Semiconductor light-emitting device

A semiconductor light-emitting device includes: a semiconductor chip having a nonpolar plane as a growth surface and configured to emit polarized light; and a reflector having a reflective surface. When a plane forming an angle of 45° relative to a direction of polarization of the polarized light is a plane L45, the reflective surface of the reflector reflects at least a part of light in the plane L45 in a normal line direction of the growth surface of the semiconductor light-emitting chip. The reflector includes a plurality of reflective surfaces, the plurality of reflective surfaces are arranged in a shape of a square in plan view, and when an angle between the direction of polarization of the polarized light and one side of the shape formed by the plurality of reflective surfaces is θ2, the angle θ2 is not less than 17° and not more than 73°.

BACKGROUND

The present invention relates to semiconductor light-emitting devices including a semiconductor light-emitting chip having a growth surface of a nonpolar plane or a semipolar plane and which emits polarized light, and a reflection member which has a reflective surface reflecting the polarized light.

Nitride semiconductors containing nitrogen (N) as a group V element have been expected as a material of a short wavelength light-emitting element because of their band gap size. Gallium nitride-based compound semiconductors, in particular, have been actively researched, and blue light-emitting diodes (LEDs), green LEDs, and blue semiconductor laser diodes that use a gallium nitride-based compound semiconductor have been also commercialized.

Gallium nitride-based compound semiconductors include a compound semiconductor obtained by substituting at least one of aluminum (Al) or indium (In) for part of gallium (Ga). Such a nitride semiconductor is represented by the general formula AlxGayInzN (where 0≦x<1, 0<y≦1, 0≦z<1, and x+y+z=1). The gallium nitride-based compound semiconductors are hereinafter referred to as GaN-based semiconductors.

When Al is substituted for Ga in a GaN-based semiconductor, this allows the band gap of the GaN-based semiconductor to be wider than that of GaN. When In is substituted for Ga in a GaN-based semiconductor, this allows the band gap of the GaN-based semiconductor to be narrower than that of GaN. Thus, not only short wavelength light, such as blue or green light, but also long wavelength light, such as orange or red light, can be emitted. From such a feature, nitride semiconductor light-emitting elements have been expected to be used for, e.g., image display devices and lighting devices.

Nitride semiconductors have a wurtzite crystal structure. InFIGS. 1A,1B, and1C, the plane orientations of the wurtzite crystal structure are expressed in four-index notation (hexagonal indices). In four-index notation, crystal planes and the orientations of the planes are expressed using primitive vectors expressed as a1, a2, a3, and c. The primitive vector c extends in a [0001] direction, and an axis in this direction is referred to as a “c-axis.” A plane perpendicular to the c-axis is referred to as a “c-plane” or a “(0001) plane.”FIG. 1Aillustrates, not only the c-plane, but also an a-plane (=(11-20) plane) and an m-plane (=(1-100) plane).FIG. 1Billustrates an r-plane (=(1-102) plane), andFIG. 1Cillustrates a (11-22) plane. Herein, the symbol “-” attached to the left of one of parenthesized numbers indicating the Miller indices expediently indicates inversion of the number.

FIG. 2Aillustrates a crystal structure of a GaN-based semiconductor using a ball-and-stick model.FIG. 2Bis a ball-and-stick model obtained by observing atomic arrangement in the vicinity of the m-plane surface from an a-axis direction. The m-plane is perpendicular to the plane of the paper ofFIG. 2B.FIG. 2Cis a ball-and-stick model obtained by observing atomic arrangement of a +c-plane surface from an m-axis direction. The c-plane is perpendicular to the plane of the paper ofFIG. 2C. As seen fromFIGS. 2A and 2B, N atoms and Ga atoms are located on a plane parallel to the m-plane. On the other hand, as seen fromFIGS. 2A and 2C, a layer in which only Ga atoms are located, and a layer in which only N atoms are located are formed on the c-plane.

Conventionally, when a semiconductor element is to be fabricated using a GaN-based semiconductor, a c-plane substrate, i.e., a substrate having a (0001) plane as its principal surface, has been used as a substrate on which a nitride semiconductor crystal is grown. In this case, spontaneous electrical polarization is induced in the nitride semiconductor along the c-axis due to the arrangements of Ga and N atoms. Thus, the “c-plane” is referred to as a “polar plane.” As a result of the electrical polarization, a piezoelectric field is generated in a quantum well layer forming a portion of a light-emitting layer of a nitride semiconductor light-emitting element and made of InGaN along the c-axis. Due to the generated piezoelectric field, the distributed electrons and holes in the light-emitting layer are displaced, and the internal quantum efficiency of the light-emitting layer is decreased due to a quantum-confined Stark effect of carriers. In order to reduce the decrease in the internal quantum efficiency of the light-emitting layer, the light-emitting layer formed on the (0001) plane is designed to have a thickness equal to or less than 3 nm.

Furthermore, in recent years, consideration has been made to fabricate a light-emitting element using a substrate having an m- or a-plane called a nonpolar plane, or a −r- or (11-22) plane called a semipolar plane as its principal surface. As illustrated inFIG. 1A, m-planes of the wurtzite crystal structure are parallel to the c-axis, and are six equivalent planes orthogonal to the c-plane. For example, inFIG. 1A, a (1-100) plane perpendicular to a [1-100] direction corresponds to one of the m-planes. The other m-planes equivalent to the (1-100) plane include a (−1010) plane, a (10-10) plane, a (−1100) plane, a (01-10) plane, and a (0-110) plane.

As illustrated inFIGS. 2A and 2B, Ga and N atoms on the m-planes are present on the same atomic plane, and thus, electrical polarization is not induced in directions perpendicular to the m-planes. Therefore, when a light-emitting element is fabricated using a semiconductor stacked structure having an m-plane as its growth surface, a piezoelectric field is not generated in a light-emitting layer, and the problem where the internal quantum efficiency is decreased due to the quantum-confined Stark effect of carriers can be solved. This applies also to the a-plane that is a nonpolar plane except the m-planes, and furthermore, even when, instead of the m-plane, the −r- or (11-22) plane called the semipolar plane is used as the growth surface, similar advantages can be provided.

A nitride semiconductor light-emitting element including an active layer having an m- or a-plane, or a −r- or (11-22) plane as a growth surface has polarization characteristics resulting from the structure of the valence band of the active layer.

For example, Japanese Unexamined Patent Publication No. 2008-109098 (FIGS. 20 and 21) describes a light-emitting diode device including light-emitting diode chips10each including a light-emitting layer12having a principal surface12a, and a package20having a chip-arrangement surface21aon which the light-emitting diode chips10are arranged, and configured such that light emitted from the principal surface12aof the light-emitting layer12has a plurality of different intensities depending on the in-plane azimuth angle of the principal surface12aof the light-emitting layer12, and at least either of the light-emitting diode chips10or the package20reduces variations in the intensity of light exiting from the package20due to the differences among the in-plane azimuth angles of the chip-arrangement surface21a, in order to reduce the variations in the intensity of light exiting from the package due to the differences among the in-plane azimuth angles of the chip-arrangement surface.

Japanese Unexamined Patent Publication No. 2009-38293 describes a light-emitting device configured such that, in order to prevent diffusion of polarized light, at least part of an inner surface of a mounting base on which a light-emitting element is mounted forms a specular surface.

Japanese Unexamined Patent Publication No. 2009-88353 describes a light-emitting device including a light-emitting element and a package, in order to provide a light-emitting device emitting polarized light with a high polarization ratio. The light-emitting element has a first end surface from which first polarized light is emitted, and a second end surface from which second polarized light is emitted. The package has a first inner wall surface that faces the first end surface and extends in parallel with the first end surface, and a second inner wall surface off which second polarized light is reflected toward the first inner wall surface.

SUMMARY

The conventional nitride semiconductor light-emitting device including an active layer having a nonpolar or semipolar plane as a growth surface has required more appropriate control over the luminous intensity distribution of outgoing light and the degree of polarization thereof.

It is therefore an object of the present disclosure to more appropriately control the luminous intensity distribution while reducing the degree of polarization of light.

In order to solve the problem, a semiconductor light-emitting device according to an aspect of the present disclosure includes: a semiconductor light-emitting chip having a growth surface that is a nonpolar or semipolar plane, and emitting polarized light; and a reflection member having a reflective surface off which the polarized light is reflected, wherein the reflective surface reflects at least a part of light in a plane L45in a normal line direction of the growth surface of the semiconductor light-emitting chip, where the plane L45represents a plane oriented at an angle of 45° to a polarization direction of the polarized light, the reflective surface of the reflection member includes a plurality of reflective surfaces, and the plurality of reflective surfaces are arranged such that a shape formed by the reflective surfaces when viewed in plan is square, and an angle θ2 is not less than 17° and not more than 73°, where the angle θ2 is an angle between the direction of polarization of the polarized light and a side of the shape formed by the reflective surfaces.

According to the semiconductor light-emitting device of the present disclosure, the luminous intensity distribution and the degree of polarization of light can be more appropriately controlled. The light distribution angle, in particular, can be controlled, and the degree of polarization of light, in particular, can be reduced.

DETAILED DESCRIPTION

A semiconductor light-emitting device according to an embodiment of the present disclosure includes: a semiconductor light-emitting chip having a growth surface that is a nonpolar or semipolar plane, and emitting polarized light; and a reflection member having a reflective surface off which the polarized light is reflected, wherein the reflective surface reflects at least a part of light in a plane L45in a normal line direction of the growth surface of the semiconductor light-emitting chip, where the plane L45represents a plane oriented at an angle of 45° to a polarization direction of the polarized light.

In an embodiment, the reflective surface may have a circular or elliptical shape when viewed in plan, and the reflection member may have a configuration in which the reflective surface reflects emitted light having an azimuth angle χ within the range from 40° to 80°, where the azimuth angle χ is an angle formed between a direction of the light emitted from the semiconductor light-emitting chip and the normal line direction of the growth surface of the semiconductor light-emitting chip.

In this case, the reflection member may have a configuration in which the reflective surface reflects emitted light having an azimuth angle χ within the range from 50° to 80°.

In an embodiment, the reflective surface may have a circular or elliptical shape when viewed in plan, the cross section of the reflective surface taken along a direction perpendicular to the growth surface of the semiconductor light-emitting chip may include a line, a curve, or a combination thereof, and an arithmetic average inclination angle Δθ1 may be not less than 20° and not more than 40°, where the arithmetic average inclination angle Δθ1 represents an angle between the reflective surface and the direction of the normal line to the growth surface of the semiconductor light-emitting chip when the reflective surface is viewed in cross section.

In this case, the arithmetic average inclination angle Δθ1 may be not less than 25° and not more than 40°.

In an embodiment, the reflective surface may have a circular or elliptical shape when viewed in plan, and may be a reflective surface configured such that the light intensity in the direction of the normal line to the growth surface of the semiconductor light-emitting chip is five or more times as high as the light intensity obtained in the case where the reflective surface is not provided.

In an embodiment, the reflection member may have a plurality of reflective surfaces, which are arranged such that a shape formed by the reflective surfaces when viewed in plan is square, and θ2 may be not less than 17° and not more than 73°, where θ2 represents an angle between the polarization direction of the polarized light and a side of the shape formed by the reflective surfaces when viewed in plan.

In this case, the angle θ2 may be not less than 30° and not more than 60°.

In an embodiment, the reflection member may have a plurality of reflective surfaces, which are arranged such that a shape formed by the reflective surfaces when viewed in plan is rectangle, and θ2 may be not less than 20° and not more than 70°, where θ2 represents an angle between the polarization direction of the polarized light and a long side of the shape formed by the reflective surfaces when viewed in plan.

In this case, the angle θ2 may be not less than 35° and not more than 55°.

In an embodiment, the cross section of the reflective surface taken along a direction perpendicular to the growth surface of the semiconductor light-emitting chip may include a line, a curve, or a combination thereof, and an arithmetic average inclination angle Δθ1 may be not less than 20° and not more than 40°, where the arithmetic average inclination angle Δθ1represents an angle between the reflective surface and the direction of the normal line to the growth surface of the semiconductor light-emitting chip when the reflective surface is viewed in cross section.

In an embodiment, corner portions of the shape formed by the reflective surfaces when viewed in plan may have a curved surface, and a curvature R of the curved surface is less than a length of each of sides of the semiconductor light-emitting chip.

In an embodiment, the semiconductor light-emitting chip may include at least two semiconductor light-emitting chips, and the at least two semiconductor light-emitting chips may be arranged such that directions of polarization of light from the at least two semiconductor light-emitting chips are identical.

In an embodiment, the semiconductor light-emitting chip may include at least four semiconductor light-emitting chips, the at least four semiconductor light-emitting chips may be arranged in a matrix such that directions of polarization of light from the at least four semiconductor light-emitting chips are identical, and D2may be less than D1, where D1represents a distance between adjacent two of the at least four semiconductor light-emitting chips arranged in a direction perpendicular to the directions of polarization of the light, and D2represents a distance between adjacent two of the at least four semiconductor light-emitting chips arranged in a direction parallel to the directions of polarization of the light.

In an embodiment, a protrusion/recess structure may be formed on a light extraction surface of the semiconductor light-emitting chip.

The semiconductor light-emitting device of the embodiment may further include: a light-transmissive member covering the semiconductor light-emitting chip.

The semiconductor light-emitting device according to the embodiment may further include: a wavelength conversion member covering the semiconductor light-emitting chip.

In an embodiment, a linear reflectivity of the reflective surface may be higher than a diffuse reflectivity of the reflective surface.

In an embodiment, a surface roughness of the reflective surface may be not more than 100 nm.

Incidentally, a nitride semiconductor active layer having an m-plane as a growth surface emits light having a high electric field intensity principally along the a-axis. When a light-emitting element emits polarized light, it is theoretically predicted that the light emitted from the light-emitting element will exhibit the luminous intensity distribution where the intensity of the emitted light increases in a direction perpendicular to the polarization direction of the light. In other words, the light emitted from the light-emitting element exhibits an uneven radiation pattern (luminous intensity distribution). Furthermore, it is theoretically predicted that light having a high electric field intensity along a specific crystal direction of a nitride semiconductor will be emitted also from each of semipolar planes, such as −r-, (20-21), (20-2-1), (10-1-3), and (11-22) planes, and other nonpolar planes, such as a-planes, and the emitted light will exhibit the luminous intensity distribution where the intensity of the emitted light increases in a direction perpendicular to the polarization direction of the light.

The polarization direction of light from a nitride semiconductor active layer having an a-plane as a growth surface has been known to be along the m-axis. Therefore, it is predicted that the light will exhibit the luminous intensity distribution where the intensity of the emitted light increases in a direction perpendicular to the m-axis.

The polarization direction of light from a nitride semiconductor active layer having a (20-2-1) or (20-21) plane that is a semipolar plane as a growth surface has been known to correspond to the [−12-10] direction. Therefore, it is predicted that the light will exhibit the luminous intensity distribution where the intensity of the emitted light increases in a direction perpendicular to the [−12-10] direction.

When the In content of a nitride semiconductor active layer having a (10-1-3) plane that is a semipolar plane as a growth surface is high, the polarization direction of light from the nitride semiconductor active layer has been known to correspond to the [−12-10] direction, and when the In content of the nitride semiconductor active layer is low, the polarization direction of the light has been known to correspond to the [11-23] direction. Therefore, it is predicted that the light will exhibit the luminous intensity distribution where when the In content of the active layer is high, the intensity of the emitted light increases in a direction perpendicular to the [−12-10] direction, and when the In content of the active layer is low, the intensity of the emitted light increases in a direction perpendicular to the [11-23] direction.

When the In content of a nitride semiconductor active layer having a (11-22) plane that is a semipolar plane as a growth surface is high, the polarization direction of light from the nitride semiconductor active layer has been known to be along the m-axis, and when the In content of the nitride semiconductor active layer is low, the polarization direction of the light has been known to correspond to the [−1-123] direction. Therefore, it is predicted that the light will exhibit the intensity distribution where when the In content of the active layer is high, the intensity of the emitted light increases in a direction perpendicular to the m-axis, and when the In content of the active layer is low, the intensity of the emitted light increases in a direction perpendicular to the [−1-123] direction.

Light having a high electric field intensity along a specific direction is herein referred to as “polarized light.” For example, light having a high electric field intensity along an X-axis is referred to as “polarized light along the X-axis,” and in this case, a direction along the X-axis is referred to as a “polarization direction.” The “polarized light along the X-axis” does not mean only linearly polarized light along the X-axis, and may include linearly polarized light along other axes. More specifically, the “polarized light along the X-axis” means light including a light component that transmits through a “polarizer having a polarization transmission axis along the X-axis” and has higher intensity (electric field intensity) than a light component transmitting through a “polarizer having a polarization transmission axis along another axis.” Therefore, the “polarized light along the X-axis” includes incoherent light including not only linearly polarized light and elliptically polarized light along the X-axis, but also linearly polarized light and elliptically polarized light in various directions.

When the polarization transmission axis of a polarizer is rotated about the optical axis, the degree of polarization of light is defined by the following expression (A):
Degree of Polarization=|Imax−Imin|/|Imax+Imin|  (A)
where Imax is the highest electric field intensity of light transmitting through the polarizer, and Imin is the lowest electric field intensity thereof.

When the polarization transmission axis of the polarizer is parallel to the X-axis, the electric field intensity of “light polarized along the X-axis” and transmitting through the polarizer is Imax, and when the polarization transmission axis of the polarizer is parallel to the Y-axis, the electric field intensity of the light transmitting through the polarizer is Imin. The electric field intensity Imin of completely linearly polarized light is equal to 0, and thus, the degree of polarization is equal to one. By contrast, the difference between the electric field intensity Imax of completely depolarized light and the electric field intensity Imin thereof is equal to zero, and thus, the degree of polarization is equal to zero.

A nitride semiconductor light-emitting element including an active layer having an m-plane as a growth surface emits polarized light principally along the a-axis as described above. In this case, the nitride semiconductor light-emitting element emits also polarized light along the c-axis and polarized light along the m-axis. However, the intensity of each of the polarized light along the c-axis and the polarized light along the m-axis is lower than that of the polarized light along the a-axis.

Herein, an active layer having an m-plane as a growth surface is used as an example, and attention is focused on polarized light along the a-axis. However, also when a semipolar plane, such as a −r-, (20-21), (20-2-1), (10-1-3), or (11-22) plane, or another nonpolar plane, such as an a-plane, is used as the growth surface, similar statements apply to polarized light in a specific crystal direction.

Herein, “m-planes” include not only planes completely parallel to the m-planes, but also planes inclined at an angle of about ±5° or less from the m-planes. The “m-planes” herein also include step-like surfaces each including a plurality of m-plane regions parallel to the m-planes. Planes inclined slightly from the m-planes are much less affected by spontaneous electrical polarization. Furthermore, the planes inclined slightly from the m-planes microscopically have properties similar to those of step-like surfaces including many m-plane regions that are not inclined from the m-planes. In addition, in some cases, in a crystal growth technique, a semiconductor layer is more easily epitaxially grown on a substrate having a crystal orientation inclined slightly from a desired orientation than on a substrate having a crystal orientation exactly identical with the desired orientation. Therefore, it may be useful to slightly incline a crystal plane in order to improve the crystal quality of the semiconductor layer to be epitaxially grown or increase the crystal growth rate of the semiconductor layer while reducing the influence of spontaneous electrical polarization to a sufficient level.

Similar statements apply to “a-planes,” “(20-21) planes,” “(20-2-1) planes,” “(10-1-3) planes,” “−r-planes,” and “(11-22) planes,” and thus, the “a-planes,” the “(20-21) planes,” the “(20-2-1) planes,” the “(10-1-3) planes,” the “−r-planes,” and the “(11-22) planes” herein each include not only planes completely parallel to corresponding ones of the “a-planes,” the “(20-21) planes,” the “(20-2-1) planes,” the “(10-1-3) planes,” the “−r-planes,” and the “(11-22) planes,” but also planes inclined at an angle of about ±5° or less from the corresponding ones of the “a-planes,” the “(20-21) planes,” the “(20-2-1) planes,” the “(10-1-3) planes,” the “−r-planes,” and the “(11-22) planes.”

A nitride semiconductor light-emitting device includes a semiconductor light-emitting chip made of a nitride semiconductor, and a reflector. The reflector may be referred to as a cavity. The nitride semiconductor light-emitting device is placed on a mounting substrate. The mounting substrate may be referred to as a package. A surface of the mounting substrate on which the semiconductor light-emitting chip is held is referred to as a mounting surface. The reflector has a reflective surface configured to change the direction of light emitted from the semiconductor light-emitting chip.

Conventionally, the azimuth angle dependence of the luminous intensity distribution of a semiconductor light-emitting chip emitting polarized light and the azimuth angle dependence of the degree of polarization of light from the semiconductor light-emitting chip have not been examined to an adequate degree; therefore, the influence of a reflective surface of a reflector on the luminous intensity distribution and the degree of polarization of light has not been revealed.

Japanese Unexamined Patent Publication No. 2008-109098 describes a method for placing a semiconductor light-emitting chip, and the shape of each of a mounting surface and a reflector surface, in order to reduce the asymmetry of the luminous intensity distribution. However, no consideration has been given to the degree of polarization of light.

Japanese Unexamined Patent Publication No. 2009-38293 describes a reflector having a reflective surface serving as a specular surface, in order to maintain the degree of polarization of light. However, no consideration has been given to the luminous intensity distribution.

Japanese Unexamined Patent Publication No. 2009-88353 describes a reflector structure configured to allow the polarization direction of light emitted from a second end surface of a nitride semiconductor light-emitting chip to be identical with the polarization direction of light emitted from a first end surface thereof, in order to increase the degree of polarization of light. However, no consideration has been given to the luminous intensity distribution.

<Degree of Polarization of Light From Semiconductor Light-Emitting Chip Emitting Polarized Light and Luminous Intensity Distribution of Semiconductor Light-Emitting Chip>

Prior to description of embodiments, the degree of polarization of light from a semiconductor light-emitting chip emitting polarized light and the luminous intensity distribution of the semiconductor light-emitting chip will be described.

First, definitions of directions of light emitted from a semiconductor light-emitting chip100made of a nitride semiconductor, and a method for measuring the luminous intensity distribution and the degree of polarization of the light will be described with reference toFIGS. 3A-3D. First, the direction perpendicular to an m-plane that is a growth surface of an active layer of the semiconductor light-emitting chip100corresponds to a Z-axis, the polarization direction of light emitted from the active layer corresponds to an X-axis, and the direction perpendicular to both the Z-axis and the X-axis corresponds to a Y-axis. The Z-axis is referred to also as the normal line direction. When the growth surface of the active layer is an m-plane, the Z-axis corresponds to the m-axis, the X-axis corresponds to the a-axis, and the Y-axis corresponds to the c-axis.

A plane L perpendicularly intersecting the active layer106is defined. The angle between the plane L and the polarization direction of light, i.e., the X-axis, is defined as φ, and when the angle φ is a specific value φ1 (unit: degree [°]), the plane L is defined as a plane Lφ1. Furthermore, in the plane Lφ1, the angle between the Z-axis (the normal line direction) and emitted light is defined as an azimuth angle χ. A plane used to measure the luminous intensity distribution is defined by the plane Lφ1, and the azimuth angle within which the luminous intensity distribution is measured is defined by the azimuth angle χ. A cross-sectional view taken along the plane Lφ1is referred to as the “cross-sectional view along the plane Lφ1.”

FIGS. 3B,3C, and3D illustrate specific examples in each of which the growth surface of the active layer is an m-plane.

FIG. 3Billustrates measurement axes along which the luminous intensity distribution in a plane L0and the degree of polarization of light therein are measured, where the growth surface of the active layer is an m-plane. In this case, the plane L0corresponds to the plane defined by the m-axis and the a-axis.

FIG. 3Cillustrates measurement axes along which the luminous intensity distribution in a plane L45and the degree of polarization of light therein are measured, where the growth surface of the active layer is an m-plane. In this case, the plane L45includes the m-axis, and corresponds to a plane inclined at an angle of 45° from the a-axis.

FIG. 3Dillustrates a measurement axis along which the luminous intensity distribution in a plane L90and the degree of polarization of light therein are measured when the growth surface of the active layer is an m-plane. In this case, the plane L90corresponds to the plane defined by the m-axis and the c-axis.

The luminous intensity distribution of the semiconductor light-emitting chip100including the active layer emitting polarized light and the profile indicating the degree of polarization of light emitted from the semiconductor light-emitting chip100vary among the measurement planes, i.e., the plane L0, the plane L45, and the plane L90. This phenomenon will be described in detail in comparative examples described below.

The luminous intensity distribution in the plane L45is similar to that in the plane L90, and when the azimuth angle χ is in the range from −80° to −10° or the range from 10° to 80°, the light intensity is much higher than when the azimuth angle χ is equal to 0°, i.e., the intensity of light emitted along the normal line direction.

When the azimuth angle χ is in the range from −80° to +80°, the intensity of light in the plane L90is high, and a high degree of polarization of light in the plane L90is maintained. When the azimuth angle χ is 0°, the degree of polarization of light in the plane L0is highest, and when the absolute value of the azimuth angle χ is greater than 80, the degree of polarization of the light gently decreases. Similarly to the degree of polarization of the light in the plane L0, when the azimuth angle χ is 0°, the degree of polarization of light in the plane L45is highest. However, when the absolute value of the azimuth angle χ is greater than 80, the degree of polarization of light in the plane L45significantly decreases, and when the azimuth angle χ is in the range from −40° to 40°, the degree of polarization of the light therein is reduced to substantially one half or less of that obtained when the azimuth angle χ is equal to 0°. Furthermore, when the azimuth angle χ is −50° or less and 50° or more, the degree of polarization of light in the plane L45is reduced to substantially one third or less of that obtained when the azimuth angle χ is equal to 0°. The azimuth angle dependence of each of the luminous intensity distribution and the degree of polarization of light has not been known.

The present inventors arrived at the following embodiments based on new characteristics, i.e., the azimuth angle dependence of each of the luminous intensity distribution and the degree of polarization of light. That is, the present inventors focused attention on the following properties: the intensity of light emitted in the plane L45to have an azimuth angle χ within the range from −80° to −40° or within the range from 40° to 80° is extremely high, and the degree of polarization of the light is low.

Specifically, when light emitted in the plane L45to have an azimuth angle χ within the range from −80° to −40° or within the range from 40° to 80° is concentrated in the normal line direction, the degree of polarization of the light in the normal line direction can be reduced while the intensity of the light in the normal line direction is increased. Alternatively, when light emitted in the plane L45to have an azimuth angle χ within the range from −80° to −50° or within the range from 50° to 80° is concentrated in the normal line direction, the degree of polarization of the light in the normal line direction can be further reduced while the intensity of the light in the normal line direction is increased.

First Embodiment

A semiconductor light-emitting device according to a first embodiment of the present disclosure will be described with reference toFIGS. 4A and 4B.

FIG. 4Ais a plan view illustrating a configuration of the semiconductor light-emitting device according to the first embodiment, andFIG. 4Bis a cross-sectional view illustrating the configuration along the line X-X′ inFIG. 4A. The cross section along the line X-X′ corresponds to the plane L45. The semiconductor light-emitting device according to this embodiment includes a mounting substrate101, a semiconductor light-emitting chip100mounted on the mounting substrate101and emitting polarized light, a reflector120that is a reflection member having reflective surfaces surrounding the semiconductor light-emitting chip100, and a light-transmissive member121covering the semiconductor light-emitting chip100and filling the interior of the reflector120.

As illustrated inFIG. 4B, the nitride semiconductor light-emitting chip100includes a substrate104having a GaN layer having an m-plane as the principal surface and the growth surface (hereinafter referred to as the m-plane GaN layer), an n-type nitride semiconductor layer105formed on the principal surface of the GaN layer of the substrate104, an active layer106formed on the n-type nitride semiconductor layer105and made of a nitride semiconductor, a p-type nitride semiconductor layer107formed on the active layer106, a p-side electrode108formed on and in contact with the p-type nitride semiconductor layer107, and an n-side electrode109formed on and in contact with an exposed region of the n-type nitride semiconductor layer105. The active layer106has a nonpolar or semipolar plane as the growth surface, and emits polarized light. In this embodiment, a light-emitting diode (LED) chip can be used as the semiconductor light-emitting chip100. Similar statements apply to the following variations and other embodiments.

The growth surface of each of the n-type nitride semiconductor layer105, the active layer106, and the p-type nitride semiconductor layer107is substantially parallel to m-planes. In other words, the layers105,106, and107are stacked along the m-axis. Another layer may be formed between the n-type nitride semiconductor layer105and the active layer106. Furthermore, another layer may be formed between the active layer106and the p-type nitride semiconductor layer107. Here, a GaN-based semiconductor will be described as an example nitride semiconductor. The GaN-based semiconductor includes a semiconductor represented by the general expression AlxInyGazN (where 0≦x<1, 0≦y<1, 0<z≦1, and x+y+z=1).

The semiconductor light-emitting chip100is mounted such that its p-side electrode108and its n-side electrode109each face a corresponding one of interconnect electrodes102placed on a surface of the mounting substrate101. Specifically, the semiconductor light-emitting chip100is electrically connected through bumps103to the interconnect electrodes102on the mounting substrate101, and is held on the interconnect electrodes102with the bumps103interposed therebetween. Such a structure is referred to as the flip-chip structure. One of the interconnect electrodes102is connected to the p-side electrode108, and the other one thereof is connected to the n-side electrode109. An insulative material, such as alumina (aluminum oxide), aluminum nitride (AlN), or a glass epoxy resin, a metal material containing, e.g., aluminum (Al), copper (Cu), or tungsten (W), a semiconductor material, such as silicon (Si) or germanium (Ge), or a composite of the materials can be used as the principal material forming the mounting substrate101. Metal, such as aluminum (Al), silver (Ag), gold (Au), or copper (Cu), can be used as a material of the interconnect electrodes102.

The substrate104may be made of only a GaN layer, or may include a layer except a GaN layer. The layer except the GaN layer may be an m-plane GaN substrate, an m-plane SiC substrate, an r-plane sapphire substrate, an m-plane sapphire substrate, or an a-plane sapphire substrate. Furthermore, the substrate104may be removed.

The active layer106includes a plurality of barrier layers made of InYGa1-YN (where 0≦Y<1), and at least one well layer vertically interposed between an adjacent pair of the barrier layers and made of InxGa1-xN (where 0<X≦1). The well layer included in the active layer106may be a single layer. Alternatively, the active layer106may have a multiple quantum well (MQW) structure in which well layers and barrier layers are alternately stacked. The wavelength of light emitted from the semiconductor light-emitting chip100depends on the In content ratio x of an InxGa1-xN semiconductor that is a semiconductor composition of the well layer.

The p-type nitride semiconductor layer107is made of, e.g., a p-type AlsGatN (where 0≦s≦1, 0≦t≦1, and s+t=1) semiconductor. For example, magnesium (Mg) can be used as a p-type dopant. As the p-type dopant, instead of Mg, zinc (Zn) or beryllium (Be), for example, may be used. The Al content ratio s of the p-type nitride semiconductor layer107may be uniform along the thickness thereof, or may vary along the thickness thereof in a continuous or stepwise manner. The thickness of the p-type nitride semiconductor layer107is, e.g., about 0.05-2 μm. The Al content ratio s of a portion of the p-type nitride semiconductor layer107near an upper surface thereof, i.e., a portion thereof near the interface between the p-type nitride semiconductor layer107and the p-side electrode108, may be zero. In other words, the portion of the p-type nitride semiconductor layer107near the upper surface thereof may be a GaN layer. In this case, the GaN layer may contain a high concentration of p-type impurities, and may function as a contact layer with the p-side electrode108.

The p-side electrode108may cover substantially the entire surface of the p-type nitride semiconductor layer107. The p-side electrode108is made of, e.g., a layered structure (Pd/Pt) in which a palladium (Pd) layer and a platinum (Pt) layer are stacked. In order to increase the reflectivity of emitted light, a layered structure (Ag/Pt) in which a silver (Ag) layer and a platinum (Pt) layer are stacked, or a layered structure (Pd/Ag/Pt) in which a Pd layer, an Ag layer, and a Pt layer are sequentially stacked may be used as the p-side electrode108.

The n-side electrode109is made of, e.g., a layered structure (Ti/Pt) in which a titanium (Ti) layer and a platinum (Pt) layer are stacked. In order to increase the reflectivity of emitted light, a layered structure (Ti/Al/Pt) in which a Ti layer, an Al layer, and a Pt layer are sequentially stacked may be used.

The semiconductor light-emitting chip100is one of pieces into which a wafer including stacked semiconductor layers is singulated along the a- and c-axes and which are square or rectangular when viewed in plan. In this case, a c-plane of a nitride semiconductor is easily cleaved, and thus, a singulation process step can be simplified. Alternatively, the semiconductor light-emitting chip100may be one of pieces into which the wafer is singulated along directions inclined at an angle of not less than 0° and not more than 45° from the a- and c-axes. In this case, planes that are difficult to be cleaved are exposed on the side surfaces of the semiconductor light-emitting chip100. This exposure tends to cause the side surfaces of the semiconductor light-emitting chip100to be uneven. The uneven surfaces improve the light extraction efficiency at which emitted light is extracted from the uneven surfaces.

An epoxy resin or a silicone resin can be used as a material of the light-transmissive member121. Alternatively, the light-transmissive member121may contain a color conversion material excited by light from the active layer106to generate light having a longer wavelength than the light from the active layer106. The surface of the light-transmissive member121may be flat, or may have a shape different from the flat shape.

In this embodiment, the reflective surfaces125of the reflector120improve the symmetry of the luminous intensity distribution, and play a significant role in controlling the degree of polarization of light. The reflector120has a portion of the reflective surface125configured to reflect light emitted from the semiconductor light-emitting chip100.

Here, the reflective surface125may have a circular shape when viewed in plan. A shape such as the circular shape having a high degree of symmetry easily reduces the asymmetry of the luminous intensity distribution. Moreover, when the reflective surface has the circular shape, the positional relationship relative to the reflector does not change even when the semiconductor light-emitting chip100rotates during its mounting process. Thus, the advantages provided by the present embodiment can be ensured.

When light output from the semiconductor light-emitting chip100in the direction of the azimuth angle χ has an angle θ1 which is one half of the azimuth angle χ, the light is reflected off the reflective surface125in the normal line direction, where the angle θ1 represents an angle formed between the reflective surface125and the direction of the normal line to the active layer when viewed in cross section. Therefore, in order to reflect emitted light having an azimuth angle χ within the range from 40° to 80° in the normal line direction, the angle θ1 can be within the range from 20° to 40°. Furthermore, in order to reflect emitted having an azimuth angle χ within the range from 50° to 80° in the normal line direction, the angle θ1 can be within the range from 25° to 40°.

Moreover, when the reflective surface125has a cross-sectional structure improving the light intensity in the normal line direction of the growth surface of the active layer so that the light intensity is 5.5 or more times as high as the light intensity obtained in the case without the reflective surface125, the degree of polarization of light in the normal line direction can be reduced to one half or less.

A metal material such as silver (Ag) or aluminum (Al) can be used as a material of the reflective surface125. Alternatively, a white resin material may be used. When the linear reflectivity of the reflection property on the reflective surface125is high, the light distribution angle is easily controlled. Moreover, when the diffuse reflectivity of the reflection property on the reflective surface125is high, the degree of polarization is easily reduced. In the present embodiment, even when a material having a high linear reflectivity is used, the asymmetry of the luminous intensity distribution is reduced, and the degree of polarization is also reduced.

FIGS. 5-10illustrate cross-sectional configurations along the Z-axis of the semiconductor light-emitting device according to variations of the first embodiment.

(First Variation of First Embodiment)

FIG. 5illustrates a semiconductor light-emitting device according to a first variation of the first embodiment. As illustrated inFIG. 5, the angle θ1 at the cross section of a reflective surface125of a reflector120according to the first variation is not one type, but includes a plurality of angles θ1a and θ1b. When reflective surfaces having different angles are combined, the light distribution angle can be more suitably controlled. In the present variation, the angles θ1a and θ1b can be set within the range from 20° to 40°. Alternatively, the angles θ1a and θ1b can be set within the range from 25° to 40°.

(Second Variation of First Embodiment)

FIG. 6illustrates a semiconductor light-emitting device according to a second variation of the first embodiment. As illustrated inFIG. 6, a reflector120according to the second variation is formed to have a portion having an angle θ1 greater than or equal to 0° and less than 20° in a cross-sectional shape near a connection portion of a reflective surface125to the mounting substrate101.FIG. 6illustrates an example in which the reflector120has a portion forming an angle θ1 of 0° near the connection portion of the reflective surface125to the mounting substrate101. The intensity of light emitted in the plane L45to have an azimuth angle χ greater than 80° is low, and thus, the portion of the reflector120near the connection portion of the reflective surface125to the mounting substrate101has a small effect on the luminous intensity distribution and the degree of polarization. That is, the portion of the reflective surface125near the connection portion to the mounting substrate101has a small effect on the luminous intensity distribution and the degree of polarization. Thus, even when the reflective surface125has a portion having an angle θ1 greater than or equal to 0° and less than 20° near the connection portion of the reflective surface125to the mounting substrate101, it is possible to reduce the degree of polarization of light in the normal line direction.

(Third Variation of First Embodiment)

FIG. 7illustrates a semiconductor light-emitting device according to a third variation of the first embodiment. As illustrated inFIG. 7, a reflective surface125of a reflector120of the third variation has a curved cross-sectional shape.

In this variation, the angle Δθ1 can be set within the range from 20° to 40°, where Δθ1 represents the arithmetic average inclination angle Δθ1 of each of the reflective surfaces125relative to the direction of the normal line to the growth surface of a semiconductor light-emitting chip100. Furthermore, the angle Δθ1 can be set within the range from 25° to 40°. Here, while the definition of the arithmetic average inclination angle Δθ1 herein is similar to that defined in Japanese Industrial Standard (JIS) B0601-1994, the reference direction of the angle herein is different from that of the angle defined in JIS B0601-1994. In other words, while the arithmetic average inclination angle RΔa defined in JIS is an angle relative to a horizontal direction, the arithmetic average inclination angle Δθ1 herein is an angle relative to the normal line direction. Specifically, the arithmetic average inclination angle Δθ1 herein is given by the following expression 1:

In order to actually measure the arithmetic average inclination angle Δθ1, the arithmetic average inclination angle RΔa of a reflective surface125is measured using a laser microscope, and the measured value is subtracted from 90° to obtain the arithmetic average inclination angle Δθ1 herein. Specifically, even when a region of the reflective surface125has an angle θ1 that is not within the range from 20° to 40° relative to the normal line direction, the effect of reducing the degree of polarization of light herein can be obtained as long as regions of the reflective surface125have an average angle within the range from 20° to 40° relative to the normal line direction.

As such, each of reflective surfaces125does not need to be linear when viewed in cross section. A plurality of lines may be combined together to form the reflective surface125, or the reflective surface125may be curved. Alternatively, a line and a curve may be combined together.

Furthermore, even when a region of the reflective surfaces125having an angle Δθ1 greater than or equal to 0° and less than 20° is located near the mounting substrate101, it is possible to reduce the degree of polarization of light in the normal line direction.

(Fourth Variation of First Embodiment)

FIG. 8illustrates a semiconductor light-emitting device according to a fourth variation of the first embodiment. As illustrated inFIG. 8, the surface of a light-transmissive member121according to the fourth variation is not flat, but is convex. In this variation, the luminous intensity distribution of light having a degree of polarization reduced by reflective surfaces125can be controlled by the surface shape of the light-transmissive member121.

For example, when the surface of the light-transmissive member121is convex, this can further reduce the light distribution angle. In contrast, although not specifically shown, when the surface of the light-transmissive member121is concave, this can increase the light distribution angle. Alternatively, although not specifically shown, when microscopic protrusions/recesses are formed on the surface of the light-transmissive member121to scatter light, it is possible to further reduce the degree of polarization of light.

(Fifth Variation of First Embodiment)

FIG. 9illustrates a semiconductor light-emitting device according to a fifth variation of the first embodiment. As illustrated inFIG. 9, in the fifth variation, a light-transmissive member121on a mounting substrate101does not cover reflective surfaces125of a reflector120, but covers a semiconductor light-emitting chip100. This configuration enables the formation of the reflector120after the formation of the light-transmissive member121.

Moreover, when the surface of the light-transmissive member121is convex as in the fourth variation, this can reduce the light distribution angle. In contrast, although not specifically shown, when the surface of the light-transmissive member121is concave, this can increase the light distribution angle. Alternatively, although not specifically shown, when microscopic protrusions/recesses are formed on the surface of the light-transmissive member121to scatter light, it is possible to further reduce the degree of polarization of light.

(Sixth Variation of First Embodiment)

FIG. 10illustrates a semiconductor light-emitting device according to a sixth variation of the first embodiment. As illustrated inFIG. 10, in the sixth variation, a wavelength conversion member122is further formed on a light-transmissive member121. The wavelength conversion member122converts the wavelength of at least one part of light emitted from a semiconductor light-emitting chip100. The wavelength conversion member122can be made of a resin material or glass containing phosphors configured to convert the light wavelength. Alternatively, it may be made of a sintered object having phosphors configured to convert the light wavelength as the main ingredient.

(Seventh Variation of First Embodiment)

FIGS. 11A and 11Brespectively illustrate a plan configuration and a cross-sectional configuration of a semiconductor light-emitting device according to a seventh variation of the first embodiment. As illustrated inFIGS. 11A and 11B, a protrusion/recess structure130is formed on a light extraction surface of a semiconductor light-emitting chip100according to the seventh variation. In the present variation, the protrusion/recess structure130is formed on the light extraction surface of the semiconductor light-emitting chip100, so that it is possible to further reduce the degree of polarization of light in the normal line direction. The size of each of protrusions or each of recesses of the protrusion/recess structure130can be not less than 100 nm and not more than 10 μm.

(Eighth Variation of First Embodiment)

FIG. 12illustrates a plan configuration of a semiconductor light-emitting device according to an eighth variation of the first embodiment. As illustrated inFIG. 12, a reflective surface125of a reflector120according to the eighth variation has an elliptical shape when viewed in plan. Also in the present variation, the cross-sectional shape of the reflective surface125may be configured such that light emitted in the plane L45to have an azimuth angle χ within the range from 40° to 80° is concentrated in the normal line direction. Therefore, the shape of the reflective surface125when viewed in plan is not necessarily perfectly circular, but may be elliptic. However, when the ellipticity of an ellipse is high, the luminous intensity distribution in the major axial direction of the ellipse and the luminous intensity distribution in the minor axial direction of the ellipse are significantly asymmetric. Thus, in order to reduce the asymmetry of the luminous intensity distribution, the length of the major axis of the ellipse can be two or less times as long as the length of the minor axis of the ellipse.

(Ninth Variation of First Embodiment)

FIG. 13illustrates the configuration of a semiconductor light-emitting device according to a ninth variation of the first embodiment when viewed in plan. As illustrated inFIG. 13, the semiconductor light-emitting device according to the present variation includes a plurality of semiconductor light-emitting chips100, four semiconductor light-emitting chips100here, arranged on a mounting substrate101such that the polarization directions of light from the semiconductor light-emitting chips100are identical. The distance D2can be less than the distance D1, where D1represents the distance between two of the semiconductor light-emitting chips100adjacent to each other in a direction perpendicular to the polarization direction of the light (along the c-axis when the growth surface of an active layer is an m-plane), and D2represents the distance between two of the semiconductor light-emitting chips100adjacent to each other in a direction identical with the polarization direction of the light (along the a-axis when the growth surface of the active layer is an m-plane). The distance D2can be less than the distance D1because a comparison between the luminous intensity distribution in the direction perpendicular to the polarization direction of the light (the luminous intensity distribution in the plane L90) and the luminous intensity distribution in the direction identical with the polarization direction of the light (the luminous intensity distribution in the plane L0) shows that in the luminous intensity distribution in the direction perpendicular to the polarization direction of the light (the luminous intensity distribution in the plane L90), even when the absolute value of the azimuth angle χ is great, the light intensity is high. Specifically, when the distance D2is less than the distance D1, this can prevent light beams emitted from the adjacent semiconductor light-emitting chips100from interfering with each other.

(Tenth Variation of First Embodiment)

FIG. 14illustrates the cross-sectional configuration of a semiconductor light-emitting device according to a tenth variation of the first embodiment. As illustrated inFIG. 14, a semiconductor light-emitting chip100according to the tenth variation is mounted on a mounting substrate101by wire bonding. Specifically, the semiconductor light-emitting chip100is held with a substrate104facing a mounting surface of the mounting substrate101. A p-side electrode108and an n-side electrode109are each electrically connected to a corresponding one of interconnect electrodes102on the mounting substrate101through a corresponding one of wires110made of gold (Au) or aluminum (Al). A p-type nitride semiconductor layer107has a light extraction surface124. The substrate104may be conductive, or may be nonconductive. The substrate104may be, for example, an insulative substrate, such as a sapphire substrate.

(Eleventh Variation of First Embodiment)

FIG. 15illustrates the cross-sectional configuration of a semiconductor light-emitting device according to an eleventh variation of the first embodiment. As illustrated inFIG. 15, a semiconductor light-emitting chip100according to the eleventh variation is mounted on a mounting substrate101by wire bonding. Specifically, the semiconductor light-emitting chip100is held with a p-side electrode108facing a mounting surface of the mounting substrate101. The p-side electrode108is electrically connected to a corresponding one of interconnect electrodes102on the mounting substrate101with solder of, e.g., gold-tin (AuSn). An n-side electrode109is electrically connected to a corresponding one of the interconnect electrodes102on the mounting substrate101through a wire110made of gold (Au) or silver (Ag). A substrate104has a light extraction surface124. In this case, the substrate104is conductive.

As such, processes for connecting each of the p-side electrode108and the n-side electrode109and a corresponding one of the interconnect electrodes102on the mounting substrate101together vary between flip-chip bonding and wire bonding. However, other configurations of the semiconductor light-emitting chip100mounted by wire bonding are substantially similar to those of the semiconductor light-emitting chip100mounted by flip-chip bonding, and operational advantages of a semiconductor light-emitting device including the semiconductor light-emitting chip100mounted by wire bonding are also similar to those of the semiconductor light-emitting device including the semiconductor light-emitting chip100mounted by flip-chip bonding according to the first embodiment.

When an active layer106emits polarized light, the first embodiment and its variations allow the polarization characteristics to be reduced. Therefore, also when the active layer106has a nonpolar plane, such as an m-plane or an a-plane, or a semipolar plane, such as −r-plane, a (11-22) plane, or a (20-2-1) plane, as a growth surface, this embodiment and its variations can improve the luminous intensity distribution, and allows the degree of polarization of light to be reduced.

Also in each of the tenth and eleventh variations of the first embodiment, a reflector120having a cross-sectional shape illustrated in any one ofFIGS. 5-7can be used.

A light-transmissive member121having a surface with the shape illustrated in any one ofFIGS. 8 and 9can be combined with each of the tenth and eleventh variations.

The wavelength conversion member122illustrated inFIG. 10can be combined with each of the tenth and eleventh variations.

A method for fabricating a semiconductor light-emitting device according to the first embodiment will be described hereinafter with reference toFIGS. 4A and 4B.

First, an n-type nitride semiconductor layer105is epitaxially grown on the principal surface of a substrate104having an m-plane as its principal surface and made of n-type GaN by metal organic chemical vapor deposition (MOCVD) or any other method. Specifically, for example, silicon (Si) is used as an n-type dopant, trimethylgallium (TMG (Ga(CH3)3)) being a gallium (Ga) source, and ammonia (NH3) being a nitrogen (N) source are supplied to the substrate104, and the about 1-3-μm-thick n-type nitride semiconductor layer105made of GaN is formed at a growth temperature approximately 900-1100° C. In this stage, the substrate104is a substrate at the wafer level, and a plurality of light-emitting structures forming semiconductor light-emitting devices can be fabricated at once.

Next, an active layer106made of a nitride semiconductor is grown on the n-type nitride semiconductor layer105. The active layer106has an InGaN/GaN multiple quantum well (MQW) structure in which, for example, 3-15-nm-thick well layers made of In1-xGaxN and 6-30-nm-thick barrier layers made of GaN are alternately stacked. When the well layers made of In1-xGaxN are formed, the growth temperature may be decreased to about 700-800° C. to ensure incorporation of indium (In) into the well layers being grown. The wavelength of emitted light is selected based on the intended use of the semiconductor light-emitting device, and the In content ratio x is determined based on the wavelength. For example, when the wavelength is 450 nm (blue light wavelength), the In content ratio x can be determined to be 0.25-0.27. When the wavelength is 520 nm (green light wavelength), the In content ratio x can be determined to be 0.40-0.42. When the wavelength is 630 nm (red light wavelength), the In content ratio x can be determined to be 0.56-0.58.

Next, a p-type nitride semiconductor layer107is epitaxially grown on the active layer106. Specifically, for example, Cp2Mg (bis(cyclopentadienyl) magnesium) is used as p-type impurities, TMG and NH3are supplied, as materials, to the substrate104, and the about 50-500-nm-thick p-type nitride semiconductor layer107made of p-type GaN is formed on the active layer106at growth temperature approximately 900-1100° C. The p-type nitride semiconductor layer107may contain an about 15-30-nm-thick p-type AlGaN layer. The formation of the p-type AlGaN layer can reduce the overflow of electrons that are carriers. An undoped GaN layer may be formed between the active layer106and the p-type nitride semiconductor layer107.

Next, in order to activate Mg with which the p-type nitride semiconductor layer107is doped, the p-type nitride semiconductor layer107is thermally treated at temperatures of about 800-900° C. for about 20 minutes.

Next, a semiconductor stacked structure including the substrate104, the n-type nitride semiconductor layer105, the active layer106, and the p-type nitride semiconductor layer107is partially etched by lithography and dry etching using a chlorine (Cl2) gas. Thus, a recess112is formed by removing a portion of the p-type nitride semiconductor layer107, a portion of the active layer106, and a portion of the n-type nitride semiconductor layer105to expose a region of the n-type nitride semiconductor layer105.

Next, an n-side electrode109is selectively formed on and in contact with the exposed region of the n-type nitride semiconductor layer105. Here, for example, a multilayer film (Ti/Pt layer) of titanium (Ti) and platinum (Pt) is formed as the n-side electrode109.

Next, a p-side electrode108is selectively formed on and in contact with the p-type nitride semiconductor layer107. For example, a multilayer film (Pd/Pt layer) of palladium (Pd) and platinum (Pt) is formed as the p-side electrode108. Thereafter, heat treatment is performed to alloy a region between the Ti/Pt layer and the n-type nitride semiconductor layer105and a region between the Pd/Pt layer and the p-type nitride semiconductor layer107. The order in which the n-side electrode109and the p-side electrode108are formed is not particularly limited.

Next, a (back) surface of the substrate104opposite to the n-type nitride semiconductor layer105is polished to reduce the thickness of the substrate104by a predetermined amount.

The wafer-level substrate104is singulated into individual semiconductor light-emitting chips100corresponding to a plurality of semiconductor light-emitting devices fabricated as above. Examples of this singulation process include various processes, such as laser dicing and cleavage. The individual semiconductor light-emitting chips100into which the substrate104has been singulated are mounted on a mounting surface of a mounting substrate101.

Examples of a method for forming a reflector120include a method in which a recess is formed in the mounting substrate101itself, and a method in which a separately fabricated reflector120is bonded to the mounting substrate101.

Processes of the method in which a recess is formed in the mounting substrate101itself vary depending on the principal material of the mounting substrate101. When the principal material of the mounting substrate101is a metal material containing, e.g., aluminum (Al), silver (Ag), copper (Cu), or tungsten (W), the recess can be formed by pressing with dies. When the principal material of the mounting substrate101is a sintered material, such as alumina (aluminum oxide) or aluminum nitride (AlN), the previous formation of protrusions/recesses on the inner surfaces of dies enables the formation of a predetermined recess after sintering. When the principal material of the mounting substrate101is a semiconductor material, such as silicon (Si) or germanium (Ge), or a composite of the materials, a predetermined recess can be formed by etching after the formation of a mask.

When a reflector120is bonded to the mounting substrate101, the semiconductor light-emitting chip100may be mounted on the mounting substrate101before the reflector120is bonded to the mounting substrate101. Alternatively, after the reflector120has been bonded to the mounting substrate101, the semiconductor light-emitting chip100may be mounted on the mounting substrate101. When a reflector120is bonded to the mounting substrate101, the principal material of the reflector120can be different from the principal material of the mounting substrate101. For example, when the reflector120is made of a metal material containing, e.g., aluminum (Al), silver (Ag), copper (Cu), or tungsten (W), the reflector120can be manufactured by pressing with dies. When the reflector120is made of a resin material or a plastic material, the reflector120can be manufactured by, e.g., injection molding or machining. In this case, a metal material containing, e.g., aluminum (Al), silver (Ag), copper (Cu), or tungsten (W), an insulative material, such as alumina (aluminum oxide) or aluminum nitride (AlN), a semiconductor material, such as silicon (Si) or germanium (Ge), or a composite of the materials can be used as the principal material of the mounting substrate101.

In order to increase the reflectivity of the reflector120, Al or Ag, for example, may be deposited on the reflective surface125by vapor deposition or plating. Alternatively, a high-reflectivity resin material containing titanium dioxide (TiO2) particles may be deposited on the reflective surface125.

A metal film for forming interconnect electrodes is formed on the surface of the mounting substrate101through a film formation process, such as sputtering or plating. Thereafter, a desired resist pattern is formed on the formed metal film by, e.g., lithography. Thereafter, the resist pattern is transferred to the metal film by dry etching or wet etching to form interconnect electrodes102each having a desired electrode shape.

Next, a plurality of bumps103are formed on predetermined portions of the interconnect electrodes102. Gold (Au) is preferably used as a constituent material of the bumps103. The bumps103each having a diameter of about 40-80 μm can be formed with a bump bonder. The bumps103can be formed by Au plating instead of with a bump bonder. Subsequently, the interconnect electrodes102on which the plurality of bumps103are formed and the electrodes of the semiconductor light-emitting chip100are electrically connected together by, e.g., ultrasonic welding.

As such, the semiconductor light-emitting device according to the first embodiment can be obtained.

Second Embodiment

A semiconductor light-emitting device according to a second embodiment of the present disclosure will be described hereinafter with reference toFIGS. 16A and 16B. InFIGS. 16A and 16B, the same characters as those inFIGS. 4A and 4Bare used to represent equivalent components, and thus, description thereof is omitted. Here, the difference between the first and second embodiments will be described.

FIG. 16Aillustrates the configuration of the semiconductor light-emitting device according to the second embodiment when viewed in plan.FIG. 16Billustrates a cross-sectional configuration taken along the line XVIb-XVIb inFIG. 16A. The cross section taken along the line XVIb-XVIb corresponds to the plane L45. A plurality of reflective surfaces125of a reflector120are arranged such that a shape formed by the reflective surfaces125when viewed in plan is square. The angle θ2 of not less than 17° and not more than 73° allows the normalized degree of polarization to be reduced to one half or less, where θ2 represents the angle between a side of the square shape formed by the reflective surfaces125and the polarization direction of light from a semiconductor light-emitting chip100. The angle θ2 of not less than 30° and not more than 60° allows the normalized degree of polarization to be reduced to one fifth or less. The angle θ2 of an angle 45° allows the normalized degree of polarization to be reduced to one tenth. The normalized degree of polarization of light is a value obtained by normalizing the value relative to the polarity of a configuration in which the reflector120is not provided, i.e., the configuration of a first comparative example which will be described later.

When the shape formed by the reflective surfaces125when viewed in plan is square, and one side of the square and the direction of polarization of light form the angle θ2, another side adjacent to the one side of the square and the direction of polarization of light form an angle obtained by subtracting θ2 from 90.

When the reflector120has a quadrangular shape when viewed in plan, and light is reflected off each corner of the quadrangle formed the reflective surfaces125, the polarization direction of the reflected light rotates. That is, the phenomenon of rotation of the plane of polarization occurs. When attention is focused on a corner120aof the square formed by the reflective surfaces125, a polarization direction Es of first reflected light on a first reflective surface125srotates anti-clockwise relative to the polarization direction of light from the semiconductor light-emitting chip100. On the other hand, on a second reflective surface125tadjacent to the first reflective surface125s, a polarization direction Et of second reflected light rotates clockwise relative to the polarization direction of the light from the semiconductor light-emitting chip100. Thus, composite light of the first reflected light and the second reflected light is elliptically polarized, so that the degree of polarization of the light is reduced. Moreover, when attention is focused on the plane L45, emitted light having a high light intensity and a low degree of polarization is concentrated in the normal line direction. As a result, the degree of polarization of light in the normal line direction can be sufficiently reduced.

As described in the first embodiment, each of the reflective surfaces125does not need to be linear when viewed in cross section. A plurality of lines may be combined together to form the reflective surface125, or the reflective surface125may be curved. Alternatively, a line and a curve may be combined together. In this case, the reflective surface125can be determined to have a portion forming an angle Δθ1 of not less than 20° and not more than 40°, where the arithmetic average inclination angle Δθ1 represents the angle between the reflective surface125and the direction of the normal line to the growth surface of each of the semiconductor light-emitting chips100. Furthermore, also when a portion of the reflective surface125having an angle Δθ1 greater than or equal to 0° and less than 20° is located near the mounting substrate101, the degree of polarization of light in the normal line direction can be reduced.

(First Variation of Second Embodiment)

FIG. 17illustrates the plan configuration of a semiconductor light-emitting device according to a first variation of the second embodiment. As illustrated inFIG. 17, a reflector120of the semiconductor light-emitting device according to the present variation has a reflective surface125having corner portions each with a curved surface. The curvature R of the curved surface can be less than the length of each of sides of the semiconductor light-emitting chip100.

(Second Variation of Second Embodiment)

FIG. 18illustrates the plan configuration of a semiconductor light-emitting device according to a second variation of the second embodiment. As illustrated inFIG. 18, the semiconductor light-emitting device according to the present variation includes a plurality of semiconductor light-emitting chips100, four semiconductor light-emitting chips100here, arranged on a mounting substrate101such that the directions of polarization of light from the semiconductor light-emitting chips100are identical. The distance D2can be less than the distance D1, where D1represents the distance between two of the semiconductor light-emitting chips100adjacent to each other in a direction perpendicular to the direction of polarization of the light, that is, along the c-axis when the growth surface of an active layer is an m-plane, and D2represents the distance between two of the semiconductor light-emitting chips100adjacent to each other in a direction identical with the direction of polarization of the light, that is, along the a-axis when the growth surface of the active layer is an m-plane. The distance D2can be less than the distance D1because a comparison between the luminous intensity distribution in the direction perpendicular to the direction of polarization of the light (the luminous intensity distribution in the plane L90) and the luminous intensity distribution in the direction identical with the direction of polarization of the light (the luminous intensity distribution in the plane L0) shows that in the luminous intensity distribution in the direction perpendicular to the direction of polarization of the light (the luminous intensity distribution in the plane L90), even when the azimuth angle χ is large, the light intensity is high. Specifically, when the distance D2is less than the distance D1, this can prevent light beams emitted from the adjacent semiconductor light-emitting chips100from interfering with each other.

Although, in the second embodiment and its variations, only a flip-chip structure was described, a wire bonding structure as illustrated inFIGS. 14 and 15can also be used.

Alternatively, the light-transmissive member121having any surface form illustrated inFIGS. 8 and 9can be combined with the present embodiment.

Alternatively, the wavelength conversion member122illustrated inFIG. 10can be combined with the present embodiment.

Moreover, when an active layer106emits polarized light, the present embodiment and its variations allow the polarization characteristics to be reduced. Therefore, also when the active layer106has a nonpolar plane, such as an m-plane or an a-plane, or a semipolar plane, such as −r-plane, a (11-22) plane, or a (20-2-1) plane, as a growth surface, this embodiment and its variations can improve the luminous intensity distribution, and allow the degree of polarization of light to be reduced.

Third Embodiment

A semiconductor light-emitting device according to a third embodiment of the present disclosure will be described hereinafter with reference toFIGS. 19A and 19B. InFIGS. 19A and 19B, the same characters as those inFIGS. 4A and 4Bare used to represent equivalent components, and thus, description thereof is omitted. Here, the difference between the first and second embodiments will be described.

FIG. 19Aillustrates the configuration of the semiconductor light-emitting device according to the third embodiment when viewed in plan.FIG. 19Billustrates a cross-sectional configuration taken along the line XIXb-XIXb inFIG. 19A. The cross section taken along the line XIXb-XIXb corresponds to the plane L45. A plurality of reflective surfaces125of a reflector120are arranged such that a shape formed by the reflective surfaces125when viewed in plan is rectangular. The angle θ2 of not less than 20° and not more than 70° allows the normalized degree of polarization to be reduced to one half or less, where θ2 represents the angle between a long side of the rectangular shape formed by the reflective surfaces125and the polarization direction of light from a semiconductor light-emitting chip100. The angle θ2 of not less than 35° and not more than 55° allows the normalized degree of polarization to be reduced to one third or less.

As described in the second embodiment, when the plurality of reflective surfaces125of the reflector120are arranged such that the shape formed by the reflective surfaces125when viewed in plan is quadrangular, and light is reflected off each of corners of the quadrangle formed by the reflective surfaces125, the phenomenon of rotation of the polarization direction of the reflected light (rotation of the plane of polarization) occurs. Thus, composite light of first reflected light and second reflected light is elliptically polarized, thereby reducing the degree of polarization of light. However, since the degree of the symmetry at the corner in the third embodiment is lower than that in the second embodiment, the effect of the second reflective surface125tserving as a reflective surface extending in the long side direction is more significant than that of the first reflective surface125sserving as a reflective surface extending in a short side direction. Thus, the effect of reducing the degree of polarization at each corner of the quadrangle is small, compared to that of the case where a square shape is formed by the reflective surfaces125. However, emitted light having a high light intensity and having a low degree of polarization in the plane L45is concentrated in the normal line direction, so that it becomes possible to sufficiently reduce the degree of polarization of the light in the normal line direction.

Moreover, as described in the first embodiment, each reflective surface125does not need to be linear when viewed in cross section. A plurality of lines may be combined together to form the reflective surface125, or the reflective surface125may be curved. Alternatively, a line and a curve may be combined together. In this case, when the angle between the reflective surface125and the direction of the normal to the growth surface of each of the semiconductor light-emitting chips100is defined by the arithmetic average inclination angle Δθ1, the reflective surface125can be determined such that the angle Δθ1 include an angle of not less than 20° and not more than 40°. Even when the reflective surface125having an angle Δθ1 of not less than 0° and less than 20° is formed near a portion of the reflective surface125connected to the mounting substrate101, the degree of polarization of light in the normal direction tends to be reduced.

(First Variation of Third Embodiment)

FIG. 20illustrates the plan configuration of a semiconductor light-emitting device according to a first variation of the third embodiment. As illustrated inFIG. 20, a reflector120of the semiconductor light-emitting device according to the first variation has a reflective surface125having corner portions each with a curved surface. The curvature R of the curved surface can be less than the length of each of sides of the semiconductor light-emitting chip100.

(Second Variation of Third Embodiment)

FIG. 21illustrates the plan configuration of a semiconductor light-emitting device according to a second variation of the third embodiment. As illustrated inFIG. 21, the semiconductor light-emitting device according to the second variation includes a plurality of semiconductor light-emitting chips100, four semiconductor light-emitting chips100here, arranged on a mounting substrate101in a matrix such that the directions of polarization of light from the semiconductor light-emitting chips100are identical. The distance D2can be less than the distance D1, where D1represents the distance between two of the semiconductor light-emitting chips100adjacent to each other in a direction perpendicular to the direction of polarization of the light, that is, along the c-axis when the growth surface of an active layer is an m-plane, and D2represents the distance between two of the semiconductor light-emitting chips100adjacent to each other in a direction identical with the direction of polarization of the light, that is, along the a-axis when the growth surface of the active layer is an m-plane. The distance D2can be less than the distance D1because a comparison between the luminous intensity distribution in the direction perpendicular to the direction of polarization of the light (the luminous intensity distribution in the plane L90) and the luminous intensity distribution in the direction identical with the direction of polarization of the light (the luminous intensity distribution in the plane L0) shows that in the luminous intensity distribution in the direction perpendicular to the direction of polarization of the light (the luminous intensity distribution in the plane L90), even when the azimuth angle χ is large, the light intensity is high. Specifically, when the distance D2is less than the distance D1, this can prevent light beams emitted from the adjacent semiconductor light-emitting chips100from interfering with each other.

Although, in the second embodiment and its variations, only a flip-chip structure was described, a wire bonding structure as illustrated inFIGS. 14 and 15can also be used.

A light-transmissive member121having a surface with the shape illustrated in any one ofFIGS. 8 and 9can be combined with each of this embodiment.

The wavelength conversion member122illustrated inFIG. 10can also be combined with each of this embodiment.

Furthermore, when an active layer106emits polarized light, this embodiment and its variations allow the degree of polarization of light to be reduced. Therefore, also when the active layer106has a nonpolar plane, such as an m-plane or an a-plane, or a semipolar plane, such as −r-plane, a (11-22) plane, or a (20-2-1) plane, as a growth surface, this embodiment and its variations can improve the luminous intensity distribution, and allow the degree of polarization of light to be reduced.

EXAMPLES

First Example

A semiconductor light-emitting device according to a first example will be described hereinafter with reference toFIGS. 22A-22D. The dimensions inFIGS. 22A-22Dare expressed in units of millimeters (mm). The same characters as those in the first embodiment are used to represent equivalent components. The same applies to the following examples.

First, a method for fabricating a semiconductor light-emitting chip100forming a portion of the semiconductor light-emitting device according to the first example and including an active layer having a growth surface that is an m-plane will be schematically described.

First, a 2-μm-thick n-type nitride semiconductor layer made of n-type GaN, an active layer having a three-period quantum well structure including a quantum well layer made of InGaN and a barrier layer made of GaN, and a 0.5-μm-thick p-type nitride semiconductor layer made of p-type GaN were formed on a wafer-level n-type GaN substrate having an m-plane as its principal surface by, e.g., MOCVD.

A Ti/Al layer was formed as an n-side electrode, and an Ag layer was formed as a p-side electrode. Thereafter, the back surface of the n-type GaN substrate was polished to reduce the thickness of the n-type GaN substrate to a thickness of 100 μm.

Subsequently, grooves having a depth of about several tens of μm from the surface of the wafer were formed in the wafer including light-emitting structures along the c-axis, i.e., the [0001] direction, and the a-axis, i.e., the [11-20] direction, with laser beams. Thereafter, the wafer was broken into semiconductor light-emitting chips100made of an m-plane GaN-based semiconductor and having sides each having a length of 450 μm.

Subsequently, one of the fabricated semiconductor light-emitting chips100was mounted on a mounting substrate101made of AlN by flip-chip mounting. The thickness of the mounting substrate101made of AlN is about 0.7 mm. Interconnect electrodes102each having a thickness of about 4 μm and made of silver (Ag) were formed on the mounting substrate101.

As such, a semiconductor light-emitting device including the active layer having a growth surface that is an m-plane was fabricated. In this state, no reflector120is provided. The measured wavelength of light emitted from the semiconductor light-emitting device at an operating current of 10 mA was 445 nm. The polarization direction of the emitted light is along the a-axis, and the degree of polarization of light measured along the m-axis corresponding to the normal line direction was 0.68. Such a semiconductor light-emitting device that does not include a reflector120corresponds to a semiconductor light-emitting device according to a first comparative example.

Separately from the semiconductor light-emitting chip100, four circular reflectors C1, C2, C3, and C4made of aluminum and each having a circular reflective surface125when viewed in plan was fabricated by press molding. The fabricated circular reflectors C1-C4each have a portion of the reflective surface125having a height of 100 μm from the top surface of the mounting substrate101and having an angle θ1 of 0°.

FIG. 23illustrates results of measuring the reflectivities of one of the reflective surfaces125of the circular reflectors C1-C4. In the measurement of the reflectivities, light having a wavelength within the range of wavelengths from 350 nm to 800 nm was measured using a spectrophotometer (UV-VIS) made by JASCO Corporation. In the measurement, the linear reflectivity and the diffuse reflectivity of the light were measured, and the sum of the linear reflectivity and the diffuse reflectivity was defined as the total reflectivity.FIG. 23shows that the total reflectivity of a reflective surface of the fabricated reflector120made of aluminum is greater than or equal to 73%, and the proportion of the liner reflectivity to the total reflectivity is greater than or equal to 95%. This shows that the square reflector S1is a reflector having high linear reflectivity.

As such, the circular reflectors C1-C4made of aluminum and fabricated separately from the mounting substrate101were each adhered to the mounting substrate101on which one of the semiconductor light-emitting chips100was mounted, thereby fabricating four types of semiconductor light-emitting devices according to the first example each including one of the four circular aluminum reflectors C1-C4.

Table 1 provides the range of azimuth angles χ of light reflected off a reflective surface125of each of the circular reflectors C1-C4, the angle θ1 between the reflective surface125and the normal direction, the normalized degree of polarization of the light in the normal direction, and the normalized intensity of the light in the normal direction. Table 1 also provides the properties of the semiconductor light-emitting device that does not include a reflector120according to the first comparative example. Here, the range of azimuth angles χ of light reflected off a reflective surface125of each of the circular reflectors C1-C4and the angle θ1 between the reflective surface125and the normal direction are designed values for the reflectors120. The normalized degree of polarization of the light in the normal direction, and the normalized intensity of the light in the normal direction are values obtained by measuring the actually fabricated semiconductor light-emitting devices, and are values normalized with respect to the properties of the semiconductor light-emitting device that does not include a reflector125according to the first comparative example.

The circular reflectors C1and C3are designed such that a value twice as large as the angle θ1 is included in the range of the azimuth angle χ of light reflected off the reflective surface125. That is, the circular reflectors C1and C3are designed such that light emitted from the semiconductor light-emitting chip100in a direction in which the azimuth angle χ is twice as large as θ1 is reflected off the reflective surface125in the normal line direction.

The circular reflectors C2and C4are structured such that light emitted from the semiconductor light-emitting chip100in a direction in which the azimuth angle χ is twice as large as θ1 is reflected off the portion of the reflective surface125formed near a connection portion of the reflective surface125to the mounting substrate101and having an angle θ1 of 0°. Thus, the design of the circular reflectors C2and C4results in a deviation from an optimum value.

FIGS. 24A and 24Bshow the degree of polarization and the luminous intensity distribution of a semiconductor light-emitting device provided with the circular reflector C1. The thin solid line in these figures illustrates the properties in the plane L0, the broken line therein illustrates the properties in the plane L45, and the thick solid line therein illustrates the properties in the plane L90. From the degree of polarization shown inFIG. 24A, it can be seen that when the azimuth angle χ is in the range from −20° to +20°, the degree of polarization is substantially constant, where the degree of polarization is approximately form 0.21 to 0.25, and that the degree of polarization is reduced, compared to 0.68 obtained in the case where the reflector is not provided. The luminous intensity distribution illustrated inFIG. 24Bshows that the light distribution angle in the plane L0is 39.0°, and the light distribution angle in the plane L90is 42.5°. Here, the light distribution angle is a full width at half maximum, and corresponds to the angle range within which when the light intensity in the normal direction is 100, the light intensity is 50. The light distribution angle is referred to also as the angle of beam spread or the divergence angle of light.

From the results, it can be seen that the angle range in which the degree of polarization of light can be reduced substantially corresponds to the range of the light distribution angle, and that the degree of polarization of major portions of light emitted from the semiconductor light-emitting chip100is reduced. In the plane L90and the plane L45of the semiconductor light-emitting device in which the reflector is not provided, the light intensity has characteristically high peaks when the azimuth angle χ is about ±60°. However, such high peaks are not observed in the semiconductor light-emitting device provided with the circular reference C1.

As described above, in the semiconductor light-emitting device provided with the circular reflector C1designed to reflect light emitted at an azimuth angle χ within the range from about 40° to about 80°, the degree of polarization of light can be reduced and the light distribution angle can be reduced while the asymmetry of the luminous intensity distribution is reduced.

FIGS. 25A and 25Bshow the degree of polarization and the luminous intensity distribution of a semiconductor light-emitting device provided with the circular reflector C2. The thin solid line in these figures illustrates the properties in the plane L0, the broken line therein illustrates the properties in the plane L45, and the thick solid line therein illustrates the properties in the plane L90. From the degree of polarization shown inFIG. 25A, it can be seen that the degree of polarization of light in the normal line direction is 0.31, and that the degree of polarization is reduced, compared to 0.68 obtained in the case where the reflector is not provided. Moreover, the degree of polarization shows a minimum value at an azimuth angle χ of ±15°. The luminous intensity distribution illustrated inFIG. 25Bshows that the light distribution angle in the plane L0is 37.0°, and the light distribution angle in the plane L90is 59.5°, and thus the difference between the angles is large. In the plane L90and the plane L45of the semiconductor light-emitting device in which the reflector is not provided, the light intensity has characteristically high peaks when the azimuth angle χ is about ±60°. However, such high peaks are not observed in the luminous intensity distribution of the semiconductor light-emitting device provided with the circular reference C2, and thus the degree of polarization of light is reduced.

As described above, since the design value of the reflective surface125of the circular reflector C2deviates from the optimal value, a direction in which the degree of polarization of light is minimum deviates from the normal line direction. Moreover, the difference between the angle of light distribution in the plane Loand the light distribution angle in the plane L90becomes significant.

FIGS. 26A and 26Bshow the degree of polarization and the luminous intensity distribution of a semiconductor light-emitting device provided with the circular reflector C3. The thin solid line in these figures illustrates the properties in the plane L0, the broken line therein illustrates the properties in the plane L45, and the thick solid line therein illustrates the properties in the plane L90. From the degree of polarization shown inFIG. 26A, it can be seen that when the azimuth angle χ is in the range from −10° to +10°, the degree of polarization of light is substantially constant and is 0.18, and that the degree of polarization is reduced, compared to 0.68 obtained in the case where the reflector is not provided. The luminous intensity distribution illustrated inFIG. 26Bshows that the light distribution angle in the plane L0is 22.0°, and the light distribution angle in the plane L90is 32.0°. From the results, it can be seen that the angle range in which the degree of polarization of light is reduced substantially corresponds to the range of the light distribution angle, and that the degree of polarization of major portions of light emitted from the semiconductor light-emitting chip100is reduced. In the plane L90and the plane L45of the semiconductor light-emitting device in which the reflector is not provided, the light intensity has characteristically high peaks when the azimuth angle χ is about ±60°. However, such high peaks are not observed in semiconductor light-emitting device provided with the circular reference C3.

As described above, in the circular reflector C3designed to reflect light emitted at an azimuth angle χ within the range from about 50° to about 80°, the degree of polarization of light can be reduced and the light distribution angle can be reduced while the asymmetry of the luminous intensity distribution is reduced. The effect of reducing the degree of polarization of light is more significant than that in the case of using the circular reflector C1.

FIGS. 27A and 27Bshow the degree of polarization and the luminous intensity distribution of a semiconductor light-emitting device provided with the circular reflector C4. The thin solid line in these figures illustrates the properties in the plane L0, the broken line therein illustrates the properties in the plane L45, and the thick solid line therein illustrates the properties in the plane L90. From the degree of polarization shown inFIG. 27A, it can be seen that the degree of polarization of light in the normal line direction is 0.35, and that the degree of polarization of light is reduced, compared to 0.68 obtained in the case where the reflector is not provided. Moreover, the degree of polarization of light shows a minimum value at an azimuth angle χ of ±13°. The luminous intensity distribution illustrated inFIG. 27Bshows that the light distribution angle in the plane L0is 35.2°, and the light distribution angle in the plane L90is 46.5°. Two characteristically high peaks of light intensity are observed from the luminous intensity distribution because the effect of the reflective surface125is insufficient in the plane L90. As described above, since the design value of the reflective surface125of the circular reflector C4deviates from the optimal value, a direction in which the degree of polarization of light is minimum deviates from the normal line direction. Moreover, the difference between the light distribution angle in the plane L0and the light distribution angle in the plane L90becomes significant.

The circular reflector C4designed to have a narrow range of the azimuth angle χ of light reflected off the reflective surface125and a value of the angle θ1 which deviates from the optimal value is least effective in reducing the normalized degree of polarization in the normal line direction. As can be seen from Table 1, in the configuration provided with the circular reflector C4, the normalized intensity of light in the normal line direction is a low value of 2.4. That is, the effect of concentrating light in the normal line direction of the upper surface of the semiconductor light-emitting chip100is small, and consequently, the effect of reducing the degree of polarization of light is also small.

After the circular reflector C4, the circular reflector C2designed to have the largest range of the azimuth angle χ of light reflected off the reflective surface125and an angle θ1 whose value deviates from the optimal value is second least effective in reducing the normalized degree of polarization in the normal line direction.

FIG. 28shows the normalized light intensity in the normal line direction, and the normalized degree of polarization in the normal line direction in the semiconductor light-emitting devices provided with the circular reflectors C1, C2, C3, and C4. As can be seen fromFIG. 28, the semiconductor light-emitting devices provided with the circular reflectors C2and C4in which the design value of the reflective surface125deviates from an optimal value exhibit small values of the normalized light intensity in the normal line direction. Consequently, the value of the normalized degree of polarization increases. On the other hand, the semiconductor light-emitting devices provided with the circular reflectors C1and C3in which the design value of the reflective surface125is in the range of optimal values exhibit large values of the normalized light intensity in the normal line direction, and small values of the normalized degree of polarization. It can be seen fromFIG. 28that as long as the reflective surface125is designed to increase the light intensity in the normal line direction by a factor of about five or more, the degree of polarization of light in the normal line direction can be reduced to about one half or less.

Second Example

A semiconductor light-emitting device according to a second example will be described hereinafter with reference toFIGS. 22A-22D, andFIGS. 11A and 11B.

The second example is different from the first example in that the protrusion/recess structure130as illustrated inFIGS. 11A and 11Bis formed on a light extraction surface of a semiconductor light-emitting chip100of the second example. The formed protrusion/recess structure130is composed of two-dimensionally arranged hemispherical raised portions having a radius of about 5 μm. To form the protrusion/recess structure130, a patterned resist mask was formed on a wafer-level substrate104provided with light-emitting structure, and then dry etching using a chlorine-based gas was performed. After the formation of the protrusion/recess structure130, the wafer-level substrate104was singulated into semiconductor light-emitting chips100, and one of the semiconductor light-emitting chips100was mounted on a mounting substrate101. The second example is the same as the first example except for the formation of the protrusion/recess structure130. As such, a semiconductor light-emitting device including the active layer having a growth surface that is an m-plane and the protrusion/recess structure formed on the light extraction surface was fabricated. In this state, no reflector120is provided. The measured wavelength of light emitted from the semiconductor light-emitting device at an operating current of 10 mA was 445 nm. The polarization direction is along the a-axis, and the degree of polarization of light measured along the m-axis corresponding to the normal line direction was 0.29. Such a semiconductor light-emitting device that does not include a reflector120corresponds to a semiconductor light-emitting device according to a second comparative example. The protrusion/recess structure130formed on the light extraction surface of the semiconductor light-emitting chip100scatters outgoing light, thereby reducing the degree of polarization of the light in the normal line direction compared to the first example.

Similar to the first example, the circular reflectors C1-C4made of aluminum and fabricated separately from the mounting substrate101were each adhered to the mounting substrate101on which one of the semiconductor light-emitting chips100was mounted, thereby fabricating four types of semiconductor light-emitting devices according to the second example each including one of the four circular aluminum reflectors C1-C4.

Table 2 provides the range of azimuth angles χ of light reflected off a reflective surface125of each of the circular reflectors C1-C4, the angle θ1 between the reflective surface125and the normal direction, the normalized degree of polarization of the light in the normal direction, and the normalized intensity of the light in the normal direction. Table 2 also provides the properties of the semiconductor light-emitting device that does not include a reflector120according to the second comparative example.

FIG. 29shows the normalized light intensity in the normal line direction, and the normalized degree of polarization in the normal line direction in the semiconductor light-emitting devices provided with the circular reflectors C1, C2, C3, and C4. As can be seen fromFIG. 29, the semiconductor light-emitting devices provided with the circular reflectors C2and C4in which the design value of the reflective surface125deviates from an optimal value exhibit small values of the normalized light intensity in the normal line direction. Consequently, the value of the normalized degree of polarization increases. On the other hand, the semiconductor light-emitting devices provided with the circular reflectors C1and C3in which the design value of the reflective surface125is in the range of optimal values exhibit large values of the normalized light intensity in the normal line direction, and small values of the normalized degree of polarization.

WhenFIG. 29is compared withFIG. 28, the two graphs inFIGS. 29 and 28substantially match each other. Whether or not the protrusion/recess structure130is provided on the light extraction surface of the semiconductor light-emitting chip100, the relationship between the normalized light intensity in the normal line direction and the normalized degree of polarization in the normal line direction is substantially maintained. Therefore, it can be seen that irrelevant to the state of the light extraction surface, the effect of reducing the degree of polarization of light by the circular reflectors C1-C4is maintained. It can be seen that as long as the reflective surface125is designed to increase the light intensity in the normal line direction by a factor of about five or more, the degree of polarization of light in the normal line direction can be reduced to one half or less.

Third Example

A semiconductor light-emitting device according to a third example will be described hereinafter with reference toFIGS. 22A-22D.

In the semiconductor light-emitting device according to the third example, a growth surface of an active layer of a semiconductor light-emitting chip100is a semipolar (20-2-1) plane. A wafer-level n-type GaN substrate having a (20-2-1) plane as its principal surface was used as a substrate of the semiconductor light-emitting chip100. In a process of singulating the substrate into semiconductor light-emitting chips100, grooves having a depth of about several tens of μm from the surface of the wafer were formed in the wafer, which is provided with a light-emitting structure, along the [10-14] direction and the [1-210] direction with laser beams. Thereafter, the wafer was broken into semiconductor light-emitting chips100having sides each having a length of 450 μm. Other processes are similar to those in the first example. As such, a semiconductor light-emitting chip100including an active layer having a growth surface that is a semipolar (20-2-1) plane was fabricated. In this state, no reflector120is provided. The measured wavelength of light emitted from the semiconductor light-emitting device at an operating current of 10 mA was 441 nm. The polarization direction of the emitted light is along the [1-210] direction, and the degree of polarization of light measured along the [20-2-1] direction corresponding to the normal line direction was 0.65, which corresponds to a value obtained in a third comparative example in which a reflector120is not provided.

Similar to the first example, the circular reflectors C1-C4made of aluminum and fabricated separately from the mounting substrate101were each adhered to the mounting substrate101on which one of the semiconductor light-emitting chips100was mounted, thereby fabricating four types of semiconductor light-emitting devices according to the third example each including one of the four circular aluminum reflectors C1-C4.

Table 3 provides the range of azimuth angles χ of light reflected off a reflective surface125of each of the circular reflectors C1-C4, the angle θ1 between the reflective surface125and the normal direction, the normalized degree of polarization of the light in the normal direction, and the normalized intensity of the light in the normal direction. Table 3 also provides the properties of the semiconductor light-emitting device that does not include a reflector120according to the third comparative example.

FIG. 30shows the normalized light intensity in the normal line direction, and the normalized degree of polarization in the normal line direction in the semiconductor light-emitting devices provided with the circular reflectors C1, C2, C3, and C4. As can be seen fromFIG. 30, the semiconductor light-emitting devices provided with the circular reflectors C2and C4in which the design value of the reflective surface125deviates from an optimal value exhibit small values of the normalized light intensity in the normal line direction. Consequently, the value of the normalized degree of polarization increases. On the other hand, the semiconductor light-emitting devices provided with the circular reflectors C1and C3in which the design value of the reflective surface125is in the range of optimal values exhibit large values of the normalized light intensity in the normal line direction, and small values of the normalized degree of polarization.

WhenFIG. 28andFIG. 30are compared with each other, it can be seen that the two graphs match each other in the tendency that the normalized degree of polarization in the normal line direction decreases as the normalized light intensity in the normal line direction increases. That is, it is shown that the degree of polarization of light of the semiconductor light-emitting chip configured to emit polarized light can be reduced by the circular reflectors C1-C4. It can be seen that as long as the reflective surface125is designed to increase the light intensity in the normal line direction by a factor of about six or more, the degree of polarization of light in the normal line direction can be reduced to one half or less.

Fourth Example

A semiconductor light-emitting device according to a fourth example will be described hereinafter with reference toFIG. 31. The dimensions inFIG. 31are expressed in units of millimeters (mm). As illustrated inFIG. 31, a semiconductor light-emitting chip100including an active layer having an m-plane as a growth surface was formed in a method similar to that in the first example, and the formed semiconductor light-emitting chip100was mounted on a mounting substrate101. Here, a protrusion/recess structure was not formed on a light extraction surface of the semiconductor light-emitting chip100. In this state, the measured wavelength of light emitted from the semiconductor light-emitting device at an operating current of 10 mA was 445 nm. The polarization direction of the emitted light is along the a-axis, and the degree of polarization of light measured along the m-axis corresponding to the normal line direction was 0.68.

An aluminum reflector S1was formed by press molding separately from the semiconductor light-emitting chip100, where the aluminum reflector S1includes four reflective surfaces125arranged such that a shape formed by the four reflective surfaces125when viewed in plan is square. The azimuth angle χ of light reflected off each reflective surface125of the square reflector S1was in the range from 42.5° to 78.7°. The angle θ1 between each reflective surface125and the normal line direction was 28.6°. The cross-sectional structure of the reflective surface125of the square reflector S1was similar to that of the circular reflector C1.

The square reflector S1made of aluminum and fabricated separately from a mounting substrate101was bonded onto the mounting substrate101provided with the semiconductor light-emitting chip100. A plurality of semiconductor light-emitting devices in which the angles θ2 are 0°, 6°, 8°, 12°, 13°, 18°, 25°, 30°, 40°, and 45° were fabricated, where θ2 represents an angle between the polarization direction of light from the semiconductor light-emitting chip100and a side of the square formed by the reflective surfaces125when viewed in plan.

Here, when the reflective surfaces125are arranged such that the shape formed by the reflective surfaces125when viewed in plan is square, the square has high symmetry when viewed in plan; therefore, when the angle θ2 is greater than 45°, the properties of such a semiconductor light-emitting device are equivalent to those obtained when the angle θ2 is equal to the angle θ2 subtracted from 90°. For this reason, the properties of semiconductor light-emitting devices in which the angles θ2 are within the range from 0° to 45° merely needs to be examined.

FIGS. 32A and 32Billustrate the degree of polarization of light from and the luminous intensity distribution of a semiconductor light-emitting device including a reflector S1in which the angle between the direction of polarization of polarized light and a side of the square formed by reflective surfaces125is set at 0°. The thin solid line in these figures illustrates the properties in the plane L0, the broken line therein illustrates the properties in the plane L45, and the thick solid line therein illustrates the properties in the plane L90. As illustrated inFIG. 32A, the degree of polarization of light in the normal direction (χ=0°) is 0.53, and the degree of polarization of light in the normal direction is kept higher than when a circular reflector is used. The luminous intensity distribution illustrated inFIG. 32Bshows that the light distribution angle is 73.0° in the plane L0, and is 69.1° in the plane L90.

FIGS. 33A and 33Billustrate the degree of polarization of light from and the luminous intensity distribution of a semiconductor light-emitting device including a reflector S1in which the angle θ2 is set at 45°. The thin solid line in these figures illustrates the properties in the plane L0, the broken line therein illustrates the properties in the plane L45, and the thick solid line therein illustrates the properties in the plane L90. As illustrated inFIG. 33A, the degree of polarization of light in the normal direction (χ=0°) is 0.07, and the degree of polarization of light in the normal direction is much lower than when the angle θ2 is 0°. Furthermore, the degree of polarization of light in the normal direction is lower than when a circular reflector is used. The luminous intensity distribution illustrated inFIG. 33Bshows that the light distribution angle is 70.6° in the plane L0, and is 71.4° in plane L90.

FIG. 34illustrates the relationship between the angle θ2 and the degree of polarization of light in the normal direction. The broken line in this figure illustrates 0.68, i.e., the degree of polarization of light from a semiconductor light-emitting device that does not include a reflector according to a first comparative example in the normal direction. When the angle θ2 is greater than 10°, the degree of polarization of light in the normal direction sharply decreases.

FIG. 35illustrates the relationship between the angle θ2 and the normalized degree of polarization of light in the normal direction. Here, the normalized degree of polarization of light is a value normalized by the degree of polarization of light in the normal direction where the angle θ2 is 0°.FIG. 35shows that the angle θ2 of not less than 17° and not more than 73° allows the normalized degree of polarization to be reduced to substantially one half or less. The angle θ2 of not less than 30° and not more than 60° allows the normalized degree of polarization to be reduced to substantially one fifth or less. The angle θ2 of 45° allows the normalized degree of polarization to be reduced to substantially one tenth.

Fifth Example

A semiconductor light-emitting device according to a fifth example will be described below. In a semiconductor light-emitting device having a configuration similar to that of the second example, a protrusion/recess structure130including two-dimensionally arranged hemispherical raised portions having a radius of about 5 μm was formed on a light extraction surface of a semiconductor light-emitting chip100including an active layer having an m-plane as a growth surface.

In this state, the measured wavelength of light emitted from the semiconductor light-emitting device at an operating current of 10 mA was 445 nm. The polarization direction of the emitted light is along the a-axis, and the degree of polarization of light measured along the m-axis corresponding to the normal line direction was 0.29.

A square reflector S1having a configuration similar to that of the fourth example was bonded onto a mounting substrate101provided with the semiconductor light-emitting chip100. The azimuth angle χ of light reflected off each reflective surface125of the square reflector S1is in the range from 42.5° to 78.7°. Moreover, the angle θ1 between each reflective surface125and the normal line direction is 28.6°. A plurality of semiconductor light-emitting devices in which the angles θ2 are 0°, 9°, 12°, 15°, 16°, 21°, 30°, 41°, and 45° were fabricated, where θ2represents an angle between the polarization direction of light from the semiconductor light-emitting chip100and a side of the square formed by the reflective surfaces125when viewed in plan.

Here, when the plurality of reflective surfaces125are arranged such that a shape formed by the reflective surfaces125when viewed in plan is square, the square has high symmetry when viewed in plan. For this reason, the properties of semiconductor light-emitting devices in which the angles θ2are within the range from 0° to 45° merely needs to be examined.

FIG. 36illustrates the relationship between the angle θ2 and the degree of polarization of light in the normal line direction. The broken line in this figure illustrates 0.30, i.e., the degree of polarization of light in the normal line direction from the semiconductor light-emitting device that does not include a reflector according to the second comparative example. WhenFIG. 36is compared withFIG. 34, it can be seen that providing the protrusion/recess structure130on the light extraction surface can reduce the degree of polarization of light as a whole.

FIG. 37shows the relationship between the angle θ2 and the normalized degree of polarization in the normal line direction. Here, the normalized degree of polarization is obtained by normalization using the degree of polarization of light in the normal line direction where the angle θ2 is 0°. WhenFIG. 37is compared withFIG. 35, the two graphs substantially match each other. Whether or not the protrusion/recess structure130is provided on the light extraction surface of the semiconductor light-emitting chip100, the relationship between the angle θ2 and the normalized degree of polarization is substantially maintained. Therefore, it can be seen that irrelevant to the state of the light extraction surface, the effect of reducing the degree of polarization of light by the square reflector is maintained.

FIG. 37shows that the angle θ2 of not less than 17° and not more than 73° allows the normalized degree of polarization to be reduced to substantially one half or less. The angle θ2 of not less than 30° and not more than 60° allows the normalized degree of polarization to be reduced to one fifth or less. The angle θ2 of 45° allows the normalized degree of polarization to be reduced to substantially one tenth.

Sixth Example

A semiconductor light-emitting device according to a sixth example will be described below. In the sixth example, a semiconductor light-emitting chip100including an active layer having a semipolar (20-2-1) plane as a growth surface was formed in a manner similar to that of the third example, and mounted on a mounting substrate101. In this state, the measured wavelength of light emitted from the semiconductor light-emitting device at an operating current of 10 mA was 441 nm. The polarization direction of the emitted light is along the [1-210] direction, and the degree of polarization of light measured along the [20-2-1] direction corresponding to the normal line direction was 0.65.

A square reflector S1having a configuration similar to that of the fourth example was bonded onto a mounting substrate101provided with the semiconductor light-emitting chip100. The azimuth angle χ of light reflected off each reflective surface125of the square reflector S1is in the range from 42.5° to 78.7°. Moreover, the angle θ1 between each reflective surface125and the normal line direction is 28.6°. A plurality of semiconductor light-emitting devices in which the angles θ2 are 0°, 9°, 12°, 15°, 16°, 21°, 30°, 41°, and 45° were fabricated, where θ2 represents an angle between the polarization direction of light from the semiconductor light-emitting chip100and a side of the square formed by the reflective surfaces125when viewed in plan.

Here, when the plurality of reflective surfaces125are arranged such that a shape formed by the reflective surfaces125when viewed in plan is square, the square has high symmetry when viewed in plan. For this reason, the properties of semiconductor light-emitting devices in which the angles θ2 are within the range from 0° to 45° merely needs to be examined.

FIG. 38illustrates the relationship between the angle θ2 and the degree of polarization of light in the normal line direction. The broken line in this figure illustrates 0.65, i.e., the degree of polarization of light in the normal line direction from the semiconductor light-emitting device that does not include a reflector according to the third comparative example.

FIG. 39illustrates the relationship between the angle θ2 and the normalized degree of polarization of light in the normal line direction. Here, the normalized degree of polarization of light is a value obtained by normalizing the degree of polarization of light relative to the degree of polarization of light in the normal line direction from a semiconductor light-emitting device in which the angle θ2 is 0°. WhenFIG. 39is compared withFIGS. 35 and 37, these three graphs have substantially the same shape. Thus, it is shown that the semiconductor light-emitting devices according to the fourth through sixth examples, i.e., according to the second embodiment can reduce the degree of polarization of light irrelevant to the direction of the growth surface of the active layer.

FIG. 39shows that the angle θ2 of not less than 15° and not more than 75° allows the normalized degree of polarization to be reduced to one half or less. The angle θ2 of not less than 20° and not more than 80° allows the normalized degree of polarization to be reduced to one fifth or less. The angle θ2 of not less than 25° and not more than 65° allows the normalized degree of polarization to be reduced to one tenth.

Seventh Example

A semiconductor light-emitting device according to a seventh example will be described hereinafter with reference toFIG. 40. As illustrated inFIG. 40, a semiconductor light-emitting chip100including an active layer having an m-plane as a growth surface was fabricated in a manner similar to that in the first example, and was mounted on a mounting substrate101. A protrusion/recess structure was not formed on the light extraction surface of the semiconductor light-emitting chip100. In this state, the measured wavelength of light emitted from the semiconductor light-emitting device at an operating current of 10 mA was 445 nm. The direction of polarization of the emitted light is along the a-axis, and the measured degree of polarization of light emitted along the m-axis corresponding to the normal direction was 0.68.

Similarly to the first example, a rectangular reflector S2made of aluminum and having a plurality of reflective surfaces125arranged such that a shape formed by the reflective surfaces when viewed in plan is rectangle was fabricated by press molding. The azimuth angle χ of light reflected off reflective surfaces125acorresponding to the long sides of the rectangle among the reflective surfaces125of the rectangular reflector S2is within the range from 42.5° to 78.7°, and the azimuth angle χ of light reflected off reflective surfaces125bcorresponding to the short sides of the rectangle is within the angle range from 57.1° to 84.8°. The angle θ1 between each of the reflective surfaces125aand125band the normal line direction is 28.6°. The rectangular reflector S2was bonded onto a mounting substrate101on which the semiconductor light-emitting chip100was previously mounted. A plurality of semiconductor light-emitting devices in which the angles θ2 are 0°, 10°, 28°, 30°, 34°, 45°, 49°, 52°, 60°, 68°, 79°, 84°, and 90° were fabricated, where θ2 represents an angle between the polarization direction of light from the semiconductor light-emitting chip100and each of the long sides of the rectangle formed by the reflective surfaces125when viewed in plan.

FIGS. 41A and 41Billustrate the degree of polarization of light from a semiconductor light-emitting device including a rectangular reflector S2in which the angle θ2 is set at 0°, and the luminous intensity distribution of the semiconductor light-emitting device, respectively. The thin solid line in each of these figures illustrates the corresponding property in the plane L0, the broken line therein illustrates the corresponding property in the plane L45, and the thick solid line therein illustrates the corresponding property in the plane L90. As illustrated inFIG. 41A, the degree of polarization of light in the normal line direction (χ=0°) is 0.50, and the degree of polarization of light in the normal line direction is kept higher than when any one of the circular reflectors is used.

FIGS. 42A and 42Billustrate the degree of polarization of light from a semiconductor light-emitting device including a rectangular reflector S2in which the angle θ2 is set at 45°, and the luminous intensity distribution of the semiconductor light-emitting device, respectively. The thin solid line in each of these figures illustrates the corresponding property in the plane L0, the broken line therein illustrates the corresponding property in the plane L45, and the thick solid line therein illustrates the corresponding property in the plane L90. As illustrated inFIG. 42A, the degree of polarization of light in the normal line direction (χ=0°) is 0.16, which is much lower than when the angle θ2 is 0°. Furthermore, the degree of polarization of light in the normal line direction is lower than when any one of the circular reflectors is used.

FIGS. 43A and 43Billustrate the degree of polarization of light from a semiconductor light-emitting device including a rectangular reflector S2in which the angle θ2 is set at 90°, and the luminous intensity distribution of the semiconductor light-emitting device, respectively. The thin solid line in each of these figures illustrates the corresponding property in the plane L0, the broken line therein illustrates the corresponding property in the plane L45, and the thick solid line therein illustrates the corresponding property in the plane L90. As illustrated inFIG. 43A, the degree of polarization of light in the normal line direction (χ=0°) is 0.44, and the degree of polarization of light in the normal line direction is kept higher than when any one of the circular reflectors is used.

FIG. 44illustrates the relationship between the angle θ2 and the degree of polarization of light in the normal line direction. The broken line in this figure illustrates 0.68, i.e., the degree of polarization of light in the normal line direction from the semiconductor light-emitting device that does not include a reflector according to the first comparative example. When the angle θ2 is 45°, the degree of polarization of light is lowest. Unlike the square reflector S1according to the fourth example, the rectangular reflector S2has low symmetry when viewed in plan. Thus, the degree of polarization of light varies between when the angle θ2 is 0° and when the angle θ2 is 90°. When the angle θ2 is 0°, i.e., when the angle between the polarization direction of light from the semiconductor light-emitting chip100and the long side of the rectangle formed by the reflective surfaces125is 0°, the degree of polarization of light is kept higher than when the angle θ2 is 90°.

FIG. 45illustrates the relationship between the angle θ2 and the normalized degree of polarization of light in the normal line direction. Here, the normalized degree of polarization of light is a value obtained by normalizing the degree of polarization of light relative to the degree of polarization of light in the normal line direction from a semiconductor light-emitting device in which the angle θ2 is 0°.FIG. 45shows that when the angle θ2 is not less than 20° and not more than 70°, the normalized degree of polarization of light can be reduced to one half or less. Furthermore, when the angle θ2 is not less than 35° and not more than 55°, the normalized degree of polarization of light can be reduced to one third or less.

First Comparative Example

The semiconductor light-emitting device according to the first comparative example will be described hereinafter with reference toFIGS. 46A and 46B.

As illustrated inFIGS. 46A and 46B, the semiconductor light-emitting device according to the first comparative example has a configuration in which a semiconductor light-emitting chip100including an active layer having an m-plane as a growth surface is provided but a reflector120is not provided. A protrusion/recess structure is not formed on a light extraction surface of the semiconductor light-emitting chip100.

A semiconductor light-emitting chip100including an active layer having a growth surface that is an m-plane was fabricated in a manner similar to that in the first example, and was mounted on a mounting substrate101. In this state, the measured wavelength of light emitted from the semiconductor light-emitting device at an operating current of 10 mA was 445 nm. The degree of polarization of light emitted along the normal line direction was 0.68.

FIGS. 47A and 47Billustrate the degree of polarization of light from the semiconductor light-emitting device according to the first comparative example, and the luminous intensity distribution of the semiconductor light-emitting device, respectively. The thin solid line in each of these figures illustrates the corresponding property in the plane L0, the broken line therein illustrates the corresponding property in the plane L45, and the thick solid line therein illustrates the corresponding property in the plane L90.

First, also when the azimuth angle χ is within the range from −80° to +80°, the degree of polarization of light in the plane L90is kept high as illustrated inFIG. 47A. When the azimuth angle χ is 0°, the degree of polarization of light in the plane L0is highest, and with increasing absolute value of the azimuth angle χ, the degree of polarization of light in the plane L0gently decreases. The degree of polarization of light in the plane L45is similar to that in the plane L0in that when the azimuth angle χ is 0°, the degree of polarization of light is highest; however, with increasing absolute value of the azimuth angle χ, the degree of polarization of light in the plane L45significantly decreases. Specifically, when the azimuth angle χ is not less than 40°, the degree of polarization of light is reduced to one half or less of the degree of polarization of light obtained when the azimuth angle χ is 0°. Furthermore, when the azimuth angle χ is not less than 50°, the degree of polarization of light is reduced to one third or less of the degree of polarization of light obtained when the azimuth angle χ is 0°. As such, the degree of polarization of light from a semiconductor light-emitting chip emitting polarized light varies among the planes L0, L45, and L90.

In contrast, the luminous intensity distribution in the plane L45is similar to that in the plane L90as illustrated inFIG. 47B, and when the azimuth angle χ is about ±60°, both of the luminous intensity distributions characteristically have a peak. When the azimuth angle χ is within the range from 10° to 80°, the light intensity is higher than that obtained when the azimuth angle χ is equal to 0°, i.e., that in the normal line direction. The luminous intensity distribution characteristic in the plane L0has high light intensities when the azimuth angle χ is within the range from −30° to +30°, and the light intensity monotonously decreases when the absolute value of the azimuth angle χ is greater than 30. As such, the luminous intensity distribution of a semiconductor light-emitting chip100emitting polarized light in the plane L0is different from the luminous intensity distribution in each of the planes L45and L90.

Second Comparative Example

The semiconductor light-emitting device according to the second comparative example will be described below.

The semiconductor light-emitting device according to the second comparative example includes a protrusion/recess structure provided on a light extraction surface of the semiconductor light-emitting chip100of the semiconductor light-emitting device without the reflector illustrated inFIGS. 46A and 46B. The protrusion/recess structure includes two-dimensionally arranged hemispheric raised portions having a radius of about 5 μm. Here, the protrusion/recess structure is not illustrated in the figure.

A semiconductor light-emitting chip100including an active layer having a growth surface that is an m-plane was fabricated in a manner similar to that in the second example, and was mounted on a mounting substrate101. In this state, the measured wavelength of light emitted from the semiconductor light-emitting device at an operating current of 10 mA was 445 nm. The degree of polarization of light emitted along the normal line direction was 0.42.

FIGS. 48A and 48Billustrate the degree of polarization of light from the semiconductor light-emitting device according to the second comparative example, and the luminous intensity distribution of the semiconductor light-emitting device, respectively. The thin solid line in each of these figures illustrates the corresponding property in the plane L0, the broken line therein illustrates the corresponding property in the plane L45, and the thick solid line therein illustrates the corresponding property in the plane L90.

First, also when the azimuth angle χ is within the range from −80° to +80°, the degree of polarization of light in the plane L90is kept substantially constant as illustrated inFIG. 48A. When the azimuth angle χ is 0°, the degree of polarization of light in the plane L0is highest, and with increasing absolute value of the azimuth angle χ, the degree of polarization of light in the plane L0gently decreases. The degree of polarization of light in the plane L45is similar to that in the plane L0in that when the azimuth angle χ is 0°, the degree of polarization of light is highest; however, with increasing absolute value of the azimuth angle χ, the degree of polarization of light in the plane L45significantly decreases. Specifically, when the azimuth angle χ is not less than 45°, the degree of polarization of light is reduced to substantially one half or less of the degree of polarization of light obtained when the azimuth angle χ is 0°. Furthermore, when the azimuth angle χ is not less than 50°, the degree of polarization of light is reduced to substantially one third or less of the degree of polarization of light obtained when the azimuth angle χ is 0°. As such, the degree of polarization of light from a semiconductor light-emitting chip emitting polarized light varies among the planes L0, L45, and L90.

In contrast, the luminous intensity distribution in the plane L45is similar to that in the plane L90as illustrated inFIG. 48B, and when the azimuth angle χ is about ±60°, both of the luminous intensity distributions characteristically have a peak. When the azimuth angle χ is within the range from 10° to 80°, the light intensity is higher than that obtained when the azimuth angle χ is equal to 0°, i.e., that in the normal line direction. The luminous intensity distribution characteristic in the plane L0has high light intensities when the azimuth angle χ is within the range from −30° to +30°, and the light intensity monotonously decreases when the absolute value of the azimuth angle χ is greater than 30. As such, the luminous intensity distribution of a semiconductor light-emitting chip emitting polarized light in the plane L0is different from the luminous intensity distribution in each of the planes L45and L90.

Third Comparative Example

The semiconductor light-emitting device according to the third comparative example will be described below.

The semiconductor light-emitting device according to the third comparative example is a semiconductor light-emitting device which includes an active layer having a semipolar (20-2-1) plane as a growth surface and in which a reflector is not provided. Note that in the present comparative example, a protrusion/recess structure is not provided on a light extraction surface of the semiconductor light-emitting chip100.

A semiconductor light-emitting chip100including an active layer having a growth surface that is a (20-2-1) plane was fabricated in a manner similar to that in the third example, and was mounted on a mounting substrate101. This provides a semiconductor light-emitting device having a configuration similar to that of the semiconductor light-emitting device illustrated inFIGS. 46A and 46B. In this state, the measured wavelength of light emitted from the semiconductor light-emitting device at an operating current of 10 mA was 441 nm. The degree of polarization of light emitted along the normal line direction was 0.68.

FIGS. 49A and 49Billustrate the degree of polarization of light from the semiconductor light-emitting device according to the third comparative example, and the luminous intensity distribution of the semiconductor light-emitting device, respectively. The thin solid line in each of these figures illustrates the corresponding property in the plane L0, the broken line therein illustrates the corresponding property in the plane L45, and the thick solid line therein illustrates the corresponding property in the plane L90.

First, also when the azimuth angle χ is within the range from −80° to +80°, the degree of polarization of light in the plane L90is kept high as illustrated inFIG. 49A. When the azimuth angle χ is 0°, the degree of polarization of light in the plane L0is highest, and with increasing absolute value of the azimuth angle χ, the degree of polarization of light in the plane L0gently decreases. The degree of polarization of light in the plane L45is similar to that in the plane L0in that when the azimuth angle χ is 0°, the degree of polarization of light is highest; however, with increasing absolute value of the azimuth angle χ, the degree of polarization of light in the plane L45significantly decreases. Specifically, when the azimuth angle χ is not less than 40°, the degree of polarization of light is reduced to substantially one half or less of the degree of polarization of light obtained when the azimuth angle χ is 0°. Furthermore, when the azimuth angle χ is not less than 60°, the degree of polarization of light is reduced to one third or less of the degree of polarization of light obtained when the azimuth angle χ is 0°. As such, the degree of polarization of light from a semiconductor light-emitting chip emitting polarized light varies among the planes L0, L45, and L90.

In contrast, the luminous intensity distribution in the plane L45is similar to that in the plane L90as illustrated inFIG. 49B, and when the azimuth angle χ is about ±60°, both of the luminous intensity distributions characteristically have a peak. When the azimuth angle χ is within the range from 10° to 80°, the light intensity is higher than that obtained when the azimuth angle χ is equal to 0°, i.e., that in the normal line direction. Meanwhile, when the azimuth angle χ is about ±40°, the luminous intensity distribution in the plane L0characteristically has a peak. As such, the luminous intensity distribution of a semiconductor light-emitting chip emitting polarized light in the plane L0is different from the luminous intensity distribution in each of the planes L45and L90.

Note that each embodiment and each variation described above can be accordingly combined with the configuration of another one of the embodiments or the variations thereof. Although in the embodiments and the variations described above, specific shapes of the reflector in plan view have been used as examples, the shape of the reflector is not limited to those described above. For example, the reflector may have another polygonal shape, or a shape other than a polygonal shape in plan view. The shape of the reflective surface in plan view is not limited to those described in the embodiments and the variations, but the reflective surface may have another polygonal shape, or a shape other than a polygonal shape.

A semiconductor light-emitting device according to an aspect of the present disclosure is applicable to, for example, lighting equipment, a headlamp of a vehicle, or a spot lamp.