Semiconductor light emitting device

According to one embodiment, a semiconductor light emitting device includes: a stacked structural body, a first electrode; and a second electrode. The stacked structural body includes a first semiconductor layer of n-type, a second semiconductor layer of p-type, and a light emitting portion provided therebetween. The first electrode includes a first contact electrode portion. The second electrode includes a second contact electrode portion and a p-side pad electrode. A sheet resistance of the second contact electrode portion is lower than a sheet resistance of the first semiconductor layer. The p-side pad electrode is provided farther inward than a circumscribed rectangle of the first contact electrode portion, and the first contact electrode portion is provided farther outward than a circumscribed rectangle of the p-side pad electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-175650, filed on Aug. 4, 2010 and the prior Japanese Patent Application No. 2011-014116, filed on Jan. 26, 2011; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor light emitting device.

BACKGROUND

Utilizing the wide band gap characteristic of group III-V nitride compound semiconductors, group III-V nitride compound semiconductors have been applied to high luminance Light Emitting Diodes (LEDs) emitting from purple to blue or green light and Laser Diodes (LDs) emitting from violet to blue light. However, there is still room for improvement in the uniformization of current density distribution and light extraction efficiency.

DETAILED DESCRIPTION

In general, according to one embodiment, a semiconductor light emitting device includes: a stacked structural body, a first electrode; and a second electrode. The stacked structural body includes a first semiconductor layer of n-type, a second semiconductor layer of p-type, and a light emitting portion provided therebetween. a part of the first semiconductor layer is exposed when viewed in a first direction from the second semiconductor layer to the first semiconductor layer. The first electrode includes a first contact electrode portion. The second electrode includes a second contact electrode portion and a p-side pad electrode. A sheet resistance of the second contact electrode portion is lower than a sheet resistance of the first semiconductor layer. The p-side pad electrode is provided farther inward than a circumscribed rectangle of the first contact electrode portion, and the first contact electrode portion is provided farther outward than a circumscribed rectangle of the p-side pad electrode.

Exemplary embodiments of the invention will now be described in detail with reference to the drawings.

The drawings are schematic or conceptual; and the relationships between the thickness and width of portions, the proportions of sizes among portions, etc., are not necessarily the same as the actual values thereof. Further, the dimensions and proportions may be illustrated differently among drawings, even for identical portions.

In the specification and drawings of the application, components similar to those described in regard to a drawing thereinabove are marked with like reference numerals, and a detailed description is omitted as appropriate.

FIG. 1is a schematic plan view illustrating a semiconductor light emitting device according to a first embodiment.

FIG. 2is a schematic cross-sectional view taken along the line A-A′ illustrated inFIG. 1.

As illustrated inFIG. 2, a semiconductor light emitting device110according to the first embodiment includes a stacked structural body70, a first electrode40, and a second electrode50. The stacked structural body70includes a first semiconductor layer10of a first conductivity type, a second semiconductor layer20of a second conductivity type, and a light emitting portion30provided between the first semiconductor layer10and the second semiconductor layer20.

In this embodiment, a first conductivity type is n-type, and a second conductivity type is p-type.

The first electrode40includes a first contact electrode portion41in contact with a face10aof the first semiconductor layer10exposed by selectively removing the second semiconductor layer20and the light emitting portion30of a first major surface70aon a second semiconductor layer20side of the stacked structural body70. In other words, a part of the first semiconductor layer10is exposed when viewed in a first direction from the second semiconductor layer20to the first semiconductor layer10. The second electrode50includes a second contact electrode portion51that has translucency and is in contact with the second semiconductor layer20

A sheet resistance Rt of the second contact electrode portion51is less than a sheet resistance of the first semiconductor layer10(in this embodiment, a sheet resistance Rn of the hereinafter described n-type contact layer12)

Here, the sheet resistance Rt is a sheet resistance of a portion of the second contact electrode portion51having a homogenous thickness with the exception of a portion T where the second semiconductor layer20and the light emitting portion30have been selectively removed.

Additionally, the sheet resistance Rn is a sheet resistance of a portion of the first semiconductor layer10having a homogenous thickness (the n-type contact layer12) with the exception of the portion T described above.

Sheet resistance is measured according to, for example, the method stipulated in Japanese Industrial Standard (JIS) C2525.

Note that in the semiconductor light emitting device110according to this embodiment, a relationship between a resistance of the second contact electrode portion51and a resistance of the first semiconductor layer10is defined by sheet resistance, but can also be defined by volume resistivity. In other words, in the semiconductor light emitting device110according to this embodiment, a value of a volume resistivity divided by a thickness of the second contact electrode portion51is less than a value of a volume resistivity divided by a thickness of the first semiconductor layer10.

In such a semiconductor light emitting device110it is possible to use an electrode structure that achieves the uniformization of current density distribution while suppressing the loss of light extraction efficiency.

The semiconductor light emitting device110according to this embodiment is, for example, a nitride semiconductor Light Emitting Diode (LED).

In the semiconductor light emitting device110, for example, a buffer layer2is provided on a substrate1made from, for example, a C face sapphire; and, for example, an undoped nitride semiconductor layer11and the n-type contact layer12are provided thereon. GaN is used, for example, for the n-type contact layer12. GaN is used, for example, for the undoped nitride semiconductor layer11. The n-type contact layer12is included in the first semiconductor layer10. In this embodiment, for convenience, the undoped nitride semiconductor layer11is also included in the first semiconductor layer10.

A multiple stacked body35is provided on the n-type contact layer12. In the multiple stacked body35, for example, a plurality of first layers and a plurality of second layers are alternately stacked. The multiple stacked body35has, for example, a superlattice structure.

The light emitting portion30(active layer) is provided on the multiple stacked body35. The light emitting portion30has, for example, a Multiple Quantum Well (MQW) structure. Specifically, the light emitting portion30includes a structure in which a plurality of barrier layers and a plurality of well layers are repeatedly, alternately stacked. In the light emitting portion30, the groups of barrier layers sandwiching the well layers may have a Single Quantum Well (SQW) structure provided per group.

For example, a p-type AlGaN layer21, a p-type (i.e. Mg doped) GaN layer22, and a p-type contact layer23are subsequently provided on the light emitting portion30. The p-type AlGaN layer21functions as, for example, an electron overflow preventing (suppressing) layer. GaN is used, for example, for the p-type contact layer23. The p-type AlGaN layer21, the Mg doped GaN layer22, and the p-type contact layer23are included in the second semiconductor layer20. Additionally, the second contact electrode portion51that is a transparent electrode is provided on the p-type contact layer23.

Moreover, a portion of the n-type contact layer12that is the first semiconductor layer10, and the multiple stacked body35, the light emitting portion30, and the second semiconductor layer20that correspond to that portion are removed. The first contact electrode portion41is provided on the exposed face10aof the n-type contact layer12.

A stacked structure of, for example, Ti/Al/Ta/Ti/Pt is used for the first contact electrode portion41. Additionally, an n-side pad electrode42nis provided on the first contact electrode portion41. A stacked structure of, for example, Ni/Au is used for the n-side pad electrode42n. The n-side pad electrode42nmay be provided on a portion of the first contact electrode portion41or on an entirety of the surface of the first contact electrode portion41.

A p-side pad electrode52pis provided on a portion of the second contact electrode portion51. Transparency of the p-side pad electrode52pis lower than transparency of the second contact electrode portion51. A stacked structure of, for example, Ni/Au is used for the p-side pad electrode52p.

The materials described for the first contact electrode portion41, the n-side pad electrode42n, the second contact electrode portion51, and the p-side pad electrode52p, are given as examples and are not limited to this embodiment.

With an electrode arrangement such as in the semiconductor light emitting device110, the first electrode40and the second electrode50are on the same side in a “face-up” configuration. In the “face-up” semiconductor light emitting device110, containment in a package is easy. On the other hand, current density distribution in a chip is prone to becoming uneven. As such, in this embodiment, an electrode structure such as follows is used.

As illustrated inFIG. 1, in the semiconductor light emitting device110according to this embodiment, when viewed planarly from the second semiconductor layer20side of the stacked structural body70, the p-side pad electrode52pis provided farther inward than a circumscribed rectangle BR1of the first contact electrode portion41. Furthermore, the first contact electrode portion41is provided farther outward than a circumscribed rectangle BR2of the p-side pad electrode52p.

In this embodiment, “circumscribed rectangle” refers to rectangles that contact each outer periphery of the electrodes41and52p. Furthermore, “circumscribed rectangle” refers to rectangles along two orthogonal directions (in the drawing, an X direction and a Y direction: a second direction) of a planarly viewed outer periphery of the semiconductor light emitting device110.

Thereby, current flows in a radiation direction from the p-side pad electrode52ptoward the first contact electrode portion41, and, due to the current density distribution being dispersed, uniformization of the luminescence distribution is achieved.

FIG. 3is a schematic plan view illustrating lengths of opposing portions of the electrodes that face each other.

In this drawing, a rectangular first contact electrode portion41is provided so as to surround a periphery of the p-side pad electrode52p.

A first length L1illustrated in this drawing is a length of the p-side pad electrode52p, of the opposing portion facing an extending part411, along an X direction of the first contact electrode portion41.

Additionally, a second length L2illustrated in this drawing is a length of the extending part411of the first contact electrode portion41, of the opposing portion facing the p-side pad electrode52p.

In the semiconductor light emitting device110according to this embodiment, the first length L1is shorter than the second length L2.

The relationship between the first length L1and the second length L2is the same for extending parts412to414as for the first contact electrode portion41. Due to such a relationship, current flows in a radiation direction from the p-side pad electrode52ptoward the first contact electrode portion41and the dispersion of current density distribution is achieved. Thereby, in the semiconductor light emitting device110, luminescence distribution is made uniform.

Hereinafter, an example of the semiconductor light emitting device will be described.

FIG. 4is a schematic plan view illustrating a first example.

As illustrated inFIG. 4, in a semiconductor light emitting device111according to the first example, the rectangular first contact electrode portion41is provided so as to surround an entirety of the periphery along the first major surface70aof the p-side pad electrode52p.

The semiconductor light emitting device111has a removed portion T where a portion of the n-type contact layer12, and the multiple stacked body35, the light emitting portion30, and the second semiconductor layer20corresponding to that portion are rectangularly removed. The first contact electrode portion41is provided along the removed portion T, and is in contact with the n-type contact layer12at a bottom surface of the removed portion T (the face10aillustrated inFIG. 2).

A bulged portion410that is, for example, rounded is provided in at least one corner of the rectangular first contact electrode portion41. The n-side pad electrode42nis provided in the bulged portion410. A shape of the n-side pad electrode42nis, for example, circular or rectangular. If the n-side pad electrode42nis circular, a diameter can be, for example, approximately not less than 50 micrometers (μm) and not more than 100 μm. If the n-side pad electrode42nis rectangular, one side can be, for example, approximately not less than 50 μm and not more than 100 μm. A thickness of the first contact electrode portion41can be approximately not less than 100 nanometers (nm) and not more than 500 nm, and is preferably approximately 300 nm.

A size of the n-side pad electrode42nis a size that allows for connectability of bonding wire, and is less than or equal to a size of the bulged portion410of the first contact electrode portion41. The n-side pad electrode42nmay be provided on a portion of the first contact electrode portion41or may be provided on the entirety of the first contact electrode portion41.

The second contact electrode portion51that is a transparent electrode is, for example, Indium Tin Oxide (ITO). A film thickness of the second contact electrode portion51can be, for example, approximately not less than 100 nm and not more than 300 nm. In this embodiment, the sheet resistance Rt of the second contact electrode portion51is less than the sheet resistance Rn of the n-type contact layer12.

Here, in the n-type contact layer12, an amount of silicon (Si) that the layer is doped with is preferably approximately not less than 1.0×1018/cm3and not more than 1.0×1019/cm3. On the other hand, when using ITO for the second contact electrode portion51, a sheet resistance Rt of the ITO is variable depending on film forming conditions and film thickness. For example, the sheet resistance Rt is not less than 5Ω/square and not more than 12Ω/square, preferably and not more than 10Ω/square, and more preferably and not more than 8Ω/square. With the range of conditions described above, sheet resistance Rt<sheet resistance Rn is made to be satisfied.

The p-side pad electrode52pis provided on a portion of the second contact electrode portion51. A shape of the p-side pad electrode52pis, for example, circular or rectangular. In this embodiment, a circular p-side pad electrode52pis described as an example. A size of the p-side pad electrode52pis a size that allows for connectability of bonding wire.

Additionally, an extending electrode521is provided in the p-side pad electrode52pas desired. In the semiconductor light emitting device111illustrated inFIG. 4, four of the extending electrodes521are provided, extending from the p-side pad electrode52ptoward each corner of the rectangular first contact electrode portion41. Specifically, in a corner of the first contact electrode portion41, a distance from the periphery of the circular p-side pad electrode52pto an extension of the first contact electrode portion41along a normal direction is longer compared to other portions. Therefore, the extending electrodes521are provided extending from the p-side pad electrode52ptoward each corner of the first contact electrode portion41, and lengthening of the distance described above is prevented. The extending electrode521provided extending toward the corner having the bulged portion410is shorter than the other extending electrodes521. Thereby, current density distribution is balanced.

In the semiconductor light emitting device111, the p-side pad electrode52pis provided on an inner side of the rectangular first contact electrode portion41. Specifically, the p-side pad electrode52pis provided on an inner side of a circumscribed rectangle of the first contact electrode portion41when viewed planarly. Additionally, the first contact electrode portion41is provided on an outer side of a circumscribed rectangle of the p-side pad electrode52pwhen viewed planarly.

Thereby, current flows in a radiation direction from the p-side pad electrode52ptoward the first contact electrode portion41, and dispersion of the current density distribution is achieved. As a result, luminescence distribution of the semiconductor light emitting device111is made uniform.

FIG. 5is a schematic plan view illustrating a second example.

As illustrated inFIG. 5, in a semiconductor light emitting device112according to the second example, the circular first contact electrode portion41is provided so as to surround the entirety of the periphery along the first major surface70aof the p-side pad electrode52p.

The semiconductor light emitting device112has a removed portion T where a portion of the n-type contact layer12, and the multiple stacked body35, the light emitting portion30, and the second semiconductor layer20corresponding to that portion are circularly removed. The first contact electrode portion41is provided along the removed portion T, and is in contact with the n-type contact layer12at a bottom surface of the removed portion T (the face10aillustrated inFIG. 2).

A bulged portion410that is, for example, rounded is provided in at least one location of the first contact electrode portion41. The n-side pad electrode42nis provided in the bulged portion410. A shape of the n-side pad electrode42nis, for example, circular or rectangular. The n-side pad electrode42nmay be provided on a portion of the first contact electrode portion41or may be provided on the entirety of the first contact electrode portion41.

The second contact electrode portion51that is a transparent electrode is, for example, Indium Tin Oxide (ITO). The sheet resistance Rt of the second contact electrode portion51is less than the sheet resistance Rn of the n-type contact layer12.

With the exception of the bulged portion410, the p-side pad electrode52pin contact with the second contact electrode portion51is provided in a center of the circular first contact electrode portion41. A shape of the p-side pad electrode52pis circular. Specifically, the p-side pad electrode52pis provided on an inner side of the circumscribed rectangle of the first contact electrode portion41when viewed planarly. Additionally, the first contact electrode portion41is provided on an outer side of the circumscribed rectangle of the p-side pad electrode52pwhen viewed planarly.

In such a disposition of the p-side pad electrode52pand the first contact electrode portion41, a minimum distance LS between the outer periphery of the p-side pad electrode52pand the inner periphery of the first contact electrode portion41is equivalent along an entire circumference of the outer periphery of the p-side pad electrode52p.

Thereby, current flows in a radiation direction from the p-side pad electrode52ptoward the first contact electrode portion41, and dispersion of the current density distribution is achieved. In the semiconductor light emitting device112, the minimum distance LS is equivalent along the entire circumference of the outer periphery of the p-side pad electrode52p. Therefore, a uniform current density distribution from the p-side pad electrode52ptoward the first contact electrode portion41can be realized. As a result, luminescence distribution of the semiconductor light emitting device112is made uniform.

FIG. 6is a schematic plan view illustrating a third example.

As illustrated inFIG. 6, in a semiconductor light emitting device113according to the third example, the first contact electrode portion41is provided so as to surround not less than 180 degrees of the periphery along the first major surface70aof the p-side pad electrode52p. In other words, the first contact electrode portion41surrounds not less than 180 degrees of the periphery of the p-side pad electrode52palong the second direction.

In the first contact electrode portion41illustrated inFIG. 6, an extending part413extends in the X direction and an extending part414extends in the Y direction from the bulged portion410provided in a corner of the semiconductor light emitting device113. Additionally, an extending part412extends in the Y direction from an end of a side of the extending part413opposite the bulged portion410. The extending part412extends partway along a side of the semiconductor light emitting device113along the Y direction. Additionally, an extending part411extends in the X direction from an end of a side of the extending part414opposite the bulged portion410. The extending part411extends partway along a side of the semiconductor light emitting device113along the X direction.

Specifically, the first contact electrode portion41is provided so as to surround not less than 180 degrees but less than 360 degrees of a periphery along the first major surface70aof the p-side pad electrode52p.

Additionally, an extending electrode521is provided in the p-side pad electrode52pas desired. In the semiconductor light emitting device113illustrated inFIG. 6, four of the extending electrodes521are provided, extending from the p-side pad electrode52ptoward each corner of the rectangular first contact electrode portion41.

In the semiconductor light emitting device113, the p-side pad electrode52pis provided on an inner side of the circumscribed rectangle of the first contact electrode portion41when viewed planarly. Additionally, the first contact electrode portion41is provided on an outer side of the circumscribed rectangle of the p-side pad electrode52pwhen viewed planarly.

Thereby, current flows in a radiation direction from the p-side pad electrode52ptoward the first contact electrode portion41, and dispersion of the current density distribution is achieved. As a result, luminescence distribution of the semiconductor light emitting device113is made uniform.

FIG. 7is a chart showing a relationship between current and luminous efficiency of the semiconductor light emitting devices.

FIG. 8is a chart showing a relationship between current and voltage of the semiconductor light emitting devices.

FIG. 9is a chart showing a relationship between current and wall plug efficiency of the semiconductor light emitting devices.

InFIGS. 7 to 9, the relationships for the semiconductor light emitting device112and a semiconductor light emitting device190according to a comparative example are each shown. The semiconductor light emitting device190according to the comparative example has a structure in which a circular p-side pad electrode is provided on a periphery, having a first contact electrode portion41in contact with the n-type contact layer12as a center.

As illustrated inFIG. 7, in the semiconductor light emitting device112according to this embodiment, compared with the semiconductor light emitting device190according to the comparative example, luminous efficiency per current is high. Particularly, a difference in luminous efficiency is significantly displayed as the current is increased.

As illustrated inFIG. 8, in the semiconductor light emitting device112according to this embodiment, compared with the semiconductor light emitting device190according to the comparative example, voltage per the same current is low. In other words, the semiconductor light emitting device112displays lower resistance than the semiconductor light emitting device190.

As illustrated inFIG. 9, in the semiconductor light emitting device112according to this embodiment, compared with the semiconductor light emitting device190according to the comparative example, wall plug efficiency per current is high. Here, when input voltage is V, current is I, and output is Po, the wall plug efficiency WPE is expressed as WPE=Po/(I·V).

FIGS. 10A and 10BandFIGS. 11A and 11Billustrate luminous intensity at locations between the p-side and the n-side electrodes.

FIGS. 10A and 10Billustrate an example of luminous intensity of the semiconductor light emitting device112according to this embodiment andFIGS. 11A and 11Billustrate an example of luminous intensity of the semiconductor light emitting device190according to the comparative example.

BothFIG. 10AandFIG. 11Aillustrate luminescence distributions between the p-side and the n-side electrodes in light/dark shades, and bothFIG. 10BandFIG. 11Bare graphs showing luminescence distributions between the p-side and the n-side electrodes. In each ofFIG. 10AandFIG. 11A, darker shades indicate lower luminous intensities, and lighter shades indicate higher luminous intensities.

As illustrated inFIGS. 10A and 10BandFIGS. 11A and 11B, the semiconductor light emitting device112according to this embodiment, compared with the semiconductor light emitting device190according to the comparative example, achieves uniform luminous intensity.

Next, a semiconductor light emitting device according to a second embodiment will be described.

The semiconductor light emitting device according to the second embodiment is an example in which a plurality of first contact electrode portions41are provided.

Hereinafter, an example of the semiconductor light emitting device according to the second embodiment is described. In the following example, descriptions will be centered on the placement of electrodes of each semiconductor light emitting device, when viewed planarly.

FIG. 12is a schematic plan view illustrating a first example. As illustrated inFIG. 12, in a semiconductor light emitting device121illustrating a first example, a p-side pad electrode52pis provided between two first contact electrode portions41A and41B.

The two first contact electrode portions41A and41B are disposed in diagonally opposite corners of the rectangular semiconductor light emitting device121. The p-side pad electrode52pis disposed between the two first contact electrode portions41A and41B, for example, in a center of the semiconductor light emitting device121, when viewed planarly.

In the semiconductor light emitting device121, the p-side pad electrode52pis provided on an inner side of a circumscribed rectangle BR1of the two first contact electrode portions41A and41B when viewed planarly. Additionally, the two first contact electrode portions41A and41B are each provided on an outer side of a circumscribed rectangle BR2of the p-side pad electrode52pwhen viewed planarly.

Thereby, current flows from the p-side pad electrode52ptoward each of the two first contact electrode portions41A and41B, and dispersion of the current density distribution is achieved. As a result, luminescence distribution of the semiconductor light emitting device121is made uniform.

FIG. 13is a schematic plan view illustrating a second example.

As illustrated inFIG. 13, in a semiconductor light emitting device122illustrating a second example, a p-side pad electrode52pis provided between the two first contact electrode portions41A and41B.

The two first contact electrode portions41A and41B are disposed in opposite corners of the rectangular semiconductor light emitting device122. The p-side pad electrode52pis disposed between the two first contact electrode portions41A and41B, for example, in a center of the semiconductor light emitting device122, when viewed planarly.

In the semiconductor light emitting device122, two extending parts411A and414A are included in the first contact electrode portion41A. Additionally, two extending parts412B and413B are included in the first contact electrode portion41B.

The extending part411A extends in the X direction from a bulged portion410A. The extending part414A extends in the Y direction from the bulged portion410A. Additionally, the extending part412B extends in the Y direction from a bulged portion410B. The extending part413B extends in the X direction from the bulged portion410B.

In the semiconductor light emitting device122, the p-side pad electrode52pis provided on an inner side of a circumscribed rectangle BR1of the two first contact electrode portions41A and41B when viewed planarly. Additionally, the two first contact electrode portions41A and41B are each provided on an outer side of a circumscribed rectangle BR2of the p-side pad electrode52pwhen viewed planarly.

Thereby, current flows from the p-side pad electrode52ptoward each of the two first contact electrode portions41A and41B, and dispersion of the current density distribution is achieved. As a result, luminescence distribution of the semiconductor light emitting device122is made uniform.

FIG. 14is a schematic plan view illustrating a third example.

As illustrated inFIG. 14, in a semiconductor light emitting device123illustrating in the third example, a p-side pad electrode52pis provided between four first contact electrode portions41A,41B,41C, and41D.

The four first contact electrode portions41A,41B,41C, and41D are disposed in each of the four corners of the rectangular semiconductor light emitting device123. The p-side pad electrode52pis disposed between the four first contact electrode portions41A,41B,41C, and41D, for example, in a center of the semiconductor light emitting device123, when viewed planarly.

In the semiconductor light emitting device123, the p-side pad electrode52pis provided on an inner side of a circumscribed rectangle BR1of the four first contact electrode portions41A,41B,41C, and41D when viewed planarly. Additionally, the four first contact electrode portions41A,41B,41C, and41D are each provided on an outer side of a circumscribed rectangle BR2of the p-side pad electrode52pwhen viewed planarly.

Thereby, current flows from the p-side pad electrode52ptoward each of the two first contact electrode portions41A and41B, and dispersion of the current density distribution is achieved. As a result, luminescence distribution of the semiconductor light emitting device123is made uniform.

FIG. 15is a schematic plan view illustrating a fourth example.

As illustrated inFIG. 15, in a semiconductor light emitting device124illustrating in the fourth example, a p-side pad electrode52pis provided between four first contact electrode portions41A,41B,41C, and41D.

The four first contact electrode portions41A,41B,41C, and41D are disposed in each of the four corners of the rectangular semiconductor light emitting device124. The p-side pad electrode52pis disposed between the four first contact electrode portions41A,41B,41C, and41D, for example, in a center of the semiconductor light emitting device124, when viewed planarly.

In the semiconductor light emitting device124, two extending parts411A and414A are included in the first contact electrode portion41A. Additionally, two extending parts412B and413B are included in the first contact electrode portion41B. Additionally, two extending parts411C and412C are included in the first contact electrode portion41C. Additionally, two extending parts413D and414D are included in the first contact electrode portion41D.

The extending part411A extends in the X direction from a bulged portion410A. The extending part414A extends in the Y direction from the bulged portion410A. Additionally, the extending part412B extends in the Y direction from a bulged portion410B. The extending part413B extends in the X direction from the bulged portion410B. The extending part411C extends in the X direction from a bulged portion410C. The extending part412C extends in the Y direction from the bulged portion410C. Additionally, the extending part413D extends in the X direction from a bulged portion410D. The extending part414D extends in the Y direction from the bulged portion410D.

In the semiconductor light emitting device124, the p-side pad electrode52pis provided on an inner side of a circumscribed rectangle BR1of the four first contact electrode portions41A,41B,41C, and41D when viewed planarly. Additionally, the four first contact electrode portions41A,41B,41C, and41D are each provided on an outer side of a circumscribed rectangle BR2of the p-side pad electrode52pwhen viewed planarly.

Thereby, current flows from the p-side pad electrode52ptoward each of the four first contact electrode portions41A,41B,41C, and41D, and dispersion of the current density distribution is achieved. As a result, luminescence distribution of the semiconductor light emitting device124is made uniform.

In the examples described above, examples having two and four of the first contact electrode portions41are described, but three or five or more of the first contact electrode portions41may be provided.

Additionally, the shapes, when viewed planarly, of the p-side pad electrode52pand the first contact electrode portion41are not limited to the examples described above.

Next, a semiconductor light emitting device according to a third embodiment will be described.

The semiconductor light emitting device according to the third embodiment is an example in which the first conductivity type is p-type, and the second conductivity type is n-type.

FIG. 16is a schematic plan view illustrating a semiconductor light emitting device according to a third embodiment.

FIG. 17is a schematic cross-sectional view taken along the line B-B′ illustrated inFIG. 16.

As illustrated inFIG. 17, a semiconductor light emitting device130according to the third embodiment includes a stacked structural body70, a first electrode40, and a second electrode50. The stacked structural body70includes a p-type (the first conductivity type) first semiconductor layer10, an n-type (the second conductivity type) second semiconductor layer20, and a light emitting portion30provided between the first semiconductor layer10and the second semiconductor layer20.

The first electrode40includes a first contact electrode portion41in contact with a face10aof the first semiconductor layer10exposed by selectively removing the second semiconductor layer20and the light emitting portion30of a first major surface70aon a second semiconductor layer20side of the stacked structural body70. In other words, a part of the first semiconductor layer10is exposed when viewed in a first direction from the second semiconductor layer20to the first semiconductor layer10. The second electrode50includes a second contact electrode portion51that has translucency and is in contact with the second semiconductor layer20.

A sheet resistance of the second contact electrode portion51is less than a sheet resistance of the first semiconductor layer10.

A p-side pad electrode42pis provided on the first contact electrode portion41. Additionally, an n-side pad electrode52nis provided on the second contact electrode portion51.

As illustrated inFIG. 16, in the semiconductor light emitting device130according to this embodiment, when viewed planarly from the second semiconductor layer20side of the stacked structural body70, the n-side pad electrode52nis provided farther outward than a circumscribed rectangle BR1of the first contact electrode portion41. Furthermore, the first contact electrode portion41is provided farther inward than a circumscribed rectangle BR2of the n-side pad electrode52n.

Thereby, current flows in a radiation direction from the first contact electrode portion41provided with the p-side pad electrode42ptoward the n-side pad electrode52n, and, due to the current density distribution being dispersed, uniformization of the luminescence distribution is achieved.

FIGS. 18 to 20are graphs showing output against position when the p-side pad electrode that is a p-side electrode and the first contact electrode portion that is an n-side electrode are disposed symmetrically.

In these graphs, positions between the p-side and the n-side electrodes are shown on the horizontal axes and luminous intensities Po are shown on the vertical axes.

FIG. 18illustrates a case where the sheet resistance Rt of the second contact electrode portion51is less than the sheet resistance Rn of the n-type contact layer12.

In this case, because current is prone to accumulate in the n-side electrode, the luminous intensity Po increases from a position partway between the p-side and the n-side electrodes to the n-side electrode.

FIG. 19illustrates a case where the sheet resistance Rt is greater than the sheet resistance Rn.

In this case, because current is prone to accumulate in the p-side electrode, the luminous intensity Po is greatest in the vicinity of the p-side electrode, and the luminous intensity Po decreases with proximity to the n-side electrode.

FIG. 20illustrates a case where the sheet resistance Rt and the sheet resistance Rn are equivalent.

In this case, the luminous intensity Po is greatest in the vicinity of the p-side and the n-side electrodes, and the luminous intensity Po decreases with proximity to a midpoint between the p-side and the n-side electrodes.

FIGS. 21 to 23are graphs showing output against position when the first contact electrode portion that is an n-side electrode is disposed circularly around the p-side pad electrode that is a p-side electrode.

In these graphs, positions between the p-side and the n-side electrodes are shown on the horizontal axes and luminous intensities Po are shown on the vertical axes.

FIG. 21illustrates a case where the sheet resistance Rt of the second contact electrode portion51is less than the sheet resistance Rn of the n-type contact layer12.

In this case, current is prone to accumulate in the n-side electrode. However, because the n-side electrode is provided so as to surround the p-side electrode, the current flows radially from the p-side electrode toward the n-side electrode. In other words, the current is dispersed from the p-side electrode toward the n-side electrode. Therefore, because of the compounding of the accumulation of current at the n-side electrode due to the sheet resistance Rt<sheet resistance Rn relationship and the dispersion of the current from the p-side electrode to the n-side electrode, uniform luminous intensity Po is obtained from the p-side electrode to the n-side electrode.

FIG. 22illustrates a case where the sheet resistance Rt is greater than the sheet resistance Rn.

In this case, current is prone to accumulate in the p-side electrode. Moreover, the current is also dispersed from the p-side electrode to the n-side electrode. Therefore, the luminous intensity Po is greatest in the vicinity of the p-side electrode, and the luminous intensity Po decreases significantly when distanced from the p-side electrode.

FIG. 23illustrates a case where the sheet resistance Rt and the sheet resistance Rn are equivalent.

In this case, the luminous intensity Po gradually decreases from the p-side electrode to the n-side electrode.

The semiconductor light emitting device according to this embodiment displays the characteristics illustrated inFIG. 21. Specifically, because of the compounding of the luminescent characteristics of the sheet resistance Rt being less than the sheet resistance Rn and the current dispersing and flowing from the p-side electrode to the n-side electrode, a uniform luminous intensity Po is obtained.

As described above, with the semiconductor light emitting device according to this embodiment, it is possible to improve light extraction efficiency.

Note that in this specification, the term, “nitride semiconductor” includes semiconductors of all compositions wherein composition ratios of x, y, and z in the formula BxInyAlzGa1-x-y-zN fall within the respective ranges of 0≦x≦1, 0≦y≦1, 0≦z≦1, and x+y+z≦1. Furthermore, in the formula described above, “nitride semiconductor” shall also be understood to include semiconductors further including group V elements other than N (nitrogen), semiconductors further including various elements added to suppress various physical properties such as conductivity type and the like, and semiconductors further including various elements that are included unintentionally.