Patent Description:
Conventionally, as one of semiconductor lasers, there has been known a vertical cavity-type semiconductor surface emitting laser (hereinafter also simply referred to as a surface emitting lase) including a semiconductor layer that emits a light by application of voltage and multilayer reflectors opposed to one another with the semiconductor layer interposed therebetween. For example, <CIT> discloses a vertical cavity-type semiconductor laser having an n-electrode and a p-electrode each connected to an n-type semiconductor layer and a p-type semiconductor layer.

<CIT> discloses methods and structures for forming vertical-cavity light-emitting devices. An n-side or bottom-side layer may be laterally etched to form a porous semiconductor region and converted to a porous oxide. The porous oxide can provide a current-blocking and guiding layer that aids in directing bias current through an active area of the light-emitting device. Distributed Bragg reflectors may be fabricated on both sides of the active region to form a vertical-cavity surface-emitting laser. The light-emitting devices may be formed from III-nitride materials.

<CIT> discloses a surface-mount compatible vcsel array.

<CIT> discloses a micro light emission element including a compound semiconductor in which an N-side layer, a light emission layer, and a P-side layer are laminated sequentially from a side of a light emitting surface, in which an N-electrode coupled to the N-side layer and a P-electrode coupled to the P-side layer are disposed on another surface opposite to the light emitting surface. The P-electrode is disposed on the light emission layer. The N-electrode is disposed in an isolation region which is a boundary region of the micro light emission element and isolates the light emission layer from a light emission layer of another micro light emission element. A surface of the N-electrode on a side of the other surface and a surface of the P-electrode on the side of the other surface are flush with each other. The N-electrode and the P-electrode are both formed of a single interconnection layer.

<CIT> discloses a surface-emitting semiconductor laser which is provided with: a first light emitting region that outputs first light; and a second light emitting region, which is provided by being separated from the first light emitting region, and which has a phase shift section, said second light emitting region outputting second light. A far-field pattern of the first light and that of the second light are different from each other.

<CIT> discloses a reflector which includes a low refractive index layer and a high refractive index layer. The low refractive index layer has a first average refractive index and has a laminated structure in which an AlN layer and a GaN layer are alternately laminated. The high refractive index layer has a second average refractive index higher than the first average refractive index and includes an InGaN layer.

For example, an optical resonator is formed with opposed reflectors in a vertical cavity light-emitting element such as a surface emitting laser. For example, in the surface emitting laser, by application of voltage to a semiconductor layer via electrodes, a light emitted from the semiconductor layer resonates in the optical resonator to generate a laser light.

However, as an example of a problem, for example, a vertical cavity-type semiconductor laser element has luminous efficiency lower than that of a horizontal cavity-type semiconductor laser element having a resonator in an in-plane direction of a semiconductor layer including an active layer.

The present invention has been made in consideration of the above-described points and it is an object to provide a vertical cavity light-emitting element having the high luminous efficiency.

In accordance with the present invention, a vertical cavity light-emitting element as set forth in the appended claims is provided. In particular, a vertical cavity light emitting element of the present invention includes a substrate, a first multilayer reflector, a semiconductor structure layer, an electrode layer, and a second multilayer reflector. The first multilayer reflector is formed on the substrate. The semiconductor structure layer includes a first semiconductor layer, a light-emitting layer, and a second semiconductor layer. The first semiconductor layer has a first conductivity type formed on the first multilayer reflector. The light-emitting layer is formed on the first semiconductor layer. The second semiconductor layer is formed on the light-emitting layer and has a second conductivity type opposite to the first conductivity type. The electrode layer is formed on an upper surface of the semiconductor structure layer and is electrically in contact with the second semiconductor layer of the semiconductor structure layer in one region of the upper surface. The second multilayer reflector is formed to cover the one region on the electrode layer and constitutes a resonator with the first multilayer reflector. The semiconductor structure layer has one recessed structure including one or a plurality of recessed portions passing through the light-emitting from the upper surface in a region surrounding the one region.

The recessed structure is disposed to overlap with the second multilayer reflector when viewed from a direction perpendicular to an in-plane direction of the semiconductor structure layer.

The following describes embodiments in detail.

While the first, third, and fifth embodiments are embodiments of the present invention falling into the scope of the claims, the second and fourth embodiments are not falling into the scope of the claims but are useful for understanding the present invention.

While, in the following description, a description will be made using a semiconductor surface emitting laser element (a semiconductor laser) as an example, the present invention is applicable not only to a surface emitting laser but also to various kinds of vertical cavity light-emitting elements, such as a vertical cavity-type light-emitting diode.

<FIG> is a perspective view of a vertical cavity surface emitting laser (VCSEL, hereinafter also simply referred to as a surface emitting laser) <NUM> according to Embodiment <NUM>.

A substrate <NUM> is a gallium-nitride-based semiconductor substrate, for example, a GaN substrate. The substrate <NUM> is, for example, a substrate having a rectangular upper surface shape. On the substrate <NUM>, a first multilayer reflector <NUM> made of a semiconductor layer that has been grown on the substrate <NUM> is formed.

The first multilayer reflector <NUM> is a semiconductor multilayer reflector in which a low refractive-index semiconductor film having a composition of AlInN and a high refractive-index semiconductor film having a GaN composition and having a refractive index higher than that of the low refractive-index semiconductor film are alternately laminated. In other words, the first multilayer reflector <NUM> is a Distributed Bragg Reflector (DBR) made of a semiconductor material. For example, on an upper surface of the substrate <NUM>, a buffer layer having the GaN composition is disposed, and alternately forming films of the high refractive-index semiconductor film and the low refractive-index semiconductor film described above on the buffer layer forms the first multilayer reflector <NUM>.

Note that the upper surface of the substrate <NUM>, that is, the surface on which the buffer layer having the GaN composition is disposed is preferred to be a C-plane or a surface offset by within <NUM>° from the C-plane. This is for providing, for example, satisfactory crystallinity of a semiconductor structure layer <NUM>, which will be described later.

The semiconductor structure layer <NUM> is a laminated structure made of a plurality of semiconductor layers formed on the first multilayer reflector <NUM>. The semiconductor structure layer <NUM> has an n-type semiconductor layer (a first semiconductor layer) <NUM> formed on the first multilayer reflector <NUM>, a light-emitting layer (or an active layer) <NUM> formed on the n-type semiconductor layer <NUM>, and a p-type semiconductor layer (a second semiconductor layer) <NUM> formed on the active layer <NUM>.

The n-type semiconductor layer <NUM> is a semiconductor layer formed on the first multilayer reflector <NUM>. The n-type semiconductor layer <NUM> is a semiconductor layer that has the GaN composition and is doped with Si as n-type impurities. The n-type semiconductor layer <NUM> has a prismatic-shaped lower portion 17A and a column-shaped upper portion 17B disposed on the lower portion 17A. Specifically, for example, the n-type semiconductor layer <NUM> has the column-shaped upper portion 17B projecting from an upper surface <NUM> of the prismatic-shaped lower portion 17A. In other words, the n-type semiconductor layer <NUM> has a mesa-shaped structure including the upper portion 17B.

The active layer <NUM> is a layer that is formed on the upper portion 17B of the n-type semiconductor layer <NUM> and has a quantum well structure including a well layer having an InGaN composition and a barrier layer having the GaN composition. In a surface emitting laser <NUM>, a light is generated in the active layer <NUM>.

The p-type semiconductor layer <NUM> is a semiconductor layer having the GaN composition formed on the active layer <NUM>. The p-type semiconductor layer <NUM> is doped with Mg as p-type impurities.

An n-electrode <NUM> is a metal electrode that is disposed on the upper surface <NUM> of the lower portion 17A of the n-type semiconductor layer <NUM> and is electrically connected to the n-type semiconductor layer <NUM>. The n-electrode <NUM> is formed into a ring shape so as to surround the upper portion 17B of the n-type semiconductor layer <NUM>.

An insulating layer <NUM> is a layer made of an insulator formed on the p-type semiconductor layer <NUM>. The insulating layer <NUM> is formed of, for example, a substance having a refractive index lower than that of a material forming the p-type semiconductor layer <NUM>, such as SiO<NUM>. The insulating layer <NUM> is formed into a ring shape on the p-type semiconductor layer <NUM> and is provided with an opening (not illustrated) that exposes the p-type semiconductor layer <NUM> at the center portion.

A p-electrode <NUM> is a metal electrode formed on the insulating layer <NUM>. The p-electrode <NUM> is electrically connected to an upper surface of the p-type semiconductor layer <NUM> exposed from the above-described opening of the insulating layer <NUM> via a transparent electrode (not illustrated) made of a metal oxide film, such as ITO or IZO.

A second multilayer reflector <NUM> is a dielectric multilayer reflector in which a low refractive index dielectric film made of Al<NUM>O<NUM> and a high refractive index dielectric film made of TazOs and having a refractive index higher than that of the low refractive index dielectric film are alternately laminated. In other words, the second multilayer reflector <NUM> is the Distributed Bragg Reflector (DBR) made of a dielectric material.

<FIG> is a top view of the surface emitting laser <NUM>. As described above, the surface emitting laser <NUM> has the semiconductor structure layer <NUM> including the n-type semiconductor layer <NUM> formed on the substrate <NUM> having the rectangular upper surface shape, the active layer <NUM> having the circular-shaped upper surface, and the p-type semiconductor layer <NUM> (see <FIG>). On the p-type semiconductor layer <NUM>, the insulating layer <NUM> and the p-electrode <NUM> are formed. On the p-electrode <NUM>, the second multilayer reflector <NUM> is formed.

The insulating layer <NUM> has an opening <NUM> as a circular-shaped opening that exposes the p-type semiconductor layer <NUM> of the above-described insulating layer <NUM>. As illustrated in <FIG>, the opening <NUM> is formed at the center of the insulating layer <NUM> when viewed from an upper side of the surface emitting laser <NUM> and is covered with the second multilayer reflector <NUM> when viewed from the upper side of the surface emitting laser <NUM>. In other words, the opening <NUM> is covered with the second multilayer reflector <NUM> in the upper surface of the p-type semiconductor layer <NUM>. Yet in other words, the opening <NUM> is formed in a region opposed to a lower surface of the multilayer reflector <NUM> of the insulating layer <NUM>.

The p-electrode <NUM> is formed at the center of the insulating layer <NUM> when viewed from the upper side of the surface emitting laser <NUM> and has an opening <NUM> that surrounds the opening <NUM>. That is, the opening <NUM> is an opening larger than the opening <NUM>. For example, the opening <NUM> has a circular shape concentric to the shape of the opening <NUM>.

As illustrated by the dashed line in <FIG>, a groove <NUM> in a circular ring shape is formed on the upper surface of the p-type semiconductor layer <NUM>, that is, the upper surface of the semiconductor structure layer <NUM>. The groove <NUM> is formed in an outside region of the opening <NUM> and the opening <NUM>. That is, the groove <NUM> is a groove provided in a ring shape when viewed from a direction perpendicular to an in-plane direction of the semiconductor structure layer <NUM>.

In this embodiment, the groove <NUM> is formed so as to be covered by the second multilayer reflector <NUM> on the upper surface of the p-type semiconductor layer <NUM>. That is, in this embodiment, the groove <NUM> is formed at a position opposed to a lower surface of the second multilayer reflector <NUM>.

<FIG> is a cross-sectional view of the surface emitting laser <NUM> taken along the line <NUM>-<NUM> in <FIG>. As described above, the surface emitting laser <NUM> has the substrate <NUM> as the GaN substrate, and the first multilayer reflector <NUM> is formed on the substrate <NUM>. Note that a lower surface of the substrate <NUM> may be applied with an AR coating.

The semiconductor structure layer <NUM> is formed on the first multilayer reflector <NUM>. The semiconductor structure layer <NUM> is a laminated body made by forming the n-type semiconductor layer <NUM>, the active layer <NUM>, and the p-type semiconductor layer <NUM> in this order.

The groove <NUM> formed in the semiconductor structure layer <NUM> is formed so as to surround a projecting portion 21P projecting at the center on the upper surface of the p-type semiconductor layer <NUM> and passes through the active layer <NUM> from the upper surface of the p-type semiconductor layer <NUM> to reach the n-type semiconductor layer <NUM>.

Thus, in the surface emitting laser <NUM> according to Embodiment <NUM>, the groove <NUM> is formed so as to pass through the active layer <NUM>. In other words, the groove <NUM> forms a clearance in the active layer <NUM>.

The insulating layer <NUM> is formed so as to cover the upper surface of the p-type semiconductor layer <NUM> and an inner surface of the groove <NUM>. As described above, the insulating layer <NUM> is made of a material having a refractive index lower than that of the p-type semiconductor layer <NUM>. The insulating layer <NUM> has the opening <NUM> that exposes the projecting portion 21P. For example, as illustrated in <FIG>, the opening <NUM> is in a circular shape. For example, the opening <NUM> and the projecting portion 21P have similar shapes, and an inner surface of the opening <NUM> and an outer surface of the projecting portion 21P are in contact with one another.

A light transmissive electrode layer <NUM> is a layer made of a conductive body having translucency formed so as to cover the insulating layer <NUM> and the projecting portion 21P exposed from the opening <NUM> of the insulating layer <NUM>. That is, the light transmissive electrode layer <NUM> is electrically in contact with the p-type semiconductor layer <NUM> in a region exposed by the opening <NUM> on the upper surface of the p-type semiconductor layer <NUM>. The light transmissive electrode layer <NUM> is formed of, for example, a metal oxide having translucency relative to an emitted light from the active layer <NUM>, such as ITO or IZO.

As described above, the p-electrode <NUM> is the metal electrode and is formed so as to cover the light transmissive electrode layer <NUM>. That is, the p-electrode <NUM> is electrically in contact with the light transmissive electrode layer <NUM>. Accordingly, the p-electrode <NUM> is electrically in contact with or electrically connected to the p-type semiconductor layer <NUM> via the light transmissive electrode layer <NUM> in a region exposed by the opening <NUM> on the upper surface of the p-type semiconductor layer <NUM>. The p-electrode <NUM> has the opening <NUM> that exposes the light transmissive electrode layer <NUM> at the center. The opening <NUM> is an opening with a width larger than that of the opening <NUM>.

The second multilayer reflector <NUM> is formed so as to cover the opening <NUM> and the groove <NUM>. The second multilayer reflector <NUM> is formed so as to fill a space formed of the opening <NUM> and so as to be in contact with the light transmissive electrode layer <NUM>. The second multilayer reflector <NUM> is formed so as to fill a space formed of the groove <NUM>.

In the surface emitting laser <NUM>, the first multilayer reflector <NUM> has reflectivity slightly lower than that of the second multilayer reflector <NUM>. Accordingly, a part of the light resonated between the first multilayer reflector <NUM> and the second multilayer reflector <NUM> transmits through the first multilayer reflector <NUM> and the substrate <NUM> to be taken out to the outside.

As described above, in the surface emitting laser <NUM> according to Embodiment <NUM>, the groove <NUM> is formed so as to pass through the active layer <NUM>. In other words, the groove <NUM> forms the clearance in the active layer <NUM>. The groove <NUM> is formed after the semiconductor structure layer <NUM> is formed. Afterwards, the insulating layer <NUM> is formed before the light transmissive electrode layer <NUM>, the p-electrode <NUM>, and the second multilayer reflector <NUM> are formed.

Accordingly, after the semiconductor structure layer <NUM> is formed, forming the groove <NUM> that reaches the active layer <NUM> forms a space or the clearance in a direction along an in-plane of the active layer <NUM>. This clearance reduces a distortion generated in an in-layer direction of the active layer <NUM> or in a layer surface direction of the semiconductor structure layer <NUM> when the active layer <NUM> is formed.

Specifically speaking, the active layer <NUM> has a crystalline structure distorted by a difference of lattice constants between InGaN and GaN forming the quantum well structure when the active layer <NUM> is formed to cause a piezoelectric polarization to cause a piezoelectric field. The generation of this piezoelectric field lowers a recombination probability of the electrons and the holes injected to the light-emitting layer to contribute to lower the internal quantum efficiency.

In the surface emitting laser <NUM>, the groove <NUM> reaching the active layer <NUM> is formed in the semiconductor structure layer <NUM>. The clearance by this groove is considered to reduce the distortion generated in the in-layer direction of the active layer <NUM> during the growth of the active layer <NUM>, and thus, the internal quantum efficiency in the active layer <NUM> is improved.

Here, an operation of the surface emitting laser <NUM> will be described. In the surface emitting laser <NUM>, when a voltage is applied between the n-electrode <NUM> and the p-electrode <NUM>, a current flows inside the semiconductor structure layer <NUM> as indicated by the one-dot chain bold line in the drawing, and the light is emitted from the active layer <NUM>. The light emitted from the active layer <NUM> is repeatedly reflected between the first multilayer reflector <NUM> and the second multilayer reflector <NUM> to reach a resonant state (to laser oscillate).

In the surface emitting laser <NUM>, the current is injected only from a portion exposed by the opening <NUM> to the p-type semiconductor layer <NUM>. Since the p-type semiconductor layer <NUM> is considerably thin, the current hardly spreads in the in-plane direction, that is, the direction along the in-plane of the semiconductor structure layer <NUM> inside the p-type semiconductor layer <NUM>. Accordingly, in the surface emitting laser <NUM>, the current is supplied only to the region immediately below the opening <NUM> in the active layer <NUM>, and the light is emitted only from this region. That is, in the surface emitting laser <NUM>, the opening <NUM> has a current confinement structure that restricts a supply range of the current in the active layer <NUM>.

As described above, in the embodiment, the first multilayer reflector <NUM> has the reflectivity slightly lower than that of the second multilayer reflector <NUM>. Accordingly, a part of the light resonated between the first multilayer reflector <NUM> and the second multilayer reflector <NUM> transmits through the first multilayer reflector <NUM> and the substrate <NUM> to be taken out to the outside. Thus, the surface emitting laser <NUM> emits the light from the lower surface of the substrate <NUM> toward the direction perpendicular to the lower surface of the substrate <NUM> and the in-plane direction of the respective layers of the semiconductor structure layer <NUM>.

The projecting portion 21P of the p-type semiconductor layer <NUM> of the semiconductor structure layer <NUM> and the opening <NUM> of the insulating layer <NUM> define a luminescence center as a center of a light emission region in the active layer <NUM> to define a center axis (a luminescence center axis) AX of a resonator OC. The center axis AX of the resonator OC passes through a center of the projecting portion 21P of the p-type semiconductor layer <NUM> and extends along a direction perpendicular to the in-plane direction of the semiconductor structure layer <NUM>.

Note that the light emission region of the active layer <NUM> means, for example, a region having a predetermined width from which a light having a predetermined intensity or more is emitted in the inside of the active layer <NUM>, and its center is the luminescence center. For example, the light emission region of the active layer <NUM> means is a region to which a current having a predetermined density or more is injected in the inside of the active layer <NUM>, and its center is the luminescence center. A straight line that passes through the luminescence center and is perpendicular to the upper surface of the substrate <NUM> or the in-plane direction of the respective layers of the semiconductor structure layer <NUM> is the center axis AX. The luminescence center axis AX is a straight line extending along a resonator length direction of the resonator OC constituted of the first multilayer reflector <NUM> and the second multilayer reflector <NUM>. The center axis AX corresponds to an optical axis of the laser light emitted from the surface emitting laser <NUM>.

Here, exemplary configurations of respective layers of the first multilayer reflector <NUM>, the semiconductor structure layer <NUM>, and the second multilayer reflector <NUM> and exemplary dimensions of the groove <NUM> in the surface emitting laser <NUM> will be described. In the embodiment, the first multilayer reflector <NUM> is made of a GaN base layer of <NUM> and <NUM> pairs of n-GaN layers and AlInN layers formed on the upper surface of the substrate <NUM>.

The n-type semiconductor layer <NUM> is an n-GaN layer having a layer thickness of <NUM>. The active layer <NUM> is made of an active layer having a multiple quantum well structure in which four pairs of GaInN layers of <NUM> and GaN layers of <NUM> are laminated. On the active layer <NUM>, an AlGaN electronic barrier layer doped with Mg is formed, and the p-type semiconductor layer <NUM> made of a p-GaN layer of <NUM> is formed thereon. The second multilayer reflector <NUM> is a lamination of <NUM> pairs of Nb<NUM>O<NUM> and SiO<NUM>. The resonant wavelength in this case was <NUM>.

The groove portion <NUM> formed in the semiconductor structure layer <NUM> has an outer diameter of <NUM>, a depth of <NUM>, and a width of <NUM>. The light transmissive electrode layer <NUM> formed on the semiconductor structure layer <NUM> is a layer made of ITO of <NUM>, and the second multilayer reflector <NUM> is formed on the light transmissive electrode layer <NUM> and the p-electrode <NUM> with a spacer layer of Nb<NUM>O<NUM> of <NUM> interposed.

Aback surface of the substrate <NUM> is a polished surface, and two layers of AR coatings of Nb<NUM>O<NUM> and SiO<NUM> are formed on this polished surface.

The p-type semiconductor layer <NUM> may have a layer thickness of <NUM> in the projecting portion 21P and a layer thickness of <NUM> in the other portions. That is, the p-type semiconductor layer <NUM> may have different layer thicknesses in the projecting portion 21P and the other regions. The insulating layer <NUM> has an upper surface configured to be arranged at a height position identical to an upper surface of the projecting portion 21P of the p-type semiconductor layer <NUM>. These are merely one example.

The following describes optical features inside the surface emitting laser <NUM>. As described above, in the surface emitting laser <NUM>, the insulating layer <NUM> has a refractive index lower than that of the p-type semiconductor layer <NUM>. Layer thicknesses of the other layers between the first multilayer reflector <NUM> and the second multilayer reflector <NUM> are the same at any positions in the plane insofar as in the same layer.

Accordingly, an equivalent refractive index (an optical distance between the first multilayer reflector <NUM> and the second multilayer reflector <NUM>, and corresponds to a resonant wavelength) in the resonator OC formed between the first multilayer reflector <NUM> and the second multilayer reflector <NUM> of the surface emitting laser <NUM> differs in a column-shaped central region CA having an upper surface shape defined by the opening <NUM> and in a pipe-shaped peripheral region PA around the central region CA by a difference in refractive indexes between the p-type semiconductor layer <NUM> and the insulating layer <NUM>.

Specifically, between the first multilayer reflector <NUM> and the second multilayer reflector <NUM>, the equivalent refractive index in the peripheral region PA is lower than the equivalent refractive index in the central region, that is, an equivalent resonant wavelength in the central region CA is smaller than the equivalent resonant wavelength in the peripheral region PA. Note that, as described above, where the light is emitted in the active layer <NUM> is the region immediately below the opening <NUM>. That is, the light emission region where the light is emitted in the active layer <NUM> is a portion overlapping with the central region CA in the active layer <NUM>, in other words, a region inside the opening <NUM> of the insulating layer <NUM> in top view.

Thus, in the surface emitting laser <NUM>, the central region CA including the light emission region of the active layer <NUM> and the peripheral region PA that surrounds the central region CA and has the refractive index lower than that of the central region CA are formed. This reduces an optical loss by diffusion (radiation) of a standing wave within the central region CA into the peripheral region PA. That is, a large amount of light remains in the central region CA, and a laser light LB is taken out to the outside in this state. Accordingly, the large amount of light concentrates in the central region CA in the peripheral area of the luminescence center axis AX of the resonator OC to ensure generating and emitting a laser light with high output and high density.

As described above, in the surface emitting laser <NUM> of the embodiment, the groove <NUM> that reaches the active layer <NUM> from the upper surface of the p-type semiconductor layer <NUM> is formed in the semiconductor structure layer <NUM>. With this groove <NUM>, the distortion generated in the in-layer direction of the active layer <NUM> is reduced in the active layer <NUM>, and the internal quantum efficiency in the active layer <NUM> is improved, thereby ensuring achieving improved luminous efficiency.

The following describes one example of a method for manufacturing the surface emitting laser <NUM>. First, a c-plane n-GaN substrate is prepared as the substrate <NUM>, and an n-GaN layer (a layer thickness of <NUM>) is formed as a base layer on the substrate by Metal-Organic Vapor Phase Epitaxy method (MOVPE). Subsequently, <NUM> pairs of n-GaN/AlInN layers are film-formed on the base layer to form the first multilayer reflector <NUM>.

Next, the active layer <NUM> is formed by forming Si-doped n-GaN (a layer thickness of <NUM>) on the first multilayer reflector <NUM> to form the n-type semiconductor layer <NUM> and then, laminating four pairs of layers made of GaInN (a layer thickness of <NUM>) and GaN (a layer thickness of <NUM>) on the n-type semiconductor layer <NUM>.

Next, the electronic barrier layer (not illustrated) made of Mg-doped AlGaN is formed on the active layer <NUM>, and then, p-GaN layer (a layer thickness of <NUM>) is film-formed on the electronic barrier layer to form the p-type semiconductor layer <NUM>.

Next, a peripheral portion of the p-type semiconductor layer <NUM>, the active layer <NUM>, and the n-type semiconductor layer <NUM> is etched to form a mesa shape such that the upper surface <NUM> of the n-type semiconductor layer <NUM> is exposed in the peripheral portion. In other words, in this process, the semiconductor structure layer <NUM> including the column-shaped portion made of the n-type semiconductor layer <NUM>, the active layer <NUM>, and the p-type semiconductor layer <NUM> in <FIG> is completed.

Next, the groove <NUM> passing through the active layer <NUM> from the upper surface of the p-type semiconductor layer <NUM> is formed by etching. Subsequently, the insulating layer <NUM> is formed by forming a film of SiO<NUM> on the semiconductor structure layer <NUM> and removing a part of the film to form the opening <NUM>.

Next, the light transmissive electrode layer <NUM> is formed by forming film of ITO of <NUM> on the insulating layer <NUM>, and then, the p-electrode <NUM> and the n-electrode <NUM> are formed by forming films of Au on the light transmissive electrode layer <NUM> and on the upper surface <NUM> of the n-type semiconductor layer <NUM>, respectively.

Next, Nb<NUM>O<NUM> of <NUM> is film-formed as a spacer layer (not illustrated) on the p-electrode <NUM> and the light transmissive electrode layer <NUM>, and then, by forming a film of <NUM> pairs of layers made of Nb<NUM>O<NUM>/SiO<NUM> in one pair on the spacer layer, the second multilayer reflector <NUM> is formed.

Next, the back surface of the substrate <NUM> is polished, and then, by forming an AR coating made of Nb<NUM>O<NUM>/SiO<NUM> on the polished surface, the surface emitting laser <NUM> is completed.

The following describes a surface emitting laser <NUM> as Embodiment. The surface emitting laser <NUM> is different from the surface emitting laser <NUM> in that the groove <NUM> of the semiconductor structure layer <NUM> is formed outside the second multilayer reflector <NUM> in top view.

<FIG> illustrates a perspective view of the surface emitting laser <NUM> according to Embodiment <NUM>. <FIG> illustrates a cross-sectional view of the surface emitting laser <NUM> cut along a cross section similar to the one illustrated in Embodiment <NUM> described above. As illustrated in <FIG> and <FIG>, in the surface emitting laser <NUM>, the groove <NUM> of the semiconductor structure layer <NUM> is formed outside the second multilayer reflector <NUM> on the upper surface of the p-type semiconductor layer <NUM>. That is, on the upper surface of the p-type semiconductor layer <NUM>, the groove <NUM> is exposed from a second formation region.

On an upper surface of the p-electrode <NUM> formed on the p-type semiconductor layer <NUM> via the insulating layer <NUM>, a groove structure <NUM> formed by inheriting the shape of the groove <NUM> is formed. That is, the groove structure <NUM> is formed on the groove <NUM> in a shape approximately identical to that of the groove <NUM>.

As illustrated in <FIG>, also in the surface emitting laser <NUM>, similarly to the surface emitting laser <NUM>, the groove <NUM> that reaches the active layer <NUM> from the upper surface of the p-type semiconductor layer <NUM> is formed in the semiconductor structure layer <NUM>. With this groove <NUM>, the distortion generated in the in-layer direction of the active layer <NUM> is reduced in the active layer <NUM>, and the internal quantum efficiency in the active layer <NUM> is improved, thereby ensuring achieving improved luminous efficiency. In the surface emitting laser <NUM>, it is not necessary to form the second multilayer reflector <NUM> on the p-electrode <NUM>. That is, since it is not necessary to form the second multilayer reflector <NUM> across a level difference, it is possible to further enhance accuracy of formation of the second multilayer reflector <NUM>.

The following describes a surface emitting laser <NUM> as Embodiment <NUM> of the present invention. The surface emitting laser <NUM> is different from the surface emitting laser <NUM> in that the electrode connected to the n-type semiconductor layer <NUM> is disposed on the back surface of the substrate <NUM> or the like.

<FIG> is a perspective view of the surface emitting laser <NUM>. A substrate <NUM> is, for example, a substrate having a rectangular upper surface shape. The substrate <NUM> is a substrate made of a conductive material such as n-GaN. On a back surface of the substrate <NUM>, an n-electrode <NUM> made of metal is formed.

On the substrate <NUM>, a first multilayer reflector <NUM> made of a semiconductor layer that has been grown on the substrate <NUM> is formed. The first multilayer reflector <NUM> is a semiconductor multilayer reflector with conductivity in which a low refractive-index semiconductor film having a composition of AlInN and a high refractive-index semiconductor film having an n-GaN composition and having a refractive index higher than that of the low refractive-index semiconductor film are alternately laminated. In other words, the first multilayer reflector <NUM> is the Distributed Bragg Reflector (DBR) made of a semiconductor material. For example, on an upper surface of the substrate <NUM>, a buffer layer having an n-GaN composition is disposed, and alternately forming films of the high refractive-index semiconductor film and the low refractive-index semiconductor film described above on the buffer layer forms the first multilayer reflector <NUM>.

The semiconductor structure layer <NUM> is a laminated structure made of a plurality of semiconductor layers formed on the first multilayer reflector <NUM>. The semiconductor structure layer <NUM> has the n-type semiconductor layer (the first semiconductor layer) <NUM> formed on the first multilayer reflector <NUM>, the light-emitting layer (or the active layer) <NUM> formed on the n-type semiconductor layer <NUM>, and the p-type semiconductor layer (the second semiconductor layer) <NUM> formed on the active layer <NUM>.

The n-type semiconductor layer <NUM> is a semiconductor layer formed on the first multilayer reflector <NUM>. The n-type semiconductor layer <NUM> is a semiconductor layer that has the GaN composition and is doped with Si as n-type impurities.

The active layer <NUM> is a layer that is formed on the n-type semiconductor layer <NUM> and has the quantum well structure including the well layer having the InGaN composition and the barrier layer having the GaN composition. In the surface emitting laser <NUM>, a light is generated in the active layer <NUM>.

The insulating layer <NUM> is a layer made of the insulator formed on the p-type semiconductor layer <NUM>. The insulating layer <NUM> is formed of, for example, a substance having a refractive index lower than that of the material forming the p-type semiconductor layer <NUM>, such as SiO<NUM>. The insulating layer <NUM> is formed into a ring shape on the p-type semiconductor layer <NUM> and is provided with the opening (not illustrated) that exposes the p-type semiconductor layer <NUM> at the center portion.

The p-electrode <NUM> is a metal electrode formed on the insulating layer <NUM>. The p-electrode <NUM> is electrically connected to the upper surface of the p-type semiconductor layer <NUM> exposed from the above-described opening of the insulating layer <NUM> via the transparent electrode (not illustrated) made of the metal oxide film, such as ITO or IZO.

The second multilayer reflector <NUM> is a dielectric multilayer reflector in which the low refractive index dielectric film made of Al<NUM>O<NUM> and the high refractive index dielectric film made of TazOs and having a refractive index higher than that of the low refractive index dielectric film are alternately laminated. In other words, the second multilayer reflector <NUM> is the Distributed Bragg Reflector (DBR) made of a dielectric material.

<FIG> is a top view of the surface emitting laser <NUM>. As described above, the surface emitting laser <NUM> has the semiconductor structure layer <NUM> including the n-type semiconductor layer <NUM> formed above the substrate <NUM> having the rectangular upper surface shape, the active layer <NUM>, and the p-type semiconductor layer <NUM> (see <FIG>). On the p-type semiconductor layer <NUM>, the insulating layer <NUM> and the p-electrode <NUM> are formed. On the p-electrode <NUM>, the second multilayer reflector <NUM> is formed.

The insulating layer <NUM> has the opening <NUM> as a circular-shaped opening that exposes the p-type semiconductor layer <NUM> of the above-described insulating layer <NUM>. As illustrated in <FIG>, the opening <NUM> is formed at the center of the insulating layer <NUM> when viewed from an upper surface of the surface emitting laser <NUM> and is covered with the second multilayer reflector <NUM> when viewed from the upper surface of the surface emitting laser <NUM>. In other words, the opening <NUM> is covered with the second multilayer reflector <NUM> on the upper surface of the p-type semiconductor layer <NUM>. Yet in other words, the opening <NUM> is disposed in a region opposed to the lower surface of the multilayer reflector <NUM> of the upper surface of the p-type semiconductor layer <NUM>.

The p-electrode <NUM> is formed at the center of the insulating layer <NUM> when viewed from the upper surface of the surface emitting laser <NUM> and has the opening <NUM> that surrounds the opening <NUM>. That is, the opening <NUM> is an opening larger than the opening <NUM>. For example, the opening <NUM> has a circular shape concentric to the shape of the opening <NUM>.

As illustrated by the dashed line in <FIG>, a groove <NUM> in a circular ring shape is formed on the upper surface of the p-type semiconductor layer <NUM>, that is, on the upper surface of the semiconductor structure layer <NUM>. The groove <NUM> is formed in an outside region of the opening <NUM> and the opening <NUM>. In this embodiment, the groove <NUM> is formed so as to be covered with the second multilayer reflector <NUM> on the upper surface of the p-type semiconductor layer <NUM>. That is, in this embodiment, the groove <NUM> is formed at a position opposed to the lower surface of the second multilayer reflector <NUM>.

<FIG> is a cross-sectional view of the surface emitting laser <NUM> taken along the line <NUM>-<NUM> in <FIG>. As described above, the surface emitting laser <NUM> has the substrate <NUM> as the n-GaN substrate, and the first multilayer reflector <NUM> is formed on the substrate <NUM>.

In a back surface 51A of the substrate <NUM>, a projecting portion 51P is formed. The projecting portion 51P is formed in a region corresponding to the projecting portion 21P when viewed from a normal direction of the substrate <NUM>. The projecting portion 51P is a protrusion remained due to a removal of a peripheral area of the projecting portion 51P by dry etching after the back surface 51A is polished. Accordingly, a top surface of the projecting portion 51P is a polished surface, and the peripheral region of the projecting portion 51P of the back surface 51A of the substrate <NUM> has a surface where the polished surface is dry-etched. The n-electrode <NUM> is formed in the peripheral region of the projecting portion 51P of the back surface 51A of the substrate <NUM>, that is, in a region excluding the projecting portion 51P. Because the projecting portion 51P has a top surface serving as an opening through which the emitted light is emitted outside so as not to obstruct the emitted light by the n-electrode <NUM>. That is, the projecting portion 51P has a structure in which it projects from the opening of the n-electrode <NUM>.

An anti-reflection layer <NUM> is formed so as to cover the projecting portion 51P in the back surface 51A of the substrate <NUM>. The anti-reflection layer <NUM> is made of, for example, a dielectric multilayer film, and has a structure, for example, in which Ta<NUM>O<NUM> layers and SiO<NUM> layers are alternately laminated a plurality of times. The anti-reflection layer <NUM> is a so-called AR coating that suppresses the light emitted from the active layer <NUM> from being reflected on the top surface of the projecting portion 51P of the substrate <NUM>.

On the first multilayer reflector <NUM>, the semiconductor structure layer <NUM> is formed. The semiconductor structure layer <NUM> is a laminated structure made by forming the n-type semiconductor layer <NUM>, the active layer <NUM>, and the p-type semiconductor layer <NUM> in this order.

The p-type semiconductor layer <NUM> has the projecting portion 21P projecting upward in a columnar shape at the center of the upper surface of the p-type semiconductor layer <NUM>. The groove <NUM> formed in the semiconductor structure layer <NUM> is formed so as to surround the projecting portion 21P on the upper surface of the p-type semiconductor layer <NUM> and passes through the active layer <NUM> from the upper surface of the p-type semiconductor layer <NUM> to reach the n-type semiconductor layer <NUM>.

Thus, in the surface emitting laser <NUM> according to Embodiment <NUM>, similarly to the surface emitting lasers <NUM> and <NUM> in the above-described embodiments, the groove <NUM> is formed so as to pass through the active layer <NUM>. In other words, the groove <NUM> forms the clearance in the active layer <NUM>.

The insulating layer <NUM> is formed so as to cover the upper surface of the p-type semiconductor layer <NUM> and the inner surface of the groove <NUM>. As described above, the insulating layer <NUM> is made of a material having a refractive index lower than that of the p-type semiconductor layer <NUM>. The insulating layer <NUM> has the opening <NUM> that exposes the projecting portion 21P. For example, as illustrated in <FIG>, the opening <NUM> is in a circular shape. For example, the opening <NUM> and the projecting portion 21P have similar shapes, and the inner surface of the opening <NUM> and the outer surface of the projecting portion 21P are in contact with one another.

The light transmissive electrode layer <NUM> is a layer made of a conductive body having translucency formed to cover the insulating layer <NUM> and the projecting portion 21P exposed from the opening <NUM> of the insulating layer <NUM>. The light transmissive electrode layer <NUM> is formed of, for example, a metal oxide having translucency relative to the emitted light from the active layer <NUM>, such as ITO or IZO.

As described above, the p-electrode <NUM> is the metal electrode and is formed so as to cover the light transmissive electrode layer <NUM>. The p-electrode <NUM> has the opening <NUM> that exposes the light transmissive electrode layer <NUM> at the center. The opening <NUM> is an opening with a width larger than that of the opening <NUM>.

Accordingly, after the semiconductor structure layer <NUM> is formed, forming the groove <NUM> that reaches the active layer <NUM> forms the clearance in a direction along the in-plane direction of the active layer <NUM>. This clearance reduces a distortion generated in the in-layer direction of the active layer <NUM> or in the in-plane direction of the semiconductor structure layer <NUM> when the active layer <NUM> is formed.

Specifically speaking, as described above, the active layer <NUM> has a crystalline structure distorted by the difference of lattice constants between InGaN and GaN forming the quantum well structure when the active layer <NUM> is formed, which causes the piezoelectric polarization so as to generate the piezoelectric field. This piezoelectric field lowers the recombination probability of the electrons and the hole injected to the light-emitting layer to lower the internal quantum efficiency.

In the surface emitting laser <NUM>, similarly to the case in the surface emitting laser <NUM>, the current is injected only from a portion exposed by the opening <NUM> to the p-type semiconductor layer <NUM>. Since the p-type semiconductor layer <NUM> is considerably thin, the current hardly spreads in the in-plane direction inside the p-type semiconductor layer <NUM>, that is, the direction along the in-plane of the semiconductor structure layer <NUM>. Accordingly, in the surface emitting laser <NUM>, the current is supplied only to the region immediately below the opening <NUM> in the active layer <NUM>, and the light is emitted only from this region. That is, in the surface emitting laser <NUM>, the opening <NUM> has the current confinement structure that restricts the supply range of the current in the active layer <NUM>.

As described above, in the embodiment, the first multilayer reflector <NUM> has the reflectivity slightly lower than that of the second multilayer reflector <NUM>. Accordingly, a part of the light resonated between the first multilayer reflector <NUM> and the second multilayer reflector <NUM> transmits through the first multilayer reflector <NUM> and the substrate <NUM> to be taken out to the outside from the projecting portion 51P. Thus, the surface emitting laser <NUM> emits the light toward the direction perpendicular to the lower surface of the substrate <NUM> and the in-plane direction of the respective layers of the semiconductor structure layer <NUM>.

The description of the luminescence center axis AX and the like will be omitted because it is the same as that of the surface emitting laser <NUM> according to Embodiment <NUM>.

Exemplary configurations of respective layers of the first multilayer reflector <NUM>, the semiconductor structure layer <NUM>, and the second multilayer reflector <NUM> and exemplary dimensions of the groove <NUM> in the surface emitting laser <NUM> will be described. In the embodiment, the first multilayer reflector <NUM> is made of the n-GaN base layer of <NUM> and <NUM> pairs of n-GaN layers and AlInN layers formed on the surface of the substrate <NUM>.

The n-type semiconductor layer <NUM> is the n-GaN layer doped with Si having a layer thickness of <NUM>. The active layer <NUM> is made of an active layer having a multiple quantum well structure in which four pairs of GaInN layers of <NUM> and GaN layers of <NUM> are laminated. On the active layer <NUM>, the AlGaN electronic barrier layer doped with Mg is formed, and the p-type semiconductor layer <NUM> made of the p-GaN layer of <NUM> is formed thereon. The second multilayer reflector <NUM> is a lamination of <NUM> pairs of and SiO<NUM>.

The groove portion <NUM> formed in the semiconductor structure layer <NUM> has an outer diameter of <NUM>, a depth of <NUM>, and a width of <NUM>. The light transmissive electrode layer <NUM> formed on the semiconductor structure layer <NUM> is a layer made of ITO of <NUM>, and the second multilayer reflector <NUM> is formed on the light transmissive electrode layer <NUM> and the p-electrode <NUM> with the spacer layer of NbzOs of <NUM> interposed.

The p-type semiconductor layer <NUM> may have a layer thickness of <NUM> in the projecting portion 21P and a layer thickness of <NUM> in the other regions. That is, the p-type semiconductor layer <NUM> may have different layer thicknesses in the projecting portion 21P and the other regions. The insulating layer <NUM> has an upper surface configured to be arranged at a height position identical to the upper surface of the projecting portion 21P of the p-type semiconductor layer <NUM>. These are merely one example.

Description of the optical features inside the surface emitting laser <NUM> is omitted because it is similar to the optical features of the surface emitting laser <NUM>.

As described above, similarly to the surface emitting laser <NUM> according to Embodiment <NUM>, in the surface emitting laser <NUM> of the embodiment, the groove <NUM> that reaches the active layer <NUM> from the upper surface of the p-type semiconductor layer <NUM> is formed in the semiconductor structure layer <NUM>. With this groove <NUM>, the distortion generated in the in-layer direction of the active layer <NUM> is reduced in the active layer <NUM>, and the internal quantum efficiency in the active layer <NUM> is improved, thereby ensuring achieving improved luminous efficiency.

The following describes a surface emitting laser <NUM> according to Embodiment <NUM>. The surface emitting laser <NUM> is different from the surface emitting laser <NUM> in that the groove <NUM> of the semiconductor structure layer <NUM> is formed on an outside of the second multilayer reflector <NUM> in top view.

<FIG> illustrates a perspective view of the surface emitting laser <NUM> according to Embodiment <NUM>. <FIG> illustrates a cross-sectional view of the surface emitting laser <NUM> cut along a cross section similar to the one illustrated in Embodiment <NUM> described above. As illustrated in <FIG> and <FIG>, in the surface emitting laser <NUM>, the groove <NUM> of the semiconductor structure layer <NUM> is formed outside the second multilayer reflector <NUM> on the upper surface of the p-type semiconductor layer <NUM>. That is, on the upper surface of the p-type semiconductor layer <NUM>, the groove <NUM> is exposed on the outside of the second multilayer reflector.

On the upper surface of the p-electrode <NUM> formed on the p-type semiconductor layer <NUM> via the insulating layer <NUM>, the groove structure <NUM> formed by inheriting the shape of the groove <NUM> is formed. That is, the groove structure <NUM> is formed on the groove <NUM> in a shape approximately identical to that of the groove <NUM>. As illustrated in <FIG>, also in the surface emitting laser <NUM>, similarly to the surface emitting laser <NUM>, the groove <NUM> that reaches the n-type semiconductor layer <NUM> from the upper surface of the p-type semiconductor layer <NUM> is formed in the semiconductor structure layer <NUM>. With this groove <NUM>, the distortion generated in the in-layer direction of the active layer <NUM> is reduced in the active layer <NUM>, and the internal quantum efficiency, for example, slope efficiency in the active layer <NUM> is improved, thereby ensuring achieving improved luminous efficiency. Note that, in the surface emitting laser <NUM>, it is not necessary to form the second multilayer reflector <NUM> on the p-electrode <NUM>. That is, since it is not necessary to form the second multilayer reflector <NUM> across the level difference, it is possible to further enhance accuracy of formation of the second multilayer reflector <NUM>.

In the above-described embodiments, a case where the groove <NUM> formed in the semiconductor structure layer <NUM> has a circular ring shape has been described. However, the groove <NUM> may have other shapes.

For example, as illustrated in <FIG>, the groove <NUM> may be a groove structure including a recessed portion GV (or a groove GV) formed intermittently instead of a perfect ring in a ring-shaped region CR (the region enclosed by the one-dot chain line in the drawing). That is, the groove <NUM> may have a recessed structure including a plurality of recessed portions. In other words, the groove <NUM> may have a ring-shaped structure formed intermittently. For example, the groove <NUM> may have an intermittently formed ring-shaped structure that surrounds a region exposed by the opening <NUM> of the upper surface of the p-type semiconductor layer <NUM>.

Note that, when the groove <NUM> is formed by a plurality of recessed portions, to equally reduce the distortion in the active layer <NUM>, the plurality of recessed portions are preferably formed in two or more directions when viewed from the above-described luminescence center axis AX. That is, when the groove <NUM> is formed by the plurality of recessed portions, in top view of the surface emitting laser <NUM>, the recessed portions are preferably formed in two or more directions when viewed from the light emission region including the luminescence center axis AX and have a structure that sandwiches the light emission region between the recessed portions. To equally reduce the distortion in the active layer <NUM>, the recessed portions forming the groove <NUM> are further preferably disposed rotationally symmetrically with respect to the luminescence center axis AX. In other words, the recessed portions forming the groove <NUM> are preferably disposed rotationally symmetrically when viewed from a direction perpendicular to the in-plane direction of the semiconductor structure layer <NUM>.

Note that, as described above, it is also possible to make a degree of reduction of the distortion in the active layer <NUM> anisotropic to control polarization of the light emitted from the surface emitting laser of the above-described embodiments by changing the shape of the groove <NUM>, for example, by forming the groove <NUM> with the plurality of recessed portions. For example, in the case of the surface emitting laser illustrated in <FIG>, when viewed from the opening <NUM>, that is, from the central region CA, the distortion of the active layer <NUM> is further reduced in a direction where the recessed portion GV forming the groove <NUM> exists. This allows increasing an optical gain in a direction (the right-left direction in the drawing) where the recessed portion GV forming the groove <NUM> exists when viewed from the opening <NUM> and obtaining a large amount of light having a polarization direction along the direction.

To reduce the distortion of the above-described active layer <NUM> and to make a degree of reduction of the above-described distortion anisotropic to control the polarization of the light emitted from the surface emitting laser, the groove <NUM> is preferably formed near the luminescence center axis AX. Accordingly, for example, like the surface emitting laser <NUM> according to Embodiment <NUM> and the surface emitting laser <NUM> according to Embodiment <NUM>, the groove <NUM> is preferably formed below the second multilayer reflector <NUM>. Note that, to reduce the distortion of the active layer <NUM>, the groove <NUM> or the plurality of grooves GV are preferably formed, for example, at a distance within <NUM> from an outer edge of the light emission region. That is, the ring-shaped region CR forming the groove <NUM> is preferably disposed at a distance within <NUM> from the outer edge of the light emission region or the central region CA.

In the above-described embodiment, while the case where a circular-shaped laser light is emitted from the surface emitting laser has been described as an example, a configuration in which a ring-shaped laser light is emitted may be employed. That is, when viewed from above the surface emitting laser of the above-described embodiment, a circular-shaped insulating layer may be formed at the center of the opening <NUM> of the insulating layer <NUM>. Yet in other words, the insulating layer <NUM> may have a circular ring-shaped hole portion, and via the circular ring-shaped hole portion, the upper surface of the p-type semiconductor layer <NUM> may be exposed, and the light transmissive electrode layer <NUM> and the p-type semiconductor layer <NUM> may be electrically in contact with one another.

In that case, an inside recessed portion IG may be further formed inside the groove <NUM> of the semiconductor structure layer <NUM>. This recessed portion IG also passes through the active layer <NUM> from the upper surface of the p-type semiconductor layer <NUM> similarly to the groove <NUM>.

<FIG> is a top view of a modification in which a column-shaped inside recessed portion IG is formed in the surface emitting laser <NUM> according to Embodiment <NUM>. <FIG> is a top view of a modification in which a cylindrical-shaped inside recessed portion IG is formed in the surface emitting laser <NUM> according to Embodiment <NUM>. Thus, forming the inside recessed portion IG allows further reducing the distortion of the active layer <NUM>.

The following describes a surface emitting laser <NUM> according to Embodiment <NUM> of the present invention. The surface emitting laser <NUM> of this embodiment is different from the surface emitting laser <NUM> according to Embodiment <NUM> in that a C-plane GaN substrate that is inclined (offset) in a m-plane (<NUM>-<NUM>) direction from c-plane is used as the substrate <NUM> and an aspect of the groove <NUM> is different. Note that the surface emitting laser <NUM> can be formed by a manufacturing method similar to that of the surface emitting laser <NUM> according to Embodiment <NUM>.

<FIG> is a perspective view when viewed from obliquely above in front of the surface emitting laser <NUM>. <FIG> is a top view of the surface emitting laser <NUM>. As described above, the surface emitting laser <NUM> has the substrate <NUM> whose upper surface is a surface that is offset to the m-plane from the c-plane of a GaN crystal plane.

Specifically, the upper surface of the substrate <NUM> is a surface that is inclined by <NUM>° toward the m-plane direction from the c-plane. In other words, the substrate <NUM> is a GaN substrate having a principal surface that is offset by <NUM>° toward the m-plane from the c-plane. Note that, in <FIG>, an axis AX1 is an axis along an m-axis direction perpendicular to the m-plane of the substrate <NUM> and in the in-plane including the upper surface of the substrate <NUM>, and an axis AX2 is an axis that is perpendicular to the axis AX1 and in the in-plane including the upper surface of the substrate <NUM>.

In the surface emitting laser <NUM>, the grooves <NUM> are constituted of two grooves GV extending parallel to one another along the axis AX2. In other words, the grooves <NUM> are constituted of two grooves GV extending with the axis AX2 interposed. That is, in the direction along the axis AX1, the grooves <NUM> are disposed so as to sandwich the opening <NUM> of the insulating layer <NUM> that overlaps with the light emission region of the active layer <NUM>.

On the upper surface of the p-type semiconductor layer <NUM>, each of the grooves GV extends from a region immediately below the second multilayer reflector <NUM> up to an outside of the second multilayer reflector <NUM>. In other words, both end portions of the respective grooves GV are disposed outside the second multilayer reflector <NUM>. Accordingly, the groove structures <NUM> having shapes similar to the grooves <NUM> also extend from the region immediately below the second multilayer reflector <NUM> up to the outside of the second multilayer reflector <NUM>.

In the surface emitting laser <NUM>, no groove GV is formed in a region in the direction along the axis AX2 when viewed from the opening <NUM>. That is, in the surface emitting laser <NUM>, the grooves GV are formed only in the region in the direction along the axis AX1 when viewed from the opening <NUM>.

The following describes the polarization direction of the emitted light in the surface emitting laser <NUM>. When the semiconductor layer is grown in a growth surface offset to the m-plane of the substrate <NUM> like the surface emitting laser <NUM> of this embodiment, an optical gain having the polarization direction in the m-axis direction becomes larger than the other direction, and thus, the laser light having the polarization direction in the m-axis direction easily oscillates. Thus, in the light emitted from the central region CA of the surface emitting laser <NUM>, a large amount of light has the polarization direction in the m-axis direction.

Furthermore, as described above, the surface emitting laser <NUM> has the groove structures <NUM> in which the grooves GV are formed only in the region in the direction along the axis AX1 along the m-axis direction when viewed from the opening <NUM>. Thus, in the direction in which the grooves GV are formed, that is, in the direction along the axis AX1 when viewed from the opening <NUM>, that is, the central region CA as the light emission region, the distortion of the active layer <NUM> is significantly reduced.

According to the surface emitting laser <NUM>, this increases the gain around the direction along the axis AX1 along the m-axis direction and thus, and thus, in addition to an effect by the above-described offset, allows obtaining a large amount of laser light having the polarization direction in the direction along the m-axis direction. Note that, in obtaining the above-described offset effect, the upper surface of the substrate <NUM> is preferably inclined in a range of <NUM>° to <NUM>° from the c-plane toward the m-plane.

While the surface emitting laser <NUM> is formed by growing the semiconductor structure layer <NUM> by a method similar to that of the surface emitting laser <NUM> according to Embodiment <NUM> described above, by performing heat treatment after forming the groove <NUM>, it is possible to obtain a surface emitting laser capable of obtaining a larger amount of laser light having the polarization direction in the direction along the m-axis direction.

Specifically, after forming the groove <NUM>, before forming the insulating layer <NUM>, performing heat treatment at temperature of, for example, <NUM> allows forming a surface emitting laser capable of obtaining a larger amount of laser light having the polarization direction in the direction along the m-axis direction. It is considered that this is because, in the p-type semiconductor layer <NUM>, among current paths to the active layer <NUM>, the heat treatment increases the conductivity in the current path in the direction along the axis AX1.

The increase of the conductivity in the current path in the direction along the axis AX1 is due to detachment of hydrogen from p-GaN forming the p-type semiconductor layer <NUM> exposed in the groove <NUM> and thus, the increase of the conductivity of the p-type semiconductor layer <NUM> around the portion exposed from the groove <NUM>.

In addition to the increase of the laser light with the polarization direction along the axis AX direction due to reduction of distortion of the active layer <NUM> in the axis AX1 and the offset of the growth surface of the substrate <NUM>, performing the above-described heat treatment allows further increase of the laser light with the polarization direction along the axis AX direction in the surface emitting laser <NUM>.

Note that it is only necessary that the heat treatment performed before forming the insulating layer <NUM> after forming the groove <NUM> is performed at a temperature where detachment of hydrogen from p-GaN forming the p-type semiconductor layer <NUM> is generated. Specifically, for example, to generate detachment of hydrogen from p-GaN, the heat treatment is preferably performed at equal to or more than <NUM>.

To increase the effect of increasing the light having the polarization direction in the direction along the above-described axis AX1, the groove <NUM> is preferably formed to be symmetry with respect to the axis AX2. The groove <NUM> preferably has a shape along the outer edge of the light emission region. Accordingly, also in the surface emitting laser <NUM>, as illustrated on <FIG>, it is preferred that the groove <NUM> having a shape along an arc as illustrated in <FIG> is formed.

In the above-described embodiment, to reduce the distortion of the active layer <NUM>, the groove <NUM> is preferably formed in the circular-shaped region of <NUM> or less from the outer edge/ of the light emission region. For controlling the polarization direction of the above-described laser light, furthermore, the groove <NUM> is preferably formed in a region in which the active layer has emission intensity of <NUM>% or less of an emission peak of the active layer when the surface emitting laser is viewed from above.

In other words, it is preferred that the region to form the groove <NUM>, for example, the ring-shaped region CR in <FIG> is a region at a distance of <NUM> or less from the outer edge of the light emission region and is a region in which the active layer has the emission intensity of <NUM>% or less of the emission peak of the active layer when the surface emitting laser is viewed from above.

This is because a confinement effect by the groove <NUM> that confines the light emitted from the active layer <NUM> inside the formation region of the groove <NUM> is not generated. Generation of the confinement effect fluctuates the polarization direction in directions other than the direction along the axis AX1 compared with a case where the confinement effect is not generated, and thus, it is preferable not to generate the confinement effect.

Note that the groove <NUM> is preferably formed so as not to overlap with the opening <NUM> in the direction along the axis AX2. Thus, generation of reduction of the distortion in the active layer <NUM> in the direction along the axis AX2 is suppressed and generation of the light having the polarization direction in the direction along the axis AX2 is reduced.

In other words, increasing a difference of reduction of the distortion in the active layer <NUM> between the direction along the axis AX1 and the direction along the axis AX2 to increase anisotropy of the reduction of the distortion allows increasing a proportion of the light having the polarization direction in the direction along the axis AX1 in the light emitted from the surface emitting laser <NUM>.

Note that, while, in Embodiment <NUM>, the case where the upper surface of the substrate <NUM> is offset from the c-plane to the m-plane as a non-polar plane has been described, the upper surface of the substrate <NUM> may be offset from the c-plane to an a-plane as the other non-polar plane. In that case, in the surface emitting laser <NUM> according to Embodiment <NUM>, the axis AX1 becomes an axis along an a-axis and the groove GV is formed in a region in the direction along the axis AX1 when viewed from the opening <NUM>.

As described above, according to the surface emitting laser according to Embodiment <NUM>, it becomes possible to obtain the light including a large amount of linearly polarized light having the polarization direction in a specific direction, that is, the light in which the polarization direction is aligned. Thus, since the emitted light itself from the surface emitting laser <NUM> according to Embodiment <NUM> is the light in which the polarization direction is aligned, it becomes possible to suppress loss of light to a minimum due to use of an optical system such as a liquid crystal or a polarization element and easily obtain a light having a specific polarization direction.

For example, the surface emitting laser such as the surface emitting laser <NUM> according to Embodiment <NUM> is useful when obtaining a sensor light that requires a light in which the polarization direction is aligned, for example, a light for communication such as Li-Fi.

In the above-described embodiment, while the insulating layer <NUM> is disposed to generate the current confinement by forming the insulating region and to form the region in which the refractive index is low, instead of disposing the insulating layer <NUM>, the current confinement may be generated and a region in which the refractive index is low may be generated by another method. For example, by etching the surface of the semiconductor structure layer <NUM> where the insulating layer <NUM> is disposed in the above-described embodiment, an insulating region and a region in which the refractive index is low may be formed. By implanting ions on the surface of the semiconductor structure layer <NUM> where the insulating layer <NUM> is disposed, an insulating region and a region having a low refractive index may be formed to generate an effect similar to that of forming the insulating layer <NUM> in the above-described embodiment. When ion implantation is performed, for example, B ions, Al ions, or oxygen ions are implanted into the semiconductor structure layer <NUM>.

In the surface emitting laser element as described above, the semiconductor structure layer <NUM> may be formed by laminating the p-GaN layer, an active layer similar to that of the above-described embodiment, and the n-GaN layer on the n-type semiconductor layer <NUM> in this order. In this case, in the p-GaN layer, a tunnel joining layer constituted of an n+-GaN layer and a p+-GaN may be formed in a portion where the central region CA of the above-described embodiment overlaps in top view in a region in contact with the n-type semiconductor layer <NUM>.

In the semiconductor structure layer having this structure, a current flows from the p-GaN layer to the n-type semiconductor layer <NUM> only from a portion of the tunnel joining layer. Thus, it becomes possible to generate the current confinement similar to that of forming the above-described insulating layer <NUM>.

Claim 1:
A vertical cavity light-emitting element comprising:
a gallium-nitride-based semiconductor substrate (<NUM>);
a first multilayer reflector (<NUM>) made of a nitride semiconductor formed on the substrate (<NUM>);
a semiconductor structure layer (<NUM>) including a first semiconductor layer (<NUM>), an active layer (<NUM>), and a second semiconductor layer (<NUM>), the first semiconductor layer (<NUM>) being made of a nitride semiconductor having a first conductivity type formed on the first multilayer reflector (<NUM>), the active layer (<NUM>) being made of a nitride semiconductor formed on the first semiconductor layer (<NUM>), the second semiconductor layer (<NUM>) being formed on the active layer (<NUM>) and made of a nitride semiconductor having a second conductivity type opposite to the first conductivity type;
a first electrode layer (<NUM>) that is electrically in contact with the first semiconductor layer (<NUM>) of the semiconductor structure layer (<NUM>);
a second electrode layer (<NUM>) formed on an upper surface of the semiconductor structure layer (<NUM>), the second electrode layer (<NUM>) being electrically in contact with the second semiconductor layer (<NUM>) of the semiconductor structure layer (<NUM>) in one region of the upper surface; and
a second multilayer reflector (<NUM>) formed to cover the one region on the second electrode layer (<NUM>), the second multilayer reflector (<NUM>) constituting a resonator with the first multilayer reflector (<NUM>), wherein
the semiconductor structure layer (<NUM>) has one recessed structure including one or a plurality of recessed portions (<NUM>) passing through the active layer from the upper surface in a region surrounding the one region, and
the recessed structure is disposed to overlap with the second multilayer reflector (<NUM>) when viewed from a direction perpendicular to an in-plane direction of the semiconductor structure layer (<NUM>).