Patent Description:
Conventionally, as one of semiconductor lasers, there has been known a vertical cavity-type surface emitting laser that includes a semiconductor layer for emitting light by application of a voltage and multilayer film reflecting mirrors opposed across the semiconductor layer to one another. In the semiconductor laser, for example, an electrode electrically connected to the semiconductor layer is disposed. For example, <CIT> discloses a vertical cavity-type semiconductor laser that has an n-electrode and a p-electrode respectively connected to an n-type semiconductor layer and a p-type semiconductor layer.

<CIT> discloses a surface light-emitting laser and was used as a basis for the preamble of claim <NUM>. The surface-emitting laser includes a laser element section that includes a first multi-layer film reflecting mirror, a first semiconductor layer of a first conductivity type, an active layer, a second semiconductor layer of a second conductivity type, a second multi-layer film reflecting mirror, a nitride semiconductor layer of the second conductivity type, and a light output surface in this order. The laser element section further includes an electrode that injects a current into the active layer.

For example, in a vertical cavity light-emitting element, such as a surface emitting laser, an optical resonator is formed by opposing reflecting mirrors. For example, in the surface emitting laser, by applying a voltage to a semiconductor layer via an electrode, light emitted from the semiconductor layer resonates inside the optical resonator, and a laser light is generated.

Here, in order to cause laser oscillation at a low threshold in the surface emitting laser, for example, a current injected into the semiconductor layer via the electrode is preferably converted into light with high efficiency in the semiconductor layer. Therefore, for example, the vertical cavity light-emitting element, such as a surface emitting laser, preferably has an electrode configuration that can inject the current into the semiconductor layer with low resistance.

The present invention has been made in consideration of the above-described points and an object of which is to provide a vertical cavity light-emitting element that performs a highly efficient light-emitting operation by performing a highly efficient current injection.

A vertical cavity light-emitting element according to the present invention is provided as set forth in claim <NUM>. Preferred embodiments of the present invention may be gathered from the dependent claims.

The following describes embodiments of the present invention in detail. In the following embodiments, a case where the present invention is exploited as a surface emitting laser (semiconductor laser) will be described. However, the present invention is not limited to the surface emitting laser and is applicable to various kinds of vertical cavity light-emitting elements, such as a vertical cavity light-emitting diode.

<FIG> is a schematic top view of a vertical cavity surface emitting laser (VCSEL, which is hereinafter referred to as a surface emitting laser) according to Embodiment <NUM>. <FIG> is a cross-sectional view of the surface emitting laser <NUM>. <FIG> is a cross-sectional view taken along the line <NUM>-<NUM> in <FIG>. Using <FIG> and <FIG>, a configuration of the surface emitting laser <NUM> will be described.

The surface emitting laser <NUM> has a mount substrate <NUM>, a p-electrode (connection electrode) <NUM> formed on the mount substrate <NUM>, and a first multilayer film reflecting mirror (hereinafter simply referred to as a first reflecting mirror) <NUM> formed so as to be embedded in the p-electrode <NUM> and partially exposed from the p-electrode <NUM>.

In this embodiment, the first reflecting mirror <NUM> has a structure in which a first dielectric film (hereinafter referred to as a low refractive index dielectric film) <NUM> and a second dielectric film (hereinafter referred to as a high refractive index dielectric film) <NUM> having a higher refractive index than the low refractive index dielectric film <NUM> are alternately laminated. In this embodiment, the first reflecting mirror <NUM> constitutes a distributed Bragg reflector (DBR) made of a dielectric material.

In this embodiment, the p-electrode <NUM> has an opening portion on an upper surface from which the first reflecting mirror <NUM> is partially exposed. The first reflecting mirror <NUM> has an exposed portion 12E that is exposed from the p-electrode <NUM> while projecting from the p-electrode <NUM> at the opening portion of the p-electrode <NUM>.

In this embodiment, the first reflecting mirror <NUM> has a buried multilayer film part embedded in the p-electrode <NUM> and a projecting multilayer film part projecting so as to decrease in width in stages from the buried multilayer film part. In this embodiment, the projecting multilayer film part is a part of the first reflecting mirror <NUM> projecting in a cylindrical shape from the buried multilayer film part so as to decrease in diameter in two stages.

Further, in this embodiment, the projecting multilayer film part in the first reflecting mirror <NUM> has a lower part (lower stepped portion in this embodiment) having a side surface that is covered by the p-electrode <NUM> and an upper part (upper stepped portion in this embodiment) having a side surface and an upper surface that project from the p-electrode <NUM> and are exposed. That is, in this embodiment, the exposed portion 12E of the first reflecting mirror <NUM> includes the upper surface of the lower part of the projecting multilayer film part and the side surface and the upper surface of the upper part. The exposed portion 12E of the first reflecting mirror <NUM> has a circular shape in a top view.

The surface emitting laser <NUM> includes a light transmissive electrode (first electrode) <NUM> formed on the p-electrode <NUM> while covering the exposed portion 12E of the first reflecting mirror <NUM>. In this embodiment, the first reflecting mirror <NUM> has a through hole that passes from the mount substrate <NUM> side to the light transmissive electrode <NUM> side. The p-electrode <NUM> passes partially through the first reflecting mirror <NUM> and is connected to the light transmissive electrode <NUM>. In this embodiment, the first reflecting mirror <NUM> has the through hole formed in a tubular shape, and the p-electrode <NUM> passes through the first reflecting mirror <NUM> in a tubular shape and is connected to the light transmissive electrode <NUM>.

The surface emitting laser <NUM> includes an insulating layer <NUM> that is formed on the p-electrode <NUM> and the light transmissive electrode <NUM> and has an opening portion 14A exposing the light transmissive electrode <NUM> on the exposed portion 12E of the first reflecting mirror <NUM>.

In this embodiment, the light transmissive electrode <NUM> has an exposed portion 13E exposed from the opening portion 14A of the insulating layer <NUM>. In this embodiment, the exposed portion 13E of the light transmissive electrode <NUM> has a circular-shaped top surface shape.

For example, the mount substrate <NUM> is made of a material having a high thermal conductivity, for example, a ceramic material such as AlN. The p-electrode <NUM> is made of a metallic material, such as Au, Al, and Cu. The low refractive index dielectric film <NUM> in the first reflecting mirror <NUM> is made of SiO<NUM>, and the high refractive index dielectric film <NUM> is made of Nb<NUM>O<NUM>. The light transmissive electrode <NUM> is made of a transparent conductive film, such as ITO and IZO. The insulating layer <NUM> is made of SiO<NUM>, SiN, and the like.

The surface emitting laser <NUM> includes an optical semiconductor layer <NUM> that is formed on the insulating layer <NUM> and connected to the exposed portion 13E of the light transmissive electrode <NUM> at the opening portion 14A of the insulating layer <NUM>. For example, the optical semiconductor layer <NUM> includes a plurality of semiconductor layers made of a nitride semiconductor. The exposed portion 13E of the light transmissive electrode <NUM> functions as a contact region that electrically connects the light transmissive electrode <NUM> (p-electrode <NUM>) to the optical semiconductor layer <NUM>.

In this embodiment, the optical semiconductor layer <NUM> includes a p-type semiconductor layer (first semiconductor layer having a first conductivity type) 15P formed on the insulating layer <NUM> while being in contact with the exposed portion 13E of the light transmissive electrode <NUM>, a light-emitting layer (active layer) 15A formed on the p-type semiconductor layer 15P, and an n-type semiconductor layer (second semiconductor layer, which is a semiconductor layer having a second conductivity type opposite to the first conductivity type) 15N formed on the light-emitting layer 15A.

In this embodiment, the n-type semiconductor layer 15N has a GaN composition and contains Si as n-type impurities. The light-emitting layer 15A has a quantum well structure that includes a well layer having an InGaN composition and a barrier layer having a GaN composition. The p-type semiconductor layer 15P has a GaN-based composition and contains Mg as p-type impurities.

The configuration of the optical semiconductor layer <NUM> is not limited to this. For example, the n-type semiconductor layer 15N may have a plurality of n-type semiconductor layers having different compositions from one another. The light-emitting layer 15A may have a single quantum well structure or may have a single layer structure.

The p-type semiconductor layer 15P may have a plurality of p-type semiconductor layers having different compositions from one another. For example, the p-type semiconductor layer 15P may have a contact layer (not illustrated) for forming an ohmic contact with the light transmissive electrode <NUM>. In this case, for example, it is only necessary for the p-type semiconductor layer 15P to have a GaN layer as a clad layer between the contact layer and the light-emitting layer 15A.

The optical semiconductor layer <NUM> may have, for example, between the light-emitting layer 15A and the p-type semiconductor layer 15P, an electron-blocking layer (not illustrated) that avoids electrons injected into the light-emitting layer 15A overflowing into the p-type semiconductor layer 15P. For example, the electron-blocking layer may have an AlGaN composition. The electron-blocking layer may contain impurities, and for example, may have p-type impurities and may have a p-type conductivity type.

The surface emitting laser <NUM> includes a second multilayer film reflecting mirror (hereinafter simply referred to as a second reflecting mirror) <NUM> formed on the optical semiconductor layer <NUM>. The second reflecting mirror <NUM> is arranged opposed across the optical semiconductor layer <NUM> to the first reflecting mirror <NUM>. Together with the first reflecting mirror <NUM>, the second reflecting mirror <NUM> constitutes a resonator 10C having a direction perpendicular to the optical semiconductor layer <NUM> (direction perpendicular to the mount substrate <NUM>) as a resonator length direction.

In this embodiment, the second reflecting mirror <NUM> has a structure in which a first semiconductor film (hereinafter referred to as a low refractive index semiconductor film) <NUM> and a second semiconductor film (hereinafter referred to as a high refractive index semiconductor film) <NUM> having a higher refractive index than the low refractive index semiconductor film <NUM> are alternately laminated. That is, in this embodiment, the second reflecting mirror <NUM> constitutes a distributed Bragg reflector made of a semiconductor material.

For example, each of the low refractive index semiconductor film <NUM> and the high refractive index semiconductor film <NUM> in the second reflecting mirror <NUM> is made of the same kind of semiconductor material as the optical semiconductor layer <NUM>, which is a nitride semiconductor material in this embodiment. For example, the low refractive index semiconductor film <NUM> is made of AlInN, and the high refractive index semiconductor film <NUM> is made of GaN.

Further, in this embodiment, the second reflecting mirror <NUM> has an n-type conductivity type. In this embodiment, each of the low refractive index semiconductor film <NUM> and the high refractive index semiconductor film <NUM> contains n-type impurities. For example, in this embodiment, the low refractive index semiconductor film <NUM> and the high refractive index semiconductor film <NUM> are an AlInN film and a GaN film that contain Si, respectively.

The surface emitting laser <NUM> includes a semiconductor substrate <NUM> formed on the second reflecting mirror <NUM>. The semiconductor substrate <NUM> is made of the same kind of semiconductor material as the optical semiconductor layer <NUM> and the second reflecting mirror <NUM>, which is a nitride semiconductor material in this embodiment. The semiconductor substrate <NUM> has a light-transmissive property to light emitted from the light-emitting layer 15A.

In this embodiment, the semiconductor substrate <NUM> is a growth substrate used for crystal growth of the optical semiconductor layer <NUM> and the second reflecting mirror <NUM>. For example, the semiconductor substrate <NUM> has a GaN composition. Further, in this embodiment, a buffer layer (not illustrated) having a GaN composition is included between the semiconductor substrate <NUM> and the second reflecting mirror <NUM>.

Further, in this embodiment, the semiconductor substrate <NUM> has an n-type conductivity type. In this embodiment, the semiconductor substrate <NUM> is made of a semiconductor material having n-type impurities, and is a GaN substrate containing Si in this embodiment.

The semiconductor substrate <NUM> has an upper surface <NUM> and a projecting portion 17P projecting from the upper surface <NUM>. The projecting portion 17P has a top surface 17PS that is mirror-finished by polishing. Further, the projecting portion 17P has a damage layer 17A that is formed in a region of a predetermined depth from the top surface 17PS and in which a conductive property is impaired by the polishing.

In this embodiment, the projecting portion 17P is a part projecting in a cylindrical shape from the upper surface <NUM> in the semiconductor substrate <NUM>. The projecting portion 17P is formed so as to be arranged at a position where the central axis of the projecting portion 17P passes through the center of the exposed portion 13E in the light transmissive electrode <NUM> (that is, a contact region with the optical semiconductor layer <NUM>). In this embodiment, the projecting portion 17P has a width (diameter) D2 larger than a width (diameter) D1 of the exposed portion 13E of the light transmissive electrode <NUM>.

In this embodiment, the upper surface <NUM> of the semiconductor substrate <NUM> is a surface region of the semiconductor substrate <NUM> that has been removed by etching. More specifically, the upper surface <NUM> of the semiconductor substrate <NUM> is a surface region of the semiconductor substrate <NUM> that appears by removing the polished surface by dry etching after the polishing. Therefore, the upper surface <NUM> of the semiconductor substrate <NUM> is a region showing the n-type conductivity type. In this embodiment, the projecting portion 17P of the semiconductor substrate <NUM> is a surface region of the semiconductor substrate <NUM> in which the polished surface remains without being dry-etched.

The surface emitting laser <NUM> includes an n-electrode (second electrode) <NUM> that is formed on the upper surface <NUM> of the semiconductor substrate <NUM> and has an opening portion 18A surrounding the projecting portion 17P. In this embodiment, the n-electrode <NUM> is made of a metallic material, such as Au, Al, and Cu.

In this embodiment, the n-electrode <NUM> is formed on the semiconductor substrate <NUM> in a layered shape. The opening portion 18A of the n-electrode <NUM> has an opening width larger than the width of the projecting portion 17P of the semiconductor substrate <NUM> and is formed to be separated from the projecting portion 17P.

The surface emitting laser <NUM> has an anti-reflection layer <NUM> formed on the n-electrode <NUM> so as to bury the projecting portion 17P of the semiconductor substrate <NUM>. The anti-reflection layer <NUM> is made of, for example, a dielectric multilayer film, and in this embodiment, has a structure in which a Ta<NUM>O<NUM> layer and an SiO<NUM> layer are alternately laminated multiple times. The anti-reflection layer <NUM> suppresses reflection of the light emitted from the light-emitting layer 15A by the top surface 17PS of the projecting portion 17P of the semiconductor substrate <NUM>.

In this embodiment, the exposed portion 13E of the light transmissive electrode <NUM> (that is, the opening portion 14A of the insulating layer <NUM>) defines a luminescence center that is the center of a luminescence region of the light-emitting layer 15A and defines a center axis (hereinafter referred to as a luminescence center axis) AX of the resonator 10C. The luminescence center axis AX of the resonator 10C passes through the center of the exposed portion 13E of the light transmissive electrode <NUM> and extends along a direction perpendicular to the optical semiconductor layer <NUM>.

The luminescence region of the light-emitting layer 15A is, for example, a region having a predetermined width where light having a predetermined intensity or higher is emitted within the light-emitting layer 15A, and the center of the luminescence region is the luminescence center. Further, for example, the luminescence region of the light-emitting layer 15A is a region into which a current having a predetermined density or higher is injected within the light-emitting layer 15A, and the center of the luminescence region is the luminescence center. A straight line perpendicular to the mount substrate <NUM> passing through the luminescence center is the luminescence center axis AX. The luminescence center axis AX is a straight line extending along the resonator length direction of the resonator 10C composed of the first reflecting mirror <NUM> and the second reflecting mirror <NUM>. The luminescence center axis AX corresponds to an optical axis of a laser light exiting from the surface emitting laser <NUM>.

In this embodiment, the second reflecting mirror <NUM> has a smaller light reflectivity than the first reflecting mirror <NUM>. The second reflecting mirror <NUM> has a light-transmissive property to the light emitted from the light-emitting layer 15A. The second reflecting mirror <NUM> reflects most of the light emitted from the light-emitting layer 15A and transmits a part of a laser beam LB that has resonated in the resonator 10C to exit outside the resonator 10C.

Therefore, in this embodiment, the surface emitting laser <NUM> is configured to cause the laser beam LB generated in the resonator 10C to exit from the top surface 17PS of the projecting portion 17P of the semiconductor substrate <NUM>.

In other words, the surface emitting laser <NUM> has a region of the projecting portion 17P of the semiconductor substrate <NUM> as a light extraction region and has a region of the upper surface <NUM> (which can be also referred to as a depressed portion region with respect to the projecting portion 17P) that is a region around the projecting portion 17P of the semiconductor substrate <NUM> as a contact region with the optical semiconductor layer <NUM>.

<FIG> is a drawing schematically illustrating a current path in the surface emitting laser <NUM>. In this embodiment, as illustrated by dashed lines in <FIG>, a current CR flowing between the light transmissive electrode <NUM> (p-electrode <NUM>) and the n-electrode <NUM> flows along a direction approximately perpendicular to the optical semiconductor layer <NUM> and the second reflecting mirror <NUM> (hereinafter referred to as a longitudinal direction). The path of the current CR can be said to be a path in which an electrical resistance becomes the smallest when a current is injected into the optical semiconductor layer <NUM>.

Specifically, first, in a case where opposed electrodes are arranged in the longitudinal direction similarly to the surface emitting laser <NUM>, the distance between the electrodes becomes less than about <NUM> in many cases. This is because handling is impossible unless the surface emitting laser <NUM> itself has a mechanical strength to some extent, and accordingly, in general, approximately <NUM> to <NUM> needs to be left as a thickness of the semiconductor substrate <NUM>.

On the other hand, provisionally, in a case where electrodes are arranged in a direction parallel to the optical semiconductor layer <NUM> (hereinafter referred to a lateral direction) by partially removing the optical semiconductor layer <NUM>, and the like, the current flows in the direction parallel to the optical semiconductor layer <NUM>. In this case, considering stable heat radiation characteristics and electrical characteristics, the distance of the current path between the electrodes becomes about <NUM> or more in many cases.

Here, the electrical resistance in the optical semiconductor layer <NUM> is proportional to the distance of the current path flowing in the optical semiconductor layer <NUM> and inversely proportional to a cross-sectional area of the current path. Then, in a case where the electrodes are arranged in the longitudinal direction, the cross-sectional area of the current path is large enough to cancel out the difference of the distances of the current path compared with a case where the electrodes are arranged in the lateral direction. For example, the cross-sectional area of the current path in the case of the electrode arrangement in the longitudinal direction is larger by double digits or more than the cross-sectional area of the current path in the case of the electrode arrangement in the lateral direction (which is a cross-sectional area significantly exceeding <NUM> times). Therefore, by arranging the electrodes in the longitudinal direction, the electrical resistance between the electrodes can be made much smaller than the case of the lateral direction.

Therefore, without being wasted in the optical semiconductor layer <NUM>, the current CR is injected into the light-emitting layer 15A and converted into light with high efficiency. Therefore, the optical semiconductor layer <NUM> can perform a highly efficient light-emitting operation.

In this embodiment, the laser beam LB exits from the top surface 17PS of the projecting portion 17P of the semiconductor substrate <NUM> that is mirror-finished. This is the most preferable configuration in stabilizing an output power and a beam shape of the laser beam LB.

Specifically, considering that high electrical characteristics are obtained and the laser beam LB exits without lowering the output power in the case where the electrodes are arranged in the longitudinal direction similarly to the surface emitting laser <NUM>, the semiconductor substrate <NUM> is preferably thin to some extent.

Further, considering that optical properties of the laser beam LB, such as the beam shape and an output distribution of the laser beam LB, are stabilized, the top surface 17PS of the projecting portion 17P that is an exiting surface of the laser beam LB is preferably highly flattened. In this case, for example, performing a mirror finishing process, such as polishing, is used after performing a processing that thins a growth substrate that becomes the semiconductor substrate <NUM>.

However, the inventors of this application noted that performing the polishing has a disadvantage in which a region that does not have a conductive property is formed in a proximity of the polished surface of the growth substrate. Further, the inventors of this application confirmed by an experiment that conduction to the p-electrode <NUM> was not obtained when the n-electrode <NUM> was formed on the polished surface.

In contrast to this, in this embodiment, by removing the polished surface of the growth substrate excluding a part becoming a light exiting surface, a region of the upper surface <NUM> that is a surface region of the semiconductor substrate <NUM> other than a part that becomes an optical path of the laser beam LB is used as a contact region with the n-electrode <NUM>. Therefore, sandwiching the optical semiconductor layer <NUM>, a satisfactory path of the current CR in the longitudinal direction can be formed between the upper surface <NUM> of the semiconductor substrate <NUM> and the exposed portion 13E of the light transmissive electrode <NUM>.

Therefore, the surface emitting laser <NUM> becomes a light-emitting element that can perform a highly efficient light-emitting operation by performing a highly efficient current injection. Further, the surface emitting laser <NUM> becomes a laser element that allows the stable laser beam LB to exit with high output power. By providing the anti-reflection layer <NUM> on the projecting portion 17P, the laser beam LB with high output power and optical properties can exit more stably.

The shape and size of the projecting portion 17P in the semiconductor substrate <NUM> can be designed based on, for example, the beam shape, a radiation angle, and the like of the laser beam LB. For example, setting the light-emitting layer 15A as an exiting point of the laser beam LB and considering the distance of the laser beam LB from the n-type semiconductor layer 15N to the top surface 17PS of the projecting portion 17P of the semiconductor substrate <NUM> and the radiation angle of the laser beam LB in the n-type semiconductor layer 15N, the second reflecting mirror <NUM>, and the semiconductor substrate <NUM>, the beam shape and the beam width (beam diameter) of the laser beam LB at the top surface 17PS of the projecting portion 17P of the semiconductor substrate <NUM> can be calculated.

In this embodiment, the height of the projecting portion 17P relative to the upper surface <NUM> in the semiconductor substrate <NUM> is larger than the thickness of the n-electrode <NUM> (height from the upper surface <NUM>). This suppresses absorption of an outer edge portion of the laser beam LB by the n-electrode <NUM> after the laser beam LB exits from the top surface 17PS of the projecting portion 17P. Therefore, the laser beam LB can stably exit with a designed beam shape and output power.

In this embodiment, the opening portion 18A of the n-electrode <NUM> has an opening diameter larger than the width D2 of the projecting portion 17P of the semiconductor substrate <NUM>. Therefore, the n-electrode <NUM> is separated from the side surface of the projecting portion 17P. This is preferred in production of the n-electrode <NUM>. Specifically, in a case where a metal layer that becomes the n-electrode <NUM> is formed by lift-off, burrs are generated at an end portion of the metal layer in some cases when the metal layer is lifted off. Even in this case, by forming the n-electrode <NUM> using a larger mask than the projecting portion 17P, formation of the burrs on the projecting portion 17P can be suppressed.

In this embodiment, the p-electrode <NUM> is in contact with approximately the whole surface of the mount substrate <NUM>. With this, the p-electrode <NUM> can form a heat radiation path for effectively conducting heat generated from the optical semiconductor layer <NUM> to the mount substrate <NUM>. Therefore, the surface emitting laser <NUM> becomes a light-emitting element that has a high heat radiation performance and stably operates even in a case of driving for a long time and with a large current.

In this embodiment, the p-electrode <NUM> passes through the first reflecting mirror <NUM> and is connected to the light transmissive electrode <NUM>. Therefore, the path for effectively conducting the heat from the optical semiconductor layer <NUM> to the mount substrate <NUM> can be formed. The p-electrode <NUM> is formed so as to pass through the first reflecting mirror <NUM> in a tubular shape in a manner to surround the luminescence center axis AX. With this, a large heat radiation effect can be expected.

Each of <FIG> is a cross-sectional view illustrating a manufacturing process of the surface emitting laser <NUM>. Using <FIG>, an example of a manufacturing method of the surface emitting laser <NUM> will be described. Each of <FIG> is a cross-sectional view similar to <FIG> in the manufacturing process of the surface emitting laser <NUM>.

First, as illustrated in <FIG>, a growth substrate 17W that becomes the semiconductor substrate <NUM> is prepared, and the second reflecting mirror <NUM> and the optical semiconductor layer <NUM> are grown on the growth substrate 17W. For example, for the growth of the second reflecting mirror <NUM> and the optical semiconductor layer <NUM>, a metal organic chemical vapor deposition (MOCVD method) can be used.

Specifically, first, an n-type GaN substrate having a flat plate shape was prepared as the growth substrate 17W. After an n-GaN layer as a buffer layer is grown on the GaN substrate, an n-GaN film as the high refractive index semiconductor film <NUM> and an n-AlInN film as the low refractive index semiconductor film <NUM> are alternately grown on the buffer layer multiple times. This forms the second reflecting mirror <NUM> on the growth substrate 17W.

Next, on the second reflecting mirror <NUM>, an n-GaN layer as the n-type semiconductor layer 15N, a plurality of pairs of InGaN layer and GaN layer as the light-emitting layer 15A, and a p-GaN layer as the p-type semiconductor layer 15P are each grown. This forms the optical semiconductor layer <NUM> on the second reflecting mirror <NUM>.

Subsequently, the insulating layer <NUM> is formed on the optical semiconductor layer <NUM>. In this embodiment, on the p-type semiconductor layer 15P, an SiO<NUM> layer was formed, and an opening portion was formed in a part of the SiO<NUM> layer. This forms the insulating layer <NUM> having the opening portion 14A.

Next, the light transmissive electrode <NUM> is formed on the insulating layer <NUM>. In this embodiment, ITO as the light transmissive electrode <NUM> was formed in a layered shape on the insulating layer <NUM> so as to be in contact with the upper surface of the p-type semiconductor layer 15P at the opening portion 14A of the insulating layer <NUM>.

Subsequently, a layer-shaped electrode 11A constituting a part of the p-electrode <NUM> is formed on the insulating layer <NUM>. In this embodiment, as the layer-shaped electrode 11A, a metal layer that has an opening portion 11B having an opening width larger than the width D1 of the opening portion 14A of the insulating layer <NUM> was formed. The opening portion 11B of the layer-shaped electrode 11A was arranged so as to overlap the opening portion 14A of the insulating layer <NUM> when viewed in a direction perpendicular to the layer-shaped electrode 11A (so as to surround the opening portion 14A in this embodiment).

Next, as illustrated in <FIG>, the growth substrate 17W is cut and polished from the surface of the growth substrate 17W on the opposite side to the second reflecting mirror <NUM>. Specifically, first, the growth substrate 17W is cut or severed to decrease the thickness of the growth substrate 17W. Then, a grinding and a polishing processes are performed on the cut surface. This forms a growth substrate 17WG in which the surface of the growth substrate 17W on the opposite side to the second reflecting mirror <NUM> is mirror-finished.

Here, by performing the polishing process of the growth substrate 17W, the n-type conductive property is impaired in a proximity of the surface that has been polished. Therefore, on the growth substrate 17WG after the polishing, a high resistance region that has a very high resistance and comes into non-ohmic contact even if the n-electrode is directly formed, that is, a surface region that becomes the damage layer 17A of the semiconductor substrate <NUM>, is formed.

Subsequently, as illustrated in <FIG>, on the layer-shaped electrode 11A, a dielectric multilayer film <NUM> composed of the high refractive index dielectric films <NUM> and the low refractive index dielectric films <NUM>, which becomes the first reflecting mirror <NUM>, is formed so as to embed the opening portion 11B. In this embodiment, as the high refractive index dielectric film <NUM> and the low refractive index dielectric film <NUM>, an Nb<NUM>O<NUM> film and an SiO<NUM> film Nb<NUM>O<NUM> were alternately laminated multiple times, respectively.

Next, as illustrated in <FIG>, a part of the dielectric multilayer film <NUM> is removed to expose the layer-shaped electrode 11A. In this embodiment, a region on which the dielectric multilayer film <NUM> is removed in a tubular shape is formed such that the opening portion 11B of the layer-shaped electrode 11A is surrounded in an annular shape by the part of the layer-shaped electrode 11A exposed from the dielectric multilayer film <NUM>.

Further, in this embodiment, the dielectric multilayer film <NUM> is removed such that the part of the layer-shaped electrode 11A exposed from the dielectric multilayer film <NUM> is arranged in a region on the light transmissive electrode <NUM>. By partially removing the dielectric multilayer film <NUM>, the first reflecting mirror <NUM> is formed on the layer-shaped electrode 11A.

Subsequently, as illustrated in <FIG>, a burying electrode 11C constituting the p-electrode <NUM> is formed so as to bury the first reflecting mirror <NUM> and so as to be in contact with the layer-shaped electrode 11A exposed from the first reflecting mirror <NUM>. The upper surface of the burying electrode 11C is flattened. The burying electrode 11C is made of, for example, a metallic material similar to the layer-shaped electrode 11A. With this, the whole of the layer-shaped electrode 11A and the burying electrode 11C becomes the p-electrode <NUM> that buries the first reflecting mirror <NUM> while partially exposing the first reflecting mirror <NUM>.

Next, as illustrated in <FIG>, the growth substrate 17WG is joined to the mount substrate <NUM> from the p-electrode <NUM> side. For example, after a ceramic substrate is prepared as the mount substrate <NUM> and a metal layer (not illustrated) is formed on the upper surface of the ceramic substrate, the p-electrode <NUM> is joined to the metal layer. With this, on the mount substrate <NUM>, the growth substrate 17WG is mounted together with the optical semiconductor layer <NUM>, the first reflecting mirror <NUM>, and the second reflecting mirror <NUM>.

Subsequently, as illustrated in <FIG>, the growth substrate 17WG is partially removed from a damage region 17DA side. For example, for the partial removal of the growth substrate 17WG, a processing technique, such as dry etching, can be used. With this, the part that has not been removed of the growth substrate 17WG projects from the surface that has been removed and exposed.

Further, on the part that has not been removed, the damage region 17DA remains. On the other hand, the part that has been removed does not have the damage region 17DA and becomes a part showing the n-type conductivity type. This forms the semiconductor substrate <NUM> that has the upper surface <NUM> and the projecting portion 17P projecting from the upper surface <NUM> and has the damage layer 17A on the upper surface of the projecting portion 17P.

Next, as illustrated in <FIG>, a metal layer is formed on the semiconductor substrate <NUM>, and an opening portion that exposes the projecting portion 17P is formed on the metal layer. This forms the n-electrode <NUM>. By forming a multilayer film of dielectric material on the n-electrode <NUM> while embedding the projecting portion 17P of the semiconductor substrate <NUM>, the anti-reflection layer <NUM> is formed. The surface emitting laser <NUM> can be manufactured, for example, in this way.

In this embodiment, a case where the semiconductor substrate <NUM> has the top surface 17PS that is mirror-finished on the projecting portion 17P and has the damage layer 17A in which a conductive property is impaired in a proximity of the top surface 17PS has been described. However, the configuration of the semiconductor substrate <NUM> is not limited to this. It is only necessary for the semiconductor substrate <NUM> to at least have the upper surface <NUM> on which the n-electrode <NUM> is formed and the projecting portion 17P that projects from the upper surface <NUM> and functions as a light exiting surface. This allows a conduction in the longitudinal direction via the semiconductor substrate <NUM> and a satisfactory light to exit from the projecting portion 17P.

In this embodiment, a case where the upper surface <NUM> that is the surface region other than the projecting portion 17P in the semiconductor substrate <NUM> is a surface region of the semiconductor substrate <NUM> that appears by dry etching has been described. However, it is only necessary for the upper surface <NUM> of the semiconductor substrate <NUM> to be a surface region showing the n-type conductivity type, and a forming method of the upper surface <NUM> is not limited to etching.

In this embodiment, a case where the first reflecting mirror <NUM> is formed so as to be embedded in the p-electrode <NUM> and has the exposed portion 12E projecting and exposed from the p-electrode <NUM> has been described. Further, a case where the light transmissive electrode <NUM> is connected to the p-electrode <NUM> has been described. However, the configurations of the p-electrode <NUM>, the first reflecting mirror <NUM>, and the light transmissive electrode <NUM> are not limited to these.

For example, it is only necessary for the surface emitting laser <NUM> to at least have the first reflecting mirror <NUM> and the light transmissive electrode <NUM> that functions as a p-side electrode formed on the first reflecting mirror <NUM>. Further, a case where the insulating layer <NUM> is disposed on the light transmissive electrode <NUM> has been described. However, the insulating layer <NUM> does not have to be disposed. For example, as long as a part of a region on the light transmissive electrode <NUM> on the p-type semiconductor layer 15P is lowered in resistance, this region functions as a current injection region. Further, the anti-reflection layer <NUM> does not have to be disposed.

Thus, in this embodiment, the surface emitting laser <NUM> includes the first reflecting mirror <NUM>, the light transmissive electrode (first electrode) <NUM>, the p-type semiconductor layer 15P (first semiconductor layer), the light-emitting layer 15A, the n-type semiconductor layer 15N, the second reflecting mirror <NUM>, the semiconductor substrate <NUM>, and the n-electrode <NUM>. The light transmissive electrode <NUM> is formed on the first reflecting mirror <NUM>. The p-type semiconductor layer 15P is formed on the light transmissive electrode <NUM>. The light-emitting layer 15A is formed on the p-type semiconductor layer 15P. The n-type semiconductor layer 15N is formed on the light-emitting layer 15A. The second reflecting mirror <NUM> is formed on the n-type semiconductor layer 15N and composed of a plurality of semiconductor films having the n-type conductivity type (second conductivity type). The semiconductor substrate <NUM> is formed on the second reflecting mirror <NUM>, has the upper surface <NUM> and the projecting portion 17P projecting from the upper surface <NUM>, and has the n-type conductivity type. The n-electrode <NUM> is formed on the upper surface <NUM> of the semiconductor substrate <NUM>. Therefore, the surface emitting laser <NUM> (vertical cavity light-emitting element) that performs a highly efficient light-emitting operation by performing a highly efficient current injection can be provided.

<FIG> is a top view of a surface emitting laser <NUM> according to Embodiment <NUM>. <FIG> is a cross-sectional view taken along the line <NUM>-<NUM> in <FIG>, which is a cross-sectional view of the surface emitting laser <NUM>. Using <FIG> and <FIG>, a configuration of the surface emitting laser <NUM> will be described.

In this embodiment, the surface emitting laser <NUM> includes a first reflecting mirror <NUM> having a plurality of exposed portions 21E, an insulating layer <NUM> having a plurality of opening portions 23A corresponding to the respective exposed portions 21E, a light transmissive electrode <NUM> having a plurality of exposed portions 22E, and a semiconductor substrate <NUM> having a plurality of projecting portions 24P. That is, the surface emitting laser <NUM> has a plurality of light exiting portions and has a plurality of luminescence center axes AX.

More specifically, the first reflecting mirror <NUM> has a structure in which a low refractive index dielectric film <NUM> and a high refractive index dielectric film <NUM> that are respectively similar to the low refractive index dielectric film <NUM> and the high refractive index dielectric film <NUM> in the first reflecting mirror <NUM> are alternately laminated. The first reflecting mirror <NUM> has a plurality of exposed portions 21E that are each exposed from the p-electrode <NUM>. In this embodiment, the first reflecting mirror <NUM> constitutes a resonator 20C together with the second reflecting mirror <NUM>.

The light transmissive electrode <NUM> is formed on the first reflecting mirror <NUM> while covering each of the plurality of exposed portions 21E of the first reflecting mirror <NUM>. The insulating layer <NUM> has the opening portions 23A that expose the light transmissive electrode <NUM> at regions on the exposed portions 21E of the first reflecting mirror <NUM> in the light transmissive electrode <NUM>. With this, the light transmissive electrode <NUM> has the plurality of exposed portions 22E that are each exposed from the insulating layer <NUM>. That is, on the p-type semiconductor layer 15P of the optical semiconductor layer <NUM>, a plurality of contact regions with the light transmissive electrode <NUM> are formed.

The semiconductor substrate <NUM> has an upper surface <NUM> and the plurality of projecting portions 24P that are formed on the respective plurality of exposed portions 22E of the light transmissive electrode <NUM> and each exposed from the upper surface <NUM>. Each of the projecting portions 24P has a damage layer 24A in a proximity of its upper surface.

The surface emitting laser <NUM> has an n-electrode <NUM> that is formed on the upper surface <NUM> of the semiconductor substrate <NUM> and has a plurality of opening portions 25A surrounding the respective plurality of projecting portions 24P. The surface emitting laser <NUM> has an anti-reflection layer <NUM> formed so as to cover the projecting portions 24P of the semiconductor substrate <NUM> and the n-electrode <NUM>. The surface emitting laser <NUM> includes pad electrodes <NUM> connected to the n-electrode <NUM>.

Claim 1:
A vertical cavity light-emitting element (<NUM>) comprising:
a first multilayer film reflecting mirror (<NUM>);
a light transmissive first electrode (<NUM>) formed on the first multilayer film reflecting mirror (<NUM>);
a first semiconductor layer (15P) formed on the first electrode (<NUM>) and having a first conductivity type;
a light-emitting layer (15A) formed on the first semiconductor layer (15P);
a second semiconductor layer (15N) formed on the light-emitting layer (15A) and having a second conductivity type opposite to the first conductivity type;
a second multilayer film reflecting mirror (<NUM>) formed on the second semiconductor layer (15N) and composed of a plurality of semiconductor layers having the second conductivity type, the second multilayer film reflecting mirror (<NUM>) constituting a resonator (10C) together with the first multilayer film reflecting mirror (<NUM>);
a semiconductor substrate (<NUM>) formed on the second multilayer film reflecting mirror (<NUM>), having an upper surface (<NUM>) and a projecting portion (17P) projecting from the upper surface (<NUM>), and having the second conductivity type; and
a second electrode (<NUM>) formed on the upper surface (<NUM>) of the semiconductor substrate (<NUM>);
characterized in that
the projecting portion (17P) of the semiconductor substrate (<NUM>) has a top surface (17PS) that is mirror-finished by polishing; and
the projecting portion (17P) of the semiconductor substrate (<NUM>) has a damage layer (17A) formed along the top surface (17PS) of the projecting portion (17P), and the damage layer (17A) has the second conductivity type impaired by the polishing.