A surface-emitting semiconductor laser includes a substrate, a first electrode provided in contact with the substrate, a first light reflection layer provided over the substrate, a second light reflection layer provided over the substrate, an active layer provided between the second light reflection layer and the first light reflection layer, a current confining layer that is provided between the active layer and the second light reflection layer and includes a current injection region, a second electrode provided over the substrate, with the second light reflection layer being interposed between the second electrode and the substrate, and a contact layer that is provided between the second electrode and the second light reflection layer and includes a contact region that is in contact with the second electrode, in which the contact region has a smaller area than an area of the current injection region.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase of International Patent Application No. PCT/JP2018/043192 filed on Nov. 22, 2018, which claims priority benefit of Japanese Patent Application No. JP 2017-230071 filed in the Japan Patent Office on Nov. 30, 2017. Each of the above-referenced applications is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present technology relates to a surface-emitting semiconductor laser including a current confining layer.

BACKGROUND ART

The surface-emitting semiconductor lasers have many advantages over edge-emitting semiconductor lasers. Therefore, the surface-emitting semiconductor lasers have been under development (for example, see PTL 1). Examples of the surface-emitting semiconductor lasers include a VCSEL (Vertical Cavity Surface Emitting LASER).

CITATION LIST

Patent Literature

SUMMARY OF THE INVENTION

It has been desired to improve radiation characteristics of beams of the surface-emitting semiconductor lasers. Examples of the beams with high radiation characteristics include a beam having a single-peak intensity distribution profile, for example.

Therefore, it is desirable to provide a surface-emitting semiconductor laser that makes it possible to improve radiation characteristics of beams.

A surface-emitting semiconductor laser according to an embodiment of the present technology includes a substrate, a first electrode provided in contact with the substrate, a first light reflection layer provided over the substrate, a second light reflection layer provided over the substrate, with the first light reflection layer being interposed between the second light reflection layer and the substrate, an active layer provided between the second light reflection layer and the first light reflection layer, a current confining layer that is provided between the active layer and the second light reflection layer and includes a current injection region, a second electrode provided over the substrate, with the second light reflection layer being interposed between the second electrode and the substrate, at least a portion of the second electrode being provided at a position overlapping the current injection region, and a contact layer that is provided between the second electrode and the second light reflection layer and includes a contact region that is in contact with the second electrode, in which the contact region has a smaller area than an area of the current injection region.

In the surface-emitting semiconductor laser according to an embodiment of the present technology, the area of the contact region is smaller than the area of the current injection region. This makes it possible to increase current density around a center of the current injection region, and this makes it easy to cause oscillation in a low-order transverse mode.

In the surface-emitting semiconductor laser according to an embodiment of the present technology, the area of the contact region is smaller than the area of the current injection region. This makes it easy to obtain a beam having a single-peak intensity distribution profile. Accordingly, it is possible to improve radiation characteristics of beams.

It is to be noted that the above-described contents are mere examples of the present disclosure. The effects of the present disclosure are not limited to the description above, and the effects of the present disclosure may be other effects, or may further include other effects.

MODES FOR CARRYING OUT THE INVENTION

Next, with reference to drawings, details of an embodiment of the present technology are described. It is to be noted that, the description is given in the following order.

1. First Embodiment

Semiconductor laser in which area of contact region is smaller than area of current injection region

Example in which second light reflection layer includes diffusion region

Embodiment

FIG.1andFIG.2each illustrate a schematic configuration of a surface-emitting semiconductor laser (a semiconductor laser1) according to an embodiment of the present technology.FIG.1illustrates a partial cross-sectional configuration of the semiconductor laser1viewed from an obliquely upward direction.FIG.2illustrates an enlarged cross-sectional configuration of the portion illustrated inFIG.1. The semiconductor laser1includes a stacked structure10of semiconductors on one surface (a front surface) of a substrate11, and includes an antireflective film23on the other surface (a back surface) of the substrate11. The stacked structure10is provided in a mesa region11M of the substrate11, and includes a first light reflection layer12, an active layer13, a current confining layer14, a second light reflection layer15, and a contact layer16in this order from substrate11side. The semiconductor laser1includes a first electrode21and a second electrode22. The first electrode21is in contact with the substrate11, and the second electrode22is in contact with the contact layer16. In the semiconductor laser1, light generated in the stacked structure10provided on the front surface side of the substrate11comes out from the back surface side of the substrate11. Therefore, the semiconductor laser1is a so-called back-emitting VCSEL.

The substrate11includes a gallium arsenide (GaAs) substrate, for example. The substrate11includes material that is highly transparent to the light generated in the stacked structure10(more specifically, the active layer13). The substrate11may include indium phosphide (InP), gallium nitride (GaN), indium gallium nitride (InGaN), sapphire, silicon (Si), silicon carbide (SiC), or the like.

The mesa region11M is provided in a selective region in the substrate11. The mesa region11M includes the stacked structure10that has been subjected to etching to have a predetermined shape. A planar shape (an XY-plane inFIG.1) of the mesa region11M is a circular shape, for example. The mesa region11M includes the stacked structure10having a substantially cylindrical shape. The substrate11may include a plurality of the mesa regions11M. The respective stacked structures10provided in the plurality of mesa regions11M are apart from each other.

The first light reflection layer12provided on the front surface of the substrate11is a DBR (Distributed Bragg Reflector) layer interposed between the substrate11and the active layer13. The first light reflection layer12opposes the second light reflection layer15with the active layer13interposed therebetween. The first light reflection layer12is configured to resonate the light generated in the active layer13, between the first light reflection layer12and the second light reflection layer15.

The first light reflection layer12has a stacked structure in which a low refractive index layer and a high refractive index layer are alternately stacked on each other. The low refractive index layer is n-type AlX1Ga(1-X1)As (0<X1<1) having an optical film thickness of λ/4, for example. λ represents an oscillation wavelength of the semiconductor laser1. The high refractive index layer is n-type AlX2Ga(1-X2)As (0≤X2<X1) having an optical film thickness of λ/4, for example.

The active layer13provided between the first light reflection layer12and the second light reflection layer15includes aluminum gallium arsenide (AlGaAs)-based semiconductor material, for example. The active layer13is configured to receive electrons injected from the second electrode22via the current confining layer14(specifically, a current injection region14A to be described later) and generate dielectric emission light. For example, undoped AlX4Ga(1-X4)As (0≤X4<1) is usable as the active layer13. The active layer13may have a multi quantum well (MQW) structure of GaAs and AlGaAs, for example. The active layer13may have a multi quantum well structure of InGaAs and AlGaAs.

It is also possible to provide a first spacer layer13abetween the first light reflection layer12and the active layer13(FIG.2). The first spacer layer13amay include n-type AlX3Ga(1-X3)As (0≤X3<1), for example. Examples of n-type impurities include silicon (Si), selenium (Se), and the like.

It is also possible to provide a second spacer layer13bbetween the active layer13and the current confining layer14(FIG.2). The second spacer layer13bmay include p-type AlX5Ga(1-X5)As (0≤X5<1), for example. Examples of p-type impurities include carbon (C), zinc (Zn), magnesium (Mg), beryllium (Be), and the like.

The active layer13, the first spacer layer13a, and the second spacer layer13bmay include semiconductor material of aluminum indium gallium arsenide (AlInGaAs)-based, aluminum gallium indium phosphorus (AlGaInP)-based, aluminum indium gallium nitride (AlInGaN)-based, or the like in accordance with constituent material of the substrate11, for example.

The current confining layer14provided between the active layer13and the second light reflection layer15has a substantially circular current injection region14A at a central part of the mesa region11M in plan view (in the XY-plane inFIG.1), for example (FIG.1andFIG.3described later). A portion of circumference side of the mesa region11M in the current confining layer14has high resistance, and is a current confining region. For example, the portion of the circumference side of the current confining layer14is oxidized and thereby have high resistance. The current injection region14A is provided in a manner that the current injection region14A is surrounded by the current confining region. By providing the current confining layer14in such a way, it is possible to confine electric currents injected into the active layer13by the second electrode22and increase current injection efficiency. This makes it possible to reduce a threshold current. The radius R14(FIG.3) of the substantially circular current injection region14A is 20 μm to 50 μm, for example.

The current confining layer14includes p-type AlX6Ga(1-X6)As (0≤X6<1), for example. The current confining region is formed by oxidizing AlX6Ga(1-X6)As from the circumference of the mesa region11M. The current confining region includes aluminum oxide (AlOX), for example. A portion of the second light reflection layer15may also be provided between the second spacer layer13band the current confining layer14.

The second light reflection layer15is a DBR layer provided between the current confining layer14and the contact layer16. The second light reflection layer15opposes the first light reflection layer12with the active layer13and the current confining layer14interposed therebetween. The second light reflection layer15has a stacked structure in which a low refractive index layer and a high refractive index layer are alternately stacked on each other. The low refractive index layer is p-type AlX1Ga(1-X1)As (0<X7<1) having an optical film thickness of λ/4, for example. The high refractive index layer is p-type AlX8Ga(1-X8)As (0≤X8<X7) having an optical film thickness of λ/4, for example.

The contact layer16is provided between the second light reflection layer15and the second electrode22. The contact layer16includes a contact region16A in a region overlapping the current injection region14A in the plan view (the XY-plane inFIG.2). The contact region16A is provided at the central part of the contact layer16in the plan view, for example. The second electrode22is in contact with the contact region16A in the contact layer16. In other words, the contact region16A is a region in which the second electrode22is in contact with the stacked structure10.

FIG.3illustrates a shape of the contact region16A in the plan view (the XY-plane) with the current injection region14A. The contact region16A has a substantially circular shape in the plan view, for example. For example, the contact region16A is provided in a manner that the whole area of the contact region16A overlaps the current injection region14A. The contact region16A is preferably provided at a position at which the center (a center C16) of the contact region16A overlaps the center (a center C14) of the current injection region14A in plan view. In other words, the contact region16A is preferably concentric with the current injection region14A.

In the present embodiment, the area of the contact region16A is smaller than the area of the current injection region14A. This makes it possible to increase current density of electric currents injected by the second electrode22near the center of the current injection region14A and this makes it easy to cause oscillation in a low-order transverse mode. Details thereof are described later. The radius R16of the substantially circular contact region16A is 5 μm to 15 μm, for example. The area of the contact region16A is preferably less than or equal to the half of the area of the current injection region14A.

FIG.4illustrates another example of placing the contact region16A and the current injection region14A. The contact region16A is preferably provided at a position at which the center C16of the contact region16A is close to the center C14of the current injection region14A in plan view. However, it is also possible to provide the contact region16A in a manner that the center C16of the contact region16A is shifted from the center C14of the current injection region14A.

As illustrated inFIG.5andFIG.6, the contact region16A and the current injection region14A may have substantially rectangular shapes in plan view. In this case, for example, the lengths of all sides of the contact region16A are shorter than the lengths of sides of the current injection region14A. The contact region16A and the current injection region14A may have triangular shapes, or polygonal shapes having five or more sides in plan view. In other words, the contact region16A and the current injection region14A may have substantially circular shapes or polygonal shapes in plan view.

The contact layer16with such a contact region16A includes p-type AlX6Ga(1-X9)As (0≤X9<1), for example. The contact layer16may be a portion of the second light reflection layer15. The portion of the second light reflection layer15is a closest part to the second electrode22.

The second electrode22installed on the stacked structure10is provided in a region in which at least a portion of the second electrode22overlaps the current injection region14A in plan view. The second electrode22has substantially the same shape as the shape of the contact region16A in plan view, for example. The second electrode22has a substantially circular shape having substantially the same radius as the radius of the contact region16A in plan view, for example. The second electrode22is provided in the contact region16A. The second electrode22includes a metal film such as gold (Au), germanium (Ge), silver (Ag), palladium (Pd), platinum (Pt), nickel (Ni), titanium (Ti), vanadium (V), tungsten (W), chromium (Cr), aluminum (Al), copper (Cu), zinc (Zn), tin (Sn), indium (In), or the like for example. The second electrode22may include a single-layered metal film or may include a metal film having a stacked structure.

The first electrode21is provided in contact with the front surface of the substrate11, for example. For example, the first electrode21is provided outside the mesa region11M in a manner that the first electrode21surrounds the mesa region11M. The first electrode21is an annular electrode, for example. The first electrode21may be provided in contact with the back surface of the substrate11. The first electrode21includes a metal film such as gold (Au), germanium (Ge), silver (Ag), palladium (Pd), platinum (Pt), nickel (Ni), titanium (Ti), vanadium (V), tungsten (W), chromium (Cr), aluminum (Al), copper (Cu), zinc (Zn), tin (Sn), indium (In), or the like, for example. The first electrode21may include a single-layered metal film or may include a metal film having a stacked structure.

The antireflective film23attached to the back surface of the substrate11is provided in a manner that the antireflective film23opposes the stacked structure10. The antireflective film23is configured to suppress reflection of light at the back surface of the substrate11and efficiently extract light from the back surface of the substrate11. The antireflective film23includes silicon oxide (SiO2), silicon nitride (SiN), or the like, for example.

Such a semiconductor laser1is produced as described below, for example.

First, the first light reflection layer12, the first spacer layer13a, the active layer13, the second spacer layer13b, the current confining layer14, the second light reflection layer15, and the contact layer16are stacked on the substrate11in this order. This layered product is formed through an epitaxial crystal growth method using molecular-beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), or the like, for example.

Next, for example, a flat circular resist film is formed on the contact layer16. Using the resist film as a mask, etching is performed from the contact layer16to the first light reflection layer12while. The etching is performed by reactive-ion etching (RIE), for example. This makes it possible to form the substantially cylindrical stacked structure10in the mesa region11M on the substrate11. After the etching, the resist film is removed.

Next, the current confining layer14is subjected to oxidation treatment at high temperature in a water-vapor atmosphere. The oxidation treatment makes it possible to form the current confining region in a certain region starting from the circumference of the mesa region11M, and form the current injection region14A at the central part of the mesa region11M. Subsequently, the second electrode22is formed in the contact region16A on the contact layer16, and the first electrode21is formed in the front surface of the substrate11. Finally, the substrate11is thinned, and the semiconductor laser1is completed.

When predetermined voltage is applied between the first electrode21and the second electrode22in the semiconductor laser1, electric currents confined by the current confining layer14are injected into the active layer13via the current injection region14A. This makes it possible to emit light through electron-hole recombination. The light is reflected between the first light reflection layer12and the second light reflection layer15, travels therebetween, generates laser oscillation at a predetermined wavelength, and is extracted as laser light from the first light reflection layer12(substrate11) side. For example, respective beams of light emitted from a plurality of the mesa regions11M overlap each other and the overlapped beams of light are extracted from the semiconductor laser1.

In the semiconductor laser1according to the present embodiment, the area of the region in which the second electrode22is in contact with the stacked structure10, that is, the area of the contact region16A is smaller than the area of the current injection region14A. This makes it possible to increase current density around the center of the current injection region14A, and this makes it easy to cause oscillation in a low-order transverse mode. Hereinafter, such workings and effects are described with reference to a comparative example.

FIG.7andFIG.8each schematically illustrate a configuration of a semiconductor laser (a semiconductor laser100) according to the comparative example. In the semiconductor laser100, light generated in the active layer13is extracted from the substrate11side. In other words, the semiconductor laser100is a back-emitting semiconductor laser. In the semiconductor laser100, a second electrode (a second electrode122) is in contact with a whole surface of the contact layer16, and a contact region (a contact region116A) includes the whole area of the contact layer16. The area of the contact region116A is larger than the area of the current injection region14A. This is a difference between the semiconductor laser100and the semiconductor laser1.

In the semiconductor laser100, electric currents I (FIG.8) injected from vicinity of a circumference of the second electrode122concentrate around the circumference of the current injection region14A. Therefore, current density around the circumference of the current injection region14A is likely to be higher than current density at the center of the current injection region14A.

FIG.9is a calculated result of a relationship between current densities and positions in the current injection region14A in the semiconductor laser100. As illustrated inFIG.9, it is recognized that the current density around the circumference of the current injection region14A is higher than the current density at the center of the current injection region14A in the semiconductor laser100.

When the current density around the circumference of the current injection region14A is high, oscillation in a high-order transverse mode has an advantage over the oscillation in the low-order transverse mode, and beams resulting from the oscillation in the high-order transverse mode are generated. Examples of the transverse mode include an LP mode (Linearly Polarized Mode). The beams resulting from the oscillation in the high-order transverse mode have a multiple-peak intensity distribution profile, or a wide emission angle, for example. In particular, when the current injection region14A has a large area, many high-order transverse modes are permitted. This makes it easy to generate the beams resulting from the oscillation in the high-order transverse modes.

FIG.10illustrates an example of light intensity distribution of beams emitted from the semiconductor laser100. The beams emitted from the semiconductor laser100have a multiple-peak intensity distribution profile as illustrated inFIG.10. In addition, the beams have wide emission angles.

In a case where the current injection region14A has a small area, the oscillation in the low-order transverse mode tends to have an advantage. Therefore, it is also possible to connect a plurality of the stacked structures10including the current injection regions14A each having a small area in parallel and output prescribed light. For example, approximately several hundreds to a thousand of stacked structures10including substantially circular current injection regions14A each having a radius of 4 μm or less are connected in parallel. This makes it possible to cause all the stacked structures10to simultaneously emit light. Therefore, it is necessary for the respective stacked structures10to have same light output characteristics, and it is necessary to surely connect the plurality of stacked structures10.

However, it is difficult to prepare the plurality of current injection regions14A of the same size on a wafer surface due to oxidation process characteristics, because the radius of the current injection regions14A is as small as approximately 4 μm. Accordingly, a yield may decrease when the approximately several hundred to thousand stacked structures10are connected in parallel as described above. In addition, the stacked structures10have heights of approximately several μm, for example. It is difficult to form an embedded structure of such a height in which the heights of all the stacked structures10are uniform. In addition, it is also difficult to form all the stacked structures10having uniform openings for connecting the first electrode21to the second electrode122. In addition, it is also difficult to completely eliminate breaks caused by unevenness. As described above, it is difficult to surely connect several hundred or more stacked structures10, and the yield may decrease.

On the other hand, as illustrated inFIG.11, the area of the contact region16A in the semiconductor laser1according to the present embodiment is smaller than the area of the current injection region14A. Therefore, the electric currents I injected from the second electrode22concentrate around the center of the current injection region14A.

FIG.12illustrates a calculation result of a relationship between current densities and positions in the current injection region14A in the semiconductor laser1.FIG.12also illustrates a result of the semiconductor laser100illustrated inFIG.9in addition to the result of the semiconductor laser1. In the semiconductor laser1including the smaller contact region16A, current density around the center of the current injection region14A is higher than the circumference of the current injection region14A.

This makes it possible to give an advantage on oscillation in the low-order transverse mode, or more specifically, a 0-th-order mode (an LP01 mode), and the semiconductor laser1emits beams resulting from the oscillation in the 0-th-order mode.

FIG.13illustrates light intensity distribution of beams emitted from the semiconductor laser1. The beams emitted from the semiconductor laser1have a single-peak intensity distribution profile as illustrated inFIG.13. In addition, the beams have small emission angles. For example, the size of the current injection region14A of the semiconductor laser1(FIG.13) is the same as that of the semiconductor laser100(FIG.10). Therefore, it is possible for the semiconductor laser1to emit beams having the single-peak intensity distribution profile even in a case where the current injection region14A has a large area.

FIG.14Aillustrates a relationship between a size of the area of the contact region16A and output angles of an FFP obtained in a case where an area of the current injection region14A is an area A1, andFIG.14Billustrates a relationship between a size of the area of the contact region16A and the output angles of the FFP obtained in a case where the area of the current injection region14A is an area A2(A1and A2are values of the area of the current injection region14A, and satisfy a relationship of A1<A2). In this manner, it is recognized that the output angle of the FFP decreases when the area of the contact region16A is smaller than the area of the current injection region14A.

FIG.15illustrates calculation results of relationships between light output and injection currents of the semiconductor lasers1and100. The semiconductor laser1makes it possible to obtain similar output as the semiconductor laser100.

As described above, the area of the contact region16A in the semiconductor laser1is smaller than the area of the current injection region14A. This gives an advantage on oscillation in the low-order transverse mode even in a case where the current injection region14A has a large area. Therefore, it is possible to achieve high output power by increasing the area of the current injection region14A, and it is also possible to emit beams having a single-peak intensity distribution profile resulting from the oscillation in the low-order transverse mode. In addition, the increase in the area of the current injection region14A makes it possible to drastically reduce the number of stacked structures10connected to each other. This makes it easy for the respective stacked structures10to have uniform light output characteristics, and this makes it possible to increase the yield.

As described above, according to the present embodiment, the area of the contact region16A is smaller than the area of the current injection region14A. This makes it easier to obtain beams having a single-peak intensity distribution profile. Accordingly, it is possible to improve radiation characteristics of the beams. In addition, even in a case where the current injection region14A has a large area, the oscillation in the low-order transverse mode tends to have an advantage. This makes it possible to achieve both high output power and improvement in radiation characteristics. In addition, when the plurality of stacked structures10is connected in parallel, it is easier for the respective stacked structures10to have uniformed light output characteristics. In addition, it is also possible to improve the yield.

In addition, it is also possible to use the semiconductor laser1to cause the plurality of stacked structures10to independently emit light, and, for example, change irradiation light patterns over time. In the independently driving-use, a structure of wiring lines and the like become complicated. However, when using the semiconductor laser1that achieves high output power and single transverse-mode oscillation, it is possible to reduce the number of stacked structures10used for achieving same light output, as compared to the semiconductor laser100, for example. Therefore, it is possible to design with an allowance wiring lines even in a case of independently driving the stacked structures10.

In addition, with an increase in the area of the current injection region14A, light output from each of the stacked structures10increases. Therefore, for example, this makes it easier to adjust the number of stacked structures10to match their individual driving patterns. Accordingly, it is possible to design the semiconductor laser1more freely.

In addition, when using the semiconductor laser1, it is possible to suppress concentration of electric currents around the circumference of the current injection region14A as compared to the semiconductor laser100. This makes it possible to suppress deterioration around the circumference of the current injection region14A resulting from the concentration of electric currents, and this makes it possible to improve reliability.

In addition, a production process of the semiconductor laser1is substantially the same as a production process of the semiconductor laser100. For example, it is only necessary to form the second electrode22instead of the second electrode122of the semiconductor laser100. The second electrode22is smaller than the second electrode122. In other words, it is not necessary to add any production process or make any special change or the like in the production process, and it is possible to easily produce the semiconductor laser1.

In addition, in the back-emitting semiconductor laser1, front side of the substrate11on which the stacked structure10is provided is mounted on a submount via solder. This makes it possible to directly radiate heat at a short distance from a light emission part. In addition, the semiconductor laser1including the second electrode22tends to have uniform current density distribution as compared to a front-surface-emitting semiconductor laser including the annular electrode. In addition, it is easy to increase the size of the area of the current injection region14A. Accordingly, the back-emitting semiconductor laser1is more appropriate for high output power than the front-surface-emitting semiconductor laser.

Such a semiconductor laser1that makes it possible to achieve both high output power and improvement in radiation characteristics is preferably applicable to a sensing light source, a laser printer, and the like, for example. In particular, high efficacy is obtained when using the semiconductor laser1including the large mesa region11M and the large current injection region14A.

Next, a modification of the above-described embodiment is described. It is to be noted that the same components as those of the above-described embodiment are given the same reference signs, and their descriptions are omitted as appropriate.

FIG.16schematically illustrates a cross-sectional configuration of a semiconductor laser (a semiconductor laser1A) according to a modification of the above-described embodiment. The semiconductor laser1A includes a diffusion region R (an electroconductive region) in a region overlapping the contact region16A in plan view. Except the diffusion region R, the semiconductor laser1A has a configuration similar to the semiconductor laser1, and achieves workings and effects that are also similar to the semiconductor laser1.

The diffusion region R is a region in which impurities such as zinc (Zn) or the like is diffused, for example. The impurities are diffused through thermodiffusion or the like, for example. For example, the diffusion region R is selectively formed in a region in the contact layer16and the second light reflection layer15, the region overlapping the contact region16A in plan view. The diffusion region R has a higher impurity concentration than the other portion in the contact layer16and the second light reflection layer15. Therefore, the diffusion region R in the contact layer16and the second light reflection layer15has a higher electrical conductivity than the other portion. This makes it possible to increase current concentration effect around the center of the current injection region14A. It is not necessary to expand the diffusion region R to a portion of the second light reflection layer15(a portion on the current confining layer14side) in a thickness direction (in a Z direction inFIG.16).

It is preferable that the diffusion region R do not reach the active layer13. If the active layer13with highest light intensity includes the diffusion region R having high impurity concentration, the impurities absorb light and may affect a beam profile and an amount of heat generation.

In a way similar to the semiconductor laser1A, the area of the contact region16A in the semiconductor laser1A according to the present modification is smaller than the area of the current injection region14A. This makes it easier to obtain beams having a single-peak intensity distribution profile. Accordingly, it is possible to improve radiation characteristics of the beams. In addition, the region overlapping the contact region16A includes the diffusion region R having a higher electrical conductivity than the other portion. This makes it possible to achieve even higher current density around the center of the current injection region14A. Accordingly, it is possible to improve radiation characteristics of beams more effectively. In addition, it is possible to reduce driving voltage. This makes it possible to improve luminous efficacy.

The present technology has been described above with reference to the embodiment and the modification. However, the present technology is not limited thereto, and it is possible to make various kinds of modifications thereof. For example, each of the components of the semiconductor lasers1and1A exemplified in the foregoing embodiment and the like, the arrangement thereof, the number thereof, and the like are mere examples. All of the components may not necessarily be provided, or another component may be further provided. For example, in the above-described embodiment and the like, a case where the first electrode21is provided on the front surface of the substrate11has been described. However, it is only necessary for the first electrode21to be in contact with the substrate11. The first electrode21may be provided on the back surface of the substrate11.

In addition, in the above-described embodiment and the like, a case where the whole surface of the second electrode22is in contact with the contact layer16has been described. However, it is also possible to provide the second electrode22in a manner that only a portion of the second electrode22is in contact with the contact layer16. In other words, the area of the second electrode22may be different from the area of the contact region16A in plan view. For example, as illustrated inFIG.17, an insulating layer24may be provided on the contact layer16. The insulating layer24has an opening in the contact region16A. In this case, the area of the second electrode22may be larger than the area of the current injection region14A in plan view.

In addition, with reference toFIG.3toFIG.6, a case where the shape of the contact region16A is substantially similar to the shape of the current injection region14A in plan view has been described above. However, the shape of the contact region16A may be different from the shape of the current injection region14A in plan view. For example, the contact region16A may have a circular shape in plan view, and the current injection region14A may have a polygonal shape in plan view.

It is to be noted that the effects described in this specification are merely examples; therefore, effects in the present technology are not limited thereto, and the present technology may have other effects.

It is to be noted that the present technology may also be configured as follows.

A surface-emitting semiconductor laser including:

a substrate;

a first electrode provided in contact with the substrate;

a first light reflection layer provided over the substrate;

a second light reflection layer provided over the substrate, with the first light reflection layer being interposed between the second light reflection layer and the substrate;

an active layer provided between the second light reflection layer and the first light reflection layer;

a current confining layer that is provided between the active layer and the second light reflection layer and includes a current injection region;

a second electrode provided over the substrate, with the second light reflection layer being interposed between the second electrode and the substrate, at least a portion of the second electrode being provided at a position overlapping the current injection region; and

a contact layer that is provided between the second electrode and the second light reflection layer and includes a contact region that is in contact with the second electrode,

in which the contact region has a smaller area than an area of the current injection region.

The surface-emitting semiconductor laser according to (1), in which a whole area of the contact region is provided at a position overlapping the current injection region.

The surface-emitting semiconductor laser according to (1) or (2), in which the contact region and the current injection region each have a circular shape in plan view.

The surface-emitting semiconductor laser according to (1) or (2), in which the contact region and the current injection region each have a polygonal shape in plan view.

The surface-emitting semiconductor laser according to any one of (1) to (4), in which a center of the contact region in plan view is provided at a position overlapping a center of the current injection region in plan view.

The surface-emitting semiconductor laser according to any one of (1) to (5), in which current density around a center of the current injection region is higher than current density around a circumference of the current injection region.

The surface-emitting semiconductor laser according to any one of (1) to (6), in which the second light reflection layer and the contact layer have an electroconductive region provided at a position overlapping the contact region, the electroconductive region having a higher electrical conductivity than another portion.

The surface-emitting semiconductor laser according to (7), in which the electroconductive region has a higher impurity concentration than an impurity concentration of the other portion in the second light reflection layer and the contact layer.

The surface-emitting semiconductor laser according to any one of (1) to (8), in which

the substrate has a mesa region in a selective region, and

the first light reflection layer, the second light reflection layer, the active layer, and the current confining layer are provided in the mesa region.

The surface-emitting semiconductor laser according to any one of (1) to (9), in which the substrate is transparent to light generated in the active layer.

The present application is based on and claims priority of Japanese Patent Application JP 2017-230071 filed in the Japan Patent Office on Nov. 30, 2017, the entire contents of which is hereby incorporated by reference.