WO2019187666A1

WO2019187666A1 - Semiconductor laser and inspection device

Info

Publication number: WO2019187666A1
Application number: PCT/JP2019/004238
Authority: WO
Inventors: 影山健生
Original assignee: 株式会社Ｑｄレーザ
Priority date: 2018-03-30
Filing date: 2019-02-06
Publication date: 2019-10-03
Also published as: JP2019179864A

Abstract

This semiconductor laser is characterized in that: a plurality of active layers are provided, each including a first reflection layer wherein an excitation light enters and an emission light is reflected, a second reflection layer provided in the layering direction of the first reflection layer and reflecting the emission light, a light-emitting layer sandwiched in the layering direction between the first reflection layer and the second reflection layer, layered in the layering direction and emitting the emission light caused by the excitation light, and first semiconductor layers sandwiching the light-emitting layer in the layering direction; a second semiconductor layer is provided between the first semiconductor layers of adjacent active layers of the plurality of active layers, and has a second band gap energy that is greater than the first band gap energy of first semiconductor layers; and, the closer to the first reflection layer side, the shorter the layering direction widths of the active layers of the plurality of active layers become.

Description

Semiconductor laser and inspection equipment

The present invention relates to a semiconductor laser and an inspection apparatus, for example, an optically pumped surface emitting laser and an inspection apparatus.

The surface emitting laser has an active layer provided on a substrate and a pair of reflective layers sandwiching the active layer (for example, Patent Document 1). It is known to arrange an active layer so that the active layer has a plurality of active layers and becomes an antinode of a standing wave generated between a pair of reflective layers (for example, Patent Document 2).

JP-A-7-221398 JP-A-8-340149

If the number of carriers excited by excitation light in a plurality of active layers in a surface emitting laser is uneven, the laser characteristics will be degraded.

The present invention has been made in view of the above problems, and aims to improve laser characteristics.

The present invention provides a first reflective layer that receives excitation light and reflects emitted light, a second reflective layer that is provided in the stacking direction of the first reflective layer and reflects the emitted light, and the first reflective layer in the stacking direction. A light emitting layer sandwiched between the reflective layer and the second reflective layer, stacked in the stacking direction and emitting the emitted light by the excitation light, and a first semiconductor layer sandwiching the light emitting layer in the stacking direction, respectively A second active layer having a second band gap energy greater than the first band gap energy of the first semiconductor layer, the active layer being provided between the active layer and the first semiconductor layer of the active layer adjacent to the active layer. A semiconductor layer, wherein a width of the active layer in the plurality of active layers in the stacking direction becomes smaller as going to the first reflective layer side.

In the above configuration, the energy of the excitation light may be larger than the first band gap energy and smaller than the second band gap energy.

In the above configuration, a plurality of antinodes of standing waves generated between the first reflective layer and the second reflective layer may be positioned in the plurality of active layers, respectively.

In the above configuration, the light emitting layer may be a quantum well layer or a quantum dot layer.

In the above structure, each of the plurality of active layers may have a plurality of light emitting layers.

In the above-described configuration, any one of the first reflective layer and the second reflective layer changes in the stacking direction with respect to the other of the first reflective layer and the second reflective layer, whereby the wavelength of the emitted light is increased. It can be configured to change.

The present invention is an inspection apparatus including the semiconductor laser.

According to the present invention, the laser characteristics can be improved.

1 is a cross-sectional view of a semiconductor laser in Example 1. FIG. FIG. 2 is a cross-sectional view of the resonance layer in the first embodiment. FIG. 3 is a cross-sectional view of the resonance layer in Comparative Example 1. 4A and 4B are diagrams showing the excitation light intensity I (z), the standing wave light intensity, and the conduction band bottom energy Ec with respect to the position z in Comparative Example 1. FIG. FIGS. 5A and 5B are diagrams showing the excitation light intensity I (z), standing wave light intensity, and conduction band bottom energy Ec with respect to the position z in the first embodiment. FIG. 6 is a diagram illustrating the number of carriers excited in the lengths L1 to L3 in Comparative Example 1 and Example 1. FIG. 7 is a schematic diagram showing the emission intensity of the semiconductor laser with respect to the excitation light intensity in Comparative Example 1 and Example 1. FIG. 8 is a cross-sectional view of the semiconductor laser according to the second embodiment. 9A and 9B are diagrams showing the excitation light intensity I (z), standing wave light intensity, and conduction band bottom energy Ec with respect to the position z in Comparative Example 2. FIG. FIG. 10A and FIG. 10B are diagrams showing the excitation light intensity I (z), standing wave light intensity, and conduction band bottom energy Ec with respect to the position z in the second embodiment. FIG. 11 is a diagram illustrating the number of carriers excited in the lengths L1 to L3 in Comparative Example 2 and Example 2. FIG. 12 is a block diagram of an inspection apparatus according to the third embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view of a semiconductor laser in Example 1. The semiconductor laser is a photoexcited surface emitting laser. As shown in FIG. 1, a reflective layer 12, a resonance layer 14, and a reflective layer 16 are sequentially provided on a substrate 10. The substrate 10 is a semiconductor layer such as a GaAs layer. The reflective layer 12 is formed by alternately laminating a low refractive index layer 12a and a high refractive index layer 12b having a higher refractive index than the low refractive index layer 12a. The reflective layer 16 is formed by alternately laminating a low refractive index layer 16a and a high refractive index layer 16b having a higher refractive index than the low refractive index layer 16a.

When the excitation light 52 is irradiated to the resonance layer 14, the resonance layer 14 emits light. The

reflective layers

12 and 16 reflect the light emitted from the resonant layer 14. The optical length between the upper surface of the reflective layer 12 and the lower surface of 16 is set to 0.5 × natural number times the wavelength λ of light. As a result, a standing wave is generated in the resonance layer 14 and light resonates in the resonance layer 14. By making the reflectance of the reflective layer 16 slightly smaller than 1, the laser light 50 is emitted from the upper surface of the reflective layer 16.

The low

refractive index layers

12a and 16a are, for example, an Al _0.9 Ga _0.1 As layer having a thickness of 87 nm, and the high

refractive index layers

12b and 16b are, for example, a GaAs layer having a thickness of 75 nm. In the reflective layer 12, the low refractive index layer 12a and the high refractive index layer 12b are, for example, 35 pairs. In the reflective layer 16, the low refractive index layer 16a and the high refractive index layer 16b are, for example, 22 pairs. The low

refractive index layers

12a and 16a and the high

refractive index layers

12b and 16b are Al _x Ga _1-x As layers (0 ≦ x ≦ 1, GaAs when x = 0, and AlAs when x = 1). At this time, x of the low

refractive index layers

12a and 16a is made larger than x of the high

refractive index layers

12b and 16b. When x of the low refractive index layer 16a is large, the low refractive index layer 16a is easily oxidized. Therefore, the uppermost layer of the reflective layer 16 is a high refractive index layer 16b so that the low refractive index layer 16a is not exposed to the air. The reflective layer 16 may be a dielectric DBR (Distributed Bragg Reflector). In the dielectric DBR, for example, a silicon oxide film can be used as the low refractive index layer, and a silicon nitride film or a titanium oxide film can be used as the high refractive index layer.

FIG. 2 is a cross-sectional view of the resonance layer in the first embodiment. As shown in FIG. 2, the resonance layer 14 has a plurality of active layers 20. For example, when the thickness of the resonance layer 14 is 2λ, the active layer 20 has three layers. Each of the active layers 20 includes a light emitting layer 22 and a semiconductor layer 24. The active layer 20 is sandwiched between the semiconductor layers 26. Three light emitting layers 22 are provided in the semiconductor layer 24. The three light emitting layers 22 form light emitting layer groups 21a to 21c. In each light emitting layer group 21a to 21c, the light emitting layer 22 functions as a quantum well layer, and the semiconductor layer 24 functions as a barrier layer of the quantum well. The light emitting layer 22 may be a quantum dot layer. The upper surface of the resonance layer 14 is 0, and the lower direction is the z direction. The band gap energy of the semiconductor layer 26 is larger than the band gap energy of the semiconductor layer 24. The band gap energy of the semiconductor layer 26 may be lower than the excitation light energy, and the band gap energy of each semiconductor layer 26 may be different from each other. The band gap energy of the light emitting layer 22 is smaller than the band gap energy of the semiconductor layer 24. Carriers (electrons and holes) are excited by excitation light in the semiconductor layer 24 and the light emitting layer 22. As carriers are recombined in the light emitting layer 22, light is emitted from the light emitting layer 22. As the emitted light resonates between the

reflective layers

12 and 16, stimulated emission occurs from the light emitting layer 22.

The semiconductor layer 24 is, for example, a GaAs layer, and the semiconductor layer 26 is, for example, an Al _0.2 Ga _0.8 As layer. The light emitting layer 22 is, for example, an In _0.28 Ga _0.72 As layer. The semiconductor layers 24 and 26 are Al _x Ga _1-x As layers (0 ≦ x ≦ 1). At this time, x of the semiconductor layer 26 is made larger than x of the semiconductor layer 24. Thereby, the band gap energy of the semiconductor layer 26 can be made larger than the band gap energy of the semiconductor layer 24. Moreover, the light emitting layer 22 can be made into a quantum well layer by making the light emitting layer 22 into InGaAs or InAs.

In order to explain the effects of Example 1, Comparative Example 1 will be described. FIG. 3 is a cross-sectional view of the resonance layer in the first comparative example. As shown in FIG. 3, in Comparative Example 1, the semiconductor layer 26 is not provided, and the light emitting layer 22 is provided in the semiconductor layer 24. Other configurations of the resonance layer 14 are the same as those in the first embodiment, and the description thereof is omitted.

4 (a) and 4 (b) are diagrams showing excitation light intensity I (z), standing wave light intensity, and conduction band bottom energy Ec with respect to position z in Comparative Example 1. FIG. The excitation light intensity I (z) indicates the light intensity distribution in the resonance layer 14 of the excitation light 52. The standing wave light intensity indicates the light intensity of the standing wave in the resonance layer 14 generated between the

reflective layers

12 and 16. The conduction band bottom energy Ec indicates the energy of the bottom of the conduction band in the resonance layer 14. The excitation light intensity I (z) is 1 when z = 0. The standing wave light intensity and the conduction band bottom energy Ec are expressed in arbitrary units (au).

The wavelength λ of the laser beam is set to 1050 nm so that a standing wave of 2λ is generated between the

reflective layers

12 and 16. If the refractive index of GaAs is 3.5, the thickness of the resonance layer 14 is 600 nm. As shown in FIG. 4B, the upper end (z = 0 nm) and the lower end (z = 600 nm) of the resonance layer 14 are antinodes of standing waves. Three antinodes are formed in the resonance layer 14 at intervals of λ / 2 (150 nm).

As shown in FIG. 4B, the light emitting layer groups 21a to 21c are provided near the antinodes of the standing wave. In the light emitting layer groups 21a to 21c, the light emitting layer 22 is an In _0.28 Ga _0.72 As layer having a thickness of 7 nm, and the barrier layer between the light emitting layers 22 is a GaAs layer having a thickness of 15 nm. By providing the light emitting layer groups 21a to 21c near the antinodes of the standing wave, the optical gain can be efficiently obtained in the light emitting layer groups 21a to 21c.

In the photo-excited surface emitting laser, the carrier is excited by the excitation light. In order to excite carriers, the energy of the excitation light is made larger than the band gap energy of the semiconductor layer 24. Therefore, the wavelength of the excitation light is set to 808 nm, which is shorter than the wavelength corresponding to the band gap energy of GaAs. As shown in FIG. 4A, the excitation light is attenuated in the semiconductor layer 24. For this reason, the excitation light intensity distribution in the resonance layer 14 decreases as the position z increases. For this reason, the light emitting layer group 21c having a large position z has fewer carriers contributing to light emission than the light emitting layer group 21a. Thus, the carriers are unbalanced by the light emitting layer groups 21a to 21c.

FIGS. 5A and 5B are diagrams showing the excitation light intensity I (z), standing wave light intensity, and conduction band bottom energy Ec with respect to the position z in the first embodiment. As shown in FIG. 5B, the band gap energy of the semiconductor layers 26 a to 26 c is larger than the band gap energy of the semiconductor layer 24. From the semiconductor layer 26a 26c is _Al 0.2 _{Ga 0.8} As layer. The energy of the excitation light is lower than the band gap energy of the semiconductor layers 26a to 26c. Therefore, the excitation light passes through the semiconductor layers 26a to 26c. The thicknesses of the semiconductor layers 26a to 26c are 39 nm, 5 nm, and 5 nm, respectively. The excitation light intensity I (z) is as shown in FIG.

In Comparative Example 1 and Example 1, the number of carriers contributing to the light emission of each light emitting layer group 21a to 21c was calculated. In Comparative Example 1, the carriers contributing to the light emission of the light emitting layer group 21a are carriers excited at a length L1 = 225 nm from z = 0 to z = 225 nm between the light emitting

layer groups

21a and 21b. The carriers contributing to the light emission of the light emitting layer group 21b were carriers excited at a length L2 = 150 nm from z = 225 nm to z = 375 nm intermediate between the light emitting

layer groups

21b and 21c. The carriers contributing to the light emission of the light emitting layer group 21c were carriers excited at a length L3 = 225 nm from z = 375 nm to z = 600 nm. That is, in the above example of Comparative Example 1, the relationship between the lengths L1 to L3 is L2 <L1 = L3.

In Example 1, the semiconductor layers 26a to 26c serve as barrier layers against excited carriers. Therefore, the carriers contributing to the light emission of each of the light emitting layer groups 21a to 21c are carriers excited in the semiconductor layer 24 sandwiched between the semiconductor layers 26a to 26c. Therefore, the carriers contributing to the light emission of the light emitting layer group 21a are carriers excited at the length L1 = 158 nm between the semiconductor layers 26a and 26b. The carriers contributing to the light emission of the light emitting layer group 21b were carriers excited at a length L2 = 177 nm between the semiconductor layers 26b and 26c. The carrier contributing to the light emission of the light emitting layer group 21c was a carrier excited at a length L3 = 222 nm between the semiconductor layer 26c and z = 600 nm. That is, in the above example of the first embodiment, the relationship between the lengths L1 to L3 is L1 <L2 <L3. In FIG. 2, a semiconductor layer that serves as a carrier barrier is not shown under the active layer 20 including the light emitting layer group 21c, but the reflective layer 12 in FIG. 1 serves as a carrier barrier.

The number of carriers Nn excited within the length Ln (n is a natural number) is expressed by Equation 1. zn is the position of z at the end of the n-th semiconductor layer 26 where z is larger.

FIG. 6 is a diagram showing the number of carriers excited in the lengths L1 to L3 in Comparative Example 1 and Example 1. The number of carriers was calculated by simulation. As shown in FIG. 6, in Comparative Example 1, the number of carriers is not uniform from L1 to L3. In Example 1, the number of carriers is uniform from L1 to L3. This is because L1 in the region where the excitation light intensity I (z) is large is shorter than L3 in the region where the excitation light intensity I (z) is small.

FIG. 7 is a schematic diagram showing the emission intensity of the semiconductor laser with respect to the excitation light intensity in Comparative Example 1 and Example 1. When the number of carriers contributing to light emission of the light emitting layer groups 21a to 21c is not uniform as in Comparative Example 1, the light emission intensity characteristic (LL characteristic) with respect to the excitation light intensity is nonlinear. Moreover, even if the excitation light intensity is increased, the emission intensity is saturated and does not increase so much.

The reason why the LL characteristic is saturated in Comparative Example 1 will be described. In Comparative Example 1, when the excitation light intensity increases, only the light emitting layer group 21a having a large number of carriers contributes to oscillation. On the other hand, in the light emitting

layer groups

21b and 21c, the carrier density does not reach the threshold carrier density causing oscillation. Thus, in the light emitting

layer groups

21b and 21c, carriers are consumed as spontaneous emission light or heat without contributing to laser oscillation. Further, when the carrier density of the light emitting layer group 21a reaches the threshold carrier density, the light emitting

layer groups

21b and 21c do not reach the carrier density that is transparent to the oscillation light. Thus, the light emitting

layer groups

21b and 21c function as an absorption layer for oscillation light. Therefore, the optical output of the semiconductor laser is greatly limited. As a result, in order for all of the light emitting layer groups 21a to 21c to contribute to oscillation, the excitation intensity is greatly increased. For this reason, in Comparative Example 1, the LL characteristic is saturated, and a desired LL characteristic cannot be obtained.

On the other hand, in Example 1, the number of carriers contributing to the light emission of the light emitting layer groups 21a to 21c is almost uniform. Thereby, the LL characteristic becomes linear. This is because light emission does not saturate in each of the light emitting layer groups 21a to 21c even when the excitation light intensity increases. That is, in Example 1, when the light emitting layer groups 21a to 21c are irradiated with excitation light having the same intensity as in Comparative Example 1, the number of carriers generated in Comparative Example 1 is small. For this reason, the excitation light intensity, which is a threshold value at which the oscillation light oscillates in the light emitting layer groups 21a to 21c, is smaller than that of the first comparative example. However, when the excitation light intensity is greater than or equal to the threshold value, the conversion efficiency from the excitation light to the oscillation light is greatly improved as compared with Comparative Example 1. For this reason, the amount of heat generated in the light emitting layer groups 21a to 21c is reduced, so that the LL characteristics are less likely to be saturated. As a result, the maximum light output can be improved. Further, the carrier densities of the light emitting layer groups 21a to 21c are uniform. Thereby, the linearity of the Ll characteristic is improved and the kink disappears. Thus, in the first embodiment, the LL characteristics can be improved.

FIG. 8 is a cross-sectional view of the semiconductor laser in Example 2. As shown in FIG. 8, an air gap 18 is provided between the resonance layer 14 and the reflection layer 16. The reflective layer 16 is supported on the resonance layer 14 by the support layer 17. By driving the reflective layer 16 and changing the thickness of the air gap 18, the wavelength of the laser light 50 is variable. For example, the wavelength of the laser beam 50 can be set to 1050 nm ± 50 nm. When the low refractive index layer 16a is easily oxidized, the uppermost layer and the lowermost layer of the reflective layer 16 are the high refractive index layer 16b so that the low refractive index layer 16a is not exposed to the air. If the reflective layer 16 can be driven, a layer made of gas, liquid, vacuum, or solid may be provided instead of the air gap 18.

9A and 9B are diagrams showing the excitation light intensity I (z), the standing wave light intensity, and the conduction band bottom energy Ec with respect to the position z in Comparative Example 2. FIG. As shown in FIGS. 9A and 9B, the thickness of the resonance layer 14 is 2.25λ. The thickness of the air gap 18 is 1.25λ. If the interface between the air gap 18 and the resonance layer 14 is a standing wave node, the resonance layer 14 above the light emitting layer group 21a becomes 1 / 4λ thick. Thereby, the length L1 becomes 300 nm. The other configurations are the same as those in FIGS. 4A to 4B of the first comparative example.

FIGS. 10A and 10B are diagrams showing the excitation light intensity I (z), standing wave light intensity, and conduction band bottom energy Ec with respect to the position z in Example 2. FIG. As shown in FIGS. 10A and 10B, the semiconductor layer 26a becomes 1 / 4λ thick. The thickness of the semiconductor layer 26a is 114 nm. Other configurations are the same as those of the first comparative example shown in FIGS. 5A to 5B. Similar to Comparative Example 1 and Example 1, the number of carriers excited within the lengths L1 to L3 was calculated.

FIG. 11 is a diagram showing the number of carriers excited in the lengths L1 to L3 in Comparative Example 2 and Example 2. As shown in FIG. 11, in Example 2, the number of carriers is uniform from L1 to L3 compared to Comparative Example 2. As in the second embodiment, the wavelength of the semiconductor laser may be variable.

According to Examples 1 and 2, as shown in FIGS. 1, 2, and 8, the reflective layer 16 (first reflective layer) reflects the emitted light that the excitation light 52 enters and the light emitting layer 22 emits. The reflective layer 12 (second reflective layer) is provided in the stacking direction of the reflective layer 16 and reflects the emitted light. The plurality of active layers 20 are sandwiched between the

reflective layers

12 and 16 in the stacking direction, and each include a light emitting layer 22 and a semiconductor layer 24 (first semiconductor layer) sandwiching the light emitting layer 22 in the stacking direction. The semiconductor layer 26 (second semiconductor layer) is provided between adjacent active layers 20 among the plurality of active layers 20. The semiconductor layer 26 has a second band gap energy that is greater than the first band gap energy of the semiconductor layer 24. As shown in FIGS. 5B and 10B, the width (length L1 to L3) in the stacking direction of the active layers 20 in the plurality of active layers 20 becomes smaller as going to the reflective layer 16 side.

Thereby, as shown in FIGS. 6 and 11, the number of carriers excited in the semiconductor layer 24 can be made substantially uniform between the active layers 20. Therefore, laser characteristics such as LL characteristics can be improved.

The energy of the excitation light 52 is larger than the first band gap energy of the semiconductor layer 24 and smaller than the second band gap energy of the semiconductor layer 26. Thereby, the excitation light 52 is hardly attenuated in the semiconductor layer 26. Therefore, the light output can be improved.

The light emitting layer 22 is a quantum well layer or a quantum dot layer. Thereby, the light emitting layer 22 can emit light efficiently. The quantum dot layer is a layer in which a plurality of semiconductor dots such as InAs or InGaAs whose band gap energy is smaller than that of the semiconductor layer 24 are provided in the semiconductor layer 24.

The light emitting layer 22 in each active layer 20 may be a single layer. Each of the plurality of active layers 20 may have a plurality of light emitting layers 22. Thereby, the light emitting layer groups 21a to 21c can emit light efficiently. The number of light emitting layer groups and the number of light emitting layers in the light emitting layer group can be arbitrarily set.

The antinodes of a plurality of standing waves generated between the

reflective layers

12 and 16 are located in the plurality of active layers 20 respectively. Thereby, the light emitting layer 22 can emit light efficiently. It is preferable that at least one of the light emitting layers 22 in each of the light emitting layer groups 21a to 21c is located at the antinode of the standing wave. In Examples 1 and 2, the distance between the upper end of the reflective layer 12 and the lower end of the reflective layer 16 is 2λ and 3.5λ, respectively, but can be arbitrarily set within a range of a natural number multiple of λ / 2.

As in Example 2, when one of the

reflective layers

12 and 16 changes in the stacking direction with respect to the other, the wavelength of the emitted light changes. Thereby, the wavelength of the laser beam 50 becomes variable.

Example 3 is an example of an OCT (Optical Coherence Tomography) apparatus as an inspection apparatus using the wavelength tunable laser apparatus according to Example 2. FIG. 12 is a block diagram of an inspection apparatus according to the third embodiment. As shown in FIG. 12, the light emitted from the light source 60 that sweeps the wavelength (or the wavelength is variable) is divided into reflected light and transmitted light by the half mirror 62. The reflected light is reflected by the mirror 64 and becomes reference light. The reference light passes through the half mirror 62. The transmitted light that has passed through the half mirror 62 is applied to the object 68 and becomes signal light. The object 68 is, for example, a body part, for example, an eye. The signal light is reflected by the half mirror 62. The detector 66 detects the light intensity at which the signal light and the reference light interfere. The light source 60 can change the wavelength of light. The processing unit 65 generates an optical coherent tomography based on the signal from the detector 66.

Although an OCT apparatus has been described as an example of an inspection apparatus using a wavelength tunable laser apparatus, a medical or other inspection apparatus other than the OCT apparatus may be used. The inspection apparatus may include the semiconductor laser of Example 1 or 2.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

Claims

A first reflective layer on which excitation light enters and reflects emitted light;
A second reflective layer provided in the stacking direction of the first reflective layer and reflecting the emitted light;
A light emitting layer sandwiched between the first reflective layer and the second reflective layer in the stacking direction and stacked in the stacking direction and emitting the emitted light by the excitation light; and a light emitting layer sandwiching the light emitting layer in the stacking direction. A plurality of active layers each having one semiconductor layer;
A second semiconductor layer provided between first semiconductor layers of adjacent active layers of the plurality of active layers and having a second band gap energy larger than a first band gap energy of the first semiconductor layer;
With
The width of the active layer in the stacking direction of the plurality of active layers becomes smaller as going to the first reflective layer side.
2. The semiconductor laser according to claim 1, wherein the energy of the excitation light is larger than the first band gap energy and smaller than the second band gap energy.
3. The semiconductor laser according to claim 1, wherein a plurality of antinodes of a standing wave generated between the first reflective layer and the second reflective layer are located in the plurality of active layers, respectively.
4. The semiconductor laser according to claim 1, wherein the light emitting layer is a quantum well layer or a quantum dot layer.
The semiconductor laser according to any one of claims 1 to 4, wherein each of the plurality of active layers has a plurality of light emitting layers.
The wavelength of the emitted light is changed by changing one of the first reflective layer and the second reflective layer in the stacking direction with respect to the other of the first reflective layer and the second reflective layer. The semiconductor laser according to any one of 1 to 5.
An inspection apparatus including the semiconductor laser according to any one of claims 1 to 6.