Light-emitting device and ranging device

Abstract

To provide a light emitting device capable of generating a light pulse with a short light pulse width and a high peak value.SOLUTION: A light emitting device includes, on a semiconductor substrate, a semiconductor light emitting element in which a first reflecting mirror, a resonator spacer portion including an active layer, and a second reflecting mirror are laminated in this order. The semiconductor light emitting device includes a saturable absorbing layer between the semiconductor substrate and the second reflecting mirror. Further, the semiconductor light emitting device is configured to emit light having a profile which has a maximum peak value and converges to a stable value, which is a predetermined light intensity, after the maximum peak value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a light emitting device and a distance measuring device. [Background technology]

[0002] Patent Document 1 describes the use of a VCSEL (Vertical Cavity Surface Emitting LASER) as a light source for a ToF (Time of Flight) LiDAR (Light Detection and Ranging). VCSELs have the advantage of having little wavelength dependency on temperature.

[0003] In the above system, by increasing the peak value of the irradiated light pulse, it becomes easier for the light receiving side to distinguish between ambient light and the light pulse emitted by the system itself, and the S / N ratio can be increased, thereby extending the maximum measurable distance. On the other hand, from the viewpoint of eye safety, there is a limit to the peak value of the light pulse. The upper limit of the peak value from the viewpoint of eye safety depends on the width of the light pulse, and the narrower the width of the light pulse, the higher the peak value can be. Therefore, a light source that can generate a light pulse with a short light pulse width and a high peak value is desirable as a light source to be applied to a LiDAR system. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-148512 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, realizing a light emitting device capable of generating light pulses suitable for a LiDAR system has not been easy from the standpoint of VCSELs and the electrical aspects of driving the VCSELs.

[0006] An object of the present invention is to provide a light emitting device including a semiconductor light emitting element capable of generating an optical pulse having a short optical pulse width and a high peak value, and a distance measuring device using such a light emitting device. [Means for solving the problem]

[0007] According to one disclosure of the present specification, there is provided a light emitting device comprising a semiconductor light emitting element having a first reflecting mirror, a cavity spacer portion including an active layer, and a second reflecting mirror stacked in this order on a semiconductor substrate, the semiconductor light emitting element including a saturable absorbing layer between the semiconductor substrate and the second reflecting mirror, the active layer having a plurality of quantum well layers and a barrier layer provided between the plurality of quantum well layers, a band gap difference between the quantum well layers and the barrier layer being 230 meV or less, and the semiconductor light emitting element configured to emit light having a maximum peak value and a profile that converges to a stable value which is a predetermined light intensity after the maximum peak value. Effect of the Invention

[0008] According to the present invention, it is possible to realize a light emitting device including a semiconductor light emitting element capable of generating an optical pulse with a short optical pulse width and a high peak value, as well as a high performance distance measuring device using such a light emitting device. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view showing a semiconductor light emitting device according to a first embodiment of the present invention. [Diagram 2] 1 is a graph showing the Al composition dependency of the ratio of the density of carriers accumulated in a well layer to the density of carriers accumulated in a barrier layer. [Diagram 3] 11 is a graph showing an optical output waveform of a semiconductor light emitting device according to a comparative example. [Figure 4] 4 is a graph showing an optical output waveform of the semiconductor light emitting device according to the first embodiment of the present invention. [Diagram 5] 4 is a graph showing the change over time in density of carriers accumulated in an active layer and in light intensity. [Figure 6] 1 is a graph showing the relationship between the effective resonator length and the optical output waveform. [Figure 7] 1 is a graph showing the relationship between the effective resonator length and the pulse width of the optical output. [Figure 8] 1 is a graph showing the relationship between the number of quantum well layers and the peak value ratio. [Figure 9] 13 is a graph showing the relationship between the minimum number of quantum well layers required for the peak value ratio to exceed 2 and the cavity length. [Figure 10] 5 is a schematic cross-sectional view showing a semiconductor light-emitting device according to a second embodiment of the present invention. [Figure 11] FIG. 11 is a schematic cross-sectional view showing a semiconductor light-emitting device according to a third embodiment of the present invention. [Figure 12] FIG. 11 is a perspective view showing a semiconductor light emitting device according to a fourth embodiment of the present invention. [Figure 13] FIG. 11 is a top view of a semiconductor light emitting device according to a fourth embodiment of the present invention. [Figure 14] FIG. 13 is a block diagram showing a schematic configuration of a distance measuring device according to a fifth embodiment of the present invention. [Figure 15] FIG. 13 is a block diagram showing a schematic configuration of a distance measuring device according to a sixth embodiment of the present invention. [Figure 16] FIG. 13 is a schematic cross-sectional view showing an example of the configuration of a surface-emitting laser array in a distance measuring device according to a sixth embodiment of the present invention. [Figure 17] 11 is a graph showing changes in optical waveform due to changes in environmental temperature and changes in physical parameters over time in a semiconductor light emitting element of a comparative example. [Figure 18] 4 is a graph showing changes in optical waveform due to changes in environmental temperature and changes in physical parameters over time in a semiconductor light emitting device of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] [First embodiment] A semiconductor light emitting device according to a first embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a schematic cross-sectional view showing the structure of the semiconductor light emitting device according to this embodiment.

[0011] The semiconductor light emitting device 100 according to this embodiment is a vertical cavity surface emitting laser (VCSEL) having a distributed Bragg reflector (DBR). As shown in FIG. 1, the semiconductor light emitting device 100 has a semiconductor substrate 10, a lower DBR layer 12, a non-doped spacer portion 14, a resonator portion 18, an upper DBR layer 28, electrodes 40, 42, and a protective film 44. The lower DBR layer 12 is provided on the semiconductor substrate 10. The non-doped spacer portion 14 is provided on the lower DBR layer 12. The resonator portion 18 is provided on the non-doped spacer portion 14. The upper DBR layer 28 is provided on the resonator portion 18. A layer (the non-doped spacer portion 14 and the resonator portion 18) located between the lower DBR layer 12 and the upper DBR layer 28 is the resonator spacer portion.

[0012] A saturable absorbing layer 16 is provided in the undoped spacer portion 14. The resonator portion 18 is composed of an n-type layer 20 provided on the undoped spacer portion 14, an undoped spacer portion 22 provided on the n-type layer 20, and a p-type layer 26 provided on the undoped spacer portion 22. Three active layers 24 are provided in the undoped spacer portion 22. An oxide constriction layer 38 is provided in the upper DBR layer 28.

[0013] The undoped spacer portion 22, the p-type layer 26, and the upper DBR layer 28 are processed into a mesa shape. An electrode 40 electrically connected to the n-type layer 20 is provided on the n-type layer 20 exposed by processing the undoped spacer portion 22, the p-type layer 26, and the upper DBR layer 28 into a mesa shape. An electrode 42 electrically connected to the upper DBR layer 28 is provided on the upper DBR layer 28. A protective film 44 is provided on the upper surface of the n-type layer 20 except for at least a portion of the surfaces of the electrodes 40, 42 and on the side and upper surface of the mesa.

[0014] The semiconductor substrate 10 may be, for example, a GaAs substrate. The lower DBR layer 12 may be, for example, an Al0.1 GaAs layer and Al 0.9 A laminate with a GaAs layer counts as one pair, and 35 pairs of these may be laminated, where λc is the center wavelength of the high reflection band of the lower DBR layer 12, which is 940 nm in this embodiment.

[0015] The non-doped spacer portion 14 is a structure not found in typical VCSELs. The saturable absorbing layer 16 may be formed of a multiple quantum well structure including three quantum well layers, each of which has an 8-nm-thick InGaAs well layer sandwiched between 10-nm-thick AlGaAs barrier layers. The other portions of the non-doped spacer portion 14 may be formed of non-doped GaAs layers.

[0016] The resonator section 18 is composed of a pin junction made up of an n-type layer 20, an undoped spacer section 22, and a p-type layer 26. Each of the three active layers 24 arranged in the undoped spacer section 22 may be composed of a multiple quantum well including four quantum well layers, for example, an InGaAs well layer having a thickness of 8 nm sandwiched between AlGaAs barrier layers having a thickness of 10 nm. In this case, a total of 12 quantum well layers are included in the resonator section 18. The n-type layer 20 may be composed of an n-type GaAs layer, the p-type layer 26 may be composed of a p-type GaAs layer, and the other parts of the undoped spacer section 22 may be composed of undoped GaAs layers.

[0017] In this way, the resonator section 18 is made of a p-i junction that is also present in a normal VCSEL, and has a similar configuration to a resonator section that includes an active layer in an i-layer. However, the number of quantum well layers in the resonator section 18 is greater than the number of quantum well layers (approximately three) in a normal VCSEL. The effective resonator length in the resonator section 18 is 10 μm.

[0018] In this embodiment, these three active layers 24 are arranged between the antinode and the node of the standing wave, not at the antinode of the standing wave used in the design of a general VCSEL. This allows the optimization of the response characteristics of light when a drive current is injected. In addition, the light confinement factor for the standing wave is generally in the range of 1.5 to 2.0 in a normal VCSEL, but in this embodiment, it is intentionally set to about 0.35, which is low. In addition, the AlGaAs barrier layer has a smaller band gap than the barrier layer in the quantum well of a normal VCSEL, and is designed so that carriers are accumulated in the barrier layer as well. As a result, although the number of layers of the InGaAs well layer in which carriers are accumulated is 12, carriers are accumulated in the AlGaAs barrier layer as well, so that it is possible to accumulate carriers in about 20 layers in terms of a normal quantum well.

[0019] Figure 2 is a graph showing the results of calculations of the dependence of the Al composition on the ratio of the carrier density accumulated in the InGaAs well layer to the carrier density accumulated in the AlGaAs barrier layer. In Figure 2, the plots marked with ■ indicate the results when the carrier density in the well layer is 2×10 18 cm -3 The ▲ marks indicate the case where the carrier density in the well layer is 5×10 18 cm -3 The plots marked with a black circle indicate the case where the carrier density in the well layer is 9×10 18 cm -3 This is the case.

[0020] The minimum carrier density required for the stimulated amplification required for laser oscillation is 2 x 10 18 cm -3 Therefore, the density of carriers accumulated in the quantum well is set to 2×10 18 cm -3Assuming this, when the Al composition of the AlGaAs barrier layer is 0.05, the ratio of the density of carriers accumulated in the well layer to the density of carriers accumulated in the barrier layer is approximately 0.075, as shown in Figure 2. When the Al composition of the AlGaAs barrier layer increases from 0.05 to 0.1, the ratio of the density of carriers accumulated in the well layer to the density of carriers accumulated in the barrier layer decreases to approximately 0.025.

[0021] The maximum thickness that is effective as a barrier layer for accumulating carriers is roughly 1 μm, which is the diffusion length of the carriers. Furthermore, the active layer of a VCSEL is often composed of three quantum wells. If it is assumed that an amount of carriers equal to or greater than the amount accumulated in three quantum wells with a total thickness of about 25 nm is accumulated in a barrier layer with a thickness of 1 μm, then the carrier density ratio must be 0.025 or more, which is the reciprocal of the thickness ratio. In other words, the calculation results in Figure 2 show that AlGaAs with an Al composition of 0.1 or less is preferable as a barrier layer.

[0022] The energy difference between the band gap of the AlGaAs barrier layer with an Al composition of 0.1 and the emission level of the InGaAs well layer with an emission wavelength of 940 nm is 230 meV. In other words, the energy difference between the band gap of the barrier layer and the emission level of the well layer is preferably 230 meV or less. On the other hand, the lower limit of the energy difference between the band gap of the barrier layer and the emission level of the well layer is the energy equivalent to the difference with the band gap of GaAs from the viewpoint of light absorption. In other words, when oscillating at a wavelength of 940 nm, the energy difference between the band gap of the barrier layer and the emission level of the well layer is preferably 105 meV or more. From the above, the preferred range of the energy difference between the emission level of the well layer and the band gap of the barrier layer is 105 meV to 230 meV.

[0023] The upper DBR layer 28 is, for example, an Al 0.1 Ga 0.9 As layer and Al 0.9 Ga 0.1 The upper DBR layer 28 is formed by stacking 20 pairs of layers, each of which is a stack of an Al layer and an As layer.0.98 Ga 0.02 The oxidized narrowing layer 38 is formed by oxidizing a part of the As layer. The oxidized narrowing layer 38 is formed by, for example, oxidizing Al 0.98 Ga 0.02 The oxidized confinement layer 38 can be formed by oxidizing the As layer from the side of the mesa with water vapor. The oxidized confinement layer 38 has a non-oxidized portion in the center of the mesa and an oxidized portion near the side wall of the mesa. The diameter of the non-oxidized portion in plan view can be about 10 μm. As a result, the current injected into the semiconductor light emitting device 100 flows only through the non-oxidized portion, and therefore only the portion of the semiconductor light emitting device 100 that overlaps with the center of the mesa in plan view oscillates as a laser.

[0024] The laser light generated by the semiconductor light emitting device 100 may be configured to be emitted from the upper DBR layer 28 side or from the semiconductor substrate 10 side.

[0025] In this way, the semiconductor light emitting device 100 of this embodiment is based on the configuration of a normal VCSEL and further includes the following three elements. The first of the three elements added to the VCSEL is to substantially increase the volume of the active layer. For example, a normal VCSEL is composed of three quantum well layers, but this is increased to about 20 layers in terms of the volume of the quantum wells. The second is to introduce a saturable absorbing layer 16. The third is to extend the effective resonator length of the VCSEL. The effective resonator length is the resonator length felt by light in the resonator. More specifically, it is the average value of the distance that light propagates from when it transmits through the active layer in the resonance direction to when it is reflected by two reflecting mirrors that constitute the resonator and transmits through the active layer again. By adding at least one of these elements, and preferably three of them, it is possible to realize a VCSEL that can generate an optical pulse with a high peak value and a short pulse width.

[0026] Next, the operation of the semiconductor light emitting device 100 according to the present embodiment will be described with reference to FIGS. Figures 3 and 4 are graphs showing the results of calculating the optical output waveform of a semiconductor light-emitting device. Figure 3 shows the optical output waveform of a semiconductor light-emitting device according to a comparative example, and Figure 4 shows the optical output waveform of the semiconductor light-emitting device 100 according to this embodiment. The semiconductor light-emitting device according to the comparative example is a VCSEL of a general configuration that does not include a saturable absorbing layer, has three quantum well layers, and is designed with a cavity length of 1λ.

[0027] In the case of a typical semiconductor light-emitting device, oscillation begins and the optical output rises about 70 ps after the start of current injection, as shown in Figure 3. The optical output then reaches a peak in the optical waveform associated with relaxation oscillation, and then converges to a steady value.

[0028] On the other hand, the semiconductor light emitting element 100 according to this embodiment emits light having a maximum peak value and a profile that converges to a stable value, which is a predetermined light intensity, after the maximum peak value. That is, in the semiconductor light emitting element 100 according to this embodiment, as shown in FIG. 4, for example, oscillation starts about 600 ps after the start of current injection. This delay in the start of oscillation is due to the fact that the effective volume of the active layer 24 is large and that oscillation is inhibited by the absorption of light in the saturable absorbing layer 16 for a certain period of time after the start of current injection. When light is absorbed in the saturable absorbing layer 16, the absorbed light is accumulated in the saturable absorbing layer 16 as carriers. The carriers increase with the absorption of light, and when the carrier density in the saturable absorbing layer 16 reaches the transparent carrier density, the saturable absorbing layer 16 stops absorbing light. As a result, the effect of inhibiting laser oscillation disappears, and the semiconductor light emitting element starts laser oscillation.

[0029] The purpose of inhibiting laser oscillation for a certain period of time by the saturable absorbing layer 16 is to accumulate carriers exceeding a threshold carrier density in the active layer 24. Here, the threshold carrier density is the carrier density that generates the gain required for laser oscillation.

[0030] Fig. 5 is a graph showing the time variation of the density of carriers accumulated in the active layer 24 and the light intensity. The current injected into the semiconductor light emitting device has a waveform similar to that in Fig. 4, and the injection is started at 4E-10 seconds on the time axis.

[0031] 5, the carrier density in the active layer 24 starts to increase as soon as current injection begins. The threshold carrier density (the carrier density that converges after the start of oscillation) in the semiconductor light emitting device 100 of this embodiment is 2.7E+18 cm -3 However, before the laser oscillation starts, the carriers temporarily exceed the threshold carrier density and continue to accumulate. Then, when the laser oscillation starts, the carriers are rapidly consumed by stimulated emission and converge to a stable value.

[0032] In this way, in the semiconductor light emitting device 100 according to this embodiment, more carriers than the threshold carrier density are accumulated in the active layer 24. Then, after the start of laser oscillation, the carriers accumulated in the active layer 24 are converted into photons by stimulated emission. This makes it possible to output an optical pulse with a high peak value and a short half-width as shown in FIG.

[0033] Carriers exceeding the threshold carrier density can be accumulated in the active layer 24 because laser oscillation is suppressed for a certain period of time using the saturable absorbing layer 16. By realizing such a high carrier density, an optical pulse with a high peak value and a short pulse width can be generated inside the semiconductor light-emitting element after oscillation. This optical pulse is shorter than the current pulse that drives the semiconductor light-emitting element.

[0034] After the optical pulse is generated, laser oscillation continues as shown in Fig. 5. The condition for laser oscillation to continue is that the maximum gain obtained by the active layer 24 exceeds the absorption in the entire resonator. Specifically, laser oscillation can be continued when the relationship expressed by the following formula (1) is established. In formula (1), Γa is the optical confinement coefficient of the saturable absorbing layer 16, Γs is the optical confinement coefficient of the active layer 24, and gmax(Iop) is the maximum gain in the active layer 24 obtained at the current value Iop. Also, α2 is the absorption coefficient of the saturable absorbing layer 16, αm is the mirror loss, and αi is the optical absorption by the semiconductor carriers, etc. Γs×gmax(Iop) > Γa×α2+αm+αi …(1)

[0035] Considering the application of the semiconductor light emitting element 100 of this embodiment to LiDAR and the like, it is preferable that the semiconductor light emitting element continues to oscillate in a stable state after the generation of the light pulse. The reason for this is that the number of current pulses output from the driving unit of the semiconductor light emitting element is the same as the number of light pulses generated by the semiconductor light emitting element. On the other hand, when a certain current is continuously injected during a certain period of time, multiple pulses are generated from the semiconductor light emitting element, it is difficult to distinguish the first pulse from the subsequent pulses from the light receiving side, and there is a possibility that the error in calculating the distance will be large. In addition, there is a possibility that there will be a disadvantage such as a reduction in the amount of light allowed per pulse from the viewpoint of eye safety.

[0036] In this embodiment, the non-doped spacer portion 14 is used to extend the distance from the lower DBR layer 12 to the upper DBR layer 28, thereby extending the cavity length as a laser. The purpose is to widen the pulse width. The optical thickness of the cavity spacer portion is desirably equal to or greater than 5 times the resonant wavelength, and more desirably equal to or greater than 11 times the resonant wavelength. The optical thickness refers to the value obtained by multiplying the physical thickness by the refractive index of the medium.

[0037] Figure 6 shows the effective cavity length L eff6 is a graph showing the results of calculation of the optical output waveform when a rectangular current pulse is injected into a semiconductor light emitting element having a cavity length of 2 μm, 5 μm, and 10 μm. FIG. 7 is a graph showing the relationship between the effective cavity length and the pulse width of the optical output. As shown in FIG. 6 and FIG. 7, the pulse width of the optical output can be increased by increasing the effective cavity length. In the configuration of this embodiment in which the active layer 24 is equivalent to 20 quantum well layers and the saturable absorbing layer 16 is equivalent to 3 quantum well layers, the pulse width was 30 ps when the effective cavity length was 2 μm, the pulse width was 59 ps when the effective cavity length was 5 μm, and the pulse width was 110 ps when the effective cavity length was 10 μm. The pulse width here is the half-width.

[0038] For example, if the error in the timing of receiving light on the light receiving element side is 100 ps, ​​it is preferable to narrow the pulse width on the light emitting element side to the same extent, but there is little benefit in narrowing it further, for example to 10 ps. Therefore, if the pulse width required on the light emitting element side is approximately 50 ps or more, it is preferable that the effective resonator length is 4 μm or more. Also, if the pulse width required from the error in the timing of receiving light is 30 ps, ​​it is preferable that the effective resonator length is 2 μm or more.

[0039] In this embodiment, the effective resonator length is extended by increasing the layer thickness of the non-doped spacer portion 14 and the like to increase the physical distance between the lower DBR layer 12 and the upper DBR layer 28, but the method for extending the effective resonator length is not limited to this. For example, by providing a third reflecting mirror between the lower DBR layer 12 and the upper DBR layer 28 to form a coupled resonator, it is possible to effectively extend the resonator length even if the distance between the lower DBR layer 12 and the upper DBR layer 28 is shorter than that of this embodiment. In any case, it is possible to control the optical pulse width to a desired width by appropriately controlling the effective resonator length.

[0040] Next, the thickness of the active layer 24, more specifically, the required range of the number of quantum well layers that constitute the active layer 24, will be described.

[0041] Figure 8 shows the effective resonator length L eff1 is a graph showing the relationship between the number of quantum well layers and the peak value ratio in semiconductor light emitting devices with diameters of 2 μm, 5 μm, and 10 μm. The peak value ratio is the ratio between the peak value of the optical pulse waveform and the steady value after stabilization. For example, a peak value ratio of 2 means that the amount of light at the peak value is twice that of the steady value.

[0042] As shown in Fig. 8, the peak value ratio increases as the number of quantum well layers increases. In addition, when comparing at the same peak value ratio, the number of required quantum well layers increases as the effective cavity length increases.

[0043] FIG. 9 is a graph showing the relationship between the minimum number of quantum well layers required for the peak value ratio to exceed 2 and the cavity length.

[0044] As shown in FIG. 9, when the cavity length is 2 μm, the number of quantum well layers with a peak value ratio exceeding 2 is 6 or more. When the cavity length is 5 μm, the number of quantum well layers with a peak value ratio exceeding 2 is 7 or more. When the cavity length is 10 μm, the number of quantum well layers with a peak value ratio exceeding 2 is 9 or more. When the design standard for the peak value ratio in a semiconductor light-emitting device with a cavity length of 2 μm or more is assumed to be 2 or more, the number of quantum well layers required is 6 or more. From the viewpoint of the pulse width described above, it is preferable that the cavity length is 4 μm or more, in which case the number of quantum well layers required is 7 or more.

[0045] The number of quantum well layers here is the number of quantum well layers calculated by converting the layer thickness of the portion where carriers accumulate into the number of quantum well layers, and does not necessarily have to match the actual number of quantum well layers. That is, the actual number of quantum well layers can be designed according to the relationships in Figures 8 and 9. Alternatively, the actual number of quantum well layers may be less than the total number according to the relationships in Figures 8 and 9, but may be designed to allow carriers to accumulate in layers around the quantum well layers as well, so that substantially desired carriers can be accumulated.

[0046] As is clear from Figures 6 to 9, from the viewpoint of pulse width and peak value ratio, the more the number of quantum well layers, the better, and there is no particular upper limit. However, when carriers are injected into the i-layer of the pin junction by current injection, the thickness of the i-layer is limited by the degree of carrier diffusion from the p-layer and n-layer. The diffusion distance varies greatly depending on the material and composition constituting the active layer 24, but if the diffusion distance is 1 μm, the number of quantum well layers is approximately 50 layers. It is desirable to appropriately select the number of quantum well layers constituting the active layer 24 within the range of, for example, 6 layers or more and 50 layers or less.

[0047] Next, an example of a method for manufacturing the semiconductor light emitting device 100 according to this embodiment will be described below. First, the semiconductor layers constituting the lower DBR layer 12, the undoped spacer portion 14, the resonator portion 18 and the upper DBR layer 28 are grown on the semiconductor substrate 10 by metalorganic chemical vapor deposition or molecular beam epitaxy.

[0048] Next, photolithography and etching techniques are used to pattern the upper DBR layer 28, the p-type layer 26, and the non-doped spacer portion 22. As a result, a columnar mesa having a diameter of, for example, about 30 μm is formed.

[0049] Next, thermal oxidation is performed in a water vapor atmosphere at about 450° C. to remove Al from the upper DBR layer 28. 0.98 Ga 0.02 The As layer is oxidized from the sidewall of the mesa to form an oxidized constriction layer 38. At this time, by controlling the oxidation time, the Al 0.98 Ga 0.02 In the As layer, a non-oxidized portion is formed in the center of the mesa, and an oxidized portion (oxidized constriction layer 38) is formed in the vicinity of the sidewall of the mesa. 0.98 Ga 0.02 The non-oxidized portion of the As layer is controlled so that its diameter is about 10 μm.

[0050] Next, electrode 42 which will become a p-side electrode is formed on the upper surface of the mesa using photolithography and vacuum deposition, and then electrode 40 which will become an n-side electrode is formed on the upper surface of n-type layer 20 which is exposed by etching. Electrode 42 has a circular ring pattern, and the central opening becomes a circular window for light extraction.

[0051] Next, a protective film 44 is formed by photolithography and plasma CVD so as to cover the top and side surfaces of the mesa on which the electrodes 40 and 42 are provided, and the top surface of the n-type layer 20.

[0052] Next, in order to obtain good electrical characteristics, a heat treatment is performed in a nitrogen atmosphere to alloy the interface between the electrode material and the semiconductor material, completing the semiconductor light emitting device 100 of this embodiment.

[0053] As described above, according to this embodiment, it is possible to realize a semiconductor light emitting element and a light emitting device capable of generating an optical pulse with a short optical pulse width and a high peak value.

[0054] [Second embodiment] A semiconductor light emitting device according to a second embodiment of the present invention will be described with reference to Fig. 10. Fig. 10 is a schematic cross-sectional view showing the structure of the semiconductor light emitting device according to this embodiment. Components similar to those of the semiconductor light emitting device according to the first embodiment are given the same reference numerals, and descriptions thereof will be omitted or simplified.

[0055] The semiconductor light emitting device according to this embodiment is similar to the semiconductor light emitting device according to the first embodiment except for the configuration of the resonator portion 18. In this embodiment, the differences from the semiconductor light emitting device according to the first embodiment will be mainly described, and descriptions of the parts common to the semiconductor light emitting device according to the first embodiment will be omitted as appropriate.

[0056] 10, the resonator portion 18 of the present embodiment is similar to that of the first embodiment in that it is configured by a pin junction consisting of an n-type layer 20, an undoped spacer portion 22, and a p-type layer 26, and in that an active layer 24 is provided in the undoped spacer portion 22. The n-type layer 20 is a semiconductor layer with a high impurity concentration disposed between the active layer 24 and the saturable absorbing layer 16.

[0057] The resonator portion 18 of the first embodiment has three active layers 24 each including three quantum well layers in the non-doped spacer portion 22. In contrast, the resonator portion 18 of the present embodiment has one active layer 24 including four quantum well layers in the non-doped spacer portion 22. The active layer 24 may be composed of a multiple quantum well including four quantum well layers, for example, an 8 nm thick InGaAs well layer sandwiched between 10 nm thick GaAs barrier layers. The other portions of the non-doped spacer portion 22 are composed of non-doped GaAs layers.

[0058] In this way, while the resonator portion 18 of the first embodiment has an active layer 24 including a total of 12 quantum well layers, the resonator portion 18 of this embodiment has an active layer 24 including four quantum well layers. The reason why the total number of quantum well layers included in the active layer 24 of the resonator portion 18 of this embodiment can be reduced to four is because the portions of the non-doped spacer portion 22 other than the InGaAs well layer, including the barrier layers, are made of GaAs instead of AlGaAs.

[0059] By constructing the non-doped spacer portion 22 other than the InGaAs well layer with GaAs, the band gap of the barrier layer can be made smaller than when AlGaAs is used as the barrier layer. As a result, carriers can be accumulated in GaAs as well, so the amount of carriers required to achieve the effects of the present invention can be easily increased. Furthermore, since there is no need to increase the number of quantum well layers, the number of quantum well layers can be reduced from 12 to 4.

[0060] In the semiconductor light emitting device of the first embodiment, the optical confinement factor for the standing wave is set to about 0.35, which is low. On the other hand, in the semiconductor light emitting device of the present embodiment, the number of quantum well layers is reduced, so the optical confinement factor is set to about 1.4. In other words, the quantum well layers are arranged near the positions of the loops of the standing wave. This is because the product of the number of quantum well layers and the optical confinement factor is the gain of the laser resonator, and the first embodiment and the present embodiment are configured to obtain the same level of gain. By making the product of the number of quantum well layers and the optical confinement factor about the same, the relaxation oscillation frequency, that is, the pulse width during pulse generation, can be set to about the same level.

[0061] The configuration of this embodiment in which carriers are actively accumulated in the barrier layer has secondary effects in addition to the effects described above. Two secondary effects will be described below as examples.

[0062] The first effect is that the accumulated strain in the semiconductor layer can be reduced. Assuming that the oscillation wavelength is set to 940 nm, the active layer is InGaAs and the substrate is GaAs, so that the active layer grown on the substrate will have strain due to the difference in lattice constant. The more the number of quantum well layers increases, the greater the accumulated strain. Therefore, a design that reduces the band gap of the barrier layer to reduce the number of quantum well layers as in this embodiment has the effect of reducing the accumulated strain. This is not a specific effect obtained when the oscillation wavelength is 940 nm, but is an effect that is commonly obtained when the lattice constant of the constituent material of the substrate is different from the lattice constant of the constituent material of the active layer or the like crystal-grown thereon.

[0063] The second effect is that it reduces the consumption of carriers due to radiative recombination. In all semiconductors, including quantum well layers and barrier layers, when both hole and electron carriers exist simultaneously, carriers are consumed by radiative recombination (spontaneous emission). In the case of semiconductor lasers, if the amount of carrier consumption due to radiative recombination (spontaneous emission) becomes large, it is undesirable because it increases the threshold for laser oscillation and reduces the power conversion efficiency. It is known that this radiative recombination is proportional to the square of the carrier density. Therefore, even when the same amount of carriers are stored, the carrier density, i.e., the amount of carriers consumed by radiative recombination, changes depending on the volume of the part that stores the carriers.

[0064] When the total number of quantum well layers is increased to accumulate carriers as in the first embodiment, the quantum well layers have a small band gap, so the carrier density increases. In this case, there is an advantage that the total layer thickness can be thin, but the carrier density increases, so the carriers consumed by radiative recombination also increase. On the other hand, when carriers are accumulated in layers with a larger band gap than the quantum well layers as in this embodiment, the carrier density decreases due to the large band gap, and the total layer thickness of the layers accumulating carriers increases. However, the carrier density decreases, so the carrier consumption by radiative recombination decreases. In this way, in this embodiment, a larger proportion of carriers are accumulated in layers with a larger band gap than the quantum well layers, so the carrier consumption by radiative recombination can be reduced.

[0065] The n-type layer 20 is Al 0.9 It is composed of a laminated structure of a GaAs layer and a GaAsP layer. 0.9 The GaAs layer is provided between the GaAsP layer and the non-doped spacer portion 22. The Al composition of the AlGaAs layer is increased to 0.9 in order to increase the band gap and prevent carriers overflowing from the active layer 24 from flowing into the saturable absorbing layer 16. 0.9The GaAs layer is provided near the non-doped spacer portion 22. On the other hand, the GaAsP layer serves as a strain compensation layer. In this embodiment, the number of quantum well layers is reduced compared to the first embodiment, but since InGaAs layers are used for the quantum well layers, accumulated strain occurs. Therefore, the accumulated strain is reduced by inserting a GaAsP layer that generates lattice strain in GaAs in the opposite direction to that of InGaAs.

[0066] The AlGaAs layer constituting the n-type layer 20 can suppress carrier overflow even if the Al composition is 0.9 or less. In the case of AlGaAs-based materials, the increase in the band gap with increasing Al composition becomes small when the Al composition is around 0.45. In other words, the decrease in the band gap caused by decreasing the Al composition of the AlGaAs layer from 0.9 to 0.45 is small. On the other hand, if the Al composition of the AlGaAs layer exceeds 0.9, the rate of formation of a natural oxide film increases rapidly due to reaction with oxygen in the air, which is not preferable from the viewpoint of the fabrication process and the reliability of the device. From this viewpoint, the Al composition of the AlGaAs layer constituting the n-type layer 20 is preferably 0.45 or more and about 0.9 or less.

[0067] Incidentally, the design of reducing the energy difference between the quantum well emission level and the barrier layer band gap to a level where light absorption does not occur at the laser oscillation wavelength, and the design of increasing the barrier layer thickness to increase the amount of carrier accumulation are opposite to the design concept of a normal semiconductor laser. The reason is that in a normal semiconductor laser, it is preferable for the optical output to respond as quickly as possible to the increase or decrease in the input current. In a semiconductor laser, a faster response is possible by accumulating carriers only in the emission layer such as the quantum well and by making the barrier layer, where the carriers move, as thin as possible.

[0068] In many applications, including optical communications and ToF LiDAR, the amount of light is controlled by increasing or decreasing the current, and there is a great advantage to increasing or decreasing the light output in response to the rapidly changing current waveform. For example, in optical communications, the communication speed can be increased. Also, in ToF LiDAR, shortening the time width of the light emission pulse can increase the accuracy of estimating the time when the light detected by the light receiving side was generated on the light emitting side, thereby improving the distance measurement accuracy. Therefore, designs that increase the number of quantum well layers beyond the number required for oscillation or designs that increase the amount of carrier accumulation in the barrier layer are designs that should be avoided because they will worsen the ability of the light increase and decrease to follow the current waveform.

[0069] On the other hand, since the present invention is based on the idea of ​​emitting a short pulse in a VCSEL, it is not necessary to make the optical output follow the current waveform. Also, it is preferable that the peak value of the pulse is large. Therefore, in this embodiment, in a configuration including the saturable absorbing layer 16 necessary for emitting a short pulse in a VCSEL, a design is adopted in which more carriers are accumulated, including in the barrier layer, to generate an optical pulse with a short pulse width and a high peak value.

[0070] As described above, according to this embodiment, it is possible to realize a semiconductor light emitting element and a light emitting device capable of generating an optical pulse with a short optical pulse width and a high peak value.

[0071] [Third embodiment] A semiconductor light emitting device according to a third embodiment of the present invention will be described with reference to Fig. 11. Fig. 11 is a schematic cross-sectional view showing the structure of the semiconductor light emitting device according to this embodiment. Components similar to those of the semiconductor light emitting device according to the first or second embodiment are given the same reference numerals, and descriptions thereof will be omitted or simplified.

[0072] As shown in FIG. 11 , the semiconductor light emitting device 100 includes a semiconductor substrate 10, a lower DBR layer 12, a non-doped spacer portion 14, a resonator portion 18, and an upper DBR layer 28. The semiconductor light emitting device 100 further includes a lower DBR layer 30, a resonator portion 32, an upper DBR layer 36, electrodes 40, 42, and a protective film 44. The lower DBR layer 12 is provided on the semiconductor substrate 10. The non-doped spacer portion 14 is provided on the lower DBR layer 12. The resonator portion 18 is provided on the non-doped spacer portion 14. The upper DBR layer 28 is provided on the resonator portion 18. The lower DBR layer 30 is provided on the upper DBR layer 28. The resonator portion 32 is provided on the lower DBR layer 30. The upper DBR layer 36 is provided on the resonator portion 32.

[0073] The laminated structure of the lower DBR layer 12, the undoped spacer portion 14, the resonator portion 18, and the upper DBR layer 28 constitutes a first VCSEL. The laminated structure of the lower DBR layer 30, the resonator portion 32, and the upper DBR layer 36 constitutes a second VCSEL. That is, the semiconductor light emitting element 100 according to this embodiment is formed by laminating the first VCSEL and the second VCSEL in this order on the semiconductor substrate 10.

[0074] The stacked structure of the first VCSEL is the same as that of the semiconductor light emitting device 100 of the first embodiment. A saturable absorbing layer 16 is provided in the non-doped spacer portion 14. Five active layers 24 are provided in the resonator portion 18. Each active layer 24 is composed of a multiple quantum well including four quantum wells. That is, the resonator portion 18 includes 20 quantum well layers in total. As in the first embodiment, the resonator portion 18 is designed to have a smaller band gap in the AlGaAs barrier layer compared to the barrier layer used in the quantum well of a normal VCSEL, and to allow carriers to be accumulated in the AlGaAs barrier layer. As in the semiconductor light emitting device of the first embodiment, the first VCSEL has a saturable absorbing layer 16 and generates a high peak value, short pulse light pulse. The structure of the semiconductor light emitting device of the second embodiment may be applied to the first VCSEL.

[0075] The laminated structure of the lower DBR layer 30, the resonator portion 32, and the upper DBR layer 36 is processed into a mesa shape. The second VCSEL is formed on this mesa. An active layer 34 is provided in the resonator portion 32. An oxide constriction layer 38 is provided in the upper DBR layer 36. An electrode 40 electrically connected to the upper DBR layer 28 and the lower DBR layer 30 is provided on the upper DBR layer 28 exposed by processing the lower DBR layer 30, the resonator portion 32, and the upper DBR layer 36 into a mesa shape. An electrode 42 electrically connected to the upper DBR layer 36 is provided on the upper DBR layer 36. A protective film 44 is provided on the top surface of the upper DBR layer 28, excluding at least a part of the surfaces of the electrodes 40 and 42, and on the side and top surface of the mesa.

[0076] The second VCSEL oscillates when a voltage is applied between the electrodes 40 and 42 to pass a current therethrough, generating a laser beam. The wavelength of the laser beam generated by the second VCSEL is shorter than the emission wavelength of the first VCSEL, for example, 780 nm. The laser beam generated by the second VCSEL is excitation light for exciting the active layer 24 of the first VCSEL. By exciting the active layer 24 with the laser beam generated by the second VCSEL, the first VCSEL generates a high peak value, short pulsed optical pulse by a mechanism similar to that of the semiconductor light emitting element 100 of the first embodiment.

[0077] The reason why the second VCSEL is provided on the first VCSEL in the semiconductor light emitting device 100 according to this embodiment is to increase the number of layers in the active layer 24 in the first VCSEL. In the case of a configuration in which a pin junction is formed as in the first embodiment, the thickness of the i-layer is limited by the diffusion length of the carriers, in particular the diffusion length of the holes. On the other hand, when the active layer 24 is excited by irradiating light from the outside as in this embodiment, there is no restriction on the diffusion length of the carriers, so a VCSEL having more active layers 24 can be configured, which has the advantage of enabling the pulse energy to be increased.

[0078] As described above, according to this embodiment, it is possible to realize a semiconductor light emitting element and a light emitting device capable of generating an optical pulse with a short optical pulse width and a high peak value.

[0079] [Fourth embodiment] A semiconductor light emitting device according to a fourth embodiment of the present invention will be described with reference to Fig. 12 and Fig. 13. Fig. 12 is a perspective view showing the semiconductor light emitting device according to this embodiment. Fig. 13 is a top view of the semiconductor light emitting device according to this embodiment.

[0080] The semiconductor light emitting device 100 according to this embodiment is a light emitting device configured by arranging a plurality of light emitting portions 50 of the semiconductor light emitting device 100 according to the first to third embodiments in a two-dimensional array, that is, a so-called VCSEL array. The cross section along the line AA' in Fig. 13 generally corresponds to the cross section of Fig. 1, Fig. 10, or Fig. 11. Each of the light emitting portions 50 in Fig. 12 corresponds to the mesa portion in Fig. 1, Fig. 10, or Fig. 11. The semiconductor substrate 10 in Fig. 12 corresponds to the semiconductor substrate 10 to the n-type layer 20 in Fig. 1 or Fig. 10, or the semiconductor substrate 10 to the upper DBR layer 28 in Fig. 11.

[0081] 12 and 13 show only 12 light emitting units 50 arranged in a 4×3 array for simplicity of the drawings, but in a typical VCSEL array, for example, 3600 VCSELs arranged in a 60×60 array are provided on the same semiconductor substrate 10. The diameter of the light emitting units 50 is, for example, 10 μm. The light emitting units 50 are arranged such that the vertical and horizontal intervals between the centers of the light emitting units 50 in a plan view are, for example, 50 μm. The chip size of the semiconductor light emitting element 100 is, for example, 3.3 mm×3.3 mm.

[0082] The electrodes 40 corresponding to each of the light-emitting sections 50 are electrically connected to the anode common electrode 40C via wiring (not shown). The electrodes 42 corresponding to each of the light-emitting sections 50 are electrically connected to the cathode common electrode 42C. The anode common electrode 40C and the cathode common electrode 42C are electrodes common to the plurality of light-emitting sections 50 constituting the VCSEL array. Au wires (not shown) are electrically and physically connected to the anode common electrode 40C and the cathode common electrode 42C. A current for driving the semiconductor light-emitting element 100 is injected from an external circuit via the anode common electrode 40C and the cathode common electrode 42C. The anode common electrode 40C and the cathode common electrode 42C have a rectangular shape with a width of, for example, 100 μm and a length of, for example, 1.5 mm.

[0083] In this way, according to this embodiment, a VCSEL array can be realized using the semiconductor light emitting device 100 according to the first to third embodiments.

[0084] [Fifth embodiment] A distance measuring device according to a fifth embodiment of the present invention will be described with reference to Fig. 14. Fig. 14 is a block diagram showing a schematic configuration of the distance measuring device according to this embodiment.

[0085] The distance measuring device 200 according to this embodiment is a distance measuring device (LiDAR device) in which the semiconductor light emitting device 100 according to the fourth embodiment is applied to a light source section.

[0086] The distance measuring device 200 according to this embodiment may be composed of a control unit 210, a surface-emitting laser array driver 212, a surface-emitting laser array 214, an emission side optical system 218, a reception side optical system 220, an image sensor 222, and a distance data processing unit 224.

[0087] The surface-emitting laser array 214 is a packaged semiconductor light-emitting element 100 according to the fourth embodiment. The surface-emitting laser array driver 212 is a drive unit that receives a drive signal from the control unit 210, generates a drive current for oscillating the surface-emitting laser array 214, and outputs the drive current to the surface-emitting laser array 214. The surface-emitting laser array 214 and the surface-emitting laser array driver 212 may be one light-emitting device.

[0088] The light-emitting side optical system 218 is an optical system that emits laser light generated by the surface-emitting laser array 214 toward the distance measurement target range. The light-receiving side optical system 220 is an optical system that guides the laser light reflected by the measurement target 1000 to an image sensor 222. Note that, although the light-emitting side optical system 218 and the light-receiving side optical system 220 are represented by a single convex lens-shaped member in Fig. 14, they are not composed of only a single convex lens-shaped member, but are composed of a lens group combining multiple lenses.

[0089] The image sensor 222 is a photoelectric conversion device in which a plurality of pixels, each including a photoelectric conversion unit, are arranged in a two-dimensional array, and is a light receiving device that outputs an electrical signal according to incident light. The image sensor 222 may be an imaging device such as a CMOS image sensor. The distance data processing unit 224 has a function as a distance information acquisition unit that generates and outputs information regarding the distance to the measurement target object 1000 present in the distance measurement target range based on a signal from the image sensor 222. Note that the distance data processing unit 224 only needs to be electrically connected to the image sensor 222, and may be disposed in the same package as the image sensor 222 or in a package separate from the image sensor 222.

[0090] The control unit 210 is configured with an information processing device including a microcomputer and a logic circuit, and functions as a central processing device that governs the operation of the distance measuring device 200, such as controlling the operation of each unit and performing various calculation processes.

[0091] As described above, a light emitting device suitable for a LiDAR system is preferably a light emitting device capable of generating an optical pulse with a short optical pulse width and a high peak value. Specifically, the optical pulse width of a light source suitable for a LiDAR system is, for example, in the range of about 50 ps to 1 ns. On the other hand, from the electrical viewpoint of driving a VCSEL and a VCSEL, it is not easy to emit light with such a short pulse width. Since a VCSEL emits light according to the amount of current injected, in order to make the optical pulse about 50 ps to 1 ns, it is necessary to make the current pulse driving the VCSEL about the same. In other words, from the driver unit to the VCSEL, it is necessary to have excellent electrical characteristics in the high frequency band such as 1 GHz or 10 GHz as a frequency component and to handle a current exceeding 1 A. Doing so has the problem of being expensive compared to the case where an electrical transmission unit to the driver and VCSEL is configured only with an electrical circuit that handles only the frequency band below that.

[0092] Therefore, in this embodiment, the semiconductor light emitting element described in the first to fourth embodiments is used so that the VCSEL itself generates a short pulse. This avoids high costs for the driver and electrical transmission units and realizes optical pulses of about 50 ps to 1 ns, which are preferable for LiDAR systems.

[0093] Next, the operation of the distance measuring device according to this embodiment will be described with reference to FIG. First, the control unit 210 outputs a drive signal to the surface-emitting laser array driver 212. The surface-emitting laser array driver 212 receives the drive signal from the control unit 210 and injects a current of a predetermined current value into the surface-emitting laser array 214. This causes the surface-emitting laser array 214 to oscillate, and laser light is output from the surface-emitting laser array 214. At this time, the pulse width of the light emitted from the surface-emitting laser array 214 is narrower than the pulse width of the injected current, as described above.

[0094] The laser light generated by the surface-emitting laser array 214 is emitted toward the distance measurement range by the light-emitting side optical system 218. Of the laser light irradiated to the measurement object 1000 in the distance measurement range, the laser light reflected by the measurement object 1000 and incident on the light-receiving side optical system 220 is guided to the image sensor 222 by the light-receiving side optical system 220.

[0095] Each pixel of the image sensor 222 generates an electric signal pulse according to the timing of incidence of the laser light. The electric signal pulse generated by the image sensor 222 is input to the distance data processing unit 224.

[0096] The distance data processing unit 224 generates information about the distance to the measurement object 1000 along the light propagation direction, based on the reception timing of the electrical signal pulse output from the image sensor 222. By calculating the distance information based on the electrical signal pulse output from each pixel of the image sensor 222, three-dimensional information of the measurement object 1000 can be acquired.

[0097] The distance measuring device 200 of this embodiment can be applied to, for example, a control device in the field of automobiles for controlling to avoid collision with other vehicles, or a control device for controlling automatic driving by following other vehicles. The distance measuring device 200 of this embodiment can be applied not only to automobiles, but also to other moving bodies (moving devices) such as ships, aircraft, and industrial robots, and moving body detection systems. The distance measuring device 200 of this embodiment can be widely applied to equipment that uses information of objects recognized three-dimensionally, including distance information. These moving bodies can be configured to include the distance measuring device of this embodiment and a control means for controlling the moving body based on information on the distance acquired by the distance measuring device.

[0098] In addition, the three-dimensional information including the depth that can be acquired by the distance measuring device 200 of this embodiment can be used in an image capturing device, an image processing device, a display device, etc. For example, it is possible to use the three-dimensional information acquired by the distance measuring device 200 of this embodiment to display a virtual object on an image of the real world without creating a sense of incongruity. In addition, by storing the three-dimensional information together with the image information, it is also possible to correct the blur of the captured image after shooting.

[0099] As described above, according to this embodiment, it is possible to realize a high-performance distance measuring device equipped with a light emitting device capable of generating an optical pulse with a short optical pulse width and a high peak value.

[0100] [Sixth embodiment] A distance measuring device according to a sixth embodiment of the present invention will be described with reference to Figs. 15 and 16. Fig. 15 is a block diagram showing a schematic configuration of the distance measuring device according to this embodiment. Fig. 16 is a schematic cross-sectional view showing a configuration example of a surface emitting laser array in the distance measuring device according to this embodiment. Components similar to those of the semiconductor light emitting devices according to the first to fourth embodiments and the distance measuring device according to the fifth embodiment are given the same reference numerals, and descriptions thereof will be omitted or simplified.

[0101] 15, the distance measuring device 200 according to this embodiment differs from the distance measuring device according to the fifth embodiment in that the surface emitting laser array 214 further includes a light emission timing monitor unit 216. Other points of the distance measuring device 200 according to this embodiment are similar to those of the distance measuring device according to the fifth embodiment.

[0102] The surface emitting laser array 214 includes a semiconductor light emitting element 100, an emission timing monitor section 216, a base 110, and a window material 120, as shown in FIG. 16. The base 110 is a part of a package that mounts the semiconductor light emitting element 100 and the emission timing monitor section 216, and has a recess that accommodates the semiconductor light emitting element 100 and the emission timing monitor section 216. The base 110 may be made of, for example, ceramic. The window material 120 is fixed to the base 110 so as to cover the recess of the base 110 on which the semiconductor light emitting element 100 and the emission timing monitor section 216 are mounted. The semiconductor light emitting element 100 is the semiconductor light emitting element 100 according to the fourth embodiment. The emission timing monitor section 216 is made of, for example, a semiconductor substrate having a square shape of 0.3 mm square, and includes a photodiode with a light receiving area having a diameter of, for example, 100 μm.

[0103] The anode common electrode 40C and the cathode common electrode 42C of the semiconductor light emitting element 100, and the anode and cathode of the photodiode constituting the light emission timing monitor unit 216 are electrically connected to electrodes (not shown) provided on the outer periphery of the base 110. A pulse current supplied from the surface emitting laser array driver 212 is supplied to the semiconductor light emitting element 100 via the electrodes provided on the base 110. In addition, an electrical signal generated by the light emission timing monitor unit 216 is supplied to the distance data processing unit 224 via the electrodes provided on the base 110.

[0104] Next, the operation of the distance measuring device according to this embodiment will be described with reference to FIGS. First, the control unit 210 outputs a drive signal to the surface-emitting laser array driver 212. The surface-emitting laser array driver 212 receives the drive signal from the control unit 210 and injects a current of a predetermined current value into the semiconductor light-emitting element 100 of the surface-emitting laser array 214. This causes the semiconductor light-emitting element 100 to oscillate, and laser light is output from the semiconductor light-emitting element 100. At this time, the pulse width of the light emitted from the semiconductor light-emitting element 100 is narrower than the pulse width of the injected current, as described above.

[0105] The laser light generated by the semiconductor light emitting element 100 is emitted from the surface emitting laser array 214 through the window material 120, and is emitted toward the distance measurement target range by the light emitting side optical system 218. At this time, although the window material 120 is subjected to an AR coating, a part of the light is reflected by the window material 120 and enters the light emission timing monitor unit 216.

[0106] The light emission timing monitor 216 converts the incident light into an electrical signal and outputs it to the distance data processor 224. The distance data processor 224 generates information about the distance to the measurement object 1000 along the light propagation direction based on the time difference between the reception timing of the electrical signal pulse from the image sensor 222 and the reception timing of the electrical signal from the light emission timing monitor 216. Then, the distance data processor 224 calculates distance information based on the electrical signal pulse output from each pixel of the image sensor 222, thereby acquiring three-dimensional information of the measurement object 1000.

[0107] Next, the reason why the distance measuring device in this embodiment is configured as described above will be explained with reference to FIGS.

[0108] In the LiDAR system, the distance to the object is calculated based on the time difference between when the laser light is emitted and when it is reflected by the object and returns. Therefore, in order to improve the distance measurement accuracy, it is necessary to know the timing at which the light emission pulse is generated in the semiconductor light emitting element 100 with higher accuracy. For example, when the time detection accuracy on the light receiving side is about 50 ps, ​​it is preferable that the accuracy of the information on the timing of the pulse generation on the light emitting side is smaller than 50 ps.

[0109] In general VCSELs and LiDAR systems using them, a pulse current is generated by the VCSEL driver to drive the VCSEL. Since the VCSEL emits light according to the pulse current waveform, the difference between the emission timing of the VCSEL and the rising timing of the pulse current generated by the VCSEL driver is small, and the time difference does not change significantly due to fluctuations in the environmental temperature, etc. This is because the VCSEL is designed to emit light according to the injected current value. Therefore, the time from the generation timing of the current pulse in the driver to the emission timing of the VCSEL can be accurately estimated.

[0110] On the other hand, the inventors have discovered for the first time that when the time difference between the generation timing of a current pulse and the generation timing of a light pulse is estimated using the above-mentioned method, the ranging accuracy may decrease in a LiDAR system using the semiconductor light-emitting elements of the first to fourth embodiments.

[0111] In the semiconductor light-emitting devices of the first to fourth embodiments, carriers are accumulated in the active layer 24, and after the start of laser oscillation, the accumulated carriers are converted into light to generate an optical pulse. That is, for a predetermined time until carriers are accumulated in the active layer 24, the current injected into the semiconductor light-emitting device is used to accumulate carriers in the active layer 24. Then, for a predetermined time until carriers are accumulated in the active layer 24, laser oscillation of the semiconductor light-emitting device is delayed.

[0112] The timing of laser oscillation in the semiconductor light emitting device of the first to fourth embodiments is determined by the structure of the semiconductor light emitting device and the physical parameters of the materials constituting each part. Therefore, even if the current waveform generated by the surface emitting laser array driver 212 is the same, the time difference from the start of driving to the start of laser oscillation changes due to changes in the environmental temperature and changes in the physical parameters over time. And, the time difference may exceed about 50 ps, ​​which is a typical time detection accuracy on the light receiving side.

[0113] Figures 17 and 18 are graphs showing the results of calculations of changes in optical waveform due to changes in environmental temperature and changes in physical parameters over time. Figure 17 shows the calculation results for a typical VCSEL, and Figure 18 shows the calculation results for the semiconductor light-emitting device of the present invention.

[0114] 17 and 18 show enlarged optical waveforms immediately after the start of oscillation when the transparent carrier density is assumed to be at room temperature and when the transparent carrier density is assumed to be 50° C. higher than room temperature. In both figures, the characteristics that start oscillation first are those when the transparent carrier density is assumed to be at room temperature, and the characteristics that start oscillation later are those when the transparent carrier density is assumed to be 50° C. higher than room temperature.

[0115] In a typical VCSEL, as shown in FIG. 17, the time difference between the peak time of the optical pulse when the transparent carrier density is assumed to be at room temperature and the peak time of the optical pulse when the transparent carrier density is assumed to be 50° C. higher than room temperature is 13 ps.

[0116] On the other hand, in the semiconductor light-emitting device of the present invention, the time difference between the peak time of the light pulse assuming the transparent carrier density at room temperature and the peak time of the light pulse assuming the transparent carrier density at a temperature 50° C. higher than room temperature is 70 ps, ​​as shown in Fig. 18. The time difference from the timing at which current injection into semiconductor light-emitting device 100 starts to the timing at which the light output reaches the maximum peak value can vary, for example, in the range of 50 ps or more and 1 ns or less due to changes in the environmental temperature, etc.

[0117] Thus, in the semiconductor light emitting device of the present invention, changes in physical properties have a large effect on the change in oscillation timing, and the amount of change in the oscillation timing may exceed about 50 ps, ​​which is a typical time detection accuracy on the light receiving side.

[0118] From this viewpoint, in the distance measuring device 200 of this embodiment, the light emission timing of the surface-emitting laser array 214 is detected by the light emission timing monitor unit 216. Then, distance information is calculated using the light emission timing detected by the light emission timing monitor unit 216. Therefore, even if the light emission timing of the surface-emitting laser array 214 is shifted due to factors such as the environmental temperature, the distance measuring accuracy of the distance measuring device 200 is not affected, and high distance measuring accuracy can be maintained.

[0119] As described above, according to this embodiment, in a distance measuring device using an optical pulse with a high peak value and a short pulse, the effect of changes in the environmental temperature on distance measuring accuracy can be reduced.

[0120] [Modified embodiment] The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, an example in which part of the configuration of any one of the embodiments is added to another embodiment, or an example in which part of the configuration of another embodiment is substituted therefor, is also an embodiment of the present invention.

[0121] In the above first to third embodiments, GaAs, AlGaAs, and InGaAs are exemplified as semiconductor materials capable of crystal growth when a GaAs substrate is used as the semiconductor substrate 10, but the semiconductor substrate 10 is not limited to a GaAs substrate. For example, an InP substrate can also be used as the semiconductor substrate 10. Examples of semiconductor materials capable of crystal growth when an InP substrate is used as the semiconductor substrate 10 include InP, InGaAs, InGaP, and InGaAsP.

[0122] Furthermore, the DBR layer in the semiconductor light emitting device according to the first to third embodiments does not necessarily have to be made of a semiconductor material, and may be made of a material other than a semiconductor material. In this case, too, by configuring it to have the same function as the first to third embodiments, the same effect as this embodiment can be achieved.

[0123] It should be noted that the above-mentioned embodiments are merely examples of the implementation of the present invention, and the technical scope of the present invention should not be interpreted as being limited by these embodiments. In other words, the present invention can be implemented in various forms without departing from its technical concept or main features.

[0124] The disclosure of the above embodiment includes the following configurations. (Configuration 1) a semiconductor light emitting element having a first reflector, a cavity spacer portion including an active layer, and a second reflector stacked in this order on a semiconductor substrate; the semiconductor light emitting device includes a saturable absorbing layer between the semiconductor substrate and the second reflector, The semiconductor light emitting element is configured to emit light having a profile that has a maximum peak value and that converges to a stable value that is a predetermined light intensity after the maximum peak value. A light emitting device characterized by: (Configuration 2) a semiconductor light emitting element having a first reflector, a cavity spacer portion including an active layer, and a second reflector stacked in this order on a semiconductor substrate; the semiconductor light emitting device includes a saturable absorbing layer between the semiconductor substrate and the second reflector, The optical confinement coefficient of the active layer is Γs, the optical confinement coefficient of the saturable absorbing layer is Γa, the maximum gain in the active layer obtained when the current value injected from the driving unit is Iop is gmax(Iop), the absorption coefficient of the saturable absorbing layer is α2, the mirror loss is αm, and the optical absorption by carriers is αi, Γs×gmax(Iop) > Γa×α2+αm+αi Satisfying the relationship A light emitting device characterized by: (Configuration 3) The saturable absorbing layer is located between the semiconductor substrate and the active layer and also serves as the first reflector. 3. The light emitting device according to configuration 1 or 2. (Configuration 4) The saturable absorbing layer is located between the active layer and the second reflector. 3. The light emitting device according to configuration 1 or 2. (Configuration 5) The half-width of the optical pulse showing the maximum peak value is 50 ps or more. 2. The light emitting device according to configuration 1. (Configuration 6) The time difference between the timing at which current injection into the semiconductor light emitting device starts and the timing at which the optical output reaches the maximum peak value is 50 ps or more and 1 ns or less. 2. The light emitting device according to configuration 1. (Configuration 7) The active layer has a plurality of quantum well layers and barrier layers provided between the plurality of quantum well layers, and an energy difference between an emission level of the quantum well layers and a band gap of the barrier layers is in a range of 105 meV to 230 meV. 7. The light emitting device according to any one of configurations 1 to 6. (Configuration 8) the quantum well layer is made of InGaAs; The barrier layer is made of GaAs. 8. The light emitting device according to configuration 7. (Configuration 9) a semiconductor layer disposed between the active layer and the saturable absorbing layer; The semiconductor layer includes an AlGaAs layer having an Al composition in the range of 0.45 to 0.9. 9. The light emitting device according to any one of configurations 1 to 8. (Configuration 10) The semiconductor layer further includes a GaAsP layer. 10. The light emitting device according to configuration 9. (Configuration 11) The optical thickness of the cavity spacer portion is equal to or greater than five times the resonant wavelength. 11. The light emitting device according to any one of configurations 1 to 10. (Configuration 12) The optical thickness of the cavity spacer portion is equal to or greater than 11 times the resonant wavelength. 12. The light emitting device according to any one of configurations 1 to 11. (Configuration 13) The active layer includes 6 to 50 quantum well layers. 13. The light emitting device according to any one of configurations 1 to 12. (Configuration 14) The semiconductor light emitting element further includes a light receiving element mounted in the same package as the semiconductor light emitting element and receiving light emitted from the semiconductor light emitting element. 14. The light emitting device according to any one of configurations 1 to 13. (Configuration 15) a semiconductor light emitting element having a first reflector, a cavity spacer portion including an active layer, and a second reflector stacked in this order on a semiconductor substrate; The active layer includes 6 to 50 quantum well layers, a saturable absorbing layer between the semiconductor substrate and the second reflector; The optical thickness of the cavity spacer portion is equal to or greater than five times the resonant wavelength. A light emitting device characterized by: (Configuration 16) The active layer is located between an antinode and a node of a standing wave generated between the first reflecting mirror and the second reflecting mirror. 16. The light emitting device according to claim 15, (Configuration 17) a semiconductor light emitting element having a first reflector, a cavity spacer portion including an active layer, and a second reflector stacked in this order on a semiconductor substrate; the semiconductor light emitting device includes a saturable absorbing layer between the semiconductor substrate and the second reflector, the active layer includes a plurality of quantum well layers and a barrier layer provided between the plurality of quantum well layers; The barrier layer is made of GaAs. A light emitting device characterized by: (Configuration 18) The optical thickness of the cavity spacer portion is equal to or greater than five times the resonant wavelength. 18. The light emitting device according to claim 17. (Configuration 19) The optical thickness of the cavity spacer portion is equal to or greater than 11 times the resonant wavelength. 19. The light emitting device according to any one of configurations 15 to 18. (Configuration 20) A light emitting device according to any one of configurations 1 to 19, a light receiving device that receives light emitted from the light emitting device and reflected by a measurement object; a distance information acquiring unit that acquires information about a distance to the object to be measured based on a time difference between a timing at which light is emitted from the light emitting device and a timing at which the light receiving device receives the light; A distance measuring device comprising: (Configuration 21) A mobile object, A distance measuring device according to aspect 20, a control means for controlling the moving object based on information regarding the distance acquired by the distance measuring device; A moving object comprising: [Explanation of symbols]

[0125] 10...Semiconductor substrate 12,30…Lower DBR layer 14...Non-doped spacer section 16...Saturable absorbing layer 18,32...Resonator section 20...n-type layer 22...Non-doped spacer section 24,34…active layer 26...p-type layer 28,36...Top DBR layer 38…Oxidized constriction layer 40,42...electrode 44...Protective film 50…Light emitting part

Claims

1. a semiconductor light emitting device having a first reflector, a cavity spacer portion including an active layer, and a second reflector stacked in this order on a semiconductor substrate; the semiconductor light emitting device includes a saturable absorbing layer between the semiconductor substrate and the second reflector; the active layer has a plurality of quantum well layers and barrier layers provided between the plurality of quantum well layers, and a band gap difference between the quantum well layers and the barrier layers is 230 meV or less; The semiconductor light emitting element is configured to emit light having a profile that has a maximum peak value and that converges to a stable value that is a predetermined light intensity after the maximum peak value. A light emitting device characterized by:

2. The saturable absorbing layer is located between the semiconductor substrate and the active layer.

2. The light emitting device according to claim 1 .

3. The saturable absorbing layer also serves as the first reflector.

2. The light emitting device according to claim 1 .

4. The saturable absorbing layer is located between the active layer and the second reflector.

2. The light emitting device according to claim 1 .

5. The half-width of the optical pulse showing the maximum peak value is 50 ps or more.

2. The light emitting device according to claim 1 .

6. The time difference between the timing at which current injection into the semiconductor light emitting element starts and the timing at which the optical output reaches the maximum peak value is 50 ps or more and 1 ns or less.

2. The light emitting device according to claim 1 .

7. the quantum well layer is made of InGaAs; The barrier layer is made of GaAs.

2. The light emitting device according to claim 1 .

8. a semiconductor layer disposed between the active layer and the saturable absorbing layer; The semiconductor layer includes an AlGaAs layer having an Al composition in the range of 0.45 to 0.

9.

2. The light emitting device according to claim 1 .

9. The semiconductor layer further includes a GaAsP layer.

9. The light emitting device according to claim 8.

10. The optical thickness of the cavity spacer portion is equal to or greater than five times the resonant wavelength.

2. The light emitting device according to claim 1 .

11. The optical thickness of the cavity spacer portion is equal to or greater than 11 times the resonant wavelength.

2. The light emitting device according to claim 1 .

12. The active layer includes 6 to 50 quantum well layers.

2. The light emitting device according to claim 1 .

13. The semiconductor light emitting element further includes a light receiving element mounted in the same package as the semiconductor light emitting element and receiving light emitted from the semiconductor light emitting element.

2. The light emitting device according to claim 1 .

14. A light emitting device according to any one of claims 1 to 13, a light receiving device that receives light emitted from the light emitting device and reflected by a measurement object; a distance information acquiring unit that acquires information about a distance to the object to be measured based on a time difference between a timing at which light is emitted from the light emitting device and a timing at which the light receiving device receives the light; A distance measuring device comprising:

15. A mobile object, A distance measuring device according to claim 14; a control means for controlling the moving object based on information regarding the distance acquired by the distance measuring device; A moving object comprising:

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