WO2022244674A1 - 発光装置、測距装置及び移動体 - Google Patents
発光装置、測距装置及び移動体 Download PDFInfo
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- H01S5/343—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
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Definitions
- the present invention relates to a light emitting device, a distance measuring device, and a moving body.
- Patent Document 1 discloses a VCSEL (Vertical Cavity Surface Emitting Laser) as a light source for ToF (Time of Flight) LiDAR (Light Detection and Ranging). It is stated to use VCSELs have the advantage of being less wavelength dependent on temperature.
- VCSEL Vertical Cavity Surface Emitting Laser
- the peak value of the irradiated light pulse By the way, 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 the ambient light and the light pulse emitted by itself, and the S/N can be increased. , and thus the maximum measurable distance can be extended.
- the peak value of the optical pulse there is a limit to the peak value of the optical pulse.
- the upper limit of the peak value from the viewpoint of eye safety depends on the width of the optical pulse, and the narrower the width of the optical pulse, the higher the peak value can be. Therefore, as a light source to be applied to the LiDAR system, a light source capable of generating a light pulse with a short light pulse width and a high peak value is desirable.
- An object of the present invention is to provide a light emitting device including a semiconductor light emitting element capable of generating a light pulse with a short light pulse width and a high peak value, and a distance measuring device using such a light emitting device.
- a semiconductor light-emitting device in which a first reflecting mirror, a resonator spacer section including an active layer, and a second reflecting mirror are stacked in this order on a semiconductor substrate.
- the semiconductor light emitting device includes a saturable absorption layer between the semiconductor substrate and the second reflector; the semiconductor light emitting device has a maximum peak value;
- a light emitting device is provided that is configured to emit light having a profile that subsequently converges to a stable value of predetermined light intensity.
- a first reflecting mirror, a resonator spacer section including an active layer, and a second reflecting mirror are laminated in this order on a semiconductor substrate.
- the semiconductor light emitting device includes a saturable absorption layer between the semiconductor substrate and the second reflecting mirror
- the light confinement coefficient of the active layer is ⁇ s
- the saturable absorption layer ⁇ a is the optical confinement factor of
- gmax (Iop) is the maximum gain in the active layer obtained when the current value injected from the drive unit is Iop
- ⁇ 2 is the absorption coefficient of the saturable absorption layer
- the mirror loss is A light-emitting device is provided that satisfies the relationship ⁇ s ⁇ gmax(Iop)> ⁇ a ⁇ 2+ ⁇ m+ ⁇ i, where ⁇ m is light absorption by carriers and ⁇ i.
- a first reflecting mirror, a resonator spacer section including an active layer, and a second reflecting mirror are laminated in this order on a semiconductor substrate.
- the active layer includes 6 or more and 50 or less quantum well layers, further comprising a saturable absorption layer between the semiconductor substrate and the second reflector;
- a light-emitting device is provided in which the optical thickness of the cavity spacer portion is equal to or greater than a thickness corresponding to five times the resonance wavelength.
- a first reflecting mirror, a resonator spacer section including an active layer, and a second reflecting mirror are laminated in this order on a semiconductor substrate.
- the semiconductor light emitting device includes a saturable absorption layer between the semiconductor substrate and the second reflector, and the active layer includes a plurality of quantum well layers and the plurality of A light emitting device is provided including barrier layers disposed between the quantum well layers, said barrier layers comprising GaAs.
- a light-emitting device including a semiconductor light-emitting element capable of generating a light pulse with a short light pulse width and a high peak value, and a high-performance distance measuring device using such a light-emitting device are realized. can be done.
- FIG. 1 is a schematic cross-sectional view showing a semiconductor light emitting device according to a first embodiment of the invention
- FIG. 4 is a graph showing Al composition dependence of the ratio of the density of carriers accumulated in a well layer to the density of carriers accumulated in a barrier layer.
- 7 is a graph showing optical output waveforms of semiconductor light emitting devices according to comparative examples.
- 4 is a graph showing optical output waveforms of the semiconductor light emitting device according to the first embodiment of the present invention; 4 is a graph showing temporal changes in density of carriers accumulated in an active layer and light intensity.
- FIG. 4 is a graph showing the relationship between effective cavity length and optical output waveform; 4 is a graph showing the relationship between the effective cavity length and the pulse width of optical output; 4 is a graph showing the relationship between the number of quantum well layers and the peak ratio. 4 is a graph showing the relationship between the minimum number of quantum well layers required for a peak ratio exceeding 2 and the cavity length.
- FIG. 4 is a schematic cross-sectional view showing a semiconductor light emitting device according to a second embodiment of the invention
- FIG. 5 is a schematic cross-sectional view showing a semiconductor light emitting device according to a third embodiment of the invention
- FIG. 11 is a perspective view showing a semiconductor light emitting device according to a fourth embodiment of the present invention.
- FIG. 10 is a top view of a semiconductor light emitting device according to a fourth embodiment of the present invention
- FIG. 11 is a block diagram showing a schematic configuration of a distance measuring device according to a fifth embodiment of the present invention
- FIG. 11 is a block diagram showing a schematic configuration of a distance measuring device according to a sixth embodiment of the present invention
- FIG. 11 is a schematic cross-sectional view showing a configuration example of a surface emitting laser array in a distance measuring device according to a sixth embodiment of the present invention
- 7 is a graph showing changes in optical waveform due to changes in environmental temperature and changes in physical parameters over time in the semiconductor light emitting device of Comparative Example.
- 5 is a graph showing changes in optical waveform due to changes in environmental temperature and changes in physical parameters over time in the semiconductor light emitting device of the present invention.
- FIG. 1 is a schematic cross-sectional view showing the structure of a semiconductor light emitting device according to this embodiment.
- the semiconductor light emitting device 100 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 includes a semiconductor substrate 10, a lower DBR layer 12, a non-doped spacer section 14, a resonator section 18, an upper DBR layer 28, electrodes 40 and 42, and a protective film. 44 and .
- a lower DBR layer 12 is provided on the semiconductor substrate 10 .
- a non-doped spacer portion 14 is provided on the lower DBR layer 12 .
- the resonator section 18 is provided on the non-doped spacer section 14 .
- the upper DBR layer 28 is provided on the resonator section 18 .
- a layer (the non-doped spacer section 14 and the resonator section 18) located between the lower DBR layer 12 and the upper DBR layer 28 is the resonator spacer section.
- a saturable absorption layer 16 is provided in the non-doped spacer portion 14 .
- the resonator section 18 includes an n-type layer 20 provided on the non-doped spacer section 14 , a non-doped spacer section 22 provided on the n-type layer 20 , and a p-type layer provided on the non-doped spacer section 22 .
- a three-layer active layer 24 is provided in the non-doped spacer portion 22 .
- An oxidized constricting layer 38 is provided in the upper DBR layer 28 .
- the non-doped 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 non-doped 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 top surface of the n-type layer 20 excluding at least part of the surfaces of the electrodes 40 and 42 and the side and top surfaces of the mesa.
- the semiconductor substrate 10 can be composed of, for example, a GaAs substrate.
- the lower DBR layer 12 can be constructed by, for example, stacking 35 pairs of a laminate of an Al 0.1 GaAs layer and an Al 0.9 GaAs layer each having an optical thickness of 1/4 ⁇ c.
- ⁇ c is the central wavelength of the high reflection band of the lower DBR layer 12, which is 940 nm in this embodiment.
- the non-doped spacer portion 14 has a configuration that does not exist in a general VCSEL.
- the saturable absorption layer 16 can be composed of, for example, a multi-quantum well layer including three quantum well layers in which InGaAs well layers with a thickness of 8 nm are sandwiched between AlGaAs barrier layers with a thickness of 10 nm.
- Other portions of the non-doped spacer portion 14 can be composed of non-doped GaAs layers.
- the resonator section 18 is composed of a pin junction composed of an n-type layer 20, a non-doped spacer section 22 and a p-type layer .
- Each of the three active layers 24 disposed in the non-doped spacer section 22 is composed of a multi-quantum well including four quantum well layers in which, for example, InGaAs well layers with a thickness of 8 nm are sandwiched between AlGaAs barrier layers with a thickness of 10 nm. obtain.
- the resonator section 18 includes a total of 12 layers of quantum wells.
- the n-type layer 20 can be composed of an n-type GaAs layer
- the p-type layer 26 can be composed of a p-type GaAs layer
- the other portions of the non-doped spacer portion 22 can be composed of non-doped GaAs layers.
- the resonator section 18 is composed of a pin junction that is also present in a normal VCSEL, and has a configuration similar to that of a resonator section that includes an active layer in the i-layer.
- the number of quantum well layers that the resonator section 18 has is larger than the number of quantum well layers (about three layers) that a normal VCSEL has.
- the effective cavity length of the cavity portion 18 is 10 ⁇ m.
- these three active layers 24 are arranged at positions between the antinodes and nodes of the standing wave, not at the positions of the antinodes of the standing wave used in general VCSEL design.
- the optical confinement factor for standing waves is generally set in the range of 1.5 to 2.0 in a normal VCSEL, but in the present embodiment, it is intentionally set as low as about 0.35.
- the AlGaAs barrier layer has a smaller bandgap 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.
- the number of InGaAs well layers in which carriers are accumulated is 12, carriers are also accumulated in the AlGaAs barrier layers, so that approximately 20 layers of carriers are accumulated in terms of normal quantum well layers. It becomes possible to
- FIG. 2 is a graph showing the result of calculating the Al composition dependence of the ratio of the density of carriers accumulated in the InGaAs well layer and the density of carriers accumulated in the AlGaAs barrier layer.
- the ⁇ plots are for the carrier density of the well layer of 2 ⁇ 10 18 cm ⁇ 3
- the ⁇ plots are for the carrier density of the well layer of 5 ⁇ 10 18 cm ⁇ 3
- the plots marked with ⁇ are for the carrier density of the well layer of 9 ⁇ 10 18 cm ⁇ 3 .
- the minimum carrier density for generating the induced amplification required for laser oscillation is about 2 ⁇ 10 18 cm ⁇ 3 . Therefore, assuming that the density of carriers accumulated in the quantum well is 2 ⁇ 10 18 cm ⁇ 3 , when the Al composition of the AlGaAs barrier layer is 0.05, as shown in FIG. The ratio of the density to the density of carriers accumulated in the barrier layer is about 0.075. 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 about 0.025.
- a guideline for the maximum thickness that is effective as a barrier layer for accumulating carriers is 1 ⁇ m, which is the diffusion length of carriers.
- the active layer of a VCSEL is often composed of three quantum wells. Therefore, assuming that the amount of carriers accumulated in the barrier layer with a thickness of 1 ⁇ m is equal to or greater than that accumulated in the three quantum wells with a total thickness of about 25 nm, the reciprocal of the thickness ratio is A carrier density ratio of 0.025 or greater is required. In other words, from the calculation results of FIG. 2, it can be seen that AlGaAs with an Al composition of 0.1 or less is preferable for the barrier layer.
- the energy difference between the bandgap 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. That is, the energy difference between the bandgap of the barrier layer and the emission level of the well layer is preferably 230 meV or less.
- the lower limit of the energy difference between the bandgap of the barrier layer and the emission level of the well layer is the energy corresponding to the difference from the bandgap of GaAs from the viewpoint of light absorption.
- the energy difference between the bandgap of the barrier layer and the emission level of the well layer is preferably 105 meV or more. From the above, the preferable range of the energy difference between the emission level of the well layer and the bandgap of the barrier layer is 105 meV to 230 meV.
- a pair of laminates of an Al 0.1 Ga 0.9 As layer and an Al 0.9 Ga 0.1 As layer having an optical film thickness of 1/4 ⁇ c are formed into 20 layers. It can be constructed by pair lamination.
- An oxidized constricting layer 38 is provided in the upper DBR layer 28 by partially oxidizing an Al 0.98 Ga 0.02 As layer having a thickness of 30 nm.
- the oxidized constricting layer 38 can be formed, for example, by oxidizing the Al 0.98 Ga 0.02 As layer from the side surface of the mesa with water vapor during manufacturing.
- the oxidized constricting layer 38 has an unoxidized portion at the center of the mesa and an oxidized portion near the sidewalls of the mesa.
- the diameter of the non-oxidized portion in plan view can be about 10 ⁇ m.
- 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 may be configured to be emitted from the semiconductor substrate 10 side.
- the following three elements are added to the basic configuration of a normal VCSEL.
- the first of the three additions to the VCSEL is to substantially increase the volume of the active layer.
- a normal VCSEL is composed of three layers of quantum wells, but this can be increased to about 20 layers in terms of quantum well volume.
- the second is to introduce a saturable absorbing layer 16 .
- the third is to extend the effective cavity length of the VCSEL.
- the effective cavity length is the cavity length that light senses in the cavity. More specifically, it is the average value of the distance that light transmitted through the active layer in the resonance direction is reflected by two reflecting mirrors constituting the resonator and propagates until the light is transmitted through the active layer again.
- FIG. 3 and 4 are graphs showing results obtained by calculation of optical output waveforms of semiconductor light emitting devices.
- FIG. 3 shows the optical output waveform of the semiconductor light emitting device according to the comparative example
- FIG. 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 having a general configuration in which a saturable absorption layer is not provided and three quantum well layers and a cavity length of 1 ⁇ are designed.
- oscillation starts at about 70 ps from the start of current injection, and light output rises. Then, the optical output reaches the peak of the optical waveform associated with relaxation oscillation, and then converges to a stationary value.
- the semiconductor light emitting device 100 emits light having a profile that has a maximum peak value and converges to a stable value that is a predetermined light intensity after the maximum peak value. That is, in the semiconductor light emitting device 100 according to the present embodiment, oscillation starts after about 600 ps have elapsed from the start of current injection, as shown in FIG. 4, for example. This delay in the start of oscillation is due to the fact that the effective volume of the active layer 24 is increased and that the oscillation is inhibited by light absorption in the saturable absorption layer 16 for a certain period of time after the start of current injection.
- the absorbed light is accumulated in the saturable absorption layer 16 as carriers.
- the carrier density in the saturable absorption layer 16 reaches the transparent carrier density, the saturable absorption layer 16 stops absorbing light. As a result, the effect of inhibiting laser oscillation disappears, and the semiconductor light emitting element starts laser oscillation.
- the purpose of inhibiting laser oscillation for a certain period of time by the saturable absorption layer 16 is to accumulate carriers exceeding the threshold carrier density in the active layer 24 .
- the threshold carrier density is a carrier density that generates a gain necessary for laser oscillation.
- FIG. 5 is a graph showing temporal changes in the density of carriers accumulated in the active layer 24 and the light intensity. Assume that the current injected into the semiconductor light emitting device has a waveform similar to that shown in FIG. 4, and the injection starts at 4E-10 seconds on the time axis.
- the carrier density in the active layer 24 begins to rise with the start of current injection.
- the threshold carrier density (the carrier density that converges after the start of oscillation) in the semiconductor light emitting device 100 of the present embodiment is 2.7E+18 cm ⁇ 3 , but before laser oscillation starts, carriers temporarily exceed the threshold carrier density. continue to accumulate. After that, when laser oscillation starts, the carriers are rapidly consumed by stimulated emission and converge to a stable value.
- the semiconductor light emitting device 100 according to this embodiment, more carriers are accumulated in the active layer 24 than the threshold carrier density. After the start of laser oscillation, 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.
- the reason why carriers with a threshold carrier density or more can be accumulated in the active layer 24 is that the saturable absorption layer 16 is used to suppress laser oscillation for a certain period of time.
- an optical pulse with a high peak value and a short pulse width can be generated inside the semiconductor light emitting device after oscillation. This light pulse is shorter than the current pulse that drives the semiconductor light emitting device.
- the condition for continuous laser oscillation is that the maximum gain obtained by the active layer 24 exceeds the absorption in the entire cavity.
- laser oscillation can be continued when the relationship represented by the following formula (1) holds.
- ⁇ a is the optical confinement coefficient of the saturable absorption layer 16
- ⁇ s is the optical confinement coefficient of the active layer 24
- gmax(Iop) is the maximum gain in the active layer 24 obtained when the current value is Iop. is.
- ⁇ 2 is the absorption coefficient of the saturable absorption layer 16
- ⁇ m is the mirror loss
- ⁇ i is the light absorption by semiconductor carriers and the like.
- the oscillation continues in a stable state after the optical pulse is generated.
- the reason is that the number of current pulses output from the driver of the semiconductor light emitting device and the number of light pulses generated by the semiconductor light emitting device are the same.
- a constant current is continuously injected during a certain period of time and a plurality of pulses are generated from the semiconductor light-emitting element, it is difficult to distinguish between the first pulse and the subsequent pulses when viewed from the light receiving side. It is difficult and can lead to large errors in calculating the distance.
- a demerit such as a reduction in the amount of light allowed for one pulse may occur.
- the length of the cavity as a laser is extended by extending the distance from the lower DBR layer 12 to the upper DBR layer 28 using the non-doped spacer portion 14 .
- the purpose is to widen the pulse width. It is desirable that the optical thickness of the cavity spacer portion is equal to or greater than five times the resonant wavelength, more preferably equal to or greater than eleven times the resonant wavelength.
- the optical thickness refers to a value obtained by multiplying the physical thickness by the refractive index of the medium.
- FIG. 6 is a graph showing results obtained by calculation of optical output waveforms when rectangular current pulses are injected into semiconductor light emitting devices having effective cavity lengths L eff of 2 ⁇ m, 5 ⁇ m, and 10 ⁇ m.
- FIG. 7 is a graph showing the relationship between the effective cavity length and the pulse width of optical output. As shown in FIGS. 6 and 7, the pulse width of the optical output can be lengthened by lengthening the effective cavity length.
- the effective cavity length is 2 ⁇ m
- the pulse width is 30 ps
- the effective cavity length is 2 ⁇ m.
- the pulse width was 59 ps at 5 ⁇ m
- the pulse width was 110 ps at the effective cavity length of 10 ⁇ m. Note that the pulse width here is the half width.
- the effective cavity length is preferably 4 ⁇ m or more. Also, if the pulse width obtained from the error of the light receiving timing is 30 ps, the effective cavity length is preferably 2 ⁇ m or more.
- the thickness of the non-doped spacer portion 14 and the like is increased to increase the physical distance between the lower DBR layer 12 and the upper DBR layer 28, thereby extending the effective cavity length.
- the method for extending the cavity length is not limited to this.
- by providing a third reflecting mirror between the lower DBR layer 12 and the upper DBR layer 28 to form a coupled resonator the distance between the lower DBR layer 12 and the upper DBR layer 28 can be changed from that of the present embodiment. Even with a relatively short configuration, it is possible to effectively extend the resonator length. In any case, it is possible to control the optical pulse width to a preferable width by appropriately controlling the effective cavity length.
- the thickness of the active layer 24, more specifically, the required range of the number of quantum well layers forming the active layer 24 will be described.
- FIG. 8 is a graph showing the relationship between the number of quantum well layers and the peak value ratio in semiconductor light emitting devices with effective cavity lengths L eff of 2 ⁇ m, 5 ⁇ m, and 10 ⁇ m.
- the peak value ratio is the ratio between the peak value of the optical pulse waveform and the steady-state value after stabilization.
- a peak value ratio of 2 means that the amount of light at the peak value is twice the amount of light at the steady value.
- the peak value ratio increases as the number of quantum well layers increases. Further, when comparing with the same peak value ratio, the longer the effective cavity length, the more the required number of quantum well layers.
- 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.
- the number of quantum well layers with a peak value ratio exceeding 2 is 6 or more.
- the number of quantum well layers with a peak value ratio exceeding 2 is seven or more.
- the number of quantum well layers with a peak value ratio exceeding 2 is nine or more.
- the design standard for the peak value ratio is 2 or more in a semiconductor light emitting device having a cavity length of 2 ⁇ m or more, six or more quantum well layers are required.
- the resonator length is preferably 4 ⁇ m or more, and in that case, the required number of quantum well layers is 7 or more.
- the number of quantum well layers here is obtained by converting the layer thickness of the portion where carriers are accumulated into the number of quantum well layers, and does not necessarily have to match the actual number of quantum well layers. do not have. That is, the actual number of quantum well layers can be designed according to the relationships shown in FIGS. Alternatively, although the actual number of quantum well layers is smaller than the total number according to the relationship of FIGS. It may be designed to accumulate carriers.
- the number of quantum well layers should be as large as possible, and there is no particular upper limit.
- the thickness of the i-layer is restricted by the degree of carrier diffusion from the p-layer and the n-layer.
- the diffusion distance varies greatly depending on the material and composition of the active layer 24. If the diffusion distance is 1 ⁇ m, the number of quantum well layers is about 50 layers. It is desirable that the number of quantum well layers forming the active layer 24 is appropriately selected, for example, within a range of 6 layers or more and 50 layers or less.
- semiconductor layers constituting the lower DBR layer 12, the non-doped spacer section 14, the resonator section 18, and the upper DBR layer 28 are grown on the semiconductor substrate 10 by metal-organic vapor phase epitaxy or molecular beam epitaxy. .
- the upper DBR layer 28, the p-type layer 26 and the non-doped spacer section 22 are patterned. Thereby, a columnar mesa having a diameter of, for example, about 30 ⁇ m is formed.
- thermal oxidation is performed in a steam atmosphere at about 450° C. to oxidize the Al 0.98 Ga 0.02 As layer in the upper DBR layer 28 from the side walls of the mesa to form an oxidized constricting layer 38 .
- the Al 0.98 Ga 0.02 As layer has a non-oxidized portion in the central portion of the mesa and an oxidized portion (oxidized constricting layer 38) in the vicinity of the side wall of the mesa.
- the non-oxidized portion of the Al 0.98 Ga 0.02 As layer is controlled to have a diameter of about 10 ⁇ m.
- an electrode 42 that will be the p-side electrode is formed on the upper surface of the mesa, and an electrode 40 that will be the n-side electrode is formed on the upper surface of the n-type layer 20 exposed by etching. do.
- the electrode 42 has an annular pattern, and the central opening serves as a circular window for extracting light.
- a protective film 44 is formed so as to cover the upper and side surfaces of the mesa provided with the electrodes 40 and 42 and the upper surface of the n-type layer 20 .
- heat treatment is performed in a nitrogen atmosphere to alloy the interface between the electrode material and the semiconductor material, thereby completing the semiconductor light emitting device 100 of this embodiment.
- 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 denoted by the same reference numerals, and description thereof is omitted or simplified.
- the semiconductor light emitting device is the same as the semiconductor light emitting device according to the first embodiment, except that the configuration of the resonator section 18 is different from that of the semiconductor light emitting device according to the first embodiment.
- the parts different from the semiconductor light emitting device according to the first embodiment will be mainly described, and the explanation of the parts common to the semiconductor light emitting device according to the first embodiment will be omitted as appropriate.
- the resonator section 18 of the present embodiment is composed of a pin junction composed of an n-type layer 20, a non-doped spacer section 22 and a p-type layer 26, and the non-doped spacer section 22
- the point that the active layer 24 is provided in is the same as in the first embodiment.
- the n-type layer 20 is a semiconductor layer with a high impurity concentration arranged between the active layer 24 and the saturable absorption layer 16 .
- the resonator section 18 of the first embodiment had three layers of active layers 24 each including three layers of quantum wells in the non-doped spacer section 22 .
- the resonator section 18 of this embodiment has a single active layer 24 including four quantum well layers in the non-doped spacer section 22 .
- the active layer 24 can be composed of, for example, a multiple quantum well including four quantum well layers in which InGaAs well layers with a thickness of 8 nm are sandwiched between GaAs barrier layers with a thickness of 10 nm.
- Other portions of the non-doped spacer portion 22 are composed of non-doped GaAs layers.
- the resonator section 18 of the first embodiment had the active layer 24 including a total of 12 quantum well layers
- the resonator section 18 of the present embodiment has four quantum well layers. It has an active layer 24 comprising layers.
- the reason why the total number of quantum well layers included in the active layer 24 of the resonator section 18 of the present embodiment can be reduced to four is that the portions other than the InGaAs well layers of the non-doped spacer section 22, including the barrier layers, are made of AlGaAs. This is because it is made of GaAs.
- the bandgap of the barrier layer can be made smaller than when AlGaAs is used as the barrier layer.
- the amount of carriers necessary for achieving the effects of the invention according to this embodiment can be easily increased.
- the optical confinement factor for standing waves is as low as about 0.35.
- the number of quantum well layers is reduced, so the optical confinement factor is set to about 1.4.
- the quantum well layer is arranged near the position of the antinode of the standing wave. Since the product of the number of quantum well layers and the optical confinement coefficient is the gain of the laser resonator, the first embodiment and the present embodiment are configured so that the same gain can be obtained. It's for.
- the relaxation oscillation frequency that is, the pulse width at the time of pulse generation, to be approximately the same.
- the configuration of this embodiment in which carriers are actively accumulated in the barrier layer, also has a secondary effect.
- Two secondary effects will be described below as examples.
- the first effect is that the accumulated strain of the semiconductor layer can be reduced.
- the active layer is made of InGaAs and the substrate is made of GaAs. Therefore, strain is generated in the active layer grown on the substrate due to the lattice constant difference.
- the cumulative strain increases as the number of quantum well layers increases. Therefore, the design in which the bandgap of the barrier layer is reduced to reduce the number of quantum well layers as in this embodiment has the effect of reducing the cumulative strain.
- the second effect is that carrier consumption due to radiative recombination can be reduced.
- the carriers are consumed by radiative recombination (spontaneous emission).
- the threshold of laser oscillation rises and the power conversion efficiency decreases, which is not preferable.
- This radiative recombination is known to be proportional to the square of the carrier density. Therefore, even when the same amount of carriers are accumulated, the carrier density, that is, the amount of carriers consumed by radiative recombination, changes depending on the volume of the portion where carriers are accumulated.
- the carrier density increases because the quantum well layers have a small bandgap.
- the carrier density increases, so the number of carriers consumed by radiative recombination also increases.
- the carrier density is low due to the large bandgap, and the total layer thickness of the layers for accumulating carriers is large.
- the carrier density is lower, less carriers are consumed by radiative recombination.
- carriers are accumulated in a layer having a larger bandgap than in the quantum well layer at a higher rate, so carrier consumption due to radiative recombination can be reduced.
- the n-type layer 20 has a laminated structure of an Al 0.9 GaAs layer and a GaAsP layer. Specifically, an Al 0.9 GaAs layer is provided between the GaAsP layer and the non-doped spacer section 22 .
- the reason why the Al composition of the AlGaAs layer is increased to 0.9 is to increase the bandgap and prevent carriers overflowing from the active layer 24 from flowing into the saturable absorption layer 16 . Therefore, the Al 0.9 GaAs layer is provided near the non-doped spacer section 22 .
- the GaAsP layer has a role as a strain compensation layer.
- the cumulative strain is reduced by inserting a GaAsP layer that generates lattice strain in the direction opposite to that of InGaAs in GaAs.
- the AlGaAs layer forming the n-type layer 20 has the effect of suppressing carrier overflow even when the Al composition is 0.9 or less.
- the amount of increase in the bandgap with respect to the increase in the Al composition becomes small from around 0.45. In other words, the amount of reduction in bandgap caused by lowering the Al composition of the AlGaAs layer from 0.9 to 0.45 is small.
- the Al composition of the AlGaAs layer exceeds 0.9, the reaction with oxygen in the air will rapidly increase the formation rate of the natural oxide film, which is not preferable from the viewpoint of the manufacturing process and device reliability. From this point of view, the Al composition of the AlGaAs layer forming the n-type layer 20 is preferably about 0.45 or more and about 0.9 or less.
- the energy difference between the emission level of the quantum well and the bandgap of the barrier layer is reduced to the extent that light absorption does not occur at the lasing wavelength, and the thickness of the barrier layer is increased to increase the amount of carrier storage.
- the design is contrary to the general semiconductor laser design concept. The reason for this is that, in a normal semiconductor laser, it is preferable that the optical output responds as fast as possible to an increase or decrease in the input current.
- a semiconductor laser can respond at a higher speed by accumulating carriers only in a light-emitting layer such as a quantum well and by making the thickness of a barrier layer through which carriers move as thin as possible.
- the amount of light is controlled by increasing or decreasing the current, and it is advantageous to increase or decrease the light output by following the current waveform that changes at high speed.
- communication speed can be increased.
- ToF type LiDAR by shortening the time width of the light emission pulse, the accuracy of estimating the time when the light detected by the light receiving side was generated on the light emitting side can be improved, and the accuracy of distance measurement can be improved. . 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 layers, are designs that should be avoided, as they will not follow the current waveform to changes in light. .
- the present invention is based on the concept of emitting short pulses within the VCSEL, it is not necessary to make the light output follow the current waveform. Also, it is preferable that the peak value of the pulse is large. Therefore, in the present embodiment, the structure including the saturable absorption layer 16 necessary for emitting a short pulse in the VCSEL is designed to accumulate more carriers including the barrier layer, thereby reducing the pulse width. A short optical pulse with a high peak value can be generated.
- 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 denoted by the same reference numerals, and description thereof is omitted or simplified.
- the semiconductor light emitting device 100 has a semiconductor substrate 10, a lower DBR layer 12, a non-doped spacer section 14, a resonator section 18, and an upper DBR layer 28, as shown in FIG. Moreover, the semiconductor light emitting device 100 further includes a lower DBR layer 30 , a resonator section 32 , an upper DBR layer 36 , electrodes 40 and 42 and a protective film 44 .
- a lower DBR layer 12 is provided on the semiconductor substrate 10 .
- a non-doped spacer portion 14 is provided on the lower DBR layer 12 .
- the resonator section 18 is provided on the non-doped spacer section 14 .
- the upper DBR layer 28 is provided on the resonator section 18 .
- a lower DBR layer 30 is provided over the upper DBR layer 28 .
- the resonator section 32 is provided on the lower DBR layer 30 .
- the upper DBR layer 36 is provided on the resonator section 32 .
- a laminated structure of the lower DBR layer 12, the non-doped spacer section 14, the resonator section 18, and the upper DBR layer 28 constitutes the first VCSEL.
- a laminated structure of the lower DBR layer 30, the resonator section 32, and the upper DBR layer 36 constitutes a second VCSEL. That is, the semiconductor light emitting device 100 according to this embodiment is formed by stacking a first VCSEL and a second VCSEL in this order on a semiconductor substrate 10 .
- the laminated structure of the first VCSEL is the same as that of the semiconductor light emitting device 100 of the first embodiment.
- a saturable absorption layer 16 is provided in the non-doped spacer section 14 .
- Five active layers 24 are provided in the resonator section 18 .
- Each of the active layers 24 is composed of multiple quantum wells including four layers of quantum wells. That is, the resonator section 18 includes a total of 20 quantum well layers.
- the bandgap of the AlGaAs barrier layer is made smaller than that of the barrier layer used in the quantum well of a normal VCSEL so that carriers can be stored in the AlGaAs barrier layer.
- the first VCSEL like the semiconductor light emitting device of the first embodiment, has a saturable absorption layer 16 and generates high peak, short optical pulses. Note that the structure of the semiconductor light emitting device of the second embodiment may be applied to the first VCSEL.
- a laminated structure of the lower DBR layer 30, the resonator section 32, and the upper DBR layer 36 is processed into a mesa shape.
- a second VCSEL is formed on this mesa.
- An active layer 34 is provided in the resonator section 32 .
- An oxidized constricting layer 38 is provided in the upper DBR layer 36 .
- Electrodes electrically connected to the upper DBR layer 28 and the lower DBR layer 30 are provided on the upper DBR layer 28 exposed by processing the lower DBR layer 30, the resonator section 32 and the upper DBR layer 36 into a mesa shape. 40 are provided.
- 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 part of the surfaces of the electrodes 40 and 42 and the side surfaces and top surface of the mesa.
- the second VCSEL oscillates and generates laser light by applying a voltage between the electrodes 40 and 42 and causing a current to flow.
- the wavelength of the laser light generated by the second VCSEL is shorter than the emission wavelength of the first VCSEL, eg, 780 nm.
- the laser light generated by the second VCSEL is excitation light for exciting the active layer 24 of the first VCSEL.
- the first VCSEL emits a light pulse with a high peak value and a short pulse by a mechanism similar to that of the semiconductor light emitting device 100 of the first embodiment. to generate
- 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 active layers 24 in the first VCSEL.
- the thickness of the i-layer is limited by the diffusion length of carriers, particularly the diffusion length of holes.
- the active layer 24 is excited by irradiating light from the outside as in the present embodiment, there is no restriction on the diffusion length of carriers, so a VCSEL having a larger number of active layers 24 can be configured. There is an advantage that the energy can be increased.
- 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.
- the semiconductor light emitting device 100 is a so-called VCSEL array, which is a light emitting device configured by arranging a plurality of light emitting portions 50 of the semiconductor light emitting devices 100 according to the first to third embodiments in a two-dimensional array.
- a cross section along line AA' in FIG. 13 generally corresponds to the cross sectional view of FIG. 1, FIG. 10 or FIG.
- Each of the light emitting portions 50 in FIG. 12 corresponds to the mesa portion in FIG. 1, FIG. 10 or FIG.
- the semiconductor substrate 10 in FIG. 12 corresponds to the semiconductor substrate 10 to the n-type layer 20 in FIG. 1 or 10 or the semiconductor substrate 10 to the upper DBR layer 28 in FIG.
- 12 and 13 show only 12 light emitting units 50 arranged in a 4 ⁇ 3 array for the sake of simplification of the drawings, but a general VCSEL array has, for example, 60 ⁇ 60 arrays. 3600 VCSELs arranged in a shape are provided on the same semiconductor substrate 10 .
- the diameter of the light emitting portion 50 is, for example, 10 ⁇ m.
- the light-emitting portions 50 are arranged such that the distance between the centers of the light-emitting portions 50 in the vertical direction and the horizontal direction is, for example, 50 ⁇ m.
- a chip size of the semiconductor light emitting device 100 is, for example, 3.3 mm ⁇ 3.3 mm.
- the electrode 40 corresponding to each of the light emitting portions 50 is electrically connected to the anode common electrode 40C via wiring (not shown). Also, the electrode 42 corresponding to each of the light emitting portions 50 is 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 units 50 that constitute 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 device 100 is injected from an external circuit through the common anode electrode 40C and the common cathode electrode 42C.
- the anode common electrode 40C and the cathode common electrode 42C have a strip shape with a width of, for example, 100 ⁇ m and a length of, for example, 1.5 mm.
- a VCSEL array using the semiconductor light emitting device 100 of the first to third embodiments can be realized.
- FIG. 14 is a block diagram showing a schematic configuration of the distance measuring device according to this embodiment.
- a range finder 200 according to the present embodiment is a range finder (LiDAR device) in which the semiconductor light emitting device 100 of the fourth embodiment is applied to the light source section.
- the distance measuring device 200 includes a control unit 210, a surface emitting laser array driver 212, a surface emitting laser array 214, a light emitting side optical system 218, a light receiving side optical system 220, an image sensor 222, a distance A data processing unit 224 may be used.
- the surface emitting laser array 214 is obtained by mounting the semiconductor light emitting device 100 according to the fourth embodiment in a package.
- the surface emitting laser array driver 212 is a driving unit that receives a drive signal from the control unit 210 , generates a driving 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.
- the light-emitting side optical system 218 is an optical system that emits the 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 beam reflected by the measurement object 1000 to the image sensor 222 .
- the light-emitting side optical system 218 and the light-receiving side optical system 220 are represented by a single convex lens-shaped member. It consists of a lens group that combines lenses.
- the image sensor 222 is a photoelectric conversion device in which a plurality of pixels including photoelectric conversion units are arranged in a two-dimensional array, and is a light receiving device that outputs electrical signals according to incident light.
- Image sensor 222 may be an imaging device such as, for example, a CMOS image sensor.
- the distance data processing unit 224 has a function as a distance information acquisition unit that generates information regarding the distance to the measurement object 1000 existing in the range to be measured based on the signal from the image sensor 222 and outputs the information. Note that the distance data processing unit 224 may be electrically connected to the image sensor 222 and may be arranged in the same package as the image sensor 222, or may be arranged in a package separate from the image sensor 222. may have been
- the control unit 210 is composed of an information processing device including a microcomputer and a logic circuit, and has a function as a central processing device that controls operations in the distance measuring device 200, such as operation control of each unit and various arithmetic processing.
- a light-emitting device suitable for the LiDAR system is preferably a light-emitting device that can generate light pulses with a short light pulse width and a high peak value.
- the optical pulse width of a light source suitable for LiDAR systems is, for example, in the range of 50 ps to 1 ns.
- the current pulse driving the VCSEL must be of the same order in order to reduce the light pulse from 50 ps to 1 ns.
- the VCSEL itself generates a short pulse by using the semiconductor light emitting device described in the first to fourth embodiments.
- the controller 210 outputs a drive signal to the surface emitting laser array driver 212 .
- the surface emitting laser array driver 212 receives a drive signal from the control unit 210 and injects a current of a predetermined current value into the surface emitting laser array 214 .
- the surface emitting laser array 214 oscillates and laser light is output from the surface emitting laser array 214 .
- 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.
- the laser light generated by the surface emitting laser array 214 is emitted toward the distance measurement target range by the light emission side optical system 218 .
- the laser beams irradiated to the measurement object 1000 in the distance measurement target range the laser beams reflected by the measurement object 1000 and incident on the light receiving side optical system 220 are guided to the image sensor 222 by the light receiving side optical system 220. be killed.
- Each pixel of the image sensor 222 generates an electrical signal pulse according to the timing of the incident laser light.
- An electrical signal pulse generated by the image sensor 222 is input to the distance data processing section 224 .
- 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 pulses output from each pixel of the image sensor 222, the three-dimensional information of the measuring object 1000 can be obtained.
- the distance measuring device 200 of the present embodiment is, for example, in the field of automobiles, a control device for performing control so as not to collide with another vehicle, or a control device for performing control for automatically driving following another vehicle. and so on. Further, the distance measuring device 200 of the present embodiment can be applied not only to automobiles but also to other moving bodies (moving devices) such as ships, aircraft, and industrial robots, moving body detection systems, and the like. The distance measuring device 200 of the present embodiment can be widely applied to devices that use information about objects recognized three-dimensionally, including distance information. These moving bodies can be configured to include the distance measuring device of the present embodiment and control means for controlling the moving bodies based on the distance information obtained by the distance measuring device.
- the three-dimensional information including the depth that can be acquired by the distance measuring device 200 of this embodiment can be used by an image capturing device, an image processing device, a display device, and the like.
- an image capturing device an image processing device
- a display device a display device
- the three-dimensional information acquired by the distance measuring device 200 of the present embodiment it is possible to display a virtual object on an image of the real world without any sense of incongruity.
- by storing three-dimensional information together with image information it is also possible to correct blurring and the like of the shot image after shooting.
- the present embodiment it is possible to realize a high-performance rangefinder equipped with a light-emitting device capable of generating an optical pulse with a short optical pulse width and a high peak value.
- 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 denoted by the same reference numerals, and the description thereof is omitted or simplified.
- 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 has a light emission timing monitor section 216, as shown in FIG. Other points of the distance measuring device 200 according to this embodiment are the same as those of the distance measuring device according to the fifth embodiment.
- the surface emitting laser array 214 has a semiconductor light emitting element 100, an emission timing monitor section 216, a base 110, and a window member 120, as shown in FIG. 16, for example.
- the base 110 is a part of the package that mounts the semiconductor light emitting element 100 and the light emission timing monitor section 216, and has a concave portion that accommodates the semiconductor light emitting element 100 and the light emission timing monitor section 216.
- FIG. The base 110 can be made of ceramic, for example.
- the window member 120 is fixed to the base 110 so as to close the concave portion of the base 110 on which the semiconductor light emitting element 100 and the light emission timing monitor section 216 are mounted.
- the semiconductor light emitting device 100 is the semiconductor light emitting device 100 according to the fourth embodiment.
- the light emission timing monitor unit 216 is configured by a semiconductor substrate having a square shape of 0.3 mm square, for example, and has a photodiode with a light receiving area having a diameter of 100 ⁇ m, for example.
- 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 section 216 are electrically connected to electrodes (not shown) provided on the outer periphery of the base 110. It is connected to the.
- a pulse current supplied from the surface emitting laser array driver 212 is supplied to the semiconductor light emitting device 100 via electrodes provided on the base 110 .
- the electrical signal generated by the light emission timing monitor section 216 is supplied to the distance data processing section 224 via the electrodes provided on the base 110 .
- the controller 210 outputs a drive signal to the surface emitting laser array driver 212 .
- the surface emitting laser array driver 212 receives a drive signal from the control unit 210 and injects current of a predetermined current value into the semiconductor light emitting elements 100 of the surface emitting laser array 214 .
- the semiconductor light emitting device 100 oscillates and laser light is output from the semiconductor light emitting device 100 .
- the pulse width of the light emitted from the semiconductor light emitting device 100 is narrower than the pulse width of the injected current, as described above.
- a laser beam generated by the semiconductor light emitting device 100 is emitted from the surface emitting laser array 214 through the window member 120 and emitted toward the distance measurement target range by the light emitting side optical system 218 .
- the window material 120 is AR-coated, part of the light is reflected by the window material 120 and enters the light emission timing monitor section 216 .
- the light emission timing monitor unit 216 converts the incident light into an electric signal and outputs it to the distance data processing unit 224 .
- the distance data processing unit 224 calculates 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 unit 216. Generate information about distance. Three-dimensional information of the measurement object 1000 is acquired by calculating distance information based on the electrical signal pulses output from each pixel of the image sensor 222 .
- FIG. 17 the reason why the distance measuring device is configured in this way will be described with reference to FIGS. 17 and 18.
- the distance to the measurement object is calculated based on the time difference from when the laser light is emitted until it is reflected by the measurement object and returned. 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 device 100 with higher accuracy. For example, if the time detection accuracy on the light receiving side is about 50 ps, the accuracy of information on timing of pulse generation on the light emitting side is preferably less than 50 ps.
- a VCSEL driver In a general VCSEL and a LiDAR system using it, a VCSEL driver generates a pulse current to drive the VCSEL. Since the VCSEL emits light according to the pulse current waveform, the difference between the VCSEL light emission timing and the rise timing of the pulse current generated by the VCSEL driver is small, and the time difference does not change significantly due to environmental temperature fluctuations. This is because the VCSEL design is designed to emit light in response to the amount of current injected. Therefore, it is possible to accurately estimate the time from the timing at which the current pulse is generated in the driver to the timing at which the VCSEL emits light.
- the LiDAR system using the semiconductor light-emitting device of the first to fourth embodiments may have reduced accuracy in distance measurement.
- the present inventors have discovered for the first time that there is.
- carriers are accumulated in the active layer 24, and after the start of laser oscillation, the accumulated carriers are converted into light to generate light pulses. That is, the current injected into the semiconductor light emitting device is used to accumulate carriers in the active layer 24 for a predetermined time until carriers are accumulated in the active layer 24 . Then, the laser oscillation of the semiconductor light emitting device is delayed for a predetermined time until carriers are accumulated in the active layer 24 .
- the timing of laser oscillation in the semiconductor light emitting devices of the first to fourth embodiments is determined by the physical parameters of the materials composing the structure and each part of the semiconductor light emitting device. 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 environmental temperature and changes in physical parameters over time. In some cases, the time difference exceeds about 50 ps, which is the typical time detection accuracy on the light receiving side.
- FIGS. 17 and 18 are graphs showing the results of calculation of changes in optical waveforms due to changes in environmental temperature and changes in physical parameters over time.
- FIG. 17 shows calculation results for a general VCSEL
- FIG. 18 shows calculation results for the semiconductor light emitting device of the present invention.
- FIGS. 17 and 18 show enlarged optical waveforms immediately after the start of oscillation in cases where the transparent carrier density is assumed at room temperature and where the transparent carrier density is assumed to be 50° C. higher than room temperature. ing.
- the characteristic where oscillation starts first is the case where the transparent carrier density is assumed at room temperature, and the characteristic where oscillation starts later is the case where it is 50°C higher than room temperature. This is the case assuming a transparent carrier density.
- the peak of the optical pulse when assuming a transparent carrier density at room temperature and the optical pulse when assuming a transparent carrier density at 50° C. higher than room temperature are shown. is 13 ps.
- the transparent carrier density at the peak of the light pulse when the transparent carrier density at room temperature is assumed and the transparent carrier density at 50° C. higher than room temperature are assumed.
- the time difference between the peak time of the optical pulse in case is 70 ps.
- the time difference from the timing when the current injection to the semiconductor light emitting device 100 starts to the timing when the light output reaches the maximum peak value can change, for example, within a range of 50 ps or more and 1 ns or less due to changes in environmental temperature.
- changes in physical properties have a greater effect on changes in oscillation timing.
- the amount of change in the oscillation timing may exceed the typical time detection accuracy of the light receiving side, which is about 50 ps.
- the light emission timing of the surface emitting laser array 214 is detected by the light emission timing monitor section 216 . Then, the light emission timing detected by the light emission timing monitor unit 216 is used to calculate the distance information. Therefore, even if the emission timing of the surface-emitting laser array 214 deviates due to factors such as the environmental temperature, it is possible to maintain high ranging accuracy without affecting the ranging accuracy of the ranging device 200 .
- GaAs, AlGaAs, and InGaAs were exemplified as semiconductor materials capable of crystal growth when a GaAs substrate was used as the semiconductor substrate 10, but the semiconductor substrate 10 is limited to a GaAs substrate. not something.
- an InP substrate can be used as the semiconductor substrate 10 .
- InP, InGaAs, InGaP, InGaAsP, and the like are examples of semiconductor materials that allow crystal growth when an InP substrate is used as the semiconductor substrate 10 .
- the DBR layers in the semiconductor light emitting devices according to the first to third embodiments do not necessarily have to be made of a semiconductor material, and may be made of a material other than a semiconductor material. Also in this case, the same effects as in the present embodiment can be obtained by configuring the same function as in the first to third embodiments.
- SYMBOLS 10 Semiconductor substrate 12, 30... Lower DBR layer 14... Non-doped spacer part 16... Saturable absorption layer 18, 32... Resonator part 20... N-type layer 22... Non-doped spacer part 24, 34... Active layer 26... P-type layer DESCRIPTION OF SYMBOLS 28, 36 Upper DBR layer 38 Oxidation narrowing layer 40, 42 Electrode 44 Protective film 50 Light-emitting section 100 Semiconductor light-emitting element 200 Distance measuring device
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Abstract
Description
本発明の第1実施形態による半導体発光素子について、図1を用いて説明する。図1は、本実施形態による半導体発光素子の構造を示す概略断面図である。
図3及び図4は、半導体発光素子の光出力波形を計算により求めた結果を示すグラフである。図3は比較例による半導体発光素子の光出力波形であり、図4は本実施形態による半導体発光素子100の光出力波形である。比較例による半導体発光素子は、可飽和吸収層を備えておらず、量子井戸が3層、共振器長が1λに設計されている一般的な構成のVCSELである。
Γs×gmax(Iop) > Γa×α2+αm+αi …(1)
まず、半導体基板10の上に、有機金属気相成長法や分子線エピタキシー法により、下部DBR層12、ノンドープスペーサ部14、共振器部18及び上部DBR層28を構成する各半導体層を成長する。
本発明の第2実施形態による半導体発光素子について、図10を用いて説明する。図10は、本実施形態による半導体発光素子の構造を示す概略断面図である。第1実施形態による半導体発光素子と同様の構成要素には同一の符号を付し、説明を省略し或いは簡潔にする。
本発明の第3実施形態による半導体発光素子について図11を用いて説明する。図11は本実施形態による半導体発光素子の構造を示す概略断面図である。第1又は第2実施形態による半導体発光素子と同様の構成要素には同一の符号を付し、説明を省略し或いは簡潔にする。
本発明の第4実施形態による半導体発光素子について、図12及び図13を用いて説明する。図12は、本実施形態による半導体発光素子を示す斜視図である。図13は、本実施形態による半導体発光素子の上面図である。
本発明の第5実施形態による測距装置について、図14を用いて説明する。図14は、本実施形態による測距装置の概略構成を示すブロック図である。
まず、制御部210は、面発光レーザアレイドライバ212に駆動信号を出力する。面発光レーザアレイドライバ212は、制御部210からの駆動信号を受け、面発光レーザアレイ214に所定の電流値の電流を注入する。これにより、面発光レーザアレイ214が発振し、面発光レーザアレイ214からレーザ光が出力される。このとき、面発光レーザアレイ214から出射される光のパルス幅は、前述のように、注入された電流のパルス幅よりも狭い。
本発明の第6実施形態による測距装置について、図15及び図16を用いて説明する。図15は、本実施形態による測距装置の概略構成を示すブロック図である。図16は、本実施形態による測距装置における面発光レーザアレイの構成例を示す概略断面図である。第1乃至第4実施形態による半導体発光素子並びに第5実施形態による測距装置と同様の構成要素には同一の符号を付し、説明を省略し或いは簡潔にする。
まず、制御部210は、面発光レーザアレイドライバ212に駆動信号を出力する。面発光レーザアレイドライバ212は、制御部210からの駆動信号を受け、面発光レーザアレイ214の半導体発光素子100に所定の電流値の電流を注入する。これにより、半導体発光素子100が発振し、半導体発光素子100からレーザ光が出力される。このとき、半導体発光素子100から出射される光のパルス幅は、前述のように、注入された電流のパルス幅よりも狭い。
本発明は、上記実施形態に限らず種々の変形が可能である。
例えば、いずれかの実施形態の一部の構成を他の実施形態に追加した例や、他の実施形態の一部の構成と置換した例も、本発明の実施形態である。
12,30…下部DBR層
14…ノンドープスペーサ部
16…可飽和吸収層
18,32…共振器部
20…n型層
22…ノンドープスペーサ部
24,34…活性層
26…p型層
28,36…上部DBR層
38…酸化狭窄層
40,42…電極
44…保護膜
50…発光部
100…半導体発光素子
200…測距装置
Claims (21)
- 半導体基板の上に、第1の反射鏡と、活性層を含む共振器スペーサ部と、第2の反射鏡と、がこの順に積層された半導体発光素子を有し、
前記半導体発光素子は、前記半導体基板と前記第2の反射鏡との間に可飽和吸収層を含み、
前記半導体発光素子は、最大ピーク値を有し、かつ、前記最大ピーク値の後に所定の光強度である安定値へ収束するプロファイルを有する光を射出するように構成されている
ことを特徴とする発光装置。 - 半導体基板の上に、第1の反射鏡と、活性層を含む共振器スペーサ部と、第2の反射鏡と、がこの順に積層された半導体発光素子を有し、
前記半導体発光素子は、前記半導体基板と前記第2の反射鏡との間に可飽和吸収層を含み、
前記活性層の光閉じ込め係数をΓs、可飽和吸収層の光閉じ込め係数をΓa、前記駆動部から注入される電流値がIopのときに得られる前記活性層での最大利得をgmax(Iop)、前記可飽和吸収層の吸収係数をα2、ミラー損失をαm、キャリアによる光吸収をαiとして、
Γs×gmax(Iop) > Γa×α2+αm+αi
の関係を満たす
ことを特徴とする発光装置。 - 前記可飽和吸収層は、前記半導体基板と前記活性層との間に位置し、前記第1の反射鏡を兼ねる
ことを特徴とする請求項1又は2に記載の発光装置。 - 前記可飽和吸収層は、前記活性層と前記第2の反射鏡との間に位置している
ことを特徴とする請求項1又は2に記載の発光装置。 - 前記最大ピーク値を示す光パルスの半値幅が50ps以上である
ことを特徴とする請求項1に記載の発光装置。 - 前記半導体発光素子への電流の注入開始のタイミングから光出力が前記最大ピーク値に達するタイミングまでの時間差が、50ps以上、1ns以下である
ことを特徴とする請求項1に記載の発光装置。 - 前記活性層は、複数の量子井戸層と、前記複数の量子井戸層の間に設けられた障壁層と、を有し、前記量子井戸層の発光準位と前記障壁層のバンドギャップとのエネルギー差は、105meVから230meVの範囲である
ことを特徴とする請求項1乃至6のいずれか1項に記載の発光装置。 - 前記量子井戸層はInGaAsにより構成されており、
前記障壁層はGaAsにより構成されている
ことを特徴とする請求項7記載の発光装置。 - 前記活性層と前記可飽和吸収層との間に配された半導体層を更に有し、
前記半導体層は、Al組成が0.45から0.9の範囲のAlGaAs層を含む
ことを特徴とする請求項1乃至8のいずれか1項に記載の発光装置。 - 前記半導体層は、GaAsP層を更に含む
ことを特徴とする請求項9記載の発光装置。 - 前記共振器スペーサ部の光学厚さは、共振波長の5倍に相当する厚さ以上である
ことを特徴とする請求項1乃至10のいずれか1項に記載の発光装置。 - 前記共振器スペーサ部の光学厚さは、共振波長の11倍に相当する厚さ以上である
ことを特徴とする請求項1乃至11のいずれか1項に記載の発光装置。 - 前記活性層は、6層以上、50層以下の量子井戸層を含む
ことを特徴とする請求項1乃至12のいずれか1項記載の発光装置。 - 前記半導体発光素子と同じパッケージに実装され、前記半導体発光素子から射出された光を受ける受光素子を更に有する
ことを特徴とする請求項1乃至13のいずれか1項に記載の発光装置。 - 半導体基板の上に、第1の反射鏡と、活性層を含む共振器スペーサ部と、第2の反射鏡と、がこの順に積層された半導体発光素子を有し、
前記活性層は、6層以上、50層以下の量子井戸層を含み、
前記半導体基板と前記第2の反射鏡との間に可飽和吸収層を更に有し、
前記共振器スペーサ部の光学厚さは、共振波長の5倍に相当する厚さ以上である
ことを特徴とする発光装置。 - 前記活性層は、前記第1の反射鏡と前記第2の反射鏡との間に生じる定在波の腹と節との間に位置している
ことを特徴とする請求項15に記載の発光装置。 - 半導体基板の上に、第1の反射鏡と、活性層を含む共振器スペーサ部と、第2の反射鏡と、がこの順に積層された半導体発光素子を有し、
前記半導体発光素子は、前記半導体基板と前記第2の反射鏡との間に可飽和吸収層を含み、
前記活性層は、複数の量子井戸層と、前記複数の量子井戸層の間に設けられた障壁層を含み、
前記障壁層は、GaAsにより構成されている
ことを特徴とする発光装置。 - 前記共振器スペーサ部の光学厚さは、共振波長の5倍に相当する厚さ以上である
ことを特徴とする請求項17に記載の発光装置。 - 前記共振器スペーサ部の光学厚さは、共振波長の11倍に相当する厚さ以上である
ことを特徴とする請求項15乃至18のいずれか1項に記載の発光装置。 - 請求項1乃至19のいずれか1項に記載の発光装置と、
前記発光装置から射出され、測定対象物で反射した光を受ける受光装置と、
前記発光装置から光が射出されるタイミングと前記受光装置が受光するタイミングとの時間差に基づいて前記測定対象物までの距離に関する情報を取得する距離情報取得部と
を有することを特徴とする測距装置。 - 移動体であって、
請求項20に記載の測距装置と、
前記測距装置が取得した前記距離に関する情報に基づいて前記移動体を制御する制御手段と
を有することを特徴とする移動体。
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EP22804587.8A EP4343990A1 (en) | 2021-05-17 | 2022-05-12 | Light-emitting device, ranging device, and movable body |
KR1020237037684A KR20230164160A (ko) | 2021-05-17 | 2022-05-12 | 발광장치, 측거장치 및 이동체 |
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Citations (6)
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JPH11511292A (ja) * | 1995-06-07 | 1999-09-28 | ハネウエル・インコーポレーテッド | マルチ・ギガヘルツ周波数変調垂直キャビティ表面発光レーザ |
US20150311673A1 (en) * | 2014-04-29 | 2015-10-29 | Princeton Optronics Inc. | Polarization Control in High Peak Power, High Brightness VCSEL |
JP2020524910A (ja) * | 2017-06-22 | 2020-08-20 | トルンプ フォトニック コンポーネンツ ゲゼルシャフト ミット ベシュレンクテル ハフツング | 利得スイッチング動作を改良した垂直共振器面発光レーザ(vcsel) |
JP2020148512A (ja) | 2019-03-11 | 2020-09-17 | ソニーセミコンダクタソリューションズ株式会社 | 光源モジュール、測距装置及び制御方法 |
JP2021083105A (ja) | 2021-02-12 | 2021-05-27 | ジャパンエレベーターサービスホールディングス株式会社 | エレベーターの通話管理システムおよび通話管理プログラム |
JP2022065143A (ja) | 2017-01-25 | 2022-04-26 | 三洋電機株式会社 | 二次電池 |
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2022
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2023
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Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH11511292A (ja) * | 1995-06-07 | 1999-09-28 | ハネウエル・インコーポレーテッド | マルチ・ギガヘルツ周波数変調垂直キャビティ表面発光レーザ |
US20150311673A1 (en) * | 2014-04-29 | 2015-10-29 | Princeton Optronics Inc. | Polarization Control in High Peak Power, High Brightness VCSEL |
JP2022065143A (ja) | 2017-01-25 | 2022-04-26 | 三洋電機株式会社 | 二次電池 |
JP2020524910A (ja) * | 2017-06-22 | 2020-08-20 | トルンプ フォトニック コンポーネンツ ゲゼルシャフト ミット ベシュレンクテル ハフツング | 利得スイッチング動作を改良した垂直共振器面発光レーザ(vcsel) |
JP2020148512A (ja) | 2019-03-11 | 2020-09-17 | ソニーセミコンダクタソリューションズ株式会社 | 光源モジュール、測距装置及び制御方法 |
JP2021083105A (ja) | 2021-02-12 | 2021-05-27 | ジャパンエレベーターサービスホールディングス株式会社 | エレベーターの通話管理システムおよび通話管理プログラム |
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