Light emitting device and distance measuring device

Abstract

To provide a light emitting device capable of emitting a high peak value pulse light at short intervals.SOLUTION: A light emitting device includes: a first light emitting element and a second light emitting element formed on a common semiconductor substrate; and a drive part that applies a drive voltage to each of the first light emitting element and the second light emitting element. Each of the first light emitting element and the second light emitting element includes: a first reflector formed on the semiconductor substrate; a resonator formed on the first reflector and including a saturable absorption layer; and a second reflector formed on the resonator. When the drive voltage is applied to the first light emitting element and the second light emitting element at the same timing, the first light emitting element and the second light emitting element respectively emit a pulsed light at different timings.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 discloses a VCSEL (Vertical Cavity Surface Emitting Laser) capable of emitting pulsed light with a high peak power. The VCSEL has a saturable absorbing layer. The saturable absorbing layer absorbs light and accumulates carriers for a certain period of time after the start of current injection, thereby delaying the start of laser oscillation. This allows the VCSEL to accumulate carriers in its active layer that exceed the threshold carrier density, enabling it to emit high-peak pulsed light. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-176886 Summary of the Invention [Problem to be solved by the invention]

[0004] However, it is necessary to reduce the carriers accumulated in the saturable absorbing layer each time a high-peak-power pulsed light is emitted, and this requires time, making it difficult to emit high-peak-power pulsed light at short intervals.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a light emitting device and a distance measuring device that can emit high peak pulsed light at short intervals. [Means for solving the problem]

[0006] According to one disclosure of the present specification, there is provided a light-emitting device comprising: a first light-emitting element and a second light-emitting element formed on a common semiconductor substrate; and a driving unit that applies a driving voltage to each of the first light-emitting element and the second light-emitting element, wherein each of the first light-emitting element and the second light-emitting element includes a first reflector formed on the semiconductor substrate, a resonator formed on the first reflector and including a saturable absorption layer, and a second reflector formed on the resonator, wherein when the driving voltage is applied to each of the first light-emitting element and the second light-emitting element at the same timing, the first light-emitting element and the second light-emitting element each emit pulsed light at different timings. [Effects of the Invention]

[0007] According to the present invention, it is possible to realize a light emitting device and a distance measuring device that can emit high peak pulsed light at short intervals. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view of a light emitting device according to a first embodiment. [Figure 2] 1 is a cross-sectional view of a light-emitting element according to a first embodiment. [Figure 3] 4 is a diagram showing the waveform of high peak value pulsed light according to the first embodiment. FIG. [Figure 4] 10 is a diagram showing the relationship between the emission interval and light intensity of high peak pulsed light according to a comparative example. FIG. [Figure 5] FIG. 10 is a diagram showing the relationship between the emission interval and the light intensity ratio in a normal pulsed light and a high peak pulsed light according to a comparative example. [Figure 6] FIG. 4 is a cross-sectional view of a light-emitting element according to a second embodiment. [Figure 7] FIG. 10 is a cross-sectional view of a light-emitting element according to a third embodiment. [Figure 8] FIG. 10 is a plan view of a light emitting device according to a fourth embodiment. [Figure 9] FIG. 10 is a cross-sectional view of a light-emitting device according to a fourth embodiment. [Figure 10]FIG. 10 is a diagram showing the waveform of high peak value pulsed light according to the fourth embodiment. [Figure 11] FIG. 10 is a plan view of a light emitting device according to a fifth embodiment. [Figure 12] FIG. 10 is a plan view of a light emitting device according to a sixth embodiment. [Figure 13] FIG. 13 is a block diagram of an imaging system and a moving object according to a seventh embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] [First embodiment] A light emitting device 1 according to the first embodiment will be described below. Fig. 1 is a plan view of the light emitting device 1 according to this embodiment.

[0010] As shown in FIG. 1, the light emitting device 1 includes a semiconductor substrate 10, a plurality of light emitting elements 20, an anode wiring 30, a power supply pad 40, and a driving section 50. The semiconductor substrate 10 is formed in a flat plate shape and can be configured to include, for example, a gas substrate.

[0011] The plurality of light-emitting elements 20 are formed on a common semiconductor substrate 10. The plurality of light-emitting elements 20 are vertical-cavity surface-emitting lasers (VCSELs) having distributed Bragg reflectors (DBRs). The plurality of light-emitting elements 20 are arranged in an array across multiple rows and multiple columns.

[0012] In the following description, the first direction (row direction) when arranging the plurality of light-emitting elements 20 in an array will be referred to as the X direction. The second direction (column direction) when arranging the plurality of light-emitting elements 20 in an array will be referred to as the Y direction. The direction intersecting the X and Y directions will be referred to as the Z direction. The X direction, Y direction, and Z direction are typically perpendicular to each other.

[0013] The plurality of light-emitting elements 20 are configured to include light-emitting elements 20A and 20B. The reflectors of the light-emitting elements 20A and 20B have different reflectivities. The configuration of the reflectors will be described later. The light-emitting elements 20A are arranged side by side in the X direction to form a single row array. The light-emitting elements 20B are also arranged side by side in the X direction to form a single row array. The single row array of the plurality of light-emitting elements 20A and the single row array of the plurality of light-emitting elements 20B are arranged alternately in the Y direction.

[0014] The anode wiring 30 is made of a conductive material such as gold, copper, titanium, or aluminum, and is connected to the anode electrodes of the light-emitting elements 20A and 20B. The anode wiring 30 is formed in a planar shape. The anode wiring 30 supplies power from the power supply pad 40 to the plurality of light-emitting elements 20A and 20B.

[0015] The power supply pad 40 is made of a conductive material such as copper, and is formed on the semiconductor substrate 10 (on the semiconductor substrate). The power supply pad 40 is integrally formed with the anode wiring 30. The power supply pad 40 is connected to a driving unit 50. The power supply pad 40 supplies power from the driving unit 50 to the anode wiring 30.

[0016] The driving unit 50 applies driving power to the light-emitting elements 20A and 20B. Specifically, the driving unit 50 injects a current into the power supply pad 40, and injects the current into the anode electrodes of the light-emitting elements 20A and 20B via the anode wiring 30. This allows the driving unit 50 to apply the same driving power to each of the light-emitting elements 20A and 20B at the same time.

[0017] Next, the configuration of the light emitting elements 20A and 20B will be described in detail. Figure 2 is a cross-sectional view of the light emitting elements 20A and 20B according to this embodiment.

[0018] The light-emitting element 20A has a semiconductor substrate 10, a lower DBR layer (first reflector) 21, a saturable absorbing layer 22, a resonator 23, a reflector (second reflector) 24A, an anode electrode 25, a cathode electrode 26, and an insulating film 27. The lower DBR layer 21 is formed on the semiconductor substrate 10. The saturable absorbing layer 22 is formed on the lower DBR layer 21 (on the reflector). The resonator 23 is formed on the saturable absorbing layer 22. The reflector 24A is formed on the resonator 23 (on the resonator). The anode electrode 25 is formed in a ring shape on the reflector 24A. The cathode electrode 26 is formed on the back side of the semiconductor substrate 10 (the side of the semiconductor substrate 10 opposite the lower DBR layer 21). The cathode electrode 26 is connected to ground.

[0019] The lower DBR layer 21 is, for example, an Al 0.1 Gas layer and Al 0.9 The configuration may include stacking 35 pairs of layers, each layer being a stack of a gas layer, where λc is the center wavelength of the high reflection band of the lower DBR layer 21, and in this embodiment is, for example, 940 nm.

[0020] The saturable absorbing layer 22 may be configured to include 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.

[0021] The resonator 23 can be configured to include a doped spacer layer 231 formed on the saturable absorbing layer 22, an undoped spacer portion 232 formed on the doped spacer layer 231, and a doped spacer layer 233 formed on the undoped spacer portion 232.

[0022] The undoped spacer portion 232 may include an undoped spacer layer 232a formed on the doped spacer layer 231, an active portion 232b formed on the undoped spacer layer 232a, and an undoped spacer layer 232c formed on the active portion 232b.

[0023] The active section 232b may be configured to include, for example, three active layers. Each of the three active layers may be configured to include, for example, a multiple quantum well including four quantum well layers, each of which has an 8-nm-thick InGaS well layer sandwiched between 10-nm-thick AlGaS barrier layers. In this case, a total of 12 quantum well layers are included in the resonator 23. The doped spacer layer 231 may be configured by an n-type gas layer, the doped spacer layer 233 may be configured by a p-type gas layer, and the undoped spacer layers 232a and 232c may be configured by undoped gas layers.

[0024] As such, the resonator 23 is composed of a p-i-n junction that is also present in a typical VCSEL, and has a similar configuration to a resonator that includes an active region 232b in the i-layer. However, the number of quantum well layers in the resonator 23 is greater than the number of quantum well layers (approximately three) in a typical VCSEL. Furthermore, the effective resonator length of the resonator 23 is 10 μm, which is longer than that of a typical VCSEL. Here, the effective resonator length is the resonator length experienced by light within the resonator 23.

[0025] The reflector 24A may be configured to include an upper DBR layer (reflector) 241 formed on the doped spacer layer 233 of the resonator 23, a contact layer 242 formed on the upper DBR layer 241, and an upper insulating film 243a formed on the contact layer 242.

[0026] The upper DBR layer 241 is, for example, an Al 0.1 Ga 0.9 As layer and Al 0.9 Ga 0.1 The upper DBR layer 241 may be configured by stacking 20 pairs of layers, each of which is a stack of an Al layer with a thickness of 30 nm. 0.98 Ga 0.02 An oxidized constriction layer 241a, which is an As layer, is formed.

[0027] The oxidized constriction layer 241a is formed by, for example, Al 0.98 Ga 0.02The oxidized constriction layer 241a can be formed by oxidizing the As layer from the side of the mesa with water vapor. The oxidized constriction layer 241a has a non-oxidized portion in the center of the mesa and an oxidized portion near the sidewall of the mesa. The diameter of the non-oxidized portion in plan view can be approximately 10 μm. As a result, current injected into the light-emitting element 20A flows only through the non-oxidized portion, and only the portion of the light-emitting element 20A that overlaps the center of the mesa in plan view lases.

[0028] The contact layer 242 is located between the anode electrode 25 and the upper DBR layer 241 and improves the electrical contact between the anode electrode 25 and the upper DBR layer 241 .

[0029] The upper insulating film 243a is formed as a thin film and insulates the contact layer 242 while leaving part of the surface of the anode electrode 25 exposed.

[0030] In the light-emitting element 20A described above, the undoped spacer portion 232 of the resonator 23, the doped spacer layer 233 of the resonator 23, and the reflector 24A are formed in a mesa shape. An insulating film 27 is formed on the side surface of the mesa, and the insulating film 27 insulates the undoped spacer portion 232, the doped spacer layer 233, and the reflector 24A. The insulating film 27 is also formed on the doped spacer layer 231 between the mesas, and insulates the doped spacer layer 231.

[0031] In this way, the light-emitting element 20A is based on the configuration of a normal VCSEL and, by introducing the saturable absorbing layer 22, realizes a VCSEL capable of generating pulsed light with a high peak power and a short pulse width. Furthermore, while the active layer of a normal VCSEL is composed of three quantum well layers, this is increased to 12 layers, thereby increasing the volume of the active section 232b. Furthermore, the effective cavity length of the cavity 23 is extended. As a result, the light-emitting element 20A realizes a VCSEL capable of emitting more effective high peak power pulsed light.

[0032] In this embodiment, the following three elements are added to the basic configuration of a conventional VCSEL. The first of the three elements added to the VCSEL is to substantially increase the volume of the active layer. For example, a conventional VCSEL is composed of three quantum wells, but in this embodiment, the volume of the active layer is increased even further. The second is to introduce a saturable absorbing layer. The third is to extend the effective cavity length of the VCSEL. The effective cavity length is the cavity length experienced by light within the cavity. More specifically, it is the average distance that light propagates from the time it transmits through the active layer in the resonance direction to the time it is reflected by the two reflecting mirrors that make up the cavity and then transmits back through the active layer. By adding at least one of these elements, and preferably three of them, it is possible to realize a VCSEL that can generate optical pulses with high peak amplitudes and short pulse widths.

[0033] Next, the light emitting element 20B will be described. The thickness of the upper insulating film 243b of the light emitting element 20B is different from that of the light emitting element 20A, but other points are the same as those of the light emitting element 20A. Regarding the light emitting element 20B, differences from the light emitting element 20A will be described in detail, and descriptions of the same configurations will be omitted as appropriate.

[0034] The light emitting element 20B includes a semiconductor substrate 10, a lower DBR layer 21, a saturable absorbing layer 22, a resonator 23, a reflector 24B, an anode electrode 25, a cathode electrode 26, and an insulating film 27.

[0035] The reflector 24B may include an upper DBR layer 241 formed on the doped spacer layer 233 of the resonator 23, a contact layer 242 formed on the upper DBR layer 241, and an upper insulating film 243b formed on the contact layer 242.

[0036] The upper insulating film 243b is formed as a thin film and insulates the contact layer 242 while leaving a portion of the surface of the anode electrode 25 exposed. The Z-direction thickness of the upper insulating film 243b is different from the Z-direction thickness of the upper insulating film 243a. Here, the Z-direction thickness of the upper insulating film 243b is formed thinner than the Z-direction thickness of the upper insulating film 243a. The upper insulating film 243b can be formed by partially removing it by etching to make it thinner than the upper insulating film 243a, or by depositing it thinner than the upper insulating film 243a in a film formation process. In this way, by making the thicknesses of the upper insulating films different, the reflectivities of the reflectors 24A and 24B are made different, and the light emission timings of the light-emitting elements 20A and 20B are shifted. The light emission timings of the light-emitting elements 20A and 20B are described below.

[0037] FIG. 3 is a diagram showing the waveform of high-peak pulsed light according to this embodiment. The vertical axis of FIG. 3 represents light intensity, and the horizontal axis represents time. FIG. 3 illustrates high-peak pulsed light L1 emitted from light-emitting element 20A and high-peak pulsed light L2 emitted from light-emitting element 20B. The half-widths of high-peak pulsed light L1 and L2 are 50 ps to 500 ps, ​​typically about 100 ps. Even though the same driving voltage is applied to light-emitting elements 20A and 20B at the same timing, as shown in FIG. 3, the emission timing of high-peak pulsed light L1 and the emission timing of high-peak pulsed light L2 are shifted from each other. Specifically, the emission timing of high-peak pulsed light L2 is delayed by about 400 ps from the emission timing of high-peak pulsed light L1. This is because the thickness of the upper insulating film 243b of light-emitting element 20B is thinner than the thickness of the upper insulating film 243a of light-emitting element 20A. As a result, the reflectance of the reflector 24B of the light-emitting element 20B is smaller than the reflectance of the reflector 24A of the light-emitting element 20A. Specifically, the reflectance of the reflector 24B of the light-emitting element 20B is 98.0%, and the reflectance of the reflector 24A of the light-emitting element 20A is 99.1%. The light intensity of the high peak pulsed light L2 is slightly smaller (about 85%) than the light intensity of the high peak pulsed light L1. However, the light intensity is maintained at 80% or higher.

[0038] In this embodiment, the reflectance of the reflector is reduced by reducing the thickness of the upper insulating film. However, since the reflectance is generally determined in relation to the optical thickness, reducing the thickness of the upper insulating film does not necessarily reduce the reflectance. In some cases, the reflectance can also be reduced by increasing the thickness of the upper insulating film. The thickness of the upper insulating film is adjusted appropriately so that the reflectance reaches the target value.

[0039] 4(a) and (b) are diagrams showing the relationship between the emission interval and optical intensity of high-peak pulsed light from a VCSEL according to a comparative example. Fig. 4(a) shows the optical intensity of high-peak pulsed light when the emission interval between the first high-peak pulsed light L1a and the next high-peak pulsed light L2a is 15 ns. Fig. 4(b) shows the optical intensity of high-peak pulsed light when the emission interval between the first high-peak pulsed light L1b and the next high-peak pulsed light L2b is 3 ns. Figs. 4(a) and (b) also show the waveform of the current injected into the VCSEL.

[0040] As shown in Figure 4(a), when high-peak pulsed light is emitted at intervals of 15 ns, the light intensity of the high-peak pulsed light L2a is slightly smaller (about 80%) than the light intensity of the high-peak pulsed light L1a. In this case, there is no particular problem because the light intensity is maintained at 80% or more.

[0041] On the other hand, as shown in Fig. 4(b), when high-peak pulsed light is emitted at intervals of 3 ns, the light intensity of the high-peak pulsed light L2b is significantly smaller (about 50%) than the light intensity of the high-peak pulsed light L1b. This is because the interval between the emission of the high-peak pulsed light L1b and the high-peak pulsed light L2b is short, and therefore the high-peak pulsed light L2b is emitted while carriers remain in the saturable absorption layer.

[0042] Fig. 5 is a diagram showing the relationship between the emission interval and the light intensity ratio of a normal pulsed light Lc and a high-peak pulsed light Ld according to a comparative example. Here, the normal pulsed light Lc has a smaller peak (about ¼) than the high-peak pulsed light Ld. The vertical axis of Fig. 5 represents the ratio of the light intensity of the next high-peak pulsed light Ld (normal pulsed light Lc) to the light intensity of the first high-peak pulsed light Ld (normal pulsed light Lc), and the horizontal axis represents the emission interval.

[0043] As shown in FIG. 5, in the case of the normal pulsed light Lc, the ratio of the light intensity of the next normal pulsed light Lc to the light intensity of the first normal pulsed light Lc was "1" regardless of the emission interval.

[0044] On the other hand, in the case of the high-peak pulsed light Ld, as the emission interval became shorter, the ratio of the light intensity of the next high-peak pulsed light Ld to the light intensity of the first high-peak pulsed light Ld became smaller. For example, when the emission interval was 15 ns, the light intensity ratio was about 80%, but when the emission interval was 3 ns, the light intensity ratio was about 50%. For this reason, the VCSEL according to the comparative example required an emission interval of 15 ns or more, making it difficult to emit high-peak pulsed light Ld continuously in a short period of time.

[0045] In contrast, in the light-emitting device 1 according to this embodiment, the reflectors 24A and 24B have different reflectivities. With this configuration, when a drive voltage is applied to each of the light-emitting elements 20A and 20B at the same timing, the light-emitting elements 20A and 20B emit pulsed light at different timings. This allows the light-emitting device 1 to emit high-peak pulsed light L1 from the light-emitting element 20A and high-peak pulsed light L2 from the light-emitting element 20B at short intervals. The driver 50 continuously outputs the drive voltage to be applied to each of the light-emitting elements 20A and 20B at the same timing at regular intervals, allowing the light-emitting device 1 to continuously emit high-peak pulsed light at short intervals.

[0046] [Second embodiment] Next, a light emitting device 1A according to this embodiment will be described. In the following second to eighth embodiments, the same components as those in the light emitting device 1 according to the first embodiment will be denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate.

[0047] The light emitting device 1A differs from the light emitting device 1 according to the first embodiment in that the number of pairs of the laminate constituting the upper DBR layer differs in each of the two light emitting elements. The following description will focus on the differences from the first embodiment.

[0048] 6 is a cross-sectional view of light emitting elements 20C and 20D according to this embodiment. The light emitting element 20C has the same configuration as the light emitting element 20A described above.

[0049] The light emitting element 20D includes a semiconductor substrate 10, a lower DBR layer 21, a saturable absorbing layer 22, a resonator 23, a reflector 24D, an anode electrode 25, a cathode electrode 26, and an insulating film 27.

[0050] The reflector 24D may include an upper DBR layer 241c formed on the doped spacer layer 233 of the resonator 23, a contact layer 242 formed on the upper DBR layer 241c, and an upper insulating film 243a formed on the contact layer 242.

[0051] The upper DBR layer 241c is, for example, an Al 0.1 Ga 0.9 As layer and Al 0.9 Ga 0.1A stack with an As layer is counted as one pair. The number of pairs in the stack of the upper DBR layer 241c is different from the number of pairs in the stack of the upper DBR layer 241 of the light-emitting element 20C. Here, the number of pairs in the stack of the upper DBR layer 241c is smaller than the number of pairs in the stack of the upper DBR layer 241 of the light-emitting element 20C. To reduce the number of pairs in the upper DBR layer 241c, a method of removing a portion by etching or a method of regrowing only a portion of the epitaxial layer other than the upper DBR layer 241c is used. This results in the reflectance of the reflector 24D of the light-emitting element 20D being smaller than the reflectance of the reflector 24A of the light-emitting element 20C. Therefore, the emission timing of the high-peak pulsed light emitted from the light-emitting element 20D is delayed compared to the emission timing of the high-peak pulsed light emitted from the light-emitting element 20C.

[0052] As described above, light emitting device 1A includes upper DBR layers 241, 241c having multiple semiconductor layer pairs, each including two semiconductor layers with different refractive indices. The number of semiconductor layer pairs in upper DBR layer 241 of light emitting element 20C is different from the number of semiconductor layer pairs in upper DBR layer 241c of light emitting element 20D. With this configuration, light emitting device 1A can stagger the emission timings of high peak pulsed light emitted from light emitting elements 20C and 20D, thereby enabling high peak pulsed light to be emitted at short intervals.

[0053] [Third embodiment] Next, a light emitting device 1B according to this embodiment will be described. Fig. 7 is a cross-sectional view of light emitting elements 20E and 20F according to this embodiment.

[0054] The light-emitting element 20E differs from the light-emitting element 20A in that it has a transparent conductive film (e.g., ITO: Indium Tin Oxide) 243d instead of the upper insulating film 243a, but otherwise has the same configuration as the light-emitting element 20A. Regarding the light-emitting element 20E, differences from the light-emitting element 20A will be described in detail, and descriptions of the same configuration will be omitted as appropriate.

[0055] The light emitting element 20E includes a semiconductor substrate 10, a lower DBR layer 21, a saturable absorbing layer 22, a resonator 23, a reflector 24E, an anode electrode 25, a cathode electrode 26, and an insulating film 27.

[0056] The reflector 24E may include an upper DBR layer 241 formed on the doped spacer layer 233 of the resonator 23, a contact layer 242 formed on the upper DBR layer 241, and a transparent conductive film 243d formed on the contact layer 242.

[0057] The anode electrode 25 is formed on the transparent conductive film 243d. The transparent conductive film 243d allows the current injected into the anode electrode 25 to flow to the center of the upper DBR layer 241 via the contact layer 242.

[0058] Next, the light-emitting element 20F will be described. The thickness of the transparent conductive film 243e of the light-emitting element 20F is different from that of the light-emitting element 20E, but other points are the same as those of the light-emitting element 20E. Regarding the light-emitting element 20F, differences from the light-emitting element 20E will be described in detail, and descriptions of the same configurations will be omitted as appropriate.

[0059] The light emitting element 20F includes a semiconductor substrate 10, a lower DBR layer 21, a saturable absorbing layer 22, a resonator 23, a reflector 24F, an anode electrode 25, a cathode electrode 26, and an insulating film 27.

[0060] The reflector 24F may include an upper DBR layer 241 formed on the doped spacer layer 233 of the resonator 23, a contact layer 242 formed on the upper DBR layer 241, and a transparent conductive film 243e formed on the contact layer 242.

[0061] The anode electrode 25 is formed on the transparent conductive film 243e. The transparent conductive film 243e allows the current injected into the anode electrode 25 to flow to the center of the upper DBR layer 241 via the contact layer 242.

[0062] The thickness of the central portion of the transparent conductive film 243e is different from the thickness of the central portion of the transparent conductive film 243d. Here, the thickness of the central portion of the transparent conductive film 243e is formed to be thinner than the thickness of the central portion of the transparent conductive film 243d. When forming the transparent conductive film 243e, for example, a portion of the film is removed by etching to form the film thinner than the transparent conductive film 243d. As a result, the reflectance of the reflector 24F of the light-emitting element 20F is smaller than the reflectance of the reflector 24E of the light-emitting element 20E. Therefore, the emission timing of the high peak pulsed light emitted from the light-emitting element 20F is delayed compared to the emission timing of the high peak pulsed light emitted from the light-emitting element 20E.

[0063] As described above, in light emitting device 1B, the thickness of transparent conductive film 243d of light emitting element 20E is different from the thickness of transparent conductive film 243e of light emitting element 20F. With this configuration, light emitting device 1B can shift the emission timing of high peak pulsed light emitted from light emitting elements 20E and 20F, and as a result, can emit high peak pulsed light at short intervals.

[0064] In this embodiment, an example has been described in which a transparent conductive film is used instead of the upper insulating film 243a of the second embodiment, but this embodiment is not limited to this, and a transparent conductive film 243d may be present between the upper insulating film 243a and the contact layer 242.

[0065] [Fourth embodiment] Next, a light emitting device 1C according to this embodiment will be described. The light emitting device 1C differs from the other embodiments in that the light emission timing is shifted by changing the drive voltage applied to the light emitting element 20G.

[0066] FIG. 8 is a plan view of a light emitting device 1C according to this embodiment. 8, the light emitting device 1C includes a semiconductor substrate 10, a plurality of light emitting elements 20G, anode wirings 30A, 30B, and 30C, power supply pads 40A, 40B, and 40C, driving sections 50A, 50B, and 50C, and a timing control section 60.

[0067] The light emitting elements 20G are arranged in an array across multiple rows and multiple columns on the semiconductor substrate 10. That is, the light emitting elements 20G are arranged in an array across the X and Y directions.

[0068] The anode wirings 30A, 30B, and 30C each extend in the X direction and are arranged side by side in the Y direction. Here, a total of six anode wirings are arranged side by side in the Y direction in the order of anode wirings 30A, 30B, and 30C. The anode wiring 30A is connected to a plurality of light-emitting elements 20G arranged along the X direction, the anode wiring 30B is connected to other light-emitting elements 20G arranged along the X direction, and the anode wiring 30C is connected to yet another light-emitting element 20G arranged along the X direction.

[0069] The power supply pad 40A is connected to the anode wiring 30A, the power supply pad 40B is connected to the anode wiring 30B, and the power supply pad 40C is connected to the anode wiring 30C. Each of the power supply pads 40A, 40B, and 40C is connected to a corresponding driver. Here, the power supply pad 40A is connected to the driver 50A, the power supply pad 40B is connected to the driver 50B, and the power supply pad 40C is connected to the driver 50C. The power supply pad 40A supplies power from the driver 50A to the light-emitting element 20G connected to the anode wiring 30A. The power supply pad 40B supplies power from the driver 50B to the light-emitting element 20G connected to the anode wiring 30B. The power supply pad 40C supplies power from the driver 50C to the light-emitting element 20G connected to the anode wiring 30C.

[0070] The drivers 50A, 50B, and 50C apply different drive voltages to the target light-emitting element 20G at the same time. Specifically, the driver 50A applies a drive voltage (e.g., 5.0 V) to the light-emitting element 20G connected to the anode wiring 30A. The driver 50B applies a drive voltage (e.g., 4.5 V) to the light-emitting element 20G connected to the anode wiring 30B. The driver 50C applies a drive voltage (e.g., 4.0 V) to the light-emitting element 20G connected to the anode wiring 30C.

[0071] The timing control section 60 controls the drive timing of the drive sections 50A, 50B, and 50C. Specifically, the timing control section 60 controls the drive sections 50A, 50B, and 50C so that the drive voltages are applied at the same timing.

[0072] Fig. 9 is a cross-sectional view of a light emitting element 20G according to this embodiment. The light emitting element 20G has the same configuration as the light emitting element 20A shown in Fig. 2. The light emitting device 1C is made up of light emitting elements 20G that all have the same configuration.

[0073] Fig. 10 is a diagram showing the waveform of a high peak value pulsed light according to this embodiment. The vertical axis of Fig. 10 represents light intensity, and the horizontal axis represents time. Fig. 10 shows three high peak value pulsed lights L1a, L2a, and L3a, each emitted at a different timing.

[0074] The high peak pulsed light L1a is emitted from the light emitting element 20G driven by the driver 50A. The high peak pulsed light L2a is emitted from the light emitting element 20G driven by the driver 50B. The high peak pulsed light L3a is emitted from the light emitting element 20G driven by the driver 50C.

[0075] The half-widths of the high-peak pulsed light L1a, L2a, and L3a are approximately 100 ps. Even though the drive voltage is applied to each of the light-emitting elements 20G at the same timing, the emission timings of the high-peak pulsed light L1a, L2a, and L3a are shifted, as shown in FIG. 10 . Specifically, the emission timing of the high-peak pulsed light L2a is delayed by approximately 300 ps from the emission timing of the high-peak pulsed light L1a. The emission timing of the high-peak pulsed light L3a is delayed by approximately 400 ps from the emission timing of the high-peak pulsed light L2a. This is because the drive voltages applied to the light-emitting element 20G are changed by the drivers 50A, 50B, and 50C. As the drive voltage decreases, the emission timing of the high-peak pulsed light is delayed.

[0076] As described above, light emitting device 1C changes the drive voltage applied to light emitting element 20G. With this configuration, light emitting device 1C can shift the emission timing of high peak pulsed light emitted from light emitting element 20G for each drive voltage, thereby enabling high peak pulsed light to be emitted at short intervals.

[0077] [Fifth embodiment] Fig. 11 is a block diagram of a light emitting device 1D according to this embodiment. Fig. 11 illustrates a portion of the light emitting device 1D. The light emitting device 1D differs from the light emitting device 1C according to the fourth embodiment in that the drive voltage applied to the light emitting element 20G is changed by a voltage drop unit.

[0078] As shown in FIG. 11, the light emitting device 1D includes a semiconductor substrate 10, a plurality of light emitting elements 20G, anode wirings 30A, 30B, and 30C, power supply pads 40A, 40B, and 40C, a driving section 50, paths 80A, 80B, and 80C, and voltage drop sections 90B and 90C.

[0079] Paths 80A, 80B, and 80C are wirings that connect the drive unit 50 and the power supply pads. Specifically, path 80A connects the drive unit 50 and the power supply pad 40A, path 80B connects the drive unit 50 and the power supply pad 40B, and path 80C connects the drive unit 50 and the power supply pad 40C.

[0080] Voltage drop units 90B and 90C drop voltage and may be, for example, resistor elements or wiring units formed of long wiring. Voltage drop units 90B and 90C have different resistance values, and here, the resistance value of voltage drop unit 90B is smaller than the resistance value of voltage drop unit 90C. Voltage drop units 90B and 90C are provided outside semiconductor substrate 10. Voltage drop unit 90B is provided on path 80B, and voltage drop unit 90C is provided on path 80C.

[0081] The driving unit 50 applies the same driving voltage to each of the paths 80A, 80B, and 80C. As a result, the highest driving voltage is applied to the light-emitting element 20G into which current is injected via the path 80A. The second highest driving voltage is applied to the light-emitting element 20G into which current is injected via the path 80B and the voltage drop unit 90B. The lowest driving voltage is applied to the light-emitting element 20G into which current is injected via the path 80C and the voltage drop unit 90C.

[0082] As described above, the light emitting device 1D includes voltage drop units 90B and 90C provided on the path between the driver 50 and the light emitting element 20G. This configuration allows the light emitting device 1D to change the drive voltage applied to the light emitting element 20G. This allows the light emitting device 1D to shift the emission timing of the high peak intensity pulsed light emitted from the light emitting element 20G for each drive voltage, thereby enabling the high peak intensity pulsed light to be emitted at short intervals. While the voltage drop unit 90B is disposed between the driver 50 and the power supply pad 40B in this embodiment, the voltage drop unit 90B may alternatively be disposed between the power supply pad 40B and the anode wiring 30B. Similarly, the voltage drop unit 90C may be disposed between the power supply pad 40C and the anode wiring 30C.

[0083] [Sixth embodiment] Fig. 12 is a block diagram of a light emitting device 1E according to this embodiment. Fig. 12 illustrates a portion of the light emitting device 1E. The light emitting device 1E differs from the light emitting device 1D according to the fifth embodiment in that voltage drop sections 90B and 90C are formed on the semiconductor substrate 10.

[0084] The paths 80A, 80B, and 80C branch off at a branch point P on the semiconductor substrate 10, and the branched ends are connected to the corresponding power supply pads. The branch point P is connected to an external connection point G. The external connection point G is connected to the drive unit 50. According to the light emitting device 1E, the external connection points G can be consolidated into one.

[0085] [Seventh embodiment] Next, a moving body according to the seventh embodiment will be described with reference to Fig. 13. Fig. 13 is a block diagram of an imaging system and a moving body according to this embodiment.

[0086] 13(a) shows an example of the configuration of a device mounted on a vehicle as an on-board camera. The device 300 has a distance measurement unit (LiDAR) 303 that measures the distance to a measurement object, and a collision determination unit 304 that determines whether or not there is a possibility of a collision based on the distance measured by the distance measurement unit 303. The distance measurement unit 303 includes a light-emitting device described in the first to sixth embodiments, a light-receiving device having a light-receiving element, and a distance information acquisition unit. The distance information acquisition unit acquires information about the distance to the measurement object based on the time difference between the timing at which light is emitted from the light-emitting element and the timing at which the light-receiving element receives the light emitted from the light-emitting element and reflected by the measurement object.

[0087] The device 300 is connected to a vehicle information acquisition device 310 and can acquire vehicle information such as vehicle speed, yaw rate, and steering angle. The device 300 is also connected to a control ECU 320, which is a control device that outputs a control signal to generate a braking force for the vehicle based on the determination result of the collision determination unit 304. The device 300 is also connected to an alarm device 330 that issues an alarm to the driver based on the determination result of the collision determination unit 304. For example, if the collision determination unit 304 determines that a collision is highly likely, the control ECU 320 performs vehicle control to avoid a collision and mitigate damage by applying the brakes, releasing the accelerator, suppressing engine output, etc. The alarm device 330 warns the user by sounding an alarm, displaying alarm information on a screen of a car navigation system, etc., or vibrating a seat belt or steering wheel. These devices of the device 300 function as a mobile object control unit that controls the operation of controlling the vehicle as described above.

[0088] In this embodiment, the device 300 measures the distance around the vehicle, for example, the front or rear. Fig. 13(b) shows the device when measuring the distance in front of the vehicle (distance measurement range 350). The vehicle information acquisition device 310, which serves as a distance measurement control means, sends an instruction to the device 300 or the distance measurement unit 303 to perform a distance measurement operation. This configuration can further improve the accuracy of distance measurement.

[0089] Although the above describes an example of control to prevent collision with other vehicles, the present invention can also be applied to control of automatic driving by following other vehicles, control of automatic driving to prevent deviation from a lane, etc. Furthermore, the present invention is not limited to vehicles such as automobiles, but can be applied to moving objects (moving devices) such as ships, aircraft, artificial satellites, industrial robots, and consumer robots. In addition, the present invention can be applied to a wide range of devices that use object recognition or biometric recognition, such as intelligent transport systems (ITS) and surveillance systems, without being limited to moving objects.

[0090] [Modified embodiment] The present invention is not limited to the above-described embodiments and can be modified in various ways. For example, an example in which part of the configuration of one embodiment is added to another embodiment, or an example in which part of the configuration of another embodiment is replaced with another embodiment, is also an embodiment of the present invention.

[0091] For example, although the cathode electrode 26 is provided on the lower surface of the semiconductor substrate 10 in the above example, the present invention is not limited to this. For example, the cathode electrode 26 may be provided so as to be electrically connected to the doped spacer layer 231.

[0092] Although the saturable absorbing layer 22 and the resonator 23 have been described as separate components, the present invention is not limited to this. For example, both the resonator 23 and the saturable absorbing layer 22 may be formed as a resonator.

[0093] The number of light-emitting elements constituting the array is not limited to the above example, and the types of light-emitting elements with different reflectances and the driving voltage patterns are not limited to the above example.

[0094] In the above description, the mesa is formed up to above the doped spacer layer 231, but this is not limiting and it may be formed, for example, up to below the oxide constriction layer 241a. Note that the mesa is preferably formed above the saturable absorbing layer 22. This is because the formation of the mesa increases non-radiative recombination in the saturable absorbing layer 22.

[0095] The disclosure of the above embodiment includes the following configurations. (Configuration 1) a first light emitting element and a second light emitting element formed on a common semiconductor substrate; a driving unit that applies a driving voltage to each of the first light-emitting element and the second light-emitting element, Each of the first light-emitting element and the second light-emitting element is a first reflector formed on the semiconductor substrate; a cavity formed on the first reflector and including a saturable absorbing layer; a second reflector formed on the resonator; A light-emitting device characterized in that when the driving voltage is applied to the first light-emitting element and the second light-emitting element at the same timing, the first light-emitting element and the second light-emitting element emit pulsed light at different timings. (Configuration 2) 2. The light emitting device according to configuration 1, wherein the reflectance of the second reflector of the first light emitting element and the reflectance of the second reflector of the second light emitting element are different from each other. (Configuration 3) Each of the second reflectors includes a reflecting mirror and an insulating film formed on the reflecting mirror, 3. The light emitting device according to configuration 2, wherein the thickness of the insulating film of the first light emitting element and the thickness of the insulating film of the second light emitting element are different from each other. (Configuration 4) the second reflector has a plurality of semiconductor layer pairs each including two semiconductor layers having different refractive indices; The light-emitting device according to configuration 2, characterized in that the number of pairs of the semiconductor layers of the second reflector of the first light-emitting element is different from the number of pairs of the semiconductor layers of the second reflector of the second light-emitting element. (Configuration 5) each of the second reflectors includes a reflecting mirror and a transparent conductive film formed on the reflecting mirror; 3. The light emitting device according to configuration 2, wherein the thickness of the transparent conductive film of the first light emitting element and the thickness of the transparent conductive film of the second light emitting element are different from each other. (Configuration 6) 6. The light emitting device according to any one of configurations 1 to 5, wherein the drive voltage applied to the first light emitting element and the drive voltage applied to the second light emitting element are the same. (Configuration 7) 2. The light emitting device according to configuration 1, wherein the drive voltage applied to the first light emitting element and the drive voltage applied to the second light emitting element are different from each other. (Configuration 8) The drive unit is a first driving unit that applies the driving voltage to the first light-emitting element; 8. The light emitting device according to configuration 7, further comprising: a second driving section that applies to the second light emitting element a driving voltage that is different from the driving voltage applied to the first light emitting element. (Configuration 9) 8. The light emitting device according to configuration 7, further comprising a voltage drop section provided on a path between the drive section and either the first light emitting element or the second light emitting element. (Configuration 10) The light emitting device according to configuration 9, wherein the voltage drop section is formed on the semiconductor substrate. (Configuration 11) 10. The light emitting device according to configuration 9, wherein the voltage drop section is provided outside the semiconductor substrate. (Configuration 12) 12. The light emitting device according to any one of configurations 7 to 11, wherein the reflectance of the second reflector of the first light emitting element and the reflectance of the second reflector of the second light emitting element are the same. (Configuration 13) The light-emitting device according to any one of configurations 1 to 12, wherein the driving unit continuously outputs the driving voltage to be applied to each of the first light-emitting element and the second light-emitting element at the same timing at regular intervals. (Configuration 14) 14. The light emitting device according to any one of configurations 1 to 13, wherein the half width of the pulsed light is 50 ps to 500 ps. (Configuration 15) a first light emitting element and a second light emitting element formed on a common semiconductor substrate; a driving unit that applies a driving voltage to each of the first light-emitting element and the second light-emitting element, Each of the first light-emitting element and the second light-emitting element is a first reflector formed on the semiconductor substrate; a cavity formed on the first reflector and including a saturable absorbing layer; a second reflector formed on the resonator; The reflectivity of the second reflector of the first light-emitting element is different from the reflectivity of the second reflector of the second light-emitting element, A light-emitting device characterized in that when the driving voltage is applied to the first light-emitting element and the second light-emitting element at the same timing, the first light-emitting element and the second light-emitting element emit pulsed light at different timings. (Configuration 16) a first light emitting element and a second light emitting element formed on a common semiconductor substrate; a driving unit that applies a driving voltage to each of the first light-emitting element and the second light-emitting element, Each of the first light-emitting element and the second light-emitting element is a first reflector formed on the semiconductor substrate; a cavity formed on the first reflector and including a saturable absorbing layer; a second reflector formed on the resonator; the driving voltage applied to the first light-emitting element and the driving voltage applied to the second light-emitting element are different from each other; A light-emitting device characterized in that when the driving voltage is applied to the first light-emitting element and the second light-emitting element at the same timing, the first light-emitting element and the second light-emitting element emit pulsed light at different timings. (Configuration 17) a light-emitting device according to any one of configurations 1 to 16; a light receiving device that receives light emitted from the light emitting device and reflected by the object to be measured; A distance measuring device characterized by having a distance information acquisition unit that acquires information regarding the distance to the object to be measured based on the time difference between the timing at which light is emitted from the light emitting device and the timing at which light is received by the light receiving device. (Configuration 18) A mobile object, a distance measuring device according to configuration 17; A moving body comprising a control means for controlling the moving body based on information about the distance obtained by the distance measuring device. [Explanation of symbols]

[0096] 1...Light emitting device 10...Semiconductor substrate 20, 20A, 20B...Light emitting element 21…Lower DBR layer 23...Resonator 24A…Reflector 243a...Upper insulating film 243d...Transparent conductive film 50, 50A, 50B, 50C...Driver 80A, 80B, 80C...Route 90B, 90C...Voltage drop section

Claims

1. a first light emitting element and a second light emitting element formed on a common semiconductor substrate; a driving unit that applies a driving voltage to each of the first light-emitting element and the second light-emitting element, Each of the first light-emitting element and the second light-emitting element is a first reflector formed on the semiconductor substrate; a cavity formed on the first reflector and including a saturable absorbing layer; a second reflector formed on the resonator; A light-emitting device characterized in that when the driving voltage is applied to each of the first light-emitting element and the second light-emitting element at the same timing, the first light-emitting element and the second light-emitting element emit pulsed light at different timings.

2. 2. The light emitting device according to claim 1, wherein the reflectance of the second reflector of the first light emitting element is different from the reflectance of the second reflector of the second light emitting element.

3. Each of the second reflectors includes a reflecting mirror and an insulating film formed on the reflecting mirror, 3. The light emitting device according to claim 2, wherein the thickness of the insulating film of the first light emitting element and the thickness of the insulating film of the second light emitting element are different from each other.

4. the second reflector has a plurality of semiconductor layer pairs each including two semiconductor layers having different refractive indices; 3. The light emitting device according to claim 2, wherein the number of pairs of the semiconductor layer of the second reflector of the first light emitting element is different from the number of pairs of the semiconductor layer of the second reflector of the second light emitting element.

5. each of the second reflectors includes a reflecting mirror and a transparent conductive film formed on the reflecting mirror; 3. The light emitting device according to claim 2, wherein the thickness of the transparent conductive film of the first light emitting element and the thickness of the transparent conductive film of the second light emitting element are different from each other.

6. 3. The light emitting device according to claim 2, wherein the driving voltage applied to the first light emitting element and the driving voltage applied to the second light emitting element are the same.

7. 2. The light emitting device according to claim 1, wherein the driving voltage applied to the first light emitting element and the driving voltage applied to the second light emitting element are different from each other.

8. The drive unit is a first driving unit that applies the driving voltage to the first light-emitting element; 8. The light emitting device according to claim 7, further comprising: a second driving section that applies the driving voltage to the second light emitting element, the driving voltage being different from the driving voltage applied to the first light emitting element.

9. 8. The light emitting device according to claim 7, further comprising a voltage drop section provided on a path between the drive section and either the first light emitting element or the second light emitting element.

10. The light emitting device according to claim 9 , wherein the voltage drop unit is formed on the semiconductor substrate.

11. The light emitting device according to claim 9 , wherein the voltage drop section is provided outside the semiconductor substrate.

12. 8. The light emitting device according to claim 7, wherein the reflectance of the second reflector of the first light emitting element and the reflectance of the second reflector of the second light emitting element are the same.

13. 2 . The light emitting device according to claim 1 , wherein the drive section outputs the drive voltage to be applied to the first light emitting element and the second light emitting element at the same timing continuously at regular intervals.

14. 2. The light emitting device according to claim 1, wherein the half width of the pulsed light is 50 ps to 500 ps.

15. a first light emitting element and a second light emitting element formed on a common semiconductor substrate; a driving unit that applies a driving voltage to each of the first light-emitting element and the second light-emitting element, Each of the first light-emitting element and the second light-emitting element is a first reflector formed on the semiconductor substrate; a cavity formed on the first reflector and including a saturable absorbing layer; a second reflector formed on the resonator; The reflectivity of the second reflector of the first light-emitting element is different from the reflectivity of the second reflector of the second light-emitting element, A light-emitting device characterized in that when the driving voltage is applied to each of the first light-emitting element and the second light-emitting element at the same timing, the first light-emitting element and the second light-emitting element emit pulsed light at different timings.

16. a first light emitting element and a second light emitting element formed on a common semiconductor substrate; a driving unit that applies a driving voltage to each of the first light-emitting element and the second light-emitting element, Each of the first light-emitting element and the second light-emitting element is a first reflector formed on the semiconductor substrate; a cavity formed on the first reflector and including a saturable absorbing layer; a second reflector formed on the resonator; the driving voltage applied to the first light-emitting element and the driving voltage applied to the second light-emitting element are different from each other; A light-emitting device characterized in that when the driving voltage is applied to each of the first light-emitting element and the second light-emitting element at the same timing, the first light-emitting element and the second light-emitting element emit pulsed light at different timings.

17. A light emitting device according to any one of claims 1 to 16, a light receiving device that receives light emitted from the light emitting device and reflected by the object to be measured; A distance measuring device characterized by having a distance information acquisition unit that acquires information regarding the distance to the object to be measured based on the time difference between the timing when light is emitted from the light emitting device and the timing when light is received by the light receiving device.

18. A mobile object, a distance measuring device according to claim 17; A moving body comprising a control means for controlling the moving body based on information about the distance obtained by the distance measuring device.

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