Light-emitting device

Abstract

[Problem] To provide a highly reliable light-emitting device capable of reducing the dark current of a photodiode provided in a vertical cavity. [Solution] A light-emitting device according to the present embodiment comprises: a substrate that contains group III-V elements or group IV elements; a first reflection part that is provided on the substrate; a second reflection part that is provided above the first reflection part; a first semiconductor layer of a first conductivity type and a second semiconductor layer of a second conductivity type that are provided between the first reflection part and the second reflection part; an active layer that is provided between the first semiconductor layer and the second semiconductor layer and generates light of a first wavelength by applying a voltage to the first and second semiconductor layers; and a photodiode layer that is provided on the first-reflection-part side of the active layer, contains a semiconductor material provided in the state of quantum dots or quantum wires, and photoelectrically converts the light of the first wavelength to generate charge.

Description

Light-emitting device

[0001] The present disclosure relates to a light-emitting device.

[0002] Self-Mixing Interference (SMI)-VCSELs, in which a photodiode is provided inside a vertical cavity surface emitting laser (VCSEL), have been developed.

[0003] Japanese Patent No. 7174780

[0004] For infrared photodiodes, the dark current increases because the band gap of the photoelectric conversion layer is small. When such a photodiode is applied to an SMI-VCSEL, the noise level increases, making signal detection difficult. Additionally, when an SMI-VCSEL is formed using a GaAs substrate, there is no photoelectric conversion material that lattice-matches with GaAs and can sufficiently absorb infrared light. When a photoelectric conversion material that does not cause lattice mismatch is used, dark current increases due to crystal defects, leading to decreased reliability.

[0005] Therefore, the present disclosure provides a highly reliable light-emitting device capable of reducing the dark current of a photodiode provided in a vertical resonator.

[0006] According to one aspect of the present disclosure, a light-emitting device includes: a substrate containing a group III-V element or a group IV element; a first reflector provided on the substrate; a second reflector provided above the first reflector; a first semiconductor layer of a first conductivity type and a second semiconductor layer of a second conductivity type provided between the first reflector and the second reflector; an active layer provided between the first semiconductor layer and the second semiconductor layer, the active layer generating light of a first wavelength by applying a voltage to the first and second semiconductor layers; and a photodiode layer provided on the first reflector side of the active layer, the photodiode layer containing a semiconductor material provided in a state of quantum dots or quantum wires, and photoelectrically converting light of the first wavelength to generate electric charges.

[0007] The quantum dots or quantum wires have a peak of light absorption coefficient near the first wavelength.

[0008] Quantum dots or quantum wires contain one of the following materials: InAs, InGaAs, InGaN, InGaAsP, or InSb.

[0009] The photodiode layer includes a GaAs layer, and the quantum dots or quantum wires are provided on the GaAs layer.

[0010] The substrate is either a substrate containing GaAs (gallium arsenide) or a substrate containing Ge (germanium).

[0011] The first and second semiconductor layers are semiconductor layers containing group III-V elements, and the first reflective portion is a laminate of multiple semiconductor layers containing group III-V elements.

[0012] The first and second semiconductor layers are semiconductor layers containing GaAs, and the first reflective portion is a laminate of multiple GaAs layers and multiple AlGaAs layers.

[0013] The first and second semiconductor layers are semiconductor layers containing InP.

[0014] The second reflective section is a laminate of multiple dielectric layers.

[0015] The photodiode layer includes an InGaAs layer, and the quantum dots or quantum wires are provided on the GaAs layer.

[0016] The light-emitting device further comprises a first electrode electrically connected to a first semiconductor layer, a second electrode electrically connected to a second semiconductor layer, and a third electrode electrically connected to a substrate.

[0017] The second semiconductor layer includes a conductive region provided in the light-emitting region and an insulating region provided around the conductive region.

[0018] The light-emitting device further comprises a third semiconductor layer provided on the second semiconductor layer between the second reflecting portion and the second semiconductor layer, having a higher impurity concentration of the second conductivity type than the second semiconductor layer, and a fourth semiconductor layer of the first conductivity type provided on the third semiconductor layer, forming a tunnel junction with the third semiconductor layer.

[0019] The light-emitting device further comprises a fifth semiconductor layer provided on the third and fourth semiconductor layers.

[0020] The photodiode layer includes a barrier layer that mitigates, compensates for, or cancels distortion in quantum dots or quantum wires.

[0021] This is a cross-sectional view showing an example configuration of a light-emitting device according to the first embodiment. This is a plan view showing the surface of the quantum dot photodiode layer. This is a graph showing the characteristics of the light-emitting device according to the first embodiment. This is a table showing the dark current of the bulk semiconductor layer and quantum dots. This is a cross-sectional view showing an example configuration of a light-emitting device according to the second embodiment. This is a plan view showing the surface of the quantum dot photodiode layer. This is a cross-sectional view showing an example configuration of a light-emitting device according to the third embodiment. This is a diagram showing an example of the installation position of the imaging unit. This is a block diagram showing a schematic configuration example of a vehicle control system, which is an example of a mobile control system to which the technology of this disclosure can be applied.

[0022] The following describes specific embodiments of this technology with reference to the drawings. The drawings are schematic or conceptual, and the proportions of each part may not necessarily be the same as those of actual objects. In the specification and drawings, elements similar to those described above are denoted by the same reference numerals with respect to previously shown drawings, and detailed explanations are omitted as appropriate.

[0023] (First Embodiment) Figure 1 is a cross-sectional view showing an example of the configuration of a light-emitting device 1 according to the first embodiment. The light-emitting device 1 comprises a substrate 10, a first reflector 20, a photodiode layer 120, a first semiconductor layer 30, an active layer 40, a second semiconductor layer 50, a constriction layer 80, a second reflector 90, a first electrode 100, a second electrode 110, a third electrode 115, and an insulating film 105.

[0024] The light-emitting device 1 is, for example, a semiconductor light-emitting device such as an SMI-VCSEL that incorporates a photodiode. The light-emitting device 1 can be used, for example, in a distance measuring device such as a ToF (Time of Flight) device.

[0025] The light-emitting device 1 emits light by applying a voltage between the first electrode 100 and the second electrode 110, thereby injecting electrons and holes from the first and second semiconductor layers 30 and 50 into the active layer 40, and recombining the electrons and holes in the active layer 40. The light is reflected and resonates between the first reflector 20 and the second reflector 90, and is emitted as laser light from the second reflector 90 side. At this time, the photodiode layer 120 is biased between the first electrode 100 and the third electrode 115, and converts light from the active layer 40 or reflected light from the outside into photoelectric light, generating an electric charge. The charge generated in the photodiode layer 120 is detected externally via the first electrode 100 or the third electrode 115.

[0026] The substrate 10 is a semiconductor substrate containing group III-V elements or group IV elements. For example, the substrate 10 is a substrate containing n-type GaAs or a substrate containing n-type Ge.

[0027] The first reflector 20 is a so-called DBR (Distributed Bragg Reflector) and is constructed by alternately stacking multiple materials with different refractive indices. For example, the first reflector 20 has a stacked structure of multiple epitaxially grown semiconductor materials. The first reflector 20 includes an n-type first reflective layer 20a, a p-type second reflective layer 20b, and an n-type third reflective layer 20c. The first reflective layer 20a contains a material that is lattice-matched with the material of the substrate 10. The first reflective layer 20a is a semiconductor layer containing n-type Group III-V elements. The second reflective layer 20b is a semiconductor layer containing p-type Group III-V elements. The third reflective layer 20c is a semiconductor layer containing n-type Group III-V elements. For example, the first and third reflective layers 20a and 20c are stacks in which multiple n-type GaAs layers and multiple AlGaAs layers are alternately stacked one layer each. The second reflective layer 20b also contains a material that is lattice-matched with the material of the substrate 10. For example, the second reflective layer 20b is a laminate in which multiple p-type GaAs layers and multiple AlGaAs layers are alternately stacked one layer at a time.

[0028] The first reflective layer 20a is provided between the substrate 10 and the photodiode layer 120. The second reflective layer 20b is provided between the photodiode layer 120 and the cladding layer 30a. The third reflective layer 20c is provided between the cladding layer 30a and the cladding layer 30b.

[0029] The photodiode layer 120 is a layer comprising a semiconductor layer 121 and a semiconductor material in the state of quantum dots QD or quantum wires Q_Dash provided on the semiconductor layer 121. The photodiode layer 120 is provided on the first reflector 20 side of the active layer 40 and is provided between the n-type first reflector layer 20a and the p-type second reflector layer 20b. The semiconductor material in the state of quantum dots QD or quantum wires Q_Dash of the photodiode layer 120 may be a material that is not lattice-matched with the materials of the substrate 10 and the first reflector 20. For example, if the substrate 10 is GaAs, the photodiode layer 120 may be a semiconductor layer containing, for example, InAs, InGaAs, InGaN, InGaAsP, or InSb as quantum dots QD or quantum wires Q_Dash. Furthermore, the quantum dots QD or quantum wires Q_Dash of the photodiode layer 120 may contain a mixture of multiple types of materials, including InAs, InGaAs, InGaN, InGaAsP, and InSb.

[0030] The semiconductor layer (barrier layer) 121 of the photodiode layer 120 is, for example, a GaAs layer. The semiconductor layer 121 is preferably a material that mitigates, compensates for, or cancels the strain of the quantum dot QD or quantum wire Q_Dash. For example, if the quantum dot QD or quantum wire Q_Dash is InAs on a GaAs substrate 10, the semiconductor layer 121 is preferably GaAs as a composition that cancels the strain of the quantum dot QD or quantum wire Q_Dash. The photodiode layer 120 may also be constructed by stacking a plurality of semiconductor layers 121 (for example, GaAs layers) containing the above-mentioned quantum dot QD or quantum wire Q_Dash. The photodiode layer 120 absorbs light from the active layer 40 and performs photoelectric conversion. The quantum wire Q_Dash will be described in the second embodiment.

[0031] Figure 2 is a plan view showing the surface of the quantum dot photodiode layer 120. The photodiode layer 120 is not a bulk layer that covers the entire surface of the semiconductor layer (e.g., GaAs layer), but is provided in the form of quantum dots QD as shown in Figure 2. The reason for this will be explained later. The quantum wire Q_Dash will be described in the second embodiment.

[0032] Refer to Figure 1 again. The first semiconductor layer 30 is located between the photodiode layer 120 and the second reflector 90 and is a cladding layer provided on the photodiode layer 120. The first semiconductor layer 30 is a semiconductor layer containing group III-V elements, for example, a semiconductor layer containing n-type GaAs. The first semiconductor layer 30 includes cladding layers 30a and 30b. Cladding layer 30a is provided between the second reflecting layer 20b and the third reflecting layer 20c. Cladding layer 30b is provided between the third reflecting layer 20c and the active layer 40.

[0033] The active layer 40 is provided between the first semiconductor layer 30 and the second semiconductor layer 50. The active layer 40 emits light when a voltage is applied to the first and second semiconductor layers 30 and 50, causing electrons from the first semiconductor layer 30 and holes from the second semiconductor layer 50 to recombine inside the active layer 40. The active layer 40 generates light of a first wavelength. The active layer 40 consists of a multiple quantum well (MQW) layer, such as a laminated film of GaInAs and GaAsP, or a laminated film of (Al)GaInAs and (AlIn)GaAs(P). The wavelength of the multiple quantum well layer of the AlGaInAs and AlGaInAs laminated film can be arbitrarily controlled by the material composition and film thickness. It is preferable to introduce mutually opposing strains into the multiple quantum well layer and the barrier layer. In this case, for example, the magnitude of the strain can be around 1%, and the number of quantum wells can be 4 to 8.

[0034] The second semiconductor layer 50 is located between the first reflector 20 and the second reflector 90 and is a cladding layer provided on the active layer 40. The second semiconductor layer 50 is a semiconductor layer containing group III-V elements and is a semiconductor layer containing p-type GaAs that is inversely conductive to the first semiconductor layer 30. Therefore, by applying a negative voltage to the first electrode 100 and a positive voltage to the second electrode 110, electrons are supplied from the first semiconductor layer 30 to the active layer 40, and holes are supplied from the second semiconductor layer 50 to the active layer 40.

[0035] The constriction layer 80 is located between the active layer 40 and the second semiconductor layer 50. The constriction layer 80 is provided around the light-emitting region (conductive region) of the second semiconductor layer 50. In a plan view from the Z direction, the constriction layer 80 is located in a position overlapping with the electrode 110, and the opening of the constriction layer 80 overlaps with the light-emitting region (conductive region of the second semiconductor layer 50) of the second reflector 90. The constriction layer 80 narrows the region in contact between the second semiconductor layer 50 and the active layer 40, concentrating the current flow in the conductive region and constricting the current. No current flows through the constriction layer 80, but current flows through the conductive region of the second semiconductor layer 50 at the opening of the constriction layer 80. The constriction layer 80 is formed, for example, by oxidizing a part of the material of the second semiconductor layer 50 from both sides (X or Y direction). The constriction layer 80 is composed of an insulating material such as aluminum oxide (AlOx). The constriction layer 80 may be an air gap. In this case, insulating material such as aluminum oxide in the constriction layer 80 is etched away. The constriction layer 80 also concentrates light at the opening due to the refractive index difference with the second semiconductor layer 50. Therefore, the constriction layer 80 has the functions of current constriction and light constriction. The Z direction is the stacking direction of the first reflector 20, etc., the direction in which current flows through the second semiconductor layer 50, and the direction in which light resonates between the first reflector 20 and the second reflector 90.

[0036] The second reflector 90 is located above the constricted layer 80 (in the +Z direction). The second reflector 90 is a DBR and is constructed by alternately stacking multiple materials with different refractive indices, one layer at a time. For example, the second reflector 90 has a stacked structure of multiple semiconductor materials (for example, a stacked structure of p-type GaAs and AlGaAs). That is, both the first and second reflectors 20 and 90 are semiconductor DBRs composed of semiconductor materials. In this embodiment, the laser light L generated in the resonator between the first reflector 20 and the second reflector 90 is emitted from the upper surface of the second reflector 90, as indicated by the arrow in Figure 1.

[0037] The first electrode 100 is provided on the cladding layer 30a of the first semiconductor layer 30 and is electrically connected to the first semiconductor layer 30. The first electrode 100 is made of a conductive metal such as Ti, Pt, Au, a multilayer film of AuGe and Ni and Au, or a multilayer film of PdGe, Ni and Au. The first electrode 100 is electrically insulated from components other than the first semiconductor layer 30. The first electrode 100 functions as a common cathode for the laser diode and photodiode layer 120, which include the active layer 40.

[0038] The second electrode 110 is provided on the upper surface of the second reflector 90 and is electrically connected to the second reflector 90. Furthermore, the second electrode 110 is electrically connected to the second semiconductor layer 50 via the second reflector 90. The second electrode 110 is also made of a conductive metal, such as Ti, Pt, Au, a multilayer film of AuGe and Ni and Au, or a multilayer film of PdGe, Ni and Au. The second electrode 110 may be made of the same material as the first electrode 100. The second electrode 110 is provided around the light emission region of the second reflector 90. The second electrode 110 functions as the anode of the laser diode including the active layer 40.

[0039] The first and second electrodes 100 and 110 do not overlap with the light emission region of the second reflector 90 when viewed from the Z direction. Therefore, the first and second electrodes 100 and 110 do not obstruct the laser light emitted from the second reflector 90.

[0040] The third electrode 115 is formed on the back surface of the substrate 10 and is electrically connected to the substrate 10 and the first reflective layer 20a. The third electrode 115 is also made of a conductive metal such as Ti, Pt, Au, a laminated film of AuGe, Ni and Au, or a laminated film of PdGe, Ni and Au, for example. The third electrode 115 may be made of the same material as the first and second electrodes 100 and 110. The third electrode 115 functions as an electrode of the photodiode layer 120.

[0041] The insulating film 105 is provided on side surfaces of the first and second reflecting mirrors 20 and 90, the constriction layer 80, the first and second semiconductor layers 30 and 50, and the active layer 40. The insulating film 105 suppresses unintended short circuits between these elements and protects these elements. Further, the insulating film 105 electrically insulates the electrodes 100, 110 and 115 from each other.

[0042] FIG. 3 is a graph showing characteristics of the light-emitting device according to the first embodiment. In this graph, the vertical axis represents the light absorption coefficient Ab of the photodiode layer 120. The horizontal axis represents the wavelength λ of light received by the photodiode layer 120.

[0043] Hereinafter, it is assumed that the photodiode layer 120 includes quantum dots QD, and the semiconductor material of the quantum dots QD is InAs. It is assumed that the wavelength of laser light emitted from the light-emitting device 1 is about 940 nm. The same applies even when the photodiode layer 120 includes InAs quantum wires.

[0044] Line Lqd shows the characteristics of InAs quantum dots QD having a peak Pa of the light absorption coefficient Ab in the vicinity of about 940 nm, which is the same as the wavelength of the laser light. Line Lbl shows the characteristics of a bulk semiconductor layer using the same material (InAs) as the quantum dots QD of line Lqd.

[0045] As shown by line Lbl, when a bulk semiconductor layer (InAs layer) is used for the photodiode layer 120, the light absorption coefficient Ab gradually decreases as the wavelength λ of light increases. That is, when the band gap Eg is large, the density of states is small, and the light absorption coefficient tends to be small. In this case, no peak of the light absorption coefficient Ab appears. Further, the wavelength λ at which the light absorption coefficient Ab becomes zero (hereinafter also referred to as the absorption edge) is, for example, about 1040 nm. That is, the bulk band gap Eg shown by line Lbl is, for example, about 1.19 eV (1240 / 1040 = 1.19).

[0046] On the other hand, as shown by line Lqd, when InAs of quantum dots QD is used for the photodiode layer 120, the light absorption coefficient Ab tends to decrease as the wavelength λ of light increases. That is, when the band gap Eg is large, the light absorption coefficient tends to be small. This tendency is the same as that of a bulk semiconductor layer. However, for example, when the wavelength λ of light is in the vicinity of about 940 nm, a peak Pa of the light absorption coefficient Ab appears. When the wavelength λ is about 940 nm, the light absorption coefficient Ab of the quantum dots QD is about four times that of the bulk semiconductor layer. That is, the quantum dots QD can photoelectrically convert light having a wavelength of about 940 nm with an efficiency about four times higher than that of a bulk semiconductor layer. The absorption edge is about 1040 nm, which is the same as that of the bulk semiconductor layer. Therefore, the band gap Eg shown by line Lqd is about 1.19 eV.

[0047] As described above, the quantum dots QD can absorb light of a specific wavelength (for example, about 940 nm) with high efficiency while keeping the absorption edge comparable to that of a bulk semiconductor layer.

[0048] If it is attempted to obtain the same light absorption coefficient as the peak Pa of the quantum dots QD using a bulk semiconductor layer, it is necessary to use the semiconductor layer shown by line Lbl_ref for the photodiode layer 120. In this case, the wavelength λ of the absorption edge of the semiconductor layer is about 1350 nm, and the band gap Eg is about 0.92 eV.

[0049] The magnitude of the absorption edge wavelength λ (or band gap Eg) is related to the magnitude of the dark current in the photodiode layer 120. For example, if the absorption edge wavelength λ is large (band gap Eg is small), the dark current increases. If the absorption edge wavelength λ is small (band gap Eg is large), the dark current decreases.

[0050] Figure 4 is a table showing the dark currents of bulk semiconductor layers (InGaAs) and quantum dots (InAs). Here, bulk semiconductor layers (InGaAs) and quantum dots (InAs) with the same optical absorption coefficient (or absorptivity) are compared. The bulk semiconductor layer (InGaAs) is a semiconductor layer with a quantum well structure.

[0051] For example, in an environment with a temperature of 20 degrees Celsius, if the dark current of a bulk semiconductor layer (InGaAs) is set to 1, the dark current of a quantum dot (InAs) QD with the same light absorption coefficient is 0.093. The ratio of their dark currents (InAs(QD) / InGaAs(QW)) is 0.09. In other words, by using quantum dots QD in the photodiode layer 120, the dark current can be reduced to about one-tenth that of a bulk semiconductor layer while maintaining the light absorption coefficient.

[0052] Even in environments with temperatures of 50°C and 80°C, although the overall dark current due to thermal excitation increases, quantum dots (QDs) can reduce the dark current compared to bulk semiconductor layers, similar to the situation at 20°C.

[0053] Thus, when comparing quantum dots (QDs) and bulk semiconductor layers having the same optical absorption coefficient (peak Pa), as shown by lines Lsd and Lbl_ref, the wavelength λ of the absorption edge of the quantum dots (QDs) is lower than that of the bulk semiconductor layer. In other words, the band gap Eg of the absorption edge of the quantum dots (QDs) is larger than that of the bulk semiconductor layer. Therefore, it can be seen that the dark current of quantum dots (QDs) is almost orders of magnitude smaller than that of the bulk semiconductor layer.

[0054] Furthermore, because InGaAs has a large lattice constant shift compared to GaAs, a bulk InGaAs layer can only be grown as crystals of a few tens of nanometers on a GaAs layer. For example, a bulk InGaAs layer with a thickness of approximately 10 nm ０．２ Ga ０．８ When an As semiconductor layer is formed on a GaAs layer, bulk-like In ０．２ Ga ０．８ The As semiconductor layer absorbs approximately 2.7% of light with a wavelength of approximately 940 nm.

[0055] On the other hand, to absorb approximately 2.7% of light with a wavelength of approximately 940 nm in a semiconductor layer having In(Ga)As quantum dots (QD) with a thickness of approximately 1 nm, this can be achieved by stacking three or four of these quantum dot (QD) semiconductor layers. While a light absorption rate of 2.7% is too low for a photodetector, it can be used in the photodiode layer 120 of SMI-VCSEL. In other words, by stacking multiple quantum dots (QD), a sufficient absorption rate for use in the photodiode layer 120 of SMI-VCSEL can be obtained.

[0056] Although the above embodiment described quantum dots (QD), the same can be said for the quantum wire (QD_Dash in Figure 6) of the second embodiment. This is because a peak in the light absorption coefficient also appears when the quantum wire Q_Dash is used in the photodiode layer 120.

[0057] As described above, the light-emitting device 1 according to this embodiment can increase the light absorption coefficient of the photodiode layer 120 and reduce the dark current by using quantum dots or quantum wires in the photodiode layer 120. As a result, the reliability of the SMI-VCSEL can be improved.

[0058] (Second Embodiment) Figure 5 is a cross-sectional view showing an example of the configuration of the light-emitting device 1 according to the second embodiment. In the second embodiment, a quantum nanowire Q_Dash is used for the photodiode layer 120.

[0059] Figure 6 is a plan view showing the surface of the quantum dot photodiode layer 120. The photodiode layer 120 is not a bulk layer that covers the entire surface of the semiconductor layer (e.g., a GaAs layer), but is provided in the state of a quantum nanowire Q_Dash as shown in Figure 6. The material of the quantum nanowire Q_Dash can be any of the following: InAs, InGaAs, InGaN, InGaAsP, or InSb.

[0060] As described above, even when the quantum nanowire Q_Dash is used in the photodiode layer 120, a peak in the light absorption coefficient appears, so the same effect as in the first embodiment can be obtained.

[0061] (Third Embodiment) Figure 7 is a cross-sectional view showing an example of the configuration of the light-emitting device 1 according to the third embodiment. In the third embodiment, an InP-based material is used.

[0062] For example, substrate 10 is a substrate containing n-type InP. For example, the first and third reflective layers 20a and 20c are laminates in which multiple n-type AlGaInAs layers and multiple InP layers are alternately stacked one layer each. The second reflective layer 20b is a laminate in which multiple p-type AlGaInAs layers and multiple InP layers are alternately stacked one layer each. For example, cladding layers 30a and 30b are semiconductor layers containing n-type InP. For example, the second semiconductor layer 50 is a semiconductor layer containing p-type InP.

[0063] In the third embodiment, a Buried Tunnel Junction (BTJ) 60 is provided on the second semiconductor layer 50. The BTJ 60 has a laminated structure consisting of a third semiconductor layer 61 provided on the second semiconductor layer 50 and having a higher p-type impurity concentration than the second semiconductor layer 50, and a fourth semiconductor layer 62 provided on the third semiconductor layer 61 and having a higher n-type impurity concentration than the semiconductor layer 70. The third semiconductor layer 61 is, for example, p ＋ It is composed of type InP. The fourth semiconductor layer 62 is, for example, n ＋It is composed of InP. The third semiconductor layer 61 and the fourth semiconductor layer 62 form a tunnel junction and function as a BTJ 60. Therefore, current flows through the BTJ 60, but no current flows at the junction between the second semiconductor layer 50 and the fifth semiconductor layer 70 surrounding it. As a result, the current between electrodes 100 and 110 flows concentrated in the BTJ 60 and is constricted. Consequently, the BTJ 60 can promote light emission in the active layer 40 directly beneath it. In addition, the top and side surfaces of the BTJ 60 are covered with semiconductor layer 70. At the contact surface between the side surface of the BTJ 60 and the semiconductor layer 70, light is also constricted in the BTJ 60 due to the difference in refractive index of these materials. In other words, the BTJ 60 has the functions of current constriction and light constriction. Note that in the third embodiment, the constriction layer 80 is unnecessary.

[0064] The fifth semiconductor layer 70 is provided on the second semiconductor layer 50 and the BTJ 60. The fifth semiconductor layer 70 is a semiconductor layer containing n-type InP.

[0065] The second reflector 90 is provided above the constricted layer 80 (in the Z direction). The second reflector 90 is constructed by alternately stacking multiple dielectric layers with different refractive indices one layer at a time on the semiconductor layer 70 and the electrode 110. For example, the second reflector 90 has a stacked structure of multiple dielectric materials (for example, a stacked structure of silicon oxide film and titanium oxide film). That is, the first reflector 20 is a semiconductor DBR made of semiconductor material, and the second reflector 90 is a dielectric DBR made of dielectric material.

[0066] The semiconductor layer 121 of the photodiode layer 120 is preferably made of InGaAlAs, for example, when the quantum dots QD or quantum wires Q_Dash are made of InGaAlAs on an InP substrate 10. This composition is such that it can alleviate, compensate for, or cancel the strain of the quantum dots QD or quantum wires Q_Dash.

[0067] The photodiode layer 120 and the active layer 40 may be the same as those in the first embodiment. The other components of the third embodiment may be the same as those in the first embodiment.

[0068] Therefore, although the third embodiment uses an InP-based material, the same effects as the first embodiment can be obtained. Furthermore, the third embodiment may be combined with the second embodiment and use a quantum nanowire Q_Dash for the photodiode layer 120.

[0069] In the above embodiment, light with a wavelength of 940 nm was described, but similar effects can be obtained for infrared light in the range of approximately 900 nm to approximately 1300 nm. In other words, when manufacturing an SMI-VCSEL that absorbs infrared light in the range of approximately 900 nm to approximately 1300 nm on a GaAs or InP substrate 10, by using quantum dots (QD) or quantum wires (Q_Dash) in the photodiode layer 120, crystal defects in the photodiode layer 120 can be suppressed even if the material is not lattice-matched. This makes it possible to suppress dark current caused by crystal defects while maintaining a high light absorption coefficient.

[0070] Furthermore, by using quantum dots (QD) or quantum wires (Q_Dash) for the photoelectric conversion portion of the photodiode layer 120, quantum dots (QD) or quantum wires (Q_Dash) can be crystallized and grown on the GaAa semiconductor layer 121 without being affected by lattice constant shifts. The photoelectric conversion layer of quantum dots (QD) or quantum wires (Q_Dash) has a lower absorption edge and fewer crystal defects than the bulk semiconductor layer. Therefore, the light-emitting device 1 according to this embodiment has low dark current and improved reliability.

[0071] Furthermore, in SMI-VCSELs, the light absorption rate does not need to be very high, and a few layers of quantum dot (QD) semiconductor layers are sufficient. Therefore, the light-emitting device 1 according to this embodiment is easy to manufacture.

[0072] (Examples of application to mobile devices) The technology disclosed herein (the technology) can be applied to various products. For example, the technology disclosed herein may be implemented as a device mounted on any type of mobile device such as automobiles, electric vehicles, hybrid electric vehicles, motorcycles, bicycles, personal mobility devices, airplanes, drones, ships, and robots.

[0073] Figure 8 is a block diagram showing a schematic configuration example of a vehicle control system, which is an example of a mobile control system to which the technology described herein may be applied.

[0074] The vehicle control system 12000 comprises a plurality of electronic control units connected via a communication network 12001. In the example shown in Figure 8, the vehicle control system 12000 includes a drive system control unit 12010, a body system control unit 12020, an external information detection unit 12030, an internal information detection unit 12040, and an integrated control unit 12050. The functional configuration of the integrated control unit 12050 is shown in the figure, which includes a microcomputer 12051, an audio / image output unit 12052, and an in-vehicle network interface 12053.

[0075] The drivetrain control unit 12010 controls the operation of devices related to the vehicle's drivetrain according to various programs. For example, the drivetrain control unit 12010 functions as a control device for a drivetrain generating device that generates driving force for the vehicle, such as an internal combustion engine or a drive motor; a drivetrain transmission mechanism that transmits driving force to the wheels; a steering mechanism that adjusts the steering angle of the vehicle; and a braking device that generates braking force for the vehicle.

[0076] The body system control unit 12020 controls the operation of various devices mounted on the vehicle body according to various programs. For example, the body system control unit 12020 functions as a control device for a keyless entry system, a smart key system, a power window system, or various lamps such as headlights, reverse lights, brake lights, turn signals, or fog lights. In this case, the body system control unit 12020 may receive radio waves transmitted from a portable device that replaces a key or signals from various switches. The body system control unit 12020 receives these radio waves or signals and controls the vehicle's door lock system, power window system, lamps, etc.

[0077] The external information detection unit 12030 detects information from outside the vehicle equipped with the vehicle control system 12000. For example, an imaging unit 12031 is connected to the external information detection unit 12030. The external information detection unit 12030 causes the imaging unit 12031 to capture images of the outside of the vehicle and receives the captured images. Based on the received images, the external information detection unit 12030 may perform object detection processing such as detecting people, cars, obstacles, signs, or characters on the road surface, or distance detection processing.

[0078] The imaging unit 12031 is a light sensor that receives light and outputs an electrical signal corresponding to the amount of light received. The imaging unit 12031 can output the electrical signal as an image or as distance measurement information. The light received by the imaging unit 12031 may be visible light or invisible light such as infrared light.

[0079] The in-vehicle information detection unit 12040 detects information inside the vehicle. The in-vehicle information detection unit 12040 is connected to, for example, a driver status detection unit 12041 that detects the driver's state. The driver status detection unit 12041 includes, for example, a camera that captures images of the driver, and the in-vehicle information detection unit 12040 may calculate the driver's level of fatigue or concentration, or determine whether the driver is drowsy, based on the detection information input from the driver status detection unit 12041.

[0080] The microcomputer 12051 can calculate control target values ​​for the drive force generator, steering mechanism, or braking device based on information inside and outside the vehicle acquired by the external information detection unit 12030 or the internal information detection unit 12040, and output control commands to the drive system control unit 12010. For example, the microcomputer 12051 can perform cooperative control aimed at realizing ADAS (Advanced Driver Assistance System) functions, including collision avoidance or impact mitigation, following driving based on distance between vehicles, maintaining vehicle speed, vehicle collision warning, or vehicle lane departure warning.

[0081] Furthermore, the microcomputer 12051 can perform cooperative control for purposes such as autonomous driving, where the vehicle drives autonomously without driver intervention, by controlling the drive force generating device, steering mechanism, or braking device, etc., based on information about the vehicle's surroundings acquired by the external information detection unit 12030 or the internal information detection unit 12040.

[0082] Furthermore, the microcomputer 12051 can output control commands to the body system control unit 12020 based on external information acquired by the external information detection unit 12030. For example, the microcomputer 12051 can control the headlights according to the position of a preceding or oncoming vehicle detected by the external information detection unit 12030, and perform coordinated control aimed at reducing glare, such as switching from high beams to low beams.

[0083] The audio-image output unit 12052 transmits at least one of audio and image output signals to an output device capable of visually or audibly notifying the vehicle occupants or those outside the vehicle of information. In the example in Figure 8, the output devices are exemplified as an audio speaker 12061, a display unit 12062, and an instrument panel 12063. The display unit 12062 may include, for example, at least one of an onboard display and a head-up display.

[0084] Figure 9 shows an example of the installation position of the imaging unit 12031.

[0085] In Figure 9, the imaging unit 12031 includes imaging units 12101, 12102, 12103, 12104, and 12105.

[0086] The imaging units 12101, 12102, 12103, 12104, and 12105 are installed, for example, on the front nose, side mirrors, rear bumper, back door, and the upper part of the windshield inside the vehicle 12100. The imaging unit 12101 installed on the front nose and the imaging unit 12105 installed on the upper part of the windshield inside the vehicle mainly acquire images of the front of the vehicle 12100. The imaging units 12102 and 12103 installed on the side mirrors mainly acquire images of the sides of the vehicle 12100. The imaging unit 12104 installed on the rear bumper or back door mainly acquires images of the rear of the vehicle 12100. The imaging unit 12105 installed on the upper part of the windshield inside the vehicle is mainly used for detecting preceding vehicles, pedestrians, obstacles, traffic lights, traffic signs, or lanes.

[0087] Figure 9 shows an example of the imaging range of imaging units 12101 to 12104. Imaging range 12111 indicates the imaging range of imaging unit 12101 located on the front nose, imaging ranges 12112 and 12113 indicate the imaging ranges of imaging units 12102 and 12103 located on the side mirrors, respectively, and imaging range 12114 indicates the imaging range of imaging unit 12104 located on the rear bumper or back door. For example, by superimposing the image data captured by imaging units 12101 to 12104, an overhead view image of the vehicle 12100 can be obtained.

[0088] At least one of the imaging units 12101 to 12104 may have a function for acquiring distance information. For example, at least one of the imaging units 12101 to 12104 may be a stereo camera consisting of multiple image sensors, or an image sensor having pixels for phase difference detection.

[0089] For example, the microcomputer 12051, based on distance information obtained from the imaging units 12101 to 12104, can determine the distance to each object within the imaging range 12111 to 12114 and the temporal change of this distance (relative speed to the vehicle 12100). In particular, it can extract the closest object on the vehicle 12100's path that is traveling in approximately the same direction as the vehicle 12100 at a predetermined speed (e.g., 0 km / h or more) as the preceding vehicle. Furthermore, the microcomputer 12051 can set a predetermined distance to be maintained before the preceding vehicle and perform automatic braking control (including follow-and-stop control) and automatic acceleration control (including follow-and-start control), etc. In this way, cooperative control aimed at autonomous driving, where the vehicle drives autonomously without driver intervention, can be performed.

[0090] For example, the microcomputer 12051 can use distance information obtained from imaging units 12101 to 12104 to classify and extract three-dimensional object data related to three-dimensional objects, such as motorcycles, passenger cars, large vehicles, pedestrians, utility poles, and other three-dimensional objects, and use this data for automatic obstacle avoidance. For example, the microcomputer 12051 identifies obstacles around the vehicle 12100 into obstacles that are visible to the driver of the vehicle 12100 and obstacles that are difficult to see. The microcomputer 12051 then determines the collision risk, which indicates the degree of risk of collision with each obstacle. If the collision risk is above a set value and there is a possibility of collision, the microcomputer 12051 can provide driving assistance to avoid collisions by outputting a warning to the driver via the audio speaker 12061 or the display unit 12062, or by performing forced deceleration or evasive steering via the drive system control unit 12010.

[0091] At least one of the imaging units 12101 to 12104 may be an infrared camera that detects infrared light. For example, the microcomputer 12051 can recognize pedestrians by determining whether or not pedestrians are present in the images captured by the imaging units 12101 to 12104. Such pedestrian recognition is performed, for example, by a procedure to extract feature points from the images captured by the imaging units 12101 to 12104 as infrared cameras, and a procedure to perform pattern matching on a series of feature points that indicate the contour of an object to determine whether or not it is a pedestrian. When the microcomputer 12051 determines that a pedestrian is present in the images captured by the imaging units 12101 to 12104 and recognizes a pedestrian, the audio-image output unit 12052 controls the display unit 12062 to superimpose a rectangular contour line for emphasis on the recognized pedestrian. The audio-image output unit 12052 may also control the display unit 12062 to display an icon indicating a pedestrian at a desired position.

[0092] The above describes an example of a vehicle control system to which the technology described herein may be applied. The technology described herein may be applied to, for example, the imaging unit 12031, among the configurations described above.

[0093] Furthermore, this technology can be configured as follows:

[0094] (1) A light-emitting device comprising: a substrate containing a group III-V element or a group IV element; a first reflecting portion provided on the substrate; a second reflecting portion (90) provided above the first reflecting portion; a first semiconductor layer of a first conductivity type and a second semiconductor layer of a second conductivity type provided between the first reflecting portion and the second reflecting portion; an active layer provided between the first semiconductor layer and the second semiconductor layer, which generates light of a first wavelength by applying a voltage to the first and second semiconductor layers; and a photodiode layer provided on the first reflecting portion side of the active layer, which contains a semiconductor material provided in the form of a quantum dot or quantum wire, and generates an electric charge by photoelectric conversion of the light of the first wavelength.

[0095] (2) The light-emitting device according to (1), wherein the quantum dot or quantum wire has a peak of light absorption coefficient near the first wavelength.

[0096] (3) The light-emitting apparatus according to (1) or (2), wherein the quantum dot or quantum wire contains any of InAs, InGaAs, InGaN, InGaAsP, or InSb.

[0097] (4) The light-emitting device according to any one of (1) to (3), wherein the photodiode layer includes a GaAs layer, and the quantum dot or quantum wire is provided on the GaAs layer.

[0098] (5) The light-emitting apparatus according to any one of (1) to (4), wherein the substrate is a substrate containing GaAs (gallium arsenide) or a substrate containing Ge (germanium).

[0099] (6) The light-emitting device according to any one of (1) to (5), wherein the first and second semiconductor layers are semiconductor layers containing group III-V elements, and the first reflector is a laminate of a plurality of semiconductor layers containing group III-V elements.

[0100] (7) The light-emitting apparatus according to (6), wherein the first and second semiconductor layers are semiconductor layers containing GaAs, and the first reflector is a laminate of a plurality of GaAs layers and a plurality of AlGaAs layers.

[0101] (8) The light-emitting apparatus according to any one of (1) to (5), wherein the first and second semiconductor layers are semiconductor layers containing InP.

[0102] (9) The light-emitting device according to (8), wherein the second reflecting portion is a laminate of a plurality of dielectric layers.

[0103] (10) The light-emitting device according to (8), wherein the photodiode layer includes an InGaAs layer, and the quantum dot or quantum wire is provided on the InGaAs layer.

[0104] (11) The light-emitting device according to (2), further comprising: a first electrode electrically connected to the first semiconductor layer; a second electrode electrically connected to the second semiconductor layer; and a third electrode electrically connected to the substrate.

[0105] (12) The light-emitting apparatus according to any one of (1) to (11), wherein the second semiconductor layer includes a conductive region provided in the light-emitting region and an insulating region provided around the conductive region.

[0106] (13) The light-emitting device according to any one of (1) to (11), further comprising: a third semiconductor layer provided on the second semiconductor layer between the second reflecting portion and the second semiconductor layer, having a higher concentration of impurities of the second conductivity type than the second semiconductor layer; and a fourth semiconductor layer of the first conductivity type provided on the third semiconductor layer, forming a tunnel junction with the third semiconductor layer.

[0107] (14) The light-emitting device according to (13), further comprising a fifth semiconductor layer provided on the third and fourth semiconductor layers.

[0108] (15) The light-emitting apparatus according to any one of (1) to (3), wherein the photodiode layer includes a barrier layer that mitigates, compensates for or cancels the distortion of the quantum dot or quantum wire.

[0109] Furthermore, this disclosure is not limited to the embodiments described above, and various modifications are possible without departing from the gist of this disclosure. Also, the effects described herein are merely illustrative and not limiting, and other effects may exist.

[0110] 1. Light-emitting device 10. Substrate 20. First reflector 30. First semiconductor layer 40. Active layer 50. Second semiconductor layer 80. Constriction layer 90. Second reflector 100. First electrode 105. Insulating film 110. Second electrode 115. Third electrode 120. Photodiode layer 121. Semiconductor layer QD: Quantum dot Q_Dash: Quantum wire

Claims

1. A light-emitting device comprising: a substrate containing a group III-V element or a group IV element; a first reflecting portion provided on the substrate; a second reflecting portion provided above the first reflecting portion; a first semiconductor layer of a first conductivity type and a second semiconductor layer of a second conductivity type provided between the first reflecting portion and the second reflecting portion; an active layer provided between the first semiconductor layer and the second semiconductor layer, which generates light of a first wavelength by applying a voltage to the first and second semiconductor layers; and a photodiode layer provided on the first reflecting portion side of the active layer, which contains a semiconductor material provided in the form of a quantum dot or quantum wire, and generates an electric charge by photoelectric conversion of the light of the first wavelength.

2. The light-emitting device according to claim 1, wherein the quantum dot or quantum wire has a peak in its light absorption coefficient near the first wavelength.

3. The light-emitting device according to claim 1, wherein the quantum dot or quantum wire includes any of InAs, InGaAs, InGaN, InGaAsP, or InSb.

4. The light-emitting device according to claim 1, wherein the photodiode layer includes a GaAs layer, and the quantum dot or quantum wire is provided on the GaAs layer.

5. The light-emitting device according to claim 1, wherein the substrate is a substrate containing GaAs (gallium arsenide) or a substrate containing Ge (germanium).

6. The light-emitting device according to claim 1, wherein the first and second semiconductor layers are semiconductor layers containing group III-V elements, and the first reflecting portion is a laminate of a plurality of semiconductor layers containing group III-V elements.

7. The light-emitting apparatus according to claim 6, wherein the first and second semiconductor layers are semiconductor layers containing GaAs, and the first reflective portion is a laminate of a plurality of GaAs layers and a plurality of AlGaAs layers.

8. The light-emitting apparatus according to claim 1, wherein the first and second semiconductor layers are semiconductor layers containing InP.

9. The light-emitting device according to claim 8, wherein the second reflective portion is a laminate of a plurality of dielectric layers.

10. The light-emitting device according to claim 8, wherein the photodiode layer includes an InGaAs layer, and the quantum dot or quantum wire is provided on the InGaAs layer.

11. The light-emitting device according to claim 2, further comprising: a first electrode electrically connected to the first semiconductor layer; a second electrode electrically connected to the second semiconductor layer; and a third electrode electrically connected to the substrate.

12. The light-emitting device according to claim 1, wherein the second semiconductor layer includes a conductive region provided in the light-emitting region and an insulating region provided around the conductive region.

13. The light-emitting device according to claim 1, further comprising: a third semiconductor layer provided on the second semiconductor layer between the second reflective portion and the second semiconductor layer, having a higher concentration of impurities of the second conductivity type than the second semiconductor layer; and a fourth semiconductor layer of the first conductivity type provided on the third semiconductor layer, forming a tunnel junction with the third semiconductor layer.

14. The light-emitting device according to claim 13, further comprising a fifth semiconductor layer provided on the third and fourth semiconductor layers.

15. The light-emitting apparatus according to claim 1, wherein the photodiode layer includes a barrier layer that mitigates, compensates for, or cancels the distortion of the quantum dot or quantum wire.

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