Light detection element and imaging element

Abstract

The present invention provides a light detection element (10) which has good light detection performance. A light detection element (10) according to an embodiment of the present disclosure comprises: a first conductivity type semiconductor layer (1) that is formed of a first conductivity type semiconductor; a second conductivity type semiconductor layer (6) that is formed of a second conductivity type semiconductor; a photoelectric conversion layer (2) that is sandwiched between the first conductivity type semiconductor layer (1) and the second conductivity type semiconductor layer (6); and an electrode layer (7) that is positioned on the opposite side from the photoelectric conversion layer (2) when viewed from the second conductivity type semiconductor layer (6), and is connected to the second conductivity type semiconductor layer (6). The photoelectric conversion layer (2) is a multilayer body (S2) which comprises: a semiconductor quantum dot layer (21) that contains quantum dots of a first semiconductor which has a first band gap; and a semiconductor spacer layer (22) that contains a second semiconductor which has a second band gap that is larger than the first band gap.

Description

Photodetector and image sensor

[0001] The present disclosure relates to a light detection element and an imaging element.

[0002] An imaging element has been proposed in which pixels are separated by providing a diffusion region between adjacent pixels (Patent Document 1).

[0003] International Publication No. 2018 / 212175

[0004] In a photodetector, it is desirable to improve the photodetection performance.

[0005] Therefore, it is desirable to provide a photodetector element that has good photodetection performance.

[0006] A photodetector element according to one embodiment of the present disclosure includes a first conductivity type semiconductor layer made of a first conductivity type semiconductor, a second conductivity type semiconductor layer made of a second conductivity type semiconductor, a photoelectric conversion layer sandwiched between the first conductivity type semiconductor layer and the second conductivity type semiconductor layer, and an electrode layer located on the opposite side of the photoelectric conversion layer from the second conductivity type semiconductor layer and connected to the second conductivity type semiconductor layer. Here, the photoelectric conversion layer is a stacked body including a semiconductor quantum dot layer including quantum dots of a first semiconductor having a first band gap, and a semiconductor spacer layer including a second semiconductor having a second band gap larger than the first band gap.

[0007] FIG. 1 is a cross-sectional view illustrating a schematic configuration of a photodetector according to an embodiment of the present disclosure. FIG. 2 is a plan view illustrating a planar configuration of the photoelectric conversion layer illustrated in FIG. 1. FIG. 3A is a cross-sectional view illustrating a step of a method for manufacturing the photodetector illustrated in FIG. 1. FIG. 3B is a cross-sectional view illustrating a step subsequent to FIG. 3A. FIG. 3C is a cross-sectional view illustrating a step subsequent to FIG. 3B. FIG. 3D is a cross-sectional view illustrating a step subsequent to FIG. 3C. FIG. 3E is a cross-sectional view illustrating a step subsequent to FIG. 3D. FIG. 3F is a cross-sectional view illustrating a step subsequent to FIG. 3E. FIG. 4A is a schematic diagram illustrating the potential of the photodetector illustrated in FIG. 1 and its behavior when infrared light is incident thereon. FIG. 4B is a schematic diagram illustrating the potential of the photodetector illustrated in FIG. 1 and its behavior when infrared light is incident thereon. FIG. 5A is a cross-sectional view illustrating a schematic configuration of a photodetector according to a first modified example of the present disclosure. FIG. 5B is a schematic diagram showing the potential of the photodetector element shown in FIG. 5A and illustrating behavior when infrared light and visible light are incident thereon. FIG. 6A is a cross-sectional view showing a schematic configuration of a photodetector element according to a second modified example of the present disclosure. FIG. 6B is a plan view showing a schematic planar configuration of the photoelectric conversion layer shown in FIG. 6A. FIG. 7 is a cross-sectional view showing a schematic configuration of a photodetector element according to a third modified example of the present disclosure. FIG. 8A is a cross-sectional view showing a schematic configuration of a photodetector element according to a fourth modified example of the present disclosure. FIG. 8B is a schematic diagram showing the potential of the photodetector element shown in FIG. 8A and illustrating behavior when infrared light and visible light are incident thereon. FIG. 9 is a diagram showing a schematic configuration of an image sensor having the photodetector element shown in FIG. 1. FIG. 10 is a diagram showing a schematic configuration of an electronic device to which the image sensor shown in FIG. 9 is applied. FIG. 11 is a block diagram showing a schematic configuration example of a vehicle control system. FIG. 12 is an explanatory diagram showing an example of an installation position of an image sensor.

[0008] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The description will be made in the following order: 1. One embodiment 2. Modifications 2-1. Modification 1 2-2. Modification 2 2-3. Modification 3 2-4. Modification 4 3. Application example 1 4. Application example 2 5. Application example to a moving body

[0009] <Embodiment> [Configuration of Photodetection Element 10] Fig. 1 is a cross-sectional view schematically illustrating an example of a cross-sectional configuration of a photodetection element 10 according to an embodiment of the present disclosure. The photodetection element 10 is an element capable of detecting incident light. The photodetection element 10 has a plurality of pixels P, each having a photoelectric conversion layer 2, and is configured to photoelectrically convert the incident light for each pixel P to generate a signal. The photodetection element 10 can be applied to an image sensor, a distance measurement sensor, etc.

[0010] The photodetector element 10 has a stacked structure in which a first conductivity type semiconductor layer 1, a photoelectric conversion layer 2, and a multilayer wiring layer 3 are stacked in this order. In this specification, the stacking direction of this stacked structure is defined as the Z direction. The photoelectric conversion layer 2 is provided on a front surface 1FS of the first conductivity type semiconductor layer 1. A transparent electrode layer 4 and a protective film 5 are provided in this order on a back surface 1BS of the first conductivity type semiconductor layer 1. In the photodetector element 10, light irradiated onto the protective film 5 is transmitted through the transparent electrode layer 4 and the first conductivity type semiconductor layer 1 in this order and then enters the photoelectric conversion layer 2.

[0011] (First Conduction-Type Semiconductor Layer 1) The first conductivity-type semiconductor layer 1 is provided on the light incident side of the photoelectric conversion layer 2. The first conductivity-type semiconductor layer 1 is provided, for example, in common to all pixels P. The first conductivity-type semiconductor layer 1 is provided between the photoelectric conversion layer 2 and the transparent electrode layer 4. The front surface 1FS of the first conductivity-type semiconductor layer 1 is in contact with the photoelectric conversion layer 2, and the back surface 1BS of the first conductivity-type semiconductor layer 1 is in contact with the transparent electrode layer 4. The first conductivity-type semiconductor layer 1 is a region where charges discharged from the transparent electrode layer 4 move, and is composed of, for example, a compound semiconductor containing n-type impurities. As a constituent material of the first conductivity-type semiconductor layer 1, for example, n-type InP (indium phosphide) can be used as the first conductivity-type semiconductor. Another layer may be interposed between the first conductivity-type semiconductor layer 1 and the photoelectric conversion layer 2. Examples of materials for the layer interposed between the first conductivity type semiconductor layer 1 and the photoelectric conversion layer 2 include semiconductor materials such as InAlAs, Ge, Si, GaAs, and InP, but it is preferable to select a material that is lattice-matched between the first conductivity type semiconductor layer 1 and the photoelectric conversion layer 2.

[0012] (Photoelectric Conversion Layer 2) The photoelectric conversion layer 2 absorbs light of a predetermined wavelength (e.g., light of a wavelength in the infrared region) and generates charges (electrons or holes). The photoelectric conversion layer 2 has a stacked body S2 including a semiconductor quantum dot layer 21 and a semiconductor spacer layer 22. In the stacked body S2 of the photoelectric conversion layer 2, the semiconductor quantum dot layer 21 and the semiconductor spacer layer 22 are alternately stacked multiple times in the Z direction. In the configuration example of the photodetector element 10 shown in FIG. 1, multiple stacked bodies S2 are provided in the shared photoelectric conversion layer 2. Specifically, in the configuration example of the photodetector element 10, each of the multiple pixels P includes one stacked body S2. FIG. 2 is a plan view schematically illustrating the planar configuration of the photoelectric conversion layer 2. The semiconductor quantum dot layer 21 includes a thick portion 21A and a thin portion 21B that is thinner than the thick portion 21A. In the example shown in FIG. 1, the thick portions 21A are provided discretely for each pixel P. The thin portions 21B extend along a plane perpendicular to the Z direction and are provided in common to a plurality of pixels P. The stack S2 is formed by alternately stacking thick portions 21A of the semiconductor quantum dot layer 21, which are thicker than the thin portions 21B, and semiconductor spacer layers 22 multiple times in the Z direction. As shown in FIG. 2 , the plurality of stacks S2 are separated from each other in an in-plane direction perpendicular to the Z direction. In the configuration example shown in FIGS. 1 and 2 , the plurality of thick portions 21A are embedded in one semiconductor spacer layer 22 provided in common to a plurality of pixels P. However, the uppermost semiconductor quantum dot layer 21 of each stack S2 is exposed on the surface 2FS of the photoelectric conversion layer 2.

[0013] The semiconductor quantum dot layer 21 includes a plurality of quantum dots of a first semiconductor having a first band gap. Each of the quantum dots is made of a three-dimensionally minute semiconductor (having a diameter of about several nanometers) and has the property of easily capturing electric charges. The semiconductor spacer layer 22 includes a second semiconductor having a second band gap larger than the first band gap of the first semiconductor. The first semiconductor quantum dots constituting the semiconductor quantum dot layer 21 can be a compound semiconductor that absorbs infrared light, such as InAs. The second semiconductor constituting the semiconductor spacer layer 22 can be InP or GaAs.

[0014] The semiconductor spacer layer 22 has a thickness that allows tunneling of charges in the Z direction. The semiconductor spacer layer 22 has a thickness of, for example, 1 nm or more and 3 nm or less at its thinnest portion.

[0015] The second semiconductor constituting the semiconductor spacer layer 22 preferably has the same lattice constant as the first semiconductor constituting the semiconductor quantum dot layer 21 and the first conductivity type semiconductor constituting the first conductivity type semiconductor layer 1. Furthermore, the second semiconductor constituting the semiconductor spacer layer 22 preferably has the same lattice constant as the first semiconductor constituting the semiconductor quantum dot layer 21 and the second conductivity type semiconductor layer 6 described below.

[0016] (Multilayer Wiring Layer 3) The multilayer wiring layer 3 includes a second-conductivity-type semiconductor layer 6, a counter electrode 7, vias V1 and V2, and wiring layers M1 and M2. In the configuration example of the photodetector element 10 shown in FIG. 1 , each of the multiple pixels P includes a stack S3 including the second-conductivity-type semiconductor layer 6, the counter electrode 7, the via V1, the wiring layer M1, the via V2, and the wiring layer M2, stacked in this order from the photoelectric conversion layer 2 side. The multiple stacks S3 are embedded in an insulating layer Z. The insulating layer Z is made of, for example, an inorganic insulating material. Examples of such inorganic insulating materials include silicon nitride (SiN), aluminum oxide (Al2O3), silicon oxide (SiO2), and hafnium oxide (HfO2). Each of the multiple stacks S3 further includes a semiconductor spacer layer 23 between the second-conductivity-type semiconductor layer 6 and the uppermost semiconductor quantum dot layer 21 of the photoelectric conversion layer 2. The semiconductor spacer layer 23 can be made of, for example, the second semiconductor that makes up the semiconductor spacer layer 22. Furthermore, the semiconductor spacer layer 23 has a thickness that allows charge tunneling in the Z direction. The semiconductor spacer layer 23 has a thickness of, for example, 1 nm or more and 3 nm or less at its thinnest portion.

[0017] In the exemplary configuration of the photodetector element 10 shown in FIG. 1 , a plurality of second-conductivity-type semiconductor layers 6, each separated from the other, are provided for one first-conductivity-type semiconductor layer 1. A plurality of counter electrodes 7 are provided corresponding to each of the second-conductivity-type semiconductor layers 6, and each of the counter electrodes 7 is electrically connected to each of the second-conductivity-type semiconductor layers 6. The second-conductivity-type semiconductor layer 6, the counter electrode 7, the via V1, the wiring layer M1, the via V2, and the wiring layer M2 are electrically connected to each other. The wiring layer M2 is exposed on the surface 3FS of the multilayer wiring layer 3 and serves as a terminal for connection to the outside. The vias V1 and V2 and the wiring layers M1 and M2 may be made of a highly conductive material such as Cu (copper).

[0018] The second conductivity type semiconductor layers 6 are provided at intervals for each pixel P. The second conductivity type semiconductor layers 6 are regions where charges generated in the photoelectric conversion layer 2 move, and are, for example, regions containing p-type impurities (p-type impurity regions). The second conductivity type semiconductor layers 6 may be made of, for example, p-type indium phosphide (InP) as a second conductivity type semiconductor. The band gaps of the first conductivity type semiconductor constituting the first conductivity type semiconductor layer 1 and the second conductivity type semiconductor constituting the second conductivity type semiconductor layer 6 are preferably both larger than the first band gap of the first semiconductor constituting the quantum dots in the semiconductor quantum dot layer 21.

[0019] The counter electrode 7, which serves as a second electrode, is a readout electrode to which a voltage is supplied for reading out charges (holes or electrons) generated in the photoelectric conversion layer 2. The counter electrode 7 is provided for each pixel P so as to face the surface 2FS of the photoelectric conversion layer 2 across the second conductivity-type semiconductor layer 6. That is, the counter electrode 7 is located on the opposite side of the photoelectric conversion layer 2 from the second conductivity-type semiconductor layer 6. The counter electrode 7 is connected to a pixel circuit for signal readout via, for example, via vias V1 and V2 and wiring layers M1 and M2. The counter electrode 7 is connected to the semiconductor quantum dot layer 21 exposed on the surface 2FS via a semiconductor spacer layer 22. The counter electrode 7 has a planar shape of, for example, a rectangle. An insulating layer Z is filled between adjacent counter electrodes 7.

[0020] The counter electrode 7 is made of, for example, any one of Ti (titanium), W (tungsten), TiN (titanium nitride), Pt (platinum), Au (gold), Cu (copper), Ge (germanium), Pd (palladium), Zn (zinc), Ni (nickel), In (indium), and Al (aluminum), or an alloy containing at least one of these. The counter electrode 7 may be a single film of such a constituent material, or may be a laminated film consisting of two or more layers.

[0021] (Transparent Electrode Layer 4) The transparent electrode layer 4 as a first electrode is provided, for example, as a common electrode for each pixel P, covering the entire back surface 2BS (light incident surface) of the photoelectric conversion layer 2 via the first conductivity type semiconductor layer 1. The transparent electrode layer 4 is used to discharge charges generated in the photoelectric conversion layer 2 that are not used as signal charges. For example, when electrons are read out as signal charges from the counter electrode 7, holes, for example, can be discharged through the transparent electrode layer 4. The transparent electrode layer 4 is made of a transparent conductive film that can transmit incident light such as infrared light, and has a transmittance of 50% or more for light with a wavelength of 1.6 μm (1600 nm). Examples of materials that can be used for the transparent electrode layer 4 include ITO (Indium Tin Oxide) and ITiO (In2O3-TiO2).

[0022] (Protective Film 5) The protective film 5 is a passivation film that physically and chemically protects the transparent electrode layer 4, the first conductivity type semiconductor layer 1, the photoelectric conversion layer 2, etc. The protective film 5 is made of a transparent resin that can transmit incident light such as infrared rays.

[0023] [Method of Manufacturing the Photodetector 10] The photodetector 10 can be manufactured, for example, as follows: Figures 3A to 3F show the manufacturing process of the photodetector 10 in order of steps.

[0024] First, as shown in FIG. 3A , a compound semiconductor stack S11 is formed. Specifically, a semiconductor substrate 11 made of, for example, InP is prepared, and then a second conductivity-type semiconductor layer 6 made of, for example, p-type InP is formed on the semiconductor substrate 11. Next, a semiconductor spacer layer 23 is formed to cover the second conductivity-type semiconductor layer 6. Furthermore, a semiconductor quantum dot layer 21 made of InAs and a semiconductor spacer layer 22 made of InP or GaAs are alternately stacked to obtain a photoelectric conversion layer 2. Then, a first conductivity-type semiconductor layer 1 made of n-type InP is stacked to cover the photoelectric conversion layer 2, thereby obtaining the stack S11. At this time, one stack S2 is formed for each region that becomes one pixel P. The stack S11 can be formed by an epitaxy method such as molecular beam epitaxy (MBE) or migration-enhanced epitaxy (MEE). The laminate S11 may be formed by a method such as MOCVD (Metal Organic Chemical Vapor Deposition), hydride vapor phase epitaxy (HVPE) in which halogen contributes to transport or reaction, ALD (Atomic Layer Deposition), or plasma-assisted physical vapor deposition (PPD). Furthermore, an adhesive layer 12A is applied to the back surface 1BS of the first conductivity type semiconductor layer 1.

[0025] 3B, the stacked body S11 shown in FIG. 3A is turned upside down and bonded to a silicon substrate 13 via an adhesive layer 12. Specifically, an adhesive layer 12B is formed on the surface of the silicon substrate 13, and then the adhesive layer 12A and the adhesive layer 12B are placed opposite each other and bonded together to form an integrated adhesive layer 12.

[0026] Thereafter, the semiconductor substrate 11 is entirely removed from the stacked body S11 by etching, and the second conductivity type semiconductor layer 6 and the semiconductor spacer layer 23 are selectively removed, thereby forming a plurality of stacked bodies of the semiconductor spacer layer 23 and the second conductivity type semiconductor layer 6 as shown in Fig. 3C. At this time, one stacked body of the semiconductor spacer layer 23 and the second conductivity type semiconductor layer 6 is formed for each region that becomes one pixel P.

[0027] Next, as shown in FIG. 3D, the counter electrodes 7 are formed on the plurality of second conductivity type semiconductor layers 6, respectively.

[0028] 3E, vias V1, wiring layers M1, vias V2, and wiring layers M2 embedded in the insulating layer Z are formed on the plurality of counter electrodes 7. At this time, a circuit board including a readout circuit may be separately attached.

[0029] 3F, the silicon substrate 13 is peeled off from the laminate S11, and the adhesive layer 12 is removed to expose the rear surface 1BS of the first conductivity type semiconductor layer 1. Thereafter, the transparent electrode layer 4 and the protective film 5 are sequentially stacked to cover the rear surface 1BS. This completes the photodetector element 10 shown in FIG.

[0030] [Operation of Photodetection Element 10] In the photodetection element 10, light (e.g., light with a wavelength in the infrared region) is incident on the photoelectric conversion layer 2 through the protective film 5 and the transparent electrode layer 4, and the light incident on the photoelectric conversion layer 2 is absorbed by the photoelectric conversion layer 2. As a result, pairs of holes and electrons are generated in the photoelectric conversion layer 2, i.e., photoelectric conversion occurs. At this time, for example, when a predetermined voltage is applied to the counter electrode 7, a potential gradient is generated in the photoelectric conversion layer 2, and one of the generated charges migrates to the second conductivity type semiconductor layer 6 as a signal charge and is then collected from the second conductivity type semiconductor layer 6 to the counter electrode 7. This signal charge is read out by a readout circuit in the multilayer wiring layer 3.

[0031] [Functions and Effects of Photodetector Element 10] In the photodetector element 10 according to an embodiment of the present disclosure, the photoelectric conversion layer 2 including the stacked body S2 having the semiconductor quantum dot layer 21 and the semiconductor spacer layer 22 is sandwiched between the first conductivity type semiconductor layer 1 and the second conductivity type semiconductor layer 6. Therefore, charges generated when light transmitted through the first conductivity type semiconductor layer 1 is incident on the semiconductor quantum dot layer 21 can easily pass through the semiconductor spacer layer 22 and reach the second conductivity type semiconductor layer 6.

[0032] 4A and 4B are schematic diagrams showing the potential in the photodetector element 10 shown in FIG. 1 . FIG. 4A shows the behavior of charges when infrared light is incident on the photoelectric conversion layer 2, and FIG. 4B shows the behavior of charges when visible light is incident on the photoelectric conversion layer 2. As shown in FIG. 4A , when infrared light is incident on the photoelectric conversion layer 2, charges (holes and electrons) are generated in the semiconductor quantum dot layer 21. The generated holes and electrons tunnel through the semiconductor spacer layer 22, which has a higher potential than the semiconductor quantum dot layer 21, with the holes reaching, for example, the second conductivity type semiconductor layer 6 and the electrons reaching the first conductivity type semiconductor layer 1. Furthermore, as shown in FIG. 4B , when visible light is incident on the photoelectric conversion layer 2, charges (holes and electrons) are generated in the semiconductor spacer layer 22. The generated holes and electrons move to the semiconductor quantum dot layer 21, which has a potential lower than that of the semiconductor spacer layer 22, and then tunnel through the semiconductor spacer layer 22. The holes reach, for example, the second conductivity type semiconductor layer 6, and the electrons reach the first conductivity type semiconductor layer 1. This charge tunneling is possible because quantum dots in the multiple semiconductor quantum dot layers 21 stacked on either side of the semiconductor spacer layer 22 are electronically coupled due to the seepage of wave functions, forming a so-called miniband. In particular, tunneling is more likely to occur when the thinnest portion of the semiconductor spacer layer 22 has a thickness of 1 nm to 3 nm. Note that the slight difference between the lattice constant of the first semiconductor constituting the semiconductor quantum dot layer 21 and the lattice constant of the second semiconductor constituting the semiconductor spacer layer 22 allows for the fine quantum dots in the semiconductor quantum dot layer 21 to be well formed by self-formation of the SK mode.

[0033] In this way, in the photodetector element 10, charges move along the stacking direction (Z direction) of the semiconductor quantum dot layer 21 and the semiconductor spacer layer 22 in the stack S2 provided for each pixel P. This prevents charges generated in the photoelectric conversion layer 2 of a pixel P from leaking to other pixels P adjacent to that pixel P. This makes it possible to prevent crosstalk from occurring and to exhibit good photodetection performance.

[0034] Furthermore, in the photodetector element 10, leakage of electric charge to adjacent pixels P can be prevented without providing an isolation structure such as a partition between the plurality of pixels P, so the photoelectric conversion layer 2 can be provided without gaps. Therefore, light receiving sensitivity can be improved compared to the case where the above-mentioned isolation structure between pixels is provided.

[0035] Modifications and application examples of the above embodiment will be described below, but in the following description, the same components as those in the above embodiment will be given the same reference numerals and their description will be omitted as appropriate.

[0036] <Modification 1> Figure 5A is a cross-sectional view schematically illustrating the general configuration of a photodetector element 10A according to a first modification of the present disclosure. In the photodetector element 10A, a p-type impurity diffusion layer 6A is provided instead of the second conductivity type semiconductor layer 6. The impurity diffusion layer 6A is in contact with the semiconductor quantum dot layer 21 located in the uppermost layer of the stack S2 of the photoelectric conversion layer 2. Except for the above points, the configuration of the photodetector element 10A is substantially the same as the configuration of the photodetector element 10.

[0037] The photodetector element 10A of this modification can be expected to have the same effects as the photodetector element 10 of the above embodiment. In particular, in the photodetector element 10A, the impurity diffusion layer 6A serving as the second conductivity type semiconductor layer is in direct contact with the semiconductor quantum dot layer 21. Therefore, as shown in FIG. 5B , the barrier between the semiconductor quantum dot layer 21 and the counter electrode 7 is lower than in the photodetector element 10, making it easier for charges (e.g., holes) to reach the counter electrode 7 from the semiconductor quantum dot layer 21. This further improves sensitivity. Note that FIG. 5B is a schematic diagram showing the potential in the photodetector element 10A shown in FIG. 5A and its behavior when infrared light and visible light are incident thereon.

[0038] <Modification 2> FIG. 6A is a cross-sectional view schematically illustrating the general configuration of a photodetector element 10B according to a second modification of the present disclosure. FIG. 6B is a plan view schematically illustrating the planar configuration of a photoelectric conversion layer 2B in the photodetector element 10B. As shown in FIGS. 6A and 6B , in the photodetector element 10B, multiple stacked bodies S2 are provided for each of multiple second conductivity-type semiconductor layers 6. Except for the above-mentioned points, the configuration of the photodetector element 10B is substantially the same as the configuration of the photodetector element 10. Note that FIGS. 6A and 6B illustrate an example in which four stacked bodies S2 arranged in two rows and two columns are provided per pixel P, but the present disclosure is not limited to this. Two, three, or five or more stacked bodies S2 may be provided per pixel P. The layout of the stacked bodies S2 can be selected arbitrarily.

[0039] The photodetector element 10B of this modified example is also expected to have the same effects as the photodetector element 10 of the above embodiment. In particular, in the photodetector element 10B, multiple stacked bodies S2 are provided in the photoelectric conversion layer 2 corresponding to one pixel P, which improves the probability that the quantum dots will capture the charges generated in the photoelectric conversion layer 2. This makes it possible to more effectively prevent crosstalk from occurring, and to achieve better photodetection performance.

[0040] <Modification 3> Figure 7 is a cross-sectional view schematically illustrating the general configuration of a photodetector element 10C according to a third modification of the present disclosure. As shown in Figure 7, in the photodetector element 10C, some of the semiconductor spacer layers 22 constituting the stack S2 of the photoelectric conversion layer 2 are replaced with strain relaxation layers 8. Except for the above-mentioned points, the configuration of the photodetector element 10C is substantially the same as the configuration of the photodetector element 10. The strain relaxation layer 8 is made of a semiconductor having a lattice constant between the lattice constant of the first semiconductor of the semiconductor quantum dot layer 21 and the lattice constant of the second semiconductor of the semiconductor spacer layer 22. Specifically, when the quantum dots of the first semiconductor of the semiconductor quantum dot layer 21 are InAs and the second semiconductor of the semiconductor spacer layer 22 are GaAs, for example, InGaAs can be used as the material for the strain relaxation layer 8. Alternatively, as a constituent material of the strain relaxation layer 8, for example, when the first semiconductor quantum dots of the semiconductor quantum dot layer 21 are InAs and the second semiconductor of the semiconductor spacer layer 22 is InP, a semiconductor such as InGaAs with an indium composition of greater than 53% can be used.

[0041] The photodetector element 10C of this modified example can be expected to have the same effects as the photodetector element 10 of the above embodiment. In particular, in the photodetector element 10C, the strain relaxation layer 8 is inserted into the photoelectric conversion layer 2, which improves the crystallinity of the photoelectric conversion layer 2 and further improves the readout characteristics, such as suppressing the generation of dark current.

[0042] <Modification 4> Fig. 8A is a cross-sectional view schematically illustrating the general configuration of a photodetector element 10D according to a fourth modification of the present disclosure. Fig. 8B is a schematic diagram illustrating the potential of the photodetector element 10D illustrated in Fig. 8A and its behavior when infrared light and visible light are incident thereon. As illustrated in Fig. 8A, in the photodetector element 10D, a barrier layer 9 is further added between the second conductivity-type semiconductor layer 6 and the photoelectric conversion layer 2. Except for the above-mentioned points, the configuration of the photodetector element 10D is substantially the same as that of the photodetector element 10. The barrier layer 9 disposed between the first conductivity-type semiconductor layer 1 and the second conductivity-type semiconductor layer 6 is a semiconductor layer that prevents the passage of either holes or electrons. In other words, the barrier layer 9 acts as a barrier only against charges of the opposite sign to the charge to be read. For example, when holes are read out from the counter electrode 7, the barrier layer 9 can be made of a semiconductor material whose bottom of the conduction band is sufficiently higher than the potential of the semiconductor spacer layer 22 and the potential of the semiconductor quantum dot layer 21 and whose top of the valence band is equivalent to the potential of the semiconductor quantum dot layer 21. When electrons are read out as signal charges, the barrier layer 9 can be made of a semiconductor material whose top of the valence band is sufficiently lower than the potential of the semiconductor quantum dot layer 21 and the potential of the semiconductor spacer layer 22 and whose bottom of the conduction band is equivalent to the potential of the semiconductor quantum dot layer 21. For example, when the first semiconductor of the semiconductor quantum dot layer 21 is InAs and the second semiconductor of the semiconductor spacer layer 22 is GaAs, or when the first semiconductor of the semiconductor quantum dot layer 21 is InAs and the second semiconductor of the semiconductor spacer layer 22 is InP, p-type AlGaAs can be used as the semiconductor constituting the barrier layer 9.

[0043] The photodetector element 10D of this modified example is expected to have the same effects as the photodetector element 10 of the above embodiment. In particular, the photodetector element 10D has a barrier layer 9, which can suppress recombination of electrons and holes generated in the photoelectric conversion layer 2. Therefore, the photodetector element 10D has improved photodetection sensitivity compared to the photodetector element 10.

[0044] 9 shows the functional configuration of an image sensor 100 that uses the photodetector element 10 (or the photodetector elements 10A to 10D of Modifications 1 to 4) described in the above-described embodiment and the like. The image sensor 100 is, for example, an infrared image sensor, and has, on a substrate 20, for example, a pixel unit 1a and a peripheral circuit unit 230 that drives the pixel unit 1a. The peripheral circuit unit 230 has, for example, a row scanning unit 231, a horizontal selection unit 233, a column scanning unit 234, and a system control unit 232.

[0045] The pixel section 1a has a plurality of pixels P arranged two-dimensionally, for example, in a matrix. A pixel drive line Lread (e.g., a row selection line and a reset control line) is wired to each pixel row in the pixels P, and a vertical signal line Lsig is wired to each pixel column in the pixels P. The pixel drive line Lread transmits a drive signal for reading out signals from the pixels P. One end of the pixel drive line Lread is connected to an output terminal of the row scanning section 231 corresponding to each row.

[0046] The row scanning unit 231 is a pixel driving unit that is configured with a shift register, an address decoder, etc., and drives each pixel P of the pixel unit 1a, for example, row by row. Signals output from each pixel P of a pixel row selected and scanned by the row scanning unit 231 are supplied to the horizontal selection unit 233 through each vertical signal line Lsig. The horizontal selection unit 233 is configured with an amplifier, a horizontal selection switch, etc., provided for each vertical signal line Lsig.

[0047] The column scanning unit 234 is configured with a shift register, an address decoder, etc., and scans and sequentially drives each horizontal selection switch of the horizontal selection unit 233. Through the selective scanning by this column scanning unit 234, signals of each pixel transmitted through each vertical signal line Lsig are output in sequence to a horizontal signal line 235, and input through the horizontal signal line 235 to a signal processing unit (not shown) or the like.

[0048] The system control unit 232 receives externally applied clocks, data instructing the operation mode, and the like, and outputs data such as internal information of the image sensor 100. The system control unit 232 further has a timing generator that generates various timing signals, and performs drive control of the row scanning unit 231, horizontal selection unit 233, column scanning unit 234, and the like based on the various timing signals generated by the timing generator.

[0049] 4. Application Example 2 The image sensor 100 described above can be applied to various types of electronic devices, such as a camera capable of capturing images in the infrared region. Fig. 10 shows a schematic configuration of an electronic device 102 (camera) as an example. The electronic device 102 is, for example, a camera capable of capturing still images or moving images, and includes the image sensor 100, an optical system (optical lens) 310, a shutter device 311, a driver 313 that drives the image sensor 100 and the shutter device 311, and a signal processor 312.

[0050] The optical system 310 guides image light (incident light) from a subject to the image sensor 100. This optical system 310 may be composed of multiple optical lenses. The shutter device 311 controls the light irradiation period and light blocking period for the image sensor 100. The drive unit 313 controls the transfer operation of the image sensor 100 and the shutter operation of the shutter device 311. The signal processing unit 312 performs various signal processing on the signal output from the image sensor 100. The video signal Dout after signal processing is stored in a storage medium such as a memory, or is output to a monitor, etc.

[0051] Furthermore, the light detection element 10 (or the light detection elements 10A to 10D) described in the present embodiment and the like can also be applied to the following electronic devices (a capsule endoscope 10100 and a moving object such as a vehicle).

[0052] 5. Application Examples to Mobile Bodies The technology according to the present disclosure (the present technology) can be applied to various products. For example, the technology according to the present disclosure may be realized as a device mounted on any type of mobile body, such as an automobile, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, personal mobility, an airplane, a drone, a ship, or a robot.

[0053] FIG. 11 is a block diagram showing a schematic configuration example of a vehicle control system, which is an example of a mobile object control system to which the technology according to the present disclosure can be applied.

[0054] The vehicle control system 12000 includes a plurality of electronic control units connected via a communication network 12001. In the example shown in Fig. 11, the vehicle control system 12000 includes a drive system control unit 12010, a body system control unit 12020, an outside-vehicle information detection unit 12030, an inside-vehicle information detection unit 12040, and an integrated control unit 12050. Also shown as functional components of the integrated control unit 12050 are a microcomputer 12051, an audio / video output unit 12052, and an in-vehicle network I / F (interface) 12053.

[0055] The drivetrain control unit 12010 controls the operation of devices related to the drivetrain of the vehicle in accordance with various programs. For example, the drivetrain control unit 12010 functions as a control device for a drive force generating device for generating a drive force of the vehicle, such as an internal combustion engine or a drive motor, a drive force transmission mechanism for transmitting the drive force to the wheels, a steering mechanism for adjusting the steering angle of the vehicle, and a braking device for generating a braking force of the vehicle.

[0056] The body system control unit 12020 controls the operation of various devices equipped in 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 device, or various lamps such as headlamps, backup lamps, brake lamps, turn signals, and fog lamps. In this case, radio waves transmitted from a portable device that serves as a key or signals from various switches can be input to the body system control unit 12020. The body system control unit 12020 receives these radio waves or signals and controls the vehicle's door lock device, power window device, lamps, etc.

[0057] The outside-vehicle information detection unit 12030 detects information outside the vehicle equipped with the vehicle control system 12000. For example, an imaging unit 12031 is connected to the outside-vehicle information detection unit 12030. The outside-vehicle information detection unit 12030 causes the imaging unit 12031 to capture images outside the vehicle and receives the captured images. The outside-vehicle information detection unit 12030 may perform object detection processing or distance detection processing for people, cars, obstacles, signs, characters on the road surface, etc. based on the received images.

[0058] The imaging unit 12031 is an optical 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.

[0059] The in-vehicle information detection unit 12040 detects information inside the vehicle. For example, a driver state detection unit 12041 that detects the state of the driver is connected to the in-vehicle information detection unit 12040. The driver state detection unit 12041 includes, for example, a camera that captures an image of the driver, and the in-vehicle information detection unit 12040 may calculate the degree of fatigue or concentration of the driver based on the detection information input from the driver state detection unit 12041, or may determine whether the driver is dozing off.

[0060] The microcomputer 12051 can calculate control target values ​​for the driving force generating device, steering mechanism, or braking device based on the information inside and outside the vehicle acquired by the outside-vehicle information detection unit 12030 or the inside-vehicle 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 the functions of an ADAS (Advanced Driver Assistance System), including vehicle collision avoidance or impact mitigation, following driving based on the distance between vehicles, maintaining vehicle speed, vehicle collision warning, vehicle lane departure warning, etc.

[0061] In addition, the microcomputer 12051 can perform cooperative control for the purpose of autonomous driving, which allows the vehicle to travel autonomously without relying on driver operation, by controlling the driving force generating device, steering mechanism, braking device, etc. based on information about the surroundings of the vehicle obtained by the outside vehicle information detection unit 12030 or the inside vehicle information detection unit 12040.

[0062] Furthermore, the microcomputer 12051 can output a control command to the body system control unit 12020 based on the information outside the vehicle acquired by the outside information detection unit 12030. For example, the microcomputer 12051 can control the headlamps according to the position of a preceding vehicle or an oncoming vehicle detected by the outside information detection unit 12030, and perform cooperative control aimed at preventing glare, such as switching from high beams to low beams.

[0063] The audio / video output unit 12052 transmits at least one of audio and video output signals to an output device capable of visually or audibly notifying the passengers of the vehicle or the outside of the vehicle of information. In the example of Fig. 14, the output devices are exemplified by 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 on-board display and a head-up display.

[0064] FIG. 12 is a diagram showing an example of the installation position of the imaging unit 12031.

[0065] In FIG. 12, the imaging unit 12031 includes imaging units 12101, 12102, 12103, 12104, and 12105.

[0066] The imaging units 12101, 12102, 12103, 12104, and 12105 are provided, for example, at positions such as the front nose, side mirrors, rear bumper, back door, and the top of the windshield inside the vehicle cabin of the vehicle 12100. The imaging unit 12101 provided on the front nose and the imaging unit 12105 provided on the top of the windshield inside the vehicle cabin mainly acquire images of the front of the vehicle 12100. The imaging units 12102 and 12103 provided on the side mirrors mainly acquire images of the sides of the vehicle 12100. The imaging unit 12104 provided on the rear bumper or back door mainly acquires images of the rear of the vehicle 12100. The imaging unit 12105 provided on the top of the windshield inside the vehicle cabin is mainly used to detect preceding vehicles, pedestrians, obstacles, traffic lights, traffic signs, lanes, etc.

[0067] 12 shows an example of the imaging ranges of the imaging units 12101 to 12104. Imaging range 12111 indicates the imaging range of the imaging unit 12101 provided on the front nose, imaging ranges 12112 and 12113 indicate the imaging ranges of the imaging units 12102 and 12103 provided on the side mirrors, respectively, and imaging range 12114 indicates the imaging range of the imaging unit 12104 provided on the rear bumper or back door. For example, by overlaying the image data captured by the imaging units 12101 to 12104, an overhead image of the vehicle 12100 viewed from above can be obtained.

[0068] At least one of the image capturing units 12101 to 12104 may have a function of acquiring distance information. For example, at least one of the image capturing units 12101 to 12104 may be a stereo camera made up of multiple image capturing elements, or may be an image capturing element having pixels for phase difference detection.

[0069] For example, based on the distance information obtained from the imaging units 12101 to 12104, the microcomputer 12051 can calculate the distance to each three-dimensional object within the imaging ranges 12111 to 12114 and the change in this distance over time (relative speed with respect to the vehicle 12100), thereby extracting as a preceding vehicle, in particular, the three-dimensional object that is the closest three-dimensional object on the path of the vehicle 12100 and traveling in approximately the same direction as the vehicle 12100 at a predetermined speed (e.g., 0 km / h or higher). Furthermore, the microcomputer 12051 can set a vehicle-to-vehicle distance to be maintained in advance in front of the preceding vehicle, and perform automatic braking control (including follow-up stop control), automatic acceleration control (including follow-up start control), etc. In this way, cooperative control can be performed for the purpose of autonomous driving, which runs autonomously without relying on driver operation.

[0070] For example, the microcomputer 12051 classifies and extracts three-dimensional object data regarding three-dimensional objects into two-wheeled vehicles, ordinary vehicles, large vehicles, pedestrians, utility poles, and other three-dimensional objects based on distance information obtained from the imaging units 12101 to 12104, and can use the data for automatic obstacle avoidance. For example, the microcomputer 12051 distinguishes 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 a collision risk that indicates the risk of collision with each obstacle, and when the collision risk is equal to or greater than a set value and a collision is possible, the microcomputer 12051 can provide driving assistance for collision avoidance by outputting an alarm to the driver via the audio speaker 12061 or the display unit 12062, or by performing forced deceleration or avoidance steering via the drive system control unit 12010.

[0071] At least one of the image capturing units 12101 to 12104 may be an infrared camera that detects infrared rays. For example, the microcomputer 12051 can recognize a pedestrian by determining whether a pedestrian is present in the images captured by the image capturing units 12101 to 12104. Such pedestrian recognition is performed, for example, by extracting feature points from the images captured by the image capturing units 12101 to 12104 as infrared cameras and performing pattern matching on a series of feature points that indicate the outline of an object to determine whether the object is a pedestrian. When the microcomputer 12051 determines that a pedestrian is present in the images captured by the image capturing units 12101 to 12104 and recognizes the pedestrian, the audio / image output unit 12052 controls the display unit 12062 to superimpose a rectangular outline on the recognized pedestrian for emphasis. The audio / image output unit 12052 may also control the display unit 12062 to display an icon or the like indicating the pedestrian at a desired position.

[0072] The above describes an example of a vehicle control system to which the technology according to the present disclosure can be applied. The technology according to the present disclosure can be applied to, for example, the image capturing unit 12031 among the components described above. By applying the technology according to the present disclosure to the image capturing unit 12031, it is possible to obtain a captured image that is easier to see, thereby reducing driver fatigue.

[0073] Although the present technology has been described above with reference to embodiments and modified examples, the present technology is not limited to the above embodiments and can be modified in various ways. For example, the layer configuration of the photodetector element described in the above embodiments is an example, and other layers may be included. Furthermore, the material and thickness of each layer are also an example and are not limited to those described above.

[0074] In one embodiment of the photodetector element of the present disclosure, a photoelectric conversion layer including a stack having a semiconductor quantum dot layer and a semiconductor spacer layer is sandwiched between a first conductivity type semiconductor layer and a second conductivity type semiconductor layer. Therefore, charges generated when light transmitted through the first conductivity type semiconductor layer is incident on the semiconductor quantum dot layer move along the stacking direction of the semiconductor quantum dot layer and the semiconductor spacer layer. This prevents charges generated in the photoelectric conversion layer of a pixel from leaking to other pixels adjacent to that pixel. This prevents crosstalk from occurring, enabling excellent photodetection performance.

[0075] Note that the effects described in this specification are merely examples and are not limited to those described, and other effects may also be present. Furthermore, the present disclosure may also have the following configurations. <1> A photodetector element comprising: a first electrode; a first conductivity type semiconductor layer provided on the first electrode and made of a first conductivity type semiconductor; a second conductivity type semiconductor layer made of a second conductivity type semiconductor; a photoelectric conversion layer sandwiched between the first conductivity type semiconductor layer and the second conductivity type semiconductor layer; and a second electrode located on the opposite side of the photoelectric conversion layer from the second conductivity type semiconductor layer and connected to the second conductivity type semiconductor layer, wherein the photoelectric conversion layer is a stacked body including a semiconductor quantum dot layer including quantum dots of a first semiconductor having a first band gap and a semiconductor spacer layer including a second semiconductor having a second band gap larger than the first band gap. <2> The photodetector according to <1> above, wherein a plurality of the second conductivity type semiconductor layers are provided for one of the first conductivity type semiconductor layers, the plurality of second electrodes are provided corresponding to the plurality of second conductivity type semiconductor layers, and the plurality of second electrodes are electrically connected to the plurality of second conductivity type semiconductor layers. <3> The photodetector according to <2> above, wherein the photoelectric conversion layer includes a plurality of the stacked bodies separated from each other in an in-plane direction orthogonal to a stacking direction of the semiconductor quantum dot layer and the semiconductor spacer layer, and one or a plurality of the stacked bodies is provided for each of the plurality of second conductivity type semiconductor layers. <4> The photodetector according to any one of <1> to <3> above, wherein the band gap of the first conductivity type semiconductor and the band gap of the second conductivity type semiconductor are both larger than the first band gap. <5> The photodetector according to any one of <1> to <4> above, wherein the second semiconductor of the semiconductor spacer layer has a lattice constant that is the same as the lattice constant of the first semiconductor of the semiconductor quantum dot layer, and the lattice constant of both the first conductivity type semiconductor and the second conductivity type semiconductor. <6> The photodetector according to any one of <1> to <5> above, wherein the thinnest portion of the semiconductor spacer layer has a thickness of 1 nm or more and 3 nm or less.<7> The photodetector according to any one of <1> to <6>, wherein the second conductivity type semiconductor layer is a diffusion layer in contact with the semiconductor quantum dot layer. <8> The photodetector according to any one of <1> to <7>, wherein the photoelectric conversion layer further includes an additional semiconductor layer made of a third semiconductor having a lattice constant between the lattice constants of the first semiconductor and the second semiconductor. <9> The photodetector according to any one of <1> to <8>, further including a barrier layer disposed between the first conductivity type semiconductor layer and the second conductivity type semiconductor layer, which prevents the passage of either holes or electrons. <10> The photodetector according to claim 1, wherein the first semiconductor is a compound semiconductor that absorbs infrared light. <11> An imaging element comprising: a first electrode; a first conductivity type semiconductor layer provided on the first electrode and made of a first conductivity type semiconductor; a second conductivity type semiconductor layer made of a second conductivity type semiconductor; a photoelectric conversion layer sandwiched between the first conductivity type semiconductor layer and the second conductivity type semiconductor layer; and a second electrode located on the opposite side of the photoelectric conversion layer as viewed from the second conductivity type semiconductor layer and connected to the second conductivity type semiconductor layer, wherein the photoelectric conversion layer is a laminated body having a semiconductor quantum dot layer including quantum dots of a first semiconductor having a first band gap, and a semiconductor spacer layer including a second semiconductor having a second band gap larger than the first band gap.

Claims

1. A photodetector comprising: a first electrode; a first conductivity type semiconductor layer provided on the first electrode and made of a first conductivity type semiconductor; a second conductivity type semiconductor layer made of a second conductivity type semiconductor; a photoelectric conversion layer sandwiched between the first conductivity type semiconductor layer and the second conductivity type semiconductor layer; and a second electrode located on the opposite side of the photoelectric conversion layer as viewed from the second conductivity type semiconductor layer and connected to the second conductivity type semiconductor layer, wherein the photoelectric conversion layer is a laminate having a semiconductor quantum dot layer including quantum dots of a first semiconductor having a first band gap, and a semiconductor spacer layer including a second semiconductor having a second band gap larger than the first band gap.

2. The photodetector element according to claim 1, wherein a plurality of said second conductivity type semiconductor layers separated from each other are provided for one of said first conductivity type semiconductor layers, a plurality of said second electrodes are provided corresponding to each of said second conductivity type semiconductor layers, and each of said second electrodes and each of said second conductivity type semiconductor layers are electrically connected to each other.

3. The photodetector element according to claim 2, wherein the photoelectric conversion layer includes a plurality of the laminated bodies separated from each other in an in-plane direction perpendicular to a stacking direction of the semiconductor quantum dot layer and the semiconductor spacer layer, and one or a plurality of the laminated bodies are provided for each of the plurality of second conductivity type semiconductor layers.

4. The photodetector element according to claim 1, wherein the band gap of the first conductive type semiconductor and the band gap of the second conductive type semiconductor are both larger than the first band gap.

5. The photodetector according to claim 1, wherein the second semiconductor of the semiconductor spacer layer has the same lattice constant as both the lattice constant of the first semiconductor of the semiconductor quantum dot layer and the lattice constant of the second conductivity type semiconductor.

6. The photodetector element according to claim 1, wherein the thinnest portion of the semiconductor spacer layer has a thickness of 1 nm or more and 3 nm or less.

7. The photodetector element according to claim 1, wherein the second conductive type semiconductor layer is a diffusion layer in contact with the semiconductor quantum dot layer.

8. The photodetector element according to claim 1, wherein the photoelectric conversion layer further comprises an additional semiconductor layer made of a third semiconductor having a lattice constant between the lattice constants of the first semiconductor and the lattice constants of the second semiconductor.

9. The photodetector according to claim 1, further comprising a barrier layer disposed between said first conductive type semiconductor layer and said second conductive type semiconductor layer, for preventing the passage of either holes or electrons.

10. The photodetector element according to claim 1, wherein the first semiconductor is a compound semiconductor that absorbs infrared rays.

11. An imaging element comprising: a first electrode; a first conductivity type semiconductor layer provided on the first electrode and made of a first conductivity type semiconductor; a second conductivity type semiconductor layer made of a second conductivity type semiconductor; a photoelectric conversion layer sandwiched between the first conductivity type semiconductor layer and the second conductivity type semiconductor layer; and a second electrode located on the opposite side of the photoelectric conversion layer as viewed from the second conductivity type semiconductor layer and connected to the second conductivity type semiconductor layer, wherein the photoelectric conversion layer is a laminate having a semiconductor quantum dot layer including quantum dots of a first semiconductor having a first band gap, and a semiconductor spacer layer including a second semiconductor having a second band gap larger than the first band gap.

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