Light detection element and light detection device

Abstract

A light detection element comprises: a semiconductor substrate, a light absorption layer of a first conductivity type formed on the semiconductor substrate, a cap layer of the first conductivity type formed on the light absorption layer, and a semiconductor region of a second conductivity type formed in the cap layer and forming a pn junction with the cap layer. A depletion layer formed around the semiconductor region does not reach the light absorption layer when a reverse bias is not applied to the pn junction, and exceeds a position of 50% of the thickness of the light absorption layer from the cap layer side when a reverse bias of 20V is applied to the pn junction.

Description

Technical Field

[0001] The present disclosure relates to a light detecting element and a light detecting device. Background Art

[0002] As a sensor for obtaining a distance image of an object using an indirect TOF (time of flight) method, a distance image sensor is known, which includes: a semiconductor substrate provided with a photosensitive region, an insulating layer formed on the semiconductor substrate, and a grating electrode and a transfer electrode for each pixel formed on the insulating layer (for example, see Patent Document 1). In the example of the distance image sensor described in Patent Document 1, the semiconductor substrate is made of silicon, and the grating electrode and the transfer electrode are made of polycrystalline silicon.

[0003] Patent Literature

[0004] Patent Document 1: Japanese Patent Application Publication No. 2011-133464 Summary of the invention

[0005] Technical problem to be solved by the invention

[0006] In recent years, for example, in order to obtain a distance image of an object in fog or smoke, a distance image sensor that can detect light with a wavelength of about 1.5 μm is needed. However, if the semiconductor substrate constituting the distance image sensor is formed of silicon, sufficient sensitivity cannot be obtained for light with a wavelength of about 1.5 μm. Therefore, in order to obtain sufficient sensitivity for light with a wavelength of about 1.5 μm, it is conceivable to use a compound semiconductor substrate as a semiconductor substrate constituting the distance image sensor. However, in this case, it is difficult to form a grating electrode and a transfer electrode on the compound semiconductor substrate.

[0007] In addition, it is also conceivable to perform output control (transmission control) of the detection signal in the CMOS provided in the back section of the distance image sensor. However, since the output control of the detection signal at the μs level is the limit in the CMOS, the output control of the detection signal by the CMOS is not sufficient for the indirect TOF method, which requires high-speed output control of the detection signal at the level of tens of ns.

[0008] An object of the present disclosure is to provide a light detection element and a light detection device capable of realizing high-speed detection signal output control with a simple structure.

[0009] Means for solving technical problems

[0010] One aspect of the present disclosure provides a light detecting element comprising: a semiconductor substrate, a light absorbing layer of a first conductivity type formed on the semiconductor substrate, a cap layer of the first conductivity type formed on the light absorbing layer, and a semiconductor region of a second conductivity type formed in the cap layer and forming a pn junction with the cap layer, wherein a depletion layer is formed around the semiconductor region and does not reach the light absorbing layer when a reverse bias is not applied to the pn junction, and exceeds a position of 50% of the thickness of the light absorbing layer from the cap layer side when a reverse bias of 20 V is applied to the pn junction.

[0011] In this light detection element, when a reverse bias is not applied to the pn junction, since the depletion layer does not reach the light absorption layer, even if carriers (electrons and holes) are generated in the light absorption layer by the incidence of the light of the detection object, no current flows through the pn junction. That is, for example, by not applying a reverse bias to the pn junction, the detection signal can be prevented from being output from the light detection element. On the other hand, when a reverse bias of 20V is applied to the pn junction, since the depletion layer exceeds 50% of the thickness of the light absorption layer from the cap layer side, when carriers are generated in the region where the depletion layer diffuses in the light absorption layer by the incidence of the light of the detection object, a current flows through the pn junction. That is, for example, by applying a reverse bias of 20V to the pn junction, the detection signal can be output from the light detection element. Here, the potential difference of 20V is, for example, a potential difference that is difficult to affect the design of the circuit of the subsequent stage of CMOS, and is a potential difference that can be modulated at a high speed of tens of ns. Therefore, according to this light detection element, high-speed output control of the detection signal can be achieved with a simple structure.

[0012] In one aspect of the light detection element disclosed herein, when a 20V reverse bias is applied to the pn junction, the depletion layer may exceed 80% of the thickness of the light absorption layer from the cap layer side. This can improve sensitivity and responsiveness. This is particularly effective for a structure in which light is incident from the semiconductor substrate side.

[0013] The light detection element according to one aspect of the present disclosure further includes a relaxation layer of the first conductivity type formed between the light absorption layer and the cap layer, thereby making it possible to smoothly move carriers generated in a region where the depletion layer diffuses in the light absorption layer.

[0014] In the light detection element of one aspect of the present disclosure, the light absorption layer and the cap layer may be in contact with each other. This can reduce the reverse bias required for the depletion layer to exceed at least 50% of the thickness of the light absorption layer from the cap layer side.

[0015] In the light detecting element of one aspect of the present disclosure, a plurality of semiconductor regions are formed in the cap layer, and the semiconductor regions can be arranged one-dimensionally or two-dimensionally when viewed in the thickness direction of the semiconductor substrate. Thus, the light detecting element can be used to obtain a distance image.

[0016] In a light detecting element of one aspect of the present disclosure, a plurality of semiconductor regions are formed in a cap layer and are arranged one-dimensionally when viewed from the thickness direction of the semiconductor substrate, and the width of the cap layer may be smaller than the width of the semiconductor substrate in a width direction perpendicular to both the thickness direction of the semiconductor substrate and the arrangement direction of the semiconductor regions. Thus, carriers generated in the region surrounding the pn junction region can be suppressed from becoming noise.

[0017] In the light detection element according to one aspect of the present disclosure, the width of the light absorption layer may be smaller than the width of the semiconductor substrate in the width direction. This can more reliably suppress carriers generated in the region surrounding the pn junction region from becoming noise.

[0018] In the light detection element according to one aspect of the present disclosure, the first conductivity type may be n-type, and the second conductivity type may be p-type. Thus, the light detection element can be easily manufactured.

[0019] In one aspect of the present disclosure, the light detection device comprises: the above-mentioned light detection element and a signal processing unit that applies a bias voltage signal to the pn junction and obtains a detection signal output from the light detection element, and the pulse voltage is a voltage signal in which a first voltage when the depletion layer does not reach the light absorption layer and a second voltage when the depletion layer reaches the light absorption layer are alternately repeated.

[0020] According to this optical detection device, while applying a bias voltage signal to the optical detection element, information about the distance to the object can be obtained, for example, by irradiating a pulse light to which the optical detection element is sensitive to the object and allowing the pulse light reflected by the object to enter the optical detection element.

[0021] In one aspect of the light detection device of the present disclosure, the second voltage may be a voltage at which the depletion layer reaches 100% of the thickness of the light absorption layer from the cap layer side. Thus, it is possible to improve sensitivity and responsiveness. In particular, this is effective for a structure in which light is incident from the semiconductor substrate side.

[0022] In the photodetection device according to one aspect of the present disclosure, the second voltage may be a voltage of 20 V or less. This makes it possible to more reliably improve the sensitivity and responsiveness.

[0023] In the photodetection device according to one aspect of the present disclosure, the second voltage may be a voltage of 10 V or less. This makes it possible to more reliably improve the sensitivity and responsiveness.

[0024] In the photodetection device according to one aspect of the present disclosure, the second voltage may be a voltage of 5 V or less. This makes it possible to more reliably improve the sensitivity and responsiveness.

[0025] The light detection device in one aspect of the present disclosure may further include a light source that outputs a pulse to which the light detection element has sensitivity. Thus, as described above, information on the distance to the object can be obtained.

[0026] In the light detection device according to one aspect of the present disclosure, the light source may output pulse light at a frequency of 10 kHz or higher. In this way, information on the distance to the object can be appropriately obtained.

[0027] Effects of the Invention

[0028] According to the present disclosure, it is possible to provide a light detection element and a light detection device that can realize high-speed output control of a detection signal with a simple structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a structural diagram of a light detection device according to one embodiment.

[0030] Figure 2 yes Figure 1 The structural diagram of the light detection unit shown.

[0031] Figure 3 yes Figure 2 A cross-sectional view of a portion of a light detecting element is shown.

[0032] Figure 4 yes Figure 2 A cross-sectional view of a portion of a light detecting element is shown.

[0033] Figure 5 This is a timing chart for obtaining information about the distance to an object.

[0034] Figure 6 This is a cross-sectional view of a portion of a light detecting element according to a modified example.

[0035] Figure 7 It is another cross-sectional view of the light detection element of the modification.

[0036] Figure 8 This is a cross-sectional view of a portion of a light detecting element according to a modified example.

[0037] Fig. 9 It is another cross-sectional view of the light detection element of the modification. DETAILED DESCRIPTION

[0038] The embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In addition, the same or corresponding parts in each drawing are represented by the same reference numerals, and repeated descriptions will be omitted.

[0039] like Figure 1As shown, the light detection device 1 includes a light detection unit 2, a light source 3, a control unit 4, and a display unit 5. The light detection device 1 is a device that obtains a distance image (an image including information on a distance d to the object OJ) of the object OJ using an indirect TOF method.

[0040] like Figure 2 As shown, the light detection unit 2 has a signal processing circuit (signal processing unit) 6 and a light detection element 10A. The signal processing circuit 6 includes a voltage signal generating circuit 61, a CMOS readout circuit 62, a vertical scanning circuit 63, a column circuit 64, a horizontal scanning circuit 65, an amplifier 66, and a timing generating circuit 67. In this embodiment, the light detection element 10A is a back-incident type InGaAs area sensor, and a bump is connected to the CMOS readout circuit 62.

[0041] The voltage signal generating circuit 61 generates a pulse voltage signal and applies it to the light detecting element 10A. The CMOS readout circuit 62 is composed of a plurality of charge amplifiers and the like, and when a detection signal is output from each pixel of the light detecting element 10A, the signal current is integrated in each charge amplifier.

[0042] The vertical scanning circuit 63 sequentially selects the plurality of charge amplifiers of the CMOS readout circuit 62 row by row. The column circuit 64 samples and holds the signal voltage integrated in each charge amplifier of the selected row together with the reset voltage. The horizontal scanning circuit 65 sequentially transmits the voltage difference between the signal voltage sampled and held in the column circuit 64 and the reset voltage to the amplifier 66.

[0043] The amplifier 66 amplifies the voltage difference between the signal voltage and the reset voltage sequentially transmitted from the column circuit 64, and outputs the amplified voltage difference as an output voltage signal to the control section 4 (see FIG. 4 ). Figure 1 ). The timing generation circuit 67 controls the operation timing of the voltage signal generation circuit 61, the vertical scanning circuit 63, and the horizontal scanning circuit 65. Also, in the case of analog output, an amplifier 66 is provided, but in the case of digital output, an AD converter is provided instead of the amplifier 66.

[0044] like Figure 3 As shown, the light detection element 10A includes an n-type (first conductivity type) semiconductor substrate 11, an n-type light absorption layer 12, an n-type relaxation layer 13, an n-type cap layer 14, and a plurality of p-type (second conductivity type) semiconductor regions 15. The light absorption layer 12 is formed on the semiconductor substrate 11, for example, by epitaxial growth. The relaxation layer 13 is formed on the light absorption layer 12, for example, by epitaxial growth. The cap layer 14 is formed on the relaxation layer 13, for example, by epitaxial growth.

[0045] The relaxation layer 13 is composed of a plurality of layers 13a, 13b, and 13c, and is formed between the light absorbing layer 12 and the cap layer 14. The band gaps of the layers 13a, 13b, and 13c are set in such a manner as to moderate the difference between the band gaps of the light absorbing layer 12 and the band gaps of the cap layer 14. The relaxation layer 13 may be composed of a single layer if the difference between the band gaps of the light absorbing layer 12 and the band gaps of the cap layer 14 can be moderated. By providing the relaxation layer 13 in this manner, it is easier to form the cap layer 14 than when the cap layer 14 is directly formed on the light absorbing layer 12.

[0046] A plurality of semiconductor regions 15 are formed in the cap layer 14, for example, by thermal diffusion, ion implantation, etc. When viewed from the thickness direction of the semiconductor substrate 11, the plurality of semiconductor regions 15 are arranged two-dimensionally (for example, in a matrix). Each semiconductor region 15 is formed along the surface of the cap layer 14 on the opposite side to the semiconductor substrate 11, and is separated from the surface of the cap layer 14 on the semiconductor substrate 11 side. Each semiconductor region 15 forms a pn junction with the cap layer 14 and constitutes each pixel P. A depletion layer D1 is formed around each semiconductor region 15. Furthermore, the semiconductor region 15 has, for example, a 1×10 17 cm -3 An impurity region with an impurity concentration above .

[0047] In this embodiment, the semiconductor substrate 11 has a thickness of 0.5 to 5×10 18 cm -3 (For example, 1×10 18 cm -3 The carrier concentration n + -InP substrate, and has a thickness of 150 to 300 μm (for example, about 200 μm). The light absorbing layer 12 has a thickness of 3 to 10×10 14 cm -3 (For example, 5×10 14 cm -3 The carrier concentration n - -InGaAs layer, and has a thickness of 1 to 5 μm (for example, about 2 μm). The relaxation layer 13 has a thickness of 0.3 to 5×10 15 cm -3 (For example, 1×10 15 cm -3 The carrier concentration n - -InGaAs layer, and the thickness is 0.1 to 0.6 μm (for example, about 0.2 μm). The cap layer 14 has a thickness of 0.3 to 5×10 15 cm -3 (For example, 1×10 15 cm -3 The carrier concentration n --InP layer, and the thickness is 1 to 2 μm (for example, about 1.5 μm). Each semiconductor region 15 has 0.1 to 10×10 18 cm -3 (For example, 1×10 18 cm -3 The p+ region has a carrier concentration of about 0.1 μm to 1 μm (for example, about 0.5 μm).

[0048] The light detecting element 10A further includes a plurality of first electrodes 16 and a plurality of second electrodes 17. The first electrodes 16 and the second electrodes 17 are formed on an insulating film 18, and the insulating film 18 is formed on the surface of the cap layer 14 on the opposite side to the semiconductor substrate 11. The first electrodes 16 and the second electrodes 17 are formed of, for example, Ti, Pt, Cr, Ni, Au, or alloys thereof. The insulating film 18 is, for example, a silicon nitride film, a silicon oxide film, or the like.

[0049] Each first electrode 16 extends in a groove (or through hole) formed in the light absorbing layer 12, the relaxation layer 13, the cap layer 14, and the insulating film 18, and is in electrical contact with the light absorbing layer 12, the relaxation layer 13, and the cap layer 14. The groove (or through hole) is formed in a manner that does not affect the depletion layer D1. Each second electrode 17 extends in an opening (or through hole) formed in the insulating film 18, and is in electrical contact with each semiconductor region 15. Since the first electrode 16 is used as a common electrode, at least one first electrode 16 can be provided for a plurality of pixels P. Since the second electrode 17 is used as an individual electrode, it is necessary to provide a second electrode 17 for each pixel P. Furthermore, if the groove (or through hole) in which each first electrode 16 extends is formed in a manner that does not affect the depletion layer D1, it can reach any layer of the semiconductor substrate 11, the light absorbing layer 12, the relaxation layer 13, and the cap layer 14.

[0050] The light absorbing layer 12, the relaxation layer 13, and the cap layer 14 are provided with a pixel separation portion 20. The pixel separation portion 20 extends in a manner passing between adjacent pixels P (that is, in a manner passing between adjacent semiconductor regions 15). When a plurality of semiconductor regions 10a are arranged in a matrix, the pixel separation portion 20 extends in a lattice shape.

[0051] The pixel separation unit 20 is formed by forming a p-type semiconductor region 22 along the inner surface of the groove 21 formed in the light absorbing layer 12, the relaxation layer 13, and the cap layer 14. A depletion layer D2 is formed around the semiconductor region 22. The pixel separation unit 20 (i.e., the groove 21 and the semiconductor region 22) reaches the side surface of the light detecting element 10A, and the semiconductor region 22 is short-circuited at the side surface. In addition, the inner surface of the groove 21 is covered with the insulating film 18.

[0052] In each pixel P, the depletion layer D1 formed around the semiconductor region 15 does not reach the light absorbing layer 12 when a reverse bias is not applied between the first electrode 16 and the second electrode 17 (non-biased state). On the other hand, when a reverse bias of 20 V is applied between the first electrode 16 and the second electrode 17, Figure 4 As shown, the depletion layer D1 exceeds 80% of the thickness of the light absorbing layer 12 from the cap layer 14 side (the position of 80% of the thickness of the light absorbing layer 12 from the surface of the light absorbing layer 12 on the cap layer 14 side as a reference). In addition, "applying or not applying a reverse bias between the first electrode 16 and the second electrode 17" is synonymous with "applying or not applying a reverse bias to the pn junction formed by the semiconductor region 15 and the cap layer 14" (the same applies hereinafter).

[0053] In this embodiment, since the first electrode 16 is an electrode on the n-type side and the second electrode 17 is an electrode on the p-type side, a reverse bias is applied between the first electrode 16 and the second electrode 17 with the potential of the first electrode 16 as a reference and the potential of the second electrode 17 being -20 V. Figure 3 As shown, the depletion layer D1 reaches the layer 13c of the relaxation layer 13 in the unbiased state. If the depletion layer D1 does not reach the light absorption layer 12 in the unbiased state, it may also reach the other layers 13a and 13b of the relaxation layer 13, or it may not reach the relaxation layer 13 (that is, it may also be contained in the cover layer 14).

[0054] Here, the setting of various parameters of the light detection element 10A will be described. When the depletion layer D1 reaches the layer 13c of the relaxation layer 13 in the non-biased state, if it is assumed that the semiconductor region 15 is in a one-sided abrupt junction state, the reverse bias V required for the depletion layer D1 to reach the light absorption layer 12 is expressed by equation (1).

[0055] [Formula 1]

[0056]

[0057] In formula (1), W1 is the distance between the depletion layer D1 and the surface on the light absorbing layer 12 side in the layer 13c, W2 is the thickness of the layer 13b, and W3 is the thickness of the layer 13a. εr1 is the relative dielectric constant of the layer 13c, εr2 is the relative dielectric constant of the layer 13b, and εr3 is the relative dielectric constant of the layer 13a. N1 is the carrier concentration of the layer 13c, N2 is the carrier concentration of the layer 13b, and N3 is the carrier concentration of the layer 13a. q is the charge, and ε0 is the electrical constant.

[0058] Therefore, when a reverse bias is not applied between the first electrode 16 and the second electrode 17 , the condition that the depletion layer D1 does not reach the light absorbing layer 12 is expressed by equation (2).

[0059] [Formula 2]

[0060]

[0061] In addition, when the depletion layer D1 reaches the layer 13c of the relaxation layer 13 in the non-biased state, assuming that the semiconductor region 15 is in a state of a unilateral abrupt junction, the reverse bias required for the depletion layer D1 to reach the position of X% of the thickness of the light absorbing layer 12 from the cap layer 14 side (the surface of the light absorbing layer 12 on the cap layer 14 side is taken as a reference, and the position of X% of the thickness of the light absorbing layer 12 from the surface) is expressed by formula (3). In formula (3), Wab is the thickness of the light absorbing layer 12, εrab is the relative dielectric constant of the light absorbing layer 12, and Nab is the carrier concentration of the light absorbing layer 12.

[0062] [Formula 3]

[0063]

[0064] Therefore, when a reverse bias of 20 V is applied between the first electrode 16 and the second electrode 17 , the condition that the depletion layer D1 exceeds 80% of the thickness of the light absorbing layer 12 from the cap layer 14 side is expressed by equation (4).

[0065] [Formula 4]

[0066]

[0067] In this embodiment, various parameters of the light detection element 10A are set so as to satisfy equations (2) and (4). In particular, in this embodiment, when a reverse bias of 5 V is applied between the first electrode 16 and the second electrode 17, the depletion layer D1 reaches a position where the thickness of the light absorption layer 12 is 100% from the cap layer 14 side. That is, in this embodiment, various parameters of the light detection element 10A are set so as to satisfy equation (5).

[0068] [Formula 5]

[0069]

[0070] Furthermore, when the depletion layer D1 does not reach the relaxation layer 13 in the non-biased state (i.e., is contained in the cap layer 14), the term of the cap layer 14 may be added to the right side of the equations (1) to (5). In this case, when the relaxation layer 13 does not exist, the term of the relaxation layer 13 may be subtracted from the right side of the equations (1) to (5). As described above, the term corresponding to each layer may be added or subtracted from the right side of the equations (1) to (5) according to the layer structure of the light detection element 10A, etc.

[0071] like Figure 1 As shown, the light source 3 outputs pulse light L at a frequency of 10KHz or more to which the light detection element 10A has sensitivity (i.e., photoelectric conversion can occur in the light detection element 10A). In the present embodiment, the light source 3 is, for example, an infrared LED, and outputs pulse light L having a wavelength of about 1.5μm. The pulse light output from the light source 3 is irradiated to the object OJ, and the pulse light L reflected by the object OJ is incident on the light detection element 10A. The control unit 4 controls the light detection unit 2 and the light source 3, and generates a distance image of the object OJ based on the output voltage signal output from the light detection unit 2, and displays it on the display unit 5.

[0072] As described above, in the light detection element 10A, if a reverse bias is not applied between the first electrode 16 and the second electrode 17, since the depletion layer D1 does not reach the light absorption layer 12, even if carriers (electrons and holes) are generated in the light absorption layer 12 by the incidence of the pulse light L, no current flows between the first electrode 16 and the second electrode 17. That is, by, for example, not applying a reverse bias between the first electrode 16 and the second electrode 17, it is possible to prevent the signal processing circuit 6 from outputting a detection signal from the light detection element 10A. On the other hand, if a reverse bias of 20 V is applied between the first electrode 16 and the second electrode 17, since the depletion layer D1 exceeds 80% of the thickness of the light absorption layer 12 from the cap layer 14 side, when carriers are generated in the region where the depletion layer D1 in the light absorption layer 12 extends by the incidence of the pulse light L, a current flows between the first electrode 16 and the second electrode 17. That is, by applying a reverse bias between the first electrode 16 and the second electrode 17, for example, the signal processing circuit 6 can output a detection signal from the light detection element 10A. Here, the potential difference of 20V is a potential difference that is not likely to affect the design of the subsequent signal processing circuit 6, and is a potential difference that can be modulated at a high speed of several tens of nanoseconds. Therefore, according to the light detection element 10A, high-speed output control of the detection signal can be realized with a simple structure.

[0073] In particular, in the light detecting element 10A, when a reverse bias of 5 V is applied between the first electrode 16 and the second electrode 17, the depletion layer D1 reaches a position where the thickness of the light absorbing layer 12 is 100% of that of the light absorbing layer 12 from the cap layer 14 side. Since the light detecting element 10A is a back-incident type area sensor that allows light to enter from the semiconductor substrate 11 side, the application of a reverse bias of 5 V allows the depletion layer D1 to reach the surface of the light incident side of the light absorbing layer 12, which is effective in improving sensitivity and responsiveness.

[0074] Furthermore, the avalanche photodiode is also an element that detects light by applying a reverse bias, but it is fundamentally different from the light detection element 10A because it requires a potential difference of, for example, 50V as a reverse bias. In the avalanche photodiode, an electric field suppression layer is formed between the light absorption layer and the cap layer to increase the electric field strength applied to the cap layer where the multiplication layer is formed, and to reduce the electric field strength applied to the light absorption layer. In contrast, in the light detection element 10A, an electric field suppression layer is formed between the light absorption layer 12 and the cap layer 14 to reduce the electric field strength applied to the cap layer 14, and to increase the electric field strength applied to the light absorption layer 12. Furthermore, the potential difference of 50V is a potential difference that easily affects the design of the subsequent circuit of CMOS, etc., and is a potential difference that cannot be modulated at a high speed of tens of ns.

[0075] In addition, in the light detection element 10A, the n-type relaxation layer 13 is formed between the light absorption layer 12 and the cap layer 14. This allows carriers generated in the region where the depletion layer D1 diffuses in the light absorption layer 12 to be smoothly transferred.

[0076] In addition, in the light detecting element 10A, when viewed from the thickness direction of the semiconductor substrate 11, the plurality of semiconductor regions 15 are two-dimensionally arranged in the cap layer 14. Thus, a distance image of the object OJ can be obtained.

[0077] In addition, in the light detection element 10A, a pixel separation unit 20 is provided in the light absorption layer 12, the relaxation layer 13, and the cap layer 14. Thus, the generation of crosstalk between adjacent pixels P can be suppressed. In addition, even if carriers are generated in the light absorption layer 12 in the unbiased state, the carriers are captured by the depletion layer D2 formed around the semiconductor region 22. Therefore, when switching from the unbiased state to the reverse biased state, the carriers generated in the light absorption layer 12 in the unbiased state can be suppressed from becoming noise.

[0078] In the light detection element 10A, the carrier concentration of each of the light absorption layer 12, the relaxation layer 13, and the cap layer 14 is 1×10 16 cm -3 Thus, by applying a reverse bias with a potential difference of 20 V or less, the depletion layer D1 can be smoothly spread in the light absorbing layer 12 .

[0079] In addition, the light detection device 1 includes: a light detection element 10A, a signal processing circuit 6 that applies a pulse voltage signal between the first electrode 16 and the second electrode 17 and obtains a detection signal output from the light detection element 10A, and a light source 3 that outputs pulse light L to which the light detection element 10A has sensitivity at a frequency of 10 kHz or more. Thus, as in the calculation example described below, information about the distance d to the object OJ can be appropriately obtained.

[0080] refer to Figure 5 , an example of calculating the distance d to the object OJ is described. Figure 5 , the intensity signal I of the pulse light L output from the light source 3 is shown. OUT , an intensity signal I of the pulse light L reflected by the object OJ and incident on the light detection element 10A IN , and the pulse voltage signal V1 applied to the light detection element 10A (specifically, between the first electrode 16 and the second electrode 17) in the first stage IN , the pulse voltage signal V2 applied to the light detection element 10A in the second stage IN , and the pulse voltage signal V3 applied to the light detection element 10A in the third stage IN Furthermore, in this calculation example, an arbitrary pixel P is considered.

[0081] In the first stage, the intensity signal I OUT The pulse light L is output from the light source 3 and the pulse voltage signal V1 is applied to the light detection element 10A IN In the state, the output voltage signal V1 is obtained OUT . Intensity signal I OUT The pulse width T is set, for example, to 30 ns (measurable distance: 4.5 m to 5.7 m), 40 ns (measurable distance: 6.0 m to 7.6 m), or 60 ns (measurable distance: 9.0 m to 8.9 m) according to the distance to be measured. IN is the first voltage V where the depletion layer D1 does not reach the light absorption layer 12 L and the depletion layer D1 reaches the second voltage V of the light absorbing layer 12 H Alternating and repetitive voltage signal, with period, pulse width, phase and intensity signal I OUT The same voltage signal. The first voltage V L In this embodiment, it is 0V. The second voltage V H is the voltage at which the depletion layer D1 reaches 100% of the thickness of the light absorbing layer 12 from the cap layer 14 side, and is 5 V in this embodiment. At this time, since the light detecting element 10A outputs the detection signal only during the period when the second voltage VH is applied, the output voltage signal V1OUT Corresponding to the intensity signal I IN The pulse and pulse voltage signal V1 IN The integrated value of the charge Q1 of the overlapping parts of the pulses.

[0082] In the second stage, the intensity signal I OUT The pulse light L is output from the light source 3 and a bias voltage signal V2 is applied to the light detection element 10A. IN In the state, the output voltage signal V2 is obtained OUT Except for the point where the phase is shifted by 180°, the pulse voltage signal V2 IN Is the pulse voltage signal V1 IN At this time, since the light detection element 10A outputs the detection signal only during the period when the second voltage VH is applied, the output voltage signal V2 OUT Corresponding to the intensity signal I IN The pulse and pulse voltage signal V2 IN The integrated value of the charge Q2 of the overlapping parts of the pulses.

[0083] In the third stage, the pulse light L is not output from the light source 3 and the bias voltage signal V3 is applied to the light detection element 10A. IN In the state, the output voltage signal V3 is obtained OUT At this time, because the light detection element 10A is only applied with the second voltage V H The detection signal is output during the period, so if there is ambient light, the output voltage signal V3 OUT The intensity signal corresponding to the ambient light and the pulse voltage signal V3 IN The integral value of the charge amount of the overlapping parts of the pulses.

[0084] When the above first stage, second stage and third stage are implemented for each pixel P, the control unit 4 controls each pixel according to the output voltage signal V1. OUT 、V2 OUT 、V3 OUT , to calculate the distance d to the object OJ. The distance d is expressed by equation (6). In equation (6), c is the speed of light.

[0085] [Formula 6]

[0086]

[0087] As described above, in the light detection device 1, the light detection element 10A can be switched (modulated) in the order of tens of nanoseconds. OUT 、V2 OUT The second voltage V HIt is the voltage at the position where the depletion layer D1 reaches 100% of the thickness of the light absorbing layer 12 from the cap layer 14 side. Thus, it is possible to suppress the detection of carriers generated in the region where the depletion layer D1 is not diffused in the light absorbing layer 12 as a delayed component, and further, it is possible to suppress the degradation of the calculation accuracy of the distance d. In addition, in the light detection device 1, the light source 3 is a light source that emits a pulse light L having a wavelength of about 1.5 μm, and the light detection element 10 is an InGaAs area sensor having sufficient sensitivity to the pulse light L having a wavelength of about 1.5 μm. Thus, even in fog or smoke, for example, it is easy to obtain a distance image of the object OJ. In addition, the above calculation example is only an example, and information about the distance d to the object OJ can be obtained by various known calculations. In addition, the second voltage VH can also be a voltage of 20V or less (preferably a voltage of 10V or less, and more preferably a voltage of 5V or less). In this case, in the light detection device 1, it is possible to more reliably seek to improve sensitivity and responsiveness.

[0088] The present disclosure is not limited to the above-described embodiment. For example, the light detection element 10A may be configured as a linear sensor in which the semiconductor region 15 is one-dimensionally arranged in the cover layer 14. Figure 6 and Figure 7 , a light detection element 10B configured as a back-illuminated InGaAs linear sensor is shown. Figure 6 is a cross-sectional view of a portion of the light detecting element 10B along a plane parallel to the arrangement direction of the plurality of semiconductor regions 15 (hereinafter, simply referred to as “arrangement direction”), and Figure 7 1 is a cross-sectional view of the light detecting element 10B taken along a plane perpendicular to the arrangement direction.

[0089] The light detection element 10B is different from the light detection element 10A described above mainly in that an n-type relaxation layer 13 is not formed between the light absorption layer 12 and the cap layer 14, and a p-type semiconductor region 23 is formed. Figure 7 As shown, in the width direction perpendicular to both the thickness direction and the arrangement direction of the semiconductor substrate 11 (hereinafter referred to as the "width direction"), the width of the cap layer 14 is smaller than the width of the semiconductor substrate 11, and the width of the light absorbing layer 12 is equal to the width of the semiconductor substrate 11. The semiconductor region 23 is formed along the side surfaces of the cap layer 14 that are opposite to each other in the width direction, and along the surface of the light absorbing layer 12 on the opposite side to the semiconductor substrate 11 where the cap layer 14 is not formed. The semiconductor region 23 is covered by the insulating film 18.

[0090] In the light detection element 10B, as Figure 8 and Fig. 9As shown, when a reverse bias of 20 V is applied only between the first electrode 16 and the second electrode 17, the depletion layer D1 exceeds 80% of the thickness of the light absorbing layer 12 from the cap layer 14 side. Therefore, according to the light detection element 10B, similarly to the light detection element 10A, high-speed output control of the detection signal can be realized with a simple structure.

[0091] In addition, in the light detection element 10B, carriers generated in the light absorption layer 12 are captured in the non-biased state not only by the depletion layer D2 formed around the semiconductor region 22 of the pixel separation unit 20 but also by the depletion layer D3 formed around the semiconductor region 23. Therefore, when switching from the non-biased state to the reverse biased state, carriers generated in the light absorption layer 12 in the non-biased state can be suppressed from becoming noise.

[0092] In addition, in the light detection element 10B, the width of the cap layer 14 is smaller than the width of the semiconductor substrate 11 in the width direction. Thus, carriers generated in the area around the pn junction region (the region of the pixel P) can be suppressed from becoming noise. In addition, in the width direction, each of the width of the light absorption layer 12 and the width of the cap layer 14 can also be smaller than the width of the semiconductor substrate 11. In this case, carriers generated in the area around the pn junction region can be more reliably suppressed from becoming noise.

[0093] In addition, in Figure 3 In the light detection element 10A shown in FIG. 1 , the n-type relaxation layer 13 may not be formed between the light absorption layer 12 and the cap layer 14. Figure 6 and Figure 7 In the light detection element 10B shown, the n-type relaxation layer 13 may not be formed between the light absorption layer 12 and the cap layer 14. If the relaxation layer 13 is not formed and the light absorption layer 12 and the cap layer 14 are in contact with each other, the reverse bias required for the depletion layer D1 to exceed at least 50% of the thickness of the light absorption layer 12 from the cap layer 14 side can be reduced. Figure 6 and Figure 7 In the light detecting element 10B shown, when the relaxation layer 13 is formed between the light absorbing layer 12 and the cover 14, the width of the relaxation layer 13 and the width of the cover 14 in the width direction may be smaller than the width of the semiconductor substrate 11, or the width of the light absorbing layer 12, the width of the relaxation layer 13, and the width of the cover 14 in the width direction may be smaller than the width of the semiconductor substrate 11. In these cases, carriers generated in the region around the pn junction region can be more reliably suppressed from becoming noise.

[0094] In addition, Figure 3 In the light detection element 10A shown in FIG. 1 , the pixel separation unit 20 may not be provided. Figure 6 and Figure 7 In the light detection element 10B shown in FIG. 1 , the pixel separation unit 20 may not be provided. Figure 6 and Figure 7 In the photodetection element 10B shown, the semiconductor region 23 may not be formed.

[0095] In any of the above-mentioned light detecting elements 10A and 10B, when a reverse bias of 20 V is applied between the first electrode 16 and the second electrode 17, the depletion layer D1 only needs to extend from the cap layer 14 side to a position where 50% of the thickness of the light absorbing layer 12 is exceeded (a position where 50% of the thickness of the light absorbing layer 12 is reached from the surface of the light absorbing layer 12 on the cap layer 14 side as a reference). The position within the range of 50% to 100% of the thickness of the light absorbing layer 12 to which the depletion layer D1 is diffused from the cap layer 14 side by applying a reverse bias of 20 V is determined by the wavelength of the light to be detected, the incident direction of the light to be detected, and the like.

[0096] In addition, any one of the above-mentioned light detecting elements 10A and 10B may be configured as a surface incident type. In this case, the first electrode 16 is formed, for example, on the surface of the semiconductor substrate 11 on the opposite side to the light absorbing layer 12. In addition, the second electrode 17 is formed with, for example, an opening for allowing the light of the detection object to be incident on the light absorbing layer 12. In the case where each of the light detecting elements 10A and 10B is configured as a surface incident type, the band gap of the layer provided on the light incident side compared to the light absorbing layer 12 is preferably larger than the band gap of the light absorbing layer 12 from the viewpoint of suppressing light absorption in the layer. Furthermore, even in the case where the light detecting elements 10A and 10B are configured as a back-incident type, the band gap of the layer provided on the light incident side compared to the light absorbing layer 12 is preferably larger than the band gap of the light absorbing layer 12 from the viewpoint of suppressing dark current.

[0097] In addition, in any of the above-mentioned light detection elements 10A and 10B, the conductivity types of the p-type and the n-type may be opposite to those described above. In this case, since the first electrode 16 is an electrode on the p-type side and the second electrode 17 is an electrode on the n-type side, a reverse bias is applied between the first electrode 16 and the second electrode 17 in such a manner that the potential of the first electrode 16 is used as a reference and the potential of the second electrode 17 is a positive potential. And, as described above, when the semiconductor substrate 11, the light absorption layer 12, the relaxation layer 13 and the cap layer 14 are n-type, and the semiconductor region 15 is p-type, the ease of manufacturing of the light detection elements 10A and 10B can be ensured.

[0098] In addition, in any of the above-mentioned light detecting elements 10A and 10B, a layer having a different composition may be formed between the light absorbing layer 12 and the cap layer 14 or in the cap layer 14 in such a manner that the semiconductor region 15 is reliably accommodated in the cap layer 14 during manufacturing. In addition, in any of the light detecting elements 10A and 10B, an ultra-thin layer having a large carrier concentration may be formed between the light absorbing layer 12 and the cap layer 14 in such a manner that the depletion layer D1 does not reach the light absorbing layer 12 due to deviations during manufacturing, etc. even in a non-biased state. In addition, in any of the above-mentioned light detecting elements 10A and 10B, a contact layer for reducing the contact resistance with the electrode may be formed on the cap layer 14.

[0099] In addition, any of the above-mentioned light detection elements 10A and 10B can also be configured as a single unit having a semiconductor region 15 formed in the cap layer 14. In this case, high-speed detection signal output control can be achieved with a simple structure. In this case, by configuring as a light detection device 1, information about the distance d to the object OJ can also be obtained.

[0100] In addition, the materials and shapes are not limited to the above, and various materials and shapes can also be applied to the structures of the light detection elements 10A and 10B. For example, the materials of the light detection elements 10A and 10B are not limited to compound semiconductors, and can also be organic semiconductors, amorphous materials, etc. In addition, the structures in one embodiment or modification example can be arbitrarily applied to the structures in other embodiments or modification examples.

[0101] In addition, the photodetection device 1 may not include the light source 3. As the photodetection device 1 in this case, an infrared image sensor having a global shutter operation (high-speed shutter operation) required for detecting a high-speed object or signal is exemplified.

[0102] Explanation of symbols

[0103] 1... Light detection device

[0104] 3… Light source

[0105] 6……Signal processing circuit (signal processing unit)

[0106] 10A, 10B...Light detection element

[0107] 11……Semiconductor substrate

[0108] 12... Light absorbing layer

[0109] 13...Mitigation layer

[0110] 14……Capping layer

[0111] 15...Semiconductor area

[0112] 16...First electrode

[0113] 17... Second electrode

[0114] D1...depletion layer.

Claims

1. A light detection element, characterized in that: have Semiconductor substrates, a light absorbing layer of a first conductivity type formed on the semiconductor substrate, a cap layer of the first conductivity type formed on the light absorbing layer, and a semiconductor region of the second conductivity type formed in the cap layer and forming a pn junction with the cap layer, The carrier concentration of the cap layer is 1×10 16 cm -3 the following, The depletion layer formed around the semiconductor region does not reach the light absorbing layer when a reverse bias is not applied to the pn junction, and exceeds a position of 50% of the thickness of the light absorbing layer from the cap layer side when a reverse bias of 20 V is applied to the pn junction. A voltage signal in which a first voltage at which the depletion layer does not reach the light absorbing layer and a second voltage at which the depletion layer reaches the light absorbing layer are alternately and repeatedly applied to the light detecting element.

2. The light detection element according to claim 1, characterized in that When a reverse bias of 20 V is applied to the pn junction, the depletion layer exceeds a position of 80% of the thickness of the light absorbing layer from the cap layer side.

3. The light detection element according to claim 1, wherein The invention further includes a first conductivity type relaxation layer formed between the light absorbing layer and the cap layer.

4. The light detecting element according to claim 2, wherein: The invention further includes a first conductivity type relaxation layer formed between the light absorbing layer and the cap layer.

5. The light detection element according to claim 1, wherein: The light absorbing layer and the capping layer are in contact with each other.

6. The light detection element according to claim 2, characterized in that The light absorbing layer and the capping layer are in contact with each other.

7. The light detection element according to any one of claims 1 to 6, characterized in that A plurality of the semiconductor regions are formed in the cap layer, and the semiconductor regions are arranged one-dimensionally or two-dimensionally when viewed in the thickness direction of the semiconductor substrate.

8. The light detecting element according to any one of claims 1 to 6, characterized in that: forming a plurality of the semiconductor regions in the cap layer, and arranging the semiconductor regions one-dimensionally when viewed in the thickness direction of the semiconductor substrate, In a width direction perpendicular to both a thickness direction of the semiconductor substrate and an arrangement direction of the semiconductor regions, the width of the cap layer is smaller than that of the semiconductor substrate.

9. The light detection element according to claim 7, characterized in that forming a plurality of the semiconductor regions in the cap layer, and arranging the semiconductor regions one-dimensionally when viewed in the thickness direction of the semiconductor substrate, In a width direction perpendicular to both a thickness direction of the semiconductor substrate and an arrangement direction of the semiconductor regions, the width of the cap layer is smaller than that of the semiconductor substrate.

10. The light detection element according to claim 8, characterized in that In the width direction, the width of the light absorbing layer is smaller than the width of the semiconductor substrate.

11. The light detecting element according to claim 9, wherein: In the width direction, the width of the light absorbing layer is smaller than the width of the semiconductor substrate.

12. The light detection element according to any one of claims 1 to 6, characterized in that: The first conductivity type is an n-type, and the second conductivity type is a p-type.

13. The light detecting element according to claim 7, wherein: The first conductivity type is an n-type, and the second conductivity type is a p-type.

14. The light detection element according to claim 8, characterized in that The first conductivity type is an n-type, and the second conductivity type is a p-type.

15. The light detecting element according to claim 9, wherein: The first conductivity type is an n-type, and the second conductivity type is a p-type.

16. The light detection element according to claim 10, characterized in that The first conductivity type is an n-type, and the second conductivity type is a p-type.

17. The light detecting element according to claim 11, characterized in that The first conductivity type is an n-type, and the second conductivity type is a p-type.

18. A light detection device, characterized in that: have: The light detecting element according to any one of claims 1 to 17, and a signal processing unit that applies a pulse voltage signal to the pn junction and obtains a detection signal output from the light detection element, The pulse voltage is a voltage signal in which a first voltage at which the depletion layer does not reach the light absorbing layer and a second voltage at which the depletion layer reaches the light absorbing layer are repeated alternately.

19. The light detection device according to claim 18, characterized in that The second voltage is a voltage at which the depletion layer reaches a position where the thickness of the light absorbing layer from the cap layer side reaches 100%.

20. The light detection device according to claim 18, characterized in that The second voltage is a voltage of 20V or less.

21. The light detection device according to claim 19, characterized in that The second voltage is a voltage of 20V or less.

22. The light detection device according to claim 18, characterized in that The second voltage is a voltage of 10V or less.

23. The light detection device according to claim 19, characterized in that The second voltage is a voltage of 10V or less.

24. The light detection device according to claim 20, characterized in that The second voltage is a voltage of 10V or less.

25. The light detection device according to claim 21, characterized in that The second voltage is a voltage of 10V or less.

26. The light detection device according to any one of claims 18 to 25, characterized in that: The second voltage is a voltage of 5V or less.

27. The light detection device according to any one of claims 18 to 25, characterized in that: The device further includes a light source for outputting pulse light to which the light detection element has sensitivity.

28. The light detection device according to claim 26, characterized in that The device further includes a light source for outputting pulse light to which the light detection element has sensitivity.

29. The light detection device according to claim 27, characterized in that The light source outputs the pulse light at a frequency of more than 10 KHz.

30. The light detection device according to claim 28, characterized in that The light source outputs the pulse light at a frequency of more than 10 KHz.

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