JP6847878B2 - Photodetector, photodetector and lidar device - Google Patents

Description

Embodiments of the present invention relate to photodetectors, photodetectors and lidar devices.

The LIDAR (Laser Imaging Detection and Ranging) device is a distance image sensing system that uses the Time of Flight (TOF), which measures the time it takes for a laser beam to make a round trip to a target and converts it into a distance. Yes, it is applied to in-vehicle drive assist systems, remote sensing, etc.

As a problem of the photodetector used in the lidar device, when the difference in the amount of light from the subject is large, in other words, when the subject distance range is wide, the light cannot be detected accurately. For example, when the subject distance is short, the amount of reciprocating light increases. If the amount of incident light is too large, the photodetector will always be in the photon detection state, and the SN ratio will deteriorate, making it impossible to count photons accurately. Therefore, when the amount of light is large, the photodetector needs to detect the incident light with low sensitivity. On the contrary, when the subject distance is long, the amount of reciprocating light is reduced. Photodetectors cannot accurately count photons if the amount of incident light is too small. Therefore, when the amount of light is small, it is necessary to detect the light incident on the photodetector with high sensitivity. Therefore, there is a need for a photodetector that can accurately detect light even when the subject distance range is wide.

Japanese Unexamined Patent Publication No. 09-331080 JP-A-2007-158036 Japanese Unexamined Patent Publication No. 2005-265606

An embodiment of the present invention provides a photodetector that accurately detects light even when the subject distance range is wide.

To accomplish the above task, the photodetector of the embodiment includes at least one first cell that converts the incident light into a charge and at least one second cell that converts the incident light into a charge. , A separating portion provided between the first cell and the second cell, and the first cell comprises a first semiconductor layer and a second semiconductor layer provided on the light incident side of the first semiconductor layer. The second cell includes a third semiconductor layer and a fourth semiconductor layer provided on the light incident side of the third semiconductor layer, and the interface between the third semiconductor layer and the fourth semiconductor layer is the first semiconductor layer. Located on the light incident side of the interface of the second semiconductor layer, the first cell detects light with the first sensitivity when the incident light amount is larger than a predetermined light amount, and the second cell is the incident light amount. Is less than a predetermined amount of light, the light is detected with the second sensitivity.

The figure which shows the photodetector of 1st Embodiment. The figure which shows the pp'cross section of the photodetector shown in FIG. The figure which shows the relationship between the impurity concentration and the depletion layer. The figure which shows the n-type impurity concentration and p-type impurity concentration distribution of 1st cell 1 and 2nd cell 2 in the depth from a light incident side to a substrate side. The figure which shows the photodetector including the photodetector of 1st Embodiment. The figure which shows the pp'cross section of the photodetector shown in FIG. The figure which shows the n-type impurity concentration and p-type impurity concentration distribution of the 1st cell 200 and the 2nd cell 300 in the depth from the light incident side to the substrate side. The figure which shows the lidar device which concerns on 2nd Embodiment. The figure for demonstrating the measurement system of the lidar apparatus of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Those with the same reference numerals indicate those corresponding to each other. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the ratio of the sizes between the parts, and the like are not necessarily the same as those in reality. Further, even when the same parts are represented, the dimensions and ratios may be different from each other depending on the drawings.

(First Embodiment)
FIG. 1 is a view of the photodetector of the first embodiment as viewed from the incident direction of light.

As shown in FIG. 1, the photodetector according to the present embodiment includes a short-distance cell 1 (also referred to as a first cell), a long-distance cell 2 (also referred to as a second cell), and a separation unit 3. Further, the photodetector includes at least one short-distance cell 1 and one long-distance cell 2, and charges light (for example, near-infrared light) incident on each of the short-distance cell 1 and the long-distance cell 2. Light is detected by photoelectric conversion and outputting the photoconverted electric signal to a drive / read unit (omitted in the drawing).

The separation unit 3 is a region for preventing cells adjacent to each other from interfering with each other, and is a region in which light incident on the photodetector cannot be detected, and is around the short-distance cell 1 and the long-distance cell 2. Surrounding. Further, the separation unit 3 is a wiring area for outputting the electric charge converted by the short-distance cell 1 and the long-distance cell 2 to the drive / read unit (omitted in the drawing). The wiring material is, for example, aluminum or an aluminum-containing material, or other metallic material in combination with that material.

FIG. 2 is a diagram showing a pp'cross section of the photodetector shown in FIG. In FIG. 2, it is assumed that light is incident from above.

The short-range cell 1 is an Avalanche Photodiode (APD) cell that detects light by converting the incident light into an electric charge, for example, using a silicon material. The short-distance cell 1 detects light with low sensitivity (also referred to as first sensitivity) when the amount of incident light is greater than a predetermined amount of light. As shown in FIG. 2, the short-distance cell 1 has a first semiconductor layer 5 (for example, a p-type semiconductor layer) provided on the substrate 4 and a second semiconductor layer provided on the light incident side of the first semiconductor layer 5. 6 (for example, an n-type semiconductor layer), a fifth semiconductor layer 11 provided so as to be in contact with the upper surface inside the second semiconductor layer 6, and the fifth semiconductor layer 11 are surrounded by the upper surface inside the second semiconductor layer 6. The sixth semiconductor layer 12 provided apart from the above is included. Here, "above" means the light incident side.

The long-distance cell 2 is an APD using, for example, a silicon material that detects light by converting the incident light into an electric charge. The long-distance cell 2 detects light with high sensitivity (second sensitivity) when the amount of incident light is less than a predetermined amount of light. The long-distance cell 2 includes a third semiconductor layer 8 (for example, a p-type semiconductor layer) provided on the substrate 4 and a fourth semiconductor layer 9 (for example, n-type) provided on the light incident side of the third semiconductor layer 8. Semiconductor layer) and. Further, in the present embodiment, the first semiconductor layer 5 and the third semiconductor layer 8 are the same semiconductor layer, and the impurity concentrations are about the same.

Further, an oxide film 22 is provided on the short-distance cell 1, the long-distance cell 2, and the separation portion 3. In the oxide film 22, two contact portions are provided on the fifth semiconductor layer 11 and the fourth semiconductor layer 9. In the two contact portions, the first electrode 7 is provided so as to be electrically connected to the fifth semiconductor layer 11 on one side, and the second electrode 10 is provided to be electrically connected to the fourth semiconductor layer 9 on the other side. Further, a first quenching resistor 15 is provided between the first electrode 7 and the separating portion 3, and a second quenching resistor 16 is provided between the second electrode 10 and the separating portion 3. The first electrode 7 is electrically connected to the wiring of the separation unit 3 via the first quench resistor 15, and the second electrode 10 is electrically connected to the wiring of the separation unit 3 via the second quench resistor 16. Will be done. Further, a protective layer 70 is provided on the oxide film 22, the first electrode 7, and the second electrode 10.

Further, a back surface electrode 17 is provided below the short-distance cell 1 and the long-distance cell 2 in the stacking direction. Here, "below" indicates the side opposite to the light incident side. The stacking direction is a direction perpendicular to the surface. A ground 18 is electrically connected to the back electrode 17.

The overall thickness of the short-distance cell 1 and the long-distance cell 2 in the stacking direction is uniform, but both the interface between the third semiconductor layer 8 and the fourth semiconductor layer 9 (for example, the pn junction and the interfaces of the semiconductor layers 8 and 9). Is provided on the light incident side of the space between the first semiconductor layer 5 and the second semiconductor layer 6 (for example, also referred to as a pn junction or an interface between the semiconductor layers 5 and 6). That is, in the long-distance cell 2, the pn junction surface is located near the first electrode 10.

The first semiconductor layer 5 is formed by ion-implanting impurities into a silicon substrate. The impurity is, for example, B.

The second semiconductor layer 6 is formed by ion-implanting impurities into the first semiconductor layer 5. Impurities are, for example, P, As, Sb.

The third semiconductor layer 8 is formed by ion-implanting impurities into a silicon substrate. The impurity is, for example, B.

The fourth semiconductor layer 9 is formed by ion-implanting impurities into the third semiconductor layer 8. Impurities are, for example, P, As, Sb.

The first electrode 10 is driven by applying a voltage to the first semiconductor layer 5 and the second semiconductor layer 6 from a power source, and drives the electric charge converted by photoelectric between the first semiconductor layer 5 and the second semiconductor layer 6. -It is provided for sending to the reading unit (omitted in the drawing). The material of the first electrode 10 is, for example, aluminum or an aluminum-containing material, or another metal material combined with the material.

The second electrode 7 is provided to drive the third semiconductor layer 8 and the fourth semiconductor layer 9 by applying a voltage from a power source different from the power source for applying the voltage to the first electrode 10. It is provided to send the charge photoelectrically converted between the third semiconductor layer 8 and the fourth semiconductor layer 9 to the drive / read unit (omitted in the drawing). The material of the second electrode 7 is, for example, aluminum or an aluminum-containing material, or another metal material combined with the material.

The fifth semiconductor layer 11 is provided to reduce the contact resistance with the first electrode 7, and is formed by ion-implanting impurities having a higher concentration than that of the second semiconductor layer 6 into the second semiconductor layer 6. Impurities are, for example, P, As, Sb.

Since the electric field tends to concentrate around the fifth semiconductor layer 11, the sixth semiconductor layer 12 is provided to prevent this, and is formed by ion-implanting impurities having a higher concentration than that of the fifth semiconductor layer 11. Impurities are, for example, P, As, Sb.

The oxide film 22 is provided so that the first electrode 7 and the second electrode 10 are not short-circuited with the surrounding wiring. The material of the oxide film 22 is, for example, a silicon oxide film or a silicon nitride film.

The first quench resistor 15 and the second quench resistor 16 are provided to cause a voltage drop and converge the electric charges flowing from the first electrode 7 and the second electrode 10.

The back surface electrode 17 is provided to apply a voltage to the first semiconductor layer 5, the second semiconductor layer 6, the third semiconductor layer 8, and the fourth semiconductor layer 9. As the material of the back electrode 17, for example, aluminum or an aluminum-containing material, or another metal material combined with the material is used.

The ground 18 is provided to generate a potential difference.

The protective layer 70 is provided to protect the electrodes 7 and 10 from coming into contact with the outside and short-circuiting. The material of the protective layer 70 is, for example, a silicon oxide film or a silicon nitride film.

The photodetection operation of a photodetector having a short-distance cell 1 and a long-distance cell 2 will be described.
In the detection standby state, the APD included in each cell is applied with a reverse voltage higher than its breakdown reverse voltage, and operates in a region called Geiger mode. Since the gain of the APD during Geiger mode operation is very high and ^{105 to 106,} it becomes possible to measure a weak light of one photon. The phenomenon of discharging in this Geiger mode is called Geiger discharge.

A resistor is connected in series to each APD, and when one photon is incident and Geiger discharges, the voltage drop due to the resistor terminates the amplification action due to the pn junction, so that a pulsed charge is obtained. This resistance is called a quench resistance.

In Silicon Photomultipliers (SiPM) with APD connected side by side, each APD performs this function, so if Geiger discharge occurs in multiple APDs, the charge of one APD is several times the APD discharged by Geiger. The amount of charge or the charge of the pulse peak value is obtained. Therefore, since the number of APDs discharged from the electric charge, that is, the number of photons incident on SiPM can be measured, it is possible to measure each photon individually.

FIG. 3 is a diagram showing the relationship between the n-type impurity concentration, the p-type impurity concentration and the depletion layer when the same amount of the n-type impurity and the p-type impurity is injected. The case where the n-type impurity concentration and the p-type impurity concentration are high is shown in FIG. 3 (a), and the case where the n-type impurity concentration and the p-type impurity concentration are low is shown in FIG. 3 (b).

In general, when the pn junction is in an equilibrium state, n-type impurities and p-type impurities are ionized, carriers are bonded, and the charge disappears, so that a depletion layer is generated. The length of this depletion layer is longer in FIG. 3 (b) than in FIG. 3 (a). That is, the higher the n-type impurity concentration and the p-type impurity concentration, the smaller the length of the depletion layer, and the smaller the length of the depletion layer, the larger the electric field. The electric field increases even if either the n-type impurity concentration or the p-type impurity concentration increases. Since the avalanche probability that contributes to the sensitivity of the photodetector increases in proportion to the electric field described above, the sensitivity of the photodetector is improved. The avalanche probability indicates the probability of doubling the avalanche.

Next, the n-type impurity concentration near between the first semiconductor layer 5 and the second semiconductor layer 6 (for example, pn junction, also referred to as the interface between the semiconductor layers 5 and 6), the third semiconductor layer 8 and the fourth semiconductor layer 9 The n-type impurity concentration near the space (for example, pn junction, also referred to as the interface between the semiconductor layers 8 and 9) will be described with reference to FIG. Here, the vicinity refers to the vicinity up to the depletion layer formed by the pn junction.

FIG. 4 is a diagram showing n-type impurity concentrations and p-type impurity concentration distributions of the first cell 1 and the second cell 2 at a depth from the light incident side to the substrate side.

As shown in FIGS. 4A and 4B, since the first semiconductor layer 5 and the third semiconductor layer 8 have the same impurity concentration in the present embodiment, the p-type impurity concentration gradient near the pn junction is almost the same. It is the same. On the other hand, when comparing the n-type impurity concentration gradients near the pn junction of the second semiconductor layer 6 and the fourth semiconductor layer 9, the fourth semiconductor layer 8 is larger. That is, when comparing the n-type impurity concentrations in the vicinity of the pn junction of the second semiconductor layer 6 and the fourth semiconductor layer 9, the fourth semiconductor layer 8 is larger. Due to the nature of ion implantation, when the same amount of impurities is implanted, the impurities are more likely to diffuse when the impurities are implanted deeper than when they are implanted shallowly. The deeper the pn junction is in the stacking direction, the smaller the impurity concentration gradient near the pn junction. Therefore, for the reason described above, the electric field of the second cell 2 having the fourth semiconductor layer 8 having a large impurity concentration gradient is larger than that of the first cell 1.

Further, since the pn junctions are provided at different depths in the first cell 1 and the second cell 2, when a positive voltage is applied from the electrodes 7 and 10, in the first cell 1, the avalanche is multiplied by the holes. In the second cell 2, the avalanche is multiplied by an electron. In the case of silicon, the magnitudes of the electron ionization rate (α) and the hole ionization rate (β) are α> β, and the proportion of electrons contributing to avalanche multiplication is higher than that of holes. Therefore, the avalanche probability of the second cell 2 is higher than that of the first cell 1.

By providing pn junctions at depths in different stacking directions in this way, different sensitivities are obtained.

FIG. 5 is a diagram showing a photodetector 100 including the photodetector of the first embodiment.

As shown in FIG. 5, the short-distance cell 1 is connected to the short-distance TOF processing unit 19 (also referred to as the first processing unit) via the wiring of the separation unit 3. The short-distance TOF processing unit 19 calculates the electric charge from the short-distance cell 1 in the distance information by the TOF. The calculated distance information is transmitted to the distance information selection unit 21. Further, the long-distance cell 2 is connected to the long-distance TOF processing unit 20 (also referred to as a second processing unit) via the wiring of the separation unit 3. The long-distance TOF processing unit 20 calculates the distance information by TOF for the electric charge from the long-distance cell 2. The calculated distance information is transmitted to the distance information selection unit 21. The distance information selection unit 21 selects, for example, the one having the higher SN ratio from the distance information of the short-distance cell 1 and the distance information of the long-distance cell 2. An image can be created using this selected distance information.

The photodetector according to the present embodiment includes a long-distance cell 2 and a short-distance cell 1 corresponding to the length of the subject distance, so that even if the subject distance range in which a general photodetector cannot accurately detect light is wide, Accurate light detection.

Regardless of the example of FIG. 5, the distance information of the short-distance cell 1 and the distance information of the long-distance cell 2 may be combined by the distance information selection unit 21 to form one image. The synthesis method is described in, for example, International Publication No. 2012/073722.

(Second embodiment)
The points different from the first embodiment will be described.

FIG. 6 is a diagram showing a pp'cross section of the photodetector shown in FIG. In FIG. 6, it is assumed that light is incident from above.

As shown in FIG. 6, the photodetector according to the present embodiment has a seventh semiconductor having a higher impurity concentration than the first semiconductor layer 5 between the first semiconductor layer 5 and the second semiconductor layer 6 of the first embodiment. A second'cell 200 in which the layer 23 is provided and an eighth semiconductor layer 24 in which an eighth semiconductor layer 24 having a higher impurity concentration than the third semiconductor layer 8 is provided between the third semiconductor layer 8 and the third semiconductor layer 8 is provided. Includes cell 300 and.

The seventh semiconductor layer 23 is formed by ion-implanting impurities having a higher concentration than that of the first semiconductor layer 5 into the first semiconductor layer 5. The impurity is, for example, B.

The eighth semiconductor layer 24 is formed by ion-implanting impurities having a higher concentration than that of the third semiconductor layer 8 into the third semiconductor layer 8. The impurity is, for example, B.

FIG. 7 is a diagram showing n-type impurity concentrations and p-type impurity concentration distributions of the 1st cell 200 and the 2nd cell 300 at a depth from the light incident side to the substrate side.

As shown in FIGS. 7A and 7B, by providing the 7th semiconductor layer 23 and the 8th semiconductor layer 24, the p-type impurity concentration gradient near the pn junction becomes larger than that in the first embodiment. Therefore, the avalanche probability can be made higher than that of the first embodiment.

In the optical detector according to the present embodiment, the seventh semiconductor layer 23, the third semiconductor layer 8 and the third semiconductor layer 6 have a higher impurity concentration than the first semiconductor layer 5 between the first semiconductor layer 5 and the second semiconductor layer 6. An eighth semiconductor layer 24 having a higher impurity concentration than the third semiconductor layer 8 is provided between the semiconductor layers 8, between the fourth semiconductor layer 9 and the eighth semiconductor layer 24, and between the second semiconductor layer 6 and the third semiconductor layer 8. 7 A pn junction is formed between the semiconductor layers 23. The p-type impurity concentration near the pn junction in the first cell 200 and the second cell 300 of the present embodiment is the p-type impurity concentration near the pn junction in the first cell 1 and the second cell 2 of the first embodiment. Will be larger than. Therefore, in the photodetector according to the present embodiment, the electric field becomes large for the reason described above, and the sensitivity is improved.

(Third Embodiment)
FIG. 8 is a diagram showing a rider device 5001 according to a third embodiment.

The rider device 5001 according to the present embodiment includes a line light source and a lens, and can be applied to a long-distance subject detection system and the like. The lidar device 5001 has a light projecting unit that projects laser light on the object 501, a light receiving unit that receives the laser light from the target object 501, and a time for the laser light to reciprocate to the target object 501. It is equipped with an optical flight time distance measuring device (not shown) that measures and converts it into distance.

In the floodlight unit, the laser light oscillator 304 oscillates the laser light. The drive circuit 303 drives the laser light oscillator 304. The optical system 305 takes out a part of the laser beam as reference light, and irradiates the object 501 with the other laser beam through the mirror 306. The mirror controller 302 controls the mirror 306 to project laser light onto the object 501. Here, flooding means shining light.

In the light receiving unit, the reference light detector 309 detects the reference light extracted by the optical system 305. The photodetector 310 receives the reflected light from the object 500. The distance measuring circuit 308 measures the distance to the object 501 based on the difference between the time when the photodetector 309 for reference light detects the reference light and the time when the photodetector 310 detects the reflected light. The image recognition system 307 recognizes the object 501 based on the result measured by the distance measuring circuit 308.

The lidar device 5001 is a distance image sensing system that employs an optical flight time ranging method that measures the time it takes for a laser beam to reciprocate to an object 501 and converts it into a distance. The lidar device 5001 is applied to an in-vehicle drive-assist system, remote sensing, and the like. When the photodetector according to the first embodiment and the second embodiment is used as the photodetector 310, good sensitivity is exhibited particularly in the near infrared region. Therefore, the lidar device 5001 can be applied to a light source in a wavelength band invisible to humans. The rider device 5001 can be used, for example, for detecting obstacles for automobiles.

FIG. 9 is a diagram for explaining a measurement system.

The measurement system includes at least a photodetector 3001 and a light source 3000. The light source 3000 of the measurement system emits light 412 to the object 500 to be measured. The photodetector 3001 detects the light 413 transmitted, reflected, and diffused through the object 500.

As the photodetector 3001, for example, when the photodetector according to the first embodiment and the second embodiment is used, a highly sensitive measurement system is realized.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. This embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. This embodiment and its modifications are included in the scope of the invention described in the claims and the equivalent scope thereof, as well as in the scope and gist of the description.

1 ... Short-distance cell, 2 ... Long-distance cell, 3 ... Separation part, 4 ... Substrate, 5 ... 1st semiconductor layer, 6 ... 2nd semiconductor layer, 7 ... 1st electrode, 8 ...・ Third semiconductor layer, 9 ・ ・ 4th semiconductor layer, 10 ・ ・ 2nd electrode, 11 ・ ・ 5th semiconductor layer, 12 ・ ・ 6th semiconductor layer, 15 ・ ・ 1st quench resistance, 16 ・ ・ 2nd Quench resistance, 17 ... back electrode, 18 ... ground, 19 ... short-distance TOF processing unit, 20 ... long-distance TOF processing unit, 21 ... distance information sorting unit, 22 ... oxide film, 23 ... 7 semiconductor layer, 24 ... 8th semiconductor layer, 70 ... protective layer, 100 ... optical detector, 200 ... 1st cell, 300 ... 2nd cell

Claims (12)

At least one first cell that converts the incident light into an electric charge,
It comprises at least one second cell, which converts the incident light into an electric charge.
The first cell includes a first semiconductor layer and a second semiconductor layer provided on the incident side of the light with respect to the first semiconductor layer.
The second cell includes a third semiconductor layer and a fourth semiconductor layer provided on the incident side of the light with respect to the third semiconductor layer.
The interface between the third semiconductor layer and the fourth semiconductor layer is located on the incident side of the light with respect to the interface between the first semiconductor layer and the second semiconductor layer.
The first cell detects light with the first sensitivity when the amount of incident light is greater than a predetermined amount of light.
The second cell is a photodetector that detects light with a second sensitivity when the amount of incident light is less than a predetermined amount of light. The photodetector according to claim 1, wherein the first cell and the second cell are avalanche photodiodes that operate in Geiger mode. At least one first cell that converts the incident light into an electric charge,
It comprises at least one second cell, which converts the incident light into an electric charge.
The first cell includes a first semiconductor layer and a second semiconductor layer provided on the incident side of the light with respect to the first semiconductor layer.
The second cell includes a third semiconductor layer and a fourth semiconductor layer provided on the incident side of the light with respect to the third semiconductor layer.
The interface between the third semiconductor layer and the fourth semiconductor layer is located on the incident side of the light with respect to the interface between the first semiconductor layer and the second semiconductor layer.
The first cell and the second cell are photodetectors that are avalanche photodiodes that operate in Geiger mode. A first quench resistor electrically connected to the first cell,
The photodetector according to claim 2 or 3 , further comprising a second quench resistor electrically connected to the second cell. The photodetector according to any one of claims 1 to 4 , wherein the thickness of the first cell and the second cell in the stacking direction is uniform. The photodetector according to any one of claims 1 to 5 , wherein the light is near infrared light. The photodetector according to any one of claims 1 to 6 , further comprising a separating portion provided between the first cell and the second cell so that the cells do not interfere with each other. The photodetector according to any one of claims 1 to 7 , wherein the first semiconductor layer and the third semiconductor layer are the same semiconductor layer. The photodetector according to any one of claims 1 to 8.
The first processing unit that calculates the distance information from the electric signal from the first cell, and
A second processing unit that calculates distance information from the electrical signal from the second cell,
An optical detection device including a first processing unit and a distance information sorting unit that sorts distance information calculated by the second processing unit. A light source that irradiates an object with light,
The photodetector according to any one of claims 1 to 8 , which detects the light reflected by the object.
Rider device equipped with. A photodetector comprising at least one first cell that converts incident light into an electric charge and at least one second cell that converts the incident light into an electric charge.
The first processing unit that calculates the distance information from the electric signal from the first cell, and
A second processing unit that calculates distance information from the electrical signal from the second cell,
A distance information sorting unit for selecting the distance information calculated by the first processing unit and the second processing unit is provided.
The first cell includes a first semiconductor layer and a second semiconductor layer provided on the incident side of the light with respect to the first semiconductor layer.
The second cell includes a third semiconductor layer and a fourth semiconductor layer provided on the incident side of the light with respect to the third semiconductor layer.
The interface between the third semiconductor layer and the fourth semiconductor layer is located on the incident side of the light with respect to the interface between the first semiconductor layer and the second semiconductor layer.
The first cell and the second cell are photodetectors that are avalanche photodiodes. A light source that irradiates an object with light,
A photodetector that detects the light reflected by the object is provided.
The photodetector comprises at least one first cell that converts incident light into an electric charge and at least one second cell that converts the incident light into an electric charge.
The first cell includes a first semiconductor layer and a second semiconductor layer provided on the incident side of the light with respect to the first semiconductor layer.
The second cell includes a third semiconductor layer and a fourth semiconductor layer provided on the incident side of the light with respect to the third semiconductor layer.
The interface between the third semiconductor layer and the fourth semiconductor layer is located on the incident side of the light with respect to the interface between the first semiconductor layer and the second semiconductor layer.
The first cell and the second cell are lidar devices that are avalanche photodiodes.

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