Light detection device

Abstract

To provide a light detection device that can prevent generation of heat in an APD due to incidence of light and damage to a reading circuit according to a variation in voltage.SOLUTION: A first terminal 61 is connected with a first electrode 11a of an APD 11. A first circuit unit 64 and a second circuit unit 65 are connected with a second electrode 11b of the APD in parallel to each other. A second terminal 62 is connected with the second electrode through the first circuit unit. A third terminal 63 is connected with the second electrode through the second circuit unit. A first switch 66 and a resistor 68, and the second electrode and the second terminal are connected in series with each other. A second switch 67 and a capacitor 69 are connected with the second electrode in parallel to each other. The second switch, the second electrode, and the third terminal are connected in series with each other. A TIA 71 is connected in series with the capacitor and is connected with the second electrode through the capacitor.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a light detection device.

Background Art

[0002] A light detection device including a plurality of light receiving regions is known (for example, Patent Document 1). In Patent Document 1, a field effect transistor is connected in series to a photodiode forming a light receiving region. The energization state of the photodiode is switched by a switch using this field effect transistor. As a result, the photodiode to be used is selected.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When an avalanche photodiode is used as a photodiode forming a light receiving region, a bias voltage is applied to the avalanche photodiode. When light is incident on the avalanche photodiode in a state where a bias voltage is applied, the avalanche photodiode multiplies and outputs electrons generated in response to the incident light. At this time, the avalanche photodiode generates heat. The greater the bias voltage, the greater the amount of heat generated by the avalanche photodiode. The greater the number of avalanche photodiodes in the light detection device, the greater the amount of heat generated in the light detection device. In a light detection device using a plurality of avalanche diodes, there is a risk that the detection accuracy may decrease due to heat generation in each avalanche photodiode. Depending on the number of avalanche photodiodes in the light detection device, the value of the bias voltage, and the amount of incident light, the light detection device may also be damaged by the above heat generation.

[0005] Even when no light to be measured is incident on the avalanche photodiode, it can generate heat due to the incidence of ambient light such as sunlight. Therefore, it is conceivable to suppress the above-mentioned heat generation by stopping the application of a bias voltage to the avalanche photodiode when no light to be measured is incident on it. For example, in the photodetector described in Patent Document 1, the application of a bias voltage to the photodiode is stopped by disconnecting the electrical connection to the photodiode that forms the light-receiving region. Specifically, a switch connected in series with the photodiode is switched between a conduction state and an off state. When the switch is in the conduction state, a bias voltage is applied to the avalanche photodiode. When the switch is off, a bias voltage is not applied to the avalanche photodiode.

[0006] In this photodetector, a voltage corresponding to the bias voltage applied to the avalanche photodiode is applied to the readout circuit that reads the signal from the avalanche photodiode. Therefore, even if the heat generation is suppressed, fluctuations in the potential applied to the readout circuit in response to the switching between the conductive and disconnected states of the switch may damage the readout circuit in the photodetector.

[0007] Each aspect of the present invention aims to provide a photodetector capable of suppressing heat generation in an avalanche photodiode due to light incidence and damage to the readout circuit in response to voltage fluctuations. [Means for solving the problem]

[0008] A photodetector according to one aspect of the present invention comprises a plurality of photodetector units, each having a light-receiving region. Each photodetector unit includes an avalanche photodiode, a first terminal, first and second circuit sections, a second terminal, and a third terminal. The avalanche photodiode has first and second electrodes and forms a light-receiving region. The first terminal is connected to the first electrode. A first potential is applied to the first terminal. The first and second circuit sections are connected in parallel to the second electrode. The second terminal is connected to the second electrode via the first circuit section. A second potential is applied to the second terminal. The third terminal is connected to the second electrode via the second circuit section. A third potential is applied to the third terminal. In each photodetector unit, the first circuit section includes a first switch and a resistor, and the second circuit section includes a second switch, a capacitor, and a readout circuit. The first switch switches the connection state between the second electrode and the second terminal. The first switch, resistor, second electrode, and second terminal are connected in series with each other. The second switch switches the connection state between the second electrode and the third terminal. The readout circuit includes a transimpedance amplifier. The second switch and the capacitor are connected in parallel to the second electrode. The second switch, the second electrode, and the third terminal are connected in series to each other. The transimpedance amplifier is connected in series with the capacitor and also connected to the second electrode via the capacitor. The absolute value of the potential difference between the first potential and the third potential is smaller than the absolute value of the potential difference between the first potential and the second potential.

[0009] In one embodiment described above, the first terminal is connected to the first electrode of the avalanche photodiode. The first switch switches the connection state between the second electrode and the second terminal of the avalanche photodiode. The second switch switches the connection state between the second electrode and the third terminal of the avalanche photodiode. As a result, this photodetector can switch the bias voltage to the avalanche photodiode from the potential difference between the first potential applied to the first terminal and the second potential applied to the second terminal to the potential difference between the first potential applied to the first terminal and the third potential applied to the third terminal. This suppresses heat generation of the avalanche photodiode due to incident light and damage to the readout circuit in response to voltage fluctuations.

[0010] In one embodiment described above, the first switch in each photodetector unit may be connected to the second electrode via a resistor. In this case, the influence of parasitic capacitance generated in the first switch is reduced.

[0011] In one embodiment described above, the photodetector may further include a switch control unit that controls the connection state of the first and second switches according to the timing of photodetection in each photodetector unit. In this case, the photodetector can switch the bias voltage to the avalanche photodiode depending on whether or not it is time to perform photodetection.

[0012] In one embodiment described above, the switch control unit may connect the second electrode and the third terminal to the second switch when the first switch is disconnecting the connection between the second electrode and the second terminal. In this case, the photodetector can discharge the current generated when ambient light is incident on the avalanche photodiode that does not detect the light to be measured to the third terminal. As a result, damage to the readout circuit is suppressed.

[0013] In one of the above embodiments, the switch control unit may cause the second switch to disconnect the connection between the second electrode and the third terminal while the first switch is connecting the second electrode and the second terminal. In this case, heat generation in the resistor is suppressed.

[0014] In one embodiment described above, the photodetector may further include an illumination unit that emits light. The switch control unit may control the energized state of the first and second switches according to the timing of light emission from the illumination unit. In this case, the photodetector can more reliably determine whether or not it is time to perform photodetection. As a result, the photodetector can more accurately switch the bias voltage to the avalanche photodiode depending on whether or not it is time to perform photodetection.

[0015] A photodetector in another aspect of the present invention comprises a plurality of photodetectors, each having a light-receiving region. Each photodetector has an avalanche photodiode, a first terminal, first and second circuit sections, a second terminal, and a third terminal. The avalanche photodiode has first and second electrodes and forms a light-receiving region. The first terminal is connected to the first electrode. A first potential is applied to the first terminal. The first and second circuit sections are connected in parallel to the second electrode. The second terminal is connected to the second electrode via the first circuit section. A second potential is applied to the second terminal. The third terminal is connected to the second electrode via the second circuit section. A third potential is applied to the third terminal. In each photodetector, the first circuit section includes a switch and a resistor, and the second circuit section includes a diode, a capacitor, and a readout circuit. The switch switches the connection state between the second electrode and the second terminal. The switch, resistor, second electrode, and second terminal are connected in series with each other. The readout circuit includes a transimpedance amplifier. The diode and capacitor are connected in parallel to each other at the second electrode. The diode has a third electrode and a fourth electrode. The third electrode has the same polarity as the first electrode of the avalanche photodiode. The fourth electrode has the same polarity as the second electrode of the avalanche photodiode. The third electrode is connected to the third terminal. The fourth electrode is connected to the second electrode. The anode of the diode is connected to the third terminal. The transimpedance amplifier is connected in series with the capacitor and also to the second electrode via the capacitor. The absolute value of the potential difference between the first potential and the third potential is smaller than the absolute value of the potential difference between the first potential and the second potential.

[0016] In the above-described alternative embodiment, the first terminal is connected to the first electrode of the avalanche photodiode. The switch toggles the connection state between the second electrode and the second terminal of the avalanche photodiode. The fourth electrode of the diode is connected to the second electrode, and the third electrode of the diode is connected to the third terminal. The fourth electrode has the same polarity as the second electrode. The third electrode has the same polarity as the first electrode. Therefore, this photodetector can switch the bias voltage to the avalanche photodiode from the potential difference between the first potential applied to the first terminal and the second potential applied to the second terminal, to the potential difference between the first potential applied to the first terminal and the third potential applied to the third terminal. As a result, heat generation of the avalanche photodiode due to incident light and damage to the readout circuit in response to voltage fluctuations are suppressed.

[0017] In another embodiment described above, the switch in the photodetector unit may be connected to the second electrode via a resistor. In this case, the influence of parasitic capacitance generated in the switch is reduced.

[0018] In each of the above embodiments, the transimpedance amplifier may be included in a CMOS logic integrated circuit. When the transimpedance amplifier is included in a CMOS logic integrated circuit, the transimpedance amplifier can operate at a relatively high speed. However, the operating voltage range of the CMOS logic integrated circuit is limited. With the above configuration, the bias voltage applied to the avalanche photodiode can be changed while the voltage applied to the CMOS logic integrated circuit remains within the operating voltage range. Therefore, the operating speed of the transimpedance amplifier can be improved while heat generation of the avalanche photodiode and damage to the readout circuit in response to voltage fluctuations can be suppressed.

[0019] In another embodiment described above, the resistor may have an impedance greater than the input impedance of the second circuit. In this case, the signal from the avalanche photodiode can be transmitted more accurately to the transimpedance amplifier.

[0020] In the above-described alternative embodiment, the potential difference between the first potential and the second potential, and the potential difference between the first potential and the third potential, may be within the operating voltage range of the transimpedance amplifier. In this case, with a simple configuration, the operating speed of the transimpedance amplifier can be improved while suppressing heat generation of the avalanche photodiode and damage to the readout circuit in response to voltage fluctuations.

[0021] A photodetector in yet another aspect of the present invention comprises a plurality of photodetector units. Each photodetector unit has an avalanche photodiode, a first terminal, first and second circuit sections, a second terminal, and a third terminal. The avalanche photodiode has first and second electrodes. The first terminal is connected to the first electrode. The first and second circuit sections are connected in parallel to each other to the second electrode. The second terminal is connected to the second electrode via the first circuit section. The third terminal is connected to the second electrode via the second circuit section. In each photodetector unit, the first circuit section includes a first switch and a resistor, and the second circuit section includes a second switch, a capacitor, and a readout circuit. The first switch switches the connection state between the second electrode and the second terminal. The first switch, resistor, second electrode, and second terminal are connected in series to each other. The second switch switches the connection state between the second electrode and the third terminal. The readout circuit includes a transimpedance amplifier. The second switch and capacitor are connected in parallel to each other to the second electrode. The second switch, the second electrode, and the third terminal are connected in series with each other. The transimpedance amplifier is connected in series with the capacitor and also connected to the second electrode via the capacitor.

[0022] In yet another aspect described above, the first terminal is connected to the first electrode of the avalanche photodiode. The first switch switches the connection state between the second electrode of the avalanche photodiode and the second terminal. The second switch switches the connection state between the second electrode of the avalanche photodiode and the third terminal. Therefore, this optical detection device can switch the bias voltage applied to the avalanche photodiode from the potential difference between the potential applied to the first terminal and the potential applied to the second terminal to the potential difference between the potential applied to the first terminal and the potential applied to the third terminal. As a result, heat generation of the avalanche photodiode due to light incidence and damage of the readout circuit due to voltage fluctuations are suppressed.

[0023] The optical detection device in yet another aspect of the present invention includes a plurality of optical detection units. Each optical detection unit has an avalanche photodiode, a first terminal, first and second circuit portions, a second terminal, and a third terminal. The avalanche photodiode has first and second electrodes. The first terminal is connected to the first electrode. The first circuit portion and the second circuit portion are connected in parallel to the second electrode to each other. The second terminal is connected to the second electrode via the first circuit portion. The third terminal is connected to the second electrode via the second circuit portion. In each optical detection unit, the first circuit portion includes a switch and a resistor, and the second circuit portion includes a diode, a capacitor, and a readout circuit. The switch switches the connection state between the second electrode and the second terminal. The switch, the resistor, the second electrode, and the second terminal are connected in series to each other. The readout circuit includes a transimpedance amplifier. The diode and the capacitor are connected in parallel to the second electrode to each other. The diode has a third electrode and a fourth electrode. The third electrode has the same polarity as the first electrode of the avalanche photodiode. The fourth electrode has the same polarity as the second electrode of the avalanche photodiode. The third electrode is connected to the third terminal. The fourth electrode is connected to the second electrode. The transimpedance amplifier is connected in series to the capacitor and is connected to the second electrode via the capacitor.

[0024] In yet another aspect described above, the first terminal is connected to the first electrode of the avalanche photodiode. The switch switches the connection state between the second electrode of the avalanche photodiode and the second terminal. The cathode of the diode is connected to the second electrode, and the anode of the diode is connected to the third terminal. Therefore, this photodetection device can switch the bias voltage applied to the avalanche photodiode from the potential difference between the potential applied to the first terminal and the potential applied to the second terminal to the potential difference between the potential applied to the first terminal and the potential applied to the third terminal. As a result, heat generation of the avalanche photodiode due to light incidence and damage to the readout circuit due to voltage fluctuations are suppressed.

Advantages of the Invention

[0025] Each aspect of the present invention can provide a photodetection device in which heat generation of an avalanche photodiode due to light incidence and damage to a readout circuit due to voltage fluctuations are suppressed.

Brief Description of the Drawings

[0026] [Figure 1] It is a schematic diagram of the photodetection device in the present embodiment. [Figure 2] It is a schematic diagram of a light receiving portion included in the photodetection device. [Figure 3] It is a partially enlarged view of the light receiving portion. [Figure 4] It is a cross-sectional view of the light receiving portion. [Figure 5] It is a diagram for explaining the circuit of the photodetection unit. [Figure 6] It is a timing chart of control signals of different photodetection units. [Figure 7] It is a diagram showing the characteristics of the avalanche photodiode. [Figure 8] It is a diagram for explaining the circuit of the photodetection unit in a modification of the present embodiment. [Figure 9] It is a diagram for explaining the circuit of the photodetection unit in a modification of the present embodiment. [Modes for carrying out the invention]

[0027] Embodiments of the present invention will be described in detail below with reference to the attached drawings. In this description, the same reference numerals will be used for elements that are the same or have the same function, and redundant explanations will be omitted.

[0028] First, the configuration of the photodetector in this embodiment will be described with reference to Figure 1. Figure 1 is a schematic diagram showing the configuration of the photodetector in this embodiment.

[0029] The light detection device 1 measures the distance to an object by detecting light from the object. The light detection device 1 is, for example, a LiDAR (Light Detection and Ranging) system. The light detection device 1 comprises an illumination unit 2, a light receiving unit 3, and lenses L1 and L2. The illumination unit 2 has a light source 2a. The illumination unit 2 emits laser light B1 from the light source 2a. The laser light B1 emitted from the illumination unit 2 passes through lens L1 and is irradiated onto, for example, an object α. The light reflected from object α passes through lens L2 and is incident on the light receiving unit 3 as the target light B2. The light receiving unit 3 detects the incident target light B2. In addition to the target light B2, ambient light B3 is also incident on the light receiving unit 3. Ambient light B3 is, for example, sunlight.

[0030] Next, the configuration of the light-receiving unit 3 will be described with reference to Figures 2 and 3. Figure 2 is a schematic diagram of the light-receiving unit 3 of the light detection device. Figure 3 is a partially enlarged view of the light-receiving unit 3.

[0031] The light-receiving unit 3 comprises a photodetector substrate 5 and a circuit element 7. The photodetector substrate 5 and the circuit element 7 are joined to each other. In this embodiment, the photodetector substrate 5 and the circuit element 7 face each other. In this embodiment, the direction in which the photodetector substrate 5 and the circuit element 7 face each other corresponds to the Z-axis direction. Each of the photodetector substrate 5 and the circuit element 7 has a rectangular shape that extends in the XY-axis direction when viewed from the Z-axis direction. The photodetector substrate 5 and the circuit element 7 are connected to each other. In this specification, "connected" means electrical conductivity unless otherwise specified, and includes not only direct connection but also indirect connection via another member. "Connected" also includes configurations in which different elements are temporarily electrically isolated by providing a separate switch or the like between them. "Jointed" means physically connected regardless of electrical connection, and includes not only direct connection but also indirect connection via another member.

[0032] The circuit element 7 includes an integrated circuit C. In this embodiment, the circuit element 7 includes only one integrated circuit C. The circuit element 7 may include multiple integrated circuits C. The integrated circuit C is a COMS logic integrated circuit. The circuit element 7 processes the signal output from the photodetector substrate 5 in the integrated circuit C. The operating voltage range of the integrated circuit C is, for example, 20V or less.

[0033] The circuit element 7 has a port section 12. The port section 12 includes multiple electrodes. The photodetector substrate 5 and the circuit element 7 operate in accordance with the voltage applied to the port section 12. The circuit element 7 processes the signal output from the photodetector substrate 5 and outputs the processed signal to the outside of the circuit element 7 through the port section 12.

[0034] The photodetector substrate 5 and the circuit element 7 include a plurality of signal output units U. In this embodiment, the plurality of signal output units U are arranged in a two-dimensional array in the XY axis direction. In a modified version of this embodiment, the plurality of signal output units U may be arranged in a single line. As shown in Figure 3, the light receiving unit 3 includes a plurality of photodetector units 15. Each signal output unit U includes a plurality of photodetector units 15. In a modified version of this embodiment, each signal output unit U may include only one photodetector unit 15.

[0035] In this embodiment, the light receiving unit 3 performs light detection at different timings for each signal output unit U. As a variation of this embodiment, the light receiving unit 3 may perform light detection at different timings for each column or row of the signal output unit U. The light receiving unit 3 may perform light detection at the same timing for all signal output units U. Multiple light detection units 15 included in one signal output unit U perform light detection at the same timing.

[0036] Each light detection unit 15 has a light-receiving region R. The light-receiving unit 3 detects light incident on each light-receiving region R. The light detection substrate 5 converts the light incident on the light-receiving region R into electrons and transmits a signal corresponding to the electrons to the circuit element 7. In this embodiment, each light-receiving region R is formed by one avalanche photodiode 11. Hereinafter, "avalanche photodiode" will be referred to as "APD". Each APD 11 is included in the light detection substrate 5. Each APD 11 is connected to the circuit element 7.

[0037] Each photodetection unit 15 has a plurality of signal processing units P that process the signals output from the corresponding APD 11. Each signal processing unit P is included in a circuit element 7. Each signal processing unit P is included in an integrated circuit C. In this embodiment, one integrated circuit C includes a plurality of signal processing units P. The circuit element 7 processes the signals transmitted from the photodetection substrate 5 in each signal processing unit P.

[0038] Each APD11 forming a light-receiving region R is connected to a corresponding signal processing unit P. In this embodiment, as shown in Figure 3, one signal processing unit P corresponds to one light-receiving region R. One APD11 is connected to one signal processing unit P through one bump B. In other words, there is a one-to-one relationship between the signal processing unit P and the APD11.

[0039] Next, an example of the configuration of the light-receiving unit 3 will be described in detail with reference to Figure 4. Figure 4 is a cross-sectional view of the light-receiving unit. In this embodiment, the light-receiving unit 3 is a back-side incident type semiconductor photodetector.

[0040] The light-receiving unit 3 includes a light-detecting substrate 5 and a circuit element 7, as well as a glass substrate 8 and a mounting substrate 9. In this embodiment, the planes parallel to the main surfaces of the light-detecting substrate 5, the circuit element 7, the glass substrate 8, and the mounting substrate 9 correspond to the XY axis plane, and the direction perpendicular to each main surface corresponds to the Z axis direction. The glass substrate 8 faces the light-detecting substrate 5. The light-detecting substrate 5 is positioned between the circuit element 7 and the glass substrate 8. The mounting substrate 9 faces the circuit element 7. The circuit element 7 is positioned between the light-detecting substrate 5 and the mounting substrate 9.

[0041] The photodetector substrate 5 has a semiconductor substrate 10 that has a rectangular shape in plan view. The semiconductor substrate 10 is made of Si and is a P-type semiconductor substrate. The semiconductor substrate 10 has two opposing main surfaces 10a and 10b. Main surface 10a is the light incident surface on the semiconductor substrate 10.

[0042] The circuit element 7 has two opposing main surfaces 7a and 7b. In plan view, the circuit element 7 has a rectangular shape. The photodetector substrate 5 is connected to the circuit element 7. The main surfaces 7a and 10b of the substrate 5 face each other. The photodetector substrate 5 and the circuit element 7 are joined by an adhesive layer IA. The adhesive layer IA is insulating. The photodetector substrate 5 and the circuit element 7 are physically and electrically connected by a plurality of bumps B. The main surfaces 7a and 7b of the circuit element 7 are larger than the main surfaces 10a and 10b of the semiconductor substrate 10. Viewed from the Z-axis direction, the edge of the circuit element 7 surrounds the edge of the photodetector substrate 5.

[0043] The glass substrate 8 has two opposing main surfaces 8a and 8b. In plan view, the glass substrate 8 has a rectangular shape. Main surface 8b faces the main surface 10a of the semiconductor substrate 10. Main surfaces 8a and 8b are flat. The glass substrate 8 and the photodetector substrate 5 are optically bonded together by an optical adhesive OA. The glass substrate 8 may also be formed directly on the photodetector substrate 5.

[0044] The mounting substrate 9 has two opposing main surfaces 9a and 9b. Main surface 9a faces the main surface 7b of the circuit element 7. The main surface 9a of the mounting substrate 9 is larger than the main surfaces 8a and 8b of the circuit element 7. Viewed from the Z-axis direction, the edge of the mounting substrate 9 surrounds the edge of the circuit element 7. The circuit element 7 and the mounting substrate 9 are connected by bonding wires W. The mounting substrate 9 is connected to the port portion 12 via the bonding wires W.

[0045] The semiconductor substrate 10 has a plurality of APDs 11. The plurality of APDs 11 are arranged in a matrix in a two-dimensional arrangement when viewed from the Z-axis direction. Each APD 11 forms a light-receiving region R on its main surface 10a. In addition to the APDs 11, the semiconductor substrate 10 has a peripheral carrier absorption region 13. A portion of the peripheral carrier absorption region 13 is located between adjacent APDs 11 when viewed from the Z-axis direction. The peripheral carrier absorption region 13 is arranged in a grid pattern when viewed from the Z-axis direction. The peripheral carrier absorption region 13 surrounds the APDs 11. The peripheral carrier absorption region 13 is a region that absorbs carriers located at the periphery.

[0046] As shown in Figure 4, the semiconductor substrate 10 includes a semiconductor region 21 and semiconductor layers 31, 32, 33, and 34. Each of the multiple APDs 11 includes a semiconductor region 21 and semiconductor layers 31, 32, and 33. The peripheral carrier absorption section 13 includes a semiconductor region 21 and semiconductor layer 34. The peripheral carrier absorption section 13 absorbs carriers located at the periphery of the semiconductor layer 34. That is, the semiconductor layer 34 functions as a peripheral carrier absorption layer that absorbs peripheral carriers.

[0047] The semiconductor region 21 and semiconductor layers 32, 33, and 35 are of the first conductivity type, while semiconductor layers 31 and 34 are of the second conductivity type. Impurities in the semiconductor are added, for example, by diffusion or ion implantation. In this embodiment, the first conductivity type is P-type, and the second conductivity type is N-type. When the semiconductor substrate 10 is Si-based, Group 13 elements such as B are used as P-type impurities, and Group 15 elements such as P or As are used as N-type impurities. In this embodiment, semiconductor layers 32, 33, and 35 have the same impurity concentration. The impurity concentration in semiconductor layers 32, 33, and 35 is higher than that in the semiconductor region 21.

[0048] The semiconductor region 21 is located on the main surface 10b side of the semiconductor substrate 10. The semiconductor region 21 constitutes a part of the main surface 10b. The semiconductor region 21 is, for example, P-type.

[0049] The semiconductor layer 31 constitutes a part of the main surface 10b. When viewed from the Z-axis direction, the semiconductor layer 31 is in contact with the semiconductor region 21 and surrounded by the semiconductor region 21. The semiconductor layer 31 is, for example, N + This is the type. In this embodiment, the semiconductor layer 31 constitutes the cathode in the APD11.

[0050] The semiconductor layer 32 is located closer to the main surface 10a than the semiconductor layer 31. The semiconductor layer 32 is in contact with and surrounded by the semiconductor region 21. The semiconductor layer 32 is provided inside the semiconductor region 21. A portion of the semiconductor region 21 is provided between the semiconductor layer 31 and the semiconductor layer 32. The semiconductor layer 32 is, for example, a P-type semiconductor. The semiconductor layer 32 constitutes the avalanche region of the APD 11.

[0051] The semiconductor layer 33 is located closer to the main surface 10a than the semiconductor layer 32 and the semiconductor region 21. The semiconductor layer 33 constitutes the entire surface of the main surface 10a. The semiconductor layer 33 is in contact with the semiconductor region 21 on the main surface 10b side. The semiconductor layer 33 is, for example, P + It is of this type. The semiconductor layer 33 constitutes the anode of the APD11.

[0052] The semiconductor layer 34 constitutes a part of the main surface 10b. When viewed from the Z-axis direction, the semiconductor layer 34 is in contact with and surrounded by the semiconductor region 21. The peripheral carrier absorption region 13 consists of the semiconductor layer 34 and is in contact only with the semiconductor region 21 on the semiconductor substrate 10. The peripheral carrier absorption region 13 does not include a layer corresponding to the avalanche region. The semiconductor layer 34 is, for example, N + It is a type.

[0053] A groove 14 is formed in the semiconductor substrate 10. In this embodiment, the groove 14 is located closer to the edge of the semiconductor substrate 10 than the APD 11 when viewed from the Z-axis direction. The groove 14 does not penetrate the semiconductor substrate 10. The semiconductor layer 35 forms the edge of the groove 14 and a part of the main surface 10b. The semiconductor layer 35 is made of, for example, P + This is the type. The semiconductor layer 35 is in contact with the semiconductor region 21. The semiconductor layer 35 extends from the main surface 10b in the Z-axis direction and is in contact with the semiconductor layer 33. The semiconductor layer 35 constitutes the anode of the APD 11.

[0054] The photodetector substrate 5 further comprises an insulating film 41, electrodes 42 and 43, a passivation film 46, and an insulating layer 47. The insulating film 41 is laminated on the main surface 10b of the semiconductor substrate 10. The insulating film 41 is, for example, a silicon oxide film. Electrode 42 is arranged on the insulating film 41. Electrode 43 is arranged on the insulating film 41 and the edge of the groove 14. The passivation film 46 is arranged on the insulating film 41 and electrodes 42 and 43. The insulating layer 47 is arranged on the passivation film 46 and fills the groove 14, thereby forming the photodetector substrate 5 into a rectangular parallelepiped shape.

[0055] Electrode 42 penetrates the insulating film 41 and is connected to the semiconductor layer 31 of the APD11. A portion of electrode 42 is exposed from the passivation film 46 and constitutes the pad electrode 52 of the APD11. Electrode 42 outputs a signal from the APD11 at the pad electrode 52. Electrode 43 is connected to the semiconductor layer 35. A portion of electrode 43 is exposed from the passivation film 46 and constitutes the pad electrode 53 of the APD11. In this embodiment, pad electrode 52 is the pad electrode for the cathode of the APD11. Pad electrode 53 is the pad electrode for the anode of the APD11.

[0056] The pad electrodes 52 and 53 are each joined to their corresponding bumps B. Each APD11 is connected to one corresponding bump B through the pad electrode 52. Multiple APD11s are connected to different bumps B. In other words, there is a one-to-one relationship between the APD11s and the bumps B.

[0057] Next, the circuit configuration of each light detection unit 15 in this embodiment will be described with reference to Figure 5. Figure 5 is a diagram illustrating the circuit of each light detection unit.

[0058] As shown in Figure 5, each photodetection unit 15 includes an APD 11, a first terminal 61, a second terminal 62, a third terminal 63, a first circuit section 64, and a second circuit section 65. In this embodiment, the APD 11 is included in the photodetection substrate 5. The first terminal 61, the second terminal 62, the third terminal 63, the first circuit section 64, and the second circuit section 65 are included in the circuit element 7. The APD 11 has an electrode 11a and an electrode 11b. Electrode 11a is connected to the first terminal 61. Electrode 11b is connected to the first circuit section 64 and the second circuit section 65. If electrode 11a corresponds to the first electrode, then electrode 11b corresponds to the second electrode.

[0059] In this embodiment, electrode 11a is the anode of APD11. Electrode 11a corresponds to a pad electrode connected to the P-type semiconductor of APD11. In this embodiment, electrode 11a corresponds to pad electrode 53. Electrode 11b is the cathode of APD11. Electrode 11b corresponds to a pad electrode connected to the N-type semiconductor of APD11. In this embodiment, electrode 11b corresponds to pad electrode 52.

[0060] The first circuit section 64 and the second circuit section 65 are connected in parallel to each other to the electrode 11b. The second terminal 62 is connected to the electrode 11b via the first circuit section 64. The third terminal 63 is connected to the electrode 11b via the second circuit section 65.

[0061] The first circuit section 64 includes a switch 66 and a resistor 68. The switch 66 corresponds to the first switch. The switch 66 switches the connection state between electrode 11b and second terminal 62. The switch 66 switches the connection state between electrode 11b and second terminal 62 by switching between a conduction state and an interruption state. "Conditioning state" is a state in which multiple connected wires are connected. In other words, the conduction state is the ON state. "Interruption state" is a state in which multiple wires connected to each other are electrically disconnected. In other words, the interruption state is the OFF state. The switch 66, resistor 68, electrode 11b, and second terminal 62 are connected in series with each other. In other words, the switch 66 and resistor 68 are inserted in series between electrode 11b and second terminal 62. In this embodiment, the switch 66 is connected to electrode 11b via resistor 68. The resistor 68 has an impedance greater than the input impedance of the second circuit section 65.

[0062] The second circuit section 65 includes a switch 67, a capacitor 69, and a readout circuit 70. Switch 67 corresponds to the second switch. The readout circuit 70 includes a transimpedance amplifier 71. Hereinafter, the "transimpedance amplifier" will be referred to as "TIA". Switch 67 switches the connection state between electrode 11b and third terminal 63. Switch 67 switches the connection state between electrode 11b and third terminal 63 by switching between a conduction state and an interruption state. Switch 67 and capacitor 69 are connected to electrode 11b in parallel with each other. Electrode 11b, switch 67, and third terminal 63 are connected in series with each other. In other words, switch 67 is inserted between electrode 11b and third terminal 63. TIA 71 is connected in series with capacitor 69. TIA 71 is connected to electrode 11b via capacitor 69. Capacitor 69 has an input impedance lower than the input impedance of TIA 71. The impedance of resistor 68 is greater than the input impedance of both capacitor 69 and TIA71.

[0063] Switches 66 and 67 are, for example, field-effect transistors. Switches 66 and 67 are, for example, MOS-FETs. Switches 66 and 67 switch between a conduction state and an interruption state in response to the application of voltage.

[0064] In this embodiment, the switch 66, resistor 68, switch 67, capacitor 69, and TIA71 are included in one integrated circuit C. The switch 66, resistor 68, switch 67, capacitor 69, and TIA71 may each be included in different integrated circuits. At least the TIA71 is included in a CMOS logic integrated circuit.

[0065] The light receiving unit 3 further includes a switch control unit 75. The switch control unit 75 controls the switches 66 and 67 respectively. The switch control unit 75 controls the connection state of the switches 66 and 67 according to the timing of light detection in each light detection unit 15. In this embodiment, the switch control unit 75 controls the connection state of the switches 66 and 67 according to the timing of laser light B1 being irradiated from the irradiation unit 2. The switch control unit 75 switches the conduction state and the disconnection state of the switch 66. The switch control unit 75 switches the conduction state and the disconnection state of the switch 66.

[0066] The switch control unit 75 is configured, for example, by a computer. This computer has a CPU (Central Processing Unit), a main memory unit, an auxiliary memory unit, a communication control unit, an input device, and an output device. The switch control unit 75 is configured by one or more computers, which consist of this hardware and software such as programs.

[0067] In this embodiment, the switch control unit 75 is provided on the circuit element 7. In a modified version of this embodiment, the switch control unit 75 may be provided on the mounting substrate 9 separately from the circuit element 7. In a further modified version of this embodiment, the switch control unit 75 may be provided outside the light receiving unit 3.

[0068] Next, the operation of each light detection unit 15 in this embodiment will be described with reference to Figures 6 and 7. Figure 6 is a timing chart of the control signals of different light detection units. Figure 7 is a diagram showing the characteristics of the APD.

[0069] The light receiving unit 3 operates multiple signal output units U at different timings. The switch control unit 75 outputs a control signal to each signal output unit U's photodetection unit 15 instructing it to perform light detection. Each signal output unit U's photodetection unit 15 operates based on the control signal output from the switch control unit 75. The control signal output from the switch control unit 75 instructs each photodetection unit 15 on the timing to perform light detection. In this embodiment, this control signal is synchronized with the timing at which the laser beam B1 is emitted from the irradiation unit 2.

[0070] Figure 6 shows signals S1, S2, S3, and S4 as control signals output from the switch control unit 75. Signals S1, S2, S3, and S4 have different waveforms. For example, the light receiving unit 3 operates four groups of signal output units U at different timings based on signals S1, S2, S3, and S4 from the switch control unit 75. In this embodiment, each signal output unit U includes multiple photodetection units 15. The switch control unit 75 outputs signals with the same waveform to the photodetection units 15 included in the same signal output unit U.

[0071] Each of the signals S1, S2, S3, and S4 is, for example, a HighLow signal. When the signals S1, S2, S3, and S4 input to the signal output unit U are High, the photodetection unit 15 included in the signal output unit U detects the light B2 to be measured. When the signals S1, S2, S3, and S4 input to the signal output unit U are Low, the photodetection unit 15 included in the signal output unit U does not detect the light B2 to be measured.

[0072] For example, as shown in Figure 6, when signal S1 falls from a High state to a Low state, signal S2 rises from a Low state to a High state. As a result, when the photodetection unit 15 of the signal output unit U receiving signal S1 finishes detecting the target light B2, the photodetection unit 15 of the signal output unit U receiving signal S2 starts detecting the target light B2. When signal S2 falls from a High state to a Low state, signal S3 rises from a Low state to a High state. As a result, when the photodetection unit 15 of the signal output unit U receiving signal S2 finishes detecting the target light B2, the photodetection unit 15 of the signal output unit U receiving signal S3 starts detecting the target light B2.

[0073] When the photodetection unit 15 detects the target light B2, the switch control unit 75 connects the electrode 11b and the second terminal 62 to switch 66 and disconnects the electrode 11b and the third terminal 63 to switch 67. When the photodetection unit 15 does not detect the target light B2, the switch control unit 75 disconnects the electrode 11b and the second terminal 62 to switch 66 and connects the electrode 11b and the third terminal 63 to switch 67. In other words, when the photodetection unit 15 detects the target light B2, the switch control unit 75 makes switch 66 conductive and switch 67 disconnected. When the photodetection unit 15 does not detect the target light B2, the switch control unit 75 makes switch 66 disconnected and switch 67 conductive.

[0074] For example, switch 66 is in a conductive state when the control signal from switch control unit 75 is in a High state, and in an OFF state when the control signal from switch control unit 75 is in a Low state. Switch 67 is in a conductive state when the control signal from switch control unit 75 is in a Low state, and in an OFF state when the control signal from switch control unit 75 is in a High state.

[0075] A first potential is applied to the first terminal 61. A second potential is applied to the second terminal 62. A third potential is applied to the third terminal 63. A voltage corresponding to the potential difference between the first potential and the third potential, or a voltage corresponding to the potential difference between the first potential and the second potential, is applied to the APD11. The absolute value of the potential difference between the first potential and the third potential is smaller than the absolute value of the potential difference between the first potential and the second potential. The potential difference between the first potential and the second potential, and the potential difference between the first potential and the third potential, are within the operating voltage range of the TIA71. The potential difference between the first potential and the second potential is determined according to the multiplication factor set in the APD11. In this embodiment, the first potential is lower than the second and third potentials, and the third potential is lower than the second potential.

[0076] The voltage applied to the APD11 is switched according to the control of the switch control unit 75. When the light to be measured B2 is detected in the photodetection unit 15, the electrode 11b and the second terminal 62 are connected by switch 66, and the connection between the electrode 11b and the third terminal 63 is disconnected by switch 67. As a result, a voltage corresponding to the potential difference between the first potential applied to the first terminal 61 and the second potential applied to the second terminal 62 is applied to the APD11.

[0077] If the light B2 to be measured is not detected in the photodetection unit 15, the connection between electrode 11b and the second terminal 62 is disconnected by switch 66, and electrode 11b and the third terminal 63 are connected by switch 67. As a result, a voltage corresponding to the potential difference between the first potential applied to the first terminal 61 and the third potential applied to the third terminal 63 is applied to the APD 11.

[0078] In this embodiment, for example, -60V is applied to the first terminal 61 as the first potential. For example, +10V is applied to the second terminal 62 as the second potential. For example, 0V is applied to the third terminal 63 as the third potential. In this case, the third terminal 63 may be connected to ground. When the light to be measured B2 is detected in the photodetection unit 15, a voltage of 70V is applied to the APD 11 as a bias voltage. When the light to be measured B2 is not detected in the photodetection unit 15, a voltage of 60V is applied to the APD 11 as a bias voltage.

[0079] Figure 7 shows an example of the characteristics of the APD11. In Figure 7, the horizontal axis represents the bias voltage at the APD11, and the vertical axis represents the gain at the APD11. In this case, when the target light B2 is detected, the gain at the APD11 is approximately 24 times, whereas when the target light B2 is not detected, the gain at the APD11 is approximately 16 times. Thus, the gain at the APD11 decreases when the target light B2 is not detected compared to when the target light B2 is detected.

[0080] Next, with reference to Figure 8, the circuits of each photodetection unit 15A in this modified embodiment will be described. Figure 8 is a diagram illustrating the circuits of each photodetection unit 15A in this modified embodiment. This modified embodiment is generally similar to or the same as the embodiment described above. This modified embodiment differs from the embodiment described above in that a diode 80 is used instead of a switch 67. The differences between the embodiment described above and this modified embodiment will be mainly described below.

[0081] Each light detection unit 15A has an APD 11, a first terminal 61, a second terminal 62, a third terminal 63, a first circuit section 64, and a second circuit section 65A. Therefore, the light detection unit 15A differs from the light detection unit 15 in that the second circuit section 65 is the second circuit section 65A.

[0082] The second circuit section 65A includes a diode 80, a capacitor 69, and a readout circuit 70. The diode 80 has an electrode 81 and an electrode 82. Electrode 81 of the diode 80 has the same polarity as electrode 11b of the APD 11. Electrode 82 of the diode 80 has the same polarity as electrode 11a of the APD 11. Electrode 81 of the diode 80 is connected to electrode 11b. Electrode 82 of the diode 80 is connected to the third terminal 63. The diode 80 and the capacitor 69 are connected in parallel to electrode 11b. Electrode 11b, the diode 80, and the third terminal 63 are connected in series to each other. When electrode 81 corresponds to the fourth electrode, electrode 82 corresponds to the third electrode.

[0083] In this embodiment, electrode 81 connected to electrode 11b is the anode of diode 80. Electrode 82 connected to the third terminal 63 is the cathode of diode 80. As a modified example of this embodiment, when the polarity of APD11 is reversed as shown in the modified example described later using Figure 9, the cathode of diode 80 is connected to electrode 11b as electrode 81, and the anode of diode 80 is connected to the third terminal 63 as electrode 82.

[0084] In this modified example, the switch 66, resistor 68, diode 80, capacitor 69, and TIA71 are included in one integrated circuit C. The switch 66, resistor 68, diode 80, capacitor 69, and TIA71 may each be included in different integrated circuits. At least the TIA71 is included in a CMOS logic integrated circuit.

[0085] A first potential is applied to the first terminal 61. A second potential is applied to the second terminal 62. A third potential is applied to the third terminal 63. The absolute value of the potential difference between the first potential and the third potential is smaller than the absolute value of the potential difference between the first potential and the second potential. The potential difference between the first potential and the second potential, and the potential difference between the first potential and the third potential, are within the operating voltage range of the TIA71. The potential difference between the first potential and the second potential is determined according to the multiplication factor set in the APD11.

[0086] The voltage applied to the APD11 is switched according to the control of the switch control unit 75. When the light to be measured B2 is detected in the photodetection unit 15A, the electrode 11b and the second terminal 62 are connected by the switch 66. In this embodiment, the first potential is lower than the second and third potentials, and the third potential is lower than the second potential. As a result, the APD11 is subjected to a voltage corresponding to the potential difference between the first potential applied to the first terminal 61 and the second potential applied to the second terminal 62.

[0087] If the light B2 to be measured is not detected by the light detection unit 15A, the connection between electrode 11b and second terminal 62 is disconnected by switch 66. In this embodiment, the first potential is lower than the second and third potentials, and the third potential is lower than the second potential. As a result, a voltage corresponding to the potential difference between the first potential applied to the first terminal 61 and the third potential applied to the third terminal 63 is applied to the APD 11.

[0088] In this embodiment, for example, -60V is applied to the first terminal 61 as the first potential. For example, +10V is applied to the second terminal 62 as the second potential. For example, 0V is applied to the third terminal 63 as the third potential. In this case, the third terminal 63 may be connected to ground. When the light to be measured B2 is detected in the photodetection unit 15A, a voltage of 70V is applied to the APD11 as a bias voltage. When the light to be measured B2 is not detected in the photodetection unit 15, a voltage of 60V is applied to the APD11 as a bias voltage. Thus, in each photodetection unit 15A, the gain in the APD11 is lower when the light to be measured B2 is not detected compared to when the light to be measured B2 is detected.

[0089] Next, with reference to Figure 9, the circuits of each photodetector unit 15B in this modified embodiment will be described. Figure 9 is a diagram illustrating the circuits of each photodetector unit 15B in this modified embodiment. This modified embodiment is generally similar to or the same as the embodiment described above. This modified embodiment differs from the embodiment described above in that the polarity of the APD is reversed. The differences between the embodiment described above and this modified embodiment will be mainly described below.

[0090] In each photodetector unit 15B, the APD11 also has an electrode 11a and an electrode 11b. Electrode 11a is connected to the first terminal 61. Electrode 11b is connected to the first circuit section 64 and the second circuit section 65. In each photodetector unit 15B, electrode 11a is the cathode of the APD11. In this modified example, electrode 11a corresponds to a pad electrode connected to the N-type semiconductor of the APD11. Electrode 11b is the anode of the APD11. Electrode 11b corresponds to a pad electrode connected to the P-type semiconductor of the APD11.

[0091] A first potential is applied to the first terminal 61. A second potential is applied to the second terminal 62. A third potential is applied to the third terminal 63. The absolute value of the potential difference between the first potential and the third potential is smaller than the absolute value of the potential difference between the first potential and the second potential. The potential difference between the first potential and the second potential, and the potential difference between the first potential and the third potential, are within the operating voltage range of the TIA71. The potential difference between the first potential and the second potential is determined according to the multiplication factor set in the APD11. In this modified example, the first potential is higher than the second and third potentials, and the third potential is higher than the second potential.

[0092] The voltage applied to the APD11 is switched according to the control of the switch control unit 75. When the light to be measured B2 is detected in the photodetection unit 15B, the electrode 11b and the second terminal 62 are connected by switch 66, and the connection between the electrode 11b and the third terminal 63 is disconnected by switch 67. As a result, a voltage corresponding to the potential difference between the first potential applied to the first terminal 61 and the second potential applied to the second terminal 62 is applied to the APD11.

[0093] If the light B2 to be measured is not detected in the photodetection unit 15B, the connection between electrode 11b and the second terminal 62 is disconnected by switch 66, and electrode 11b and the third terminal 63 are connected by switch 67. As a result, a voltage corresponding to the potential difference between the first potential applied to the first terminal 61 and the third potential applied to the third terminal 63 is applied to the APD 11.

[0094] In this modified example, for example, +70V is applied to the first terminal 61 as the first potential. For example, 0V is applied to the second terminal 62 as the second potential. For example, +12V is applied to the third terminal 63 as the third potential. In this case, the second terminal 62 may also be connected to ground. When the light to be measured B2 is detected in the photodetection unit 15, a voltage of 70V is applied to the APD 11 as a bias voltage. When the light to be measured B2 is not detected in the photodetection unit 15, a voltage of 58V is applied to the APD 11 as a bias voltage. Thus, in each photodetection unit 15B, the gain in the APD 11 is lower when the light to be measured B2 is not detected compared to when the light to be measured B2 is detected.

[0095] Next, the operation and effects of the photodetector 1 will be explained. In each photodetector unit 15, 15B, the first terminal 61 is connected to the electrode 11a of the APD 11. Switch 66 switches the connection state between the electrode 11b of the APD 11 and the second terminal 62. Switch 67 switches the connection state between the electrode 11b of the APD 11 and the third terminal 63. Therefore, this photodetector 1 can switch the bias voltage to the APD 11 from the potential difference between the first potential applied to the first terminal 61 and the second potential applied to the second terminal 62 to the potential difference between the first potential applied to the first terminal 61 and the third potential applied to the third terminal 63.

[0096] If the bias voltage applied to the APD11 when light detection is not performed is lower than the bias voltage applied to the APD11 when light detection is performed, then heat generation of the APD11 due to incident ambient light, etc., will be suppressed when light detection is not performed. For example, in the light detection units 15 and 15B of the light detection device 1 described above, if the potential difference between the first potential and the second potential is lower than the potential difference between the first potential and the third potential, and switch 66 is in the off state and switch 67 is in the on state, then the bias voltage applied to the APD11 will decrease. As a result, heat generation of the APD11 due to incident light will be suppressed.

[0097] The bias voltage applied to the APD11 is switched between the potential difference between the first potential and the second potential, and the potential difference between the first potential and the third potential. Therefore, the fluctuation of the bias voltage in the APD11 is smaller than when the APD11 is switched between a state where a bias voltage is applied and a state where a bias voltage is not applied. As a result, fluctuations in the potential applied to the readout circuit 70 are also suppressed, and thus damage to the readout circuit 70 is also suppressed.

[0098] In the photodetector unit 15A, the first terminal 61 is connected to the electrode 11a of the APD11. The switch 66 switches the connection state between the electrode 11b of the APD11 and the second terminal 62. The electrode 81 of the diode 80 is connected to the electrode 11b, and the electrode 82 of the diode 80 is connected to the third terminal 63. Electrode 81 has the same polarity as electrode 11b. Electrode 82 has the same polarity as electrode 11a. Therefore, this photodetector 1 can switch the bias voltage to the APD11 from the potential difference between the first potential applied to the first terminal 61 and the second potential applied to the second terminal 62 to the potential difference between the first potential applied to the first terminal 61 and the third potential applied to the third terminal 63.

[0099] For example, in the photodetection unit 15A of the photodetection device 1 described above, if the switch 66 is in the off state when the potential difference between the first potential and the second potential is lower than the potential difference between the first potential and the third potential, the bias voltage applied to the APD 11 decreases. As a result, heat generation of the APD 11 due to incident light is suppressed. The bias voltage applied to the APD 11 is switched between the potential difference between the first potential and the second potential and the potential difference between the first potential and the third potential. Therefore, the fluctuation of the bias voltage in the APD 11 is smaller than when the state in which the bias voltage is applied to the APD 11 and the state in which the bias voltage is not applied to the APD 11 are switched. As a result, fluctuations in the potential applied to the readout circuit 70 are also suppressed, and damage to the readout circuit 70 is also suppressed.

[0100] In each of the photodetection units 15, 15A, and 15B, the switch 66 is connected to the electrode 11b via a resistor 68. In this case, the influence of parasitic capacitance generated in the switch 66 is reduced.

[0101] In each of the photodetection units 15, 15A, and 15B, the TIA 71 is included in a CMOS logic integrated circuit. When the TIA 71 is included in a CMOS logic integrated circuit, the TIA can operate at a relatively high speed. However, the operating voltage range of the CMOS logic integrated circuit is limited. With the above configuration, the bias voltage applied to the APD 11 can be changed while the voltage applied to the CMOS logic integrated circuit remains within the operating voltage range. Therefore, the operating speed of the TIA 71 can be improved while suppressing heat generation in the APD 11 and damage to the read circuit 70 in response to voltage fluctuations.

[0102] Each of the photodetector units 15 and 15B can operate at a relatively low operating voltage, for example, 20V or less, even when the switch 66, resistor 68, switch 67, capacitor 69, and TIA71 are all included in the same CMOS logic integrated circuit. In other words, the TIA71 can operate at a relatively high speed in a configuration where the switch 66, resistor 68, switch 67, capacitor 69, and TIA71 are all included in the same integrated circuit.

[0103] Each photodetector unit 15A can operate at a relatively low operating voltage, for example, 20V or less, even when the switch 66, resistor 68, diode 80, capacitor 69, and TIA71 are all included in the same CMOS logic integrated circuit. In other words, the TIA71 can operate at a relatively high speed in a configuration where the switch 66, resistor 68, diode 80, capacitor 69, and TIA71 are all included in the same integrated circuit.

[0104] In each of the photodetection units 15, 15A, and 15B, the resistor 68 has an impedance greater than the input impedance of the second circuit section 65. In this case, the signal from the APD 11 can be transmitted to the TIA 71 more accurately.

[0105] In each of the photodetection units 15, 15A, and 15B, the potential difference between the first potential and the second potential, and the potential difference between the first potential and the third potential, may be within the operating voltage range of the TIA71. In this case, with a simple configuration, the operating speed of the TIA71 can be improved while suppressing heat generation of the APD11 and damage to the readout circuit 70 in response to voltage fluctuations.

[0106] The photodetector 1 further includes a switch control unit 75 that controls the connection state of switches 66 and 67 according to the timing of photodetection in each photodetector unit 15, 15A, and 15B. In this case, the photodetector 1 can switch the bias voltage to the APD 11 depending on whether or not it is time to perform photodetection.

[0107] For each of the light detection units 15 and 15B, the switch control unit 75 causes switch 67 to connect electrode 11b to the third terminal 63 when switch 66 is disconnecting the connection between electrode 11b and the second terminal 62. In this case, the light detection device 1 can discharge the generated current to the third terminal 63 when ambient light B3 is incident on the APD 11 which does not detect the light to be measured B2. As a result, damage to the readout circuit 70 is suppressed.

[0108] For each of the light detection units 15 and 15B, the switch control unit 75 causes switch 67 to disconnect the connection between electrode 11b and the third terminal 63 when switch 66 is connected to electrode 11b and the second terminal 62. In this case, heat generation in resistor 68 is suppressed.

[0109] The light detection device 1 may further include an irradiation unit 2 that emits light. The switch control unit 75 controls the energized state of switches 66 and 67 according to the timing when light is emitted from the irradiation unit 2. In this case, the light detection device 1 can more reliably determine whether or not it is time to perform light detection. As a result, the light detection device 1 can more accurately switch the bias voltage to the APD 11 depending on whether or not it is time to perform light detection.

[0110] While embodiments and modifications of the present invention have been described above, the present invention is not necessarily limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention.

[0111] For example, in the embodiments and modifications described above, the APD11 operates in linear mode. However, the APD11 may also operate in Geiger mode. In this case, each photodetector unit 15 may further have a quenching circuit connected to the APD11. The quenching circuit may be provided on the photodetector substrate 5 or on the circuit element 7. The quenching circuit may be provided integrally with the resistor 68.

[0112] In the embodiments and modifications described above, the photodetector substrate 5 and the circuit element 7 are separated from each other and arranged to face each other in the Z-axis direction. However, the photodetector substrate 5 and the circuit element 7 may be integrally constructed. The photodetector substrate 5 and the circuit element 7 may be arranged in a direction intersecting the Z-axis direction.

[0113] In the embodiments and modifications described above, the photodetector substrate 5 and the circuit element 7 are connected via bumps B. However, the photodetector substrate 5 and the circuit element 7 may be directly joined together.

[0114] In the embodiments and modified examples described above, the switch control unit 75 controls switch 66 and switch 67 respectively. However, switch 66 and switch 67 may be linked. For example, switch 66 and switch 67 may be made of CMOS.

[0115] In each photodetection unit 15 and photodetection unit 15B, the switch control unit 75 opens switch 66 and closes switch 67 when the photodetection unit 15 detects the target light B2. When the photodetection unit 15 does not detect the target light B2, the switch control unit 75 closes switch 66 and opens switch 67. However, when the photodetection unit 15 does not detect the target light B2, both switch 66 and switch 67 may be opened. Even in this case, the bias voltage applied to the APD 11 is lower than when switch 66 is open and switch 67 is closed. The fluctuation of the bias voltage in the APD 11 is smaller than when the state in which a bias voltage is applied to the APD 11 and the state in which a bias voltage is not applied to the APD 11 are switched. As a result, heat generation in the APD 11 due to incident light and damage to the readout circuit 70 in response to potential fluctuations are suppressed. When switch 66 is in the off state and switch 67 is in the conductive state, heat generation in resistor 68 is suppressed compared to when both switch 66 and switch 67 are conductive.

[0116] The above-described modifications may be combined in any way. For example, in each photodetection unit 15B, a diode 80 may be used instead of the switch 67, as in the photodetection unit 15A. [Explanation of Symbols]

[0117] 1...Photodetector, 2...Irradiation unit, 11...Avalanche photodiode, 11a,11b...Electrodes, 15,15A,15B...Photodetector unit, 61...First terminal, 62...Second terminal, 63...Third terminal, 64...First circuit section, 65,65A...Second circuit section, 66,67...Switch, 68...Resistor, 69...Capacitor, 70...Readout circuit, 71...Transimpedance amplifier, 75...Switch control section, 80...Diode, 81,82...Electrodes, R...Light receiving area.

Claims

1. It comprises multiple light detection units, each having a light-receiving area. Each of the aforementioned light detection units is: An avalanche photodiode having first and second electrodes and forming the light-receiving region, A first terminal connected to the first electrode and to which a first potential is applied, The first and second circuit sections are connected in parallel to the second electrode, A second terminal connected to the second electrode via the first circuit section and to which a second potential is applied, It has a third terminal which is connected to the second electrode via the second circuit and to which a third potential is applied, In each of the aforementioned light detection units, The first circuit section includes a first switch for switching the connection state between the second electrode and the second terminal, and a resistor. The first switch, the resistor, the second electrode, and the second terminal are connected in series with respect to each other. The second circuit section includes a second switch for switching the connection state between the second electrode and the third terminal, a capacitor, and a readout circuit including a transimpedance amplifier. The second switch and the capacitor are connected in parallel to the second electrode. The second switch, the second electrode, and the third terminal are connected in series with respect to each other. The transimpedance amplifier is connected in series with the capacitor and is connected to the second electrode via the capacitor. The absolute value of the potential difference between the first potential and the third potential is smaller than the absolute value of the potential difference between the first potential and the second potential. The light detection device further includes a switch control unit that controls the connection state of the first and second switches according to the timing of light detection in each of the light detection units, The switch control unit, at the timing of light detection, connects the second electrode and the second terminal to the first switch, and disconnects the connection between the second electrode and the third terminal to the second switch. A light detection device that, when light detection is not performed, causes the first switch to disconnect the connection between the second electrode and the second terminal, and causes the second switch to connect the second electrode and the third terminal.

2. The photodetector according to claim 1, wherein in each of the photodetector units, the first switch is connected to the second electrode via the resistor.

3. It is further equipped with an irradiating section that emits light, The light detection device according to claim 1 or 2, wherein the switch control unit controls the energized state of the first and second switches in accordance with the timing at which the light is irradiated from the irradiation unit.

4. It comprises multiple light detection units, each having a light-receiving area. Each of the aforementioned light detection units is: An avalanche photodiode having first and second electrodes and forming the light-receiving region, A first terminal connected to the first electrode and to which a first potential is applied, The first and second circuit sections are connected in parallel to the second electrode, A second terminal connected to the second electrode via the first circuit section and to which a second potential is applied, It has a third terminal which is connected to the second electrode via the second circuit and to which a third potential is applied, In each of the aforementioned light detection units, The first circuit section includes a switch for switching the connection state between the second electrode and the second terminal, and a resistor. The switch, the resistor, the second electrode, and the second terminal are connected in series with respect to each other. The second circuit section includes a diode, a capacitor, and a readout circuit including a transimpedance amplifier. The diode and the capacitor are connected in parallel to the second electrode. The diode has a third electrode having the same polarity as the first electrode of the avalanche photodiode, and a fourth electrode having the same polarity as the second electrode of the avalanche photodiode. The third electrode of the diode is connected to the third terminal, The fourth electrode of the diode is connected to the second electrode, The transimpedance amplifier is connected in series with the capacitor and is connected to the second electrode via the capacitor. The absolute value of the potential difference between the first potential and the third potential is smaller than the absolute value of the potential difference between the first potential and the second potential. The light detection device further includes a switch control unit that controls the connection state of the switch according to the timing of light detection in each of the light detection units, The switch control unit connects the second electrode and the second terminal to the switch at the timing of light detection. A light detection device that, when light detection is not performed, causes the switch to disconnect the connection between the second electrode and the second terminal.

5. The photodetector according to claim 4, wherein in each of the photodetector units, the switch is connected to the second electrode via the resistor.

6. The photodetector according to any one of claims 1 to 5, wherein the transimpedance amplifier is included in a CMOS logic integrated circuit.

7. The photodetector according to any one of claims 1 to 6, wherein the resistor has an impedance greater than the input impedance of the second circuit section.

8. The photodetector according to any one of claims 1 to 7, wherein the potential difference between the first potential and the second potential, and the potential difference between the first potential and the third potential, are within the operating voltage range of the transimpedance amplifier.

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