Photodetector, photodetector array, and drive method comprising a second transistor including a channel of first conductivity type and a first transistor including a channel of second conductivity type that has polarity opposite to polarity of the first conductivity type

1. A photodetector comprising:

at least one avalanche photodiode (APD) including a first semiconductor layer of a first conductivity type and a second semiconductor layer of a second conductivity type;

a first transistor connected to the first semiconductor layer and including a channel of the second conductivity type that has polarity opposite to polarity of the first conductivity type; and

a second transistor connected to the first semiconductor layer and including a channel of the first conductivity type.

2. The photodetector according to claim 1 , wherein

the first transistor is brought into:

conduction during a reset period during which a voltage of the first semiconductor layer is reset to a first voltage; and

non-conduction during an exposure period during which the at least one APD detects light.

3. The photodetector according to claim 2 , wherein

the second transistor is brought into:

non-conduction during the reset period; and

a half-ON state during the exposure period.

4. The photodetector according to claim 3 , wherein

during the exposure period, a difference between a gate voltage of the second transistor and a second voltage is less than a breakdown voltage of the at least one APD, the second voltage being a voltage of the second semiconductor layer included in the at least one APD.

5. The photodetector according to claim 1 , wherein

the first transistor includes a first terminal connected to the first semiconductor layer and a second terminal connected to a power line,

the second transistor includes a third terminal connected to the first semiconductor layer and a fourth terminal connected to the power line, and

the second terminal and the fourth terminal are electrically connected.

6. The photodetector according to claim 2 , further comprising:

a third transistor including a channel of the first conductivity type, wherein

the second transistor is connected to the first semiconductor layer via the third transistor.

7. The photodetector according to claim 6 , wherein

during a transmission period, the third transistor transmits charge accumulated in the at least one APD to one end of the second transistor, and

the exposure period and the transmission period are a same period.

8. The photodetector according to claim 7 , further comprising:

a fourth transistor connected to a connection portion at which the second transistor and the third transistor are connected to each other and including a channel of the first conductivity type or the second conductivity type; and

a storage capacitance element connected in series with the fourth transistor.

9. The photodetector according to claim 8 , wherein

during a capacitance reset period, the second transistor and the fourth transistor are concurrently brought into conduction to reset a voltage of one end of the storage capacitance element to a third voltage V 3 ,

during an accumulation period, the fourth transistor transmits, to the storage capacitance element, the charge that has been transmitted to the one end of the second transistor during the exposure period, and

during the exposure period and the accumulation period, the second transistor is in a half-ON state.

10. The photodetector according to claim 9 , wherein

the second transistor is also in the half-ON state during a discharge period during which excessive charge accumulated in the one end of the second transistor is discharged after the transmission period.

11. The photodetector according to claim 10 , wherein

the third transistor is in the half-ON state during at least one of the exposure period, the transmission period, or the discharge period.

12. The photodetector according to claim 9 , wherein

a threshold voltage of the third transistor is higher than a threshold voltage of the second transistor.

13. The photodetector according to claim 1 , wherein

at least one of a gate area size of the first transistor or a gate area size of the second transistor is larger than a gate area size of an other transistor within the photodetector.

14. The photodetector according to claim 1 , wherein

at least one of a gate oxide film of the first transistor or a gate oxide film of the second transistor is thicker than a gate oxide film of an other transistor within the photodetector.

15. The photodetector according to claim 1 , further comprising:

a semiconductor substrate, wherein

the semiconductor substrate includes a first well of the first conductivity type and a second well of the second conductivity type,

the first transistor is disposed in the first well, and

the second transistor is disposed in the second well.

16. The photodetector according to claim 15 , wherein

at least one of the first well or the second well is in a linear shape.

17. The photodetector according to claim 15 , further comprising:

a first photodetector circuit including the at least one APD, the first transistor, and the second transistor; and

a second photodetector circuit including same elements as the first photodetector circuit, wherein

at least one of the first well or the second well is commonly used by the first photodetector circuit and the second photodetector circuit.

18. The photodetector according to claim 17 , wherein

any of a gate, a drain, and a source of the first transistor is shared by the first photodetector circuit and the second photodetector circuit.

19. The photodetector according to claim 15 , wherein

a direction of the channel of the first transistor is orthogonal to a direction of a channel of a transistor of the second conductivity type.

20. The photodetector according to claim 17 , wherein

the first photodetector circuit and the second photodetector circuit are arranged in mirror symmetry in a plan view of the semiconductor substrate.

21. The photodetector according to claim 1 , further comprising:

a first semiconductor substrate in which the at least one APD is disposed; and

a second semiconductor substrate in which the first transistor and the second transistor are disposed.

22. The photodetector according to claim 21 , wherein

the first semiconductor substrate further includes a trench, and

the trench is disposed on a light illumination surface side of the first semiconductor substrate with respect to a multiplication region of the at least one APD.

23. The photodetector according to claim 1 , wherein

the at least one APD is used in a Geiger multiplication mode.

24. A photodetector array comprising:

two or more photodetectors, the two or more photodetectors each being the photodetector according to claim 1 .

25. The photodetector array according to claim 24 , further comprising:

an isolation region between APDs adjacent to each other or between the at least one APD and the first transistor, the APDs each being the at least one APD, wherein

at least part of the isolation region is a depletion layer.

26. The photodetector array according to claim 25 , wherein

the isolation region includes neither a trench nor a contact.

27. A drive method for driving a photodetector, wherein

the photodetector includes:

at least one avalanche photodiode including a first semiconductor layer of a first conductivity type and a second semiconductor layer of a second conductivity type;

a first transistor connected to the first semiconductor layer and including a channel of the second conductivity type that has polarity opposite to polarity of the first conductivity type; and

a second transistor connected to the first semiconductor layer and including a channel of the first conductivity type, and

the drive method comprises:

during a reset period, bringing (i) the first transistor into conduction to reset a voltage of the first semiconductor layer to a first voltage and (ii) the second transistor into non-conduction; and

during an exposure period after the reset period, bringing (i) the first transistor into non-conduction and (ii) the second transistor into a half-ON state.