Abstract
We present an analysis of carrier dynamics of the single-photon detection process, i.e., from Geiger mode pulse generation to its quenching, in a single-photon avalanche diode (SPAD). The device is modeled by a parallel circuit of a SPAD and a capacitance representing both space charge accumulation inside the SPAD and parasitic components. The carrier dynamics inside the SPAD is described by time-dependent bipolar-coupled continuity equations (BCE). Numerical solutions of BCE show that the entire process completes within a few hundreds of picoseconds. More importantly, we find that the total amount of charges stored on the series capacitance gives rise to a voltage swing of the internal bias of SPAD twice of the excess bias voltage with respect to the breakdown voltage. This, in turn, gives a design methodology to control precisely generated charges and enables one to use SPADs as conventional photodiodes (PDs) in a four transistor pixel of a complementary metal-oxide-semiconductor (CMOS) image sensor (CIS) with short exposure time and without carrier overflow. Such operation is demonstrated by experiments with a 6 µm size 400 × 400 pixels SPAD-based CIS designed with this methodology.
Highlights
Single-photon avalanche diodes (SPADs) are devices capable of detecting an individual photon by generating a large current pulse due to the Geiger mode (GM) avalanche multiplication of an electron-hole pair created on initial detection of a single photon. [1,2,3,4]
Operation of a single-photon avalanche diode (SPAD) is comprised of three stages; (i) an idling stage; (ii) single-photon detection followed by a GM pulse generation; (iii) quenching the GM pulse
Numerical calculations of bipolar-coupled continuity equations (BCE) show that the carrier number in a SPAD depletion region is of the capacitive relaxation quenching in a SPAD-based CMOS image sensor (CIS)
Summary
Single-photon avalanche diodes (SPADs) are devices capable of detecting an individual photon by generating a large current pulse due to the Geiger mode (GM) avalanche multiplication of an electron-hole pair created on initial detection of a single photon. [1,2,3,4]. Rapid progress has been made in the development of SPAD-based complementary metal-oxide-semiconductor (CMOS) image sensors (CIS). Operation of a SPAD is comprised of three stages; (i) an idling stage; (ii) single-photon detection followed by a GM pulse generation; (iii) quenching the GM pulse. A SPAD is biased with a voltage (|Vex |) in “excess” of the breakdown voltage (|VBD |). During the quenching process, generated charges accumulate on any capacitive component in parallel with the SPAD. The accumulated charges are drained out through a series resistance in order to recover (recharge) the SPAD to the idling state. Conventional SPAD-based CISs have pixel circuits with many components for quenching and counting GM pulses resulting in relatively large pixel sizes and low fill factors [2,3,4,15]. If a SPAD-based CIS with a standard four-transistors
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