A new MOS photon-counting sensor operating in the above-breakdown regime

A solid-state optical sensor based on a buried-channel charge-transfer MOS structure and operated at voltages in the above, breakdown regime is proposed. In this mode of operation the MOS photosensor performs as a photon counter with, it is suggested two significant advantages over similar sensors based on p-n junction diodes, namely: self-quenching of the avalanche discharge and possible implementation in the form of a self-scanned CCD array. In this first demonstration of the proposed device, discrete structures in silicon are investigated experimentally. It is demonstrated that internal gains of 3 × 10⁶electrons/photon are possible during operation at about 10 V above breakdown. It is also shown that, after accousting for dark generation and retriggering effects, the photon-induced count rate saturates with increasing bias above breakdown. The results are in excellent agreement with the theoretical predictions from a two-dimensional model and imply that, at 10-15 V above breakdown avalanche initiation probabilities for electrons in excess of 0.9 have been attained.