NUMERICAL EXAMINATION OF SILICON AVALANCHE PHOTODIODES OPERATED IN CHARGE STORAGE MODE

The behavior of silicon-based avalanche photodiodes (APD's) operated i n the charge storage mode is examined. In the charge storage mode, the diodes are periodically biased to a sub-breakdown voltage and then op en-circuited. During this integration period, photo-excited and therma lly generated carriers are accumulated within the structure. The dynam ics of this accumulation and its effects upon the avalanching of the d iode warrants a detailed, fully numerical analysis. The salient featur es of this investigation include device sensitivity to the input photo -current including the self-quenching effect of the diode and its limi tations in sensing low light levels, the dependence of the response on the bulk lifetime and hence on the generation current within the devi ce, the initial gain, transient response, dependence of the device uni formity upon performance, and the quantity of storable charge within t he device. To achieve these tasks our device simulator, STEBS-2D, was utilized. A modified current-controlled boundary condition is employed which allows for the simulation of the isolated diode after the initi al reset bias has been applied. With this boundary condition, it is po ssible to establish a steady-state voltage on the ohmic contact and th en effectively remove the device from the external circuit while still including effects from surface recombination, trapped surface charge, and leakage current from the read-out electronics.