Effect of the Series Resistance on the Current Response of a HgCdTe Avalanche Photodiode Under High-intensity Nanosecond Irradiation

Abstract

We investigate the nonlinear signal current response of a Hg0.72Cd0.28Te avalanche photodiode (APD) irradiated by high-intensity, finite-duration laser pulses. At high irradiation levels and/or high gains, carrier-induced perturbations in the junction electric field and avalanche gain strongly influence the temporal behavior of the APD current. The total series resistance will play a major role here, and four values of the series resistance were used for mapping out the APD response. When striving for maximum achievable bandwidth, the internal junction capacitance and the internal series resistance set the ultimate limits for an APD. A signal analysis of these high-intensity nonlinear gain effects should therefore begin with an intrinsic APD, and proceed with adding appropriate external series resistances. A simultaneous modeling of the entire external circuit is then required. To this end, we have combined full-band Monte Carlo (MC) transport simulation in the active multiplication zone with conventional circuit modeling outside. We demonstrate how overshoot/undershoot and rapid oscillations in the signal current evolve in time as a function of the chosen external series resistances at two different high-intensity irradiation levels. Oscillations are shown to persist slightly beyond the duration of the laser pulse when operating the diode within the junction transit time-limited regime. The periodicity of the oscillations is related to the junction transit time and remains only weakly dependent on irradiation levels and external resistance values until we enter the resistance–capacitance (RC)-limited case. Here, a change occurs where oscillations are smoothed out as external series resistances are increased further.