  An approximate iterative model of avalanche process in a pixel of micropixel
avalanche photodiode initiated by a single photoelectron is presented. The
model describes development of the avalanche process in time, taking into
account change of electric field within the depleted region caused by internal
discharge and external recharge currents. Conclusions obtained as a result of
modelling are compared with experimental data. Simulations show that typical
durations of the front and rear edges of the discharge current have the same
magnitude of less than 50 ps. The front of the external recharge current has
the same duration, however duration of the rear edge depends on value of the
quenching micro-resistor. It was found that effective capacitance of the pixel
calculated as the slope of linear dependence of the pulse charge on bias
voltage exceeds its real capacitance by a factor of two, while the total pixel
voltage drop equals twice the value of bias overvoltage.
