SPECTRAL PROPERTIES OF PHOTOCURRENT FLUCTUATIONS IN AVALANCHE PHOTODIODES

We provide a stochastic model that describes the time dynamics of double-carrier multiplication in an avalanche photodiode (APD) and obtain the autocorrelation function and the spectral characteristics of the photoelectric current. The photoelectric pulse generated by an APD as a result of a single injected photoelectron is regarded as a nonstationary random function of time (the impulse response function). A discrete stochastic model for the electron/hole motion and multiplication is defined on a spatio-temporal lattice and used to derive recursive equations for the mean, the variance, and the autocorrelation of the impulse response as functions of time. Correlation properties of the impulse response are studied for a conventional and a multilayer (superlattice) APD with the same mean gain and carrier-ionization rate ratio. The power spectral density of the photocurrent in response to a Poisson-distributed stream of photons of uniform rate is evaluated.