Avalanche gain distribution of X-ray avalanche photodiodes

Realistic Monte Carlo simulations have been performed to study the direct effect of avalanche gain distribution on the energy resolution of X-ray APDs. The dependence of the gain distribution on the incident photon energy, detector material pair creation energy, ionization coefficient ratio, dead space, position of charge injection and the mean gain itself are analyzed. The results suggest that the distribution of avalanche gain narrows significantly when the number of carriers generated per photon increases. Initiation of the impact ionization process with carriers´ with the higher ionization coefficient as well as the presence of dead space were also found to narrow avalanche gain distribution.