Computer simulation of photoconductivity decay in AgBr microcrystals: Relaxation model

Abstract

Previous workers have explained photoconductivity decay in AgBr microcrystals by proposing a model involving lattice relaxation following shallow surface trapping of electrons. This model is investigated using Monte Carlo simulations in which the electron and hole undergo a random walk in the volume of the microcrystals and are shallowly trapped at the surface. The decay rate is controlled by the thermal barrier that must be overcome to achieve a lower-energy lattice configuration, as well as by the density and cross section of the shallow surface traps. The simulation results lend support to the lattice relaxation model, but also suggest a significant role of free-electron/trapped-hole recombination in the photoconductivity decay. The experimentally observed increase in decay time with increasing microcrystal size is also seen in the simulations. This size dependence is due to the effect of the surface-to-volume ratio on the distribution between free and shallowly trapped states for the electron.