Modeling of recombination lifetimes in charge-separation device structures

摘要

Recombination processes in semiconductors are inhibited by charge-separation mechanisms that are produced in structures such as pn junctions. In this work, we calculated the recombination rates in Si and GaAs n~+p junction structures by both analytical and numerical techniques. Transport effects can be divided into three physical phenomena. The first is the flow of carriers that results in the build up of a junction voltage or charge-separation. The time constant of this effect is determined by the junction dopant concentrations and the mobilities. The second is the flow of carriers due to diffusion. The time constant of this event is a function of the carrier diffusion coefficient and physical width of the absorbing medium. In most semiconductor structures, this time constant is relatively short relative to the recombination lifetime. The third effect is the discharge of the open-circuit voltage of the junction by minority carrier charge injection. A heuristic analysis of the long-term decay in this regime indicates that the decay time varies as CkT/qJ_0, where C is the junction capacitance and J_0 is the dark current. In this regime, the decay time is a function of recombination lifetime through the dependence of J_0, but the measured excess carrier decay time is often not the true recombination lifetime of the underlying materials.