Impact of Trap Filling on Carrier Diffusion in MAPbBr_{3} Single Crystals

We present experimental evidence showing that the effective carrier diffusion length (L_{d}) and lifetime ({\tau}) depend on the carrier density in MAPbBr_{3} single crystals. Independent measurements reveal that both L_{d} and {\tau} decrease with an increase in photo-carrier density. Scanning photocurrent microscopy is used to extract the characteristic photocurrent I_{ph} decay-length parameter, L_{d}, which is a measure of effective carrier diffusion. The L_{d} magnitudes for electrons and holes were determined to be ~ 13.3 {\mu}m and ~ 13.8 {\mu}m respectively. A marginal increase in uniform light bias ({\leq} 5 {\times} 10^{15} photons/cm^{2}) increases the modulated photocurrent magnitude and reduces the L_{d} parameter by a factor of two and three for electrons and holes respectively, indicating that the recombination is not monomolecular. The L_{d} variations were correlated to the features in photoluminescence lifetime studies. Analysis of lifetime variation shows intensity-dependent monomolecular and bimolecular recombination trends with recombination constants determined to be ~ 9.3 {\times} 10^{6} s^{-1} and ~ 1.4 {\times} 10^{-9} cm^{3}s^{-1} respectively. Based on the trends of L_{d} and lifetime, it is inferred that the sub-band-gap trap recombination influences carrier transport in the low-intensity excitation regime, while bimolecular recombination and transport dominate at high intensity.