Theoretical study of time-resolved luminescence in semiconductors. II. Pulsed excitation

In the second part of this series, we studied TRL decay on semiconductor layers and thin film homostructures after a pulsed excitation by simulation with Synopsys TCAD (R) and by mathematical approximation. Again, our working example is Cu(In, Ga)Se-2. We investigate the influence of the excitation pulse length, axial diffusion, bulk-defects, and defects at the contacts, as well as space charge on the TRL-decay separately by quasi one-dimensional simulations of semiconductor layers and semiconductor homostructures. Material parameters like defect density, carrier mobility, and surface recombination velocity are varied in a wide range, such that the calculations are applicable to other semiconductors. We further study the influence of multi-pulse excitation. We show how material parameters such as carrier lifetime and carrier mobility can be extracted from the TRL transients and how the samples can be characterized by excitation dependent measurements in the open circuit case. We can explain some effects found in luminescence experiments, like an increased decay in semiconductor junctions due to the electric field in the space charge region. However, we also discuss the effect of charge storage which may lead to decreased decay. It is revealed that under high injection conditions single layers within a semiconductor stack can be characterized in terms of carrier lifetime. (C) 2014 AIP Publishing LLC.