UC Berkeley

We use transient absorption spectroscopy to measure carrier lifetimes in the multiband semiconductor GaPyAs1-x-yNx. These measurements probe the electron populations in the conduction band, intermediate band, and valence band as a function of time after an excitation pulse. Following photoexcitation of GaP0.32As0.67N0.01, we find that the electron population in the conduction band decays exponentially with a time constant τCB=23 ps. The electron population in the intermediate band exhibits bimolecular recombination with recombination constant r=2×10-8 cm3/s. In our experiment, an optical pump pulse excites electrons from the valence band to the intermediate and conduction bands, and the change in interband absorption due to absorption saturation and induced absorption is probed with a delayed white-light pulse. We model the optical properties of our samples using the band anticrossing model to extract carrier densities as a function of time. These results not only identify the short minority-carrier lifetime as a key factor affecting the performance of GaPyAs1-x-yNx-based intermediate-band solar cells but also provide guidance on ways to address this issue.