Exploring defect level position and occupation in GaAsP via recombination analysis

1. Exploring defect level position and occupation in GaAsP via recombination analysis KyungTaek Lim and Tim Gfroerer, Davidson College, Davidson, NC Mark Wanlass, National Renewable Energy Lab, Golden, CO Abstract When electron-hole pairs are created in a semiconductor, recombination can occur either radiatively or nonradiatively. We measure the radiative efficiency (the fraction of recombination that is radiative) as a function of laser excitation intensity and temperature to characterize recombination mechanisms and predict how defects will impact solar cell performance. In a 1.6eV-bandgap GaAsP heterostructure, we observe complex changes in the photoluminescence spectrum and radiative efficiency with excitation and temperature. The changes suggest that two defect bands may be contributing to recombination in this alloy. Further evidence for the presence of these bands is obtained by modeling the defect level occupation and recombination statistics. The analysis suggests that thermal activation out of shallow defect levels can improve the performance of solar cells incorporating GaAsP. • Conclusions, Significance, and Acknowledgement • We observe complex changes in the radiative efficiency of GaAsP with excitation and temperature. • The changes suggest that 2 defect bands may be contributing to recombination. • The presence of 2 bands, with expected characteristics, is confirmed by modeling the defect level occupation and recombination statistics. • Thermal activation out of shallow defect levels can reduce the negative impact of these states on GaAsP-based solar cell performance. • We thank Jeff Carapella for growing the test structure and • we acknowledge the Donors of the American Chemical Society – Petroleum Research Fund for supporting this work.