Spectral response of steady-state photoluminescence from GaAs_1-xP_x layers grown on a SiGe/Si system

Measuring the spectral response of photoluminescence (SR_PL) in solar cells has recently attracted attention as it can be used as a contactless relative measure of external quantum efficiency (EQE) prior to full device fabrication. However, this technique requires that the monitored PL spectrum originates mainly from a region in the solar cell with uniformly distributed majority carriers. For a stack of thin films with a similar material composition, the slightly different emission spectrum from each layer may lead to the superposition of several luminescence peaks. This letter presents the measurement of the SR_PL from GaAsP tandem solar cells and outlines a method for separating the individual layer contributions. Good agreement between measured SR_PL and EQE at short wavelengths has been achieved, and the deviations at longer wavelengths have been analyzed. This study also reveals unexpected bandgap narrowing resulting from a variable material composition within the active region.