How does diffusion affect radiative efficiency measurements?

Defect-related recombination can lower the efficiency of many semiconductor devices. We measure the radiative efficiency (the ratio of emitted to incident light) as a function of excitation laser power to investigate defect-related recombination in GaAs. Images of the emitted light reveal isolated dark regions where the radiative efficiency is reduced. When the laser is focused onto one of these defective regions, the dependence of the radiative efficiency on excitation power is dramatically different. Using these results, we model the distribution of defect-related energy levels near and far from the isolated defect. But our defect-related recombination model is incomplete because it does not account for diffusion. Our radiative efficiency measurements depend strongly on laser focusing, suggesting that diffusion is important. We seek to understand how diffusion modifies our experimental results.