We construct a theory for the quantum efficiency of radiation in bulk semiconductor crystals as observed in PL measurements. The general form of the external quantum efficiency (EQE), which is directly measured from the PL intensity, is formulated by considering the self-absorption in the sample. For a better understanding of the physical concept behind the EQE, we derive a simple analytical formula for EQE in a weak photoexcitation condition and discuss the relation between EQE and internal quantum efficiency (IQE). We find that, in contrast to IQE, EQE is affected by two kinds of light-extraction efficiencies, ηopt and ηself. ηopt gives the fraction of luminescence passing through the sample surface without the optical Fresnel reflection. Meanwhile, ηself gives the fraction of luminescence reaching the sample surface that overcomes the self-absorption process inside the sample. ηself strongly depends on the spatial carrier distribution, because of which carrier-diffusion phenomena have a large impact on EQE. We also show an example calculation of the theoretical calibration curve of EQE to determine the concentration of nonradiative recombination centers (NRCs) in semiconductor samples. The NRC concentration estimated from the calibration curve is consistent with the recent omnidirectional photoluminescence measurements, and the sensitivity is high enough to quantify defect concentrations for power-device applications.
ASJC Scopus subject areas
- Physics and Astronomy(all)