Abstract
A model based on the exciton theory has been presented for lineshape analysis of photoreflectance (PR) spectra. Experimental PR spectra of high‐quality thick GaAs epilayers of different purity were measured to verify the theoretical results. It has been shown that excitonic effects completely prevail over the one‐electron theory in the formation of photoreflectance spectrum even at high electric fields and room temperature, giving evidence of the existence of Franz–Keldysh oscillations enhanced by excitonic effects. A comparison of PR spectra simulated using the exciton theory and the one‐electron approximation has shown that the semiperiods of the oscillations were practically similar. This demonstrates the validity of using the simple “high‐field” model of Aspnes and Studna to determine surface electric fields. In photoreflectance of thick ultrapure GaAs epilayers an oscillating structure was experimentally observed in the region between the excitonic and the fundamental bandgap. This provides a possibility for contactless characterization not only for doped (N ∼ 10^14^–10^18^ cm^–3^) but also for ultrapure (N ∼ 10^11^–10^13^ cm^–3^) GaAs epilayers as well as other semiconductor materials. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)