Photoreflectance measurements of unintentional impurity concentrations in undoped GaAs

Abstract

Modulated photoreflectance is used to measure the unintentional impurity concentrations in undoped epitaxial GaAs. A photoreflectance signal above the band gap spreads with the unintentional impurity concentrations and shows well-defined Franz–Keldysh peaks whose separation provide a good measure of the current carrier concentrations. In samples less than 3 μm thick, a photoreflectance signal at the band edge contains a substrate-epilayer interface effect which precludes the analysis of the data by using the customary third derivative functional fits for low electric fields.