Elimination of an artifact in the photoluminescence spectra of heavily doped C-GaAs epitaxial layers on undoped GaAs substrates

Selective absorption of light in the undoped GaAs substrate is shown to be responsible for a spurious but prominent feature observed in the photoluminescence spectra of C-doped epitaxial GaAs layers that have smaller band gaps than the substrate. It is shown that the feature is an optical artifact and, indeed, an intrinsic characteristic of luminescence spectroscopy techniques when they are used for analysis of epitaxial layers on semiconductor substrates. The artifact may lead to false interpretation of data and hinder quantitative photoluminescence analysis of the electronic structure of heavily doped GaAs epilayers. We show experimental and analytical methods that can be easily implemented to remove the artifact and, thereby, restore the true emission spectrum.