Photoreflectance on wide bandgap nitride semiconductors

Extensive research has been reported on the wide band gap nitride materials system in the past few years. Despite the development of many well-working GaN based opto- and electronic devices, theoretical and experimental understanding of many fundamental properties remains still incomplete. In this paper, we show the unique benefits that can be drawn from optical modulation spectroscopy as applied to nitride materials, despite the difficulties in working in the UV spectral range, that is required for the photoreflectance measurements of wide band gap semiconductors. By performing PR spectroscopy at low temperature in cubic phase GaN layers grown on c-SiC pseudosubstrates, the different valence band excitons are measured and compared with theoretical calculations, allowing the determination of residual strain inside the epitaxial layer. The second part of the paper is devoted to emphasize the unique interest of PR spectroscopy in the Franz Keldysh oscillations regime, especially in the case of wurtzite phase GaN/AlGaN quantum structures, in order to extract the piezoelectric field in a non-destructive all-optical experiment. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.