Optical properties of wurtzite GaN epilayers grown on<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>A</mml:mi></mml:math>-plane sapphire

Abstract

The exciton binding energies are measured in GaN grown on $A$-plane sapphire. A value of $25\ifmmode\pm\else\textpm\fi{}1\mathrm{meV}$ is found to be consistent with reflectance and photoreflectance experiments. This 25 meV value matches very well the results obtained on GaN epilayers grown on $C$-plane sapphire with strong biaxial compression, and seems to indicate that exciton energies in GaN epilayers are predominantly influenced by strain fields. From the in-plane anisotropy of optical response, we deduce a value of $\ensuremath{-}2.4\mathrm{eV}$ for the ${C}_{5}$ deformation potential in GaN.