Dependence of the fundamental band gap of AlxGa1−xN on alloy composition and pressure

Optical absorption studies were performed to investigate the dependence of the fundamental band gap of AlxGa1−xN epitaxial films on Al content and applied hydrostatic pressure. The results of absorption measurements performed at atmospheric pressure yielded the variation of the band-gap energy E(x)=3.43+1.44x+1.33x2 eV for the AlxGa1−xN system. Optical absorption edge associated with the direct Γ band gap shifts linearly towards higher energy under applied pressure. By examining the pressure dependence of the absorption edge in samples with different AlN mole fractions and taking into account the difference of compressibility between the epitaxial films and sapphire substrate, the pressure coefficients for the direct Γ band gaps of AlxGa1−xN were determined.