Pressure and Temperature Dependence of the Absorption Edge in GaN

Abstract

Measurements of the absorption edge of single‐crystal and polycrystal GaN were made as a function of hydrostatic pressure up to 10 kbar at temperatures of 296 and 77 K. Its shift with stress, 4.2±0.4 meV/kbar at 296 K, is similar to the value 5.3±1.0 meV/kbar, calculated for the E₀ transition by Camphausen, Connell, and Paul. The absorption near the gap could be separated into a strongly temperature‐dependent component for α≳600 cm⁻¹ giving ∂E_g/∂T =−6.7×10⁻⁴ eV/K and a less sensitive component for α−1. The latter is interpreted as defect‐ or impurity‐induced absorption. The band structure proposed by Van Vechten was adjusted and the results now compare more favorably with our measurements and recent reflectance data.