Absorption coefficient, energy gap, exciton binding energy, and recombination lifetime of GaN obtained from transmission measurements

The absorption coefficient for a 0.4-μm-thick GaN layer grown on a polished sapphire substrate was determined from transmission measurements at room temperature. A strong, well defined exciton peak for the A and B excitons was obtained. The A, B, and C excitonic features are clearly defined at 77 K. At room temperature, an energy gap Eg=3.452±0.001 eV and an exciton binding energy ExA,B=20.4±0.5 meV for the A and B excitons and ExC=23.5±0.5 meV for the C exciton were determined by analysis of the absorption coefficient. From this measured absorption coefficient, together with the detailed balance approach of van Roosbroek and Shockley, the radiative constant B=1.1×10−8 cm3/s was obtained.