Temperature-dependent absorption measurements of excitons in GaN epilayers

Optical absorption measurements were performed on a series of thin GaN epilayers. Sharp spectral features were observed due to the Is A and B exciton transitions. Using polarization dependent absorption, the C exciton transition was identified. A broad absorption feature was observed at similar to 3.6 eV, which is attributed to indirect exciton-phonon absorption. The excitonic structure was found to persist well above room temperature. A fit to the Varshni formula yielded a temperature dependence of E(T) = E(T = 0) -11.8 x 10(-4)T(2)(1414 + T) eV for the A and B excitons. The exciton absorption linewidth was studied as a function of temperature, indicating that GaN exhibits very large exciton-phonon coupling. (C) 1997 American Institute of Physics.