Photocurrent and photoluminescence measurements in the near-band-edge region of 6H GaN

Abstract
The optical transitions near the band edge in molecular-beam epitaxy grown 6H GaN films on sapphire have been studied by photocurrent (PC) and photoluminescence (PL) measurements. The low-temperature PC spectra show well-resolved free-exciton transitions, which allow us to determine the A, B, and C free-exciton energies and the corresponding direct band gaps. PL measurements were performed to check the assignment of the excitonic transitions and to derive strain-dependent excitonic parameters from the energetic position of the free A exciton transition, which serve as an input to the fit function for the PC spectra. Variation of the sample temperature between 5 and 300 K allows us to extract the temperature dependence of the band gap.