PHOTOCURRENT AND PHOTOLUMINESCENCE MEASUREMENTS IN THE NEAR-BAND-EDGEREGION OF 6H GAN

The optical transitions near the band edge in molecular-beam epitaxy g rown 6H GaN films on sapphire have been studied by photocurrent (PC) a nd photoluminescence (PL) measurements. The low-temperature PC spectra show well-resolved free-exciton transitions, which allow us to determ ine 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 par ameters from the energetic position of the free A exciton transition, which serve as an input to the fit function for the PC spectra. Variat ion of the sample temperature between 5 and 300 K allows us to extract the temperature dependence of the band gap. (C) 1998 American Institu te of Physics.