Photoreflectance spectroscopy as a powerful tool for the investigation of GaN-AlGaN quantum well structures

Room-temperature photoreflectance spectroscopy is performed on a series of GaN-AlGaN quantum wells grown by molecular beam epitaxy. We show that the p otentialities of this powerful investigation method previously demonstrated to many low-dimensional systems can be extended to nitride-based quantum w ells for accurate large scale characterisation. In particular, this techniq ue allows us to get rid of optical interferences that usually prevent the o bservation of free-exciton transitions below the band-gap of GaN. Such tran sitions occur in wide quantum wells, because of large built-in electric fie lds which also quench the oscillator strength of the transitions. Also, thi s technique allows us to magnify the features of confined excited states, w hich are difficult to observe by standard reflectance. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.