Photoreflectance spectroscopy 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 on 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, due to large built-in electric fields which also quench the oscillator strength of the transitions. Also, this te chnique allows us to magnify the features of confined excited states, which are difficult to observe by standard reflectance.