Optical investigation of AlxGa1-xN epitaxial films grown on AlN buffer layers

In this study we investigate AlxGa1-xN/AlN heterostructure layers grown on c-plane sapphire by RF-plasma enhanced molecular beam epitaxy. The Al mole fraction was varied through the entire range of compositions (0less than or equal toxless than or equal to1), and was determined from Rutherford backscattering (RBS) analysis and X-ray diffraction (XRD). The thicknesses of the AlxGa1-xN layers ranged from 650 nm to approximate to2 mum, and those of the AlN buffer layers from approximate to100 nm to approximate to400 nm. Reflection and cathodoluminescence measurements were carried out in the photon energy range between 3.0 and 6.2 eV at various cryogenic temperatures down to liquid helium temperature. The reflection measurements yield a bowing parameter b = (0.91 +/- 0.14) eV for the dependence of the band-gap energy on the alloy composition. (C) 2002 Elsevier Science B.V. All rights reserved.