Direct evidence of compositional pulling effect in AlxGa1-xN epilayers

We report the investigation on the compositional-pulling effect of crystalline AlxGa1-xN/(0 0 0 1) sapphire epilayers by cross-sectional cathodoluminescence (CL) and energy-dispersive X-ray (EDX) analyses. Direct evidence for the compositional distribution was found in the AlxGa1-xN (0 < x < 0.3) layers, which accompany the different optical phenomena arising from the change of the band gap. The band gap variation of the 1.7 mu m AlxGa1-xN epilayers with the Al content rising from x = 11% to 30% was observed. It is consistent with the result of depth-resolved CL spectra acquired with increasing electron energies, which can also be used to reveal the spatial composition distribution along the growth direction. We emphasize here that the selective-wavelength CL image is a very powerful tool in exploring the correlation between the specific emission and the composition of inhomogeneous alloys. (c) 2006 Elsevier B.V. All rights reserved.