Probing the AlxGa1−xN spatial alloy fluctuation via UV-photoluminescence and Raman at submicron scale

Abstract

We present a straightforward method for the study of alloy spatial compositional distribution at the submicron scale via photoluminescence and Raman spectroscopy. The spatial dependence of the band gap light-emission energy of AlxGa1−xN alloys at composition 0⩽x⩽1 was studied via deep UV-photoluminescence and Raman microscopy in order to address the issue of the spatial alloy fluctuation. The data were acquired in a random fashion from an area of ∼1 mm2 on the sample at steps of ∼1–200 μm utilizing the 244 nm laser line of probing spot size ∼300 nm radius. Our study indicates that the photoluminescence emission energy exhibits random type variations depending on locality: the alloys of composition x=0.12, x=0.22, x=50, and x=0.70 exhibit average variations of ∼10, 30, 45, and 25 meV, respectively. The photoluminescence of the pure GaN exhibits no significant spatial fluctuation. The stress contribution to the observed photoluminescence fluctuations was investigated via Raman analysis and was taken into account in order to estimate the local compositional fluctuation Δx. Our results indicate that for the higher Al composition alloys x=0.50 and 0.70 the stress and the compositional fluctuation can be resolved, resulting in average spatial fluctuations of Δx=0.004 and 0.002, respectively.