Probing the Al_cGa_(1-c)N Atomic Distribution via UV-Photoluminescence and Raman at Sub-Jim Scale

摘要

The spatial dependence of the band-gap light-emission energy of Al_xGa_(1-x)N alloys at composition 0 ≤ x ≤ 1 was studied via deep UV-photoluminescence (PL) and Raman microscopy. The data were acquired in a random fashion from an area of ～ 1mm~2 on the sample at steps of ～ 1 μm ― 200 μm utilizing the 244 nm laser line of probing spot size ～300 nm radius. Our study indicates that the PL emission energy exhibits random type variations depending on locality: the alloys of composition x=0.12, x=0.22, and x=0.70 exhibit variations of ～ 10 meV, 30 meV, and 25 meV respectively. The PL of the pure GaN exhibits no spatial dependence while the alloy of x=0.50 exhibits a variation around ～ 45 meV. Moreover, the functional dependence of the band-gap E_g, on the composition was found to be E_g(x)=3.4(1-x)+6.2x-1.2x(1-x) from which the compositional variation, Δx, can be computed for a given variation in the PL emission energy after accounting for the stress effect in the alloys.