Compositional ordering in In xGa 1-xN and its influence on optical properties

In _xGa _1-xN layers grown with compositions with the predicted miscibility gap have been studied using Transmission Electron Microscopy (TEM), x-ray diffraction and optical measurements (photoluminescence and absorption). The samples (0.34 <x <0.8) were deposited by Molecular Beam Epitaxy at 800°C using 200 nm AlN buffer layer grown directly on sapphire substrates. Another sample with x = 0.34 was grown on a GaN buffer layer. Dislocation densities in the InGaN layers were typically in the mid-10 ¹⁰ cm ^-2 to10 ¹¹ cm ^-2 range. Edge dislocations were the most prevalent. For In concentration x = 0.5 compositional ordering is observed leading to extra diffraction spots in electron and x-ray diffraction. The ordering was not observed for the sample with x=0.34 grown on GaN. Based on TEM measurements the estimated period of ordering Δ was about Δ = 45 Å for x = 0.5 and Δ = 65Å for x = 0.78. The sample with x = 0.5 had the highest dislocation density. In addition to the presence of threading dislocations two types of domain boundaries on (0001) and (0110) planes were also observed in this sample. This sample has a broader photoluminescence (PL) that is redshifted compared to the absorption edge ("Stokes shift"). © 2005 Materials Research Society.