The effect of annealing on the surface morphology of strained and unstrained InxAl1−xN thin films

InxAl1−xN is a particularly useful group-III nitride alloy because by adjusting its composition it can be lattice matched to GaN. Such lattice-matched layers may find application in distributed Bragg reflectors (DBRs) and high electron mobility transistors (HEMTs). However, compared with other semiconducting nitride alloys, InxAl1-xN has not been researched extensively. In this study, thin InxAl1−xN epilayers were grown by metal-organic vapour phase epitaxy (MOVPE) on GaN and AlyGa1−yN layers. Samples were subjected to annealing at their growth temperature of 790 °C for varying lengths of time, or alternatively to a temperature ramp to 1000 °C. Their subsequent surface morphologies were analysed by atomic force microscopy (AFM). For both unstrained InxAl1−xN epilayers grown on GaN and compressively strained epilayers grown on AlyGa1−yN, surface features and fissures were seen to develop as a consequence of thermal treatment, resulting in surface roughening. It is possible that these features are caused by the loss of In-rich material formed on spinodal decomposition. Additionally, trends seen in the strained InxAl1−xN layers may suggest that the presence of biaxial strain stabilises the alloy by suppressing the spinode and shifting it to higher indium compositions.