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Comparison of Thin GaN and AlN Layers Deposited by Plasma Assisted Molecular Beam Epitaxy on 6H-SiC

We have studied the effect of the deposition temperature and high temperature annealing on the quality of thin GaN and AlN layers on 6H-SiC substrates. By systematic characterization using reflection high electron energy diffraction (RHEED) and atomic force microscopy (AFM), we have shown that the two nitrides act differently in the early stage of growth. GaN undergoes a Stransky-Krastanov transition enhanced by the post growth annealing. AlN is less sensitive to the effect of annealing and the layers are comparatively smoother than the GaN ones. GaN gives easily the cubic phase at low temperatures whereas it is less feasible for AlN. For each material, better morphology and crystallinity are achieved at the highest temperature studied (800°C) but AlN is preferable to GaN as no islands are formed with AlN.