Critical thickness as a function of the indium molar fraction in cubic In_xGa_1-xN and the influence in the growth of nanostructures

The critical thickness for the relaxation of cubic (beta) InxGa1-xN layers grown over (002) beta-GaN/MgO, with different indium content, particularly of 17, 44, and 70% have been determined experimentally. The layers were grown by plasma-assisted molecular beam epitaxy. In all the samples studied, the critical thickness (hc) of the pseudomorphic layer was measured with a frame-by-frame analysis of reflection high energy electron diffraction (RHEED) patterns. The growth mode transition during layer growth was identified via RHEED patterns, from layer by layer or 2D to 3D growth mode by gradually transitioning from a streaky to a spotty pattern. The experimental he value of beta-InxGa1-xN on beta-GaN was compared to values calculated from the Fisher model. For the indium concentration of x = 0.44, the self-assembling epitaxial nanostructures were successfully grown in the Stranski-Krastanov growth mode with a critical thickness of 1.8 +/- 0.7 nm. The beta-In0.44Ga0.56N nanostructures showed a variation in morphology and density depending on the deposition time; self-assembled nanodots and nano-bars were confirmed by atomic force microscopy. Photoluminescence spectra of beta-In0.44Ga0.56N nanostructures showed emissions associated with quantum confinement; these peaks indicate a blue shift with respect to the bulk.