Initial stages of growth of thin films of III-V nitrides and silicon carbide polytypes by molecular beam epitaxy

The morphology and interface chemistry occurring during the initial deposition of BN, AlN and GaN films via metal evaporation and N₂ decomposition under UHV conditions have been determined. FTIR spectroscopy and TEM revealed the consecutive deposition of an initial 20angstrom layer of a-BN, 20-60angstrom of oriented h-BN, and a final layer of polycrystalline c-BN. This sequence is attributed primarily to increasing intrinsic compressive stress in the films. XPS analysis revealed the growth of GaN on sapphire to occur via the Stranski-Krastanov mode; growth on SiC showed characteristics of three-dimensional growth. AlN grew layer-by-layer on both substrates. Vicinal 6H-SiC(0001) substrate surfaces contain closely spaced, single bilayer steps. During deposition of Si and C at 1050°C, 6H layers initially form and step bunching occurs. The latter phenomenon results in more widely spaced steps, the nucleation of 3C-SiC both on the new terraces and at the larger steps and formation of double position boundaries. The C/Si ratio in the gaseous reactants also affects the occurrence of these three phenomena.