Microstructural evolution and defect formation during the initial stages of the growth of silicon carbide and aluminum nitride on α(6H) -SiC(0001) substrates

The effect of gas flow ratios (C₂H₄/Si₂H₆ = 1,2,10) on the growth mode of SiC thin films on vicinal α(6H)-SiC(0001) substrates by gas-source molecular beam epitaxy (GSMBE) at 950-1150°C has been investigated. Step flow, step bunching and the deposition of 6H-SiC occurred at the outset of the exposure of the (1 × 1) surface to the reactants using any flow ratio. Subsequent deposition resulted in either step flow and continued growth of 6H films using C₂H₄/Si₂H₆ = 1 or nucleation and coalescence of 3C-SiC islands on the 6H terraces using C₂H₄/Si₂H₆ = 2 and 10. The initial stage of A1N film growth on these substrates and the occurrence of defects has also been investigated. Essentially atomically flat A1N surfaces, indicative of two-dimensional growth, were obtained using on-axis substrates. Island-like features were observed on the vicinal surfaces. The coalescence of the latter features gave rise to double positioning boundaries as a result of the misalignment of the Si/C bilayer steps with the A1/N bilayers in the growing films. The quality of the thicker A1N films was strongly influenced by the concentration of these boundaries. The following sections describe the procedures used to deposit and analyze these two materials as well as detail the results and conclusions of this research.