Microstructural evolution and defect formation during the initial stages of the growth of silicon carbide and aluminum nitride on alpha(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 alpha(6H)-SiC(0001) substrates by gas source molecular beam epitaxy (GSMBE) at 950-1150 degrees C has been investigated. Step flow, step bunching and the deposition of 6H-SiC occurred at the outset of the exposure of the (1 x 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 AlN film growth on these substrates and the occurrence of defects has also been investigated. Essentially atomically flat AlN 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 Al/N bilayers in the growing films. The quality of the thicker AlN 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.