Mechanism for improved quality B₁₂As₂ epitaxial films on (0001) 4H-SiC substrates offcut towards [1-100]

Epitaxial growth of icosahedral boron arsenide (B₁₂As ₂, abbreviated here as IBA) on 4H-SiC substrates intentionally misoriented from (0001) towards [1-100] is shown to eliminate rotational twinning. Comparisons of IBA on on-axis and off-axis c-plane 4H-SiC by synchrotron white beam x-ray topography (SWBXT) and high resolution transmission electron microscopy (HRTEM) confirm the single crystalline nature and much higher quality of the films on the latter substrates. Furthermore, no intermediate layer between the epilayer and substrate was observed for IBA on off-axis 4H-SiC. It is shown that the vicinal steps formed by hydrogen etching on the off-axis 4H-SiC substrate surface before deposition cause the film to adopt a single orientation, a process that is not seen on substrates with either no misorientation, or those tilted toward the [11-20] direction. This work demonstrates that c-plane 4H-SiC with 7° offcut toward [1-100] is potentially a good substrate choice for the growth of high-quality, untwinned IBA epilayers for future device applications.