Suppression of Rotational Twin Formation in Virtual GaP/Si(111) Substrates for III-V Nanowire Growth

Planar GaP epilayers on Si(111) are considered as virtual substrates for III-V-related optoelectronic devices such as high efficiency nanowire-based tandem absorber structures for solar energy conversion, next generation LEDs, and fast photodetectors. Rotational twin domains in such heteroepitaxial epilayers are found to strongly impede vertical nanowire growth. We investigate the twin-induced defect density and surface morphology of B-type GaP/Si(111) virtual substrates in dependence on the GaP nucleation process by metalorganic chemical vapor deposition. By employing quantitative high-resolution X-ray diffraction (HR-XRD)), scanning electron and atomic force microscopy (SEM and AFM), we reveal the significant influence of nucleation temperature and substrate miscut direction on the formation of rotational twin domains during a two-step GaP growth approach. The epilayer defect density is drastically decreased by low temperature GaP nucleation on Si(111) misoriented 3 degrees toward [112], where rotational twin domains are suppressed below 5% and the layers exhibit a smooth surface morphology. We demonstrate that these virtual substrates are highly suitable for vertical GaP nanowire growth.