In situ control of step formation on Si(100) surfaces during MOVPE preparation for III-V-on-Si solar cells

One of the fundamental problems for III-V-on-Si growth relates to the difference in atomic structure which manifests itself in the polarity of the III-V material as opposed to the non-polar nature of the silicon substrate. As a consequence, the step structure of the substrate is vital for defect-free heteroepitaxy, with single-layer steps on the substrate initiating anti-phase disorder in the III-V material, while a double-layer stepped substrate in principle enables anti-phase-free III-V growth. We have investigated step formation on Si(100) surfaces in H₂ process gas environment. D_A-type double layer steps, which are considered energetically least favorable on both the clean and the monohydride-terminated Si(100) surface, can be prepared on 2° misoriented substrates. We attribute D_A step formation to vacancy generation due to the reactive process environment, and subsequent vacancy diffusion and annihilation at step edges. In situ reflection anisotropy spectroscopy (RAS) enables direct observation of the domain content of the surface during processing and the interaction between Si(100) and H₂ process gas.