Preparation of single-domain Si(100) surfaces with in situ control in CVD ambient

III-V films grown heteroepitaxially on Si(100) substrates by metal-organic chemical vapor deposition (MOCVD) are desired for the combination of optoelectronics with microelectronic devices. Difficulties regarding device quality are related to the formation of the crucial III-V/Si(100) interface, where single-layer steps on the substrate surface induce antiphase disorder in the epitaxial film. In principle, double-layer steps on the Si(100) substrate prevent the occurrence of antiphase disorder. While the preparation of silicon surfaces is well-established in UHV, preparation in H₂ ambient differs considerably. Considered energetically least favorable on both the clean and the monohydride-terminated Si(100) surface, single domain surfaces with double layer steps in the unusual D_A configuration were recently prepared in MOCVD ambient. The D_A step formation on Si(100) with 2° offcut in CVD ambient is suggested to originate in vacancy generation and diffusion on the terraces accompanied by preferential annihilation at the step edges. Here, we investigate Si removal and vacancy formation on Si(100) substrates with large terraces under CVD preparation conditions. With in situ reflection anisotropy spectroscopy (RAS), we directly observe the domain formation in dependence of the preparation route. Oscillations in transient RA measurements indicate layer by layer Si removal during annealing in hydrogen. Based on scanning tunneling microscopy results, we conclude that vacancy island formation and anisotropic expansion preferentially in parallel to the dimer rows of the terraces explains the layer-by-layer Si removal process.