Domain-sensitive in situ observation of layer-by-layer removal at Si(100) in H2 ambient
Double-layer step formation on Si(100) substrates is a crucial prerequisite for antiphase-domain free III–V compound semiconductor heteroepitaxy. Due to its unequaled relevance in microelectronics, the (100) oriented surface of silicon is by far the most studied semiconductor surface. However, Si(100) preparation in hydrogen process gas ambient, which is commonly employed for Si and III–V device preparation, is completely different from preparation in ultra-high vacuum due to strong interaction between H2 and the Si surface, leading to a kinetically driven different step formation. Here, we observe chemical layer-by-layer removal of surface atoms from the terraces at the Si(100) surface during annealing in hydrogen ambient. Mutually perpendicularly oriented dimers on subsequently removed monolayers induce oscillations in the in situ reflection anisotropy spectroscopy (RAS) signal. Scanning tunneling microscopy measurements support a model, where surface atom removal proceeds by formation and anisotropic expansion of vacancy islands on the terraces. We determined an activation energy Ed of 2.75 ± 0.20 eV for Si etching in H2 ambient by transient in situ RAS measurements. In situ control of the highly reactive Si(100) surface preparation is essential for subsequent defect-free III–V heteroepitaxy.