Mechanism of atomic-scale passivation and flattening of semiconductor surfaces by wet-chemical preparations

Atomic arrangements of Si(001), Si(110) and 4H-SiC(0001) surfaces after wet-chemical preparations are investigated with scanning tunneling microscopy. Their passivated structures as well as the surface formation mechanisms in aqueous solutions are discussed. On both Si(001) and Si(110) surfaces, simple 1 × 1 phases terminated by H atoms are clearly resolved after dilute HF dipping. Subsequent etching with water produces the surfaces with 'near-atomic' smoothness. The mechanisms of atomic-scale preferential etching in water are described in detail together with first-principles calculations. Furthermore, 4H-SiC(0001), which is a hard material and where it is difficult to control the surface structure by solutions, is flattened on the atomic scale with Pt as a catalyst in HF solution. After a mechanism is proposed based on electroless oxidation, the flattened surface mainly composed of a 1 × 1 phase is analyzed. The obtained results will be helpful from various scientific and technological viewpoints.