Hydrogen passivation of interfacial gap state defects at UHV-prepared ultrathin SiO2 layers on Si(1 1 1), Si(1 1 0), and Si(1 0 0)

A complete in situ process from preparation and hydrogen passivation to interface gap state analysis by near-UV photoelectron spectroscopy (NUV-PES) without breaking ultrahigh vacuum (UHV) conditions is applied to ultrathin oxide layers on Si(1 1 1), (1 1 0), and (1 0 0). RF plasma oxidation with thermalized neutral oxygen atoms allows the growth of homogeneous ultrathin SiO2 layers (<2 nm) and the preparation of compositionally and structurally abrupt Si/SiO2 interfaces with minimal amounts of suboxides ranging from 2% on Si(1 0 0) to 4% on Si(1 1 0). The oxide growth is independent of the crystallographic orientation. Appropriate plasma treatment with nearly thermalized hydrogen atoms (Ekin<1 eV) leads to significant passivation of dangling bonds at the ultrathin-SiO2/Si interfaces and is most efficient on Si(1 0 0). In contrast, energetic hydrogen plasma treatment of these interfaces with kinetic energies exceeding 120 eV, which is conventionally applied for polycrystalline Si thin-film solar cells, imparts large amounts of energy and deteriorates the electrical properties as is reflected in interface degradation and increased densities of defect states.