Formation of germanates on germanium by chemical vapor treatment

The surface of a single crystal Germanium wafer was transformed to fluoride and oxide crystals upon exposure to a vapor of HF and HNO₃ chemical mixture. Ellipsometry, X-ray, SEM and photoluminescence were used to investigate the physical properties of the resultant surface structure. The analysis indicates that the transformation results in a polycrystalline hexagonal ammonium fluogermanates and a hexagonal α-Germanium oxide clusters with a preferential crystal growth orientation in <101> direction. The fluogermanates grow particularly around the germanium oxide clusters as evidenced by electron dispersive spectroscopy profiling. Local vibrational mode analysis confirm the presence of N-H and Ge-F vibrational modes of NH₄⁺ and GeF₆^- ions. The vibrational modes at around 840 cm^{- 1} is significative of GeO_x stretching bands originating from the partial coverage surface oxide formed together with the fluogermanates and clusters on the Germanium. Electronic band structure as probed by ellipsometry is typical of Ge and any discrepancy was associated with disorder induced band tailing effects originating possibly from the effect of oxide clustering.