Chemical Modification of Surface Steps on SI(111) Vicinal Wafers: a Bonding Model for Phase Changes in Second Harmonic Generation

Abstract

ABSTRACTThere have been several studies of second harmonic generation (SHG) from chemically-modified vicinal Si(111) wafers. The SH fields contain one-fold (ψ) and three-fold (3ψ) symmetry contributions, which originate respectively from the terrace and surface step atoms. The phase of these contributions are different for native oxides, and are a function of the frequency of the incident radiation, ω. To identify the origin of these different phases for the terrace and step SH fields, we use a classical anharmonic oscillator model based on two assumptions: (a) a significant fraction of Si atoms at the steps have dangling bonds when oxides are formed below ∼850°C, and (b) these step atoms are linked to atoms at the bottom of the steps by O-Si-O groups following annealing at >900°C.