Growth Rate and Temperature Dependence of Oxygen Incorporation in Si_1-XGe_x Thin Films

Abstract

A series of Si1-x Ge x heterostructures was grown at different substrate temperatures using molecular beam epitaxy (MBE) on Si <100> substrates, where the composition x was varied in a “staircase” pattern by stepping down the Ge flux between constant composition layers while maintaining a constant Si flux, and vice versa. The Ge composition and oxygen concentration of these staircase structures were then measured using secondary ion mass spectroscopy (SIMS). From the SIMS profiles, it is evident that the oxygen concentration is inversely proportional to and linear with growth rate, regardless of how that rate is changed. This observation implies that the dominant source of oxygen is the residual background in the MBE chamber. Further, the oxygen concentration retains its linearity in growth rate when changing substrate growth temperature. The oxygen concentration increases at lower growth temperature, and shows an exponential dependence in substrate growth temperature for a given rate.