Growth of heterojunctions in Si–Ge alloy nanowires by altering AuGeSi eutectic composition using an approach based on thermal oxidation

Abstract

Understanding the growth mechanism of heterojunctions in silicon–germanium alloy (Si–Ge) nanowires is helpful for designing adequate physical properties in the material for device applications. We examine the formation of the heterojunction in low Ge-content Si–Ge nanowires by an approach of thermal oxidation, which produces an atomically abrupt interface with an obvious concentration change. Forming heterojunctions in Si–Ge nanowires by this approach involves more complicated reaction routes than direct growth of heterojunction nanowires using the vapor–liquid–solid method. At the beginning of the oxidation process, the AuGeSi eutectic liquid at the nanowire tip significantly etches the Si–Ge alloy nanowires. Selective oxidation of Si results in a change of the relative amount of Ge to Si in the eutectic liquid, which further modulates the solubility of Ge and Si atoms. The compositional variation in the Au–Ge–Si ternary alloy system during the oxidation process accounts for the observed concentration profile in the heterojunction nanowire. The thermal oxidation approach is applied on a low Ge-content Si–Ge thin film that is coated with Au nanoparticles. Si–Ge nanodots, which exhibit a higher Ge concentration, are precipitated epitaxially in the film, as a result of compositional modulation in the AuGeSi eutectic liquid.