Nanocrystalline Ge Synthesis by Reduction of Si1-xGexO2 Formed by High Pressure Oxidation

Abstract

ABSTRACTNanocrystalline Ge suitable for photoluminescence studies was synthesized from hydrothermally oxidized alloys of Si60Ge40 using steam at 25 MPa and 475°C. Annealing in either an inert atmosphere (UHP N2) or in flowing forming gas (80:20 N2:H2) results in Ge precipitation. In the first case the Ge precipitates are large and concentrated in the bottom portion of the oxide and result from Si reduction of GeO2. In the case of flowing forming gas the Ge precipitates are distributed diroughout die oxide and are formed by reaction between H2 and GeO2. The precipitated samples were analyzed using Raman spectroscopy and cross sectional TEM. Preliminary photoluminescence data reveal that oxide samples excited by the 325 nm line of a HeCd laser after annealing in H2 at both 750 and 800°C for 30 min show strong visible luminescence while unannealed samples do not.