GeSi nanocrystals formed by high temperature annealing of GeO/SiO_2 multilayers: structure and optical properties

摘要

The structural and optical properties of Ge and GeSi nanocrystals, formed by annealing of GeO/SiO_2 multilayers have been investigated. According to Raman spectroscopy, the formation of pure Ge nanocrystals is observed after post growth annealing at 700 ℃. Annealings at 800℃-900℃ leads to the formation of intermixed Ge_xSi_(1-x) nanocrystals. High resolution transmission electron microscopy shows that the structure and the size of the nanocrystals strongly depend on annealing temperature. Spatial redistribution of Ge with the formation of large faceted clusters located near the Si substrate as well as GeSi intermixing at the substrate/film interface were observed. In the case of the sample containing 20 pairs of GeO/SiO_2 layers annealed at 900 ℃, some clusters exhibit a pyramid-like shape. FTIR absorption spectroscopy measurements demonstrate that intermixing between the GeO and SiO_2 layers occurs leading to the formation of a SiGe02 glass. Low temperature (10 K-100 K) photoluminescence was observed in the spectral range 1400-2000 nm for samples containing nanocrystals. The temperature dependence of the photoluminescence is studied.