Luminescence in GeOx films containing germanium nanoclusters

Abstract

Metastable GeO_x films have been deposited onto a Si substrate by the electron beam evaporation of GeO₂ powder in high vacuum. The optical properties of Ge nanoclusters in GeO_x films after a series of annealing are studied by Raman spectroscopy, ellipsometry, cathodoluminescence, and photoluminescence. After the annealings, the cathodoluminescence peaks are first found in GeO_x films in the visible spectral range (400 and 660 nm) at room temperature. The cathodoluminescence may be associated both with the existence of nonground (excited) levels in Ge nanoclusters and allowed optical transitions from an excited to ground level and surface states at Ge/GeO₂-matrix interface or defects inside a Ge nanocluster. The photoluminescence signals in a yellow-green region (2.1–2.4 eV), which are observed for GeO_x films after annealings, can be explained by quasi-direct optical transitions in Ge nanoclusters.