Revealing the role of the native oxide and the surface roughness in the visible luminescence of Ge epitaxial films

Abstract

We report here the first observation of a visible luminescence from planar, relaxed germanium films epitaxially grown on silicon (001) wafers. Even the as-grown films exhibit a bright blue-green (2.4eV) emission at room temperature. The Ge surface was subsequently etched in RF SF6 remote plasma in order to form Ge nanodots. The photoluminescence measurements of the etched surface reveal an additional emission at 2.8eV. We combine morphological characterizations with photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS) analysis to explain the origin of the observed visible luminescence. The measured emissions did not show an excitonic behavior expected for quantum confined carriers in the nanostructures. It is found that the defects in the GeO2 layer natively formed on the Ge surface are responsible for the blue-green emission of the films before and after the etching process. For the etched surface, the role of the interface Ge/GeO2 defects in the blue emission (2.8eV) will also be discussed.