Visible photoluminescence from the nanophase film prepared by GeAl co-evaporation

Abstract

Abstract Nanocluster-assembled thin films have been prepared by a GeAl co-evaporation technique. The nanoclusters were deposited on crystalline silicon (c-Si) and quartz substrates and then coated with a layer of NaCl to prevent the nanoclusters from oxidation in air. The composition of the thin films is about 86 at.% Ge and 14 at.% Al. From transmission electron microscopy and X-ray diffraction patterns, it is clear that the thin films consist of Ge nanocrystals (NCs) and amorphous Ge (a-Ge) nanoclusters with incorporated Al atoms, and the mean diameter of Ge NCs is estimated to be about 5 nm. In the absorption spectrum, a shoulder peak appears at 3.44–4.05 eV, which results from the Ge NCs. Under 3.54 eV excitation, the photoluminescence (PL) peaks appear at 2.30, 2.43, and 2.82–3.02 eV. The strong PL peak at 2.82–3.02 eV is ascribed to a-Ge nanoclusters with incorporated Al atoms; the two weak PL peaks at 2.30 and 2.43 eV are assigned to Ge NCs and can be explained by the quantum confinement effect.