Optical properties of cluster-based nanofilms prepared by Ge–Al co-evaporation

Three GeAl thin nanofilms have been prepared by Ge–Al co-evaporation technique. The measurements of transmission electron microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) indicate that the films consist of Ge nanocrystals (NCs) and a-Ge nanoclusters with incorporated Al atoms, and the average size of the nanoclusters are estimated to be ∼12,5 and 3 nm. The XRD also suggests that Ge NCs are preferentially oriented to (1 1 0) plane growth due to the stacking faults of Ge atoms during crystallization at low temperatures. The absorption spectra changed drastically. The interband transition absorption in bulk Ge disappeared, and the absorption edge is shifted to high energy. These spectral changes can be qualitatively explained by quantum confinement effect.