Photo-oxidation of germanium nanostructures deposited by the cluster-beam evaporation technique

The photo-oxidation of germanium (Ge) nanostructures deposited by the cluster-beam evaporation technique is systematically studied. The significant photo-oxidation is found in the Ge-liquid nitrogen temperature (LNT) film, which was deposited on substrates whose temperature was kept at liquid nitrogen temperature during the deposition but not in the Ge-RT film, whose substrate temperature was room temperature. The difference in photo-oxidation of both types of Ge films is explained by denseness of Ge nanostructures. The threshold photon energy for photo-oxidation is close to the optical band gap estimated from the absorption spectrum of the as-deposited Ge-LNT film. The modified electron-active oxidation model is proposed to explain the photo-oxidation of Ge nanostructures. It is also hypothesized that the final size of Ge cores is determined by the incident photon energy and that the size of Ge cores becomes more uniform for prolonged photo-oxidation.