Optical properties of tetragonal germanium nanocrystals deposited by the cluster-beam evaporation technique: New light emitting material for future

Abstract

The germanium (Ge) nanocrystals were deposited on substrates whose temperature was kept at room or liquid nitrogen (LN₂) temperature by the cluster-beam evaporation technique. The deposited films are found to consist of the tetragonal crystalline structure rather than the diamond structure of bulk Ge. Such a phase-transition has been theoretically predicted for sizes smaller than 4 nm, which agrees with the size measured by the transmission electron microscopy (TEM). The tetragonal Ge is expected to have a direct band gap of 1·47 eV. Furthermore, the Ge film deposited at LN₂ temperature exhibits unique properties, such as photo-oxidation and blue-light emission. The Ge-nanocrystal films deposited by the cluster-beam evaporation technique are attractive materials for application to light emitting devices in future.