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

The germanium (Ge) nanocrystals were deposited on substrates whose temperat ure was kept at room or liquid nitrogen (LN2) temperature by the cluster-be am evaporation technique. The deposited films are found to consist of the t etragonal crystalline structure rather than the diamond structure of bulk G e. Such a phase-transition has been theoretically predicted for sizes small er than 4 nm, which agrees with the size measured by the transmission elect ron microscopy (TEM), The tetragonal Ge is expected to have a direct band g ap of 1.47 eV, Furthermore, the Ge film deposited at LN, temperature exhibi ts unique properties, such as photo-oxidation and blue-light emission, The Ge-nanocrystal films deposited by the cluster-beam evaporation technique ar e attractive materials for application to light emitting devices in future.