On the Formation of IR-Light-Emitting Ge Nanocrystals in Ge:SiO2 Films

The study is concerned with light-emitting Ge nanocrystals formed during the annealing of Ge (x) [SiO2](1 -) (x) films produced by the high-vacuum cosputtering of germanium and quartz targets onto substrates at a temperature of 100A degrees C. In accordance with the conditions of growth, the Ge molar fraction was varied from 10 to 40%. By means of electron microscopy and Raman spectroscopy, amorphous Ge nanoclusters similar to 4-5 nm in dimensions are detected in as-deposited films with a Ge content higher than 20 mol %. To crystallize amorphous nanoclusters, annealing at temperatures of up to 650A degrees C is used. The kinetics of the crystallization of Ge nanoclusters is studied, and it is established that up to similar to 1/3 of the amorphous phase is retained in the system, supposedly at the interfaces between nanocrystals and the surrounding amorphous SiO2 matrix. It is found that, upon annealing in normal atmosphere, germanium nanoclusters are partially or completely oxidized (at a Ge molar fraction of 30% and smaller). An intense infrared photoluminescence signal from quantum-confined Ge nanocrystals and a visible photoluminescence signal defined by defect complexes (oxygen vacancy + excess Ge atoms) are observed.