Influence of growth and annealing conditions on photoluminescence of Ge/Si layers grown on oxidized Si surfaces

Ge/ Si structures with a layer of Ge islands grown on oxidized Si surfaces and covered with Si were recently found to exhibit intense photoluminescence ( PL) in the D1 region (similar to 0.8 eV) after annealing at high temperatures. We show that this PL is a property of the Ge/ Si structures grown at low temperatures from about 400 to 500 degrees C, at which crystal defects are introduced through the coalescence of strained three- dimensional islands. PL features are found to be independent of Ge thickness over a wide range from 0.7 to 3 nm. A monotonic increase in PL with annealing temperature is observed up to 1000 degrees C, but PL completely vanishes after annealing at higher temperatures. The transmission electron microscopy data show the presence of dense arrays of crystal defects in the Si layer capping the layer of Ge islands.