Effect of overgrowth temperature on the photoluminescence of Ge/Si islands

Ge/Si islands grown with molecular-beam epitaxy at 630 degrees C are overgrown with Si at different temperatures T-cap, and their photoluminescene spectra are recorded. Both the island-related and wetting-layer-related energy transitions redshift with lowered T-cap, which is explained by reduced material intermixing. The mandatory growth interruption, which is introduced during the temperature drop, causes island ripening and shifts the island (wetting layer) photoluminescence peaks slightly to lower (higher) energies. The growth interruption quenches the quantum efficiency of the wetting layer by more than an order of magnitude, whereas the island-related photoluminescence intensity even slightly increases. The island's superior resistance against growth interruptions, and hence interface contamination, is explained by effective carrier localization in the Ge nanostructures. Room-temperature photoluminescence is reported for Ge islands overgrown at 460 degrees C. (C) 2000 American Institute of Physics. [S0003-6951(00)02842-4].