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

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