Photoluminescence of ultrasmall Ge quantum dots grown by molecular-beam epitaxy at low temperatures

Low-temperature epitaxial growth of Si-Ge heterostructures opens possibilities for synthesizing very small and abrupt low-dimensional structures due to the low adatom surface mobilities. We present photoluminescence from Ge quantum structures grown by molecular-beam epitaxy at low temperatures which reveals a transition from two-dimensional to three-dimensional growth. Phononless radiative recombination is observed from <105> faceted Ge quantum dots with height of approximately 0.9 nm and lateral width of 9 nm. Postgrowth annealing reveals a systematic blueshift of the Ge quantum dot's luminescence and a reduction in nonradiative recombination channels. With increasing annealing temperatures Si-Ge intermixing smears out the three-dimensional carrier localization around the dot. (C) 2002 American Institute of Physics.