Breakdown of the k-conservation rule in Si1-xGex alloy nanocrystals:: Resonant photoluminescence study

Resonant photoluminescence from Si1-xGex alloy nanocrystals as small as 4 nm in diameter embedded in SiO2 thin film matrices was studied. In pure Si nanocrystals, phonon structures were clearly observed, indicating that optical transitions are assisted by momentum-conserving phonons. These structures are quenched by adding a small amount of Ge atoms in Si nanocrystals, i.e., due to the formation of Si1-xGex alloy. Furthermore, the lifetime of the radiative recombination became much faster in doped nanocrystals. These results suggest that Si1-xGex alloy formation leads to a disorder in the translation invariance of the crystalline lattice, thus resulting in the breakdown of the k-conservation rule. (C) 2000 American Institute of Physics. [S0021-8979(00)04223-7].