Phononless radiative recombination of indirect excitons in a Si/Ge type-II quantum dot

Phononless radiative recombination is observed in luminescence spectra of Ge quantum wells decorated by self-organized Stranski-Krastanow (S-K) dots grown on Si (100). External uniaxial tensile stress along [011] allows the discrimination of phonon-missing optical transitions. The phononless recombination is attributed to a dipole-allowed k diagonal Delta(1)-Gamma(25') interband transition involving the hole in the Ge wetting layer and the electron in a Si quantum dot encompassed by large S-K dots, The weak oscillator strength of the phononless recombination is evidenced by its slow decay kinetics. The results indicate that low-lying broad band features due to S-K dots are also of phononless origins. (C) 1997 American Institute of Physics.