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

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Abstract
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 Δ1-Γ25′ 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.