WHY IS A QUANTUM-CONFINED STARK SHIFT ABSENT IN TYPE-I STRAINED SI1-XGEX SI SYMMETRICAL QUANTUM-WELLS/

We report on photoluminescence studies of the quantum-confined Stark e ffect (QCS) in strained Si1-xGex/Si type-I quantum wells (QWs) with sy mmetric confinement potential. Application of a weak longitudinal elec tric field leads to an upward shift of the free-exciton peaks due to a field-driven decrease of the exciton binding energies arising from th e shallow electron confinement of SiGe QWs. The existence of the maske d QCS has been separately confirmed by observing prolonged luminescenc e decay times with increasing electric field. The insertion of an asym metric potential does not fully restore the QCS redshift, indicating t hat an enhancement in the exciton binding energy is necessary to estab lish the QCS redshift.