CHARGE ACCUMULATION EFFECTS IN INGAAS GAAS [111]-ORIENTED PIEZOELECTRIC MULTIPLE-QUANTUM WELLS/

We show that charge accumulation in piezoelectric [111]-oriented multi ple quantum wells (MQWs), with average electric Gelds opposing the fie ld in the barriers, inhibits the shift of optical transitions by exter nally applied electric fields. This effect is due to the screening of the average electric field as photogenerated electrons and holes drift towards the opposite edges in the MQW region due to this average fiel d. The resulting dipole flattens the envelope potential and hence prec ludes the change of energy levels with variations of external voltage. This behavior has been observed in different device configurations em ploying InGaAs/GaAs MQW embedded in a p-i-n diode by low temperature p hotoluminescence (PL) and photocapacitance spectroscopies under differ ent bias conditions. In addition to these 'self-locked' transitions we also observed other peaks in the PL spectra related to the charge acc umulation effect and that are qualitatively explained using Hartree ca lculations. (C) 1997 Elsevier Science Ltd.