Oscillatorstrengthofexcitonsandchargedexcitonsin ZnSe=ZnMgSSeQWswitha2DEGoflowdensity

We report on reectivity studies of negatively charged excitons (trions) and exciton states in ZnSe=(Zn,Mg)(S,Se) quantum wells with a two-dimensional electron gas of low density (ne61:2 10 11 cm 2 ). The radiative damping (i.e. oscillator strength) of the trion states grows linearly with increasing electron concentration. The exciton radiative damping is weakly sensitive to the electron concentration, but we found a strong contribution of exciton{electron scattering processes to the broadening of the exciton resonance. An optical method to determine the electron concentration of diluted 2DEG is developed. ? 2000 Elsevier Science B.V. All rights reserved.