Oscillator strength of excitons and charged excitons in ZnSe/ZnMgSSe QWs with a 2DEG of low density

We report on reflectivity 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 (ne⩽1.2×1011 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.