Oscillator strengths of charged excitons: combining magnetoabsorption and photoluminescence dynamics in semimagnetic quantum wells

We present a systematic study of the oscillator strength of the positively charged excitons (X+) in Cd1-xMnxTe quantum wells. CW-absorption and time-r esolved photoluminescence measurements were combined as two approaches for the determination of the oscillator strength. By varying (in a small magnet ic field) the spin subband hole distribution at constant total concentratio n, we observe an increase of the oscillator strength in absorption, proport ional to the hole concentration in one spin subband (the one which allows t he X+ formation). The measurements done for different, total hole concentra tions show an important decrease of the X+ oscillator strength per carrier when increasing the total concentration. On the contrary the radiative life time, measured in time-resolved PL experiment, is found to be constant over the whole range of hole gas concentrations, and equal to the value which w e deduce from transmission in the limit of vanishing hole concentration. (C ) 2000 Published by Elsevier Science B.V. All rights reserved.