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-resolved photoluminescence measurements were combined as two approaches for the determination of the oscillator strength. By varying (in a small magnetic field) the spin subband hole distribution at constant total concentration, we observe an increase of the oscillator strength in absorption, proportional to the hole concentration in one spin subband (the one which allows the X+ formation). The measurements done for different, total hole concentrations show an important decrease of the X+ oscillator strength per carrier when increasing the total concentration. On the contrary the radiative lifetime, 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 we deduce from transmission in the limit of vanishing hole concentration. (C) 2000 Published by Elsevier Science B.V. All rights reserved.