Free-carrier effects on the excitonic absorption of n-type modulation-doped Zn1-xCdxSe/ZnSe multiple quantum wells

We investigated the effect of the free-electron density on the heavy-hole exciton transitions in n-type, modulation-doped Zn1-xCdxSe/ZnSe multiple quantum wells. Exciton binding energy and oscillator strength were determined from optical-absorption spectra and were found to be strongly influenced by the free-carrier concentration. Complete saturation of the excitonic absorption could be induced at sufficiently high doping levels. Comparison with theoretical predictions suggests that phase-space filling and short-range exchange interactions may account for exciton bleaching. The corresponding critical density was found to increase with Cd content as a consequence of the increasing exciton stability.