THERMAL AND ELECTROSTATIC STABILITY OF BIEXCITONS IN ZN1-XCDXSE ZNSE QUANTUM-WELLS/

We investigated the density and temperature dependence of biexciton re combination in Zn1-xCdxSe/ZnSe quantum wells grown by molecular beam e pitaxy. Modulation-doped structures allowed us to investigate the elec trostatic stability of biexcitons in the presence of a precise concent ration of free carriers. Doping was introduced in the central part of the barrier up to a doping concentration of 3.4 x 10(18) cm(3). The co mparison between the two sets of samples allowed us to clarify the rol e of each elementary excitation as far as lasing is concerned. Althoug h the biexciton binding energy in our undoped samples was sufficiently higher than in III-V materials, biexcitons are not stable at temperat ures greater than 50 K. Moreover, the electrostatic screening and many -body effects caused by free-carriers decrease the biexciton binding e nergy so that biexcitons are not observed in modulation-doped samples. We found that the vicinity of the stimulated emission line at thresho ld with the peak of biexcitonic recombination, is not a sufficient cri terion to conclude that lasing is biexcitonic in origin. (C) 1998 Else vier Science B.V. All rights reserved.