Thermal and electrostatic stability of biexcitons in Zn1-xCdxSe/ZnSe quantum wells

We investigated the density and temperature dependence of biexciton recombination in Zn1-xCdxSe/ZnSe quantum wells grown by molecular beam epitaxy. Modulation-doped structures allowed us to investigate the electrostatic stability of biexcitons in the presence of a precise concentration 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 comparison between the two sets of samples allowed us to clarify the role of each elementary excitation as far as lasing is concerned. Although the biexciton binding energy in our undoped samples was sufficiently higher than in III-V materials, biexcitons are not stable at temperatures greater than 50 K. Moreover, the electrostatic screening and many-body effects caused by free-carriers decrease the biexciton binding energy so that biexcitons are not observed in modulation-doped samples. We found that the vicinity of the stimulated emission line at threshold with the peak of biexcitonic recombination, is not a sufficient criterion to conclude that lasing is biexcitonic in origin. (C) 1998 Elsevier Science B.V. All rights reserved.