TEMPERATURE-DEPENDENCE OF EXCITON-CAPTURE AT IMPURITIES IN GAAS ALXGA(1-X)AS QUANTUM-WELLS/

In this paper we present an investigation of the exciton capture proce ss in GaAs/Al.3Ga.7As quantum wells using a picosecond time-resolved p hotoluminescence technique. We demonstrate that there are significant differences in the capture mechanism for narrow quantum wells in compa rison to bulk material. In particular the initial capture efficiency i s shown to increase with temperature. This behaviour is understood in terms of the role of localisation of the free exciton in the potential s caused by the interface roughness. Higher temperatures destroy this localisation process which otherwise limits the total capture rate for the exciton to the impurity. The effect of localisation on capture is also shown to be stronger for narrower wells. We conclude that the re lative weakness of bound exciton recombination in the near bandgap lum inescence of doped quantum wells can in part be understood by the redu ction of capture efficiency due to localisation.