Carrier dynamics in shallow GaAs/AlGaAs quantum wells

We report a comprehensive study of carrier relaxation, recombination and escape mechanisms in a set of nine high-quality GaAs/AlxGa1-xAs shallow quantum wells (SQW), under various conditions of applied electric field, temperature and excitation energy, by means of time-integrated and time-resolved photoluminescence. Our experimental findings are analyzed theoretically and bring a better understanding of SQW properties as well as conventional QWs. In a biased SQW at low temperature, it is shown that photo-carrier escape via direct tunneling results in a strong quenching of the luminescence at fields one order of magnitude smaller than what prevails in conventional QWs. Apart from the field-activated escape process, we demonstrate the existence of thermally activated escape dynamics due to the low effective barrier height in SQWs. Time-resolved photoluminescence at low temperature reveals both a major increase in the relaxation times and radiative recombination times in SQWs, in good agreement with our theoretical model. (C) 1998 Elsevier Science B.V. All rights reserved.