Journal of Luminescence 92 (2001) 43–56 Consequences of thermalization on the photoluminescence dynamics of shallow quantum well heterostructures Ph. Roussignol*, J. Tignon, G. Bastard Laboratoire de Physique de la Matie `re Condense ´e de l’Ecole Normale Supe ´rieure, 24 rue Lhomond, F-75005 Paris, France Received 24 March 2000; accepted 26 June 2000 Abstract We calculate the time-resolved photoluminescence signal of a thermalized population of excitons in quantum wells. The excitons are assumed to be in thermal equilibrium with free carriers either in the well or in the barrier. The results of our calculations based on rate equations for particle and energy losses are compared to experimental data on GaAs/ Ga 1  x Al x As shallow quantum wells with Al concentration varying between 1.5 and 17.8%. These structures are shown to be particularly sensitive to thermalization effects over different subbands, to such an extent that the time decay of their excitonic photoluminescence has very little to do with the true exciton radiative lifetime. # 2001 Elsevier Science B.V. All rights reserved. PACS: 73.20.Dx; 78.47.+p; 78.55.Cr; 71.35.  y Keywords: Time-resolved photoluminescence; Carrier thermalization; Semiconductor quantum well heterostructures 1. Introduction Time-resolved photoluminescence (TRPL) is a very popular tool of investigation of carrier dynamics in semiconductor heterostructures. Nu- merous time-resolved experiments, in particular those done on quantum wells, are analyzed in terms of luminescent levels with a radiative lifetime t r , often of excitonic origin, fed by an upper level at a rate 1@t a . A fit to the experimental data allows to extract t a and t r . The time t r is then claimed to be the recombination time of excitons and its dependencies upon various external parameters (temperature, electric and magnetic fields, etc.) are then compared to various models (see, for example, Ref. [1]). Recent time-resolved experi- ments of excitonic PL have been undertaken on high-quality shallow GaAs/Ga 1  x Al x As quantum wells with x ranging from 0.5% to 17.8% [2]. For these samples the band offset varies between 7 and 240 meV. In these shallow quantum wells, at low temperature, a strong increase of the PL decay time is observed as x decreases. For x ¼ 1:5 and 17.8% we measured PL decay times of about 600 and 200 ps, respectively. However, an accurate theory of excitons in these structures reveals that very little variation with x is expected for the excitonic oscillator strength (less than 10%) [3]. This indicates that the interpretation of t r as the *Corresponding author. Tel.: +33-1-44-32-25-57; fax: +33- 1-44-32-38-40. E-mail address: philippe.roussignol@ipmc.ens.fr (Ph. Roussignol). 0022-2313/01/$ - see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0022-2313(00)00245-3