Materials Science and Engineering B82 (2001) 185 – 187 Renormalization of the exciton parameters in piezoelectric nitride quantum structures: the effects of injection intensity and temperature P. Bigenwald a, *, A. Kavokin b , P. Christol a , B. Gil c a Department de Physique -UFR Sciences, 33 rue Pasteur, F -84000 Aignon, France b LASMEA-CNRS, Uniersite ´ Blaise Pascal, 24 aenue des Landais, F -63177 Aubie `re Cedex, France c GES -CNRS, Uniersite ´ Montpellier II, Place Euge `ne Bataillon, F -34095 Montpellier Cedex, France Abstract Exciton properties have been calculated for polarized GaN/AlGaN quantum well (QW) as a function of the injection intensity for various temperatures. A self-consistent process is performed to solve Schro ¨ dinger and Poisson equations, and a trial function that takes into account quantum exclusion principle in the filling of the reciprocal space is chosen for the exciton. When carriers are injected in the quantum structure, three different regimes are evidenced before the complete bleaching of the electron – hole interaction at large excitation intensities. We show that, for a given structure, the critical injection intensity of carriers at which this exciton starts to dissociate due to kinetic effects increases with the temperature of the lattice. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Exciton; Polarization; Quantum well; Temperature www.elsevier.com/locate/mseb 1. Introduction Nitrides have huge potentialities for different opto- electronic applications, but 30 years after Pankove [1], very little is known about their intimate properties. After the observation of significant red-shifts of lu- minescence peaks in quantum structures [2–5] ex- plained by intrinsic electric fields, theoretical studies [6,7] have elucidated the spontaneous and piezoelectric polarizations and confirmed their huge orders of mag- nitude in the wu ¨ rtzite lattice. We propose in this com- munication to investigate theoretically the combined effect of carrier injection intensity ( ) and temperature (T ) on the optical properties of polarized AlGaN/GaN single quantum wells. There are three basic aspects in the electron–hole plasma effect on excitons in GaN/AlGaN quantum wells (QWs): first, the free carriers screen the polariza- tion fields thus stabilizing the exciton, second, they screen the exciton itself, and third, an effect that is often neglected but appears to be of key importance at high pumping intensities, the band-filling affects the exciton wave function via the quantum exclusion effect. Here we study the relative importance of these three factors for the exciton energy and oscillator strength behavior in GaN/AlGaN QWs as a function of the optical pumping intensity and temperature. 2. Formalism Our sample structure is an Al 0.11 Ga 0.89 N/GaN single QW with the binary layer compressed to the ternary. The bandgap discontinuity E g is 231 meV of which 62% are attributed to the conduction band. Our well width is equal to 15 monolayers (MLs) or 3.9 nm. Concerning the electric fields, we assumed the barriers are not polarized whereas the GaN layer is submitted to F =450 kV cm -1 , a value independent on the QW width [5]. In the presence of electron–hole pairs with an in-plane density , the initial field is screened and we have to solve self consistently Poisson and Schro ¨ dinger equations to obtain the correct electron and hole eigen- * Corresponding author. Tel.: +33-90144463; fax: +33-90144469. E-mail address: pierre.bigenwald@univ-avignon.fr (P. Bigenwald). 0921-5107/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0921-5107(00)00787-X