Comprehensive description of the dynamical screening of the internal electric fields of AlGaN/GaN quantum wells in time-resolved photoluminescence experiments
We present a combined theoretical and experimental analysis to describe the interplay between polarization field, charge screening, and radiative and nonradiative recombinations in AlGaN/ GaN-based nanostructures. We perform the study of photoluminescence (PL) in both stationary and time-resolved PL (TR-PL) conditions, considering also the effect of temperature on the different recombination mechanisms, and especially on nonradiative recombinations. The theoretical analysis is obtained by coupling a complete self-consistent solution of Schrodinger and Poisson equations to determine the electronic states in the nanostructure with a rate equation model to account for time-dependent effects of charge rearrangement. We review the topic of polarization field screening taking into account the most recent results on the evaluation of the very strong coefficients for spontaneous and piezoelectric polarizations that have recently been predicted for III-V nitride semiconductors with natural wurtzite symmetry, and we show how the screening influences both static and dynamic recombination mechanisms. Experimental results are obtained for high-quality GaN/AlGaN multiple quantum wells by means of both continuous-wave (cw) and TR-PL techniques. The case of single quantum well is also considered. The PL measured decays show a time dependence that is not only controlled by radiative lifetimes, which depend on the fields inside the GaN wells, but also on the carrier recombinations through nonradiative channels. We demonstrate that PL emission is influenced by charge accumulation in the well, and a loss of carriers from the ground level induced by an interplay between radiative and nonradiative recombination processes. Moreover, from the analysis of the temperature dependence of the TR-PL decays, we deduce important confirmations of a thermally activated detrapping mechanism that strongly affects the nonradiative recombination processes. (C) 2003 American Institute of Physics.