Evolution of the optical transitions in Al_xGa_(1-x)As/GaAs quantum well structures grown on GaAs buffers with different surface treatments by molecular beam epitaxy

摘要

Al_(0.3)Ga_(0.7)As/GaAs Quantum Well structures were grown by molecular beam epitaxy (MBE) on a 500 nm thick GaAs buffer layer subjected to the following surface processes: a) in-situ Cl_2 etching at 70 ℃ and 200 ℃, b) air-exposure for 30 min. The characteristics of these samples were compared to those of a continuously grown sample with no processing (control sample). We obtained the quantum wells energy transitions using photoreflectance spectroscopy as a function of the temperature (8-300 K), in the range of 1.2 to 2.1 eV. The sample etched at 200 ℃ shows a larger intensity of the quantum well peaks in comparison to the others samples. We studied the temperature dependence of the excitonic energies in the quantum wells (QWs) as well as in GaAs using three different models; the first one proposed by Varshni [4], the second one by Vina et al. [5], and the third one by Passler and Oelgart [6]. The Passler model presents the best fitting to the experimental data.