Optical properties of n- and p-type modulation doped GaAsBi/AlGaAs quantum well structures

Abstract

In this work, optical properties of n- and p-type modulation doped GaAsBi/AlGaAs single quantum well (QW) heterostructures are investigated via temperature-and excitation power-dependent photoluminescence (PL) and integrated photoluminescence (IPL) studies and the results are compared to the nand p-type GaAs/AlGaAs QW structures to determine the influence of Bi and doping type on the optical properties. The results of the temperature dependent PL peak energy reveal that, as an effect of doping type, the temperature dependence of the PL peak energy exhibit different characteristic for n-and p-type samples. The temperature dependence of the PL peak energy reveals S-shaped trend for the n-type GaAsBi/AlGaAs QW sample. On the other hand, the characteristic follows Varshni law for the p-type GaAsBi/AlGaAs QW sample. The observed S-shaped behaviour for the n-type sample is explained by considering the contribution of the Bi-induced states above valence band (VB) to the PL. As for p-type sample, the localised states-related contribution to the PL signal is drastically diminished, resulting in an almost S-shape free temperature dependence of the optical transition energy, which can be explained by the compensation of acceptor-like states. The observed PL spectra of n-and p-type samples successfully reconstructed by two Gaussian peaks, which are assigned to optical transitions due to recombination of free and localised excitons. The localised exciton-related peak is observed to be very weak in p-type sample compared to that in n-type one. The allowed transitions in GaAsBi QW is calculated by selfconsistently solving the Schr_odinger-Poisson equation to identify the origin of the observed transitions. A comparison of the PL results of the Bi-containing samples with the results of the Bi-free ones is exhibited approximately 80 meV/Bi% decrease in the fundamental optical transition. Using the excitation-dependent IPL measurements, it is found that at low temperatures and under low excitations, recombination process is under the effect of Shockley-Read-Hall (SRH) non-radiative process. When the excitation power density increases, radiative recombination becomes dominant. At higher-temperatures and in the high-intensity regime, we observed Auger effect in recombination process for n-and p-type GaAsBi samples, but the effect of Auger loss is observed to be much less in the p-type GaAsBi sample due to enhanced spin orbit split-off energy as a result of incorporation of bismuth. Furthermore, when we compare the result for Bi-free and Bi-containing p-type samples, again, Auger recombination is found to be less effective for the Bi-containing sample. (C) 2017 Elsevier B.V. All rights reserved.