Ab initio molecular dynamics simulation of the radiation damage effects of GaAs/AlGaAs superlattice

Abstract

In the past several decades, the radiation tolerance of semiconductor superlattices has been extensively investigated to improve their performance under radiation environment. In the literature, it has been reported that the GaAs/AlGaAs superlattice is more radiation resistant than the GaAs/AlAs superlattice; however, the underlying physical origin still remains unknown. In this study, an ab initio molecular dynamics simulation of low-energy radiation response of the GaAs/AlGaAs superlattice confirms the experimental observation that the radiation resistance of GaAs/AlAs suplerlattice is enhanced by the introduction of Ga to AlAs layer. Also, it turns out that a large number of antisite defects are created during the dynamic process of the displacement events for the GaAs/AlGaAs superlattice. These antisite defects have low formation energies and increase the energy barrier for further defect generation, thus resulting in enhanced radiation tolerance. The presented results unveil the underlying mechanism for the enhanced radiation tolerance induced by introducing Ga to AlAs layer in the GaAs/AlAs superlattice, which will be beneficial to design highly radiation-resistant semiconductor superlattices for their applications as optical and electronic devices.

Introduction

Impurity induced compositional disordering of GaAs/AlAs superlattice (SL) has been reported for impurities like Zn [1] and Si [2,3], in which diffusion or ion implantation of such impurity atoms into the SL brings different properties from the original. By line-and-space scan of Ga ion into the superlattice epitaxial wafer, Yoshiro et al. fabricated a multi-dimensional GaAs/Al_xGa_1-xAs SL with higher photoluminescence peak energy, which is more suitable for designing laser diode [4]. Now, the semiconductor SLs have been widely used in the different applications like the optoelectronic devices, quantum cascade laser, high-frequency oscillators and thermoelectric devices [[5], [6], [7], [8]]. It is noticeable that the degradation of the semiconductor SLs’ performance may occur when they are bombarded by high-energy charged particles during the applications of aerospace, astronomy and nuclear related areas [[9], [10], [11], [12], [13]]. The interaction between particles and the atoms in the semiconductor SLs causes the displacement in the atoms, which results in the creation of different types of defects. These defects may cause the changes in the microstructure and ultimately deteriorate their optical and electronic properties, which may lead to permanent failure. For example, Li et al. studied the radiation damage effects of the AlGaAs/GaAs based solar cell under 100 keV∼10 MeV proton irradiation, and found that short-circuit current, open-circuit voltage and power conversation efficiency decrease with the increasing radiation energy [14]. Therefore, it is of great importance to study the radiation damage effects of GaAs/AlGaAs SL under radiation environment.

In recent years, the radiation effects of GaAs/AlGaAs SLs have been investigated experimentally. Hamdi et al. investigated the change in strain of Al_xGa_1-xAs/GaAs SLs under Si ion radiation at the room temperature [15]. They suggested that the damaged end states overall increase the average strain of SL structures and the damage caused by implantation is largely reversible upon annealing at ∼420 °C [15]. Laiadi et al. investigated the radiation effects on the electrical properties of AlGaAs/GaAs based solar cell under electron and proton irradiation [16]. They demonstrated that the short-circuit current shows a strong degradation from 23.86 to 14.36 mA/cm² at 10¹⁶ cm⁻² electron fluence, and the open-circuit voltage decreases from 1.01 to 0.69 V under proton irradiation [16]. Cullis et al. have studied the radiation responses of Al_xGa_1-xAs/GaAs (x = 0.2 and 0.85) samples to Kr⁺ and Xe⁺ irradiation and reported that the AlGaAs layer is more resistant to amorphization than GaAs layer and the resistance increases with the increasing Al content [17]. In our previous study, we employed an ab initio molecular dynamics (AIMD) method to simulate the responses of GaAs/AlAs SL to electron irradiation and found that the AlAs layer behaves more robustly than GaAs layer under electron irradiation [18]. In spite of these investigations, no theoretical simulation of dynamic processes in GaAs/AlGaAs SL under irradiation has been reported in the literature thus far. Besides, there still lacks theoretical understanding of the different radiation tolerances between GaAs/AlAs and GaAs/AlGaAs SLs.

In this study, the AIMD method [[19], [20], [21], [22], [23]] is employed to investigate the response behaviors of GaAs/AlGaAs SL under radiation environment, i.e., how the defects are created, what types of defects are generated and how these defects are distributed in the material. The aim of this study is to investigate how the introduction of Ga into AlAs layer of GaAs/AlAs SL influences the defect generation and radiation resistance at an atomic level. The threshold displacement energies have been determined, and the pathways for defect generation have been provided. Meanwhile, the origin of the difference in the radiation susceptibility between GaAs/AlGaAs and GaAs/AlAs SLs has been explored. The presented results provide a fundamental insight into the microscopic mechanism of displacement events in GaAs/AlGaAs SL, and will advance the understanding of the radiation damage effects of GaAs/AlGaAs SL.