First-principles Study On The GaAs And The Quaternary GaAs_1-x-yN_xBi_y Alloy

Recently, with the rapid development of global technology, the world today has entered the information age. In the information age, photovoltaic technologies have a vital role. As an important part of photovoltaic technologies, semiconductor materials with its good performance characteristics rapidly expand its application field. And GaAs compound semiconductor occupies an important position in the semiconductor materials.GaAs saturable absorbers have achieved passive Q-switching for it’s a variety of advantages. As is known, the main mechanism of passive Q-switching is the effect of EL2 deep level defect, which is generated by the defects of GaAs raw materials. In order to design its saturable absorption property accurately, it is essential to understand the effects of native point defects, and that will be helpful in ascertaining the origin of EL2 deep-level defect in GaAs.First-principles calculations are performed for the effects of intrinsic defects in GaAs, including VGa,VAs, GaAs, AsGa,Gai and Asi. Among these intrinsic defects, four types of Gai, Tetra[Ga-Ga],Tetra[Ga-As], Split[Ga-Ga] and Split[Ga-As], have been studied respectively. In the same way, four types of Asi, Tetra [As-As], Tetra [As-Ga], Split [As-As] and Split [As-Ga], have also been mainly calculated. Since density functional theory (DFT) using the local density approximation (LDA) or the generalized gradient approximation (GGA) often severely underestimates the band gap and overestimates the lattice constants, the state-of-the-art computational method with the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional in VASP has been performed to obtain the correct band structures. In this paper, defect energy levels corresponding to these point defects and their electrical characteristics are analyzed from the aspects of band structures and density of states. And the partial band decomposed charge density of the defect energy levels are also been studied. Besides, the quaternary GaAs1-x-yNxBiy alloy lattice-matched to GaAs has also been studied, including the electronic and optical properties (dielectric function, absorption coefficient, refractive index, energy loss function, and reflectivity). It is believed that our calculated results will be useful for the device applications of GaAs and GaAs1-x-yNxBiy quaternary alloys especially in optoelectronic devices such as solid-state lasers, high-efficiency multijunction solar cells, and so on.