研究目的
The purpose of these calculations is to investigate the electronic and optical properties of Al-doped GaAs and GaSb for solar cell design and optical applications.
研究成果
In this article, the electronic and optical properties of Ga1?xAlxAs and Ga1?xAlxSb are simulated by means of first principle based on full-potential linearised augmented plane wave method using the Wein2k code. The lattice constant is optimised for Al-doped GaAs/Sb and found that the increase in lattice constant due to increase in dopant concentration (i.e. replacement of Al ions by Ga) increases the bandgap of the studied materials. This shows that the bandgap of the studied materials can be tuned by varying the dopant composition to obtain the desired energy range for increased solar cell efficiency. The calculated negative value of enthalpy shows that the studied materials are thermodynamically stable, and the stability increases with increase in Al contents in GaAs/Sb. The bandgap values calculated from Im ε(ω) threshold limit are slightly overestimated because of the approximations in the DFT computations. However, the detailed analysis of optical properties shows that there is maximum absorption of light in UV and visible region and also minimum loss of energy and reflection in functional (UV and visible) regions. This predicts the strong potential of the studied alloys for solar cell applications.
研究不足
The bandgap values calculated from Im ε(ω) threshold limit are slightly overestimated because of the approximations in the DFT computations.
The electronic and optical characteristics of Al-doped GaAs and GaSb alloys are depicted by DFT-dependent full-potential linearised augmented plane wave method that simulated in Wein2k code. The zinc-blende structures of studied compounds are optimised and relaxed by PBEsol approximations because it calculates ground states parameter more exact than local density approximation (LDA) and GGA. The optimised structures are converged by self-consistent field to find the Hamiltonian of the system. The exchange-correlation energy (Exc) term in the Hamiltonian is usually approximated by well-known LDA, GGA, PBEsol, or hybrid approximations. The ground state parameters are accurately found from these approximations, while excited state properties are underestimated. For example, the bandgap reports through these approximations are sturdily underestimated. The problem associated with aforementioned approximations to underestimate the bandgap is self-interaction error that restricts derivative discontinuity that is important when we compare the Kohn–Sham and experimental bandgaps. On the other hand, the hybrid functional is more expensive and LDA + U/GGA + U are limited to localised states (3d and 4f electrons). Consequently, to solve the above difficulties, Tran and Blaha and Koller improved the Backe-Johnson potential (TB-mBJ) that exactly calculates the electronic structures of semiconductors, insulators, and metal oxides. This potential is successfully implemented in the present calculations to elaborate the electronic structure and bandgap-dependent optical properties. Moreover, the wave function splits into two regions; the core electrons are confined in the muffin-tin region having spherical harmonic-type solution, and the rest of the region has plane wave-like wave function. However, the potential in both regions kept the same through the FP-LAPW method. The basic set of inputs is adjusted as the Kmax × RMT = 8.0 and Gmax = 16, respectively. Furthermore, the k-mesh grid of 4000 k-points has been used for the accurate convergence through iteration process up to 10?4 Ry. We have chosen the k-mesh grid of 4000 k-points because at and above this value the energy release from the alloys during charge/energy convergence becomes constant.
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