Electronic structure, thermodynamics, and thermoelectric properties of YxAl1−xN semiconductor alloys for new promising optoelectronics and energy conversion: Ab Initio study

Abstract

Key characteristics such as structural, electronic, thermodynamic, and thermoelectric of wurtzite yttrium aluminum nitride (YxAl1−xN) semiconductor alloys (with 0≤ x ≤ 0.375) were investigated using Ab Initio density functional simulation within powerful full-potential linear augmented plane wave (FP‒LAPW) method. The equilibrium structural parameters (a0, c0, c0/a0,V0) were determined using the revised GGA−PBEsol approach in perfect agreement with experiments. The lattice a0-parameter varies almost linearly with yttrium concentration with a bowing of −0.08597 Å, while the c0-parameter has a bowing of −0.5715 Å. The lattice dynamics of doped YxAl1−xN systems were analyzed based on formation energy and phonon frequencies. Electronic structures of wurtzite YxAl1−xN described from a modern nKTB−mBJ potential show bandgap engineering with a range of [6.10 eV–3.85 eV] for x varies from 0 to 0.375, covering emission wavelengths [203 nm–322 nm] in the ultraviolet spectrum. The electron charge density contours indicate ionic bonding in wurtzite YxAl1−xN. Using the quasi-harmonic Debye model, thermodynamic properties of YxAl1−xN alloys, including volume (V0), mass modulus (B0), specific heat (Cv), thermal expansion (α), entropy (S), Debye temperature (ΘD) and Grüneisen parameter (γ), were calculated and analyzed under temperature and pressure effects. Moreover, electronic transport properties, such as the Seebeck coefficient (S), electrical conductivity (σ/τ), power factor, thermal conductivity (κel/τ), and figure of merit (ZT), of YxAl1−xN alloys were determined using BoltzTraP code. YxAl1−xN (at x = 0.25 and T = 600 K) exhibited the largest magnitude of S, with a value of ∼213.9 μV/K, and ZT ∼ 0.72. It also had the lowest value of κ/τ ∼9.9 × 1013 W m−1.K−1.s−1. Wurtzite YxAl1−xN crystal appears to be an extremely interesting candidate for potential applications in optoelectronics (UV) and future green energy system.