Structural, optoelectronic, and thermodynamic properties of Y $$_x$$ x Al $$_{1-x}$$ 1 - x N semiconducting alloys

Abstract

The structural, electronic, optical, and thermodynamic properties of Y\(_x\)Al\(_{1-x}\)N alloys were computed using first-principles calculations. The effects of exchange and correlation have been considered by means of the generalized gradient approximation (GGA) with the Perdew–Burke–Ernzerhof parametrization. In addition, the Tran–Blaha-modified Becke–Johnson potential (TB-mBJ) was applied to give a better description of the band-gap energies and optical spectra. The lattice parameters, bulk modulus, and band-gap energy show nonlinear dependence on concentration x. Results for rock-salt Y\(_x\)Al\(_{1-x}\)N alloys show that the band gap undergoes an indirect (\(\Gamma \rightarrow X\))-to-direct (\(\Gamma \rightarrow \Gamma \)) transition at a given yttrium composition, followed by a direct (\(\Gamma \rightarrow \Gamma \))-to-indirect (\(\Gamma \rightarrow X\)) transition in a higher yttrium concentration. For wurtzite Y\(_x\)Al\(_{1-x}\)N alloys, the band gap presents a direct (\(\Gamma \rightarrow \Gamma \))-to-indirect (\(M\rightarrow \Gamma \)) transition at a given yttrium composition, followed by an indirect (\(M\rightarrow \Gamma \))-to-indirect (\(M\rightarrow \Sigma \)) transition in a higher yttrium concentration. The real dielectric function, imaginary dielectric function, refractive index, and extinction coefficient were calculated using the TB-mBJ potential. Using a regular solution model, slightly lower mixing enthalpies for wurtzite Y\(_x\)Al\(_{1-x}\)N alloys were found. The mixing enthalpy for a given concentration differs depending on structures, and on the interaction between atoms of constituents. The effect of temperature on the volume, bulk modulus, Debye temperature, and the heat capacity for Y\(_x\)Al\(_{1-x}\)N alloys was analyzed using the quasi-harmonic Debye model. Results show that the heat capacity is fairly sensitive to composition as temperature increases.