Structural, elastic, and opto-electronic conduct of half Heusler Li(Ca, Mg, Zn)N alloys: Ab initio computation

Abstract

In this study, we investigated the half-Heusler semiconductor LiYN (Y = Ca, Mg and Zn) under pressure using DFT implemented in Wien2k to find materials more suitable for optoelectronic applications. At a pressure of 10 GPa, we observe a transition in bandgap type for LiCaN and LiMgN, from indirect to direct bandgaps for LiCaN, and from direct to indirect for LiMgN. This transition was determined by analyzing the critical points of the valence and conduction bands, as well as the associated wave vectors, via electronic band structure calculations. For LiZnN, on the other hand, the band gap remains direct at 10 GPa, confirming the stability of this compound's optical character under pressure. The gap energy values increase with increasing pressure in percentages 16.8 %, 17.9 % and 81.4 % for LiCaN, LiMgN and LiZnN, respectively. The elements studied have cubic structures with three main elastic coefficients: C₁₁, C₁₂ and C₄₄. These constants, which are key to understanding material stabilities, vary with increasing pressure. Optical properties such as the imaginary and real parts of the dielectric complex function, absorption coefficient, reflectivity and refractive index are calculated and described in detail.