First principle study of strain tunable electronic and optical properties of half-Heusler alloys XCoGe (X=V, Nb, Ta)

Abstract

Half-Heusler alloys are gaining considerable attention for designing novel optoelectronic and renewable energy device applications. In the present work, we performed the first principle study of structural, electronic, and optical properties of XCoGe(X=V,Nb,andTa) half-Heusler alloys under external strain (0–8%). All compounds exhibit cubic crystal structures with an F-43m space group. The lattice constant and bond length increase (decrease) with increasing tensile (compressive) strain. The calculated formation energy of XCoGe systems is negative and increases (decreases) with varying the tensile (compressive) strain from 0 to 8%, indicating the stability of these systems. All XCoGe compounds possess an indirect band gap nature and are retained under strain. The band gap reduces under tensile strain and considerably widens by external compressive strain. The X-s state and Co-s state mainly contribute to the valence band maximum and conduction band minimum in XCoGe systems. Interestingly, the optical absorption spectra reveal maximum absorption in the visible energy range for both unstrained and strained systems. Interestingly, the red- and blue-shift under tensile and compressive strain in XCoGe make them good candidates for optoelectronic applications. The results pave the path for the practical utilization of XCoGe compounds for optoelectronic and light detection applications.