Thermodynamic, optical and electronic properties of Ge₂Te₅As₂ and Ge₂Te₄As₂: ab initio insights

Using ab initio DFT and the WC-mBJ potential, we analyze and compare the structural, electronic, optical, and thermodynamic characteristics of two germanium telluride arsenide compounds: the stable Ge₂Te₅As₂ and its Ge₂Te₄As₂ sub-stoichiometric analogue, characterized by an ordered tellurium depletion. Our calculations reveal that this stoichiometric modification fundamentally alters the electronic structure, driving a transition from an indirect semiconducting character in Ge₂Te₅As₂ (with a calculated band gap of 0.423 eV) to a distinct metallic state in Ge₂Te₄As₂, as evidenced by a finite density of states at the Fermi level. This drastic shift governs the optical characteristics, significantly modifying the absorption spectrum and complex dielectric function. Furthermore, thermodynamic stability assessments confirm the viability of both structures. These findings unequivocally highlight the profound impact of periodic structural reconfigurations on adapting the fundamental characteristics of functional materials for potential applications in optoelectronics and phase-change memory devices.