Systematic Simulations of Structural Stability, Phonon Dispersions, and Thermal Expansion in Zinc-Blende ZnO

Zinc oxide (ZnO) has recently gained considerable attention due to its exceptional properties, including higher electron mobility, good thermal conductivity, high breakdown voltage, and a relatively large exciton-binding energy. These characteristics helped engineers to develop low dimensional heterostructures (LDHs)-based advanced flexible/transparent nanoelectronics, which were then integrated into thermal management systems. Coefficients of thermal expansion αT, phonon dispersions ωj(q→), and Grüneisen parameters γjq→ can play important roles in evaluating the suitability of materials in such devices. By adopting a realistic rigid-ion model in the quasi-harmonic approximation, this work aims to report the results of a methodical study to comprehend the structural, lattice dynamical, and thermodynamic behavior of zinc-blende (zb) ZnO. Systematic calculations of ωj(q→), γjq→, and αT have indicated negative thermal expansion (NTE) at low T. Soft transverse acoustic shear mode gammas γTA at critical points offered major contributions to NTE. Our results of ωj(q→) at ambient pressure compare reasonably well with Raman scattering spectroscopy measurements and first-principles calculations. By adjusting the layers of materials with positive and negative thermal expansion, it is possible to create LDHs with near-zero αT. Such a nanostructure might experience a minimal dimensional change with T fluctuations, making it ideal for devices where precise dimensional stability is crucial.