First-Principles Investigation of Pressure-Dependent Structural, Electronic, Vibrational, and Thermodynamic Properties of Zinc Blende CdTe under Hydrostatic Pressure

Abstract

This study presents a comprehensive first-principles investigation of the structural, electronic, vibrational, and thermodynamic properties of zinc blende (ZB) CdTe under hydrostatic pressure up to 50 GPa, using density functional theory (DFT) within the PBE-GGA framework as implemented in the CASTEP code. Cadmium telluride (CdTe) is a technologically important semiconductor widely used in thin-film photovoltaic devices, where CdTe-based solar cells have achieved conversion efficiencies of approximately 22%. The structural analysis reveals a monotonic reduction in the lattice parameter and unit cell volume with increasing pressure, confirming isotropic compression behavior consistent with the Birch-Murnaghan equation of state. The electronic band gap exhibits a pronounced non-monotonic pressure dependence, increasing from 1.59 eV at ambient pressure to a maximum of 2.22 eV at approximately 20 GPa, followed by a decrease to 1.63 eV at 50 GPa. This behavior is attributed to pressure-induced orbital redistribution and modifications at the band edges, primarily involving Te-5p and Cd-5s states, as elucidated by density of states (DOS) analysis. Vibrational properties, analyzed through Raman spectra, show a continuous blueshift in phonon wavenumbers with pressure, indicating bond stiffening and increased interatomic force constants, accompanied by significant variations in spectral intensity due to anharmonic effects. The thermodynamic response, including enthalpy, Gibbs free energy, heat capacity, and Debye temperature, demonstrates strong pressure sensitivity, reflecting modified lattice dynamics and reduced thermodynamic stability under compression. It is important to note that calculations beyond approximately 20 GPa were performed under constrained zinc blende symmetry to explore property trends and should be interpreted as indicative of metastable behavior. The results establish CdTe as a pressure-tunable semiconductor and identify ~20 GPa as a significant threshold for changes in its electronic and vibrational behavior, providing a valuable reference for future experimental and theoretical studies on CdTe under extreme conditions.