Ab-initio simulations of ZnSe point defects revealed

Abstract

Point defects in ZnSe are well characterized thermodynamically (formation energies, charge transition levels), yet no first-principles vibrational fingerprint exists to identify them non-destructively in real crystals via terahertz (THz) spectroscopy. This gap is practically relevant: residual native defects limit the optical quality of ZnSe and ZnSe:Fe used as infrared windows and as gain media for mid-infrared Fe2+/Cr2+:ZnSe lasers, and several weak absorption features below 90 cm⁻¹ in measured THz/IR transmission spectra (300 K and 77 K series, 5–300 cm⁻¹) remain unassigned. We address this by combining density-functional perturbation theory (DFPT, Quantum ESPRESSO) with a charge-state-resolved defect vibrational catalogue, aiming to link local mode frequencies to specific native defects (vacancies, antisites, interstitials) and their charge states, and ultimately to fit the experimental T(ω) spectra with a Lorentz-oscillator model. As a first validation step, the full phonon and dielectric response of the pristine ZnSe host lattice was converged (Γ-point DFPT, Born effective charges), correctly reproducing the known reststrahlen band (205–252 cm⁻¹). Structural relaxation of the ten dominant native point defects and their charge states (prioritizing V_Zn and V_Se, identified as thermodynamically dominant in prior hybrid-functional studies) is underway, correctly capturing symmetry-lowering distortions expected for open-shell defect levels. This work aims to close the gap between existing defect thermodynamics and a predictive, charge-resolved vibrational assignment usable for THz-based defect diagnostics of ZnSe-based optical and laser materials.

Speaker

Nikulchin Egor
Prokhorov General Physics Institute of the Russian Academy of Sciences
Russia

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