Study on haze defects in CVD-ZnSe: Performance, microstructure and suppression

Abstract

Haze is a prevalent defect limiting the optical performance and utilization of bulk CVD-ZnSe infrared windows. In this work, four CVD-ZnSe batches with different haze levels were prepared by varying the Zn/Se molar ratio of the reactants. Spectrophotometry, haze values, transmission polarizing microscopy, stress-birefringence mapping, EBSD, and TEM/HRTEM were combined to quantify performance, resolve microstructural origins, and propose strategies for haze suppression. The results show that haze mainly decreases visible-band transmittance. Microstructurally, grains are composed of twin lamellae with varying thickness. Σ3 lamellar twin boundaries with clustered stacking faults locally convert zinc blende stacking into hexagonal sequences, producing intrinsic birefringence that scatters light. Hazy samples thus include more twin boundaries. A semi-empirical internal-interface scattering model fitted to spectra reproduces both the curve trend and the wavelength dependence of the transmittance loss, corroborating internal scattering from hexagonally stacked lamellae as the primary haze mechanism. Haze value is introduced to describe scattering in materials to characterize defects. The haze value enables a four-grade classification (severe, moderate, slight, and clear) that is consistent with visible-band transmittance, macroscopic appearance, and microstructural indicators, and provides a practical quality criterion. In part of slightly hazy CVD-ZnSe, abnormal columnar growth introduces anisotropy and residual stress that dominate in-plane optical nonuniformity. Reducing twins and stabilizing equiaxed growth are crucial for haze suppression. Zn/Se molar ratio of reactants (≈1.2) and CVD chamber flow-field uniformity suppress haze defects, improve transmittance, and enhance consistency in CVD-ZnSe.