Annealing modification and defect analysis of Hg2Br2 crystal

Abstract

With the urgent demand for wavelength extension of acousto-optic devices in military and civil fields, long wavelength infrared acousto-optic crystals with high performance have become indispensable. In this context, Hg2Br2 crystals with dimensions of Ф 50 × 40 mm3 were successfully obtained by a self-designed physical vapor transport furnace. The transmittance spectra reflect that the Hg2Br2 crystal has a wide spectral transmission range, and the maximum transmittance in the UV–vis IR range exceeds 80%. Annealing is proven to be an effective measure to optimize crystal properties, and the optimal annealing temperature of the Hg2Br2 crystal is defined. The crystal quality and transmittance of the Hg2Br2 crystal are improved, and the stress is reduced after annealing at the optimal temperature. In addition, the dislocation defects of the Hg2Br2 (110) and (001) wafers were characterized via the thermal etching method. The average defect density was assessed on the order of magnitude of ∼105 cm−2, which indicates the high quality of the as-grown Hg2Br2 crystal.