Growth And Characterization Of AgGaS₂ Single Crystals

Silver gallium sulfide(AgGaS2) is a excellent nonlinear infrared optical material. It is transparent in the region from 0.45-13 U m, it has large nonlinear optical coefficient (d36=18 x 10~12m/V), adequate birefringence and lower dispersion. AgGaS2 crystals can not only realize phase matching for the second-harmonic generation fundamental wavelength in the region from 1.8 to 11 um, but can also support three-wave mixing processes, optical parametric oscillation, sum- and difference-frequency generation. Nonlinear optical devices made by AgGaSa crystals can generate multi-frequency output light from 1.8 to 11 um, Especially through sum-frequency switching, they can transform weak infrared signals into strong visible light signals. Thus, AgGaSa crystals have wide application potentials such as for radar detection with COa laser, infrared remote control laser communication, infrared guidance as well as in environment science fields.This paper reports a new procedure of polycrystalline synthesis and a new technique of single crystal growth on AgGaSa, i.e. two-zone temperature vapor transporting and descending crucible with rotation. A single phase dense AgGaSa polycrystalline ingot was synthesized, and a crack-free AgGaS2 single crystal with 10 mm in diameter and 25 mm in length was grown by the technique mentioned above. Structure integrity of the crystal was studied by the X-ray diffraction technique. Six order X-rays spectra from the {011} face of the crystal were obtained, and an anomalous phenomenon was observed for the first time that intensity of the higher order diffraction peak is much stronger than that of the lower order diffraction peaks, which prove the ingot we have received is perfect crystalline. Some properties of AgGaSa were studied. Etching-pits of the crystal were observed by the scanning electron microscope (SEM). Infrared transmission spectra (IR) and X-ray photoelectron energy spectrum indicate the ingot contains the secondary deposit; by DTA and Pseudobinary Ag2S-Ga2S3 phase diagram, we know the secondary deposit isAg2Ga20S31. The results shows the descending ampoule with rotation method is a promising method for growth of AgGaSa single crystals. In order to receive higher-quality crystal, we should anneal crystal. Only after annealed, crystal could be used for devices. The paper also calculate some values about the secondary harmonic wave.