Effect of Thermal Annealing Treatment and Defect Analysison AgGaGeS 4 Single Crystals

AgGaGeS4 is a new promising nonlinear-optical crystal for frequency-shifting a 1.064 μm laser into mid-IR. This quaternary compound single crystal has been successfully grown by a modified vertical Bridgman method. Although it has high transparency in the 0.5–11.5 μm spectral range, the nonideal transparency at 2.9, 4, and 10 μm restricts further optical experiments and applications. Therefore, in this work, AgGaGeS4 wafers were annealed in vacuum and with a AgGaGeS4 polycrystalline powder at different temperatures. After annealing, under certain conditions, the optical quality of AgGaGeS4 wafers shows evident improvement, and it is found that volatile GeS2 easily results in stoichiometric deviation, even decomposition, so that the choice of temperature plays a pivotal role in the annealing treatment. Conclusively, the results confirm that thermal annealing could effectively improve the optical quality of the as-grown AgGaGeS4 crystal and annealings with a AgGaGeS4 polycrystalline powder at 550 °C and in ...