Numerical simulation for growing Large-scale and High-quality Zinc germanium phosphide crystals

Abstract

The mid-infrared nonlinear crystals have shown great promise for the usage in the fields of sum frequency generation, optical parametric amplifier and optical parametric oscillator. These motivations are empowered by high-quality ZnGeP2 optical devices with high second-order dielectric susceptibility, thermal conductivity and hardness. However, the rapid development of large-sized ZnGeP2 single crystals with high optical quality is limited by traditional time-consuming and unpredictable growth route. Herein, for the first time, a strategy of comprehensive unsteady computer modeling is implemented to stimulate the Vertical Bridgman growth process of large-sized ZnGeP2 single crystal by the Crystal Growth Simulator (CGSim) software. The accurate simulations of temperature field, crystal growth rate, crystallization interface shape and thermal stress evolution are achieved by using this established numerical model. The accuracy and feasibility have been confirmed by the agreement between stimulated and experimental results of the temperature field curves and crystallization interface shape. The optimal parameters for growing large-sized (Φ = 60 mm) ZnGeP2 single crystal are determined: pulling speed of 0.3 mm/h, temperature gradient of 5 K/cm and slow cooling regime. The large-sized (Φ = 60 mm) ZnGeP2 single crystal with better quality is thus successfully obtained in the crystal-growth experiment in our lab, further verifying the accuracy of the constructed numerical model. Our work provides a new way to predict and guide the growth of large ZnGeP2 single crystal and other similar single crystals.