Simulation Study Of The Large Sapphire Single Crystal Kyropoulos Furnace Warm Field

Due to good optical properties,chemical stability and mechanical strength,the sapphire crystal is widely used in satellite space technology,infrared military devices,high-intensity laser windows and other military fields.Because of its lattice constant close to GaN and mature growth process,sapphire single crystal is widely used in SOS microelectronic circuits,LED lamp beads and other substrate industry.Owing to its high hardness and dielectric constant conformed to the requirements of capacitive screen,sapphire crystal is used in the field of wearable equipment window.And because of the special properties of the atomic energy level transition,sapphire crystal is used as gain medium of high power laser.Sapphire demand is increasing with the rapid development of these industries,the growth of large size,high quality sapphire single crystal has become particularly urgent.Therefore,the study of the large-size sapphire single crystal furnace temperature field has great application value.In this thesis,combining with the simulation software and the actual results of crystal growth experiments,the reasons of single crystal furnace temperature field aging has been explored.The composition,microstructure and reflectivity of the molybdenum screen of aged single crystal furnace were measured by metallographic microscope,scanning electron microscope(SEM)and interferometer.The results showed that the aging mechanism of the upper,middle and bottom molybdenum screen of the single crystal furnace were obviously different: In the upper molybdenum screen region,due to the long-term working in the low temperature,the molybdenum screen was attached by the volatile of Al,O,Mo,W and other objects and generated different sizes black attachments.The black volatiles changed the reflectivity of the molybdenum screen and reduced its insulation effect.In the middle molybdenum screen region,because the work area temperature didn’t reach its maximum operating temperature,surface morphology changed little and reflectivity was not changed to much.In the bottom molybdenum screen region,owing to long-term working in the high temperature,molybdenum elements were volatilized.Thus a lot of chaotic direction and different sizes micro-mirror was formed on the surface.The molybdenum screen insulation effect was reduced because of the scattering of micro-mirror.The measured molybdenum screen reflectivity was introduced into the computer.The simulation results show that the temperature gradient,the solid-liquid surface and the melt flow have been changed due to the changing of the molybdenum screen insulation effect.In comparison with the original temperature field.The crystal quality serious declined.By using the sapphire single crystal simulation software CGSim,the properties of temperature field formed by zirconia,alumina and metal were studied.A new insulation system was proposed,in which apart of molybdenum screen was replaced by zirconia the bottom and alumina on the outside,respectively.The simulation results showed that the insulation effect of the temperature field was deteriorated by changing the thickness of the molybdenum screen to alumina.By keeping the layer of internal molybdenum screen unchanged,the insulation effect of temperature field was significantly enhanced with increasing the thickness of external zircon or alumina,proofed by the decrease of power consumption.But increasing to a certain thickness further,the power consumption declined in slow.By simulating the temperature field with different crucible size,the temperature field performance of 120 kg,200kg and 300 kgwas explored.The simulation results showed that the insulation effect of the temperature field was deteriorated and the power consumption was increased with the increase of the crucible size.It was also observed that the growth angle was increased,and the stress was increased and enriched.Temperature gradient was decreased.Melt flow remained unchanged.Therefore,enhancing side and lower insulation effect and the interface between seed crystal and crystal are favorable for prevent the phenomenon of stress enrichment,when designing large-size single crystal furnace.