Studies on thermal and interface optimization for CdZnTe crystals by unseeded Traveling Heater Method

A stable thermal field and a controlled convex growth interface are essential for the stable growth of large-size CdZnTe crystals by the Traveling Heater Method (THM). However, the crucible wall temperature always increases due to the deposition of CdZnTe crystals with low thermal conductivity at the bottom of the crucible. A comprehensive two-dimensional simulation model for THM growth of CdZnTe is developed and implemented to study the heat and mass transfer. The effect of increasing wall temperature on interface shape and concentration distribution is discussed. Experimental results show that a dummy crystal with a thermal conductivity similar to that of the CdZnTe crystal helps to stabilize the wall temperature. In a stable thermal field, low constant rotation is assumed to be sufficient to weaken natural convection flow and to make the interface convex in THM. Simulation results show that low constant rotation rates of 2.5 RPM for 2-in. crystal and of 1.25 RPM for 3-in. crystal are effective in interface optimization. Several ingots with a diameter of 2 in. and 3 in. were grown by unseeded THM. Convex interfaces were observed both in 2-in. and 3-in. crystals by applying simulated rotation rates after fast cooling.