Boron Oxide Encapsulated Vertical Bridgman: a Method for Preventing Crystal-Crucible Contact in the CdZnTe Growth

One of the reasons for the formation of twins and grain boundaries during the CdZnTe (CZT) crystal growth is the crystal-crucible interaction, typical of the vertical Bridgman technique. Particularly detrimental seems to be the use of quartz crucibles that ease the sticking of the crystal to the crucible walls. Due to this reason, many authors suggest the use of graphite crucibles or of carbon coated quartz crucibles. In order to avoid the contact between the growing crystal and the crucible, it was proposed to opportunely control the wetting angle. However, it was shown that this is possible only under microgravity conditions or by imposing a pressure difference between the melt and the solidifying crystal. In this work, we show that it is possible to avoid the contact between the crystal and the crucible by interposing a thin liquid boron oxide layer. This condition can be obtained in a vertical Bridgman furnace by covering the polycrystalline charge with a boron oxide pellet. In this way, crystals with large single grains were obtained also in quartz crucibles. Moreover, the crystals show low dislocation density, as expected in the case of crystals grown without contact with the crucible.