New AIG Method of Growing Alkali Halide Crystals and Potential Application to CZT

Abstract

The new AIG (Advance Interface Growth) method has been successfully applied to alkali halide scintillation crystals at PhotoPeak, Inc. for the last four years. It produces single, stress‐free crystals having a low level of defects and has resulted in increasing the yield of usable CsI(Tl) crystals to 75–85%. Essentially it is a low gradient method but has the capability to adapt the gradient to that needed by an individual crystal for the most successful growth. High quality crystals have been supplied to national laboratories and the nuclear medicine market. For example, a blank CsI(Tl) crystal 2 in diameter and 2 in length was produced having a measured energy resolution of 6.5% at 662 keV on a 2 ‐diameter PMT having a standard blue bialkali photocathode. This far exceeds the best resolution, 8.5–9.5%, obtained for CsI(Tl) crystals grown by the conventional Bridgman method. It is expected that this method can be successfully applied to grow high quality CZT crystals with substantially higher yield, 25–35%, than the presently existing 5–10%. The reasons for the expected improved yield of CZT crystals are that the phase diagram of CZT material has a narrow range of stability and CZT crystals should benefit from growth in a low gradient environment. Since the AIG method does not involve any moving parts, the temperature control and stability are much higher than for the conventional Bridgman method. The experience with CsI crystals indicates that imperfections like twinning, sparks, and multiplicities can be substantially reduced or even eliminated in CZT crystals. The expected higher yield and improved spectroscopic quality of CZT should allow many commercial applications to become a reality.