ELECTRODRIFT PURIFICATION OF MERCURIC IODIDE FOR IMPROVED GAMMA-RAY DETECTOR PERFORMANCE

The primary problems with mercuric iodide for use in room-temperature radiation detectors are the low yield of high quality devices and the problems with detector stability. It is believed that one of the prime causes of these failures is the presence of certain detrimental impur ities. Previous experiments have demonstrated that these impurities ca n be introduced during processing and that they can strongly affect de tector performance. Significant effort has been expended to develop an d utilize various mercuric iodide purification schemes. While these te chniques are effective to some degree, the level of impurities in dete ctor materials is still higher than that found in more established sem iconductors. In this work we developed and investigated a new purifica tion scheme that is based on the mobility of many of the impurities id mercuric iodide under an applied electric field. In this ''electrodri ft'' process undesirable metallic impurities are removed from a portio n of a bulk mercuric iodide charge to produce higher purity material f or detector crystal growth. The lower level of impurities results in f ewer charge-trapping centers and therefore there is the potential for significant improvements in the carrier lifetimes and detector stabili ty. This paper reports on some preliminary results of the effectivenes s of this method.