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 impurities. Previous experiments have demonstrated that these impurities can be introduced during processing and that they can strongly affect detector performance. Significant effort has been expended to develop and utilize various mercuric iodide purification schemes. While these techniques are effective to some degree, the level of impurities in detector materials is still higher than that found in more established semiconductors. In this work we developed and investigated a new purification scheme that is based on the mobility of many of the impurities in mercuric iodide under an applied electric field. In this “electrodrift” process undesirable metallic impurities are removed from a portion of a bulk mercuric iodide charge to produce higher purity material for detector crystal growth. The lower level of impurities results in fewer charge-trapping centers and therefore there is the potential for significant improvements in the carrier lifetimes and detector stability. This paper reports on some preliminary results of the effectiveness of this method.