Impurities in CdZnTe crystal grown by vertical Bridgman method

The impurity segregation in CdZnTe grown by vertical Bridgman method and its corresponding effects on the crystal optical and electrical properties have been studied in detail. Inductively coupled plasma mass spectrometry reveals that impurities Al and Ga with segregation coefficient larger than one centralize in the first-to-freeze portion of the ingot, while impurities Li, Na, Mn, and Cu with segregation coefficient less than one enrich in the last-to-freeze portion of the ingot. At the same time, all impurities enrich in the grain boundaries. Hall measurement indicates that there exists an approximate linear monotonously increasing relationship between the free-carrier density and the sum of all the impurities concentration, which leads to an increase in the infrared transmission with the increase of wave number within the impurity enriching portions caused by the free carrier absorption. It is also found that the resistivity decreases with the concentration of Li, Na, and Cu, but increases with the concentration of Al, Mn, and Ga. An annealing processing is adopted to extract the impurities and therefore improve the crystal properties.