Internal Electric Field in (cd,mn)te and (cd,mg)te Studied by the Pockels Effect

(Cd,Mn) Te and (Cd,Mg) Te bulk crystals are among the materials which have recently attracted attention in the field of room-temperature nuclear detector applications, where uniform semi-insulating (> 10(9) Omega cm) crystals with superior quality and homogenous distribution of internal electric field are required. We discuss crystals obtained using the low-pressure Bridgman method. The electric field distribution within the doped as-grown (Cd,Mn) Te and (Cd, Mg) Te crystals and its relationship with the resistivity are studied using the Pockels effect and a technique which uses the time-dependent charge principle. The (Cd,Mn) Te crystals are more uniform in terms of crystal quality than the (Cd,Mg) Te ones. A (Cd,Mn) Te sample which has non-uniform resistivity distribution was studied to elucidate the dependence between sample resistivity and the electric field within it. The cathode effects have been highlighted. A higher electric field observed next to the cathode is attributed to the presence of a rectifying metal-semiconductor interface. In (Cd,Mg) Te crystal a non-uniform field distribution is observed, primarily due to a strong inclination of the crystal towards twin formation. Thus, the (Cd,Mn) Te crystals seem to be more promising for nuclear detector applications than the (Cd,Mg) Te ones.