Electrical Properties Study of Three Highly Purified CdTe Ingots

Three high resistivity CdTe ingots have been prepared with highly purified materials. The three starting Te components were purified through three different purification processes: horizontal zone refining, vacuum distillation and by a combination of both processes. The three crystals growths were achieved by the THM method. The purity studies were achieved by the determination of the concentration of 21 impurities, using the Atomic Absorption (AASGF) method. The resistivity ρ measurements along the length of the three CdTe ingots at room temperature showed a nearly constant ρ value within the range of 109 - 1010 Ω.cm. This represents a motivating result, in net advance with the general behavior of classic THM materials, where it began by high ρ at the starting point, and then it decreased by few decades. Values of drifting motilities μ were measured for all ingots and showed interesting high values: μe =1100cm2/Vs for electrons and μh =90 cm2/Vs for holes. The position in the band gap and eventually the nature of the corresponding electrical defects levels, involved in the trapping process was studied by using the PICTS method. The uniformity of ρ, the high mobility μ and the low concentration values of impurities in all our CdTe ingots confirm the high electronic grade quality of these CdTe materials, which is better than 6N purity.