Improving and Characterizing (Cd, Zn) Te Crystals for Detecting Gamma-Ray Radiation

Cd0.9Zn0.1 Te ingots were synthesized from pure components (6N purity Cd, Zn, and Te with In as the dopant) and subsequently grown from the melt under an argon overpressure. Graphite crucibles (with and without an inner coating of pyrolytic BN) were used. The temperature gradient in the solidification zone was 7-30 K/cm, and the growth rate was 0.6-1.0 mm/hour. We investigated the chemical composition, structure, and electrical properties of the as-grown crystals, and established relationships between the crystal properties and the growth conditions. The bottom, middle, and top of the ingots had n-type conductivity, but slightly different properties. Resistivity reached a maximum in the middle of the ingots ((2.5 - 5.0) x 10(10) Ohm-cm), and was less at the edges similar to 0.8 x 10(10) Ohm-cm. The value of the bandgap was minimal in the middle of the ingots (similar to 1.5 eV), and 1.53-1.55 eV at the edges. The compensation degree (N-d/N-a) of the energy level responsible for the low dark conductivity showed a maximum value at the bottom of the ingots (similar to 60 - 90%), and a minimum in the middle part (1-2%). The crystals were then used to fabricate Cd(Zn) Te detectors for gamma-ray radiation.