Improving and characterizing the quality of (Cd,Zn)Te crystals for detecting gamma radiation

Cd_0.9Zn_0.1Te ingots were synthesized from pure components (6N purity Cd, Zn, Te, with In and Fe as dopants) 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 ~15-30 K/cm, and the growth rate was 0.6-1 mm/hour. We investigated the chemical composition, structure, and electrical properties of the grown crystals, and established the relationships with their growth conditions. The beginning, middle, and top of the ingot had n-type conductivity, but slightly different properties. Resistivity reached a maximum in the middle of the ingot ((2.5-5)×10¹⁰ Ohm-cm), and was less at the edges ~0.8×10¹⁰ Ohm-cm. The value of the band-gap was minimal in the middle of the ingot (~1.5 eV), and 1.53-1.55 eV at its edges. The compensation degree (Nd/Na) of the energy level, responsible for the dark conductivity, showed a maximum value at the beginning of the ingot (~60-90 %), and a minimum in the ingot´s middle part (1-2 %). High-temperature Hall-effect measurements of CdTe:In samples ([In]~2×10¹⁷ cm^-3) demonstrated the possibility of restoring the initial sample´s high resistivity (decreased after eliminating inclusions using Cd overpressure annealing) by treatment under a Te overpressure at ~870 K. The crystals were then used to fabricate Cd(Zn)Te detectors for gamma radiation.