Role of Zn in obtaining of semi-insulating CdZnTe crystals for ionizing radiations detectors

TL;DR

This study investigates how zinc influences the formation of semi-insulating CdZnTe crystals, focusing on vacancy control to improve their properties for ionizing radiation detectors.

Contribution

It explains the role of zinc in self-regulating cadmium vacancies, leading to improved control of crystal properties during growth and annealing.

Findings

Reducing cadmium vacancies increases hole mobility-lifetime product.

Zinc addition stabilizes vacancy concentration, reducing pressure dependence.

Annealing at 600°C decreases vacancy-related photoluminescence and photoconductivity bands.

Abstract

Studies of n-CdZnTe crystals (photoluminescence, extrinsic photoconductivity, Hall effect, time-of-flight technique) have shown that the excess concentration of vacancies of cadmium (Vcd) is the main reason of low, as a rule, values of product of mobility to life time of holes (mhth). The reduction of the concentration of cadmium vacancies (decreasing of the intensity of near 1eV photoluminescence band and an intensity of the (0.9-1.3) eV extrinsic photoconductivity band) by annealing of the crystals at 600 C results in increasing of value of mhth. Influence of Zn on formation of the basic photoelectric properties of CdZnTe crystals has been explained by "self-control" of a concentration of cadmium vacancies Vcd due to addition of Zn results in formation of divacancies of metal, which in part dissociate and provide a crystal with necessary quantity of monovacancies for processes of complex formation. That makes process of obtaining of semi-insulating CdZnTe crystals less dependent from pressure Pcd in comparison with CdTe. However with the purpose of obtaining CdZnTe crystals with high value of mhth (i.e. with small concentration of the free vacancies of cadmium) it is necessary to control Pcd above the crystal at stages of its growth and annealing.