Post-growth annealing of Bridgman-grown CdZnTe and CdMnTe crystals for room-temperature nuclear radiation detectors

Abstract

a b s t r a c tBridgman-grown cadmium zinc telluride (CdZnTe or CZT) and cadmium manganese telluride (CdMnTe or CMT) crystals often have Te inclusions that limit their performances as X-ray-and gamma-raydetectors. We present here the results of post-growth thermal annealing aimed at reducing and eliminating Te inclusions in them. In a 2D analysis, we observed that the sizes of the Te inclusions declined to 92% during a 60-h annealing of CZT at 510 1C under Cd vapor. Further, tellurium inclusions were eliminated completely in CMT samples annealed at 570 1C in Cd vapor for 26 h, whilst their electrical resistivity fell by an order of 10 2 . During the temperature-gradient annealing of CMT at 730 1C and an 18 1C/cm temperature gradient for 18 h in a vacuum of 10 À 5 mbar, we observed the diffusion of Te from the sample, so causing a reduction in size of the Te inclusions. For CZT samples annealed at 700 1C in a 10 1C/cm temperature gradient, we observed the migration of Te inclusions from a lowtemperature region to a high one at 0.022 μm/s. During the temperature-gradient annealing of CZT in a vacuum of 10 À 5 mbar at 570 1C and 30 1C/cm for 18 h, some Te inclusions moved toward the hightemperature side of the wafer, while other inclusions of the same size, i.e., 10 mm in diameter, remained in the same position. These results show that the migration, diffusion, and reaction of Te with Cd in the matrix of CZT-and CMT-wafers are complex phenomena that depend on the conditions in local regions, such as composition and structure, as well as on the annealing conditions.

Thermal Annealing of CdMnTe Material Being Developed for Nuclear Radiation Detection Applications

“…Some of the smaller inclusions in the upper side of the image have been eliminated while other were replaced with much smaller inclusions. The change in shape, reduction in size, and elimination could be attributed to two major processes [14], viz. reaction between Te inclusions and Cd that diffused into the CdMnTe matrix, and diffusion of Te within the matrix.…”

“…One method of removing these performance-limiting Te inclusions is post-growth thermal annealing. There are two primary approaches to post-growth thermal annealing [14]: 1) annealing the crystal at a constant temperature (around or above the melting point of Te) in a Cd vapor, and 2) annealing under a temperature gradient to induce the migration of Te inclusions to the hightemperature side of the crystal. In temperature gradient annealing the migration of Te particles leaves regions with fewer and smaller Te inclusions, which can be harvested for detector fabrication.…”

Analysis of Te and TeO<sub>2</sub> on CdZnTe Nuclear Detectors Treated with Hydrogen Bromide and Ammonium-Based Solutions

“…The start materials are typically high purity cadmium telluride (CdTe) and zinc telluride (ZnTe) [17]. Typical data on Cd 1-x Zn x Te, with x = 0.1, grown by Bridgman technique in our research group at Brookhaven National Laboratory is reported in [4] [17]. The CdTe and ZnTe start materials were commercially obtained with data on their composition.…”

“…The CdZnTe crystals are grown under tellurium-rich environments to attain high resistivity that is needed for the detector to operate at room temperature [4]. The major requirements need for detectors to operate at room temperature include high atomic number, large energy band gap, high density, and high electrical resistivity [2] [3].…”

Study of Detector-Grade CdMnTe:In Crystals Obtained by a Multi-Step Post-Growth Annealing Method

“…Generally, one annealing method only contains one step. For example, in order to reduce Te inclusions, CdTe-based crystals are generally annealed under a Cd atmosphere [11][12][13].…”