Abstract-Te inclusions existing at high concentrations in CdZnTe (CZT) material can degrade the performance of CZT detectors. These microscopic defects trap the free electrons generated by incident radiation, so entailing significant fluctuations in the total collected charge and thereby strongly affecting the energy resolution of thick (long-drift) detectors. Such effects were demonstrated in thin planar detectors, and, in many cases, they proved to be the dominant cause of the low performance of thick detectors, wherein the fluctuations in the charge losses accumulate along the charge's drift path. We continued studying this effect using different tools and techniques. We employed a dedicated beam-line recently established at BNL's National Synchrotron Light Source for characterizing semiconductor radiation detectors, along with an IR transmission microscope system, the combination of which allowed us to correlate the concentration of defects with the devices' performances. We present here our new results from testing over 50 CZT samples grown by different techniques. Our goals are to establish tolerable limits on the size and concentrations of these detrimental Te inclusions in CZT material, and to provide feedback to crystal growers to reduce their numbers in the material.

No abstract

In the past, various virtual Frisch-grid designs have been proposed for cadmium zinc telluride (CZT) and other compound semiconductor detectors. These include three-terminal, semi-spherical, CAPture, Frisch-ring, capacitive Frisch-grid and pixel devices (along with their modifications). Among them, the Frisch-grid design employing a non-contacting ring extended over the entire side surfaces of parallelepiped-shaped CZT crystals is the most promising. The defect-free parallelepiped-shaped crystals with typical dimensions of 5x5~12 mm3 are easy to produce and can be arranged into large arrays used for imaging and gamma-ray spectroscopy. In this paper, we report on further advances of the virtual Frischgrid detector design for the parallelepiped-shaped CZT crystals. Both the experimental testing and modeling results are described.

Our first-principles calculations show that the ordering of stoichiometric cation vacancies in Ga2Se3 has a large influence on the bandgap, up to 0.55 eV. Therein, the zigzag-line vacancy-ordered Ga2Se3 has the maximum bandgap (∼2.56 eV direct bandgap), and the straight-line vacancy-ordered Ga2Se3 has the minimum bandgap (∼1.99 eV indirect bandgap) at 0 K, according to scGW calculations. The bandgap difference (0.55 eV) is almost the same for normal density functional theory (DFT) calculations, hybrid DFT calculations and GW calculations. The calculation results are consistent with the experimental bandgap range of 2.0-2.6 eV at room temperature. Also, hydrostatic pressure (<9 GPa) tends to increase the bandgap, consistent with the experiments in the literature.

No abstract

No abstract

No abstract

We observe that pressure-induced amorphization of Ga 2 SeTe 2 (a III-VI semiconductor) is directly influenced by the periodicity of its intrinsic defect structures.Specimens with periodic and semi-periodic two-dimensional vacancy structures become amorphous around 10-11 GPa in contrast to those with aperiodic structures, which amorphize around 7-8 GPa. The result is a notable instance of altering material phase-change properties via rearrangement of stoichiometric vacancies as opposed to adjusting their concentrations. Based on our experimental findings, we posit that periodic two-dimensional vacancy structures in Ga 2 SeTe 2 provide an energetically preferred crystal lattice that is less prone to collapse under applied pressure. This is corroborated through first-principles electronic structure calculations, which demonstrate that the energy stability of III-VI structures under hydrostatic pressure is highly dependent on the configuration of intrinsic vacancies.