Elgin E. Eissler

Current issues of high-pressure Bridgman growth of semi-insulating CdZnTe

The availability of large-size, detector-grade CdZnTe crystals in large volume and at affordable cost is a key to the further development of radiation-detector applications based on this II-VI compound. The high pressure Bridgman technique that supplies the bulk of semiinsulating CdZnTe crystals used in X-ray, γ-ray detector and imaging devices at present is hampered by material issues that limit the yield of large-size and high-quality crystals. These include ingot cracking, formation of pipes, material homogeneity and the reproducibility of the material from growth to growth. The incorporation of macro defects in the material during crystal growth poses both material quality limitations and technological problems for detector fabrication. The effects of macro defects such as Te inclusions and pipes on the charge-transport properties of CdZnTe are discussed in this paper. Growth experiments designed to study the origin and formation of large defects are described. The importance of material-crucible interactions and control of thermodynamic parameters during crystal growth are also addressed. Opportunities for growth improvements and yield increases are identified.

Deep electronic levels in high-pressure Bridgman Cd1−xZnxTe

Abstract The behavior of deep electronic levels was studied as a function of Zn concentration in CdZnTe crystals grown by the high-pressure Bridgman technique using thermoelectric effect spectroscopy. A significant increase of the thermal ionization energies of hole traps was observed with the increasing Zn content of the ternary compound. The effect explains the stronger hole trapping and the resulting much shorter hole lifetime usually observed in CdZnTe as compared to CdTe. The behavior also suggests increased carrier recombination and explains the strong deterioration of electron collection in detectors fabricated from CdZnTe of high Zn concentration.

Radiation detector performance of CdTe single crystals grown by the conventional vertical Bridgman technique

The charge transport properties and radiation detector performance of semi-insulating CdTe single crystal grown by the conventional vertical Bridgman technique in this paper. The measured room-temperature electrical resistivity of the crystals is below the theoretical maximum allowed by the band gap of CdTe indicating incomplete electrical compensation of the material. The crystals show excellent spectroscopic performance in the 15 keV - 662 keV energy range, with reduced low-energy tailing in the photopeaks. The energy resolution of the best detector was 2.7 keV full width half maximum (FWHM) at 59.5 keV, 4.5 keV FWHM at 122 keV, and 20.1 keV FWHM at 662 keV. This improved performance is attributed to the improved hole transport over the typical HPB CdZnTe. The measured mobility-lifetime product of holes, (mu) (tau) h approximately equals 2.3 X 10-4 cm2/V, is significantly higher than that typical for HPB CdZnTe crystals. The measured electron (mu) (tau) e approximately equals 1.6 X 10-3 cm2/V of these CdTe crystals suggest somewhat poorer electron transport than in a spectroscopic grade HPB material.