## Overview of Tellurium Inclusions in CZT
Tellurium (Te) inclusions are microscopic regions of excess elemental Te within the CdZnTe crystal lattice. In hemispherical CZT detectors, these inclusions act as localized defects that disrupt the uniformity of the crystal’s electronic properties. Their presence affects charge transport, trapping, and recombination, which directly influences spectroscopic performance, particularly energy resolution and peak shape.
## Impact on Charge Transport
Te inclusions create regions of distorted electric field and localized potential barriers. Electrons drifting toward the small anode may be deflected or slowed when passing near these inclusions. This increases the likelihood of trapping or recombination, particularly for interactions occurring deeper in the detector bulk. The net effect is a reduction in collected charge and an increase in variability between events, degrading spectral resolution.
## Generation of Low-Energy Tailing
Interactions near or around Te inclusions often result in partial charge collection, producing pulses with reduced amplitude. These events manifest in the energy spectrum as low-energy tails or asymmetrical peaks. In hemispherical detectors, where electron collection dominates, the effect is particularly pronounced for events far from the anode, where carriers must traverse larger distances and encounter more inclusions.
## Spatial Non-Uniformity Effects
High inclusion density leads to spatially varying charge collection efficiency across the detector volume. This non-uniformity introduces event-to-event variability, complicating depth-of-interaction corrections and calibration procedures. For hemispherical detectors, the radial electric field amplifies the impact of local defects on charge collection, making uniformity essential for accurate spectroscopy.
## Contribution to Leakage Current and Noise
Te inclusions near surfaces or at interfaces can act as localized conductive paths, increasing surface or bulk leakage currents. Elevated leakage contributes to shot noise, which reduces the signal-to-noise ratio, particularly at low energies. This noise further degrades energy resolution and limits the detector’s effective low-energy threshold.
## Mitigation and Quality Control
Minimizing Te inclusion density requires careful crystal growth and post-growth selection. Advanced characterization techniques such as infrared imaging, X-ray topography, or optical microscopy are used to identify inclusions before detector fabrication. In hemispherical detectors, positioning the small anode to collect electrons from the most uniform regions of the crystal helps mitigate the impact of inclusions.
## Summary
Te inclusions in CZT hemispherical detectors degrade spectroscopic performance by disrupting charge transport, increasing trapping, producing low-energy tailing, and introducing spatial non-uniformity. They can also contribute to elevated leakage current and electronic noise. High-quality crystals with low inclusion density, careful anode placement, and pre-fabrication characterization are essential to preserve energy resolution and reliable single-carrier electron collection in hemispherical geometries.
CdZnTe Association (CdZnTe.com)
https://www.cdznte.com/blog/how-does-te-inclusion-density-degrade-spectroscopic-performance-in-a-czt-hemispherical-detector.html
