## Nature of Te Inclusions in CZT Crystals
Tellurium (Te) inclusions are microscopic precipitates or clusters of excess Te that form during the growth of CZT crystals. Even in high-quality CZT, small Te inclusions are present, and their size, density, and spatial distribution influence the electrical and transport properties of the detector. These inclusions are electrically active defects that can act as trapping centers for charge carriers, creating localized regions of reduced carrier mobility-lifetime (μτ) product.
## Impact on Electron and Hole Mobility
Te inclusions introduce localized scattering sites within the CZT crystal. Electrons and holes encountering these regions experience increased recombination or trapping, reducing their effective drift velocity and μτ product. In planar detectors, where electrons primarily contribute to the anode signal, high Te inclusion density can reduce electron collection efficiency, broaden spectral peaks, and increase low-energy tailing. Holes, which are already less mobile and more prone to trapping, are similarly affected, compounding charge loss effects.
## Spatial Non-Uniformity and Localized Charge Loss
High-density or clustered Te inclusions create spatially non-uniform charge transport. As carriers traverse the crystal, regions with higher inclusion density produce localized signal deficits, resulting in position-dependent variations in energy measurement. In large-area planar detectors, this manifests as non-uniform spectral response across the detector surface, requiring calibration maps or correction algorithms to compensate for regional charge collection losses.
## Influence on Leakage Current and Noise
Te inclusions can also increase dark current by forming electrically active paths along the crystal. Although the effect is less pronounced in high-quality CZT, higher inclusion densities may contribute to elevated leakage currents locally, adding shot noise and baseline fluctuations in the readout electronics. This noise reduces the signal-to-noise ratio and further degrades energy resolution.
## Interaction with Bias Voltage and Electric Field
The impact of Te inclusions on charge transport depends on the applied bias voltage. Stronger electric fields can partially mitigate trapping by accelerating carriers more rapidly through inclusion-affected regions, reducing recombination probability. However, in thick planar detectors, carriers still drift over longer distances, increasing the likelihood of encountering multiple inclusions and sustaining cumulative charge loss. Thus, Te inclusion density sets an intrinsic limit on achievable energy resolution, even under optimized bias conditions.
## Correlation with Spectroscopic Performance
Detectors with lower Te inclusion density exhibit higher and more uniform μτ products, producing sharper spectral peaks and reduced low-energy tailing. Conversely, high-density inclusion regions correlate with broadened full-width at half-maximum (FWHM) and depth-dependent signal distortions. For thick planar CZT detectors, controlling inclusion density during crystal growth is critical to achieving consistent spectroscopic performance and reliable calibration across the active area.
## Summary
Te inclusion density in CZT planar detectors directly affects charge transport by introducing trapping sites, localized recombination centers, and scattering regions. High inclusion density reduces electron and hole mobility-lifetime products, generates spatial non-uniformities in charge collection, increases leakage current, and degrades energy resolution. Minimizing Te inclusion density is therefore essential for maintaining high-quality, uniform spectroscopic performance in planar CZT detectors.
CdZnTe Association (CdZnTe.com)
https://www.cdznte.com/blog/how-does-te-inclusion-density-affect-charge-transport-properties-in-a-high-quality-czt-planar-detector.html
