## Structural Nature of Twins Symmetric about the {111} Plane in CdZnTe
Twins symmetric about the {111} plane in CdZnTe crystals are a specific type of planar defect where the atomic arrangement on one side of the twin boundary is a mirror image of the other side with respect to the {111} crystallographic plane. This twin boundary represents a coherent but abrupt interruption in the regular lattice structure and alters the local atomic stacking sequence. Due to the zincblende structure of CdZnTe, the {111} planes are close-packed and play a critical role in crystal growth and defect formation. Such twins often form during growth or post-growth thermal processes and introduce regions of lattice mismatch strain and localized structural perturbations.
## Influence on Charge Carrier Scattering and Mobility
The presence of {111} twin boundaries acts as an effective scattering site for charge carriers — both electrons and holes — traveling through the CdZnTe crystal. When carriers approach these boundaries, the abrupt change in lattice symmetry and potential energy landscape causes deflection and scattering of their trajectories. This scattering reduces the average carrier mobility by increasing the probability of momentum relaxation and carrier trapping. Additionally, the twin boundary may introduce localized electronic states or perturbations in the band structure that can serve as trapping centers, further limiting carrier transport.
## Impact on Charge Carrier Lifetime and Trapping
Twins symmetric about the {111} plane contribute to the generation of recombination centers due to the presence of structural disorder and strain fields localized at the boundary. These centers trap charge carriers, reducing their effective lifetime before recombination. The reduced carrier lifetime directly impacts the charge collection efficiency, as fewer carriers can reach the electrodes to contribute to the signal. The accumulation of trapped charges near the twin boundary can create local space charge regions, modifying the internal electric field and causing additional charge collection inefficiencies.
## Effects on Electric Field Distribution and Charge Collection Uniformity
The localized strain and defect states associated with the {111} twin boundary distort the internal electric field within the detector volume. These distortions alter the drift paths of charge carriers, causing deviations from ideal straight-line trajectories toward the electrodes. The result is spatial nonuniformity in charge collection efficiency, where regions near the twin boundary demonstrate degraded response compared to bulk crystal areas. This spatial variation leads to spectral artifacts such as peak broadening and low-energy tailing in gamma-ray detection, adversely affecting energy resolution and quantitative accuracy.
## Contribution to Increased Leakage Currents and Noise
Structural imperfections around the {111} twin boundary can facilitate leakage current pathways by lowering the local resistivity and forming conductive channels. Increased leakage currents raise the electronic noise floor in CdZnTe detectors, thereby reducing the signal-to-noise ratio. The elevated noise further complicates the accurate detection of low-energy events and limits the detector’s overall sensitivity and stability under prolonged operation.
## Summary
Twins symmetric about the {111} plane in CdZnTe crystals introduce significant disruptions to charge transport through scattering, trapping, and modification of local electronic states. These boundaries reduce carrier mobility and lifetime, distort the internal electric field, and degrade charge collection uniformity, which collectively diminish detector performance in terms of energy resolution, sensitivity, and operational stability. Effective control of twin formation and mitigation of their impact is critical for advancing the performance of CdZnTe-based radiation detectors.
CdZnTe Association (CdZnTe.com)
https://www.cdznte.com/blog/how-do-twins-symmetric-about-the-111-plane-affect-charge-transport-in-cdznte-detectors.html
