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Description
Transmittance imaging enables the localization and mapping of various crystal features, such as defects and inclusions, within CdTe and CZT crystals [1]. By converting these identified locations into point clouds, we can analyse defect relationships using advanced computational tools, including neural networks. The resulting maps allow us to estimate crystal quality before the materials are processed and integrated into radiation detectors.
Charge collection properties can be verified using transient current measurements. By treating detector surfaces to allow laser pulse penetration, we can generate electron-hole pairs at depths determined by the laser's wavelength. Furthermore, by mounting samples on an XYZ-stage, specific internal regions of the detector can be systematically scanned [2-3].
When using a wavelength close to the bandgap, energy deposition from the laser pulse is continuous along its entire path. This inherent limitation of the Single Photon Absorption (SPA) technique can be overcome by utilizing ultra-fast laser pulses with a wavelength approximately double that of the bandgap. In this Two-Photon Absorption (TPA) technique, electron-hole pairs are generated within a much more confined volume inside the bulk.
In this contribution, we discuss the characterization of various CdTe crystals using transmittance imaging and transient current measurements. These detector materials are evaluated using both SPA and TPA techniques, performed with a standard TCT setup and the laser facility at ELI Beamlines in Dolní Břežany, Czechia.
[1] M Väänänen et al., J. Inst. 19 (2024), C12004
[2] M Bezak et al., J. Inst. 20 (2025), C01021
[2] M Bezak et al., J. Inst. 18 (2023), C02004