Investigation and manufacture of CZT and CdTe sensors
- CdTe and CdZnTe gamma-ray semiconductor sensors
- Production process of CdZnTe, CdTe and ZnSe sensors for detector modules
- I-V Characteristics of Au/CdZnTe/Au detectors
- Investigation of the radiation hardness of CdTe and CdZnTe detectors
CdTe and CdZnTe gamma-ray semiconductor sensors↑
A new generation of detectors of ionizing radiation on the basis of CdTe and CdZnTe semiconductor compounds is developed in NSC KIPT. They have high count efficiency, high energy spectral resolution, high sensitivity to radiation and small size, and, what is important, they do not require cryogenic (77 К) cooling
Production process of CdZnTe, CdTe and ZnSe sensors for detector modules↑
Thermal processing↑
Contacts↑
Palladium ohmic contact on semiinsulating CdZnTe: Palladium ohmic contact on the semiinsulating CdZnTe Pd coating is harder than golden coating (3-5 times), able to soldering even after being in corrosive environment, have greater wear resistance compared with Au-covers.
A new chemical process of application of Pd- and Au-Pd-contacts was developed. The contacts have high adhesive ability, increased mechanical strength and possibility of adjusting the coating thickness. Au-Pd-contacts ensure operating performances not worse than standard Au-contacts.
Passivation↑
Methods of passivation of lateral surface of CZT sensors:
Chemical Passivation ↑A method of chemical passivation in peroxide solutions and Е-etchant is used for improving detector temporal stability and prevention of increase of leakage current.
Ion-Plasma Passivation↑A method is developed for passivation of the lateral surface of detectors by chemically and mechanically stable oxide coatings of МеО2 (TiO2, Al2O3, ZrO2, HfO2) by ion-plasma sputtering. It allows to increase the resistance of CdZnTe detectors to ~ 2×1011 Ohm and to decrease substantially leakage currents.
The best performances of CdZnTe detectors are obtained with plasma-chemical coating of HfO2. [A.V. Rybka et al.]
A method of electrical isolation CdZnTe gamma-ray detectors by lateral surface passivation with polymeric coating of parylene (poly-para-xylylene) is developed.
The cover is applied from the gas phase, after preliminary sample cleaning in the magnetron discharge, and ensures reliable isolation of a surface of the detector from effect of the various factors of an environment.
After parylene passivation the dark current is decreased to ~ 3 nA (at 300 V), charge collection carriers is improved and the temporal stability of work, i.e. service life of detectors is considerably increased.
I-V Characteristics of Au/CdZnTe/Au detectors ↑
Traditional manufacturing of detector contacts: etching in at 5 % bromine-methanol and chemical sedimentation Au from a solution of chloroauric acid.
The structure Au-p-CdZnTe-Au, received by a chemical Au sedimentation, has linear ohmic I/V characteristic in a broad range of bias voltages.
The knowledge of the temperature dependence of CdTe and CdZnTe detectors resistivity in the range from - 30 to + 70°C, has allowed to optimize operational modes of the detectors and to account for a single-error correction in dosimetry measurements in current operational mode.
Investigation of the radiation hardness of CdTe and CdZnTe detectors ↑
Stable radiation defects are accumulated during lasting gamma irradiation and despite of small cross-section of their formation at large doses deteriorate the material. The limiting absorbed dozes for CdTe and CdZnTe make ~200 kGy and ~800 kGy correspondingly. The doze limit for dosimetry detectors is substantially larger than for spectrometric devices.
Samples were irradiated by Bremsstrahlung at an electron linac (11 MeV) and average beam current 430 μA. The Bremsstrahlung absorbed dose rate was 7.5 Mrad/h (75 kGy/h).
