We investigated the response function of a planar Cd(Zn)Te detector designed for measurement of electron energy spectra and experimentally measured the response of Cd(Zn)Te detector to radiation of 90Sr/90Y reference radiation source. The obtained experimental spectra were compared with the spectra simulated by the Monte-Carlo method with Geant4 package. We managed to agree the simulated response with the experimental one using only two fitting parameters: products of mobility and average lifetime for electrons and holes. Thereby determined transport parameters of charge carriers were independently verified through the measurement of the positions of low energy 133Ba photopeaks of a reference gamma-ray source.
We investigated the spectroscopic properties of several Cd(Zn)Te detectors with a Schottky contact and simulated them via a computer code. The responses were determined of 0.5-mm-thick surface-barrier Ni/Cd(Zn)Te/Ni detectors to gamma-rays from reference sources of 241Am, 133Ba, 152Eu, 137Cs and 60Co. The best measured energy-resolution at 661.67 keV (137Cs) of these detectors under 800 V of displacement voltage was better than 1.5%. The detectors’ response functions, simulated with Geant4 toolkit, agreed satisfactorily with our experimental data.
We explored the influence of Cd(Zn)Te detectors on the detector’s dark current for different methods of
contact formation and passivation of the side surfaces. Our findings suggest that the dark current of a
homogeneous detector with ohmic contacts is limited by the detector’s resistivity and the operating voltage.
Detectors with a rectifying barrier have a markedly lower dark current at the same voltage and contact
geometry than those without such a barrier, and their sides have a larger space charge than those of untreated
ones. The major factor lowering the detector’s dark current is the formation of a rectifying barrier that occurs
while creating contacts to the detector; the role of passivation of the lateral surface in this case is minimal.
However, passivation plays the main role in the formation of leakage current in homogeneous detectors with
ohmic contacts, where the uniformity of the electric field is important inside the detector, or in other studies
used for determining the bulk resistivity of the detector material. We formed a surface-barrier structure on a
semi-insulating Cr-Cd(Zn)Te-Cr crystal (n-type) with a resistivity of 1010 Ohm-cm at room temperature. The
measured leakage current of this detector was less than 3 nA at 1500 V. We discuss our findings on this
detector’s structural properties.
Considerable variations in the charge-carrier transport parameters necessitate individual calibration of CdZnTe gammaray
detectors for many applications. We carried out a set of experiments wherein we determined that the main region of
interest for the energy dependence of CdZnTe-detectors’ sensitivity lay in the gamma-quantum energy range of 0.03- to
3-MeV. This finding was satisfactorily verified and reconstructed from our measurements of pulse-height distributions
using 241Am-, 137Cs-, and 60Co-sources. We discuss our comparison of the quality-of-fit of the approximation formulae with our detailed calculations of the sensitivity of CdZnTe detectors via a Monte-Carlo method.
KEYWORDS: Sensors, Spectroscopy, Monte Carlo methods, Gamma radiation, Data modeling, Absorption, Sensor performance, Electron transport, Electroluminescence, Physics
We investigated the influence of the ratio of the electron and hole mobility-lifetime products, (μτ)e,h and (μτ)e/(μτ)h, on
the resolution of CdZnTe planar radiation detectors via Monte-Carlo simulations. Preliminary results show that this ratio
exercises a larger effect than that of any other parameter on the detector’s peak-to-valley ratio and resolution. We
determined the range of values of the ratio (μt)e/(μτ)h where the fast degeneration of the photopeak in CdZnTe detectors
takes place at a gamma-ray energy 661.7 keV (137Cs). We offer an explanation, based on the results of some of our
experimental data, on the spectrometric performance of CdZnTe detectors.
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