We developed a new concept of X- and γ-ray radiation semiconductor detectors based on a large area graphene/semi-insulating single crystal CdTe Schottky-type heterojunction. These two terminal electronic devices can be easily fabricated by forming a Van der Waals contact between large area chemical vapor deposited graphene and CdTe substrates in air and at room temperature. This approach significantly reduces the fabrication cost and improves the reproducibility and stability of electrical properties. A detailed analysis of their AC and DC electrical properties was carried out in order to determine the width of the space charge region and dominant charge transport mechanisms at reverse bias. The unoptimized graphene/CdTe heterojunction detectors exhibited a promising spectral resolution of 241Am (59 keV) and 137Cs (662 keV) isotope radiation at room temperature.
An influence of laser-induced stress and shock waves on photoelectric properties of epitaxial n-Cd 0.28 Hg 0.72 Te (CMT) films with a cellular structure was studied. Irradiation of CMT films with nanosecond ruby laser pulses resulted in a modification of photoconductivity spectra and an increase in the photosensitivity because of segregation of electrically active point defects at the cell boundaries (acting as sinks) and also because of changes in their electron states as a result of action of the laser-generated stress and shock waves. Using the calculations of the temperature of the samples, the depth of shock wave formation and the amplitude of shock wave at laser irradiation, it was established that the strongest photosensitization of CMT took place in deep-seated layers where the shock wave was formed. This deduction was confirmed by an increase in the photosensitivity of purpose-designed samples coated with copper foil in such a way as to exclude the photo-and thermal effects under laser irradiation of CMT solid solutions.
A significant improvement in electrical characteristics of Schottky diodes designed for X-and-ray detectors has been achieved using semi-insulating CdTe single crystals and unified technology, where both Schottky and near-ohmic contacts were formed by the deposition of the same metal (Ni) on the opposite surfaces of the crystal pre-treated by chemical etching and Ar ion bombardment with different parameters. Reduction of injection of minority carriers from the near-ohmic contact in the neutral part of the diode and high Schottky barrier for holes provides low leakage current even at high bias voltage (50 nA cm 2 at 2000 V and at room temperature). The current-voltage characteristics of the detectors with Ni/CdTe/Ni electrode configuration in the low-voltage range are described by the generation-recombination Sah-Noyce-Shockley theory. The results of the reproducibility and time stability of the fabricated diodes are reported. Index Terms-Charge carrier processes, leakage currents, Schottky diodes, X-and gamma-ray detectors.
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