Abstract
Schottky CdTe X-ray detectors exhibit excellent spectroscopic performance but suffer from instabilities. Hence it is of extreme relevance to investigate their electrical properties. A systematic study of the electric field distribution and the current flowing in such detectors under optical perturbations is presented here. The detector response is explored by varying experimental parameters, such as voltage, temperature, and radiation wavelength. The strongest perturbation is observed under 850 nm irradiation, bulk carrier recombination becoming effective there. Cathode and anode irradiations evidence the crucial role of the contacts, the cathode being Ohmic and the anode blocking. In particular, under irradiation of the cathode, charge injection occurs and peculiar kinks, typical of trap filling, are observed both in the current-voltage characteristic and during transients. The simultaneous access to the electric field and the current highlights the correlation between free and fixed charges, and unveils carrier transport/collection mechanisms otherwise hidden.
Highlights
Understanding charge carrier transport in radiation detectors is of extreme relevance as detectors rely on the efficient collection of photo-generated charge pairs
Schottky detectors based on high quality SI CdTe have been produced for more than ten years; they sustain high operating voltages with sufficiently low currents and show excellent spectroscopic performance [1]
We use optical radiation of different wavelengths to identify the mechanisms perturbing the electrical properties of Schottky CdTe detectors, by measuring the electric field distributions by Pockels effect and the photocurrent, under various experimental conditions
Summary
Understanding charge carrier transport in radiation detectors is of extreme relevance as detectors rely on the efficient collection of photo-generated charge pairs. Under high X-ray radiation flux, all CdTe detectors, both with Ohmic and Schottky contacts, experience a reduction in counting rate and spectroscopic performance with time [5,6,7] This radiation induced polarization, still related to a space charge build-up, and to a strong distortion of the electric field distribution, is characterized by a progressive decrease of the carrier lifetime [7]. We use optical radiation of different wavelengths (above and below the band gap) to identify the mechanisms perturbing the electrical properties of Schottky CdTe detectors, by measuring the electric field distributions by Pockels effect and the photocurrent, under various experimental conditions. The role of contacts is extensively discussed throughout the paper and, in particular, in Section 6 where the relation between injection mechanisms and photocurrent is tackled
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