Electrical and dosimetric characterization of a CVD diamond detector with high sensitivity

A prototype detector has been built using commercial high quality single crystal epitaxial diamond and novel electrical contacts resulting in two asymmetric Schottky junctions able to operate the detector at zero bias like a photodiode. Aiming at evaluating the detector suitability for radiotherapy applications we report on results related to signal dynamics, linearity with the dose and dose rate, signal stability and measurement repeatability determined in a Co-60 reference beam. In addition, we measured the detector sensitivity and its dependence on the applied bias voltage. The detector has a wide active volume leading to high current signal values. The signal dynamics is wide, with a dark current of 3.2 × 10−14 A at zero bias and a current of 6.8 × 10−10 A under irradiation with a dose rate of 0.95 Gy min−1. The sensitivity to ionizing radiation increases with the bias voltage and values up to 104 nC Gy−1 mm−3 have been evaluated at −300 V. When operated at −5 V, the detector shows a linear response on a wide range of Co-60 dose rates from 1.3 × 10−3 Gy min−1 to 1.2 Gy min−1 following the Fowler's power law with a coefficient Δ = 0.99 ± 0.01. The device also shows rise and fall times of less than 1.0 s with a stability of the signal under irradiation better than 0.3%. The characteristics of the detector, as determined in the Co-60 beam, appear suitable for radiotherapy dosimetry, when fast response on the transient, wide signal dynamics, linearity and high sensitivity are required.

► The linearity with the dose rate is spread over three orders of magnitude from 1.3 × 10−3 Gy min−1 to 1.2 Gy min−1.
► The dependence on the dose rate follows a power law with a coefficient of linearity Δ = 0.99 ± 0.01 at −5 V.
► The sensitivity to ionizing radiation is dependent on the voltage and values of 104 nC Gy−1 mm−3 at −300 V have been evaluated.
► Rise and fall times of less than 1.0 s, the stability of the signal under irradiation of 0.2% with a bias voltage of −5 V.