Modeling of the Transport Properties of Diamond Radiation Sensors

Abstract

A fully quantitative model of electronic transport in polycrystalline chemical vapour deposited (pCVD) diamond sensors is presented, predicting the conductivity behavior of diamond devices during and after exposure to ionizing radiation. The model takes into account a widely adopted qualitative picture of the diamond band gap, based on two distributions of defect levels: a mid-gap group of recombination centers and a distribution of traps closer to one of the band edges. Analytical expressions for the radiation-induced currents (RIC) and persistent radiation-induced currents (PIC) are derived from the solutions of a complete set of rate equations, and the experimental data are well fitted by assuming the distribution of the trap centers to be formed from the superposition of several uniform bands, with different cross sections, energies and concentrations. The model is validated against experimental data from a set of diamond detectors whose charge collection distance ranges over an order of magnitude (from 15 μm to 250 μm), i.e., from highly defective to the state-of-the-art material. A rationale is then proposed for the relationship between material quality and trap parameters, also with regard to the changes in the material properties caused by high irradiations of fast neutrons.