Influence of radiation and high temperatures on electronic properties of diamond detectors

Abstract

Due to its ultra-wide bandgap, diamond is a material that offers a unique combination of excellent electrical, mechanical and thermal properties. Contrary to silicon, the operation of diamond-based radiation detectors should thus be possible under specific harsh conditions. In this work, hardness against temperature and radiation damage was investigated with two custom-designed thermally resilient diamond detectors. High purity single crystal diamond samples were used, with tungsten electrodes deposited on the opposing crystal faces. The operation of diamond as a radiation detector was investigated by exposure to fast ions in the MeV energy range, focused on a micrometer spot with the ion microprobe setup. By changing the ion energy and mass, the penetration depth or ionization density can be modified. These capabilities provide information about the interaction volume between the radiation particles and the device, which was exploited in two experimental scenarios: to probe the electronic properties by inducing ionization in the detector (probing ions), or to deposit the radiation damage by exposure to a higher ion dose (damaging ions). The analysis of the induced signal gives us the possibility to extract important parameters related to both the macroscopic detector performance, and the fundamental semiconductor properties of the diamond material used. Charge transport at elevated temperatures was characterized by measuring charge collection efficiency, mobility-lifetime product and drift time of electrons and holes, using both charge- and current-sensitive pulse-processing electronics. Testing the detector for nuclear spectroscopy operation revealed a highest operating temperature of 720 K, at which the energy resolution and collection efficiency of the detector remained virtually unaffected by thermal effects. It was also found that the radiation hardness, after deposition of the radiation damage with 5 MeV protons, deteriorates with elevating temperature. However, the decrease is stopped at temperatures above 660 K, which can be attributed to the beneficial mechanism of thermally induced detrapping of charge carriers. Analysis of the time evolution of the transient charge signal in the detector provided a framework to extract the energy levels of the responsible deep traps. These results are particularly important for the development and new applications of diamond radiation detectors in high-temperature and high-radiation conditions. Finally, an additional investigation was performed to understand the influence of the space-charge-limited regime on the charge carrier dynamics. It was demonstrated that exposure to elevated temperatures led to depolarization of the detector, whereupon the adverse effects on the charge transport were mitigated and collection efficiency was restored