Characterization of ion beam induced polarization in scCVD diamond detectors using a microbeam probe

Abstract

Diamond detectors are increasingly being used in many multidisciplinary areas due to their good spectroscopy properties. However, in certain cases of diamond employment as a nuclear detector, a significant deterioration of the signal properties due to the trapping of free charge carriers by defects can be observed. This phenomenon is known as polarization. Experimentally, a good understanding of the free carrier transport mechanisms can be obtained from direct measurements of the Charge Collection Efficiency (CCE) using the ion beam induced charge technique (IBIC). In this work IBIC was performed by focused proton and carbon ion beams of different energies in the MeV range, to probe the polarization induced changes of the CCE. The detectors being used in this study include a thin scCVD membrane detector (thickness 6 μm) and a scCVD crystal of 65 μm thickness. Furthermore, the detectors have been damaged with transmitted protons to study the influence of defects on polarization. The results that are presented show that the ion microprobe technique IBIC can be successfully used to fully characterize the polarization development in terms of time evolution in scCVD diamonds. More specifically, we show for the thin membrane detectors at high count rates and longer time irradiation a clear dependence of the pulse height signal decrease, induced by the polarization effect, with levels of radiation damage. A significant deterioration of the signal was observed in regions damaged with fluences between 1012 and 1014 ions/cm2 for both types of charge carriers. The results have shown that the energies used for the probing ion beams allow us to explore the electronic features from shallow to deeply penetration range and that has an effective impact on the temporal evolution of the build-up space charge. The experiments carried out have also shown that light can be used to suppress or amplify the polarization phenomena in damaged regions depending on the dominant type of charge carriers.