Evidence of localised charge build-up mechanisms in CVD diamond as observed using micro-X-ray beam analysis

Abstract

Geometrical non-uniformities in the photoconduction properties of polycrystalline diamond detection devices are known and can be attributed to the spatial variation of the electric field distribution in the vicinity of grain boundaries. In this study, we provided further insights into these spatial variations of the sensitivity by using a monochromatic X-ray source in order to locally create carriers in diamond under a narrow spot size with a focal point size below 1μm in diameter. In this way, photo-sensitivity maps can be probed, and since the variation of the photon energies leads to modified penetration depths, the tool also enables the probing of the non-uniformity of the device throughout the volume of the device. Here we have also particularly focused on non-stable mechanisms that are known to affect the device performances, namely polarisation effects and charge build-up. This study therefore highlights several mechanisms that can be observed in diamond radiation detectors and that motivates their study: (i) limitations in sensitivity due to the saturation of the velocity of carriers, (ii) non-uniform photo-sensitivity, (iii) polarisation and (iv) charge build-up.