Ion microbeam analysis of CVD diamond

In order to investigate the homogeneity of the transport properties in diamond, IBIC (Ion Beam Induced Charge) technique has been widely used, in consideration of the very high electrical resistivity of undoped CVD diamond. However, even if detailed maps of the combined electron-hole drift or collection length have been obtained, some effects occurring during measurements, mainly due to space-charge produced by trapped charge, probably contribute to mask reality. These effects could be responsible for electrical polarisation, by means of which the collection efficiency may decay with time, or even for the dependence of the results on the pulse counting rate. The strong polarisation observed in some samples is an indication of poor electronic properties. Good samples do not polarise at all, but in all cases display collection efficiency maps which depend both on the type of radiation used, on its energy and on total dose delivered to them. In general, but not always, the collection efficiency improves both in average value and in homogeneity through the sample: this could be an indication that the sample is not totally depleted by the applied bias because of space charge. There are also indications that the material quality improves from the substrate side to the growth side, and that drift length for electrons is longer than for holes, at least in some samples. These and other observations and conclusions gathered during years of IBIC measurements will be presented and discussed, in order to illuminate this still relatively unknown material, CVD diamond.