Ion microbeam analysis of CVD diamond

In order to investigate the homogeneity of the transport properties in diam ond, IBIC (ion beam induced charge) technique has been widely used, in cons ideration of the very high electrical resistivity of undoped CVD diamond. H owever, even if detailed maps of the combined electron-hole drift or collec tion 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 polaris ation, 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 stro ng polarisation observed in some samples is an indication of poor electroni c 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 al ways, the collection efficiency improves both in average value and in homog eneity through the sample: this could be an indication that the sample is n ot 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 conclusi ons gathered during years of IBIC measurements will be presented and discus sed, in order to illuminate this still relatively unknown material, CVD dia mond. (C) 1999 Elsevier Science S.A. All rights reserved.