A MICRO-IBIC COMPARISON BETWEEN NATURAL AND CVD DIAMOND

Micro-IBIC (ion beam-induced current) by means of a proton microbeam i s a powerful tool for mapping the distribution of charge collection le ngths at the surface and in the bulk of diamond samples. Up to now, an evident correspondence between the morphological columnar structure o f chemical vapour-deposited (CVD) diamond and the ''stripy'' shape of IBIC maps has been found. This points out the presence of a microcryst alline ''electric'' structure and the harmful effects of defects assoc iated to grain boundaries on transport properties. In this work we pre sent for the first time a comparison between micro-IBIC maps of cross- sections of a natural IIa diamond and maps obtained in CVD diamond sam ples. In natural IIa diamond, IBIC maps are homogeneous and the global IBIC spectrum is peaked al a mean collection efficiency of about 10% at an electric field of 7500 V cm(-1). Strong ii-radiation produces a uniform increase of the mean collection length in natural IIa diamond whereas, in CVD diamond, it produces an homogenisation of the space ch arge with an increase of the counting rate without any evident Increas e of the average collection length. (C) 1997 Elsevier Science S.A.