<0001> channeling stopping power of MeV He + ions in 4H- and 6H-SiC.
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channeling stopping power of MeV He+ ions in 4H- and 6H-SiC. Roberta Nipoti and Fabrice Letertre1 CNR-IMM Sezione di Bologna, via Gobetti 101, I-40129 Bologna, Italy 1 SOITEC S.A., Parc Technologique des Fontaines, 38190 France ABSTRACT 4H-SiC and 6H-SiC thin films as top surface layers of SiCOI wafers and Rutherford Back Scattering experiments with He+ ions in the energy range 0.9 - 2.2 MeV were used for measuring the He+ ions channeling stopping power with respect to the SiC random one. The film thicknesses were in the range 270-360 nm. The ratio between axial and random stopping power values decreased for increasing energy values and was higher for the 6H polytype with respect to the 4H one, i.e. it ranged from 0.85 to 0.72 for the former and from 0.80 to 0.66 for the latter. INTRODUCTION The energy loss of energetic ions along the major directions of crystals has been the subject of many studies. In fact, this phenomenon has relevance in several fields as nuclear physics, ion beam analysis and material modification by ion implantation. Thin selfsupporting targets and transmission experiments are the traditional approach to the stopping power measurement of swift ions in crystalline materials [1-3]. In spite of the many advantages of this method, the experimental results strongly depend on the preparation of the self-supported thin crystals, which must be planar and with homogeneous thickness to give accurate and reliable data. In the last decade alternative approaches have been proposed. All of them used thick targets and backscattering experiments. These targets were bulk crystals [4,5] or substrates with on the top a perfect crystalline film [6,7]. Generally, the simulation of the back scattering channeling spectra was used to derive the channeling stopping power values by assuming a known dependence of the dechanneling function on the ion energy. The best fits between the spectrum yield and the spectrum energy edges were used to evaluate the channeling stopping power that played as variable parameter in the simulation process. In the panorama given above, the literature concerning SiC is limited to experiments of the more recent type and to the use of bulk SiC polytypes [5]. But, times are mature to perform experiments also by using thin crystalline SiC films. In fact, now days, such films of the 4H and 6H polytypes are manufactured from bulk SiC wafers by the Smart-Cut® process [8]. These SiC film have electronic quality [9], are few hundred nanometer thick, lay on the top of a thick SiO2 layer that lay on the top of a Si wafer. Such a structure is called “Silicon Carbide On Insulator” or SiCOI. This paper presents the axial stopping power measurements both in 4H- and 6H-SiC done by using SiCOI wafers and Rutherford Back Scattering (RBS) experiments. EXPERIMENTAL on axis 6H-SiC and 8° off axis 4H-SiC SiCOI wafers were used for this study. The SiC films had nominal thickness < 350 nm and 50 mm diameter, while the Si wafer had 100 mm diameter and the SiO2 layer was thicker than 1 µm. The Rutherford B
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