Vacancy-Type Defects in as-Grown and Proton-Irradiated 6H-SiC
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WERNER PUFF *,PETER MASCHER **,and ADAM G. BALOGH * Institut fUr Technische Physik, Technische Universitit Graz, Petersgasse 16, A-8010 Graz, Austria, [email protected] ** Centre for Electrophotonic Materials and Devices, Department of Engineering Physics, McMaster University, Hamilton, Ont. L8S 4L7, Canada *** FB Materialwissenschaft, FG Diinne Schichten, Technische Hochschule Darmstadt, PetersenstraBe 23, 64287 Darmstadt, Germany ABSTRACT Annealing of defects in as-grown and proton irradiated bulk n- and p-type 6H-SiC has been investigated by positron lifetime spectroscopy and Doppler-broadening measurements. The grown-in defects do not anneal out until 1600 °C, whereas the radiation induced defects show three main annealing stages well below this temperature. During annealing, the formation of larger defect complexes can be observed. INTRODUCTION Silicon carbide is a promising candidate for specific high-temperature, high-power, or highfrequency devices. Nevertheless, the behaviour of native and irradiation induced defects has not yet been studied sufficiently. In the recent years, some progress has been made in this field resulting in a few comprehensive reviews [1-3]. There have been quite a few electron spin resonance studies done on 3C-SiC and 6H-SiC. The results may be summarized as follows: Both silicon and carbon vacancies are formed upon electron irradiation [4, 5]. Whereas the silicon vacancy is in the negative charge state [4], the situation for the carbon vacancy is more complicated. It is suggested that after proton irradiation, the neutral carbon vacancy exists in n-type material while it is positively charged in p-type material [6]. After electron irradiation, the positively charged carbon vacancy was found in ntype samples [7]. Positron annihilation experiments on electron-irradiated 6H-SiC detected both carbon and silicon vacancies in n-type material, whereas in p-type material no vacancies were detected [8, 9]. After proton irradiation, however, vacancies were detected also in p-type material [ 10,111. EXPERIMENTAL DETAILS The samples consisted of ten sets of research grade 6H-SiC single crystalline wafers obtained from Cree Res. Inc., seven n-type with carrier concentrations in the range from 2.Ox 1017 cm- 3 to 3.2x10 1 8 cm- 3, two p-type (3.8x10' 8 cm-3 and 6.2x101 8 cm- 3), and one semi-insulating sample (for details see Tables. 1 and 2). The samples were irradiated with 5 MeV protons to fluences of lxl014 cm-2 , lxlO15 cm-2 or lx1016 cm-2, respectively (cf. Table. 2). The temperature of the specimens was kept below 220 K during irradiation. The 20 min isochronal annealing was done in air from room temperature to 1000 'C and in an Ar atmosphere to the highest temperatures. The positron annihilation lifetime and Doppler-broadening measurements were performed at room temperature. For the lifetime measurements, a conventional spectrometer was used with a 261
Mat. Res. Soc. Symp. Proc. Vol. 512 © 1998 Materials Research Society
time resolution of 136 ps full width at half maximum (FWHM). T
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