Deep-Level Defects in Electron Irradiated 6H-SiC
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1246-B05-03
Deep-Level Defects in Electron Irradiated 6H-SiC Michal S. Kozubal1, Pawel Kaminski1, Stanislaw Warchol2, Katarzyna Racka-Dzietko1, Krzysztof Grasza1, 3 and Emil Tymicki1 1
Institute of Electronic Materials Technology, ul. Wolczynska 133, 01-919 Warszawa, Poland Institute of Nuclear Chemistry and Technology, ul. Dorodna 16, 03-195 Warszawa, Poland 3 Institute of Physics Polish Academy of Sciences , Al. Lotnikow 32/46, 02-668 Warszawa, Poland 2
ABSTRACT An effect of electron irradiation on the concentrations of deep-level centers in C-rich and Si-rich 6H-SiC wafers is investigated. In the former material, the main deep-level centers with activation energies of Ec-0.50, Ec-0.64 and Ec-0.67 eV are found to be related to dicarbon interstitials and CiNC complexes located in hexagonal and quasi-cubic lattice sites, respectively. In the latter material, the dicarbon interstitials are dominant after the irradiation with 1.5-MeV electrons. At the energy of bombarding electrons equal to 0.3 and 0.7 MeV, the activation energies of the dominant deep-level centers are Ec-0.38 and Ec-0.52 eV, respectively. The first center is related to carbon vacancies and the second to silicon interstitials. INTRODUCTION The quality of SiC single crystals is strongly affected by defect centers resulting from the material non-stoichiometry. Depending on the growth conditions, the SiC crystals can be Si- or C-rich with a vast majority of native point defects in carbon or silicon sublattice, respectively. Thus, the essential technological issue is to control the deviation from the stoichiometric composition of the SiC crystals. In this paper, we report new experimental results obtained by deep-level transient spectroscopy (DLTS) on the electron properties of non-stoichiometry-related defect centers in 6H-SiC bulk crystals grown by physical vapor transport (PVT). The changes in the concentrations of deep defect centers induced in C-rich and Si-rich samples by the electron irradiation at an energy ranging from 0.3 to 1.5 MeV with a dose of 2x1017 cm-3 are shown. EXPERIMENT Deep defect centers were studied in two wafers with a thickness of ~1.2 mm, labeled as A and B, cut off from the [0001] boules obtained in two selected PVT growth processes. The wafers A and B originated from the n-type C-rich and Si-rich 6H-SiC single crystals, respectively. The both sides of the wafers were mirror-polished. The samples used in our experiment were Schottky diodes prepared on the wafers. Before making the contacts, the wafers were etched for 5 min in 5% hydrofluoric acid solution to remove the oxide layer. The Schottky contacts were made by evaporating a 20-nm layer of Cr and a 300-nm layer of Au on the front side of the wafers (Si face) through a shadow mask. The diameter of the Schottky contacts was 0.5 mm. Ohmic Al contacts of large area were deposited on the back side of the wafers by electron beam evaporation. The wafer with the contacts was cut into chips of 5 x 5 mm2 in area
which were used for measurements of capacitance-voltage (C-V) char
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