Epitaxial 4H-Silicon Carbide and High-Purity/Low-Doped Silicon; Irradiation-Induced Point Defects
B. G. Svensson 1,2, E. V. Monakhov1, G. Alfieri1, M. L. David1,3, M. K. Linnarsson2, M. S. Janson2, A. Yu. Kuznetsov1,2 P. Lévêque2, A. Hallén2, J. Wong-Leung4, C. Jagadish4, B. S. Avsett5, U. Grossner1 and J. Grillenberger1
1, University of Oslo, Department of Physics, Physical Electronics, P.B. 1048 Blindern, N-0316 Oslo, NORWAY
2, Royal Institute of Technology, Microelectronics and Information Technology, SE-164 40 Kista-Stockholm, SWEDEN
3, Lab de Métallurgie, University of Poitiers, Bd Marie at Pierre Curie, BP 30179, 86962 Futuroscope-Chasseneuil, FRANCE
4, The Australian National University, Electronic Materials Engineering, Canberra, ACT 0200, AUSTRALIA
5, SINTEF Electronics and Cybernetics, P.O. Box 124 Blindern, N-0314 Oslo, NORWAY
Because of its intrinsic properties silicon carbide (SiC) is considered as a material of choice for devices operating at high powers, high frequencies and high temperatures. Moreover, SiC is usually associated with detectors for ionising radiation since the material is anticipated to be radiation hard. However, recent results have revealed that the generation of point defects in nitrogen-doped 4H-SiC epitaxial layers during particle irradiation as well as during device processing involving energetic ions (ion implantation and reactive ion etching) is about one order of magnitude higher than in n-type silicon at room temperature. Evidence is obtained for deactivation of the nitrogen donors and formation of electrically neutral complexes containing nitrogen.
For fabrication of particle detectors, high-purity and low-doped (~5 x 1012 cm-3) n-type float zone silicon (FZ-Si) is, however, still the material mainly used. In the late 1990's, it was reported that oxygenation of high-purity FZ-Si by diffusion at 1100-1200 °C for an extended duration (~50-100 h) (DOFZ-Si) substantially increased the radiation hardness of the detectors. We have investigated DOFZ-Si samples after low-dose irradiation with MeV protons and electrons using ordinary deep level transient spectroscopy (DLTS) and Laplace-DLTS. In particular, annealing of the prominent divacancy (V2) center is found to give rise to a new double negative acceptor center with levels close to those of V2, but readily resolved by Laplace-DLTS. A close proportionality holds between the loss of V2 and the growth of the new center, which is tentatively ascribed to a divacancy-oxygen complex. Further, the annealing kinetics of V2 in Czochralski-grown, FZ and DOFZ n-type samples are compared and the efficiency of interstitial oxygen as trap for migrating V2 centers is discussed.