Photo EPR Study of Trapping and Recombination Processes in Semi-Insulating 4H-SiC Crystals as Function of Temperature
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Photo EPR Study of Trapping and Recombination Processes in Semi-Insulating 4H-SiC Crystals as Function of Temperature E.N. Kalabukhova1, S.N. Lukin1, A. Saxler2, W.C. Mitchel2, S R. Smith2, J.S. Solomon2, and A.O. Evwaraye3 1 Institute of Semiconductor Physics, NASU, Kiev, Ukraine, 2 Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, U.S.A. 3 University of Dayton, Physics Department, Dayton, U.S.A. ABSTRACT Photo-Electron Paramagnetic Resonance (photo-EPR) measurements of semi-insulating (s.-i.) 4H SiC have been made at 37 GHz including photo excitation and photo quenching techniques in the temperature interval from 77 K to 50 K. At T = 77 K in the dark the EPR spectrum consists of a low intensity line due to boron on the cubic lattice site and a single line with isotropic g|| = g⊥ = 2.0025 due to a carbon-related surface defect. During illumination with ultraviolet light the EPR lines of hexagonal boron and cubic nitrogen appear in the EPR spectrum and persist after the illumination is removed. Subsequent illumination of the sample with sub-band gap, visible, light resulted in the quenching of the EPR lines from nitrogen and appearance of the IP1 EPR line with g|| = 2.0048, g⊥ = 2.0030 caused by direct transfer of electrons from nitrogen donor to the P1 center. The lifetime of the photo-generated carriers trapped by the P1 centers is found to be more than 15- 20 hours after the photo-excitation was turned off. The deep donor P1 local center is suggested to be the as yet unidentified deep level located at EC – 1.1 eV which pins the Fermi level in this sample at this energy in the dark. As the temperature is lowered from 77K and the quasi Fermi level positions reach shallow donor and acceptor states, an additional EPR line, ID, with g|| = 2.0063, g⊥ = 2.0006, appears at 50 K in the excitation EPR spectrum and is attributed to the antisite defect Sic− with an energy level shallower than nitrogen. At the same time the ratio of the photo-excited EPR line intensities k : I h , returns to the value observed at responsible for boron on the cubic and hexagonal sites, I B B 77 K and becomes equal to 0.4 at 50 K, showing that the concentration of boron in the hexagonal site is higher than on the cubic site. INTRODUCTION There is current interest in deep levels in SiC for the production of semi-insulating substrates for use in microwave devices. Among the deep levels, the dominant recombination centers (i.e. the life-time-limiting defects), despite their essential importance, are still unknown. One of the suitable experimental techniques which are sensitive to carrier recombination and can give the detailed information about electronic structure of the defects is the photo EPR technique. In this work a systematic and comprehensive photo-Electron Paramagnetic Resonance (photo-EPR) study of s.-i. 4H SiC has been carried out in an attempt to reveal and investigate the defects playing important roles in the trapping and recombination (TR) process.
E9.4.1
EXPERIMENTAL DETAILS Photo-EPR
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