Papers by Author: Junichi Isoya

Abstract: We present an electrically detected electron-spin-resonance (ESR) study on SiO2-SiC interface regions of n-channel lateral 4H-SiC MOSFETs with hydrogen annealing. This characterization technique can reveal electrically active defects that interact with channel currents of the MOSFETs. The defects were observed at 20 K, and were labeled “PH0” and “PH1”, one of which (PH1) exhibited a 1H hyperfine splitting of 5.3 mT.

Abstract: DLTS measurements show bistable behavior of the previously reported EH5 peak in low- and high-energy electron irradiation 4H-SiC. Both reconfiguration processes (A ! B and B ! A) take place above 700 ±C. By isothermal annealing, the reconfiguration rates were determined and the reconfiguration energy was calculated to EA = 2.4±0.2 eV. Since the defect is present already after low-energy electron irradiation, which mainly affects the C atom in SiC, the EH5 peak may be related to defects associated with C-vacancies or C-interstitials

Abstract: After low-energy electron irradiation of epitaxial n-type 4H-SiC, the DLTS peak amplitudes of the defects Z1/2 and EH6/7, which were already observed in as-grown layers, increased and the commonly found peaks EH1 and EH3 appeared. The bistable M-center, previously seen in high-energy proton implanted 4H-SiC, was detected. New bistable defects, the EB-centers, evolved after annealing out of the M-center, EH1 and EH3. The reconfiguration energies for one of the two EB-centers were determined to be about 0.96 eV for both transitions: from configuration I to II and from configuration II to I. Since low-energy electron irradiation (<220 keV) affects mainly the carbon atom in SiC, both the M- and EB-centers are likely to be carbon related defects.

Abstract: Electron paramagnetic resonance (EPR) was used to study high-purity semi-insulating 4H-SiC irradiated with 2 MeV electrons at room temperature. The EPR signal of the EI4 defect was found to be dominating in samples irradiated and annealed at ~750°C. Additional large-splitting 29Si hyperfine (hf) lines and also other 13C and 29Si hf structures were observed. Based on the observed hf structures and annealing behaviour, the complex between a negative carbon vacancy-carbon antisite pair (VCCSi–) and a distance positive carbon vacancy ( ) is tentatively proposed as a possible model for the EI4 defect.

Abstract: Photoexcitation electron paramagnetic resonance (photo-EPR) was used to determine deep levels related to the carbon vacancy (VC) in 4H-SiC. High-purity free-standing n-type 4H-SiC epilayers with concentration of intrinsic defects (except the photo-insensitive SI1 center) below the detection limit of EPR were irradiated with low-energy (200 keV) electrons to create mainly VC and defects related to the C sublattice. The simultaneous observation of and signals, their relative intensity changes and the absence of other defects in the sample provide a more straight and reliable interpretation of the photo-EPR results. The study suggests that the (+|0) level of VC is located at ~EC–1.77 eV in agreement with previously reported results and its single and double acceptor levels may be at ~ EC–0.8 eV and ~ EC–1.0 eV, respectively.

Abstract: Defects introduced by electron irradiation at ~80-100 K in 3C-, 4H- and 6H-SiC were studied by electron paramagnetic resonance (EPR). A number of EPR spectra, labelled LE1-10, were detected. Combining EPR and supercell calculations, we will show that the LE1 center in 3C-SiC with C2v symmetry and an electron spin S=3/2 is related to the (VSi-Sii)3+ Frenkel pair between the silicon vacancy and a second neighbour Sii interstitial along the <100> direction. Results on other centers, possibly also related to interstitials, are discussed.

Abstract: We identify the negatively charged dicarbon antisite defect (C2 core at silicon site) in electron irradiated n-type 4H-SiC by means of combined electron paramagnetic resonance (EPR) studies and first principles calculations. The pair of HEI5 and HEI6 EPR centers (S = 1/2, C1h symmetry) are associated with the cubic and hexagonal dicarbon antisite defects, respectively. This assignment is based on the comparison of the measured and calculated hyperfine tensors of 13C and 29Si atoms. We investigated the creation and annihilation of this defect as a function of electron-dose and annealing temperature.

Abstract: The Tv2a center in 4H-SiC irradiated by electrons at room temperature has been studied by pulsed EPR. Various techniques such as pulsed ELDOR (electron-electron double resonance), 2-pulse echo decay, 3-pulse inversion recovery, pulsed ENDOR (electron nuclear double resonance), and 3-pulse ESEEM (electron spin echo envelope modulation) have been applied to perform the detailed structure determination and to exploit applicability for the coherent spin control experiments.

Abstract: We report photo-induced electron paramagnetic resonance (photo-EPR) data for irradiated n-type 4H-SiC. Energy levels and associated photo-induced transitions are discussed for silicon vacancy (VSi), carbon vacancy (VC), carbon antisite-vacancy pair (CSiVC), and divacancy (VSiVC).

Abstract: In EPR (electron paramagnetic resonance) identification of point defects, hyperfine (HF) interaction is decisive information not only for chemical identity but also for the local geometry and the electronic state. In some intrinsic defects in SiC, the wave function of the unpaired electron extends quite unevenly among major atoms comprising the defects. In such a case, the determination of the number of equivalent atoms and the chemical identity (Si or C) of those atoms even with weak HF splitting are useful to compare with HF parameters obtained theoretically. For vacancy-related defects of relatively deep levels, the sum of the spin densities on the nearest-neighbor shell is found to be 60-68%.