Papers by Author: Hisayoshi Itoh

Abstract: This paper investigates the transient induced currents by energetic carbon ions in 6H-SiC MOSFETs and the carrier dynamic response due to such a heavy ion collision is simulated by Technology Computer Aided Design (TCAD). It was found that a heavy ion strike induces a bipolar effect on the transistor, whereby the current transients can vary in both polarities. And this has been attributed to the inherent in the MOSFET is a parasitic bipolar junction transistor.

Abstract: Intrinsic defects in 3C-SiC are generated by implantation of H+- and He+-ions or irra¬diation with high energy electrons. The defect parameters and the thermal stability of the observed defects are determined. The capture-cross-section of the W6-center is directly measured by variation of the filling pulse length. The charge state of the W6-center is obtained from double-correlated DLTS investigations according to the Poole-Frenkel effect.

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: The effect of the fabrication process of n-channel 6H-SiC MOSFETs on their radiation resistance is investigated. MOSFETs that post implantation annealing for source and drain was carried out with carbon coating on the sample surface are compared to MOSFETs that post implantation annealing was carried out without carbon coating. The radiation resistance (gamma-rays) of the carbon-coated MOSFETs is higher than that of non-coated ones. The channel mobility for MOSFETs whose gate oxide was formed using pyrogenic or dry oxidation process dose not change by gamma-ray irradiation below 1x105 Gy. The value of channel mobility slightly increases with increasing dose above 1x105 Gy. No significant increase in irradiation induced interface traps is observed.

Abstract: N-channel MOSFETs are irradiated with gamma-rays (g-rays) up to 3.16 MGy(SiO2) at room temperature. Above 1 MGy, the effective channel mobility increases with increasing absorbed dose. A similar increase is observed for the Hall mobility in the inversion layer. In addition, the Hall-effect measurements indicate a reduction of the interface trap density.

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: The charge generated in 6H-SiC n+p diodes by gold (Au) ion irradiation at an energy of 12 MeV was evaluated using the Transient Ion Beam Induced Current (TIBIC). The signal peak of the transient current increases, and the fall-time decreases with increasing applied reverse bias. The value of collected charge experimentally obtained is smaller than the ideal value. The Charge Collection Efficiency (CCE) of 6H-SiC n+p diodes irradiated with Au ions is approximately 50 % in spite that the CCE of 100 % is obtained in the case of oxygen (O) ion irradiation.

Abstract: In this paper we give a comparative study of two types of gate oxidation of n-channel 6HSiC MOSFETs. One set of transistors was fabricated using pyrogenic oxidation with no postoxidation annealing, and for the second set the oxide was grown in dry O2 with post-oxidation annealing. The lateral MOSFETs show a Hall mobility of ~ 75 cm2/Vs which is essentially same for both types of oxide. From the IV characteristics curves, the latter devices exhibit an average effective channel mobility of 72 (± 5) cm2/Vs, whereas the former has a value of 30 (± 3) cm2/Vs. From the capacitance and conductance measurements, the interface trap density for pyrogenicgrown oxide using is roughly a factor of 2 greater than those grown by dry oxidation. We found that the pyrogenic post-oxidation anneal at 1073K helps to reduce the interface states density and improves the effective channel mobility of 6H-SiC MOSFETs.

Abstract: Impurity atoms in a high-purity semi-insulating 4H-SiC substrate fabricated by sublimation and an n-type 3C-SiC substrate fabricated by Chemical Vapor Deposition (CVD) were evaluated by neutron activation analysis. Cr, Fe, Zn, As, Br, Mo, Sb, Eu, Yb, Hf, Ta, W and Au atoms were detected in the 4H-SiC fabricated by sublimation. In the 3C-SiC fabricated by CVD, Cr, Zn, As, Br, Mo, Sb, La Sm and Hf atoms were found. The concentration of these atoms tends to decrease with increasing atomic number.