Papers by Author: John R. Williams

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Authors: J. Neil Merrett, David C. Sheridan, John R. Williams, Chin Che Tin, J.D. Cressler
Authors: Sokrates T. Pantelides, G. Duscher, M. Di Ventra, Ryszard Buczko, K. McDonald, M.B. Huang, Robert A. Weller, Israel J.R. Baumvol, Fernanda Chiarello Stedile, C. Radtke, S.J. Pennycook, G.Y. Chung, Chin Che Tin, John R. Williams, J.H. Won, Leonard C. Feldman
Authors: Gil Yong Chung, Mark J. Loboda, M.J. Marninella, D.K. Schroder, Tamara Isaacs-Smith, John R. Williams
Abstract: The pulsed MOS-C (Metal Oxide Semiconductor-Capacitor) technique was used to measure generation lifetimes in 4H-SiC epitaxial wafers. The ratio of generation to recombination lifetime has been investigated to understand the dominant defect for generation lifetime. The EH6/7 defect level is considered to limit generation lifetime and field enhanced emission is proposed to explain extremely large variation of generation lifetime in a small area. Generation lifetime is limited by dislocations when they are above a threshold density of about 106cm-2. Generation lifetimes measured on 4 and 8 degree off-cut angle epi-substrates are very comparable.
Authors: A.V. Adedeji, Ayayi Claude Ahyi, John R. Williams, M.J. Bozack, S.E. Mohney, B. Liu, James D. Scofield
Abstract: Composite ohmic contacts designed for SiC devices operating in air at 350°C have been studied. Ohmic contacts to n- and p-4H-SiC were protected against inter-diffusion and oxidation by Ta-Si-N layers obtained by sputter deposition from a TaSi2 target in a mixture of Ar and N2. Platinum was sputter-deposited at 250°C to promote adhesion between the Ta-Si- N barrier layer and a thick Au cap layer. Platinum also acts as a barrier to the diffusion of Au. The electrical and mechanical characteristics of the composite contacts were stable after hundreds of hours of annealing in air at 350°C. We report the effects of thermal aging on the specific contact resistance and the semiconductor sheet resistance, and the results of wire bond pull and shear tests following aging for Ta-Si-N / Pt / Au stacks deposited on both SiO2 dielectric layers and the ohmic contact layers.
Authors: David C. Sheridan, J. Neil Merrett, J.D. Cressler, Stephen E. Saddow, John R. Williams, C. Ellis, G. Niu
Authors: Alberto F. Basile, John Rozen, X.D. Chen, Sarit Dhar, John R. Williams, Leonard C. Feldman, Patricia M. Mooney
Abstract: The electrical properties of the SiC/SiO2 interface resulting from oxidation of the n-type 6H-SiC polytype were studied by hi-lo CV, temperature dependent CV and constant capacitance deep level transient spectroscopy (CCDLTS) techniques. Several trap species differing in energy and capture cross section were identified. A trap distribution at 0.5 eV below the 6H-SiC conduction band energy and a shallower density of states in both the 6H and 4H polytyes are passivated by post-oxidation NO annealing. However, other ultra-shallow and deeper defect distributions remain after nitridation. The latter may originate from semiconductor traps.
Authors: C.Y. Lu, James A. Cooper, G.Y. Chung, John R. Williams, K. McDonald, Leonard C. Feldman
Authors: Alberto F. Basile, Sarit Dhar, John R. Williams, Leonard C. Feldman, Patricia M. Mooney
Abstract: Temperature dependent capacitance-voltage (C-V) and constant capacitance transient spectroscopy (CCDLTS) measurements have been performed to investigate the role of N in improving the transport properties of 4H-SiC MOS transistors. The higher channel mobility in the N pre-implanted transistors is due at least in part to activation of a small fraction of the implanted N near the SiO2/SiC interface as donors in SiC during oxidation, thus reducing the effects of interface trapping. In addition, the absence of oxidation-induced near-interface defects, which were observed in NO-annealed capacitors, may contribute to the improved mobility in N pre-implanted transistors.
Authors: J. Neil Merrett, John R. Williams, J.D. Cressler, A.P. Sutton, Lin Cheng, V. Bondarenko, Igor Sankin, D. Seale, Michael S. Mazzola, Bharat Krishnan, Yaroslav Koshka, Jeff B. Casady
Abstract: 4H-SiC vertical depletion-mode trench JFETs were fabricated, packaged, and then irradiated with either 6.8 Mrad gamma from a 60Co source, a 9x1011 cm-2 dose of 4 MeV protons, or a 5x1013 cm-2 dose of 63 MeV protons. 4H-SiC Schottky diodes were also fabricated, packaged and exposed to the same irradiations. The trench VJFETs have a nominal blocking voltage of 600 V and a forward current rating of 2 A prior to irradiation. On-state and blocking I-V characteristics were measured after irradiation and compared to the pre-irradiation performance. Devices irradiated with 4 MeV proton and gamma radiation showed a slight increase in on resistance and a decrease in leakage current in blocking mode. Devices irradiated with 63 MeV protons, however, showed a dramatic decrease in forward current. DLTS measurements were performed, and the results of these measurements will be discussed as well.
Authors: Ayayi Claude Ahyi, S.R. Wang, John R. Williams
Abstract: The effects of gamma radiation on field effect mobility and threshold voltage have been studied for lateral n-channel 4H-SiC MOSFETs passivated with nitric oxide. MOS capacitors (n and p) and n-channel lateral MOSFETs were irradiated unbiased (floating contacts) for a total gamma dose of 6.8Mrad (Si). The MOS capacitors were used to study the radiation-induced interface traps and fixed oxide charge that affect the performance of the MOSFETs. Radiationinduced interface traps were observed near the SiC valence band edge and just above mid-gap, and field effect channel mobility was reduced by 18-20% following irradiation. Even so, 4HMOSFETs appear to be more radiation tolerant than Si devices.
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