Papers by Author: Marek Skowronski

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Authors: Gil Yong Chung, Mark J. Loboda, Jie Zhang, Jian Wei Wan, E.P. Carlson, T.J. Toth, Robert E. Stahlbush, Marek Skowronski, R. Berechman, Siddarth G. Sundaresan, Ranbir Singh
Abstract: Improvements in the quality and consistency of 4H-SiC epitaxy wafers are now starting to enable growth of commercial SiC power device applications in areas such as inverters for photo-voltaic systems and power supplies. Recent work has achieved very low epitaxy surface roughness and very low BPD (Basal plane dislocation) in the on 4 degree off-axis substrates. In this paper, we report characterization of the very low BPD epitaxy wafers and a newly observed triangular defect.
Authors: Seo Young Ha, William M. Vetter, Michael Dudley, Marek Skowronski
Authors: Joseph J. Sumakeris, Mrinal K. Das, H. McD. Hobgood, Stephan G. Müller, Michael J. Paisley, Seo Young Ha, Marek Skowronski, John W. Palmour, Calvin H. Carter Jr.
Authors: Seo Young Ha, P. Mieszkowski, L.B. Rowland, Marek Skowronski
Authors: Philip G. Neudeck, J. Anthony Powell, David J. Spry, Andrew J. Trunek, X. Huang, William M. Vetter, Michael Dudley, Marek Skowronski, Jin Qiang Liu
Authors: V.D. Heydemann, W.J. Everson, Rick D. Gamble, David Snyder, Marek Skowronski
Authors: E.R. Glaser, B.V. Shanabrook, W.E. Carlos, Hun Jae Chung, Saurav Nigam, A.Y. Polyakov, Marek Skowronski
Abstract: We have employed low-temperature photoluminescence to estimate the total residual N concentration in semi-insulating (SI) SiC substrates where all N shallow donors are compensated in the dark. The ratio of the nitrogen-bound exciton line (Qo) to the free excitonic emission (I77) as a function of excitation power density (Pexc) was tracked for several SI 4H-SiC samples with varying residual N concentration (~ 7x1014 – 5.2x1016 cm-3). Most notably, a linear relationship was found between Qo/I77 and [N] for [N] < 1x1016 cm-3 while a sub-linear behavior was observed for samples with higher N levels. This technique should be particularly valuable to map [N] where the levels are close to or below the present SIMS detection limit of ~ 5-7 x 1014 cm-3. Results obtained for a limited number of low n-type and SI 6H-SiC substrates are also presented.
Authors: Sung Wook Huh, A.Y. Polyakov, Hun Jae Chung, Saurav Nigam, Marek Skowronski, E.R. Glaser, W.E. Carlos, Mark A. Fanton, N.B. Smirnov
Abstract: Deep electron and hole traps were studied in a series of high purity 6H-SiC single crystals grown by Halide Chemical Vapor Deposition (HCVD) method at various C/Si flow ratios and at temperatures between 2000 oC and 2100 oC. Characterization included Low Temperature Photoluminescence (LTPL), Deep Level Transient Spectroscopy (DLTS), Minority Carrier Transient Spectroscopy (MCTS), and Thermal Admittance Spectroscopy (TAS) measurements. Concentrations of all deep traps were shown to strongly decrease with increased C/Si flow ratio and with increased growth temperature. The results indicate that the majority of deep centers in 6H-SiC crystals grown by HCVD are due to native defects or complexes of native defects promoted by Si-rich growth conditions. The observed growth temperature dependence of residual donor concentration and traps density is explained by increasing the effective C/Si ratio at higher temperatures for the same nominal ratio of C and Si flows.
Authors: Sung Wook Huh, Joseph J. Sumakeris, A.Y. Polyakov, Marek Skowronski, Paul B. Klein, B.V. Shanabrook, Michael J. O'Loughlin
Abstract: Carrier lifetimes and the dominant electron and hole traps were investigated in a set of thick (9-104mm) undoped 4H-SiC epitaxial layers grown by CVD homoepitaxy. Deep trap spectra were measured by deep level transient spectroscopy (DLTS) with electrical or optical injection, while lifetimes were measured by room temperature time-resolved photoluminescence (PL). The main electron traps detected in all samples were due to Ti, Z1/Z2 centers, and EH6/EH7 centers. Two boron-related hole traps were observed with activation energies of 0.3 eV (boron acceptors) and 0.6 eV (boron-related D centers). The concentration of electron traps decreased with increasing layer thickness and increased toward the edge of the wafers. PL lifetimes were in the 400 ns-1800 ns range with varying injection and generally correlated with changes in the density of Z1/Z2 and to a lesser extent the EH6/EH7 electron traps. However, the results of DLTS measurements on p-i-n diode structures suggest that the capture of injected holes is much more efficient for the Z1/Z2 traps compared to the EH6/EH7 centers making the Z1/Z2 more probable candidates for the role of lifetime killers. A good fit of the thickness dependence of the measured lifetimes to the usual analytical form was obtained assuming that Z1/Z2 is the dominant hole recombination center and that the surface recombination velocity was 2500 cm/sec.
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