Papers by Author: J. Anthony Powell

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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: Andrew J. Trunek, Philip G. Neudeck, J. Anthony Powell, David J. Spry
Authors: N.D. Bassim, Mark E. Twigg, Michael A. Mastro, Philip G. Neudeck, Charles R. Eddy, R.L. Henry, R.N. Holm, J. Anthony Powell, Andrew J. Trunek
Abstract: Through the use of specially-prepared on-axis SiC substrates with patterned mesa tops completely free of atomic-scale surface steps, we have previously reported the growth of highquality GaN heteroepitaxial films with greatly reduced threading dislocation densities on the order of 107/cm2. In these films, we reported a defect substructure in which lateral a-type dislocations are present in the nucleation layer but do not bow into threading dislocations during the subsequent GaN growth. This study focuses further on the role of SiC substrate surface steps in the generation of misfit, a-type, and threading dislocations at the heteroepitaxial interface. By using weak-beam imaging (both to eliminate Moiré effects and to observe narrow dislocation images) from plan-view transmission electron microscopy (TEM), we identify dislocations generated on stepped and unstepped mesas and compare their geometries. We observe that misfit dislocations nucleated on an unstepped SiC mesa are confined to one set of a-type Burgers vectors of the form g=1/3 [2110] _ _ , straight and well-ordered so that they are less likely to interact with each other. On the other hand, misfit dislocation structures on a stepped SiC mesa surface are not nearly as well-ordered, having bowed structure with threading dislocations that appear to nucleate at SiC surface steps.
Authors: J. Anthony Powell, David J. Larkin, Andrew J. Trunek
Authors: Philip G. Neudeck, J. Anthony Powell, Andrew J. Trunek, X. Huang, Michael Dudley
Authors: Andrew J. Trunek, J. Anthony Powell, Philip G. Neudeck, M. Mrdenovich
Abstract: We report on new observations made, when 4H-SiC, Si-face substrate mesas, having either low tilt-angle (< 1°) with steps or step-free top surfaces, were exposed to three separate HCl etching conditions for five minutes at temperatures of 1130°C, 1240°C and 1390°C. We observed that HCl was ineffective at 1130°C, as etching was incomplete with abundant surface contamination. At 1240°C, screw dislocations were aggressively etched by HCl, while multiple shallow flat-bottomed etch pits were formed on step-free mesa surfaces. At 1390°C, step-flow etching dominated as large etch pits were formed at screw dislocations and previously step-free surfaces etched inward from mesa edges to form parallel rows of organized steps.
Authors: Philip G. Neudeck, J. Anthony Powell, Andrew J. Trunek, David J. Spry, Glenn M. Beheim, Emye Benavage, Phillip B. Abel, William M. Vetter, Michael Dudley
Authors: Andrew J. Trunek, Philip G. Neudeck, Andrew A. Woodworth, J. Anthony Powell, David J. Spry, Balaji Raghothamachar, Michael Dudley
Abstract: Lateral expansion of small mixed polytype 4H/6H-SiC and 6H-SiC slivers were realized by hot wall chemical vapor deposition (HWCVD). Small slivers cut from m-oriented (11 ̅00) SiC boule slices containing regions of 4H and 6H-SiC or just single polytype 6H-SiC were exposed to HWCVD conditions using standard silane/propane chemistry for a period of up to eight hours. The slivers exhibited approximately 1500 μm (1.5 mm) of total lateral expansion. Initial analysis by synchrotron white beam x-ray topography (SWBXT) confirms, that the lateral growth was homoepitaxial, matching the polytype of the respective underlying region of the seed sliver.
Authors: Wolfgang J. Choyke, J. Anthony Powell, T.T. Cheng, P. Pirouz
Authors: Michael Dudley, William M. Vetter, X. Huang, Philip G. Neudeck, J. Anthony Powell
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