@article{hartman_roskowski_reitmeier_tracy_davis_nemanich_2003, title={Characterization of hydrogen etched 6H-SiC(0001) substrates and subsequently grown AlN films}, volume={21}, ISSN={["0734-2101"]}, DOI={10.1116/1.1539080}, abstractNote={Wafers of n-type, 6H–SiC(0001) with (ND–NA)=(5.1–7.5)×1017 and 2.5×1018 were etched in a flowing 25%H2/75%He mixture within the range of 1500–1640 °C at 1 atm. Equilibrium thermodynamic calculations indicated that the presence of atomic hydrogen is necessary to achieve etching of SiC. Atomic force microscopy, optical microscopy, and low energy electron diffraction of the etched surface revealed a faceted surface morphology with unit cell and half unit cell high steps and a 1×1 reconstruction. The latter sample also exhibited a much larger number of hexagonal pits on the surface. Annealing the etched samples under ultrahigh vacuum (UHV) at 1030 °C for 15 min resulted in (1) a reduction of the surface oxygen and adventitious hydrocarbons below the detection limit of Auger electron spectroscopy, (2) a (√3×√3)R30° reconstructed surface and (3) a Si-to-C peak-to-peak height ratio of 1.2. By contrast, using a chemical vapor cleaning (CVC) process consisting of an exposure to 3000 Langmuir (L) of silane at 1030 °C for 10 min under UHV conditions resulted in a (3×3) surface reconstruction, a Si-to-C ratio of 3.9, and islands of excess silicon. Continued annealing of the latter material for an additional 10 min at 1030 °C resulted in a (1×1) LEED pattern with a diffuse ring. Films of AlN grown via MOCVD at a sample platter temperature of 1274 °C for 15 min on hydrogen etched wafers having a doping concentration of 8.7×1017 cm−3 and cleaned via annealing had a rms roughness value of ≈0.4 nm.}, number={2}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Hartman, JD and Roskowski, AM and Reitmeier, ZJ and Tracy, KM and Davis, RF and Nemanich, RJ}, year={2003}, pages={394–400} }
 @article{tracy_hartlieb_einfeldt_davis_hurt_nemanich_2003, title={Electrical and chemical characterization of the Schottky barrier formed between clean n-GaN(0001) surfaces and Pt, Au, and Ag}, volume={94}, ISSN={["0021-8979"]}, DOI={10.1063/1.1598630}, abstractNote={Platinum, gold, and silver formed abrupt, unreacted, smooth, and epitaxial metal–semiconductor interfaces when deposited from the vapor onto clean, n-type GaN(0001) films. The Schottky barrier heights, determined from data acquired using x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, capacitance–voltage, and current–voltage measurements agreed to within the experimental error for each contact metal and had the values of 1.2±0.1, 0.9±0.1, and 0.6±0.1 eV for Pt, Au, and Ag, respectively. The band bending and the electron affinity at the clean n-GaN surface were 0.3±0.1 and 3.1±0.1 eV, respectively. The barrier height is proportional to the metal work function, indicating that the Fermi level is not pinned at the GaN surface. However, discrepancies to the Schottky–Mott model were found as evidenced by a proportionality factor of 0.44 between the work function of the metal and the resulting Schottky barrier height. The sum of these discrepancies constitute the interface dipole contributions to the Schottky barrier height which were measured to be ∼1.4, 1.3, and 0.7 eV for Pt, Au, and Ag, respectively.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Tracy, KM and Hartlieb, PJ and Einfeldt, S and Davis, RF and Hurt, EH and Nemanich, RJ}, year={2003}, month={Sep}, pages={3939–3948} }
 @article{cook_fulton_mecouch_tracy_davis_hurt_lucovsky_nemanich_2003, title={Measurement of the band offsets of SiO2 on clean n- and p-type GaN(0001)}, volume={93}, ISSN={["0021-8979"]}, DOI={10.1063/1.1559424}, abstractNote={The band alignment at the SiO2-GaN interface is important for passivation of high voltage devices and for gate insulator applications. X-ray photoelectron spectroscopy and ultraviolet photoemission spectroscopy have been used to observe the interface electronic states as SiO2 was deposited on clean GaN(0001) surfaces. The substrates, grown by metallorganic chemical vapor deposition, were n- (1×1017) and p-type (2×1018) GaN on 6H-SiC(0001) with an AlN(0001) buffer layer. The GaN surfaces were atomically cleaned via an 860 °C anneal in an NH3 atmosphere. For the clean surfaces, n-type GaN showed upward band bending of 0.3±0.1 eV, while p-type GaN showed downward band bending of 1.3±0.1 eV. The electron affinity for n- and p-type GaN was measured to be 2.9±0.1 and 3.2±0.1 eV, respectively. To avoid oxidizing the GaN, layers of Si were deposited on the clean GaN surface via ultrahigh vacuum e-beam deposition, and the Si was oxidized at 300 °C by a remote O2 plasma. The substrates were annealed at 650 °C for densification of the SiO2 films. Surface analysis techniques were performed after each step in the process, and yielded a valence band offset of 2.0±0.2 eV and a conduction band offset of 3.6±0.2 eV for the GaN-SiO2 interface for both p- and n-type samples. Interface dipoles of 1.8 and 1.5 eV were deduced for the GaN-SiO2 interface for the n- and p-type surfaces, respectively.}, number={7}, journal={JOURNAL OF APPLIED PHYSICS}, author={Cook, TE and Fulton, CC and Mecouch, WJ and Tracy, KM and Davis, RF and Hurt, EH and Lucovsky, G and Nemanich, RJ}, year={2003}, month={Apr}, pages={3995–4004} }
 @misc{linthicum_gehrke_davis_thomson_tracy_2003, title={Methods of fabricating gallium nitride microelectronic layers on silicon layers}, volume={6,602,764}, number={2003 Aug. 5}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Linthicum, K. J. and Gehrke, T. and Davis, R. F. and Thomson, D. B. and Tracy, K. M.}, year={2003} }
 @article{tracy_mecouch_davis_nemanich_2003, title={Preparation and characterization of atomically clean, stoichiometric surfaces of n- and p-type GaN(0001)}, volume={94}, ISSN={["1089-7550"]}, DOI={10.1063/1.1596369}, abstractNote={It is demonstrated that in situ exposure of the (0001) surface of n- and p-type GaN thin films to flowing ammonia at 860 °C and 10−4 Torr removes hydrocarbon and oxygen/hydroxide species below the detectable limits of x-ray and ultraviolet photoelectron spectroscopies (UPS) and decreases the Ga/N ratio from 1.3 to 1.0. Additional indications of the efficacy of this ammonia-based chemical vapor cleaning (CVC) process were the shifts in the Ga 3d and the N 1s core level positions from the as-loaded to the CVC surfaces of the n-type samples from 21.0±0.1 to 20.6±0.1 eV and from 398.3±0.1 to 398.0±0.1 eV, respectively, and the change in the UPS measured low energy spectrum turn on from 3.9±0.1 (as-loaded samples) to 3.0±0.1 eV (cleaned samples) below the Fermi level. Analogous changes in the p-type samples were from 19.6±0.1 to 18.9±0.1 eV and from 397.1±0.1 to 396.3±0.1 eV for the Ga 3d and the N 1s core levels, and from 3.0±0.1 to 1.1±0.1 eV for the UPS valence band maximum (VBM). The VBM values of the CVC samples indicate band bending of ∼0.3 eV upward on n type and ∼0.8 eV downward on p type. Electron affinities of 2.8±0.1 and 2.6±0.1 eV were determined for the clean n-type and p-type surfaces, respectively. Irrespective of doping, the CVC process left unchanged the (1×1) low energy diffraction pattern, the terraced microstructure, and the root mean square roughness observed for the surfaces of the as-loaded samples, i.e., the surface microstructure was not damaged during the high temperature exposure to ammonia at low pressure.}, number={5}, journal={JOURNAL OF APPLIED PHYSICS}, author={Tracy, KM and Mecouch, WJ and Davis, RF and Nemanich, RJ}, year={2003}, month={Sep}, pages={3163–3172} }
 @article{preble_tracy_kiesel_mclean_miraglia_nemanich_davis_albrecht_smith_2002, title={Electrical, structural and microstructural characteristics of as-deposited and annealed Pt and Au contacts on chemical-vapor-cleaned GaN thin films}, volume={91}, ISSN={["0021-8979"]}, DOI={10.1063/1.1432127}, abstractNote={Schottky contacts of Pt(111) and Au(111) were deposited on chemical-vapor-cleaned, n-type GaN(0001) thin films. The growth mode of the deposition, as determined by x-ray photoelectron spectroscopy analysis, followed the two-dimensional Frank–van der Merwe growth model. The resulting as-deposited metal films were monocrystalline and epitaxial with a (111)//(0002) relationship with the GaN. Selected samples were annealed for three minutes at 400 °C, 600 °C or 800 °C. The rectifying behavior of both contacts degraded at 400 °C; they became ohmic after annealing at 600 °C (Au) or 800 °C (Pt). High-resolution transmission electron micrographs revealed reactions at the metal/GaN interfaces for the higher temperature samples. X-ray diffraction results revealed an unidentified phase in the Pt sample annealed at 800 °C. A decrease in the room temperature in-plane (111) lattice constant for both metals, ranging from −0.1% to −0.5%, was observed as the annealing temperature was increased from 400 to 800 °C. This plastic deformation was caused by tensile stresses along the [111] direction that exceeded the yield strength as a result of the large differences in the coefficients of thermal expansion between the metal contacts and the GaN film.}, number={4}, journal={JOURNAL OF APPLIED PHYSICS}, author={Preble, EA and Tracy, KM and Kiesel, S and McLean, H and Miraglia, PQ and Nemanich, RJ and Davis, RF and Albrecht, M and Smith, DJ}, year={2002}, month={Feb}, pages={2133–2137} }
 @article{platow_wood_tracy_burnette_nemanich_sayers_2001, title={Formation of cobalt disilicide films on (root 3 x root 3)6H-SiC(0001)}, volume={63}, ISSN={["1550-235X"]}, DOI={10.1103/physrevb.63.115312}, abstractNote={This paper presents a detailed study of thin Co films grown directly, sequentially, and by codeposition with Si on the $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})\ensuremath{-}R30\ifmmode^\circ\else\textdegree\fi{}$ surface of $6H\ensuremath{-}\mathrm{SiC}(0001).$ The structure, chemistry, and morphology of the films were determined using x-ray absorption fine structure, x-ray photoelectron spectroscopy, Auger electron spectroscopy, and atomic force microscopy. For directly deposited Co films (1--8 nm) graphite layers form on top of the film surface during annealing, whereas Co stays mainly unreacted over a temperature range of 300--1000 \ifmmode^\circ\else\textdegree\fi{}C. The formation of ${\mathrm{CoSi}}_{2}$ is achieved by sequential and codeposition of Co and Si. Films annealed at 550 \ifmmode^\circ\else\textdegree\fi{}C are polycrystalline and further annealing to 650 \ifmmode^\circ\else\textdegree\fi{}C causes no C segregation, but there is islanding of the films. Attempts to improve film morphology and homogeneity including applying a template method and varying growth temperature are also reported.}, number={11}, journal={PHYSICAL REVIEW B}, author={Platow, W and Wood, DK and Tracy, KM and Burnette, JE and Nemanich, RJ and Sayers, DE}, year={2001}, month={Mar} }
 @misc{linthicum_gehrke_davis_thomson_tracy_2001, title={Methods of fabricating gallium nitride microelectronic layers on silicon layers and gallium nitride microelectronic structures formed thereby}, volume={6,255,198}, number={2001 July 3}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Linthicum, K. J. and Gehrke, T. and Davis, R. F. and Thomson, D. B. and Tracy, K. M.}, year={2001} }
 @article{ward_hartman_hurt_tracy_davis_nemanich_2000, title={Schottky barrier height and electron affinity of titanium on AIN}, volume={18}, ISSN={["1071-1023"]}, DOI={10.1116/1.1303733}, abstractNote={Approximately 100 or 1000 Å of AlN was deposited on the (0001)Si-face of on-axis n-type 6H–SiC. The surfaces were examined by ultraviolet photoemission spectroscopy (UPS) utilizing the He I α (21.2 eV) and the He II α (40.8 eV) excitation. Experimental difficulties are discussed. Titanium was deposited on the clean surface of in situ grown AlN. The titanium–AlN interface was also characterized with UPS. Two approaches are presented to identify the valence band maximum (VBM) and the electron affinity χ of the clean surface of AlN was found to be either 0 to 1 eV depending upon the position of the valence band edge. The same assumptions were applied to the analysis of the Ti/AlN interface and, for the case of χ=0 eV, the position of the valence band maximum is 3.4 eV below the position of the Fermi level. For the case of χ=1 eV, the position of the valence band maximum is 4.4 eV below the position of the Fermi level. Therefore, the p-type Schottky barrier height of titanium on AlN is measured to be 3.4±0.2 or 4.4±0.2 eV for χ=0 eV and χ=1 eV, respectively. Independent of the selection of the valence band maximum, the observed Schottky barrier differed from that predicted by the Schottky–Mott model by 1.5±0.2 eV.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Ward, BL and Hartman, JD and Hurt, EH and Tracy, KM and Davis, RF and Nemanich, RJ}, year={2000}, pages={2082–2087} }
 @article{linthicum_gehrke_thomson_tracy_carlson_smith_zheleva_zorman_mehregany_davis_1999, title={Process routes for low defect-density GaN on various substrates employing pendeo-epitaxial growth techniques}, volume={4S1}, number={G4.9}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Linthicum, K. J. and Gehrke, T. and Thomson, D. B. and Tracy, K. M. and Carlson, E. P. and Smith, T. P. and Zheleva, T. S. and Zorman, C. A. and Mehregany, M. and Davis, R. F.}, year={1999} }