@article{coppa_fulton_hartlieb_davis_rodriguez_shields_nemanich_2004, title={In situ cleaning and characterization of oxygen- and zinc-terminated, n-type, ZnO{0001} surfaces}, volume={95}, ISSN={["1089-7550"]}, DOI={10.1063/1.1695596}, abstractNote={A layer containing an average of 1.0 monolayer (ML) of adventitious carbon and averages of 1.5 ML and 1.9 ML of hydroxide was determined to be present on the respective O-terminated (0001̄) and Zn-terminated (0001) surfaces of ZnO. A diffuse low-energy electron diffraction pattern was obtained from both surfaces. In situ cleaning procedures were developed and their efficacy evaluated in terms of the concentrations of residual hydrocarbons and hydroxide and the crystallography, microstructure, and electronic structure of these surfaces. Annealing ZnO(0001̄) in pure oxygen at 600–650 °C±20 °C reduced but did not eliminate all of the detectable hydrocarbon contamination. Annealing for 15 min in pure O2 at 700 °C and 0.100±0.001 Torr caused desorption of both the hydrocarbons and the hydroxide constituents to concentrations below the detection limits (∼0.03 ML=∼0.3 at. %) of our x-ray photoelectron spectroscopy instrument. However, thermal decomposition degraded the surface microstructure. Exposure of the ZnO(0001̄) surface to a remote plasma having an optimized 20% O2/80% He mixture for the optimized time, temperature, and pressure of 30 min, 525 °C, and 0.050 Torr, respectively, resulted in the desorption of all detectable hydrocarbon species. Approximately 0.4 ML of hydroxide remained. The plasma-cleaned surface possessed an ordered crystallography and a step-and-terrace microstructure and was stoichiometric with nearly flat electronic bands. A 0.5 eV change in band bending was attributed to the significant reduction in the thickness of an accumulation layer associated with the hydroxide. The hydroxide was more tightly bound to the ZnO(0001) surface; this effect increased the optimal temperature and time of the plasma cleaning process for this surface to 550 °C and 60 min, respectively, at 0.050 Torr. Similar changes were achieved in the structural, chemical, and electronic properties of this surface; however, the microstructure only increased slightly in roughness and was without distinctive features.}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={Coppa, BJ and Fulton, CC and Hartlieb, PJ and Davis, RF and Rodriguez, BJ and Shields, BJ and Nemanich, RJ}, year={2004}, month={May}, pages={5856–5864} }
 @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{smith_mecouch_miraglia_roskowski_hartlieb_davis_2003, title={Evolution and growth of ZnO thin films on GaN(0001) epilayers via metalorganic vapor phase epitaxy}, volume={257}, ISSN={["1873-5002"]}, DOI={10.1016/S0022-0248(03)01469-6}, abstractNote={Zinc oxide thin films have been grown via metalorganic vapor phase epitaxy at 450°C and 250 Torr total pressure on O-terminated areas and micro-regions of native oxide formed on GaN(0 0 0 1) epilayers during exposure to the oxygen reactant. Analyses of the Ga3d core level spectra acquired from films grown for progressively longer times and comparisons of these data with both thermodynamic models of growth processes and associated atomic force micrographs revealed that the ZnO nucleated and grew via the Stranski–Krastanov mode. Considerations of (1) differences in surface energetics of the polar (0 0 0 1) surfaces of ZnO and GaN and that of the Ga-based oxide as well as (2) the relatively low stress generated by the moderate lattice mismatches in the a-axis lattice parameters of these compounds supported the observed growth mode. The shifts in the position of the Ga3d core level with increasing deposition time and decreasing peak intensity were caused by surface charging and increasing sampling volumes of the Ga-based oxide as well as the growing ZnO layer. The island/ocean morphology of the Ga-based oxide controlled the morphology of the initial ZnO layer, which, in turn controlled the locations and the morphologies of the subsequently nucleated ZnO islands. Scanning electron microscopy of thicker ZnO films revealed a highly textured microstructure.}, number={3-4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Smith, TP and Mecouch, WJ and Miraglia, PQ and Roskowski, AM and Hartlieb, PJ and Davis, RF}, year={2003}, month={Oct}, pages={255–262} }
 @article{hartlieb_roskowski_davis_platow_nemanich_2003, title={Response to "Comment on 'Pd growth and subsequent Schottky barrier formation on chemical vapor cleaned p-type GaN surfaces' [J. Appl. Phys. 91, 732 (2002)]"}, volume={93}, ISSN={["0021-8979"]}, DOI={10.1063/1.1542911}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Hartlieb, PJ and Roskowski, A and Davis, RF and Platow, W and Nemanich, RJ}, year={2003}, month={Mar}, pages={3679–3679} }
 @article{hartlieb_roskowski_davis_nemanich_2002, title={Chemical, electrical, and structural properties of Ni/Au contacts on chemical vapor cleaned p-type GaN}, volume={91}, ISSN={["1089-7550"]}, DOI={10.1063/1.1471578}, abstractNote={Chemical vapor cleaned, Mg-doped, p-type GaN(0001) surfaces and Ni/Au contacts deposited on these surfaces have been studied using several characterization techniques. Stoichiometric surfaces without detectable carbon and an 87% reduction in the surface oxygen to 2±1 at. % were achieved. The binding energies of the Ga 3d and N 1s core level photoelectron peaks were reduced by 0.5±0.1 eV following the chemical vapor clean. The band bending at the clean surface was measured to be 0.8±0.1 eV. As-deposited Ni/Au contacts on chemical vapor cleaned surfaces exhibited significantly less rectification in the low voltage region (<2 V) compared to identical contact structures on conventional HCl treated surfaces. The specific contact resistance of these contacts deposited on chemical vapor cleaned surfaces and subsequently annealed at 450 °C for 30 seconds was 3±2 Ω cm2. Improved ohmic behavior and a specific contact resistance of 4±2 Ω cm2 was obtained for contacts deposited on HCl treated surfaces and annealed using the same schedule. The formation of Au:Ga and Au:Ni solid solutions was observed for contacts on HCl treated surfaces following the 450 °C anneal. There were significantly less interfacial reactions for annealed contacts on chemical vapor cleaned surfaces. The values of specific contact resistance, sheet resistance, and transfer length of the annealed contacts deposited on both chemical vapor cleaned and HCl treated surfaces and measured from room temperature to 140 °C did not change during three successive thermal cycles within this range.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={Hartlieb, PJ and Roskowski, A and Davis, RF and Nemanich, RJ}, year={2002}, month={Jun}, pages={9151–9160} }
 @article{hartlieb_roskowski_davis_platow_nemanich_2002, title={Pd growth and subsequent Schottky barrier formation on chemical vapor cleaned p-type GaN surfaces}, volume={91}, ISSN={["1089-7550"]}, DOI={10.1063/1.1424060}, abstractNote={Characterization of chemical vapor cleaned, Mg-doped, p-type GaN(0001) surfaces and Pd contacts sequentially deposited on these surfaces has been conducted using x-ray and ultraviolet photoelectron spectroscopies and low-energy electron diffraction. The band bending and the electron affinity at the cleaned p-GaN surface were 1.4±0.1 eV and 3.1±0.1 eV, respectively. A previously unidentified band of surface states was observed at ∼1.0 eV below the Fermi level on this surface. The Pd grew epitaxially on the cleaned surface in a layer-by-layer mode and formed an abrupt, unreacted metal–semiconductor interface. The induced Fermi level movement with Pd deposition has been attributed to a complex interaction between extrinsic and intrinsic surface states as well as metal induced gap states. The final Schottky barrier height at the Pd/p-GaN interface was 1.3±0.1 eV; the interface dipole contribution was 0.4±0.1 eV.}, number={2}, journal={JOURNAL OF APPLIED PHYSICS}, author={Hartlieb, PJ and Roskowski, A and Davis, RF and Platow, W and Nemanich, RJ}, year={2002}, month={Jan}, pages={732–738} }
 @article{ronning_hofsass_stotzler_deicher_carlson_hartlieb_gehrke_rajagopal_davis_2000, title={Photoluminescence characterization of Mg implanted GaN}, volume={5}, number={2000}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Ronning, C. and Hofsass, H. and Stotzler, A. and Deicher, M. and Carlson, E. P. and Hartlieb, P. J. and Gehrke, T. and Rajagopal, P. and Davis, R. F.}, year={2000}, pages={U622–628} }
 @article{ronning_linthicum_carlson_hartlieb_thomson_gehrke_davis_1999, title={Characterization of Be-implanted GaN annealed at high temperatures}, volume={4S1}, number={G3.17}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Ronning, C. and Linthicum, K. J. and Carlson, E. P. and Hartlieb, P. J. and Thomson, D. B. and Gehrke, T. and Davis, R. F.}, year={1999} }