@article{losego_paisley_craft_lam_sachet_mita_collazo_sitar_maria_2016, title={Selective area epitaxy of magnesium oxide thin films on gallium nitride surfaces}, volume={31}, ISSN={["2044-5326"]}, DOI={10.1557/jmr.2015.332}, abstractNote={Abstract}, number={1}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Losego, Mark D. and Paisley, Elizabeth A. and Craft, H. Spalding and Lam, Peter G. and Sachet, Edward and Mita, Seiji and Collazo, Ramon and Sitar, Zlatko and Maria, Jon-Paul}, year={2016}, month={Jan}, pages={36–45} }
 @article{paisley_craft_losego_lu_gruverman_collazo_sitar_maria_2013, title={Epitaxial PbxZr1-xTiO3 on GaN}, volume={113}, ISSN={["1089-7550"]}, DOI={10.1063/1.4792599}, abstractNote={Epitaxial integration of PbxZr1−xTiO3 (PZT) (111) with GaN (0002) presents the possibility of polarity coupling across a functional-oxide/nitride heteropolar interface. This work describes the synthesis and characterization of such thin film heterostructures by magnetron sputtering, with specific attention given to process optimization. Using x-ray diffraction and electrical characterization, the growth of epitaxial PZT (∼250 nm) on GaN and PZT on MgO/GaN stacks was verified. A two-stage growth process was developed for epitaxial PZT with a deposition temperature of 300 °C and an ex-situ anneal at 650 °C, which was effective in mitigating interfacial reactions and promoting phase-pure perovskite growth. Electrical analysis of interdigital capacitors revealed a nonlinear and hysteretic dielectric response consistent with ferroelectric PZT. Piezoresponse force microscopy (PFM) characterization shows clear evidence of ferroelectric switching, and PFM hysteresis loop analysis shows minimal evidence for direct polarity coupling, but suggests that band offsets which accompany the oxide-nitride heterostructures influence switching.}, number={7}, journal={JOURNAL OF APPLIED PHYSICS}, author={Paisley, E. A. and Craft, H. S. and Losego, M. D. and Lu, H. and Gruverman, A. and Collazo, R. and Sitar, Z. and Maria, J. -P.}, year={2013}, month={Feb} }
 @article{paisley_craft_losego_lu_gruverman_collazo_sitar_maria_2013, title={Epitaxial lead zirconate titanate on gallium nitride (vol 113, 074107, 2013)}, volume={114}, number={23}, journal={Journal of Applied Physics}, author={Paisley, E. A. and Craft, H. S. and Losego, M. D. and Lu, H. and Gruverman, A. and Collazo, R. and Sitar, Z. and Maria, J. P.}, year={2013} }
 @article{craft_rice_collazo_sitar_maria_2011, title={Spectroscopic measurements of the surface stoichiometry of chemical vapor deposited GaN}, volume={98}, ISSN={["0003-6951"]}, DOI={10.1063/1.3554762}, abstractNote={We report on the surface stoichiometry of Ga-polar GaN films grown by metalorganic chemical vapor deposition as studied by x-ray photoelectron spectroscopy. GaN film surfaces are found to be Ga-rich, with Ga:N ratios ranging from 1.3:1 to 3.2:1. In vacuo ion-beam sputter/annealing studies show that these treatments drive the apparent Ga:N surface composition farther from unity, either through a decrease in surface contamination, oxidation of the surface, or both. Simple annealing experiments decrease the Ga:N ratio. The measured GaN ratio is correlated with the GaN growth time, suggesting that residual Ga precursor after growth interacts with the GaN surface as it cools.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={Craft, H. S. and Rice, A. L. and Collazo, R. and Sitar, Z. and Maria, J. -P.}, year={2011}, month={Feb} }
 @article{losego_craft_paisley_mita_collazo_sitar_maria_2010, title={Critical examination of growth rate for magnesium oxide (MgO) thin films deposited by molecular beam epitaxy with a molecular oxygen flux}, volume={25}, ISSN={["0884-2914"]}, DOI={10.1557/jmr.2010.0096}, abstractNote={The authors report a study of molecular beam deposition of MgO films on amorphous SiO2 and (0001) GaN surfaces over a large range of temperatures (25–400 °C) and molecular oxygen growth pressures (10−7–10−4 Torr). This study provides insight into the growth behavior of an oxide with volatile metal constituents. Unlike other materials containing volatile constituents (e.g., GaAs, PbTiO3), all components of MgO become volatile at normal epitaxial growth temperatures (≥250 °C). Consequently, defining which species is the adsorption controller becomes ambiguous. Different growth regimes are delineated by the critical substrate temperature for Mg re-evaporation and the Mg:O flux ratio. These regimes have impact on phase purity, quartz crystal microbalance calibration, and film microstructure. The universal decay in deposition rate above growth 10−5 Torr O2 is also considered. By introducing a third flux of inert argon gas, rate reduction is attributed to increased molecular scattering and not oxidation of the metal source.}, number={4}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Losego, Mark D. and Craft, H. Spalding and Paisley, Elizabeth A. and Mita, Seiji and Collazo, Ramon and Sitar, Zlatko and Maria, Jon-Paul}, year={2010}, month={Apr}, pages={670–679} }
 @article{losego_fitting kourkoutis_mita_craft_muller_collazo_sitar_maria_2009, title={Epitaxial Ba0.5Sr0.5TiO3–GaN heterostructures with abrupt interfaces}, volume={311}, ISSN={0022-0248}, url={http://dx.doi.org/10.1016/j.jcrysgro.2008.11.085}, DOI={10.1016/j.jcrysgro.2008.11.085}, abstractNote={Abstract Epitaxial heterostructures incorporating the complex ferroelectric oxide Ba 0.5 Sr 0.5 TiO 3 (BST) and GaN were prepared using a combination of RF magnetron sputtering and metalorganic chemical vapor deposition for the respective layers. The heterostructures were grown on c -plane sapphire substrates and were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning transmission electron microscopy (STEM). This analysis showed that at substrate temperatures of 650 °C, BST films grow epitaxially on GaN with a {1 1 1} orientation and that the GaN–BST interface is smooth and abrupt, with disorder confined to grain boundaries and the interface plane. The film morphology is grainy indicating a 3-D growth mode. High-temperature post-deposition annealing studies suggest no interface reactions up to 900 °C. These results demonstrate that complex oxides like BST can be integrated with wide bandgap semiconductors like GaN and open exciting possibilities for new multifunctional devices.}, number={4}, journal={Journal of Crystal Growth}, publisher={Elsevier BV}, author={Losego, M.D. and Fitting Kourkoutis, L. and Mita, S. and Craft, H.S. and Muller, D.A. and Collazo, R. and Sitar, Z. and Maria, J.-P.}, year={2009}, month={Feb}, pages={1106–1109} }
 @article{paisley_losego_aygun_craft_maria_2008, title={Barrier layer mechanism engineering in calcium copper titanate thin film capacitors through microstructure control}, volume={104}, ISSN={["1089-7550"]}, DOI={10.1063/1.3033166}, abstractNote={A peak permittivity greater than 10 000 has been achieved for calcium copper titanate (CCT) thin films by engineering a thin film microstructure that maximizes space charge contributions to polarizability. This permittivity is an order of magnitude greater than previous polycrystalline thin film efforts. This unique microstructure control is accomplished using a chemical solution deposition process flow that produces highly dense parallel layers ∼100 nm in thickness. We observe a thickness dependent permittivity where the entire film thickness constitutes the conducting region of a barrier layer capacitor despite the presence of multiple grain boundaries within that thickness. The model predictions are in good agreement with experimental data and are consistent with existing literature reports. These trends in permittivity with dielectric thickness raise new questions regarding the nature of barrier layers in CCT—and specifically, these results suggest that grain boundaries may not always participate as high resistance interlayers.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={Paisley, E. A. and Losego, M. D. and Aygun, S. M. and Craft, H. S. and Maria, J. -P.}, year={2008}, month={Dec} }
 @article{lebeau_jur_lichtenwalner_craft_maria_kingon_klenov_cagnon_stemmer_2008, title={High temperature stability of Hf-based gate dielectric stacks with rare-earth oxide layers for threshold voltage control}, volume={92}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2901036}, DOI={10.1063/1.2901036}, abstractNote={The thermal stability of DyOx∕HfSiON and HoOx∕HfSiON gate dielectric stacks on silicon was studied by scanning transmission electron microscopy techniques and correlated with their electrical characteristics. Intermixing of the rare-earth elements with the HfSiON was observed, but there was no diffusion into the interfacial SiO2. Rapid thermal annealing (1000°C) produced little detectable change in the concentration profile of the rare-earth elements but caused thinning of the interfacial SiO2 layer along with a corresponding increase in the rare-earth oxide layer thickness. These reactions could be explained with oxygen deficiency in the rare-earth oxide layer and its greater thermodynamic stability relative to SiO2. Negative flat band voltage shifts were observed relative to a control sample with no DyOx or HoOx. Mechanisms by which the observed microstructure changes could give rise to negative flatband voltage shifts are discussed.}, number={11}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={LeBeau, James M. and Jur, Jesse S. and Lichtenwalner, Daniel J. and Craft, H. Spalding and Maria, Jon-Paul and Kingon, Angus I. and Klenov, Dmitri O. and Cagnon, Joël and Stemmer, Susanne}, year={2008}, month={Mar}, pages={112912} }
 @article{craft_collazo_losego_mita_sitar_maria_2008, title={Spectroscopic analysis of the epitaxial CaO (111)-GaN (0002) interface}, volume={92}, ISSN={["0003-6951"]}, DOI={10.1063/1.2887878}, abstractNote={We report an x-ray photoelectron spectroscopy (XPS) study of the CaO∕GaN interface. Epitaxial films of CaO (111) were grown on GaN (0002) and analyzed in situ using XPS. We observe Stranski–Krastanov growth, in which CaO coalesces rapidly, then converts to a three-dimensional mode. Data suggest coalescence within the first nanometer of film growth, indicating growth behavior different from published reports of the analogous MgO–GaN system. We find 1.0±0.2eV for the valence band offset and a 2.5±0.2eV conduction band offset. The results are discussed in terms of their utility in oxide-nitride electronic devices.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={Craft, H. S. and Collazo, R. and Losego, M. D. and Mita, S. and Sitar, Z. and Maria, J. -P.}, year={2008}, month={Feb} }
 @article{craft_collazo_losego_sitar_maria_2008, title={Surface water reactivity of polycrystalline MgO and CaO films investigated using x-ray photoelectron spectroscopy}, volume={26}, ISSN={["0734-2101"]}, DOI={10.1116/1.3000058}, abstractNote={The authors report a study comparing the surface reactivities of the alkaline earth oxides MgO and CaO with respect to water vapor under ultrahigh and high vacuum conditions. Using x-ray photoelectron spectroscopy and a series of in vacuo exposures spanning ∼10−10Torr vacuum, to 10−6Torr flowing oxygen, the extent of surface hydroxylation was investigated by monitoring the O 1s photoelectron line. After the most aggressive exposures, the MgO surface reacted to form a maximum hydroxyl coverage of ∼1.3 ML (monolayer), while the CaO surface reached a maximum coverage of ∼3.0 ML. Both surface hydroxides could be removed by in vacuo thermal anneals; exposure to 250 and 500°C were required for MgO and CaO, respectively. These results are framed in terms of the suitability of these oxides in complex oxide-compound semiconductor heteroepitaxial multifunctional devices and with respect to understanding the development of surface morphology in epitaxial 111-oriented CaO and MgO thin films.}, number={6}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Craft, H. S. and Collazo, R. and Losego, M. D. and Sitar, Z. and Maria, J. -P.}, year={2008}, month={Nov}, pages={1507–1510} }
 @article{craft_collazo_losego_mita_sitar_maria_2007, title={Band offsets and growth mode of molecular beam epitaxy grown MgO (111) on GaN (0002) by x-ray photoelectron spectroscopy}, volume={102}, ISSN={["1089-7550"]}, DOI={10.1063/1.2785022}, abstractNote={MgO is a proposed dielectric for use as a tunneling barrier in devices integrating GaN and ferroelectric oxides. In this study, we present data regarding the growth mode and band offsets of MgO grown epitaxially on GaN (0002) surfaces using molecular beam epitaxy. Using in situ x-ray photoelectron spectroscopy (XPS) and molecular beam epitaxy, we determine, from sequential growth experiments, that the growth of MgO proceeds via the Volmer-Weber (three-dimensional) mode, and full coalescence of the film does not occur until approximately 12nm of MgO has been deposited. The observation of a three-dimensional growth mode is in agreement with previously published data. For the valence band offset, we find a value of 1.2±0.2eV, which corresponds to a 3.2eV conduction band offset. XPS measurements suggest a chemically abrupt interface and no effect on band lineup due to the slow coalescence behavior.}, number={7}, journal={JOURNAL OF APPLIED PHYSICS}, author={Craft, H. S. and Collazo, R. and Losego, M. D. and Mita, S. and Sitar, Z. and Maria, J.-P.}, year={2007}, month={Oct} }
 @article{craft_ihlefeld_losego_collazo_sitar_maria_2006, title={MgO epitaxy on GaN (0002) surfaces by molecular beam epitaxy}, volume={88}, ISSN={["1077-3118"]}, DOI={10.1063/1.2201041}, abstractNote={We report on the epitaxial deposition of magnesium oxide films with [111] crystallographic orientation on (0002) GaN by molecular beam epitaxy. Specifically, we use an adsorption controlled growth mechanism to initiate the growth process. Electron diffraction shows a spotty intense pattern without intensity fluctuations during growth and evidence of in-plane twinning. X-ray diffraction reveals the films to be epitaxial with full width at half maximum values of 0.3°, 0.5°, and 1° in 2θ, ϕ, and χ circles, respectively. Wet etching of the GaN surface with a HCl:HF mixture prior to growth is critical for achieving high crystalline quality. Epitaxial growth is observed between room temperature and 650°C, with negligible changes in crystalline quality with increased temperature. Atomic force microscopy analysis shows grainy surfaces with feature sizes near 10nm and rms roughness values of 1.4Å over 1μm2 areas. X-ray diffraction analysis suggests MgO film stability up to 850°C in ex situ air annealing.}, number={21}, journal={APPLIED PHYSICS LETTERS}, author={Craft, H. S. and Ihlefeld, J. F. and Losego, M. D. and Collazo, R. and Sitar, Z. and Maria, J. -P.}, year={2006}, month={May} }
 @article{craft_collazo_sitar_maria_2006, title={Molecular beam epitaxy of Sm2O3, Dy2O3, and Ho2O3 on Si (111)}, volume={24}, ISSN={["2166-2746"]}, DOI={10.1116/1.2216721}, abstractNote={We report on the epitaxial deposition of Sm2O3, Dy2O3, and Ho2O3 films on Si (111) substrates as progress towards developing a predictive model for gate oxide selection. To date, films have been characterized by reflection high-energy electron diffraction, x-ray diffraction (XRD), and x-ray photoemission spectroscopy (XPS). In the case of Sm2O3, difficulty was encountered in achieving the growth of phase pure films; growth of the desired bixbyite oxide phase was accompanied by significant amounts of monoclinic oxide as detected by XRD. Dy2O3 and Ho2O3 films can be produced free of unwanted phases when deposited using a background pressure of 1×10−6torr O2∕O3 and a substrate temperature between 425 and 550°C. Dy2O3 films with an x-ray peak width of 0.6° in ω were obtained. XPS studies of the Dy2O3∕Si interface are in progress, and verify the phase purity of the films.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Craft, H. S. and Collazo, R. and Sitar, Z. and Maria, J. P.}, year={2006}, pages={2105–2110} }
 @article{edge_schlom_rivillon_chabal_agustin_stemmer_lee_kim_craft_maria_et al._2006, title={Thermal stability of amorphous LaScO3 films on silicon}, volume={89}, ISSN={["1077-3118"]}, DOI={10.1063/1.2222302}, abstractNote={The thermal stability of amorphous LaScO3 thin films deposited by molecular-beam deposition directly on (001) Si was investigated by high-resolution transmission electron microscopy (HRTEM), transmission infrared absorption spectroscopy (IRAS), and x-ray diffraction (XRD). IRAS indicated that the as-deposited films contained <0.1Å of SiO2 at the interface between LaScO3 and silicon. XRD studies showed that the films remained amorphous after annealing in N2 at 700°C, although HRTEM showed structural order on an ∼1nm length scale even in the as-deposited films. By 800°C, the LaScO3 had started to crystallize and formed a ∼5nm thick Sc-deficient interlayer between it and silicon.}, number={6}, journal={APPLIED PHYSICS LETTERS}, author={Edge, L. F. and Schlom, D. G. and Rivillon, S. and Chabal, Y. J. and Agustin, M. P. and Stemmer, S. and Lee, T. and Kim, M. J. and Craft, H. S. and Maria, J. -P. and et al.}, year={2006}, month={Aug} }
 @article{sivasubramani_kim_gnade_wallace_edge_schlom_craft_maria_2005, title={Outdiffusion of La and Al from amorphous LaAlO3 in direct contact with Si(001)}, volume={86}, ISSN={["1077-3118"]}, DOI={10.1063/1.1928316}, abstractNote={We have evaluated the thermal stability of Al2O3/LaAlO3/Si (001) stacks with atomic force microscopy, x-ray diffraction, transmission electron microscopy, and secondary ion mass spectrometry using a back side polishing approach. Crystallization of the amorphous LaAlO3 film was found to occur for rapid thermal anneals (RTA) above 935 °C for 20 s, in flowing N2. Penetration of Al and La into the underlying Si (001) is clearly observed for RTA at or above 950 °C for 20 s in flowing N2.}, number={20}, journal={APPLIED PHYSICS LETTERS}, author={Sivasubramani, P and Kim, MJ and Gnade, BE and Wallace, RM and Edge, LF and Schlom, DG and Craft, HS and Maria, JP}, year={2005}, month={May} }