Lynnette D. Madsen

Microstructure and electronic properties of the refractory semiconductor ScN grown on MgO(001) by ultra-high-vacuum reactive magnetron sputter deposition

ScN layers, 180 nm thick, were grown on MgO(001) substrates at 750 °C by ultra-high-vacuum reactive magnetron sputter deposition in pure N2 discharges. N/Sc ratios, determined by Rutherford backscattering spectroscopy, were 0.98±0.02. X-ray diffraction θ–2θ scans and pole figures combined with plan-view and cross-sectional transmission electron microscopy showed that the films are strongly textured, both in plane and along the growth direction, and have a columnar microstructure with an average column width near the film surface of 30±5 nm. During nucleation and the early stages of film growth, the layers consist of approximately equal volume fractions of 002- and 111-oriented grains. However, preferred orientation evolves toward a purely 111 texture within ≃40 nm as the 002 grains grow out of existence in a kinetically limited competitive growth mode. 002 grains exhibit local cube-on-cube epitaxy with an orientation relationship (001)ScN∥(001)MgO and [010]ScN∥[010]MgO while 111 grains have a complex four...

Composition, structure, and dielectric tunability of epitaxial SrTiO3 thin films grown by radio frequency magnetron sputtering

Epitaxial (001) oriented SrTiO3 films have been deposited on LaAlO3(001) substrates by off-axis radio frequency magnetron sputtering in Ar:O2 gas mixtures at substrate temperatures ranging from 650 to 850 °C. For the deposition conditions used, stoichiometric targets yielded 20% Sr-deficient films, whereas Sr-enriched targets (Sr1.1Ti0.9O3.0) resulted in stoichiometric films. The Sr-deficient films had a mosaic structure and a larger lattice parameter in comparison to bulk SrTiO3. The stoichiometric films on the other hand had a much higher crystalline quality in the as-deposited condition. The mosaicity of the latter films was primarily limited by the crystalline quality of the LaAlO3 substrates. The lattice parameters of the stoichiometric films were also smaller than the Sr-deficient ones and closer to the bulk value. The dielectric properties of the stoichiometric films were superior to the Sr-deficient films. For films with a thickness of ∼300 nm, the typical dielectric constants as measured at ∼77 K...

Microstructure and microwave dielectric properties of epitaxial SrTiO3 films on LaAlO3 substrates

Sr-deficient and stoichiometric epitaxial (001) SrTiO3 films, deposited on (110)rhombohedral LaAlO3 substrates by rf magnetron sputtering, have been characterized using high-resolution transmission electron microscopy. A subsequent heat treatment in oxygen had a positive influence on the dielectric properties. Sr-deficiency had a large negative impact on the microwave dielectric constant of the films. These changes were correlated to changes in lattice parameters. In all samples, at the film/substrate interface, were misfit dislocations present. The residual elastic strain compressed the SrTiO3 unit cell in the substrate surface plane and expanded it an equal amount in the [001] direction. X-ray diffraction revealed that the tetragonal distortion, due to the mismatch strain, was concentrated to a narrow region closest to the film/substrate interface.

Temperature stable Pd ohmic contacts to p-type 4H-SiC formed at low temperatures

The formation of low resistivity Pd-based ohmic contacts to p-type 4H-SiC below 750/spl deg/C are reported herein. The electrical properties of the contacts were examined using I-V measurements and the transmission-line model (TLM) technique. Contact resistivity as a function of annealing was investigated over the temperature range of 600/spl deg/C-700/spl deg/C. The lowest contact resistivity (5.5/spl times/10/sup -5/ /spl Omega/cm/sup 2/) was obtained after annealing at 700/spl deg/C for 5 min. Atomic force microscopy of the as-deposited Pd layer showed a root-mean-square roughness of /spl sim/8 nm, while after annealing at 700/spl deg/C, agglomeration occurred, increasing the roughness to 111 nm. Auger electron spectroscopy depth profiles revealed that with annealing, interdiffusion had resulted in the formation of Pd-rich silicides. However, X-ray diffraction and Rutherford backscattering showed that the majority of the film was still (unreacted) Pd. The thermal stability and reliability of the Pd contacts were examined by aging and temperature dependence electrical tests. The contacts annealed at 700/spl deg/C were stable at prolonged heating at a constant temperature of 500/spl deg/C and they showed thermal stability in air at operating temperatures up to 450/spl deg/C. This stability was not found for contacts formed at lower temperatures of 600/spl deg/C or 650/spl deg/C.

In Situ Doping of Silicon Films Prepared by Low Pressure Chemical Vapor Deposition Using Disilane and Phosphine

The low pressure chemical vapor deposition (LPCVD) of in situ doped silicon from disilane (Si 2 H 6 ) and phosphine (PH 3 ) was investigated using response surface methodology experimental design. TEM and associated analytical techniques were employed in characterizing films deposited over the range of 475 o -700 o C. Polycrystalline films with a resistivity of ∼770 μΩ-cm after a 850 o C, 30 min anneal with less than 5% thickness variation were deposited at approximately 60 A-min -1 over 100 mm wafers

Epitaxial cerium oxide buffer layers and YBa 2 Cu 3 O 7−δ thin films for microwave device applications

CeO 2 films with thicknesses ranging from 8.8 to 199 nm were grown on Al 2 O 3 (1 1 02) (R-cut) substrates by off-axis rf magnetron sputtering. X-ray diffraction showed an epitaxial relationship with the CeO 2 (001) planes parallel to the Al 2 O 3 (1 1 02) planes for all film thicknesses. Atomic force microscopy (AFM) revealed a rough surface morphology consisting of crystallites with lateral dimensions of 10–90 nm. In the thinnest film, these crystallites were regularly shaped and uniformly distributed on the substrate, while they were rectangularly shaped and oriented mainly in two directions, orthogonal to each other, in the thicker films. The surface roughness of the films increased with increasing layer thickness. Characterization of the microstructure was done by cross-sectional transmission electron microscopy (XTEM) and showed a polycrystalline, highly oriented, columnar structure with a top layer terminated by (111)-facets. High-quality YBa 2 Cu 3 O 7−δ (YBCO) thin films were deposited directly onto the CeO 2 layers. XTEM, rather surprisingly, showed a smooth interface between the YBCO and CeO 2 layer. Postdeposition ex situ annealing was carried out on two CeO 2 films and evaluated by AFM. Upon annealing samples at 930 °C, a relatively smooth morphology without facets was obtained. Annealing films at 800 °C caused no appreciable change in surface morphology, whereas igniting a YBCO plasma during a similar anneal clearly altered the sample surface, giving facets that were rounded.

Morphology and microstructure of epitaxial Cu(001) films grown by primary ion deposition on Si and Ge substrates

A low‐energy, high‐brightness, broad beam Cu ion source is used to study the effects of self‐ion energy Ei on the deposition of epitaxial Cu films in ultrahigh vacuum. Atomically flat Ge(001) and Si(001) substrates are verified by in situ scanning tunneling microscopy (STM) prior to deposition of 300 nm Cu films with Ei ranging from 20 to 100 eV. Film microstructure, texture, and morphology are characterized using x‐ray diffraction ω‐rocking curves, pole figure analyses, and STM. Primary ion deposition produces significant improvements in both the surface morphology and mosaic spread of the films: At Ei>37 eV the surface roughness decreases by nearly a factor of 2 relative to evaporated Cu films, and at Ei≂35 eV the mosaic spread of Cu films grown on Si substrates is only ≂2°, nearly a factor of 2 smaller than that of evaporated Cu. During deposition with Ei≂25 eV on Ge substrates, the film coherently relaxes the 10% misfit strain by formation of a tilt boundary which is fourfold symmetric toward 〈111〉. T...

Growth and characterization of Na0.5K0.5NbO3 thin films on polycrystalline Pt80Ir20 substrates

Na0.5K0.5NbO3 thin films have been deposited onto textured polycrystalline Pt80Ir20 substrates using radio frequency magnetron sputtering. Films were grown in off- and on-axis positions relative to ...

Reduction of surface particles on YBa2Cu3O7−∂ thin films through the use of nonstoichiometric sputtering targets and N2O in the sputtering gas

High quality YBa2Cu3O7−∂ (YBCO) thin films that combine good electrical properties and smooth surfaces without particles are important for many future applications. Today most films with good electrical properties have secondary phases in the form of copper‐rich surface particles and small Y2O3 inclusions in the film. This work investigates how the surface particle coverage and superconducting properties of dc‐magnetron sputtered thin films change as a function of target stoichiometry and the use of Ar:O2 or Ar:O2:N2O as sputtering gases. In an attempt to eliminate the copper‐rich surface particles, sputtering was performed using targets deficient in copper (by up to 28%). However, only a small reduction in the number of the surface particles was achieved with an Ar:O2 sputtering gas mixture and little change in the superconducting properties was found. No new secondary phases could be detected. When nitrous oxide (N2O) was added to the sputtering gas, the superconducting properties deteriorated and Ba2Cu...

A NEW SILICON PHOSPHIDE, SI12P5: FORMATION CONDITIONS, STRUCTURE, AND PROPERTIES

The formation conditions, structure, and properties of the recently discovered phosphide, Si12P5 (initially assigned Si7P3), have been studied using x-ray diffraction, high-resolution transmission electron microscopy, photospectrometry, and a four-point probe. The phosphide formed in amorphous Si–P alloy thin films with 30, 35 and 44 at. % P after annealing at 1000 °C for 30 min. During annealing at 1100 °C, the phosphide dissociated through P evaporation. The Si12P5 phase is proposed to have rhombohedral symmetry with a P31m space group and a C5W12 structure. The hexagonal lattice parameters measured were a=6.16±0.05 A and c=13.17±0.01 A. The optical band gap and the electrical resistivity of the phosphide were determined to be 1.55 eV and 5 mΩ cm, respectively. The Gibbs free energy diagram for the Si–P system was modified to include this new Si12P5 phase.