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30 May 2005

Volume 86, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 223902 (2005); http://dx.doi.org/10.1063/1.1938253 (3 pages)

Philip J. Lee, Paul J. Hung, Robin Shaw, Lily Jan, and Luke P. Lee
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Ultrathick, low-stress nanostructured diamond films

S. O. Kucheyev, J. Biener, J. W. Tringe, Y. M. Wang, P. B. Mirkarimi, T. van Buuren, S. L. Baker, A. V. Hamza, K. Brühne, and H.-J. Fecht

Appl. Phys. Lett. 86, 221914 (2005); http://dx.doi.org/10.1063/1.1943492 (3 pages) | Cited 6 times

Online Publication Date: 25 May 2005

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We describe a hot-filament chemical vapor deposition process for growing freestanding nanostructured diamond films, ∼ 80 μm thick, with residual tensile stress levels ≲90 MPa. We characterize the film microstructure, mechanical properties, chemical bond distribution, and elemental composition. Results show that our films are nanostructured with columnar grain diameters of ≲150 nm and a highly variable grain length along the growth direction of ∼ 50–1500 nm. These films have a rms surface roughness of ≲200 nm for a 300×400 μm2 scan, which is about one order of magnitude lower than the roughness of typical microcrystalline diamond films of comparable thickness. Soft x-ray absorption near-edge structure (XANES) spectroscopy indicates a large percentage of sp3 bonding in the films, consistent with a high hardness of 66 GPa. Nanoindentation and XANES results are also consistent with a high phase and elemental purity of the films, directly measured by x-ray and electron diffraction, Rutherford backscattering spectrometry, and elastic recoil detection analysis. Cross-sectional transmission electron microscopy reveals a large density of planar defects within the grains, suggesting a high rate of secondary nucleation during film growth. These films represent a new class of smooth, ultrathick nanostructured diamond.
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68.60.Bs Mechanical and acoustical properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
78.70.Dm X-ray absorption spectra
68.55.A- Nucleation and growth
68.55.Nq Composition and phase identification
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Generation of terahertz monochromatic acoustic phonon pulses by femtosecond optical excitation of a gallium nitride/aluminium nitride superlattice

C. E. Martinez, N. M. Stanton, P. M. Walker, A. J. Kent, S. V. Novikov, and C. T. Foxon

Appl. Phys. Lett. 86, 221915 (2005); http://dx.doi.org/10.1063/1.1941475 (3 pages) | Cited 6 times

Online Publication Date: 25 May 2005

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We describe the generation of pulses of monochromatic acoustic phonons by ultrafast laser excitation of a gallium nitride/aluminium nitride superlattice (SL). The SL response to the optical excitation was studied using femtosecond pump-probe measurements. Superconducting bolometers were used to detect the phonons that leak out of the SL and propagate across the substrate. We see that, for excitation wavelengths around 430 nm, a pronounced enhancement in the longitudinal acoustic phonon signal occurs. The results are consistent with similar measurements using GaAs/AlAs SL’s, where propagating monochromatic phonons were generated under resonant photoexcitation [ Appl. Phys. Lett. 81, 3497 (2002) ].
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.47.-p Spectroscopy of solid state dynamics
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Pure-edge dislocation network for strain-relaxed SiGe/Si(001) systems

Akira Sakai, Noriyuki Taoka, Osamu Nakatsuka, Shigeaki Zaima, and Yukio Yasuda

Appl. Phys. Lett. 86, 221916 (2005); http://dx.doi.org/10.1063/1.1943493 (3 pages) | Cited 18 times

Online Publication Date: 26 May 2005

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We have grown strain-relaxed SiGe layers on Si(001) substrates with a pure-edge dislocation network buried at the heterointerface and analyzed dislocation morphology depending on growth conditions. The process employed here consists of pure-Ge film growth on Si(001) and subsequent high temperature annealing for solid-phase intermixing of the Ge film and Si deposited on the top to form a SiGe alloy layer. Transmission electron microscopy revealed morphological changes of shorter pure-edge dislocation segments initially formed at the Ge/Si interface into a network structure consisting of longer and regularly spaced dislocations during post-deposition annealing. The dislocation network was explicitly preserved even after the intermixing of Si and Ge and predominantly contributed to in-plane strain relaxation of the SiGe layer. Applicability of the pure-edge dislocation network to strain-relaxed SiGe buffer layers on Si(001) substrates is discussed.
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68.60.Bs Mechanical and acoustical properties
61.72.Cc Kinetics of defect formation and annealing
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations

Ultraviolet photovoltage characteristics of SrTiO3−δ/Si heterojunction

Kun Zhao, Yanhong Huang, Qingli Zhou, Kui-Juan Jin, Huibin Lu, Meng He, Bolin Cheng, Yueliang Zhou, Zhenghao Chen, and Guozhen Yang

Appl. Phys. Lett. 86, 221917 (2005); http://dx.doi.org/10.1063/1.1943495 (3 pages) | Cited 37 times

Online Publication Date: 26 May 2005

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A photovoltaic effect is observed in the heterostructure of p-Si/n-SrTiO3−δ (p: hole carrier type, n: electron carrier type). The current–voltage curve exhibits a good rectifying characteristic similar to that of the traditional diode. The junction shows the open circuit voltage of 126 mV/mJ, the short circuit current of 1.78 mA/mJ, and the response time faster than 10 ns for ultraviolet pulsed laser of 25 ns in duration at room temperature, suggesting the promising potential of this junction as a new type of ultrafast ultraviolet detectors with high sensitivity for application.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.47.-p Spectroscopy of solid state dynamics
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
73.40.Ei Rectification
81.05.Cy Elemental semiconductors

Kinetically controlled thin-film growth of layered β- and γ-NaxCoO2 cobaltate

J. Y. Son, Bog G. Kim, and J. H. Cho

Appl. Phys. Lett. 86, 221918 (2005); http://dx.doi.org/10.1063/1.1943498 (3 pages) | Cited 7 times

Online Publication Date: 27 May 2005

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We report growth characteristics of epitaxial β-Na0.6CoO2 and γ-Na0.7CoO2 thin films on (001) sapphire substrates grown by pulsed-laser deposition. Reduction of the deposition rate could change the structure of the NaxCoO2 thin film from a β phase with an island growth mode to a γ phase with a layer-by-layer growth mode. The γ-Na0.7CoO2 thin film exhibits spiral surface growth with multiterraced islands and highly crystallized texture compared to that of the β-Na0.6CoO2 thin film. This heterogeneous epitaxial film growth can give an example of the strain effect of physical properties and growth dynamics of NaxCoO2 as well as the subtle nature of structural change.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
68.35.B- Structure of clean surfaces (and surface reconstruction)
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Epitaxial growth of CoSi2 in a decanano contact opening on a (100) silicon substrate

Ho-Jung Sun, Young-Jin Lee, Soo-Hyun Kim, Joo-Wan Lee, Ja-Chun Ku, Hyun-Chul Sohn, Jin-Woong Kim, Uisik Kim, and Nak-Kyun Sung

Appl. Phys. Lett. 86, 221919 (2005); http://dx.doi.org/10.1063/1.1943500 (3 pages)

Online Publication Date: 27 May 2005

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The behavior of cobalt silicidation was investigated in a 45-nm-wide contact opening on (100) silicon substrate. A Co film was deposited using sputtering techniques with elongated target-to-wafer spacing and a CoSi2 phase was developed after being annealed using rapid thermal processing at 750 °C for 30 s. It was revealed that the CoSi2 was grown epitaxially both on {111} and (100) Si at the same time, resulting in a faceted single crystal. Type A epitaxy on {111} Si was developed due to the coepitaxial growth. It was suggested that the tendency for the epitaxial growth of CoSi2 was strong in such a highly confined contact opening.
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81.07.Lk Nanocontacts
81.07.Bc Nanocrystalline materials
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering
85.40.Sz Deposition technology
61.46.-w Structure of nanoscale materials

Stacking faults in Si nanocrystals

Y. Q. Wang, R. Smirani, and G. G. Ross

Appl. Phys. Lett. 86, 221920 (2005); http://dx.doi.org/10.1063/1.1943501 (3 pages) | Cited 4 times

Online Publication Date: 27 May 2005

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Si nanocrystals (Si nc) were formed by the implantation of Si+ into a SiO2 film on (100) Si, followed by high-temperature annealing. High-resolution transmission electron microscopy has been used to examine the microstructure of the Si nc produced by a high-dose (3×1017 cm−2) implantation. It is shown that there are only stacking-fault (SF) defects in some nanocrystals; while in others the stacking faults (SFs) coexist with twins. Two kinds of SFs, one being an intrinsic SF, the other being an extrinsic SF, have been observed inside the Si nc. More intrinsic SFs have been found in the Si nc, and the possible reasons are discussed. These microstructural defects are expected to play an important role in the light emission from the Si nc.
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81.07.Bc Nanocrystalline materials
81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.46.-w Structure of nanoscale materials
68.47.Fg Semiconductor surfaces
61.72.up Other materials
61.72.Nn Stacking faults and other planar or extended defects
81.16.-c Methods of micro- and nanofabrication and processing
68.37.Lp Transmission electron microscopy (TEM)
52.77.Dq Plasma-based ion implantation and deposition
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.82.Rx Nanocrystalline materials

Cu-Si bilayers as storage medium in optical recording

A. E. T. Kuiper, R. J. M. Vullers, D. Pasquariello, and E. P. Naburgh

Appl. Phys. Lett. 86, 221921 (2005); http://dx.doi.org/10.1063/1.1944205 (3 pages) | Cited 12 times

Online Publication Date: 27 May 2005

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Instead of a phase change or a dye layer, a Cu/Si bilayer can be applied as the recording medium in a write-once Blu-ray Disc. The write process basically comprises the formation of a CuSi alloy containing 25–30 at. % Si, while any excess of Si is left behind as unreacted film. Auger analyses of the laser-written layers indicate that recording consists primarily of the diffusion of Si into Cu. The data allow for discrimination between the various models presented in literature for Cu/Si-based recording and to optimize the stack. Very low jitter levels of typically 4% proved to be achievable with equally thick films of Cu and Si as recording medium.
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81.05.Bx Metals, semimetals, and alloys
42.79.Vb Optical storage systems, optical disks
79.60.Bm Clean metal, semiconductor, and insulator surfaces
66.30.-h Diffusion in solids
42.62.-b Laser applications

Theory of compositionally graded ferroelectrics and pyroelectricity

M. Marvan, P. Chvosta, and J. Fousek

Appl. Phys. Lett. 86, 221922 (2005); http://dx.doi.org/10.1063/1.1940729 (3 pages) | Cited 9 times

Online Publication Date: 27 May 2005

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A thermodynamic theory of compositionally graded materials is developed, based on a term in the Landau formula for free energy of the form γPgradc, where P, c, and γ stand for the polarization, the atomic concentration, and a phenomenological coefficient, respectively. The consequence of this term is the following: (1) the original equivalence of two states with spontaneous polarization +PS and −PS is upset and the sample has the tendency to become oriented along one of the originally equivalent directions; (2) an additional polarization is induced. The consequences of the modified free energy for pyroelectricity are discussed.
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77.80.-e Ferroelectricity and antiferroelectricity
77.70.+a Pyroelectric and electrocaloric effects
65.40.G- Other thermodynamical quantities

Relaxation processes in strained Si layers on silicon-germanium- on-insulator substrates

Norio Hirashita, Naoharu Sugiyama, Eiji Toyoda, and Shin-ichi Takagi

Appl. Phys. Lett. 86, 221923 (2005); http://dx.doi.org/10.1063/1.1944208 (3 pages) | Cited 9 times

Online Publication Date: 27 May 2005

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Misfit defects in strained Si layers on silicon-germanium-on-insulator (SGOI) substrates were studied using transmission electron microscopy. With increasing strained-layer thickness, stacking faults with 90° Shockley partial dislocations at strained-Si–SiGe interfaces are found to be increasingly formed in the strained Si layers, extending from the surface to the interface. This fact indicates that generation and glide on {111} planes of the 90° partial dislocations are responsible for the relaxation of the cumulative tensile strain in strained Si layers on SGOI substrates.
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81.05.Cy Elemental semiconductors
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Nn Stacking faults and other planar or extended defects
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p-ZnO/n-GaN heterostructure ZnO light-emitting diodes

Dae-Kue Hwang, Soon-Hyung Kang, Jae-Hong Lim, Eun-Jeong Yang, Jin-Yong Oh, Jin-Ho Yang, and Seong-Ju Park

Appl. Phys. Lett. 86, 222101 (2005); http://dx.doi.org/10.1063/1.1940736 (3 pages) | Cited 128 times

Online Publication Date: 24 May 2005

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We report on the characteristics of a ZnO light-emitting diode (LED) comprised of a heterostructure of p-ZnO/n-GaN. The LED structure consisted of a phosphorus doped p-ZnO film with a hole concentration of 6.68×1017 cm−3 and a Si-doped n-GaN film with an electron concentration of 1.1×1018 cm−3. The I–V of the LED showed a threshold voltage of 5.4 V and an electroluminescence (EL) emission of 409 nm at room temperature. The EL emission peak at 409 nm was attributed to the band gap of p-ZnO which was reduced as the result of the band offset at the interface of p-ZnO and n-GaN.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence

Zero-field spin splitting in modulation-doped AlxGa1−xN/GaN two-dimensional electron systems

K. S. Cho, Tsai-Yu Huang, Hong-Syuan Wang, Ming-Gu Lin, Tse-Ming Chen, C.-T. Liang, Y. F. Chen, and Ikai Lo

Appl. Phys. Lett. 86, 222102 (2005); http://dx.doi.org/10.1063/1.1929876 (3 pages) | Cited 20 times

Online Publication Date: 24 May 2005

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Low-temperature magnetotransport measurements were performed on AlxGa1−xN/GaN two-dimensional electron systems. By studying the beating pattern in the Shubnikov–de Haas oscillations in a perpendicular magnetic field, we are able to measure the zero-field spin-splitting energies in our systems. Our experimental results demonstrate that the Rashba term due to structural inversion asymmetry is the dominant mechanism which gives rise to the measured zero-field spin splitting in our wurzite AlGaN/GaN structures. By utilizing the persistent photoconductivity (PPC) effect, we are able to increase the carrier density n in our AlGaN/GaN two-dimensional electron system. It is found that the Rashba spin-orbit splitting parameter α decreases with increasing n. We suggest that the formation of long-lived electron-hole pairs induced by the PPC effect decreases the large electric field near the AlGaN/GaN interface, causing α to decrease with increasing n.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ey III-V semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Observation of large electron drift velocities in InN by ultrafast Raman spectroscopy

K. T. Tsen, C. Poweleit, D. K. Ferry, Hai Lu, and William J. Schaff

Appl. Phys. Lett. 86, 222103 (2005); http://dx.doi.org/10.1063/1.1931048 (3 pages) | Cited 37 times

Online Publication Date: 24 May 2005

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Electron transport in an InN film grown on GaN has been studied by transient Raman spectroscopy at T = 300 K. Our experimental results demonstrate that under the subpicosecond laser excitation and probing, electron drift velocity of carriers in the Γ valley can exceed its steady-state value by as much as 40%. Electron velocities have been found to cut off at around 2×108 cm/s, significantly larger than those observed for other III-V semiconductors, such as GaAs and InP. These experimental results have been compared with ensemble Monte Carlo simulations and good agreement has been obtained.
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73.61.Ey III-V semiconductors
78.30.Fs III-V and II-VI semiconductors

General model and segregation coefficient measurement for ultrashallow doping by excimer laser annealing

Jean-Numa Gillet, Jean-Yves Degorce, and Michel Meunier

Appl. Phys. Lett. 86, 222104 (2005); http://dx.doi.org/10.1063/1.1927275 (3 pages) | Cited 8 times

Online Publication Date: 24 May 2005

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A general model of ultrashallow doping by excimer laser annealing is derived from only one diffusion-segregation equation. In our model, the relative dopant profile after some laser shots reaches a stationary distribution, which only depends on the segregation and liquid-phase diffusion coefficients of the dopant but not on the laser-process parameters. From this result, a one-point method is proposed to experimentally determine the out-of-equilibrium segregation coefficient k. Only the relative dopant concentration at the material surface has to be measured prior to determine the k value. Experimental dopant profiles are compared to simulations generated with experimental k values.
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64.75.-g Phase equilibria
66.30.J- Diffusion of impurities
61.72.S- Impurities in crystals
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Electronic properties of a semiconducting oligomer/silicon (111) interface: Influence of silicon doping

V. Papaefthimiou and S. Kennou

Appl. Phys. Lett. 86, 222105 (2005); http://dx.doi.org/10.1063/1.1929073 (3 pages) | Cited 1 time

Online Publication Date: 24 May 2005

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The interface formation between a semiconducting oligomer and the p-doped Si(111) surface was investigated by X-ray and ultraviolet photoelectron spectroscopies (UPS) and the results were compared to the same oligomer/Si (n-doped) interface. The position of the energy levels of the bulk oligomer film was identical in both interfaces, while differences appeared at the first steps of the interface formation. The band bending at the interfaces was assessed from X-ray photoelectron spectra while the interfacial dipoles from the UPS results. A ∼ 0.30 eV dipole layer was observed at the oligomer/Si (p-doped) interface whereas the oligomer/Si (n-doped) interface is dipole free. The valence-band offset between silicon and the oligomer was found ∼ 0.40 eV in both cases.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.60.Jv Interfaces; heterostructures; nanostructures
73.20.At Surface states, band structure, electron density of states
61.72.uf Ge and Si

High-mobility nanocrystalline silicon thin-film transistors fabricated by plasma-enhanced chemical vapor deposition

Czang-Ho Lee, Andrei Sazonov, and Arokia Nathan

Appl. Phys. Lett. 86, 222106 (2005); http://dx.doi.org/10.1063/1.1942641 (3 pages) | Cited 53 times

Online Publication Date: 24 May 2005

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Hydrogenated nanocrystalline silicon (nc-Si:H) films were deposited by using 13.56 MHz plasma-enhanced chemical vapor deposition at 260 °C by means of a silane (SiH4) plasma heavily diluted with hydrogen (H2). The high-quality nc-Si:H film showed an oxygen concentration (CO) of ∼ 1.5×1017 at./cm3 and a dark conductivity (σd) of ∼ 10−6 S/cm, while the Raman crystalline volume fraction (Xc) was over 80%. Top-gate nc-Si:H thin-film transistors employing an optimized ∼ 100 nm nc-Si:H channel layer exhibited a field-effect mobility (μFE) of ∼ 150 cm2/V s, a threshold voltage (VT) of ∼ 2 V, a subthreshold slope (S) of ∼ 0.25 V/dec, and an ON∕OFF current ratio of ∼ 106.
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85.30.Tv Field effect devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Cd2+/NH3 treatment-induced formation of a CdSe surface layer on CuGaSe2 thin-film solar cell absorbers

M. Bär, S. Lehmann, M. Rusu, A. Grimm, I. Kötschau, I. Lauermann, P. Pistor, S. Sokoll, Th. Schedel-Niedrig, M. Ch. Lux-Steiner, Ch.-H. Fischer, L. Weinhardt, C. Heske, and Ch. Jung

Appl. Phys. Lett. 86, 222107 (2005); http://dx.doi.org/10.1063/1.1942638 (3 pages) | Cited 5 times

Online Publication Date: 25 May 2005

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CuGaSe2 (CGSe)-based high-gap thin-film solar cells have to date not reached their potential level of electrical performance. In order to elucidate possible shortcomings of the electronic interface structure, we have studied the initial stage of the CdS/CGSe interface formation by use of a simple Cd2+/NH3 treatment. As in the case of low-gap chalcopyrites, we find a Cd-containing surface layer, in the present case comprised of approximately one monolayer of CdSe. The results indicate that the CdS/CGSe interface is not abrupt, but contains intermediate layers. Furthermore, they shed light on possible surface modification schemes to enhance the overall performance of high-gap CGSe chalcopyrite solar cells.
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81.05.Dz II-VI semiconductors
84.60.Jt Photoelectric conversion
81.65.-b Surface treatments
68.35.Ct Interface structure and roughness

Deep impurity transitions involving cation vacancies and complexes in AlGaN alloys

K. B. Nam, M. L. Nakarmi, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 86, 222108 (2005); http://dx.doi.org/10.1063/1.1943489 (3 pages) | Cited 37 times

Online Publication Date: 26 May 2005

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Deep ultraviolet (UV) photoluminescence (PL) spectroscopy has been employed to study deep impurity transitions in AlxGa1−xN (0 ⩽ x ⩽ 1) epilayers. Two groups of deep impurity transitions were observed, which are assigned to the recombination between shallow donors and two different deep level acceptors involving cation vacancies (Vcation) and Vcation complexes in AlxGa1−xN alloys. These acceptor levels are pinned to two different energy levels common to AlxGa1−xN alloys (0 ⩽ x ⩽ 1). The deep impurity transitions related with Vcation complexes were observed in AlxGa1−xN alloys between x = 0 and 1, while those related with Vcation were only observed in AlxGa1−xN alloys between x = 0.58 and 1. This points out to the fact that the formation of Vcation is more favorable in Al-rich AlGaN alloys, while Vcation complexes can be formed in the whole range of x between 0 and 1. The implications of our findings to the UV optoelectronic devices using AlGaN alloys are also discussed.
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71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.J- Point defects and defect clusters

Effect of inclined quantum wells on macroscopic capacitance-voltage response of Schottky contacts: Cubic inclusions in hexagonal SiC

K.-B. Park, Y. Ding, J. P. Pelz, M. K. Mikhov, Y. Wang, and B. J. Skromme

Appl. Phys. Lett. 86, 222109 (2005); http://dx.doi.org/10.1063/1.1935757 (3 pages) | Cited 7 times

Online Publication Date: 26 May 2005

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Finite-element calculations of Schottky diode capacitance-voltage (C-V) curves show that an array of subsurface inclined quantum wells (QWs) produce negligible change in shape and slope of C-V curves, but significantly reduce the intercept voltage. This is particularly important for hexagonal SiC, in which current- or process-induced cubic inclusions are known to behave as electron QWs. These calculations naturally explain the surprisingly large effect of cubic inclusions on the apparent 4H–SiC Schottky barrier determined by C-V measurements, and together with the measured C-V data indicate the QW subband energy in the inclusions to be ∼ 0.51 eV below the host 4H–SiC conduction band.
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85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices
73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.At Surface states, band structure, electron density of states
73.63.Hs Quantum wells
73.21.Fg Quantum wells
71.20.Nr Semiconductor compounds
02.70.Dh Finite-element and Galerkin methods
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Magnetic resonance signatures of grown-in defects in GaInNP alloys grown on a GaAs substrate

I. P. Vorona, T. Mchedlidze, M. Izadifard, I. A. Buyanova, W. M. Chen, Y. G. Hong, H. P. Xin, and C. W. Tu

Appl. Phys. Lett. 86, 222110 (2005); http://dx.doi.org/10.1063/1.1943487 (3 pages) | Cited 4 times

Online Publication Date: 27 May 2005

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Dilute-nitride Ga0.44In0.56NyP1−y alloys with y = 0–0.02, grown on a GaAs substrate using gas-source molecular beam epitaxy, are studied by the optically detected magnetic resonance (ODMR) technique. Grown-in paramagnetic defects were found to act as centers of nonradiative recombination. Resolved hyperfine structure for one of the detected ODMR signals suggests involvement of a Ga-interstitial or an As-antisite in the structure of the related defect.
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81.05.Ea III-V semiconductors
76.30.Mi Color centers and other defects
61.72.J- Point defects and defect clusters

n-type doping of (001)-oriented single-crystalline diamond by phosphorus

Hiromitsu Kato, Satoshi Yamasaki, and Hideyo Okushi

Appl. Phys. Lett. 86, 222111 (2005); http://dx.doi.org/10.1063/1.1944228 (3 pages) | Cited 56 times

Online Publication Date: 27 May 2005

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n-type doping of (001)-oriented single-crystalline diamond has been achieved using PH3 as doping gas and applying a newly optimized homoepitaxial growth technique based on plasma-enhanced chemical vapor deposition. Hall-effect measurements indicate n-type conductivity with highest mobilities of ∼ 350 cm2/Vs. Phosphorus doping is confirmed by secondary-ion mass spectroscopy.
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61.72.up Other materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Cw Elemental semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
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Enhanced magnetic and bolometric sensitivity of La0.7Ce0.3MnO3 thin films due to 200 MeV Ag ion irradiation

R. J. Choudhary, Ravi Kumar, S. I. Patil, Shahid Husain, J. P. Srivastava, and S. K. Malik

Appl. Phys. Lett. 86, 222501 (2005); http://dx.doi.org/10.1063/1.1941479 (3 pages) | Cited 8 times

Online Publication Date: 24 May 2005

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The parameters for bolometric performance [temperature coefficient of resistance (TCR) and noise value] and magnetic sensitivity of pulsed-laser-deposited thin films of La0.7Ce0.3MnO3 and their dependence on the 200 MeV Ag ions irradiation are studied. It is observed that the TCR value and magnetic sensitivity can be tuned in different temperature regime by controlling the irradiation fluence value. It turns out that irradiation with a fluence value of 5×1010 ions/cm2 changes the TCR value in a positive direction and enhances magnetic sensitivity at room temperature, while irradiation with a fluence value of 1×1012 ions/cm2 enhances these parameters at 200 K. The observations are explained on the basis of structural and electrical transport modifications induced by the 200 MeV Ag ion irradiation.
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71.30.+h Metal-insulator transitions and other electronic transitions
72.70.+m Noise processes and phenomena
75.70.Ak Magnetic properties of monolayers and thin films
61.80.Jh Ion radiation effects

High critical current properties of MgB2 bulks prepared by a diffusion method

Shinya Ueda, Jun-ichi Shimoyama, Isao Iwayama, Akiyasu Yamamoto, Yukari Katsura, Shigeru Horii, and Kohji Kishio

Appl. Phys. Lett. 86, 222502 (2005); http://dx.doi.org/10.1063/1.1939071 (3 pages) | Cited 29 times

Online Publication Date: 24 May 2005

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Highly dense MgB2 bulks with high purity were synthesized by the newly developed PICT-diffusion method, starting from magnesium and boron which were separately packed in sealed stainless tubes. Critical current density, Jc, systematically improved with a decrease of grain size of the samples. A sample reacted at 800 °C for 60 h exhibited the highest Jc of ∼ 0.86 MA/cm2 at 20 K in self-field, which was almost three times higher than that of conventional porous MgB2 bulks prepared by the solid-state reaction. Besides an increase of effective current pass, small grains with 30–100 nm in size and good grain connectivity resulted in the dramatically enhanced Jc.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Sv Critical currents
81.40.Gh Other heat and thermomechanical treatments

Ferromagnetism in nanocrystalline epitaxial Co:TiO2 thin films

A. K. Pradhan, D. Hunter, J. B. Dadson, T. M. Williams, Kai Zhang, K. Lord, B. Lasley, R. R. Rakhimov, Jun Zhang, D. J. Sellmyer, U. N. Roy, Y. Cui, A. Burger, C. Hopkins, N. Pearson, et al.

Appl. Phys. Lett. 86, 222503 (2005); http://dx.doi.org/10.1063/1.1944209 (3 pages) | Cited 7 times

Online Publication Date: 25 May 2005

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We report on the observation of remarkable room-temperature ferromagnetism in nanocrystalline epitaxial Co:TiO2 films grown on sapphire (0001) substrates by a pulsed-laser deposition technique using high-density targets. The films were characterized by x-ray measurements, atomic force microscopy, micro-Raman, electron-paramagnetic resonance, and magnetization studies. The films exhibit three-dimensional islandlike growth that contains nanocrystalline particles. Our experimental results suggest that the remarkable ferromagnetism in Co:TiO2 films is controlled either by the interstitial Co2+ ions or small clusters, which are mainly present at the interface and on the surface of the films. Our work clearly indicates that Co interstitials and nanoclusters cause room-temperature ferromagnetism in Co-doped TiO2.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Tt Fine-particle systems; nanocrystalline materials
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.30.-v Electron paramagnetic resonance and relaxation
61.72.J- Point defects and defect clusters
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
78.30.Hv Other nonmetallic inorganics
78.66.Li Other semiconductors

Preparation of highly conductive Mn-doped Fe3O4 thin films with spin polarization at room temperature using a pulsed-laser deposition technique

Mizue Ishikawa, Hidekazu Tanaka, and Tomoji Kawai

Appl. Phys. Lett. 86, 222504 (2005); http://dx.doi.org/10.1063/1.1942640 (3 pages) | Cited 37 times

Online Publication Date: 25 May 2005

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We report on the preparation of MnxFe3−xO4 (x = 0, 0.1, or 0.5) epitaxial thin films using a pulsed-laser deposition technique. Conditions for modified film formation are discussed, in addition to their electrical and magnetic properties in relation to the potential development of room temperature spin electronics devices. The film with x = 0.1 could be fabricated at a higher substrate temperature (600 °C) than the Fe3O4 thin film without Mn doping. The doped films exhibited low resistivity of about 7.0×10−3(x = 0.1)–9.0×10−2(x = 0.5) Ω cm at room temperature. Moreover, a spin polarization of the carrier of MnxFe3−xO4 (x = 0, 0.1, or 0.5) films was confirmed at room temperature by examination of anomalous Hall coefficient measurements.
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75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films
68.55.A- Nucleation and growth
81.15.Fg Pulsed laser ablation deposition
73.61.Ng Insulators
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.S- Impurities in crystals
72.25.-b Spin polarized transport
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