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3 Dec 2007

Volume 91, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 232101 (2007); http://dx.doi.org/10.1063/1.2818712 (3 pages)

T. Kita, D. Chiba, Y. Ohno, and H. Ohno
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Lattice relaxation mechanism of ZnO thin films grown on c-Al2O3 substrates by plasma-assisted molecular-beam epitaxy

S. H. Park, T. Hanada, D. C. Oh, T. Minegishi, H. Goto, G. Fujimoto, J. S. Park, I. H. Im, J. H. Chang, M. W. Cho, T. Yao, and K. Inaba

Appl. Phys. Lett. 91, 231904 (2007); http://dx.doi.org/10.1063/1.2813021 (3 pages) | Cited 12 times

Online Publication Date: 4 December 2007

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We report on the lattice relaxation mechanism of ZnO films grown on c-Al2O3 substrates by plasma-assisted molecular-beam epitaxy. The lattice relaxation of ZnO films with various thicknesses up to 2000 nm is investigated by using both in situ time-resolved reflection high energy electron diffraction observation during the initial growth and absolute lattice constant measurements (Bond method) for grown films. The residual strain in the films is explained in terms of lattice misfit relaxation (compression) at the growth temperature and thermal stress (tension) due to the difference of growth and measurement temperatures. In thick films (>1 μm), the residual tensile strain begins to relax by bending and microcrack formation.
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81.05.Dz II-VI semiconductors
68.60.Bs Mechanical and acoustical properties
52.77.-j Plasma applications
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Assessing the critical sizes for shear band formation in metallic glasses from molecular dynamics simulation

Qi-Kai Li and Mo Li

Appl. Phys. Lett. 91, 231905 (2007); http://dx.doi.org/10.1063/1.2821832 (3 pages) | Cited 11 times

Online Publication Date: 5 December 2007

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The size effect on the strength and fracture behavior of metallic glasses reported earlier by the authors is further examined in a mode I fracture from extensive molecular dynamics simulation using multimillion atoms and a method for atomic strain. In sharp contrast to the notch-free and notched samples, with small dimensions, in the large samples, shear bands easily initiate at the notch tips and grow into maturity. We identified two critical length scales for nucleating a shear band: the nucleation zone size d of about 10–20 nm and the shear length ξ that is at least twice as large as d. The shape anisotropy of the critical nucleus described by the two length scales d and ξ may contribute to deformation anisotropy.
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81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.43.Fs Glasses

Sodium reconstruction on surface of silicate glasses in transmission electron microscope

Nan Jiang, Dong Su, and John C. H. Spence

Appl. Phys. Lett. 91, 231906 (2007); http://dx.doi.org/10.1063/1.2822402 (3 pages) | Cited 4 times

Online Publication Date: 5 December 2007

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We find that irradiated Na ions in silicate glasses undergo reconstruction on the surfaces before being repelled from the irradiated area by electron excitations. These results are based on evidence from time-dependent electron energy-loss spectroscopy. The process of reconstruction involves an irreversible change of the Na+→Na0→Na+, in which the initial and final Na+ ions have different bonding environments. The phenomenon is the result of the elimination of nonbridging oxygen associated with Na.
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61.43.Fs Glasses
61.80.Jh Ion radiation effects
68.37.Lp Transmission electron microscopy (TEM)
79.20.Uv Electron energy loss spectroscopy

Surface plasmon enhanced ultraviolet emission from ZnO films deposited on Ag/Si(001) by magnetron sputtering

J. B. You, X. W. Zhang, Y. M. Fan, S. Qu, and N. F. Chen

Appl. Phys. Lett. 91, 231907 (2007); http://dx.doi.org/10.1063/1.2822404 (3 pages) | Cited 24 times

Online Publication Date: 5 December 2007

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The ZnO films were grown on Ag/Si(001) substrates by sputtering Ag and ZnO targets successively in a pure Ar ambient. A significant enhancement of ZnO ultraviolet emission and a reduction of its full width of half maximum have been observed while introducing a 100 nm Ag interlayer between ZnO film and Si substrate. Furthermore, a complete suppression of the defect related visible emission was also found for the ZnO/Ag/Si sample. This improved optical performance of ZnO is attributed to the resonant coupling between Ag surface plasmon and ultraviolet emission of ZnO.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.55.Cr III-V semiconductors
78.66.Hf II-VI semiconductors
81.15.Cd Deposition by sputtering

Strong perturbation of the guided light within Y2O3:Eu3+ thin-film phosphors coated with two-dimensional air-hole photonic crystal arrays

Young Kwang Lee, Jeong Rok Oh, Young Rag Do, and Young-Duk Huh

Appl. Phys. Lett. 91, 231908 (2007); http://dx.doi.org/10.1063/1.2820389 (3 pages) | Cited 13 times

Online Publication Date: 5 December 2007

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Two-dimensional (2D) triangular-lattice air-hole nanoarrays of either SiO2 or SiNx were fabricated with nanosphere lithography as photonic crystal layers (PCLs) on sol-gel derived Y2O3:Eu3+ thin-film phosphors (TFPs). The effects of varying the air fill factor of the 2D PCLs on the light extraction efficiency of the TFPs were investigated. The integrated and normally directed photoluminescence extraction efficiencies were found to be improved by coating with 2D SiNx PCLs by factors of above 5.9 and 9.4, respectively; the 2D SiNx PCLs perturb the guided light more effectively than the 2D SiO2 PCLs because of their larger refractive index contrast.
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78.66.-w Optical properties of specific thin films
78.55.Hx Other solid inorganic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Qs Photonic bandgap materials

Enhanced photoelectrochemical responses of ZnO films through Ga and N codoping

Kwang-Soon Ahn, Yanfa Yan, Sudhakar Shet, Todd Deutsch, John Turner, and Mowafak Al-Jassim

Appl. Phys. Lett. 91, 231909 (2007); http://dx.doi.org/10.1063/1.2822440 (3 pages) | Cited 46 times

Online Publication Date: 5 December 2007

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We report on the crystallinity and photoelectrochemical (PEC) response of ZnO thin films codoped by Ga and N. The ZnO:(Ga,N) thin films were deposited by cosputtering at room temperature and followed by postannealing at 500 °C in air for 2 h. We found that ZnO:(Ga,N) thin films exhibited significantly enhanced crystallinity compared to ZnO doped solely with N at the same growth conditions. Furthermore, ZnO:(Ga,N) thin films exhibited enhanced N incorporation over ZnO doped solely with N at high temperatures. As a result, ZnO:(Ga,N) thin films achieved dramatically improved PEC response, compared to ZnO thin films doped solely with N at any conditions. Our results suggest a general way to improve PEC response for wide-band-gap oxides.
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82.50.-m Photochemistry
81.15.Cd Deposition by sputtering
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Localization-induced inhomogeneous screening of internal electric fields in AlGaN-based quantum wells

Hideaki Murotani, Takuya Saito, Nobuo Kato, Yoichi Yamada, Tsunemasa Taguchi, Akihiko Ishibashi, Yasutoshi Kawaguchi, and Toshiya Yokogawa

Appl. Phys. Lett. 91, 231910 (2007); http://dx.doi.org/10.1063/1.2817749 (3 pages) | Cited 1 time

Online Publication Date: 5 December 2007

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The influence of both localization and internal electric field on the microscopic photoluminescence (PL) properties of AlGaN-based quantum wells (QWs) has been studied by means of scanning near-field optical microscopy (SNOM). SNOM-PL images of three QWs with different well-layer thicknesses were measured under an illumination-collection mode. A correlation was observed between the PL intensity and the PL peak wavelength: a shorter-PL wavelength indicates a stronger intensity for a wider QW. The correlation is caused by an inhomogeneous screening of the internal electric field.
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78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors

Evaluation of plasticity driven material damage using Lamb waves

Christoph Pruell, Jin-Yeon Kim, Jianmin Qu, and Laurence J. Jacobs

Appl. Phys. Lett. 91, 231911 (2007); http://dx.doi.org/10.1063/1.2811954 (3 pages) | Cited 27 times

Online Publication Date: 5 December 2007

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This letter reports on the experimental observation of a direct correlation between the acoustic nonlinearity measured with Lamb waves and the level of plasticity in a metal specimen. This correlation implies that even though Lamb waves are multimodal and dispersive, they will interact with a material’s plasticity in a manner similar to longitudinal and Rayleigh waves; there is a fundamental relationship between material plasticity and acoustic nonlinearity that is independent of wave type. As a result, Lamb waves can be used to quantitatively assess plasticity driven material damage using established higher harmonic generation techniques.
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81.40.Lm Deformation, plasticity, and creep
68.35.Gy Mechanical properties; surface strains
68.35.Iv Acoustical properties
62.65.+k Acoustical properties of solids
43.25.Dc Nonlinear acoustics of solids

Size dependency of the elastic modulus of ZnO nanowires: Surface stress effect

Guofeng Wang and Xiaodong Li

Appl. Phys. Lett. 91, 231912 (2007); http://dx.doi.org/10.1063/1.2821118 (3 pages) | Cited 25 times

Online Publication Date: 5 December 2007

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Relation between the elastic modulus and the diameter (D) of ZnO nanowires was elucidated using a model with the calculated ZnO surface stresses as input. We predict for ZnO nanowires due to surface stress effect: (1) when D>20 nm, the elastic modulus would be lower than the bulk modulus and decrease with the decreasing diameter, (2) when 20 nm>D>2 nm, the nanowires with a longer length and a wurtzite crystal structure could be mechanically unstable, and (3) when D<2 nm, the elastic modulus would be higher than that of the bulk value and increase with a decrease in nanowire diameter.
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62.25.-g Mechanical properties of nanoscale systems
68.35.Gy Mechanical properties; surface strains
62.20.D- Elasticity

Lattice contraction and magnetic and electronic transport properties of Mn3Zn1−xGexN

Ying Sun, Cong Wang, Yongchun Wen, Kaigui Zhu, and Jingtai Zhao

Appl. Phys. Lett. 91, 231913 (2007); http://dx.doi.org/10.1063/1.2822813 (3 pages) | Cited 33 times

Online Publication Date: 6 December 2007

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The lattice and electronic and magnetic transport properties of the antiperovskite structure Mn3Zn1−xGexN compounds were investigated. For Mn3ZnN, there is a magnetic transition from antiferromagnetic to paramagnetic near 185 K. Correspondingly, the resistivity shows an abrupt drop, but any sudden change of lattice parameters is not found. However, it is interesting that the partial substitution of Ge for Zn induces a lattice contraction near the magnetic transition temperature, where a drop of the resistivity remain, and the transition temperature point increases and the temperature range is broadened with increasing doped Ge contents. The thermodynamics properties were also investigated.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.20.-b Electron density of states and band structure of crystalline solids
61.66.Fn Inorganic compounds

Strain-compensated AlGaN/GaN/InGaN cladding layers in homoepitaxial nitride devices

R. Czernecki, S. Krukowski, G. Targowski, P. Prystawko, M. Sarzynski, M. Krysko, G. Kamler, I. Grzegory, M. Leszczynski, and S. Porowski

Appl. Phys. Lett. 91, 231914 (2007); http://dx.doi.org/10.1063/1.2823587 (3 pages) | Cited 5 times

Online Publication Date: 6 December 2007

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One of the most important problems in III-nitride violet laser diode technology is the lattice mismatch between the AlGaN cladding layers and the rest of the epitaxial structure. For efficiently working devices, it is necessary to have both a high Al content and thick claddings. This leads, however, to severe sample bowing and even cracking of the upper layer. In this work, we propose a cladding structure of strain-compensated AlGaN/GaN/InGaN superlattice grown by metal-organic vapor phase epitaxy on bulk GaN substrates. Various thicknesses and compositions of the layers were employed. We measured the radius of bowing, lattice mismatches, aluminum and indium contents, and densities of threading dislocations. The proposed cladding structures suppress bowing and cracking, which are the two parasitic effects commonly experienced in laser diodes with bulk AlGaN claddings. The suppression of cracking and bowing is shown to occur due to modified strain energy distribution of the superlattices structure.
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81.65.-b Surface treatments
42.55.Px Semiconductor lasers; laser diodes
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Lm Deformation, plasticity, and creep
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.Nq Composition and phase identification
68.60.Bs Mechanical and acoustical properties

The structural evolution of boron carbide via ab initio calculations

James E. Saal, Shunli Shang, and Zi-Kui Liu

Appl. Phys. Lett. 91, 231915 (2007); http://dx.doi.org/10.1063/1.2818661 (3 pages) | Cited 15 times

Online Publication Date: 6 December 2007

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The distribution of boron and carbon atoms in boron carbide (B4C), the third hardest naturally occurring material, is a hotly debated subject. In the current work, an ab initio approach is applied to the entire composition range of boron carbide ( ∼ 8–20 at. % C) to determine what disordering mechanisms are responsible for such a large single-phase region. Based on the correctly predicted crystal structures, enthalpy of formation, and infrared phonon modes, we reveal direct evidence in support of a new defect model for boron carbide, where mixing occurs in the icosahedron for carbon-rich compositions and in the chain for boron-rich compositions.
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61.66.Fn Inorganic compounds

An optical method to determine the thermodynamics of hydrogen absorption and desorption in metals

R. Gremaud, M. Slaman, H. Schreuders, B. Dam, and R. Griessen

Appl. Phys. Lett. 91, 231916 (2007); http://dx.doi.org/10.1063/1.2821376 (3 pages) | Cited 25 times

Online Publication Date: 6 December 2007

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Hydrogenography, an optical high-throughput combinatorial technique to find hydrogen storage materials, has so far been applied only to materials undergoing a metal-to-semiconductor transition during hydrogenation. We show here that this technique works equally well for metallic hydrides. Additionally, we find that the thermodynamic data obtained optically on thin Pd–H films agree very well with Pd–H bulk data. This confirms that hydrogenography is a valuable general method to determine the relevant parameters for hydrogen storage in metal hydrides.
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68.43.Mn Adsorption kinetics
68.47.De Metallic surfaces
71.30.+h Metal-insulator transitions and other electronic transitions

Sedimentation of isotope atoms in monatomic liquid Se

Tsutomu Mashimo, Masao Ono, Xinsheng Huang, Yusuke Iguchi, Satoru Okayasu, Katsura Kobayashi, and Eizo Nakamura

Appl. Phys. Lett. 91, 231917 (2007); http://dx.doi.org/10.1063/1.2819070 (3 pages) | Cited 3 times

Online Publication Date: 7 December 2007

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A strong gravitational field resulted in the sedimentation of isotope atoms in monatomic liquid. The concentration ratio 82Se/76Se increased by greater than 3.5% in specimen ultracentrifuged at (0.7–0.9)×106 G and at 300 °C. The recovered sample had a feather-shaped crystalline morphology. The concentration gradient was nearly twice that of the steady state analytical result (ideal gas system), indicating a nonideal system diffusion. The present result is evidence of sedimentation of substitutional atoms in condensed matter via self-diffusion and suggestes its possible application to isotope separation, crystalline control, and matter dynamics in massive star.
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61.20.Ne Structure of simple liquids
66.10.C- Diffusion and thermal diffusion

Shock-induced lattice deformation of CdS single crystal by nanosecond time-resolved Laue diffraction

Kouhei Ichiyanagi, Shin-ichi Adachi, Shunsuke Nozawa, Yoichiro Hironaka, Kazutaka G. Nakamura, Tokushi Sato, Ayana Tomita, and Shin-ya Koshihara

Appl. Phys. Lett. 91, 231918 (2007); http://dx.doi.org/10.1063/1.2819617 (3 pages) | Cited 8 times

Online Publication Date: 7 December 2007

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We report a single-shot nanosecond time-resolved Laue diffraction measurement of cadmium sulfide (CdS) single crystal under laser-induced shock compression. The observed Laue diffraction pattern maintains sixfolding axis of the wurtzite structure for 10 ns at a shock pressure of 3.92 GPa, which is above the threshold pressure of phase transition to a rocksalt structure. This result shows that a transient wurtzite structure is observed above its threshold pressure to a rocksalt structure on a nanosecond time scale. Uniaxial compression was confirmed by the c/a value of the transient structure obtained from the (201) and (302) peaks.
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61.66.Fn Inorganic compounds

Effect of current crowding on whisker growth at the anode in flip chip solder joints

Fan-Yi Ouyang, Kai Chen, K. N. Tu, and Yi-Shao Lai

Appl. Phys. Lett. 91, 231919 (2007); http://dx.doi.org/10.1063/1.2822446 (3 pages) | Cited 9 times

Online Publication Date: 7 December 2007

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Owing to the line-to-bump configuration in flip chip solder joints, current crowding occurs when electrons enter into or exit from the solder bump. At the cathode contact, where electrons enter into the bump, current crowding induced pancake-type void formation has now been observed widely. At the anode contact, where electrons exit from the bump, we report here that whisker is formed. Results of both eutectic SnPb and SnAgCu solder joints are presented and compared. The cross-sectioned surface in SnPb showed dimple and bulge after electromigration, while that of SnAgCu remained flat. The difference is due to a larger back stress in the SnAgCu, consequently, electromigration in SnAgCu is slower than that in SnPb. Nanoindentation markers were used to measure the combined atomic fluxes of back stress and electromigration.
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68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
61.72.Qq Microscopic defects (voids, inclusions, etc.)
66.30.Qa Electromigration

Ultrafast switching by controlling Rabi splitting

Gianluca Manzacca, Gabriella Cincotti, and Kurt Hingerl

Appl. Phys. Lett. 91, 231920 (2007); http://dx.doi.org/10.1063/1.2822820 (3 pages) | Cited 10 times

Online Publication Date: 7 December 2007

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We analyze the behavior of a quantum dot embedded in an add-drop filter for optical signal processing applications. The joint effects of dipole induced transparency and electromagnetic induced transparency, which shift the transparency peak induced by a dipole in an add-drop filter due to vacuum Rabi splitting, have been considered. The mathematical model and some different conditions for tuning the transparency peak are derived for application to all optical switching and wavelength tunable devices.
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78.67.Hc Quantum dots
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Qs Photonic bandgap materials

Etching of lithium niobate using standard Ti indiffusion technique

Vijay Sivan, Arnan Mitchell, Lam Bui, Anthony Holland, Suresh Bhargava, and Timothy Priest

Appl. Phys. Lett. 91, 231921 (2007); http://dx.doi.org/10.1063/1.2821111 (3 pages) | Cited 3 times

Online Publication Date: 7 December 2007

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We present evidence of etching LiNbO3 when annealing two wafers in contact with an intermediate Ti strip. Etched features are characterized qualitatively using atomic force microscopy. The impact of the Ti strip thickness on the depth and roughness of the etched surface is quantified. Etched trenches of similar depths to the original Ti film are achieved with very smooth etched surface.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.65.Cf Surface cleaning, etching, patterning
81.40.Gh Other heat and thermomechanical treatments
68.37.Ps Atomic force microscopy (AFM)

Intrinsic lattice thermal conductivity of semiconductors from first principles

D. A. Broido, M. Malorny, G. Birner, Natalio Mingo, and D. A. Stewart

Appl. Phys. Lett. 91, 231922 (2007); http://dx.doi.org/10.1063/1.2822891 (3 pages) | Cited 39 times

Online Publication Date: 7 December 2007

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We present an ab initio theoretical approach to accurately describe phonon thermal transport in semiconductors and insulators free of adjustable parameters. This technique combines a Boltzmann formalism with density functional calculations of harmonic and anharmonic interatomic force constants. Without any fitting parameters, we obtain excellent agreement (<5% difference at room temperature) between the calculated and measured intrinsic lattice thermal conductivities of silicon and germanium. As such, this method may provide predictive theoretical guidance to experimental thermal transport studies of bulk and nanomaterials as well as facilitating the design of new materials.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
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A few-electron vertical In0.56Ga0.44As quantum dot with an insulating gate

T. Kita, D. Chiba, Y. Ohno, and H. Ohno

Appl. Phys. Lett. 91, 232101 (2007); http://dx.doi.org/10.1063/1.2818712 (3 pages)

Online Publication Date: 3 December 2007

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Using an Al2O3 gate insulator by atomic layer deposition and air-bridge drain electrode, we fabricated a quantum dot with few electrons based on an In0.56Ga0.44As resonant tunneling diode structure. Artificial atomic properties manifested themselves in magnetotransport, enabling the determination of effective electron g factors. Results show that the insulating gate structure used here is effective for realizing quantum dots made of narrow-gap semiconductors for studying spin-related phenomena.
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85.30.Kk Junction diodes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Kinetics of Ni3Si2 formation in the Ni2Si–NiSi thin film reaction from in situ measurements

J. A. Kittl, M. A. Pawlak, C. Torregiani, A. Lauwers, C. Demeurisse, C. Vrancken, P. P. Absil, S. Biesemans, C. Detavernier, J. Jordan-Sweet, and C. Lavoie

Appl. Phys. Lett. 91, 232102 (2007); http://dx.doi.org/10.1063/1.2822411 (3 pages) | Cited 3 times

Online Publication Date: 3 December 2007

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The kinetics of Ni3Si2 formation in the Ni2Si–NiSi thin film reaction were determined from simultaneous in situ x-ray diffraction (XRD) measurements, performed using a synchrotron source, and sheet resistance measurements. Samples consisted of 90 nm Ni/100 nm polycrystalline-Si/SiO2 stacks, of interest for fully silicided gate applications, on (100) Si. After initial formation of a Ni2Si/NiSi bilayer, these films reacted to form Ni3Si2. The evolution of sheet resistance and of the intensity of XRD peaks were used to extract the fraction of Ni3Si2 formed during ramp and isothermal annealings. A Kissinger analysis was performed for ramp annealing with ramp rates of 1, 3, 5, 9, and 27 °C/s, obtaining the activation energy of Ni3Si2 formation, Ea = 1.92±0.15 eV. A Kolmogorov-Johnson-Mehl-Avrami analysis was performed for isothermal anneals, finding an Avrami exponent of 2.1±0.2, suggesting two-dimensional growth. This is consistent with a nucleation controlled process for Ni3Si2 formation, with nucleation sites at different positions in the thin film, and subsequent lateral two-dimensional propagation of the transformation front parallel to the film surface. Implications for Ni fully silicided gate applications are discussed.
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81.40.Gh Other heat and thermomechanical treatments
73.61.At Metal and metallic alloys

Low nonalloyed Ohmic contact resistance to nitride high electron mobility transistors using N-face growth

Man Hoi Wong, Yi Pei, Tomás Palacios, Likun Shen, Arpan Chakraborty, Lee S. McCarthy, Stacia Keller, Steven P. DenBaars, James S. Speck, and Umesh K. Mishra

Appl. Phys. Lett. 91, 232103 (2007); http://dx.doi.org/10.1063/1.2820381 (3 pages) | Cited 14 times

Online Publication Date: 3 December 2007

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Nonalloyed Ohmic contacts on Ga-face n+-GaN/AlGaN/GaN high electron mobility transistor (HEMT) structures typically have significant contact resistance to the two-dimensional electron gas (2DEG) due to the AlGaN barrier. By growing the HEMT structure inverted on the N-face, electrons from the contacts were able to access the 2DEG without going through an AlGaN layer. A low contact resistance of 0.16 Ω mm and specific contact resistivity of 5.5×10−7 Ω cm2 were achieved without contact annealing on the inverted HEMT structure.
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85.30.Tv Field effect devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Tungsten nanocrystal memory devices improved by supercritical fluid treatment

C. H. Chen, T. C. Chang, I. H. Liao, P. B. Xi, C. T. Tsai, P. Y. Yang, Joe Hsieh, Jason Chen, U. S. Chen, and J. R. Chen

Appl. Phys. Lett. 91, 232104 (2007); http://dx.doi.org/10.1063/1.2803937 (3 pages) | Cited 3 times

Online Publication Date: 4 December 2007

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A supercritical CO2 (SCCO2) fluid technique is proposed to improve electrical characteristics for W nanocrystal nonvolatile memory devices, since the thickness and quality of tunnel oxide are critical issues for the fabrication of nonvolatile memory devices. After SCCO2 treatments, C-V curves are restored to normal, as well as the leakage current of W nanocrystal memory devices are reduced significantly. It reveals that W nanocrystal memory devices could be formed with shorter oxidation time, moreover, dangling bonds and trapping states initially created within an incomplete oxidized film will be efficiently repaired after SCCO2 treatment.
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85.35.-p Nanoelectronic devices

Kondo effect in a semiconductor quantum dot coupled to ferromagnetic electrodes

K. Hamaya, M. Kitabatake, K. Shibata, M. Jung, M. Kawamura, K. Hirakawa, T. Machida, T. Taniyama, S. Ishida, and Y. Arakawa

Appl. Phys. Lett. 91, 232105 (2007); http://dx.doi.org/10.1063/1.2820445 (3 pages) | Cited 27 times

Online Publication Date: 4 December 2007

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Using a laterally fabricated quantum-dot (QD) spin-valve device, we experimentally study the Kondo effect in the electron transport through a semiconductor QD with an odd number of electrons (N). In a parallel magnetic configuration of the ferromagnetic electrodes, the Kondo resonance at N = 3 splits clearly without external magnetic fields. With applying magnetic fields (B), the splitting is gradually reduced, and then the Kondo effect is almost restored at B = 1.2 T. This means that, in the Kondo regime, an inverse effective magnetic field of B ∼ 1.2 T can be applied to the QD in the parallel magnetic configuration of the ferromagnetic electrodes.
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73.63.Kv Quantum dots
73.40.Sx Metal-semiconductor-metal structures
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)

Metallic conductivity at the CaHfO3/SrTiO3 interface

Keisuke Shibuya, Tsuyoshi Ohnishi, Mikk Lippmaa, and Masaharu Oshima

Appl. Phys. Lett. 91, 232106 (2007); http://dx.doi.org/10.1063/1.2816907 (3 pages) | Cited 9 times

Online Publication Date: 5 December 2007

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The transport and photoluminescence properties of interfaces between amorphous CaHfO3 films and SrTiO3 single crystal substrates were investigated. Although both materials are band-gap insulators, the interfaces were metallic. The sheet carrier density was found to depend strongly on the laser fluence used during the CaHfO3 layer fabrication by pulsed laser deposition, indicating the presence of oxygen vacancies at the interface. The Hall mobility of the heterostructures saturated at 2000 cm2/V s at low temperature. Photoluminescence spectra showed an oxygen vacancy-related emission band at around 420 nm.
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73.40.-c Electronic transport in interface structures
78.55.Hx Other solid inorganic materials
78.66.Nk Insulators
73.61.Ng Insulators
72.20.My Galvanomagnetic and other magnetotransport effects
81.15.Fg Pulsed laser ablation deposition
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