bluuebunny/crossref_metadata_2025 huggingface dataset:
Gain spectroscopy on InGaN/GaN quantum well diodes
Authors: Kuball M. , Jeon E.-S. , Song Y.-K. , Nurmikko A. V. , Kozodoy P. , Abare A. , Keller S. , Coldren L. A. , Mishra U. K. , DenBaars S. P. , Steigerwald D. A.
Published: July 2002

We have investigated spectroscopically the emergence of gain in InGaN/GaN quantum well diodes under high current injection (>kA/cm2). The spectral characteristics suggest that the electronic states responsible for blue laser action in this material are strongly influenced by the presence of microscopic crystalline disorder.
Photorefractive damage removal in annealed-proton-exchanged LiNbO3 channel waveguides
Authors: Robertson Elaine E. , Eason Robert W. , Yokoo Yoshiatsu , Chandler Peter J.
Published: July 2002

Ion beam implantation has been used as a postprocessing technique to dramatically reduce the photorefractive effect in lithium niobate channel waveguides. The waveguides were fabricated by proton exchange and then annealed 1.0 MeV H+ ions were implanted through the existing channel waveguides such that the “damaged layer” was created beneath the existing channel waveguide. The output characteristics from the waveguides were subsequently examined. Highly stable single-mode outputs were observed with the waveguides retaining up to 95% of their original transmission. It is thought that this decrease in photorefractive susceptibility can be explained by the implant changing the defect structure and hence photovoltaic properties of the material.
In situ electron-spin-resonance measurements of film growth of hydrogenated amorphous silicon
Authors: Yamasaki Satoshi , Umeda Takahide , Isoya Junichi , Tanaka Kazunobu
Published: July 2002

In situ electron-spin-resonance (ESR) measurements of film growth of hydrogenated amorphous silicon (a-Si:H) using a remote hydrogen plasma technique have been performed. The Si dangling-bond signal in a-Si:H during and after deposition has been detected, in addition to the gas-phase ESR signals both of atomic hydrogen and radicals related with silane molecules. Dynamic changes of the Si dangling-bond signal intensity have been observed in real-time, where the signal intensity increases with deposition time and decreases after stopping the deposition due to a structural relaxation. High potentiality of in situ ESR techniques for microscopic understanding of film growth and surface reaction has been demonstrated.
Indium diffusion in n-type gallium arsenide
Authors: Li W. M. , Cohen R. M. , Simons D. S. , Chi P. H.
Published: July 2002

Diffusion of indium markers at T=900 °C have been measured in undoped and Te-doped GaAs epilayers grown by organometallic vapor phase epitaxy. The diffusivity was found to be a linear function of electron concentration over the range n=2×1017–1.5×1019 cm−3. The results are consistent with the interdiffusion of AlAs–GaAs superlattices, and the diffusivities of In and Al in GaAs at 900 °C are found to be essentially identical within experimental noise. The results strongly suggest that group III interdiffusion in GaAs is controlled by a Ga vacancy with a charge of −1.
Modeling of stress-induced leakage current in ultrathin oxides with the trap-assisted tunneling mechanism
Authors: Chou Anthony I. , Lai Kafai , Kumar Kiran , Chowdhury Prasenjit , Lee Jack C.
Published: July 2002

Stress-induced leakage current (SILC) in ultrathin oxide metal–oxide–semiconductor devices has been quantitatively modeled by the trap-assisted tunneling mechanism. These results are compared with experimental data on samples with oxide thickness ranging from 40 to 80 Å. This model accurately describes the electric-field dependence of SILC, and also predicts the increase, then decrease in SILC, with decreasing oxide thickness, which is observed experimentally.
Redshifting of a bound-to-continuum GaAs/AlGaAs quantum-well infrared photodetector response via laser annealing
Authors: Sengupta D. K. , Horton T. , Fang W. , Curtis A. , Li J. , Chuang S. L. , Chen H. , Feng M. , Stillman G. E. , Kar A. , Mazumder J. , Li L. , Liu H. C.
Published: July 2002

The effect of laser annealing on important detector characteristics such as dark current, spectral response, and absolute responsivity is investigated for bound-to-continuum GaAs/AlGaAs quantum-well infrared photodetectors (QWIPs) operating in the 8–12 μm wavelength regime. A set of experiments was conducted on QWIPs fabricated from both as-grown and laser-annealed multiple-quantum-well structures. Compared to the as-grown structure, the peak spectral response of the laser-annealed structure was shifted to longer wavelengths, though absolute responsivity was decreased by about a factor of two. In addition, over a wide range of bias levels, the laser-annealed QWIPs exhibited a slightly lower dark current compared to the as-grown QWIPs. Thus, the postgrowth control of GaAs/AlGaAs quantum-well composition profiles by laser annealing offers unique opportunities to fine tune various aspects of a QWIP’s response.
Bright high efficiency blue organic light-emitting diodes with Al2O3/Al cathodes
Authors: Tang H. , Li F. , Shinar J.
Published: July 2002

The behavior of bright, efficient, low-driving-voltage blue organic light-emitting diodes based on amino-oxadiazole-fluorenes (AODFs) with Al2O3/Al cathodes is described. It is shown that the thin Al2O3 buffer layer sharply enhances current injection, increases the device efficiency, and reduces the driving voltage; the performance of devices with the optimal oxide buffer layer thickness approaches those with Mg0.9Ag0.1 cathodes. The effects of the Al2O3 buffer layer are believed to result from the removal of interface gap states induced by defects and chemical bonds between the AODF and Al, which trap carriers and quench singlet excitons nonradiatively.
Optimized growth conditions for the epitaxial nucleation of β-GaN on GaAs(001) by molecular beam epitaxy
Authors: Brandt Oliver , Yang Hui , Trampert Achim , Wassermeier Matthias , Ploog Klaus H.
Published: July 2002

Ultrathin (5–7 monolayers) nucleation layers of GaN are deposited on (2×4)-GaAs(001) by plasma-assisted molecular beam epitaxy. Reflection high-energy electron diffraction applied in situ reveals these layers to be epitaxial β-GaN. Transmission electron microscopy confirms this result and reveals in addition that the layers are highly connected and have an atomically abrupt interface to the GaAs substrate. The rms roughness of these layers, as measured by atomic force microscopy, is as low as 1.4 Å.
“Resonant conducting” in nano-patterning the hydrogen-passivated Si(100) by atomic force microscopy
Authors: Luo E. Z. , Wilson I. H. , Xu J. B. , Ma J. X.
Published: July 2002

By monitoring the electric current image during conducting atomic force microscopy nano-patterning, a phenomenon that we term “resonant conducting” was found. This was characterized by a sharp peak at V=2.45±0.05 V in the averaged current-voltage plot. The electrical current is irreversible and decays very rapidly after repeat scanning, which implies that the resonant current is associated with the transient process from a hydrogen de-passivation to an oxygen passivation under the specific electrical field. On the practical side, “resonant conducting” provides a very sensitive method for visualization of H passivation of silicon on a nano-meter scale.
The effect of surface reconstructions on the surface morphology during in situ etching of GaAs
Authors: Ritz M. , Kaneko T. , Eberl K.
Published: July 2002

The influence of surface reconstructions on the surface morphology during in situ layer-by-layer etching of GaAs(001) has been studied based on the observation of reflection high-energy electron-diffraction measurements. For the etching, AsBr3 is used as a reactive source etchant under solid source molecular beam epitaxy conditions, focusing on a high temperature region in which the etching rate is limited by a supply rate of AsBr3 resulting in a constant value. Despite the fact that the etching starts on a layer-by-layer basis, an initially smooth surface turns considerably rougher depending on the stoichiometry associated with the surface reconstruction. The best morphology after a removal of 250 nm is obtained in the Ga-rich (3×1) reconstruction region close to the phase transition boundary to the As-rich (2×4). This is also verified by the measurement of scanning electron microscopy and atomic force microscopy.
Formation of buried p-type conducting layers in diamond
Authors: Walker R. , Prawer S. , Jamieson D. N. , Nugent K. W. , Kalish R.
Published: July 2002

Deeply buried boron doped layers are realized in single crystal diamond using MeV ion implantation. Contact to the buried layers is accomplished using pulsed focused laser irradiation which is selectively absorbed in the implanted layer to form a graphite column up to the surface. The contacts are ohmic over a wide range of applied voltage. Implantation induced defects that are responsible for compensation of the acceptors are identified. It is found that removal of these defects requires annealing temperatures of about 1450 °C, but once these defects are removed the buried B doped layer displays excellent activation of the acceptors with an activation energy of 0.372 eV.
Trap-mediated excitation of Er3+ photoluminescence in Er-implanted GaN
Authors: Kim S. , Rhee S. J. , Turnbull D. A. , Li X. , Coleman J. J. , Bishop S. G. , Klein P. B.
Published: July 2002

Site-selective photoluminescence (PL) spectra obtained at 6 K from the 1540 nm I413/2→I415/2 emissions characteristic of four distinct Er3+ centers in Er-implanted films of GaN are compared with the Er3+ PL excited by 325 nm above-gap pump light. Two of the site-selective 1540 nm Er3+ PL spectra pumped by below-gap, trap-mediated excitation bands dominate the Er3+ PL spectrum excited by above-gap light. A third broad band-excited spectrum and a fourth spectrum pumped by direct Er3+ 4f-band absorption are apparently not strongly excited by above-gap light. These results indicate that trap-mediated excitation dominates above-gap pumping of Er3+ emission in GaN:Er, and suggest an explanation for the reduced thermal quenching of Er3+ emission in GaN.
Enhanced electron attachment to highly excited molecules using a plasma mixing scheme
Authors: Pinnaduwage Lal A. , Ding Weixing , McCorkle Dennis L.
Published: July 2002

We present preliminary results on a glow discharge-based technique to populate highly excited states of molecules using a novel excitation transfer process, and to efficiently produce negative ions via electron attachment to those excited states.
Nanoscale field-effect transistors: An ultimate size analysis
Authors: Pikus F. G. , Likharev K. K.
Published: July 2002

We have used a simple, analytically solvable model to analyze the characteristics of dual-gate metal-oxide-semiconductor field-effect transistors (MOSFETs) with 10 nm-scale channel length L. The model assumes ballistic dynamics of two-dimensional electrons in an undoped channel between highly doped source and drain. When applied to silicon n-MOSFETs, calculations show that the voltage gain (necessary for logic applications) drops sharply at L∼10 nm, while the conductance modulation remains sufficient for memory applications until L∼4 nm.
Thick stress-free amorphous-tetrahedral carbon films with hardness near that of diamond
Authors: Friedmann T. A. , Sullivan J. P. , Knapp J. A. , Tallant D. R. , Follstaedt D. M. , Medlin D. L. , Mirkarimi P. B.
Published: July 2002

We have developed a process for making thick, stress-free, amorphous-tetrahedrally bonded carbon (a-tC) films with hardness and stiffness near that of diamond. Using pulsed-laser deposition, thin a-tC films (0.1–0.2 μm) were deposited at room temperature. The intrinsic stress in these films (6–8 GPa) was relieved by a short (2 min) anneal at 600 °C. Raman and electron energy-loss spectra from single-layer annealed specimens show only subtle changes from as-grown films. Subsequent deposition and annealing steps were used to build up thick layers. Films up to 1.2 μm thick have been grown that are adherent to the substrate and have low residual compressive stress (<0.2 GPa). The values of hardness and modulus determined directly from an Oliver–Pharr analysis of nanoindentation experimental data were 80.2 and 552 GPa, respectively. We used finite-element modeling of the experimental nanoindentation curves to separate the “intrinsic” film response from the measured substrate/film response. We found a hardness of 88 GPa and Young’s modulus of 1100 GPa. From these fits, a lower bound on the compressive yield stress of diamond (∼100 GPa) was determined.
Red–green–blue light emission from hydrogenated amorphous silicon carbide films prepared by using organic compound xylene as carbon source
Authors: Ma Tianfu , Xu Jun , Chen Kunji , Du Jiafang , Li Wei , Huang Xinfan
Published: July 2002

We fabricated hydrogenated amorphous silicon carbide (a-Si1-XCX:H) films by the plasma-enhanced chemical vapor deposition technique using organic compound xylene (C8H10) as the carbon source, which was initially attempted by W. A. Nevin H. Yamagishi, M. Yamaguchi, and Y. Tawada, Nature 368, 529 (1994). Here we used different preparation conditions from those authors to produce xylene-based a-Si1-XCX:H films, and a different light emission behavior of the films has been observed at room temperature. The light emission wavelength can be shifted from 630 nm to 450 nm by changing the optical band gap (Eopt) of the films from 2.3 eV to 3.5 eV, nearly covering the whole visible light range, which was never reported previously. Fourier transform infrared spectra showed that the configuration of the material was a combination of organic aromatic rings and inorganic SiC networks.
Manipulation of passivated gold clusters on graphite with the scanning tunneling microscope
Authors: Durston P. J. , Palmer R. E. , Wilcoxon J. P.
Published: July 2002

Chemically passivated gold nanoclusters deposited on the surface of graphite have been manipulated with the scanning tunneling microscope (STM) in ultrahigh vacuum. The controlled clearing of a definite shape in a cluster layer is demonstrated. Clusters embedded in a close-packed array could not be removed from the surface, apparently because of the attractive interaction between neighboring ligand chains. A minority channel of cluster fragmentation has been identified and leads to the creation of platelets which can be further manipulated by the STM tip.
Factors affecting resolution in scanning electron beam induced patterning of surface adsorption layers
Authors: Hui Frank Y. C. , Eres Gyula , Joy David C.
Published: July 2002

The monoatomic hydride layer on silicon was used as a prototype for resistless electron beam lithography. Arbitrary patterns with linewidths below 60 nm have been achieved. The variation of the linewidth with electron energy, electron dose, and substrate thickness was studied to determine the mechanisms that govern surface hydrogen desorption and subsequent pattern formation. Unlike in resist based lithography, no resolution enhancement was observed with decreasing substrate thickness. The experimental data in combination with Monte Carlo simulations of the backscattered and transmitted electrons suggest that surface hydrogen desorption and pattern formation are not strongly related to the backscattered electrons and the secondary electrons (energies <50 eV) associated with the backscattered electrons.
Magnetization reversal in submicron magnetic wire studied by using giant magnetoresistance effect
Authors: Ono T. , Miyajima H. , Shigeto K. , Shinjo T.
Published: July 2002

The magnetization reversal phenomenon in a submicron magnetic wire with a trilayer structure consisting of NiFe(200 Å)/Cu(100 Å)/NiFe(50 Å) was investigated by measuring the electric resistance in an external magnetic field. A giant magnetoresistance (GMR) effect of about 0.8% was observed when the magnetizations in two NiFe layers are oriented antiparallel. It is demonstrated that magnetization reversal phenomena can be very sensitively investigated by utilizing the GMR effect.
Chemical vapor deposition of ultrathin Ta2O5 films using Ta[N(CH3)2]5
Authors: Son K.-A. , Mao A. Y. , Sun Y.-M. , Kim B. Y. , Liu F. , Kamath A. , White J. M. , Kwong D. L. , Roberts D. A. , Vrtis R. N.
Published: July 2002

Tantalum oxide films were deposited on Si substrates by chemical vapor deposition using the precursor Ta[N(CH3)2]5, and an oxidizing agent—O2, H2O, or NO. Temperatures ranged between 400 and 500 °C and total pressures between 10−3 and 9 Torr. NO did not lead to satisfactory film growth rates. Insignificant (<1 at. %) N and up to a few percent C are incorporated when O2 is the oxidant and the total pressure is in the Torr regime. In the milliTorr regime, the Ta2O5 films, grown using either O2 or H2O, contain readily detectable amounts of C and N. For the films grown with O2 in the Torr regime, leakage currents were significantly lowered when the flow rate of O2 increased from 100 to 900 sccm.
Investigation of the interface formation between calcium and tris-(8-hydroxy quinoline) aluminum
Authors: Choong V.-E. , Mason M. G. , Tang C. W. , Gao Yongli
Published: July 2002

X-ray and ultraviolet photoemission spectroscopy investigations reveal strong interactions between Ca and tris-(8-hydroxy quinoline) aluminum (Alq3) during the Ca/Alq3 interface formation. The details of the interaction depend on the direction of the interface formation. For the case of Ca deposited on Alq3, a staged interface reaction is observed. For low Ca coverages (ΘCa⩽4 Å), negatively charged Alq3 radical anions are formed by electron transfer from the Ca. The emergence of new states in the energy gap is observed in the UPS spectra. At higher coverages, the Ca reacts with the phenoxide oxygen resulting in the decomposition of the Alq3 molecule. On the other hand, for the case of Alq3 deposited on Ca, a strong chemical reaction takes place as soon as Alq3 is deposited, and Ca attacks every constituent of Alq3. Finally, no interaction occurs between Alq3 and the Ca substrate if the substrate has been passivated by oxygen prior to the Alq3 deposition.
Controlled spontaneous lifetime in microcavity confined InGaAlAs/GaAs quantum dots
Authors: Graham L. A. , Huffaker D. L. , Deng Q. , Deppe D. G.
Published: July 2002

Controlled spontaneous lifetimes are demonstrated in InGaAlAs/GaAs quantum dots confined in planar microcavities. Due to their independent and spectrally sharp light emission, the quantum dot emitters provide an excellent means for studying the spontaneous lifetime dependence on microcavity tuning, while maintaining experimental parameters such as temperature and pump intensity constant. The measured lifetime changes are compared with calculated results and show good agreement.
Hydrogen poor cationic silicon clusters in an expanding argon–hydrogen–silane plasma
Authors: Kessels W. M. M. , van de Sanden M. C. M. , Schram D. C.
Published: July 2002

Cationic silicon clusters SinHm+ with up to ten silicon atoms have been detected mass spectrometrically in an expanding argon–hydrogen–silane plasma used for fast deposition of amorphous hydrogenated silicon. A reaction pathway is proposed in which initial silane ions are produced by dissociative charge exchange between argon and hydrogen ions emanating from the plasma source and the admixed silane followed by chain reactions of the created ions with silane. The silicon clusters are hydrogen poor, which is ascribed to the high gas temperature as the initial argon–hydrogen plasma is thermal in origin.
Band edge versus deep luminescence of InxGa1−xN layers grown by molecular beam epitaxy
Authors: Grandjean N. , Massies J. , Leroux M. , De Mierry P.
Published: July 2002

In x Ga 1−x N  (0<x<0.2) thin layers were grown on GaN-coated sapphire substrates by molecular beam epitaxy (MBE) using ammonia as the nitrogen source. Their optical properties have been investigated by low- and room-temperature photoluminescence (PL) and photothermal deflection spectroscopy. It is shown that high-quality InxGa1−xN layers with x∼0.1 can be grown by MBE using NH3. The PL linewidths are 48 and 80 meV at 9 and 300 K, respectively. A bowing parameter of 1 eV is deduced for the band-edge luminescence energy. On the other hand, when the growth conditions slightly move aside the optimum, the PL spectra exhibit broad and deep luminescence. The variation of the PL energy of this deep luminescence as a function of the In composition is then discussed.
Photoacoustic phase transition of the ceramic BaTiO3
Authors: Castañeda-Guzmán R. , Villagrán-Muniz M. , Saniger-Blesa J. M. , Pérez-Martı́nez O.
Published: July 2002

Photoacoustic signals from the ceramic BaTiO3 are analyzed, as a function of temperature close to structural phase transition from tetragonal to cubic at 110 °C. The amplitude of the signals depends on the changes of the thermoelastic properties in the ceramic with temperature. The Curie temperature value for the phase change was reproducible and was found to be 109±6 °C. A comparative analysis of this result with the differential thermal analysis and permittivity techniques is performed. Two changes of sign in the photoacoustic signal are observed, associated with the thermal expansion coefficient behavior in this material near the transition.
Microwave near-field imaging of electric fields in a superconducting microstrip resonator
Authors: Thanawalla Ashfaq S. , Dutta S. K. , Vlahacos C. P. , Steinhauer D. E. , Feenstra B. J. , Anlage Steven M. , Wellstood F. C. , Hammond Robert B.
Published: July 2002

We describe the use of a cryogenic near-field scanning microwave microscope to image microwave electric fields from superconducting and normal-metal microstrip resonators. The microscope employs an open-ended coaxial probe and operates from 77 to 300 K in the 0.01–20 GHz frequency range with a spatial resolution of about 200 μm. We describe the operation of the system and present microwave images of Cu and Tl2Ba2CaCu2O8 microstrip resonators, showing standing wave patterns at the fundamental and second harmonic frequencies.
A photomodulated reflectance study of InAs/GaAs self-assembled quantum dots
Authors: Rowland G. L. , Hosea T. J. C. , Malik S. , Childs D. , Murray R.
Published: July 2002

Photomodulated reflectance (PR) spectra have been measured for self-assembled InAs/GaAs quantum dot (QD) structures consisting of a pair of QD layers, with a GaAs spacer either 50 or 100 Å thick. The PR clearly reveals five confined-state QD transitions, at both 80 and 300 K, as well as features from the two-dimensional confining and GaAs layers. The measured QD transition energies correlate well with photoluminescence spectra at 13 K, using high laser excitation powers to incur level filling. Annealing one of the samples produces a strong blueshift in the QD transitions.
Measurement of gain current relations for InGaN multiple quantum wells
Authors: Abare A. C. , Mack M. P. , Hansen M. , Speck J. S. , Coldren L. A. , DenBaars S. P. , Meyer G. A. , Lehew S. L. , Cooper G. A.
Published: July 2002

Pulsed operation of in-plane laser diodes with InGaN multiple quantum well active regions was achieved. For uncoated chemically assisted ion beam etched facets, we obtained threshold current densities as low as 10.6 kA/cm2. The external differential quantum efficiency dependence on bar length was used to determine the internal optical loss and internal quantum efficiency of these devices and to calculate the modal gain in the device as a function of the terminal current density. Values of facet reflection were determined by a self-consistent analysis. We have measured 90 cm−1 of modal gain and estimate material gain exceeding 900 cm−1, at 20 kA/cm2.
Finite-element modeling of diamond deformation at multimegabar pressures
Authors: Merkel Sébastien , Hemley Russell J. , Mao Ho-kwang
Published: July 2002

Finite-element modeling calculations reveal the origin of the remarkably large elastic strains in diamond observed in recent experiments at multimegabar pressures. This approach provides a means to determine the pressure dependence of the yield strength of strong materials used in the gasket, and allows us to examine quantities that are not accessible experimentally such as the stress and strain relations in diamond. Stress tensor elements are obtained near the tip where large modifications in the optical properties of diamond have been observed.
Formation of aluminum oxynitride diffusion barriers for Ag metallization
Authors: Wang Y. , Alford T. L.
Published: July 2002

Aluminum oxynitride (AlxOyNz) diffusion barriers have been formed in the temperature range of 400–725 °C by annealing Ag/Al bilayers on oxidized Si substrates in an ammonia (NH3) ambient. Rutherford backscattering spectrometry showed that the out-diffused Al reacted with ammonia and oxygen in the ambient and encapsulated the Ag films. The resulting Ag resistivity values are 1.75±0.35 μΩ cm. Higher processing temperatures and thinner original Al layers showed to improve the resistivity of the encapsulated Ag layers. The thermal stability of these diffusion barriers was evaluated by depositing 50 nm of Cu films onto the encapsulated samples, and then annealing in either vacuum or flowing He-0.5%H2. Results showed that these barriers sustained interdiffusion between Cu and Ag up to 620 °C at least for 30 min in either ambient. This temperature is a 200 °C improvement over previously reported values for the self-encapsulated Cu and Ag films.
Time-resolved photoluminescence studies of an ionized donor-bound exciton in GaN
Authors: Mair R. A. , Li J. , Duan S. K. , Lin J. Y. , Jiang H. X.
Published: July 2002

Time-resolved photoluminescence (PL) spectroscopy has been used to study the radiative recombination of excitons bound to ionized donors in GaN doped with both Mg and Si at concentrations of 5×1018/cm3 and 1.5×1017/cm3, respectively. Low temperature (T∼10K) time-resolved, as well as integrated PL spectra, identify an ionized donor-bound (Si) exciton peak (D+X) approximately 11.5 meV below and a neutral acceptor-bound exciton (A0X) 20.5 meV below the free exciton peak. Rapid decay of the free exciton emission (⩽20 ps) implies that excitons are quickly captured by acceptors and ionized donors. We find the (A0X) emission lifetime is consistent with previous measurements for GaN:Mg epilayers, while the (D+X) lifetime of 160 ps is longer than that of the well studied neutral donor-bound exciton (D0X). The measured (D+X) lifetime, in comparison with (D0X) and (A0X), suggests that the state is stable at low temperature.
Charge sensitivity of radio frequency single-electron transistor
Authors: Korotkov Alexander N. , Paalanen Mikko A.
Published: July 2002

A theoretical analysis of the charge sensitivity of the radio frequency single-electron transistor (rf-SET) is presented. We use the “orthodox” approach and consider the case when the carrier frequency is much less than I/e where I is the typical current through rf-SET. The optimized noise-limited sensitivity is determined by the temperature T, and at low T it is only 1.4 times worse than the sensitivity of conventional single-electron transistor.
Third-order susceptibilities of asymmetric pentaazadentate porphyrin-like metal complexes
Authors: Sun Wenfang , Byeon Clare C. , Lawson Chris M. , Gray Gary M. , Wang Duoyuan
Published: July 2002

The third-order nonlinear optical properties of a series of asymmetric pentaazadentate porphyrin-like metal complexes ([(R–APPC)M]Cln) with different conjugated R groups and metal centers have been investigated by degenerate four wave mixing experiments using 40 ps laser pulses at 532 nm. The molecular second-order hyperpolarizabilities (γ) for these complexes range from 1.1×10−31 to 1.2×10−30 esu and depend strongly on both the nature of the metal and the R group. The γ values of the [(R–APPC)Cd]Cl complexes are 2–7 times larger than those of PbPc(CP)4 and SiNc, two of the most promising nonlinear optical materials for optical limiting applications. Measurements of the individual components of the χ(3) tensor indicate that the nonlinearity is predominantly electronic in origin when 40 ps laser pulses are used.
Observation of growth modes during metal-organic chemical vapor deposition of GaN
Authors: Stephenson G. B. , Eastman J. A. , Thompson C. , Auciello O. , Thompson L. J. , Munkholm A. , Fini P. , DenBaars S. P. , Speck J. S.
Published: July 2002

We present real-time surface x-ray scattering measurements during homoepitaxial growth of GaN by metal-organic chemical vapor deposition. We observed intensity oscillations corresponding to the completion of each monolayer during layer-by-layer growth. The growth rate was found to be temperature independent and Ga-transport limited. Transitions between step-flow, layer-by-layer, and three-dimensional growth modes were determined as a function of temperature and growth rate.
Subnanosecond magnetization dynamics measured by the second-harmonic magneto-optic Kerr effect
Authors: Crawford T. M. , Silva T. J. , Teplin C. W. , Rogers C. T.
Published: July 2002

We have measured the in-plane magnetization dynamics of Ni81Fe19 films using the surface- and interface-sensitive second-harmonic magneto-optic Kerr effect. The dynamical magnetization was measured on patterned Ni81Fe19 stripes as a function of an in-plane magnetic field applied parallel to the anisotropy axis. The excitation sources were 100 ps risetime magnetic field impulses and steps. The minimum magnetization switching times were <300 ps, and precessional free-induction decay was observed. The dynamics for both impulse and step excitation are fitted to the Landau–Lifshitz equation, yielding values for the anisotropy field, gyroscopic splitting factor, and damping. The local surface precessional frequency and anisotropy are different from the average bulk values, demonstrating that this technique possesses the necessary sensitivity to detect variations in localized surface and interface dynamics.
Ultraviolet-light-enhanced luminescence in SiC thin films grown on Si by hot filament chemical vapor deposition and ultraviolet-light-induced luminescence in anodized SiC
Authors: Wang J. N. , Chen Z. M. , Woo P. W. , Ge W. K. , Wang Y. Q. , Yu M. B.
Published: July 2002

Intense wide-band photoluminescence (PL) was observed at room temperature from both SiC thin films grown on silicon substrates by hot-filament chemical vapor deposition and anodized SiC thin films formed by electrochemical anodization in HF–ethanol solution. It was found that prolonged irradiation with ultraviolet light from a He–Cd laser (325 nm, 10 mW) generally enhanced the PL intensity of as-grown SiC but induced a new PL band in anodized SiC at room temperature. The light-induced PL emission in anodized SiC was centered at the energy between 2.1 and 2.2 eV in comparison with the initial peak position of about 1.9 eV. These effects were also temperature dependent.
Evidence for multiple atomic structure for the {101̄0} inversion domain boundaries in GaN layers
Authors: Potin V. , Nouet G. , Ruterana P.
Published: July 2002

Atomic structure investigation has been carried out on {101̄0} inversion domain boundaries in GaN layers grown by molecular beam epitaxy. A method based on the comparison of the stacking sequences of GaN on both sides of the boundary is proposed in order to distinguish between different models. Experimental evidence is shown for two atomic configurations of the boundary plane. Depending probably on the growth conditions, the Holt model, which has been theoretically characterized as highly energetic, can also exist for the {101̄0} inversion domain boundaries in GaN epitaxial layers.
The inverse Meyer–Neldel rule in thin-film transistors with intrinsic heterogeneous silicon
Authors: Meiling H. , Schropp R. E. I.
Published: July 2002

The electron transport in undoped heterogeneous silicon deposited by hot-wire chemical vapor deposition is found to exhibit conventional as well as greatly pronounced inverse Meyer–Neldel behavior, when including this type of silicon in a field-effect device. The heterogeneous nature of the semiconductor in the channel region near to the gate insulator allows the Fermi level to be pushed deeply into the conduction-band tail states of the amorphous constituent of the material, which is the transport-limiting phase. By considering the band alignment at the interface of the crystalline inclusions and the amorphous phase, the occurrence of an activation energy smaller than 0.1 eV (required to observe the inverse Meyer–Neldel behavior) can be expected.
On-line laser photoacoustic detection of ethene in exhaled air as biomarker of ultraviolet radiation damage of the human skin
Authors: Harren F. J. M. , Berkelmans R. , Kuiper K. , te Lintel Hekkert S. , Scheepers P. , Dekhuijzen R. , Hollander P. , Parker D. H.
Published: July 2002

The exhaled air and volatile emission by the skin of human subjects were analyzed for traces of ethene (C2H4) by means of CO2 laser photoacoustic trace gas detection. Due to the extreme sensitivity of the detection system (6 part per trillion volume, 6:1012), these measurements could be performed on-line and noninvasively. Exhaled ethene was used as a biomarker for lipid peroxidation in the skin of human subjects exposed to ultraviolet (UV) radiation from a solarium. A change in the ethene concentration was already observed in the exhaled air after 2 min. Adaptation of the skin to UV exposure and direct skin emission could also be observed.
Boron-enhanced diffusion of boron from ultralow-energy ion implantation
Authors: Agarwal Aditya , Gossmann H.-J. , Eaglesham D. J. , Herner S. B. , Fiory A. T. , Haynes T. E.
Published: July 2002

We have investigated the diffusion enhancement mechanism of boron-enhanced diffusion (BED), wherein boron diffusivity is enhanced four to five times over the equilibrium diffusivity at 1050 °C in the proximity of a silicon layer containing a high boron concentration. It is demonstrated that BED is driven by excess interstitials injected from the high boron concentration layer during annealing. For evaporated layers, BED is observed above a threshold boron concentration between 1% and 10%, though it appears to be closer to 1% for B-implanted layers. For sub-keV B implants above the threshold, BED dominates over the contribution from transient-enhanced diffusion to junction depth. For 0.5 keV B, this threshold implantation dose lies between 3×1014 and 1×1015 cm−2. It is proposed that the excess interstitials responsible for BED are produced during the formation of a silicon boride phase in the high B concentration layers.
Atomic force microscopy of work functions on the nanometer scale
Authors: O’Boyle M. P. , Hwang T. T. , Wickramasinghe H. K.
Published: July 2002

The Kelvin probe force microscope, introduced some years ago, has opened up several avenues of investigation. In this letter, we demonstrate that the technique is capable of distinguishing constituents of a metal alloy through their work-function differences. The intermetallics in the alloy are clearly resolved. We discuss the basic principles of the measurement technique and present our results on aluminum/copper surfaces. The limits of the technique are also discussed.
Vacuum-tunneling magnetoresistance: The role of spin-polarized surface states
Authors: Wiesendanger R. , Bode M. , Getzlaff M.
Published: July 2002

We have studied magnetoresistance effects in Fe–vacuum–Gd tunnel junctions as a function of the applied bias voltage by using a scanning tunneling microscope operated under ultra-high-vacuum conditions. We found that the vacuum-tunneling magnetoresistance (VTMR) can be maximized by tunneling into highly spin-polarized surface states. By tuning the applied bias to the energetic positions of the spin-polarized surface states, a VTMR response as much as 31% at 70 K was obtained. This result is explained in terms of an enhancement caused by the spin-polarized surface state and a suppression of spin-flip tunneling processes compared to tunnel junctions with oxide barriers.
Carrier transport through boron-doped amorphous diamond-like carbon p layer of amorphous silicon based p–i–n solar cells
Authors: Lee Chang Hyun , Lim Koeng Su
Published: July 2002

The current transport mechanisms in boron-doped amorphous diamond-like carbon (p-a-DLC:H) used as part of the p layer of hydrogenated amorphous silicon (a-Si:H) solar cells are investigated by studying the temperature dependence of the dark current–voltage characteristics of the solar cell. The cell structure is glass/SnO2/p-a-DLC:H/p-a-SiC:H/i-a-Si:H/n-μc-Si:H/Al. The temperature dependence of the reverse saturation current and the ideality factor shows that carriers transport dominantly over the p-a-DLC:H by thermionic emission at higher temperatures above about 300 K and through the tunneling process by a hopping mechanism in the p-a-DLC:H at lower temperatures. Using the Schottky barrier model, it is shown that the lowering of the Schottky barrier height by inserting the interfacial p-a-DLC:H between the SnO2 and p-a-SiC:H causes the open circuit voltage and the short wavelength response of the cells to be enhanced.
Patterning of (Pb, La)(Zr, Ti)O3 waveguides for fabricating micro-optics using wet etching and solid-phase epitaxy
Authors: Nashimoto K. , Haga K. , Watanabe M. , Nakamura S. , Osakabe E.
Published: July 2002

The patterning process of (Pb, La)(Zr, Ti)O3 heterostructure waveguides was examined for fabricating micro-optics, including channels and lenses. After the patterning of the amorphous thin films derived from spin-cast methoxyethoxide precursors by a wet etching, the patterned amorphous film was crystallized by solid-phase epitaxy. A 5-μm-wide ridge-type channel waveguide was fabricated in a Pb0.91La0.09(Zr0.65Ti0.35)O3/Pb(Zr0.52Ti0.48)O3 heterostructure on a SrTiO3 (100) substrate by the process. The optical confinement was successfully observed. A mode index lens was also fabricated in the Pb0.91La0.09(Zr0.65Ti0.35)O3/Pb(Zr0.30Ti0.70)O3 heterostructure on the SrTiO3 (100) substrate. A deflection of the collimated light by the lens was observed.
Bound-to-continuum intersubband photoconductivity of self-assembled InAs quantum dots in modulation-doped heterostructures
Authors: Lee S.-W. , Hirakawa K. , Shimada Y.
Published: July 2002

We have designed and fabricated a quantum dot infrared photodetector which utilizes the lateral transport of photoexcited carriers in the modulation-doped AlGaAs/GaAs two-dimensional (2D) channels. A broad photocurrent signal has been observed in the photon energy range of 100–300 meV due to the bound-to-continuum intersubband absorption of normal incidence radiation in the self-assembled InAs quantum dots. A peak responsivity was as high as 4.7 A/W. The high responsivity is realized mainly by a high mobility and a long lifetime of photoexcited carriers in the modulation-doped 2D channels. Furthermore, it is found that the observed photosensitivity survives up to 190 K.
Fine structures of photoresponse spectra in quantum well infrared photodetector
Authors: Li Ning , Fu Y. , Karlsteen M. , Willander M. , Li Na , Liu X. Q. , Yuan X. Z. , Lu W. , Shen S. C.
Published: July 2002

We study the fine structures in the photoresponse spectra of GaAs/AlGaAs quantum well infrared photodetectors and the influences from γ irradiation (1-16 Mrad), rapid time annealing (800, 850 and 900 °C for 30 s) and ion implantation (450 keV 0.7×, 1.0× and 5.0×1015 cm−2). With the theoretical analysis a ±-monolayer change has been concluded in the well width of the as-grown GaAs quantum wells in our photodetector. The γ irradiation decreases the carrier lifetime (the relaxation energy Γ increases with the irradiation dose α in the manner of Γ∝α1.5), while the rapid thermal annealing and ion-implantation processes enhance the Al diffusion across the GaAs/AlGaAs heterointerfaces the relaxation energy increases at the same time.
Switching asymmetries in closely coupled magnetic nanostructure arrays
Authors: Dunin-Borkowski R. E. , McCartney M. R. , Kardynal B. , Smith David J. , Scheinfein M. R.
Published: July 2002

Cobalt nanostructures (220 and 300 nm×275 nm×30 nm) were fabricated using electron beam lithography into ordered, close proximity (170 nm) arrays. Domain configurations with accompanying hysteresis loops were measured using off-axis electron holography. Measurements were compared to solutions of the Landau–Lifshitz–Gilbert equations. Both exhibit switching asymmetries due to strong intercell coupling and the presence of a field normal to the cell surface. Magnetic domain configurations during switching depended strongly on the initial conditions, as well as the direction of the perpendicular field relative to the in-plane hysteresis-field direction.
Dynamic response of the electro-optic effect in epitaxial KNbO3
Authors: Hoerman B. H. , Nichols B. M. , Nystrom M. J. , Wessels B. W.
Published: July 2002

The dynamic response of the electro-optic coefficient of epitaxial KNbO3 thin films was measured at room temperature. The effective electro-optic coefficient for these films at 100 kHz is 12 pm/V. The magnitude of the electro-optic response increased by seventy percent as the duration of the applied field was increased from 10 ns to 10 μs. A dispersion of the electro-optic coefficient is observed which follows a power law given by Atm.
Optimization of blazed quantum-grid infrared photodetectors
Authors: Rokhinson L. P. , Chen C. J. , Choi K. K. , Tsui D. C. , Vawter G. A. , Yan L. , Jiang M. , Tamir T.
Published: July 2002

In a quantum-grid infrared photodetector (QGIP), the active multiple quantum well material is patterned into a grid structure. The purposes of the grid are, on the one hand, to create additional lateral electron confinement and, on the other, to convert part of the incident light into parallel propagation. With these two unique functions, a QGIP allows intersubband transition to occur in all directions. In this work, we focused on improving the effectiveness of a QGIP in redirecting the propagation of light using a blazed structure. The optimization of the grid parameters in terms of the blaze angle and the periodicity was performed by numerical simulation using the modal transmission-line theory and verified by experiment. With a blazed structure, the sensitivity of a QGIP can be improved by a factor of 1.8 compared with a regular QGIP with rectangular profiles.
Size dependence of the energy relaxation in silver nanoparticles embedded in dielectric matrices
Authors: Halté V. , Bigot J.-Y. , Palpant B. , Broyer M. , Prével B. , Pérez A.
Published: July 2002

The electron dynamics is studied in silver nanoparticles of different sizes embedded either in a silicate glass or in a porous alumina matrix, using time-resolved optical spectroscopy. The femtosecond pump–probe measurements, made under various conditions of excitation, reveal that the energy relaxation is faster as the particle size decreases. For particles with identical size and excitation conditions, the relaxation time is found to be faster for clusters in the alumina matrix. The influence of the surface acoustic modes and of the heat conductivity of the matrix on the energy relaxation is discussed.
Relaxation of an epitaxial InGaAs film on a thin twist-bonded (100) GaAs substrate
Authors: Senz St. , Kästner G. , Gösele U. , Gottschalch V.
Published: July 2002

A 30 nm (100) GaAs layer was transferred by twist wafer bonding to a (100) GaAs handling wafer. A similar structure was proposed in the literature as a “compliant substrate.” Transmission electron microscopy and x-ray diffraction of 40 and 300 nm epitaxial InGaAs films (0.5% misfit) showed no evidence of a relaxation mechanism specifically attributed to a compliant substrate. The 40 nm film was nearly pseudomorphic without any evidence of a relaxation mechanism, like grain-boundary sliding. The possibility of grain-boundary slip along the twist-bonded interface is discussed.
Structures and optical properties of silicon nanocrystallites prepared by pulsed-laser ablation in inert background gas
Authors: Suzuki Nobuyasu , Makino Toshiharu , Yamada Yuka , Yoshida Takehito , Onari Seinosuke
Published: July 2002

Silicon (Si) nanocrystallites have been synthesized using pulsed-laser ablation in inert background gases, for studying the structures and optical properties as one of the quantum confinement effects. We extracted a process condition where well-dispersed Si nanocrystallites devoid of droplets and debris are prepared, by varying excitation laser conditions. Furthermore, we investigate the influence of the inert background gas pressures on transition from amorphous-like thin films to nanocrystallites. It was clarified that there is a processing window of the inert background gas pressure in which the quantum confinement effects for carriers and phonons become apparent.
Effects of alloy disorder on the transport properties of AlxGa1−xN epilayers probed by persistent photoconductivity
Authors: Zeng K. C. , Lin J. Y. , Jiang H. X.
Published: July 2002

The effects of alloy fluctuations on the transport properties of AlxGa1−xN alloys (x∼0.35) have been probed through the use of persistent photoconductivity (PPC). In the PPC state, the electron mobility, μe, as a function of electron concentration, n, in a single sample can be obtained under controlled light illumination conditions. It was found that μe is a constant when n is below a critical value nc and it then increases with n at n>nc. This mobility behavior was attributed to the effects of alloy fluctuations in AlxGa1−xN alloys. As a result, the initial PPC buildup kinetics seen in AlxGa1−xN alloys was quite different from those in better understood semiconductor alloys, such as AlGaAs and ZnCdSe, and is a direct consequence of the observed unique dependence of μe on n. From these measurements, the total density of the tail states below the mobility edge in the conduction band was estimated to be 1.46×1017 cm−3 in a Al0.35Ga0.65N sample. The results were compared with those in II–VI semiconductor alloys and their implications on III-nitride device applications were discussed.
Effects of energy back transfer on the luminescence of Yb and Er ions in YAG
Authors: Vega-Durán J. T. , Barbosa-Garcı́a O. , Diáz-Torres L. A. , Meneses-Nava M. A. , Sumida D. S.
Published: July 2002

The back-energy-transfer process from acceptors to donors is included to predict and explain the nonradiative energy-transfer processes among Yb–Er ions in a YAG matrix. This process is in addition to the direct Yb-to-Er energy transfer and the migration of energy among Yb ions. The two measured Yb transients are well fitted by the corresponding solution of the master equations that give the dynamics of the energy-transfer processes.
Gigantic resistivity and band gap changes in GdOyHx thin films
Authors: Miniotas A. , Hjörvarsson B. , Douysset L. , Nostell P.
Published: July 2002

In this letter we show that GdOyHx thin films allow one to tailor the electric and the optical properties by controlling the hydrogen and oxygen content. By changing the O/H ratio, one can shift the optical band gap from 2.4 eV in the trihydride to 5.4 eV in the pure oxide. The GdOxHy (x<1.5, y<2) thin films are insulating, and a resistivity as high as 1010 Ω cm, as compared to 10−4 Ω cm in the metallic state, is obtained. The thermal stability of the films depends strongly on the oxygen concentration. Samples with low oxygen content can be switched between the insulating and conducting state by reducing the hydrogen content. A reversible resistivity change of 106 Ω cm is demonstrated.