bluuebunny/crossref_metadata_2025 huggingface dataset:
Room-temperature diode-pumped continuous-wave SrY4(SiO4)3O: Yb3+, Er3+ crystal laser at 1554 nm
Authors: Souriau J. C. , Romero R. , Borel C. , Wyon C. , Li C. , Moncorgé R.
Published: July 2002

Continuous-wave (cw) laser operation at room temperature of an Yb3+, Er3+ doped oxyapatite single crystal SrY4(SiO4)3O pumped at 980 nm by an InGaAs diode laser has been achieved around the eye-safe laser wavelength of 1554 nm.
Degradation of rapid thermal oxides due to the presence of nitrogen in the oxidation ambient
Authors: Hames G. A. , Wortman J. J. , Beck S. E. , Bohling D. A.
Published: July 2002

Ultrathin rapid thermal oxides have been formed in oxygen with varying levels of nitrogen incorporated into the oxidation ambient. Metal-oxide-semiconductor capacitors were subsequently fabricated and tested. It was observed that the interface trap density and the frequency of low field breakdowns increased with increasing nitrogen concentration in the oxidation ambient. No improvement in the interface state generation rate due to nitrogen incorporation in the oxidation ambient was observed in this study.
Infrared luminescence of residual iron deep level acceptors in gallium nitride (GaN) epitaxial layers
Authors: Baur J. , Maier K. , Kunzer M. , Kaufmann U. , Schneider J. , Amano H. , Akasaki I. , Detchprohm T. , Hiramatsu K.
Published: July 2002

A characteristic infrared luminescence band, dominated by a zero-phonon line at 1.30 eV has been consistently detected in gallium nitride (GaN) epitaxial layers. It is assigned to the intra-3d-shell transitions 4T1(G)→6A1(S) of omnipresent iron trace impurities, Fe3+Ga(3d5). Another infrared emission is often also observed at 1.19 eV. This is tentatively assigned to chromium trace impurities, Cr4+Ga(3d2). The role of iron and chromium as minority-carrier lifetime killers in GaN-based optoelectronic devices is suggested from these data.
Strained state of Ge(Si) islands on Si: Finite element calculations and comparison to convergent beam electron-diffraction measurements
Authors: Christiansen S. , Albrecht M. , Strunk H. P. , Maier H. J.
Published: July 2002

In this letter we present calculations by three-dimensional finite element method and measurements by convergent beam electron diffraction of the displacement field resulting from misfitting Ge0.85Si0.25 islands on Si(001). A good agreement between the results of both methods indicates that the three-dimensional finite element method is a reliable tool to calculate the strain, and thus the stress field, in such nanostructures. As a result both methods show that the substrate substantially takes part in the elastic relaxation process in such heteroepitaxial systems.
Blue light generation using bulk single crystals of niobium-doped KTiOPO4
Authors: Cheng L. T. , Cheng L. K. , Harlow R. L. , Bierlein J. D.
Published: July 2002

We report here new solid-solution KTiOPO4 (KTP) isomorphs, namely K1−xNbxTi1−xOPO4 and K1−xTaxTi1−xOPO4, suitable for the second-harmonic generation (SHG) of blue light. Aliovalent substitution of the Ti4+-K+ pair in KTP with Nb5+ or Ta5+ increases substantially the optical birefringence (nz−ny,x) of KTP, and blueshifts the SHG cutoff wavelengths for propagation along the x and y axes. A birefringence increase of ∼70%, and a SHG cutoff wavelength as short as 892 nm have been experimentally observed in crystals of K1−xNbxTi1−xOPO4. Detailed single-crystal x-ray structure determination reveals that the Nb substitution is ordered, with Nb strongly favoring the cis-Ti(1) sites. We discuss possible correlation between this preferential substitution and the observed compositional dependence of nonlinear susceptibilities d24, and d15. Optimal solid-solution compositions for the noncritically phase-matched frequency doubling of the 1.064 and 0.946 μm lines of Nd:YAG lasers are presented, and potential applications for these new materials are outlined.
Thin SiC films prepared by pyrolysis of polyimide Langmuir–Blodgett films on silicon
Authors: Yang Beifang , Zhou Yue , Cai Weili , He Pingsheng , Ruan Yaozhong , Huang Yunlan , Liu Xianming , Zhou Guien
Published: July 2002

The quasi-single-crystal SiC thin films were grown on silicon (111) by pyrolysis of polyimide LB films at 1000 °C in vacuum. The chemical and structural characterizations were studied by x-ray diffraction, infrared absorption, x-ray photoelectron spectroscopy, and Laue photography.
Room-temperature electroluminescence at wavelengths of 5–7 μm from HgCdTe heterostructure diodes
Authors: Ashley T. , Elliott C. T. , Gordon N. R. , Hall R. S. , Maxey C. D. , Matthews B. E.
Published: July 2002

Room-temperature electroluminescence at peak wavelengths of 5–7 μm has been observed in metalorganic vapor phase epitaxy-grown mercury cadmium telluride, fully impurity doped, heterostructure, mesa diodes. The internal quantum efficiency at low injection for 5 μm emission is around 4×10−4. Maximum output power at 295 K is 6 nW from an 80 μm diameter device (120 μW cm−2) at 50% duty cycle. The dependence of intensity on current, the emission spectra, and an infrared microscope image of the emission are presented.
Low pressure microwave electron cyclotron resonance plasma deposition of amorphous Ta2O5 films
Authors: Laviale D. , Oberlin J. C. , Devine R. A. B.
Published: July 2002

Deposition of Ta2O5 from Ta(OC2H5)5 and O2 has been studied using a distributed electron cyclotron resonance plasma. Carbon contamination levels as low as 1.5% have been obtained when the Ta(OC2H5)5 vapor is introduced ‘‘downstream’’ away from the plasma volume. Electrical measurements (current density/voltage, capacitance/voltage) suggest the films have dielectric constants ∼22 and leakage currents ∼10−10 A cm−2 for 2 V operation (50 nm thick, 10 nm a-SiO2 equivalent). These values are obtained without the necessity for high temperature annealing and recrystallization. The conduction mechanism is attributed to the Poole–Frenkel effect.
Dependence on the In concentration of the piezoelectric field in (111)B InGaAs/GaAs strained heterostructures
Authors: Sánchez-Rojas J. L. , Sacedón A. , González-Sanz F. , Calleja E. , Muñoz E.
Published: July 2002

A series of (111)B InxGa1−xAs/GaAs multiple quantum well p-i-n structures have been investigated via low temperature photocurrent and photoluminescence spectroscopies. The indium mole fraction was in the range of 0.07–0.23. Evolution of the experimental blueshifts of the transition energies, with the external bias, agreed very well with the theoretical calculations. This allowed us to obtain precise information about the piezoelectric constant, e14, for the various In compositions. For the range of x investigated, we have found e14(x) to be linear with x but significantly lower than predicted by a simple linear interpolation of the accepted values for GaAs and InAs.
Midinfrared lead salt multi-quantum-well diode lasers with 282 K operation
Authors: Shi Z. , Tacke M. , Lambrecht A. , Böttner H.
Published: July 2002

IV-VI multiple-quantum-well lasers with seven wells made from molecular-beam-epitaxy grown PbSe/PbSrSe have been operated in pulsed mode up to 282 K at a wavelength of λ=4.2 μm. This is the highest midinfrared quantum well laser operation temperature observed to date.
Bias-enhanced nucleation of highly oriented diamond on titanium carbide (111) substrates
Authors: Wolter S. D. , McClure M. T. , Glass J. T. , Stoner B. R.
Published: July 2002

The bias-enhanced nucleation (BEN) technique has been applied to TiC(111) substrates and resulted in deposition of oriented diamond particles. The orientation was observed via scanning electron microscopy. A dense region of oriented particles was not observed on the samples, presumably due to the excessive twinning of the diamond. However, micrographs taken throughout the substrate showed diamond particles having similar orientation with respect to each other. Some of the diamond particles showed evidence of azimuthal twist and tilting, resulting most likely from the ∼21% lattice mismatch. Raman spectra of the diamond crystals show a strong feature at 1332 cm−1, which is indicative of diamond, and smaller features at 1480 and 1602 cm−1 due to sp2-bonded carbon.
Extremely high electron mobility in Si/SiGe modulation-doped heterostructures
Authors: Ismail K. , Arafa M. , Saenger K. L. , Chu J. O. , Meyerson B. S.
Published: July 2002

We report record high electron mobility in modulation-doped Si/SiGe. Samples grown by ultrahigh vacuum chemical vapor deposition (UHV-CVD) with mobility values in the range of 3.2–5.2×105 cm2/V s have been measured at 0.4 K. The current and temperature dependence of the magnetoresistance in those samples have been examined and the scattering times are deduced from these measurements. At high magnetic field (≳10 T), fractional quantum Hall filling factors have been observed, and the corresponding activation energies have been calculated. These are significantly larger than previously reported values in Si/SiGe, and are comparable to those in GaAs/AlGaAs modulation-doped heterostructures with mobility higher than 1×106 cm2/V s.
Two-photon excitation 4Pi confocal microscope: Enhanced axial resolution microscope for biological research
Authors: Hänninen P. E. , Hell S. W. , Salo J. , Soini E. , Cremer C.
Published: July 2002

The applicability of two photon excitation 4Pi confocal fluorescence microscopy to biological imaging is demonstrated. We show that 4Pi confocal microscopy in combination with a simple deconvolution algorithm allows axial localization and quantification with 0.14 μm resolution in a biological sample. The 4Pi-confocal microscope extends the applicability of far field fluorescence microscopy to high resolution three-dimensional imaging and quantification of subcellular structures.
Ultrathin foils for Coulomb-explosion experiments
Authors: Both G. , Kanter E. P. , Vager Z. , Zabransky B. J. , Zajfman D.
Published: July 2002

We have examined the properties of very thin foils used for electron stripping of MeV molecular ions in Coulomb-explosion experiments. Carbon foils with a nominal thickness of 0.2 μg/cm2 proved to be thicker than 1 μg/cm2. It was not possible to reduce their thickness by bombardment with 2-MeV Kr+ or H2O+ ions or by heating to a red glow. We succeeded in producing Formvar films of about 0.5 μg/cm2, which are supported by a nickel mesh.
Fiber optics for Raman scattering at low temperatures and high-magnetic fields
Authors: Isaacs E. D. , Heiman D.
Published: July 2002

A versatile and compact fiber-optic system for Raman scattering and photoluminescence is described. This optical fiber system was used for inelastic light-scattering experiments at temperatures down to T=0.35 K and dc magnetic fields to B=30 T. We believe this is the first observation of Raman scattering in either of these environments, both of which are normally inaccessible with optical Dewars. The portable head has a 1-cm o.d. and permits measurements longitudinal and transverse to the applied magnetic field. Observation of spin-flip Raman scattering from donor bound magnetic polarons in (Cd, Mn)Se demonstrates this system at the extremes of both magnetic field and temperature.
‘‘Tracking’’ tunneling microscopy
Authors: Pohl D. W. , Möller R.
Published: July 2002

Simple modification of the electronics of a STM allows operation in various tracking modes. Profiles of steepest inclination, equal height, equipotential, electrical field lines, etc., can be traced out. The tunnel tip can also be locked to a surface extremity for indefinite time. Some of these possibilities were tested experimentally.
20-ps timing resolution with single-photon avalanche diodes
Authors: Cova S. , Lacaita A. , Ghioni M. , Ripamonti G. , Louis T. A.
Published: July 2002

Single photon avalanche diodes (SPADs) are avalanche photodiodes specifically designed for reverse bias operation above the breakdown voltage and used for detecting single optical photons. A new silicon epitaxial device structure was designed to give improved timing performance with respect to previous SPADs. Extensive tests were carried out in order to establish the timing resolution of the device in time correlated photon counting (TCPC). The timing resolution of the SPAD in terms of its full-width at half-maximum (FWHM) contribution to the overall instrumental response width is 20 ps with the detector cooled to −65 °C, and 28 ps at room temperature. This is the highest resolution so far reported for solid-state single-photon detectors. In vacuum tubes, comparable results are obtained only with special microchannel-plate photomultipliers (MCP-PMT). Results from time-resolved photoluminescence measurements in GaAs demonstrate the power of the TCPC technique when used with the new SPAD detector. With the excellent timing resolution of the SPAD and the well-known advantages of TCPC systems (high sensitivity, linearity, etc.), various applications are foreseen in areas so far dominated by streak cameras.
Scanning tunneling microscope instrumentation
Authors: Kuk Y. , Silverman P. J.
Published: July 2002

A review is presented of the basic operating principles of scanning tunneling microscopy and spectroscopy. The physical and electronic design of the scanning tunneling microscope is discussed, and other new microscopes using similar concepts are described. Some examples of the past accomplishments of scanning tunneling microscopy are given, and prospects for future applications are assessed.
A sensitive time-resolved radiation pyrometer for shock-temperature measurements above 1500 K
Authors: Boslough Mark B. , Ahrens Thomas J.
Published: July 2002

An optical system has been developed which can determine time-resolved temperatures in shocked materials by measuring the spectral radiance of light emitted from shocked solid samples in the visible and near-infrared wavelength range (0.5–1.0 μm). It can measure temperatures as low as 1500 K and has been successfully used to observe shock-induced chemical reactions in powder samples. The high sensitivity of this radiation pyrometer can be attributed to the large angular aperture (0.06 sr), the large bandwidth per channel (up to 0.1 μm), the large photodiode detection areas (1.0 cm2 ), and the small number of calibrated channels (4) among which light is divided. Improved calibration techniques, as well as the layout of the instrument, eliminate certain sources of error encountered in previous shock-temperature experiments. Errors in the measured spectral radiance were reduced by: (1) recalibration before every experiment to account for changes in optical components; (2) direct calibration of voltage recorded at each digitizer to prevent transfer error by an intermediate step; (3) use of a spectral irradiance calibration lamp to exclude errors due to spatial inhomogeneities associated with spectral radiance sources; and (4) obtaining a large spatial average of light at each wavelength from the same portion of the sample to eliminate errors from possible inhomogeneities in the sample. The magnitude each of these errors could previously contribute was 1%–2% of the total signal. Absolute temperature uncertainties, determined from the standard deviation of the measured spectral radiances from the least-squares-fit values, are typically about 5%. Emissivities are poorly constrained by spectral radiance data because of a weak functional dependence, and uncertainties can easily exceed 50% for temperatures of around 2000 K.
Properties of a four-electrode adjustable electron mirror as an aberration corrector
Authors: Shao Zhifeng , Wu Xiao Dong
Published: July 2002

A numerical analysis of a four-electrode electron mirror is presented. It is shown that this system can have adjustable aberration coefficients, opposite to the aberrations of conventional electron optical systems. Therefore, it is possible to use such an electron mirror as an aberration corrector to further improve resolutions in electron microscopes.
An accurate method for the refractive index measurements of liquids: Application of the Kramers–Kronig relation in the liquid phase
Authors: Marteau Ph. , Montixi G. , Obriot J. , Bose T. K. , St. Arnaud J. M.
Published: July 2002

An accurate method for the precise determination of the refractive index of liquids in the visible and in the infrared is described. The method is based on two laser interferometers where one measures the sample thickness variation in air and the other the change in the optical path length of the liquid sample. In this way, the refractive index of the liquid is directly derived from the two fringe counts without resorting to the measurements of angles or geometrical thicknesses. The experimental results of the refractive index of CCl4 and CS2 in the infrared agree well with the theoretical prediction based on the Kramers–Kronig relation.
Island formation during growth of Ge on Si(100): A study using photoluminescence spectroscopy
Authors: Sunamura H. , Usami N. , Shiraki Y. , Fukatsu S.
Published: July 2002

We present a photoluminescence (PL) study on the growth mode changeover during growth of Ge on Si(100) substrates. Intense PL signals originating from both the flat Ge layer and the three-dimensional (3D) Ge islands are observed from Si/Ge/Si quantum wells with various Ge coverage. The onset of the 3D island formation is determined to be 3.7 monolayers (ML). It is also found that the 3D islands grow with only 3.0 ML of the flat Ge layer retained. This implies that only the 3.0 ML Ge is thermodynamically stable on Si(100) and hence corresponds to the ‘‘equilibrium’’ critical thickness.
High quantum efficiency for a porous silicon light emitting diode under pulsed operation
Authors: Linnros Jan , Lalic Nenad
Published: July 2002

A high quantum efficiency for a porous silicon light emitting diode (LED) is demonstrated under pulsed operation. The LED is fabricated from a p+nn+ structure by anodic/hydrofluoric etching followed by deposition of a transparent gold contact. The LED shows a rectifying behavior and emits orange-red light under forward bias with a spectral width significantly narrower than the corresponding photoluminescence spectrum. By calibrated measurements, we here demonstrate electroluminescence external quantum efficiencies of ∼0.2% under pulsed operation corresponding to internal quantum efficiencies of a few percent.
Spectroscopic ellipsometry on the millisecond time scale for real-time investigations of thin-film and surface phenomena
Authors: An Ilsin , Li Y. M. , Nguyen H. V. , Collins R. W.
Published: July 2002

Submonolayer sensitivity to thin-film nucleation and growth in real time on the millisecond scale has been achieved with a unique rotating polarizer multichannel ellipsometer. Continuous spectra in the ellipsometry angles {ψ(hv),Δ(hv)} consisting of ∼50 points from hv=1.5 to 4.3 eV have been obtained with acquisition and repetition times as short as 16 and 32 ms, respectively. As an example of the instrument capabilities, we present results for hydrogenated amorphous silicon (a-Si:H) growth on c-Si by plasma-enhanced chemical vapor deposition at a rate of 400 Å/min. In this example, the acquisition and repetition times are both 64 ms, and at this speed a precision in (ψ,Δ) of ∼0.02–0.03° is obtained under optimum conditions. We observe a-Si:H nucleation in the first 2 s of deposition, and detect relaxation of nucleation-induced surface roughness with submonolayer sensitivity.
Friction effects in the deflection of atomic force microscope cantilevers
Authors: Warmack R. J. , Zheng X.-Y. , Thundat T. , Allison D. P.
Published: July 2002

The conventional deflection-mode atomic force microscope operates by optically monitoring the slope near the end of a microcantilever in contact with the sample surface. This signal is usually interpreted as a measure of height change. Lateral forces from friction, surface geometry, or inclination of the cantilever to the surface also affect the slope due to cantilever buckling. We calculate the deflection of a hollow triangular model cantilever subject to both lateral and normal forces. The measured response of the servo circuit to an inclined, loaded cantilever is then determined. This shows (1) errors are always present in height measurements of structures on inhomogeneous surfaces; (2) the sensitivity to buckling can be reduced by repositioning the laser; (3) friction measurements can be accurately made by scanning in two directions and applying the proper calibration.
Atomic force microscope tip deconvolution using calibration arrays
Authors: Markiewicz Peter , Goh M. Cynthia
Published: July 2002

An algorithm for the deconvolution of the probe tips used with the atomic force microscope from the images of calibration grids made using very large scale integrated technology, which is useful in visualization of the tip before or after imaging for the elucidation of the condition of the stylus, is presented. This procedure described is of general applicability: it makes no assumptions about the tip geometry and requires no pretreatment of the data, such as filtering. Grids having circular depressions are shown to reproduce the geometries of circular and conical tips faithfully, but are limited when imaging those which are square pyramidal. Slight variations in the size and shapes of the depressions within a grid pattern limit the accuracy of the tip reconstruction.
Parametric back-action effects in a high-Q cyrogenic sapphire transducer
Authors: Cuthbertson B. D. , Tobar M. E. , Ivanov E. N. , Blair D. G.
Published: July 2002

The construction and operation of a high-quality factor microwave sapphire resonator transducer coupled to a 1 kHz niobium membrane acoustic oscillator are presented in this paper. A four-stage passive vibration isolation system was included in the design to permit the measurement of the transducer’s parametric properties. The isolation system was shown to sufficiently suppress mechanical noise above 100 Hz and an upper limit to the displacement sensitivity of the transducer was measured to be 3.0±0.6×10−16 m/√Hz. The parametric behavior of the transducer with a single pump readout was measured for several transducer configurations, and the results were found to be in good agreement with theory. The measurements presented here display for the first time the complete parametric behavior in a high electrical Q system, where the transducer’s bandwidth is less than the mechanical oscillator’s frequency. The high stability and low losses of our system may allow the transducer to be configured as a back-action evasion or quantum nondemolition device.
Traveling wave method for measurement of thermal conductivity of thin films
Authors: Bhusari D. M. , Teng C. W. , Chen K. H. , Wei S. L. , Chen L. C.
Published: July 2002

We present here the design of a novel and simple setup for measuring the thermal conductivity of thin films. This method is based on the well known principle of phase lag of a traveling thermal wave. In the present setup, the traveling thermal wave is generated in the thin film by irradiating its one edge by an infrared laser. The phase lag (Δθ) between the excitation wave and the resulting thermal wave, at a variable distance d from the edge of the sample, is determined by measuring the deflection of another “probe-laser.” The thermal diffusivity is then directly calculated from the slope of the plot between Δθ and d. This method offers an accuracy of better than ±5%.
Localized surface elasticity measurements using an atomic force microscope
Authors: DeVecchio Derik , Bhushan Bharat
Published: July 2002

Magnetic recording, microelectro mechanical systems, and other microelectronics industries use ultrathin continuous films as well as composite films. The motivation of this research was to identify and map differences in the stiffness or elasticity of these ultrathin films at the very near surface (up to a few nm) by using the force modulation technique. We have shown that this technique amplitudes on samples can yield quantitative elasticity data on samples with an elastic modulus up to a few tens of GPa. This technique provides an alternative to current elasticity measurements that require forces higher than 1 μN, and which can only make single point measurements. With this technique it is possible to make quantitative measurements with loads as low as a few tenths of a μN. By choosing tips that match the stiffness of the sample, the depth of the indentation during the elasticity measurement is kept small, thus eliminating significant plastic deformation of samples of any hardness and any stiffness. The technique has been applied to quantitatively measure the elasticity of polytetrafluoroethylene and to qualitatively map magnetic tape samples to reveal sharp variations in the surface elasticity due to the composite nature of the polymer matrix with magnetic and abrasive particles.
A new angle into time-resolved photoacoustic spectroscopy: A layered prism cell increases experimental flexibility
Authors: Autrey Tom , Foster Nancy S. , Klepzig Kim , Amonette James E. , Daschbach John L.
Published: July 2002

A new pulsed photoacoustic calorimetry cell that uses transmission of light through a pair of dovetail prisms is discussed. The layered prism cell (LPC) combines the enhanced time-resolution capabilities of the “layered” front-face irradiation geometry with the zero-background and broadband flexibility of the classical cuvette geometry. This work provides a phenomenological description of photoinduced pressure changes to yield an analytical expression to calculate the magnitude of the photoinduced acoustic pressure wave in a series of solvents. The mechanical to electrical conversion efficiency for an ultrasonic transducer coupled to the LPC is presented to provide a comparison of the experimentally observed photoinduced acoustic signal amplitudes to the empirically calculated acoustic signal amplitudes. An analysis of the background signals due to absorption and electrostriction of the media provides insight into the issues of sensitivity and limitations of pulsed photoacoustic experiments. The LPC provides several benefits to increase the flexibility of the photoacoustic spectroscopy: (1) greater sensitivity, (2) enhanced time resolution, and (3) the ability to obtain kinetic data in complex solvent mixtures. Under optically dilute conditions in the layered cell geometry, the acoustic transient time, τa, approaches zero because the photoinduced acoustic wave homogeneously expands against the walls of the photoacoustic cell. To demonstrate the unique capabilities of the LPC, rates of hydrogen abstraction by tert-butoxyl radical from solvent mixtures containing ethyl and methyl alcohol are presented.
Fast pulsed hollow cathode capillary discharge device
Authors: Choi P. , Favre M.
Published: July 2002

A fast pulsed capillary discharge device has been developed and implemented. The device combines the features of a transient hollow cathode discharge with the inherent characteristics of the capillary discharge, to obtain VUV to XUV radiation with ns rise time. The discharge operates in a 0.8 mm inner diameter alumina capillary, at 10–30 kV applied voltage. On axis discharge initiation is assisted by electron beams, which are characteristic of the hollow cathode effect. A short, 5 ns full width at half maximum XUV pulse is produced in association with a ∼1 kA, 5 ns current pulse.
A reproducible method to fabricate atomically sharp tips for scanning tunneling microscopy
Authors: Nakamura Yoshiaki , Mera Yutaka , Maeda Koji
Published: July 2002

The electrochemical etching method by Ibe et al. [J. Vac. Sci. Technol. A 8, 3570 (1990)] to fabricate sharp tips for scanning tunneling microscopy was modified by shortening the cutoff time of the etching current after the material wire drops off at the air-electrolyte interface. The tip radius measured by field ion microscopy was successfully reduced to 8 nm when the cutoff time was shortened to 50 ns. The dependence of the field-emitting electron current from the sharpest tips was close to one expected from the Fowler–Nordheim formula with a reasonable value for the emitting area of the tip.
Nanoscale elasticity measurement with in situ tip shape estimation in atomic force microscopy
Authors: Yamanaka Kazushi , Tsuji Toshihiro , Noguchi Atsushi , Koike Takayuki , Mihara Tsuyoshi
Published: July 2002

For a quantitative evaluation of nanoscale elasticity, atomic force microscopy, and related methods measure the contact stiffness (or force gradient) between the tip and sample surface. In these methods the key parameter is the contact radius, since the contact stiffness is changed not only by the elasticity of the sample but also by the contact radius. However, the contact radius is very uncertain and it makes the precision of measurements questionable. In this work, we propose a novel in situ method to estimate the tip shape and the contact radius at the nanoscale contact of the tip and sample. Because the measured resonance frequency sometimes does not depend so sensitively on the contact force as expected from the parabolic tip model, we introduced a more general model of an axial symmetric body and derived an equation for the contact stiffness. Then, the parameters in the model are unambiguously determined from a contact force dependence of the cantilever resonance frequency. We verified that this method is able to provide an accurate prediction of the cantilever thickness, the tip shape, and the effective elasticity of soft and rigid samples.
Spatially resolved photoluminescence spectroscopy of lateral p-n junctions prepared by Si-doped GaAs using a photon scanning tunneling microscope
Authors: Saiki T. , Mononobe S. , Ohtsu M. , Saito N. , Kusano J.
Published: July 2002

An accurate correspondence between the local optical responses and the structures of semiconductor light-emitting devices is demonstrated by using an illumination-mode photon scanning tunneling microscope with noncontact atomic force microscope technique. We study the novel-structured lateral p-n junctions grown on patterned GaAs(111)A substrate. Measuring the spatially resolved photoluminescence spectra with a 200 nm apertured probe, we precisely determine the position and the width of the transition region of p-n junctions. The illumination-collection hybrid mode is also employed to map the two-dimensional emission efficiency with higher resolution, which is not affected by carrier diffusion.
Auger lifetime in InAs, InAsSb, and InAsSb-InAlAsSb quantum wells
Authors: Lindle J. R. , Meyer J. R. , Hoffman C. A. , Bartoli F. J. , Turner G. W. , Choi H. K.
Published: July 2002

The intensity-dependent photoconductive response to 2.06 μm excitation has been used to determine Shockley-Read and Auger lifetimes for InAs, InAs0.91Sb0.09, and an InAs0.85Sb0.15-InAlAsSb multiple quantum well. The Auger rate at 77 K correlates with the proximity to resonance between the energy gap and the split-off gap. Thus the Auger coefficient in the alloy decreases with decreasing temperature, whereas that in the quantum well increases by nearly a factor of 5 between 300 and 77 K.
Controlled photon emission in porous silicon microcavities
Authors: Pavesi Lorenzo , Mazzoleni Claudio , Tredicucci Alessandro , Pellegrini Vittorio
Published: July 2002

We demonstrate the preparation of narrow-band porous-silicon reflectors integrated on porous-silicon layers by electrochemical etching. By carefully tuning the resulting photon cavity mode around the maximum of the porous silicon photoluminescence, we have obtained both a narrowing and enhancement of the emission line, and a highly concentrated radiation pattern. These results show that the porous silicon spontaneous emission is modified because of the coupling with the photon cavity mode.
Band-tail photoluminescence in polycrystalline silicon thin films
Authors: Savchouk A. U. , Ostapenko S. , Nowak G. , Lagowski J. , Jastrzebski L.
Published: July 2002

We have found a new photoluminescence (PL) band with a maximum at 0.9 eV and a halfwidth of 0.1 eV at 4.2 K in polycrystalline Si thin films deposited on glass at 625 °C. The PL band strongly shifts toward low energy with increasing the temperature (1.3 meV/K) and toward high energy with increasing the excitation intensity. Hydrogenation of polycrystalline Si enhances the PL intensity by factor of 3 to 5. The luminescence characteristics are consistent with radiative recombination of electrons and holes trapped in tail states of the conduction and the valence band, respectively. Excellent agreement is achieved between the 0.9 eV band shape and theoretical calculations based on a band-tail recombination. It is also argued that a corresponding luminescence spectroscopy provides a new possibility for band-tail diagnostics in polycrystalline Si thin films.
Nanofabrication of a two-dimensional array using laser-focused atomic deposition
Authors: Gupta R. , McClelland J. J. , Jabbour Z. J. , Celotta R. J.
Published: July 2002

Fabrication of a two-dimensional array of nanometer-scale chromium features on a silicon substrate by laser-focused atomic deposition is described. Features 13±1 nm high and having a full-width at half maximum of 80±10 nm are fabricated in a square array with lattice constant 212.78 nm, determined by the laser wavelength. The array covers an area of approximately 100 μm×200 μm. Issues associated with laser-focusing of atoms in a two-dimensional standing wave are discussed, and potential applications and improvements of the process are mentioned.
Screening effects on the band-gap renormalization of strained InGaAs/InGaAsP quantum well lasers lattice matched to GaAs
Authors: Park Seoung-Hwan , Ahn Doyeol
Published: July 2002

The screening effects on the band-gap renormalization (BGR) of strained InGaAs/InGaAsP (Eg=1.6 eV) QW lasers lattice matched to GaAs are investigated theoretically, taking into account the valence-band mixing and multisubband effects. These results are also compared with those of InGaAs/GaAs QW lasers. Without the screening effect, the BGR significantly depends on both the carrier density and the In composition. On the other hand, with the screening effect, these dependencies are expected to be reduced considerably. The BGR with the screening effect in InGaAs/GaAs lasers show weaker dependence on the In composition compared to InGaAs/InGaAsP lasers.
Deep levels in the upper band-gap region of lightly Mg-doped GaN
Authors: Hacke P. , Nakayama H. , Detchprohm T. , Hiramatsu K. , Sawaki N.
Published: July 2002

Deep levels in undoped and weakly Mg-doped n-type GaN films fabricated by metalorganic chemical vapor deposition were examined with deep level transient spectroscopy. Deep levels measured at 0.26 and 0.62 eV below the conduction band were found in relatively low concentrations of ∼2×1013 cm−3 in undoped GaN. Addition of small quantities of the Mg acceptor species by means of bis-cyclopentadienyl magnesium (Cp2Mg) during growth corresponded to a significant increase in the concentration of the level at 0.62 eV. The concentration of the shallower level, found to be independent of the Cp2Mg addition, remained unchanged. These deep levels may detrimentally affect optical and electrical properties when fabricating p-type GaN.
Simulation of cluster evaporation and transient enhanced diffusion in silicon
Authors: Rafferty C. S. , Gilmer G. H. , Jaraiz M. , Eaglesham D. , Gossmann H.-J.
Published: July 2002

The evaporation of {311} self-interstitial clusters has recently been linked to the phenomenon of transient enhanced diffusion in silicon. A theory of cluster evaporation is described, based on first-order kinetic equations. It is shown to give a good account of the data over a range of temperatures. The theory simultaneously explains several of the unexpected features of transient enhanced diffusion, including the apparently steady level of the enhancement during its duration, and the dependence of the duration on implant energy and dose. The binding energy used to match the theory to data is in good agreement with molecular dynamics calculations of cluster stability in silicon.
Assessment of nondiamond carbon levels present in chemical vapor deposited diamond by analysis of the plasmon loss features of x-ray photoelectron spectra
Authors: Haq S. , Tunnicliffe D. L. , Sails S. , Savage J. A.
Published: July 2002

The plasmon loss region of x-ray photoelectron spectra has been analyzed for chemically vapor deposition diamond in order to assess the nondiamond carbon (NDC) levels present. A semiquantitative method for expressing the quality of the diamond, based upon the ratio of the diamond bulk plasmon to the main carbon 1s line is presented and a figure of merit defined. A comparison with Raman spectroscopy shows that this technique compares well in terms of range and sensitivity to NDC levels.
Etching of InP at ≳1 μm/min in Cl2/Ar plasma chemistries
Authors: Lee J. W. , Hong J. , Pearton S. J.
Published: July 2002

A simple Cl2/Ar plasma chemistry without additional sample heating is found to produce etch rates above 1 μm/min for InP under high microwave power (1000 W) electron cyclotron resonance conditions. While the etch rate increases essentially linearly with Cl2 composition the root-mean-square (RMS) surface roughness measured by atomic force microscopy is strongly dependent on the Cl2-to-Ar ratio. Under optimized conditions (10Cl2/5Ar), RMS roughness of ∼2.6 nm is obtained on samples etched more than 1 μm, a typical unetched control sample displays a RMS value of 1.3–1.6 nm. The high ion current under ECR conditions appears to promote efficient sputter desorption of the InCl3 etch product and prevents buildup of the usual selvedge layer that requires elevated sample temperatures to desorb under more conventional reactive ion etching conditions. The result is a simplified plasma chemistry with avoidance of the polymer deposition and hydrogen passivation associated with CH4/H2 discharges.
Identification of Cr in p-type silicon using the minority carrier lifetime measurement by the surface photovoltage method
Authors: Mishra Kamal
Published: July 2002

The effect of CrB pair dissociation on the minority carrier lifetime in p-type silicon is studied using the surface photovoltage (SPV) and deep level transient spectroscopy (DLTS) methods. Experiments were conducted using Cr doped samples (0.5×1012–5×1012 cm−3) with resistivity ranging from 1 to 50 Ω cm. The minority carrier lifetime, increased after the dissociation of CrB by a factor ranging, depending upon resistivity, approximately from 2.0 to 10. This is in contrast to a tenfold reduction observed in the minority carrier lifetime following the dissociation of FeB pairs. The resistivity dependence of the minority carrier lifetime in Cr doped sample can be successfully predicted according to the Shockley–Reed–Hall (SRH) model. It is demonstrated that the defects with energy levels of Ev+0.27 eV and Ec −0.22 eV are the main recombination centers for CrB and Cri, respectively.
Compensation of n-type GaN
Authors: Yi Gyu-Chul , Wessels Bruce W.
Published: July 2002

Compensation in Se-doped n-type GaN prepared by atmospheric pressure metalorganic vapor phase epitaxy was studied. Hydrogen selenide was the dopant source. The carrier concentration is linearly proportional to the H2Se pressure for low partial pressures and proportional to the cube root at high partial pressures. Carrier concentrations as high as 6×1019 cm−3 at 295 K were achieved. From Hall-effect measurements, the Se-doped GaN was shown to be highly compensated even for heavily n-type material. The defects responsible for the compensation were investigated using low-temperature photoluminescence. A strong acceptor-related transition at 3.447 eV at 15 K was observed in the heavily doped layer. The observed doping dependence of Se in GaN is attributed to compensation by triply charged vacancies which is consistent with recent theoretical calculations on defect formation in n-type material.
Continuous-wave operation of InGaN multi-quantum-well-structure laser diodes at 233 K
Authors: Nakamura Shuji , Senoh Masayuki , Nagahama Shin-ichi , Iwasa Naruhito , Yamada Takao , Matsushita Toshio , Sugimoto Yasunobu , Kiyoku Hiroyuki
Published: July 2002

Continuous-wave (cw) operation of InGaN multiquantum-well-structure laser diodes (LDs) was demonstrated at 233 K. The threshold current and voltage of the LD were 210 mA and 11 V, respectively. During room-temperature cw operation, the LDs were easily broken within one second due to heat generation. At 233 K, the lifetime of the LDs was longer than 30 min, and the emission spectra could be measured under cw operation. Only a single peak was observed under cw operation with increasing forward current above the threshold current. The characteristic temperature of the threshold current of the LDs was 162 K.
Pulsed electroluminescence from organic bilayer light emitting diodes
Authors: Tak Y. H. , Pommerehne J. , Vestweber H. , Sander R. , Bässler H. , Hörhold H. H.
Published: July 2002

Transient electroluminescence (EL) from organic bilayer light emitting diodes featuring an interfacial blockade for holes and electrons was studied. At the end of the driving voltage pulse an EL spike is observed whose magnitude exceeds the cw-EL intensity by up to two orders of magnitude. The effect is attributed to an increase of the recombination probability of minority carriers (electrons) with majority carriers upon switching off the external field.
Interactions of ion-implantation-induced interstitials with boron at high concentrations in silicon
Authors: Haynes T. E. , Eaglesham D. J. , Stolk P. A. , Gossmann H.-J. , Jacobson D. C. , Poate J. M.
Published: July 2002

Ion implantation of Si (60 keV, 1×1014/cm2) has been used to introduce excess interstitials into silicon predoped with high background concentrations of B, which were varied between 1×1018 and 1×1019/cm3. Following post-implantation annealing at 740 °C for 15 min to allow agglomeration of the available interstitials into elongated {311} defects, the density of the agglomerated interstitials was determined by plan-view transmission electron microscopy observation of the defects. We report a significant reduction in the fraction of excess interstitials trapped in {311} defects as a function of boron concentration, up to nearly complete disappearance of the {311} defects at boron concentrations of 1×1019/cm3. The reduction of the excess interstitial concentration is interpreted in terms of boron-interstitial clustering, and implications for transient-enhanced diffusion of B at high concentrations are discussed.
A high sensitivity, wide dynamic range magnetometer designed on a xylophone resonator
Authors: Givens R. B. , Murphy J. C. , Osiander R. , Kistenmacher T. J. , Wickenden D. K.
Published: July 2002

A novel magnetometer based on a classical xylophone resonator is described. The device consists of an aluminum bar supported by two wires placed at the nodal points of the fundamental resonance frequency. The wires also supply current of this frequency to the bar. In the presence of a magnetic field, the Lorentz force causes the resonator to vibrate. The amplitude of this vibration is proportional to a vector component of the magnetic field. The device is intrinsically linear, and by altering the drive current the sensitivity can range from nanoteslas to teslas.
Excited states of individual quantum dots studied by photoluminescence spectroscopy
Authors: Hessman D. , Castrillo P. , Pistol M.-E. , Pryor C. , Samuelson L.
Published: July 2002

The photoluminescence from individual InP quantum dots embedded in a matrix of GaInP has been studied. In addition to the ground state emission that consists of several peaks, we observe excited states of the dot. These states are observed either via state filling or with photoluminescence excitation spectroscopy. We observe a fast relaxation to the set of states with lowest energy but no relaxation between these states.
Single-atom point contact devices fabricated with an atomic force microscope
Authors: Snow E. S. , Park D. , Campbell P. M.
Published: July 2002

The fabrication of atomic point contacts by using anodic oxidation of thin Al films with an atomic force microscope is reported. In situ electrical measurements were used as feedback to control the fabrication of Al nanowires that were subsequently anodized through their cross section to form point contacts. When the conductance of a point contact is reduced below ∼5×10−4 S it starts to decrease in discrete steps of ∼2e2/h. In some devices we are able to stabilize the conductance at a value near 2e2/h which corresponds to a single, atomic-sized conducting channel.
Optical transition in SiGe self-organized dots
Authors: Chen H. , Cheng W. Q. , Xie X. G. , Huang Q. , Zhou J. M.
Published: July 2002

It is found that the SiGe alloy self-organizers into uniform quantum dots embedded in the Si layer during the growth of a strained Si/Ge short period superlattice on a Si(001) substrate at a temperature of 800 °C by molecular beam epitaxy. The peak of photoluminescence from the quantum dots is at an energy higher than the band gap of Si. The intensity is two orders of magnitude higher than that of SiGe/Si quantum well.
Recycling of guided mode light emission in planar microcavity light emitting diodes
Authors: De Neve H. , Blondelle J. , Van Daele P. , Demeester P. , Baets R. , Borghs G.
Published: July 2002

Results are presented on planar microcavity light emitting diodes with different device diameters. A record external quantum efficiency of 20% is achieved for a 1.5 mm light emitting diode. The strong dependence of the quantum efficiency on current density and device size are compared with theoretical results. A good correspondence is obtained when spectral broadening and photon recycling are taken into account.
Electrical properties and crystal structure of (Ba,Sr)TiO3 films prepared at low temperatures on a LaNiO3 electrode by radio-frequency magnetron sputtering
Authors: Chu Chung Ming , Lin Pang
Published: July 2002

(Ba,Sr)TiO3 films on a LaNiO3 underlayer were prepared by radio-frequency magnetron sputter deposition. The onset of crystallization of the films occurred at a deposition temperature (Td) as low as 200 °C. Good crystallinity was observed at Td⩾350 °C. A moderate high dielectric constant (εr∼170–250) of the films was obtained at relatively low Td∼200–300 °C. The value of εr showed a much slower increase with Td⩾350 °C than that expected from the progress of crystallinity. The deviation was attributed to an interdiffusion layer formed between the film and underlayer, which also caused an abnormal contact potential barrier and a decline of the εr value of the samples postannealed at 350 °C. Annealing at 300 °C under O2 atmosphere lessened the oxygen deficiency in the film and enhanced the dielectric constant without forming an interfacial layer.
Tunable InGaAs/GaAs/InGaP laser
Authors: Dutta N. K. , Hobson W. S. , Lopata J. , Zydzik G.
Published: July 2002

The fabrication and performance characteristics of a tunable InGaAs/GaAs/InGaP laser emitting near 980 nm are reported. The tunability is achieved using the thermoelectric effect of the substrate. A tuning range of >6 nm has been demonstrated using ∼60 mA of thermoelectric controller current.
Exciton-phonon interaction in InGaN/GaN and GaN/AlGaN multiple quantum wells
Authors: Smith M. , Lin J. Y. , Jiang H. X. , Khan A. , Chen Q. , Salvador A. , Botchkarev A. , Kim W. , Morkoc H.
Published: July 2002

The exciton-phonon coupling has been studied in InxGa1−xN/GaN and GaN/AlxGa1−xN multiple quantum wells (MQWs) and compared with that in InxGa1−xN and GaN epilayers. Phonon replicas with up to four phonons can be well resolved only in the alloy regions of the MQWs (InxGa1−xN or AlxGa1−xN) and was independent of the structure (well or barrier), while no phonon replicas of the exciton transitions were observed for the free-exciton transitions in the GaN and the localized exciton transitions in the InxGa1−xN epilayers. It thus suggests that the symmetry properties of MQWs, which modifies the phonon dispersion relation, together with alloy disorder are responsible for the enhanced exciton-phonon interaction in III-nitride MQW. The coupling constant S of the exciton-phonon interaction is extracted for an InxGa1−xN/GaN and GaN/AlxGa1−xN MQW, and is found to be S=0.802 and 0.556, respectively. The implications of the modified exciton-phonon coupling in MQWs in terms of understanding the fundamental physics of this system as well as practical device applications are discussed.