bluuebunny/crossref_metadata_2025 huggingface dataset:
Goniometric optical scatter instrument for out-of-plane ellipsometry measurements
Authors: Germer Thomas A. , Asmail Clara C.
Published: July 2002

A goniometric optical scatter instrument has been developed at the National Institute of Standards and Technology which can readily perform measurements of optical scatter and its associated polarization in directions out of the plane of incidence. In this article the coordinate transformations that are required to operate such a goniometer with respect to sample-specific coordinates are described. We present new methods for measuring the 3×3 nonhanded Mueller matrix elements using dual rotating half-wave retarders, and present a subset of the Mueller matrix, referred to as the bidirectional ellipsometric parameters which have been shown to simplify the interpretation of the data. The results of out-of-plane Mueller matrix and bidirectional ellipsometric measurements from a titanium nitride layer on silicon are presented.
Type-II quantum-well lasers for the mid-wavelength infrared
Authors: Meyer J. R. , Hoffman C. A. , Bartoli F. J. , Ram-Mohan L. R.
Published: July 2002

We discuss an improved mid-wave infrared diode laser structure based on InAs-Ga1−xInxSb- InAs-Ga1−xAlxSb Type-II multiple quantum wells. The proposed design combines strong optical coupling, 2D dispersion for both electrons and holes, suppression of the Auger recombination rate, and excellent electrical and optical confinement.
Giant magnetoresistive memory effect in Nd0.7Sr0.3MnOz films
Authors: Xiong G. C. , Li Q. , Ju H. L. , Bhagat S. M. , Lofland S. E. , Greene R. L. , Venkatesan T.
Published: July 2002

A novel giant magnetoresistance memory effect has been observed in epitaxial Nd0.7Sr0.3MnOz thin films which have previously been found to exhibit a linear increase in conductivity on first application of magnetic field B. The resistivity of the films depends not only on the instantaneous applied field but also on the magnetic history of the sample. At T well below the temperature Tp, where the zero-field resistivity has a peak, the film enters a high-conductivity state (upon application of a magnetic field) which persists even when B is reduced to zero. The original ‘‘zero’’ field state is not recovered until the sample is warmed to T∼Tp. Surprisingly, the dc magnetization exhibits only a weak irreversibility while the magnetoconductivity is markedly hysteretic. A possible explanation is proposed.
Temperature dependence of the photoluminescence of Zn1−xCdxSe/ZnSe strained-layer quantum wells
Authors: Tournié E. , Morhain C. , Leroux M. , Ongaretto C. , Faurie J. P.
Published: July 2002

We investigate by temperature-dependent photoluminescence (PL) spectroscopy between 9 K and 300 K Zn1−xCdxSe/ZnSe strained-layer quantum wells (QWs) with Cd contents ranging between 12% and 19% and QW thicknesses between 9 and 175 Å, i.e., with confinement energies up to 220 meV. In the whole temperature range the PL spectra are dominated by E1-HH1 free-exciton recombinations. Between 9 and 300 K the intensity of this line is reduced by three to four orders of magnitude while transitions involving excited states progressively emerge. An analysis of the thermal quenching of the PL intensity reveals that for all confinement energies the escape of excitons out of the QWs is the mechanism responsible for this quenching near 300 K.
Highly sensitive and wideband optical detection in patterned YBa2Cu3O7−δ thin films
Authors: Tanaka Ken’ichi , Arikawa Yoshiro , Sekine Matsuo , Ohtsu Motoichi , Harada Yuichi , Danerud Martin
Published: July 2002

We have measured the optical responses up to 18 GHz in patterned YBa2Cu3O7−δ thin films at various wavelengths by optical heterodyne mixing. The responsivity of the detectors is higher than 50 V/W below 1 Hz at various wavelengths and the responsivity is 20 mV/W at 780 nm and 150 mV/W at 1.55 μm wavelengths in the regime of the modulation frequency from 3 GHz to 18 GHz.
1.2 K Shubnikov–de Haas measurements and self-consistent calculation of silicon spreading in δ- and slab-doped In0.53Ga0.47As grown by molecular beam epitaxy
Authors: McElhinney M. , Vögele B. , Holland M. C. , Stanley C. R. , Skuras E. , Long A. R. , Johnson E. A.
Published: July 2002

Magnetotransport measurements are reported for In0.53Ga0.47As layers grown by molecular beam epitaxy (MBE) at different substrate temperatures (Ts) and either δ- or slab-doped with Si. Multiple subband densities deduced from the Fourier analysis of 1.2 K Shubnikov–de Haas measurements are compared with those derived from self-consistent calculations which include nonparabolicity and the doping profile width wSi as a fitting parameter. Significant spreading of the Si donors away from the doping plane is deduced for deposition at Ts≊520 °C, while no measurable migration is inferred for Ts≤470 °C, leading to near-ideal δ-doping behavior. Contrary to previous results [McElhinney et al., J. Cryst. Growth 150, 266 (1995)], no evidence for amphoteric behavior has been found for Si areal densities up to 4×1012 cm−2.
Diffusion of ion implanted boron in preamorphized silicon
Authors: Jones K. S. , Zhang L. H. , Krishnamoorthy V. , Law M. , Simons D. S. , Chi P. , Rubin L. , Elliman R. G.
Published: July 2002

Transient enhanced diffusion of boron in preamorphized and subsequently regrown Si was studied by secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM). A comparison of 4 keV, 1× 1014/cm2 boron implants into crystalline and Ge+ preamorphized silicon was undertaken. Upon annealing the B+ implant into crystalline material exhibited the well-known transient enhanced diffusion (TED). In this case the peak of the boron distribution was relatively immobile and only B in the tail showed TED. In the second set of samples, the surface was first preamorphized by a 180 keV, 1×1015/cm2 Ge+ implant which produced an amorphous layer 2300 Å deep, which then was implanted with boron. After implantation the tail of the B distribution extended to only 700 Å. Upon annealing, TED of the boron in the regrown Si was also observed, but the diffusion profile was very different. In this case the peak showed no clustering, so the entire profile diffused. The time for the TED to decay was around 15 min at 800 °C. TEM results indicate that the (311) defects in the end of range damage finish dissolving between 10 and 60 min at 800 °C. These results indicate that for these Ge preamorphization conditions, not only do the end of range defects not block the flow of interstitials into the regrown silicon, the (311) defects in the end of range damage act as the source of interstitials. In addition, boron does not appear to cluster in regrown silicon.
AlGaN/InGaN/GaN blue light emitting diode degradation under pulsed current stress
Authors: Osiński Marek , Zeller Joachim , Chiu Pei-Chih , Scott Phillips B. , Barton Daniel L.
Published: July 2002

This study focused on the performance of commercial AlGaN/InGaN/GaN blue light emitting diodes (LEDs) under high current pulse conditions. The results of deep level transient spectroscopy (DLTS), thermally stimulated capacitance, and admittance spectroscopy measurements performed on stressed devices, showed no evidence of any deep-level defects that may have developed as a result of high current pulses. Physical analysis of stressed LEDs indicated a strong connection between the high intrinsic defect density in these devices and the resulting mode of degradation.
Strain in InAs islands grown on InP(001) analyzed by Raman spectroscopy
Authors: Groenen J. , Mlayah A. , Carles R. , Ponchet A. , Le Corre A. , Salaün S.
Published: July 2002

Raman scattering has been used to investigate strained InAs islands grown on InP(001), in correlation with transmission electron microscopy. Symmetry arguments, selective resonance at the InAs E1-like transition and comparison with a single-quantum-well structure allowed to distinguish between the islands and remaining wetting layer signals. Whereas the vibrational modes of the 2D thin layers are greatly affected by interface roughness and confinement, strain effects mainly account for the phonon frequency shifts in the islands.
High-resolution x-ray diffraction study of piezoelectric InGaAs/GaAs multiquantum well p-i-n photodiodes grown on (111)B GaAs
Authors: Sanz-Hervás A. , Aguilar M. , Sánchez-Rojas J. L. , Sacedón A. , Calleja E. , Muñoz E. , Abril E. J. , López M.
Published: July 2002

High-resolution x-ray diffractometry has been applied to the structural characterization of piezoelectric strained InGaAs/GaAs multiquantum well p-i-n diodes grown by molecular beam epitaxy on (111)B GaAs substrates. Reference samples simultaneously grown on (001) GaAs have been also characterized. Diodes with 3, 7, and 10 periods and different well to barrier thickness ratio have been studied. Symmetric and asymmetric reflections at various azimuths were measured and the scans were fitted with theoretical curves obtained through a dynamical simulation program developed in our lab. The comparison between experimental and simulated profiles has enabled us to determine the main structural parameters of the samples. High-resolution x-ray diffractometry provided accurate data about period and capping layer thicknesses, indium content in the wells and state of relaxation, information which cannot be always obtained in (111)B samples from other characterization techniques such as photoluminescence or photocurrent spectroscopies.
Structural and optical properties of strained (Ga,In)Sb/GaSb quantum wells grown by molecular-beam epitaxy
Authors: Bertru N. , Klann R. , Mazuelas A. , Brandt O. , Ploog K. H. , Gaillard S.
Published: July 2002

Strained (Ga,In)Sb/GaSb quantum wells were grown by molecular-beam epitaxy which exhibit excellent structural properties as well as intense and narrow photoluminescence transitions. The coincidence of these transitions with resonances in electroreflectance spectra demonstrates their intrinsic nature. The spectral position of the emission peak shifts to lower energies with increasing thickness of the quantum well, showing that the transitions truly originate from quantum confined states. However, the emission energy is much lower than that calculated in the frame of the envelope function model when assuming the commonly accepted parameters for the strained (Ga,In)Sb band gap. We propose that these parameters have to be revised.
Uncooled thermal imaging using a piezoresistive microcantilever
Authors: Oden P. I. , Datskos P. G. , Thundat T. , Warmack R. J.
Published: July 2002

The operation of an uncooled, microcantilever-based infrared (IR) imaging device is demonstrated. Bending of the microcantilever is a function of the IR radiation intensity incident on the cantilever surface. The infrared image of the source is obtained by rastering a microfabricated cantilever over the image formed at the focal plane of a concave mirror. The bending variation of the microcantilever, as it scanned the focal plane of the mirror, is used to construct an infrared image of the source in front of the mirror. The thermal image obtained by scanning a single element cantilever is presented.
Influences of deposition temperature on thermal stability and moisture resistance of chemical vapor deposited fluorinated silicon oxide by using indirect fluorinating precursor
Authors: Chang Kow Ming , Wang Shih Wei , Wu Chin Jen , Yeh Ta Hsun , Li Chii Horng , Yang Ji Yi
Published: July 2002

In this letter, fluorinated silicon oxide (FxSiOy) films were deposited in the electron cyclotron resonance (ECR) chemical vapor deposition system with SiH4, O2, and CF4 as the reaction gases. The CF4, in contrast to SiF4 or FSi(OC2H5)3 used in other reports, is an indirect fluorinating source. The fluorinating mechanism is similar to that of the etching of oxide by fluorocarbon plasma, therefore, the thermal stability of the incorporated fluorine must strongly depend on the deposition temperature. It is found that the thermal stability and moisture resistance are greatly improved by increasing the deposition temperature. However, the higher deposition temperature also results in a higher compressed stress and dielectric constant. Besides, to get the moisture resistance, the deposition temperature must be above 300 °C. On the other hand, ECR-SiO2 (without fluorination), even deposited at room temperature, is shown to have a good water resistance. Therefore, by choosing deposition temperature for FxSiOy to have enough thermal tolerance and capping with ECR-SiO2, the moisture resistor is suggested for the inter metal dielectric applications.
Influence of microstructure on electromigration dynamics in submicron Al interconnects: Real-time imaging
Authors: Riege S. P. , Prybyla J. A. , Hunt A. W.
Published: July 2002

Systematic studies of the influence of local microstructure on electromigration (EM) dynamics in submicron Al (0.5 wt % Cu) interconnects were performed using in situ transmission electron microscopy. This approach has allowed us to observe, in real time, voids forming, growing, migrating, pinning, failing a runner, and healing all with respect to the detailed local microstructure of the runners. In this letter, we report and describe how grain boundaries dramatically influence almost all aspects of EM-induced void and failure dynamics in submicron runners. In addition, we report that EM voids nucleate at grain boundaries long before open-circuit failures occur. These findings have important implications for electromigration modeling.
Laterally structured ZnCdSe/ZnSe superlattices by diffusion induced disordering
Authors: Kuttler M. , Strassburg M. , Türck V. , Heitz R. , Pohl U. W. , Bimberg D. , Kurtz E. , Landwehr G. , Hommel D.
Published: July 2002

Thermally induced disordering of ZnCdSe/ZnSe superlattices was studied by secondary-ion-mass-spectroscopy and cathodoluminescence. The structures were grown by molecular beam epitaxy and annealed in Zn, H2, or Se atmosphere. In Zn atmosphere the superlattice was found to be stable up to 500 °C, whereas a heat treatment in H2 and Se atmosphere leads to a complete intermixing at temperatures of 450 and 430 °C, respectively. A Si3N4 stripe was used to protect the superlattice locally from the annealing atmosphere and to achieve a laterally structured intermixing. The disordering area is controlled to better than 600 nm.
Hall mobility analysis in low-temperature-grown molecular-beam epitaxial GaAs
Authors: Betko J. , Morvic M. , Novák J. , Förster A. , Kordos̆ P.
Published: July 2002

Temperature dependent conductivity and Hall effect measurements were carried out on molecular-beam epitaxial GaAs layers grown at 200–420 °C and separated from the substrate. An analysis of experimental data with and without considering the hopping Hall mobility was made. An extremely low room temperature Hall mobility of 0.14 cm2 V−1 s−1 was measured in the 250 °C layer, which could be interpreted as the hopping Hall mobility. The room temperature band Hall mobility (μHb) increases from 500 to 6000 cm2 V−1 s−1 and the power (n) of the temperature dependence of μHb (∼T−n) increases from 0.5 to 1.2 with increasing growth temperature from 300 to 420 °C.
Hot carrier dynamics in a (GaInSb/InAs)/GaInAlAsSb superlattice multiple quantum well measured with mid-wave infrared, subpicosecond photoluminescence upconversion
Authors: Jang D.-J. , Olesberg J. T. , Flatté M. E. , Boggess Thomas F. , Hasenberg T. C.
Published: July 2002

We have extended the technique of subpicosecond photoluminescence upconversion to the mid-wave infrared spectral region and have used this system to investigate the energy relaxation of hot, optically injected electron-hole pairs in a narrow-band-gap (2.32 μm) (GaInSb/InAs)/ GaInAlAsSb superlattice multiple quantum well. These and similar structures are currently of interest as the active region for mid-wave infrared diode lasers. The measurements demonstrate that carriers, which are injected with nearly 1 eV of excess energy, are well described by a hot, thermalized distribution in the wells within 2 ps after excitation. For a carrier density of 1017 cm−3, cooling by optical phonon emission is essentially complete 15 ps after injection. By fitting the time dependence of the carrier temperature, we estimate an effective carrier- optical-phonon scattering time of 1.2 ps.
Diffusion of metals into organic films
Authors: Probst M. , Haight R.
Published: July 2002

The temporal evolution of Ga and Ca vacuum deposited onto thin films of tris (8-hydroxy quinoline) aluminum (Alq) was studied with valence and atomic core level photoelectron spectroscopy. It was found that Ga, which exhibits weak reactivity with the Alq diffused into the organic at room temperature. Conversely Ca, a significantly more reactive metal, shows strong interaction with the organic surface. Effects of the initial morphology of the deposited materials on diffusivity will be described.
Unusual capacitance behavior of quantum well infrared photodetectors
Authors: Ershov M. , Liu H. C. , Li L. , Buchanan M. , Wasilewski Z. R. , Ryzhii V.
Published: July 2002

We report experimental and simulation results of capacitance of quantum well infrared photodetectors (QWIPs). We found that the QWIP capacitance displays unusual behavior as a function of voltage and frequency, deviating far from the constant geometric capacitance value. At high voltages, capacitance starts with a negative value at low frequencies, increases above zero with frequency, and eventually decays to the geometric capacitance value. The magnitude of negative capacitance exceeds the geometric capacitance by more than two orders of magnitude. Negative capacitance arises when the transient current in response to a voltage step is nonmonotonic with time. Simulation shows that this effect is due to nonequilibrium transient electron injection from the emitter resulting from the properties of the injection barrier and inertia of the QW recharging processes.
Temperature dependence of energy gap in GaN thin film studied by thermomodulation
Authors: Li Y. , Lu Y. , Shen H. , Wraback M. , Brown M. G. , Schurman M. , Koszi L. , Stall R. A.
Published: July 2002

The thermomodulation spectrum from metal organic chemical vapor deposition grown GaN has been measured in the temperature range of 20–310 K. A theoretical model is established to explain the spectrum by considering the modulation of dielectric constant and epilayer thickness. It is found that the latter is especially important for a material system with a large difference in refractive indices between the epilayer and the substrate. The band gap energy and broadening parameter are determined using a lineshape analysis. Varshni coefficients of the energy gap are determined. The temperature dependence of broadening parameter is also measured.
InN-based Ohmic contacts to InAlN
Authors: Donovan S. M. , MacKenzie J. D. , Abernathy C. R. , Pearton S. J. , Ren F. , Jones K. , Cole M.
Published: July 2002

The ability to form low resistance Ohmic contacts to InAlN using refractory metallization on In-containing contact layers has been investigated. The crystal quality as measured by surface roughness and x-ray diffraction was found to be a determining factor in the contact resistance which could be obtained using WSix contacts. InN growth conditions which resulted in poorer structural quality, such as the use of GaAs rather than sapphire substrates, low nitrogen flows, and low growth temperatures, resulted in contact resistances of 10−4–10−3 Ω cm2, as compared to ∼10−5 cm2 for InAlN alone. Using optimized conditions, contact resistances to InAlN of ∼3.5×10−6 Ω cm2 were obtained.
Stable amorphous-silicon thin-film transistors
Authors: Meiling H. , Schropp R. E. I.
Published: July 2002

Hydrogenated amorphous silicon, a-Si:H, prepared with the hot-wire chemical vapour deposition technique is incorporated in thin-film transistors (TFTs). High-quality TFTs are fabricated with this type of a-Si:H, which we deposited at a rate of 17 Å/s. TFTs with a current switching ratio of 5×105, a threshold voltage of 6.3 V, and an electron field-effect mobility in the saturation regime of 0.6 cm2/V s are obtained. These TFTs do not show any threshold voltage shift upon prolonged gate voltage application, in contrast to conventional a-Si:H TFTs. This has been achieved by optimizing the electronic properties of the hot-wire layer, and by optimizing the interface between the gate dielectric and the hot-wire layer.
Metal organic vapor phase epitaxy growth of GaAsN on GaAs using dimethylhydrazine and tertiarybutylarsine
Authors: Ougazzaden A. , Le Bellego Y. , Rao E. V. K. , Juhel M. , Leprince L. , Patriarche G.
Published: July 2002

GaAsN layers with good structural quality and surface morphology have been successfully grown on a GaAs substrate using atmospheric pressure metal organic vapor phase epitaxy. A new combination of precursors namely, dimethylhydrazine for nitrogen and tertiarybutylarsine instead of conventional arsine for arsenic, greatly facilitated growths at temperatures as low as 500 °C. Layers with N content as high as 3% and corresponding to room temperature photoluminescence (PL) peak wavelength of 1.17 μm (1.064 eV) have been obtained.
Relaxed Si1−xGex/Si1−x−yGexCy buffer structures with low threading dislocation density
Authors: Osten H. J. , Bugiel E.
Published: July 2002

We demonstrate the growth of a relaxed, only 1 μm thick, stepwise graded buffer based on a combination of Si1−xGex and Si1−x−yGexCy. This buffer concept relies on the retardation of dislocation glide in Si1−x−yGexCy relative to strain equivalent Si1−xGex on silicon. The homogeneous Si1−xGex layer with x=30% on top of the buffer structure is (73±5)% relaxed. For the nonoptimized buffer growth, we already find a threading dislocation density below 105 cm−2. A stepped Si1−xGex buffer with the identical thickness and strain profile grown with the same temperature ramp yields a threading dislocation density above 107 cm−2. This indicates that the addition of carbon is a promising way for new relaxed buffer concepts with low threading dislocation densities.
Deposition of n-type diamondlike carbon by using the layer-by-layer technique and its electron emission properties
Authors: Park Kyu Chang , Moon Jong Hyun , Chung Suk Jae , Jang Jin , Oh Myung Hwan , Milne W. I.
Published: July 2002

We have studied the electron emission behavior of the diamondlike carbon (DLC) films by plasma enhanced chemical vapor deposition using a layer-by-layer deposition, in which the deposition of a thin layer of DLC and a CF4 plasma exposure on its surface were carried out alternatively. The electron emission current increases with CF4 plasma exposure time. The increase in emission current appears to be due to the n-type behavior of the DLC.
Second harmonic generation in electric poled X-cut MgO-doped LiNbO3 waveguides
Authors: Sonoda Shinichiro , Tsuruma Isao , Hatori Masami
Published: July 2002

We demonstrate that quasi-phase-matched second harmonic generation occurs in annealed proton-exchanged (APE) X-cut MgO 5 mol % doped LiNbO3 (MgO:LN) waveguides supporting a TE-mode guided wave. Formation of a domain inversion was achieved by applying electric fields in X-cut and Y-cut MgO:LN. The depth of the formed domain inversion was 1 μm with a period of 4.75 μm. Anomalous characteristics of current versus voltage (I–V) of samples having domain inversion formed therein were found to have similar properties to a diode. A blue light having a wavelength of 475 nm and a power of 2.2 mW has been obtained with a normalized second harmonic conversion efficiency of 60%/W cm2 with uniform grating of 6 mm by using a Ti:Al2O3 laser as a fundamental wave source.
5-μm-wide YBa2Cu3O7−δ coplanar line with low transmission loss
Authors: Hattori W. , Yoshitake T. , Tahara S.
Published: July 2002

Narrow and low-loss YBa2Cu3O7−δ (YBCO) transmission lines for use in multichip modules have been attempted to be developed. 18-cm-long YBCO coplanar transmission lines with widths down to 5 μm were prepared by a composite patterning process combining Ar-ion milling and wet-etching. The transmission losses of the packaged 5-, 10-, and 25-μm-wide lines, respectively, were −1.57, −0.85, and −0.55 dB at 20 GHz and 55 K. These values provide similar surface resistances of 0.59–0.80 mΩ at 20 GHz and 55 K. This indicates successful fabrication of a 5-μm-wide YBCO coplanar line without notable extrinsic loss increase resulting from process damage. The attenuation constants of these lines are approximately two orders of magnitude lower than for 10-μm-wide Cu microstrip lines. These results show that the YBCO coplanar lines with widths down to 5 μm have great potential for use in multi-chip modules.
Heterogeneous nucleation of coherently strained islands during epitaxial growth of Ge on Si(110)
Authors: Krishnamurthy M. , Yang Bi-Ke , Weil J. D. , Slough C. G.
Published: July 2002

We report on the molecular beam epitaxial growth of Ge on Si(110) surfaces. High temperature cleaning (oxide desorption) results in the formation of shallow faceted pits distributed randomly on the Si(110) surface. Deposition of Ge at temperatures between 600 and 725 °C leads to preferential nucleation along the pit edges forming elongated islands, which subsequently grow to compact three-dimensional coherent islands. The observation of strained islands in close proximity to each other offers insights into their nucleation behavior and strain relaxation. Our observations suggest heterogeneous nucleation as a possible method for fabricating assemblies of quantum dots.
Electro-optic birefringence in semiconductor vertical-cavity lasers
Authors: Hendriks R. F. M. , van Exter M. P. , Woerdman J. P. , van Geelen A. , Weegels L. , Gulden K. H. , Moser M.
Published: July 2002

Birefringence induced by the electro-optic effect is demonstrated in vertical-cavity surface-emitting lasers (VCSEL). This is done by comparing two types of optically pumped VCSELs: VCSELs with standard pin-doping and VCSELs with symmetrical pip-doping. The observed birefringence in these VCSELs differs by an order of magnitude, a difference that we ascribe to the presence and absence, respectively, of electro-optic birefringence.
Direct correlation of structural and optical properties of InAs self-assembled dots deposited on InP(100)
Authors: Fréchengues S. , Drouot V. , Lambert B. , Lemoine D. , Loualiche S. , Le Corre A. , L’Haridon H.
Published: July 2002

The optical properties of self-assembled InAs dots on InP have been measured by photoluminescence, and using a selective chemical etching of the InP cap layer, the geometrical properties of the same dots have been determined by atomic force microscopy. From the dot dimensions, the calculated (n=1) electron to heavy hole transition energies with a simple model are strongly correlated to the measured photoluminescence spectra. This technique allows a better understanding of the correlation between structural and optical properties of self-assembled dots.
Magnetic field-induced noise in directly coupled high Tc superconducting quantum interference device magnetometers
Authors: Milliken F. P. , Brown S. L. , Koch R. H.
Published: July 2002

We have measured the noise of several directly coupled high Tc superconducting quantum interference device (SQUID) magnetometers as we change a static magnetic field B while the devices are superconducting. Devices without “flux dams” show an increase in noise at relatively low magnetic fields B∼1 μT. Devices with flux dams can show no deterioration of the noise characteristics for B as large as 34 μT. The flux dams are part of the pickup loop and limit the circulating current Icirc. If Icirc is kept sufficiently low no vortices are forced into the SQUID loop and the noise performance of the magnetometer remains good.
Optical properties of AlxGa1−xN/GaN heterostructures on sapphire by spectroscopic ellipsometry
Authors: Yu G. , Ishikawa H. , Umeno M. , Egawa T. , Watanabe J. , Jimbo T. , Soga T.
Published: July 2002

A method of analysis of spectroscopic ellipsometry (SE) measurement data is proposed for AlxGa1−xN/GaN heterostructures grown on sapphire substrates. The SE data measured at three angles of incidence, 40°, 50°, and 60°, are simultaneously fitted assuming the dielectric function to consist of a Sellmeir dispersion equation and a free-exciton absorption term. The refractive index n and the extinction coefficient k of undoped AlxGa1−xN films are determined in the spectral range of 1.5–4.13 eV of photon energy. The transition energy of the free exciton, which is in excellent agreement with the reported results for GaN in a previous paper, is found to vary from 3.44 to 3.95 eV when the composition x varies from 0 to 0.151. The refractive index n of AlxGa1−xN has also been compared with those reported results.
Space-charge-limited charge injection from indium tin oxide into a starburst amine and its implications for organic light-emitting diodes
Authors: Giebeler Carsten , Antoniadis Homer , Bradley Donal D. C. , Shirota Yasuhiko
Published: July 2002

We have investigated the hole-injection characteristics from indium tin–oxide (ITO) into 4,4′,4″-tris{N,-(3-methylphenyl)-N-phenylamino}triphenylamine (m-MTDATA) and have measured the hole-carrier drift mobility of this compound in single-layer ITO/m-MTDATA/Au structures. We have found that ITO is able to provide trap-free space-charge-limited currents over a wide range of film thicknesses and have established unambiguously that the ITO/m-MTDATA is an ideal Ohmic contact at high electric fields. Our observations clarify the role of m-MTDATA as a voltage-lowering hole-injecting buffer layer in organic light-emitting diodes.
Incorporation of oxygen and nitrogen in ultrathin films of SiO2 annealed in NO
Authors: Baumvol I. J. R. , Ganem J.-J. , Gosset L. G. , Trimaille I. , Rigo S.
Published: July 2002

The areal densities of oxygen and nitrogen incorporated into ultrathin films of silicon dioxide during rapid thermal processing in nitric oxide, as well as the regions where these incorporations took place, were determined by combining nuclear reaction analysis and narrow nuclear resonance depth profiling with isotopic enrichment of the processing gas. Oxygen is seen to incorporate in the near-surface and near-interface regions of the oxynitride films, whereas nitrogen is incorporated only in the near-interface regions. The growth of the oxynitride film is very moderate as compared to that of a SiO2 film in dry O2. The thermal oxynitridation of ultrathin SiO2 films takes place by two mechanisms in parallel: the major part of the NO molecules, which react with the silica, decompose in the near-surface region, the O atoms being exchanged for O atoms preexistent in this region of the SiO2 films; a minor portion of the NO molecules diffuse through the silica film in interstitial sites, without reacting with it, to react at the oxynitride/Si interface.
Spin-dependent tunneling through layered ferromagnetic nanoparticles
Authors: Inomata K. , Saito Y.
Published: July 2002

Spin-dependent tunneling has been investigated for nanostructured ferromagnetic tunnel junctions, in which an insulating nanostructured film made of layered hard ferromagnetic Co80Pt20 nanoparticles dispersed in an insulating SiO2 matrix is sandwiched between two soft ferromagnetic electrodes, an Fe/Co80Pt20 as a bottom electrode and a Co9Fe as a top electrode. The junctions investigated have three tunnel barriers and exhibited tunnel magnetoresistance of 9% at room temperature with a small resistance at a low field. The charging energy of the particles with an average diameter of 7 nm was estimated to be 45 meV from the temperature dependence of the resistance. Coulomb blockade was not observed for the junctions because of the low junction resistance.
Yellow luminescence depth profiling on GaN epifilms using reactive ion etching
Authors: Tu L. W. , Lee Y. C. , Chen S. J. , Lo I. , Stocker D. , Schubert E. F.
Published: July 2002

Depth profiling measurements of photoluminescence on GaN epitaxial films grown on c-plane sapphire with metalorganic chemical vapor deposition have been performed. Dry etching technique of reactive ion etching is used with reactive gas of CCl2F2/H2/Ar under an operation power of 200 W. Before and after each etching, reflectivity and photoluminescence spectra are measured. Film thickness is determined from both the scanning electron microscopy and the interference oscillations of the reflectivity spectra. An excellent steady etching rate of 19.2 nm/min is established. The photoluminescence measurements show that both the near-band-edge and the yellow luminescence remain fairly constant until the film thickness of about 700 nm, and a large drop is obtained in the ratio of near-band-edge to yellow emission intensity under about 300 nm. Analysis shows that the yellow luminescence emitters are mostly confined within the near interface region, and supports the origin of yellow luminescence to be due to native defects instead of impurities.
Analysis of current–voltage characteristics of organic light emitting diodes having a LiF/Al cathode and an Al–hydroxyquinoline/diamine junction
Authors: Matsumura Michio , Jinde Yukitoshi
Published: July 2002

The electron injection from the composite cathode consisting of a very thin LiF layer and an Al layer (LiF/Al) into Al–hydroxyquinoline (ALQ) layers showed the voltage and temperature dependence, which is characteristic to the Schottky emission mechanism. The barrier formed at the interface is lower than that formed at the interfaces between the conventional cathodes and the ALQ layer. The current–voltage characteristics of the light emitting diodes having the LiF/Al cathode and the ALQ/diamine junction were well explained on the basis of the properties of the electron injection into the ALQ layer and the hole injection into the diamine layer.
Local modification of magnetic properties by an electron beam
Authors: Allenspach R. , Bischof A. , Dürig U. , Grütter P.
Published: July 2002

Magnetic anisotropies can be modified locally by intense electron beams with keV energy. In ultrathin epitaxial Co films grown on Pt(111), switching of the easy axis from parallel to perpendicular to the surface can be induced, and the domain size can be enlarged by one order of magnitude.
Enhancing electron emission from silicon tip arrays by using thin amorphous diamond coating
Authors: Xu N. S. , She J. C. , Huq S. E. , Chen J. , Deng S. Z.
Published: July 2002

A thin (∼2 nm thick) amorphous diamond coating was prepared on single crystal silicon tip arrays by using a filtered vacuum arc plasma deposition technique. The coating has a microscopically uniform morphology. As compared to uncoated tips, the electron emission of the coated tip arrays is enhanced, showing an increase in the total current, lower turn-on field and a lower-slope Fowler–Nordheim plot. We propose that field-emitted electrons could tunnel through such a thin coating with few scattering events. It is shown that the low potential barrier at the interface is the major cause of the enhancing effects instead of the negative surface electron affinity of the coating.
Formation of oriented particles in an amorphous host: ZnS nanocrystals in silicon
Authors: Meldrum A. , Zuhr R. A. , Sonder E. , Budai J. D. , White C. W. , Boatner L. A. , Ewing R. C. , Henderson D. O.
Published: July 2002

Processes for incorporating randomly oriented crystalline precipitates in an amorphous host can be traced back to the 17th century when Cassius produced “gold ruby” glass. In this glass, octahedral colloidal precipitates of gold scatter light by the Mie process to produce a deep red color. In contrast to gold ruby glass, we describe a type of material in which the crystalline precipitates are crystallographically aligned in a coherent manner—even though they are dispersed in an amorphous matrix. Ion implantation and thermal processing are first used to form zinc sulfide nanocrystals that are coherently oriented with respect to a crystalline Si host. The Si is then amorphized by ion irradiation leaving the highly radiation-resistant ZnS precipitates in an aligned crystalline state. The process is anticipated to find applications in the creation of surfaces with unique optoelectronic properties.
CdSe fractional-monolayer active region of molecular beam epitaxy grown green ZnSe-based lasers
Authors: Ivanov S. V. , Toropov A. A. , Sorokin S. V. , Shubina T. V. , Sedova I. V. , Sitnikova A. A. , Kop’ev P. S. , Alferov Zh. I. , Lugauer H.-J. , Reuscher G. , Keim M. , Fischer F. , Waag A. , Landwehr G.
Published: July 2002

This letter reports on the self-organized growth of nanoscale dot-like CdSe-based islands during molecular beam epitaxy of CdSe/ZnSe nanostructures with a CdSe thickness between 0.75 and 3.0 monolayers. An increase in the nominal CdSe thickness results in a higher density of islands (up to 2×1010 cm−2) and is accompanied by dramatic enhancement of the photoluminescence efficiency. The density of large relaxed islands appears to saturate at a value of (3–4)×109 cm−2. Room temperature (Zn, Mg)(S, Se)-based optically pumped lasers with an extremely low threshold (less than 4 kW/cm2), as well as (Be, Mg, Zn)Se-based injection laser diodes using a single (2.5–2.8) monolayer thick CdSe active region, both demonstrating significantly enhanced degradation stability, have been fabricated and studied.
Determination of energy levels of surface states in GaAs metal–semiconductor field-effect transistor using deep-level transient spectroscopy
Authors: Choi Kyoung Jin , Lee Jong-Lam
Published: July 2002

The energy levels of surface states at the surface of GaAs were determined through capacitance deep-level transient spectroscopy of GaAs metal–semiconductor field-effect transistor with large gate periphery. Two types of hole-like traps are observed in the spectra. These originate from the surface states at the ungated regions between gate and source/drain electrodes. The activation energies of both surface states are determined to be 0.65±0.07 and 0.88±0.04 eV, which agree well with the energy levels of AsGa+ and AsGa++ within band gap of GaAs, responsible for the Fermi level pinning at the surface.
Study of the angular-dependent exchange coupling between a ferromagnetic and an antiferromagnetic layer
Authors: Xi Haiwen , Kryder Mark H. , White Robert M.
Published: July 2002

The angular dependence of the exchange coupling between a Permalloy film and an antiferromagnetic Cr45.5Mn45.5Pt9 film has been measured. We show that this complex angular dependence of the exchange coupling can be understood by a simple Stoner–Wohlfarth model involving only a uniaxial anisotropy and a unidirectional exchange coupling at the interface. Numerical results are in excellent agreement with the experimental data.
Observation of built-in electric field in InP self-assembled quantum dot systems
Authors: Davydov V. , Ignatiev I. , Ren H.-W. , Sugou S. , Masumoto Y.
Published: July 2002

Strong Franz–Keldysh oscillations were observed in the nonlinear reflection spectra of heterostructures with InP self-assembled quantum dots. These oscillations manifest a built-in electric field of about 30 kV/cm. We propose that this field originates from electric charge captured by the intrinsic defects on the dot interface. The presence of acceptor-like intrinsic defect states is found to be a general feature of the InP/InGaP interface but was not observed in other structures with quantum dots such as InAs/GaAs.
Magnetostatic interdot coupling in two-dimensional magnetic dot arrays
Authors: Guslienko K. Yu.
Published: July 2002

In this letter the calculations of the magnetostatic coupling energy are done for the typical cylindrical dot arrays. The square lattice of submicron-size dots and rectangular “herringbone” lattice of nanoscaled dots are considered. The ground state of the square dot lattice is shown to be continuously degenerated noncollinear antiferromagnetic. For the herringbone dot lattice the uniaxial anisotropy induced by magnetostatic coupling is calculated. Some experimental results on the submicron dots and nanometer scaled Co dots are discussed.
Selective electroluminescence from a single stack of sidewall quantum wires on patterned GaAs (311)A substrates
Authors: Ma Wenquan , Nötzel Richard , Ramsteiner Manfred , Jahn Uwe , Schönherr Hans-Peter , Kostial Helmar , Ploog Klaus H.
Published: July 2002

A p-i-n light-emitting diode (LED) with a single stack of sidewall quantum wires in the center of the intrinsic region has been fabricated by molecular-beam epitaxy on patterned GaAs (311)A substrates with all-Si n- and p-type doping. For small injection currents, the electroluminescence (EL) measured at low temperatures solely originates from the quantum wires without emission from the surrounding quantum wells within the patterned LED of 220 μm diameter. The selectivity of the EL emission is gradually reduced with increasing temperature, but the emission intensity per unit area in the wire regions is still two orders of magnitude larger than that in the well regions at room temperature. A model based on the lateral diffusion of injected electrons and holes is proposed to explain the selective carrier injection into the quantum wires.
Possible cooling by resonant Fowler-Nordheim emission
Authors: Korotkov Alexander N. , Likharev Konstantin K.
Published: July 2002

A method of electronic refrigeration based on resonant Fowler-Nordheim emission is analyzed. In this method, a bulk emitter is covered with a-few-nm-thick film of a widegap semiconductor, creating an intermediate step between electron energies in the emitter and in vacuum. An external electric field tilts this potential profile, forming a quantum well at the semiconductor-vacuum boundary. Alignment of its lowest two-dimensional subband with the energy of the hottest electrons of the emitter (a few kBT above the Fermi level) leads to a resonant, selective emission of these electrons, providing emitter cooling. Calculations show that cooling power of at least 30 W/cm2, and temperatures down to 10 K may be achieved using this effect.
A five-period normal-incidence (In, Ga)As/GaAs quantum-dot infrared photodetector
Authors: Pan Dong , Towe Elias , Kennerly Steve
Published: July 2002

We have measured the optical and electrical properties of a five-period normal-incidence (In, Ga)As/GaAs quantum-dot infrared photodetector. A primary intersubband transition peak is observed at the wavelength of 10.2 μm and a secondary one at 9.4 μm. Excellent electron transport and peak detectivity of 7×109 cm Hz1/2/W are achieved at 30 K, with a low bias responsivity of up to 70 mA/W at 0.6 V. We believe that an observed avalanche gain process is initiated by intersubband absorption in the quantum dots. The maximum responsivity due to this avalanche multiplication process is about 4 A/W at a bias of 1.0 V.
Role of Si1−xGex buffer layer on mobility enhancement in a strained-Si n-channel metal–oxide–semiconductor field-effect transistor
Authors: Sugii Nobuyuki , Nakagawa Kiyokazu , Yamaguchi Shinya , Miyao Masanobu
Published: July 2002

Strained-Si n-channel metal–oxide–semiconductor field-effect transistors (MOSFETs) were fabricated on molecular-beam epitaxially grown strained Si with various Si1−xGex buffer layers. Effective electron mobility in n-MOSFETs with a Si1−xGex (x=0.2, 0.3) graded buffer layer was 60% higher than that in an unstrained-Si n-MOSFET. However, mobility of samples with a Si1−xGex buffer layer on a low-temperature grown Si buffer layer was not increased as much as that of samples on a graded buffer layer. Atomic-force microscopic observation suggests that the power spectrum of surface roughness of the strained-Si layer varies according to the buffer layer, and this variation may affect the enhancement of mobility.
Erasable nanometer-scale modification at the Au/Si interface by ballistic electron emission microscopy
Authors: Hasegawa Y. , Akiyama K. , Ono M. , Kahng S.-J. , Xue Q. K. , Nakayama K. , Hashizume T. , Sakurai T.
Published: July 2002

We report that local modification and its erasing with a nanometer-scale size can be performed at a Au/Si(111) interface using ballistic electron emission microscopy (BEEM). By applying a negative voltage on the tip, a region was created where no BEEM current flows at the interface and was imaged with BEEM. The modified area can be erased by applying a voltage with the opposite polarity. It is found that the minimum size of writing and erasing corresponds to Au grains, suggesting a method of rewritable memory on a nanometer-scale dimension.
Role of self- and boron-interstitial clusters in transient enhanced diffusion in silicon
Authors: Mannino G. , Cowern N. E. B. , Roozeboom F. , van Berkum J. G. M.
Published: July 2002

We investigate the nucleation and evolution of boron-interstitial clusters (BIC), driven by high interstitial supersaturations, S(t), during Si implant damage annealing. The BICs are “fabricated” in a narrow band by overlapping the Si implant damage tail with a lightly doped B buried layer. The BIC band is found to be a net sink for interstitials at supersaturations S(t)>104. Our results suggest that silicon self-interstitial defects are the primary source of interstitials driving transient enhanced diffusion, and that BICs act as a secondary “buffer” for the interstitial supersaturation.
Cubic GaN epilayers grown by molecular beam epitaxy on thin β-SiC/Si (001) substrates
Authors: As D. J. , Frey T. , Schikora D. , Lischka K. , Cimalla V. , Pezoldt J. , Goldhahn R. , Kaiser S. , Gebhardt W.
Published: July 2002

The molecular beam epitaxy of cubic GaN on Si(001) substrates, which were covered by a 4 nm thick β-SiC layer, is reported. The structural and optical properties of the cubic GaN epilayers were studied by transmission electron microscopy, high-resolution x-ray diffraction, and low-temperature photoluminescence measurements. We find clear evidence for the growth of cubic GaN layers almost free of hexagonal inclusions. The density of extended defects and the near band edge photoluminescence of the cubic GaN layers grown at substrate temperatures of 835 °C is comparable to that of high quality cubic GaN epilayers grown by molecular beam epitaxy on GaAs (001) substrates.
Importance of coupling between longitudinal and transverse components for the creation of acoustic band gaps: The aluminum in mercury case
Authors: Sigalas M. M. , Garcı́a N.
Published: July 2002

Using the finite-difference time-domain method, we theoretically study elastic waves propagating in a two-dimensional composite consisting of aluminum cylinders embedded in mercury. The importance of the transverse components of the aluminum scatterers in the creation of the gaps is shown by switching off the transverse waves inside the aluminum. In that case, there are very narrow gaps or no gaps at all. In contrast, when the transverse components are on, as they should be, wide full band gaps appear for longitudinal incident waves. Since mercury supports only longitudinal waves, these are full elastic band gaps.
Si complementary single-electron inverter with voltage gain
Authors: Ono Yukinori , Takahashi Yasuo , Yamazaki Kenji , Nagase Masao , Namatsu Hideo , Kurihara Kenji , Murase Katsumi
Published: July 2002

A Si complementary single-electron inverter in which two identical single-electron transistors (SETs) are packed is fabricated on a silicon-on-insulator substrate. For the fabrication, the vertical pattern-dependent oxidation method, which enables the formation of two tiny SETs aligned in parallel, is modified so that the two SETs can be connected in series to realize an inverter configuration. The resultant circuit occupies a very small area: 100×100 nm for each SET. For complementary operation, the electrical characteristics of one of the SETs are shifted using a side gate situated near the SET. Input–output transfer with a voltage gain larger than unity is demonstrated at 27 K.