bluuebunny/crossref_metadata_2025 huggingface dataset:
Low temperature annealing of ion-implantation-induced defects in GaAs by minority carrier injection
Authors: Wada K. , Nakanishi H. , Yamada K.
Published: July 2002

This letter demonstrates that minority-carrier injection entirely removes ion-implantation- induced defects in GaAs at temperatures as low as 200 °C, where no annealing is observed as a result of a simple thermal annealing. The enhancement mechanism is discussed within the framework of recombination-enhanced defect reaction. The present findings have opened the door to ‘‘room temperature semiconductor material processing.’’
Barrier height enhancement of Schottky diodes on n-In0.53Ga0.47As by cryogenic processing
Authors: Lee H. J. , Anderson W. A. , Hardtdegen H. , Lüth H.
Published: July 2002

Schottky contacts on n-In0.53Ga0.47As have been made by metal deposition on substrates cooled to a temperature of 77 K. The current-voltage and capacitance-voltage characteristics showed that the Schottky diodes formed at low temperature had a much improved barrier height compared to those formed at room temperature. The Schottky barrier height φB, was found to be increased from ∼0.2 to 0.60 eV with Ag metal. For the low temperature diode, the saturation current density, J0, was about four orders smaller than for the room temperature diode. Deep level transient spectroscopy studies of n-InGaAs low temperature diodes exhibited one electron trap located at Ec-0.23 eV. This trap level was identified as a bulk trap.
Electroluminescence at room temperature of a SinGem strained-layer superlattice
Authors: Engvall Jesper , Olajos Janos , Grimmeiss Hermann G. , Presting Hartmut , Kibbel Horst , Kasper Erich
Published: July 2002

We report for the first time on room temperature electroluminescence in the region 1.3–1.7 μm from a strain-adjusted Si6Ge4 superlattice. These results, together with photoluminescence, short-circuit photocurrent spectroscopy, and voltage-intensity and current-intensity measurements indicate that the observed electroluminescence consists of two emission bands which are believed to be caused by defect and interband recombination processes.
Morphological instability and Si diffusion in nanoscale cobalt silicide films formed on heavily phosphorus doped polycrystalline silicon
Authors: Pramanick S. , Erokhin Yu. N. , Patnaik B. K. , Rozgonyi G. A.
Published: July 2002

In this letter we examine the interdiffusion and reaction of deposited cobalt layers during the formation of nanoscale (<35 nm) silicide films on heavily phosphorus doped polycrystalline silicon films. The onset of morphological instability is indicated by an increase of layer resistivity. Cross-section transmission electron micrographs of high resistance films, which were formed by rapid thermal annealing at 700 °C for 30 s, show a series of disconnected ‘‘islands’’ of CoSi2 with or without a highly disordered (amorphous) Si-rich top surface layer. A continuous band of voids, attributed to the Kirkendall effect and to phase transformation induced volume changes, initially appear at the CoSi/CoSi2 interface. In the highly agglomerated films, these voids separate the buried CoSi2 islands and buried polycrystalline Si from the disordered surface layer. The sequence of events is analyzed in terms of grain boundary diffusion, grain boundary grooving, and the impact of phosphorus concentration (∼1020 cm−3) on Si diffusivity.
Reduced threshold all-optical bistability in etched quantum well microresonators
Authors: Rivera T. , Ladan F. R. , Izraël A. , Azoulay R. , Kuszelewicz R. , Oudar J. L.
Published: July 2002

All-optical bistability is demonstrated in GaAs/AlGaAs multiple quantum well microresonators fabricated by SiCl4 reactive ion etching. A fabrication process has been developed in order to obtain low threshold bistability. The studied samples are two-dimensional 15×15 arrays of cylindrical microresonators of 4 μm diam and 6 μm height. Owing to lateral carrier and light confinement, bistability is observed with a strongly reduced threshold power, below 100 μW. This result was obtained without post-etching surface treatment. The low bistability threshold suggests that the surface recombination rate is reasonably small, possibly due to some self-passivation occurring during the etching process.
Temporal behavior of resonant-optical-waveguide phase-locked diode laser arrays
Authors: Ramanujan Sujatha , Winful Herbert G. , Felisky Marc , DeFreez Richard K. , Botez Dan , Jansen Michael , Wisseman Phil
Published: July 2002

Measurements of the temporal and spatial behavior of resonant optical waveguide (ROW) laser arrays with significant interelement loss reveal the presence of sustained self-pulsations in the output intensity of the laser. The mechanism responsible for pulsations is believed to be saturable absorption arising from the presence of absorbers in the interelement regions. This is experimentally confirmed in that reduction or elimination of the interelement loss suppresses the pulsations. Quiescent behavior is obtained to at least 0.45 W continuous wave power and 3.4 times threshold in near-diffraction-limited beams from devices with negligible interelement loss.
Self-organizing growth of erbium arsenide quantum dots and wires in gallium arsenide by molecular beam epitaxy
Authors: Singer K. E. , Rutter P. , Peaker A. R. , Wright A. C.
Published: July 2002

Gallium arsenide doped with erbium has been grown by molecular beam epitaxy. At growth temperatures in the range 540–605 °C, and with arsenic to gallium flux ratios of 2 and more, the erbium forms uniform crystalline microprecipitates of ErAs when the concentration exceeds 7×1017 cm−3. The diameter can be varied in the range 11–21 Å by altering the growth temperature. Reducing the arsenic to gallium flux ratio to close to stoichiometry changes the growth mode to one yielding quantum wires aligned in the growth direction. Subtle changes in growth conditions lead to bifurcated structures, which we refer to as quantum trees.
High T
c Josephson junctions combining a grain boundary and local strain, using NdGaO3 bicrystal substrates
Authors: Quincey P. G.
Published: July 2002

The bicrystal substrate approach to high Tc Josephson junctions has previously used substrates with cubic (isotropic) structure. NdGaO3, which has orthorhombic structure, has excellent lattice match to YBa2Cu3O7−x and good dielectric properties. When bicrystals are made with NdGaO3 in the usual (110) orientation, the anisotropy means that there will be thermally induced local strain at the grain boundary in any overlaid film. Several junctions have been made with this novel variation on the bicrystal technique, showing values of IcRN around 400 μV at 77 K.
Nanometer-scale lithography on Si surface by decomposition of ferrocene molecules using a scanning tunneling microscope
Authors: Thibaudau F. , Roche J. R. , Salvan F.
Published: July 2002

We describe lithography experiments on boron doped Si substrates using the decomposition of ferrocene molecules with a scanning tunneling microscope tip. On the basis of writing conditions we propose that field ionization of the molecules is the key to the writing process and is responsible for the nanometer definition of the pattern edge.
Thermal annealing effect on low temperature molecular beam epitaxy grown GaAs: Arsenic precipitation and the change of resistivity
Authors: Luo J. K. , Thomas H. , Morgan D. V. , Westwood D.
Published: July 2002

The post-growth annealing effects on the electrical properties of low temperature (LT-) GaAs grown by molecular beam epitaxy have been investigated. It was found that the resistivity of the LT-GaAs layer increased exponentially with annealing temperature TA, resulting in an activation energy of 2.1 eV. This activation energy is related to the activation energy of arsenic precipitation. Based on hopping conduction theory, an As cluster density NT, has been estimated from the resistivities of the LT-GaAs layers. The change of density of arsenic clusters with TA, was found to be of the form NT=NT0 exp(−T/T0), in agreement with values obtained by transmission electron microscopy measurements. The breakdown voltage of the LT-GaAs layer remained almost unchanged as TA was increased up to 650 °C, but the breakdown characteristic became soft. The formation of As clusters is held responsible for the soft breakdown of the LT-GaAs layer after annealing.
Selective growth of Ge in GeF4-Si2H6 system
Authors: Yamamoto Masaji , Takada Yoshiharu , Hanna Jun-ichi
Published: July 2002

Selective growth of Ge in GeF4-Si2H6 system was investigated on SiO2 patterned Si substrates and its characteristics were discussed in comparison with those of W chemical vapor deposition in WF6-SiH4 system which is similar in terms of a combination of redox materials including a fluorinated substance. The selectivity was governed primarily by the growth temperature. The selective growth on a SiO2 patterned Si substrate was achieved at a wide range of the gas flow ratios (Si2H6/GeF4) at 375 °C, where the characteristics of film growth were distinguished clearly from those at the temperatures over 400 °C larger quality degraded. The experimental results indicated that the selectivity was deeply rooted in the growth mechanisms of the film themselves which were separated around 400 °C.
Laser-induced breakdown by impact ionization in SiO2 with pulse widths from 7 ns to 150 fs
Authors: Du D. , Liu X. , Korn G. , Squier J. , Mourou G.
Published: July 2002

Results of laser-induced breakdown experiments in fused silica (SiO2) employing 150 fs–7 ns, 780 nm laser pulses are reported. The avalanche ionization mechanism is found to dominate over the entire pulse-width range. Fluence breakdown threshold does not follow the scaling of Fth∼ √τp, when pulses are shorter than 10 ps. The impact ionization coefficient of SiO2 is measured up to ∼3×108 V/cm. The relative role of photoionization in breakdown for ultrashort pulses is discussed.
Dielectric properties of electron-beam deposited Ga2O3 films
Authors: Passlack M. , Hunt N. E. J. , Schubert E. F. , Zydzik G. J. , Hong M. , Mannaerts J. P. , Opila R. L. , Fischer R. J.
Published: July 2002

We have fabricated high quality, dielectric Ga2O3 thin films. The films with thicknesses between 40 and 4000 Å were deposited by electron-beam evaporation using a single-crystal high purity Gd3Ga5O12 source. Metal-insulator-semiconductor (MIS) and metal-insulator-metal structures (MIM) were fabricated in order to determine dielectric properties, which were found to depend strongly on deposition conditions such as substrate temperature and oxygen pressure. We obtained excellent dielectric properties for films deposited at substrate temperatures of 40 °C with no excess oxygen and at 125 °C with an oxygen partial pressure of 2×10−4 Torr. Specific resistivities ρ and dc breakdown fields Em of up to 6×1013 Ω cm and 2.1 MV/cm, respectively, were measured. Static dielectric constants between 9.93 and 10.2 were determined for these films. Like in other dielectrics, the current transport mechanisms are found to be bulk rather than electrode controlled.
Wavelength-selective detector based on a quantum well in a standing wave
Authors: Carraresi L. , De Souza E. A. , Miller D. A. B. , Jan W. Y. , Cunningham J. E.
Published: July 2002

We present an example of a new class of optoelectronic devices realized by placing thin absorbers in a standing wave. Using quantum wells as absorbers and measuring the photocurrent from each of them separately it is possible to realize devices which accomplish complex tasks like separately detecting more than one wavelength at the same time or measuring the wavelength of a quasimonochromatic beam. In this letter we demonstrate a wavelength-selective detector based on a single quantum well. It detects at 850 nm with a bandwidth <10 nm, while rejecting at the shorter wavelength of 835 nm by a factor of 120.
Pulsed excimer laser deposition of potassium titanyl phosphate films
Authors: Xiong Fulin , Chang R. P. H. , Hagerman M. E. , Kozhevnikov V. L. , Poeppelmeier K. R. , Zhou Haitain , Wong G. K. , Ketterson J. B. , White C. W.
Published: July 2002

Nonlinear optical thin films of potassium titanyl phosphate (KTP) have been successfully fabricated by pulsed excimer laser deposition on substrates of sapphire and Si. The films deposited on sapphire substrates in the temperature ranges of 450–550 °C show good crystallinity with preferential (100) and (011) orientations; on silicon, the films are polycrystalline. The stoichiometry of the films has been found to be Ti rich (about 20% higher). The effective refractive index of the films has been evaluated by spectroscopic ellipsometry with values between 1.75 and 2.0 in the spectral region 0.3–0.9 μm, consistent with the bulk value. The deposited films show a promising nonlinear optical response with high second-harmonic generation efficiency, comparable to that of single-crystal KTP.
Thermal expansion of polycrystalline diamond produced by chemical vapor deposition
Authors: Pickrell D. J. , Kline K. A. , Taylor R. E.
Published: July 2002

The in-plane thermal expansion of thick freestanding polycrystalline diamond films produced by hot filament chemical vapor deposition was measured by dilatometry. Measurements were obtained from two different diamond wafers over a temperature range of −200 to +800 °C. Within experimental error of the measurements, values agree with those reported for natural single-crystal diamond. Quantification of the thermal expansion of chemically vapor deposited (CVD) diamond is important for determining thermal stresses which will be encountered during deposition of diamond on various substrate materials and during use of diamond in various applications.
Deep photoluminescence in Si/Si1−xGex/Si quantum wells created by ion implantation and annealing
Authors: Sturm J. C. , Amour A. St. , Lacroix Y. , Thewalt M. L. W.
Published: July 2002

Strong broad photoluminescence similar to that observed in some materials grown by molecular beam epitaxy (MBE) has been observed in Si/Si1−xGex/Si quantum wells grown by chemical vapor deposition. As grown, the samples exhibited SiGe band-edge phonon-resolved bound-exciton luminescence, but after being self-implanted with silicon and annealed at 600 °C, a deep broad luminescence band 80–100 meV below the excitonic gap was observed. This strong luminescence disappeared with an 800 °C anneal and had a pump power and temperature dependence similar to that observed in MBE samples. This is the first time that such luminescence has been observed in material other than that grown by MBE.
Spiral growth of GaAs by metalorganic vapor phase epitaxy
Authors: Hsu C. C. , Lu Y. C. , Xu J. B. , Wilson I. H.
Published: July 2002

Growth spirals are observed on metalorganic vapor phase epitaxy grown GaAs surfaces by atomic force microscopy. The growth mechanism is according to the classical Burton–Cabrera–Frank theory. Spirals originate from screw dislocations. Successive turns of steps are sent out by the dislocations. These steps are of monolayer height (0.28 nm) and the interstep distance is around 150 nm. The spiral steps are well developed around the screw dislocations, while the adjacent vicinal steps lack the regularity of the spiral steps. Two-dimensional nucleation islands are also observed on the vicinal steps.
Nitrogen-doped ZnSe grown on 4°-misoriented GaAs(100) and GaAs(211) by molecular beam epitaxy
Authors: Zhu Ziqiang , Ebisutani Takashi , Takebayashi Kazuhisa , Tanaka Kiyotake , Yao Takafumi
Published: July 2002

This letter presents the growth and characterization of N-doped ZnSe grown on (100)GaAs misoriented 4° off toward (110), and (010), and (211)GaAs-A and -B. The effects of the surface steps on the formation of deep donors are investigated by comparing photoluminescence properties and net-acceptor concentration of ZnSe:N epilayers grown on misoriented (100) surfaces with those grown on the exact (100)GaAs. It is shown that the use of the misoriented (100) surfaces suppresses the generation of deep donors and enhances the net acceptor concentration. The effects of bond natures at Zn sites on the N-incorporation process are studied through the comparison of the net-acceptor concentration of N-doped ZnSe epilayers grown on the (211)A surface with those on the (211)B surface. It is found that the N incorporation is limited by a single-dangling bond at the Zn sites.
Growth of high quality amorphous silicon films with significantly improved stability
Authors: Dalal Vikram L. , Ping E. X. , Kaushal Sanjeev , Bhan Mohan K. , Leonard Mark
Published: July 2002

We report on the results of a systematic series of experiments aimed at improving the stability of amorphous silicon (a-Si:H) films. We find that very low levels (0.2–0.4 ppm) of compensation by boron, when combined with growth conditions that favor a robust microstructure in the material, results in films with significantly improved stability and very low defect density. The films were grown using a reactive plasma beam technique using a remote plasma beam from an electron-cyclotron-resonance source. The improvement in stability is seen under both short-term (a few minutes) light soaking, and also under light soaking under high intensity (10×sun) illumination conditions. We conclude that the improvement in initial stability is a result of compensation of native donors (probably oxygen) in the material by boron. The surprising reduction in long term instability and corresponding defect density upon compensation implies that the microstructure and structural changes around the native impurities may play a role in the long-term instability of the material.
Quantum wire microcavity laser made from GaAs fractional layer superlattices
Authors: Chavez-Pirson A. , Ando H. , Saito H. , Kanbe H.
Published: July 2002

We report the first demonstration of lasing action in a quantum wire microcavity semiconductor laser made from an array of (AlAs)1/4(GaAs)3/4 fractional-layer superlattice (FLS) quantum wires. The FLS growth method produces uniform, densely packed, damage-free arrays of nanometer-size quantum wires which are integrated into an optical microcavity that is the size of the wavelength of the light. We obtain room temperature optically pumped lasing for wavelengths from 670 to 690 nm. The lasing output is linearly polarized parallel to the quantum wires, reflecting the higher optical gain for polarization direction parallel to the wires. The combination of a semiconductor quantum wire active material with an optical microcavity offers the possibility of ultimately compact, highly efficient laser sources.
Kinetic pattern formation of Gd-silicide films in lateral growth geometry
Authors: Molnár G. , Petô G. , Horváth Z. E. , Zsoldos E.
Published: July 2002

The solid phase reaction of gadolinium thin film and silicon substrate was investigated in lateral growth geometry with the help of periodic titanium protective stripes by optical microscopy. In the lateral reaction zone the shape of the interface between gadolinium and Gd silicide was very complicated and showed pattern formation. This silicide growth can be described as a kinetic process modified by the structure of the Gd film in contrast to the previously proposed simple nucleation.
Detection of hydrogen-plasma-induced defects in Si by positron annihilation
Authors: Asoka-Kumar P. , Stein H. J. , Lynn K. G.
Published: July 2002

We report a positron annihilation study of defects created in Si by rf hydrogen-plasma exposure at 275 °C. Analysis of positron annihilation spectroscopy data indicates voidlike structures in a defective ayer extending to ≊14 nm from the surface at a concentration of 1.9±0.5×1020 cm−3. The Doppler broadening parameter for the annihilation gamma rays is strongly correlated to the hydrogen coverage of the void surfaces, voids remain in the Si to at least 800 °C while the hydrogen is desorbed from their surfaces between 600 and 800 °C.
Candela-class high-brightness InGaN/AlGaN double-heterostructure blue-light-emitting diodes
Authors: Nakamura Shuji , Mukai Takashi , Senoh Masayuki
Published: July 2002

Candela-class high-brightness InGaN/AlGaN double-heterostructure (DH) blue-light-emitting diodes (LEDs) with the luminous intensity over 1 cd were fabricated. As an active layer, a Zn-doped InGaN layer was used for the DH LEDs. The typical output power was 1500 μW and the external quantum efficiency was as high as 2.7% at a forward current of 20 mA at room temperature. The peak wavelength and the full width at half-maximum of the electroluminescence were 450 and 70 nm, respectively. This value of luminous intensity was the highest ever reported for blue LEDs.
Fullerenes as precursors for diamond film growth without hydrogen or oxygen additions
Authors: Gruen Dieter M. , Liu Shengzhong , Krauss Alan R. , Luo Jianshu , Pan Xianzheng
Published: July 2002

Diamond films are predominantly grown using approximately 1% of a hydrocarbon precursor in hydrogen gas. Hydrogen is generally believed to be necessary for the diamond thin-film growth process. However, hydrogen in varying amounts is inevitably incorporated in the growing diamond lattice, leading to structural defects. We report here the successful growth of diamond films using fullerene precursors in an argon microwave plasma, a unique development achieved without the addition of hydrogen or oxygen. We speculate that collisional fragmentation of C60 to give C2 could be responsible for the high growth rate of the very-fine-grained diamond films.
Improved performance of large-area InP/InGaAs metal-semiconductor-metal photodetectors by sulfur passivation
Authors: Schade U. , Kollakowski St. , Böttcher E. H. , Bimberg D.
Published: July 2002

We report on sulfur based surface passivation technique for InGaAs metal-semiconductor-metal (MSM) photodetectors with an InP barrier enhancement layer. We show that excessive leakage current and photocurrent gain, which are the two major performance-limiting factors in MSM detectors, can be largely suppressed by a treatment of the InP surface with ammonium polysulfide. The dark current and photocurrent characteristics of such passivated devices were monitored over a period of half a year and were found to be stable. The improved performance of the device characteristics is explained in terms of a passivation-induced reduction of surface charging effects.
Photoluminescence, intersubband absorption, and double crystal x-ray diffraction in p-doped InGaAs/AlGaAs strained multiple quantum wells
Authors: Chin V. W. L. , Tansley T. L. , Zhang D. H. , Radhakrishnan K. , Yoon S. F. , Clark A.
Published: July 2002

We report the correlation of photoluminescence (PL), infrared intersubband absorption, and double crystal x-ray diffraction (DCXRD) data for a p-doped InGaAs/AlGaAs strained multi- ple-quantum-well structure grown by molecular beam epitaxy. A PL doublet at 1.476 and 1.563 eV involves two confined holes states and their 87 meV separation is in good agreement with the measured intersubband absorption of about 14.5 μm (85 meV). Furthermore, when the well width obtained from DCXRD measurement is included excellent agreement with an envelope function calculation is found for the energy levels determined by PL and intersubband absorption energy.
Preparation of La-modified PbTiO3 thin films on the oxide buffer layers with NaCl-type structure
Authors: Fujii Satoru , Tomozawa Atsushi , Fujii Eiji , Torii Hideo , Takayama Ryoichi , Hirao Takashi
Published: July 2002

La-modified PbTiO3(PLT: Pb0.9La0.1Ti0.975O3) thin films by rf magnetron sputtering were prepared on the preferred (100)-oriented oxide buffer layers with NaCl-type structure, which were prepared by plasma-enhanced metalorganic chemical vapor deposition. Fused silica, (111)Si, soda-lime glass, and stainless steel were used as the substrates to prepare the oxide buffer layers. The c-axis and a-axis preferred oriented PLT thin films were obtained on the buffer layer, independent of the kind of substrate. Further, highly c-axis oriented PLT thin films were obtained when the substrate had a large thermal expansion coefficient. Significant pyroelectric currents were detected without a poling treatment. The NiCr/PLT/(100)Pt/(100)MgO/stainless steel structure had a dielectric constant of 250, a dielectric loss factor tan δ of 0.8%, and a pyroelectric coefficient of 3.8×10−4 C/m2 K.
Franz–Keldysh effect in an optical waveguide containing a resonant tunneling diode
Authors: McMeekin S. G. , Taylor M. R. S. , Vögele B. , Stanley C. R. , Ironside C. N.
Published: July 2002

Optical modulation in a waveguide containing a resonant tunneling diode has been observed. The observations are in agreement with a model which assumes that the modulation effect is due to a Franz–Keldysh band-edge shift produced by the electric field developed over a depletion region association with operation of the resonant tunneling diode. The effect has device potential for optical modulation at microwave frequencies.
Photoinduced light scattering in LiTaO3:Nd crystal
Authors: Wu Xinglong , Zhang Ming-sheng , Chen Xiaoyuan , Meng Xiangkang , Feng Duan
Published: July 2002

Photoinduced light scattering of LiTaO3:Nd crystal (0.1 wt %) was examined by using a focused He-Ne laser beam. When an ordinary incident beam illuminates the sample along the y axis, the scattered light is asymmetrical in the xy plane, and the scattered intensities display a time-dependent distribution with a gradual increase and decrease for the ordinary and extraordinary beams, respectively. The situation is reversed for an extraordinary incident beam. When an incident beam with ordinary or extraordinary polarizations illuminates the sample along the x axis, two scattered specklons are dependent upon the crossing angle with almost the same intensity. We attribute them to a new photorefractive effect due to the microstructure change in LiTaO3 crystal with Nd doping. In addition, Raman spectra concerning the observed scattered structures are also measured and elucidated.
Tunneling escape time of electrons from a quantum well with Γ-Χ mixing effect
Authors: Zhang Yumin , Zheng Houzhi
Published: July 2002

By using the envelope function method we calculated the tunneling escape time of electrons from a quantum well. We adopted a simplified interface matrix to describe the Γ-Χ mixing effect, and employed a wave packet method to determine the tunneling escape time. When the Γ state in the well was in resonance with the Χ state in the barrier, the escape time reduced remarkably. However, it was possible that the wave functions in two different channels, i.e., Γ-Γ-Γ and Γ-Χ-Γ, could interfere destructively, leading the escape time greater than that of pure Γ-Γ-Γ tunneling.
Very low loss channel waveguides in polymethylmethacrylate
Authors: Mukherjee Anadi , Eapen Ben Joy , Baral Swapan K.
Published: July 2002

A unique ultraviolet laser fabrication technique of very low loss channel waveguides in polymethylmethacrylate (PMMA) is reported. Beside low surface and sidewall scattering, the role of bulk scattering in polymeric waveguides was addressed. Linear propagation loss of 0.08 dB/cm in channel waveguides of PMMA at 633 nm was achieved. The experimentally observed one order of magnitude reduction of linear loss due to a selection of maximum size polymers used is qualitatively explained from Mie scattering simulation from bulk polymer medium. This points to the possibility of further reduction of linear propagation loss in polymeric waveguides with reduced dimension of constituent polymers.
Multicolor infrared detection using a voltage tunable bandpass filter
Authors: Tidrow M. Z. , Choi K. K. , Farley C. W. , Chang F.
Published: July 2002

It was demonstrated that an electron energy bandpass filter placed next to a quantum well infrared photodetector (QWIP) is not only able to suppress dark current, but also is able to select photocurrents of different energies. Since the bandpass energy of the filter changes with an applied bias across the filter, this mechanism can be used to control the detection width and the cutoff wavelength of the detector. If the photoresponse of the QWIP has more than one energy peak, the same filter can also be used to intercept a particular photoelectron peak and achieve voltage tunable multicolor infrared detection. In this work, we also show that the bandpass filter increases the background limited temperature and the detectivity of the QWIP by filtering away the lower energy dark current and the unused photocurrent.
Seeded epitaxy of metals by sputter deposition
Authors: Harp G. R. , Parkin S. S. P.
Published: July 2002

It is not generally appreciated that crystalline metallic thin film structures can be prepared using sputter deposition techniques by growth onto single crystalline substrates. Three systems, fcc Co/Cu(100), bcc Co/Cr(100), and hcp Co/Ru(101̄3) multilayers are described in detail from a comprehensive study of more than 40 different systems. It is shown that the use of thin ‘‘seed’’ layers readily allows the preparation of different crystal structures and/or crystal orientations for the same substrate.
Photodetector for microwave signals based on the synchronous drift of photogenerated carriers with a moving interference pattern
Authors: Dolfi D. , Merlet Th. , Mestreau A. , Huignard J.-P.
Published: July 2002

We present the principle of a new photodetector based on the synchronous drift in a semiconductor of photogenerated carriers with a moving interference pattern. It provides a large detection volume which could be suitable for the optical generation of microwave signals. A theoretical analysis is detailed and followed by an experimental demonstration in a MBE grown GaAs layer illuminated with a moving interference pattern. We study the evolution of the detected signal at frequency f=1.6 GHz as a function of applied electric field, carrier lifetime, and fringe period.
Electron emission from diamond coated silicon field emitters
Authors: Liu J. , Zhirnov V. V. , Wojak G. J. , Myers A. F. , Choi W. B. , Hren J. J. , Wolter S. D. , McClure M. T. , Stoner B. R. , Glass J. T.
Published: July 2002

Polycrystalline diamond thin films have been formed on single crystal silicon field emitters using bias-enhanced nucleation in a microwave plasma chemical vapor deposition system. A diamond nucleation density greater than 1010/cm2 with small grain sizes (<25 nm) was achieved on the surfaces of silicon emitters with nanometer scale curvature. Field emission from these diamond coated silicon emitters exhibited significant enhancement compared to the pure Si emitters both in total emission current and stability. Using a Fowler–Nordheim analysis a very large effective emitting area of nearly 10−11 cm2 was obtained from the diamond coated Si emitters compared to that of uncoated Si emitters (10−16 cm2). This area was found to be comparable to the entire tip surface area.
Influence of X-valley superlattice on electron blocking by multiquantum barriers
Authors: Yen S. T. , Lee C. P. , Tsai C. M. , Chen H. R.
Published: July 2002

Four n-i-n GaAs/AlGaAs diodes have been used to demonstrate that at room temperature the carrier blocking is influenced by the X-valley superlattice in a multiquantum barrier. The diode with a Γ-X crossover multiquantum barrier has a current at least three orders lower than the corresponding diode with only a bulk barrier. However, diodes without Γ-X crossover barriers have resistance as low as 10 Ω in spite of whether a multiquantum barrier exists or not. This indicates that the X-valley superlattice plays an important role in blocking the current flowing across/through a multiquantum barrier.
Improved poling and thermal stability of sol-gel nonlinear optical polymers
Authors: Kalluri Srinath , Shi Yongqiang , Steier William H. , Yang Zhixin , Xu Chengzeng , Wu Bo , Dalton Larry R.
Published: July 2002

An aminosulfone dye chromophore was covalently incorporated into a sol-gel network for second-order nonlinear optics applications by functionalizing both ends of the chromophore. Covalent incorporation allows for high chromophore loading densities (∼35%) and locking in both ends of the chromophore improves thermal stability. Short term stability of the nonlinearity at 200 °C and long term stability over 500 h at 100 °C was demonstrated. Two different temperature profiles for corona poling were investigated and one found superior to the other. A second harmonic coefficient, d33 of 27 pm/V at the 1064 nm fundamental wavelength was measured.
Phase-matched second-harmonic generation in a Ta2O5/KTiOPO4 waveguide
Authors: Doumuki Tohru , Tamada Hitoshi , Saitoh Masaki
Published: July 2002

Highly efficient phase-matched second-harmonic generation (TEω00-like mode to TE2ω10-like mode) using waveguide modal dispersions is reported. The waveguide is composed of a KTiOPO4 substrate, a Ta2O5 thin-film core, and a SiO2 clad in the strip-loaded configuration. Normalized conversion efficiency of around 1000%/W cm2 and the blue (413 nm) second-harmonic power of 13 mW were achieved with a 4.1-mm-long waveguide. The output beam of the second-harmonic wave showed a single-peak power profile, in spite of being first-order mode in the film thickness directions.
Direct observation of the interface structure of thin YBa2Cu3Ox film (<500 Å) deposited on SrTiO3(001) utilizing grazing incidence x-ray diffraction
Authors: Gau Tsai-Sheng , Chang Shih-Lin , Hung Hsueh-Hsing , Lee Chih-Hao , Huang Tung-Wuu , Lu Horng-Bor , Yang Sheng-Jenn , Hsu Shu-En
Published: July 2002

The structure near the interface of thin YBa2Cu3Ox films (<500 Å) deposited on SrTiO3(001) with laser ablation was revealed utilizing grazing incidence x-ray diffraction. The structure consists of a layer with large crystal mosaicity just above the interface, a c-oriented tetragonal layer with lattice constants a=b=3.883±0.001 Å, and a well textured but strained orthorhombic layer with lattice constants a≂3.887 Å, b≂3.867 Å in the middle, and a thin air-contaminated top layer. The thicknesses of the differently structured layers determined from x-ray reflectivity data are 50±4.7, 20±2.2, 200±5.5, and 12.56±0.14 Å, from the interface to the top layer, respectively. Since there are no additional phases appearing in this system aside from those mentioned, we conclude that the film remains strained at a distance about 300 Å above the interface.
Interaction of 300–5000 eV ions with GaAs(110)
Authors: Wang X.-S. , Pechman R. J. , Weaver J. H.
Published: July 2002

The interaction of 0.3–5 keV Ar+ and Xe+ ions with GaAs(110) in the initial stages of sputtering was studied with scanning tunneling microscopy. At normal incidence, these ions create pits typically of 1–5 unit cells and, on average, each ion leads to the removal of about 1.5 surface atoms from the surface. The sputtering yield depends weakly on ion mass and energy. The bombardment events are mainly in the single knock-on regime, with some in the linear cascade regime. The mechanism of ion-surface impact is discussed.
Imaging of single polymer chains based on their elasticity
Authors: Akari S. O. , van der Vegte E. W. , Grim P. C. M. , Belder G. F. , Koutsos V. , ten Brinke G. , Hadziioannou G.
Published: July 2002

In this work we apply a force modulation technique to a standard atomic force microscope (AFM) in order to study the elasticity of individual polystyrene molecules. The sample mounted on a piezoelectric tube was forced to vibrate along the z direction. The corresponding modulation of the cantilever, which reflects the spring constant of the sample, was phase sensitively detected and measured as a function of the surface topography. The image contrast in these images is based on local variations of the surface elasticity. Compared to the conventional AFM topography image, the elasticity image shows an enhanced contrast with pronounced molecular structure.
Nanometer-scale modification of the tribological properties of Si(100) by scanning force microscope
Authors: Teuschler T. , Mahr K. , Miyazaki S. , Hundhausen M. , Ley L.
Published: July 2002

Hydrogen-terminated Si(100) surfaces were patterned on the nanometer scale using a conducting-probe scanning force microscope (SFM) operating in air ambient. To generate the nanostructures, negative voltages were applied to the conductive SFM tip with respect to the sample while scanning in contact mode. After structuring, the same SFM tip was used to measure simultaneously the sample topography and the friction force between tip and sample. An increase in height by about three nanometers resulting from field-enhanced oxidation is observed in areas where the tip had been negatively biased with constant voltages above 7 V. The topographical change is accompanied by a relative increase of the friction force of about 20% over the structured areas.
Si diffusion and intermixing in AlGaAs/GaAs structures using buried impurity sources
Authors: Beernink K. J. , Thornton R. L. , Anderson G. B. , Emanuel M. A.
Published: July 2002

Si diffusion and impurity-induced layer intermixing from a buried impurity source have been studied by transmission electron microscopy and secondary ion mass spectroscopy of isolated, Si-doped GaAs layers in an undoped Al0.4Ga0.6As/GaAs superlattice and by photoluminescence measurements on Si-doped GaAs quantum wells with undoped Al0.4Ga0.6As barriers. In annealed samples, the Si profile suggests a Si diffusion process involving multiply ionized column III vacancies. The width of the resulting Si profile and the spatial extent and completeness of intermixing strongly depend on the initial Si concentration in the doped layer.
Crystalline orientation of YBa2Cu3Oy film prepared by liquid-phase epitaxial growth on NdGaO3 substrate
Authors: Kitamura Tasuku , Yoshida Manabu , Yamada Yasuji , Shiohara Yuh , Hirabayashi Izumi , Tanaka Shoji
Published: July 2002

Superconducting YBa2Cu3Oy films were grown by liquid-phase epitaxy on NdGaO3(110) single-crystalline substrates by a modified top-seeded solution growth method. Two different melt compositions were used. In the case of Cu-poor melt compositions (Ba:Cu=3.0:5.0), only c-axis oriented growth was observed. However, if we used Cu-rich melt compositions (Ba:Cu=3.0:6.5), both c-axis and a-axis oriented films were obtained. In the latter case the crystalline orientations of the YBa2Cu3Oy films were dependent on the temperature of the surface of the melt. At lower temperatures, c-axis oriented films were obtained, whereas the films showed a-axis orientation at higher temperatures. The width of the temperature region over which the orientation changes is less than 3 °C, which is very narrow compared to the width observed in conventional vapor phase depositions (typically 50 °C). We propose that changes in orientation during the liquid-phase epitaxial growth is due to the unique properties of the phase diagram of the Y–Ba–Cu–O system.
Intersubband lasing lifetimes of SiGe/Si and GaAs/AlGaAs multiple quantum well structures
Authors: Sun G. , Friedman L. , Soref R. A.
Published: July 2002

The feasibility of population inversion is studied for the SiGe/Si system and compared with that of GaAs/AlGaAs. Because of the absence of strong polar optical phonon scattering in SiGe/Si, the lifetime difference of the upper and lower lasing levels, to which the population inversion and laser gain are proportional, is consistently an order of magnitude larger than that of GaAs/AlGaAs; nor does it show the sudden drop to zero or negative values when the lasing energy exceeds the optical phonon energy. Both systems studied are superlattices, each period of which consists of three coupled quantum wells and barriers.
Study of μm-scale spatial variations in strain of a compositionally step-graded InxGa1−xAs/GaAs(001) heterostructure
Authors: Rammohan K. , Rich D. H. , Goldman R. S. , Chen J. , Wieder H. H. , Kavanagh K. L.
Published: July 2002

The relaxation of strain in compositionally step-graded InxGa1−xAs layers grown on GaAs(001) has been examined with cathodoluminescence (CL) wavelength and linearly polarized imaging approaches. A polarization anisotropy in CL is found, and this correlates with spectral shifts in the peak positions of excitonic luminescence. Varying asymmetries in misfit dislocation densities from transmission electron microscopy are found to be consistent with the μm-scale spatial variations in strain that is deduced from the CL.
Direct heterobonding of lithium niobate onto lithium tantalate
Authors: Eda Kazuo , Sugimoto Masato , Tomita Yoshihiro
Published: July 2002

A new method to bond directly different electro-optic materials (lithium niobate on lithium tantalate) for fabricating an optical waveguide is reported. Its fabrication process, interface microstructure, and usefulness for optical devices are also related.
A study of gettering efficiency and stability in Czochralski silicon
Authors: McHugo Scott A. , Weber E. R. , Mizuno M. , Kirscht F. G.
Published: July 2002

Internal gettering efficiencies and stabilities of high and low carbon doped silicon have been compared with standard and ramped annealing conditions. The gettering efficiency of low carbon silicon has been found to be greatly enhanced with ramped annealing by creating a high concentration of oxygen precipitates and related defects. This ramped low carbon material and both the standard and ramped high carbon materials have a greatly enhanced oxygen precipitation rate, relative to the standard low carbon standard anneal. However, the high carbon material’s gettering efficiency and stability are low, compared to the ramped low carbon material, due to a reduction of the oxygen precipitate’s strain field and concentration of related defects.
Chemical bonding and atomic structure of Rb+ exchanged KTiOPO4 waveguides probed by micro-Raman spectroscopy
Authors: Tuschel David D. , Paz-Pujalt Gustavo R. , Risk William P.
Published: July 2002

Channel waveguides of Rb+ exchanged single-crystal KTiOPO4 were studied by micro-Raman spectroscopy. Rb+ exchange causes a disruption of the long-range translational (crystal) symmetry of the lattice and a tilting of the TiO6 octahedra. The ability to nondestructively map the chemical and physical structure related to the optical properties of channel waveguides is demonstrated.
Fabrication of YBa2Cu3Ox thin-film flux transformers using a novel microshadow mask technique for in situ patterning
Authors: Strikovski M. D. , Kahlmann F. , Schubert J. , Zander W. , Glyantsev V. , Ockenfuss G. , Jia C. L.
Published: July 2002

A novel microshadow mask technique for in situ patterning of multilayers is presented. It is ideally suited to fabricate YBa2Cu3Ox(YBCO) and insulator lines with gently sloping edges, needed for high quality insulated superconducting crossovers. The critical current density jc (T=77 K) of a YBCO/SrTiO3/YBCO crossover exceeds 2×106 A/cm2 in both the bottom and the top YBCO stripline. The insulating SrTiO3 layer of 200 nm thickness displays a high resistivity of ρ≳108 Ω cm (T=77 K). The extremely smooth morphology of the edges has been revealed by cross sectional transmission electron microscopy, indicating a stepflow mechanism of YBCO growth. Multiturn flux transformers with a 15 μm linewidth input coil spiral have been fabricated by this microshadow mask technique. A transformer with a pickup loop area of 7 mm2 has been coupled to a 1 mm2 washer dc SQUID in flip chip geometry. In comparison to the bare SQUID a magnetic flux gain factor of 9 has been obtained. The white noise level of this setup was determined to be 8×10−5 Φ0/Hz1/2 at 77 K. It was entirely due to the intrinsic noise of the employed dc SQUID itself. The 1/f noise level increased a factor of 2.
Visible luminescence from one- and two-dimensional silicon structures produced by conventional lithographic and reactive ion etching techniques
Authors: Nassiopoulos A. G. , Grigoropoulos S. , Gogolides E. , Papadimitriou D.
Published: July 2002

Visible luminescence from silicon nanostructures fabricated by using conventional lithographic and reactive ion etching techniques and final thinning by high temperature thermal oxidation was obtained at room temperature under 488 nm argon laser excitation. Highly anisotropic vertical silicon pillars with aspect ratios as high as 25:1 and diameter below 0.1 μm, as well as silicon walls of the same sizes were first produced, which were further thinned by several cycles of thermal oxidation and oxide removal by HF dip. Sub-10 nm diameter silicon pillars and same thickness silicon walls with height in the μm range were thus produced. The fabrication process involved high resolution deep-UV lithography, highly anisotropic silicon etching, and final thinning of the silicon structures by oxidation and oxide removal. The initial pattern of dots and lines was defined by optical lithography using the well known silylation process. The resolution of the process in dot and line size definition was equal to 0.22 μm but lower dimensions down to less than 0.1 μm were obtained in overexposed regions during dry development in a plasma reactor. Three different masks were used for the silicon etching: Cr or Al metal masks or silylated photoresist, all being resistant to the silicon etchants. Highly anisotropic reactive ion etching was achieved by a process using a mixture of SF6 and CHF3 gases at room temperature.
Quantum wirelike induced morphology in InGaAs wells grown on InyAl1−yAs tensile buffer layers over (100)InP vicinal surfaces
Authors: Peiró F. , Cornet A. , Morante J. R. , Georgakilas A. , Wood C. , Christou A.
Published: July 2002

The appearance of quantum wirelike morphology on InGaAs single quantum well structures grown by molecular beam epitaxy on (100)InP vicinal surfaces is reported. The results of transmission electron microscopy reveal that the misorientation of the substrate drives the development of a lateral contrast modulation related to In-rich or Al-rich regions oriented along {133} or {122} planes that initiate on the InAlAs tensile buffer layer and propagate across the structure, giving rise to an anisotropic rippling of the InGaAs well. Conversely, a misfit dislocation network at the InAlAs/InP interface was observed for the same layers grown on exact (100) surface. A comparison of the two structures suggest that the development of such modulated configuration is apparently a strain relieving mechanism.
Quasi-one-dimensional single AlGaAs/GaAs Hall bar quantum wires grown on patterned substrates
Authors: Shitara T. , Tornow M. , Kurtenbach A. , Weiss D. , Eberl K. , Klitzing K. v.
Published: July 2002

Hall bars with widths down to about 250 nm were prepared by overgrowth on patterned GaAs(001) substrates using molecular beam epitaxy. This fabrication method generates a lateral confinement potential determined by AlGaAs barriers. The four-terminal magnetoresistance of a single wire, measured at 1.3 K after illumination, displays the well-known features of quasi-one-dimensional electron systems. We estimate the electron mobility in a ∼250 nm wide wire to be larger than 51 000 cm2/V s at a carrier concentration of 3.3×1011 cm−2.This mobility is comparable to the one measured in a wide reference sample fabricated under identical conditions.
Low noise YBa2Cu3O7−x–SrTiO3–YBa2Cu3O7−x multilayers for improved superconducting magnetometers
Authors: Ludwig F. , Koelle D. , Dantsker E. , Nemeth D. T. , Miklich A. H. , Clarke John , Thomson R. E.
Published: July 2002

We have fabricated YBa2Cu3O7−x–SrTiO3–YBa2Cu3O7−x (YBCO–STO–YBCO) trilayers, in which each layer is patterned photolithographically, capping the first YBCO film with an in situ STO film. Atomic force microscopy demonstrates that the capping process dramatically improves the quality of the surface of the second layer, allowing the growth of an upper YBCO film with a substantially reduced level of low-frequency flux noise. A magnetometer with a multiturn flux transformer coupled to a dc superconducting quantum interference device achieved a magnetic field noise of 74 fT Hz−1/2 at 1 Hz, improving to 31 fT Hz−1/2 at 1 kHz.