bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical waveguide formed by cubic silicon carbide on sapphire substrates
Authors: Tang Xiao , Wongchotigul Kobchat , Spencer Michael G.
Published: July 2002

Optical confinement in beta silicon carbide (β-SiC) thin films on sapphire substrate is demonstrated. Measurements are performed on waveguides formed by the mechanical transfer of thin β-SiC films to sapphire. Recent results of epitaxial films of SiC on sapphire substrates attest to the technological viability of optoelectronic devices made from silicon carbide. Far-field mode patterns are shown. We believe this is the first step in validating a silicon carbide optoelectronic technology.
Reduction of recombination centers in C-doped p+-GaAs/n-AlGaAs heterojunctions by post-growth annealing
Authors: Watanabe Kazuo , Yamazaki Hajime , Yamada Kohji
Published: July 2002

The effect of post-growth annealing at 500, 600, and 700 °C on the electrical characteristics of C-doped p+-GaAs/n-AlGaAs junction diodes fabricated with metalorganic chemical vapor deposition layers has been investigated. Recombination current is reduced by post-growth annealing at 600 and 700 °C, but not at 500 °C. The current reduction is primarily attributed to the dramatic reduction of 0.55 eV deep levels, which may be oxygen related complex levels. Under present annealing conditions, no degradation of carrier profiles near the p+-n junction is detected. Thus, post-growth annealing at temperatures of 600 °C or higher is a promising method for reducing recombination centers in the C-doped p+-GaAs/n-AlGaAs junction.
Cation termination at ion-polished and chemically etched (001)YBa2Cu3O7 crystal surfaces: An ion channeling study
Authors: Fiory A. T. , Hebard A. F. , Eick R. H. , Schneemeyer L. F. , Waszczak J. V. , Gossmann H.-J.
Published: July 2002

Local cation order approaching ideal bulk termination was found for cleaned (001) surfaces of YBa2Cu3O7 crystals by ion-channeling surface-peak analysis. Surfaces etched in dilute CH3OH:Br2 and ultrasonically agitated in CH3OH to dislodge the Br2 appear terminated preferentially by the Cu-O ‘‘double-plane’’ sequence, containing less than 1/2-cation monolayer of surface disorder. Planar polishing with ion beams incident at a glancing angle on a rotating crystal leaves residual disorder as low as ∼8 Å, damage which is readily removed by a light chemical etch.
Optimization by numerical simulation of the focusing properties of self-magnetically insulated ion diodes
Authors: Westermann Thomas
Published: July 2002

We present two-dimensional electromagnetic computer simulation results performed in order to investigate the focusing properties of self-magnetically insulated ion diodes. A particle-in-cell code self-consistently computes the electromagnetic fields inside the anode-cathode gap and an optimization code changes the shape of the anode in order to improve the focusing behavior. It has been shown computationally that in the case of the self-magnetically Bθ-insulated diode the power density can be improved by a factor of 7 by changing the anode surface.
Detection of ferromagnetic resonance in metallic glass by fiber interferometric strain measurement
Authors: Dagenais D. M. , Bucholtz F. , Koo K. P. , Vohra S. , Pond J. M.
Published: July 2002

We report the first detection of ferromagnetic resonance in a magnetostrictive amorphous alloy using a fiber interferometer. By measuring the strain at the difference frequency resulting from the application of two rf magnetic fields, we observe a natural (zero field) ferromagnetic resonance near 400 MHz. We discuss novel features of this technique and outline modifications to the existing theory of dynamic magnetostriction suggested by the results.
Quadrupole interaction of 111Cd in the semiconductor CdS
Authors: Bertholdt E. , Frank M. , Gubitz F. , Kreische W. , Ott Ch. , Röseler B. , Schwab F. , Stammler K. , Weeske G.
Published: July 2002

The time differential perturbed angular correlation technique was applied to study the electric quadrupole coupling of 111Cd in the II-VI semiconductor CdS (20 K≤T≤1000 K). Two kinds of sample preparation were used: implantation and diffusion. Obtained results for the regular lattice sites were independent of the preparation. The measured electric field gradient (EFG) was between 6.7±0.4 MHz and 9.1±0.2 MHz. Data were confirmed by point-charge calculations. Implantation however caused a second EFG (≊78 MHz) that was assigned to a defect due to the preceding irradiation.
Latent image measurements in electron beam exposed polymethylmethacrylate
Authors: Shaw Jerry C. , Rishton Stephen A. , Jackson Robert R. , O’Boyle Martin P.
Published: July 2002

Undeveloped and unbaked paterns or latent images (LI) in polymethylmethacrylate (PMMA) have been observed and measured using different measurement techniques. Results from two common-path baseband optical techniques have been compared with the results of profiling LI using an atomic force probe. These results indicate that 5 Å detection limits in optical path length measurements are easily achievable at near video rates using simple optical systems.
High-speed 1.3 μm InGaAs/GaAs metal-semiconductor-metal photodetector
Authors: Jagannath C. , Choudhury A. N. M. Masum , Negri A. , Elman B. , Haugsjaa P.
Published: July 2002

A high frequency, low dark current, 1.3 μm metal-semiconductor-metal photodetector on GaAs is reported. The measured frequency response of this photodetector up to 10 GHz agrees with a model that assumes different collection times for electrons and holes.
Phase-shifted distributed feedback laser with linearly chirped grating for narrow linewidth and high-power operation
Authors: Zhou Ping , Lee G. S.
Published: July 2002

Phase-shifted distributed feedback laser with linearly chirped grating (PS-CG-DFB) was analyzed. The field distribution, threshold gain difference between the lasing mode and the next lowest threshold gain mode, linewidth of the lasing mode, and output power of PS-CG-DFB were self-consistently calculated under different injection levels. It is found that the lasing mode pattern and the carrier concentration distribution are ‘‘locked’’ at high injection level due to the strong interaction between carriers and photons. The chirped grating compensates the spatial hole burning effect to the mode stability and makes the mode stable in the whole injection region.
Resonant indirect Fowler–Nordheim tunneling in Al0.8Ga0.2As barrier
Authors: Lu S. S. , Lee K. , Nathan M. I. , Wright S. L.
Published: July 2002

Oscillatory current-voltage characteristics of n+-GaAs/semi-insulating Al0.8Ga0.2As/nGaAs heterojunction barriers (400 Å thick) grown by molecular beam epitaxy on n+-GaAs (100) substrates are observed at 4 K when the heterostructures are placed under the transverse uniaxial stress along 〈011〉 direction (perpendicular to current direction) above 4 kbar. We attribute these oscillations to the resonant indirect Fowler–Nordheim tunneling via 〈011〉 oriented transverse X valleys, where the change of wave vector is required for tunneling.
Grazing angle optical emission interferometry for end-point detection
Authors: Angell David , Oehrlein Gottlieb S.
Published: July 2002

Light emitted from a plasma during reactive ion etching and reflected by the wafer surface at a grazing angle is utilized to determine the remaining film thickness with an accuracy of ±30 Å. This promises a more flexible etching approach, e.g., tailoring the final stage of etching to minimize lattice damage.
Quantum well infrared photodetectors: Monte Carlo simulations of transport
Authors: Artaki M. , Kizilyalli I. C.
Published: July 2002

This letter describes some Monte Carlo simulations of electron transport in quantum well infrared photodetectors designed to operate in the 10 μm wavelength range. These GaAs/AlGaAs superlattice photodetectors absorb radiation between a bound state in the wells and the continuum of states above the wells. We have studied the collection efficiency of the photoexcited electrons at 70 K as a function of bias across the device, as well as the response time. It is concluded that the quantum mechanical well capture transition rate through interaction with LO phonons, between the extended states in the continuum and the bound state, has to be considered for agreement with the experimental results.
Preparation of stable and photoconductive hydrogenated amorphous silicon from a Xe-diluted silane plasma
Authors: Matsuda A. , Mashima S. , Hasezaki K. , Suzuki A. , Yamasaki S. , McElheny P. J.
Published: July 2002

Photoconductive and stable hydrogenated amorphous silicon thin films, prepared by plasma-enhanced chemical vapor deposition using a Xe-silane mixture at a substrate temperature of 250 °C, did not show any photo-induced degradation of the photoconductivity after 104 min light soaking (air mass-1, 100 mW/cm2). The network structure of these films is inhomogeneous and includes a large amount of clustered hydrogen as indicated by the low-temperature thermal effusion and the large, broad component in the nuclear magnetic resonance spectrum.
In situ patterning of contamination resists in metalorganic chemical vapor deposition for fabrication of quantum wires
Authors: Takahashi T. , Arakawa Y. , Nishioka M.
Published: July 2002

We demonstrated a novel selective growth technology for the fabrication of quantum microstructures utilizing in situ patterning of contamination resist in the metalorganic chemical vapor deposition system. The results indicate that a GaAs quasi-quantum wire structure, as narrow as 700 nm, can be successfully fabricated, showing that this technique may be applied to fabrication technologies for quantum microstructures.
Role of negatively charged vacancies in secondary grain growth in polycrystalline silicon during rapid thermal annealing
Authors: Park Keunhyung , Batra Shubneesh , Banerjee Sanjay
Published: July 2002

It has been reported that there is a drastic increase of grain size in polycrystalline silicon because of secondary grain growth in ultrathin, heavily n-type doped films upon conventional furnace annealing. There has been very limited work on secondary grain growth during rapid thermal annealing (RTA). This letter presents for the first time extensive data on secondary grain growth in heavily n-type, P-doped amorphous silicon-on-oxide films during RTA. Grains as large as 16 μm in diameter have been obtained in 160-nm-thick films which represent the largest secondary grains and largest grain size to film thickness reported in the literature. The role of charged silicon vacancies is invoked in a new way to explain the observed lower activation energy for grain boundary mobility during secondary grain growth than during normal grain growth.
Synthesis under ambient pressure of 80 K superconducting YBa2Cu4O8 powders via coprecipitation
Authors: Ho J. S. , Chang C. T. , Liu R. S. , Edwards P. P.
Published: July 2002

Sub-micron homogeneous powders of YBa2Cu4O8 having Tc∼80 K were synthesised from aqueous solutions containing Y, Ba, Cu salts, and oxalic acid as a precipitant via a chemical coprecipitation method using triethylamine as a base. An accelerated formation−within 24 h−of nearly single phase YBa2Cu4O8 powders was achieved. The intragrain critical current density at 5 K and H=1 T was determined to be 3.9×107 A/cm2. This process may have considerable potential in the large-scale preparation of YBa2Cu4O8.
Effects of metalorganic chemical vapor deposition growth conditions on the GaAs/Ge solar cell properties
Authors: Chen J. C. , Ristow M. Ladle , Cubbage J. I. , Werthen J. G.
Published: July 2002

We have studied the effects of metalorganic chemical vapor deposition (MOCVD) growth conditions on the properties of GaAs solar cells grown upon Ge substrates, and in particular the GaAs/Ge interface. The interface properties were found to strongly depend on growth conditions. By small changes in the growth temperature, the GaAs/Ge interface was altered from active to passive. Only a narrow temperature window (600–630 °C) for the initial GaAs layer growth gave the passive-Ge junction together with good surface morphology. Accordingly, a high efficiency (19%, AM0) GaAs solar cell was grown by atmospheric pressure MOCVD on a Ge substrate without any junction in the Ge.
pnp lateral magnetotransistor and influence of n+-buried layer on sensitivity
Authors: Ristic Ljubisa , Maenaka Kazusuke , Smy Tom , Nakamura Tetsuro , Doan My The
Published: July 2002

An analysis of the sensitivity of a pnp lateral magnetotransistor (LMT) fabricated in bipolar technology is presented. In addition, the role of the n+-buried layer is studied. The devices were designed as differential LMTs. It has been found that the change in sensitivity of pnp LMT increases by one order of magnitude if the n+-buried layer is not omitted. The obtained sensitivity is the highest ever reported for a pnp LMT.
Admittance of Al/GaAs Schottky contacts under forward bias as a function of interface preparation conditions
Authors: Muret P. , Elguennouni D. , Missous M. , Rhoderick E. H.
Published: July 2002

Admittance measurements have been made under forward bias on two types of Al/n-GaAs contacts. The Al and n-GaAs layers have been prepared by molecular beam epitaxy on an n+-GaAs wafer. In the first type, which shows ideal current-voltage characteristics, only an inductive effect was observed and no effect attributable to interface states was detected. In the second type, differing only in the n-GaAs surface which was prepared under inferior vacuum conditions, nonideality of current-voltage characteristics and excess capacitances were both seen. The back contact being the same in both types of samples, the onset of excess capacitances must be related to the change in surface characteristics. A model which assumes a U-shaped density of extrinsic interface states accounts simultaneously for the behavior of conductance, capacitance, and ideality factor as functions of temperature, voltage, and frequency.
Electron paramagnetic resonance of a multistable interstitial-carbon-substitutional-phosphorus pair in silicon
Authors: Zhan X. D. , Watkins G. D.
Published: July 2002

Two new electron paramagnetic resonance centers are reported, Si-L8 and Si-L9, which are identified with the stable and one of the four metastable configurations, respectively, of a multistable defect recently discovered by deep level transient capacitance spectroscopy in electron-irradiated phosphorus-doped silicon. Resolved 31P hyperfine interactions and stress-induced alignment effects are detected in the spectra which serve to confirm the identification as a Ci-Ps pair and lead to a model for the atomic structure in the stable configuration.
New method for the evaluation of brittleness in ceramics
Authors: Nishi Yoshitake , Katagiri Tatsuo , Yamano Takehide , Kanai Fumiyuki , Ninomiya Nobuyuki , Uchida Satoshi , Oguri Kazuya , Morishita Tadae , Endo Takashi , Kawakami Mamoru
Published: July 2002

Using Vickers indentation method, plastic deformation (Ef) is suggested to be a convenient measurement to determine the ductility (brittleness) of brittle new materials. It was found that Ef is related empirically to KIC and GIC through a logarithmic linear relationship.
Room-temperature photoconductivity of InGaAs/GaAs strained-layer superlattices
Authors: Salokatve A. , Hovinen M. , Pessa M.
Published: July 2002

InGaAs/GaAs strained-layer superlattices have been grown by molecular beam epitaxy and characterized with photoconductivity measurements. The layers were doped p type by diffusion of Zn in an ohmic contact annealing process. A sudden reduction in room-temperature photoconductivity of the p-type samples was observed at photon energies slightly below the GaAs band gap in all of the samples. This spectral feature is proposed to originate from photoionization of acceptor-like defect states in GaAs, and a model accounting for this phenomenon is discussed.
Asymptotic treatment of the Elenbaas–Heller equation
Authors: Kuiken H. K.
Published: July 2002

When the maximum temperatures within a high-pressure gas discharge arc are lower than the ionization temperature of the gas molecules by an order of magnitude, an asymptotic treatment of the temperature equation is possible. This is illustrated by means of the Elenbaas–Heller equation [e.g., M. F. Hoyaux, Arc Physics (Springer, Berlin, 1968), p. 36] for a nonradiating wall-stabilized arc. The asymptotics lead to a closed-form expression for the relationship between the arc current and the axis temperature. An expression for the heat loss per unit length is also given.
Ultrahigh-efficiency optical modulation (≳20 W/A) by interferometric frequency→intensity conversion of gain-levered semiconductor lasers
Authors: Lau K. Y.
Published: July 2002

It is theoretically and experimentally demonstrated that a peculiar amplitude/phase coupling characteristic between the modulated and noise output of gain-levered lasers leads to a simultaneous increase in the modulation efficiency and a reduction in the intensity noise by interferometric frequency→intensity conversion.
Ti-implanted Bragg reflectors on LiNbO3:Ti stripe waveguides
Authors: Fouchet S. , Ladan F. R. , Huet F. , Carenco A. , Carre M. , Gao Y.
Published: July 2002

The first demonstration of Ti-implanted Bragg reflectors on Ti-indiffused LiNbO3 waveguides is reported here. A bandwidth of 7 Å, around 1.52 μm, with reflection coefficients ≳99%, has been achieved for TE polarization on X-cut, Y-propagating guides.
Pulsed laser deposition and ferroelectric characterization of bismuth titanate films
Authors: Buhay H. , Sinharoy S. , Kasner W. H. , Francombe M. H. , Lampe D. R. , Stepke E.
Published: July 2002

Stoichiometric films of bismuth titanate, Bi4Ti3O12, have been grown for the first time by the technique of pulsed excimer laser deposition. Ferroelectric films were obtained at temperatures as low as 500 °C on Si(100), MgO(110), and Pt-coated Si(100) substrates. Hysteresis measurements using a Pt-coated Si sample yielded a saturation polarization value of about 28 μC/cm2, consistent with a randomly oriented titanate film structure. A preliminary metal-insulator-semiconductor sandwich structure of the form Bi4Ti3O12-CaF2(100 Å)-Si was grown and used to examine polarization induced memory switching effects.
Photoluminescence of deep levels in ion-implanted AlxGa1−xAs
Authors: Gillin W. P. , Homewood K. P. , Sealy B. J. , Roberts J.
Published: July 2002

We have studied the effect of ion implantation of donors into AlxGa1−xAs epilayers and have shown the presence of two deep level luminescence centers whose emission energies are strongly dependent on aluminum concentration. The variation of the intensity of these levels with annealing conditions gives an activation energy for their annihilation and this is found to be in agreement with that obtained from electrical data. From this, a model for the electrical activation of sulphur-implanted GaAs is proposed.
Superconducting whiskers and crystals of the high T
c Bi2Sr2Ca2Cu3O10 phase
Authors: Matsubara Ichiro , Tanigawa Hideo , Ogura Toru , Yamashita Hiroshi , Kinoshita Makoto , Kawai Tomoji
Published: July 2002

Whiskers of the high Tc Bi2Sr2Ca2Cu3O10  (2223) phase have been prepared by annealing Bi2Sr2CaCu2O8  (2212) whiskers in a Bi2Sr2Ca4Cu6Pb0. 5Ox powder. By the same method, single-crystal sheets of the 2212 phase have also been converted to the 2223 phase, resulting in 2223 sheet crystals as large as approximately 1 mm2. Although the original sample outlines are retained after the phase conversion, the smooth surfaces were lost due to contact with the powder during annealing. A zero-resistance temperature of 107 K and a maximum Jc value of 7.3×104 A/cm2 at 77 K in a zero magnetic field were obtained for the 2223 whisker.
Quantum molecular dynamics treatment for the electronic relaxation of high-density plasmas in two-dimensional structures
Authors: Joshi R. P. , Kriman A. M. , Kann M. J. , Ferry D. K.
Published: July 2002

We examine effects of the exchange interaction on the thermalization dynamics of high-density photogenerated plasmas in quantum wells. A technique for simulating the transient dynamics is presented which combines the conventional Ensemble Monte Carlo method for the carrier-phonon scattering, with a molecular dynamics scheme for treating the many-body contributions to the long-range Coulomb potentials. Account is taken of the exchange-energy interactions in keeping with the exclusion principle and the Fermi nature of the system. Our results indicate that the exchange corrections slow the cooling of the photogenerated plasma at carrier densities above 1012 cm−2. The effect is due primarily to a weakening of the direct Colomb force, and demonstrates that calculations based on simple carrier–carrier scattering alone would underestimate thermalization time constants.
Heavily phosphorus-doped epitaxial Si deposited by low-temperature plasma-enhanced chemical vapor deposition
Authors: Baert K. , Vanhellemont J. , Vandervorst W. , Nijs J. , Konagai M.
Published: July 2002

Heavily P-doped Si layers have been grown at very low temperature (<600 °C) by rf plasma chemical vapor deposition. Films grown by vapor phase epitaxy (VPE) or solid phase epitaxy (SPE) are compared. By VPE growth, fully electrically activated films with a P concentration in excess of 1021 cm−3 and steep doping profiles (≤4 nm/dec) were obtained. SPE films are not fully activated and an anomalously fast P diffusion is observed during the crystallization at 600 °C. On the other hand, the Hall mobility of VPE films is significantly lower than that of SPE films.
Novel etching technique for a buried heterostructure GaInAs/AlGaInAs quantum-well laser diode
Authors: Kasukawa A. , Bhat R. , Caneau C. , Zah C. E. , Koza M. A. , Lee T. P.
Published: July 2002

A novel etching technique for the 1.5-μm GaInAs/AlGaInAs buried heterostructure quantum-well laser diode is developed. Tartaric acid is used for the etching of GaInAs and AlGaInAs layers for the first time. Using a three-step material-selective etching, a 3-μm-high mesa with about 1.5-μm-wide active layer and 3-μm-wide contact layer can be achieved with good reproducibility. Nearly flat surfaces were obtained after a two-step organometallic chemical vapor deposition growth. A low threshold current of 11 mA was obtained for a 570-μm-long cavity device.
Timing jitter and pulse energy fluctuations in a passively mode-locked two-section quantum-well laser coupled to an external cavity
Authors: Sanders Steve , Schrans Thomas , Yariv Amnon , Paslaski Joel , Ungar Jeffrey E. , Zarem Hal A.
Published: July 2002

Stability of pulse energy and timing in a passively mode-locked two-section quantum-well laser is measured. Spectral analysis of the 546-MHz pulse train reveals rms timing jitter of 5.5 ps above 50 Hz and rms pulse energy fluctuations of <0.52% above 200 Hz.
Hybrid soliton pulse source using a silica waveguide external cavity and Bragg reflector
Authors: Morton P. A. , Adar R. , Kistler R. C. , Henry C. H. , Tanbun-Ek T. , Logan R. A. , Coblentz D. L. , Sergent A. M. , Wecht K. W.
Published: July 2002

We describe the first results for a hybrid soliton pulse source, combining a mode-locked semiconductor laser with a silica waveguide external cavity and Bragg reflector. Near transform limited pulses at 1.55 μm have been obtained at pulse widths and repetition rates compatible with practical soliton transmission system. A novel new mechanism of cavity length detuning is described, which gives the device an extended operating frequency range over which useful mode locking occurs.
High reflectivity 1.55 μm InP/InGaAsP Bragg mirror grown by chemical beam epitaxy
Authors: Choa F. S. , Tai K. , Tsang W. T. , Chu S. N. G.
Published: July 2002

We report the chemical-beam epitaxial (CBE) growth of InP/InGaAsP Bragg mirrors around 1.55 μm wavelength region. Mirrors with nearly 100% reflectivity and with more than 400 Å flat top region in the Bragg band have been achieved by using 45 pairs of InP (1348 Å) and InGaAsP (1216 Å, λg=1.45 μm) quarter wavelength layers which have a total thickness of 11.5 μm. Excellent uniformity of the layer thickness and optical quality in both horizontal and vertical directions were obtained. This demonstrates the unique capability of CBE in maintaining uniform and reproducible growth of InP/InGaAsP during a long growth period.
Poly(methylphenylsilane) film as a hole transport layer in electroluminescent devices
Authors: Kido Junji , Nagai Katsutoshi , Okamoto Yoshiyuki , Skotheim Terje
Published: July 2002

Electroluminescent devices were fabricated using poly(methylphenylsilane) and 8-hydroxyquinoline aluminum complex as the hole transport layer and the emitting layer, respectively. The cell structure of glass substrate/indium-tin-oxide/hole transport layer/emitting layer/Mg/Ag was employed. Smooth hole injection from the electrode through the polymer layer and concomitant efficient electroluminescence from the emitting layer were observed. Green emission with a luminance of over 1000 cd/m2 was achieved at a current density of 100 mA/cm2.
Removing native oxide from Si(001) surfaces using photoexcited fluorine gas
Authors: Aoyama Takayuki , Yamazaki Tatsuya , Ito Takashi
Published: July 2002

This letter discusses the reaction between (001) oriented Si surfaces and photoexcited fluorine gas resulting in the removal of the native Si oxide. For an F2/Ar gas system, the bulk Si was etched in areas where the native Si oxide had been completely removed. However, by using an F2/H2 gas system, only the native Si oxide was removed. We used this method to remove the native Si oxide in Si epitaxial growth. A high-quality single-crystal Si film surface was obtained up to a maximum temperature of 600 °C through this Si growth process. We also characterized the etching of a thermal oxide, silicon nitride, and silicon carbide.
Systematic observation of strain-induced lateral quantum confinement in GaAs quantum well wires prepared by chemical dry etching
Authors: Tan I-Hsing , Lishan David , Mirin Richard , Jayaraman Vijay , Yasuda Takashi , Hu Evelyn L. , Bowers John
Published: July 2002

HCl radical beam etching has been used to produce strain-induced lateral confinement in a GaAs quantum well. This confinement was generated in the GaAs quantum well by radical beam etching a grating pattern into a pseudomorphic, strained layer of In0.35Ga0.65As which overlies the GaAs quantum well. The photoluminescence spectrum showed two peaks, corresponding to the GaAs quantum well both beneath the strained layer and in regions where the strained overlayer had been etched away. The peak due to strain-induced confinement displayed a redshift that increases with etch time; the maximum shift observed was 20 meV. The after-etch photoluminescence intensity and the systematic peak shift with etch time are indicators of the degree of control and low-damage nature of the etch process used.
Boundary conditions for tunneling through potential barriers in nonparabolic semiconductors
Authors: Nag B. R.
Published: July 2002

A wave equation is formulated by using the energy-wave-vector relation for nonparabolic bands and it is shown that the resultant boundary condition is in agreement with the condition of the continuity of probability current density. The condition is shown to involve the velocity effective mass with the derivatives of the wave function, in place of the energy effective mass, used earlier. Calculated results are also presented for the probability of tunneling through a single rectangular barrier in the Ga0.47In0.53As/InP/Ga0.47In0.53As system, which show that the nonparabolicity reduces significantly the value of the probability from those estimated by using the energy effective mass in the boundary condition.
Two-dimensional electron gas modulated resonant tunneling transistor
Authors: Longenbach K. F. , Wang Y. , Wang W. I.
Published: July 2002

Operation of a novel three-terminal resonant tunneling device which consists of an AlGaAs/GaAs modulation-doped structure grown on top of an AlAs/GaAs double-barrier resonant tunneling heterostructure has been demonstrated. In this device, the drain-to-source voltage is used to directly control the bias across a resonant tunneling structure, while the gate voltage controls the number of carriers available for the tunneling process by modulating the density of carriers in a two-dimensional electron gas. Device operation is demonstrated at 80 K as well as room temperature with peak current densities of 420 A/cm2 and peak-to-valley ratios as high as 5:1. Operation into the hundred gigahertz range is predicted for an optimized device structure.
(InAs)1/(GaAs)4 superlattices quantum-well laser
Authors: Dutta N. K. , Chand Naresh , Lopata J. , Wetzel R.
Published: July 2002

We report the fabrication and performance characteristics of (InAs1)/(GaAs)4 short-period superlattice (SPS) strained quantum-well lasers emitting near 1 μm. The SPS consists of 6 periods of 1 and 4 ML of InAs and GaAs, respectively. The 250-μm-long ridge waveguide lasers have a threshold current of 10 mA, an external differential quantum efficiency of 0.35 mW/mA facet, and have operated to a temperature of 200 °C.
Mode-locked GaAs vertical cavity surface emitting lasers
Authors: Jiang W. B. , Mirin R. , Bowers J. E.
Published: July 2002

The first mode-locked GaAs vertical cavity surface emitting laser is reported. Pulses of 324 fs pulsewidth with 64 W peak power were generated by compressing the output from the mode-locked laser.
Principle differences between the transport properties of normal AlGaAs/InGaAs/GaAs and inverted GaAs/InGaAs/AlGaAs modulation doped heterostructures
Authors: Schweizer T. , Köhler K. , Ganser P.
Published: July 2002

The electrical properties of Al0.3Ga0.7As/InxGa1−xAs modulation doped heterostructures grown on GaAs substrates were studied. We found for the normal and inverted heterostructures principal differences of the transport properties. For an InAs mole fraction of 0.2 the inverted modulation doped heterostructures show a stronger decrease in the electron mobility of the two-dimensional electron gas if the critical layer thickness of the In0.2Ga0.8As layer is exceeded, in comparison to the normal heterostructures. This behavior can be explained by the relaxation process of the In0.2Ga0.8As layer. For InxGa1−xAs heterostructures with x≳0.3 the growth mode changes from two-dimensional to three-dimensional growth, which leads to interface roughness, degrading the transport properties of the normal heterostructure. Thus for high InAs mole fractions the inverted heterostructures show better transport properties in comparison to the normal heterostructures.
Metal-intrinsic semiconductor-semiconductor structures using polycrystalline diamond films
Authors: Miyata K. , Dreifus D. L. , Kobashi K.
Published: July 2002

The electrical characteristics of a metal-intrinsic semiconductor-semiconductor structure formed by Al-undoped polycrystalline diamond-B-doped polycrystalline diamond were investigated. Boron-doped diamond films containing B-to-C ratios of 400 and 4000 ppm in gas phase were deposited on (111)-oriented B-doped Si substrates. Subsequently, undoped diamond layers were deposited on the B-doped diamond films for 60 min. The existence of a bilayer structure in terms of the atomic B concentration was confirmed by a secondary-ion mass spectroscopy. Significant improvements in the rectifying characteristics could be obtained with the introduction of an undoped diamond layer.
Electron accumulation in AlGaSb/InAs/AlGaSb quantum well system
Authors: Ideshita S. , Furukawa A. , Mochizuki Y. , Mizuta M.
Published: July 2002

The mechanism of the electron accumulation in the AlGaSb/InAs/AlGaSb QW system with Al composition higher than 0.5 is discussed. In this QW system, it is found that the dominant electron source is donor levels in AlGaSb rather than interface levels which have, so far, been proposed as the electron source. We have found two contradictory results, that undoped AlGaSb shows p-type conduction and Be-doping is compensated electrically, are satisfactorily explained by the model of coexistence of donors and a larger concentration of deep acceptors. Electron accumulation in InAs QW is shown to be controllable by shifting the quantum level with respect to the deep acceptor level.
Phosphorous doping in low temperature silicon molecular beam epitaxy
Authors: Friess E. , Nützel J. , Abstreiter G.
Published: July 2002

Phosphorus doping with silicon molecular beam epitaxy was studied using a novel design of a solid doping source based on evaporation of highly doped silicon. Doping concentrations up to the level of the source material are possible. Bulklike Hall mobilities can be achieved. No memory effect was detectable in the course of this work. Phosphorus incorporation in the growing silicon film was investigated with secondary ion mass spectrometry. A drastic increase of segregation with growth temperature was found between 320 and 540 °C. This temperature range represents a kinetically limited regime, which also explains the observed enhancement of segregation with reduced growth rate.
Photoluminescence from hot carriers in low-temperature-grown gallium arsenide
Authors: van Driel H. M. , Zhou X.-Q. , Rühle W. W. , Kuhl J. , Ploog K.
Published: July 2002

Band-to-band photoluminescence spectra of GaAs grown at 200 °C by molecular beam epitaxy have been measured as a function of lattice temperature (10<TL<290 K), laser photon energy (1.62<Ep<2.07 eV) and excitation intensity during 5 ps excitation. Carrier recombination, previously reported to be as fast as 300 fs in this material, displays at most a weak density dependence, consistent with a monomolecular mechanism. The spectra correspond to quasi-steady-state carrier distributions which evolve from nonthermal to thermal character as the density increases from 1016 to 1018 cm−3. For the thermal distributions, the characteristic temperature depends strongly on Ep; values near 1000 K are obtained for Ep≳1.85 eV. The results are related to ultrafast carrier recombination, intervalley transfer, and thermalization.
High quality GaAs on Si by conformal growth
Authors: Pribat D. , Gerard B. , Dupuy M. , Legagneux P.
Published: July 2002

We propose a simple technique which allows the growth of low defect density GaAs films on Si substrates. This technique is based on conformal vapor phase epitaxy and uses a Si3N4 capping layer, as well as the Si surface itself for growth confinement. The as-grown conformal GaAs films exhibit a spectacular reduction in the density of dislocations, because of the latter blocking either on the Si3N4 cap or on the Si substrate. Dislocation densities below 5×105 cm−2 have been obtained in submicrometer-thick conformal GaAs films.
Raman study of disorder and strain in epitaxial ZnSxSe1−x films on a GaAs substrate
Authors: Kanemitsu Yoshihiko , Yamamoto Aishi , Matsue Hitoshi , Masumoto Yasuaki , Yamaga Shigeki , Yoshikawa Akihiko
Published: July 2002

Quantitative characterization of disorder and strain in ZnSxSe1−x/GaAs lattice-mismatched semiconductor heterostructures was successfully done by means of Raman spectroscopy. The alloy disorder and the phonon coherence length in epitaxial ZnSxSe1−x films were estimated from the Raman linewidth of the ZnSe-like LO phonon by using a spatial correlation model. The strain due to the lattice mismatch near the interface between ZnSxSe1−x and GaAs was deduced from the linewidth of the GaAs LO phonon.
Optically detected transient thermal response of high T
c epitaxial films
Authors: Levey C. G. , Etemad S. , Inam A.
Published: July 2002

A thermally induced transient absorption is found to accompany the unusually fast and sensitive bolometric response of thin YBa2Cu3O7 films. We utilize this optical signature as an internal thermometer to investigate thermal transients in both superconducting films and their undoped isomorphs. In the temperature range 10–300 K we find that the combination of a small thermal film mass and a large film-substrate interface resistance results in large transient temperatures. Superconducting and nonsuperconducting films show comparable temperature rises and kinetics.
Effects of thin SiO2 capping layer on silicon-on-insulator formation by lateral solid-phase epitaxy
Authors: Kusukawa K. , Ohkura M. , Moniwa M. , Miyao M.
Published: July 2002

The effects of a SiO2 capping layer over an amorphous Si surface on the lateral solid-phase epitaxy of Si are investigated. A thin SiO2 layer (about 5 nm) chemically grown on the deposited amorphous layer reduces the lateral crystal growth length. In addition, observations using a transmission electron microscope reveal that crystal defects are formed during lateral growth at the interface of the surface SiO2 and the deposited amorphous Si layer. These crystal defects are thought to be responsible for the reduction in crystal growth.
Photoquenching of hopping conduction in low-temperature-grown molecular-beam-epitaxial GaAs
Authors: Fang Z.-Q. , Look D. C.
Published: July 2002

We have observed IR photoquenching of the hopping conduction in GaAs samples grown by molecular beam epitaxy at the low temperature of 250 °C and annealed at temperatures from 300 to 600 °C. A key element in the success of this study is removal of the layers from their substrates. The hopping conduction recovers at about 140 K, with a thermal activation energy of about 0.3 eV.
Kinetics of selective epitaxial deposition of Si1−xGex
Authors: Kamins T. I. , Vook D. W. , Yu P. K. , Turner J. E.
Published: July 2002

The kinetics of selective deposition of epitaxial Si1−xGex layers in an atmospheric-pressure reactor have been examined. Adding HCl to the SiH2Cl2/GeH4/H2 system decreases the Si component of the deposition rate more than the Ge component, increasing the Ge fraction in the deposited layer. HCl addition also decreases boron incorporation. When deposited selectively on oxide-patterned wafers, lateral transport of the depositing materials causes the deposition rate and the Ge fraction to be higher in small patterns than in large patterns and also to be higher near the edges of patterns than at their centers.
Fluorinated diphenyl-diacetylene and tolane liquid crystals with low threshold voltage
Authors: Wu Shin-Tson , Hsu Chain-Shu , Chen Yee-Nan , Wang Show-Ru
Published: July 2002

Several new fluoro-alkoxy and alkenyloxy (alkoxy with a carbon-carbon double bond) diphenyl-diacetylene and tolane liquid crystals are synthesized and their physical properties evaluated. Double bond position is found to make a pronounced effect on elastic constant, phase transition temperature and heat fusion enthalpy, but little change on birefringence, dielectric anisotropy, and viscosity. These compounds exhibit a high birefringence, low viscosity, and low threshold voltage, and are particularly attractive for infrared light valves and polymer-dispersed liquid crystal displays.
Enhanced Tm3+ blue emission in Tm, Yb, co-doped fluorophosphate glasses due to back energy transfer processes
Authors: Özen G. , Denis J. P. , Goldner Ph. , Wu Xu , Genotelle M. , Pellé F.
Published: July 2002

Up-conversion emission spectra of fluorophosphate glasses doped with Tm3+ and co-doped with Tm3+ and Yb3+ ions were obtained under two different excitation wavelengths (657 and 683 nm). Both samples show a stronger emission centered at 450 nm than the ones centered at 478 and 363 nm when 3F2 level of Tm3+ is excited at 657 nm. If 3F3 level of Tm3+ is excited with the 683 nm light the 478 nm emission of the double doped sample becomes much stronger (about 200 times) than the same emission of the single doped sample. We propose an up-conversion mechanism to explain the spectra which is in agreement with quadratic dependence of the emission intensities on the excitation power under both excitations.
Investigations of quantum trench tunneling diodes
Authors: Peck A. J. , Bending S. J. , von Klitzing K. , Ploog K.
Published: July 2002

We report on the realization of a new type of lateral tunneling diode with the potential for ultrahigh frequency (THz) operation. The diodes, which are fabricated by etching tiny quantum trenches into the surface of a GaAs/AlGaAs heterostructure, display extremely nonlinear current-voltage characteristics. Tunneling barrier heights are obtained from a study of thermally activated current, and results are compared to those of a theoretical model of the structure based on the finite difference form of the Poisson equation.
Simultaneous occurrence of multiphases in the interfacial reactions of ultrahigh vacuum deposited Hf and Cr thin films on (111)Si
Authors: Hsieh W. Y. , Lin J. H. , Chen L. J.
Published: July 2002

Simultaneous occurrence of multiphases were observed in the interfacial reactions of ultrahigh vacuum deposited Hf and Cr thin films on (111)Si by high-resolution transmission electron microscopy in conjunction with fast Fourier transform diffraction analysis and image simulation. For Hf/Si system, an amorphous interlayer, Hf5Si3 as well as FeB and CrB types of HfSi were found to form simultaneously in samples annealed at 530 °C for 40–80 min. For Cr/Si system, an amorphous interlayer, Cr5Si3, CrSi, and CrSi2 were observed to form in samples annealed at 375 °C for 30 min. The formation of multiphases appeared to be quite general in the initial stages of interfacial reactions of ultrahigh vacuum deposited refractory thin films. The results called for a reexamination of generally accepted ‘‘difference’’ in reaction sequence between bulk and thin-film couples.
Strained GaxIn1−xP multiple quantum wire light-emitting diodes: A luminescence polarization study
Authors: Pearah P. J. , Stellini E. M. , Chen A. C. , Moy A. M. , Hsieh K. C. , Cheng K. Y.
Published: July 2002

Strongly polarized photoluminescence and electroluminescence spectra have been obtained from strained GaxIn1−xP quantum wire heterostructures grown on (100) oriented, on-axis GaAs substrates by an in situ epitaxial technique. The phenomenon of strain-induced lateral layer ordering has been exploited in order to create lateral superlattices of GaxIn1−xP compositionally modulated in the [110] direction with a modulation period of 96 Å. The previous and subsequent growth of lattice-matched Ga0.51In0.49P ternary alloy epilayers results in the formation of compressively strained quantum wires. Transmission electron microscopy shows the wire cross sections to be ∼48×200 Å. These structures exhibit 77 K photoluminescence spectra at 1.79 eV that are strongly (96%) polarized parallel to the wires due to strain resulting from the lateral compositional modulation. The intensity of this emission depends critically on the polarization of the incident excitation. Electroluminescence spectra from multiple quantum wire light-emitting diodes display anisotropic polarization as well. The energies and optical anisotropies of these luminescence bands are consistent with a simple theoretical analysis.
Steplike behavior of photoluminescence peak energy and formation of p-type porous silicon
Authors: Zhang Shu-Lin , Ho Kuok-san , Hou Yongtian , Qian Bidong , Diao Peng , Cai Shengmin
Published: July 2002

The photoluminescence spectra from a series of porous silicon samples formed in HF concentrations at constant current density and fixed forming times, are presented. A novel steplike behavior of photoluminescence peak energy was observed. A formation mechanism based on the quantum confinement of porous Si walls has been proposed to explain the experimental results.
Scanning force microscopy measurement of edge growth rate enhancement in selective area epitaxy
Authors: Cotta M. A. , Hamm R. A. , Staley T. W. , Yadvish R. D. , Harriott L. R. , Temkin H.
Published: July 2002

Using scanning force microscopy we have studied the growth rate enhancement at the edge of InP and lattice matched InGaAs layers grown into openings on SiO2-masked InP substrates by selective area epitaxy. The growth method was metalorganic molecular beam epitaxy. The growth rates were measured at the center and at the edge of the openings using a scanning force microscope. We have found that the growth rate enhancement can be minimized by using lower metalorganic and hydride flows, and that diffusion is the dominant process at work in the formation of the edge. The migration length of the species depends on the arrival rate of the precursor molecules to the substrate, determined by the absolute group III and V flows, and not on the nominal V/III ratio used for the growth.
Electron-temperature control by movable pins installed in a hollow cathode for discharge plasmas
Authors: Sato N. , Iizuka S. , Koizumi T. , Takada T.
Published: July 2002

In order to control electron energy distributions in discharge plasmas, we have developed a new hollow cathode with pins inside. With an increase in the pin length, the electron temperature is observed to decrease continuously by an order of magnitude, being accompanied by a change of local plasma structure, in weakly magnetized low-pressure Ar dc discharge plasmas.
Tin oxide gated metal-insulator-semiconductor switch diode for room-temperature high speed gas sensing applications
Authors: Fang Y. K. , Chen F. Y. , Hwang J. D. , Fang B. C. , Chen Jiann-Ruey
Published: July 2002

This letter shows the turn on–off current-voltage curves of a tin oxide gated metal-insulator-semiconductor switch diode at room temperature in air, ethanol gas, and hydrogen gas ambient, respectively. Also, the gate turn-off capability and turn-off response time of the device under these gas ambients are investigated. The experimental results show that the device has higher sensitivity and higher speed features in sensing these flammable gases than that of other reported devices at room temperature. The causes which lead to the high sensitivity and high speed features of the sensor were studied in detail and are described.
Normal incidence intersubband transitions in Si-doped InGaAs multiple quantum wells
Authors: Peng Lung-Han , Fonstad Clifton G.
Published: July 2002

Angle- and polarization-resolved infrared techniques have been used to study the polarization selection rules of intersubband transitions in Si-doped InGaAs multiple quantum wells (MQWs). Intersubband transitions are found to be active for light, polarized both parallel and perpendicular to the MQW plane, and to show a strain dependent splitting between the corresponding transition energies. Previously reported intersubband data measured in the Brewster angle configuration for the same lattice-matched and strained Si-doped InGaAs MQWs were also reproduced.
Charge transfer from poly( p-phenylene vinylene) into molecularly doped polymer
Authors: Antoniadis H. , Hsieh B. R. , Abkowitz M. A. , Stolka M.
Published: July 2002

We describe photoinduced charge transfer process in a bilayer device comprised of poly(p-phenylene vinylene) (PPV) layer and a trap-free molecularly doped polymer containing diaryldiamine (TPD) dispersed in polycarbonate (PC). The time resolved charge transfer from PPV to TPD:PC in the presence of an electric field is analyzed. The injection (transfer) efficiency of the photoinduced holes from PPV into TPD:PC is about 25% holes/photons at electric fields at 4×105 V/cm or higher. Minimal trapping of photocarriers at the interface region between the two polymer layers is associated with this transfer.
High power blue light generation by frequency doubling of a laser diode in a periodically domain-inverted LiTaO3 waveguide
Authors: Yamamoto Kazuhisa , Mizuuchi Kiminori , Kitaoka Yasuo , Kato Makoto
Published: July 2002

We report high power and stable blue-light generation by frequency doubling a laser diode, stabilized by a grating feedback technique, in a periodically domain-inverted LiTaO3 waveguide. Due to the deep domain-inverted regions and strong waveguide confinement formed by proton-exchange and a quick heat treatment, high efficiency second harmonic generation (SHG) has been obtained. Locking the oscillation wavelength of a laser diode through the waveguide by a grating feedback technique, 8 mW of stable blue SHG has been demonstrated.