bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of irradiant wavelength during porous silicon formation
Authors: Malone Crona , Jorne Jacob
Published: July 2002

Photoelectrochemical etching of silicon using light assistance of various wavelengths has been studied. As the etching process proceeds, a blueshift is noted in the photoluminescence spectra. However, after a certain period of etching, under a fixed current density, a saturation point is reached, below which no further shift to higher energies is detected. This cutoff point occurs at approximately 2 eV, even if a much higher energy irradiant light source is used during the formation process. These results provide strong evidence for the surface-state mechanism of luminescence and render the pure quantum confinement model unlikely.
New ripple patterns observed in excimer-laser irradiated SiO2/polycrystalline silicon/SiO2 structures
Authors: Giust G. K. , Sigmon T. W.
Published: July 2002

A new ripple formation mechanism is observed in excimer-laser irradiated polycrystalline silicon (polysilicon) films on oxidized silicon wafers. The ripples form for polysilicon films capped with a thin oxide, and for laser fluences that completely melt the buried polysilicon. The resulting ripples are unlike those previously reported in that (1) their wavelength cannot be predicted by Rayleigh’s diffraction condition, (2) their wave fronts are arranged in chaotic patterns, rather than parallel lines, and (3) the wave fronts can be manipulated by changing the polysilicon surface topology. The characteristics of these ripples are investigated in the context of understanding the underlying physics.
Observation of trap states in Er-doped InP by photoreflectance
Authors: Nukeaw Jiti , Yanagisawa Jun , Matsubara Naoteru , Fujiwara Yasufumi , Takeda Yoshikazu
Published: July 2002

We have investigated room-temperature photoreflectance (PR) spectra in Er-doped InP grown by low-pressure organometallic vapor phase epitaxy. A new feature is clearly observed at 1.31 eV, accompanied with a feature due to the bandgap transition at 1.35 eV. The new feature is attributed to a transition involving an Er trap. The transition energy is independent of both doping processing techniques and concentrations of Er in the layers. The PR spectral width of the trap transition energy described by the broadening parameter, increases linearly with the logarithm of Er concentrations.
Evidence for strong spatially localized band-filling effects at interface islands
Authors: Ding Y. J. , Reynolds D. C. , Lee S. J. , Khurgin J. B. , Rabinovich W. S. , Katzer D. S.
Published: July 2002

We have observed saturation of photoluminescence peak at extremely low pump intensities in growth-interrupted and undoped asymmetric-coupled quantum-well structures. We believe the saturation is due to filling of the exciton states localized at the interface islands. The exciton density required to completely fill the localized exciton states at the interface islands for one of the samples is two orders of magnitude lower than that for the previous sample. We have demonstrated that even under the same growth condition, two samples with the same structure exhibit distinctly different photoluminescence spectra and saturation characteristics.
Z-scan measurements with Fourier analysis in ion-doped solids
Authors: Mendonça C. R. , Misoguti L. , Zilio S. C.
Published: July 2002

We report on the measurement of nonlinear refraction in ion-doped solids with a method that combines the single-beam Z-scan technique and a Fourier analysis of the transmittance time evolution. The laser beam is modulated at a frequency f and the Fourier components at f and 2f are shown to be related, respectively, to linear and nonlinear refractions. Their ratio is used to eliminate spurious linear effects as a way of increasing the sensitivity of the measurement. With this method we are able to measure nonlinear phase changes of a few tens of mrad, corresponding to wave front distortions smaller than λ/105. Moreover, the technique can discriminate nonlinear processes with different relaxation times.
Single variant ordering in GaInAs/InP
Authors: Wirth R. , Seitz H. , Geiger M. , Scholz F. , Hangleiter A. , Mühe A. , Phillipp F.
Published: July 2002

Spontaneously ordered Ga0.47In0.53As grown on substrates with the (001) surface tilted 4° towards {111}B are studied using spectroscopic methods as well as x-ray diffraction, transmission electron diffraction and dark-field transmission electron microscopy. The single variant ordering is proved by the absence of one class of the ordering induced 12{111}B superlattice spots in transmission electron diffraction patterns as well as by the tilted polarization of the photoluminescence emerging from the samples cleaved edge. The temperature dependence of the luminescence peak position shows an anomalous behavior at low temperatures and a strong dependence of the peak position on the excitation power. From low temperature absorption measurements, we find a band gap reduction of 37 meV and a valence band splitting of 13.2 meV.
Correlation of two diamagnetic bands of the magnetic circular dichroism of the optical absorption with EL2 in GaAs
Authors: Wietzke K. H. , Koschnick F. K. , Krambrock K.
Published: July 2002

In a previous investigation, a diamagnetic band of the magnetic circular dichroism of the optical absorption (MCDA) in semi-insulating GaAs centered at 1.19 eV was observed and attributed to the neutral diamagnetic charge state of EL2, EL20. In this letter, we show a direct correlation between the signal intensities of two diamagnetic MCDA bands located at 0.93 and 1.19 eV and the concentration of neutral diamagnetic EL20 centers in different GaAs samples. A calibration factor is presented for the absolute MCDA intensities. This opens up the possibility of measuring the concentrations of EL20 and EL2+ using the same technique.
A Si bistable diode utilizing interband tunneling junctions
Authors: Zhu X. , Zheng X. , Pak M. , Tanner M. O. , Wang K. L.
Published: July 2002

A forward S-type bistability was observed in a Si diode with two double δ-doped Si tunnel junctions between the p and n contacts. The conductivity in the two branches of the bistable I–V curve changes by seven orders of magnitude. This, coupled with the all-silicon nature of the device, makes it a very attractive multistate device for practical applications. The bistability is explained by a mechanism, referred to as “band switching,” which is supported by temperature dependence of the I–V characteristics.
Surface morphology of GaN films determined from quantitative x-ray reflectivity
Authors: Lederman D. , Yu Zhonghai , Myers T. H. , Richards-Babb M. R.
Published: July 2002

The surface of two GaN films grown under Ga-rich conditions by molecular beam epitaxy was characterized using x-ray reflectivity, assuming a self-affine/fractal surface morphology. The surface height fluctuations were similar for both samples at the largest lateral length scales at which the fractal description is valid, although this lateral length was significantly greater and the “jaggedness” significantly smaller for the sample grown under higher Ga flux. Previous atomic force microscopy images revealed a higher density of large features on the surface for the sample grown under lower Ga flux. The lateral size of the features are dominated by a convolution of the atomic force microscopy tip shape and the actual features on the surface, which precludes an accurate determination of the surface structure at length scales smaller than the tip radius. This study illustrates the importance of using different techniques to evaluate the film surface morphology at different length scales.
Effect of capping layers on activation of Be/As-implanted semi-insulating InP:Fe
Authors: Lee Dongsoo , Jeong Jichai
Published: July 2002

Be/As-coimplanted semi-insulating InP:Fe samples have been activated by rapid thermal annealing using two different capping layers to protect the surface during activation. Activated samples are investigated using Hall measurements, transmission electron microscopy, and secondary ion mass spectrometry. It is found that borosilicate glass capping results in more abrupt Be profiles as compared with aluminum oxide. Aluminum oxide capped samples show better electrical properties. However, an electrically dead layer and dislocation loop at the surface are observed in aluminum oxide capped samples. These results can be related to stress in the capped films during the activation process.
Resonance Raman and photoluminescence investigations of micro-twins in homoepitaxially grown chemical vapor deposited diamond
Authors: Vohra Yogesh K. , Israel Andrew , Catledge Shane A.
Published: July 2002

Resonance Raman and photoluminescence (PL) investigations of the {100}〈111〉 penetration twin that forms during homoepitaxial diamond growth on (100) diamond substrates by microwave plasma chemical vapor deposition is reported on. A homoepitaxially grown diamond film of 0.13 mm thickness and 1.6 mm diameter was studied with blue (457.9 nm), green (514.5 nm), and red (647.1 nm) laser excitation. The amorphous carbon incorporated in the twin crystal shows resonance Raman enhancement with 647.1 nm excitation. PL spectroscopy reveals increased incorporation of nitrogen-vacancy (N-V) and nitrogen di-vacancy (N-V2) defects in the twin as well as a new defect not observed in the bulk of the film. The present studies show that once the micro-twins are nucleated they form a preferential site for the incorporation of amorphous carbon and other nitrogen-based defects.
Photothermal approach to magnetoresistance monitoring in magnetic multilayers
Authors: Roger J. P. , Boccara A. C. , Valet T.
Published: July 2002

Photothermal methods were used to monitor thermal effects related to magnetoresistance of epitaxial magnetic metallic multilayers, in a direction perpendicular to the layers, as a function of the applied magnetic field. Photothermal signal changes induced by thermal conductivity variations were modeled in order to determine the suitable experimental conditions according to the technique used. Both photothermal microscopy and mirage detection were successfully applied to such measurements. For the sample studied here, a magneto induced perpendicular conductivity variation of ∼6% was determined.
ZnSe epitaxy on a GaAs(110) surface
Authors: Miwa S. , Kuo L. H. , Kimura K. , Ohtake A. , Yasuda T. , Jin C. G. , Yao T.
Published: July 2002

ZnSe molecular beam epitaxial growth on GaAs(110) substrates has been studied using reflection high-energy electron diffraction (RHEED), atomic force microscopy, and transmission electron microscopy. An atomically flat and low defect homoepitaxial buffer GaAs(110) was grown with high V/III ratio (⩾150) and at low growth temperature (∼430 °C). At the beginning of ZnSe growth on a GaAs(110) buffer epitaxial layer, RHEED oscillation was observed and no facet was seen on a pseudomorphic ZnSe(110) surface. Low defect ZnSe films (defect density ⩽105 cm−2) were also obtained without the Zn preexposure process necessary for low defect ZnSe(001) growth.
Thermal stability of YBa2Cu3O7−x single crystal surfaces investigated by the ion channeling technique
Authors: Wang F. , Zama H. , Ohtsuka H. , Sato M. , Morishita T.
Published: July 2002

We have performed ion channeling characterizations on the (001) and (100) surfaces of YBa2Cu3O7−x single crystals, using 950 keV He+ ions at temperatures ranging from 20 to 780 °C. In oxygen pressures below 5×10−5 Torr, we directly observed the surface changes as the sample temperature was increased, and found that the compositional and structural changes occurred from around 400 °C. At higher oxygen pressures, we heated the crystals and performed channeling analysis before and after the heating. We found that the YBa2Cu3O7−x crystal surfaces were stable at temperatures up to 780 °C in the oxygen pressure range of 1 mTorr–1 Torr. Beyond this range, the surfaces deteriorated at high temperatures.
Modeling of electrical conductance variation in substrate during initial growth of ultra thin film
Authors: Song Seok-Kyun , Jung Hyung-Jin , Koh Seok-Keun , Baik Hong-Koo
Published: July 2002

A model of the electrical conductance of a resistive or semiconductive substrate, as a function of the average thickness d of a deposited film in initial growth on the substrate is proposed. The total conductance has two terms: one proportional to d2/3 for three-dimension (3D) growth, and one proportional to d for 2D growth or for increasing number of islands. The model was applied to the conductance of a Sn film deposited on a SiOx substrate showing that the initial growth is dominated by 3D growth. The proposed model may be useful for in situ study of the growth of ultra thin films prior to the onset of tunneling conductance.
Laser-induced acoustic desorption of electrons and ions
Authors: Golovlev V. V. , Allman S. L. , Garrett W. R. , Chen C. H.
Published: July 2002

Laser irradiation of absorbing materials can be used to generate acoustic pulses with extremely high amplitude and short pulse duration. Such acoustic pulses can transfer energy and momentum to atomic particles on solid surfaces to cause desorption of the particles. We report experimental observations of the effect of laser-induced acoustic desorption (LIAD) of electrons from metal film surfaces and hydrogen ions from the surface of palladium saturated with hydrogen. We believe LIAD can be used as a gentle technique to transfer analyte molecules and ions into gas phase for mass analysis and for other applications.
Pt/
p
-strained-Si Schottky diode characteristics at low temperature
Authors: Chattopadhyay S. , Bera L. K. , Ray S. K. , Maiti C. K.
Published: July 2002

The Schottky barrier height and ideality factor of Pt on p-type strained Si (grown on a graded relaxed Si0.82Ge0.18 buffer layer) have been investigated in the temperature range (90–150 K) using the current-voltage characteristics and are found to be temperature dependent. While the ideality factor decreases with an increase in temperature, the barrier height increases. Simulation based on a drift-diffusion emission model has been used to explain the experimental results.
Using strained (AlxGa1−x)yIn1−yAszP1−z system materials to improve the performance of 850 nm surface- and edge-emitting lasers
Authors: Sale T. E. , Amamo C. , Ohiso Y. , Kurokawa T.
Published: July 2002

We compute the optical gain of various quantum wells for use in 850 nm lasers. In particular, we investigate compressively strained wells of AlGaInAs, InGaAs, or InGaAsP without any assumptions of the material quality. Reductions of up to 43% in the radiative current and 24% in the sheet carrier density can be expected, compared with GaAs/AlGaAs wells. For the case of vertical-cavity surface-emitting lasers and distributed feedback lasers, compressive strain is particularly attractive in reducing the temperature sensitivity and fabrication tolerances for low threshold and efficient operation.
Field and temperature effects on oxide charge detrapping in a metal–oxide–semiconductor field effect transistor by measuring a subthreshold current transient
Authors: Chiang Lu-Ping , Zous N. K. , Wang Tahui , Chang T. E. , Shen K. Y. , Huang C.
Published: July 2002

A technique to characterize oxide charge detrapping in a Fowler–Nordheim stressed n-metal–oxide–semiconductor field effect transistor is proposed. This technique consists of two alternating phases, an oxide charge detrapping phase and a subthreshold current measurement phase. An analytical model relating a subthreshold current transient to oxide charge density and detrapping time constants was derived. By varying the gate bias in the detrapping phase and the ambient temperature, the field and temperature dependences of oxide charge detrapping can be obtained from the subthreshold current transients measured.
Dislocation-related photoluminescence peak shift due to atomic interdiffusion in SiGe/Si
Authors: Shum Kai , Mooney P. M. , Chu J. O.
Published: July 2002

Low-temperature photoluminescence (PL) spectroscopy was used to study electronic states associated with threading dislocations (D lines) in strain-relaxed Si1−xGex layers. The structures investigated were grown by ultrahigh vacuum chemical vapor deposition at 550 °C and consist of a Si(001) substrate, followed by a stepwise graded buffer layer, followed by a thick uniform composition Si1−xGex layer. The PL peak positions of the four D lines after isochronal annealing at temperatures between 600 and 800 °C were measured. We show that the large energy shift of the D1 line is due to a change in the local band gap energy at the dislocation core due to strain-driven diffusion of Ge atoms away from the dislocation core with an activation energy Ea, which varies with Ge mole fraction x.
Indirect enhancement of PbS photoconductivity by ferroelectric field effect in a PbS/PbTiO3/Si heterostructure
Authors: Pintilie I. , Pintilie L. , Dragoi V. , Petre D. , Botila T.
Published: July 2002

A lead sulphide/lead titanate/silicon (PbS/PbTiO3/Si) heterostructure was manufactured by successive deposition of PbTiO3 and PbS thin film on a single crystalline, p-type, Si substrate. Chemical methods were used for deposition. A three electrode configuration was used to control the photoconductivity of PbS thin film by field effect, through the ferroelectric PbTiO3 thin film. The spectral distribution of the photoconductive signal shows two maxima, situated at 1.1 and 2.45 μm. It was found that the photoconductive signal at 1 μm varies of about eight times when the voltage applied on the Si substrate is varied between −1 and +1 V. At 2 μm the photoconductive signal is almost independent of the applied voltage on the Si substrate. The observed results are explained considering a ferroelectric field effect by which the photogenerated carriers in Si influence the photoconductive signal in the PbS thin film.
Fourth power law of time dependence of Si adsorbate diffusion on a Si(001) surface
Authors: Doi Takahisa , Ichikawa Masakazu , Hosoki Shigeyuki
Published: July 2002

Diffusion of Si adsorbates deposited on a Si(001) surface is investigated by reflection electron microscopy. At temperatures up to about 600 °C, the diffused length x of the adsorbates is proportional to t1/4 before the critical time tc, where t is the heating time. At ttc, the diffused length x is proportional to t1/2, where x is determined by thermal diffusion of the adsorbates.
Surface roughness determination using the acousto-optic technique: Theory and experiment
Authors: Briers R. , Leroy O. , Devolder S. , Wevers M. , De Meester P.
Published: July 2002

With the acousto-optic nondestructive testing technique, phase shifts between the incident and the reflected ultrasound are measured at critical angles of the investigated material. This letter is focusing theoretically as well as experimentally on the influence of a small surface roughness (some micrometers) of a thick material on the phase information.
Intrinsic modulation bandwidth of strained GaInP/AlGaInP quantum well lasers
Authors: Moritz A. , Wirth R. , Heppel S. , Geng C. , Kuhn J. , Schweizer H. , Scholz F. , Hangleiter A.
Published: July 2002

We have investigated the intrinsic modulation response of GaxIn1-xP/AlGaInP quantum well lasers. The differential gain resulting from the measurement of the frequency response, is in good agreement with calculations based on a 6-band kp-theory and direct measurements of the optical gain. We find a maximum value of 3.8×10−16 cm2 for a strongly compressively strained sample, which is less than in InGaAs lasers according to the larger effective masses. The maximum bandwidth we observed is 9.3 GHz at −3 dB. We show that the bandwidth is limited by catastrophic optical damage and not by intrinsic mechanisms.
An aluminum-wire grid polarizer fabricated on a gallium–arsenide photodiode
Authors: Doumuki Tohru , Tamada Hitoshi
Published: July 2002

An aluminum-wire grid polarizer fabricated directly on a gallium–arsenide photodiode is used to realize a polarization-selective photodetector. Since all of the light transmitted through the wire grid, including higher-order diffraction components, can be detected at the photodiode and since a resonance of incident electromagnetic waves is utilized, the required grid period can be significantly larger. With a grid period of 600 nm and normal incident light at 715 nm, an extinction ratio of 16 can be obtained both for light detected at the photodiode and light reflected from the surface. If light detected at the photodiode is to be optimized, a higher extinction ratio of 30 and a loss of 30% have been experimentally obtained as well. These experimental results are in good agreement with our theoretical simulation.
Ideal Ohmic contact to n-type 6H-SiC by reduction of Schottky barrier height
Authors: Teraji T. , Hara S. , Okushi H. , Kajimura K.
Published: July 2002

We formed ideal Ti Ohmic contacts on an n-type 6H-SiC epitaxial layer by reducing Schottky barrier heights. The ideal contacts were realized by utilizing ideal SiC surfaces formed under processes that intend to lower the density of surface states. As the first process to form the ideal surfaces, SiC surfaces were flattened by oxidation followed by HF etching. Further, the ideal SiC surfaces in terms of passivation of surface states were formed by immersing the flat SiC surfaces in boiling water. Ti electrodes thus formed had Ohmic properties with excellent I–V characteristic linearity without the use of heavy doping and high-temperature annealing.
Lattice relaxation of GaAs islands grown on Si(100) substrate
Authors: Asai Koyu , Kamei Kazuhito , Katahama Hisashi
Published: July 2002

Initial stage of lattice relaxation of GaAs islands grown on Si(100) substrate were investigated by combination of reflection high-energy electron diffraction and molecular beam epitaxy. In addition to the lattice constants in horizontal direction (a∥) to the substrate surface, we first measured directly those in vertical one (a⊥). At the beginning of the growth, the rapid increase of a∥ and the larger Poisson’s ratios than that of bulk were observed. Atomic bond flexibility and extension induced by surface effects might cause this rapid increase of a∥ and large Poisson’s ratios.
Hot-carrier-induced modifications to the noise performance of polycrystalline silicon thin-film transistors
Authors: Giovannini S. , Carluccio R. , Mariucci L. , Pecora A. , Fortunato G. , Reita C. , Plais F. , Pribat D.
Published: July 2002

Modifications of noise performances induced by hot-carrier degradation in polycrystalline silicon thin-film transistors, made by excimer laser crystallization, are presented. In particular, the normalized drain current spectral density of these devices shows an evident 1/f behavior, and as the device characteristics are degraded by prolonged bias stressing, the noise performances worsen. Hot-carrier degradation results in the formation of both interface states, that have been evaluated through the analysis of the sheet conductance, as well as of oxide traps near the insulator/semiconductor interface, as evidenced by the 1/f noise measurements. A strong correlation between interface state and oxide trap densities has been found, suggesting a common origin for the generation mechanism of the two types of defects.
Simulation of carrier capture in semiconductor quantum wells: Bridging the gap from quantum to classical transport
Authors: Register Leonard F. , Hess Karl
Published: July 2002

The effects of lost phase coherence on carrier capture by semiconductor quantum wells are simulated using Schrödinger Equation Monte Carlo. Results are shown for polar-opticalphonon-induced capture of both electrons and holes, and for both monoenergetic and thermal distributions of incident charge carriers. Results suggest that semiclassical modeling of hole capture may be sufficient, provided that quantum mechanical reflection from the individual heterointerfaces still is taken into account. However, for a quantum well laser optimized to operate at an electron capture resonance, semiclassical calculations blind to the resonance structure would underestimate the capture rate, while Golden-Rule calculations, which assume complete phase coherence, could somewhat overestimate it.
Calculation of valence-band offsets of lattice-matched GaInTlP/InP heterostructures and of Schottky barrier heights of metal–GaInTlP contacts
Authors: Mönch Winfried
Published: July 2002

Quaternary Ga0.18(1−y)InyTl0.82(1−y)P alloys are lattice matched with InP and their band gaps were predicted to be direct and to vary from zero width to 1.35 eV, the value of InP. This study calculates the branch points of the interface-induced gap states of the binary compound TlP and of the ternary GaTlP and InTlP as well as some quaternary GaInTlP alloys using an empirical tight-binding approach. Several predictions are made. First, the band lineup of lattice-matched InP/Ga0.18(1−y)InyTl0.82(1−y)P heterostructures is of type I. Second, the conduction-band discontinuities are larger than the valence-band offsets. And third, metal/Ga0.18(1−y)InyTl0.82(1−y)P contacts are naturally ohmic for indium contents y smaller than approximately 0.5.
Terahertz wave amplification, stimulated by dc electric current, in grating coupled low-dimensional electron systems
Authors: Mikhailov S. A. , Savostianova N. A.
Published: July 2002

We present an analytic theory of the transmission of electromagnetic waves through a structure “two-dimensional electron system with a flowing current – grating coupler.” The transmission coefficient T(ω,vdr) is calculated as a function of frequency, drift velocity vdr, and other physical and geometrical parameters of the structure. Threshold conditions for amplification [T(ω,vdr)>1] are analyzed. A number of ideas for a reduction of the threshold velocity and an enhancement of the amplification are proposed. Our results can be used for designing tunable solid-state terahertz wave amplifiers (generators), based on the grating coupled low-dimensional electron systems.
Pyroelectrically induced optical emission from potassium titanyl phosphate crystals
Authors: Cooke D. W. , Bennett B. L. , Muenchausen R. E. , Wayne D. M.
Published: July 2002

We have observed optical scintillations and corresponding electric current pulses when uniformly heating potassium titanyl phosphate (KTP) crystals at 0.1–0.4 K/s over the temperature range 8–300 K. The scintillations correspond to molecular nitrogen emission occurring during the electrical breakdown of air near the crystal surface, and imply the existence of pyroelectrically induced peak electric fields at the crystal surface exceeding 30 kV/cm, which is ten times larger than dc electric fields reported to induce electrochromic (EC) damage in this material. Recent optical damage studies on KTP under high repetition rate, high average-power laser irradiation reveal an EC-like damage, implying the existence of an internal electric field arising during laser irradiation. Our observation of a sizable total pyroelectric response suggests one possible mechanism for the origin of these internal fields in KTP and other nonlinear optical materials.
Trivalent behavior of palladium in silicon
Authors: Sachse J.-U. , Jost W. , Weber J. , Lemke H.
Published: July 2002

Palladium is known to exhibit an acceptor state at EC−0.22 eV in n-type Si and a donor state at EV+0.31 eV in p-type Si. We have identified a third level at EV+(0.140±0.005) eV and attribute it to the double donor state of substitutional Pd. The Pd level positions are very similar to the corresponding levels for Pt. The double donor states of both metals show an electric field dependence of the emission rates and a thermal activation of the hole capture cross sections.
Nanolithography with metastable neon atoms: Enhanced rate of contamination resist formation for nanostructure fabrication
Authors: Rehse S. J. , Glueck A. D. , Lee S. A. , Goulakov A. B. , Menoni C. S. , Ralph D. C. , Johnson K. S. , Prentiss M.
Published: July 2002

We report a sevenfold improvement in the rate of contamination resist formation over previous experiments by using metastable neon atoms for nanolithography. Chemically assisted ion beam etching was used to transfer the resist pattern into the substrate. We demonstrate the fabrication of 50-nm-wide features in GaAs with well-defined edges and an aspect ratio >2:1. These are the best resolution and highest aspect ratio features that have been achieved with metastable atom lithography. The resist formation rate by the metastable neon atoms and the etch selectivity of the contamination resist with GaAs were measured.
Continuously tunable, 6–14 μm silver-gallium selenide optical parametric oscillator pumped at 1.57 μm
Authors: Chandra Suresh , Allik Toomas H. , Catella Gary , Utano Richard , Hutchinson J. Andrew
Published: July 2002

An angle tuned silver gallium selenide (AgGaSe2) optical parametric oscillator (OPO), pumped by the fixed wavelength 1.57 μm output of a noncritically phase-matched KTiOPO4 OPO, yielded radiation continuously tunable from 6 to 14 μm. Energies of up to 1.2 mJ/pulse with bandwidths of ∼5 cm−1   (full width at half-maximum) were obtained using a 6.5×6.5×35.3  mm long, type I AgGaSe2 crystal.
Oxygen displacement in a Ag17+107 ion irradiated Bi2Sr2CaCu2O8 single crystal
Authors: Sudershan Y. S. , Rastogi Amit , Bhat S. V. , Grover A. K. , Yamaguchi Y. , Oka K. , Nishihara Y. , Senapati L. , Kanjilal D.
Published: July 2002

We have studied the magnetic field (H∥c) dependent rf dissipation (Hrf∥a) in an as-grown Bi2Sr2CaCu2O8 single crystal prior to and after irradiation with 250 MeV Ag17+107 ions. In a comparison of the responses from the as-grown crystal with an air-annealed crystal, features due to oxygen deficient regions acting as weak links in the former are identified. These features disappear immediately after irradiation of the as-grown crystal. We attribute such behavior to the displacement of oxygen from columnar tracks to deficient regions thus eliminating the weak links. Losses from the same irradiated as-grown crystal stored at 300 K for 60 days show that the features similar but not identical to those observed in the pristine state have reappeared implying that the displaced oxygen is in a metastable configuration in the deficient regions and hence is mobile due to thermal effects even at 300 K.
Improvement in critical current density under magnetic field in heavily Pb-doped Bi2Sr2CaCu2Ox superconducting tape
Authors: Funahashi Ryoji , Matsubara Ichiro , Ueno Kazuo , Ishikawa Hiroshi , Mizuno Katsunori , Ohno Nobuhito
Published: July 2002

A heavily Pb-doped Bi2Sr2CaCu2Ox (Bi-2212) tape has been prepared using an isothermal partial melting method. Width of magnetic hysteresis (ΔM) normalized by ΔM under 0 Oe decreases with increasing magnetic field (H∥c axis) at 20–60 K; this occurs more rapidly in pure Bi-2212 tape (Pb-free tape) than in Pb-doped tape. Irreversibility field under the H∥c axis is elevated by Pb doping at 20–60 K. Moreover, a decrease in transport critical current density (Jc) with increasing H∥c axis is reduced by Pb doping at 20–60 K. In particular, a peak is observed at 2.0 kOe in Jc–H curves at 20 and 30 K. Hole concentration in the Pb-doped tape seems to be close to the optimum, as magnetic superconducting transition starts at 91 K. Therefore, the above results are due to production of new pinning centers induced by applying the magnetic field. It is clear that heavy Pb doping is effective for Bi-2212 polycrystalline tape in producing efficient pinning centers for the H∥c axis as reported in Bi-2212 single crystals.
Effects of quenched impurities and relative antiferroelectric/ferroelectric phase stability on the incommensurately modulated polar structures of La-modified lead zirconate titanate
Authors: Xu Z. , Dai X. H. , Li J. F. , Viehland Dwight
Published: July 2002

Structure–property relationship studies have been performed in the La-modified lead zirconate titanate (PLZT) solution as a function of quenched La impurity content and Zr/Ti ratio. For Zr/Ti ratios of 90/10 and 85/15, an incommensurate antiferroelectric state was found to be stabilized with increasing La content. Temperature-dependent investigations demonstrated that the incommensurate structure becomes pinned into long-time metastable states, rather than transforming to a commensurate phase. Also, the modulation wavelength (λ) was found to increase significantly with the decreasing Zr/Ti ratio and decreasing La content. The results of this study clearly demonstrate that the incommensurately modulated polar structures of PLZT are dependent on the relative antiferroelectric/ferroelectric phase stability, and the concentration of quenched La impurities.
Long-term stable direct current bias operation in electro-optic polymer modulators with an electrically compatible multilayer structure
Authors: Shi Yongqiang , Wang Wenshen , Lin Weiping , Olson David J. , Bechtel James H.
Published: July 2002

The drift of the direct current (dc) quadrature bias voltage was monitored in electro-optic polymer Mach–Zehnder modulators for over 600 h. Traceable bias voltage was observed in polyurethane-Disperse Red 19 modulators. Electric field relaxation analysis showed that steady state dc and alternating current (ac) field distributions on polymer layers depended on the dielectric properties of the materials. The long-term bias stability of our modulators was originated from the low conductivity of the electro-optic polymer guiding layer. A concept of material electrical compatibility is introduced as a materials selection guideline for the fabrication of polymer modulators with the minimum bias drift.
GaN exciton photovoltaic spectra at room temperature
Authors: Liu W. , Li M. F. , Chua S. J. , Zhang Y. H. , Uchida K.
Published: July 2002

Clear exciton absorption peak has been observed at room temperature by photovoltaic spectra, on a GaN layer grown on (0001)-plane sapphire by metalorganic chemical vapor deposition. From the spectra, we obtained the wurtzite GaN room temperature A and B exciton transition energies, and the energy gap to be 3.401, 3.408, and 3.426 eV, respectively. We have also performed photovoltaic measurements with varied light incidence angles, and observed the polarization behavior of exciton absorption in GaN. In conjunction with previous room temperature photoreflectance measurements, this work provided direct and reliable assessment of GaN semiconductor crystal layers.
Resonant excitation of visible photoluminescence from an erbium-oxide overlayer on Si
Authors: Kasuya A. , Suezawa M.
Published: July 2002

A thin Er2O3 layer grown on a Si surface by vapor doping of Er exhibits intense photoluminescence in the green and red regions excited by laser beams in the 800 nm and 450–490 nm ranges. These intense light emissions take place via resonant two or one step photoexcitations of the 4f levels in Er3+ ions. Our sample fabrication procedure is integrated circuit compatible and produces Er2O3 layers of excellent homogeneity and quality as demonstrated in the optical measurements.
Ultrafast carrier dynamics and intervalley scattering in ZnSe
Authors: Dougherty D. J. , Fleischer S. B. , Warlick E. L. , House J. L. , Petrich G. S. , Kolodziejski L. A. , Ippen E. P.
Published: July 2002

Intraband carrier dynamics were measured in ZnSe films by a two-wavelength pump probe technique with 180 fs resolution. A below-band pump pulse was used to heat carrier distributions in N-type samples by free carrier absorption. The electron cooling time constant was observed to be 500 fs. Intervalley scattering was seen to play a significant role in the electron dynamics and the scattering time from the L back to the Γ valley was measured to be 1.8 ps. By examining the ratio of the intervalley component to the total response as a function of pump photon energy, the bottom of the L valley was determined to lie 1.30 eV above the Γ-valley minimum.
Preservation of atomically clean silicon surfaces in air by contact bonding
Authors: Grey François , Hermansson Karin
Published: July 2002

When two hydrogen-passivated silicon surfaces are placed in contact under cleanroom conditions, a weak bond is formed. Cleaving this bond under ultrahigh vacuum (UHV) conditions, and observing the surfaces with low energy electron diffraction and scanning tunneling microscopy, we find that the ordered atomic structure of the surfaces is protected from oxidation, even after the bonded samples have been in air for weeks. Further, we show that silicon surfaces that have been cleaned and hydrogen-passivated in UHV can be contacted in UHV in a similarly hermetic fashion, protecting the surface reconstruction from oxidation in air. Contact bonding opens the way to novel applications of reconstructed semiconductor surfaces, by preserving their atomic structure intact outside of a UHV chamber.
The influence of inversion domains on surface morphology in GaN grown by molecular beam epitaxy
Authors: Romano L. T. , Myers T. H.
Published: July 2002

Growth of GaN by rf-plasma molecular beam leads to different surface morphologies for nitrogen-rich growth versus gallium-rich growth. Nitrogen-rich growth produces a significant density of pyramidal hillocks while gallium-rich growth results in flat surfaces. Differences in surface morphology were directly linked to the presence of inversion domains which originated in the nucleation layer. Nitrogen-rich growth and growth under atomic hydrogen enhanced the growth rate of inversion domains with respect to the surrounding matrix, while growth under Ga-rich conditions resulted in a more nearly equal growth rate.
Enhanced conductivity in ionic conductor-insulator composites: Experiments and numerical model
Authors: Debierre Jean-Marc , Knauth P. , Albinet Gilbert
Published: July 2002

We study ionic conductivity of the model composites, copper(I) bromide-titanium dioxyde, in a large domain of composition. The experimentally observed enhancement of conductivity is interpreted by a numerical model taking into account grain size effects and interactions between ionic conductor and insulator grains.
Comparison of the k⋅p and the direct diagonalization approaches for describing the electronic structure of quantum dots
Authors: Fu Huaxiang , Wang Lin-Wang , Zunger Alex
Published: July 2002

It is shown that the standard (decoupled) 6×6 k⋅p effective-mass approach for semiconductor quantum dots overestimates significantly the hole and electron confinement energies, and, for dots made of materials with small spin-orbit coupling (e.g., phosphides, sulphides) produces a reverse order of s- and p-like valence states. By contrasting the electronic structures of dots as obtained by a direct diagonalization (multiband) pseudopotential approach and by its k⋅p approximation, we are able to trace the systematic errors of k⋅p in dots to the k⋅p errors in the underlying bulk solids. This suggests a “diagnostic tool” and a strategy for improving the k⋅p.
n
-type delta-doped strained quantum well lasers for improved temperature-dependent performance
Authors: Buchinsky O. , Blumin M. , Fekete D.
Published: July 2002

It is demonstrated that the incorporation of Te n-type δ doping close to a single-strained InGaAs/GaAs quantum well improves the temperature stability of the laser, as indicated by the higher characteristic temperature and by the reduced sensitivity of the threshold current to temperature variations. This improvement results from the strong coupling between the quantum well and the δ-doping well.
Oxygen and the thermal stability of thin CoSi2 layers
Authors: Tung R. T.
Published: July 2002

The thermal stability of thin CoSi2 layers is demonstrated to improve with the use of oxygen-containing annealing ambients. Pinhole formation observed in 11–27 nm thick CoSi2 layers after anneals at 800 °C in nitrogen and vacuum is found to be eliminated when oxygen is used as the annealing ambient. A thin SiO2 layer grown during oxygen anneals, which curbs surface diffusion and reduces the rates of kinetic processes, is thought to be the primary reason for the retardation of layer agglomeration. The beneficial effect of air exposure and wet etches to the integrity of thin CoSi2 layers is also shown. These findings suggest the inclusion of oxygen in certain Co salicide processing steps.
Abnormal photocurrent–voltage behavior of GaAs/AlGaAs multiple shallow quantum well p-i-n diodes
Authors: Kwon O-Kyun , Lee Kyu-Seok , Chu Hye Yong , Lee El-Hang , Ahn Byung-Tae
Published: July 2002

We have observed the abnormal photocurrent–voltage (I–V) behavior in GaAs/AlGaAs multiple shallow quantum wells p-i-n diodes. Under the illumination of a laser, two current plateaus were developed at the negative conductance region of the I–V curve, along with some hystereses depending on the scan direction. At the first plateau, two major oscillations of ∼120 kHz and ∼37 MHz were observed with several minor oscillations of frequencies below the latter, while this latter component was uniquely at the other plateau. Analyzing the electrical and the optical oscillations, we explain that one hysteresis at the first plateau was due to the low frequency bias-circuit oscillations, whereas the other at the next plateau was attributed to the intrinsic behavior of the p-i-n diode.
Spectral characteristics of an InP/InGaAs distributed absorbing Bragg reflector
Authors: Ogawa Kensuke , Matsui Yasuhiro , Itatani Taro , Ouchi Kiyoshi
Published: July 2002

An InP/In0.53Ga0.47As distributed absorbing Bragg reflector is investigated by reflectance and group-delay-time spectroscopy. The measured reflectance is suppressed and shows a minimum at the low-wavelength side of the high-reflectance band. This suppression of reflectance is due to an enhancement of optical absorption. The enhancement of optical absorption originates from an increase in the overlap of the optical field with the absorbing InGaAs layers since an intense optical field is confined near the surface in the spectral range of the enhancement.
Use of a helicon-wave excited plasma for aluminum-doped ZnO thin-film sputtering
Authors: Yamaya K. , Yamaki Y. , Nakanishi H. , Chichibu S.
Published: July 2002

Successful sputtering deposition of aluminum-doped zinc oxide (ZnO:Al) thin films was carried out using the helicon-wave excited plasma (HWP). The films deposited on soda-lime glass substrates exhibited a dominant [0001]-oriented growth with a small full-width at half maximum (0.32 deg) of the (0002) x-ray diffraction peak. The film deposited at 300 °C showed a resistivity of 5×10−4 Ω cm without any additional annealings. High optical transmittance greater than 80% was achieved in the visible spectral wavelengths. Similar to the success of the laser ablation technique, the HWP-sputtering method is expected to be developed as one of the versatile techniques for the preparation of semiconductor thin films.
Optical mixing to 211 GHz using 50 nm gate pseudomorphic high electron mobility transistors
Authors: Ali M. E. , Bhattacharya D. , Fetterman H. R. , Matloubian M.
Published: July 2002

We report optical mixing with difference frequencies to 211 GHz in 50 nm gate pseudomorphic InP-based high electron mobility transistors (HEMTs). To our knowledge, this is the highest frequency optical mixing signal obtained in three terminal devices. To detect the signals at these frequencies, a novel three-wave-mixing configuration was employed. To demonstrate the wide tunability of this setup, a sweep of frequencies from 160 to 190 GHz was performed. The optically generated millimeter wave signals were downconverted to 97 GHz and radiated. For the radiation experiments, tunable baseband signals were also added by injection into the gate terminal of our HEMTs, thereby providing a method to transmit information.
Observation of an anomalously large blueshift of apparent donor–acceptor pair transition peak in compensation-doped quantum wells
Authors: Ding Y. J. , Korotkov R. , Khurgin J. B. , Rabinovich W. S. , Katzer D. S.
Published: July 2002

We have observed an anomalously large blueshift of the apparent donor–acceptor pair transition peak as the laser intensity increases in compensation-doped coupled quantum wells. The mechanism for the blueshift is the change of the Coulomb interaction energy between the recombined donors and acceptors due to the decrease in their separation as the laser intensity increases. The blueshift is accompanied by the saturation of the relative donor–acceptor pair transition peak intensity due to filling of the impurity states.
Temperature dependence of the current-phase relation for YBa2Cu3O7−x step-edge Josephson junctions
Authors: Il’ichev E. , Zakosarenko V. , Schultze V. , Meyer H.-G. , Hoenig H. E. , Glyantsev V. N. , Golubov A.
Published: July 2002

The current-phase relation (CPR) of YBa2Cu3O7−x step-edge Josephson junctions was investigated experimentally at various temperatures. The investigated junctions were incorporated into a washer-shaped superconducting ring with inductance L∼300 pH. The ring was inductively coupled to a tank circuit with a resonance frequency between 9 MHz and 40 MHz. The CPR was obtained from the measurement of the impedance of the phase-biased junction. At high temperatures and low critical current the experimentally observed CPR is sinusoidal. The same results were obtained at low temperatures when the rms flux noise in the ring is negligible. In the case of larger critical current and finite noise, deviations of the apparent CPR from sinusoidal dependence were found. The deviations can be described by thermal fluctuations of the magnetic flux in the ring.
Electromagnetic characterization of vertical-cavity surface-emitting lasers based on a vectorial eigenmode calculation
Authors: Burak D. , Binder R.
Published: July 2002

A complete theoretical approach to the electromagnetic properties of vertical-cavity surface-emitting lasers (VCSELs) is presented. The solution of the 3D vector Maxwell equations is obtained by means of a generalized vectorial transform matrix. Results for the characterization of laser modes include modal frequencies, cavity losses, and eigenmode light-field vector patterns. As an example, modal properties of air-post index-guided VCSELs are analyzed for various cavity design parameters. Scattering losses due to modal mismatch at cavity interfaces are found to be small and, hence, would not overcompensate potential cavity design improvements based on increased relative index steps.
Addition energies in semiconductor quantum dots: Role of electron–electron interaction
Authors: Rontani Massimo , Rossi Fausto , Manghi Franca , Molinari Elisa
Published: July 2002

We show that the addition spectra of semiconductor quantum dots in the presence of magnetic field can be studied through a theoretical scheme that allows an accurate and practical treatment of the single-particle states and electron–electron interaction up to large numbers of electrons. The calculated addition spectra exhibit the typical structures of Hund-like shell filling, and account for recent experimental findings. A full three-dimensional description of Coulomb interaction is found to be essential for predicting the conductance characteristics of few-electron semiconductor structures.
SrBi
2
Ta
2
O
9
memory capacitor on Si with a silicon nitride buffer
Authors: Han Jin-Ping , Ma T. P.
Published: July 2002

We have made ferroelectric memory capacitors by depositing a SrBi2Ta2O9 thin film on a Si substrate separated by an ultrathin buffer layer of silicon nitride film. The hysteresis in the capacitance–voltage curves suggests a sizable memory window of 2 V with a programming voltage swing of ±7 V. The switching time is estimated to be on the order of nanosecond based on the results of a one-shot pulse experiment. The results from the fatigue test indicate a slight degradation of the memory window after 1011 switching cycles. These properties are encouraging for the development of ferroelectric memory transistors.