bluuebunny/crossref_metadata_2025 huggingface dataset:
Low threshold quasi-three-level 946 nm laser operation of an epitaxially grown Nd:Y3Al5O12 waveguide
Authors: Hanna D. C. , Large A. C. , Shepherd D. P. , Tropper A. C. , Chartier I. , Ferrand B. , Pelenc D.
Published: July 2002

We report the 946 nm laser operation of an epitaxially grown Nd:YAG planar waveguide. The incident and absorbed power thresholds of 4 and 1.2 mW, respectively, are lower than those reported for bulk lasers when using a similar experimental setup. We also report the use of Ga doping of the active layer to increase the refractive index difference to allow the production of very small guiding layers.
Novel surface emitting GaAs/AlGaAs laser diodes based on surface mode emission
Authors: Köck A. , Seeberg A. , Rosenberger M. , Gmachl C. , Gornik E. , Thanner C. , Korte L.
Published: July 2002

We present a novel concept to achieve surface emission from conventional semiconductor laser diodes. This new type of laser diode is modified to allow a coupling of the laser mode to a transverse electric polarized surface mode. As a result we achieve surface emission from GaAs/AlGaAs double heterostructure laser diodes with a beam divergence of 0.2%. This novel concept has a high potential for the realization of a beam steering device.
New continuous wave infrared Ar-Xe laser at intermediate gas pressures pumped by a transverse radio frequency discharge
Authors: Udalov Y. B. , Peters P. J. M. , Heeman-Ilieva M. B. , Ernst F. H. J. , Ochkin V. N. , Witteman W. J.
Published: July 2002

An atomic Xe laser with a transverse rf excitation has been operated in a cw mode in the intermediate pressure regime. The laser output spectrum consisted of 5 Xe lines with wavelengths of 2.03, 2.63, 2.65, 3.37, and 3.51 μm. The unoptimized total output power of 330 mW was obtained for a gas mixture Ar:He:Xe=59:40:1 at a pressure of 85 Torr and a rf input power of 150 W and excitation frequency of 121 MHz.
Multiple peak photoluminescence of porous silicon
Authors: Cheah K. W. , Chan Tommy , Lee W. L. , Teng Da , Zheng W. H. , Wang Q. M.
Published: July 2002

The photoluminescence (PL) response of porous silicon is usually in the form of a single broad peak. Recently, however, PL response with two peaks has been reported. Here we report the observation of multiple peaks in the PL spectrum of porous silicon. A simple modeling of the line shape indicates that four peaks exist within the response curve, and analysis suggests that the PL of porous silicon is derived from quantum confinement in the silicon crystallites. The line shapes can be due to either minibands within the conduction and valence bands or crystallite size variation or a combination of the two.
Josephson coupling in a-axis YBa2Cu3O7−δ/Pr1−xYxBa2Cu3O7−δ /YBa2Cu3O7−δ sandwich-type junctions
Authors: Umezawa T. , Lew D. J. , Streiffer S. K. , Beasley M. R.
Published: July 2002

We have studied Josephson coupling in a-axis YBa2Cu3O7−δ/Pr1−xYxBa2Cu3O7−δ /YBa2Cu3O7−δ sandwich-type superconductor/normal/superconductor (SNS) junctions. Growth parameters for the films were optimized for smoothness of the barrier interfaces and the films were well characterized by scanning electron microscopy, atomic force microscopy, and cross-sectional transmission electron microscopy. Transport of the barrier material was highly dependent upon the doping: for x=0, the resistivity followed a T−1/4 behavior and was ∼105 Ω cm at 4.2 K; for x=0.45, the resistivity was nearly metallic and was 10−1 Ω cm at 4.2 K. In the small junction regime W<λj, the critical current scaled with junction area, and was modulated by a magnetic field. We have compared our results to other SNS work and found that the coupling strength of the barrier increases with the conductivity of the barrier material. Possible sources of the coupling are discussed.
Positron annihilation in porous silicon
Authors: Itoh Yoshiko , Murakami Hideoki , Kinoshita Akira
Published: July 2002

Three lifetime components, one of which is extremely long (25±2 ns), have been observed in experimental studies of positron annihilation in porous silicon, made by anodization in hydrofluoric acid. The Doppler-broadened spectrum of the porous silicon is sharp compared with that of crystal silicon and becomes even narrower in an applied magnetic field. The positronium yield in the porous silicon therefore is concluded from the long lifetime, narrow Doppler spectrum and its narrowing in a magnetic field. The porous structure is the cause of positronium formation.
Deep hole trap properties of p-type ZnSe grown by molecular beam epitaxy
Authors: Ando K. , Kawaguchi Y. , Ohno T. , Ohki A. , Zembutsu S.
Published: July 2002

The characteristics of deep hole traps in p-type ZnSe are studied by means of a transient capacitance spectroscopy technique. p-type ZnSe layers were grown by molecular beam epitaxy using radical N2 (nitrogen) doping. A major deep hole trap with a thermal hole activation energy of ΔE=720±30 meV is detected for two different sample structures: (a) n+-p ZnSe diodes and (b) Au-p ZnSe double-Schottky diodes. The trap concentration tends to increase as the net acceptor (N) concentration increases. The deep hole trap has revealed an exponential temperature dependence of hole capture rates, indicating a strong electron-lattice coupling in carrier capture/emission processes.
Structure and magnetic properties of Sm2Fe14Ga3Cx (x=0–2.5) compounds prepared by arc melting
Authors: Shen Bao-Gen , Kong Lin-Shu , Wang Fang-Wei , Cao Lei
Published: July 2002

A novel hard magnetic compound series with composition Sm2Fe14Ga3Cx (x=0, 0.5, 1.0, 1.5, 2.0, and 2.5) was prepared by arc melting. The carbides crystallize in the rhombohedral Th2Zn17-type structure and are single phase except for Sm2Fe14Ga3 and Sm2Fe14Ga3C0.5 which contain some amounts of α-Fe. The substitution of Ga is found to play an important role in the stability of high carbon rare-earth iron compounds with 2:17-type structure. The Curie temperatures of Sm2Fe14Ga3Cx are 200–240 K higher than that of Sm2Fe17. All compounds with x=0–2.5 exhibit an easy c-axis anisotropy at room temperature. The anisotropy fields increase with increasing carbon concentration from 70 kOe for x=0 to at least 90 kOe for x≥1.5. A room-temperature coercivity of 15 kOe is obtained in Sm2Fe14Ga3C1.5 prepared by melt spinning at a speed of 30 m/s.
Improving the thermal stability by anchoring both ends of chromophores in the side-chain nonlinear optical polymers
Authors: Shi Yongqiang , Ranon Peter M. , Steier William H. , Xu Chengzeng , Wu Bo , Dalton Larry R.
Published: July 2002

We report our study of a new side-chain second-order nonlinear optical polymer in which both ends of the chromophores are anchored by thermal crosslinking during electric field poling. A sizable second-harmonic generation coefficient d33 of 60 pm/V was measured at 1064 nm fundamental wavelength with corona poling. After anchoring both ends of the chromophores, the thermal stability of the poling alignment was greatly improved and the nonlinear optical properties were shown to be stable at both 90 and 125 °C. Channel waveguides were defined in the polymer thin films by reactive ion etching.
Synthesis and luminescence of silicon remnants formed by truncated glassmelt-particle reaction
Authors: Risbud Subhash H. , Liu Li-Chi , Shackelford James F.
Published: July 2002

We have obtained nanometer sized silicon remnants sequestered in glass matrices by terminating the reaction of pure silicon powders dispersed in the viscous melt at a temperature of 1400 °C. Repeated use of this truncated melt-particle reaction process dilutes the amount and size of silicon remnants, and bulk samples containing nanosize silicon crystallites embedded in a glass matrix were eventually obtained. These quantum dot sized silicon-in-glass materials emit greenish luminescence with peak wavelengths from ≊480 to 530 nm, considerably shorter than the reddish luminescence (at about 700–850 nm) observed in porous silicon structures prepared by electrochemical etching techniques; upon complete digestion of Si particles by the melt, the luminescence peaks disappear. Since our silicon-in-glass preparation method does not involve etching, the origin of the luminescence is not likely to be due to Si-O-H compounds (e.g., siloxene) postulated recently. The location of the luminescence peaks and the observed silicon crystallite size suggest quantum confinement leading to a widened silicon band gap arising from remnants in the glass matrix smaller than the exciton diameter of bulk silicon (10 nm).
Nonresonant electron capture in GaAs/AlAs/AlGaAs double-barrier quantum well infrared detectors
Authors: Schneider H. , Vinattieri A. , Shah J. , Ehret S. , Larkins E. C. , Rossmanith M.
Published: July 2002

We have investigated electron and hole capture times in n-type double-barrier quantum well (DBQW) infrared (3–5 μm) detector structures. Photoluminescence upconversion allows us to observe the relaxation of photoexcited carriers from AlAs/(AlGa)As/AlAs barriers into GaAs quantum wells. For 2 nm AlAs, 25 nm Al0.3Ga0.7As and 5 nm GaAs, the electron capture process is non-resonant, with a capture time of 47 ps at a temperature of 5 K and 28 ps at 77 K. Theoretical calculations show that electron tunneling across the 2 nm AlAs layers mainly occurs via the Γ-minimum, and that the Γ-X contribution is negligible.
Strain symmetrization effects in pseudomorphic Si1−yCy/Si1−xGex superlattices
Authors: Eberl K. , Iyer S. S. , LeGoues F. K.
Published: July 2002

We report on strain and stability measurements on pseudomorphic Si1−yCy/Si1−xGex superlattices which are synthesized by solid source molecular beam epitaxy on silicon (100) substrate. The strain in the superlattices alternates between tensile and compressive in the individual Si1−yCy and Si1−xGex alloy layers, respectively. A symmetrical strain distribution can be achieved directly on silicon by adjusting the carbon and the germanium content and/or the thickness of the individual layers. X-ray diffraction and transmission electron microscopy are applied to investigate the structural properties and the thermal stability.
Four-channel YBa2Cu3O7−y dc SQUID magnetometer for biomagnetic measurements
Authors: Tanaka S. , Itozaki H. , Toyoda H. , Harada N. , Adachi A. , Okajima K. , Kado H. , Nagaishi T.
Published: July 2002

A four-channel YBa2Cu3O7−y thin film dc SQUID magnetometer was fabricated. Biomagnetic measurements were performed by using the four-channel system at 77 K in a magnetically shielded room. We have successfully measured four-channel magnetocardiac signals clearly in real-time mode. The best magnetic field resolution of the four SQUIDs was 370 fT/Hz1/2 at 10 Hz and 200 fT/Hz1/2 in the white noise region.
Logarithmically graded quantum well far-infrared modulator
Authors: Hopkins P. F. , Campman K. L. , Bellomi G. , Gossard A. C. , Sundaram M. , Yuh E. L. , Gwinn E. G.
Published: July 2002

We have designed and fabricated a remotely doped ‘‘logarithmic’’ potential well intended to have a tunable, narrow band absorption at far-infrared frequencies. A surface gate, epitaxially grown backgate, and contact to the electron gas in the quantum well allow independent control of the absorption frequency and the integrated absorption strength. The resonance frequency is dominated by the well curvature at the potential minimum and can be Stark shifted from ω/2πc=35 cm−1 to a frequency of 125 cm−1 by moving the electron gas through the asymmetric well.
Surface degradation of superconducting YBa2Cu3O7−δ thin films
Authors: Russek S. E. , Sanders S. C. , Roshko A. , Ekin J. W.
Published: July 2002

The surface degradation of c-axis oriented YBa2Cu3O7−δ thin films due to air, CO2, N2, O2, and vacuum exposure has been studied with reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy, and contact resistivity measurements. The formation of an amorphous surface reaction layer upon exposure to air and CO2 is monitored with RHEED and correlated with an increase in contact resistivity. The contact resistivity of samples exposed to air increases with time t as ρc = (1.0 × 10−7 Ω cm2)e√t/640 min. Surfaces exposed to CO2 show a similar degradation while surfaces exposed to N2 showed a slightly different degradation mechanism. Vacuum exposed surfaces how little increase in contact resistivity, indicating no long-term surface oxygen loss.
Dynamics of laser-ablated iron in nitrogen atmosphere
Authors: Ohkoshi M. , Yoshitake T. , Tsushima K.
Published: July 2002

Fast photography with a framing streak camera is applied to investigate the dynamics of ablated Fe particles by a pulsed excimer laser when a nitrogen atmosphere is present. Two stages of expansion are found in the generated plume. The first one starts just after the laser irradiation where the hemispherical and unidirectional plumes are found simultaneously. The dynamics of the unidirectional plume is described by a drag model for 300 ns. The second stage occurs at 300 ns, and the unidirectional plume expands again in agreement with a delayed blast wave model. The thickness distribution of the deposited Fe-N film is well correlated with the change in the plume geometry, then with the nitrogen pressure.
Capture and recombination of acceptor bound excitons in the transition region from a two-dimensional to a quasi-three-dimensional GaAs/AlGaAs system
Authors: Zhao Q. X. , Holtz P. O. , Harris C. I. , Monemar B. , Veje E.
Published: July 2002

The capture and recombination processes for acceptor bound excitons (BEs) have been studied for GaAs/AlGaAs multiple quantum well structures, by varying the barrier thickness for a constant 100 Å well width. The observed decay time for the acceptor BE increases rapidly with decreasing barrier width, and is determined by the relative confinement of the electron and hole wave functions. The capture rate of free excitons to the BE state of the neutral acceptor increases by about a factor 7 from a two-dimensional to a three-dimensionlike system.
Carrier temperature and spectral holeburning dynamics in InGaAsP quantum well laser amplifiers
Authors: Willatzen M. , Mark J. , Mo/rk J. , Seltzer C. P.
Published: July 2002

An experimental and theoretical study of ultrafast gain dynamics in InGaAsP multiple quantum well laser amplifiers is presented. A transition from pump-induced heating of the carriers to pump-induced cooling is observed by change of the pump-probe wavelength. The experimental results are in good agreement with a theoretical model including the effects of carrier temperature dynamics, spectral holeburning, and two-photon absorption.
In-plane effective masses and quantum scattering times of electrons in narrow modulation-doped InGaAs/InP quantum wells
Authors: Wiesner U. , Pillath J. , Bauhofer W. , Kohl A. , Mesquida Küsters A. , Brittner S. , Heime K.
Published: July 2002

In-plane effective masses m*∥ and quantum scattering times are derived from temperature-dependent Shubnikov–de Haas oscillations measured on a series of modulation-doped InxGa1−xAs/InP quantum wells with x=0.53 and 0.75, and for well widths ranging from 3 to 7 nm. The values for m*∥ are consistently higher by 30%–70% than the respective bulk data. This result is in good agreement with recent theoretical calculations which predict an increase of m*∥ with decreasing well width. The scatter of the mass values for nominally identical quantum wells is assumed to reflect corresponding variations of the well widths. The ratio of quantum to classical scattering times and the carrier density dependence of the electron mobilities indicate that Coulomb scattering is important even in extremely narrow quantum wells.
Doping of polycrystalline diamond by boron ion implantation
Authors: Kalish R. , Uzan-Saguy C. , Samoiloff A. , Locher R. , Koidl P.
Published: July 2002

Polycrystalline diamond films, heavily implanted with boron ions (2×1016 cm−2, 60 keV) are found to exhibit, following annealing and graphite removal, electrical properties similar to those obtained for chemical vapor deposited diamond, heavily doped with B during film growth. Control experiments in which carbon ions were implanted and annealed under identical conditions did not show any significant electrical conductivity, verifying that the measured effects are caused by chemical doping due to the presence of B. It is therefore concluded that doping of polycrystalline diamond by ion implantation is possible and graphitization along grain boundaries, that one might have expected to occur as a result of implantation and annealing, does not seem to severely affect the electrical properties of the implantation-doped material.
Full band structure calculation of the linear electro-optic susceptibility
Authors: Ghahramani Ed , Sipe J. E.
Published: July 2002

We have derived a complete microscopic quantum mechanical expression for the frequency-dependent (clamped lattice) linear electro-optic (EO) susceptibility, χ⇊(2) (−ω;ω,0), of crystalline solids in the independent particle approximation. The expression is free of the unphysical divergent terms at zero frequency which often plague such calculations. Using these expressions and utilizing a linear combination of Gaussian orbitals technique in conjunction with the Xα method we have carried out a full band structure calculation of the frequency-dependent linear EO susceptibility of GaAs. Our calculated results are in good agreement with the available experimental measurements.
Self-irradiation in potassium halide thermoluminescent crystals
Authors: Barboza-Flores M. , Pérez Salas R. , Aceves R. , Pashchenko L. P. , Medvedev L. L. , Piters T. M.
Published: July 2002

A self-irradiation process has been observed in potassium halide thermoluminescent crystals. The 0.0117% abundance of the radioactive nuclide 40K in natural potassium, with a halflife of 1.28×109 years, is responsible for about 4.9 μGy/h of self-irradiation dose. The present finding is of importance in relation to the performance and limitations of recently proposed solid state dosimeters based on doped potassium halide crystals.
Si/Ge/S multilayer passivation of GaAs(100) for metal-insulator-semiconductor capacitors
Authors: Lu Z. H. , Landheer D. , Baribeau J.-M. , Huang L. J. , Lau W. W.
Published: July 2002

We describe a new multilayer passivation method on GaAs(100), an ex situ method that doesn’t require GaAs epitaxy. Thin 20 Å Si films or thin films consisting of 15 Å Si and 5 Å Ge were grown on (NH4)2S cleaned and S passivated GaAs(100) wafers. High-energy resolution x-ray photoelectron spectroscopy has been used to study the chemical structure of the buried GaAs surfaces. As and Ga 3d core level studies show that the surface is free of gallium and arsenic oxides as well as elementary As. The Ga-S-Ga bridge bond termination is found preserved on the buried GaAs surface. SiNx/Si/Ge/S/GaAs and SiNx/Si/S/GaAs capacitors have been made and analyzed using quasistatic and high frequency capacitance-voltage measurements. Using the high-low method, an interface state density of about 1012 cm−2 eV−1 is obtained. The modulation of the surface potential is the highest reported for a method not requiring GaAs epitaxy.
Inherent bandwidth limits in semiconductor lasers due to distributed microwave effects
Authors: Tauber Daniel A. , Spickermann Ralph , Nagarajan Radhakrishnan , Reynolds Thomas , Holmes Archie L. , Bowers John E.
Published: July 2002

This letter studies the inherent bandwidth limits in high speed semiconductor lasers caused by microwave signal propagation along the device. We show experimentally and theoretically that microwave propagation at high frequency is dominated by loss and slow wave effects. The primary conclusions from this study are (1) the standard treatment of a diode laser as a lumped electrical element is invalid above 25 GHz for device lengths on the order of 300 μm and (2) the frequency dependence of the microwave loss results in rolloff in the modulation response at high frequency. This roll off results in bandwidth degradation relative to the simplistic lumped element case and leads to new length and electrode considerations in the design of high speed lasers.
Vibrational mode for nitrogen in zinc selenide
Authors: Stein H. J.
Published: July 2002

The first observation of a localized vibrational mode for N in ZnSe by infrared absorption is reported. Nitrogen was introduced into internal reflection plates of polycrystalline ZnSe by ion implantation. Isotopic substitution confirmed assignment of the absorption to N, and the band frequency is consistent with N on Se sites. Coimplantation with deuterium decreased the N band intensity and introduced a band for Zn—D. These deuterium effects which increase upon annealing between 200 and 300 °C are ascribed to a breaking of Zn—N bonds to form Zn—D bonds and a relaxation of N toward threefold coordination.
Effects of disturbing pulses on the switchable polarization of Pb(ZrTi)O3 thin film capacitors
Authors: Taylor D. J. , Larsen P. K. , Cuppens R.
Published: July 2002

The effect of disturbing pulses on the switchable polarization in ferroelectric films of PbZrxTi1−xO3 with x=0.36 and 0.71 has been investigated. The two compositions were selected because of their different hysteresis shapes. Pulse measurements were carried out with a varying number of disturbing pulses at different amplitudes, interrupted by single shot read/write pulses. It was found that the composition with the squarer loop (x=0.36) showed less sensitivity to disturbing pulses, i.e., the switchable polarization did not significantly degrade with 109 disturbing pulses of amplitude 1.2 V. In addition, these results demonstrate that degradation of the stored polarization due to parasitic disturbing voltages in high density ferroelectric random access memories can be kept at an acceptable level.
Phase-matched second-harmonic generation by periodic poling of fused silica
Authors: Kashyap Raman , Veldhuis Gerrit J. , Rogers David C. , Mckee Paul F.
Published: July 2002

90° phase matching in periodically poled fused silica is achieved over approximately 2 mm at a wavelength of 1064 nm. Electrical poling was done at 5 kV for 120 min using photolithographed periodic electrodes on fused silica glass at 250 °C. A nonlinearity equivalent to d11/200 of quartz is estimated from measurements. Several phase-matched interactions are reported and the implications for device applications discussed.
Photoluminescence study of (111)-oriented GaAs/GaAsP strained-layer quantum well structure
Authors: Zhang Xiong , Karaki Koichi , Yaguchi Hiroyuki , Onabe Kentaro , Ito Ryoichi , Shiraki Yasuhiro
Published: July 2002

A GaAs/GaAs1−xPx (x=0.13) strained-layer quantum well structure has been grown on (111)B-oriented GaAs substrate by means of low-pressure (60 Torr) metalorganic vapor phase epitaxy and characterized by photoluminescence (PL) spectroscopy. Despite the partial relaxation of the tensile strain confined in the GaAsP barrier layers, our sample exhibits smooth surface morphology and intense optical emission. Moreover, an evident blue shift of the excitonic transition peak attributed to the screening of the strain-induced internal electric field by the photoexcited carriers, has been observed in the PL measurement.
Approach of selective nucleation and epitaxy of diamond films on Si(100)
Authors: Jiang X. , Boettger E. , Paul M. , Klages C.-P.
Published: July 2002

Heteroepitaxial diamond films were selectively nucleated and grown on mirror-polished single crystalline (100) silicon by microwave plasma assisted chemical vapor deposition (MWCVD). The silicon substrates were coated by 0.5 μm thick SiO2 films patterned by a standard photolithography process. The selective nucleation was performed under a negative substrate bias condition. Results show that fine patterns of (100) oriented diamond films can be obtained with high deposition selectivity and fine-line definition. In spite of the relatively large crystal size a structure edge roughness of <0.3 μm was achieved.
Laser demonstration of neodymium-doped strontium chlorovanadate
Authors: DeLoach Laura D. , Payne Stephen A. , Chai Bruce H. T. , Loutts George
Published: July 2002

Nd:Sr5(VO4)3Cl has been successfully lased using a Ti:sapphire pump laser operating at 810 nm. A slope efficiency of 52% for the 1.065 μm laser line and a lasing threshold of only a few tens of milliwatts have been measured. These favorable results are comparable to another Nd-doped vanadate apatite, Sr5(VO4)3F. A brief survey of the spectroscopy of Nd3+ in Sr5(VO4)3Cl, Sr5(VO4)3F, and Ca5(VO4)3F reveals properties which suggest the vanadate-based apatite crystals as a whole may represent a useful new class of Nd-laser hosts.
Z-scan measurement of χ(3) using top-hat beams
Authors: Zhao W. , Palffy-Muhoray P.
Published: July 2002

Z-scan measurements of third-order optical nonlinearities are usually carried out with Gaussian beams. Good quality Gaussian beams are not readily available, however, and to overcome this limitation, we analyze the Z-scan experiment using top-hat beams. A graphical method is developed which allows straightforward determination of the nonlinear refraction and absorption coefficients from experimental data. The advantage of using top-hat beams is that it allows Z-scan measurements using a wide variety of laser sources, including dye lasers. χ(3) values obtained using Z-scan measurements with top-hat and Gaussian beams are compared for the liquid crystal 5CB (4-cyano-4′-n-pentybiphenyl).
Se-rich phase of ZnSe(100) predicted by total-energy calculations
Authors: García Alberto , Northrup John E.
Published: July 2002

The relative stability of various ZnSe(100) surface reconstructions is investigated by means of first-principles pseudopotential calculations. A c(2×2) reconstruction with half-monolayer coverage of twofold coordinated Zn atoms is stable in the Zn-rich limit. Under moderately Se-rich conditions, the surface adopts a (2×1) Se-dimer phase. In the extreme Se-rich limit, realizable at low growth temperatures, we predict the stability of a new phase covered with one and a half monolayers of Se. The new structure can account for observed growth rates in atomic layer epitaxy and migration enhanced epitaxy experiments.
Nucleation of GaAs on CaF2/Si(111) substrates
Authors: Li Weidan , Anan Takayoshi , Schowalter Leo J.
Published: July 2002

Two different nucleation modes in epitaxial growth of GaAs on CaF2/Si(111) substrates have been identified. At low temperature (below 500 °C). GaAs nucleates on CaF2(111) surface with a three-dimensional mode. When Ts is high (higher than 590 °C), two-dimensional nucleation of GaAs can be achieved on the CaF2/Si(111) surface under a proper As flux. A thorough investigation of this phenomenon has been carried out using Rutherford backscattering spectrometry. A stable As layer has been observed on the CaF2(111) surface when the CaF2/Si(111) substrates are treated at high temperatures and under a high enough As flux (≥2×10−5 mbar). The formation of this As layer is understood as a consequence of a chemical reaction between As adatoms and the CaF2 surface. The existence of the As layer modifies the surface free energy of CaF2/Si(111) substrates and leads to a transition in the GaAs nucleation mode. By controlling the nucleation mode, high quality GaAs has been grown on the top of CaF2/Si(111) substrates without using electron-beam modification of the CaF2 surface, and, thus, avoids irradiation damage of the epitaxial initiation surface.
Photoluminescence of a staggered In0.5Ga0.5P/AlxGa1−xAs heterojunction
Authors: Kim Kwan-Shik , Lee Jong Boong , Choe Byung-Doo , Jeong Weon Guk , Lim H.
Published: July 2002

Photoluminescence of the In0.5Ga0.5P/AlxGa1−xAs heterojunction with Al mole fractions x=0.29 and x=0.19 is presented. Below-band-gap photoluminescence with a peak energy less than both band gap energies of the constituent materials was observed. As the laser excitation intensity was decreased, the peak energy of the luminescence shifted to the lower energy side and showed a saturation behavior. The full width at half maximum of the peak also decreased as the laser excitation intensity was decreased. These phenomena indicate that the heterojunction has a staggered band alignment at each value of the Al mole fractions. The expected band alignment of the heterojunction at various Al mole fractions is presented.
Defect alignment in grain boundaries as quantum wells
Authors: Mataré Herbert F.
Published: July 2002

Improvements of optical absorption bandwidth in high-density dislocation layers and enhanced solar-cell efficiency through application of ion-implanted defect layers as well as the electro-optical properties of porous silicon, are seen to connect earlier results on grain boundaries with defined parameters and their electro-optic properties with quantum wells (QW). These well-defined grain boundaries are also those which enhance optical sensitivity and critical current (Ic) densities in high-temperature superconductors (HTS) by a flux-pinning effect and are useful for the production of superconducting quantum-interference devices (SQUIDS).
Mediation of strain from In0.36Ga0.64As layers through GaAs barriers in multiple quantum well structures
Authors: Ekenstedt M. J. , Chen W. Q. , Andersson T. G. , Thordson J.
Published: July 2002

The strain mediation in multiple quantum well structures consisting of In0.36Ga0.64As layers separated by GaAs barriers has been investigated by photoluminescence. Strain in layers grown by molecular beam epitaxy was evaluated by comparing the photoluminescence-peak energies with calculated recombination energies in strained quantum wells using the effective-mass Schrödinger equation. In structures consisting of two 40 Å thick In0.36Ga0.64As layers separated by a GaAs barrier, onset of relaxation is not observed until the barrier thickness is reduced below 100 Å. The corresponding value is 180 Å in a structure with two 50 Å thick In0.36Ga0.64As layers. Results also show that strain mediation increases with the number of strained In0.36Ga0.64As layers. In multiple quantum well structures with four 50 Å thick In0.36Ga0.64As layers, the barrier thickness required to stop strain mediation increases to 225 Å. In similar structures with eight and twenty 50 Å thick In0.36Ga0.64As layers this value is 275 Å.
Thermal stability of sulfur passivated InP(100)-(1×1)
Authors: Anderson G. W. , Hanf M. C. , Norton P. R. , Lu Z. H. , Graham M. J.
Published: July 2002

Auger electron spectroscopy, low-energy electron diffraction, thermal desorption spectroscopy, and scanning electron microscopy have been utilized to investigate the thermal stability of S-passivated InP(100). S-passivated InP(100) is shown to be thermally stable up to ∼730 K, where S removal and sample evaporation begins. This evaporation results in the formation of a roughened, but clean, InP(100) surface, showing the characteristic (4×2) reconstruction.
Modification of the second-order optical susceptibility in AlxGa1−xAs by ion-beam induced amorphization
Authors: Janz S. , Buchanan M. , Chatenoud F. , McCaffrey J. P. , Normandin R. , Akano Usman G. , Mitchell Ian V.
Published: July 2002

The optical second-harmonic (SH) response of GaAs and Al0.6Ga0.4As bombarded with 1.2-MeV energy As+ ions has been measured for doses ranging from 5×1012 to 2×1014 ions cm−2. The measured SH response vanishes at an ion dose of 2×1014 ions cm−2 as a result of ion induced amorphization. Thermal annealing at 600 °C greatly reduced the damage induced optical absorption, for λ=1.06 μm light, but had no effect on the SH susceptibility.
Coherent photoelectron bunch generation and quantum efficiency enhancement in a photocathode optical resonator
Authors: Hartemann F. V. , Fochs S. N. , McNally J. D. , Burns S. , Luhmann N. C. , Perry M. D. , Chu K. R.
Published: July 2002

A novel scheme producing multiple, coherently phased, high charge (nC), short duration (ps) electron bunches in a radio-frequency (rf) photoinjector is presented. In this configuration, the mirror photocathode is an integral part of an optical resonator. The ultrashort laser pulse is reflected off the photocathode and recirculated through the optical cavity at a subharmonic of the rf drive frequency after extracting a photoelectron bunch. This new technique can dramatically increase the effective quantum efficiency of metals and produce high current, high brightness, prebunched electron beams ideally suited for high power coherent microwave generation. A proof-of-principle experiment operating at 0.250 GHz and using a frequency-quadrupled, mode-locked Nd:YAG laser has shown the production of a train of coherently phased photoelectron bunches, with a measured effective quantum efficiency enhancement of 4.2.
Self-consistent calculation of the modulation response for quantum well laser diodes
Authors: Grupen Matt , Hess Karl
Published: July 2002

Modulation responses for a set of strained-layer InGaAs quantum well lasers as calculated by a new version of Minilase are presented and compared to experiment. Based upon the agreement with measured data, Minilase is used further to associate gain saturation and low frequency rolloff with carrier capture in the quantum well. The capture rates, therefore, influence the modulation response in a significant way even if the time constants are much shorter than the inverse frequency of the modulation signal.
Theoretical investigation of minority carrier leakages of high-power 0.8 μm InGaAsP/InGaP/GaAs laser diodes
Authors: Diaz J. , Eliashevich I. , Yi H. , He X. , Stanton M. , Erdtmann M. , Wang L. , Razeghi M.
Published: July 2002

We report a theoretical model that accurately describes the effects of minority carrier leakage from the InGaAsP waveguide into InGaP cladding layers in high-power aluminum-free 0.8 μm InGaAsP/InGaP/GaAs separate confinement heterostructure lasers. Current leakage due to the relatively low band-gap discontinuity between the active region and the InGaP barrier can be eliminated by employing laser diodes with cavity length longer than 500 μm. Experimental results for lasers grown by low-pressure metalorganic chemical vapor deposition are in excellent agreement with the theoretical model.
Heteroepitaxial Si/Si1−xGex/Si structures produced using pulsed UV-laser processing
Authors: Kramer K.-Josef , Talwar Somit , Sigmon Thomas W. , Weiner Kurt H.
Published: July 2002

High quality heteroepitaxial regrowth of arsenic-implanted a-Si on Si1−xGex layers with Ge fractions between 0 and 0.2 is accomplished using pulsed laser induced epitaxy (PLIE). The structures of boron-doped Si1−xGex on Si(100) are created beforehand using a combination of (PLIE) and gas immersion laser doping. A small amount of Ge and B backdiffusion from the Si1−xGex film into the top Si layer is observed. During the laser pulse, the implanted arsenic diffuses up to the maximum melt depth so that melt depth and junction depth coincide. The a-Si is sputter deposited to a thickness of 900 Å, and the As is implanted to a dose of 5×1014 cm−2 at 40 keV. A single XeCl excimer laser pulse with an energy fluence to be selected between 0.6 and 0.8 J/cm2 is sufficient to heteroepitaxially regrow the a-Si and activate the implanted arsenic.
Misfit dislocations lying along 〈100〉 in [001] GaAs/In0.25Ga0.75As/GaAs quantum well heterostructures
Authors: Zou J. , Chou C. T. , Cockayne D. J. H. , Sikorski A. , Vaughan M. R.
Published: July 2002

Misfit dislocations in [001] GaAs/In0.25Ga0.75As/GaAs multiquantum well heterostructures are studied by transmission electron microscopy. Two sets of misfit dislocation networks have been observed; one is a set of conventional 60° misfit dislocations lying along 〈110〉, and the other is a set of edge dislocations lying along 〈100〉. The location of these misfit dislocations with respect to the strained layers is investigated. A qualitative explanation for the generation mechanism of the misfit dislocations lying along 〈100〉 is given.
Reverse biased photoconductive detectors and switches with separate absorption and detection area
Authors: Riel P. , Greger E. , Reingruber K. , Ennes M. , Kiesel P. , Kneissl M. , Döhler G. H. , Tränkle G. , Weimann G.
Published: July 2002

We report on reverse biased photoconductive detectors with novel design and improved high-frequency performance. Taking advantage of the ‘‘giant ambipolar diffusion constant’’ which has been observed previously in n-i-p-i doping superlattices very fast carrier transfer from the inner absorption area to the outer detection area is achieved. The combination of narrow contact spacings and small RC and diffusion time constants results in very high gain-bandwidth products (≳20 GHz) with adjustable 3 dB frequencies.
Band-structure tailoring by electric field in a weakly coupled electron-hole system
Authors: Naveh Y. , Laikhtman B.
Published: July 2002

A novel semiconductor switching device is proposed. It is based on unique control over the two-dimensional band structure of an AlSb-GaSb-InAs-AlSb heterostructure. By applying small electric fields, virtually any value can be achieved for such parameters as the energy gaps, effective masses, and carrier types and densities in the material. The proposed heterostructure can be readily fabricated with existing epitaxial techniques.
Heteroepitaxial nucleation of diamond on Si(001) in hot filament chemical vapor deposition
Authors: Stubhan F. , Ferguson M. , Füsser H.-J. , Behm R. J.
Published: July 2002

Heteroepitaxial nucleation of diamond on mirror-polished Si(001) substrates was achieved in a conventional hot filament reactor. The key to this achievement was the development of a bias-enhanced nucleation process step analogous to the procedure for heteroepitaxial nucleation in microwave plasma chemical vapor deposition. The nucleation and subsequent growth of diamond were characterized by means of scanning electron microscopy, scanning tunneling microscopy, and Raman spectroscopy. Well-developed diamond (001) crystal faces are observed even for very thin (∼0.3 μm) diamond films. High-resolution scanning electron microscopy investigations of the early stage of growth revealed oriented crystallites on the substrate surface with a nucleation density of 109 cm−2.
Measurement of nonlinear absorption and refraction in titanium dioxide single crystal by using a phase distortion method
Authors: Watanabe Yuichi , Ohnishi Masato , Tsuchiya Toshio
Published: July 2002

A phase distortion method is applied to examine the optical nonlinearity in titanium dioxide single crystal. The two-photon absorption coefficient obtained agrees with that reported previously, while the nonlinear index of refraction is larger than that predicted theoretically by a factor of 10. One of the reasons for the discrepancy is given as the applicable limit of the simple theory in which a two-parabolic band model has been assumed in the analysis.
The role of the substrate in photoenhanced metalorganic chemical vapor deposition
Authors: Maayan E. , Kreinin O. , Veinger D. , Thon A. , Bahir G. , Salzman J.
Published: July 2002

A GaAs laser diode has been used as the light source for the selective epitaxial growth of GaAs by photoenhanced metalorganic chemical vapor deposition (PE-MOCVD). The use of GaAs/InGaP layered structures as substrates for these experiments permitted to accurately control the availability of photoexcited carriers reaching the GaAs growth surface. The experimental results obtained rule out pure pyrolysis and photolysis as possible mechanisms responsible for the PE growth rate, and indicate that photoexcited carriers are directly involved in the PE process. The experimental data are consistent with a kinetic model that invokes surface recombination as the main physical mechanism for the PE growth rate effect.
Measurements of sheath electric fields in a high pressure helium radio frequency discharge
Authors: Bowden M. D. , Choi Y. W. , Muraoka K. , Maeda M.
Published: July 2002

The importance of capacitively coupled radio frequency (rf) discharges has resulted in many attempts, by experiment and by simulation, to understand the dynamics of the discharge. Because of the time varying nature of the sheath potential, the sheath region is of special interest in these plasmas. Direct measurements are reported of the sheath electric fields in a helium plasma obtained using a laser induced fluorescence method. In the interpretation of these measurements, the time dependence of the fluorescence spectrum had to be considered. The measured electric field distributions can be used to deduce sheath widths.
Electron beam irradiation of n-type porous silicon obtained by photoelectrochemical etching
Authors: Maurice J.-L. , Rivière A. , Alapini A. , Lévy-Clément C.
Published: July 2002

The effects of electron beam irradiation on luminescence and microstructure of n-type porous silicon (PS) have been investigated, using cathodoluminescence (CL) in the scanning electron microscope (SEM), and electron energy loss spectroscopy in the transmission electron microscope (TEM). In the SEM, the CL rapidly decreased with irradiation. It could be fully restored by boiling the samples in de-ionized water. In the TEM, freshly restored PS emerged as Si nano-crystallites embedded in an unstable silicon oxide. The effect of irradiation was to suppress the oxide, and also, in the case of proximity of carbon from the foil holding the sample, to change the crystallite composition to β-SiC.
Effects of electrode structure on output electron energy distribution of microchannel plates
Authors: Koshida Nobuyoshi
Published: July 2002

The output energy distribution of microchannel plates with different output electrode structures has been studied experimentally. It is shown that the penetration depth of the output electrode into the microchannel plates ω is a very important factor affecting both the output energy spread and the gain. When ω becomes twice the length of a channel diameter, the unfavorable tail component in the energy distribution can be suppressed. Improvement in the output energy spread, however, results in a considerable gain reduction. These characteristics are clarified by the internal current behavior in MCPs inferred from two operating dynode currents at the input and output ends.
Polycrystalline silicon oxidation method improving surface roughness at the oxide/polycrystalline silicon interface
Authors: Jun Myung-Chul , Kim Yong-Sang , Han Min-Koo , Kim Jin-Won , Kim Ki-Bum
Published: July 2002

A polycrystalline silicon oxidation method, which considerably improves the surface roughness at the oxide/polycrystalline silicon interface, is presented. The surface roughness at the interface is observed by transmission electron microscopy and is also evaluated by atomic force microscopy after the oxide layer is removed using buffered HF acid. The oxide/polycrystalline silicon interface by the new oxidation method with the 50 Å thick intermediate oxide has the rms surface roughness of 30 Å, while that of the interface by the conventional method is 120 Å.
New UHV dilatometer for precise measurement of internal stresses in thin binary-alloy films from 20 to 750 K
Authors: Moske M. , Samwer K.
Published: July 2002

We describe a new dilatometric device for internal stress measurements of thin binary-alloy films, able to operate in ultrahigh vacuum in the temperature range 20–750 K. Using a three-terminal capacitor method, the displacement of the free end of a thin cantilever substrate is monitored by the capacitance change. With a sensitivity of 1 nm for substrate displacements, the resolution for stress detection is 105 Pa in a 100-nm-thick film. Simultaneously with the stress measurement, the electrical resistivity of the film can be determined on the same substrate. The direct comparison of electrical and mechanical thin-film properties gives the ability to obtain additional information on the growth process and on the thin-film structure. Measurements of a crystalline Cu film and an amorphous Zr20 Co80 alloy film are shown.
Blue light emission from a laser diode pumped ring resonator with an organic second-harmonic generation crystal of 8-(4′-acetylphenyl)-1,4-dioxa-8-azaspirol[4.5]decane
Authors: Sagawa M. , Kagawa H. , Kakuta A. , Kaji M. , Saeki M. , Namba Y.
Published: July 2002

A laser diode pumped ring resonator was built with a new organic second-order nonlinear optical crystal, 8-(4′-acetylphenyl)-1,4-dioxa-8-azaspiro[4.5] decane. Ultraprecision diamond polishing was used for the crystal and optically flat surfaces and roughnesses of less than λ/10 were achieved. The surfaces were dip coated with a perfluorinated polymer thin film to suppress surface reflection loss. Under resonant conditions, fundamental power was enhanced and a blue second-harmonic emission with wavelength of 405.5 nm was observed.
Photoluminescence of modulation-doped ordered–disordered GaInP2 homojunctions: Intrinsic versus extrinsic emissions
Authors: Driessen F. A. J. M. , Hageman P. R. , Olsthoorn S. M. , Giling L. J.
Published: July 2002

Photoluminescence (PL) measurements are reported on modulation-doped ordered-GaInP2/ disordered-GaInP2 homojunctions. These junctions exhibit extremely high carrier densities of the two-dimensional (2D) electron gas. A luminescence peak that involves recombination of these intrinsic 2D electrons and photoexcited holes shows a very large redshift as a result of the spatially separated carriers. However, no inverted S shaped behavior of PL energy is observed for this signal upon increasing temperature. This result affirms that the inverted S PL behavior of bulk ordered GaInP2 has an extrinsic nature.
A scanning tunneling microscope based on a motorized micrometer
Authors: Stupian Gary W. , Leung Martin S.
Published: July 2002

A scanning tunneling microscope (STM) that uses a motorized micrometer to provide for coarse mechanical motion of the specimen relative to the tunneling tip is described. The specimen is attached directly to the micrometer spindle. No additional motion reduction mechanisms, such as levers, are necessary. After positioning the tip optically about 0.2–0.3 mm from the specimen, tunneling current is established automatically under the control of the system computer by a sequence of mechanical motions of the micrometer combined with extensions of a tubular piezoelectric scanner. Tunneling current is typically acquired in 10–15 min.
Aging of critical currents and irreversibility line in melt textured YBa2Cu3O7
Authors: Martínez B. , Sandiumenge F. , Piñol S. , Vilalta N. , Fontcuberta J. , Obradors X.
Published: July 2002

The critical currents and the irreversibility line of bulk melt textured YBa2Cu3O7 have been found to evolve with the increase of the oxygenation time. A strong field-dependent reduction of the critical currents is observed which finally leads to a downward shift of the irreversibility line. Transmission electron microscopy micrographs of aged samples display a huge increase in the concentration of stacking faults near the microcracks and at the YBa2Cu3O7-Y2BaCuO5 interfaces. Low field ac susceptibility measured with H∥ab shows a strong reduction of the screening capability thus meaning that nonsuperconducting planar defects parallel to the ab planes have been created. We suggest that an enhanced two-dimensional behavior of the vortex flux lattice occurs when H∥c as a consequence of this layered defective structure.
Evolution of strain relaxation in step-graded SiGe/Si structures
Authors: Mooney P. M. , Jordan-Sweet J. L. , Chu J. O. , LeGoues F. K.
Published: July 2002

Strain relaxation in a series of step-graded SiGe/Si structures has been quantitatively investigated by high-resolution x-ray diffraction measurements. We show that beyond a critical thickness, dislocations nucleate continuously as layers with higher Ge mole fraction are added to the structure and that the mismatch strain at which nucleation occurs is therefore essentially constant. It had been found empirically that a lower growth temperature is required to suppress roughening of layers with higher Ge mole fraction, even in graded structures. We prove that this is not because the strain increases, but rather because of the lower melting temperature of layers with higher Ge content.