bluuebunny/crossref_metadata_2025 huggingface dataset:
Low off-state leakage current thin-film transistor using Cl incorporated hydrogenated amorphous silicon
Authors: Lee Keun Soo , Choi Jong Hyun , Kim Sung Ki , Jeon Hong Bin , Jang Jin
Published: July 2002

We have studied the fabrication of low off-state leakage current amorphous silicon thin-film transistor (TFT) using Cl incorporated amorphous silicon [a-Si:H(:Cl)] as an active layer. The room temperature conductivity and conductivity activation energy of a-Si:H(:Cl) deposited by adding 10% SiH2Cl2 into silane plasma are much less than those of undoped hydrogenated amorphous silicon because the a-Si:H(:Cl) shows a p-type conduction. The off-state leakage currents of the a-Si:H(:Cl) TFT under light illumination are much less than that of conventional a-Si:H TFT without degrading the field effect mobility because the photoconductivity of a-Si:H(:Cl) is much less than that of a-Si:H.
Deposition of thermally stable, low dielectric constant fluorocarbon/SiO2 composite thin film
Authors: Kim Dong S. , Lee Young H. , Park Nae-Hak
Published: July 2002

Low dielectric fluorocarbon/SiO2 composite films are developed that exhibit good thermal stability and low dielectric constant by using hexamethyldisiloxane (HMDSO) and prefluorobenzene (C6F6) as the monomer source gases, and argon and oxygen as the carrier gases in a dual frequency, inductively-coupled high-density plasma reactor. Fourier transform infrared measurements of the films show that they consisted of both SiO2 and amorphous perfluoro tetra fluoroethylene, and the amount of each can be controlled by changing the feed monomer gas ratio. The dielectric constant of the film ranges between 2 and 4 depending on the feed monomer gas ratio. For example, when the monomer gas ratio [HMDSO/(HMDSO+C6F6)] is 0.2, the dielectric constant of the film is ∼2.5. Such a composite film shows good thermal stability and good adhesion on a silicon substrate.
Physical origins of temperature variation and background radiation associated with pyrometric interferometry measurement during III–V molecular-beam-epitaxy growth
Authors: Zhou J. J. , Li Y. , Thompson P. , Sato D. L. , Lee H. P. , Kuo J. M.
Published: July 2002

The physical origins of temperature variation and background radiation associated with in situ pyrometric interferometry (PI) monitoring during III–V molecular-beam epitaxy are examined. By means of complementary PI and diffused reflectance spectroscopy measurements on GaAs and GaAs/AlAs structures grown at different temperature, the temperature variations due to the changes of sample emissivity and radiative heating from the Knudsen cells are identified and characterized. The studies will lead to more accurate modeling of PI signal and better control of substrate temperature.
Boron redistribution in a shallow δ-doped Si structure after solid phase epitaxial growth
Authors: Huang M. B. , Mitchell I. V.
Published: July 2002

A combination of nuclear reaction analysis, high-resolution sectioning methods, and time-resolved reflectivity have been used to study the boron redistribution from a shallow δ-doped layer in silicon, following deep amorphization and subsequent solid phase epitaxial growth (SPEG). A significant fraction of the boron was found to move into the top 20 nm undoped Si cap layer after SPEG. Over the temperature range of 550–600 °C, the fraction of boron accumulating in the cap layer is increased with the SPEG temperatures. Boron redistribution was enhanced in the sample which was etched in HF prior to SPEG. Possible contributing factors are discussed.
Superconducting complementary output switching logic operating at 5–10 Gb/s
Authors: Jeffery Mark , Perold Willem , Van Duzer T.
Published: July 2002

We present experimental results of superconducting voltage-state complementary output switching logic gates operating 10 Gb/s and 2-bit encoder circuits clocked at 5–8 Gb/s. The logic gates and circuits were designed using a Monte Carlo optimization process so that they have a high theoretical yield at 5–10 Gb/s in spite of existing Josephson junction process variations.
Conductance anomaly in a quantum well
Authors: Kim Chang Sub , Olendski Oleg
Published: July 2002

A single quantum well under the influence of vertical electric and in-plane magnetic fields is considered theoretically. Within an effective mass and independent-electron approximation, the spectroscopy of energy levels and the lateral currents are obtained. We found an interesting anomaly in our calculations of transverse differential conductance which suggests the possibility of a novel field-effect concept.
Synthesis of InP-based 1.3 μm band gap pseudoalloy by organometallic vapor phase epitaxy
Authors: Emerson D. T. , Shealy J. R.
Published: July 2002

Synthesis of short period GaInAs/InP superlattices, or pseudoalloys, by organometallic vapor phase epitaxy for replacement of the mixed crystal GaInAsP deposited on InP is discussed. Raman scattering, double crystal x-ray diffraction, photoluminescence, and atomic force microscopy are used to investigate accumulative interface roughening and layer intermixing in the pseudoalloy. We demonstrate that pseudoalloy quality is not necessarily comprised by the presence of unintentional interfacial layers and show that thick (>2500 Å) InP-based pseudoalloys with structural and optical properties that compare favorably with those of the random alloy can be synthesized. Finally, we present results on broad area 1.3 μm lasers incorporating the pseudoalloy as the optical gain media in separate confinement heterostructure devices.
Hot-electron power loss in a doped GaAs/AlGaAs superlattice at intermediate temperature studied by infrared differential spectroscopy
Authors: Hilber W. , Helm M. , Alavi K. , Pathak R. N.
Published: July 2002

The power loss of electrons in a strongly coupled n-type GaAs/AlxGa1−xAs superlattice is studied by analyzing the temperature and electric-field dependence of the interminiband absorption. Electrons are heated by an electric-field pulse and the resulting change of the infrared absorption spectrum is monitored by a step-scan Fourier transform spectrometer operated in a time-resolved, gated mode. The measured power loss is higher than predicted by a simple three-dimensional calculation including acoustic (deformation potential and piezoelectric) and polar-optical phonon emission. Possible explanations for this, such as relaxation via folded acoustic phonons or coupled plasmon–phonon modes, are discussed. The energy relaxation time, which can be extracted from the power balance, decreases from 300 ps at 15 K to 20 ps at 48 K.
Multiple cross switching in a two-mode semiconductor laser
Authors: Ku Pei-Cheng , Lin Ching-Fuh , Lee Bor-Lin
Published: July 2002

A multiple cross switching phenomenon is observed in a two-mode semiconductor laser in an external cavity. Its physical origins are investigated. The changing temperature or injection current causes the variation of the refractive index and the length of the laser diode, leading to the shift of the modulated gain peaks of the anti-reflection-coated laser diode in the external cavity. Consequently, the two modes experience different gains periodically and the strong gain competition then leads to the multiple cross switching.
Copper nitride and tin nitride thin films for write-once optical recording media
Authors: Maruyama Toshiro , Morishita Tomonori
Published: July 2002

The feasibility of using copper nitride and tin nitride thin films as write-once optical recording media was explored. The Cu3N and SnNx films were obtained by the reactive sputtering method. They were thermally decomposed into Cu and Sn films at 470 and 550 °C, respectively. The Cu film obtained by the thermal decomposition showed a large difference in reflectance which is applicable to the optical recording media. The Sn film obtained by the thermal decomposition included SnO, and consequently it showed a small difference in reflectance from that of SnNx film.
Dopant impurity-induced defects in p-type doped hydrogenated amorphous germanium
Authors: Comedi D. , Chambouleyron I.
Published: July 2002

The defect density (ND) in hydrogenated amorphous germanium (a-Ge:H) doped p-type by aluminum, gallium, or indium was studied as a function of the dopant impurity concentration (Nimp) by using photothermal deflection spectroscopy. ND remains roughly constant with increasing Nimp for Nimp<2×1019 cm−3 and increases linearly for larger Nimp for Al, Ga, or In doping, On the other hand, the dependence of ND on the Fermi energy (as deduced from conductivity measurements) is different for the different dopant impurities, contrary to predictions of charge-induced weak bond–dangling bond conversion models. A mechanism involving direct dangling bond formation induced by sp2 bonded dopant impurities qualitatively accounts for the observed results.
Hyperfine properties of bond-center muonium and hydrogen in diamond
Authors: Chawla Sanjay , Messmer Richard P.
Published: July 2002

The bond-center (BC) hydrogen/muonium defect is of considerable interest both as a model for the theoretical description of defects in semiconductors, and because of its possible role in affecting the opto-electronic properties of polycrystalline silicon and diamond. Its identification requires a reliable calculation of its hyperfine couplings (HFCs) both in the bulk and in strained bonds that occur at grain boundary sites. Using a novel multiconfigurational perturbative approach we have calculated the HFCs of BC muonium/hydrogen in diamond. To our knowledge the method provides the best compromise between accuracy and computational efficiency. Our results for the bulk BC muonium defect are in very good agreement with experiment. As an application of this method, we have obtained the HFCs for hydrogen in strained C-C bonds.
Dissipation anisotropy of highly c-axis-oriented(Bi,Pb)2Sr2Ca2Cu3Ox silver sheathed tapes
Authors: Sun Yuping , Xu Guoyang , Jiang Liudi , Du Jiaju , Zhang Yuheng , Duan Zhenzhong , Tang Xiande , Xi Zhengping , Zhou Lian
Published: July 2002

Dissipation anisotropy of a highly c-axis-oriented (Bi,Pb)2Sr2Ca2Cu3Ox silver-sheathed tape in the vicinity of Tc(T/Tc>0.9) has been investigated by measuring the dependence of the magnetoresistance on the applied field, the temperature and the angle (θ) between the magnetic field direction and the tape surface. The results show that the dissipation anisotropy increases with the increase of the field and the temperature. It is found that the dissipation is only related to the magnetic field component perpendicular to the tape surface (c-axis component), i.e., R(H,θ)=R(Hsinθ). The experimental results can be accounted for in terms of the easy motion of two-dimensional (2D) pancake vortices along the CuO2 planes.
Enhanced electro-optic modulation by integration of nonradiative centers in a resonant tunneling light emitting diode
Authors: Alphenaar B. W. , Baumberg J. J. , Köhler K.
Published: July 2002

We create a reservoir of hole traps in a resonant tunneling light emitting diode by etching the p-type contact into an array of nanometer scale pillars. In the off state, the charge reservoir keeps the light output extremely low, even at relatively high currents. The device can be switched on to produce light by raising the electron emitter past a confined electron state allowing holes to escape from the nonradiative region. The resulting electro-optic switch has an on/off ratio of at least 1000:1, a large improvement over conventional resonant tunneling light emitting diodes.
Effect of α-HgI2 epitaxial growth on the defect structure of CdTe:Ge substrates
Authors: Panin G. , Piqueras J. , Sochinskii N. , Dieguez E.
Published: July 2002

The α-HgI2/CdTe:Ge heterostructures have been studied by cathodoluminescence (CL) in the scanning electron microscope. The α-HgI2 expitaxial growth was shown to cause an enhancement of the CL intensity in a layer of the substrate extending up to about 500 μm from the α-HgI2/CdTe:Ge interface. CL spectra of the layer reveal the appearance of a band related to tellurium vacancies as well as the decrease of the emission attributed to defect complexes involving Ge. The data obtained indicate that Ge-impurity gettering and VTe generation at the interface take place during α-HgI2 epitaxial growth.
XeF
(C–A)
laser pumped by formed-ferrite open discharge radiation
Authors: Sentis M. L. , Tcheremiskine V. I. , Delaporte Ph. C. , Mikheev L. D. , Zuev V. S.
Published: July 2002

A study of a high-power blue–green XeF(C–A) laser photolytically pumped by an open discharge along a formed-ferrite surface is presented. A laser output energy of 1.3 J was extracted from a gas mixture of 4 Torr XeF2, 230 Torr N2, and 680 Torr Kr, with a stable optical resonator. With a flat optical resonator, a laser output energy of 1 J was obtained. In this case, we observed an oscillating regime of the laser power, which indicates that the unsaturated gain value was close to the laser action threshold. Perspectives of optical pumping schemes are presented.
Double-end crosslinked electro-optic polymer modulators with high optical power handling capability
Authors: Shi Yongqiang , Wang Wenshen , Lin Weiping , Olson David J. , Bechtel James H.
Published: July 2002

Integrated Mach–Zehnder and straight channel electro-optic modulators have been fabricated with a double-end crosslinked polymer containing amino-sulfone chromophores. The optical power handling capability of these modulators was tested at 1.32 μm wavelength and at input optical power levels compatible with commercial analog transmitters. At a cw peak intensity of 0.9 MW/cm2 inside the waveguide, the double-end crosslinked polymer waveguide modulators exhibited no observable increase in optical loss or degradation of nonlinearity during the experiment period. The poled polymer showed a long-term thermal stability of the electro-optic coefficient at 100 °C and photochemical stability at 633 nm wavelength.
Back gating of a two-dimensional hole gas in a SiGe quantum well
Authors: Emeleus C. J. , Sadeghzadeh M. A. , Phillips P. J. , Parker E. H. C. , Whall T. E. , Pepper M. , Evans A. G. R.
Published: July 2002

A device comprising a low-resistivity, n-type, Si substrate as a back gate to a p-type (boron), remote-doped, SiGe quantum well has been fabricated and characterized. Reverse and forward voltage biasing of the gate with respect to the two-dimensional hole gas in the quantum well allows the density of holes to be varied from 8×1011 cm−2 down to a measurement-limited value of 4×1011 cm−2. This device is used to demonstrate the evolution with decreasing carrier density of a re-entrant insulator state between the integer quantum Hall effect states with filling factors 1 and 3.
Method for fabricating submicron silicide structures on silicon using a resistless electron beam lithography process
Authors: Drouin D. , Beauvais J. , Lemire R. , Lavallée E. , Gauvin R. , Caron M.
Published: July 2002

A novel resistless lithography process using a conventional electron beam system is presented. Metallic lines with widths of less than 50 nm were produced on silicon substrates. The process is based on localized heating with a focused electron beam of thin platinum layers deposited on silicon. It is demonstrated that silicide formation occurs at the Pt-Si interface. By using a dilute solution of aqua regia, it is possible to obtain a sufficient difference in etch rates between exposed and unexposed regions of the platinum thin film to selectively remove only the unexposed areas.
Elastic constants and crystal anisotropy of titanium diboride
Authors: Spoor P. S. , Maynard J. D. , Pan M. J. , Green D. J. , Hellmann J. R. , Tanaka T.
Published: July 2002

In this study, the elastic constants of a titanium diboride (TiB2) single crystal were measured using resonant ultrasound spectroscopy. In contrast to previous work, the current results are consistent with the measured elastic constants of TiB2 polycrystals. In addition, the crystal anisotropy of TiB2 was examined. The current data show that the elastic properties of TiB2 are much more isotropic than previously considered.
Effect of bumps on the wafer on ion distribution functions in high-density argon and argon-chlorine discharges
Authors: Woodworth J. R. , Aragon B. P. , Hamilton T. W.
Published: July 2002

The presence of bumps on or near the wafer in plasma processing reactors can significantly affect plasma parameters. We have used a gridded energy analyzer to measure ion fluxes, energy distributions, and angular distributions near such bumps on a grounded electrode in an inductively coupled discharge in a Gaseous Electronics Conference Reference Cell. We find that the bumps affect the ion energy distributions only slightly, lower the ion fluxes by more than a factor of 2 and dramatically alter the ion angular distributions.
Structural study of InAs quantum boxes grown by molecular beam epitaxy on a (001) GaAs-on-Si substrate
Authors: Lacombe D. , Ponchet A. , Gérard J.-M. , Cabrol O.
Published: July 2002

InAs quantum boxes have been obtained by molecular beam epitaxy on a GaAs-on-Si substrate using the strained-induced 2D–3D transition. The boxes are examined by transmission electron microscopy and compared with those obtained under the same growth conditions on a GaAs substrate. Although there exist 107 dislocations per cm2 in the GaAs-on-Si substrate, high quality coherent strained islands are observed with a density slightly higher than on GaAs substrate. The behavior of the threading dislocations originating from the Si–GaAs interface when they cross the island plane is also investigated. Although some dislocations are bent in the island plane, the island distribution is apparently not affected by the vicinity of a threading dislocation.
Improved performance of laterally oxidized GaInP/AlGaInP lasers by thermal annealing
Authors: Floyd P. D. , Treat D. W.
Published: July 2002

The improvement of efficiency and threshold of visible AlGaInP/GaInP laser diodes, which use buried AlAs native oxides for carrier and optical confinement, is described. Annealing of completed laser bars in an inert atmosphere lowers the threshold current and dramatically increases the external differential quantum efficiency. The characteristic temperature of the devices also increases from 74.8 to 125 K, indicating that the electron confinement is greatly enhanced in the annealed lasers, resulting in the observed improved performance. Secondary-ion mass spectrometry measurements reveal a reduction in hydrogen concentration in the laser cladding regions. This suggests that the improved electron confinement can be attributed to increased acceptor activation due to reduced hydrogen passivation.
Novel method to determine the off-diagonal element of the dielectric tensor in a magnetic medium
Authors: You Chun-Yeol , Shin Sung-Chul
Published: July 2002

A new method to determine the off-diagonal element of the dielectric tensor from the measurements of p- and s-wave Kerr rotation angles, without measuring the ellipticity is reported on in this letter. The method has been verified by determining the off-diagonal elements of Cu/Co multilayer having in-plane magnetization and Co/Pd multilayer having perpendicular magnetization.
Alternating Be and C doping for strain compensated GaAs/AlAs distributed Bragg reflectors
Authors: Mazuelas A. , Hey R. , Jenichen B. , Grahn H. T.
Published: July 2002

We demonstrate a new type of strain compensated, p-type distributed Bragg reflector (DBR) using alternating doping of Be in GaAs and C in AlAs with carbon concentrations as high as 2×1020 cm−3. These DBRs exhibit simultaneously a high crystalline quality, an excellent surface morphology, and no misfit dislocations, which cannot be achieved in undoped or Be-doped DBRs. The absolute optical reflectivity is as high as in the undoped DBR. The differential resistance of these structures is comparable to best reported values in Be-doped DBRs.
Ionization and pulse lethargy effects in inverse Cherenkov accelerators
Authors: Sprangle P. , Hafizi B. , Hubbard R. F.
Published: July 2002

Ionization processes and pulse lethargy limit the pulse duration, accelerating gradient, and maximum energy gain in the inverse Cherenkov accelerator (ICA). These limits are obtained for two ICA waveguide configurations: (i) lined with a dielectric or (ii) filled with a neutral gas. Ionization of the dielectric or gas, by the electromagnetic driver, can modify the dispersive properties, altering the accelerating field phase velocity, causing particle slippage, and disrupting the acceleration. In addition, the electrons can outrun the pulse (pulse lethargy), terminating the acceleration. Limitations due to ionization and pulse lethargy on the accelerating gradient, pulse duration, and maximum energy gain are obtained and illustrated by several examples.
Chirp of monolithic colliding pulse mode-locked diode lasers
Authors: Hofmann M. , Bischoff S. , Franck T. , Prip L. , Brorson S. D. , Mo/rk J. , Fröjdh K.
Published: July 2002

Spectrally resolved streak camera measurements of picosecond pulses emitted by hybridly colliding pulse mode-locked (CPM) laser diodes are presented in this letter. Depending on the modulation frequency both blue-chirped (upchirped) and red-chirped (downchirped) pulses can be observed. The two different regimes and the transition between them are characterized experimentally and the behavior is explained on the basis of our model for the CPM laser dynamics.
Sound-echo experiments in (100)-cut diamond at 70 and 150 GHz
Authors: Scheffold B. , Weis O.
Published: July 2002

We report on sound-echo experiments at 70 and 150 GHz using a 3-mm-thick type IIa diamond with a (100) cut. Longitudinal sound was piezoelectrically excited and detected by means of a sputtered ZnO film. The method of linear frequency modulation of a continuous wave was applied. The temperature dependence of sound attenuation could be measured at 70 GHz up to a temperature of 200 K where an attenuation of about 1 dB/mm was observed.
Pressure and strain sensors based on intervalley electron transfer in AlGaAs
Authors: Lee S. J. , Khurgin J. B. , Wang K. L. , Alt K. , Ehrlich M. J. , Wagner J. W.
Published: July 2002

A novel sensor, based on the intervalley transfer of electrons in AlxGa1−xAs (x∼0.3) subjected to hydrostatic pressure and/or strain is proposed. The operation characteristics are evaluated, optimized theoretically, and demonstrated experimentally.
Annular Josephson junctions as superconductive nuclear particle detectors
Authors: Nappi C. , Cristiano R.
Published: July 2002

A new geometrical configuration for superconductive tunnel junctions as high energy resolution particle detectors is presented. The proposed configuration is based on annular junctions, in which fluxons are trapped in the central hole during the superconducting transition. Such a configuration overcomes some important drawbacks of the traditional geometries. The suppression of the Josephson critical current by a magnetic field that does not need to be sustained during the whole detection time and the absence of Fiske steps, which compromise the stability of the bias point, are automatically reached with the new configuration.
Intracavity gain and absorption dynamics of hybrid modelocked semiconductor lasers using multiple quantum well saturable absorbers
Authors: Gee S. , Coffie R. , Delfyett P. J. , Alphonse G. , Connolly J.
Published: July 2002

Time resolved intracavity gain, saturable absorption dynamics, intracavity intensity pulse profiles, and their corresponding spectrograms, were measured in an external cavity hybrid mode-locked semiconductor diode laser. These measurements were performed to obtain fundamental information of the mode-locking dynamics and to determine their role in the pulse shaping and chirping dynamics. The results of these experiments show that the integrating nonlinearity associated with gain depletion, coupled with group velocity dispersion, leads to asymmetric intensity pulse profiles with predominantly cubic temporal phase, while saturable absorption coupled with group velocity dispersion tends to linearize the chirp. Exploitation of these dynamics may allow researchers to generate optical pulses with higher peak intensities than previously reported.
Kinks induced by free-carrier absorption in weakly index guided semiconductor lasers
Authors: ten Cate J. W. R. , Weegels L. M. , van Bakel A. H. , van der Poel C. J. , Ambrosius H. P. M. M.
Published: July 2002

The time dependence of the kink power in weakly index guided high power stripe lasers in the AlGaAs system are investigated. A periodic dependence of the kink power on the length of the laser is observed in continuous and pulsed modes, but the pulsed mode kink curve is shifted with respect to the continuous one. This is observed to be proportional to 1/τ, where τ is the pulse width. The kink is due to phase locking of the modes of the waveguide resulting from a shift of the effective indexes, which is driven by self-heating due to free-carrier absorption of the laser mode.
GaAs/AlGaAs quantum-well infrared photodetectors on GaAs-on-Si substrates
Authors: Sengupta D. K. , Fang W. , Malin J. I. , Li J. , Horton T. , Curtis A. P. , Hsieh K. C. , Chuang S. L. , Chen H. , Feng M. , Stillman G. E. , Li L. , Liu H. C. , Bandara K. M. S. V. , Gunapala S. D. , Wang W. I.
Published: July 2002

In this letter, we describe the characteristics of molecular beam epitaxy GaAs/AlGaAs quantum-well infrared photodetectors (QWIP’s) grown on a GaAs substrate, and on a GaAs-on-Si substrate produced by metalorganic chemical-vapor deposition. Important issues for QWIP applications such as dark current, spectral response, and absolute responsivity are studied. We find that compared to a similar detector structure grown on a GaAs substrate, the detector grown on a GaAs-on-Si substrate exhibits similar dark current and absolute responsivity while displaying a small blueshift in the spectral response.
Spatially resolved detection of mutually locked Josephson junctions in arrays
Authors: Keck M. , Doderer T. , Huebener R. P. , Traeuble T. , Dolata R. , Weimann T. , Niemeyer J.
Published: July 2002

Mutual locking due to the internal coupling in two-dimensional arrays of Josephson junctions was investigated. The appearance of Shapiro steps in the current versus voltage curve of a coupled on-chip detector junction is used to indicate coherent oscillations in the array. A highly coherent state is observed for some range of the array bias current. By scanning the array with a low-power electron beam, mutually locked junctions remain locked while the unlocked junctions generate a beam-induced additional voltage drop at the array. This imaging technique allows the detection of the nonlocked or weakly locked Josephson junctions in a (partially) locked array state.
Proton damage effects in YBa2Cu3O7/YBa2Cu2.79Co0.21O7/YBa2Cu3O7 Josephson junctions
Authors: Jackson E. M. , Weaver B. D. , Summers G. P.
Published: July 2002

The effects of proton-induced defects on the properties of superconductor-normal-superconductor Josephson junctions with YBa2Cu2.79Co0.21O7 barriers have been investigated. The resistance (R) increases linearly and the critical current (Ic) decreases exponentially with fluence, respectively. Changes in Ic and R occur only at fluences which also reduce Tc. The results indicate that point defects probably have little influence on the uniformity of the Ic and R in junction arrays.
Dielectric properties of silicon nitride films deposited by microwave electron cyclotron resonance plasma chemical vapor deposition at low temperature
Authors: Ye Chao , Ning Zhaoyuan , Shen Mingrong , Wang Hao , Gan Zhaoqiang
Published: July 2002

The dielectric properties of amorphous silicon nitride (SiNx) films that were prepared by microwave electron cyclotron resonance plasma chemical vapor deposition at low temperature in the frequency range 5 Hz–1 MHz have been investigated. The dielectric dispersion in the frequency range exhibits two fractional power laws of (ε′−ε∞′)∝ω−p1 and (ε′−ε∞′)∝ωn1−1 with p1=0.12–0.18 and n1=0.95–0.96. These are close to the result predicted by the many-cluster anomalous conduction theory of fractal structure.
Laser emission from photonic dots
Authors: Röhner M. , Reithmaier J. P. , Forchel A. , Schäfer F. , Zull H.
Published: July 2002

Laser emission was observed in photonic semiconductor dots with a discretized optical mode spectrum. The photonic dots with lateral sizes between 1 and 5 μm provide a three-dimensional optical confinement by using in the vertical direction AlAs/GaAs Bragg mirrors and in the lateral directions the refractive index discontinuity at the etched surfaces. In the optically pumped structures, the laser emission takes place on the fundamental mode of the microcavities. External threshold excitation densities of 200 W/cm2, which correspond to a very low internal optical excitation power of 0.15 μW per microcavity post, were measured for microcavity structures with a lateral size of 2.7 μm.
Texture analysis of indium films grown on GaAs(100) by molecular beam epitaxy
Authors: Kečkéš J. , Ortner B. , Németh Š. , Grietens B. , Borghs G.
Published: July 2002

X-ray diffraction texture analysis is employed to study heteroepitaxial layers of indium grown on GaAs(100) surfaces by molecular beam epitaxy. The results document the epitaxial relationships In{101}∥GaAs{111} and In〈100〉∥GaAs〈110〉. Furthermore, an In{101} plane is oriented nearly parallel to another GaAs{111} plane, with angular deviation less than 3.9°. Due to the symmetry of the zincblende structure, for each GaAs(111) plane, In crystallites are detected in three equivalent positions. The growth of In layers was strongly influenced by the polar character of the GaAs structure, because indium was found to grow preferably on {111}A planes.
Temperature dependence of excitonic energy in isolated Se chains formed in channels of AlPO4-5 crystals
Authors: Sun H. D. , Tang Z. K. , Zhao W. M. , Wong George K. L.
Published: July 2002

Optical absorption spectra of Se chains formed in channels of AlPO4-5 (AFI) crystals are measured in the temperature range from 80 to 298 K. The excitonic energy of the isolated Se chains is observed to shift to lower energy linearly with increasing temperatures, in sharp contrast to the positive temperature coefficient in trigonal-Se crystal. The marked change in the temperature behavior of the excitonic energy is attributed to the greatly diminished interchain interaction in Se–AFI as well as the weakening of the electron-optical-phonon coupling in a low-dimensional system.
Semiconductor based light emitters powered by tritium
Authors: Ruda Harry E. , Jedral Lech Z. , Mannik L.
Published: July 2002

We report on radioluminescence (RL) studies of the wide band gap semiconductors GaP and GaInAsP exposed to tritium gas. All samples were prepared by liquid phase epitaxy. RL tests were performed as a function of tritium pressure, sample temperature, and time, enabling the limiting factors for developing high efficiency visible RL sources to be identified. The studies were complemented by photoluminescence (PL) and cathodoluminescence (CL) measurements. Reduction of surface recombination velocity was shown to be essential for obtaining low threshold CL response and improved PL efficiency. This factor resulted in tritium-activated RL visible to the naked eye. With appropriate materials optimization, these structures should be suitable for developing high efficiency RL devices.
Thermal limitation of self-pulsation in 650 nm AlGaInP laser diodes with an epitaxially integrated absorber
Authors: Summers H. D. , Rees P.
Published: July 2002

Self-pulsation within 650 nm, AlGaInP laser diodes can be achieved via the use of a saturable absorbing, epitaxial layer within the structure. A rate equation model of this type of device is presented, which includes the process of thermally activated charge transfer from the quantum well and gain region to the absorbing layer. The results indicate that this thermal leakage mechanism saturates the absorber and hence destroys the self-pulsation at high temperatures. Comparison of the model with recently published experimental data shows good agreement and provides a consistent explanation for the loss of pulsation at temperatures in excess of 60 °C.
Molecular scale alignment strategies: An investigation of Ag adsorption on patterned fullerene layers
Authors: Dunn A. W. , Cotier B. N. , Nogaret A. , Moriarty P. , Beton P. H. , Beaumont S. P.
Published: July 2002

We have developed a procedure for atomic scale alignment with respect to macroscopic objects. Metallic and etched registration marks on clean reconstructed Si surfaces are used to guide the tip of a scanning tunnelling microscope. The metallic marks are formed from Ta and can withstand thermal cycling up to 1500 K. These procedures have been used to investigate the interaction of Ag with a patterned fullerene multilayer deposited on Si(111)-7×7.
Photoluminescence determination of the Be binding energy in direct-gap AlGaAs
Authors: Galbiati N. , Gatti C. , Grilli E. , Guzzi M. , Pavesi L. , Henini M.
Published: July 2002

The Be binding energy [EABe(x)] as a function of the Al content in AlxGa1−xAs has been determined by photoluminescence measurements of direct-gap Be-doped AlxGa1−xAs (0⩽x⩽0.315) samples grown by molecular beam epitaxy. It has been found EABe(x)=27.5+98x2 (meV) which is systematically lower than other literature values.
Indexing the hopper shaped {111} face produced in chemical vapor deposited diamond
Authors: Menon Prabhjot Mehta , Feigerle C. S. , Thundat T. , Heatherly L. , Clausing R. E.
Published: July 2002

The hopper shaped {111} face frequently observed in cubo octahedral crystallites of diamond has been analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The diamond was grown via hot filament assisted chemical vapor deposition with a feed gas composition of 1% methane in hydrogen. The SEM images of these crystallites show that the {100} faces are usually flatter than the {111}. The hopper shaped {111} faces have been imaged using the tapping mode of the AFM and the angles between planes and their orientations determined. The planes comprising the hoppered {111} face were found to belong to the {221} and {331} family. The implications of the presence of higher index planes as well as other growth features on the growth mechanisms involved are presented.
Annealing effects in ZnSe/GaAs heterostructure grown by molecular beam epitaxy
Authors: Leem J. Y. , Son J. S. , Lee C. R. , Kim C. S. , Cho Y. K. , Lee Hwack J. , Noh S. K. , Bae I. H.
Published: July 2002

In the ZnSe/GaAs heterostructure, the problems of interdiffusion and thermal stability are very crucial. We have investigated the effects of annealing on ZnSe grown on GaAs by photoluminescence and double-crystal x-ray measurement. In order to investigate annealing effects of the ZnSe/GaAs heterostructure, we used 1.0-μm-thick and 0.2-μm-thick samples. Samples were annealed in the temperature range of 200–500 °C in an N2 ambient for 3 min using a face-to-face configuration with ZnSe epitaxial layer as a cap layer. In the annealing temperature above 450 °C, new emission peaks appeared in the range of 2.62–2.72 eV. The biaxial compressive strain due to lattice mismatch at the growth temperature is mostly relaxed at 400 °C, and the epilayer annealed at 500 °C has a biaxial tensile strain.
Structure of high index proton exchange LiNbO3 waveguides with undegraded nonlinear optical coefficients
Authors: Rams J. , Agulló-Rueda F. , Cabrera J. M.
Published: July 2002

A structural study is presented on proton exchanged LiNbO3 waveguides prepared in benzoic acid vapor which, for z-cut substrates, were previously reported to simultaneously exhibit high index jump, very low losses, and undegraded nonlinear optical coefficients. X-ray rocking curves of z-cut guides show a unique, intense peak with the same bandwidth as the substrate peak, located at the κ2-phase position of HxLi1−xNbO3, as well as a small α-phase contribution. For x-cut guides only the β1-phase peak is obtained, with a bandwidth about 60% greater than the substrate peak. Distinctive features of κ2 and β1 guides are also shown in micro-Raman spectra.
Intersubband emission in double-well structures with quantum interference in absorption
Authors: Faist Jérôme , Capasso Federico , Sirtori Carlo , Hutchinson Albert L. , West Ken W. , Pfeiffer L. N.
Published: July 2002

Intersubband electroluminescence is investigated in structures where two excited states are coupled by tunneling to a common continuum, and exhibit a clear sign of destructive interference in absorption spectroscopy. We show that, in addition to the nonreciprocity between the matrix elements for absorption and emission, the difference between the absorption and emission profiles has its origin also in the electron distribution of the injector.
Strain induced interface roughness of Si1−xCx δ layers on Si(001)
Authors: Falta J. , Bahr D. , Hille A. , Materlik G. , Osten H. J.
Published: July 2002

Ultra thin buried Si1−xCx films (δ layers) of monolayer thickness and high carbon concentration (x>0.1) in a Si matrix have been prepared by molecular beam epitaxy and were structurally characterized by high resolution x-ray diffraction, i.e., measurements of crystal truncation rods. The average interface roughness of the δ layers is in the order of 6–10 Å. A larger carbon deposit results in the formation of thicker Si1−xCx δ layers with lower carbon concentrations and smoother interfaces. This effect is attributed to a reduction of the strain in the δ layer due to the lower carbon concentration.
Guest-host electro-optic switching in spin-coated polymer ferroelectric liquid crystal film
Authors: Okazaki Shoji , Uto Sadahito , Ozaki Masanori , Yoshino Katsumi , Skarp Kent , Helgee Bertil
Published: July 2002

We have proposed an electro-optic effect in dichroic-dye-doped polymer ferroelectric liquid crystal thin films prepared by a spin-coating technique. A high-quality homeotropically aligned film has been realized. Guest-host type electro-optic switching is confirmed in the dye-doped film, and basic properties such as electric field dependence of the response time are studied.
Origin of high bandwidth performance of graded-index plastic optical fibers
Authors: Shi R. F. , Koeppen C. , Jiang G. , Wang J. , Garito A. F.
Published: July 2002

Observations in high bandwidth graded-index plastic optical fibers (GI POFs) are reported of strong mode coupling and its characteristic square root-like fiber length dependence of the optical pulse broadening. We have further found that the measured refractive index profile is not parabolic, but consists of two markedly different regions. Analysis of the index profile reveals that strong mode coupling increases the GI POF bandwidth from its profile-determined value of 0.43 GHz to its measured value of 3.0 GHz for 100 m.
High performance electro-optic polymer waveguide device
Authors: Lee Hyang-Mok , Hwang Wol-Yon , Oh Min-Cheol , Park Heuk , Zyung Taehyoung , Kim Jang-Joo
Published: July 2002

A high performance electro-optic polymer modulator is fabricated by utilizing a thermally curable cladding polymer. Half-wave modulation voltage as low as 3.7 and 4.8 V under 500 Hz operation is obtained with a 1.5 cm long electrode at wavelengths of 1.3 and 1.55 μm, respectively. The modulator also shows stable dc bias voltage to be traceable and low poling-induced optical loss. This work implies that proper selection of a cladding material is as important as the electro-optic materials in the electro-optic waveguide devices.
High power mid infrared operation of the atomic xenon laser
Authors: Wendland J. J. , Morley R. J. , Baker H. J. , Hall D. R.
Published: July 2002

We report high power cw operation of a slab waveguide atomic xenon laser in a spectral region of low atmospheric absorption. Using transverse radio frequency discharge excitation at 49 MHz and a hybrid waveguide-unstable resonator, with a sharp band edge on the reflectivity versus wavelength curve of the laser mirrors, 50 mW was obtained on the 3.869 μm transition and 210 mW on the 3.895 μm line.
Magnetospectroscopy of high-purity InP grown by gas source molecular beam epitaxy
Authors: Shi X. H. , Liu P. L. , Shi G. L. , Hu C. M. , Chen Z. H. , Shen S. C. , Chen J. X. , Xin H. P. , Li A. Z.
Published: July 2002

Magneto-photoconductivity spectra related to the bound phonons and resonant polaron effect on Si donors in high-purity InP have been investigated. Not only the transition from the 1s ground state to bound phonon state (1s+LO) of Si donors, but also the antilevel crossings of the (3, 1, 0) metastable state with the bound phonon states (1s+LO) and (2p−1+LO) are clearly observed in high magnetic fields. The results demonstrate the bound phonon in Si-doped InP consists of both electron and phonon via multiphonon processes and there is a resonant interaction between LO phonons and impurity-bound electrons in InP.
Growth of single-phase PrBa0.7Sr1.3Cu3O7 thin films and the role of lattice strain on the transport properties
Authors: Zhao Y. G. , Dong Z. W. , Rajeswari M. , Sharma R. P. , Venkatesan T.
Published: July 2002

Single-phase PrBa0.7Sr1.3Cu3O7 thin films with the Sr dopant concentration exceeding the solid solubility limit were epitaxially grown on (001) SrTiO3 and (001) LaAlO3 substrates by pulsed laser deposition (PLD) method. The resistivity of the doped films grown on LaAlO3 was significantly lower than that of PrBa2Cu3O7. For most of the films grown on SrTiO3, the resistivity was higher than that of PrBa2Cu3O7. The results were explained by considering the Sr-doping effect and lattice-mismatch-induced strain effect. This work shows the potential of PLD to grow single-phase films with the dopant concentration exceeding the solid solubility limit.
Simultaneous optimization of membrane reflectance and tuning voltage for tunable vertical cavity lasers
Authors: Sugihwo F. , Larson M. C. , Harris J. S.
Published: July 2002

Micromachined wavelength tunable vertical cavity lasers are attractive for applications ranging from wavelength division multiplexing to spectroscopy. An improved tunable structure that incorporates a partial anti-reflection coating to increase coupling between the air gap and the semiconductor cavity, and a more flexible micromachine process that enables independent optimization of the central reflector region and deformable membrane structure are described. This combination of structural and process modifications enables decoupling the tradeoffs between wavelength tuning rate and threshold current, as well as the tradeoffs between top mirror reflectance and tuning voltage. With these improved approaches, a 2.5 pair dielectric distributed Bragg reflector hybrid membrane top mirror produced singlemode devices with a 23 nm wavelength tuning range and multi-transverse-mode devices with a 30 nm wavelength tuning range. Threshold current, differential quantum efficiency, and lasing mode are characterized as a function of membrane bias.
How to achieve in-phase locking in small-inductance Josephson junction ladder arrays
Authors: Basler M. , Krech W. , Platov K. Yu.
Published: July 2002

We present the results of an analytical study of phase locking in externally loaded two-dimensional Josephson junction ladder arrays with small, but non-vanishing ring inductances. A Lyapunov stability based condition is found controlling realization of the radiating in-phase oscillation regime.
Photoinduced surface deposition of Ag on Ag-rich Ag–Ge–S films: Optimal Ag content and film thickness for applications in optical recording devices
Authors: Kawaguchi Takeshi
Published: July 2002

The photosensitivity of the photosurface deposition (PSD) effect and the durability in air of Agx(Ge0.3S0.7)100−x films (40⩽x⩽83) with thicknesses of 50–700 nm have been studied. Films of 60–65 at. % Ag and 200–300 nm thick were found to be optimal for applications in optical recording devices. Crystallized samples have been examined to obtain structural information on the Ag-rich films. It is suggested that excess Ag+ ions, which contribute to the PSD, exist in a disordered Ag8GeS6 phase of the Ag-rich films.
Bistable electroluminescence in p-i-n light-emitting tunnel-diodes enhanced by aperiodic-superlattice injectors
Authors: Cao S. M. , Willander M. , Toropov A. A. , Shubina T. V. , Mel’tser B. Ya. , Kop’ev P. S. , Lundström T. , Holtz P. O. , Bergman J. P. , Monemar B.
Published: July 2002

A p-i-n resonant tunnel diode is designed and investigated using photoluminescence (PL) spectroscopy. The device is based on an Al0.4Ga0.6As/GaAs graded-index waveguide heterostructure enhanced by aperiodic-superlattice injectors for simultaneous resonant injection of electrons and heavy holes. The bias-dependent study of photocurrent, electroluminescence (EL) and PL show strong resonance behavior in the optical intensity confirming the field-dependent resonant injection of the excited states in the emission layers. Pronounced voltage-current bistability due to injection efficiency leads to multiple-wavelength EL and lasing action.
Localized switching in photorefractive ferroelectrics induced by spatially inhomogeneous electric fields
Authors: Fousek J. , Marvan M. , Cudney R. S.
Published: July 2002

We examine theoretically the stability of 180° domain patterns that may form inside photorefractive ferroelectric crystals when an optically induced spatially modulated electric field is present. By analyzing the total free energy of a ferroelectric crystal subjected to an applied field and with free charges contained within, we find under what conditions (magnitude of the applied field, amplitude of the optically induced electric field, and domain-wall energy density) the spontaneous polarization of the crystal tends to switch throughout the whole crystal and under which only partial switching occurs.
Annealing effect on concentration of EL6-like deep-level state in low-temperature-grown molecular beam epitaxial GaAs
Authors: Darmo J. , Dubecký F. , Kordoš P. , Förster A.
Published: July 2002

A deep-level donor state with signatures similar to the EL6 level observed in low-temperature-grown molecular beam epitaxial (MBE) GaAs grown at 250 °C and annealed in the temperature range 310–370 °C was studied. The annealing kinetics of this level suggest a confined pair recombination, likely VGa and Asi. A correlation between the deep level observed and recently published photoluminescence data of low-temperature-grown MBE GaAs is found.
Exchange-biased spin valves combining a high magnetoresistance ratio with soft-magnetic behavior
Authors: Kools J. C. S. , Lardoux S. , Roozeboom F.
Published: July 2002

We report on the preparation of bottom spin valves combining a high giant magnetoresistance effect (above 10%) with a soft-magnetic behavior (coercivities of a few hundreds of A/m). By optimization of film composition and preparation conditions, it is possible to obtain materials having magnetoresistance values around 16%, which display minor loop coercivities of 0.2 kA/m, and sensitivities of 11%/kA/m.
In situ monitoring of Raman scattering and photoluminescence from silicon surfaces in HF aqueous solutions
Authors: Ren B. , Liu F. M. , Xie J. , Mao B. W. , Zu Y. B. , Tian Z. Q.
Published: July 2002

In situ Raman spectra of SiHx, Si–F, and Si–Si vibrations from Si surfaces in HF aqueous solutions are obtained using a highly sensitive confocal microprobe Raman system. Electrochemical roughening pretreatment and laser-assisted roughening procedure enable good quality surface Raman spectra to be obtained. The surface Raman and photoluminescence spectra from the Si surface in the etching environment and the correlation of the two types of spectra are discussed. The Raman spectroscopy is shown to have high potential in serving as an important tool for in situ investigating of Si surface bonding during the etching process.