bluuebunny/crossref_metadata_2025 huggingface dataset:
New photodefinable glass etch masks for entirely dry photolithography: Plasma deposited organosilicon hydride polymers
Authors: Weidman Timothy W. , Joshi Ajey M.
Published: July 2002

The low energy plasma induced dehydrogenative polymerization of various monosubstituted silanes (RSiH3) is shown to provide photosensitive films characterized as organosilicon hydride network materials with extensive Si—Si bonding. Plasma deposited films may be photo-oxidatively patterned with mid-deep ultraviolet light producing glasslike Si–O–Si crosslinked materials in exposed areas. Patterns can be developed by chlorine reactive ion etching with up to 5:1 selectivity, and transferred into underlying organic layers with ≳50:1 selectivity and sub-half-micron resolution. This provides a versatile, completely dry photolithographic process useful with current exposure and etching tools and is well-suited for integration into cluster tool technologies.
Fast degradation of boron-doped strained Si(1−x)Gex layers by 1-MeV electron irradiation
Authors: Vanhellemont J. , Trauwaert M.-A. , Poortmans J. , Caymax M. , Clauws P.
Published: July 2002

Fast degradation is reported of p+ boron-doped Si(1−x)Gex strained layers by 1-MeV electron irradiations performed at room temperature. n+p+ diodes with x=0, 0.12, and 0.16 are fabricated on conventional p-type Czochralski silicon substrates. Current/voltage, capacitance/voltage, and capacitance/temperature characteristics are studied before and after irradiation as a function of the electron fluence. A possible degradation mechanism is discussed.
Acoustic phonon peak splitting and satellite lines in Raman spectra of semiconductor superlattices
Authors: Zhang P. X. , Lockwood D. J. , Baribeau J.-M.
Published: July 2002

Folded longitudinal acoustic phonon peak splitting and sets of satellite lines are observed in high resolution Raman spectra of Si/Si1−xGex superlattices. Analysis shows that the phonon peak splittings are possibly due to a variation in the superlattice periodicity and the sets of satellite lines originate from the interference of the folded longitudinal acoustic phonons and the confined acoustic phonons in the superlattice film. These fine structures in Raman spectra enable a detailed characterization of the superlattices.
Resonant Raman scattering and photoluminescence at the E0 band gap of carbon-doped AlAs
Authors: Wagner J. , Fischer A. , Ploog K.
Published: July 2002

Carbon-doped AlAs grown by solid source molecular beam epitaxy has been studied by Raman and photoluminescence spectroscopy. Doping levels exceeding 2×1019 cm−3 have been obtained using a heated graphite filament as the carbon source. For excitation just above the AlAs E0 band-gap energy radiative recombination is observed across that band gap, which involves nonthermalized photogenerated electrons occupying the Γ-conduction-band minimum rather than the lowest indirect X minima. Raman spectra excited in resonance with the E0 band gap show a hole-plasmon-longitudinal-optical-phonon coupling similar to that found in p-type GaAs. Resonantly excited Raman spectra further reveal a vibrational mode at ≂635 cm−1, which is assigned to the local vibrational mode of the CAs acceptor in AlAs.
Impurity induced disordering of CdZnSe/ZnSe strained layer superlattices by germanium diffusion
Authors: Yokogawa T. , Floyd P. D. , Hashemi M. M. , Merz J. L. , Luo H. , Furdyna J. K.
Published: July 2002

We report the first confirmation of disordering of CdZnSe/ZnSe strained layer superlattices (SLSs) by Ge diffusion. Both the as-grown sample and the sample annealed without a Ge layer showed several orders of well-resolved double crystal x-ray satellite peaks due to SLS periodic structure. However, the satellite peaks completely disappeared in the Ge-diffused sample, indicating that the SLS structure was disordered by the Ge diffusion and not caused by the annealing process. PL measurements at 1.4 K of both the as-grown and the annealed samples without Ge diffusion show identical, sharp excitonic emission around 483 nm. After Ge diffusion, the PL peaks shift to higher energy confirming the layer disordering of the SLS.
Ultrathin textured polycrystalline oxide with a high electron conduction efficiency prepared by thermal oxidation of thin polycrystalline silicon film on n+ polycrystalline silicon
Authors: Wu Shye Lin , Lee Chung Len , Lei Tan Fu
Published: July 2002

This letter presents an ultrathin textured polycrystalline oxide (polyoxide) (≤100 Å) prepared by thermal oxidation of thin polycrystalline silicon (polysilicon) film on n+ polysilicon. The presented textured polyoxide exhibits a much higher electron injection efficiency, a much smaller electron trapping rate, and a much larger charge to breakdown than the normal polyoxide. The value of Qbd of the textured polyoxide could be more than 3000 C/cm2 even under 100 mA/cm2 stressing.
Use of the Talbot effect to couple the phases of lasers
Authors: Latimer Paul
Published: July 2002

Antyukhov et al. [JETP Lett. 44, 78 (1986)] first proposed that a normal and partly reflecting mirror be placed a distance a2/λ in front of a laser array to synchronize and phase lock them. Then the Talbot effect, said to produce source ‘‘self-imaging,’’ forms an ‘‘array image’’ on the array. However, a basic relation of Fresnel diffraction is now found to indicate that the method as used is inherently flawed. The Talbot effect actually introduces phase shifts into some of the reflected light which make the total output nonuniform in phase. This produces a complex amplitude pattern in Talbot planes different from the grating output. Then the various lasers will not emit in phase.
Observation of the DX center in Pb-doped GaAs
Authors: Willke U. , Maude D. K. , Sallese J. M. , Fille M. L. , el Jani B. , Gibart P. , Portal J. C.
Published: July 2002

Pb in GaAs introduces a DX center-like (metastable) defect level that is (229±16) meV above the Γ-conduction-band edge, in a similar energetic position to the Si and Sn related DX centers in GaAs. The persistent photoconductivity effect quenches at approximately 50 K, indicating that the barrier to capture for the Pb and Sn dopants are similar. Despite the quite different atomic parameters of the Pb atom compared with the Sn atom, no significant chemical shifts have been found.
Field-induced absorption edge merging in tensile strained GaAsP quantum wells
Authors: Gomatam Badri N. , Anderson Neal G. , Agahi Farid , Musante Charles F. , Lau Kei May
Published: July 2002

Field-induced merging of electron-to-light-hole (e-lh) and electron-to-heavy-hole (e-hh) excitonic absorption edges in tensile-strained quantum wells is demonstrated for the first time. Photocurrent spectra (77 K) of a GaAs0.92P0.08/Al0.37Ga0.63As multiple-quantum-well structure embedded in a p-i-n diode clearly show reduction and eventual elimination of a zero-bias ∼7 meV splitting between the e-lh and e-hh exciton peaks with increasing reverse bias. The unique ‘‘light-hole-up’’ valence subband configuration required for this field-induced merging is achieved through a combination of tensile strain and quantum-size effects in the ∼95 Å GaAs0.92P0.08/Al0.37Ga0.63As multiple quantum wells. The ability to control and eliminate the splitting between the e-lh and e-hh absorption edges via an applied electric field offers possibilities for improving the performance of electroabsorption modulators.
Tristable operation of injection laser diodes coupled to absorbers of narrow spectral bandwidth
Authors: Maeda Yoshinobu
Published: July 2002

Tristable longitudinal modes of a laser diode for an injection current were observed. Transmitting these laser lights through an Er-doped yttrium aluminum garnet crystal, which has an absorption peak of narrow spectral bandwidth, results in changes in these wavelengths of the laser diode that could be converted into intensity changes and take tristable optical outputs for the same injection current value. It is suggested that an optical inverter and memory could be realized and a new type three-valued logic would be constructed by making use of these phenomena.
Dynamics of the 5 eV optical absorption in SiO2 glass
Authors: Tsai T. E. , Jewell J. M. , Sanghera J. S.
Published: July 2002

The optical absorption at 5 eV in SiO2 glass was observed, using laser calorimetry, to change reversibly depending on the intensity of UV light. The generation and bleaching of an absorption band at 5 eV by two- and one-photon absorption processes, respectively, can explain these reversible changes. This observation supports the structural model of unrelaxed oxygen deficiency center for the 5 eV absorption band in silica.
Alkaline metal dopants and photodarkening in colored filter glass
Authors: Yanagawa T. , Nakano H. , Ishida Y. , Kubodera K.
Published: July 2002

It is clearly shown for the first time that alkaline metal ions assist the photodarkening effect in colored filter glass. Time responses of samples vary depending on the kind of alkaline metal dopants involved as additive compounds for improving glass quality. Energy relaxation times of photoexcited carriers after laser beam irradiation change following weight quotients of potassium oxides from sodium oxides. The fastest response after irradiation can be obtained when the quotient is approximately two. This quotient corresponds to compositions showing conspicuous mixed-alkali effects from potassium and sodium.
Near-millimeter-wave response of high T
c ramp-type Josephson junctions
Authors: Gupta R. , Hu Qing , Terpstra D. , Gerritsma G. J. , Rogalla H.
Published: July 2002

We have studied the response of a YBCO/PBCO/YBCO ramp-type junction to coherent radiation at 176 and 270 GHz. The I-V characteristic of the junction closely resembles the prediction of the RSJ model. The IcRn product of the junction is 0.25 mV at 5 K. The millimeter-wave radiation is coupled to the junction via a quasioptical structure that focuses the radiation onto the junction through a yttrium-stabilized ZrO2 substrate. At 176 GHz, we have observed as many as six Shapiro steps at the maximum power level of our Gunn oscillator-pumped frequency doubler. Shapiro steps are still clearly seen up to 65 K. The amplitudes of the zeroth, first, and second Shapiro steps, as functions of the square root of the radiation power, agree remarkably well with a Bessel function fit, indicating the junction is voltage-biased at the radiation frequency (rf). At 270 GHz, due to a combination of the heavy rf loss in the ZrO2 substrate and the lack of radiation power, we have observed only the first Shapiro step.
Study of Ge movement during thermal reactions between Pt and GeSi/Si heterostructures
Authors: Zhong Peixin , Zheng Youdou
Published: July 2002

Germanium movement in the thermal reaction between Pt and the Ge0.15Si0.85/Si heterostructure was studied by Auger electron spectroscopy. The compounds formed were identified by x-ray diffraction after various anneals from 300 to 760 °C. Pt2Ge and Pt2Si formed at low annealing temperatures. At higher temperatures, Pt(GexSi1−x) formed. Two types of Ge segregation were observed. Ge was rich at the surface and the PtGeSi/GeSi interface. Some Ge was pushed inward during thermal reaction at all of the above conditions. This procedure was enhanced by higher annealing temperature. Some Ge in the PtGeSi layer segregated to the surface. Both types of Ge segregation were strong after a 3 h, 300 °C anneal. The mechanism of the phenomena is discussed. This will have certain affects on the properties of PtGeSi/GeSi Schottky devices.
High resolution Si position sensor
Authors: Scott K. A. M. , Sharma A. K. , Wilson C. M. , Mullins B. W. , Soares S. F. , Brueck S. R. J.
Published: July 2002

We report on a simple 80-μm-diam Ni-Si-Ni back-to-back Schottky photodiode with a demonstrated vibration-limited optical-position sensitivity of <4-nm transverse to an incident laser beam. This is two orders of magnitude higher than the previous best resolution reported for a solid-state noninterferometric position sensor. The response time of the unbiased device was measured to be 350 ps. The position sensitivity limit resulting from background electronic noise is as low as 0.25 pm/√Hz. The short circuit photocurrent response is linear across the detector gap and is insensitive to changes in wavelength and laser spot sizes within the gap. The bandwidth of the sensor was found to be 2 GHz. A simple model, based primarily on the symmetry of the device, provides a qualitative understanding of these results.
Dependence of electron accumulation in AlSb/InAs quantum well on thin surface materials of InAs and GaSb
Authors: Furukawa A.
Published: July 2002

The role of thin surface material in electron accumulation of an AlSb/InAs quantum-well system is reported. Electron density transferred from surface to well is much smaller when InAs was grown at the surface than when GaSb was grown at the surface. This result is explained by the difference of surface pinning positions between InAs and GaSb. The surface pinning position of InAs is obtained to be lower by 0.2 eV than that of GaSb.
Enhancement of diffusion length of pregettered multicrystalline silicon solar cells by hydrogen ion implantation at the end of the process
Authors: Sivoththaman S. , Rodot M. , Muller J. C. , Hartiti B. , Ghannam M. , Elgamel H. E. , Nijs J. , Sarti D.
Published: July 2002

2×2 cm2 n+pp+ multicrystalline silicon solar cells have been fabricated using thin wafers less than 200 μm thick. A large electron diffusion length has been achieved in these wafers after metallic impurity gettering using a heavy phosphorus diffusion prior to cell processing. Further improvements in the electron diffusion length (Ln) and in the short circuit current (Jsc) of these cells are brought out by hydrogen ion implantation carried out through the back surface of the finished cell. A 25% increase in Ln and a 5.5% increase in Jsc are obtained.
Effects of ion beam defect engineering on carrier concentration profiles in 50 keV P+-implanted Si(100)
Authors: Zhao Qing-tai , Wang Zhong-lie , Xu Tian-bing , Zhu Pei-ran , Zhou Jun-si
Published: July 2002

Shallower carrier concentration profiles in 50 keV P+-implanted Si(100) after annealing at 1000 °C for 1 h have been observed when a buried amorphous layer was formed by an additional irradiation of 1.0 MeV Si+ ions prior to annealing (i.e., ion beam defect engineering process). The secondary defects formed in the MeV Si+ damaged region act as gettering sites for the collection of interstitials from the shallower depths which are responsible for the transient diffusion of P, and therefore the transient diffusion of P is reduced and the carrier concentration profiles become shallower.
Chemically induced shifts in the photoluminescence spectra of porous silicon
Authors: Li K.-H. , Tsai C. , Sarathy J. , Campbell J. C.
Published: July 2002

The observation of photoluminescence (PL) spectral shifts during anodization of porous Si and after immersion in different chemical solutions is reported. These shifts in the PL spectra are attributed to changes in the surface chemistry achieved by changing the composition of the electrolyte in which the samples are immersed. Using this approach the emission has been repeatedly cycled (≳100 times) between green and red.
Polarization properties of a vertical cavity surface emitting laser using a fractional layer superlattice gain medium
Authors: Chavez-Pirson A. , Ando H. , Saito H. , Kanbe H.
Published: July 2002

We investigate the polarization properties of a vertical cavity surface emitting laser that uses an (Al0.5Ga0.5As)1/2(GaAs)1/2 fractional-layer superlattice (FLS) as an anisotropic gain medium. The anisotropy in the gain enables us to both control and switch the polarization state of the optically pumped lasing output. We obtain room-temperature lasing for wavelengths from 690 to 720 nm. The output is linearly polarized and the polarization direction is fixed, either parallel or perpendicular to the FLS layers. By tuning the cavity resonance wavelength, we demonstrate high contrast switching between two orthogonal linear polarization states in the FLS surface emitting laser.
Effect of carrier escape time on the performance of semi-insulating photorefractive self-electro-optic effect devices
Authors: Partovi A. , Glass A. M. , Zydzik G. J. , O’Bryan H. M. , Chiu T. H. , Knox W. H.
Published: July 2002

We report on the effect of carrier escape time on the performance of semi-insulating photorefractive self-electro-optic effect devices by investigating three samples of Cr-doped GaAs/AlxGa1−xAs multiple quantum wells of varying barrier thickness and height. Reduction of barrier thickness from 100 to 35 Å and Al fraction from 0.42 to 0.29 results in a three orders of magnitude increase in diffraction efficiency at a given voltage. The effect of shorter carrier escape and sweep-out times on the diffraction efficiency, resolution, and sensitivity of these devices is discussed.
Selective area deposition of metal films by the ionized cluster beam method
Authors: Urban Frank K. , Hosseini-Tehrani Atoosa , Feng Susan W. , Nainaparampil Josekutty J.
Published: July 2002

Shrinkage of ultralarge scale integrated circuit design rules to below 0.5 μm is placing new demands upon thin-film interconnect, especially for filling vias in insulating material to conductors lying below. Selective area deposition which will lead to enhanced via filling is investigated here using cluster beams, with a distribution peaking at 2200 atoms in average size, in which every cluster is positively ionized. A positive repelling voltage is placed on a conducting plate immediately behind test substrates which consist of an insulator with overlying conductive test patterns held at ground. Depositing metal selectively coated the conductive patterns while the repelling voltage essentially eliminated deposition onto insulating areas.
Superior flux pinning in in situ synthesized silver-sheathed superconducting tape of Tl0.5Pb0.5Sr1.6Ba0.4Ca0.8Y0.2Cu2Oy
Authors: Ren Z. F. , Wang J. H.
Published: July 2002

In situ synthesis has been developed for the first time to fabricate the Tl-based silver-sheathed superconducting tapes. Tapes of Tl0.5Pb0.5Sr1.6Ba0.4Ca0.8Y0.2Cu2Oy (Tl-1212) made by the in situ synthesis method under optimal oxygen partial pressure were found to have transport Jc of 7000 A/cm2 in the absence of external magnetic field. In low magnetic field (<0.2 T) the Jc decreases rapidly with field due to weak links. But the Tl-1212 tapes exhibited flux-pinning properties superior to those of Tl-1223 tapes when measured by SQUID at 77 K. XRD pattern of the powdered superconducting material shows it to be a single 1212 phase. Both transport measurement by the four-probe method and magnetization measurement by SQUID also show that it is a single phase with zero resistance and onset transition temperatures of 97.5–99.0 and 101–103 K, respectively, under a measuring current of 150 mA.
Modeling of piezo-Hall effects in n-doped silicon devices
Authors: Nathan A. , Manku T.
Published: July 2002

The output response for n-type 〈100〉 and 〈110〉 silicon Hall geometries is presented for various device (current flow) orientations, in the presence of both magnetic field and stress. The results are based on a systematic formulation of the piezo-Hall current density equation which accounts for the effects of stress on the galvanomagnetic carrier transport. The equation is presented in a generic form, thus providing an accurate means of interpreting pertinent Hall measurement data in strained materials as well as to reliably predict the output response (including offsets) associated with integrated Hall sensors under stress.
Observation of electromigration of hydrogen in polycrystalline silicon using poly emitter bipolar transistors
Authors: Zhao J. , Li G. P. , Liao K. Y. , Chin M. R. , Sun J. Y.-C.
Published: July 2002

Electromigration of hydrogen inside polycrystalline silicon (polysilicon) has been observed for the first time. Experiments were conducted on polysilicon emitter (poly emitter) n-p-n transistors with and without atomic hydrogen inside polysilicon. The current gain (β) of n-p-n was selected to monitor electromigration of hydrogen during current stress because of its high sensitivity to hydrogen passivation of dangling bonds. The major characteristics of hydrogen electromigration are shown in this letter.
Electrical properties of Y-doped CaCuO2 films prepared by organometallic chemical vapor deposition
Authors: Kobayashi Kenkichiro , Ishihara Yozo , Matsushima Shigenori , Okada Genji
Published: July 2002

Y-doped CaCuO2 films have been formed on SrTiO3 (100) substrates in the range of 730–790 °C. The lattice constants of Y-doped CaCuO2 films are c=3.180–3.183 Å, which are shorter than that of an undoped CaCuO2 film. Although the resistivity of a Y-doped CaCuO2 film is significantly decreased in comparison with an undoped CaCuO2 film, no superconductivity is found in the Y-doped CaCuO2 films at a temperature higher than 12 K.
Experimental observation of multiple current-voltage curves and zero-bias memory phenomena in quantum well diodes with n−-n+-n− spacer layers
Authors: Gullapalli K. K. , Tsao A. J. , Neikirk D. P.
Published: July 2002

We report the observation of a new room-temperature storage phenomenon based on quantum interference. Multiple, stable current-voltage curves extending continuously through zero bias have been observed in GaAs/AlAs double barrier quantum well diodes containing n−-n+-n− spacer layers. Once placed on a particular branch, the devices retain memory of the branch they lie on, even when held at zero bias for extended periods of time. The devices can be repetitively switched between the different branches of the current-voltage characteristics. The experimental observations are consistent with the multiple self-consistent solutions to the coupled Schrödinger and Poisson equations found for diodes that combine heterostructure tunneling barriers with n−-n+-n− spacer layers.
Hydrostatic pressure dependence of the Cu-acceptor level in In0.53Ga0.47As
Authors: Gerling M. , Tilly L. P.
Published: July 2002

Low-temperature photoluminescence measurements have been used to study the evolution of the Cu-acceptor level in In0.53Ga0.47As as a function of hydrostatic pressure. In the pressure range up to 37 kbar the Cu related emission closely tracks the near-band-edge emission. A pressure coefficient of the Cu-acceptor level relative to the valence-band edge of 0±0.5 meV/kbar was determined, and the corresponding pressure coefficient of the Cu-acceptor level relative to the conduction-band edge was found to be 10.9±0.2 meV/kbar.
Deformation induced deep levels in p-CdTe
Authors: Hümmelgen I. A. , Schröter W.
Published: July 2002

α and β dislocations are separately investigated in p-CdTe by deep level transient spectroscopy. Two lines, whose amplitudes increase with increasing dislocation density are found. The defect concentration is found to be higher in case of β dislocations. One line, at Ev+0.44 eV, is Gaussian broadened, while the second, at Ev+0.35 eV, shows unusual capture characteristics.
Radiation linewidth of phase-locked distributed array in the submillimeter wave range
Authors: Bi Baokang , Han Siyuan , Lukens James E.
Published: July 2002

The radiation linewidth of a phase-locked distributed Josephson junction array source at 250 GHz has been measured as a function of temperature using an integrated submillimeter wave receiver/source. The measured total linewidth (including signal and local oscillator arrays, having 10 junctions each) is 10 MHz at 1.6 K. The measured data agree, within 50% uncertainty, with the linewidth obtained from computer simulation assuming the Nyquist noise current spectral density generated by the junction shunt resistors.
Optical data storage based on magnetic circular dichroism
Authors: Schlichting W. , Milster T. D. , Campillo C. J.
Published: July 2002

An alternative to differential detection in optical data storage is magnetic circular dichroism (MCD) detection. The MCD system has increased light efficiency when compared to the commonly used differential detection method. Also, the signal amplitude for MCD detection can be twice as large as for differential detection when an s-p phase difference of 90° is introduced in the medium. Modeling results show that a thin-film device can introduce the necessary s−p phase difference. Our signal-to-noise analysis indicates that the MCD system rejects polarization noise. Experimental results on coupon samples verify that the signal from MCD detection can be twice as large as from differential detection.
Compensation of shallow silicon donors by deep copper acceptors in gallium arsenide
Authors: Roush Randy A. , Stoudt David C. , Mazzola Michael S.
Published: July 2002

Electrical compensation in n-type, silicon-doped, GaAs (GaAs:Si) has been achieved for several different silicon doping densities. The introduction of deep copper acceptors into GaAs:Si through a thermal diffusion process has produced semi-insulating GaAs:Si:Cu. The density of diffused copper is shown to be predicted, to a good approximation, by knowledge of both the annealing temperature at which compensation is observed, and the initial free-electron density. Also, a model based on Fermi–Dirac statistics has demonstrated the same qualitative behavior as the data.
Efficient poling and thermal crosslinking of randomly bonded main-chain polymers for stable second-order nonlinearities
Authors: Ranon Peter M. , Shi Yongqiang , Steier William H. , Xu Chengzeng , Wu Bo , Dalton Larry R.
Published: July 2002

We report our second-harmonic generation study of a new crosslinked main-chain polymer system for second-order nonlinear optics (NLO). In this unique polymer system, the rigid second-order NLO chromophores are randomly bonded in the main chain with flexible links between the rigid chromophores to allow electric poling at or above the glass transition temperature. A thermal crosslinker is added to crosslink the polymer backbone during electric poling. The combination of the flexible chain segments and crosslinking allows us to achieve a high degree of alignment (〈cos3θ〉≊0.34) and long-term (≳2500 h) temporal stability of the nonlinearities.
Quantitative study of exciton migration effects on photoluminescence of quantum well
Authors: Ping Er-Xuan
Published: July 2002

The effects, induced by the exciton (EX) migration and the inherent interface roughness, on the photoluminescence (PL) in a quantum well (QW) have been studied by a model which includes the inter- and intra-growth-island EX transfer. Analytical expressions, showing the redshifting and linewidth reduction in the PL spectrum, are obtained at low and high temperatures. The inconsistency of the PL and PL excitation spectra has been reexamined and quantitatively obtained, under the influence of the EX migration, as a function of the temperature, the quality, and the structure of the QW.
Observation of separate electron and hole escape rates in unbiased strained InGaAsP multiple quantum well laser structures
Authors: Takasaki B. W. , Preston J. S. , Evans J. D. , Simmons J. G. , Puetz N.
Published: July 2002

We report on the first time-resolved photoconductivity measurements in strained InGaAsP multiple quantum well 1.3 μm laser structures. The photoconductive response is characterized by two exponential time constants, a fast time constant of less than 500 ps and a long time constant between 10 and 20 ns. We attribute these to the escape of electrons and holes from the wells, respectively.
Determination of barrier traversal time by modulation of the incident wave
Authors: Hagmann M. J.
Published: July 2002

The semiclassical expression for barrier traversal time results from a variety of theoretical procedures, but it appears that an opaque barrier is required in each derivation. Following Büttiker and Landauer [IBM J. Res. Dev. 30, 451 (1986)], we use two interfering plane waves as the incident wave and determine the traversal time by attributing differences in the transmitted and incident waves to the ratio of dispersion in the transit time to the modulation period. Calculations are made for rectangular barriers with different sizes. There is essentially agreement with Büttiker and Landauer for opaque barriers which they considered, but the present solution does not diverge for energies near the top of the barrier.
High quality In0.2Ga0.8As/AlxGa1−xAs (x=0−0.32) strained single quantum wells grown by molecular beam epitaxy
Authors: Hayakawa Toshiro , Horie Hideyoshi , Nagai Masaharu , Niwata Yoshihisa
Published: July 2002

The effect of the Al composition on photoluminescence (PL) in the In0.2Ga0.8As/AlxGa1−xAs single strained quantum wells with the well width of 6 nm has been studied. The samples have been grown by molecular beam epitaxy. The PL intensity measured at RT very rapidly increases with the AlAs mole fraction possibly due to the suppression of the carrier leakage from a quantum well. It increases by a factor of 300 when the AlAs mole fraction x is increased from 0 to 0.32. The full width at half maximum of the PL spectrum measured at 10 K is as small as 3.0, 4.4, and 4.9 meV for x=0, 0.14, and 0.32, respectively. The increase in the PL linewidth can be explained by the increased effect of heterobarrier height on the quantized energy. The present results suggest that performance characteristics of devices can be improved by employing the high-quality AlGaAs barrier instead of GaAs.
Superconducting Y1Ba2Cu3O7−x/Nd1.85Ce0.15CuO4−y bilayer thin films
Authors: Mao S. N. , Xi X. X. , Li Qi , Takeuchi I. , Bhattacharya S. , Kwon C. , Doughty C. , Walkenhorst A. , Venkatesan T. , Whan C. B. , Peng J. L. , Greene R. L.
Published: July 2002

Bilayers of Y1Ba2Cu3O7−x(YBCO)/Nd1.85Ce0.15CuO4−y(NCCO), in which both layers were superconducting, were fabricated in situ by pulsed laser deposition. Using N2O as the reactive gas, we were able to meet the conflicting processing requirements, oxygenation for YBCO, and reduction for NCCO, in the same sample with a specific cooling procedure. The bilayer thin films were c-axis oriented with a transition temperature, Tco, of 88.5 K for YBCO and 18.5 K for NCCO. Supercurrent was observed across the interface of the YBCO and NCCO superconducting layers, indicating the phase coherence between these superconductors.
Epitaxial YBa2Cu3O7−y bolometers on micromachined windows in silicon wafers
Authors: Li Q. , Fenner D. B. , Hamblen W. D. , Hamblen D. G.
Published: July 2002

Epitaxial YBCO thin-film bolometers have been successfully fabricated on thin Si(100) substrates. Substrates included prethinned wafers ranging from 400 μm down to 4 μm thick, and a window, 0.75 μm thick, micromachined into a 400-μm wafer. As the Si is made thinner, the speed and responsivity both improve considerably. A 500-μs rise time was achieved on the micromachined window bolometer (0.75-μm-thick Si) under chopped infrared illumination. Calculations of heat flow in Si windows are in excellent agreement with the observed window-bolometer response waveform.
Monte Carlo calculation of electron relaxation times in perfect and disordered quantum wire laser structures
Authors: Vurgaftman Igor , Singh Jasprit
Published: July 2002

We calculate the electron relaxation times in GaAs quantum wires of 100×100 Å and 200×200 Å cross sections by a Monte Carlo simulation with the inclusion of electron-phonon and electron-electron interactions for the wire band structure computed by solving the one-band Schrödinger equation with and without structural disorder at the wire interface. The electron relaxation time is found to be greater than a hundred picoseconds for the 100×100 Å wire, while it is approximately 10 ps for the wire with the 200×200 Å cross section with the results converging to the case of bulk material for increased wire cross section. The influence of disorder on carrier relaxation in quantum wires is found to be negligible. The unusually slow carrier equilibration process is attributed to the combined effect of the sharply peaked one-dimensional density of states and the absence of randomizing intrasubband carrier-carrier scattering processes in quasi-one-dimensional systems. The dependence of electron relaxation times on the size of the quantum wire appears to be extremely sensitive.
Photoinduced refractive index change in a photoconductive electro-optic polymer
Authors: Kawakami T. , Sonoda N.
Published: July 2002

We report the photorefraction in polymeric materials such as a polyvinylcarbazole doped with nonlinear optical dye and a copolymer of a NLO dye-pendant monomer and a monomer with carbazolyl group. In the latter polymer, diffraction efficiency was on 10−6 order, the change of the refractive index was reversible and its decay was accelerated by photoirradiation. The observed photorefraction was mainly due to the molar refraction change of carbazolyl groups caused by photoinduced ionization, and this is evidence that trapped ion radicals exist in the polymer forming grating, which is necessary for the real photorefractives.
Kinetics of recovery of the light-induced defects in hydrogenated amorphous silicon under illumination
Authors: Gleskova H. , Morin P. A. , Wagner S.
Published: July 2002

The results of a study of the kinetics of the light-induced annealing of defects in hydrogenated amorphous silicon (a-Si:H) are presented. Our results show that at temperatures between 92 and 152 °C illumination increases the rate of annealing compared to annealing in the dark. The rates of annealing in the dark and under illumination exhibit the same functional dependence on the defect density. This observation suggests that the mechanisms for ‘‘dark’’ and ‘‘light’’ annealing are identical.
Long range disordering of GaAs-AlGaAs multiquantum wells by isoelectronic antimony implants
Authors: Rao E. V. K. , Juhel M. , Krauz Ph. , Gao Y. , Thibierge H.
Published: July 2002

We show here for the first time that the width of implant damage disordered regions in GaAs-AlGaAs MQWs can be extended to depths as far as ∼30 times the implant projected range (Rp). This is accomplished by performing room-temperature implants of isoelectronic Sb+ (Rp∼0.09 μm) in thick 130 period multiquantum well structures consisting of alternate layers of ∼100 Å GaAs (Lz) and ∼100 Å Al0.3Ga0.7As (Lb). Subsequent to high temperature (850 °C) and long duration (up to 4 h) furnace anneals, the disordering has been monitored using photoluminescence spectroscopy and secondary ion mass spectroscopy for depth dependence. The data is tentatively explained assuming a long range migration of defects both during implantation and annealing processes.
Chemically deposited epitaxial Si1−xGex thin film growth at atmospheric pressure
Authors: Kühne H.
Published: July 2002

A so-called ‘‘three-partial-rates’’ model of Si1−x Gex chemical vapor deposition that describes total growth rate as well as layer composition is applied to experimental data obtained at atmospheric pressure in hydrogen along with germane. The kind of silicon source gas was varied in that investigation using silane, dichlorosilane, and disilane, whereas all the other deposition conditions were maintained constant. Theoretical expectations drawn on the background of the above model agree fairly well with the experimental findings. All the experimental results this letter is related to were independently obtained and published [T. I. Kamins and D. J. Meyer, Appl. Phys. Lett. 61, 190 (1992)].
Fabrication of periodic domain inversion in an x-cut LiTaO3
Authors: Mizuuchi Kiminori , Yamamoto Kazuhisa , Sato Hisanao
Published: July 2002

We report on the fabrication of periodic domain inversion on the x face of LiTaO3 by selective proton exchange and quick heat treatment. Observation of domain formation in –c-cut LiTaO3 indicates an inside field model where electric field caused by proton diffusion reverses the orientation of domains. Based on this model, it has been found that an effective inside field to form domain inversion is also induced in x-cut LiTaO3 by using selective proton exchange. Accordingly, periodic domain inversion at 10 μm intervals has been successfully formed on the x face of LiTaO3.
Raman scattering from square profile, sinusoidal profile, and tilted AlxGa1−xAs/AlyGa1−yAs superlattices
Authors: Johnson F. G. , Wicks G. W.
Published: July 2002

The Al-like and Ga-like longitudinal optic phonons from square profile, sinusoidal profile, and tilted AlxGa1−xAs/AlyGa1−yAs superlattices are examined using Raman spectroscopy. The Raman spectrum from a superlattice with a square composition profile and an Al composition modulation of 18% (x−y=0.18) exhibits Al- and Ga-like longitudinal optic phonon peaks that are doublets. These doublets are no longer resolvable for a square profile superlattice with a 10% composition modulation (x−y=0.1), and the spectrum contains only single, broadened Al- and Ga-like longitudinal optic phonon peaks. The spectra from sinusoidal profile superlattices also exhibit single, broadened phonon peaks for composition modulations that are less than or equal to 22% (x−y≤0.22). The spectrum of a tilted superlattice is similar to that of a square profile superlattice with a 10% composition modulation and to that of a sinusoidal profile superlattice with a composition modulation of 16%. The assignment of the sinusoidal profile with a 16% composition modulation to the tilted superlattice is consistent with a previous photoluminescence study of tilted superlattices.
X-ray diffraction investigation of single step and step-graded SiGe alloy buffers for the growth of short-period SimGen superlattices using reciprocal space mapping
Authors: Koppensteiner E. , Hamberger P. , Bauer G. , Pesek A. , Kibbel H. , Presting H. , Kasper E.
Published: July 2002

Double crystal and triple axis x-ray diffractometry was used to characterize the structural properties of short period Si6Ge4 superlattices grown by molecular beam epitaxy on either a thin (20 nm) single step Si0.6Ge0.4 alloy buffer or on a thick step-graded Si1−xGex(0<x<0.4, 700 nm thick) buffer followed by a 550 nm Si0.6Ge0.4 layer. Reciprocal space maps around the (004) and (224) reciprocal lattice points yield direct information on the strain status of the buffer and superlattice layers. For the thick step-graded buffer indeed all layers with different Ge content are fully relaxed and thus the growth of an almost freestanding superlattice is possible.
Experimental proof for nanoparticle origin of photoluminescence in porous silicon layers
Authors: Koós Margit , Pócsik István , Vázsonyi Éva B.
Published: July 2002

A series of nonlinear phenomena in the excitation intensity dependence of photoluminescence (PL) was observed in porous silicon (PS) at room temperature. From a low level of excitation, the blue shift of the PL spectra was detected followed by complete saturation of the integrated PL intensity, without detectable change in the spectral position. This behavior may well be experimental proof of the nonparticle origin of PS light emission.
Gas phase reactions of trimethylamine alane in low pressure organometallic vapor phase epitaxy of AlGaAs
Authors: Pitts B. L. , Emerson D. T. , Shealy J. R.
Published: July 2002

We have investigated the effects of gas phase reactions between trimethylamine alane (TMAA), triethylgallium (TEG), and arsine on AlxGa1−xAs films grown by low pressure organometallic vapor phase epitaxy. The reactor used in this study provides for independent observation of the effects of TEG-TMAA and TMAA-arsine gas phase reactions. Gas phase reactions involving TMAA and TEG result in the formation of nonvolatile compounds upstream, which condense on the reactor wall, resulting in a reduction of growth rate and a degradation of the deposition uniformity. The TMAA-arsine reaction produces a compositional dependence on the gas phase stoichiometry (V/III ratio). Both of these effects are more severe for higher TMAA fluxes. High quality AlGaAs with excellent thickness and compositional uniformity was produced by spatially separating the TMAA and TEG in the gas phase which minimizes the parasitic reactions.
Metalorganic chemical vapor deposition of double-sided YBa2Cu3O7 thin films
Authors: DeSisto W. J. , Newman H. S. , Henry R. L. , Cestone V. C.
Published: July 2002

Thin films of YBa2Cu3O7−δ were deposited on both sides of (100) LaAlO3 substrates by metalorganic chemical vapor deposition. Using a gold-coated wafer carrier, improvements in both the transition temperature and critical current density of the film exposed to the carrier (first side) were demonstrated. Tc’s of 86–88 K and Jc’s≥106 A/cm2 at 77 K were achieved. The microwave surface resistance of both sides of double-sided samples measured at 77 K was approximately 8 mΩ at 36 GHz, scaling to less than 700 μΩ at 10 GHz.
X-ray photoelectron spectroscopic studies of the chemical nature of as-prepared and NaOH-treated porous silicon layer
Authors: Murakoshi Kei , Uosaki K.
Published: July 2002

The effect of various surface treatments of a porous silicon layer (PSL) including etching in NaOH solution on the chemical nature of the surface was studied using x-ray photoelectron spectroscopy. As-prepared PSL, which is formed by anodic oxidation of silicon in ethanolic HF solution, is covered with silicon oxide. NaOH treatment removes the surface oxide almost completely. Chemical states of surface silicon at the NaOH-treated PSL surface are very close to that at the HF-treated silicon surface. Surface oxygen on the NaOH-treated PSL surface seems to be in the form of Si-OH.
Demonstration of a new tool for degradation of amorphous hydrogenated silicon and the importance of the Fermi level shift
Authors: Kočka J. , Štika O. , Klíma O.
Published: July 2002

We introduce the pulsed Ruby laser as a new efficient degradation tool for amorphous hydrogenated silicon (a-Si:H). We present the degradation dynamics and the saturated values of the density of states (DOS) and the room temperature conductivity. Comparison of two samples with different impurity content indicates the impurity-related initial Fermi level shift. By a simple model we illustrate the influence of this shift on the initial stage of degradation (its acceleration or delay) and consequently, also on the saturated DOS.
Correlation of optical and structural properties of light emitting porous silicon
Authors: Lee H.-J. , Seo Y. H. , Oh D.-H. , Nahm K. S. , Suh E.-K. , Lee Y. H. , Lee H. J. , Hwang Y. G. , Park K.-H. , Chang S. H. , Lee E. H.
Published: July 2002

Microscopic structures of light emitting porous silicon layers have been studied. The samples prepared in an aqueous HF solution by anodizing p-type silicon substrates show a strong positional dependence of photoluminescence and Raman spectra. The photoluminescence peaks are broad around 1.8 eV, where the photoluminescence intensities are comparable to that of GaAs at 5 K. We have found from Raman studies showing two characteristic peaks at 500 and 520 cm−1 that microscopic structures reveal gradual changes from porous silicon to a mixture of polycrystalline and hydrogenated amorphous phases as the probing spot is moved to the edge of the sample. This is explained by the redeposition of silicon atoms on top of the porous silicon layers near the edge of the sample as a result of liquid flow caused by bubbles of hydrogen gas which was produced near the surface of the sample during the anodization process.
Distributed-Bragg reflectors and 90° couplers for cylindrical wave devices
Authors: Jiang Yuan , Hacker Jill
Published: July 2002

Multilayer reflectors for cylindrical waves, and grating distributed reflectors and 90° couplers for guided cylindrical waves, are important components for optical devices. We find that the spacings of the multilayers and grating steps should not be multiple of a quarter wavelength as suggested by the periodic-phase-change argument. We outline the design principles for these components. Explanations and solutions to the skewed-wave pattern and multimode-lasing problems observed in the concentric-circle-grating-laser experiments are provided.
Diode-laser-pumped InGaAs/GaAs/AlGaAs heterostructure lasers with low internal loss and 4-W average power
Authors: Le H. Q. , Goodhue W. D. , Maki P. A. , Cecca S. Di
Published: July 2002

Optically pumped InGaAs/GaAs/AlGaAs heterostructure lasers exhibit differential quantum efficiencies that are not sensitive to output coupling or active length, indicating low free carrier absorption loss. A broad-stripe 2.5-mm-long device yielded 4-W average power and 20-W peak power.
Rapid thermal annealing of Si-implanted GaAs using the Ga-doped spin-on glass films
Authors: Nishitsuji Mitsuru , Tamura Akiyoshi
Published: July 2002

We have studied rapid thermal annealing (RTA) of Si-implanted GaAs using Ga-doped spin-on glass (SOG) film for the first time. Three kinds of films such as Ga-doped SOG, undoped SOG, and SiO2 formed by the chemical vapor deposition (CVD) method were compared. The annealed GaAs layers were characterized by sheet resistance, capacitance-voltage (C-V), deep level transient spectroscopy (DLTS), and photoluminescence (PL) measurements. The secondary ion mass spectroscopy (SIMS) measurement was also performed to investigate the atomic behavior at the insulating film/GaAs interface during annealing. Ga-doped SOG film as an anneal cap of GaAs offers activation efficiency as compared with CVD-SiO2 and undoped SOG film. The PL spectra for the annealed sample with Ga-doped SOG cap exhibited the lowest intensity at 1.36 eV broad band emission, which suggests the suppression of the generation of Ga-vacancy related acceptor level during annealing.
Photosensitive Coulomb blockade in semiconductor p-n tunnel diodes
Authors: Hess K. , Holonyak N. , Richard T. A.
Published: July 2002

Data and arguments are presented identifying the old phenomenon (1960) of the ‘‘zero-bias anomaly’’ in III-V semiconductor p-n tunneling as a manifestation of the Coulomb blockade. Tunneling involving a Au-Ge complex in GaAs, which acts as a photosensitive ‘‘quantum dot’’ controlling the p-n tunneling, provides the basis for a light-sensitive Coulomb blockade and serves also as a model, an explanation, for the zero-bias anomaly (V=0) observed in III-V p-n tunneling.
Electronic structure of periodic random superlattice [(GaAs)m/(AlAs)n]l
Authors: Wang E. G. , Xu J. H. , Su W. P. , Ting C. S.
Published: July 2002

The electronic structure of a realistic three-dimensional periodic random superlattice (SL) [(GaAs)m/(AlAs)n]l are calculated for the first time using the large-cluster recursion method within the tight-binding framework. It is found that the localized valance band-tail states of the random SL, which are almost independent of the AlAs concentration, extend to the band-gap region of the corresponding ordered SL. The central peaks in the Al s and Ga s states which vary with the Al concentration are studied, and comparison with the alloy AlxGa1−xAs is made. Our results provide a guide to the band-gap engineering of the random superlattices.
Morphology of molecular beam epitaxy grown NiAl on GaAs studied by scanning tunneling microscopy
Authors: Hirono S. , Tanimoto M. , Takigami T. , Osaka J. , Inoue N.
Published: July 2002

Extended terraces, steps along the 〈110〉 directions, and trenches between the terraces were observed on 100 nm thick NiAl films grown on GaAs by molecular beam epitaxy at 600 °C. Atomically smooth surfaces as large as 100 nm across could be obtained at this growth temperature, but at 450 °C, mounds rather than terraces were formed. We propose models for the formation of these features.
High-quality resonant tunneling through a random multibarrier superlattice
Authors: Xiong Shijie
Published: July 2002

The transmission of electrons through a random array of a number of identical multibarriers has been studied. Although most of the electrons are reflected by such a random structure, there still exist electrons with special energies which are completely unscattered. This produces a high-quality resonant tunneling with a peak transmission coefficient much narrower than that of the tunneling through a single double barrier. The current-voltage characteristics of this structure are calculated and the special negative differential conductivity is exhibited.