bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical bistability in an InGaAs/InP multiple quantum well waveguide Fabry–Perot cavity
Authors: Ehrlich J. E. , Neilson D. T. , Walker A. C. , Kennedy G. T. , Grant R. S. , Sibbett W. , Hopkinson M. , Pate M.
Published: July 2002

We report measurements of quasi-cw optical bistability in an InGaAs/InP multiple quantum well waveguide Fabry–Perot cavity at 1.47 μm wavelength. This operating wavelength is detuned from the band-edge resonance by 0.07 μm, where an enhanced free-carrier contribution to the nonlinear refractive index due to 2D confinement of carriers in the quantum wells accounts for the large index variations. The effect of any thermally induced nonlinear response is negligible.
Intrasubband plasmons in delta-doped InGaAs single quantum wells
Authors: Peng L. H. , Fonstad C. G.
Published: July 2002

Polarization-resolved infrared techniques have been applied to study the optical properties of the quasi-two-dimensional electron gas in doped InGaAs quantum wells and to show that inter- and intrasubband processes can be distinguished by their polarization sensitivity. Distinct excitations of inter- and intrasubband transitions at the Γ(q=k=0) point in delta-doped narrow InGaAs/AlAs single quantum wells were resolved through the use of quantum well structures designed to increase their energy difference and thus diminish the coupling between these two processes. Longitudinal qz intrasubband plasmons were observed at 1550 cm−1 and were excited by transverse-magnetic (TM) polarized light; the intersubband transitions occurred at around 4000 cm−1 and were both transverse-electric (TE) and TM polarization active.
Beryllium δ doping studies in InP and Ga0.47In0.53As during metalorganic molecular beam epitaxy
Authors: Ritter Dan , Hamm R. A. , Panish M. B. , Geva M.
Published: July 2002

A secondary ion mass spectroscopy study of δ and bulk doped layers demonstrates that the incorporation efficiency of Be in Ga0.47In0.53As and InP during metalorganic molecular beam epitaxy is much lower than unity. This effect is attributed to the removal of Be atoms from the surface by the organic gases in the growth chamber. The upper limit for δ doping of Ga0.47In0.53As before the onset of diffusion is 7×1012 cm−2, and in InP it is less than 5×1011 cm−2.
Effects of electron-beam-assisted dry etching on optical and electrical properties
Authors: Watanabe Heiji , Ochiai Yukinori , Matsui Shinji
Published: July 2002

The degree of damage induced by electron-beam (EB)-assisted dry etching is optically and electrically characterized and compared with ion-beam-assisted etching (IBAE). The optical and electrical damage are evaluated using the photoluminescence (PL) from GaAs/AlGaAs quantum well (QW) structures and the Hall effect in two-dimensional electron gas (2DEG) heterostructures, respectively. These layered samples are etched by a newly proposed EB-assisted selective dry etching technique using Cl2 and SF6 gases. EB-assisted dry etching is proven to produce no degradation of either type of property, whereas a 54% reduction in PL intensity from a 30-nm-deep QW and 8% reduction in Hall mobility in a 51-nm-deep 2DEG are observed for IBAE.
Evidence for hydrogen accumulation at strained layer heterojunctions
Authors: Sobiesierski Z. , Clegg J. B.
Published: July 2002

The incorporation of hydrogen into strained InxGa1−xAs/GaAs quantum wells results in the formation of shallow, H-related radiative states which compete with, and quench, the intrinsic band-to-band luminescence. By comparing the photoluminescence data obtained from hydrogenated material with secondary ion mass spectroscopy profiles from deuterated material, it is possible to deduce that the H-related radiative states are associated with H which is accumulated at the well interfaces.
Proton exchanged depth determination in LiNbO3 from laser induced pyroelectric voltage measurements
Authors: Tuli Suneet , Bhattacharyya A. B.
Published: July 2002

We report a new nondestructive technique for the determination of depth of proton exchanged (PE) layers in LiNbO3. Relying on the difference in the magnitudes of measured pyroelectric voltages, induced by an intensity modulated laser beam, on the exchanged and unexchanged regions, the depth of the PE layer has been measured and corroborated by a conventional optical characterization method.
Dipole relaxation current in n-type AlxGa1−xAs
Authors: Scalvi L. V. A. , de Oliveira L. , Minami E. , Siu-Li M.
Published: July 2002

We report for the first time the thermally stimulated depolarization current (TSDC) spectrum for a direct band-gap AlGaAs sample, where the presence of DX centers is clearly observed by photoconductivity measurements. A TSDC band is obtained, revealing the presence of dipoles, which could be attributed to DX−-d+ pairs as indeed predicted by O’Reilly [Appl. Phys. Lett. 55, 1409 (1989)]. The data are fitted by relaxation time distribution approach yielding an average activation energy of 0.108 eV. This is the most striking feature of our data, since this energy has approximately the same value of the DX center binding energy.
Stoichiometry control over a wide composition range of sputtered CuGaxIn(1−x)Se2
Authors: Hernández-Rojas J. L. , Lucía M. L. , Mártil I. , González-Díaz G. , Santamaria J. , Sánchez-Quesada F.
Published: July 2002

Films of CuGaxIn(1−x)Se2 (CGIS) have been grown by rf sputtering from stoichiometric single targets with different Ga/In ratios. Adjusting growth temperature and argon pressure we are able to deposit films with a wide range of Cu contents: From CGIS Cu-poor (16 at. %) to Cu2Se. Reevaporation of (Ga,In)2Se3 binaries is observed when substrate temperature is increased at a constant argon pressure (20 mTorr). An increase in Ar pressure from 5 to 150 mTorr at a growth temperature of 450 °C, produces a decrease in Cu atomic percentage from 24% to 16% due to a preferential diffusion of Cu sputtered atoms in the plasma. The relevant film properties of the analyzed films are found to be ruled by the Cu content. Graded composition absorbers with adequate physical properties for the fabrication of photovoltaic devices are grown with a proper choice of growth parameters.
Single-domain layers formed in multidomain LiTaO3 by proton exchange and heat treatment
Authors: Åhlfeldt Henrik , Webjörn Jonas
Published: July 2002

Proton exchange and subsequent heat treatment can yield single-domain layers at the surfaces of initially multidomain z-cut LiTaO3. The thickness of these single-domain layers is equal to the thickness of the domain-inverted layer that the same processing parameters cause in initially single-domain samples. This letter also describes how the domain structure develops when heat treatment is carried out above the Curie temperature. The results are discussed in relation to a recently proposed model for the domain-inversion mechanism.
Demonstration of high energy extraction efficiency in a laser-diode pumped high gain Nd:YAG regenerative amplifier
Authors: Naito Kenta , Ohmi Masato , Ishikawa Koji , Akatsuka Masanori , Yamanaka Masanobu , Nakatsuka Masahiro , Nakai Sadao , Sato Tsuyoshi
Published: July 2002

High energy extraction efficiency of 48±4% for the cavity mode cross section (17.5%±1% for the entire lasant cross section) and high energy gain of 71±1 dB have been demonstrated simultaneously, for the first time, in a laser-diode pumped Nd:YAG regenerative amplifier (RA). The RA was operated at an initial small-signal gain of 3.15±0.20, an input pulse energy of 0.5±0.1 nJ (pulse width of 910±12 ps), an amplified output pulse energy of 6.0±0.3 mJ (pulse width <1 ns), and a repetition rate of 50 Hz. The dependence of energy extraction efficiency on initial small-signal gain of the RA was shown to be well fitted with the theory of Lowdermilk and Murray [J. Appl. Phys. 51, 2436 (1980)].
Influence of Ag-Au and Ag-Cu alloys on Bi2Sr2CaCu2Ox superconductor
Authors: Nomura K. , Sasaoka T. , Sato J. , Kuma S. , Kumakura H. , Togano K. , Tomita N.
Published: July 2002

The influence of Ag-Au and Ag-Cu alloy substrates on the microstructure and superconducting properties of Bi2Sr2CaCu2Ox (Bi-2212) was studied. The critical current density (Jc) of Bi-2212/(Ag-Au) was not degraded by increasing the Au content of the Ag-Au alloy, while the Jc of Bi-2212/(Ag-Cu) was drastically degraded by increasing the Cu content of the Ag-Cu alloy. The microstructure of Bi-2212 on the Ag-Au alloy was uniform and no precipitates were observed. The Jc degradation of Bi-2212 in contact with the Ag-Cu alloy was understood by the fact that Cu absorption of Bi-2212 from the Ag-Cu alloys changed the composition of the oxide layer. Ag-Au alloys are superior substrate materials for Bi-2212 for power current leads for superconducting magnets, taking into account their low thermal conductivity.
N+-implantation induced enhanced adhesion of amorphous-SiC films deposited on stainless steel
Authors: Laidani Nadhira , Miotello Antonio , Guzman Luis , Calliari Lucia
Published: July 2002

Amorphous a-SiC films were deposited by rf magnetron sputtering on stainless steel and N+ implantations were performed at room temperature over a fluence range of 1×1016–1×1017 ions/cm2 at 30 and 160 keV. Chemical characterization of the a-SiC/steel interface and compositional depth profiles were obtained by Auger electron spectroscopy. Adhesion properties of the films were examined using a scratch tester in conjunction with scanning electron microscopy. A strong adhesion enhancement (about a factor of eight) along with an improvement of the fracture toughness were observed in the implanted a-SiC/steel specimens. The key mechanisms envisaged to explain the enhanced adhesion is mainly related to the new chemical bondings, involving C and N in Si—(N,C)—Cr complexes formation at the a-SiC/steel interface.
Electroluminescence spectroscopy of resonantly coupled GaAs-AlAs superlattices
Authors: Bertram D. , Lage H. , Grahn H. T. , Ploog K.
Published: July 2002

The resonant coupling of different electronic subbands between adjacent wells in GaAs-AlAs superlattices is investigated with electroluminescence (EL) spectroscopy as a function of the applied forward bias. The EL efficiency, i.e., the EL intensity normalized to the current, exhibits a resonant behavior. An efficient occupation of the second subband by sequential resonant tunneling is observed at higher bias.
Field-induced metastable states in ultrathin films of fcc Fe/Cu(100)
Authors: Hembree G. G. , Drucker Jeff , Healy S. D. , Heim K. R. , Yang Z. J. , Scheinfein M. R.
Published: July 2002

The thickness dependence of both the perpendicular and in-plane magnetization is observed for pseudomorphic ultrathin, fcc Fe epitaxial films grown on room temperature Cu(100). Ferromagnetically ordered 3.5-monolayer-thick films display both in-plane and perpendicular remanence. Perpendicular remanence, lost after a 9.0 kOe static field is applied perpendicular to the film plane, can be restored by either heating or applying large in-plane fields. These field-induced metastable states are interpreted in terms of magnetoelastic effects which modify the exchange and anisotropy constants both perpendicular to and within the film plane.
Device model for pulsing in silicon p-i-n structures
Authors: Perera A. G. U. , Matsik S.
Published: July 2002

We report experimental data and modeling results based on device physics and circuit parameters for the spontaneous firing patterns for silicon p-i-n structures at 4.2 K controlled by a constant current source. The model provides insights into the sensitivity of the pulsing rate and explains the wide range of behavior observed. The knowledge on the effect of these parameters on pulsing is critical for designing uniform arrays, which will have a major impact on applications such as infrared detectors and neural net models. The model will also serve as the first step towards obtaining high temperature pulsing arrays using quantum well structures.
Ultrashallow p-type layer formation by rapid vapor-phase doping using a lamp annealing apparatus
Authors: Kiyota Yukihiro , Matsushima Masaru , Kaneko Yutaka , Kanetomo Masafumi , Tamaki Youichi , Muraki Kazuhiko , Inada Taroh
Published: July 2002

Ultrashallow p-type layers below 30 nm were formed by a rapid vapor-phase doping involving a lamp annealing system. A new one-wafer-type apparatus with tungsten lamps has been developed for use in this process. Temperatures at five different points on a 4-in. wafer are in situ monitored by infrared radiative thermometers with optical fibers to maintain a uniform temperature profile across the wafer. By using hydrogen and B2H6 gas, an ultrashallow boron-doped layer of below 30 nm with the surface boron concentration of 5.8×1019 cm−3 was formed after 10 s of 900 °C annealing with a B2H6 flow rate of 100 ml/min.
Towards magnetic centering of the discharge in a krypton flashlamp
Authors: Loveland D. G. , Candev N. , Marode E.
Published: July 2002

The filamentary surface discharge, which occurs in a 2 bar krypton flashlamp before complete breakdown of the whole gas volume, has been guided along a rectilinear path using an earthed, external strip conductor. It has then been pushed away from the tube wall with an impulsionally applied magnetic field of order 0.2 T, reaching the axis of the 5-mm internal diameter lamp in a time of less than 1 ms.
Analysis of origin of nonlinear gain in 1.5 μm semiconductor active layers by highly nondegenerate four-wave mixing
Authors: Kikuchi K. , Amano M. , Zah C. E. , Lee T. P.
Published: July 2002

The origin of the nonlinear gain effect in 1.5 μm semiconductor active layers is investigated by using highly nondegenerate four-wave mixing, where the pump-probe detuning is extended up to 2 THz. From the signal intensity measured as a function of the detuning frequency we find that both the spectral hole burning and the dynamic carrier heating contribute to the four-wave mixing. The dynamic carrier heating, however, creates the index grating rather than the gain grating, and hence, the spectral hole burning is the main origin of the nonlinear gain effect.
1.9 picosecond high-sensitivity sampling optical temporal analyzer
Authors: Chen Yi , Williamson Steve , Brock Tim
Published: July 2002

An all solid-state, high-sensitivity sampling optical temporal analyzer has been demonstrated by integrating two interdigitated picosecond metal-semiconductor-metal photodetectors into a coplanar transmission line structure. The full width at half-maximum of the response time is 1.9 ps. The noise equivalent optical power is 500 pW, and the dynamic range is more than 60 dB.
Morphology of plasma polymerized methyl methacrylate films
Authors: Li Guifang , Tobin Jeffrey A. , Denton Denice D.
Published: July 2002

The surface morphology of plasma polymerized methyl methacrylate films was investigated using atomic force microscopy. It was found that the plasma polymer surfaces consist of nanometer scale growth columns. The average grain size of the growth columns increases with deposition time. For the same deposition time, the average grain size is proportional to pressure and deposition power. It was deduced that microscopic properties of plasma polymers are not uniform through the bulk of the plasma polymer films even though the external deposition parameters are held constant.
Structural characterization and microwave loss of Nd1.85Ce0.15CuO4−y superconducting thin films on yttria-stabilized zirconia buffered sapphire
Authors: Mao S. N. , Xi X. X. , Mao Jian , Wu D. H. , Li Qi , Anlage S. M. , Venkatesan T. , Beesabathina D. Prasad , Salamanca-Riba L. , Wu X. D.
Published: July 2002

We have grown superconducting Nd1.85Ce0.15CuO4−y (NCCO) thin films on (11̄02) sapphire using a yttria-stabilized zirconia (YSZ) buffer layer, which has been demonstrated to be the best material for the growth of n-type superconducting NCCO thin films. The films are c-axis oriented, epitaxially grown with a small mosaic spread of 0.2° and a Rutherford backscattering spectroscopy channeling yield of ∼9%. Cross-sectional transmission electron microscopy images reveal a sharp interface between NCCO and YSZ. The microwave surface resistance of NCCO films on YSZ buffered sapphire at 9.6 GHz is only 80 μΩ at 4.2 K in zero magnetic field, which is comparable to Y1Ba2Cu3O7−y films at similar reduced temperature, as a consequence of the decrease of structural imperfection in the film. The temperature dependence of the surface resistance and magnetic penetration depth in these films further confirms the s-wave BCS nature of NCCO.
Improved modulator characteristics using tensile strain in long-wavelength InGaAs/InGaAsP multiple quantum wells
Authors: Tütken T. , Hawdon B. J. , Zimmermann M. , Queisser I. , Hangleiter A. , Härle V. , Scholz F.
Published: July 2002

We have measured the field dependent Stark shift and exciton oscillator strength in tensile strained, compressively strained, and unstrained 1.5 μm InGaAs/InGaAsP modulator structures. We find that the exciton oscillator strength is much less field dependent for tensile strained structures, which operate at the light hole transition. We conclude that tensile strained structures should lead to improved modulator performance.
Direct observation of the etching of damaged surface layers from natural diamond by low-energy oxygen ion bombardment
Authors: Beerling T. E. , Helms C. R.
Published: July 2002

The interaction of oxygen ions with diamond surfaces is reported. Using electron energy loss spectroscopy (EELS), we found that 200 eV oxygen ion bombardment removed surface damaged layers (non-sp3 bonded), recovering diamond EELS features in the surface region, Higher-energy oxygen ion bombardment does not produce surfaces as ideal as the 200 eV case. The oxygen surface concentration after the 200 eV oxygen ion irradiation, examined using Auger electron spectroscopy, was determined to be ∼1×1015 cm−2.
Analysis of normal-incident absorption in a proposed p-type very-narrow-quantum-well infrared photodetector
Authors: Man P. , Pan D. S.
Published: July 2002

A p-type very-narrow-quantum-well infrared photodetector is proposed and studied in this letter. Direct transitions between extended-state heavy-hole-like subbands and bound-state light-hole-like subbands are utilized. A first-principles k⋅p calculation of normal-incident absorption is performed with no adjustable parameter. Despite quantum wells only 17 Å wide, integrated absorption is found to be stronger in the proposed structure (at T=77 K, from λ=8 μm to λ=10 μm) than in a conventional p-type quantum-well infrared photodetector with the same cutoff wavelength. The integrated responsivity is estimated to be more than twice as high, while the integrated shot-noise-limited detectivity can be improved by a factor of 2. The proposed structure may also be implemented as a two-color photodetector.
High-resolution x-ray characterization of low-temperature GaAs/As superlattice grown by molecular-beam epitaxy
Authors: Cheng T. M. , Chang C. Y. , Chang T. C. , Huang J. H. , Huang M. F.
Published: July 2002

High-resolution x-ray analysis of Si delta-doped GaAs grown by molecular-beam epitaxy at a low substrate temperature (230 °C) is presented. Superlattice satellite peaks in the rocking curve are observed for the sample annealed at 700 °C for 10 min. The peak intensity increases with increasing postgrowth annealing temperature and reaches the maximum value for the 900 °C annealed sample. The evolution of the x-ray rocking curves can be explained consistently by the formation of a GaAs/As superlattice during the annealing period based on the transmission electron microscope observations.
Giant capacitance oscillations related to the quantum capacitance in GaAs/AlAs superlattices
Authors: Zhang Yaohui , Li Yuexia , Jiang Desheng , Yang Xiaoping , Zhang Penghua
Published: July 2002

We have observed periodic current and capacitance oscillations with increasing bias on doped GaAs/AlAs superlattices at a temperature of 77 K. The maximum of the observed capacitance is larger than usual geometric capacitances in superlattices, being comparable to the quantum capacitance of the two-dimensional (2D) electron system proposed by Luryi. A model based on well-to-well sequential resonant tunneling due to the movement of the boundary between the electric field domains in superlattice was proposed to explain the origin of the giant capacitance oscillations. It was demonstrated that the capacitance at the peaks of capacitance-voltage (C-V) characteristics reflects the quantum capacitance of the space-charge region at the boundary between the domains (a novel 2D electron system).
Doubly resonant second harmonic generation of 2.0 μm light in coupled InGaAs/AlAs quantum wells
Authors: Chui H. C. , Martinet E. L. , Woods G. L. , Fejer M. M. , Harris J. S. , Rella C. A. , Richman B. I. , Schwettman H. A.
Published: July 2002

We demonstrate intersubband absorption and second harmonic generation (SHG) in asymmetric coupled In0.6Ga0.4As/AlAs n-type quantum wells (QWs) grown on a GaAs substrate. Intersubband absorption at 4.1 and 2.1 μm wavelengths, corresponding to the 1 to 2 and 1 to 3 transitions, respectively, are observed. SHG of 2.0 μm light is demonstrated in this doubly resonant QW. This is the shortest wavelength SHG to date in any n-type QW system. The second order nonlinear susceptibility χ(2) is measured using a free electron laser by interference of the second harmonic fields from the QW and substrate. At a pump wavelength of 4.0 μm, a large asymmetry in the SHG power with rotation angle of the sample arising from SHG from the QW is observed, and a χ(2) of magnitude 20±8 nm/V, approximately 100 times that of bulk GaAs, and phase 63°±34° relative to the GaAs substrate is measured. Comparison of both the linear and nonlinear properties to a simple model is discussed.
Generation of high repetition rate far-infrared laser pulses
Authors: Mueller E. R. , Wilson T. E. , Waldman J. , Kennedy J. T. , Hart R. A.
Published: July 2002

We report the generation of pulsed optically pumped far-infrared (FIR) radiation with a repetition rate of 200 kHz. These pulses were obtained in a straightforward method by pumping a FIR resonator with a high repetition rate, rf-excited, waveguide CO2 laser. Pulses approximately 50 ns wide were generated both at 432.6 μm in HCOOH, and 117.7 μm in CH2F2. The pulse width of the FIR radiation was studied as a function of the CO2 pulse width, and the relative delay between the two was measured. Based on this data we conclude that the FIR radiation was gain switched and of a duration which was a function of either the gain bandwidth of the FIR transition, or more likely the FIR cavity parameters.
Scanning tunneling microscopy observation of hydrogen-terminated Si(111) surfaces at room temperature
Authors: Usuda K. , Kanaya H. , Yamada K. , Sato T. , Sueyoshi T. , Iwatsuki M.
Published: July 2002

Scanning tunneling microscopy has been applied to observe hydrogen-terminated Si(111) surfaces at room temperature. A clear image was easily observed for a Si surface prepared by rinsing in pure water with very low dissolved oxygen after removal of native oxide by 1% HF solution dipping. A smooth surface in an atomic scale was exhibited in a 50×50 nm area. Completely triangular-shaped holes were observed on the surface. The holes were surrounded by steps which were very likely directed toward 〈112̄〉. The treatment of the surface was remarkably stable even after a 3 h air exposure. Furthermore, nm size pits were found at the bottom part of the triangular-shaped holes. The results imply that the nm size pits appeared to be due to microdefects and that the pits might be the origin of surface etching at the Si surface.
Temperature and carrier density dependence of mobility in a heavily doped quantum well
Authors: Somerville Mark H. , Greenberg David R. , del Alamo Jesús A.
Published: July 2002

Interest in heterostructure field-effect transistors (HFETs) utilizing narrow, heavily doped channels motivates a study of mobility in heavily doped quantum wells. We have measured electron mobility as a function of carrier concentration and temperature in an In0.15Ga0.85As quantum well with a doping of ND=6×1012 cm−2. Mobility is found to rise significantly as the ratio of electron to impurity concentration increases. Even at T=300 K, μ climbs by nearly a factor of 2 as carrier concentration in the well is increased from 1×1012 to 5×1012 cm−2. The results agree qualitatively with recently published theoretical predictions, and suggest that device models utilizing constant mobility are not appropriate for HFETs using doped two-dimensional channels.
Far-infrared study of a quasi-one-dimensional electron gas formed by molecular beam epitaxial regrowth on patterned GaAs
Authors: Arnone D. D. , Burroughes J. H. , Pepper M. , Grimshaw M. P. , Ritchie D. A. , Jones G. A. C.
Published: July 2002

A quasi-one-dimensional electron gas has been realized by using molecular beam epitaxy to grow a high electron mobility transistor (HEMT) on a patterned GaAs structure consisting of alternate layers of p-GaAs and n-GaAs. Independently contacting the p-GaAs and n-GaAs creates a patterned backgate, which is used to electrostatically induce a lateral modulation of the electron gas in the HEMT. Far-infrared cyclotron resonance spectra demonstrate that lateral confinement energies over the range 1.3–3.3 meV may be selected via tuning of the biases applied to the p-GaAs and n-GaAs layers.
High uniformity of threshold voltage for GaAs/AlGaAs high electron mobility transistors grown on a Si substrate
Authors: Aigo Takashi , Jono Aiji , Tachikawa Akiyoshi , Hiratsuka Ryuichi , Moritani Akihiro
Published: July 2002

We report on a study of microscopic distribution of threshold voltage ( Vth) for GaAs/AlGaAs high electron mobility transistors (HEMTs) on a Si substrate grown by metal-organic chemical vapor deposition (MOCVD). Using selective dry etching, the superior microscopic distribution of Vth comparable to that for GaAs substrates is obtained, namely the standard deviation of threshold voltage (σ Vth) of 8.96 mV with the Vth of −101.3 mV for 150 points of the HEMT in a 1.95×1.9-mm2 area. From the evaluation of macroscopic (full wafer) and microscopic Vth distribution, high-density dislocations in the GaAs/Si are found not to affect the uniformity of Vth. This result indicates that HEMT/Si technology has a potential to lead the GaAs/Si to GaAs integrated circuit applications in which large-diameter wafers are beneficial.
Theoretical study on threshold energy and impact ionization coefficient for electrons in Si1−xGex
Authors: Yeom Keesoo , Hinckley John M. , Singh Jasprit
Published: July 2002

Threshold energy and electron impact ionization coefficients (α) are calculated for unstrained and strained Si1−xGex on {100} silicon substrate using nonparabolic and ellipsoidal band structure for conduction band and k⋅p method for valence band. The threshold energy in the unstrained Si1−xGex is smaller than that in pure silicon due to the reduced band-gap energy. The strain causes band degeneracy lifting for both the conduction band and valence band. It gives an additional band-gap narrowing which leads to a much smaller threshold energy. On the basis of these results, the electron impact ionization coefficient is estimated up to 30% germanium using a Monte Carlo simulation. The reduced threshold energy is found to be the most dominant factor in determining α in the strained Si1−xGex. As a result, the strained Si1−xGex has much larger α than pure silicon while the unstrained Si1−xGex does not due to the effect of alloy scattering and the relatively small change of the threshold energy.
Very long-wavelength GaAs/AlxGa1−xAs infrared hot electron transistor
Authors: Gunapala S. D. , Park J. S. , Lin T. L. , Liu J. K. , Bandara K. M. S. V.
Published: July 2002

We have demonstrated a bound-to-continuum state GaAs/AlxGa1−xAs infrared hot electron transistor which has a peak response at λp=16.3 μm. This device utilizes a bound-to-continuum quantum well infrared photodetector as a photosensitive emitter and a wide AlxGa1−xAs barrier between the base and the collector as an energy discriminating filter. An excellent photocurrent transfer ratio of αp=0.12 and very low dark current transfer ratio of αd=7.2×10−5 is achieved at a temperature of T=60 K.
New superconducting three-terminal device based on externally controlled critical currents
Authors: Downar H. , Peterreins Th. , Scherber W. , Ziemann P.
Published: July 2002

It is demonstrated that at 4.2 K the critical current Ic of a superconducting Nb micro (μ) bridge (typical thickness 30 nm, length 200 μm, width 10 μm) can be reversibly varied over a wide range by applying electrical fields of the order of 108 V/m at an insulated gate prepared on top of the Nb μbridge. The preparation and the electrical characteristics of these metal/insulator/superconductor field effect transistor-like devices of the type M/NbOx/Nb, where M represents Al, Au, or Nb gate metals, are described. Additional experiments in external magnetic fields revealed that the gate-controlled effect on Ic is based on depinning due to an electric field-induced ‘quasimetallic’ state of the typically 10-nm-thick NbOx. Under optimized conditions, a gate power of less than 200 μW is needed to switch the superconducting Nb μbridge into the normal conducting state.
Observation of optical response of avalanche photodiodes at photon-counting light levels
Authors: Hunt J. H. , Holmes R. B.
Published: July 2002

We have demonstrated all-optical spatial light modulation at photon-counting light levels. Modulation is performed with a silicon avalanche photodiode operating as a Fizeau interferometer with optical thickness modulated by optically initiated, avalanche-induced heating. Modulation of 32% is achieved with off-the-shelf devices with writing beams using as few as 10 photons per pulse. The results represent the first spatially and temporally resolved measurements of avalanche breakdown.
Activation energy for Ostwald ripening of Al2Cu in Al(4 wt. % Cu) thin films using a lateral diffusion couple
Authors: Colgan E. G.
Published: July 2002

The activation energy Ea for Ostwald ripening (coarsening) of Al2Cu(Θ phase) precipitates in Al(4 wt. % Cu) thin films was determined using a lateral diffusion couple. A 1 μm thick Al(4 wt. % Cu) blanket film was deposited on lines of Al2Cu embedded in SiO2. With annealing at temperatures between 400 and 450 °C (1.4–2.5 wt. % Cu in solution) for 1 to 80 h, Θ precipitates were dissolved in regions between 10 and 110 μm wide parallel to the Al2Cu lines. The width of this region increased as the square root of the annealing time. The Ea was determined to be 2.5±0.5 eV from an Arrhenius plot. This value is much larger than both the activation energies for Cu lattice and grain-boundary diffusion in Al. Understanding the coarsening kinetics of Al2Cu is important since the reliability of Al(Cu) metallizations is strongly dependent on the microstructure.
Threshold current density of strained InGaAs/InGaAsP quantum well lasers lattice matched to GaAs
Authors: Park Seoung-hwan , Jeong Weon-guk , Choe Byung-doo
Published: July 2002

The theoretical study on the threshold current density (Jth) of InxGa1−xAs/InGaAsP quantum well (QW) lasers lattice matched to GaAs is presented. The results are also compared with those of InxGa1−xAs/GaAs QW lasers. For relatively long cavity length (≳1000 μm), two lasers have similar values of the Jth for x<0.25, in particular, for the wavelength of 0.98 μm. On the other hand, for x≳0.25, InGaAs/InGaAsP lasers show lower values of the Jth than InGaAs/GaAs lasers for all cavity lengths. The results indicate that InGaAs/InGaAsP lasers are expected as a promising light source for optoelectronic applications.
Ultrafast dynamics of the optical mode of a 1.5 μm multiple quantum well optical amplifier
Authors: Botkin D. , Weiss S. , Sucha G. , Chemla D. S. , Wiesenfeld J. M.
Published: July 2002

Time-resolved measurements of the mode profile of semiconductor multiple quantum well amplifiers reveal ultrafast dynamic changes which contribute to the nonlinear gain of such devices.
GaAs-InGaAs quantum-well resonant-tunneling switching device grown by molecular beam epitaxy
Authors: Liu Wen-Chau , Guo Der-Feng , Yih Shiuh-Ren , Liang Jing-Tong , Liah Lih-Wen , Lyuu Gau-Ming
Published: July 2002

In this letter, a new switching device having a p-type delta-doped sheet in the center of an InGaAs-GaAs quantum well is presented. An N-shaped negative-differential-resistance (NDR) phenomenon resulting from the resonant tunneling effect through the miniband under a proper anode-to-cathode voltage is observed. From the experimental results, it is seen that the temperature plays an important role in the device operation.
Improved efficiency of crystalline silicon solar cells due to He+ implantation
Authors: Bruns J. , Seifert W. , Wawer P. , Winnicke H. , Bräunig D. , Wagemann H. G.
Published: July 2002

The influence of He+ implantation on the properties of crystalline silicon solar cells has been investigated. The implantation of 550 keV He+ ions into the masked surface of solar cells was used to form a two-dimensional defect layer inside the cell space-charge region. For suitable implantation doses it is possible to increase the photocurrent without degenerating the values for open circuit voltage thus resulting in an improved efficiency of the cells.
Investigation of AlxGayIn1−x−yP as a Schottky layer of AlInAs/GaInAs high electron mobility transistors
Authors: Chough K. B. , Caneau C. , Hong W.-P. , Song J.-I.
Published: July 2002

The use of high band gap strained AlxGayIn1−x−yP as a Schottky layer of AlInAs/GaInAs high electron mobility transistors on InP has been investigated. A Schottky layer with a small AlP mole fraction (Al0.1Ga0.1In0.8P or Al0.2In 0.8P) significantly increases the Schottky barrier height, leading to significant reduction of gate leakage currents. Devices with an Al0.2In0.8P Schottky layer yield gate breakdown voltages as high as −15.5 V in addition to improving drain breakdown voltages (∼8 V). With devices having a gate length of 0.5 μm, we have achieved a maximum transconductance (gm) of 480 mS/mm, current gain cutoff frequency (fT) of 68 GHz, and power gain cutoff frequency (fmax) of 130 GHz.
Arsenic pressure dependence of first-order phase transition on InAs (001) surface
Authors: Yamaguchi Hiroshi , Horikoshi Yoshiji
Published: July 2002

The role of As pressure in the first-order phase transition between As-covered (2×4) and In-covered (4×2) structures on InAs (001) surfaces is investigated using reflection high-energy electron diffraction. The dependence of transition temperatures on As pressure is well explained by Monte Carlo simulation with a two-dimensional lattice gas model, and the interaction energy is quantitatively obtained. The influence of metastability on As desorption is also clarified by comparing the experiments and simulations.
Mutual phase locking of two high-Tc Josephson junctions from 0.2 to 1 THz
Authors: Edstam J. , Olsson H. K.
Published: July 2002

We have demonstrated mutual phase locking of two YBa2Cu3O7 Josephson junction oscillators in the frequency range from 0.2 to 1 THz. A maximum power of 0.2 μW was delivered to a distributed 8 Ω load at 0.7 THz. The corresponding dc locking current, ‖IL‖, was 43 μA. A maximum locking current of 75 μA at 0.44 THz or 7% of the critical current agrees well with a calculated maximum value of 6% for this circuit. The excellent high frequency operation is due to the use of a lumped microstrip circuit and a high characteristic voltage of the grain boundary junctions (1.7 mV at 4 K). This circuit was continuously tunable for all frequencies and was operated from 4 to 60 K.
Dimerization induced incorporation nonlinearities in GaAsP
Authors: Cunningham J. E. , Santos M. B. , Goossen K. W. , Williams M. D. , Jan W.
Published: July 2002

We find that the incorporation of As and P into GaAs1−yPy, when using gas-source molecular beam epitaxy, does not depend linearly upon the atomic fluxes within the reactor. Rather, incorporation of As and P into GaAsP goes as the square of the atomic fluxes, i.e., y=fP2/(fP2+βfAs2), where fP(As) is the flux of P(As). β is a fitting parameter and that differs for relaxed and strained GaAsP. The deviation in y from a linear model [y=fP/(fP+fAs)] is as high as a factor of two, whereas our quadratic model is never more than a few percent off. We interpret this as due to surface pairing between two like species (dimerization) in order for them to incorporate into the crystal.
Dry etching and implantation characteristics of Al0.5Ga0.5P
Authors: Pearton S. J. , Abernathy C. R. , Ren F.
Published: July 2002

Highly anisotropic pattern transfer into AlGaP was achieved using low pressure (1 mTorr) microwave BCl3/Ar or CH4/H2/Ar discharges. Much faster etch rates were obtained with the chlorine-based discharges and etching was initiated at lower dc biases. The electrical activation of implanted Si+ and Be+ ions was investigated at fixed dose (5×1014 cm−2) as a function of annealing temperature (500–1000 °C). Activation efficiencies of ∼50% were obtained for Be+ implantation after annealing at ≥750 °C. Activation of Si+ was less efficient and required higher annealing temperatures than for Be+. Thermally stable high resistance (≳108 Ω/⧠) regions were formed in initially n+ AlGaP by O+ implantation at doses ≳1014 cm−2 while normal damage-induced compensation was observed for lower O+ doses. No thermally stable isolation was found in O+-implanted p+ AlGaP.
Kinetic suppression of islanding in impurity-mediated heteroepitaxial growth of germanium on silicon
Authors: Osten H. J.
Published: July 2002

The impurity-mediated suppression of islanding in molecular beam epitaxy growth experiments of Ge on Si(100) can be understood by a kinetic reduction of surface diffusion. Besides the energy barrier for surface diffusion, an energy barrier for a site exchange mechanism between Ge adatoms and the impurity atoms also has to be considered in a simple phenomenological approach that describes this effect. We found satisfactory agreement with different experimental results, like dependence of kinetic suppression of islanding on temperature and/or submonolayer coverage with impurities and germanium flux density.
Low-temperature growth of high resistivity GaAs by photoassisted metalorganic chemical vapor deposition
Authors: Roberts J. C. , Boutros K. S. , Bedair S. M. , Look D. C.
Published: July 2002

We report the photoassisted low-temperature (LT) metalorganic chemical vapor deposition (MOCVD) of high resistivity GaAs. The undoped as-grown GaAs exhibits a resistivity of ∼106 Ω cm, which is the highest reported for undoped material grown in the MOCVD environment. Photoassisted growth of doped and undoped device quality GaAs has been achieved at a substrate temperature of 400 °C in a modified atmospheric pressure MOCVD reactor. By using silane as a dopant gas, the LT photoassisted doped films have high levels of doping and electron mobilities comparable to those achieved by MOCVD for growth temperatures, Tg≳600 °C.
Hydrogenation of p-type gallium nitride
Authors: Brandt M. S. , Johnson N. M. , Molnar R. J. , Singh R. , Moustakas T. D.
Published: July 2002

Hole concentrations of up to 1019 cm−3 have been reported for GaN:Mg films grown by molecular beam epitaxy without any post-growth treatment. Comparing results from Hall measurements and secondary ion mass spectrometry, we observe doping efficiencies of up to 10% at room temperatures in such p-type material. By hydrogenating at temperatures above 500 °C, the hole concentration can be reduced by an order of magnitude. A new photoluminescence line at 3.35 eV is observed after this treatment, both in p-type and unintentionally doped n-type material, which suggests the introduction of a hydrogen-related donor level in GaN.
Effective surface resistance of LuBa2Cu3O7−δ thin films
Authors: Pinto R. , Chourey A. G. , Apte P. R.
Published: July 2002

Superconducting LuBa2Cu3O7−δ thin films have been grown in situ on 〈100〉 LaAlO3 by pulsed laser deposition and their effective surface resistance, Reff, has been measured at 10 GHz at various temperatures and for various thicknesses using microstrip resonator technique. The results show that the films are highly c-axis oriented with a high critical current density, Jc, in the range 4–5×106 A cm−2 at 77 K and a low value of intrinsic surface resistance Rs, of 320 μΩ for 10 GHz at 77 K. Thicker films (≳3000 Å) however, have shown degraded values presumably due to the strain caused by the small ionic radius of lutetium which, as shown by Somasundaram et al. [Mater. Res. Bull. 25, 331 (1990)], makes LuBa2Cu3O7−δ unstable in bulk.
Thermal-wave-modulated superconducting quantum interference device susceptometry for thin magnetic layers
Authors: Enichlmair H. , Krenn H.
Published: July 2002

Thermal waves are excited by a chopped nonresonant light wave in a 3.2 μm EuTe layer on a crystalline BaF2 substrate. The glass fiber optic sample holder is at rest within the pickup coil of a superconducting quantum interference device susceptometer. The thermal wave amplitude (simulated by a two-dimensional heat conduction model) is a function of temperature and chop rate of illumination and modulates only the magnetic properties of the epitaxial layer. Therefore, the novel method has an enhanced dynamic range and sensitivity (resolution of magnetic moment ≤2×10−9 emu) and resolves the antiferromagnetic phase transition of the EuTe layers at TN=9.8 K even for small magnetic fields of 10 G.
Reactive ion etching of high-aspect-ratio 100 nm linewidth features in tungsten
Authors: Chu W. , Foster K. W. , Shirey L. M. , Rhee K. W. , Kosakowski J. , Isaacson I. P. , McCarthy D. , Eddy C. R. , Dobisz E. A. , Marrian C. R. K. , Peckerar M. C.
Published: July 2002

The subtractive patterning of fine-linewidth (sub-250-nm) tungsten absorbers for x-ray masks requires the ability to etch features with high aspect ratios and vertical sidewalls. In this letter, a reactive-ion-etching process which meets these requirements is described. The etch gases used are SF6 and H2. It is further shown that an intermittent etch process, whereby the sample is vented to atmosphere in between etches results in an etch profile with vertical tungsten sidewalls. This interrupted etching is compared with the results from continuous etching. The straighter sidewalls in the case of the interrupted etch suggests a passivation of the sidewalls which occurs during the venting process. Results are presented to show etching of 100 nm gratings and 200 nm dot arrays. An in situ endpoint detection method developed for the reactive-ion-etching system is presented.
Reduced mass of an exciton in a monolayer-wide-InAs/GaAs quantum well from magnetophotoluminescence measurements
Authors: Dosanjh S. S. , Bowser E. F. , Harris J. J.
Published: July 2002

Magnetophotoluminescence experiments were conducted on samples consisting of nominally one-monolayer-wide InAs quantum wells (QWs) with GaAs barriers grown on (001) substrate. From these measurements, we have for the first time deduced the reduced mass of the exciton associated with the InAs QW. The reduced mass is found to be lower than that predicted theoretically using bulk effective masses, the reduction probably arising from a reduction in InAs heavy-hole mass due to heavy- and light-hole subband mixing in the QW.
Local hydrogen environments in Gd1−xFex thin films amorphous alloys from effusion experiments
Authors: Vergnat M. , Chatbi H. , Marchal G.
Published: July 2002

Thin films of hydrogenated Gd1−xFex (0.25≤x≤0.90) amorphous alloys were prepared by reactive evaporation. Effusion experiments, showing several hydrogen release peaks, allowed us to describe the site distribution of hydrogen in these alloys. The different local environments correspond to tetrahedral sites and the stability of these sites increases with the number of rare-earth neighbors.
Determination of anisotropic refractive indices of a single-crystal organic thin film by attenuated total reflection Raman spectroscopy
Authors: Yoshikawa M. , Gotoh T. , Mori Y. , Iwamoto M. , Ishida H.
Published: July 2002

We have determined the dispersion of the anisotropic refractive indices of a single-crystal organic thin film using attenuated total reflection (ATR) Raman spectroscopy. ATR Raman spectroscopy simultaneously gives information about the molecular orientation of thin organic films and the dispersion of anisotropic refractive indices.
Growth and microstructure of interfacially oriented large-crystalline-grain C60 sheets
Authors: Fartash A.
Published: July 2002

C60 films reaching sheet thicknesses of ∼10 μm have been grown in vacuum by using a custom-built effusion cell generating a beam of C60 molecules at flux rates several times higher than rates achieved by conventional methods. High quality films are grown epitaxially on Muscovite 2M1 mica substrates with double domain structures. X-ray diffraction measurements show that in the [111] direction, the structural coherency of the films reaches ∼5000 Å. Since with increasing thickness the mosaic structures of the films do not disorder significantly, the film grains remain well oriented away from the interface.
Dynamics of beam defocusing and induced absorption in CdZnTe alloys
Authors: Hönerlage B. , Ohlmann D. , Benhmida M. , Lévy R. , Grun J. B.
Published: July 2002

We study the optical nonlinear properties of bulk Cd0.13Zn0.87Te monocrystals at room temperature near the band gap. In time-resolved test and pump experiments, they manifest themselves by a defocalization and an induced absorption of the test beam in the presence of the pump beam. By measuring the spatial intensity profile of the test pulse transmitted through the sample, we determine the real and the imaginary parts of the refractive index as functions of the photon energy and time delay between pump and test pulses.
Photoinduced Bragg reflector in As2S3 glass
Authors: Shiramine K. , Hisakuni H. , Tanaka K.
Published: July 2002

Bragg reflectors have been fabricated in As2S3 glasses through the photoinduced refractive-index change process. Illumination of single monochromatic beams can produce Bragg reflectors with a half Bragg width of 2 nm in wavelength and the reflectivity estimated from the transmission decrease at 10%–20%. The reflectors can be erased with annealing and polychromatic illumination.
Simple Diophantine test for the validity of conventional deep level transient spectroscopy
Authors: Batovski Dobri , Hardalov Chavdar
Published: July 2002

An experimental test is proposed to check the validity of the conventional theoretical model used to interpret deep level transient spectroscopy (DLTS) spectra. The test is based on the conventional DLTS technique with time points determined from a corresponding Diophantine equation. The test is simple, fast, and can be realized during each experimental DLTS measurement.
Materials characterization with the acoustic microscope
Authors: Hirsekorn S. , Pangraz S.
Published: July 2002

The material signature of the acoustic microscope in reflection is calculated taking into account exactly aberration and phase shifts caused by different sound path lengths. The results allow to evaluate elastic material properties from the distance between an interference maximum and the maximum from specular reflection of measured V(z) curves. This is necessary if rigid materials such as ceramics are investigated because in these cases high frequency acoustic microscopes yield V(z) curves with only one maximum besides that from specular reflection.
Microwave compatible YBa2Cu3O7−δ films on (001)MgF2 substrates
Authors: Harshavardhan K. S. , Pique A. , Green S. M. , Patel K. , Zhang J. R. , Belohoubek E. , Edwards R. , Venkatesan T. , Denlinger E. J. , Pendrick V. , Kalokitis D. , Fathy A. , Wu X. D. , Rajeswari M. , Smith A.
Published: July 2002

High quality YBa2Cu3O7−δ (YBCO) films have been epitaxially grown on low dielectric constant, low loss tangent (001)MgF2 substrates using a double buffer layer scheme. The YBCO films are (001) oriented, exhibit Tc’s of 88–89 K with transition widths ≤0.5 K and Jc’s of 4×106 A/cm2 at 77 K in zero field. Dielectric resonator experiments indicate unloaded Q values in excess of 30 000 at 77 K and 24 GHz in the unpatterned films. Films patterned into meanderline resonators and operating at 10 GHz, 79 K, exhibit surface resistance (Rs)<1 m Ω suggesting near-future realization of low loss superconducting components in the millimeter-wave region.