bluuebunny/crossref_metadata_2025 huggingface dataset:
Tailoring the intersubband absorption in quantum wells
Authors: Trzeciakowski W. , McCombe B. D.
Published: July 2002

Optical transitions between quantum well subbands have large oscillator strengths and narrow linewidths so that they can be used for the detection of infrared light. Here we show that the intersubband separation can be varied over a wide energy range by depositing a thin barrier layer of AlGaAs in the middle of a GaAs well. In a sufficiently narrow well it should be possible to push the subbands out of the well, i.e., perform the transition from the quasi-two-dimensional case to the quasi-three-dimensional case.
Uniaxial stress dependence of current-voltage characteristics in GaAs-AlxGa1−xAs-GaAs heterojunction barriers
Authors: Lu S. S. , Lee K. , Nathan M. I. , Heiblum M. , Wright S. L.
Published: July 2002

Current-voltage characteristics of nGaAs-iAlxGa1−xAs-nGaAs heterojunction barriers grown on (100) substrates have been measured under uniaxial stress along 〈100〉 at 77 K. The results show that thermionic emission current through longitudinal X valleys becomes dominant over Fowler–Nordheim tunneling current through Γ or transverse X valleys, as stress increases. From the stress-dependent thermionic emission current the rate of change with stress of the band-edge energy difference between Γ in GaAs and longitudinal X in AlGaAs is deduced to be 14±2 meV/kbar, which leads to an X-valley shear deformation potential of 9.6±1.8 eV.
Single quantum well photoluminescence in ZnSe/GaAs/AlGaAs grown by migration-enhanced epitaxy
Authors: Kobayashi Naoki
Published: July 2002

Photoluminescence in ZnSe/GaAs/Al0.4Ga0.6As single quantum well heterostructures is reported for the first time. These structures are grown by migration-enhanced epitaxy, resulting in flat and abrupt ZnSe/GaAs heterointerfaces. The quantum size effect is clearly observed. Photoluminescence intensities of ZnSe/GaAs/Al0.4Ga0.6As single quantum well structures are comparable to those of Al0.4Ga0.6As/GaAs/Al0.4Ga0.6As, indicating a reasonable quality of the ZnSe layer as well as the ZnSe/GaAs heterojunctions. From the GaAs well width dependence of photoluminescence wavelength, the conduction- and valence-band-edge discontinuities are estimated to be 0.03–0.05 eV and 1.21–1.23 eV, respectively.
Mg diffusion during metalorganic vapor phase epitaxy of InP
Authors: Veuhoff E. , Baumeister H. , Treichler R. , Brandt O.
Published: July 2002

The diffusion mechanism of Mg has been studied during low-pressure metalorganic vapor phase epitaxy of InP. The Mg dopant profiles were measured by secondary-ion mass spectroscopy. The analysis reveals that abrupt Mg dopant profiles are possible; the Mg diffusion, however, strongly depends on the Mg concentration in the crystal lattice. Simultaneous doping with Si leads to a distinct decrease of the Mg diffusion. This behavior is consistent with a model assuming that Mg diffuses as a complex involving a deep donor.
Ultraviolet laser-induced low-temperature epitaxy of GaP
Authors: Sudarsan U. , Cody N. W. , Dosluoglu T. , Solanki R.
Published: July 2002

An ArF excimer laser has been used to achieve homoepitaxy of GaP at 500 °C using trimethylgallium and tertiarybutylphosphine as the precursor gases. Dependence of epitaxial growth on several parameters is examined. It is found that at 500 °C, in the presence of laser radiation, higher growth rate and superior crystalline properties of GaP are achieved compared to purely thermal growth. Electrical properties of p-n diodes fabricated via Zn doping have also been examined.
As-grown superconducting Bi(-Pb)-Sr-Ca-Cu-O films by electron cyclotron resonance plasma sputtering
Authors: Masumoto H. , Goto T. , Hirai T.
Published: July 2002

Bi(-Pb)-Sr-Ca-Cu-O thin films were prepared on MgO(100) single-crystal substrates by electron cyclotron resonance (ECR) plasma sputtering at substrate temperatures from room temperature to 590 °C. Pb-doped superconducting as-grown films were obtained above 560 °C. The Tc values of the Pb-doped films prepared at 570–590 °C were 58–64 K which increased with increasing substrate temperature. Pb-undoped as-grown films obtained at 590 °C showed superconduction (Tc =30 K), but the films obtained below 580 °C were semiconductors. The grain sizes and contents of the 37 Å phase (110 K phase) were increased by the Pb doping into the as-grown Bi-Sr-Ca-Cu-O films.
Surface-emitting two-dimensional coherent semiconductor laser array
Authors: Buus J. , Williams P. J. , Goodridge I. , Robbins D. J. , Urquhart J. , Webb A. P. , Reid T. , Nicklin R. , Charles P. , Reid D. C. J. , Carter A. C.
Published: July 2002

We describe a new surface-emitting semiconductor structure, its fabrication, and its performance. Phase-locked emission takes place from a region much larger than the wavelength in two dimensions; therefore we term this device a two-dimensional coherent array. The key feature of our device is that the radiation is coupled directly from the active region using a nonresonant grating coupler, i.e., the grating is of noninteger order.
Low-temperature diamond growth in a microwave discharge
Authors: Hsu W. L. , Tung D. M. , Fuchs E. A. , McCarty K. F. , Joshi A. , Nimmagadda R.
Published: July 2002

A new regime for plasma-assisted chemical vapor deposition (CVD) of diamond is reported in which high quality diamond films can be deposited on silicon with relatively high ratios of methane in hydrogen mixtures and at significantly lower substrate temperatures than previously reported. The deposition was achieved in a microwave plasma discharge with a feed gas consisting of a mixture of only methane and hydrogen. The surface temperature of a molybdenum sample, when exposed to the same plasma environment, was measured at 500 °C with an infrared scanning camera. This substrate temperature is substantially lower than the 700–1000 °C range generally regarded as the optimal regime for CVD diamond growth. Analysis by Raman spectroscopy showed that films deposited with a 2% methane in hydrogen mixture produced a near graphite-free diamond film at our reported low-temperature regime, while deposition at 1000 °C resulted in films with a much higher graphitic content.
Atomic layer epitaxy of device quality GaAs
Authors: Colas E. , Bhat R. , Skromme B. J. , Nihous G. C.
Published: July 2002

Device quality GaAs was grown in a conventional organometallic chemical vapor deposition reactor, using sequential group III (trimethylgallium, TMG) and group V (arsine) reactant gas exposures typical of atomic layer epitaxy (ALE). The results show that, at a given temperature, impurity (e.g., carbon) incorporation is controlled by the effective V/III ratio at the growing surface, which is determined by the sequence used in the growth cycles. This effect, specific to ALE, is quantified by solving the diffusion equation that describes concentration transients at the growing surface. Detailed photoluminescence experiments identified C and Mg as the residual acceptors and Ge as the sole residual donor in a 3×1015 cm−3 n-type background layer with mobilities of 5600 cm2/V s at room temperature and 35 000 cm2/V s at 77 K. A higher purity sample showed reduced levels of Ge, with traces of S, Si, and Te donors and only C acceptors.
Photoelectrochemical etching of n-InP in a thin-film cell
Authors: Grebel H. , Iskandar B. , Sheppard K. G.
Published: July 2002

The laser-induced photoelectrochemical etching of n-InP using a thin-film cell has been studied. A minimum in the reaction time was found as a function of etchant concentration for a given laser intensity. External potential biasing enhanced the reaction only for relatively low etchant concentrations.
Conduction-band offset in strained Al0.15Ga0.85As/In0.15Ga0.85As/GaAs pseudomorphic structures
Authors: Lin S. Y. , Tsui D. C. , Lee H. , Ackley D.
Published: July 2002

We report a first determination of the conduction-band offset in the strained-layer Al0.15Ga0.85As/In0.15Ga0.85As/GaAs pseudomorphic structure. Two-dimensional electron density and its effective mass are independently measured by Shubnikov–de Haas and cyclotron resonance experiments for a series of samples with a range of spacer thickness from 30 to 100 Å. Using a charge transfer model, the conduction-band offset at the Al0.15Ga0.85As/In0.15Ga0.85As interface is found to be (255±35) meV.
Highly stable W/p-In0.53Ga0.47As ohmic contacts formed by rapid thermal processing
Authors: Katz A. , Weir B. E. , Maher D. M. , Thomas P. M. , Soler M. , Dautremont-Smith W. C. , Karlicek R. F. , Wynn J. D. , Kimerling L. C.
Published: July 2002

Tungsten contacts to Zn-doped In0.53Ga0.47As have been formed by rapid thermal processing. Contacts to layers with a Zn doping concentration of 5×1018 cm−3 were rectifying as sputter deposited as well as after heat treatments at temperatures lower than 450 °C. Higher processing temperatures caused a linear decrease of the contact resistivity values from 0.6 as deposited to 0.15 Ω mm after heating at 550 °C. Rapid thermal processing at these higher temperatures stimulated the Schottky-to-ohmic contact conversion with a minimum contact resistance value of 8.5×10−5 Ω cm2 and a sheet resistance value of 150 Ω/⧠ as a result of heating at 600 °C for 30 s. By increasing the p-InGaAs doping level to 1×1019 cm−3, the specific resistance of this contact was dropped to the minimum of 7.5×10−6 Ω cm2 as a result of heating at 600 °C for 30 s. The W/p-In0.53Ga0.47As contact showed excellent thermal stability over the temperature range of 300–750 °C, with an abrupt and almost unreacted metal-semiconductor interface. Heating at temperatures of 800 °C or higher caused degradation of the contact. This was reflected by a distinct increase in the heterostructure sheet resistance as a result of the intensive interfacial reaction which took place at the contact, accompanied by outdiffusion of both In and As.
Mobility of silver on tin oxide surfaces
Authors: Sears W. M. , Colbow Konrad
Published: July 2002

We report on the observation of the rapid drift mobility of metallic silver under an applied electric field on the surface of a pyrolitically deposited tin oxide film. Silver dag contacts were applied to the surface of the film which was maintained in air at a temperature of 330 °C under a potential difference of a few volts. Under these conditions metallic silver was seen to migrate across the film forming both fractal and dense packed structures.
Electroluminescence from sulfur impurities in a p-n junction formed in epitaxial silicon
Authors: Bradfield P. L. , Brown T. G. , Hall D. G.
Published: July 2002

We characterize the behavior of electroluminescence from a sulfur-related impurity complex in a p-n junction formed in epitaxial silicon. The spectrum of the electroluminescence matches that of previously reported photoluminescence from sulfur impurities and persists to ∼150 K. In our structure, we find that the electroluminescence exhibits an external quantum efficiency of 0.2–0.5%.
High performance InP/InGaAs heterostructure bipolar transistors grown by metalorganic vapor phase epitaxy
Authors: Nottenburg R. N. , Chen Y. K. , Tanbun-Ek T. , Logan R. A. , Humphrey D. A.
Published: July 2002

We demonstrate high performance InGaAs/InP heterostructure bipolar transistors grown by metalorganic vapor phase epitaxy. A unity current gain cutoff frequency fT=78 GHz and a maximum oscillation frequency fmax=42 GHz are achieved in transistors with emitter size 2.5×11 μm2. Ring oscillators using nonthreshold logic show a propagation delay of 31 ps.
Variation of the spacer layer between two resonant tunneling diodes
Authors: Wolak E. , Park B. G. , Lear K. L. , Harris J. S.
Published: July 2002

The effect of changing the length of the spacer layer between two vertically integrated resonant tunneling diodes (RTDs) is experimentally determined. Three different wafers, each containing two RTDs, were grown by molecular beam epitaxy, with spacer layers of 1200, 700, and 200 Å, respectively. A fourth wafer with a single such RTD was grown as a control sample. Two of the control samples wired in series show two current peaks, the temperature dependence of the current-voltage (I-V) curves being correctly predicted by a nonlinear load model. The I-V characteristics of the stacked devices with 1200 and 700 Å quantum wells between the RTDs also show two current peaks, confirming that the bulk of electrons lose longitudinal wave function coherence between the two double-barrier structures. The first derivative of the I-V curve for the samples with 700 and 1200 Å spacers displays evidence of quantum interference between the cathode well and the central spacer as a second-order effect. The first major peak in the structure with a 200 Å spacer between the quantum wells differs from the first peak in the other structures, and the difference is attributed to quantum interference effects.
Transient and steady-state excess carrier lifetimes in p-type HgCdTe
Authors: Fastow R. , Nemirovsky Y.
Published: July 2002

The transient and steady-state excess carrier lifetimes in p-type Hg0.775Cd0.225Te have been measured as a function of temperature. It is demonstrated that the transient lifetime can be greater than the steady-state lifetime by as much as a factor of 16 at 77 K. This difference is attributed to minority-carrier trapping, and explains, in part, the large range of lifetimes which have been reported for this material.
Magnetic field controlled levitation and suspension of a magnet above and below type II superconductors
Authors: Takamori Takeshi , Boland John J. , Dove Derek B.
Published: July 2002

Observations are presented on levitation and suspension of a permanent magnet by combination of a variable magnetic field and a type II superconductor (YBa2Cu3Ox). It has been found that a continuous range of distances exists where stable levitation and suspension may be obtained, and that the orientation of magnetic moment of the levitated or suspended magnet is also adjustable over a range of angles. In addition, the incorporation of the magnetic element makes it possible to suspend much higher mass than observed previously.
Photoluminescence studies of Si (100) doped with low-energy (≤1000 eV) As+ ions during molecular beam epitaxy
Authors: Noël J.-P. , Greene J. E. , Rowell N. L. , Kechang S. , Houghton D. C.
Published: July 2002

Low-temperature (4.2K) photoluminescence (PL) has been used to characterize Si(100) films doped with EAs =200, 500, and 1000 eV 75 As+ ions during growth by molecular beam epitaxy on n+ Sb-doped substrates at temperatures Ts between 500 and 800 °C. Sharp no-phonon, transverse-optical, and transverse-acoustic phonon-assisted bound-exciton (BE) Peaks associated with As dopant species, together with broader, weaker, Sb-related BE peaks, were the dominant PL features obtained from 5-μm-thick layers. No peaks ascribable to residual ion-induced damage were observed in films grown at 650 °C with EAs =200 eV or Ts =800 °C with EAs =200, 500, and 1000 eV. However, reducing the film growth temperature to 500 °C with Eas =200 eV gave rise to a strong ion-damage PL peak at 1039.7 meV. Furthermore, both undoped and As ion-doped films grown at 500 °C exhibited a gradual increase in the PL background below 890 meV which we believe was due to quenched-in point defects. Complementary deep level transient spectroscopy measurements showed electron trap states (concentrations≂1014 cm−3) at energies of 0.06 an d-0.52 eV below the conduction-band edge for films grown at 500 °C with EAs =200 eV. No traps were observed in the ion-doped Ts=650 and 800 °C samples.
Growth of YBaCuO thin films on random and (100) aligned ZrO2 substrates
Authors: Li Q. , Meyer O. , Xi X. X. , Geerk J. , Linker G.
Published: July 2002

The growth quality of thin, superconducting YBaCuO films has been compared on random and (100) oriented yttrium-stabilized zirconia substrates using x-ray diffraction and ion channeling experiments. Superior growth is observed on (100) substrates with narrow mosaic distributions (0.4°) and a minimum yield value of 10% in the channeling experiment. The lattice matching required for epitaxial growth is achieved by azimuthal adjustment of the film plane with respect to the substrate. The superior growth is reflected in the film properties like the critical current density yielding values of 2×106 A/cm2 at 77 K.
Fabrication of heteroepitaxial YBa2Cu3O7−x-PrBa2Cu3O7−x-YBa2Cu3O7−x Josephson devices grown by laser deposition
Authors: Rogers C. T. , Inam A. , Hegde M. S. , Dutta B. , Wu X. D. , Venkatesan T.
Published: July 2002

We have fabricated Josephson weak links from in situ laser-deposited four-layer structures of YBa2Cu3O7−x/PrBa2Cu3O7−x/YBa2Cu3O7−xAu. These devices show superconductor/normal-metal/superconductor-like current-voltage characteristics with good areal scaling of both the critical currents Ic and resistances Rj, with IcRj≊3.5 mV. Constant-voltage current steps observed in response to 84 GHz mm-wave radiation and modulation of the dc supercurrent in a transverse magnetic field demonstrate that both the ac and dc Josephson effects occur in these devices.
Effect of processing geometry in oxygen incorporation and i
n s
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u formation of YBa2Cu3O7 superconducting thin films by pulsed laser evaporation technique
Authors: Singh R. K. , Ganapathi L. , Tiwari P. , Narayan J.
Published: July 2002

I n situ formation of YBa2 Cu3 O7 superconducting thin films by the pulsed laser evaporation technique is critically dependent on the processing conditions (substrate temperature, oxygen partial pressure, subsequent annealing, etc.) and on the deposition setup, including the nozzle geometry required for the incorporation of oxygen. We have studied the recovery of the superconducting properties as a function of location of the oxygen jet relative to a fixed substrate-target setup at a substrate temperature of 550 °C and an oxygen partial pressure of 200 mTorr. Several experiments were performed with the oxygen jet directed on the target and/or on the substrate. During the deposition process, a dc bias voltage of +300 V was applied on an interposing ring, which has resulted in formation of superconducting thin films at a low temperature of 500 °C. Excellent superconducting properties with the Tc zero of 88 K were obtained on films fabricated at 550 °C with the nozzle directed onto the substrate. In contrast, films formed with the oxygen jet directed at the target showed poor superconducting properties, with a Tc0 of approximately 50 K. The x-ray diffraction studies on these films showed much sharper Bragg peaks and higher oxygen content for films fabricated with the oxygen jet directed on the substrate compared to that of the target.
Growth of epitaxial NiSi2 on Si(111) at room temperature
Authors: Tung R. T. , Schrey F.
Published: July 2002

Epitaxial type B NiSi2 thin layers have been grown at room temperature on Si(111). Deposition of a few monolayers of nickel followed by codeposition of NiSi2 has led to the growth of high quality single-crystal layers, with ion channeling χmin <2%. No disorder was found at the interfaces of these layers. The topography of the original substrate has a predominant effect on the structure of line defects at the NiSi2 interface. Codeposition at room temperature on annealed silicide thin layers also led to the overgrowth of high quality NiSi2. These results are suggestive of type B NiSi2 formation on Si(111) upon deposition of a few monolayers of nickel at room temperature.
Epitaxial growth of superconducting YBa2Cu3O7−x thin films by reactive magnetron sputtering
Authors: Xiong G. C. , Wang S. Z.
Published: July 2002

Perfect epitaxial growth of superconducting YBa2Cu3O7−x thin films have been achieved on (100) SrTiO3, (110) SrTiO3, and (100) ZrO2 substrates using a modified planar dc magnetron sputtering system. The films exhibit zero resistances at 87–90 K with transition widths of about 2 K. The critical current density of 1.4×106 A/cm2 at 77 K so far has been measured on the (100) SrTiO3 substrate. The epitaxial orientation of the thin films was influenced by the substrate orientation, the substrate temperature, and the oxygen partial pressure. The quality of growth and the epitaxial orientation of the films were examined by electron channeling, x-ray diffraction, and reflection high-energy electron diffraction techniques. The preferential epitaxial orientation is discussed.
Effect of oxygen partial pressure on the transformation between high T
c and low T
c phases in a Bi-Pb-Sr-Ca-Cu-O system
Authors: Lee H. K. , Lee K. W. , Ha D. H. , Park K. , Park J. C.
Published: July 2002

The effect of oxygen partial pressure on the stability of the high Tc phase (>100 K) in a Bi-Pb-Sr-Ca-Cu-O system has been studied using resistivity, x-ray diffraction, and ac susceptibility measurements. It was observed that part of the high Tc phase formed by sintering at 840 °C in a low oxygen partial pressure of 1/10 atmosphere was transformed into a low Tc phase (∼80 K) and an insulating phase by heating at the same sintering temperature in O2 of one atmosphere. The original high Tc phase was restored upon retreatment at the same temperature in a low oxygen partial pressure of 1/10 atmosphere.
Epitaxial growth of YBa2Cu3O7−δ thin films on LiNbO3 substrates
Authors: Lee S. G. , Koren G. , Gupta A. , Segmüller Armin , Chi C. C.
Published: July 2002

I n situ epitaxial growth of YBa2Cu3O7−δ thin films on Y-cut LiNbO3 substrates using a standard laser ablation technique is reported. Resistance of the films shows a normal metallic behavior and a very sharp (<1 K) superconducting transition with Tc(R=0) of 92 K. High critical current density of Jc(77 K)=2×105 A/cm2 is observed, which is in accordance with epitaxial growth. Film orientation observed from x-ray diffraction spectra indicates that the c axis is normal to the substrate plane and the a axis is at 45° to the [11.0] direction of the hexagonal lattice of the substrate with two domains in mirror image to the (110) plane.
Low etch pit density GaAs on Si grown by metalorganic chemical vapor deposition
Authors: Soga Tetsuo , Jimbo Takashi , Umeno Masayoshi
Published: July 2002

GaAs was grown on a Si substrate by metalorganic chemical vapor deposition using GaAs/GaAsP strained-layer superlattice (SLS) intermediate layers. The dislocation density decreases at the interface between GaAs and the SLS, but does not decrease in the SLS. When a GaAs/GaAsP SLS is used as the intermediate layer, part of the threading dislocation propagates into the top GaAs layer because of the lattice mismatch of GaAs and SLS. The low etch pit density of (3–5)×105 cm−2 was obtained by using the intermediate layer of a GaAs/GaAsP SLS and an AlAs/GaAs superlattice with thermal cycle annealing.
Base doping limits in heterostructure bipolar transistors
Authors: Jalali B. , Nottenburg R. N. , Levi A. F. J. , Hamm R. A. , Panish M. B. , Sivco D. , Cho A. Y.
Published: July 2002

Heterostructure bipolar transistors are used to experimentally determine band offsets in lattice-matched In0.53Ga0.47As devices. Valence-band offsets of ΔEV=0.24 eV for Al0.48In0.52As/In0.53Ga0.47As and ΔEV=0.34 eV for InP/In0.53Ga0.47As are measured. Because of band filling in the base, these values place important constraints on p-type doping levels and emitter injection efficiency in practical devices.
Effect of alignment layer conductivity on the bistability of surface-stabilized ferroelectric liquid-crystal devices
Authors: Chieu T. C. , Yang K. H.
Published: July 2002

Recent experimental results indicate that bistability is difficult to achieve in surface-stabilized ferroelectric liquid-crystal devices with high spontaneous polarization (Ps) materials. We formulated the basic equations to analyze the bistability as a function of the conductivity and thickness of the alignment layers using Ps as a parameter. It is found that a threshold value of the conductivity, which approximately scales with both the thickness and Ps, exists to achieve good bistability. Numerical results are given to provide important guidances for choosing the alignment layer materials to obtain excellent bistability using high Ps materials.
I
n s
i
t
u low-temperature deposition and properties of Bi(Pb)-Sr-Ca-Cu-O thin films prepared by magnetron sputtering
Authors: Jedamzik D. , Barnard B. R. , Harrison M. R. , Freeman W. G. , Howard P. J.
Published: July 2002

Superconducting thin films of the Bi-Sr-Ca-Cu-O system with and without lead doping were prepared by rf magnetron sputtering onto (100)MgO substrates. Although the superconducting properties of the thin films are very sensitive to the deposition and soak temperatures, reproducible results were obtained. Our in situ deposition process with processing temperatures not exceeding 600 °C yielded films with zero resistance at 82 K and Jc=7×105 A cm−2 measured at 4 K for the two-layer Bi phase. Our initial results with lead-doped Bi-Sr-Ca-Cu-O thin films will also be discussed.
Thermal processing of strained GaInAs/GaAs high hole mobility transistor structures
Authors: Gillin W. , Tang Y. S. , Whitehead N. J. , Homewood K. P. , Sealy B. J. , Emeny M. T. , Whitehouse C. R.
Published: July 2002

We have studied the resistance to thermal processing of a realistic strained-layer device structure: a GaAs/GaInAs p-type modulation-doped field-effect transistor layer. The integrity of the structure was monitored using the photoluminescence from the strained quantum well in the active region of the structure. No evidence of mixing or strain relaxation was observed when samples were annealed at 750 °C for 5 h. At higher temperatures, 900 °C and above, mixing is observed and values for the interdiffusion constants and the activation energy obtained.
Formation and decay of metastable fluorine atoms in pulsed fluorocarbon/oxygen discharges monitored by laser-induced fluorescence
Authors: Hansen S. G. , Luckman G. , Nieman George C. , Colson Steven D.
Published: July 2002

The temporal profiles of metastable F(4 P3/2) and Ar(1s5) and emitting F(4D05/2 ) and Ar(2p2) in a sharp-edged, pulsed CF4/O2/Ar (87.5/10.4/2.1) discharge are discussed. All four states are so short lived that there is no net accumulation during the discharge pulse and the profiles merely reflect the formation rate. For Ar, electron impact on the ground state leads to both excited states. Their similar profiles mirror the electron excitation function. For excited F, two channels are open: electron impact on CF4, and electron impact on ground-state F which accumulates during the discharge pulse. The fact that metastable F is rapidly quenched in the gas phase indicates that it is not a major etchant of silicon or silicon nitride as was recently suggested in the literature.
All high T
c edge junctions and SQUIDs
Authors: Laibowitz R. B. , Koch R. H. , Gupta A. , Koren G. , Gallagher W. J. , Foglietti V. , Oh B. , Viggiano J. M.
Published: July 2002

We present the first observations of superconducting quantum interference in multilevel, all high Tc, lithographically patterned edge junction structures. The current-voltage characteristics are nonhysteretic and have well-defined critical currents. The dynamic resistance is independent of current above the critical current. These devices show periodic sensitivity to magnetic fields and low levels of magnetic hysteresis up to temperatures around 60 K.
Photoluminescence of the D lines in silicon containing a high concentration of carbon after a two-step isochronal anneal
Authors: Wijaranakula W. , Mollenkopf H. , Matlock J. H.
Published: July 2002

Photoluminescence at the photon energies of 0.808 and 0.874 eV was observed in silicon containing a high concentration of carbon after a two-step isochronal anneal. The annealing sequence consisted of a low-temperature isochronal anneal and a 1050 °C anneal, respectively. The observed luminescence had the photon energies corresponding to those of the D lines which are known to arise from the interstitial-type dislocation loops. In silicon containing a high concentration of carbon, a formation of the dislocation loops was hypothesized to occur via a condensation of the excess silicon interstitials, originated from the agglomerates of interstitial carbons.
Electron-hole transition energies and atomic steps at the interfaces of thin InGaAs/InP quantum wells
Authors: Zachau M. , Grützmacher D.
Published: July 2002

We measure the absorption of thin InGaAs/InP quantum wells with a well width between 0 and 20 Å. The discretization of the transition energies due to the quantization of the well width by monolayers is clearly observed for both the heavy and light hole excitons. The dependences of the heavy and light hole transition energies on the InGaAs growth time are investigated and show striking differences. This is discussed in relation to the atomic steps at the interfaces of the wells. The measured heavy and light hole transition energies agree well with calculation, which takes the split-off holes into account.
Microstrain and macrostrain profiles in ZnSe epitaxial layers
Authors: Krost A. , Richter W. , Brafman O.
Published: July 2002

We present a microprobe Raman scattering study of the strain in a ZnSe heterostructure with GaAs, Ge, and Si. Measurements taken at adjacent sites of different distances from the interface prove Raman scattering to be a very powerful tool for detecting the strain and distinguishing between local high strains and macroscopic low strains.
Photoluminescence studies of Si (100) doped with low-energy (100–1000 eV) B+ ions during molecular beam epitaxy
Authors: Noël J.-P. , Greene J. E. , Rowell N. L. , Houghton D. C.
Published: July 2002

Temperature-dependent photoluminescence (PL) measurements have been used to characterize 5-μm-thick Si(100) epitaxial layers doped in situ during molecular beam epitaxial growth with low-energy (100, 500, and 1000 eV) 11 B+ ions at growth temperatures of 500, 650, and 800 °C. Moderate doping (NB ∼1017 cm−3) yielded PL features comprised of both sharp and broad peaks in the boron bound exciton (B-BE) region. At 4.2 K a broad B-BE feature near 1086 meV dominated, although the sharp transverse optical phonon-assisted B-BE peak (B1TO ) at 1092.5 meV was resolvable for NB<1017 cm−3. Increasing the PL sample temperature above 4.2 K caused a rapid decay of the broad B-BE peak intensity, thus permitting comparison of B1TO intensity for a range of ion energies and growth temperatures. At 10 K, a bulk-like spectrum containing a sharp B1TO peak with weaker multiexciton peaks B2TO and B3TO was observed for the film growth at the highest temperature and lowest ion energy (800 °C and 100 eV). However, the intensity of the B1TO peak decreased with decreasing growth temperature (constant ion energy) and with increasing ion energy (constant growth temperature). Samples grown at the lowest temperature (500 °C) displayed very different PL spectra with much weaker line emission, a rising PL background, and additional lines near 1040 meV due to ion-induced residual lattice defects. Quenching of B1TO and the other sharp B-BE peaks was accompanied by an increase in the N1 peak at 745.7 meV.
Linewidth enhancement factor in strained quantum well lasers
Authors: Dutta N. K. , Wynn J. , Sivco D. L. , Cho A. Y.
Published: July 2002

The linewidth enhancement factor α in an In0.2Ga0.8As/GaAs strained-layer multiple quantum well (MQW) laser has been determined from the spontaneous emission spectra below threshold. The measured α at the lasing wavelength is found to be 1.0 compared to a value of 5 typically observed for InGaAsP/InP double-heterostructure lasers. The smaller α shows that single wavelength strained MQW lasers may have smaller chirp width under modulation and also smaller cw linewidth.
Impact ionization mechanism in rare earth activated sulfides
Authors: Świa̧tek K. , Suchocki A. , Godlewski M.
Published: July 2002

In this letter we present the theoretical estimation of the 3+■2+ ionization energies of rare earth (RE) ions in sulfides. It is shown that for Yb, Eu, Sm, Tm, and Pr the RE2+ energy level is located in the forbidden gap of wide-gap sulfides [ZnS (except Pr), CaS, SrS, BaS, MgS]. For these RE ions the possibility of a new efficient excitation mechanism (impact ionization) of electroluminescence is indicated. Highly efficient electroluminescence can be obtained if the ionized RE center rapidly recaptures a free carrier either directly or indirectly via the RE3+ excited state. This prediction is confirmed by the recent experimental results for Pr-doped SrS. Further experimental results supporting the presented calculations are discussed.
Effect of conventional and rapid thermal annealing on platinum silicide Schottky barrier diodes
Authors: Dimitriadis C. A.
Published: July 2002

The effects of rapid thermal annealing (RTA) on the material properties and on the performance of Pt Schottky barriers on Si are investigated and compared with the effects of corresponding furnace annealings. For fabrication of platinum silicide-silicon Schottky diodes, furnace annealing degrades the minority-carrier diffusion length, while Schottky diodes prepared by RTA have better performance without degradation of the diffusion length.
Capacitance-voltage characteristics of alternating-current thin-film electroluminescent devices
Authors: McArthur R. C. , Davidson J. D. , Wager J. F. , Khormaei I. , King C. N.
Published: July 2002

The capacitance-voltage (C-V) technique is proposed as a method for characterization of the electrical properties of alternating-current thin-film electroluminescent (ACTFEL) display devices. Analysis of the C-V and aging characteristics of ZnS:Mn ACTFEL devices indicates that the C-V technique is complementary to the charge-voltage technique in the extraction of device physics information.
1.3 μm monolithically integrated waveguide-interdigitated metal-semiconductor-metal photodetector on a GaAs substrate
Authors: Jagannath C. , Silletti A. , Choudhury A. N. M. M. , Elman B. , Melman P.
Published: July 2002

An InGaAs/GaAs strained-layer single quantum well waveguide-photodetector combination operating at a wavelength of 1.3 μm was fabricated on a GaAs substrate. An interdigitated metal-semiconductor-metal detector was deposited on top of the waveguide using Ti/Pt/Au for Schottky contacts. As expected, the responsivity of the detector increased with increasing single quantum well absorption in the waveguide and was sensitive to the polarization of the incident light. For TM polarization the responsivity of the detector was an order of magnitude lower at 1284 nm, compared to TE polarization, and exhibited weak dependence on wavelength, consistent with the transmission data. These results demonstrate for the first time a monolithically integrated 1.3 μm waveguide photodetector fabricated on a GaAs substrate.
Fabrication of Tl-Ca-Ba-Cu-O superconducting thin films on LaAlO3 substrates
Authors: Subramanyam G. , Radpour F. , Kapoor V. J.
Published: July 2002

For the first time, fabrication of high-temperature superconducting Tl-Ca-Ba-Cu-O (TlCaBaCuO) thin films on LaAlO3 substrates is reported. TlCaBaCuO thin films were deposited by rf magnetron sputtering of a single composite powder target in a pure argon plasma. The films were sintered in an excess thallium ambient at 850 °C for 15 min followed by a 30 min oxygen annealing at 750 °C. Scanning electron microscopy and x-ray diffraction results showed the smooth and highly c-axis oriented nature of the thin films. The temperature dependence of resistance showed the onset of critical transition temperature (Tc) at 114 K, and zero resistance at 103 K.
Exchange interaction effects in quantum well infrared detectors and absorbers
Authors: Choe J.-W. , O Byungsung , Bandara K. M. S. V. , Coon D. D.
Published: July 2002

Infrared excitation energies between the ground-state subband and the first excited-state subband in quantum wells are analyzed including the effect of exchange interactions on the ground-state subband. Analytic and numerical calculations relevant to infrared absorption and infrared detection are performed. Previous work on exchange interaction effects in narrow wells is extended to deal with well widths which can provide absorption peaks and photocurrent peaks throughout the long-wavelength infrared and very-long-wavelength infrared regime. Exchange effects are shown to be substantial.
Etching of SiO2 in an electron cyclotron resonance argon plasma
Authors: Salimian S. , Cooper C. B. , Ellingboe A.
Published: July 2002

Etching of SiO2 with low-energy Ar ions has been studied in an electron cyclotron resonance (ECR) based etching system. Ion energies were controlled by a capacitively coupled 13.56 MHz bias of the substrate. Etch rates of over 100 Å/min have been achieved at ion energies below 100 V. The variation in etch rate has been studied as a function of ECR power, self-induced bias, and position of the wafer relative to the ECR source. This low-energy process can be utilized for cleaning of semiconductor surfaces prior to chemical vapor deposition or metallization processes.
Electrical properties of the interface between YBa2Cu3Ox films and various substrates
Authors: Ying Q. Y. , Kwok H. S.
Published: July 2002

The electrical properties of the interfacial layers between YBCO films and various substrates were studied using in situ resistivity measurements. It was found that this method is sensitive to even a 10-Å-thick interface layer. Moreover, it yields the resistivity of the interfacial layer and the YBCO film during deposition. For yttria-stabilized zirconia, the interface has a very low resistivity. For MgO and sapphire the interface has a high resistivity; SrTiO3 falls between these two cases. Sapphire shows a large reaction layer and evidence for nucleated growth, which are probably responsible for its relatively poor superconducting properties.
Thermally induced epitaxial recrystallization of NiSi2 and CoSi2
Authors: Ridgway M. C. , Elliman R. G. , Thornton R. P. , Williams J. S.
Published: July 2002

Time-resolved reflectivity and Rutherford backscattering spectrometry combined with channeling have been used to measure the epitaxial recrystallization kinetics of amorphous NiSi2 and CoSi2 layers. Epitaxial metal silicide layers, fabricated on (111) Si substrates by metal deposition and thermal reaction, were implanted with low-energy Si ions to form amorphous surface layers. Such layers recrystallized epitaxially from the underlying crystalline metal silicide during thermal annealing at temperatures of 60–176 °C. Post-anneal disorder consisted of dislocation networks as observed with transmission electron microscopy. Reduced recrystallization rates were apparent in samples implanted with O and Ar ions. Activation energies of 1.09±0.03 and 1.17±0.03 eV were determined for the epitaxial recrystallization of amorphous NiSi2 and CoSi2 layers, respectively.
Increase in the flux-pinning energy of YBa2Cu3O7−δ by shock compaction
Authors: Weir S. T. , Nellis W. J. , Kramer M. J. , Seaman C. L. , Early E. A. , Maple M. B.
Published: July 2002

Magnetic flux relaxation data on a composite specimen of YBa2Cu3O7−δ +Ag shock compacted at 167 kbar show that the flux-pinning energy at 70 K and 10 kOe is enhanced by a factor of 2–3. This enhancement persists after annealing at 890 °C in oxygen for 24 h. The increased pinning energy is apparently caused by shock-induced 〈100〉 and 〈110〉 line defects having a density up to 1012 cm−2. Annealing replaces line defects with (001) extrinsic stacking faults having displacement vectors of 1/6[031]. The average separation of the stacking faults in the [001] direction is 0.04 μm, which is comparable to the separation between fluxoids at 10 kOe. These results indicate that intragranular critical current densities can be increased significantly in bulk materials by shock processing. High densities of flux-pinning sites could be induced efficiently in industrial-scale quantities of bulk high Tc oxides by explosives.
Microstructure of epitaxial YBa2Cu3O7−x thin films
Authors: Nieh C. W. , Anthony L. , Josefowicz J. Y. , Krajenbrink F. G.
Published: July 2002

We have investigated the microstructure of epitaxial YBa2Cu3O7−x thin films on SrTiO3(100), LaGaO3(100), and LaAlO3 (100) with particular emphasis on how the final microstructure is developed. Cross-sectional transmission electron microscopy as well as plan-view transmission electron microscopy combined with sputter depth profiling were used to study the change in microstructure with the increase in film thickness. For a thin film or near the substrate/film interface of a thick film, the YBa2Cu3O7−x film is composed primarily of grains oriented with c axis normal to the substrate surface and a small volume fraction of grains with c axis parallel to the substrate surface. As the film grows thicker, the c-axis parallel grains increase in size and grow over the top of the c-axis normal grains. The volume fraction of c-axis parallel grains increases rapidly as the film thickness increases and eventually the entire film surface is covered by c-axis parallel grains. However, the number density of the c-axis parallel grains remains constant throughout the whole film thickness. A growth model is proposed to explain the observed microstructure. Based on this model, a computer simulation is carried out. The simulated microstructure agrees well with the experimental result.
Use of cathodoluminescence microscopy to distinguish semiconducting from metallic phases in high T
c superconductors
Authors: Miller J. H. , Hunn J. D. , Holder S. L. , DiBianca A. N. , Bagnell C. R.
Published: July 2002

We show that semiconducting and insulating metal-oxide phases emit substantially greater luminescence when irradiated with 10–30 keV electrons than metallic, candidate high Tc superconducting phases. The use of a cathodoluminescence (CL) detector in a scanning electron microscope to form high-resolution CL images of Y2O3, BaCO3, Y2BaCuO5, oxygen-depleted YBa2Cu3O7−x(x>0.5), and oxygen-annealed YBa2Cu3O7−x(x∼0) is reported. The spatial resolution obtained in CL micrographs of YBa2Cu3O7−x is found to be about 0.1 μm when the electron beam current is 190 nA. The use of CL microscopy in combination with energy-dispersive x-ray analysis may be a promising technique for identifying candidate superconducting phases of novel stoichiometry in complex multiphase samples.
Accelerated formation of 110 K high T
c phase in the Ca- and Cu-rich Bi-Pb-Sr-Ca-Cu-O system
Authors: Huang Y. T. , Liu R. G. , Lu S. W. , Wu P. T. , Wang W. N.
Published: July 2002

The crystal structure and superconducting properties of the Bi-Pb-Sr-Ca-Cu-O system with Ca- and Cu-rich nominal composition were investigated. A nearly single-phased 110 K high Tc superconductor can be obtained with 852 °C/20 h sintering from the starting composition of Bi1.7Pb0.4Sr1.6Ca2.4Cu3.6Oy. X-ray diffraction patterns, resistivity measurement, diamagnetic susceptibility results, and scanning electron micrographs all indicate that the Ca- and Cu-rich nominal composition would result in better superconducting properties than those of Ca:Sr=1:1 Bi-Pb-Sr-Ca-Cu-O compounds in a much shorter sintering time.
Fabrication of Tl-Ba-Ca-Cu-O films by annealing rf-sputtered Ba-Ca-Cu-O films in thallium oxide vapors
Authors: Shah S. I. , Herron N. , Fincher C. R. , Holstein W. L.
Published: July 2002

Thin, superconducting Tl-Ba-Ca-Cu-O films were grown using a two-step fabrication process which involved the growth of Ba-Ca-Cu-O films by reactive magnetron sputtering followed by ex situ high-temperature crystallization and thallination under thallium oxide vapors. Films were thallinated with both Tl2O3 and Tl2Ba2CuO6 as the source for thallium oxide vapors. Highly oriented films were obtained with the c axis perpendicular to the surface of the film. Best films had a Tc (R=0) of 104 K and a critical current density of 5×104 A/cm2 at 77 K.
Properties of epitaxial YBa2Cu3O7 thin films on Al2O3 {1̄012}
Authors: Char K. , Fork D. K. , Geballe T. H. , Laderman S. S. , Taber R. C. , Jacowitz R. D. , Bridges F. , Connell G. A. N. , Boyce J. B.
Published: July 2002

Epitaxial YBa2Cu3O7 films were grown on Al2O3 {1̄012} by a laser ablation technique. X-ray diffraction shows that films are epitaxial with the c axis perpendicular to the substrate surface and ‘‘123’’ [110] aligned with sapphire [101̄1], although the full width at half maximum of the rocking curve is larger than those of epitaxial films on SrTiO3. Typical Tc’s are between 85 and 88 K with transition widths between 0.5 and 3 K. The normal-state resistivity is 270 μΩ cm at 300 K and extrapolates to zero at zero temperature while the magnetization Jc is as high as 5×106 A/cm2 at 4.2 K. High-frequency loss measurements show that 2000-Å-thick epitaxial films on Al2O3 {1̄012} have a surface impedance about 1 mΩ at 13 GHz at 4.2 K.
Light-induced defect studies in hydrogenated amorphous silicon by exoelectron emission
Authors: Bhide R. S. , Manorama V. , Pawar S. K. , Babras Suvarna , Bhoraskar S. V. , Bhide V. G.
Published: July 2002

Exoelectron emission was observed from previously light soaked, glow discharge prepared a-Si:H films by thermal stimulation. The energy analysis of exoelectrons was incorporated by a 127° cylindrical deflection analyzer (CDA). Observed energies of exoelectrons (4–8 eV) suggest that the delocalized electron gains energy during emission either from the Coulomb potential or from the exchange of energy from dangling bond annihilation. Several models of dangling bond creation are discussed; however, the actual mechanism appears to be more complex.
Resonant cavity enhanced AlGaAs/GaAs heterojunction phototransistors with an intermediate InGaAs layer in the collector
Authors: Ünlü M. S. , Kishino K. , Chyi J-I. , Arsenault L. , Reed J. , Mohammad S. Noor , Morkoç H.
Published: July 2002

Gain and spectral response of heterojunction phototransistors (HPTs) having a thin (0.1 μm) InGaAs strained absorbing layer in the collector has been investigated. Low dark current ∼ 5 pA (1×10−8 A/cm2) and large optical gain as high as 500 were observed. A resonant cavity composed of an AlAs/GaAs buried mirror structure (reflectivity R=0.9) and the epilayer surface (R=0.3) was used to enhance the otherwise small quantum efficiency η (at InGaAs absorption wavelength). For a 1000 Å absorbing layer an improvement of η from 6.7 to 43% (6.4-fold) was demonstrated, in agreement with calculations, through the spectral analysis of the HPTs with and without resonant cavities.
Efficient GaInAsSb/AlGaAsSb diode lasers emitting at 2.29 μm
Authors: Eglash S. J. , Choi H. K.
Published: July 2002

Diode lasers emitting at 2.29 μm have been fabricated from lattice-matched double heterostructures having a GaInAsSb active layer and AlGaAsSb confining layers grown by molecular beam epitaxy on GaSb substrates. For pulsed room-temperature operation these devices have exhibited threshold current densities as low as 1.7 kA/cm2 and differential quantum efficiencies as high as 18% per facet, the highest room-temperature efficiency reported for any semiconductor diode laser emitting beyond 2 μm.
Analysis of the two-dimensional dark currents in quantum well devices
Authors: Brennan Kevin , Wang Yang
Published: July 2002

We present approximate analytical expressions for the principal forms of dark current, thermionic emission, and tunneling, which arise within a two-dimensional quantum well photodetector. A simple closed form expression for the two-dimensional thermionic emission current is obtained as well as a numerical result for the tunneling current. Though the dark currents are calculated making use of the usual approximation for the wave function of that for an infinite square well, these expressions are expected to yield reasonable estimates. These formulas can be applied to properly assess the resulting dark currents in photodetectors which utilize quantum well states for either detection or multiplication.
Photoluminescence study of hydrogen passivation in GaAs and AlGaAs by the photochemical vapor deposition system
Authors: Chen Yang-Fang , Tsai Chong-Sheng , Chang Yuanhei
Published: July 2002

It is shown for the first time that hydrogen passivation can be made by using a photochemical vapor deposition system. Unlike the common methods, this new method of hydrogenation has no electron or ion bombardment, thus the sample surface will not be damaged during processing. The effects of hydrogenation are confirmed by the enhancement of photoluminescence intensity. A strong increase in the luminescence intensity (a factor of 23) has been observed which is comparable to the results of rf glow discharge systems.