bluuebunny/crossref_metadata_2025 huggingface dataset:
Resistive dissipation in imperfect crystals of YBa2Cu3O7−δ
Authors: Kwok W. K. , Welp U. , Vandervoort K. G. , Fang Y. , Crabtree G. W. , Liu J. Z.
Published: July 2002

We have measured ac magnetoresistance in fields up to 8 T in a variety of YBa2Cu3O7−δ single crystals containing (a) twin boundaries only in one direction, (b) multi-twin domain structure, and (c) growth steps. We find two components of the resistance: an angular dependent Lorentz force induced ‘‘excess resistivity’’ superimposed on an angular independent resistivity. The temperature and magnetic field dependence of the angular-dependent resistivity exhibit a strong correlation with crystal defects, whereas the angular-independent resistivity remains virtually unchanged. In addition, we find crystals exhibiting both ohmic and non-ohmic behavior in their I-V characteristics depending on crystal imperfections.
Deep levels associated with α and β dislocations in n-type InP
Authors: Zozime Alain , Schröter Wolfgang
Published: July 2002

We describe an experimental method which allows us to investigate α and β dislocations in compound semiconductors separately by deep level transient spectroscopy. We use two linear configurations of hardness indentations surrounding a key-shaped metal-insulator-semiconductor contact on {100} planes of n-type InP to generate either α or β dislocations beneath the contact. We observe significant differences in the point defect concentration generated by the motion of the two types of dislocations.
Raman scattering verification of nonpersistent optical control of electron density in a heterojunction
Authors: Richards D. , Fasol G. , Ploog K.
Published: July 2002

We report electronic Raman scattering measurements of the plasmon mode in a single GaAs/AlGaAs heterojunction, with a δ layer of acceptors in the GaAs buffer a well-defined distance from the interface. Under illumination above the band gap of the AlGaAs barrier, a dynamic charge-transfer effect occurs in which the quasi-two-dimensional electron concentration of the hetrojunction decreases. From Raman measurements of the plasmon mode we directly determine the change in carrier concentration with excess illumination. We obtain a time of τ=120 ps for the transfer of electrons from the AlGaAs barrier into the two-dimensional channel.
Bias circuit effects on the current-voltage characteristic of double-barrier tunneling structures: Experimental and theoretical results
Authors: Belhadj C. Y. , Martin K. P. , Ben Amor S. , Rascol J. J. L. , Higgins R. J. , Potter R. C. , Hier H. , Hempfling E.
Published: July 2002

Using the stable, dc current-voltage (I-V) curve measured from a double-barrier resonant tunneling structure, we have studied the effects of external circuit elements on device oscillations. A simulation, using the experimental I-V and a simple circuit model for the biasing arrangement, showed that hysteresis and vertical jumps appear in the current-voltage curve when the circuit oscillates. This observation is supported by experimental results obtained on the same device with external circuit elements intentionally added to the biasing configuration.
Evidence for a stretched-exponential description of optical defect generation in hydrogenated amorphous silicon
Authors: Bube Richard H. , Echeverria Lisa , Redfield David
Published: July 2002

It is shown that a growing number of experimental results, including some that are very recent and detailed, provide a strong support for a stretched-exponential description of optically induced degradation in hydrogenated amorphous silicon. This support consists of the confirmation of predictions of intensity-independent saturation of the density of light-induced defects, as well as several effects involved in the time dependence of degradation. These rate effects include variations with (a) light intensity, (b) temperature during degradation, (c) the range of density variation, and (d) the optical properties of the material.
Interface impurities of low-temperature (900 °C) deposited Si epitaxial films prepared by HF treatments
Authors: Miyauchi Akihiro , Inoue Yousuke , Suzuki Takaya , Akiyama Mikio
Published: July 2002

Impurities at the interfaces of HF-treated Si (100) substrates and Si films prepared by low-temperature (900 °C) chemical vapor deposition using SiH2 Cl2 were measured by secondary-ion mass spectroscopy. Si substrates were prepared by 49% HF, 5% HF, and 0.05% HF acid solutions and loaded into the growth chamber without a water rinse. Carbon, fluorine, oxygen and chlorine were detected at the interfaces for 49% HF and 0.05% HF treated substrates, but they were not detected for 5% HF-treated samples. Desorption of the contaminants appeared to be sensitively related to a difference in chemical states of the HF-treated surfaces.
Grain growth kinetics during ion beam irradiation of chemical vapor deposited amorphous silicon
Authors: Spinella C. , Lombardo S. , Campisano S. U.
Published: July 2002

The amorphous to polycrystal transition during Kr ion beam irradiation of chemical vapor deposited silicon layers has been studied in the temperature range 320–480 °C. At each irradiation temperature the average grain diameter increases linearly with the Kr dose, while the grain density remains constant within the experimental accuracy. The growth rate follows a complex behavior which can be described by dynamic defect generation and annihilation. The absolute value of the grain growth rate is equal to that of the ion-assisted epitaxial layer by layer crystallization in the silicon (111) orientation. This result can be related to the crystal grain structure and morphology.
On the linewidth enhancement factor in semiconductor lasers
Authors: Olofsson L. , Brown T. G.
Published: July 2002

The linewidth enhancement factor α is known to have an important impact on semiconductor laser frequency stability. We determine under what general circumstances the value of α for a semiconductor laser may depend upon the longitudinal laser structure. A longitudinal modulation of the modal refractive index is shown not to have any influence on α, while our results indicate that a longitudinal modulation of the modal gain such as would be used in a gain-coupled laser will in general change the linewidth enhancement factor.
Asymmetric distribution of microtwins in a GaAs/Si heterostructure grown by molecular beam epitaxy
Authors: Xie Q. H. , Fung K. K. , Ding A. J. , Cai L. H. , Huang Y. , Zhou J. M.
Published: July 2002

The distribution of microtwins in GaAs epilayer grown on Si (001) substrates tilted towards the [1̄11] direction by molecular beam epitaxy has been studied by transmission electron microscopy. An asymmetric distribution of microtwins attributed to substrate misorientation and two-dimensional (2D) growth mode has been found. Orthogonal [1̄10] and [110] cross sections are identified by the angle of tilt in large-angle convergent beam electron diffraction Tanaka patterns [J. Electron. Microsc. 29, 408 (1980)] taken across the GaAs/Si interface. It is found that (11̄1) microtwins are preferentially grown in GaAs epilayers on a tilted Si (001) substrate where the growth mode is 2D, while symmetrical (1̄1̄1) and (111) twins are observed when there is a reversal of twin distribution and the growth mode is 3D.
As-deposited Sb-doped Bi-Pb-Sr-Ca-Cu-O thin films prepared by pulsed laser deposition
Authors: Mao X. L. , Russo R. E. , Liu H. B. , Ho J. C.
Published: July 2002

Superconducting Bi-Pb-Sr-Ca-Cu-O films doped with Sb have been fabricated on MgO single-crystal substrates without post-annealing, using pulsed excimer laser deposition. Deposition at 800 °C in 0.2 Torr oxygen environment from a target doped with Sb yielded as-deposited superconducting films with zero resistance at 70 K. X-ray diffraction data show the films are c-axis oriented 2212 phase material. Scanning electron micrographs indicate that doping with Sb enhances grain growth. These results demonstrate that Sb acts to stabilize the 2212 phase in the as-deposited films.
Expansion of amorphous carbon in W/C multilayers after annealing
Authors: Jiang Xiaoming , Xian Dingchang , Wu Ziqin
Published: July 2002

Dynamical optical dispersion theory is employed to analyze the variations of the positions and intensities of x-ray diffraction peaks from the W/C multilayer. It is confirmed that the thickness of the C layer expands with the annealing temperature and the multilayer remains undamaged until 800 °C. There is an obvious drop of interfacial root mean square (rms) roughness at 600–800 °C.
Effects of substrate misorientation on ordering in GaAs0.5P0.5 grown by organometallic vapor phase epitaxy
Authors: Chen G. S. , Jaw D. H. , Stringfellow G. B.
Published: July 2002

Effects of (001) GaAs substrate misorientation on the formation of the group V sublattice {111} (CuPt) ordered structure are studied for the first time for GaAs0.5P0.5. It is found that the direction of substrate misorientation has a strong effect on the determination of which variants are formed. Two of the four possible ordered variants appear for epilayers grown on exact (001) substrates. The same two variants also appear for the epilayers grown on the (001) substrates misoriented by 6° towards [110]. Only one variant appears on epilayers grown on (001) substrates misoriented by 6° towards the [1̄10] direction. Most significantly, all the ordered-induced diffraction spots in GaAsP are found to occur on the [110] cross section. Thus, the variants found in GaAsP are exactly the same as for GaInP, an alloy with CuPt ordering on the group III sublattice. This result is contradictory to expectations based on the bond-length model proposed previously for GaInP alloys. In addition, for all the 6° misorientated GaAs substrates, independent of the direction of misorientation, large ordered domains with dimensions on the order of micrometers are found in the GaAsP alloys. This has not been reported for other ternary or quaternary alloy systems.
Texture growth processing of plasma-sprayed Y-Ba-Cu-O superconducting deposits
Authors: Wang H. , Herman H. , Wiesmann H. J. , Zhu Y. , Xu Youwen , Sabatini R. L. , Suenaga M.
Published: July 2002

A partial melt/texture growth process has been applied to plasma-sprayed YBa2Cu3O7−x deposits. The length of the aligned grains is in the range 300–500 μm. Small-angle grain boundaries with a misorientation between 3° and 5° are commonly observed. The critical current density, using a four-probe method with continuous direct current, is in excess of 5000 A/cm2 under an applied field of 1 T at 77 K.
Photoluminescence and reflection high-energy electron diffraction study of GaAs/AlxGa1−xAs(100) single quantum wells grown via molecular beam epitaxy employing two forms (As2 and As4) of arsenic
Authors: Kim J. Y. , Bassi D. , Ellis J. , Jostad L.
Published: July 2002

Photoluminescence (PL) and intensity behavior of a reflected high-energy electron diffraction (RHEED) beam are examined for GaAs/AlxGa1−xAs (x=0.5 and 0.7) single quantum wells grown via molecular beam epitaxy under dimeric (As2) and tetrameric (As4) arsenic pressures. The growth conditions for AlxGa1−xAs and GaAs layers in a single quantum well are determined via RHEED. Results show that PL linewidth and intensity are correlated with RHEED intensity and that the dual arsenic source scheme produces superior quality GaAs/AlxGa1−xAs heterostructures.
Localized two-dimensional electron gas formation by focused Si ion beam implantation into GaAs/AlGaAs heterostructures
Authors: Sasa S. , Miller M. S. , Li Y. J. , Xu Z. , Ensslin K. , Petroff P. M.
Published: July 2002

We have demonstrated the localized formation of a two-dimensional electron gas (2DEG) using focused Si ion beam implantation (100 keV) into undoped GaAs/AlGaAs heterostructures. We found that to achieve a good-quality 2DEG without also forming a 3DEG it is essential to use a double instead of a single interface heterostructure. The low-temperature mobility of the 2DEG was as high as 1.0×104 cm2/V s at a carrier concentration of 1×1012 cm−2. This 2DEG mobility in the double heterostructure was a factor of 3 larger than the 2DEG mobility in the single heterostructures.
Reflection high-energy electron diffraction dynamics study of GaAs, AlAs, and Al0.5Ga0.5As layer growth under As4 and/or As2 molecular beam species
Authors: Kim J. Y. , Bassi D. , Jostad L.
Published: July 2002

Reflection high-energy electron diffraction intensity dynamic behavior was examined on GaAs, AlAs, and Al0.5Ga0.5As layers using As4 and/or As2 flux to establish optimum growth conditions for heterointerfaces. Results show that As4 is preferable for the growth of AlAs and Al0.5Ga0.5As, while As2 is better for GaAs. This finding is explained on the basis of the expected dynamic surface kinetic processes. Low-temperature photoluminescence line width of a quantum well (20 monolayer GaAs well/100 monolayer Al0.5Ga0.5As barriers) grown under the optimized growth condition is 4.5 meV.
Low threshold and high power output 1.5 μm InGaAs/InGaAsP separate confinement multiple quantum well laser grown by chemical beam epitaxy
Authors: Tsang W. T. , Wu M. C. , Tanbun-Ek T. , Logan R. A. , Chu S. N. G. , Sergent A. M.
Published: July 2002

We have demonstrated the first successful preparation of InGaAs/InGaAsP multiple quantum well (MQW) lasers grown by chemical beam epitaxy. The broad-area threshold current densities of standard (not graded index) separate confinement heterostructure (SCH) MQW lasers were as low as 860 and ∼590 A/cm2 for cavity lengths of 500 and 1500–3500 μm. Such values are similar to those obtained from MQW wafers employing the more advanced graded index SCH(GRIN-SCH) grown by metalorganic vapor phase epitaxy. Buried-heterostructure lasers also have similar threshold currents, i.e., 25–40 mA for 300–1500 long cavities. Pulsed and cw output power at 1.57 μm as high as 216 and 140 mW were obtained from 1-mm-long buried-heterostructure lasers having antireflection and high reflection coatings of ∼5% and ∼85%. The layer thickness uniformity is better than ±1% across a 2-in.-diam wafer.
50 Hz current-dependent losses of Bi2Sr2Ca1Cu2O8+x/Ag wires
Authors: Zannella S. , Tenbrink J. , Heine K. , Ottoboni V. , Ricca A. , Ripamonti G.
Published: July 2002

50 Hz current-dependent loss measurements were carried out at 4.2 K on short straight samples of Bi2Sr2Ca1Cu2O8+x /Ag wires having high critical current densities of up to 1.5×104 A/cm2 at 26 T. The ac power losses vary proportional to the square of the transport current which is not consistent with the simple Bean model. On the other hand the losses depend linearly on the frequency of the alternating current which would be compatible with hysteresis as the dominant loss mechanism. Loss values are found to be rather high and are not strongly influenced by bias magnetic fields up to 1 T. Several effects may contribute to the loss enhancement and its current dependence, however the reason for this behavior remains to be clarified.
Intersubband infrared absorption in a GaAs/Al0.3Ga0.7As quantum well structure
Authors: Manasreh M. O. , Szmulowicz F. , Fischer D. W. , Evans K. R. , Stutz C. E.
Published: July 2002

The linewidth, total integrated area, and peak position (ν0) of the intersubband transition (IT) in a GaAs/Al0.3Ga0.7As multiple quantum well, with doping in the barrier, are studied as a function of temperature using the infrared absorption technique. From the temperature dependence of the linewidth and the configuration coordinate model we find that the electrons in the GaAs well are weakly coupled to the GaAs normal optical phonon mode. The electron density (σ) in the quantum well is extracted from the total integrated area of the IT. From the temperature-dependence of σ we conclude that the Fermi energy is also temperature dependent and that at 5 K it is about 36 meV above the ground state energy. We also find that ν0 increases as the temperature decreases. We calculated the absorption spectrum for the quantum well in a nonparabolic-anisotropic envelope function approximation including temperature-dependent effective masses, nonparabolicity, conduction-band offsets, the Fermi level, and line shape broadening. Our results indicate that a large many-body correction, in particular an exchange interaction for the ground state, is necessary to account for the experimental peak position and blue shift as the temperature is lowered.
Ion beam enhanced epitaxial growth of Ge (001)
Authors: Chason E. , Bedrossian P. , Horn K. M. , Tsao J. Y. , Picraux S. T.
Published: July 2002

An enhancement in surface smoothness during molecular beam epitaxial growth of Ge on Ge (001) by 200 eV Xe ion bombardment has been measured with reflection high-energy electron diffraction. We show that the steady-state surface is smoother during simultaneous ion bombardment and growth at 400 °C than during ion bombardment or growth alone. The smoothest surface is obtained when the rate of deposition is approximately equal to the rate of production of ion-induced surface defects. It is suggested that the smoothening is the consequence of the ion-induced vacancy-like defects annihilating with surface atoms and/or destabilizing small clusters.
High-mobility CdTe films grown by molecular beam epitaxy with excess Cd
Authors: Wu Y. S. , Waag A. , Bicknell-Tassius R. N.
Published: July 2002

We report the fact that n-type conducting CdTe can be grown by molecular beam epitaxy (MBE) with excess Cd flux and show for the first time details of the CdTe/Cd surface phase reconstruction diagram.The surface phase diagram has been mapped over the substrate temperature range 180–375 °C using Cd/CdTe ratios between 0.0 and 1.0. At low Cd/CdTe ratios and high temperatures a (2×1) reconstruction is observed and at high Cd/CdTe flux ratios we observe a c(2×2) reconstruction. We have also observed a strong influence of substrate illumination on the surface reconstruction.
Recovery of original superconducting properties in ion-irradiated Y1Ba2Cu3O7−x thin films
Authors: Vadlamannati S. , England P. , Stoffel N. G. , Ramesh R. , Ravi T. S. , Hwang D. M. , Findikoglu A. , Li Q. , Venkatesan T. , McLean W. L.
Published: July 2002

The changes in the superconducting properties of in situ pulsed laser deposited Y1Ba2Cu3O7−x thin films caused by irradiation with 200 keV He+ ions are due to both oxygen loss as well as oxygen and cationic displacements induced by the irradiation. This is demonstrated by a study of the recovery of these defects by plasma oxidation and relatively low temperature (∼600 °C) annealing in oxygen. Plasma oxidation of films irradiated to low fluences enables the replacement of oxygen atoms in the lattice, leading to a substantial recovery of Tc0, Jc, and normal state resistivity. Irradiation-induced oxygen and cationic displacements and other microscopic defects can be further annealed out at relatively low temperatures leading to an almost full recovery of Tc0, Jc, and normal state resistivity. A transmission electron microscope study of irradiated films shows evidence that they are structurally disordered.
Transport critical current density in epitaxial Bi2Sr2CaCu2O8+x films: Effects of the substrate twinning
Authors: Balestrino G. , Foglietti V. , Marinelli M. , Milani E. , Paoletti A. , Paroli P.
Published: July 2002

Epitaxial Bi2Sr2CaCu2O8+x films have been grown by the liquid phase technique on twinned LaGaO3 and untwinned SrTiO3 substrates. Crystallographic properties and transition temperatures are comparable, but the transport critical current density Jc depends dramatically on the substrate. Films grown on SrTiO3 have Jc comparable with single crystals, while films grown on LaGaO3 have Jc values extrapolated at 4.2 K in the 104–105 A cm−2 range. This effect is demonstrated to be a consequence of the presence of twinning domains in the substrate.
Large critical current densities in YBa2Cu3O7−x thin films made at high deposition rates
Authors: Wu X. D. , Muenchausen R. E. , Foltyn S. , Estler R. C. , Dye R. C. , Garcia A. R. , Nogar N. S. , England P. , Ramesh R. , Hwang D. M. , Ravi T. S. , Chang C. C. , Venkatesan T. , Xi X. X. , Li Q. , Inam A.
Published: July 2002

Critical current densities (Jc) in YBa2Cu3O7−x films made at deposition rates from 0.1 to 14.5 nm/s (∼50 μm/h) were measured using a direct transport method. As the deposition rate was increased by two orders of magnitude, the films exhibited no marked degradation in current carrying capability with Jc of ∼4×106 A/cm2 at 77 K and zero field. Jc for all the films showed similar behavior under a magnetic field up to 8 T, although extra structural defects were found in the films deposited at the higher rates. The results from this experiment indicate the feasibility for coating wires, tapes, and other macroscopic shapes with high Tc superconductors using proper vapor deposition techniques.
Processing controlled stacking faults in YBa2Cu3O7−δ and their effect on flux pinning
Authors: Kramer M. J.
Published: July 2002

There has been considerable interest in inserting controlled defects in high-temperature superconductors to enhance their flux pinning potential. One means of obtaining controlled defects in the YBa2Cu3O7−δ (Y123) structure is to decompose YBa2Cu4O8 (Y124). However, not only is the decomposition of the Y124 to optimize pinning difficult to control, sintering dense compacts of Y124 is very difficult. It is shown that the addition of 1.2 wt% CuO to Y123 sintered at 830 °C results in evenly spaced 1/6[031] extrinsic stacking faults. These stacking faults have also been shown to increase pinning energy, and are stable to at least to 900 °C. Intragranular Jc, as calculated from the hystersis loops, shows a significantly reduced temperature dependence at high fields. Jc dropped only a factor of 30 from 2×106 at 10 K to 6×104 A/cm2 at 70 K at 1 T.
Differential photoreflectance from modulation-doped heterojunctions
Authors: Sydor Michael , Badakhshan Ali , Engholm James R. , Dale Daniel A.
Published: July 2002

We present a new photoreflectance (PR) technique for studies of layered electronic materials. Using the technique, we isolate the reflected signal from buried interfaces and extract the signature from the two-dimensional electron gas in high electron mobility transistor. We compare the results from the technique with conventional PR measurements performed on sequentially etched samples. The results indicate that the new technique picks out the PR from buried interfaces and provides data on the in situ electric fields at the interfaces.
High quality planar HgCdTe photodiodes fabricated by the organometallic epitaxy (Direct Alloy Growth Process)
Authors: Ghandhi S. K. , Parat K. K. , Ehsani H. , Bhat I. B.
Published: July 2002

Hg1−xCdxTe, grown by the alloy organometallic vapor phase epitaxy technique, was used in the fabrication of p-n junction photodiodes. Hg1−xCdxTe layers, capped with a CdTe cap, were grown in a continuous run by the direct alloy growth process. These layers were p type due to column II vacancies, with a concentration of 3–4×1016/cm3. n-type regions were obtained by selectively annealing the Hg1−xCdxTe layer after opening windows in the CdTe cap layer. Vertical p-n junction diodes, with CdTe as the junction passivant, were thus formed in a planar configuration. Photodiodes, with cutoff wavelengths of 4.5 μm at 77 K, had R0 A products in excess of 9×107 Ω cm2.
Saturation of Si atom concentration in Si planar-doped InP layers grown by metalorganic chemical vapor deposition
Authors: Ishikawa Hideto , Miwa Shiro , Maruyama Toshiyuki , Kamada Mikio
Published: July 2002

A mechanism which causes saturation in Si atom concentration in planar-doped InP layers was investigated. The layers were grown by atmospheric metalorganic chemical vapor deposition (MOCVD) and planar doping was performed by supplying Si2H6 in PH3 atmosphere. We found that the sheet Si atom concentration of the layers saturated as a function of doping time. We propose a new model which can describe the saturation as competition between adsorption and desorption. This model will describe the doping time dependence and the PH3 flow rate dependence of sheet Si atom concentration of planar-doped InP layers grown by MOCVD.
IcR products of tunnel junctions with depressed order parameter
Authors: Mannhart J. , Martinoli P.
Published: July 2002

I cR N products of tunnel junctions with depressed order parameters are calculated. It is shown that in contrast to abrupt, classical tunnel junctions, IcRN products of junctions with depressed order parameter are a function of Ic with IcRN(Ic) ≤ πΔ0/2e.
High critical current densities in YBa2Cu3O7−x thin films formed by metalorganic chemical vapor deposition at 730 °C
Authors: Li Y. Q. , Zhao J. , Chern C. S. , Huang W. , Kulesha G. A. , Lu P. , Gallois B. , Norris P. , Kear B. , Cosandey F.
Published: July 2002

YBa2Cu3O7−x superconducting thin films with a critical current density of 2.3×106 A/cm2 at 77.7 K and 0 T were prepared by a metalorganic chemical vapor deposition process. The films were formed in situ on LaAlO3 at a substrate temperature of 730 °C in 2 Torr partial pressure of N2O. Resistivity and magnetic susceptibility measurements of the as-deposited films show a sharp superconducting transition temperature of 89 K with a narrow width of less than 1 K. Critical current densities were measured by the dc transport method with a patterned bridge of 120 μm×40 μm. Both x-ray diffraction and high-resolution electron microscopy measurements indicate that films grew epitaxially with the c axis perpendicular to the surface of the substrate.
Identification of the first nucleated phase in the interfacial reactions of ultrahigh vacuum deposited titanium thin films on silicon
Authors: Wang M. H. , Chen L. J.
Published: July 2002

The first nucleated phase in ultrahigh vacuum deposited Ti thin films on silicon has been unambiguously identified utilizing high-resolution transmission electron microscopy (HREM) in conjunction with optical diffractometry. Ti5Si3 was found to form first at the interface of the Ti overlayer and the amorphous interlayer. For plan-view specimens of the samples annealed at 450 °C for 30 min, 1 and 2 h, all 15 silicide diffraction rings corresponding to interplanar spacings longer than 0.098 nm could be attributed to Ti5Si3. Ti5Si3 was also the only silicide phase that could match the symmetry and lattice spacings of the HREM images. The observation is consistent with a kinetic model which predicts that the crystalline phase with composition and structure nearest to that of the amorphous interlayer will be first nucleated.
Photoluminescence and magnetic resonance studies of Er3+ in MeV ion-implanted GaAs
Authors: Klein P. B. , Moore F. G. , Dietrich H. B.
Published: July 2002

The effects of post-implantation annealing have been studied in MeV Er-implanted GaAs by monitoring the Er3+ electron paramagnetic resonance (EPR) signal as well as the Er3+ and near-band-edge photoluminescence (PL) spectra as a function of the anneal temperature. Er3+ PL is observed from several distinct Er sites in the annealed material. In addition, the observed dependences upon anneal temperature suggest that the Er3+ PL is emitted from centers that are not in the Er3+ state at equilibrium. Absolute EPR measurements of the Er3+ concentration indicate that only a small fraction (<0.1%) of the Er in the sample is Er3+.
Poled polymers for frequency doubling of diode lasers
Authors: Rikken G. L. J. A. , Seppen C. J. E. , Nijhuis S. , Meijer E. W.
Published: July 2002

We report on the design and characterization of methylmethacrylate copolymers with nonlinear optical 4-alkoxy-4′-alkylsulfone stilbene sidechains, which are transparent down to 410 nm. A fairly stable, polar orientation has been obtained by means of electric field poling, resulting in a reasonably high nonlinearity (d33≤9 pm/V).
Gas-source molecular beam epitaxy growth of highly strained device quality InAsP/InP multiple quantum well structures
Authors: Hou H. Q. , Tu C. W. , Chu S. N. G.
Published: July 2002

InAsxP1−x/InP strained multiple quantum wells with strain as high as 2.5% were grown by gas-source molecular beam epitaxy. Successful control of the arsenic composition over a wide range was achieved by two different growth techniques. Structural and optical studies, such as high-resolution x-ray rocking curve, cross-sectional transmission electron microscopy, photoluminescence, and absorption measurement, indicate that we have obtained high quality multiple quantum wells that are suitable for optoelectronic applications.
Single electron transport in a two-dimensional electron gas system with modulated barriers: A possible dc current standard
Authors: Odintsov A. A.
Published: July 2002

A small laterally confined area of the two-dimensional electron gas (2DEG) separated from two wide 2DEG regions by potential barriers is considered. Transparencies of the barriers can be controlled by the split gate voltages. The analysis shows that the dc current through the device can be quantized in units of ef, where f is frequency of the gate voltage modulation.
Magnetization of (100)NiFe films deposited on (100)Pd/Cu/Si(100)
Authors: Chang Chin-An
Published: July 2002

(100) oriented NiFe films have been deposited on (100)Si using the (100)Pd/Cu seed layers. Three Ni/Fe compositions are compared, 80/20, 50/50, and 20/80, all show the (100) orientation. The observed lattice spacings indicate an face-centered cubic structure for the 80/20 alloy, and a body-centered cubic one for the 50/50 and 20/80 alloys. When the magnetization of the NiFe alloys is compared with that obtained from pure Ni and Fe using the additivity rule, an increasing deviation is seen with increasing Fe concentration in the alloys. In-plane magnetization along different crystalline edges shows the same magnetocrystalline anisotropy for the alloys as those of Ni and Fe. This is due to the epitaxial relation between Ni and Fe, with Ni[011]∥Fe[010], the two edges with higher magnetization than those of Ni[010] and Fe[011], respectively.
Characterization of the early stages of electromigration at grain boundary triple junctions
Authors: Genut M. , Li Z. , Bauer C. L. , Mahajan S. , Tang P. F. , Milnes A. G.
Published: July 2002

The formation and growth of holes and hillocks at grain boundary triple junctions in thin-film conductors of gold on gallium arsenide and thin-film conductors of aluminum-1 wt. % silicon on (oxidized) silicon during the early stages of electromigration have been investigated through measurement of fractional change of electrical resistance ΔR/R and microstructural characterization by scanning and transmission electron microscopy. Each grain boundary triple junction is characterized by a unique structure factor ΔY, which defines the degree of cumulative flux divergence and, consequently, the degree of susceptibility to formation and growth of holes or hillocks. Resultant holes are characterized by a shape factor  f, which defines the degree of noncircularity and, consequently, relates fractional change of hole area to ΔR/R. Estimates of the upper limit for ΔY and the average value of  f  are in good agreement with measured values of ΔR/R and consistent with observed microstructure.
In situ synchrotron studies of the structural properties of Y-Ba-Cu-O thin films during growth
Authors: Zheng J. Q. , Wang X. K. , Shih M. C. , Williams S. , So J. , Lee S. J. , Dutta P. , Chang R. P. H. , Ketterson J. B.
Published: July 2002

We report the first real time, in situ synchrotron x-ray studies of Y-Ba-Cu-O thin-film growth on (100) SrTiO3 using a miniature, faced-magnetron sputtering system. A combination of the substrate temperature and the deposition rate determines whether the film grows along the a, c, or multiple axes.
High-contrast, large optical bandwidth field-induced guide/antiguide modulator
Authors: Huang T. C. , Chung Y. , Dagli N. , Coldren L. A.
Published: July 2002

We report an electric field induced-guide/antiguide optical intensity modulator which has a very wide optical bandwidth from 1 to 1.55 μm (ON/OFF ratio ≳ 13 dB from 1 to 1.55 μm for both TE and TM modes), which is the largest ever reported before for an intensity modulator. A TE mode ON/OFF ratio larger than 21 dB at 1.15 μm, and a propagation loss ∼1 dB at 1.3 μm has been measured. The electro-optic effects, along with carrier effects have been exploited to increase the refractive index under the guide and adjacent antiguide electrodes by applying reverse biases to them.
Quenched-in defect removal through silicide formation by rapid thermal processing
Authors: Mathiot Daniel
Published: July 2002

We report on a detailed study of the influence of TiSi2 silicidation on the formation of the quenched-in defects usually created by rapid thermal processing (RTP). It is shown that TiSi2 growth during RTP leads to a total removal of the defects, whereas the presence of TiSi2 by itself (without growth) has no influence. It is concluded that the defect removal is caused by the strong vacancy injection induced by the silicide growth.
Identification of a paramagnetic nitrogen dangling bond defect in nitrided silicon dioxide films on silicon
Authors: Chaiyasena I. A. , Lenahan P. M. , Dunn G. J.
Published: July 2002

We report the first observation of a nitrogen dangling bond center in nitrided thermally grown silicon dioxide films on silicon. Interpretation of the 14N hyperfine parameters indicates that the unpaired electron wave function is strongly localized on the central nitrogen and that the wave function is highly p in character.
Preferred alignment of twin boundaries in YBa2Cu3Ox thin films and YBa2Cu3Ox/PrBa2Cu3Ox superlattices on SrTiO3
Authors: Budai J. D. , Chisholm M. F. , Feenstra R. , Lowndes D. H. , Norton D. P. , Boatner L. A. , Christen D. K.
Published: July 2002

The structure of YBa2Cu3Ox thin films and YBa2Cu3Ox/PrBa2Cu3Ox superlattice films grown on (00L) SrTiO3 substrates has been studied using x-ray diffraction and transmission electron microscopy. The films consist of four symmetry-equivalent domains related by mutually perpendicular (hh0) and (hh̄0) twin boundaries. One twin orientation is often highly favored over the other. We have correlated this in-plane symmetry breaking with small miscuts of the substrate surface towards the [HH0] direction and propose that interfacial steps act as nucleation sites for twins. Thus, by controlling the surface normal, a technique is described for producing films containing aligned twin boundaries.
Thin buried cobalt silicide layers in Si(100) by channeled implantations
Authors: Dekempeneer E. H. A. , Ottenheim J. J. M. , Zalm P. C. , Bulle-Lieuwma C. W. T. , Vandenhoudt D. E. W. , Naburgh E. P.
Published: July 2002

Si(100) wafers have been implanted with 50 keV Co ions at elevated substrate temperatures (320 °C) in the dose range 7.8×1014–7.8×1016 at. cm−2. A comparison is made between channeled (along the Si 〈100〉 surface normal) and random (tilted by 7°) implantations. Co depth distributions are measured with secondary-ion mass spectrometry and compared to marlowe and trim simulations. Annealed samples are characterized by Rutherford backscattering spectrometry and transmission electron microscopy. Our data indicate that for channeled implantations the sputtering effect is strongly reduced as compared to random implantations. Also, the average penetration depth is increased by about 20%. As a consequence, annealing of our high-dose implanted samples yields either a discontinuous surface silicide layer (random case) or a pinhole-free buried silicide layer (channeled case).
Growth of gallium arsenide on hydrogen passivated Si with low-temperature treatment (∼600 °C)
Authors: Fang S. F. , Salvador A. , Morkoç H.
Published: July 2002

Epitaxial growth of GaAs on Si commonly employs a high-temperature (≳850 °C) oxide desorption step. In this letter, we report the first epitaxial growth of GaAs on Si without the need for this high-temperature treatment. This method utilizes a final HF treatment whereby the Si surface dangling bonds are terminated by hydrogen with a resultant (1×1) bulk-like surface structure. Upon medium temperature heat treatment (×500 °C), hydrogen leaves the surface leading to the common orthogonal 2×1 surface reconstruction. High quality GaAs epitaxial layers were successfully grown on these 2×1 reconstructed Si surfaces with the pregrowth substrate preparation temperatures of as low as 600 °C.
Cd-H pairs in GaAs: Identification and stability
Authors: Pfeiffer W. , Deicher M. , Keller R. , Magerle R. , Recknagel E. , Skudlik H. , Wichert Th. , Wolf H. , Forkel D. , Moriya N. , Kalish R.
Published: July 2002

The Cd-H complex in 111mCd-doped GaAs implanted with low-energy (150–400 eV) hydrogen atoms is identified and studied by perturbed angular correlation spectroscopy using radioactive 111mCd as a probe. By measuring the fraction of Cd-H pairs in an isochronal annealing experiment, the stability of the pairs is deduced yielding a dissociation energy of ED=1.35(10) eV. After 111mCd implantation but preceding the H loading, the GaAs samples have to be annealed at temperatures exceeding 900 K in order to form Cd-H pairs. These temperatures are in agreement with the temperature range required for electrical activation of Cd implants, suggesting that a Coulombic interaction is responsible for the formation of Cd-H pairs in GaAs.
1.3 mJ XeCl laser pumped by microwaves
Authors: Klingenberg H. H. , Gekat F.
Published: July 2002

A microwave discharge pumped XeCl laser of a pulse energy of 1.3 mJ was demonstrated for the first time with nonrelativistic microwave sources. The pulse duration was measured to be 16 ns. This corresponds to peak powers of the order of 100 kW. The repetition frequency was so far 10 Hz.
Use of ultraviolet/ozone cleaning to remove C and O from GaAs prior to metalorganic molecular beam epitaxy and metalorganic chemical vapor deposition
Authors: Pearton S. J. , Ren F. , Abernathy C. R. , Hobson W. S. , Luftman H. S.
Published: July 2002

Ultraviolet/ozone cleaning of GaAs substrates prior to metalorganic molecular beam epitaxy at 500 °C is shown to reduce the interfacial C and O concentrations by more than two orders of magnitude. Metal-semiconductor field-effect transistors (MESFETs) utilizing this cleaning prior to growth of the component epitaxial layers display superior current voltage (I-V) saturation characteristics compared to identical devices grown without the cleaning step. By contrast, provided the GaAs surface is not contaminated with silicates, the atomic hydrogen generated at the growth surface during growth by metalorganic chemical vapor deposition (MOCVD) leads to lower O and C interfacial concentrations, thereby circumventing the need for ozone cleaning. MESFETs grown by MOCVD with or without this cleaning have excellent I-V characteristics.
Properties of silicon surface cleaned by hydrogen plasma
Authors: Ishii M. , Nakashima K. , Tajima I. , Yamamoto M.
Published: July 2002

Properties of the silicon surface cleaned by the irradiation of the hydrogen electron cyclotron resonance plasma has been studied by x-ray photoelectron spectroscopy, reflection high-energy electron diffraction, and Fourier transform infrared spectroscopy. It was confirmed that the irradiation of the hydrogen plasma eliminated both a native oxide layer and a contaminated carbon layer from the silicon surface. In addition, it was found that the surface has the retardation effect on the air oxidation at room temperature. However, the plasma irradiation caused the minute roughness on the surface and hydrogen penetration into the bulk.
Effect of x-y coupling on the beam breakup instability
Authors: Bosch R. A. , Gilgenbach R. M.
Published: July 2002

In solenoidal beam transport systems, motions in the x and y directions are coupled by the v×B force. A two-dimensional coupled mode description of the beam breakup (BBU) instability is presented; its dispersion relation is derived and compared with the one-dimensional BBU dispersion relation. In the two-dimensional description, instability growth is doubled and two additional wave modes are found in the regime of strong focusing. In the weak focusing regime, the two-dimensional description gives the same dispersion relation as the one-dimensional model.
Electroluminescence from a pseudomorphic Si0.8Ge0.2 alloy
Authors: Robbins D. J. , Calcott P. , Leong W. Y.
Published: July 2002

Electroluminescence due to recombination of electrons and holes at the band edges of strained Si1−xGex alloy is reported for the first time. This is demonstrated by comparison of the luminescence energy with the photoconductivity threshold of a p-i-n diode incorporating Si0.8Ge0.2, and with the calculated energy gap for the pseudomorphic alloy. The luminescence is strong at low temperature and persists to 220 K. The high intensity of the no-phonon line relative to the momentum-conserving phonon replica in the spectrum shows the scattering in the random alloy is a practical and effective mechanism for enhancing the recombination probability in this indirect semiconductor.
Critical currents and processing of wound coils of Ag-sheathed Bi-2223 high T
c tape: Microstructural and pinning effects
Authors: Motowidlo L. R. , Gregory E. , Haldar P. , Rice J. A. , Blaugher R. D.
Published: July 2002

Using a ‘‘powder-in-tube’’ process long lengths of high Tc prototype tape have been fabricated with high critical currents at liquid-nitrogen temperature and excellent high field properties at liquid-helium temperature. A Pb-doped bismuth-based 2223 powder was initially prepared then packed into silver tubes. Using a combination of cold work and heat treatment, a high degree of texture and good compaction with uniform properties was achieved. Current densities exceeding 10 000 A/cm2 at 77 K and 50 000 A/cm2 at 4.2 K in zero field were measured. At the 4.2 K temperature, the material still carried approximately 14 000 A/cm2 at 8 T. Tests on spirally wound and reacted coils, 52 cm long, have also demonstrated high current carrying capability. Effects of process variations and observed microstructure on superconducting properties are described.
Reflectance modulator based on tandem Fabry-Perot resonators
Authors: Fritz I. J. , Klem J. F. , Wendt J. R.
Published: July 2002

We present calculations and data on a novel, electrically tunable reflector structure consisting of tandem Fabry–Perot resonators grown as a single epitaxial device. The device consists of three mirrors (quarter-wave stacks of AlGaAs and AlAs) separated by two cavities (one an AlGaAs alloy and the other a GaAs/AlGaAs superlattice) on a GaAs substrate. The tandem cavities produce a characteristic double-dipped reflectance spectrum which can be modulated by tunable electro-optic effects in the superlattice cavity. Our demonstration device has a modulation depth of ≳10% over a 20 nm bandwidth with <4 V of bias swing.
Remote plasma hydrogenation of ion beam amorphized silicon
Authors: Kar S. , Pankove J. I. , Tsuo Y. S.
Published: July 2002

In this investigation, the efficacy of remote plasma hydrogenation, in the passivation of bonding and other electronic defects in amorphous silicon, has been compared with those of ion beam and radio-frequency plasma hydrogenations. The amorphous silicon film was obtained by amorphization of the subsurface of ultrapure crystalline silicon by a Si ion beam. Electrical measurements indicated remote plasma hydrogenation to be a promising low- temperature defect removal technique, without the damaging effect of a plasma or the etching effects of low-energy hydrogen ions.
Liquid phase epitaxy of yttrium aluminum garnet: Reduction of growth rate by germanium oxide
Authors: Gualtieri D. M.
Published: July 2002

Germanium is found to be a growth inhibitor in the liquid phase epitaxy of yttrium aluminum garnet. Germanium oxide additions to PbO/B2O3 fluxed melts for the liquid phase epitaxy of Y3Al5O12 and Ce:Y3Al5O12 on Y3Al5O12 substrates reduce the epitaxial growth rate in an effect similar to that with calcium oxide additions to melts for the growth of Y3Fe5O12. In contrast, cerium oxide additions to Y3Al5O12 melts have no measurable effect on growth rate. Germanium oxide additions reduce the growth rate sensitivity with supercooling, at saturation temperatures near 900 °C, as an essentially linear decreasing function of the germanium oxide concentration, GeO2/(GeO2+2Al2O3), where GeO2 and Al2O3 are the molar concentrations of germanium and aluminum oxide in the melt.
Photoluminescence enhancement monitored in real time during photowashing of GaAs
Authors: Kauffman J. F. , Richmond G. L.
Published: July 2002

We have observed the luminescence emitted from GaAs during the surface treatment process known as photowashing. This allows us to probe the extent of surface quality improvement in real time as the treatment proceeds. We observe a tenfold increase in photoluminescence (PL) intensity during photowashing, which provides unambiguous proof that PL enhancement does not require an activation step following photowashing. We also observe that the PL enhancement persists for at least 1 h under continued photowashing. Studies performed to elucidate the chemistry of PL enhancement indicate that sample history has a critical influence on experimental results, and that experimental details cannot be overlooked when comparing different experiments. We quantify the improvement in surface quality by measuring surface minority trapping velocities from luminescence decay profiles following picosecond optical excitation.
Strain-relaxed epitaxial layers for high-speed electronic devices
Authors: Wang G. W.
Published: July 2002

A new approach of high-speed electronic devices beyond the limit of pseudomorphic heterostructures is investigated. Metal-semiconductor field-effect transistors (MESFETs) are fabricated on InGaAs layers which have intentionally relaxed crystal lattice on GaAs substrate to take advantage of the small effective electron mass of bulk InGaAs materials. 0.25 μm gate MESFETs with an unstrained In0.15Ga0.85As layer and In0.25Ga0.75As layer show state-of-the-art current gain cutoff frequencies of 120 and 126 GHz, respectively. These results imply a trade-off between dislocation density and effective electron mass.
Atomic ordering in InAs0.5P0.5 grown by organometallic vapor phase epitaxy
Authors: Jaw D. H. , Chen G. S. , Stringfellow G. B.
Published: July 2002

InAsP epilayers grown by organometallic vapor phase epitaxy have been investigated using transmission electron microscopy. Electron diffraction studies using 〈110〉 cross sections indicate the formation of CuPt-like ordering on the group V sublattice. Only two of the four possible ordered variants are observed for epilayers grown on the exactly (001) oriented InP substrates. All the order-induced diffraction spots for InAsP are found to occur on the [110] cross section. Thus, the variants found in InAsP are 1/2(1̄11) and 1/2(11̄1), exactly the same as those found in GaInP, an alloy with CuPt ordering on the group III sublattice. This result is in agreement with recent studies on GaAsP and is contradictory to expectations based on the bond-length model proposed previously for GaInP alloys. The direction of substrate misorientation has a strong effect on the formation of ordered structures for normally (001) oriented InP substrates.
Ferroelectric switching of a field-effect transistor with a lithium niobate gate insulator
Authors: Rost Timothy A. , Lin He , Rabson Thomas A.
Published: July 2002

A field-effect transistor in which the ferroelectric lithium niobate (LiNbO3) replaces the oxide in a conventional metal-oxide-semiconductor transistor has been fabricated. The channel conductance of this device has been shown to be strongly affected by the application of voltage pulses between the gate of the device and the substrate. A reduction of channel current of nearly 140 μA was observed after the application of a voltage pulse of −30 V and partially restored with a+10-V pulse. This behavior was found to be consistent with the influence of the polarization charge of the LiNbO3 layer on the carriers in the channel. This is the first observation of such behavior in a metal-ferroelectric-semiconductor field-effect transistor without the growth of a buffer layer between the semiconductor and ferroelectric to prevent charge injection.