bluuebunny/crossref_metadata_2025 huggingface dataset:
Adjustable surface emission from AlGaAs/GaAs laser diodes based on first-order-grating coupled surface mode emission
Authors: Golshani A. , Köck A. , Freisleben S. , Gmachl C. , Gornik E. , Korte L.
Published: July 2002

Strongly improved surface emitting laser diodes based on surface mode emission are presented. A first-order-grating was utilized for the excitation of the surface modes. This results in an efficient quasi-single-beam surface emission with low divergence and a significant narrowing in the emission spectrum. A variation in the emission wavelength of up to 4 nm is achieved by adjusting the surface waveguide thickness, which demonstrates the wavelength selection mechanism of the SME technique. The decisive advantage of the SME laser diodes in comparison to DFB/DBR laser diodes is their high flexibility in fabrication, which makes them very suitable for wavelength division multiplexing applications.
Raman polarization-selective feedback schemes for all-optical microwave frequency standards
Authors: Liu Z. D. , Juncar P. , Bloch D. , Ducloy M.
Published: July 2002

All-optical locking of the frequency difference between two laser diodes onto a Raman transition is demonstrated. The properties of Raman-type polarization spectroscopy are discussed and exemplified in the cases of the 3.036 GHz Raman resonance of the 85Rb D2 line. The generation of a polarization-selective Raman resonant optical feedback ensures the Raman optical locking of the slave diode laser onto the master oscillator.
Dielectric response process in relaxor ferroelectrics
Authors: Gui Hong , Zhang Xiaowen , Gu Binglin
Published: July 2002

The dielectric constant ε*(ω,T)=ε′(ω,T)+iε″(ω,T) of relaxor ferroelectrics is simulated by the Monte Carlo method. It is proved that the polar microregions switch among different polarization directions as a whole under the electrical field, giving rise to the high dielectric constant. The relaxor characteristics are caused by the randomly distributed interactions between the polar microregions. Factors which influence the dielectric response process are discussed.
Gain characteristics of gain-guided II–VI laser diodes
Authors: Yoshida H. , Gonno Y. , Nakano K. , Taniguchi S. , Hino T. , Ishibashi A. , Ikeda M. , Chuang S. L. , Hegarty J.
Published: July 2002

We have studied the gain characteristics of gain-guided quantum well II–VI laser diodes by measuring the amplified spontaneous emission spectra under several pulsed conditions. The temperature rise during one current pulse affects the gain characteristics and the L-I characteristics. The net modal gain at constant peak current increases with the pulse width. The peak gain for long pulses shows a superlinear dependence on injection current. In this case, the L-I curve is very steep above threshold and sometimes shows an internal quantum efficiency of more than unity. This leads to an underestimation of the internal cavity loss giving a value inconsistent with the one obtained from the gain spectra. With short pulse currents (<200 ns), the peak gain shows a weak sublinear dependence on injection current. The cavity losses obtained from the gain spectra and the L-I characteristics at short pulses are consistent. As a result, we obtain the intrinsic gain characteristics of gain-guided quantum well II–VI laser diodes.
Fabrication and characterization of modulation-doped-field-effect-transistors with antidot-patterned passivation layers
Authors: Hwang S. W. , Yu Y. S. , Ha W. I. , Kim T. G. , Han C. K. , Park J. H. , Kim M. S. , Kim E. K. , Min S. K.
Published: July 2002

A gate passivation technique for modulation-doped-field-effect-transistors has been proposed and demonstrated. This technique incorporates an antidot-patterned (net-shaped), polymer passivation layer deposited between the gate metal and the heterojunction wafer. Characterization results of the device with the patterned passivation layer show that independent engineering of the threshold voltage and the transconductance has been achieved.
Calculation of diamond chemical vapor deposition region in C–H–O phase diagram
Authors: Rakov E. G.
Published: July 2002

Thermodynamic calculations of graphite yield at the interaction of gaseous components of the C–H–O system were performed. Their results proved to be in satisfactory agreement with experimental data published on the lower concentration boundary of the diamond deposition region. The calculations indicate an influence of the substrate temperature, total pressure, and concentrations of inert and active additives on this boundary’s location. These data confirm an inference that a diamond deposition mechanism might include spontaneous growth-etch cycles due to fluctuations of the gas concentrations.
High resolution electron energy loss spectroscopy: A new probe of subgap absorption in amorphous solids
Authors: Lopinski G. P. , Lannin J. S.
Published: July 2002

The use of high resolution electron energy spectroscopy (HREELS) as a new method for studies of subgap absorption in thin films of amorphous semiconductors is demonstrated. For a-Si films, the α(ω) values extracted from the measured loss spectra are in quantitative agreement with previous optical measurements. The method is also applied to both threefold and diamond-like amorphous carbon films, yielding α(ω) down to considerably lower energies (∼50 meV) than previously reported. The HREELS method is shown to be complementary to existing techniques in that it can access the regime of low energies and ultrathin films which is difficult to investigate with the conventional methods.
Co-doped ferrite single domains and the effect of metallic nanoinclusions
Authors: Multigner M. , Läkamp S. , Pourroy G. , Hernando A. , Valenzuela R.
Published: July 2002

Magnetic properties measurements were performed on metal–ferrite composites prepared by coprecipitation of Co and Fe chlorides at various Co/Fe ratios. The microstructure can be described as octahedrally shaped ferrite particles with nanometric CoFe alloy inclusions. Upon elimination of the metallic fraction, and increase in coercive field Hc and a decrease in saturation magnetization Ms were observed. Scanning electron microscopy observations revealed that ferrite particles were in micron range, with a narrow size distribution. The composite magnetic properties can be interpreted in terms of a nanostructured exchanged-coupled system, while the ferrite-only magnetic behavior is close to a single-domain, Stoner–Wohlfarth system.
Aharonov–Bohm effect induced by light in a fiber
Authors: Kulik Igor O. , Shumovsky Alexander S.
Published: July 2002

A weakly coupled normal-metal ring surrounding an optical fiber is considered under the condition that the frequency of light in fiber is larger than the conduction bandwidth of the metal. It is shown that in the presence of static magnetic field parallel to the fiber axis, the resistance of the ring is a nonmonotone function of the optical intensity and an oscillating function of the static magnetic flux with period equal to flux quantum hc/e. The temperature dependence of oscillations requires that inelastic mean free path of electrons is larger than the ring size, and does not relate to the energy level spacing to temperature ratio.
Iodine use in solid-source III–V molecular-beam epitaxy
Authors: Micovic M. , Flack F. , Streater R. W. , SpringThorpe A. J.
Published: July 2002

Use of iodine for in situ etching of GaAs, AlAs, and InAs in solid-source molecular-beam epitaxy has been explored. Reflectance high-energy electron-diffraction intensity oscillations have been observed during iodine etching of GaAs and InAs, indicating a molecular layer-by-layer nature of material removal. Etch rates of GaAs and InAs determined from the period of the oscillations are comparable for a given iodine flux. Secondary-ion-mass spectroscopy depth profiles indicate that the etching of AlAs is negligible, and that iodine can be used as a selective etch which stops on AlAs or AlGaAs layers. Electrical properties of GaAs layers grown with an iodine beam impinging on the surface are comparable to those of the layers grown without iodine. Use of iodine for the surface cleaning of GaAs has also been examined. Our results show that iodine etching prior to growth reduces the level of carbon contamination at the substrate epilayer interface.
Control of field screening effects in GaInAs(P)/GaInAsP quantum-confined Stark effect modulator structures
Authors: König P. , Geiger M. , Ottenwälder D. , Scholz F. , Hangleiter A.
Published: July 2002

We compare the field screening behavior of quantum-confined Stark effect modulator structures where the GaInAsP/InP heterojunction is in the intrinsic (standard structure) or in the doped regions (modified structure) at working wavelengths of 1.55 and 1.3 μm. The modified structures are obtained by expanding the GaInAsP confinement layers into the p-doped and n-doped regions without changing the total intrinsic layer thickness. The effectiveness of the InP heterobarriers for the holes on the p-side and for the electrons on the n-side is thereby lowered. A significant reduction of field screening for the modified structures is achieved.
A novel multilayer circuit process using YBa2Cu3Ox/SrTiO3 thin films patterned by wet etching and ion milling
Authors: Li H. Q. , Ono R. H. , Vale L. R. , Rudman D. A. , Liou S. H.
Published: July 2002

A process combining hydrofluoric acid (HF) and Ar+ ion milling has been used to make YBa2Cu3Ox/SrTiO3/YBa2Cu3Ox(YBCO/STO/YBCO) multilayer test circuits. Low-angle steps can be readily etched in STO and YBCO films with this process. YBCO lines crossing 5° steps have about the same critical temperature Tc (89–90 K) and critical current density Jc (≳1×106 A/cm2 at 86 K) as lines on planar surfaces. Via connections have the same Tc as other circuit components and adequate critical currents for most circuit designs.
Coherent islands as preferential sites for sticking of Ge atoms in Si/Ge multilayers: Formation of conical shaped defects
Authors: Carlino E. , Tapfer L. , von Känel H.
Published: July 2002

In this work we investigate the role of coherent islands in the strain relaxation mechanism of Si/SixGe1−x multilayers by using conventional transmission electron microscopy, high-resolution transmission electron microscopy, and transmission electron spectroscopic imaging. The samples investigated were grown by molecular beam epitaxy and they differ in the number of periods, period thickness, and in the Si/Ge layer thickness ratio. The formation of defect free coherent islands in strained SixGe1−x layers is at the origin of the peculiar morphology of the interfaces (waviness). We show that coherent islands act as preferential sticking sites for Ge adatoms, producing regions of higher Ge concentration. The higher concentration of Ge corresponding to the greater lattice spacing on the top of the coherent islands depletes the relevant strained layers. The corresponding accumulation of strain energy produces the formation of ‘‘conical-shaped defects.’’ Inside these conical-shaped defects the elastic energy is relieved by nucleation of dislocations.
Hypercooling of completely miscible alloys
Authors: Wilde G. , Görler G. P. , Willnecker R.
Published: July 2002

Calorimetric measurements and undercooling investigations were performed on the high-melting, completely miscible binary systems (Co, Ni, Fe)-Pd. The alloys, characterized by phase diagrams with concavous liquidus and solidus lines, exhibit heat-of-fusion values considerably lower than calculated assuming ideal solution behavior. As a consequence, these metallic systems offer the possibility to achieve the hypercooling regime at a reduced extent of undercooling. Investigations on the undercoolability of the liquid alloys indicate the surmounting of the calculated hypercooling limit. Time-resolved radiation thermometry experimentally proved the appearance of complete isenthalpic solidification. Metallographic investigations of samples solidified from different levels of undercooling revealed the corresponding stages of microstructural evolution.
A kinetic mechanism for the formation of aligned (Bi,Pb)2Sr 2Ca2Cu3O10 in a powder-in-tube processed tape
Authors: Wang Y.-L. , Bian W. , Zhu Y. , Cai Z.-X. , Welch D. O. , Sabatini R. L. , Suenaga M. , Thurston T. R.
Published: July 2002

A two-step process is proposed for the formation of c-axis aligned (Bi,Pb)2Sr2Ca2Cu3O10+δ  [Bi(2:2:2:3)] platelets in a silver sheath. The process involves: (1) the formation of c-axis aligned (Bi,Pb)2Sr2CaCu2O8+δ  at early stage of heat treatment and (2) the subsequent intercalation of Ca–Cu–O layers to form Bi(2:2:2:3). This is based on the measurements of (1) the rocking curves for c-axis alignment and the two theta scans for the Bi(2:2:2:3) conversion ratio, both by a transmission x-ray technique, and (2) a quantitative study of the phase conversion due to intercalation of Ca–Cu–O layers into existing Bi(2:2:1:2) by transmission electron microscopy.
He-plasma assisted epitaxy for highly resistive, optically fast InP-based materials
Authors: Mitchell D. B. , Robinson B. J. , Thompson D. A. , Qian Li , Benjamin S. D. , Smith P.W. E.
Published: July 2002

InP and related quaternaries (InGaAsP) have been grown by conventional gas source molecular beam epitaxy while simultaneously exposing the growth surface to a He plasma stream generated by electron cyclotron resonance. For growth temperatures from 400 to 450 °C, the InP produced by this process displays greatly increased resistivity, as high as 105 Ω cm, compared to growth without plasma where resistivities are typically less than 1 Ω cm. An InGaAsP quaternary, with band-gap wavelength of 1.55 μm, grown with the plasma displays a sharp band edge and fast photoresponse (15 ps).
Ohmic contacts on n-type CdTe and CdZnTe using coherently grown neodymium
Authors: Brun-Le Cunff D. , Daudin B. , Rouvière J. L.
Published: July 2002

Low resistance metallic contacts have been realized on n-type doped CdTe and CdZnTe layers grown by molecular beam epitaxy. The n-type doping of the layers was achieved using iodine or indium as a dopant. The metal/II–VI semiconductor heterostructures were realized with neodymium that was found to grow coherently on CdTe and CdZnTe substrates, with formation of a reacted compound at the interface. This interfacial layer is noted IL(Nd). The specific contact resistance, ρc, of the Nd/IL(Nd)/n-CdTe and Nd/IL(Nd)/n-CdZnTe heterostructures was measured using the transmission line model. The best result of 2.5×10−5 Ω cm2 is obtained for Nd/IL(Nd)/n-CdTe and for a doping level of about 6×1018 cm−3. An exponential increase of the ρc value is found when increasing zinc concentration in the CdZnTe alloys.
The energies of microvoid formation in Si as a function of applied hydrostatic stress
Authors: Cuendet Nicolas , Halicioglu Timur , Tiller William A.
Published: July 2002

Using a Tersoff-type empirical potential energy function, the free energy of formation for microvoids in silicon containing 24 and 57 vacancies was calculated at 1000 K as a function of externally applied hydrostatic stress in the range of −10 kbar (tensile) to 10 kbar (compressive). The results indicate that bigger microvoids are more sensitive to the applied stress than the smaller ones.
Measurement of the interwell carrier transport lifetime in multiquantum-well optical amplifiers by polarization-resolved four-wave mixing
Authors: Paiella Roberto , Hunziker Guido , Vahala Kerry J. , Koren Uzi
Published: July 2002

Polarization-resolved four-wave mixing spectroscopy is used to study interwell carrier dynamics in an alternating-strain multiquantum-well optical amplifier. The experimental data are found to be in good agreement with a simple model based on quantum capture/escape and diffusion processes. The results suggest that the interwell transport in this structure is mainly limited by carrier escape, and give an estimate of 16 ps for the overall transport lifetime.
Observation of spontaneous emission microcavity effects in an external-cavity surface-emitting laser structure
Authors: Sandusky J. V. , Brueck S. R. J.
Published: July 2002

We report both enhancement and inhibition of spectrally integrated, cavity-normal room temperature spontaneous emission (SpE) in an external-microcavity surface-emitting laser as the cavity length is varied. The use of an external cavity permits changes in resonator length without altering the semiconductor properties. Measurements of the SpE radiation pattern and spectrum under conditions of enhancement and inhibition are compared to the macrocavity continuum limit. A transition of continuum behavior occurs as the cavity length is increased beyond the spontaneous emission coherence length.
Optimization of four-wave mixing conversion efficiency in the presence of nonlinear loss
Authors: Darwish A. M. , Ippen E. P. , Le H. Q. , Donnelly J. P. , Groves S. H.
Published: July 2002

We analyze the effect of nonlinear loss on four-wave mixing (FWM) conversion efficiency. Maximum conversion efficiency is geometry independent and equal to e−2|χ(3)/Im{χ(3)}|2 when nonlinear loss dominates. Optimum device length and operating conditions are obtained and theoretical results are verified with a picosecond pulse FWM experiment.
Pressure and power dependence of self-bias, sheath thickness, and deposition rate in confined methane plasmas at 13.56 MHz
Authors: Hytry R. , Boutard-Gabillet D.
Published: July 2002

A capacitively coupled asymmetric rf discharge has been confined by means of a grounded metal grid above the powered electrode. The dc self-bias, optical sheath thicknesses and deposition rates in methane plasmas have been measured versus gas pressure, absorbed rf power, and gas flow rate. While the self-bias increases as a power law of the absorbed power for a given pressure, the evolution with pressure shows two domains for a given absorbed power. This may be attributed to the variation of the plasma potential due to the small, confined configuration. Otherwise the pressure variation of the deposition rates was also found to depend on the gas flow in the present conditions.
Monolithic waveguide smart pixels for high-contrast and high-gain all-optical switching
Authors: Hilburger U. , Kneissl M. , Kiesel P. , Knüpfer B. , Döhler G. H. , Grothe H.
Published: July 2002

We demonstrate a novel and simple smart pixel which combines free space optics for the input signal and waveguide configuration for the output beam. Our monolithic smart pixels consist of a threshold switch with high photoconductive gain and a Franz–Keldysh waveguide modulator. The switch provides sufficiently high current to control directly the output beam via the modulator. A high switching contrast of ≳17 dB and a fan-out ≳230 at an optical output power of ≳130 μW has been achieved with our first monolithic smart pixels, which are still far from being optimized.
Instabilities in electroluminescent porous silicon diodes
Authors: Linnros J. , Lalic N. , Knápek P. , Luterová K. , Kočka J. , Fejfar A. , Pelant I.
Published: July 2002

The stability of high quantum efficiency, porous silicon (PS) electroluminescent (EL) diodes have been analyzed under pulsed operation. The results show that EL exhausting is due to a charging of the PS network which recovery is thermally activated (Er∼0.4 eV). This suggests a charge trapping mechanism at larger crystallites with low bandgap, inhibiting further injection of carriers. Also, forward current is found to be thermally activated, however, with a distinctly lower activation energy (Ej∼0.1–0.2 eV), possibly related to jumping of carriers over barriers between nearby crystallites. Finally, high current densities may lead to thermal runaway causing permanent damage to the structure.
High-speed GaAs metal-semiconductor-metal photodetectors with recessed metal electrodes
Authors: Yuang R.-H. , Chien Y.-J. , Shieh J.-L. , Chyi J.-I.
Published: July 2002

The GaAs metal-semiconductor-metal photodetector (MSM-PD) with recessed metal electrodes have been fabricated and characterized. The recessed structure allows very short photocarrier sweep-out time because of both a strengthened electric field in the active region and a shortened distance for the photocarriers to reach the electrodes. Improved high-speed performance and enhanced peak amplitude in the temporal response can thus be obtained simultaneously. There is about a 60% and 50% improvement in the fall time and peak amplitude of the temporal response at 5 V bias over the conventional device, respectively. The measured results also show that high-speed operation can be achieved at a lower bias voltage for the GaAs MSM-PD with recessed metal electrodes as compared to the conventional one. Two-dimensional simulation was carried out to give an insight into the operation principle of this device.
Evidence for electron trapping by Sm dimer and trimer centers in Sm doped CaF2
Authors: Beck W. , Ricard D. , Flytzanis C.
Published: July 2002

Using coherent anti-Stokes Raman and linear absorption spectroscopy we present experimental evidence for a novel electron trapping mechanism in Sm doped CaF2. The appearance of additional Raman lines after ionization of the Sm2+ ions, their dependence on the Sm3+ concentration and their behavior due to an enhancement by the lowest 4f→5d transition of Sm2+, support strongly that electrons can be trapped by dimers or trimers of Sm3+ ions in a CaF2 lattice. The resulting color change is reversible due to a possible reionization of the traps, rendering this material photochromic.
Control of structure and optical anisotropy in porous Si by magnetic-field assisted anodization
Authors: Nakagawa Takashi , Koyama Hideki , Koshida Nobuyoshi
Published: July 2002

The effects of an applied magnetic field during anodization on the structural and optical isotropy of luminescent porous silicon (PS) are investigated. The PS layers are prepared by anodizing p-type Si wafers in HF solutions with an external magnetic field of 0–1.7 T applied perpendicular to the Si surface. It is shown that the photoluminescence intensity of PS significantly increases with increasing magnetic field. This effect is accompanied by an increase in both the porosity and the optical isotropy without affecting the surface chemical composition. The structural uniformity in the PS layer and at the PS-substrate interface are also improved. These results suggest that an external magnetic field during anodization regulates the supply of holes from the substrate and produces well-controlled optical and structural properties of PS.
Frequency-stable, narrow linewidth oscillation of red diode laser with phase-conjugate feedback using stimulated photorefractive backscattering
Authors: Shiratori Akira , Obara Minoru
Published: July 2002

Frequency-stable, narrow linewidth oscillation of a 638 nm AlGaInP diode laser has been achieved with an external photorefractive BaTiO3 phase conjugator in a novel configuration. The mechanism of the phase conjugation in this configuration is the stimulated photorefractive backscattering process with the measured phase-conjugate reflectivity of <1.8×10−3%. With this new phase-conjugate feedback method, the laser linewidth was reduced to ∼0.1 nm (within the resolution limit of the spectrum analyzer used) and the oscillation frequency was highly stabilized, while it was impossible with a conventional cat conjugator.
Dipole tip model investigation of resonance effects in scanning tunneling microscopy
Authors: Kalotas T. M. , Lee A. R. , Liesegang J. , Alexopoulos A.
Published: July 2002

The distribution of the tunneling current in the semiclassical mode of operation of the scanning tunneling microscope is studied using an axially symmetric 3-D tip. The tip is taken as an equipotential of a dipole, thus giving an analytical form for the potential and the field lines between the tip and the surface, with the latter taken to be atomically flat and corresponding to the zero equipotential plane. Field emission resonance calculations are made, allowing conductance and tip-to-surface separation to be determined as functions of bias voltage at constant current. Results are compared with the measurements of Becker, Golovchenko, and Swartzentruber [Phys. Rev. Lett. 55, 987 (1985)].
Delta-doped InGaP grown by low pressure metalorganic chemical vapor deposition
Authors: Malacký L. , Kúdela R. , Morvic M. , Černianský M. , Peiner E. , Wehmann H.-H.
Published: July 2002

Silicon-delta-doped In0.49Ga0.51P layers were grown at 560 °C, 640 °C, and 720 °C by low pressure metalorganic chemical vapor deposition. For the growth temperature 560 °C, the electron sheet concentration saturated at 5.9×1012 cm−2, which corresponds to a three-dimensional (3D) concentration of 1.5×1019 cm−3. The sheet concentration increases by factor 3.5 and even by factor 11 for growth temperatures 640 °C and 720 °C, respectively. The widths of doping profiles were less than 6 nm, indicating a strong carrier confinement in the V-shaped quantum well. Electron mobility in samples grown at 560 °C indicates the presence of acceptor impurities at a high density. In InGaP grown at 640 °C, compensation effects of background acceptors do not occur resulting in extremely sharp profiles with a full width at half-maximum of 1.9 nm and a peak concentration of 2.1×1019 cm−3. The highest electron sheet concentrations were obtained in samples grown at 720 °C.
Intersubband absorption in Si/Si1−x−yGexCy quantum wells
Authors: Boucaud P. , Lourtioz J.-M. , Julien F. H. , Warren P. , Dutoit M.
Published: July 2002

Intersubband absorption in the valence band of Si–Si1−x−yGexCy multiquantum wells is reported. The quantum wells with x≊17% and y≊1% and thicknesses around 3 nm are grown pseudomorphically by rapid thermal chemical vapor deposition on Si(001). The carbon is incorporated in substitutional site using methylsilane as the gas precursor. The quantum wells exhibit near-band-edge photoluminescence with no-phonon and phonon-assisted replica. The energy position of the no-phonon and phonon-assisted replica are shifted to high energy with respect to bulk alloys due to the quantum confinement of the first heavy hole subband. The intersubband absorption between confined subbands is measured in a multipass waveguide geometry under optical pumping. Absorptions for light with an electric field polarized either parallel or perpendicular to the growth axis are observed in both SiGe and SiGeC quantum wells. The absorptions peak at 100 and 130 meV and involve bound-to-bound and bound-to-continuum transitions. The spectral positions of the intersubband absorptions are discussed from numerical calculations accounting for the band gap variation induced by carbon.
Molecular-beam epitaxy of high-quality ZnSe homo-epitaxial layers on solid-phase recrystallized substrates
Authors: Tournié E. , Brunet P. , Faurie J.-P. , Triboulet R. , Ndap J. O.
Published: July 2002

We study through reflection high-energy electron diffraction (RHEED) and low-temperature photoluminescence (PL) spectroscopy the molecular-beam epitaxy of ZnSe homoepitaxial layers on solid-phase recrystallized substrates. We show that with a proper ex situ substrate polishing a two-dimensional (2D) RHEED pattern is readily observed when introducing the substrate into the growth chamber at low temperature. We demonstrate that the in situ pre-growth treatment has a dramatic influence on ZnSe nucleation and that a suitable preparation leads to direct 2D growth of ZnSe layers which exhibit superior optical properties. The PL spectra are dominated by the near-band edge emission, with no deep-level and defect-related lines.
Phototransformation in visible and near-IR femtosecond pump-probe studies of C60 films
Authors: Fleischer S. B. , Pevzner B. , Dougherty D. J. , Ippen E. P. , Dresselhaus M. S. , Hebard A. F.
Published: July 2002

The ultrafast non-linear optical dynamics of C60 thin films were investigated at low excitation levels. The pump-probe response observed at low power is found to differ significantly from the ultrafast non-exponential behavior observed at higher intensity. It is determined that the ultrafast relaxation processes measured at higher fluence levels are affected by phototransformation of C60.
Periodic poling and waveguide frequency doubling in RbTiOAsO4
Authors: Risk W. P. , Loiacono G. M.
Published: July 2002

We report the demonstration of a guided-wave nonlinear process in the material rubidium titanyl arsenate (RTA). Quasi-phase-matched frequency doubling of 874.5 nm light was achieved in a Cs:RTA waveguide, with a normalized conversion efficiency of 225%/W cm2. We also report phase matching characteristics for bulk periodically poled RTA.
InGaN-GaN based light-emitting diodes over (111) spinel substrates
Authors: Yang J. W. , Chen Q. , Sun C. J. , Lim B. , Anwar M. Z. , Khan M. Asif , Temkin H.
Published: July 2002

In this letter we report the deposition of high quality GaN-InGaN double-heterostructure pn junctions over (111) spinel substrates using low-pressure metalorganic chemical vapor deposition. A ten-period undoped GaN-In0.1Ga0.9N multiple quantum well was used for the active region. Mesa-type light-emitting diode (LED) structures were fabricated which under forward bias exhibited only strong band-edge electroluminescence. The spectral emission was centered at 385 nm and had a linewidth of 15 nm. This is similar to what is measured for similar LED structures over sapphire substrates.
Preparation of large area and investigation of initial film growth of YBa2Cu3O7 by scanning pulsed laser deposition
Authors: Wu K. H. , Wang R. C. , Chen S. P. , Lin H. C. , Juang J. Y. , Uen T. M. , Gou Y. S.
Published: July 2002

A pulsed laser deposition system with a rotating reflector, which can generate an extended plume with a diameter of about 40 mm, has been proven to be viable in producing large area YBa2Cu3O7 (YBCO) thin films. Films with uniformity of thickness and electrical properties to within a few percents were obtained. By making a further modification on this laser scanning system, YBCO films with various thicknesses can be deposited in situ on several pieces of substrates under essentially identical deposition conditions, and particularly, in a continuous fashion. The atomic force microscopy (AFM) images reveal that films grown on NdGaO3 follow the Stranski–Krastanov (layer then island growth) mode, while films grown on as-polished MgO and on annealed MgO follow the Volmer–Weber (islands without layer growth) mode and step-flow mode, respectively.
Low temperature current imaging tunneling spectroscopy on wet chemically etched quantum wires
Authors: Smoliner J. , Eder C. , Böhm G. , Weimann G.
Published: July 2002

In this letter, low temperature current imaging tunneling spectroscopy studies on wet chemically etched quantum wires are reported. On the wires, symmetric current voltage curves are observed. Between the wires, however, significant current is only observed for negative sample bias. Through this behavior, topographic and current imaging profiles of quantum wires are obtained. In liquid helium, the current profiles of the wires are clearly smaller than the topographic profiles, which is used to determined the edge depletion width directly.
Gain analysis for surface emission by optical pumping of wurtzite GaN
Authors: Domen K. , Kondo K. , Kuramata A. , Tanahashi T.
Published: July 2002

We analyzed optically pumped surface emissions by calculating the optical gain in bulk GaN. We found that GaN has a large gain of over 104 cm−1 and no gain saturation up to 25 000 cm−1 . This high optical gain is generated by the high joint-density of states due to the three valence bands close to band edge and the large effective mass of the conduction band. As a result, although the gain required for lasing in the vertical direction is very high, the high excitation of carriers can achieve this without an intentional high reflection structure.
Outdoor evaluation of the thermoluminescent properties of α-Al2O3 crystals
Authors: Muñoz J. A. , Cussó F. , de Cárcer I. Aguirre , Jaque F. , Muñiz J. L. , Delgado A. , Castañeda B. , Barboza-Flores M. , Pérez-Salas R. , Aceves R. , Pashchenko L. P.
Published: July 2002

In this work, the thermoluminescence response of α-Al2O3 under solar irradiation has been studied. This material exhibits selective excitation with a narrow response, with a maximum at 313 nm, in the ultraviolet-B range.
Oxidation kinetics of TiN layers: Exposed and beneath Pt thin films
Authors: McIntyre Paul C. , Summerfelt Scott R. , Maggiore Carl J.
Published: July 2002

Oxidation kinetics are reported for thin films of TiN, both directly exposed to a dry oxygen ambient and beneath polycrystalline Pt films of ∼100 nm thickness. Oxygen resonance backscattering spectrometry was used to detect thin oxide layers at the Pt/TiN interface produced by oxidation annealing at 550–650 °C. A linear oxidation rate law was observed for the buried TiN film, indicating the oxidation rate is independent of average titanium oxide thickness. The linear rate constant had an activation enthalpy of 2.4±0.1 eV.
Time-frequency characterization of magnetostatic envelope soliton waves
Authors: Dragoman D. , Dragoman M.
Published: July 2002

The time-frequency characterization is used to test if measured waveforms are magnetostatic solitons. Measured bright and dark magnetostatic solitons are analyzed in the time-frequency domain using the Wigner transform.
Electrical properties of high resistivity 6H–SiC under high temperature/high field stress
Authors: Gradinaru G. , Sudarshan T. S. , Gradinaru S. A. , Mitchell W. , Hobgood H. M.
Published: July 2002

The influence of ambient temperature and applied electric field on the electrical properties of high resistivity (1–30 kΩ cm), semi-insulating (>100 kΩ cm), and insulating (1011–1012 Ω cm) single-crystal 6H–SiC is reported. Current–voltage (I–V) characteristics of lateral metal-semiconductor-metal test structures were measured in vacuum in a temperature range of 295–730 K and under moderate pulsed electric fields (0.5–80 kV/cm). It is shown that the resistivity of the undoped 6H–SiC varies strongly with the ambient temperature after a temperature/field function dominated by a factor containing the activation (ionization) energy of residual boron of 0.35 eV. The dominant activation energy of semi-insulating Vanadium-compensated material (6H–SiC:V) varies with the ambient temperature, increasing from ∼0 eV at 295–320 K to ∼0.8 eV at T⩾600 K. This result can explain the relatively low decrease of the resistivity of insulating 6H–SiC at very high ambient temperatures and its viability as a substrate for next-generation high temperature microwave integrated circuits based on large band gap semiconductors.
Ballistic electron spectroscopy of vertical superlattice minibands
Authors: Rauch C. , Strasser G. , Unterrainer K. , Gornik E. , Brill B.
Published: July 2002

We present a study of ballistic electron transport in GaAs/GaAlAs superlattices with different well widths. A three terminal device is used to inject an energy tunable electron beam via a tunneling barrier into a field free superlattice and to collect the transmitted current as a function of the injector energy. A significant increase of the collector current is observed due to miniband conduction in the superlattice. The transfer ratio α=IC/IE can be used to probe miniband positions and the miniband widths in field free superlattices. Longitudinal optical phonon replicas of the eigenstate structure are presented. The tunneling spectroscopy data agree well with self-consistent Poisson–Schrödinger calculations.
Hole perpendicular transport in GaAs–AlGaAs superlattices
Authors: Dong Bing , Lei X. L.
Published: July 2002

We investigate the hole perpendicular transport properties in semiconductor superlattices (SLs) by using the extended Lei–Ting balance equation theory for an arbitrary energy band including hole-impurity, hole-polar-optic-phonon, and hole-nonpolar-optic-phonon scatterings. Effects of heavy-hole–light-hole mixing are taken into account by means of the approximate dispersion relation suggested by O. E. Raichev [Phys. Rev. B 50, 5382 (1994)]. Numerical calculations show that the complex hole energy spectrum causes a breakdown of the negative differential conductance for the hot-hole perpendicular transport in SLs in contrast with the results corresponding to a simplified electronlike energy spectrum.
Determining the distribution of silicon monofluoride on hydrofluoric acid-treated Si (111) surface by exchange reaction with molecules at the solid/liquid interface
Authors: Mitsuya Munehisa
Published: July 2002

Silicon monofluoride (Si–F) species on hydrofluoric acid (HF)-treated silicon surface have been shown to be quantitatively replaced by nucleophilic reagents at the solid/liquid interface, but some Si–F remain intact. The chemisorption of molecules with larger dimensions results in a decrease in the proportion of fluorine that is replaced. These results can be attributed to steric hindrance by the adsorbed molecules. This is explained by a model in which Si–F are grouped together to form islands of Si–F species on a predominantly H-terminated Si surface.
Magneto-transport properties of Bi substituted thin films of La–Ca–Mn–O
Authors: Suresh Babu V. , Seehra M. S. , Srinivasan G. , Savage R. M.
Published: July 2002

This letter is on the observation of anisotropic electrical transport and magnetoresistance (MR) in rf sputtered thin films of La0.62Bi0.05Ca0.33MnO3 on Si. Films sputtered on (111)Si are polycrystalline, whereas textured films with (110) orientation are obtained from (100) Si. Both films show a reduction in the lattice constant and relatively high Curie temperatures (262–266 K vs 230 K for bulk polycrystals). Although the films have identical magnetic parameters, resistivity ρ and MR data for the (110) textured films show the following features indicative of possible dependence of magneto transport on crystallographic orientation: (i) a two order of magnitude enhancement in the low temperature ρ value compared to polycrystalline films, (ii) a semiconductorlike electrical conduction and the absence of any metallic to semiconductor transition, and (iii) a relatively large MR, as high as 80% at 40 kOe.
High continuous wave power, 0.8 μm-band, Al-free active-region diode lasers
Authors: Wade J. K. , Mawst L. J. , Botez D. , Jansen M. , Fang F. , Nabiev R. F.
Published: July 2002

Efficient, high-power, Al-free active-region diode lasers emitting at λ=0.83 μm have been grown by low-pressure metalorganic chemical vapor deposition. Threshold-current densities as low as 220 A/cm2, maximum continuous wave (cw) power of 4.6 W, and a maximum cw wallplug efficiency of 45% are achieved from 1 mm long, uncoated devices with In0.5(Ga0.5Al0.5)0.5P cladding layers. Further improvement is obtained by replacing the p-In0.5(Ga0.5Al0.5)0.5P cladding layer with thin (0.1 μm) electron-blocking layers of Al0.85Ga0.15As and In0.5(Ga0.5Al0.5)0.5P, and a p-In0.5(Ga0.9Al0.1)0.5P cladding layer. Such devices provide a record-high T0 of 160 K and reach catastrophic optical mirror damage (COMD) at a record-high cw power of 4.7 W (both facets). The corresponding COMD power-density level (8.7 MW/cm2)is ∼2 times the COMD power-density level for uncoated, 0.81-μm-emitting AlGaAs-active devices. Therefore, 0.81-μm-emitting, Al-free active-region devices are expected to operate reliably at roughly twice the power of AlGaAs-active region devices.
Synthesis of diamondlike films by an electrochemical method at atmospheric pressure and low temperature
Authors: Novikov V. P. , Dymont V. P.
Published: July 2002

A technique of carbon film synthesis based on an electrochemical process was developed. A solution of acetylene in liquid ammonia was employed as the electrolyte. Films were deposited at the metallic anode. Two types of films were produced. Films of type I are transparent and fragile, whereas those of type II are black and plastic. The films were investigated by the electron diffraction method and Raman spectroscopy. The electron diffraction data for type I films demonstrate the films’ high degree of crystallinity. Values of lattice plane spacings agree with data on cubic diamond modifications. The Raman spectrum of type I films shows a line at 1334 cm−1 (full width at half-maximum equal to 15 cm−1), inherent in that of diamond and an essentially amorphous carbon component. Spectra of the type II films do not feature the Raman peak of diamond.
Electrical properties of Ta–Sn–O films on indium tin oxide electrodes
Authors: Fujikawa Hisayoshi , Noda Koji , Tokito Shizuo , Taga Yasunori
Published: July 2002

We have found that Ta–Sn–O films prepared on indium tin oxide (ITO) electrodes by magnetron cosputtering of Ta2O5 and SnO2 have much higher breakdown field strength than the Ta2O5 films on the ITO electrodes. The highly insulating Ta–Sn–O films were obtained in the Sn concentration range of 3–40 at. %. The figure of merit, which was defined by the multiplication of the breakdown field strength by the relative dielectric constant, of the Ta–Sn–O films was found to become a maximum in the Sn concentration of about 3 at. %. The experimental results of temperature dependence of the leakage currents indicated that the conduction mechanisms at room temperature changed from Poole–Frenkel type to Fowler–Nordheim tunneling type by adding SnO2 into Ta2O5 films.
Oxidation of strained Si in a microwave electron cyclotron resonance plasma
Authors: Bera L. K. , Mukhopadhyay M. , Ray S. K. , Nayak D. K. , Usami N. , Shiraki Y. , Maiti C. K.
Published: July 2002

Electron cyclotron resonance plasma oxidation of strained Si on relaxed Si1−xGex buffer layers in O2 ambient at room temperature is reported. The electrical properties of grown oxide have been characterized and compared with thermally grown oxides using a metal-oxide semiconductor structure. At a low field, the accumulation of holes in the buried Si1−xGex layer, due to the type-II band offset, has been observed. The experimental results from thermally grown oxides have been compared with the simulation results obtained using a heterostructure Poisson solver.
Correlation of frictional losses of spinning levitated magnets with ac susceptibility in high-temperature superconductors
Authors: Rossman C. E. , Budnick J. I. , Weinberger B. R.
Published: July 2002

Measurements of both the ac magnetic susceptibility in melt processed and film Y–Ba–Cu–O and frictional losses of spinning permanent magnets levitated above Y–Ba–Cu–O are presented. A direct correlation is observed only when large susceptibility samples are studied indicative of the importance of grain boundary loss mechanisms. The increasing loss per revolution with increasing frequency for a spinning permanent magnet is explored.
Length quantization in In0.13Ga0.87As/GaAs quantum boxes with rectangular cross section
Authors: Michel M. , Forchel A. , Faller F.
Published: July 2002

By electron-beam lithography and wet chemical etching quantum boxes with a controlled shape as, e.g., a rectangular cross section, can be realized. We have fabricated quantum boxes with approximately constant widths of 50–60 nm and strongly varying lengths (150–80 nm). The luminescence of the structures shows a shift of the ground-state emission to higher energy as well as transitions between excited box states. By comparison with model calculations the changes of the emission spectra are related to the length quantization in the structures.
Anomalous luminescence peak shift of SiGe/Si quantum well induced by self-assembled Ge islands
Authors: Kim E. S. , Usami N. , Shiraki Y.
Published: July 2002

Strain effects in a strained SiGe/Si quantum well induced by self-assembled Ge islands have been studied by varying the Ge coverage. The strain by the Ge islands induces a complicated behavior in photoluminescence spectra depending on the Ge coverage. The Ge islands give the enhanced local strain to the underlying structures with the increase of the Ge coverage, at the early stage of the growth. However, as the Ge coverage increases the enhanced local strain does not continue being reinforced but is limited after once being retrogressed. These results are discussed in terms of elastic deformation due to the lattice mismatch between Si and Ge and the lattice relaxation in Ge islands.
Normal-mode theory of nonspecular phenomena for a finite-aperture ultrasonic beam reflected from layered media
Authors: Jia X.
Published: July 2002

A normal-mode formalism is developed to describe the nonspecular effects of a finite-aperture ultrasonic beam incident onto layered elastic media. Analytical expressions for the reflected field have been obtained for various structures. This model proposed a unique physical picture and resolved the conflict between various explanations made for the nonspecular reflection phenomena. Novel features of leaky wave fields were observed at interfaces of liquid-solid and liquid-solid-liquid structures. These results may be helpful for nondestructive evaluation of layered structures and determination of material signatures in the acoustic microscope.
Ballistic electron emission microscopy study of transport in GaN thin films
Authors: Brazel E. G. , Chin M. A. , Narayanamurti V. , Kapolnek D. , Tarsa E. J. , DenBaars S. P.
Published: July 2002

Ballistic electron emission microscopy (BEEM) measurements on GaN grown on sapphire substrates reveal a second conduction band minimum ∼340 meV above the absolute band minimum at the zone center (Γ point). A significant lateral variation of the energy difference between the two band minima, ±50 meV, was observed which may result from nonuniform strain in the material. The existence of two conduction bands in close proximity may affect device applications, i.e., GaN based lasers and electronic devices.
Nanosecond time-resolved emission spectroscopy from silicon implanted and annealed SiO2 layers
Authors: Pifferi A. , Taroni P. , Torricelli A. , Valentini G. , Mutti P. , Ghislotti G. , Zanghieri L.
Published: July 2002

Photoluminescence decay curves and nanosecond time-gated spectra were measured from silicon implanted SiO2 layers after thermal annealing. Different ion fluences and annealing times were tested. Three components emitting blue-green light with lifetimes of about 0.4, 2, and 10 ns were detected. The peak position of all components moves to longer wavelengths upon increasing the ion fluence. This short-wavelength emission seems to be related to the presence of extended defects acting as precursors of nanocrystals. A slower (microsecond) component, centered in the near infrared and attributed to nanocrystals, was also identified in the highest fluence implant considered (3×1017 cm−2).
Threshold sheath potential for the nucleation and growth of cubic boron nitride by inductively coupled plasma enhanced chemical-vapor deposition
Authors: Amagi Satoshi , Takahashi Daisuke , Yoshida Toyonobu
Published: July 2002

The nucleation and growth conditions of c-BN films were studied in low-pressure inductively coupled plasma enhanced chemical-vapor deposition. The threshold sheath potentials needed for the nucleation and the growth of c-BN were sustained by two step Vsheath deposition. The threshold sheath potential for the growth Vsheathg was found to be significantly lower than the threshold value required for nucleation Vsheathn. Under our experimental condition, the values of Vsheathg and Vsheathn were found to be 45 and 65 V.
Quality improvement of low-pressure chemical-vapor-deposited oxide by N2O nitridation
Authors: Lai P. T. , Jingping Xu , Lo H. B. , Cheng Y. C.
Published: July 2002

Quality of low-pressure chemical-vapor-deposited (LPCVD) oxide and N2O-nitrided LPCVD (LN2ON) oxide is investigated under high-field stress conditions as compared to thermal oxide. It is found that LPCVD oxide has lower midgap interface-state density Dit-m and smaller stress-induced Dit-m increase than thermal oxide, but exhibits enhanced electron trapping rate and degraded charge-to-breakdown characteristics, which, however, are significantly suppressed in LN2ON oxide, suggesting effective elimination of hydrogen-related species. Moreover, LN2ON oxide shows further improved Si/SiO2 interface due to interfacial nitrogen incorporation.