bluuebunny/crossref_metadata_2025 huggingface dataset:
Fermi level pinning and differential efficiency in GaInP quantum well laser diodes
Authors: Smowton P. M. , Blood P.
Published: July 2002

Analysis of spontaneous emission spectra of GaInP quantum well laser diodes above and below threshold show that the quasi-Fermi level separation pins within the quantum wells but not throughout the whole device structure. By reproducing the temperature and cavity length dependence of the external differential efficiency using these measurements it is shown that a value of internal differential efficiency which is nonunity is due to current spreading and incomplete carrier injection and that the temperature dependence is due to the temperature dependence of the efficiency with which carriers are injected into the quantum well.
Delayed luminescence induced by intersubband optical excitation in a charge transfer double quantum well structure
Authors: Rüfenacht M. , Tsujino S. , Ohno Y. , Sakaki H.
Published: July 2002

Photoluminescence processes in a novel GaAs double quantum well (DQW) structure were studied and found to be controlled by a 10 μm mid-infrared (MIR) light. In this DQW structure, photogenerated electron-hole pairs are normally separated into different wells and their radiative recombination is inhibited. However, when a MIR light pulse is supplied to induce an electron intersubband transition, electrons are efficiently transferred to the hole-rich well, resulting in a significant enhancement of luminescence. By time shifting the MIR pulse with respect to the light pulse for interband excitation, we demonstrated the generation of a delayed photoluminescence. Device potentials of this MIR to near-infrared conversion are discussed.
Unidirectional operation of waveguide diode ring lasers
Authors: Liang James J. , Lau Stanley T. , Leary Michael H. , Ballantyne Joseph M.
Published: July 2002

A method of providing asymmetric feedback in the triangular ring laser structure was devised through the simple alterations of the waveguide shape. Two kinds of alterations were designed and implemented, one being the “optical diode,” the other being the tapered waveguide. Unidirectional operation was achieved for the ring lasers, with a single-beam slope efficiency of 0.23 W/A, which was the highest single-beam slope efficiency reported for semiconductor ring lasers.
Demonstration of a frequency-modulated, pulsed optical parametric oscillator
Authors: Armstrong D. J. , Smith A. V.
Published: July 2002

We demonstrate that injection seeding a pulsed optical parametric oscillator with frequency modulated cw light with a modulation period equal to the cavity round-trip time produces pulses that have the same modulated character as the seed. A sensitivity of 10−3 was demonstrated for these pulses in frequency-modulated absorption measurements.
Atomic hydrogen enhanced reflow of copper
Authors: Miyake T. , Petek H. , Takeda K. , Hinode K.
Published: July 2002

A low temperature technique for copper metallization using sputter-reflow process is investigated. Metallization of 0.15–1.5 μm prepatterned trenches at a temperature of 320 °C by atomic hydrogen enhanced reflow of sputtered Cu films is described. Debye temperature of a single crystal Cu(110) surface measured by He atom scattering indicates that surface H reduces the surface Cu–Cu bonding strength. Moreover, atomic H efficiently removes oxygen and carbon impurities from the sputtered Cu films at surface temperatures of >150 °C.
Surface acoustic wave measurements of YBa2Cu3O7−δ thin films and single crystals
Authors: Gaffney R. , Hucho C. , Feller J. R. , McKenna M. J. , Sarma B. K. , Levy M.
Published: July 2002

Surface acoustic wave (SAW) velocity and attenuation measurements have been performed on high-temperature superconducting YBa2Cu3O7−δ (YBCO) thin films (deposited on nonpiezoelectric substrates), and YBCO single crystals. A “bridge” technique is employed in which piezoelectric substrates, patterned with interdigital transducers, are bonded to the sample under investigation. The temperature dependence of 168 MHz SAW attenuation in a single crystal near its superconducting transition has been measured in applied magnetic fields up to 1.6 T. Features are seen above the superconducting transition temperature which may be indicative of a transition in the electric polarization of the material. A field-dependent attenuation peak, seen in the superconducting state, is discussed in terms of the theory of thermally activated vortex motion.
Free carrier absorption as a probe of carrier dynamics: A Monte Carlo based study for silicon
Authors: Jiang Hongtao , Hinckley John M. , Singh Jasprit
Published: July 2002

The Monte Carlo method normally used for transport studies in semiconductors is extended and used to study free carrier absorption of subband gap radiation in semiconductors. The approach is applied to n-type silicon where we find very good agreement with experimental results and calculations based on quantum electrodynamics. This method also allows us to study free carrier absorption in semiconductors with a dc bias. With a dc bias, the absorption coefficient has a strong dependence on the polarization of the ac field. We show that the absorption coefficient can be directly related to the carrier temperature as well as the momentum and energy relaxation times. Thus important carrier dynamics information can be obtained from free carrier absorption measurements in the presence of a dc field.
Temperature sensitivity of repoling in strontium barium niobate near to the glassy transition
Authors: Smith Peter G. R. , Eason Robert W. , Brown Paul T. , Ross Graeme W.
Published: July 2002

We report the observation of an enhanced temperature sensitivity for transient repoling near to the domain freezing temperature in ferroelectric strontium barium niobate. This work has important consequences for the use of optical fields to control domain patterns in such materials. We model the repoling characteristics of the material using a Vogel–Fulcher type response and present results showing the degree of repoling as a function of field and temperature, for short duration repoling times.
Ion energy control in an insulating inductively coupled discharge reactor
Authors: Smith Brian A. , Overzet Lawrence J.
Published: July 2002

An electrically insulating plasma reactor with a Faraday shielded inductive source antenna permits direct control of the dc plasma potential of the discharge. This control may be used to provide a tailored ion energy distribution at a substrate of fixed potential or to fix the plasma potential at a chosen value. With a reactor constructed from Pyrex tubing and a Faraday shielded inductive source coil, all that is required to control the plasma potential is a small electrostatic probe in contact with the plasma. By applying a stairstep potential to the probe, it is possible to create an ion energy distribution possessing virtually any desired shape. Insulating reactors could provide a novel way to control ion production and ion energy separately without the need for direct substrate biasing. They may also provide a way to maintain a consistent plasma potential in a processing reactor in situations where the reactor walls are easily contaminated by the process.
Tunneling spectroscopy for quantum well excitons
Authors: Cao H. , Klimovitch G. , Björk G. , Pau S. , Yamamoto Y.
Published: July 2002

We have demonstrated a technique of directly measuring the exciton binding energy and the valence band split in the quantum well through a tunneling process. We have also measured the emission efficiency of quantum well heavy-hole excitons and light-hole excitons into the normal direction.
Midinfrared molecular gas lasers optically pumped by a continuously tunable infrared optical parametric oscillator
Authors: Tapalian H. Charles , Michaels Chris A. , Flynn George W.
Published: July 2002

We report the observation of midinfrared super radiant pulses emitted from molecular gases pumped by a narrow-band, continuously tunable infrared optical parametric oscillator. Molecules pumped either into a vibrational combination band or a vibrational overtone state decay by means of super radiant emission to a lower vibrationally excited state. Emission was observed in N2O at 4.5 and 8 μm, and in C2H2 at 13.6 μm and 15.7 μm. Pulse energies as high as 0.5 mJ and pulse widths as short as 7 ns make this an excellent technique for the production of intense midinfrared light.
Differential reflectance spectroscopy of GaAlAs thin films and GaAs bulk under externally applied temperature gradient
Authors: Dai N. , Feng J. F. , Chen L. Y. , Liu X. Q. , Lu W. , Zhong J. L.
Published: July 2002

Using vibrating optical beam, differential reflectance (DR) spectra have been obtained on GaAlAs thin films and GaAs bulk subjected to an externally applied temperature gradient. The DR spectra reveal all the critical points, namely, E0 and E0+Δ0 in GaAlAs and E0, E0+Δ0 and E1 in GaAs in the given energy range under study whereas, without the temperature gradient, DR spectra measured on homogeneous materials are structureless. The DR technique shows better sensitivity than photoreflectance on thin epilayers. Our investigation suggests that, combined with the application of a field gradient, DR can be made extremely useful for the characterization of semiconductors.
Characteristic improvement of tungsten photocathode by two-wavelength irradiation of the Nd:YAG laser
Authors: Ohkubo Koichi , Nakao Naoya , Mima Kunioki , Nakai Sadao , Fujita Masayuki , Imasaki Kazuo , Yamanaka Chiyoe , Watanabe Takeshi , Ishida Takayuki , Ohigashi Nobuhisa , Tsunawaki Yoshiaki
Published: July 2002

Metals or metal compounds as photocathodes provide high current density and have a high damage threshold for laser irradiation. In addition, the quantum efficiency of these cathodes is enhanced by heating to a higher operating temperature. The tungsten photocathode heated up to 1400 K and irradiated by 2ω (532 nm) of the Nd:YAG laser produced an electron beam with high current density (∼1 kA/cm2) and the quantum efficiency was about 10−5. The fundamental (1064 nm) of a Nd:YAG laser was used to further heat up the cathode instantly; the temperature rise was calculated to be 2000 K in a 10 ps time scale. Compared to the static 1400 K operation, two times enhancement of quantum efficiency was observed.
Persistent photoconductivity in high Tc grain boundary Josephson junctions
Authors: Hoffmann A. , Schuller Ivan K. , Gilabert A. , Medici M. G. , Schmidl F. , Seidel P.
Published: July 2002

We observed persistent photoconductivity in YBa2Cu3Ox bicrystal grain boundary Josephson junctions. Upon illumination of these grain boundary Josephson junctions, the normal state resistance decreases and the critical current increases. This strongly suggests that the grain boundary in these films consists of oxygen depleted YBa2Cu3Ox. A comparison with the persistent photoconductivity in oxygen depleted YBa2Cu3Ox thin films implies an average oxygen content of x=6.6±0.1 for the grain boundary. The spectral dependence has a lower threshold for persistent photoconductivity in the junctions (≈1.2 eV) than in thin films.
Transport anisotropy in spontaneously ordered GaInP2 alloys
Authors: Chernyak Leonid , Osinsky Andrei , Temkin Henryk , Mintairov Alexander , Malkina I. G. , Zvonkov B. N. , Saf’anov Yu. N.
Published: July 2002

Large anisotropy in minority carrier diffusion length and specific conductivity is observed in epitaxial layers of GaInP2 alloys with CuPtB-type ordering. Both the diffusion length and specific conductivity are enhanced, by factor of 10, in the [110] direction, parallel to the line of intersection of the ordered (1–11) and (−111) planes with the (001) growth surface. The reduction in transport length in the [1–10] direction is attributed to carrier scattering at domain boundaries. No transport anisotropy is observed in disordered GaInP2 epitaxial layers.
Conducting Sr0.7NbO3 thin film electrodes for ferroelectric capacitors
Authors: Bowman R. M. , O’Neill D. , McCurry M. , Gregg J. M.
Published: July 2002

We report the synthesis of thin films of the conducting cubic oxide Sr0.7NbO3 by pulsed laser deposition. Deposition conditions were investigated and optimized to yield both conductivity and crystallinity. Unlike most similar materials we find that successful synthesis of conducting Sr0.7NbO3 is very sensitive to oxygen pressure during deposition. Optimal properties were obtained for vacuum deposition at a substrate temperature of 750 °C. Typical resistivity was 800 μΩ cm at 300 K and independent of temperature down to 10 K. Films grew epitaxially onto {100} MgO. Functionality of the material was demonstrated by preparing MgO/Sr0.7NbO3/BaTiO3/Au capacitors. Despite their apparently excellent lattice match, these capacitors exhibited depressed Curie temperatures.
High velocity pseudosurface waves on LiNbO3 with thin overlayers
Authors: Makarov S. N. , Belkova A. L.
Published: July 2002

A numerical study is made of high velocity pseudosurface acoustic waves (HVPSAW) on coated LiNbO3. Standard YZ and 41° YX cuts are considered. In contrast to the pure substrate, the presence of typical thin overlayers leads to the appearance of a well-localized low-attenuating HVPSAW mode at certain values of the film thickness. The depth of the localization domain may be smaller than the wavelength.
Single-electron transistor fabricated by focused laser beam-induced doping of a GaAs/AlGaAs heterostructure
Authors: Baumgartner P. , Wegscheider W. , Bichler M. , Schedelbeck G. , Neumann R. , Abstreiter G.
Published: July 2002

A single-electron transistor has been fabricated by an optical fabrication method. A small dot, a source and drain reservoir, and in-plane gates are all built from the two-dimensional electron gas of an n-type GaAs/AlGaAs heterostructure. Laser-written p-doped lines are used to define this dot with a diameter of about 70 nm and to insulate it from the in-plane gates. Tunnel junctions connect the dot with source and drain. The in-plane gates are used to tune the tunnel junctions and to change the electrostatic potential of the dot. A large charging energy of 5 meV and clear Coulomb-blockade oscillations are observed at helium temperature, due to a small dot capacitance of about 3×10−17 F.
Near-infrared and visible photoluminescence from argon plasma polymerized fullerene film
Authors: Xu Can , Chen Guanghua , Xie Erqing , Gong Jinlong
Published: July 2002

Oxygenated polymeric fullerene films synthesized in argon plasma show strong photoluminescence in near-infrared and visible region (1.50–2.36 eV) at room temperature excited by a 514.5 nm argon ion laser. After being annealed at different high temperatures, photoluminescence decreased in intensity. The generation and decrease of the photoluminescence were explained in terms of the change of the fullerene C60 symmetry.
Photoluminescence study of Si1−xGex/Si surface quantum wells
Authors: Kishimoto Y. , Shiraki Y. , Fukatsu S.
Published: July 2002

We report a photoluminescence (PL) study of Si1−xGex/Si surface quantum wells (SFQWs). The PL peak energies are found to be affected by strain relaxation in Ge-rich SFQWs while a PL energy lowering was observed for x⩽0.47 as compared to buried quantum wells capped with Si. Exciton localization in the lateral direction is suggested to be the dominant PL mechanism in SFQWs rather than perpendicular confinement effects that are expected for SFQWs. PL degradation and a spectral dominance switch over to newly developing lower energy peaks were clearly observed after prolonged air exposure.
Exchange induced unidirectional anisotropy observed using Cr–Al antiferromagnetic films
Authors: Klemmer T. J. , Inturi V. R. , Minor M. K. , Barnard J. A.
Published: July 2002

Exchange induced unidirectional anisotropy has been observed in a new bilayer system consisting of a ferromagnetic FeTaN or Ni80Fe20 film coupled to an antiferromagnetic Cr–Al alloy film. Estimates of the exchange coupling energy and magnetic anisotropy constant of the antiferromagnet are made and compared to other exchange coupled systems.
Very high (>1019 cm−3) in situ n-type doping of silicon during molecular beam epitaxy using supersonic jets of phosphine
Authors: Malik R. , Gulari E. , Bhattacharya P. , Linder K. K. , Rieh J.-S.
Published: July 2002

The use of supersonically injected pulses of phosphine to achieve uniform and high levels of n-type doping in Si during gas-source molecular beam epitaxy is demonstrated. Uniform n-type doping up to levels of 5×1019 cm−3 is obtained. SiGe/Si junction diodes made with this doping technique show good doping profiles and rectifying characteristics.
Synthesis and characterization of Ag–C60 nanostructure film
Authors: Hou J. G. , Wang Yan , Xu Wentao , Zhang S. Y. , Jian Zou , Zhang Y. H.
Published: July 2002

A thin film structure with Ag nanocrystallites embedded in a polycrystalline C60 matrix was grown under high vacuum by codeposition of Ag and C60 onto the hot substrate. The structural and physical properties of the film were characterized by a transmission electron microscope and a Raman scattering spectrometer. The Ag nanoparticles were well dispersed and not aggregated. An ordered nanoscale C60 lattice was observed between the two adjacent Ag particles, and the Raman-active Ag(2) pentagonal-pinch mode of C60 shifted to lower frequency. These results imply a strong interfacial interaction and charge transfer from the Ag to the C60.
Temperature dependence of the photoquenching of EL2 in semi-insulating GaAs
Authors: Alvarez A. , Jiménez J. , González M. A. , Sanz L. F.
Published: July 2002

A model of the temperature behavior of the photoquenching of EL2 in semi-insulating GaAs is presented. The thermal emission of a hole trapped on an actuator level accounts for the very low photoquenching efficiency above 85 K. This effect is presented in terms of a set of rate equations that reproduce in a reliable way the temperature dependence of the photoquenching of EL2. The activation energy of the actuator level suggests a hole trap level other than GaAs as was previously assumed.
Intersubband stimulated emission in GaAs/AlGaAs quantum wells: Pump-probe experiments using a two-color free-electron laser
Authors: Gauthier-Lafaye O. , Sauvage S. , Boucaud P. , Julien F. H. , Prazeres R. , Glotin F. , Ortega J.-M. , Thierry-Mieg V. , Planel R. , Leburton J.-P. , Berger V.
Published: July 2002

Intersubband stimulated emission under optical pumping has been observed in the conduction band of GaAs–AlGaAs quantum wells. The asymmetric coupled quantum wells which exhibit three conduction bound levels are designed to exhibit population inversion under optical pumping. An optical excitation at λ=9.2 μm is used to bleach the absorption between the ground and second excited subband. The population inversion between excited subbands is pumped and probed on a picosecond time scale by a tunable two-color free-electron laser. The stimulated amplification is studied at low temperature in infrared waveguides as a function of the waveguide length and of the probe wavelength. A stimulated gain ≈80 cm−1 is measured at 12.5 μm in agreement with calculations.
Type II recombination and band offset determination in a tensile strained InGaAs quantum well
Authors: Lugand C. , Benyattou T. , Guillot G. , Venet T. , Gendry M. , Hollinger G. , Sermage B.
Published: July 2002

Photoluminescence measurements under different excitation powers and time-resolved photoluminescence experiments were carried out at low temperature on tensile strained In0.3Ga0.7As quantum wells with InGaAs barriers lattice matched to InP. Evidence of a type II recombination is found between carriers confined in the tensile strained layer and in the lattice matched one. This study allows us to propose a precise determination of the light holes band offset in the In0.3Ga0.7As/In0.53Ga0.47As system.
Microstructual study of the alternating current bias-enhanced nucleation and growth of diamond on (001) silicon wafers
Authors: Seong Tae-Yeon , Kim Do-Geun , Choi Kwang-Ki , Baik Young-Joon
Published: July 2002

The bias-enhanced nucleation (BEN) and growth of diamond by microwave plasma chemical vapor deposition have been investigated using transmission electron microscopy (TEM), transmission electron diffraction (TED), atomic force microscopy (AFM), and scanning electron microscopy (SEM) full stop TED results show epitaxial relations between SiC and Si, and diamond and SiC, which depend on the BEN time. The formation of highly oriented (001) diamond films is obtained after 25 min BEN, in which the heteroepitaxially oriented β-SiC and hence the heteroepitaxially oriented diamond crystallites play an important role. TEM reveals the β-SiC crystallites 2–10 nm in size and the diamond crystallites 5–30 nm across. As the nucleation time increases, the density of the β-SiC crystallites increases from ∼2.7×1011 to ∼1.6×1012 cm−2, while that of the diamond crystallites varies from ∼2.0×109 to ∼4.1×1010 cm−2. Discrepancy between the densities obtained using TEM and AFM is discussed.
Active mode locking with a hybrid neodymium laser
Authors: Yan Li , Guo Bo
Published: July 2002

A novel concept of mode locking with a hybrid laser was demonstrated in an actively mode-locked hybrid neodymium (Nd) laser, which contains both Nd:YLF and Nd:glass in a single cavity. A small gain from Nd:YLF can control the spectrum of Nd:glass and ensure good phase coherence among the lasing axial modes, generating stable, coherent pulses of 11 ps. The broadband Nd:glass can facilitate spectral broadening and produce shorter pulses than by Nd:YLF alone under the same mode-locking force.
Carbon doping and etching of AlxGa1−xAs (0⩽x⩽1) with carbon tetrachloride in metalorganic vapor phase epitaxy
Authors: Hou H. Q.
Published: July 2002

Carbon doping and the parasitic growth-rate reduction with carbon-tetrachloride (CCl4) in AlxGa1−xAs was studied in the entire Al composition range for metalorganic vapor phase epitaxial growth. The doping efficiency in AlGaAs was found to increase by two orders of magnitude when the Al composition in AlxGa1−xAs changed from 0 to 1. The parasitic growth rate reduction, however, decreased by a factor of 15 when x changed from 0 to 1. This reduction of growth rate was confirmed to be caused by the etching of the material from the surface by Cl radicals cracked from CCl4. This strong compositional selectivity of the doping and etching has potential implications for lateral definition of growth on patterned surfaces. The doping and etching behaviors were also studied as a function of the growth temperature.
Domain-orientation dependence of levitation force in seeded melt grown single-domain YBa2Cu3Ox
Authors: Shi Donglu , Qu D. , Sagar S. , Lahiri K.
Published: July 2002

Domain-orientation dependence of levitation force has been determined for single-domain YBa2Cu3Ox. The single-domain material is obtained from a seeded melt growth process. The levitation force has been found to reach a maximum as the c axis of the domain is parallel to the direction of the force. The levitation force decreases in a cosine law fashion as the angle θ (the angle between the direction of the force and the c axis) increases from 0° to 60°. A maximum anisotropy of levitation force of 2.29 has been found. A physical model is proposed to explain the observed orientation dependence.
Microstructural study of hollandite-type MnO2 nano-fibers
Authors: Benaissa M. , José-Yacamán M. , Xiao T. D. , Strutt P. R.
Published: July 2002

A new morphology of manganese oxide in the form of nano-fibers was synthesized using a novel synthetic route, and structurally characterized using high-resolution transmission electron microscopy. The obtained manganese oxide, doped with potassium, adopts a hollandite-type structure with “few useful defects” which provide an open tunneled structure in three-dimensions. This characteristic is actually believed to improve, to a high extent, the ionic conductivity of the material and exhibits the doped hollandite-type manganese oxide as a highly promising candidate for electrochemical applications such as rechargeable batteries.
Confinement potential and surface state density in deep-mesa etched quantum wires
Authors: Riege S. P. , Kurth T. , Runkel F. , Heitmann D. , Eberl K.
Published: July 2002

We present an electrostatic model to determine the surface charge density and confinement potential in etched AlGaAs/GaAs quantum wires. In far-infrared transmission experiments we have determined the resonance frequencies of the dynamic eigenmodes of the quantum wire, which gives an independent determination of the confinement potential. We find good agreement with the modeled potential, which shows that this model gives a very good description of the electronic system.
Optical force microscopy with silicone rubber waveguides
Authors: Herminghaus S. , Riedel M. , Leiderer P. , Bastmeyer M. , Stürmer C.
Published: July 2002

A simple technique is described for optically imaging the lateral distribution of normal forces exerted onto a flat surface. It is based on the detuning of a silicone rubber planar waveguide by the forces to be investigated. The method is demonstrated by imaging the contact line force of a sessile water droplet on the surface, with a force resolution better than μN. It is shown that the lateral resolution may be much better than the decay length of the waveguide modes used.
Absorption spectra of Se and HgI2 chains in channels of AlPO4-5 single crystal
Authors: Tang Z. K. , Loy Michael M. T. , Chen Jiesheng , Xu Ruren
Published: July 2002

The absorption spectra are reported for isolated Se and HgI2 semiconductor chains accommodated in AlPO4-5 (AFI) channels of diameter 7.3 Å. The lowest electronic excitation states of the isolated chains are shifted to higher energy from the band edge transitions of their bulk crystals. The blue shifts are qualitatively explained by the quantum confinement effects of carriers in a one-dimensional wire. The experimental result of the Se/AFI is in good agreement with the theoretical expectation based on the effective-mass-approximation. The result of the HgI2/AFI, however, does not agree with the calculation. The different behaviors of the Se/AFI and the HgI2/AFI are expected to result from their different electronic structures.
Inductive-coupling-nitrogen-plasma process for suppression of boron penetration in BF2+-implanted polycrystalline silicon gate
Authors: Chao T. S. , Chu C. H.
Published: July 2002

A novel and simple method to suppress the boron penetration in the BF2+-implanted polycrystalline silicon gate is presented by using the inductive-coupling-nitrogen-plasma (ICNP) process. A nitrogen layer was found at the SiO2/Si interface by using this method. The result shows that the sample with the ICNP treatment exhibits a good suppression of boron penetration and improved electrical characteristics.
1.3 μm strain-compensated InAsP/InGaP electroabsorption modulator structure grown by atmospheric pressure metal–organic vapor epitaxy
Authors: Ougazzaden A. , Devaux F. , Rao E. V. K. , Silvestre L. , Patriarche G.
Published: July 2002

High quality 15-period strain-compensated InAsP/InGaP electroabsorption (EA) modulator structures have been grown by atmospheric pressure metal–organic vapor epitaxy. The incorporation of large compressive strain (∼1.7%) in the InAsP wells and tensile strain (∼−1.8%) in the InGaP barriers necessitated the growth of a few InP monolayers between the wells and barriers. The high structural quality of such samples has been demonstrated by (cross-sectional transmission electron microscopy analysis to be free of misfit dislocations and thickness undulations. The detection of a sharp and abrupt room-temperature exciton peak both in the photoconductivity and photoluminescence measurements further confirmed their excellent optical quality. 100 μm cavity length EA modulators fabricated in these structures exhibited excellent performances namely, an extinction ratio higher than 20 dB for 2.5 V drive voltage, a 3 dB bandwidth over 20 GHz, and low coupling losses to fiber (less than 2.5 dB per facet).
Thermal lens determination of end-pumped solid-state lasers using primary degeneration modes
Authors: Ozygus Bernd , Zhang Qincheng
Published: July 2002

A simple method using the singularities of an optical resonator to determine the thermal lens of end-pumped laser crystals is reported in this letter. At certain resonator parameters the transverse structures of the laser beam become a superposition of many transverse cavity modes of equal resonance frequencies. Because the resonator parameters depend on the thermally induced lens in the active medium, the strength of the lens can be determined by means of measuring the shift of the degeneration resonator length depending on the pumping power. The method is applied to an end-pumped Nd:YAG laser.
Edge detection in phase-change optical data storage
Authors: Peng Chubing , Mansuripur M. , Kim W. M. , Kim S. G.
Published: July 2002

A direct mark edge detection scheme for readout in phase-change optical disk systems is described. The medium for edge detetection must be optimized to have a 90° phase difference between the amorphous mark and the crystalline space. Theoretical analysis and numerical simulation have shown that the readout signal using mark edge detection is as good as that using conventional detection of reflectivity for long marks and superior for short marks. Noise level at the output of differential edge detection is lower than that at the output of conventional detection. We also show experimental results that confirm these predictions.
Novel method for fabrication of integrated resistors on bilayer Ag/YBa2Cu3O7 films using Ni implantation
Authors: LaGraff J. R. , Chan H. , Murduck J. M. , Hong S. H. , Ma Q. Y.
Published: July 2002

A novel ion implantation method is described for fabricating low inductance integrated resistors on Ag/YBa2Cu3O7 (YBCO) bilayer thin films. Parallel high and low value resistors were simultaneously formed by patterning bilayer films into 10-μm-wide lines, then masking and implanting with Ni to selectively inhibit superconductivity in YBCO. Low value resistors (<1 Ω/sq) were formed at 77 K as the supercurrent bypassed the Ni-doped nonsuperconducting YBCO and was shunted through the overlying low resistivity Ag metal. High value resistors (20–140 Ω/sq) were formed by removing Ag from above the implanted YBCO forcing the current through the implanted YBCO region. The sheet resistance of both types of resistors was found to increase systematically with increasing Ni implant energy.
Raman scattering studies on Si-doped GaAs grown by hydrogen-assisted molecular beam epitaxy
Authors: Zhang J. M. , Cardona M. , Peng Z. L. , Horikoshi Y.
Published: July 2002

The surfactant effect of atomic hydrogen on the incorporation of silicon into (100)-, (111)A-, and (311)A-oriented GaAs grown by hydrogen-assisted molecular beam epitaxy has been studied with Raman spectroscopy. Local vibrational modes (LVMs) of SiGa and SiAs impurities are observed for excitation nearly resonant with the E1 energy gap. Site switch of the doping Si atoms from Ga to As lattice sites due to the surfactant effect of H during growth of the high-index doped layers was directly monitored by changes of the normalized intensity of the LVMs. An increase of the free carrier concentration in p-type samples and a decrease in n-type samples resulting from this site switch were also observed in the plasmon-phonon coupled modes as observed in Raman scattering. Similar changes in carrier concentrations were observed by means of electrical transport measurements.
Optical property of a novel (111)-oriented quantum structure
Authors: Zhang Xiong , Chua Soo-Jin , Xu Shijie , Chong Kok-Boon , Onabe Kentaro
Published: July 2002

A novel hetero tensile-unstrained-tensile-unstrained-tensile (t-u-t-u-t) quantum structure, which consists of multiple quantum wells in the unstrained (u) regions, lattice matched to a (111)-oriented substrate, and sandwiched between tensile-strained epitaxial layers (t), is proposed. The energy band configuration modified by the strain-induced piezoelectric field and the distribution of the built-in internal electric field within this hetero t-u-t-u-t quantum structure were theoretically deduced and found to be consistent with the experimental results. It was demonstrated that some nonlinear optical properties such as the energy blue shift observed in the excitation-power-dependent photoluminescence spectra are strongly dependent on the distribution of the strain-induced built-in electric field within this quantum structure and quite comparable to the analogous values for the existing quantum structures.
A scaling law for ac susceptibility of an YBa2Cu3O film in a perpendicular ac field
Authors: Han G. C. , Ong C. K. , Xu S. Y. , Li H. P.
Published: July 2002

The ac susceptibility (ACS) of an YBa2Cu3O thin film in a perpendicular ac magnetic field (Ha) from 0.22 to 30.8 G is measured as a function of temperature. The temperature dependence of the real (χ′) and imaginary (χ′′) parts of the ACS for various Ha can be well scaled onto a single curve using the peak value (χp″) and temperature (Tp) of χ′′(T) as the scaling parameters. The scaling law suggests that the critical state can be established only below Tp. Above Tp, the ACS is determined by the screening effect of the film due to the sharp decrease of its resistance. Below Tp, the scaling behavior is in agreement with the theoretical approaches based on the critical state model, only if the temperature for zero critical current density is related to the irreversibility temperature Tirr rather than Tc. From the scaling law, we found that Tirr=Tp.
Unshielded use of thin-film Nb dc superconducting quantum interference devices and integrated asymmetric gradiometers for nondestructive evaluation
Authors: Walker M. E. , Nakane H. , Cochran A. , Weston R. G. , Klein U. , Pegrum C. M. , Donaldson G. B.
Published: July 2002

Novel nondestructive evaluation measurements made using niobium dc superconducting quantum interference devices with integrated asymmetric first-order gradiometers are described. Comparative theoretical and experimental studies of their spatial response have been described, and it is shown that the gradiometric response makes operation possible in an unshielded and electromagnetically noisy environment. As a demonstration of their capabilities, subsurface defects in a multilayer aluminum structure have been located and mapped using induced eddy currents at 70 Hz, with no magnetic shielding around the specimen or cryostat.
Holographic memory with one-beam geometry in photorefractive crystal
Authors: Naruse Shinichi , Shiratori Akira , Obara Minoru
Published: July 2002

A new configuration holographic memory with a one-beam geometry in a photorefractive crystal has been proposed, and recording of ten angle-multiplexed holograms in a Fe:LiNbO3 crystal has been experimentally demonstrated. A maximum page number of 1728 pages in the LiNbO3 crystal was theoretically estimated by the angular multiplexing method at an incident beam diameter of 5.10 mm and the laser wavelength of 514.5 nm. In this new configuration, one incident beam can simultaneously play two roles as an object beam and a reference beam, therefore, an optical setup becomes simpler than conventional setups, which leads to compact and robust holographic recording system.
Self-stabilization of a continuous wave multimode green laser due to antiphase dynamics
Authors: Ustyugov V. I. , Orlov O. A. , Khaleev M. M. , Novikov G. E. , Viktorov E. A. , Mandel Paul
Published: July 2002

The stability of a diode pumped Nd:YAG laser with intracavity KTP in an L-shaped cavity is studied. The mirror which connects the two cavity arms is a dielectric which also acts as a partial polarizer. This design provides a high level of stability for the total output power, despite the instability of the separate modes: separate modes are chaotic with large amplitude noise while the total output displays reduced noise below 1% rms. A model based on the Jones matrices is studied numerically. It shows antiphase and clustering, in excellent qualitative agreement with the experimental data.
Apertureless near-field optical microscopy with differential and close-proximity detection
Authors: Fukuzawa Kenji , Tanaka Yuriko
Published: July 2002

A new method of apertureless near-field optical microscopy that combines laterally differential detection with close-proximity detection has been developed. The laterally differential detection allows the light scattered from the probe apex to be distinguished from the background light. The close-proximity detection is done using a microfabricated photosensitive cantilever; it is thought to be a form of heterodyne detection, which provides a high signal level. This method makes it possible to detect the light scattered from the probe apex, which depends on the coupling between the probe apex dipole and the sample feature dipole.
Photodarkening in 4-(N,N-diethylamino)-β-nitrostyrene solutions
Authors: Yanagawa T. , Kanbara H.
Published: July 2002

Photodarkening is reported in 4-(N,N-diethylamino)-β-nitrostyrene solutions. The photodarkening is due to the formation of new absorption bands and is thought to be a photochemical effect of the structural changes. In degenerate four-wave mixing, a resonant effect is observed around the new absorption bands but the fast response behavior does not change. After darkening, the excitation spectrum becomes complicated, which implies a multipath decay that may show the fast response in the resonant region. The solvent and concentration dependence of the darkening property is also reported.
Direct absolute measurements of the two-dimensional elastic constants in smectic C* liquid crystal films
Authors: Galerne Yves , Poinsot Isabelle , Schaegis Daniel
Published: July 2002

The orientational elastic constants of free-standing films in a tilted smectic phase are directly measured in absolute units with a new experimental method similar to light scattering in the heterodyne regime. Basically, the amplitude of the thermodynamically excited orientational fluctuations, which modulate polarized light, is measured in the direct space by means of a microscope and a video camera connected to a microcomputer. Then, with a Fourier transform, we go into the reciprocal space and deduce the two-dimensional bend and splay elastic constants of the film in a range of wave vectors simultaneously. The method, which only needs light experimental means, is simple, fast, and accurate. It can be particularly helpful in the ferroelectric smectic C* liquid crystals for determining the elastic constants and indirectly the ferroelectric polarizations, without problems for orienting the samples.
Identifying layer switching in magnetic multilayers with x-ray resonant magnetic scattering
Authors: Freeland J. W. , Chakarian V. , Idzerda Y. U. , Doherty S. , Zhu J. G. , Park J.-H. , Kao C.-C.
Published: July 2002

The order of layer switching in a NiFe/Cu/Co spin valve is determined directly using circular polarized x-ray resonant magnetic scattering. By monitoring changes in the angular dependence of the magnetic contributions to the reflectivity near the Fe L3 and Co L3 edges as a function of applied field, the order of layer switching is directly obtained.
Microstructure of sputtered TiN on Al
Authors: Eaglesham D. J. , Bower J. E. , Marcus M. A. , Gross M. , Merchant S.
Published: July 2002

We use electron microscopy and x-ray diffraction to study the microstructure of TiN deposited on Al. In contrast to previous work, we show that the TiN has a large (≈1 μm) grain size arising from its epitaxial orientation on the underlying Al. Within a single grain, the TiN has a heavily voided columnar structure that closely mimics the appearance of fine grains. The within-grain columnar structure arises from the usual shadowing mechanism for sputtered films, and has a weak dependence on the deposition temperature.
Optical control of electric field poling in LiTaO3
Authors: Ross Graeme W. , Smith Peter G. R. , Eason Robert W.
Published: July 2002

A room temperature technique is presented for optically inducing periodic domain-inverted structures in bulk (0.2 mm thick) LiTaO3. By simultaneous application of an electric field and patterned illumination using UV wavelengths (351 and 364 nm), we demonstrate modulation of the resulting domain profile. We discuss the origins of the observed optical effect and describe our results from repeated domain switching, by cycling the electric field.
Second harmonic generation of the output of an AlGaAs diode oscillator amplifier system in critically phase matched LiB3O5 and β-BaB2O4
Authors: Beier B. , Woll D. , Scheidt M. , Boller K.-J. , Wallenstein R.
Published: July 2002

Blue 403 nm laser light is generated by frequency doubling the radiation of an AlGaAs diode laser oscillator amplifier system in critically phase matched LiB3O5 (LBO) and β-BaB2O4 (BBO) crystals. The laser system emits 400 mW of single frequency 806 nm radiation in an almost diffraction limited beam. For optimum doubling efficiency the laser radiation is enhanced by a resonant external ring cavity. The nonlinear crystal is placed at a resonator internal focus. Using a 16-mm-long LBO crystal a diode laser power of 387 mW generated 98 mW of second harmonic radiation, corresponding to a conversion efficiency of 25%. The same power was obtained in a 12- mm-long BBO crystal with a laser power of 417 mW. The measured conversion efficiencies are in good agreement with the values calculated for critically phase matched conversion in these nonlinear materials.
Optical and microstructural characterization of chemically synthesized gallium nitride nanopowders
Authors: Gonsalves Kenneth E. , Rangarajan Sri Prakash , Carlson Greg , Kumar Jayant , Yang Ke , Benaissa Mohamed , José-Yacamán M.
Published: July 2002

Thermal decomposition of an amido precursor; [Ga2(NMe2)6, Me=CH3] in an ammonia atmosphere yielded nanostructured gallium nitride powder. The x-ray diffraction spectrum of the nanosized gallium nitride exhibited reflections corresponding to the lattice planes of fcc (zinc blende) GaN. High resolution transmission electron microscopy confirmed the cubic structure of the material and evidence of stacking faults within the fcc structure. Infrared spectra showed the characteristic Ga–N stretch at 550 cm−1. Transmission electron microscope measurements indicated that the GaN consisted of ≈50 nm sized particles which in turn are agglomerates of smaller particles with ≈5 nm domain sizes. The photoluminescence (PL) emission spectrum of the GaN was found to be sensitive to the excitation wavelength exhibiting peaks at 378 and 317 nm. The PL excitation spectrum showed resonances in the 200–300 nm region. These PL results suggest the effect of quantum confinement in these GaN particles.
Powder diffraction from compressed molecular hydrogen in a diamond-anvil cell
Authors: Besedin Stanislav P. , Jephcoat Andrew P. , Hanfland Michael , Häusermann Daniel
Published: July 2002

We report the first observation of x-ray powder-diffraction from molecular hydrogen in a diamond-anvil cell obtained at the European Synchrotron Radiation Facility using image-plate recording techniques. The sample was prepared by compression of hydrogen together with nickel powder in the high-pressure chamber. This result suggests that structural phase transitions in solid hydrogen could be studied directly with powder x-ray techniques.
Auger recombination dynamics of Hg0.795Cd0.205Te in the high excitation regime
Authors: Ciesla C. M. , Murdin B. N. , Phillips T. J. , White A. M. , Beattie A. R. , Langerak C. J. G. M. , Elliott C. T. , Pidgeon C. R. , Sivananthan S.
Published: July 2002

A direct measurement of carrier recombination, far from equilibrium, in Hg0.795Cd0.205Te (Nd−Na=3.3×1014 cm−3) has been made on a picosecond time scale with a pump–probe technique using a free-electron laser. Over the range of carrier densities (5×1016–3×1017 cm−3) and at the temperatures (50–300 K) studied experimentally, contributions to the recombination from Auger, Shockley–Read–Hall, and radiative mechanisms were calculated using an analytic approximation, with carrier degeneracy included, Auger-1 (CCCH) recombination rates were calculated, which also gave the Auger-7 (CHHL) rates via a simple relationship. Excellent agreement was obtained, with Auger-1 dominant at all temperatures and, significantly, for T>225 K when the sample is intrinsic, the Auger-7 contribution was found to be important.
Far-infrared study of a laterally confined electron gas formed by molecular beam epitaxial regrowth on a patterned (100) n+-GaAs substrate
Authors: Arnone D. D. , Cina S. , Burroughes J. H. , Holmes S. N. , Burke T. , Hughes H. P. , Ritchie D. A. , Pepper M.
Published: July 2002

A method of producing lateral confinement of an electron gas has been realized by using molecular beam epitaxy to grow a high mobility heterostructure on a (100) n+-GaAs layer selectively etched to create a two-dimensional array of cavities through the n+-GaAs, which are bound by higher index facets. Far-infrared cyclotron resonance (CR) spectra unambiguously demonstrate that the electron gas formed inside the cavities is confined in both lateral directions. Typical confinement energies of 30 cm−1 and widths of 2000 nm are derived from the spectra and magnetoresistance measurements. The effect of different n+-GaAs backgate biases is also investigated. Combining information from CR spectra with atomic force microscopy images provides a picture of the nature of the lateral confinement in this structure.
Novel wet chemical etch for nanostructures based on II-VI compounds
Authors: Osinsky A. , Qiu Y. , Mahan J. , Temkin H. , Gurevich S. A. , Nesterov S. I. , Tanklevskaia E. M. , Tretyakov V. , Lavrova O. A. , Skopina V. I.
Published: July 2002

A simple wet chemical etch which produces stable and oxide-free surfaces of ZnSe is described. The etchant, a low pH solution of H2SO4:H2O2:H2O, reacts with ZnSe producing an amorphous layer of Se which grows into the semiconductor. The Se layer is then dissolved in aqueous (NH4)2S resulting in a S-passivated surface. The S-passivated layer is volatile and can be desorbed by heating the sample to 300 °C. The efficacy of this process is demonstrated by the formation of 20 nm wide quantum wires of CdZnSe/ZnSe with good optical properties.
Microwave measurement of shot noise in resonant tunneling diodes
Authors: Przadka A. , Webb K. J. , Janes D. B. , Liu H. C. , Wasilewski Z. R.
Published: July 2002

The room temperature shot noise of a resonant tunneling diode was determined from microwave measurements as a function of bias. An AlAs/GaAs structure with multiple quasibound well states and asymmetric barrier thicknesses was investigated over a bias regime exceeding the first resonance. In contrast to results for single well state devices, significant noise suppression below the classical limit was also observed for bias ranges beyond the first resonance level. This suppression can be explained by competition between the first and second resonance levels for the thick barrier on the emitter side and due to predominately single barrier tunneling in the reverse polarity.
AlGaAs/GaAs high electron mobility transistor with a low-temperature grown GaAs ion damage blocking layer
Authors: Chen Ching-Hui , Ibbetson James P. , Hu Evelyn L. , Mishra Umesh K.
Published: July 2002

We have successfully used a thin layer (∼200 Å) of annealed low-temperature GaAs (LT-GaAs) to reduce ion damage that would occur during the formation of a dry-etch gate recess of a high electron mobility transistor. Compared to structures without an ion damage blocking layer, the devices with a thin layer of LT-GaAs are more robust against ion damage. This is important for the application of ion-assisted processing to the fabrication of electronic devices, such as dry etching used to achieve gate recessing.