bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical studies of the applications of resonant tunneling diodes as intersubband laser and interband excitonic modulators
Authors: Loehr J. P. , Singh J. , Mains R. K. , Haddad G. I.
Published: July 2002

We present a theoretical analysis of the optical applications of resonant tunneling diodes. The electronic properties are calculated with a self-consistent traveling-wave model that includes effective-mass mismatches. The interband optical properties are calculated from a 4×4 k⋅p band structure in the dipole approximation. We find that it is possible to operate a conventional device as an intersubband laser if the transition energy is large (∼0.5 eV) and the linewidth in minimal (∼5 meV). A bound-state device can produce a modulation ratio of 5:1 at the excitonic peak with an absorption length of ∼ 40 μm in a waveguide geometry.
Sub-100 femtosecond pulses from an external-cavity surface-emitting InGaAs/InP multiple quantum well laser with soliton-effect compression
Authors: Xiang W. H. , Friberg S. R. , Watanabe K. , Machida S. , Sakai Y. , Iwamura H. , Yamamoto Y.
Published: July 2002

We have compressed strongly chirped optical pulses from a synchronously pumped In0.53Ga0.47As/InP multiple quantum well surface-emitting laser operating with an external cavity. The pulses, initially exhibiting a strong up-chirp with a time-bandwidth product of more than 100 times the Fourier transform limit, were compressed to 77 fs using dispersion and soliton compression in a negative group-velocity-dispersion fiber. Chirp compensation using a diffraction grating pair followed by soliton compression in a fiber gave pulses as short as 21 fs.
Electron-state lifetimes in submicron diameter resonant tunneling diodes
Authors: Tewordt M. , Ritchie D. A. , Syme R. T. , Kelly M. J. , Law V. J. , Newbury R. , Pepper M. , Frost J. E. F. , Jones G. A. C. , Stobbs W. M.
Published: July 2002

We have investigated the lifetimes of electron states in the quantum wells of GaAs-AlGaAs resonant tunneling diodes with diameters down to 200 nm, as a function of the barrier thickness. The times were extracted from the magnitude of steps observed in the current-voltage characteristics, a quantum effect which reflects the quasi-one-dimensional electron transport in these devices. We find very good agreement between the experimental lifetimes, and those calculated using data from transmission electron microscopy. It is also shown that the total scattering time does not correlate with the barrier thickness and is much smaller than the electron-state lifetime.
Femtosecond time-resolved refractive index changes in CdS0.75Se0.25 and CdS
Authors: Fox E. C. , Canto-Said E. , van Driel H. M.
Published: July 2002

A pump-probe, light by light deflection technique employing 120 fs pulses at λ=620 nm has been used to measure the temporal and irradiance (I) dependence of the refractive index (n) in 100-μm-thick single crystals of CdS0.75Se0.25 and CdS at 295 K. For I<3 GW/cm2 only instantaneous negative changes in n are observed and are attributed to Stark and two-photon resonance effects while for higher I negative changes with onset times of approximately 2 ps are attributed to the cooling of two-photon generated carriers. For I≳30 GW/cm2 a partial recovery of n occurs within 10 ps and is attributed to possible threshold dependent recombination processes. The variation of probe-beam deflection with pump irradiance has been determined for different probe delays and related to two photon absorption of the pump beam.
Non-contact electrical characterization of low-resistivity p-type ZnSe:N grown by molecular beam epitaxy
Authors: Park R. M. , Troffer M. B. , Yablonovitch E. , Gmitter T. J.
Published: July 2002

The resistivity of p-type ZnSe:N/GaAs heteroepitaxial layers grown by molecular beam epitaxy using a nitrogen free-radical source has been determined as a function of both substrate temperature and the Zn-to-Se beam equivalent pressure (BEP) ratio employed during growth. Layer resistivities were determined using a noncontact inductive-coupling radio-frequency measurement technique that provided sheet conductivity data from which layer resistivities were calculated. A minimum resistivity of 0.75 Ω cm has been measured to date for p-type ZnSe:N material grown at 235 °C with a BEP ratio of 1:2. Such a resistivity would imply a free-hole density in the range 4×1017−8×1017 cm−3 assuming the hole mobility to be in the range 20−10 cm2 V−1 s−1, respectively.
Influence of nucleation procedures on stress relaxation in heterostructures: GaAs/Si (100)
Authors: Soutadé J. , Fontaine C. , Muñoz-Yagüe A.
Published: July 2002

Stress relaxation behavior at the start of molecular beam epitaxial growth of GaAs layers on Si (100) 2 ° off substrates was studied as a function of nucleation procedures. Two alternative methods were investigated: (i) the standard two-step technique in which growth is initiated at moderate temperature and growth rate, and (ii) a procedure in which a succession of amorphous thin GaAs layers are deposited and thermally crystallized at each step. The results obtained by in situ reflection high-energy electron diffraction analyses evidence a strong dependence of stress relaxation on the nucleation procedure used: in the first case, stress relaxation occurs abruptly at the start of nucleation although, in the second case, relaxation occurs progressively. These results are discussed in terms of the modes of growth involved.
Photodarkening and microcrystallite size in colored filter glasses
Authors: Yanagawa T. , Nakano H. , Sasaki Y.
Published: July 2002

It is demonstrated for the first time that photodarkening in colored filter glasses is associated with apparent growth of CdSxSe1−x microcrystallites. This is thought to be due to the attraction of impurity ions around the microcrystallites. Both a Q-switched Nd3+:YAG laser and a hybrid mode-locked dye laser are used as the light sources. Microcrystallite growth is directly observed by transmission electron microscopy and by field-emission scanning electron microscopy. Growth is also inferred from local changes in color and measured absorption spectra.
Low-threshold InGaAs/GaAs strained-layer ridge waveguide surface emitting lasers with two 45° angle etched internal total reflection mirrors
Authors: Chao Chih-Ping , Law Kwok-Keung , Merz James L.
Published: July 2002

A new type of in-plane surface emitting laser structure with two 45° mirrors has been demonstrated. The device is a ridge waveguide laser with total reflection mirrors etched at 45° to the plane of the active layer, having an epitaxially grown distributed Bragg reflector. Continuous-wave threshold current as low as 10 mA with 12% external differential quantum efficiency is achieved on a 5-μm-wide, 400-μm-long device.
Scanning tunneling microscope surface imaging and etching of single crystals of the high-temperature superconductor Tl2Ba2CuO6+δ
Authors: Parks D. C. , Wang Jihong , Clark Noel A. , Hermann A. M.
Published: July 2002

We have studied the surface morphology of single-crystal bulk superconductors in the Tl-Ca-Ba-Cu-O system by scanning tunneling microscopy, observing surface etching phenomena in air at room temperature, including the formation of lines and pits.
GaAs corrugation pattern with submicron pitch grown by Ar ion laser-assisted metalorganic molecular beam epitaxy
Authors: Yamada Takeshi , Iga Ryuzo , Sugiura Hideo
Published: July 2002

Epitaxial growth of a GaAs film with a fine pattern is realized by Ar ion laser irradiation during metalorganic molecular beam epitaxy. Corrugation patterns with 0.85 and 4 μm pitch are successfully grown on a GaAs substrate using a holographic interference technique, i.e., irradiation of the interference fringe pattern of two laser beams. The cross-section profile of the pattern is similar to a sinusoidal curve, expected from laser power distribution of interference. Vibration of a substrate during epitaxial growth is discussed comparing obtained pattern height to the theoretical one.
Millimeter wave mixing from deliberate grain-boundary weak links in epitaxial Tl2CaBa2Cu2O8 films
Authors: Hong J. P. , Kim T. W. , Fetterman H. R. , Cardona A. H. , Bourne L. C.
Published: July 2002

Millimeter mixers have been fabricated from epitaxial films of Tl2CaBa2Cu2O8, using a bowtie antenna structure integrated with grain-boundary weak links that were deliberately formed during film growth. The bowtie antenna was utilized for broadband millimeter wave coupling of the radiation into the weak links. Heterodyne mixing of signals at both V band (55 GHz) and W band (94 GHz) frequencies, and subharmonic mixing at V has been observed at liquid nitrogen temperature for zero and finite bias voltage conditions. The dependence of the IF output on temperature, bias voltage, and millimeter wave signal power has been studied. Efficient mixing with bias voltage exhibited strong signals right up to Tc (101 K).
Strain relaxation of compositionally graded InxGa1−xAs buffer layers for modulation-doped In0.3Ga0.7As/In0.29Al0.71As heterostructures
Authors: Chang J. C. P. , Chen Jianhui , Fernandez J. M. , Wieder H. H. , Kavanagh K. L.
Published: July 2002

Modulation-doped In0.3Ga0.7As/In0.29Al0.71As heterostructures have been grown on GaAs substrates by molecular beam epitaxy using a compositionally step-graded InxGa1−xAs buffer layer. We found that the buffer layer produces essentially total relaxation with <2×106/cm2 dislocations present in the In0.3Ga0.7As layer. The structural perfection of this layer is reflected in the electrical and galvanomagnetic properties of its two-dimensional electron-gas channel which has a sheet-electron density of 1.2×1012/cm2, peak mobilities of 9 300 cm2/V s at room temperature and 31 000 cm2/V s at 77 K, and a mobility anisotropy of ∼4% along orthogonal 〈110〉 directions.
Resonant-cavity InGaAlAs/InGaAs/InAlAs phototransistors with high gain for 1.3–1.6 μm
Authors: Dodabalapur Ananth , Chang T. Y.
Published: July 2002

We describe the characteristics of resonant-cavity heterojunction bipolar phototransistors (RCHPTs) grown on InP substrates. The active layers are part of a Fabry–Perot cavity in which gold is the top reflector and an InGaAlAs/InAlAs quarter-wave stack is the bottom reflector. The stack and active layer thicknesses are such that the absorption is resonantly enhanced by ∼100% at 1.28 μm in one wafer and 1.52 μm in another. An enhancement in photocurrent response also of ∼100% is obtained at resonance. A dc phototransistor current gain of 5000, corresponding to an optical gain of ∼2500 at resonance, was measured on a three-terminal device in a RCHPT wafer.
Laser diode-pumped femtosecond erbium-doped fiber laser with a sub-ring cavity for repetition rate control
Authors: Yoshida Eiji , Kimura Yasuo , Nakazawa Masataka
Published: July 2002

It is shown for the first time that the pulse repetition rate of a femtosecond erbium-doped fiber laser with a nonlinear amplifying loop mirror can be controlled by attaching a sub-ring linear cavity to the main cavity. The transit time in the sub-ring cavity is set as an inverse integer of that in the main cavity, resulting in an increase in the repetition rate of the output pulse. The pulse thus obtained has a width of 315 fs, a peak power of 12.7 W, and a repetition rate of 125 MHz.
Structural characterization of low-temperature molecular beam epitaxial In0.52Al0.48As/InP heterolayers
Authors: Claverie A. , Yu K. M. , Swider W. , Liliental-Weber Z. , O’Keefe M. , Kilaas R. , Pamulapati J. , Bhattacharya P. K.
Published: July 2002

A systematic study of the structural quality and arsenic content of as-grown In0.52Al0.48As/InP layers deposited on InP by molecular beam epitaxy at temperatures between 150 and 450 °C was performed using transmission electron microscopy and particle-induced x-ray emission. We found that the amount of As incorporated in the layers generally increases with decreasing growth temperature, with the crystalline quality of the layers being good at growth temperatures higher than 200 °C. At 150 °C, a large density of pyramidal defects is formed, the defects are related to the very large amount of excess As incorporated into the layer. The mechanisms leading to the formation of these defects are discussed. At 200 °C, however, the amount of excess As is lower than expected, and wavy streaks of diffuse scattering are seen in electron diffraction. It is shown that small ordered domains of the CuPt type on the group III atoms are responsible for these features.
InAs p-n diodes grown on GaAs and GaAs-coated Si by molecular beam epitaxy
Authors: Dobbelaere W. , De Boeck J. , Heremans P. , Mertens R. , Borghs G. , Luyten W. , Van Landuyt J.
Published: July 2002

InAs p-n diodes have been grown on GaAs and GaAs-coated Si substrates by molecular beam epitaxy. Transmission electron microscopy cross sections of the epilayers demonstrate a good structural quality. Photodiodes were obtained using a Be (p=5×1016 cm−3) and Si (n=3×1016 cm−3) doping scheme. The diodes exhibited 77 K zero-bias resistance area products of 2200 Ω cm2 for InAs/GaAs and 1500 Ω cm2 for InAs/GaAs/Si. The spectral response of the devices peaked at 2.95 μm with Johnson noise limited detectivities D* of 7.0×1011 cm Hz1/2/W for InAs/GaAs and 5.8×1011 cm Hz1/2/W for InAs/GaAs/Si. These results clearly demonstrate the feasibility of the monolithic integration of InAs infrared detectors and GaAs or Si read-out electronics.
ZnSe based multilayer pn junctions as efficient light emitting diodes for display applications
Authors: Jeon H. , Ding J. , Nurmikko A. V. , Xie W. , Kobayashi M. , Gunshor R. L.
Published: July 2002

pn junction characteristics and LED action in ZnSe-based multilayers grown by molecular beam epitaxy is demonstrated. In particular, we show that (Zn,Cd)Se/ZnSe/Zn(S,Se) structures containing (Zn,Cd)Se quantum wells, grown on p-type GaAs epilayers, and designed with a heavily doped n+-ZnSe top contact layer may be appropriate for display device applications in the blue-green portion of the spectrum.
Phase coherence and disorder in Josephson-junction arrays
Authors: Octavio M. , Whan C. B. , Lobb C. J.
Published: July 2002

We present simulations of one- and two-dimensional Josephson-junction arrays to study the effects of disorder on the coherent oscillation of such arrays. For uniformity in the critical currents comparable to that which can be achieved with present technology, two-dimensional arrays are much more stable against disorder than one-dimensional arrays. Both systems are particularly sensitive to disorder when biased near the critical current, with stability increasing at currents farther above the critical current.
Wavelength tuning characteristics of tunable twin-guide lasers with improved current-injection structures
Authors: Yamamoto E. , Hamada M. , Suda K. , Nogiwa S. , Oki T.
Published: July 2002

Tunable twin-guide distributed feedback (TTG-DFB) lasers are fabricated by the all-metalorganic vapor phase epitaxy (MOVPE) process. A very wide continuous tuning range (4.9 nm/25 mA) with single-mode operation is obtained by improving the efficiency of current-injection into the modulation layer. The side-mode suppression ratio (SMSR) is larger than 20 dB in the tuning range up to 4.3 nm.The threshold current is 16 mA and maximum output power is 5 mW.
Low-defect-density germanium on silicon obtained by a novel growth phenomenon
Authors: Malta D. P. , Posthill J. B. , Markunas R. J. , Humphreys T. P.
Published: July 2002

Heteroepitaxial Ge on Si has been grown using molecular beam epitaxy at a Si substrate temperature of 900 °C. Electron microscopy results reveal a highly faceted interface, indicating localized Ge melting and subsequent local alloying with Si. Furthermore, this phenomenon is associated with extensive threading dislocation confinement near the Ge/Si interface. Etch pit density measurements obtained on Ge heteroepitaxial films that have undergone interfacial melting are as low as 105 cm−2.
High resolution transmission electron microscopy study of a GaAs/Si heterostructure grown by chemical beam epitaxy
Authors: Xing Y. R. , Devenish R. W. , Joyce T. B. F. , Kiely C. J. , Bullough T. J. , Goodhew P. J.
Published: July 2002

We have successfully grown epitaxial GaAs on a Si(001) substrate by chemical beam epitaxy (CBE). Misfit dislocations and stacking faults in the GaAs/Si interface have been analyzed by high resolution transmission electron microscopy (HRTEM). The results indicate that the lattice mismatch between GaAs epilayer and Si substrate is completely accommodated mostly by 90° pure-edge misfit dislocations, and partly by 60° mixed misfit dislocations and stacking faults. Residual amorphous patches, presumably of SiO2, on the substrate surface appear to act as nucleation sites for stacking faults. Areas of thin amorphous layer on the substrate do not seem to prevent the epitaxial growth of GaAs on the Si substrate.
Vertical scaling in heterojunction bipolar transistors with nonequilibrium base transport
Authors: Levi A. F. J. , Jalali B. , Nottenburg R. N. , Cho A. Y.
Published: July 2002

We experimentally measure a departure from conventional scaling of current gain β with base thickness xB in abrupt junction n-p-n heterojunction bipolar transistors. It is empirically established that extreme nonequilibrium electron transport in the base causes β to vary as approximately 1/xB. In our AlInAs/InGaAs transistors this new behavior occurs for base thickness xB≲1000 Å.
Control of grain alignment to fabricate long Y-Ba-Cu-O superconductors with high current density
Authors: Selvamanickam V. , Partsinevelos C. , McGuire A. V. , Salama K.
Published: July 2002

A directional solidification method has been developed to grow YBa2Cu3Ox samples in excess of 55 mm in length with uniform grain alignment and a-b planes oriented parallel to the sample length. Using a furnace configuration that yields a negative lateral gradient, the YBa2Cu3Ox grains have been forced to nucleate and grow along the axis instead of at an angle to the sample length. X-ray pole figures analyses along the entire length at different sections show that the a-b planes are aligned parallel to the sample length with deviations less than 5° along the growth direction. Transport critical current density (Jc) measurements over the entire length and at different sections of the sample reveal a uniform current density in excess of 7000 A/cm2 at 1.5 T and 77 K.
Epitaxial growth of Be on α-Al2O3
Authors: Ruffner Judith A. , Slaughter J. M. , Falco Charles M.
Published: July 2002

We report the growth of epitaxial single-crystal (0001) hcp-Be on (0001) α-Al2O3 substrates using molecular beam epitaxy. Thin films were characterized in situ with reflection high energy electron diffraction, and ex situ with ion beam analysis, electron microscopy, atomic force microscopy, and a variety of x-ray diffraction techniques. The in-plane orientation of films grown at substrate temperatures T in the range 10 °C<T<270 °C is Be[11̄00] ∥α-Al2O3[12̄10] and Be[12̄10] ∥α-Al2O3[11̄00], while at T=500 °C the Be is aligned with the substrate. At T=10 °C the films are smooth, but the roughness increases with increasing T. At T=500 °C the crystal perfection improves dramatically but the Be forms large islands.
Mechanism of the growth of microcrystalline silicon
Authors: Jang Jin , Koh Sung Ok , Kim Tae Gon , Kim Sung Chul
Published: July 2002

We studied the behavior of hydrogen atoms bonded to Si in hydrogenated amorphous silicon (a-Si:H) films prepared by layer by layer deposition technique, in which deposition of a few tens of a-Si:H film and hydrogen radical exposure on the surface are done alternatively, with variations of each layer thickness and the exposure time to hydrogen radicals. With increasing the exposure time, the hydrogen atoms are incorporated until reaching a saturation, and then out-diffused by forming molecular hydrogen. In this process, the microcrystalline structure is formed.
Metalorganic chemical vapor deposition of low microwave surface resistance YBa2Cu3O7 on (100) LaAlO3 and (100) SrTiO3
Authors: DeSisto W. J. , Henry R. L. , Newman H. S. , Osofsky M. S. , Cestone V. C.
Published: July 2002

Thin films of YBa2Cu3O7−δ on (100) LaAlO3 and (100) SrTiO3, up to 5000 Å thick, were grown by metalorganic chemical vapor deposition. The as-deposited films were c-axis oriented, and had transition temperatures between 87 and 89 K, transition widths less than or equal to 1 K, and critical current densities of 1–3×106 A/cm2 at 77 K. Microwave surface resistance measurements at 36 GHz on (100) LaAlO3 showed significant improvements over copper metal at 77 K. Films grown on (100) SrTiO3 exhibited slightly better properties than those grown on (100) LaAlO3. Films which were slightly deficient in barium and rich in yttrium consistently demonstrated superior properties.
Step edge YBa2Cu3O7−δ dc SQUIDs on sapphire substrates
Authors: Yuan C. W. , Berezin A. B. , de Lozanne A. L.
Published: July 2002

We have made YBa2Cu3O7−δ (YBCO) thin film dc superconducting quantum interference devices (SQUIDs) on sapphire substrates that operate above 77 K. The YBCO thin films are free of weak links and have critical current densities (Jc) of 106 A/cm2 at 77 K. Across the step edge, typical Jc ranges from 105 to 103 A/cm2 at 77 K and increases linearly with decreasing temperature. Typically, we obtain IcRn products near 30 μV at 77 K. We have operated the dc SQUIDs between 4.2 and 77 K and observed voltage modulation in rough agreement with the expected values. The flux noise is typically 1×10−10 Φ20/Hz, with a corresponding noise energy, SE, of 1.3×10−29 J/Hz at 77 K and 1 kHz.
Measurements of the intensity noise of a broadly tunable, erbium-doped fiber ring laser, relative to the standard quantum limit
Authors: Sanders Steve , Dawson Jay W. , Park Namkyoo , Vahala Kerry J.
Published: July 2002

The intensity noise of an erbium-doped fiber ring laser is measured relative to the standard quantum limit. Over a tuning range of 24 nm, the noise power is within 20 dB of the shot noise floor and varies linearly with laser output power. Oscillations in the noise power spectrum are observed and attributed to beating of the lasing mode with other, strongly damped cavity modes.
Two-dimensional lattice-mismatched heteroepitaxy of germanium on silicon beyond the critical thickness by introducing a surfactant
Authors: Osten H. J. , Klatt J. , Lippert G. , Bugiel E. , Hinrich S.
Published: July 2002

Smooth germanium films have been grown on Si(100) surfaces in a two-dimensional fashion by using antimony as a surfactant. Different ways of depositing the surfactant (at the interface between substrate and growing film, after the deposition of a thin Ge layer, and by coevaporation) have been investigated. The grown films, investigated by high-resolution electron microscopy and reflection high-energy electron diffraction, show that the surfactant does not act at the interface. A kinetical approach for the description of surfactant behavior in the growing front is necessary.
Optical properties of free-standing silicon quantum wires
Authors: Sanders G. D. , Chang Yia-Chung
Published: July 2002

We present theoretical studies of the optical properties of free-standing Si quantum wires, using an empirical tight-binding model which includes d orbitals and second-neighbor interactions. The excitonic effects are included within the effective-mass approximation. The predicted exciton transition energy for a quantum wire with a width of 27 Å agrees with the observed luminescence for a sample of similar size. We found that the thermally averaged exciton oscillator strengths for quantum wires with widths around 8 Å can become comparable to that of bulk GaAs.
Single-mode selection using coherent imaging within a slab waveguide CO2 laser
Authors: Abramski K. M. , Baker H. J. , Colley A. D. , Hall D. R.
Published: July 2002

A technique for selecting a single high-order lateral mode of a rf excited slab waveguide laser is described. An in-cavity grid which matches the periodicity of the desired mode, together with slab waveguide dimensions which create coherent imaging by the Talbot effect, have produced a stable output power of 155 W in a high spectral purity, single-resonator mode.
Tunable twin-guide lasers with flat frequency modulation response by quantum confined Stark effect
Authors: Wolf T. , Drögemüller K. , Borchert B. , Westermeier H. , Veuhoff E. , Baumeister H.
Published: July 2002

For the first time results on the frequency modulation response of tunable twin-guide laser diodes utilizing the quantum confined Stark effect in a multiquantum well modulation layer are presented. The structures were grown by metalorganic vapor phase epitaxy and were processed into ridge-waveguide lasers emitting at 1555 nm. Preliminary devices exhibit single-mode output power levels of more than 10 mW and minimum linewidths around 4 MHz. The frequency modulation response is flat up to 2 GHz with a modulation efficiency of 7 GHz/V.
Bias-stress-induced creation and removal of dangling-bond states in amorphous silicon thin-film transistors
Authors: Powell M. J. , Deane S. C. , Milne W. I.
Published: July 2002

We report on the threshold voltage shift in amorphous silicon thin-film transistors, subjected to a gate bias for a prolonged period of time (bias stress). For transistors made with a silicon nitride gate insulator, the threshold voltage shift for low positive bias is due to dangling-bond-state creation in the amorphous silicon layer. For low negative bias, the threshold voltage shift is due to the bias-stress-induced removal of dangling-bond states. These results are contrasted with previously published results for oxide transistors, but both results are consistent with a defect pool model for the dangling-bond states. The difference for oxide and nitride transistors is due to a different zero-bias Fermi energy position at the interface. For nitride transistors at much larger applied bias, the dominant mechanism changes and the threshold voltage shift is dominated by charge trapping in the gate dielectric. This is found for both large negative and large positive bias.
Novel very sensitive analytical technique for compositional analysis of Hg1−xCdxTe epilayers
Authors: Bubulac L. O. , Viswanathan C. R.
Published: July 2002

This letter reports a novel analytical method using negative secondary ion mass spectrometry (SIMS) of the Te matrix element with a Cs primary ion beam to analyze and determine the composition in HgCdTe epilayers with a high sensitivity (better than Δx of 0.0015) and a depth resolution determined by SIMS. The method is based on matrix-induced ion yield variations in the Te signal observed in SIMS. The correlation between the Te− secondary ion yield and Cd mole fraction is a linear function. The material composition can be calculated by this technique when the Te yield profile is known provided that the composition of any two layers of the structure are known, or the structure contains a CdTe layer, for which case composition of no Hg1−xCdxTe layer is needed.
Growth and characterization of Zn1−xMnxTe epilayers grown by hot wall epitaxy on (001)GaAs substrates
Authors: Abramof E. , Pesek A. , Juza P. , Sitter H. , Fromherz T. , Jantsch W.
Published: July 2002

In this letter we report the first growth of Zn1−xMnxTe epitaxial films. The films were grown by hot wall epitaxy on 2° misoriented (001) GaAs substrates up to a Mn concentration of 70%. The Mn content was determined by optical reflection and x-ray diffraction. All the epilayers (0.0≤x≤0.7) grew in the [001] direction in the zinc-blende structure. The full width at half maximum of the (004) reflex of the x-ray rocking curves proved the good crystalline quality of the grown layers and increased monotonically as the Mn content increased. The relative tilt between epilayer and substrate was also determined from high resolution x-ray diffraction.
dc current-voltage characteristics of a double-quantum-well field-effect resonant tunneling transistor
Authors: Chen J. G. , Yang C. H. , Wilson R. A. , Wood C. E. C.
Published: July 2002

We reported the observation of steplike drain current and the negative transconductance, in a field-effect transistor. Our transistor has a double-quantum-well channel, and the quantum well close to the surface is depleted. We demonstrate that the novel transistor characteristics are from tunneling of electrons in between two-dimensional quantum wells. The observed current-voltage characteristic in gate tunneling current has a large peak-to-valley ratio (380–1), which is close to an idealized delta functionlike behavior.
Effective electric field in dc magnetization measurements: Comparing magnetization to transport critical currents
Authors: Hettinger J. D. , Kim D. H. , Gray K. E. , Welp U. , Kampwirth R. T. , Eddy M.
Published: July 2002

We report values of critical current (Jc) for Tl2Ba2CaCu2Ox(Tl-2212) epitaxial thin films in magnetic fields up to 5 T and at temperatures of 5, 40, and 77 K determined from dc magnetization and using a standard transport technique. Although we verify the applicability of Bean’s model [Rev. Mod. Phys. 36, 31 (1964)], these values only agree at small applied magnetic fields and at low temperatures. Our results indicate that the differences observed in Jc’s determined from the two techniques may be understood by considering only the field-dependent, nonlinear E-J characteristic and the ‘‘effective’’ electric-field criterion used in determining Jc.
Electron paramagnetic resonance study of porous silicon
Authors: Bhat S. V. , Jayaram K. , Muthu D. Victor S. , Sood A. K.
Published: July 2002

Electron paramagnetic resonance studies under ambient conditions of boron-doped porous silicon show anisotropic Zeeman (g) and hyperfine (A) tensors, signaling localization of the charge carriers due to quantum confinement.
Compatible laser emission and optical waveguide modulation at 1.5 μm using Wannier–Stark localization
Authors: Bigan E. , Harmand J. C. , Allovon M. , Carré M. , Carenco A. , Voisin P.
Published: July 2002

We investigate the electroabsorption properties of an InGaAs-InAlAs superlattice optical waveguide. When reverse biased, the structure exhibits large extinction ratios over short waveguide lengths with very low drive voltages by using low-energy oblique transitions below the superlattice band gap. Although the structure has been optimized for modulation, laser emission is observed under forward bias. The peak emission wavelength stands in the ‘‘blue-shift’’ region which opens a way to straightforward laser-modulator monolithic integration.
Optical nonlinear responses of a quantum well photodiode with a non-ohmic contact
Authors: Abe Yuji , Tokuda Yasunori , Kanamoto Kyozo , Tsukada Noriaki
Published: July 2002

The dependence of photocurrent properties on incident optical power in a quantum well p-i-n photodiode with a nonohmic contact was investigated. The experimental results showed that a significant absorption peak shift, in an extremely low optical power range, as well as a notable modification in the spectral shape at a higher power range was observed, without any external feedback element. The mechanism for the optical nonlinear responses can be explained in terms of the built-in field screening at the p-i-n junction or by taking into account the load characteristics of the Schottky-like contact.
Orientation control of YBa2Cu3O7 thin films on MgO for epitaxial junctions
Authors: Chew N. G. , Goodyear S. W. , Humphreys R. G. , Satchell J. S. , Edwards J. A. , Keene M. N.
Published: July 2002

A low-temperature argon ion milling process has been used to induce growth of c-oriented YBa2Cu3O7 on (001) MgO substrates with the in-plane film axes rotated 45° with respect to those of the substrate, and with respect to those of films grown on untreated regions of the substrate. This process is compatible with standard photolithographic processing, and has been used to produce defined areas of the two orientations on the same substrate. Josephson junctions and dc SQUIDs have been fabricated using the resulting grain boundaries.
Observation of screening effect in large-area, cold-cathode diodes
Authors: Coogan J. J. , Rose E. A.
Published: July 2002

In this work we report the first observation of the screening effect in large-area, cold-cathode diodes. A framing camera was used to observe the formation of emission centers (ECs) on a 200 cm2 velvet emitter. The density of ECs increased as a function of applied magnetic field as predicted. The current per EC decreased as the magnetic field was increased. These phenomena suggest methods of increasing the spatial and temporal uniformity of high-power electron beams.
Ultrafast (up to 39 GHz) relaxation oscillation of vertical cavity surface emitting laser
Authors: Lin J. , Gamelin J. K. , Lau K. Y. , Wang S. , Hong M. , Mannaerts J. P.
Published: July 2002

Relaxation oscillation of frequency as high as 39 GHz has been observed in a surface emitting laser (SELD). The correlation between the observed relaxation oscillation and the modulation bandwidth was studied. The experimental results suggest that SELDs have the potential to operate at several times the highest modulation speed achieved so far.
Low-dislocation-density silicon-on-insulator material produced by sequential oxygen implantation and low-temperature annealing
Authors: Venables D. , Jones K. S. , Namavar F.
Published: July 2002

Lattice strain and defect formation in oxygen-implanted silicon (SIMOX) were investigated by high-resolution x-ray diffraction and transmission electron microscopy. At doses of 1×1017 and 3×1017 cm−2 a high density of vacancy-type defects formed in a uniaxially compressed layer at the surface of the as-implanted wafer. Annealing at 900 °C for 0.5 h reduced this negative strain as the defects coarsened into observable cavities. The development of cavities upon annealing was used in a sequential-implantation and low-temperature-annealing process to produce low-threading dislocation density SIMOX. This new process offers several advantages over other methods of producing low-dislocation-density material.
Flux pinning by a-axis grains in c-axis-oriented Y-Ba-Cu-O films
Authors: Fuke H. , Yoshino H. , Yamazaki M. , Thanh T. D. , Nakamura S. , Ando K. , Kobayashi Y.
Published: July 2002

We have investigated the relationship between the microstructures and pinning forces by measuring the magnetic-field dependence and angular dependence of Jc in several kinds of YBCO thin films having different microstructures. A high-Jc value was kept even when the magnetic field was applied perpendicular to the film plane in the case of a c-axis-oriented film which was studded with a-axis-oriented grains. The boundaries between the a-axis-oriented grain and the c-axis-oriented grain are considered to be effective as pinning centers.
Observation of third-order intersubband dc Kerr effect at the midinfrared wavelengths in GaAs quantum wells
Authors: Sa’ar A. , Kuze N. , Feng J. , Gravé I. , Yariv A.
Published: July 2002

We report on the first observation of third-order intersubband nonlinearities in a quantum well structure. We have measured the dc Kerr effect in a symmetric quantum well and found that the Kerr coefficients due to intersubband transitions are six orders of magnitude larger than that of bulk GaAs. To our best knowledge this is the largest value ever measured for the third-order susceptibility. By including dc screening effects and evaluating the internal electric field in the well, a good agreement between the calculated coefficients and the experimental ones was found.
Effect of silicon source gas on silicon-germanium chemical vapor deposition kinetics at atmospheric pressure
Authors: Kamins T. I. , Meyer D. J.
Published: July 2002

Epitaxial Si1−xGex alloy layers have been deposited in an atmospheric-pressure, chemical-vapor-deposition reactor using dichlorosilane, silane, and disilane, along with germane. The deposition rate increases and the Ge content decreases with increasing reactivity of the silicon-containing gas. The rate increases monotonically with increasing Ge content in the layer for all three gases, in contrast to the behavior seen in systems operating at substantially lower total deposition pressures, suggesting that the differences in previously reported behavior are dominated by the different operating-pressure regimes, rather than the different silicon source gases.
In0.35Ga0.65P light-emitting diodes grown by gas-source molecular beam epitaxy
Authors: Masselink W. Ted , Zachau Martin
Published: July 2002

Light-emitting diodes with peak (300 K) emission centered at less than 590 nm have been fabricated from p-i-n junctions in In0.35Ga0.65P. This alloy is close to that with the largest direct band gap in the InyGa1−yP system and has lattice mismatch from the GaAs substrate of 1%. Specularly smooth surface morphology is obtained in this gas-source MBE material through the use of a unique strained-layer-superlattice buffer. Diodes exhibit good rectification and good reverse breakdown characteristics.
Improved performance of carbon-doped GaAs base heterojunction bipolar transistors through the use of InGaP
Authors: Abernathy C. R. , Ren F. , Wisk P. W. , Pearton S. J. , Esagui R.
Published: July 2002

Carbon-doped GaAs/AlGaAs heterojunction bipolar transistors (HBTs) typically exhibit severe leakage at the base-emitter interface which limits their utility for low-current applications. Furthermore, the device breakdown voltage, and hence power handling capability, is limited due to the band gap of the GaAs collector material. In this letter we will demonstrate for the first time that both of these limitations can be overcome through the use of InGaP. Since InGaP is not readily doped with carbon, it does not suffer from compensation due to carryover of carbon from the GaAs base. Hence, the ideality factor of the base-emitter junction improves from 1.3 to 1.09 when the conventional n-AlGaAs emitter layer is replaced with n-InGaP. Moreover, InGaP eliminates the crossover of the base and collector currents typically observed in heavily carbon doped GaAs HBTs. This results in the maintenance of gain even at very low collector currents. As a collector material, we have found that InGaP produces significantly higher breakdown voltage than GaAs (19 V vs 12 V) of the same thickness and doping, due to its larger band gap. As in the emitter, InGaP collectors exhibit excellent ideality factors of ∼1.05.
Evidence for quantum well asymmetry in optical absorption
Authors: Young P. M. , Ehrenreich H.
Published: July 2002

Some previously unexplained features of the experimentally determined optical spectra of GaAs/Ga1−xAlxAs heterostructures are theoretically explained in terms of unintentionally introduced asymmetries in the shape of semiconductor quantum wells which break the usual optical selection rules. Various mechanisms that may be responsible for well asymmetries are suggested. Their measurement may be a useful characterization tool in quantum well fabrication.
Radiative recombination in GaAs-AlxGa1−xAs quantum dots
Authors: Wang P. D. , Sotomayor Torres C. M. , Benisty H. , Weisbuch C. , Beaumont S. P.
Published: July 2002

We present experimental and theoretical results on the low-temperature luminescence intensity of dry-etched GaAs-AlxGa1−xAs quantum dots. The luminescence intensity was found to decrease by two orders of magnitude with the decrease of dot sizes from 1 μm to 60 nm. Our intrinsic model of the emission yield invokes slower momentum and energy relaxation mechanisms as the lateral dimensions decrease. The additional extrinsic effect considered involves carrier diffusion with a surface nonradiative recombination velocity. Combining intrinsic and extrinsic effects and using a surface recombination velocity of ∼105 cm/s for GaAs, we can obtain a good fit to the data.
X-ray photoelectron spectroscopy study for Nb Josephson junctions with overlayer structure
Authors: Shigeno Mayumi , Morohashi Shin’ichi
Published: July 2002

We studied metal/Nb structures with Al, Zr, Ta, Hf, V, and Ti as thin overlayers (all transition elements except Al) using x-ray photoelectron spectroscopy. The metal thickness sufficient to protect Nb from the formation of Nb native oxide was 2.0 nm. In structures with Al, Zr, Ta, and Hf overlayers, the oxide peaks in the photoelectron spectra, which resulted from native oxide grown on the metal surface, shifted toward higher binding energies with increasing metal overlayer thickness. These shifts were attributed to the metal coverage and the insulating oxide layers. The oxide insulating properties of the native oxides and the metal coverage of the Nb surface were studied at the same time, nondestructively, using XPS. These are essential factors for fabricating Nb junctions with excellent current-voltage characteristics.
Effect on spontaneous emission of quantum well placement in a short vertical cavity
Authors: Huffaker D. L. , Huang Z. , Lei C. , Deppe D. G. , Pinzone C. J. , Neff J. G. , Dupuis R. D.
Published: July 2002

Data are presented demonstrating the influence of the precise placement of a GaAs quantum well in a 5 μm long AlGaAs vertical cavity. It is shown that, even for this relatively long cavity, when the emitting dipoles are confined to a region significantly less than the optical wavelength, the quantum well placement influences not only the spectral shape of the emitted light but also the spectrally integrated intensity. Cavity structures are characterized using transmission measurements, spectral emission, and radiation patterns.
Passively mode locked femtosecond color center lasers in the erbium gain band
Authors: Soccolich C. E. , Islam M. N. , Möllmann K. , Gellermann W. , German K. R.
Published: July 2002

Using semiconductor saturable absorbers, we passively mode lock two color center lasers (CCL) to generate femtosecond pulses at wavelengths within the gain band of erbium-doped fiber amplifiers. For the first time to our knowledge, we passively mode lock a KCl, FA(Tl) CCL in a single cavity to generate near transform limited Gaussian pulses as short as 315 fs with pulse energies up to 600 pJ. We also extend the tuning range for a NaCl, (F 2+)H CCL to include the 1.5–1.6 μm wavelength range and generate pulses as short as 280 fs by addition of a low-loss intracavity prism filter and proper crystal preparation. The performance of the two lasers are compared as a function of wavelength.
Submicrometer modification of polymer surfaces with a surface force microscope
Authors: Jin X. , Unertl W. N.
Published: July 2002

We have used the sharp tip of a surface force microscope to make modifications with submicrometer dimensions on polymer surfaces. In this letter we show three examples: scribed grooves with widths less than 120 nm, raised areas with heights up to 1 nm above the original surface, and pits with depths of 6 nm. We also discuss possible sources of contrast in surface force microscope images that are not due to height variations in the surface topography. Because the surface force microscope can be used for both conducting and nonconducting materials, it has an advantage over the higher resolution scanning tunneling microscope.
Characterization of SiO2/Si(100) interface structure of ultrathin SiO2 films using spatially resolved electron energy loss spectroscopy
Authors: Fukuda Hisashi , Yasuda Makoto , Iwabuchi Toshiyuki
Published: July 2002

High-resolution transmission electron microscopy (HRTEM) with 0.3-nm resolution, scanning transmission electron microscopy using transmission electron diffraction and electron energy loss spectroscopy (EELS) with 0.7-nm resolution have been employed to characterize the SiO2/Si(100) interface structure of ultrathin (5–12 nm) SiO2 films grown by rapid thermal oxidation (RTO) at 1100 °C. In the HRTEM image, the SiO2/Si(100) interface of ultrathin SiO2 film grown by RTO in dry oxygen ambient seems to be uniform. The TED patterns also showed that the atomic structure abruptly changes from the crystalline silicon to amorphous oxide network across the SiO2/Si interface. The EELS plasmon-loss spectra showed that for 5-nm-thick SiO2 an intermediate oxide composition indicating a plasmon energy between Si (17.0 eV) and SiO2 (22.5 eV) is present, whereas it disappears for 12-nm-thick SiO2 film.
Diffractive elements for annular laser beam transformation
Authors: Davidson N. , Friesem A. A. , Hasman E.
Published: July 2002

A diffractive optical system for the transformation of an annular laser beam to a uniform circular beam is presented. It is composed of two diffractive elements which are recorded as surface relief transmission gratings with multilevel discrete binary steps. Our experiments with CO2 laser radiation show that high diffraction efficiencies and good uniformity of the output beam can be achieved.
Possible structural models of n-diamond: A modified form of diamond
Authors: Hirai Hisako , Kondo Ken-ichi , Sugiura Hiroshi
Published: July 2002

A few possible structural models of n-diamond, which is a modified form of diamond quenched from shock-compressed graphite, are proposed on the basis of observed electron diffraction patterns. From the structural relationship and transition mechanism, the most favored structure is composed of hexagonal-ring-planes moderately puckered with opposite direction to that of cubic (Fd3m) diamond, having a peculiar bonding state different from exact sp2 and sp3.
Simultaneous measurement of electron and hole escape times from biased single quantum wells
Authors: Cavaillès J. A. , Miller D. A. B. , Cunningham J. E. , Kam Wa P. Li , Miller A.
Published: July 2002

Picosecond pump probe measurements on waveguides containing a single GaAs/GaAlAs quantum well have enabled us to determine for the first time both electron and hole escape times from biased quantum wells. Contributions from excitonic saturation and field screening by photogenerated carriers can be clearly identified in the nonlinear transition signal and are quantitatively modeled. Preliminary analysis suggests that thermally assisted escape is dominant at room temperature, but discrepancies are found with conventional thermionic emission models.
Molecular beam epitaxy of (211)-InAs quantum sheets in GaAs
Authors: Ilg M. , Brandt O. , Ploog K.
Published: July 2002

We study the synthesis of piezoelectrically active (211)-InAs quantum sheets in GaAs by molecular beam epitaxy. The important feature of our growth technique is the modulation of the substrate temperature during the interface formation. The final structures are investigated by high-resolution x-ray diffraction and photoluminescence spectroscopy. These experiments demonstrate the necessity to consider In segregation for the optimization of the optical response of these structures, and then reveal in addition that [211]-oriented samples exhibit structural and optical properties strikingly different from those of [100]-oriented samples.
Photoluminescence study of strain-induced quantum well dots by wet-etching technique
Authors: Tan I-Hsing , Mirin Richard , Jayaraman Vijay , Shi Song , Hu Evelyn , Bowers John
Published: July 2002

Simple holographic lithography and wet etching have been used to fabricate strain-induced quantum well dot structures. Lateral confinement was generated in a GaAs quantum well (QW) by etching a double-exposed grating pattern into a pseudomorphic, strained layer of In0.3Ga0.7As which overlies the QW. By spacing three QWs of different widths at varying depth from the stressor, lateral strain confinement and vertical strain propagation are directly resolved. We have observed at 14 meV redshift in the photoluminescence spectra for the QW located 22 nm away from the stressors and have confirmed that the strain propagation depth along the material growth direction is comparable to the lateral dot dimension.