bluuebunny/crossref_metadata_2025 huggingface dataset:
Spontaneous growth of coherent tilted superlattice on vicinal (100) GaAs substrates
Authors: Tsuchiya M. , Petroff P. M. , Coldren L. A.
Published: July 2002

Periodic Al composition modulations have been observed to occur spontaneously during molecular beam epitaxy of AlGaAs on vicinal (100) substrates. The formation of the spontaneous Al modulation requires (a) the migration-enhanced epitaxy deposition and (b) one monolayer deposition of Al and Ga atoms per cycle, hence, the denomination of coherent tilted superlattice (C-TSL). Cross-sectional transmission electron microscopy clearly shows that the C-TSL has the periodicity of the surface steps. We also show that the Al-rich regions of the C-TSL form at the bottom of steps before the As flux is established. These results indicate that growth kinetics dominates the C-TSL formation.
Impact of sidewall recombination on the quantum efficiency of dry etched InGaAs/InP semiconductor wires
Authors: Maile B. E. , Forchel A. , Germann R. , Grützmacher D.
Published: July 2002

We have investigated the lateral width (Lx) dependence of the quantum efficiency of the excitonic recombination in etched InGaAs/InP wires (40 nm≤Lx≤5 μm). The analysis of data obtained at different temperatures implies that the intensity decay observed for narrow wires is due to the formation of an optically inactive (‘‘dead’’) layer and due to surface recombination.
Coherent broadband microwave spectroscopy using picosecond optoelectronic antennas
Authors: Pastol Y. , Arjavalingam G. , Halbout J.-M. , Kopcsay G. V.
Published: July 2002

We describe coherent microwave transient spectroscopy experiments using picosecond optoelectronic integrated antennas. The effectiveness of the experimental setup for the measurement of the loss and dispersion properties of materials in the 10–125 GHz range is characterized using microwave filters of predictable behavior. We also present measurements of the absorption coefficient and refractive index of fused silica over this frequency band.
Stimulated emission in quantum well laser diodes
Authors: Blood P.
Published: July 2002

We observe that stimulated emission from inhomogeneously pumped quantum well laser diodes is shifted down in energy compared with the subband transition energy. Measured spontaneous emission spectra show that this stimulated emission is due to band-to-band transitions shifted by renormalization at high injected carrier densities, and we suggest that this same mechanism explains reported observations of stimulated emission from inhomogeneously photopumped structures which previously have been interpreted as evidence for longitudinal optic (LO) phonon participation. We show that LO phonon participation cannot account for the photon energy of stimulated emission from conventional homogeneously pumped quantum well laser diodes.
Quasi-nondestructive readout of holographically stored information in photorefractive Bi12SiO20 crystals
Authors: Delboulbe A. , Fromont C. , Herriau J. P. , Mallick S. , Huignard J. P.
Published: July 2002

The hologram fixing process in a Bi12 SiO20 crystal arises due to the formation of a complementary grating of positive charges localized in shallow traps. Uniform illumination of the crystal with blue or green light erases the electronic charge pattern but leaves the positive charge grating undisturbed. Due to the smaller mobility lifetime product of holes, this grating decays at room temperature with a time constant that is much longer than that of the electronic grating. We show in this letter that the readout time constant can be further increased considerably by cooling the crystal. Images retrieved from a crystal kept at 0 °C temperature and under continuous illumination for a few hours are presented. The energy levels of the hole trapping sites involved in this process are found to be situated at 0.56 and 1.1 eV above the valence band.
Diffusion-enhanced epitaxial growth of thickness-modulated low-loss rib waveguides on patterned GaAs substrates
Authors: Colas E. , Shahar A. , Tomlinson W. J.
Published: July 2002

Rib waveguides have been fabricated without any post-crystal growth processing steps. The ribs are defined by the two nongrowth (111)B surfaces that develop at each edge of (011) mesas on a patterned GaAs substrate during organometallic chemical vapor deposition (OMCVD) of GaAs/AlGaAs structures. Propagation losses as low as 0.6 dB/cm at 1.52 μm wavelength have been obtained, which is attributed to the smoothness of the (111)B facets defining the GaAs guiding layer. This study revealed the importance of surface diffusion-enhanced crystal growth when a growth surface is adjacent to a nongrowth surface such as a (111)B facet. This effect was quantified here and its magnitude suggests that the OMCVD technique would be well suited for the growth of structures tapered in three dimensions, of interest for integrated optics applications.
Strain mapping in [111] and [001] InGaAs/GaAs superlattices
Authors: Venkateswaran U. D. , Cui L. J. , Li M. , Weinstein B. A. , Elcess K. , Fonstad C. G. , Mailhiot C.
Published: July 2002

Raman area maps measuring the strain in lattice-mismatched [111] and [001] oriented InxGa1−xAs/GaAs superlattices (x=0.1, 0.17) are presented and compared with independent x-ray rocking curve studies of the average strain in the same samples. We find that the LO phonon frequency, but not the TO frequency, is a valid measure of strain for [111] oriented superlattices exhibiting one-mode behavior. This is explained by the lack of compensation between the effects of alloying and strain for the TO mode in InxGa1−xAs. The capability to nondestructively map small growth variations in superlattice and buffer layer constituents is demonstrated.
Evidence of native gallium antisite defects in semi-insulating liquid-encapsulated Czochralski-grown GaAs
Authors: Alaya S. , Maaref H. , von Bardeleben H. J. , Bourgoin J. C.
Published: July 2002

We report the observation by photoluminescence of the gallium antisite double acceptor in As-rich GaAs grown by the liquid-encapsulated Czochralski technique. In the semi-insulating material both arsenic antisite and gallium antisite defects are present simultaneously which must be taken into account for any electrical compensation model.
Far-infrared frequency modulation by optically induced gratings in silicon
Authors: Alius H. , Dodel G.
Published: July 2002

Frequency modulation of 119 μm (2.5 THz) H2O laser radiation by optically induced gratings in Si is reported. The gratings were excited using two diode-pumped, frequency-tunable Nd:YAG lasers. Frequency shifts up to 15 MHz were generated. With 26 mW effective optical exitation power a maximal efficiency of 1.5×10−3 was achieved, with a 3 dB roll-off frequency of 35 kHz for the Si wafer used in the experiment. Results of numerical model calculations are presented, which show that efficiencies in the 10% region should be achievable with moderate optical excitation power. It is pointed out that the principle of optically induced gratings offers a promising tool to transfer frequency modulation from the near-infrared to the far-infrared spectral range.
Powder-free plasma chemical vapor deposition of hydrogenated amorphous silicon with high rf power density using modulated rf discharge
Authors: Watanabe Y. , Shiratani M. , Makino H.
Published: July 2002

Deposition of hydrogenated amorphous silicon films from SiH4/He gas mixtures was performed by using a square wave amplitude modulated rf discharge. The modulation was used for controlling radical densities in plasmas which led to a high rate deposition of good quality films. The fairly high deposition rate of 6 Å/s was obtained for a low concentration of 5% SiH4 and a high rf peak power 200 W (0.8 W/cm3) without any appreciable amount of powder particles in the reaction chamber. The optical gap of the films was 1.8–1.95 eV. Emission intensities of HeI 388.9 nm and SiH 413.5 nm linearly increased with rf peak power and were well correlated with the deposition rate.
Monolithic integration of an (Al)GaAs laser and an intracavity electroabsorption modulator using selective partial interdiffusion
Authors: O’Brien S. , Shealy J. R. , Wicks G. W.
Published: July 2002

The monolithic integration of an intracavity modulator with a multiple quantum well (Al)GaAs laser has been accomplished with the use of selective partial interdiffusion. Interdiffusion was used to create a blue-shifted and semitransparent modulator section in a ridge laser structure. In measuring the total optical output power from the devices, steady-state extinction ratios of 20 dB were measured at reverse biases of −4.6 and −3.6 V for modulator sections with lengths of 200 and 400 μm, respectively. Shifting of the lasing mode towards longer wavelengths (Δλ≊0–50 Å) was also observed making the structure useful as a tunable device and for frequency modulation applications.
High quality AlxGa1−xAs grown by organometallic vapor phase epitaxy using trimethylamine alane as the aluminum precursor
Authors: Hobson W. S. , Harris T. D. , Abernathy C. R. , Pearton S. J.
Published: July 2002

High quality AlxGa1−xAs has been grown by low-pressure (30 Torr) organometallic vapor phase epitaxy (OMVPE) using a novel precursor, trimethylamine alane (TMAAl), as the aluminum source. The epilayers exhibited featureless surface morphology, very strong room-temperature photoluminescence (PL), and excellent compositional uniformity (x=0.235±0.002 over a 40 mm diameter). The residual carbon incorporation, which determined the background doping, depended largely upon the choice of gallium precursor. Using triethylgallium, carbon incorporation could be largely suppressed ([C]≪1016 cm−3). The carbon-related emission intensity was less than the bound exciton emission in low-temperature (1.6 K) PL even at excitation powers as low as 50 μW cm−2. By sharp contrast, the use of trimethylgallium led to much higher C concentrations (2–5×1017cm−3). Under appropriate conditions, therefore, the use of TMAAl produces extremely high purity AlGaAs of superior quality to AlGaAs grown using conventional precursors.
X-ray characterization of in-plane ordering in YBa2Cu3O7−x thin films using a standard Weissenberg camera
Authors: Perrin A. , Karkut M. G. , Guilloux-Viry M. , Sergent M.
Published: July 2002

We have used a standard Weissenberg camera in the oscillating mode to characterize the in-plane structure of YBa2Cu3O7 thin films. We find that for films optimally grown on (100) MgO or (100) SrTiO3 substrates, the in-plane film axes are aligned parallel to the substrate axes. This is true both for solely c-axis oriented films (perpendicular to the film plane) and for mixed a- and c-axis oriented films. For a film grown on (110) SrTiO3, we have established that the film orientation perpendicular to the film plane is solely (103) and not (110) or a mixture of the two. In addition the in-plane film axes are colinear to the substrate axes.
Electron and hole impact ionization coefficients in GaAs/Al0.45Ga0.55As/Al0.3Ga0.7As coupled well systems
Authors: Bhattacharya P. K. , Zebda Y. , Singh J.
Published: July 2002

We have measured electron and hole multiplication factors and impact ionization coefficients in 550 Å GaAs/500 Å Al0.3Ga0.7As quantum wells with an intermediate Al0.45Ga0.55As barrier (50 and 100 Å) inserted in the well region. It is seen that while the measured value of α(E) is insensitive to the position of the intermediate barrier in the well, the value of β(E) is very sensitive. The value of α/β varies from less than unity to 5, depending on the position of this barrier. These results suggest that hole confinement and scattering play a major role in making the value of α/β greater than unity in these multilayered structures.
Improved performance of strained InGaAs/GaAs photodiodes grown on patterned GaAs substrates by molecular beam epitaxy
Authors: Li W. Q. , Bhattacharya P. K. , Tober R. L.
Published: July 2002

We have experimentally studied the photoresponse characteristics of strained InxGa1−xAs (0.05≤x≤0.20) p-i-n photodiodes grown in small holes etched in GaAs substrates where the thickness of the i region exceeds the critical thickness. The diodes exhibit enhanced quantum efficiency and no degradation of the temporal response compared with devices grown on planar substrates, indicating that reduced area growth may be a useful technique for making optoelectronic devices with strained-layer structures.
Magnetotransport of piezoelectric [111] oriented strained quantum wells
Authors: Martin R. W. , Lakrimi M. , López C. , Nicholas R. J. , Chidley E. T. R. , Mason N. J. , Walker P. J.
Published: July 2002

We report the first observation of magnetotransport in piezoelectrically active heterostructures. Well-resolved quantum Hall plateaus and magnetoresistance minima are observed for two-dimensional hole gases confined in [111] oriented strained-layer Ga1−xInxSb/GaSb quantum wells with a piezoelectric field, of order 1×105 V/cm. We discuss the enhanced carrier densities induced by the in-built field and the differences observed between [111]A and [111]B orientations. Comparisons are made with simultaneously grown [001] structures. Stark energy shifts observed in photoluminescence are well accounted for by the estimated electric field.
Surface reconstruction limited mechanism of molecular-beam epitaxial growth of AlGaAs on (111)B face
Authors: Hayakawa Toshiro , Morishima Mitsukata , Chen Samuel
Published: July 2002

We propose a model which gives a fundamental limiting factor for the growth of epilayers on (111)B face. Our model is that the As-trimer structure of As-stabilized (111)B surface with the (2×2) reconstruction disturbs the incorporation of group III atoms into lattice sites. This model gives the explanation to most of the reported properties in the growth of GaAs and AlGaAs on (111)B substrates. This model has been verified by comparing the growth rate of GaAs layers grown by molecular-beam epitaxy over mesa-shaped substrates with (111)A and (111)B sidewalls using As4 and As2. Moreover, the cause of microtwins found in transmission electron microscopy images of AlGaAs grown on (111)B GaAs at a low Ts can be at least partly explained by this model.
Measurements of nondegenerate optical nonlinearity using a two-color single beam method
Authors: Ma H. , Gomes A. S. L. , de Araujo Cid B.
Published: July 2002

A two-color ‘‘z’’ scan method is introduced to characterize the nonlinear refraction of optical materials in their absorptive region. We demonstrate the method by measuring the sign and the magnitude of the frequency nondegenerate nonlinearity in the absorptive region of semiconductor doped glasses.
GaAs field-effect transistor with an atomically precise ultrashort gate
Authors: Stormer H. L. , Baldwin K. W. , Pfeiffer L. N. , West K. W.
Published: July 2002

We present a new type of depletion-mode field-effect transistor (FET) with an inherently ultrashort gate length. The device is fabricated exclusively via molecular beam epitaxy (MBE) in GaAs/AlGaAs by cleaved-edge overgrowth of a suitably prepared MBE-grown substrate. The channel, as well as the gate, of this T-FET consists of a high-mobility, two-dimensional electron gas (2DEG) generated by modulation doping of GaAs quantum wells. The planes of the 2D systems are orthogonal to one another forming a ‘‘T’’ whose legs approach each other at the intercept to within 200 Å. In this way, the thickness of one of the quantum wells (200 Å) established the gate length of the device. All elements of the T-FET are completely immersed into the semiconductor material and all relevant length scales are established to atomic precision by MBE. Schottky barriers do not enter the device characteristics. Our first T-FET reaches transconductances of 196 and 410 mS/mm at 77 and 4.2 K, respectively.
Aluminum oxide thin films prepared by chemical vapor deposition from aluminum acetylacetonate
Authors: Maruyama Toshiro , Arai Susumu
Published: July 2002

Amorphous aluminum oxide thin films were prepared on glass and silicon (100) substrates by a low-temperature atmospheric-pressure chemical vapor deposition method. The raw material was aluminum acetylacetonate, which is nontoxic and easy to handle. The substrate temperature could be lowered to 250 °C by the thermal decomposition of aluminum acetylacetonate in air.
Optoelectronic devices based on type II polytype tunnel heterostructures
Authors: Ohno H. , Esaki L. , Mendez E. E.
Published: July 2002

We describe a new family of optoelectronic devices based on the unique properties of combinations of semiconductor tunnel junctions with type II polytype heterostructures. A typical light-emitting device structure consists of AlSb (thin barrier)/InAs(quantum well)/AlSb(thin barrier) structure clad by AlInAsSb emitter and GaSb collector. The emission source is the intersubband radiative transition between the first two subbands in the InAs well. Since the conduction-bank minimum of InAs is energetically lower than the valence-band maximum of GaSb, the device can be designed in such a way that electrons are injected only into the higher subband and extracted out only from the lower subband, both via tunneling, leading to an intraband population inversion and highly efficient radiative transitions. The same operation principle can be applied to design detector structures.
Comparative study of interface structure in GaAs/AlAs superlattices grown by molecular beam epitaxy on (001) GaAs substrates misoriented towards (111)Ga or (111)As plane
Authors: Poudoulec A. , Guenais B. , D’Anterroches C. , Auvray P. , Baudet M. , Regreny A.
Published: July 2002

The interface morphology of GaAs/AlAs superlattices grown by molecular beam epitaxy on (001) misoriented GaAs substrates has been investigated using high-resolution transmission electron microscopy observations. We show that the misorientation towards (111)Ga or (111)As plane leads to the same interfacial structure: monolayer height steps and terrace width variations are observed. But the results reveal that the misorientation towards the (111)Ga plane is the most favorable to a regular growth of superlattice structures, because the higher degree of correlation between the interfaces resulting from a smoothing of step edges.
Steps and spikes in current-voltage characteristics of oxide/microcrystallite-silicon/oxide diodes
Authors: Chou S. Y. , Gordon A. E.
Published: July 2002

SiO2/microcrystallite-Si/SiO2 diodes with different contact window sizes were fabricated and studied at room temperature, 77 K, and 4.2 K. Steps were observed in the current-voltage (I-V) characteristics at all three temperatures. These steps would appear for a certain number of measurements, depending upon measurement temperature, and then were replaced by a smooth electrical breakdown I-V characteristic. Data analysis indicates that the steps in the I-V characteristics are due to local electrical breakdowns along the edge of metal contacts instead of electron resonant tunneling through the structure. Surprisingly, however, in one diode, three repeatable spikes, instead of steps, were observed at 4.2 K; this cannot be satisfactorily explained in terms of electrical breakdown, and seems rather like electron resonant tunneling.
Carbon K edge spectroscopy of internal interface and defect states of chemical vapor deposited diamond films
Authors: Nithianandam J. , Rife J. C. , Windischmann H.
Published: July 2002

We have made carbon K edge reflectivity and absorption measurements using synchrotron radiation on diamond crystals and chemical vapor deposited diamond films to determine their electronic structures. Our spectra of diamond films show that both sp2 and sp3 bonded carbon atoms are formed during initial nucleation and growth. Transmission spectra of a diamond film with 30 nm diameter cystallites show striking features below the carbon sp3 K edge due to internal interface states and/or defects. We compare these absorption features to x-ray absorption spectra of clean diamond (111) surface, graphite, and hydrocarbon gases to understand surface chemistry involved in the deposition process.
Surfactant mediated epitaxial growth of InxGa1−xAs on GaAs (001)
Authors: Massies J. , Grandjean N. , Etgens V. H.
Published: July 2002

It is shown that Te can be used as a surfactant for the growth of highly strained InxGa1−xAs on GaAs(001). As observed by reflection high-energy electron diffraction analysis during growth, adsorption of Te on the GaAs surface prior to the growth of InxGa1−xAs drastically increases the layer thickness which can be grown in a two-dimensional layer-by-layer fashion. In analogy with the behavior of As and Sb as surfactant in the growth of Si/Ge [Copel, Reuter, Kaxiras, and Tromp, Phys. Rev. Lett. 63, 632 (1989)] Te is only slightly incorporated in the growing layer and floats at the surface.
Suppression of the spiral-growth mechanism in epitaxial YBa2Cu3O7−x films grown on miscut substrates
Authors: Lowndes Douglas H. , Zheng X.-Y. , Zhu Shen , Budai J. D. , Warmack R. J.
Published: July 2002

The growth mechanism and surface microstructures of epitaxial YBa2Cu3O7−x films are extremely sensitive to substrate miscut angle. The screw dislocation-mediated growth that is so prominent in YBa2Cu3O7−x films grown on well-aligned (001) substrates can be completely eliminated by growing YBa2Cu3O7−x on a substrate that is miscut only 2°–3° away from (001). Films grown on miscut near-(001) LaAlO3 and SrTiO3 substrates consist of overlapping tilted platelets, one c-axis unit cell thick, that are epitaxially aligned with the underlying crystal lattice. This morphology, and the absence of screw-growth features, persists even in relatively thick (∼200 nm) films. The dominance of miscut-aligned growth is explained by the large number of surface steps that act as both nucleation and rapid-growth sites on a miscut surface.
Normal incidence intersubband optical transition in GaSb/InAs superlattices
Authors: Chen H. H. , Houng M. P. , Wang Y. H. , Chang Yia-Chung
Published: July 2002

A novel intersubband optical transition, incorporating interband and p-type intersubband optical transition mechanisms, in a suitably designed GaSb/InAs superlattice is proposed. Such a structure utilizes the strong mixing of GaSb light-hole band with InAs conduction band and the heavy-hole to light-hole intervalence-subband transition in the GaSb/InAs superlattice to obtain a strong normal incidence photoabsorption coefficient (over 8.0×104 cm−1) at a wavelength near 10 μm.
Exciton lifetimes in CdTe/CdMnTe single quantum wells
Authors: Polhmann A. , Hellmann R. , Göbel E. O. , Yakovlev D. R. , Ossau W. , Waag A. , Bicknell-Tassius R. N. , Landwehr G.
Published: July 2002

The lifetime of excitons in CdTe/Cd0.75Mn0.25Te single quantum wells (SQW) has been measured by time-resolved photoluminescence for quantum wells with thicknesses from 34 to 300 Å and in the temperature range from 1.6 to 300 K. The exciton lifetimes are of the order of 150 ps at the lowest temperatures, where radiative recombination dominates. The lifetimes are only weakly dependent on well thickness and decrease from 170 to 140 ps for quantum wells with thickness decreasing from 300 to 34 Å. A comparison with a high quality GaAs/AlGaAs SQW yields comparable luminescence efficiencies at low temperatures, yet the lifetimes are considerably shorter in the CdTe/Cd0.75Mn0.25Te quantum wells due to the higher exciton oscillator strength.
Study of the pretilt angle for 5CB on rubbed polyimide films containing trifluoromethyl moiety and analysis of the surface atomic concentration of F/C(%) with an electron spectroscope for chemical analysis
Authors: Seo Dae-Shik , Kobayashi Shunsuke , Nishikawa Michinori
Published: July 2002

We have investigated the generation of the pretilt angles for nematic liquid crystal (5CB) aligned in the cells using rubbed polyimide (PI) films containing trifluoromethyl moieties as a function of rubbing strength (RS). In order to characterize the films, we have conducted an analysis of the surface atomic concentration of fluorine (F) relative to that of carbon (C), F/C(%) with an electron spectroscopy for chemical analysis (ESCA) in the shallow surface region at the depth of 3 and 12 nm. It is shown that the F/C ratio at a depth of 3 nm decreases with RS, and that the observed pretilt angle shows a high value approaching 45° in the weak RS region, and tends to decrease with increasing RS. The existence of the trifluoromethyl moiety in the special PI, and its appearance in the surface region are considered to be responsible for the generation of high pretilt angles at low RS region since a surface covered by fluorine atoms has a low surface energy and the van der Waals dispersion force is thought to be dominant and hence perpendicular LC alignment is expected. With increasing RS the surface concentration of fluorine atoms decreases and repeated triangles will be formed; a combination of the dispersion force and steric interaction between LC molecules and these structures may cause a medium or low pretilted LC conformation.
Current injection mechanism for porous-silicon transparent surface light-emitting diodes
Authors: Maruska H. Paul , Namavar F. , Kalkhoran N. M.
Published: July 2002

We present a model for the injection of minority carriers into porous silicon films which results in visible dc electroluminescence. A thin interfacial dielectric region is postulated between the surface of the porous silicon layer and a transparent conductive oxide on the surface, which allows alignment of states between the two corresponding conduction bands of these materials under bias, and hence, overlap of electron wave functions and the passage of a tunneling current. Interface state densities are calculated and a parasitic nonradiative shunt current through such states is discussed.
Study of the effect of Sn doping on the electronic transport properties of thin film indium oxide
Authors: Shigesato Yuzo , Paine David C.
Published: July 2002

High quality, low resistivity (2.6×10−4 Ω cm), 0.32-μm-thick amorphous and polycrystalline, pure and Sn-doped, In2O3 films prepared by high density plasma-assisted electron beam evaporation were used to investigate the effect of Sn doping on the electronic transport properties of this material. Amorphous films with high carrier density in the as-deposited state showed no effect of Sn doping on resistivity (ρ), Hall mobility (μ), or carrier density (n) over the range 0 to 5.3 wt % Sn. After recrystallization by annealing in air at 180 or 250 °C for 20 min, n, μ, and ρ were seen to be strongly dependent on Sn concentration in the range 0 to 1.5 wt % with a decreasing effect of Sn doping in the range 1.5 to 5.3 wt %. The data presented in this study were analyzed based on charged and neutral impurity scattering models and suggest that increasing Sn concentration leads to the formation of defect complexes which act as scattering centers but which do not contribute carriers to the material.
Negative ion mass spectra and particulate formation in radio frequency silane plasma deposition experiments
Authors: Howling A. A. , Dorier J.-L. , Hollenstein Ch.
Published: July 2002

Negative ions have been clearly identified in silane rf plasmas used for the deposition of amorphous silicon. Mass spectra were measured for monosilicon up to pentasilicon negative ion radical groups in power-modulated plasmas by means of a mass spectrometer mounted just outside the glow region. Negative ions were only observed over a limited range of power modulation frequency which corresponds to particle-free plasma conditions. The importance of negative ions regarding particulate formation is demonstrated and commented upon.
X-ray emission from laser-irradiated gas puff targets
Authors: Fiedorowicz H. , Bartnik A. , Patron Z. , Parys P.
Published: July 2002

This letter reports the first study of x-ray emission from plasma produced by laser irradiation of gas puff targets. The gas puff targets were created by the pulsed injection of gas into a vacuum chamber. To irradiate the gas puff target a Nd-glass laser was used, which generated 1-ns pulses of up to 15 J in energy. Spatial, spectral, and temporal measurements show that intense soft x-ray emission from the laser-irradiated gas puff target is produced.
Aging-free InP substrates ready for molecular beam epitaxial growth of InAlAs/InGaAs heterostructures
Authors: Katsura S. , Sugiyama Y. , Oda O. , Tacano M.
Published: July 2002

Aging-free InP substrates ready for molecular beam epitaxy have been developed by the inert gas packaging technique. The surface degradation of the InP substrate after chemical cleaning was evaluated by the quality of the 2DEG heterostructure grown on the substrate. The InP substrate in a package filled with nitrogen gas was used for MBE growth. The Hall mobility of an InAlAs/InGaAs heterostructure directly grown on the InP substrate without any pretreatment or chemical etching is larger than 10 000 cm2 /V s at 300 K. There are no aging effects on the sample stored even after six months.
Low spectral chirp and large electroabsorption in a strained InGaAsP/InGaAsP multiple quantum well modulator
Authors: Langanay J. , Starck C. , Boulou M. , Nicolardot M. , Emery J. Y. , Fortin C. , Aubert P. , Lesterlin D.
Published: July 2002

An intensity modulator based on the quantum confined Stark effect with strained InGaAsP quantum wells and InGaAsP barriers was grown using gas source molecular beam epitaxy. The highest electroabsorption effect and the first estimation of the spectral chirp ever reported with such a modulator under TE polarization mode around 1.55 μm were obtained. The attenuation was measured to be better than −30 dB with a reverse driving voltage lower than 3 V and the phase-amplitude coupling factor has been estimated to be lower than 0.2 over a large operating wavelength range.
Deposition of thin films of TiO2 from Langmuir–Blodgett film precursors
Authors: Paranjape D. V. , Sastry Murali , Ganguly P.
Published: July 2002

Excellent quality thin TiO2 films have been obtained by the thermal decomposition of n-octadecyl amine-titanyl oxalate complex multilayer Langmuir–Blodgett films. The films were characterized by x-ray diffraction and x-ray photoemission studies. X-ray diffraction studies suggest a preferred orientation of the TiO2 films.
Normal incidence infrared photodetectors using intersubband transitions in GaSb L-valley quantum wells
Authors: Zhang Y. , Baruch N. , Wang W. I.
Published: July 2002

We report on the demonstration of normal incidence (IR) detectors based on interconduction subband transitions in narrow GaSb/Ga0.6Al0.4Sb0.9As0.1 multiquantum wells in which L valley is the ground state. Strong IR absorption at 7.8 μm with an absorption coefficient of 9100 cm−1 and good photodetector response covering a wide spectrum region have been achieved. The orientation dependence of the absorption is also presented. Our results indicate the potential of this novel structure for use as normal incidence IR photodetectors.
GaAs surface passivation by deposition of an ultrathin InP-related layer
Authors: Wada Yoshinori , Wada Kazumi
Published: July 2002

A few-atomic-layer deposition of InP-related compounds on a GaAs surface greatly improves the surface properties. Tenfold enhancement in the photoluminescence intensity is observed at the GaAs band edge, which indicates a reduction in the surface recombination. Relaxation of the surface pinning, which results in photoluminescence intensity enhancement, is observed by x-ray photoelectron spectroscopy. Based on the results, we propose a novel concept of surface passivation by atomic-layer deposition, where the surface band structure of GaAs is modulated by the ultrathin strained layer.
Epitaxial integration of single crystal C60
Authors: Dura J. A. , Pippenger P. M. , Halas N. J. , Xiong X. Z. , Chow P. C. , Moss S. C.
Published: July 2002

Single crystal thin films of (111) oriented C60 are grown on epitaxial layers of single crystal antimony. The C60/Sb epitaxy is confirmed by low-energy electron diffraction which indicates that the [11̄0] in-plane directions are parallel in the two layers. X-ray diffraction shows that the C60 film is entirely (111) oriented and of high quality with sharp Bragg peaks and narrow mosaic spread. In this study the Sb films were grown on GaSb, to which they are lattice matched; however, since Sb can be epitaxially grown on surfaces with a large lattice mismatch this technique may be applied to integrate C60 single crystals onto many substrates or devices with a surface having sixfold symmetry.
Capture time versus barrier thickness in quantum-well structures measured by infrared photoconductive gain
Authors: Rosencher E. , Luc F. , Bois P. , Nagle J. , Cordier Y.
Published: July 2002

Photoconductive gain measurements in quantum-well (QW) infrared detectors are used to determine the variation of the capture time of electrons in QWs as a function of barrier thickness. The capture time is shown to be proportional to the multi-quantum-well period, which is consistent with a quantum mechanical description of the capture process. The measured values are far higher than the ones measured by time-resolved photoluminescence, ranging from 8 to 150 ps, depending on the applied electric field and barrier thickness. The reasons for this discrepancy are discussed.
Investigation of silicon interstitial reactions with insulating films using the silicon wafer bonding technique
Authors: Tsoukalas D. , Tsamis C. , Stoemenos J.
Published: July 2002

The silicon wafer bonding technique of silicon implanted with oxygen (SIMOX) wafers is used to investigate the silicon interstitial reactions with a thin thermal oxide layer formed on the surface of one of the wafers before bonding. The silicon interstitials are generated by oxidation of the surface of selectively thinned bonded samples that form a silicon on insulator structure on the top of a SIMOX wafer. By monitoring the length of pregrown oxidation stacking faults we can calculate the diffusivity of the silicon interstitials transport vehicle in the thin oxide film for a temperature range widely used in silicon technology.
Blue-green laser emission from ZnSe quantum well microresonators
Authors: Hovinen M. , Ding J. , Nurmikko A. V. , Grillo D. C. , Han J. , He L. , Gunshor R. L.
Published: July 2002

Microresonator structures have been fabricated from (Zn,Cd)Se/Zn(S,Se) quantum well material. The resonators, which are designed in the ‘‘whispering gallery’’ geometry, have been optically pumped at room temperature with threshold excitation levels of 100 kW/cm2.
Optical injection induced polarization bistability in vertical-cavity surface-emitting lasers
Authors: Pan Z. George , Jiang Shijun , Dagenais Mario , Morgan Robert A. , Kojima Keisuke , Asom Moses T. , Leibenguth Ronald E. , Guth Gregory D. , Focht Marlin W.
Published: July 2002

We report the observation of bistable polarization switching in a vertical-cavity surface-emitting laser under optical injection. The wavelength dependence of the switching is measured. It is found that this polarization switching is achieved through injection locking where both the wavelength and the polarization of the vertical-cavity laser are locked to the injected optical signal.
Electronic properties of a one-dimensional channel field effect transistor formed by molecular beam epitaxial regrowth on patterned GaAs
Authors: Burroughes J. H. , Leadbeater M. L. , Grimshaw M. P. , Evans R. J. , Ritchie D. A. , Jones G. A. C. , Pepper M.
Published: July 2002

A high mobility electron gas was grown by molecular beam epitaxy on patterned GaAs consisting of a p-GaAs/n-GaAs multilayered structure. By contacting to the p-GaAs and n-GaAs layers separately and applying the appropriate bias voltages, we were able to laterally modulate the electron gas to form narrow conduction channels. At 1.5 K we obtain an electron mobility of 5×105 cm2/V s and when operated in the field effect transistor mode a transconductance of 50 ms/mm for a device with a 50-μm source/drain separation.
Observation of spectral narrowing and emission energy shift in organic electroluminescent diode utilizing 8-hydroxyquinoline aluminum/aromatic diamine multilayer structure
Authors: Ohmori Yutaka , Fujii Akihiko , Uchida Masao , Morishima Chikayoshi , Yoshino Katsumi
Published: July 2002

Organic electroluminescent (EL) diode with a multilayer structure which consists of alternating layers of organic 8-hydroxyquinoline aluminum (Alq3) and aromatic diamine has been grown by organic molecular beam deposition. The EL emission from the multilayer structure shows spectral narrowing and the emission energy has been observed to shift to higher energy compared with that in the monolayer structure. Mechanism of spectral narrowing and the emission energy shift in the diode with the multilayer structure have been discussed.
Composition dependence of band gap and type of lineup in In1−x−yGaxAlyAs/InP heterostructures
Authors: Böhrer J. , Krost A. , Bimberg D. B.
Published: July 2002

In1−x−yGaxAlyAs is grown lattice matched by low pressure metalorganic chemical vapor deposition on InP and characterized using low temperature photoluminescence. Compositional information is obtained from energy dispersive x-ray spectroscopy and the band gap is determined as a function of Al content. We obtain Eg(y)=0.81+0.036y+2.96y2 eV at 2 K. For Al compositions larger than 22% a type II staggered band lineup is observed. At this point the conduction band discontinuity disappears (ΔEc=0). The conduction band discontinuity as a function of the Al composition is ΔEc(y)=0.245−1.179y+0.3y2 eV.
Piezoelectric-induced current asymmetry in [111] InGaAs/InAlAs resonant tunneling diodes for microwave mixing
Authors: Hernández J. M. , Izpura I. , Calleja E. , Muñoz E.
Published: July 2002

This letter predicts a strong nonlinear current density versus voltage (J-V) dependence in InAlAs/InGaAs/InAlAs double barrier resonant tunneling diodes (DBRTDs) with a strained well, grown on [111] InP. The piezoelectric field generates accumulation and depletion regions in both contact layers at zero bias, producing a high asymmetric J-V characteristic while keeping a low device series resistance. Very high cutoff frequency devices, suitable for low-level microwave mixing applications, are then proposed.
Observation of stimulated emission in the near ultraviolet from a molecular beam epitaxy grown GaN film on sapphire in a vertical-cavity, single pass configuration
Authors: Yung K. , Yee J. , Koo J. , Rubin M. , Newman N. , Ross J.
Published: July 2002

We report the first observation of stimulated emission from a GaN film grown by ion-assisted molecular beam epitaxy. The observed near-UV optical emission power was a nonlinear function of the pump power density. The characteristics of the observed stimulated emission are similar to those observed recently from films grown with low-pressure metalorganic chemical vapor deposition techniques.
Low-resistivity transparent In2O3 films prepared by reactive ion plating
Authors: Jeong J. I. , Moon J. H. , Hong J. H. , Kang J. S. , Lee Y. P.
Published: July 2002

Indium oxide films with an electrical resistivity of less than 1.5×10−4 Ω cm and good optical quality were prepared by the reactive ion plating of pure indium in an oxygen atmosphere of ∼10−4 Torr. The deposition rate was in the range of 500–900 Å/min, which is much higher than that of the ordinary evaporation. Hall effect measurement showed that the observed low resistivity is primarily due to the high electron mobility (≥70 cm2/V s) with carrier density up to 7×1020/cm3. These properties were correlated with the atomic concentration data by Auger electron spectroscopy and x-ray photoelectron spectroscopy. It has been found that the films of low resistivity had the atomic ratio of O to In of 1.29–1.31.
Strain distribution in InP/InGaAs superlattice structure determined by high resolution x-ray diffraction
Authors: Krost A. , Böhrer J. , Roehle H. , Bauer G.
Published: July 2002

Interfacial strain distribution in a short period InP/InGaAs superlattice structure is evaluated by means of high resolution x-ray diffraction. The diffraction pattern of the structure allows an unambiguous determination of interfacial strain distribution. From the numerical calculation, positively strained interfacial monolayers at the InP→InGaAs and negatively strained interfacial monolayers at the InGaAs→InP interfaces had to be introduced in order to reproduce the experimental data. At the InP→InGaAs interfaces a group V exchange reaction leading to a positively strained InAs or InAs1−xP interfacial layer is compatible with the simulation. At the InGaAs→InP interfaces negatively strained ternary or quaternary InGaAsyP1−y meet these requirements. The results are consistent with low temperature calorimetric absorption measurements which exhibit a wide band gap InGaAsP-like absorption feature at 1.48 eV beyond the InP energy gap.
Electrical properties of thermal oxide grown on n-type 6H-silicon carbide
Authors: Alok Dev , McLarty P. K. , Baliga B. J.
Published: July 2002

Measurement of current conduction in the metal/thermal oxide/n-type 6H-silicon carbide is reported. The thermal oxides were grown on nitrogen-doped n-type 6H-silicon carbide at 1275 °C in a dry oxygen ambient. Analysis indicates a Fowler–Nordheim type current conduction mechanism with a barrier height of 2.7 eV between silicon carbide and oxide. Using this value an electron affinity of 3.7–3.8 eV was determined for the Si face of 6H-silicon carbide. The breakdown field strength for the oxides grown on n-type 6H-silicon carbide was 10 MV/cm which is comparable to the breakdown field strength of thermal oxides grown on silicon. Capacitance-voltage measurements indicated that the interface between n-type silicon carbide and the thermally grown oxide has a low (5×1010 cm−2 eV−1) interface trap density (Dit). The effective charge density in the oxide was estimated to be 1×1011 cm−2. These measurements indicate that the quality of oxides thermally grown on 6H-silicon carbide is comparable to those grown on silicon.
Temperature dependence of cathodoluminescence from thin GaAs-AlGaAs multiple quantum wells
Authors: Jahn U. , Menniger J. , Hey R. , Grahn H. T.
Published: July 2002

The temperature dependence of the cathodoluminescence (CL) intensity originating from GaAs-Al0.3Ga0.7As multiple quantum wells has been measured between 5 and 300 K. The CL intensity drops exponentially by two orders of magnitude above 100 K with an activation energy of 83 meV between 140 and 200 K and 145 meV between 250 and 300 K. These energies are comparable to the effective barrier height of an electron or hole and an exciton, respectively. The decrease of the CL intensity is therefore attributed to thermal re-emission of carriers and excitons out of the quantum well.
Interface roughness during thermal and ion-induced regrowth of amorphous layers on Si(001)
Authors: Lohmeier M. , de Vries S. , Custer J. S. , Vlieg E. , Finney M. S. , Priolo F. , Battaglia A.
Published: July 2002

The roughness of Si(001) amorphous/crystalline interfaces, regrown by either solid phase epitaxy (SPE) or ion-beam-induced epitaxial crystallization (IBIEC), has been studied by measuring the scattered x-ray intensity along crystal truncation rods close to Si bulk Bragg peaks. For both regrowth methods, the interface region is well described by a discrete roughness profile. The root-mean-square roughnesses are comparable and rather small: 8.0±0.6 Å and 7.4±0.6 Å for the SPE and the IBIEC regrown sample, respectively. This indicates the presence of a common smoothing mechanism.
Germanium- and silicon-doped indium-oxide thin films prepared by radio-frequency magnetron sputtering
Authors: Maruyama Toshiro , Tago Teruoki
Published: July 2002

Indium oxide (In2O3) thin films doped with either germanium or silicon were prepared by using a radio-frequency magnetron sputtering method. The target was the In2O3 powder mixed with either Ge or Si powder. The resistivities of the films were compared with that of the film doped with tin (ITO). The Ge and Si dopings yielded lower carrier concentrations and higher Hall mobilities compared to those for Sn doping, and they gave different dependencies of resistivity on atomic ratio. The minimum resistivity of the films doped with Ge was nearly equal to that of ITO.
SiC buried layer formation by ion beam synthesis at 950 °C
Authors: Nejim A. , Hemment P. L. F. , Stoemenos J.
Published: July 2002

Carbon implantation into Si at a temperature of 950 °C and at doses in the range of 0.2×1018 to 1×1018 cm−2 at 200 keV results in the formation of β-SiC buried layers having the same orientation as the Si matrix. Under these conditions redistribution of the implanted species occurs enabling the formation of a buried layer of β-SiC with an overlayer of high quality single crystal Si which is free of structural defects. The quality of the Si overlayer and the β-SiC buried layer was investigated by Rutherford backscattering and transmission electron microscopy. A mechanism for the formation of the β-SiC without the generation of defects in the Si matrix is proposed.
Midwave infrared stimulated emission from a GaInSb/InAs superlattice
Authors: Miles R. H. , Chow D. H. , Zhang Y.-H. , Brewer P. D. , Wilson R. G.
Published: July 2002

Use of a cracked Sb source and a postgrowth anneal procedure has been found to yield significant improvements in optical efficiencies of GaInSb/InAs superlattices grown by molecular beam epitaxy. Appreciable 5 μm band-to-band luminescence has been observed at room temperature, and stimulated emission at 3.2 μm has been demonstrated in an optically pumped structure. Intrinsic properties of this class of superlattices favor them for application as efficient infrared lasers operating at comparatively high temperatures.
Regular artificial nanometer-scale structures fabricated with scanning tunneling microscope
Authors: Gu Q. J. , Liu N. , Zhao W. B. , Ma Z. L. , Xue Z. Q. , Pang S. J.
Published: July 2002

The scanning tunneling microscope (STM) has been used to fabricate grooves a few nm wide at room temperature by extracting atoms one by one from the Si(111)7×7 surfaces. When the direction of modification is parallel to the basic vector of Si(111)7×7 surfaces, grooves formed by such a process have atomically straight edges and lateral features as small as one 7×7 unit cell wide. The critical current under various voltages for fabricating grooves is measured. The modification mechanism is discussed based on the experiment data in this letter.
Observation of a vacuum tunnel gap in a transmission electron microscope using a micromechanical tunneling microscope
Authors: Lutwyche M. I. , Wada Y.
Published: July 2002

This letter reports the observation of the vacuum tunnel gap between two conductors using a high resolution transmission electron microscope. A 2.5 mm square micromachined tunneling microscope chip has been fabricated with a minimum feature size of 0.4 μm. The chip fits into a modified side-entry type transmission electron microscope holder. The tunnel gap is controlled by a purpose-built feedback controller. The micromachines work reliably during observation of the tip apex in a transmission electron microscope, allowing the voltage and current to be changed while the tunnel gap is observed.
Interband transitions in CdTe/ZnTe single quantum wells grown by temperature-gradient vapor deposition
Authors: Lee J. H. , Lee S. D. , Park H. L. , Kim T. W.
Published: July 2002

Several CdTe/ZnTe strained single quantum well structures with widths ranging from 5 to 20 Å were grown on GaAs (100) substrates by double-well temperature-gradient vapor-transport deposition. Photoluminescence (PL) measurements on the strained single quantum-well structures showed that the sharp excitonic peaks corresponding to the transitions from the first electronic subband to the first heavy-hole band (E1–HH1) below the critical thickness of the CdTe well were shifted to lower energy with increasing well width. However, the results of the PL spectra above the critical thickness of the CdTe clearly showed broad excitonic peaks, originating from the dislocations in the CdTe quantum well, corresponding to the (E1–HH1) transitions. Electronic subband energies were calculated by an envelope function approximation taking into account the strain effects, and the transition values were in good agreement with those obtained from the experimental measurements.