bluuebunny/crossref_metadata_2025 huggingface dataset:
Metal-oxide-semiconductor characteristics of chemical vapor deposited Ta2O5 films
Authors: Lo G. Q. , Kwong D. L. , Lee S.
Published: July 2002

This letter describes the metal-oxide-semiconductor characteristics of chemical vapor deposited Ta2O5 films. With the passivation of bottom ultrathin SiO2 layer (∼3.4 nm), an excellent interface (i.e., low fixed charge and interface state densities) has been achieved. In this study, different top dielectrics such as SiO2 and Si3N4 were used to be compatible with conventional polycrystalline Si-gate process. By using top dielectrics deposited on Ta2O5, such as SiO2 and Si3N4, the leakage current is found to be greatly suppressed by three orders of magnitude for −Vg. For +Vg, the leakage current behaviors are believed to be governed by the Fowler–Nordheim tunneling through the bottom SiO2 layer. Under high-field stress, however, interface state generation was found to be enhanced with the presence of the top dielectric layer.
High quantum efficiency photoluminescence from localized excitons in Si1−xGex
Authors: Lenchyshyn L. C. , Thewalt M. L. W. , Sturm J. C. , Schwartz P. V. , Prinz E. J. , Rowell N. L. , Noël J.-P. , Houghton D. C.
Published: July 2002

We report a new photoluminescence process in epitaxial Si1−xGex layers grown on Si by rapid thermal chemical vapor deposition which we attribute to the recombination of excitons localized at random alloy fluctuations. This luminescence is characterized by saturation at very low excitation densities (≂100 μW cm−2), very long decay times (≳1 ms), and high quantum efficiency at low excitation. We have directly measured an external photoluminescence quantum efficiency of 11.5±2%.
Linear electro-optic effects in polymer-dispersed ferroelectric liquid crystals
Authors: Kitzerow Heinz-S. , Molsen Henning , Heppke Gerd
Published: July 2002

We demonstrate that ferroelectric liquid crystals are suitable for application in polymer-dispersed liquid crystal (PDLC) displays. The alignment of the liquid crystal can be controlled by mechanical shear during the polymerization-induced phase separation between the liquid crystal and the UV-curable adhesive which forms the polymer matrix. Helical unwinding in the smectic SmC phase and the electroclinic effect in the smectic SmA phase have been found in these samples. Both effects lead to a rotation of the optical axis in the plane perpendicular to the electric field. Switching times are of the order 100 μs.
Scanning electron microscopy observation of excitation of the surface acoustic waves by the regular domain structures in the LiNbO3 crystals
Authors: Roshchupkin D. V. , Fournier Th. , Brunel M. , Plotitsyna O. A. , Sorokin N. G.
Published: July 2002

This letter reports a scanning electron microscope study of excitation of surface acoustic waves by the regular domain structures in LiNbO3 crystals. The regular domain structures in LiNbO3 crystals were formed by the method of aftergrowth thermoelectrical treatment. It is shown that the regular domain structures excite surface acoustic waves by the piezoelectric effect. In this case, the wavelength of the surface acoustic waves is determined by the period of the regular domain structure. These experiments have been made at CNRS (Grenoble, France) using a scanning electron microscope JSM-840.
Evaluation of the 3-level charge pumping technique for characterizing interface traps
Authors: Saks N. S. , Ancona M. G. , Chen Wenliang
Published: July 2002

Emission cross sections of Si-SiO2 interface traps have been measured as a function of trap energy with the new 3-level charge pumping technique and with standard admittance techniques. Good agreement between the different techniques is obtained, thereby validating 3-level charge pumping as a tool for characterizing interface traps.
Improvement in heteroepitaxial film quality by a novel substrate patterning geometry
Authors: Hull R. , Bean J. C. , Higashi G. S. , Green M. L. , Peticolas L. , Bahnck D. , Brasen D.
Published: July 2002

We describe a novel substrate patterning geometry which can reduce epilayer threading dislocation densities by up to two orders of magnitude in GexSi1−x/Si(100) (x∼0.15–0.20) het- eroepitaxial layers. The basic pattern consists of a two-dimensional array of ∼2 μm diameter oxide pillars which are separated from each other by varying pitch dimensions, and which are staggered slightly from their neighbors with respect to the in-plane 〈011〉 directions. This ensures that a misfit dislocation nucleating at any point within the epilayer must eventually propagate into one of the pillars, where the threading end will be terminated. Prospects for surface planarization and overgrowth of the pillars are discussed.
Hole space-charge buildup and evidence for sequential tunneling in p-type double-barrier resonant tunneling devices
Authors: Hayden R. K. , Eaves L. , Henini M. , Maude D. K. , Portal J. C. , Hill G.
Published: July 2002

Magnetoquantum oscillations in the tunnel current of a p-type double-barrier AlAs/GaAs/AlAs device are used to measure the buildup of hole space charge in the quantum well over a wide range of bias. These measurements demonstrate sequential tunneling of holes. The effective mass for hole tunneling is estimated.
Direct evidence for the amorphous silicon phase in visible photoluminescent porous silicon
Authors: Perez J. M. , Villalobos J. , McNeill P. , Prasad J. , Cheek R. , Kelber J. , Estrera J. P. , Stevens P. D. , Glosser R.
Published: July 2002

We report on micro-Raman spectroscopy studies of porous silicon which show an amorphous silicon Raman line at 480 R cm−1 from regions that emit visible photoluminescence. A Raman line corresponding to microcrystalline silicon at 510 R cm−1 is also observed. X-ray photoelectron spectroscopy data is presented which shows a high silicon-dioxide content in porous silicon consistent with an amorphous silicon phase.
Structure of serpentine superlattice quantum-wire arrays determined by transmission electron microscopy
Authors: Krishnamurthy Mohan , Miller M. S. , Petroff P. M.
Published: July 2002

The structure of serpentine superlattice (SSL) quantum-wire arrays is analyzed with transmission electron diffraction and microscopy. The lateral SSL barriers are nominally formed as a digital alloy of (AlAs)r(GaAs)p partial layers in the vertical direction. Micrographs demonstrate the predicted SSL shape and its insensitivity to systematic deposition rate errors. A diffraction pattern is synthesized to explain diffraction features and order-sensitive SSL images, which are compared with chemical contrast images. The lateral structure is observed to be incompletely segregated into wells and barriers. The length of the quantum wires is estimated to be at least on the order of 100 nm.
Optical properties of serpentine superlattices on GaAs vicinal substrates for quantum wire laser applications
Authors: Chang Yi Jong , Dagli Nadir
Published: July 2002

In this letter, the first detailed theoretical study of optical gain in serpentine superlattice quantum wire arrays grown on GaAs vicinal substrates is presented. In the calculations, the complex nature of the miniband structure due to coupling between wires and the valence band intermixing are taken into account. In addition to the ideal structure, the effects of imperfect Al segregation between GaAs wires and AlGaAs barriers are also investigated.
Ferromagnetic δ-Mn1−xGax thin films with perpendicular anisotropy
Authors: Krishnan Kannan M.
Published: July 2002

We report the structure and properties of the thermodynamically stable δ-phase Mn1−xGax single crystal thin films grown on GaAs. X-ray Θ–2Θ scans and grazing-incidence scattering measurements confirmed that the unit cell of this phase is tetragonal (a=0.279 nm, c=0.351 nm) and grows with the c-axis oriented normal to the {001} GaAs substrate surface. X-ray emission spectroscopy confirmed the composition to be 62±2% Mn. Polar Kerr rotation, SQUID and vibrating sample magnetometer measurements with the field applied along the thin-film normal showed nearly perfect square hysteresis loops confirming perpendicular anisotropy of the films. The film exhibits a Kerr rotation angle of ∼0.1° at 820 nm, a coercivity of 6.27 kOe and a saturation magnetization of 460 emu/cm3. The optical reflectivity of the film was 65%–70% over a broad range of wavelengths. This unique set of properties make it a very promising material for magneto-optic recording with the additional potential of integrating semiconductor/magnetic devices by suitable patterning techniques.
Nanometer-scale lithography using the atomic force microscope
Authors: Majumdar A. , Oden P. I. , Carrejo J. P. , Nagahara L. A. , Graham J. J. , Alexander J.
Published: July 2002

We demonstrate a new use of the atomic force microscope (AFM) for nanometer-scale lithography on ultrathin films of poly(methylmethacrylate) (PMMA). The PMMA films were chemically modified as both positive and negative resists due to energy transfer from a highly localized electron source provided by metallized AFM tips. We were able to fabricate a line pattern with 68 nm line periodicity with about 35 nm line widths.
Effect of one monolayer of surface gold atoms on the epitaxial growth of InAs nanowhiskers
Authors: Yazawa M. , Koguchi M. , Muto A. , Ozawa M. , Hiruma K.
Published: July 2002

This letter shows that selective heteroepitaxy of nanometer-scale InAs whiskers on SiO2-patterned GaAs substrates [Yazawa, Koguchi, and Hiruma, Appl. Phys. Lett. 58, 1080 (1991)] is induced by surface contamination with Au resulting from the fluorocarbon plasma etching process used to etch the SiO2 mask. We demonstrate that high densities (≂1010/cm2) of InAs nanowhiskers 20–30 nm in diameter can be epitaxially grown on InAs(111)B substrates onto which 1 monolayer of Au atoms had been deposited. This wirelike growth appears to be induced by ultrafine alloy droplets generated by the reactions between Au-clusters and InAs substrates.
Thermo-electro-optic switch based on polymer dispersed liquid crystal composite
Authors: Jain Sukhmal C. , Thakur Ravindra S.
Published: July 2002

A new type of thermo-electro-optic switch based on polymer dispersed liquid crystal (PDLC) composite is reported below. The PDLC composite has been made by dispersing a dual frequency addressable liquid crystal (LC) mixture in an isotropic polymer matrix in the form of very fine droplets of micron and submicron sizes. The PDLC cell in the presence of an electric field can be made to switch from transparent to scattering state or vice-versa by varying its temperature by ±≥1 °C, respectively. Moreover, the transition temperature of the PDLC switch can be set by varying the frequency of the electric biasing field.
Virtual-surfactant epitaxy of strained InAs/Al0.48In0.52As quantum wells
Authors: Tournié Eric , Ploog Klaus H.
Published: July 2002

The solid-source molecular beam epitaxy growth of strained InAs films embedded in an Al0.48In0.52As matrix on InP substrates is studied by in situ reflection high-energy electron diffraction. Under standard As stable conditions, the highly (3.2%) strained InAs film grows on Al0.48In0.52As in the Stranski–Krastanov mode. Islanding starts at a thickness of 8 monolayers. On the contrary, when growing InAs under In stable conditions, islanding is inhibited. The highly reactive In stable surface imposes kinetic limitations to the sticking atoms and forces two-dimensional nucleation, thus acting as a virtual surfactant. This growth technique produces samples of superior quality and opens a new route for the preparation of strained heterostructures.
Optical characterization of InAs monolayer structures grown on (113)A and (001) GaAs substrates
Authors: Meléndez J. , Mazuelas A. , Domínguez P. S. , Garriga M. , Alonso M. I. , Armelles G. , Tapfer L. , Briones F.
Published: July 2002

A study on structures consisting of one InAs monolayer in a GaAs matrix, grown on both (001) and (113)A GaAs substrates, is presented. The structures were grown simultaneously at low temperature by atomic layer molecular beam epitaxy, and were structurally characterized by the x-ray interference effect. Optical characterization was performed by means of piezoreflectance and photoreflectance. Observed InAs-related transitions can only be fitted by an envelope wave function model if a larger InAs segregation is assumed in the (113) sample than in the (001) sample, or, less plausible, the band offset is strongly direction dependent.
Low-temperature selective-area deposition of metals: Chemical vapor deposition of gold from ethyl(trimethylphosphine)gold(I)
Authors: Banaszak Holl M. M. , Seidler P. F. , Kowalczyk S. P. , McFeely F. R.
Published: July 2002

Chemical vapor deposition of high purity gold is demonstrated using ethyl(trimethylphosphine)gold(I) at temperatures as low as room temperature. Total selectivity for growth on atomically clean metallic surfaces in the presence of insulating surfaces is found over a ∼200 °C temperature range and confirmed with scanning electron microscopy and x-ray photoelectron spectroscopy. A key processing parameter is shown to be ultrahigh vacuum, particularly for growth on reactive metals such as chromium. These results suggest low-temperature selectivity can be extended to other known precursors.
Growth of GaAsN alloys by low-pressure metalorganic chemical vapor deposition using plasma-cracked NH3
Authors: Weyers Markus , Sato Michio
Published: July 2002

We present a letter on the growth of GaAs1−xNx alloys (0<x<0.016). The layers have been grown by metalorganic chemical vapor deposition at very low pressure (25 Pa). The nitrogen source NH3 has been decomposed in a remote microwave plasma, and uncracked triethylgallium and AsH3 were used. The N uptake into the layers shows a strong dependence on the growth temperature. The competition for the group V lattice sites leads to a reduction of the N content at higher AsH3 fluxes. The GaAsN layers show a strong red shift of the photoluminescence with increasing N content.
Free and bound exciton photoluminescence of quantum well affected by free carriers
Authors: Ping Er-Xuan
Published: July 2002

Free exciton (FE) and bound exciton (BE) photoluminescence (PL) of quantum well (QW) affected by free carrier (FC) is studied by a model which includes the transfer of particles among FC, FE, and BE states. It is shown that FC state is important not only at high temperature but also at low temperature. General formulas for FE and BE PL are developed. The two-dimensional law of mass action is reproduced for high temperature, and the trapping of FE by defects is obtained for low defect concentration. Temperature behavior of FE and BE PL for high defect concentration is also discussed.
Epitaxial nonlinear optical films of LiTaO3 grown on GaAs in waveguide form
Authors: Hung L. S. , Agostinelli J. A. , Mir J. M. , Zheng L. R.
Published: July 2002

Nonlinear optical films of LiTaO3 were epitaxially grown on (NH4)2Sx-treated (111) GaAs using e-beam evaporated MgO as intermediate layers. The MgO lattice was found to rotate by 180° about the [111] surface normal with respect to the GaAs substrate. The laser-ablated LiTaO3 film grew epitaxially in the preferred [0001] direction and formed a waveguide with its underlying buffer layer of MgO.
Quasiperiodic contrast inhomogeneities induced by clusters in the In0.52Al0.48As/InP interface
Authors: Peiro F. , Cornet A. , Morante J. R. , Georgakilas A. , Christou A.
Published: July 2002

The structure of In0.52Al0.48As films grown on InP (100) by molecular beam epitaxy, at growth temperatures in the range of 530–590 °C, are analyzed by transmission electron microscopy. The existence of contrast inhomogeneities along the 〈010〉 fcc soft directions, the appearance of which depends on the temperature and the distance to the substrate, is reported. It is shown that these contrast irregularities in InAlAs are related directly to the existence of precipitates in the InAlAs/InP interface, whose origin can be found in the formation of an InAs layer under an As-stabilized InP surface.
Photoluminescence from stain-etched polycrystalline Si thin films
Authors: Steckl A. J. , Xu J. , Mogul H. C.
Published: July 2002

Visible room-temperature photoluminescence (PL) has been observed from stain-etched polycrystalline Si thin films. Poly-Si thin films deposited on oxidized Si and quartz substrates became porous (PoSi) after stain-etching in a 1:3:5 solution of HF:HNO3:H2O. Under UV excitation, the stain-etched doped and undoped poly-Si films produce uniform orange-red (∼650 nm) luminescence very similar to that obtained from stain-etched crystalline Si substrates. Stained amorphous thin films did not exhibit photoluminescence. Luminescent patterns with sub-micrometer (∼0.6 μm) dimensions have been obtained for the first time from PoSi produced from poly-Si films.
Photoluminescence from ultrathin ZnSe/CdSe quantum wells
Authors: Zajicek H. , Juza P. , Abramof E. , Pankratov O. , Sitter H. , Helm M. , Brunthaler G. , Faschinger W. , Lischka K.
Published: July 2002

Self-limiting monolayer epitaxy has been used to prepare ZnSe/CdSe quantum well structures containing 1–5 monolayers (≊3–15 Å) thick CdSe quantum wells. Photoluminescence spectra of these structures show bright excitonic lines with a blue shift of maximum 870 meV for the 1 monolayer wide quantum wells. Calculations for the energetic positions of the photoluminescence peaks are in good agreement with the experimental data. The full width at half maximum of the photoluminescence lines increases from about 25 meV for the 1 ML quantum wells to about 75 meV for the 3 ML quantum wells.
Reversible changes in doping of InGaAlN alloys induced by ion implantation or hydrogenation
Authors: Pearton S. J. , Abernathy C. R. , Wisk P. W. , Hobson W. S. , Ren F.
Published: July 2002

Carrier concentrations in doped InN, In0.37Ga0.63N, and In0.75Al0.25N layers are reduced by both F+ ion implantation to produce resistive material for device isolation, and by exposure to a hydrogen plasma. In the former case, post-implant annealing at 450–500 °C produces sheet resistances ≳106 Ω/⧠ in initially n+ (7×1018–3×1019 cm−3) ternary layers and values of ∼5×103 Ω/⧠ in initially degenerately doped (4×1020 cm−3) InN. The evolution of sheet resistance with post-implant annealing temperature is consistent with the introduction of deep acceptor states by the ion bombardment, and the subsequent removal of these states at temperatures ≲500 °C where the initial carrier concentrations are restored. Hydrogenation of the nitrides at 200 °C reduces the n-type doping levels by 1–2 orders of magnitude and suggests that unintentional carrier passivation occurring during cool down after epitaxial growth may play a role in determining the apparent doping efficiency in these materials.
Efficiency of grating coupled AlGaAs/GaAs quantum well infrared detectors
Authors: Lundqvist L. , Andersson J. Y. , Paska Z. F. , Borglind J. , Haga D.
Published: July 2002

The efficiency of grating coupling of radiation into the quantum well infrared detector is studied experimentally, with special emphasis on the influence of detector mesa size. It is found that compared to a 45° polished edge detector, the integrated quantum efficiency for crossed grating detectors of mesa size as small as 45 μm is about four times larger with a waveguide included, and two times larger without a waveguide. Furthermore, the importance of a high conductivity grating metal, the use of crossed gratings instead of lamellar gratings, as well as of a dielectric reflector is demonstrated. To show the superior coupling efficiency, the detectivity is measured for a detector with a crossed grating and a waveguide, and of mesa size 500 μm, resulting in D*=1.4×1011 cm Hz1/2 W−1 at 77 K operating temperature with the detector shielded from background radiation.
Carbon doping of GaAs and (In,Ga)As in solid source molecular beam epitaxy using carbon tetrabromide
Authors: Zhang Kai , Hwang Wen-yen , Miller D. L. , Kapitan Larry W.
Published: July 2002

We have grown C-doped GaAs and (In,Ga)As epitaxial layers of device quality in a standard solid source molecular beam epitaxy system using carbon tetrabromide (CBr4) as the carbon source. Dopant incorporation was relatively efficient for both GaAs and (In,Ga)As, requiring a CBr4 beam pressure of about 1×10−6 Torr to achieve a hole density of 1.5×1020/cm3. For doping in the 1019/cm3 range, hole mobilities were comparable to or slightly higher than those of Be-doped layers with the same carrier concentrations. Modulation-doped structures grown immediately after heavily C-doped GaAs layers exhibited reduced two-dimensional electron gas mobility, but the mobility recovered to previous values within 24 h. (Al,Ga)As/GaAs heterojunction bipolar transistors (emitter size=25 μm×50 μm) with C-doped bases (p=1.2×1019 cm−3) had common emitter small signal current gains averaging 86 at an emitter current density of 970 A/cm2. The relatively low gas load during growth, the lack of long-term memory effect, and the acceptable device performance indicate that CBr4 is an attractive alternative to Be for GaAs and (In,Ga)As devices grown by solid source molecular beam epitaxy.
Charge trapping and device degradation induced by x-ray irradiation in metal-oxide-semiconductor field-effect transistors
Authors: Campbell S. A. , Lee K. H. , Li H. H. , Nachman R. , Cerrina F.
Published: July 2002

Oxide charge trapping and interface trap generation by hot carrier stress was studied with x-ray irradiated metal-oxide-semiconductor field-effect transistors. Although the threshold voltage and transconductance recovered after a hydrogen anneal at 450 °C, the irradiated and annealed devices were more susceptible to damage under hot carrier stressing, both at the Si/SiO2 interface and in the oxide bulk. The latent damage was quantified using the various gate voltage hot carrier stresses. It is found that most of the latent damage is related to oxide hole traps and interface traps. Electron trapping is present, but is less significant.
Improvement of the growth of InxGa1−xAs on GaAs (001) using Te as surfactant
Authors: Grandjean N. , Massies J. , Delamarre C. , Wang L. P. , Dubon A. , Laval J. Y.
Published: July 2002

It is demonstrated by using reflection high-energy electron diffraction and transmission electron microscopy that the epitaxial growth of highly strained InxGa1−xAs (x≳0.3) layers on GaAs(001) is improved by a preadsorbed Te surfactant layer. The formation of 3D islands is inhibited by the surfactant action and consequently the onset of plastic relaxation (i.e., the critical thickness) is significantly delayed.
Temperature field determination of InGaAsP/InP lasers by photothermal microscopy: Evidence for weak nonradiative processes at the facets
Authors: Mansanares A. M. , Roger J. P. , Fournier D. , Boccara A. C.
Published: July 2002

Photothermal microscopy was used for absolute temperature determination of InGaAsP/InP lasers. High modulation frequencies were employed in order to improve spatial contrast. The strong thermal mismatch between InGaAsP and InP induces a heat confinement in the active region as shown experimentally and confirmed by finite element calculations. Facet temperature was found to be 10 K/mW for a 2-μm-wide active layer, which is low compared to those reported for GaAlAs/GaAs and GaInP. Moreover, measurements along the cavity do not show differences in temperature when approaching the facets. Both results indicate a weak nonradiative recombination process at the facets, in agreement with the higher mirror reliability of this type of laser.
Mid-infrared interband magneto-absorption in HgTe/CdTe superlattices
Authors: Sizmann R. , Helgesen P. , Colin T. , Skauli T. , Lo/vold S.
Published: July 2002

We demonstrate that interband magneto-absorption in the mid-infrared regime is a powerful technique to characterize the electronic properties of HgTe/CdTe superlattices. The rich optical spectra permit a close comparison with theoretically evaluated band structures and provide a valuable feedback for growth. The experimentally obtained band-gap energies between hole and electron subbands for the HgTe/CdTe superlattice structure considered here are in good agreement with published values calculated for a valence-band offset of 350 meV.
Time dependence of dopant diffusion in δ-doped Si films and properties of Si point defects
Authors: Gossmann H.-J. , Rafferty C. S. , Vredenberg A. M. , Luftman H. S. , Unterwald F. C. , Eaglesham D. J. , Jacobson D. C. , Boone T. , Poate J. M.
Published: July 2002

The diffusion of Sb and B in thin Si films grown by low temperature molecular beam epitaxy is investigated in the temperature range 750–900 °C for times of 0.25–60 h. The small spatial extent of the initial δ-function-like dopant profiles allows the detection of very small diffusional displacements. The dopant atoms are used as tracers of Si point defects (vacancies and self-interstitials). Diffusion of Sb is found to be enhanced relative to equilibrium values, while that of B is retarded. We propose a model based on an initial supersaturation of vacancies. Matching this model to the experimental data allows the extraction of the vacancy diffusivity, the activation energy of vacancy formation, and the recombination lifetime of interstitials. The results show that interstitial and vacancy populations cannot be considered independent at low temperature, as has been previously suggested.
High quality ultrathin dielectric films grown on silicon in a nitric oxide ambient
Authors: Yao Z.-Q. , Harrison H. B. , Dimitrijev S. , Sweatman D. , Yeow Y. T.
Published: July 2002

High quality ultrathin silicon oxynitride films (3.5 nm) have been grown in a nitric oxide ambient using rapid thermal processing. The physical and electrical properties of these films are compared with those formed in a nitrous oxide environment. X-ray photoelectron spectroscopy (XPS) results show that the nitric oxide (NO) grown films have a significantly different nitrogen distribution compared to the nitrious oxide (N2O) grown films. The capacitance-voltage and current-voltage characteristics of the NO grown and NO-modified films are, in general, better than those of the same thickness grown in either N2O or O2.
Planar optical waveguides in Nd-doped yttrium oxy-orthosilicate
Authors: Sharp J. H. , Rodman M. J. , Chandler P. J. , Townsend P. D.
Published: July 2002

Planar waveguides have been fabricated in single-crystal Nd-doped yttrium oxy-orthosilicate (Nd:Y2SiO5) using 2.0 MeV He+ ion implantation at doses of around 1016 ions/cm2. Refractive index profiles of the waveguides are presented. The losses were found to be lower for TE polarized modes with the minimum loss achieved to date being 0.71 dB/cm after annealing. Photoluminescence studies indicate that both the spectral line shape and the radiative lifetimes of the waveguides fully recover to bulk values after annealing.
Improved GaInAs/GaAs heterostructures by high growth rate molecular beam epitaxy
Authors: Grandjean N. , Massies J. , Leroux M. , Leymarie J. , Vasson A. , Vasson A. M.
Published: July 2002

This work shows that the critical thickness for the two-dimensional–three-dimensional growth mode transition during the growth of Ga0.65In0.35As on GaAs(001) can be significantly increased by increasing the growth rate. This experimental finding is corroborated by a Monte Carlo simulation of this heteroepitaxial growth. Improved quantum well optical properties are demonstrated.
Resonant tunneling between parallel, two-dimensional electron gases: A new approach to device fabrication using in situ ion beam lithography and molecular beam epitaxy growth
Authors: Brown K. M. , Linfield E. H. , Ritchie D. A. , Jones G. A. C. , Grimshaw M. P. , Pepper M.
Published: July 2002

Using the techniques of in situ focused ion beam lithography and molecular beam epitaxy regrowth high quality, patterned back gate, double quantum well devices have been fabricated. Independent ohmic contacts were made to the two two-dimensional electron gases (2DEGs) using a ‘‘selective depletion’’ scheme, and using further gates the carrier densities in each well were controlled. Resonant tunneling between the two electron gases was observed as a function of carrier density in each 2DEG, and as a function of the bias applied between the two wells. Extremely large peak-to-valley ratios were observed, resulting from removal of unwanted parallel tunneling paths.
Electron mobility enhancement in Si using doubly δ-doped layers
Authors: Radamson H. H. , Sardela M. R. , Nur O. , Willander M. , Sernelius B. E. , Ni W.-X. , Hansson G. V.
Published: July 2002

Large enhancements in the electron mobility are reported for structures containing a pair of closely spaced Sb δ-doped layers in Si. The room-temperature mobility is enhanced by a factor of 2 compared to corresponding uniformly doped layers of singly δ-doped structures. Even higher mobilities were obtained by using a Schottky gate on top and applying a voltage to adjust the potential well. With an effective gate voltage of ∼−0.3 V the mobility was 1200 cm2 V−1 s−1 at room temperature, which is an enhancement by a factor of 10 relative to the layer with equivalent bulk doping concentration. The high mobility is attributed to wave functions with nodes at the δ-doped layers.
Diffusion length of Ga adatoms on GaAs (1̄1̄1̄) surface in the √19 ×√19 reconstruction growth regime
Authors: Yang K. , Schowalter L. J. , Thundat T.
Published: July 2002

Faceted surface morphologies of homoepitaxial films grown on exactly (1̄1̄1̄)-oriented GaAs substrates in the √19 ×√19 regime are studied with an atomic force microscope. The facets are composed of three vicinal surfaces tilted about 2° toward [21̄1̄], [1̄21̄], and [1̄1̄2] directions, respectively. The diffusion length at the growth condition is estimated from the surface morphologies and found to be at least hundreds of nanometers. It is comparable to the diffusion length on the (100) surface grown under the same conditions. Therefore, the facet formation on GaAs (1̄1̄1̄) film is unlikely caused by slower surface mobility.
Optical characterization of submonolayer and monolayer InAs structures grown in a GaAs matrix on (100) and high-index surfaces
Authors: Wang P. D. , Ledentsov N. N. , Sotomayor Torres C. M. , Kop’ev P. S. , Ustinov V. M.
Published: July 2002

We studied the optical properties of InAs/GaAs heterostructures with InAs average layer thickness ranging from 1 Å [one-third of a monolayer (ML)] to 4 ML grown on (100) and (311) surfaces. Extremely high optical quality was revealed for the structures with ultrasmall InAs coverage. We attribute the improvements to the first stage of InAs growth on the GaAs surface which we refer to as submonolayer epitaxy. Optical anisotropy found in photoluminescence (PL), as well as in PL excitation spectra indicates a highly anisotropic growth mode for InAs molecules on the GaAs (100) surface. An InAs/GaAs superlattice composed of submonolayer InAs exhibits greatly improved luminescence efficiency at room temperature and much better nonequilibrium carrier capture compared to either the (In,Ga)As alloy or an InAs/GaAs superlattice composed of monolayer-thick InAs layers with the same average In composition.
Traveling wave electro-optic phase modulator using cross-linked nonlinear optical polymer
Authors: Wang Wenshen , Chen Datong , Fetterman Harold R. , Shi Yongqiang , Steier William H. , Dalton Larry R.
Published: July 2002

We report the fabrication and characterization of a high frequency traveling wave electro-optic phase modulator made from thermally cross-linked polyurethane-Disperse Red 19 polymers. The device has been fabricated using a three layer structure with an integrated 50 Ω microstrip line circuit. The straight channel optical waveguides were defined laterally by standard photolithography and oxygen reactive ion etching. The measured half-wave voltage was in good agreement with that extrapolated from the second harmonic generation measurements. Optical modulation was observed directly on a spectrum analyzer up to 18 GHz. Long-term evaluation over an extensive length of time found no observable loss of performance.
Plastic relaxation of metamorphic single layer and multilayer InGaAs/GaAs structures
Authors: Dunstan D. J. , Kidd P. , Fewster P. F. , Andrew N. L. , Grey R. , David J. P. R. , González L. , González Y. , Sacedón A. , González-Sanz F.
Published: July 2002

The plastic relaxation of multilayer structures of strained InGaAs grown above critical thickness on GaAs is reported and compared with the relaxation of single layers and with theory. We show that a composite structure, taken as a whole, follows the same relaxation law as observed in single layers. However, departures of the strains of some component layers from theory show that misfit dislocations are easily pinned at an interface. Implications for the design of relaxed buffer layer growth are discussed.
Quantum cascade laser: Temperature dependence of the performance characteristics and high T0 operation
Authors: Faist Jerome , Capasso Federico , Sivco Deborah L. , Hutchinson Albert L. , Sirtori Carlo , Chu S. N. G. , Cho Alfred Y.
Published: July 2002

The design and temperature dependence of the performance characteristics of a quantum cascade intersubband laser operating pulsed in the midinfrared (λ≂4.3 μm) are reported. The threshold current density varies exponentially with temperature [exp(T/T0)] from ≊6.0 kA/cm2 at 50 K to ≊9.3 kA/cm2 up to the maximum operating temperature (125 K) with a T0∼112 K. This weak temperature dependence, compared to interband lasers operating at similar wavelengths, is due to the intersubband nature of the laser transition, to the physics of optical phonons scattering, and to the negligible intersubband Auger transition rates. The measured peak optical power varies from 32 mW at 10 K to 18 mW at 80 K for a 1.2-mm cavity length. The measured slope efficiency is 52 mW/A at 80 K which corresponds to an estimated differential quantum efficiency of ≂3.4×10−2 per facet per stage.
Fast neutron irradiation for Czochralski grown silicon
Authors: Xu Yuesheng , Li Yangxian , Liu Caichi , Wang Hongmei
Published: July 2002

In this investigation, Czochralski grown silicon (CZ-Si) was irradiated by a fast neutron which can introduce irradiated defects into silicon and change the quality and density of point defects in silicon, by the interaction between irradiated defects and oxygen, the controlled precipitation of oxygen, and an excellent intrinsic gettering structure in CZ-Si during heat treatment cycles can be obtained easily.
Observation and electronic characterization of two E′ center charge traps in conventionally processed thermal SiO2 on Si
Authors: Conley John F. , Lenahan P. M. , Evans H. L. , Lowry R. K. , Morthorst T. J.
Published: July 2002

We demonstrate that at least two varieties of E′ defect precursors exist in a wide variety of conventionally processed thermal SiO2 thin films. We provisionally label the defects EP and E′γp. We find that EP defect capture cross sections exceed the corresponding E′γp values by an order of magnitude, that EP centers are distributed far more broadly throughout the oxides than are the E′γp defects, and that the EP resonance, unlike the E′γp resonance is not stable at room temperature.
Structure and conductance evolution of very thin indium oxide films
Authors: Korobov V. , Leibovitch M. , Shapira Yoram
Published: July 2002

The conductance of transparent conducting oxide films as a function of their coverage has been investigated in situ. The films have been prepared by means of reactive evaporation of In in the presence of oxygen on the glass substrate at different substrate temperatures. The analysis shows that island growth, percolation, coalescence, and ohmic stages can be identified. Critical parameters of the films can be determined during the growth, such as anisotropic and percolative growth modes, resistivity, a lower limit of the effective dopant concentration. The technique shows a potential for in-depth characterization of very thin film growth.
Growth and electrical transport properties of very high mobility two-dimensional hole gases displaying persistent photoconductivity
Authors: Henini M. , Rodgers P. J. , Crump P. A. , Gallagher B. L. , Hill G.
Published: July 2002

We report on the growth by molecular beam epitaxy of modulation-doped GaAs-(Ga,Al)As heterostructures with low-temperature hole mobility exceeding 1.2×106 cm2 V−1 s−1 with carrier concentrations as low as 0.8×1011 cm−2: The highest value observed at such low densities. We also report the first observation of persistent positive photoconductivity in a two-dimensional hole gas. An analysis of the number density and temperature dependence of the mobility leads us to conclude that the mobility is limited by phonon scattering above ∼4 K and interface scattering at lower temperatures.
In0.53Ga0.47As metal-semiconductor-metal photodiodes with transparent cadmium tin oxide Schottky contacts
Authors: Gao Wei , Khan Al-Sameen , Berger Paul R. , Hunsperger R. G. , Zydzik George , O’Bryan H. M. , Sivco D. , Cho A. Y.
Published: July 2002

A metal-semiconductor-metal (MSM) In0.53Ga0.47As photodiode using a transparent cadmium tin oxide (CTO) layer for the interdigitated electrodes was investigated. The transparent contact prevents shadowing of the active layer by the electrodes, thus allowing greater collection of incident light. The barrier height (φBn) of CTO on i-In0.52Al0.48As was determined to be 0.47 eV, while the Ti/Au barrier height was 0.595 eV. The reduced barrier height for CTO is caused by tunneling through the sputter-damaged cap layer. Responsivity for 1.3 μm incident light was 0.49 and 0.28 A/W, respectively, for the CTO and Ti/Au MSM photodiodes. No antireflection (AR) coating was utilized over the bare semiconductor surface. The CTO MSM photodiode shows a factor of almost two improvement in responsivity over conventional Ti/Au MSM photodiodes.
Morphological transition of InAs islands on GaAs(001) upon deposition of a GaAs capping layer
Authors: Lin X. W. , Washburn J. , Liliental-Weber Z. , Weber E. R. , Sasaki A. , Wakahara A. , Nabetani Y.
Published: July 2002

The interaction between a GaAs cap and InAs islands grown on vicinal GaAs(001) has been studied by transmission electron microscopy and atomic force microscopy. Samples were prepared by molecular beam epitaxy at 480 °C. Upon GaAs cap deposition, it was found that the previously grown InAs islands undergo a novel type of morphological transition, i.e., a transition from disk-shaped to ring-shaped islands. InAs becomes depleted or entirely absent in the central area of what had been a disk-shaped InAs island. The GaAs cap was also shown to be virtually absent within the same central region, resulting in the formation of crater-like surface depressions.
Nature of defects in the Si-SiO2 system generated by vacuum-ultraviolet irradiation
Authors: Druijf K. G. , de Nijs J. M. M. , Drift E. V. D. , Granneman E. H. A. , Balk P.
Published: July 2002

We have used high-frequency and quasi-static capacitance-voltage measurements to study the properties of interface states generated upon vacuum-ultraviolet irradiation under positive gate bias followed by neutralization of the holes trapped in the oxide. The data indicate the exclusive generation of fast donor-type states that anneal at room temperature. We propose that these states explain the turn-around effect and annealing of positive charge.
Sharply directed emission in organic electroluminescent diodes with an optical-microcavity structure
Authors: Tsutsui Tetsuo , Takada Noriyuki , Saito Shogo , Ogino Etsuo
Published: July 2002

An optical microcavity structure was introduced into organic three-layer electroluminescent (EL) diodes with a europium complex as an emission layer. The device structure consisted of a dielectric reflector composed of SiO2/TiO2 bilayers, an indium-tin-oxide electrode, a hole transport layer, a europium complex as an emission layer, an electron transport layer, and a MgAg electrode. The dielectric reflector and the MgAg metal electrode constituted a planer microcavity. Sharply directed emission from the europium complex was observed when operated under dc drive voltage. Both angular dependences of intensity of emitted light and emission spectra of the EL diodes with the microcavity were compared with those of conventional EL diodes without microcavity.
Dark current analysis of Si homojunction interfacial work function internal photoemission far-infrared detectors
Authors: Yuan H. X. , Perera A. G. U.
Published: July 2002

A detailed theoretical investigation of dark current mechanisms is performed for a novel Si n+-i homojunction interfacial work function internal photoemission (HIWIP) far-infrared (FIR) detector. Thermionic emission, thermionic field emission and field emission currents, including the image force effect, are calculated and compared as functions of bias voltage and temperature. The bias and temperature dependence of detector noise equivalent power (NEP), limited by thermal noise and background noise, is also calculated. From these results, the optimal operating temperatures and bias voltages are determined. Results show that Si HIWIP FIR detectors may have a performance comparable to the conventional Ge FIR detectors, with some unique advantages over them.
Electron and hole energy levels in InAs self-assembled quantum dots
Authors: Medeiros-Ribeiro G. , Leonard D. , Petroff P. M.
Published: July 2002

Capacitance spectroscopy is used to determine the allowed energy levels for electrons and holes in InAs self-assembled quantum dots embedded in GaAs. Using this technique, the relative energy of the electron and hole states is measured with respect to their respective energy band minima in the GaAs. This allows the construction of an energy level diagram for these quantum dots which correlates well with previously observed photoluminescence data. By tuning the device geometry, a fine structure in the electron ground state is revealed and attributed to Coulomb charging effects.
Effect of growth conditions on crystalline quality of metalorganic chemical vapor deposition (111)B CdTe epilayers characterized by x-ray diffraction
Authors: Khanin E. , Amir N. , Nemirovsky Y. , Gartstein E.
Published: July 2002

A study of the effect of growth parameters on the resulting crystalline quality of CdTe epilayers grown by metalorganic chemical vapor deposition (MOCVD) technique is reported. The crystalline quality of the MOCVD CdTe (111)B epilayers is investigated by the double crystal rocking curve (DCRC) and Laue x-ray diffraction techniques. The rocking curve full width at half-maximum (FWHM) is used as a quantitative measure of structural perfection of the epilayers. The results indicate that a major parameter that affects the crystalline quality is the growth temperature. Epilayers grown at 480 °C exhibit high crystalline quality that is hardly affected by the partial vapor pressure of the metalorganic sources or the growth rate, whereas these growth parameters strongly affect the crystalline quality of epilayers grown at 430 °C. This phenomenon is attributed to the different mechanisms governing the growth process at these growth temperatures, namely mass transfer and surface kinetics. The crystalline quality of the MOCVD CdTe layers grown on the (111)B face of CdZnTe (4% Zn) or CdTe substrates can consistently match that of MOCVD (001) layers previously considered to have the best crystalline quality, with FWHM less than 90 arcsec for 6–7 μm thick layers. Linewidths as narrow as 56 arcsec are observed for epilayers thicker than about 11 μm. Microtwins, identified by the sixfold symmetry of Laue and double crystal 360° φ-scan diffraction patterns, are present even in epilayers with the narrowest FWHM. No straightforward correlation between visual morphology and crystalline quality was found. The growth of CdTe or CdZnTe epilayers is proposed by the MOCVD technique as buffer layers to obtain super substrates (‘‘superstrates’’) for the subsequent liquid phase epitaxy (LPE) growth of HgCdTe layers and additional heterostructures.
Effect of substrate misorientation on the growth of GaxIn1−x
P lateral quantum wells
Authors: Chen A. C. , Moy A. M. , Chou L. J. , Hsieh K. C. , Cheng K. Y.
Published: July 2002

We report the effects of misoriented GaAs substrates and varied substrate temperatures on the formation of GaxIn1−xP lateral quantum wells (LQWs) by the strain-induced lateral-layer ordering (SILO) process. Nominally [001] GaAs on-axis substrates, [001] substrates cut 2° off toward the [110] direction, and [001] substrates cut 2° off toward the [1̄10] direction were used to simultaneously grow LQWs. The samples were characterized using plan-view and cross-sectional transmission electron microscopy and polarized photoluminescence spectroscopy. We found that regardless of the substrate misorientation or substrate growth temperature, the SILO process induced LQWs always formed along the [1̄10] direction; primarily determined by the direction of the group-V dimer bonds on the surface during growth.
Atomic diffusion-induced deep levels near ZnSe/GaAs(100) interfaces
Authors: Raisanen A. D. , Brillson L. J. , Vanzetti L. , Bonanni A. , Franciosi A.
Published: July 2002

Luminescence spectroscopy measurements of ZnSe/GaAs(100) heterojunctions grown by molecular beam epitaxy reveal the formation of deep levels near ‘‘buried’’ interfaces upon thermal annealing. A pronounced emission at 1.9–2.0 eV appears at temperatures in the 300–400 °C range depending on the ZnSe growth conditions with a constant activation energy of 1.10 eV. X-ray photoemission spectroscopy indicates a correlation between this deep level and atomic diffusion of Ga and Zn across the heterointerface. Zn-rich ZnSe growth conditions dramatically reduce this emission, highlighting the importance of local interface composition on thermal stability.
Fully automated apparatus to measure the thermal conductivity of liquids by the transient hot-wire method
Authors: Kawaguchi N. , Nagasaka Y. , Nagashima A.
Published: July 2002

A new fully automated apparatus for measuring the thermal conductivity of liquids is described. This apparatus has been developed to meet the needs of industrial applications. The principle of the measurement is based on the absolute transient hot-wire method. All data acquisition and instrument control can be performed using a microcomputer. After filling with a sample liquid in a cell the apparatus can automatically measure the thermal conductivity at the desired temperature without any manual procedures. The automated procedures include an algorithm to determine onset time of natural convection. The applicability of the apparatus has been tested to measure the thermal conductivity of toluene at room temperature and the results have an estimated accuracy of ±1.0 to ±1.5% depending on a sample to be measured.
Data acquisition from a parallax bar via an RS232C interface
Authors: Trotter C. M. , Carson W. W.
Published: July 2002

A single-channel, microprocessor-based data-acquisition unit which allows readings from a simply instrumented parallax bar to be sent directly to a computer is described. The unit allows the usual manually read resolution of 0.01 mm in 40 mm to be retained. A serial ASCII, EIA RS232C data-communication format is used, with transmitted data terminated by the ASCII characters ‘‘carriage-return, line-feed.’’ This format allows simple data reception by most computers. Extension of the unit to a more general purpose, multichannel voltage acquisition device is also outlined.