bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced absorption modulation in hetero n-i-p-i structures by constructive superposition of field effect and phase space filling
Authors: Gulden K. H. , Kneissl M. , Kiesel P. , Malzer S. , Döhler G. H. , Wu X. , Smith J. S.
Published: July 2002

We report on large changes of the absorption coefficient due to a constructive superposition of the band-filling effect and Franz–Keldysh absorption in a selectively contacted In0.07Ga0.93As/GaAs hetero n-i-p-i structure. By changing the applied bias Upn from −2.5 to +0.8 V the internal fields in the GaAs layers can be tuned from 6.3×105 V/cm to 1.3×105 V/cm. Simultaneously the carrier concentration in the In0.07Ga0.93As quantum wells changes from 0 to 7.4×1012 cm−2. The maximum changes of the absorption coefficient observed at photon energies of 1.39 eV exceed 2000 cm−1 referred to the total sample thickness. This large absorption change is consistent with the theoretically expected constructive superposition of the sub-band-gap Franz–Keldysh absorption in the GaAs layers and the (red shifted) band-filling effect in the InGaAs quantum wells.
Lattice location and electrical activity of Ge co-implanted with P into InP
Authors: Kringho/j Per
Published: July 2002

The lattice location and electrical activation of Ge co-implanted with P or Se has been monitored by employing Rutherford backscattering spectrometry combined with proton-induced x-ray emission and differential Hall/resistivity measurements. The substitutional lattice location of Ge co-implanted with P is the In site, in contrast to a Ge-only implant where the Ge atoms occupy both lattice sites equally. Both P and Se co-implantation result in a significantly higher electrical activation, in agreement with the strongly reduced amphoteric behavior of Ge seen in channeling.
Fivefold multiply twinned crystallites in CuInSe2
Authors: Wada Takahiro , Negami Takayuki , Nishitani Mikihiko
Published: July 2002

The microstructure of polycrystalline CuInSe2 thin films are studied by cross-sectional high resolution electron microscopy. The CuInSe2 films were deposited on a Mo coated glass substrate by three-source evaporation. The film contained fivefold multiply twinned crystallites as well as a high density of twins in {112} planes. The formation of these defects are discussed.
Fluorine ion etching of lead zirconate-titanate thin films
Authors: Lau W. M. , Bello I. , Sayer M. , Zou Lichun
Published: July 2002

The etching reactions of lead zirconate-titanate (PZT) films with fluorine ions were studied by in situ x-ray photoelectron spectroscopic (XPS) analysis of the ion bombarded films. The bombardment was carried out with a mass separated low energy ion beam in ultrahigh vacuum and at 30 and 40 eV. It was found that the bombardment at 30 eV and a dose of 1×1017/cm2 (equivalent to 50 monolayers if a surface atom density of 2×1015/cm2 is assumed) at room temperature led to the removal of about 6 nm of PZT. This etch yield is much higher than the expected sputter yield at 30 eV, a phenomenon which clearly indicates the importance of surface chemistry. The XPS data also show that prior to bombardment, a homogeneous oxide was present but that the bombardment induced a surface enrichment of lead and the formation of metal fluorides. Heating the sample to 300 °C in vacuum desorbed virtually all metal fluorides. The results show that reactive ion etching of PZT films with fluorine chemistry is conceivable. However, the reaction mechanism appeared to be very much dependent on the bombardment energy. For example, an increase of the bombardment energy to 40 eV did not only increase the etch yield but also suppressed the surface enrichment of lead and induced the formation of oxy-fluorides.
AlGaAs/GaAs charge injection transistor/negative resistance field-effect transistor fabricated with shallow Pd/Ge ohmic contacts
Authors: Lai Jiun-Tsuen , Lee Joseph Ya-min
Published: July 2002

AlGaAs/GaAs charge injection transistor (CHINT)/negative resistance field-effect transistor (NERFET) devices are fabricated with Pd/Ge ohmic contacts. Pd and Ge are deposited by e-beam evaporation. The contact metal layers are annealed by rapid thermal annealing at 450–500 °C for 1 min. This gives a shallow ohmic contact and low specific contact resistivity. The better ρc are on the order of 10−6 Ω cm2. Using Pd/Ge contacts and rapid thermal annealing method, the metallization of CHINT/NERFET becomes much less critical. Good device performance under NERFET mode and CHINT mode is achieved. The largest peak-to-valley ratio of NERFET is about 15 at room temperature. The process developed in this work considerably simplifies the fabrication of CHINT/NERFET devices.
Low resistivity (∼10−5 Ω cm2) ohmic contacts to 6H silicon carbide fabricated using cubic silicon carbide contact layer
Authors: Dmitriev V. A. , Irvine K. , Spencer M. , Kelner G.
Published: July 2002

Silicon carbide is a wide band-gap semiconductor material which exists in more than 170 polytypes. In this work, heteropolytype epitaxy was used to decrease the specific contact resistance of ohmic contacts to the 6H-SiC polytype (band gap Eg∼3.0 eV). High quality ohmic contacts were produced by metallizing and annealing a thin cap layer of 3C-SiC (Eg∼2.3 eV) grown by chemical vapor deposition on either n- or p-type 6H-SiC. The measured specific contact resistance (rc) of the ohmic contacts to n-type 6H-SiC was found to be less than 1.7×10−5 and 2×10−5 Ω cm2 for contacts to p-type 6H-SiC.
Formation of metal silicide-silicon contact with ultralow contact resistance by silicon-capping silicidation technique
Authors: Yamada Keiichi , Tomita Kazuo , Ohmi Tadahiro
Published: July 2002

Ultralow contact resistance of metal silicide-n+-Si contact has been achieved by a novel contact metallization process employing Ta silicidation of a n+-Si contact surface by a Si-capping silicidation technique. The Si-capping silicidation has been employed to realize an ultraclean silicidation. The as-deposited Ta surface is in situ covered with a very thin Si protection layer in order to prevent the metal surface from being oxidized or contaminated. By combining the oxide-layer-free Si/metal on Si deposition process and an ultraclean ion implantation for mixing, metal silicide-n+Si structure has been formed by low temperature thermal annealing in an ultraclean Ar gas. As a result, an ultralow contact resistivity of 5.8×10−9 (Ω cm2) has been achieved.
Interfacial roughness in InAs/GaSb superlattices
Authors: Twigg M. E. , Bennett B. R. , Shanabrook B. V. , Waterman J. R. , Davis J. L. , Wagner R. J.
Published: July 2002

Using high-resolution transmission electron microscopy (HRTEM), we have studied InAs/GaSb superlattices grown by molecular beam epitaxy. Our HRTEM observations indicate that the apparent interface width is on the order of 1 monolayer for InSb-like interfaces, and on the order of 2 monolayers for GaAs-like interfaces. The combination of these results with x-ray diffraction and Raman scattering measurements leads us to conclude that these interface widths are principally due to roughness rather than to interfacial diffusion.
Maskless laser patterning of insulating films from salt solutions
Authors: von Gutfeld R. J. , Vigliotti D. R. , Wells O. C. , Khanna V. D. , O’Sullivan E. J.
Published: July 2002

Insulating thin-film patterns have been deposited on a variety of metal surfaces using focused laser light incident on samples submerged in both electrolytic and electroless nickel solutions. Deposits occur only where the laser radiation is absorbed by the substrate. For a single scan, the patterned film can have dimensions as small as 25 nm in height, 4 μm in width. Scanning electron microscope and electrical probing measurements confirm the insulating nature of the films.
Oxidation enhanced dopant diffusion in separation by implantation by oxygen silicon-on-insulator material
Authors: Crowder S. W. , Griffin P. B. , Hsieh C. J. , Wei G. Y. , Plummer J. D. , Allen L. P.
Published: July 2002

An effective interstitial surface recombination velocity for the buried Si-SiO2 interface in separation by implantation of oxygen (SIMOX) material has been used to accurately model the oxidation-enhanced diffusion of boron and phosphorous in single- and multiple-implant material. The effective recombination velocity at the SIMOX interface was found to be higher than the value for a thermally grown SiO2 interface. The enhancement of the effective recombination velocity is dependent on the material formation conditions and is empirically related to the near-interface dislocation density. Increased surface interfacial area is considered to be the most likely cause for the increased effective recombination velocity.
Effect of an augmented oxygen implant on electron trapping in buried oxides
Authors: Lambert R. J. , Bhar T. N. , Hughes H. L.
Published: July 2002

Standard silicon on insulator wafers were prepared by separation by implantation of oxygen. The standard implant of 1.8×1018 O+ cm−2 was augmented by an additional implant of 1017 O+ cm−2. The effect of this augmented implantation of oxygen on electron trap density and cross section was investigated using avalanche injection of electrons into the buried oxide. The shift in the high-frequency capacitance-voltage curve was monitored as a function of injected charge. Analysis of the mid-gap voltage shift versus charge shows no change in the effective density of electron traps. There is a factor of 6.8 decrease in the capture cross section for samples that received the supplemental oxygen implantation.
Noncritical phase matching and photorefractive damage in Sc2O3:LiNbO3
Authors: Yamamoto Joyce K. , Yamazaki T. , Yamagishi K.
Published: July 2002

The noncritical phase-matching temperature, Tpm, of Sc2O3-doped LiNbO3 was measured as a function of Sc2O3 concentration (0.0, 0.5, 1.0, and 1.5 mol % Sc2O3). Increasing the Sc2O3 concentration increased the phase-matching temperature, but to a lesser extent than reported in MgO:LiNbO3. The maximum phase-matching temperature was 46.5 °C in the 1.0 mol % Sc2O3:LiNbO3 crystal with an estimated temperature bandwidth of 1° cm. Photorefractive damage, determined by distortion in the transmitted beam, decreased with increasing Sc concentration, reaching a damage level comparable to that observed in 5.0 mol % MgO:LiNbO3 crystal in the 1.5 mol % Sc2O3:LiNbO3 crystal.
Eliminating dopant diffusion after ion implantation by surface etching
Authors: Lee Cynthia C. , Deal Michael D. , Bravman John C.
Published: July 2002

Implantation damage is believed to play a significant role in dopant diffusion. Described here is an attempt to modify the point defect damage profile of a 40 keV, 29Si implant in GaAs by chemically etching away the top 100 Å of the sample after implantation. In these samples, no Si diffusion was observed after annealing, while significant Si redistribution did occur in a similar sample which received no post-implant etch. trim simulations predict an excess Ga vacancy surface layer and excess Ga interstitials deeper in the sample. It is thought that by removing the vacancy-rich surface layer, the etch alters the implant damage profile and thus the diffusion behavior of the Si. Surface effects from etching as related to the Si diffusion are shown to be consistent with a vacancy-assisted diffusion mechanism. Evidence that this model may be applicable to B implants in Si is also shown.
Growth of heavy carbon-doped GaInAs lattice matched to InP by chemical beam epitaxy
Authors: Palmstro/m C. J. , Van der Gaag B. P. , Song J.-I. , Hong W.-P. , Schwarz S. A. , Novak S.
Published: July 2002

Successful growth of p-type (∼1×1020 holes/cm−3) C-doped lattice matched GaInAs on InP(100) has been demonstrated using chemical beam epitaxy. Carbon tetrachloride was used as the C-dopant gas and p-type GaInAs was grown by chemical beam epitaxy using trimethylindium, triethylgallium and cracked arsine. Combinations of elemental and organometallic group-III sources also resulted in p-type layers. High performance C-doped base InP/InGaAs heterojunction bipolar transistors were fabricated using chemical beam epitaxy grown material.
Thin films of the protonic conductor gadolinium-doped barium cerate by solid-source metalorganic chemical vapor deposition
Authors: Jiang N. , Buchanan R. M. , Lu Z. , Stevenson D. A. , Hiskes R. , DiCarolis S. A.
Published: July 2002

Gadolinium-doped barium cerate thin films have been grown on r-plane (11̄02) sapphire and on silver foil substrates by single solid-source metalorganic chemical vapor deposition using tetramethylheptanedionate mixed powder sources. The films have been deposited at 800 °C at a reduced pressure of 6 Torr. The bulk conductivity of the thin films, as measured by an alternating current impedance method, is close to that of sintered ceramic samples, and shows a similar hydrogen/deuterium isotope effect, providing evidence of protonic conduction.
Carrier escape time dependence on multiple quantum well structure in InGaAs/In(Ga)AlAs systems
Authors: Uenohara H. , Takahashi R. , Kawamura Y. , Iwamura H.
Published: July 2002

The dependence of carrier escape time from InGaAs/In(Ga)AlAs multiple quantum wells (MQW) on barrier width and barrier height is studied by using pump-probe measurement. Absorption saturation due to phase space filling caused by photogenerated carriers, and following electric-field screening dominates the transient electroabsorption signals. The barrier thickness strongly affects the carrier escape time. Escape time from MQW of less than 5 ps occurs under high electric field, and the escape time from the optical confinement layer is about one order of magnitude larger.
Surface roughening transition and critical layer thickness in strained-layer heteroepitaxy of EuTe on PbTe (111)
Authors: Springholz G. , Frank N. , Bauer G.
Published: July 2002

Heteroepitaxial growth of 2% lattice-mismatched EuTe on PbTe (111) by molecular beam epitaxy is investigated in the two-dimensional layer-by-layer growth regime combining in situ reflection high-energy electron diffraction and scanning tunneling microscopy (STM). At the critical layer thickness a distinct surface roughening is observed. The quantitative analysis of STM images yields an increase of the root mean square roughness by a factor of 4 at this roughening transition. Strong evidence is presented that for the used growth conditions this roughening is not caused by strain induced coherent islanding but by misfit dislocations at the onset of strain relaxation.
Smoothing effect of GaAs/AlxGa1−xAs superlattices grown by metalorganic vapor phase epitaxy
Authors: Xu Xian’gang , Huang Baibiao , Ren Hongwen , Jiang Minhua
Published: July 2002

GaAs/AlxGa1−xAs (x=0.5, 0.6, 1.0) superlattices used as buffer layers in high electron mobility transistors and photomultiplier devices can smooth out interface roughness. The mechanism of the smoothing effect has been discussed in detail. The initial stage of nucleation on the substrates has been clearly verified by examining the undulations of a 30 nm GaAs layer sandwiched between the substrate and the superlattice.
Atomic desorption of chlorine adsorbed on Si(111) with a scanning tunneling microscope
Authors: Baba Masakazu , Matsui Shinji
Published: July 2002

This letter reports the selective atomic desorption of Cl atoms adsorbed on an Si(111)7×7 surface by field evaporation using a scanning tunneling microscope (STM). After using STM to study the reaction of the Cl on the surface, the STM tip is placed on the adsorbed Cl and pulse voltage is applied. This results in selective atomic desorption of Cl. Although both desorption and readsorption are observed at a low pulse voltage of +4–+6 V, only desorption occurs at a high pulse voltage over +6 V.
Influence of deposition pressure on the bulk and interface states in low pressure chemical vapor deposited polycrystalline silicon thin-film transistors
Authors: Dimitriadis C. A. , Tassis D. H. , Economou N. A. , Giakoumakis G.
Published: July 2002

The effect of deposition pressure, p, on the bulk and interface states of undoped low pressure chemical vapor deposited polycrystalline silicon thin-film transistors (polysilicon TFTs) is investigated by field-effect conductance activation energy measurements. The bulk states consist of deep states with a characteristic wide peak near the midgap and shallow exponential tails near the conduction band. The interface states show an exponential distribution which cause a faster change of the gap states density near the conduction-band edge. For p≳40 mTorr, the bulk and interface states are controlled by the grain size and the degree of disorder of the material. For p<40 mTorr, the experimental results indicate that the films are contaminated by some impurities. The concentration of these impurities increases as p decreases and contributes mainly to the deep states generation.
Photorefractive wave mixing in undoped liquid encapsulated Czochralski GaAs at 1.5 μm: Validation of photorefractive modeling
Authors: Delaye P. , de Montmorillon L. A. , von Bardeleben H. J. , Roosen G.
Published: July 2002

We present photorefractive measurements in undoped GaAs performed at 1.06 μm, 1.32 μm, and at 1.55 μm. Using concentrations of EL20/+ that we determined through optical absorption and electron paramagnetic resonance measurements in the same sample, we show that a single defect model with an electron-hole competition quantitatively explains our results of photorefractive wave mixing.
Passivation of InGaAs/InP surface quantum wells by ion-gun hydrogenation
Authors: Chang Ying-Lan , Tan I-Hsing , Reaves Casper , Merz James , Hu Evelyn , DenBaars Steve , Frova A. , Emiliani V. , Bonanni B.
Published: July 2002

We have investigated the optical properties of an InGaAs/InP surface quantum well before and after room-temperature low-energy ion-gun hydrogenation. The luminescence efficiency of the surface quantum well was enhanced by up to two orders of magnitude after hydrogenation. Our experiments also reveal that the nonradiative recombination centers at the etched surface can be saturated by increasing excitation density for the photoluminescence measurement. To ‘‘unmask’’ the effects of the saturation of recombination sites, for a true comparison of passivation effects brought about by different surface treatments, an excitation density below 1 W/cm2 is required.
In situ monitoring of electron cyclotron resonance plasma processing of GaAs surfaces by optical reflection spectroscopy
Authors: Weegels L. M. , Saitoh T. , Oohashi H. , Kanbe H.
Published: July 2002

In situ reflection spectroscopy is demonstrated to be a useful technique for monitoring the damage to the surface of GaAs substrates induced by ions from an electron cyclotron plasma. Distinct differences in the reflectance spectra of GaAs substrates are observed between etching by argon ions and chemical cleaning by hydrogen ions. For argon it is found that the damage layer thickness increases linearly with the argon ion energy. Hydrogen ions induce a damage layer of 3.1 nm and arsenic atoms are preferentially removed from the surface as the ion energy increased.
Visible spectrum optical absorption in Te2 vapor
Authors: De Young Russell J.
Published: July 2002

The absorption spectrum of Te2 vapor has been measured throughout the visible spectrum. The absorption cross section (A state) was determined to be 2.18×10−18 cm2. At wavelengths above 500 nm, absorption takes place from vibrational levels above the ground level, allowing more efficient absorption of visible (solar) spectrum light. From an absorption point of view, Te2 appears to be a good candidate for a direct solar-pumped laser.
Observation of slow positron annihilation in silicide films formed by solid state interaction of Co/Ti/Si and Co/Si
Authors: Liu Ping , Lin Chenglu , Zhou Zuyao , Zou Shichang , Weng Huiming , Han Rongdian , Li Bingzong
Published: July 2002

Slow positron beam was used to investigate the solid state reaction of Co/Si and Co/Ti/Si. Variable-energy (0–20 keV) positrons were implanted into samples at different depths. The Doppler broadening of the annihilation γ-ray energy spectra measured at a number of different incident positron energies were characterized by a line-shape parameter ‘‘S.’’ It was found that the measured S parameters were sensitive to thin-film reaction and crystalline characteristics. In particular, the S parameter of epitaxial CoSi2 formed by the ternary reaction was quite different with that of the polycrystalline CoSi2 formed by direct reaction of Co with Si.
Charge trapping levels in vacuum evaporated polyvinylidene fluoride films
Authors: Chand Suresh , Bhatheja R. C. , Sharma G. D. , Chandra Subhas
Published: July 2002

Thermally stimulated discharge current (TSD) behavior of vacuum evaporated polyvinylidene fluoride films (∼5000 Å) has been studied at different polarization fields (2.0×103–1.8×104 V cm−1) and temperatures (333–393 K). The TSD spectra of these films show a single relaxation peak the position and activation energy of which depends on the polarization parameters. The origin of the peak has been attributed to the migration of the charge carriers, injected from the electrodes, at the macroscopic distances and their subsequent trapping; the trapping levels being distributed in their energies and lie between 0.46 and 0.72 eV, respectively.
New interface structure for A-type CoSi2/Si(111)
Authors: Chisholm M. F. , Pennycook S. J. , Jebasinski R. , Mantl S.
Published: July 2002

A new model of a CoSi2/Si(111) interface structure has been generated using images produced by Z-contrast scanning transmission electron microscopy. The images indicate that the top and bottom interfaces between the type-A buried CoSi2 layer and Si(111) both have eightfold coordinated Co atoms. This is accomplished by converting the one interface structure from sevenfold to eightfold coordination by locating a twinned layer of Si at the interface. The preference for this interface over the sevenfold type-A structure is in agreement with theoretical predictions.
Transmission electron microscopy characterization of InxGa1−xAs substrates grown by heteroepitaxial lateral overgrowth
Authors: McCaffrey J. P. , Bryskiewicz B. , Bryskiewicz T. , Jiran E.
Published: July 2002

InxGa1−xAs (x=0.04) ingots have been grown by liquid phase electroepitaxy (LPEE) on GaAs (001) substrates covered with a 0.2 μm thick SiO2 layer using a heteroepitaxial lateral overgrowth technique. Growth begins in 10 μm wide oxide-free seeding windows oriented at approximately 30° to the {110} planes of the substrate, and proceeds laterally over adjacent 90 μm wide oxide strips. Transmission electron microscopy (TEM) analysis of the resulting material reveals a decrease in dislocation densities in the alloy layer, as dislocation nucleation occurs only at the seeding windows, while growth proceeds defect-free over the oxide. Etching the seeding windows slightly into the substrate results in an increase in dislocation propagation into the substrate and under the oxide layer, and a lower dislocation density in the overlayer. The combination of the lateral overgrowth technique and the deeper window etching results in a significantly lower defect density in the InxGa1−xAs overlayer.
Threshold voltage shift of amorphous silicon thin film transistors with atmospheric pressure chemical vapor deposition silicon dioxide
Authors: Kim Jeong Hyun , Oh Eui Yeol , Yoon Jung Kee , Park Yong Suk , Hong Chan Hee
Published: July 2002

The threshold voltage (Vth) shift of hydrogenated amorphous silicon thin film transistors (a-Si:H TFTs) have been investigated for the atmospheric pressure chemical vapor deposition (APCVD) silicon dioxide (SiO2) gate insulator. For both positive and negative gate bias stress, the threshold voltage was shifted in the positive direction and was dominated by the defect creation near the a-Si:H/SiO2 interface. There was little charge trapping into the APCVD SiO2 gate insulator under the gate bias stress. For the positive gate bias stress, the threshold voltage shifts of a-Si:H TFTs with the a-Si:H/SiO2 interface were smaller than those of the conventional a-Si:H TFTs with the a-Si:H/SiNx interface.
Writing electronic nanometer structures into porous Si films by scanning tunneling microscopy
Authors: Enachescu M. , Hartmann E. , Koch F.
Published: July 2002

Under conditions of increased tunnel current and voltage, with the electron flow directed towards the sample, nanometer-scale structures have been written into ultrathin (∼20 nm) light-emitting porous silicon (PS) films using scanning tunneling microscopy in a high-vacuum environment. For the writing process, a threshold voltage of ∼4.5 V is observed and the resulting dimensions range between 20 and 50 nm. Depending on the writing parameters, the modified regions relax or remain stable during the observation time of several days at room temperature. These results can be assigned, in the first case, to a disruption of a small number of bonds, followed by reconfiguration, and a charging of dangling bond sites, followed by carrier release, in near surface regions. In the latter case, the creation of time-stable defect states within the PS layer is proposed.
Study of reactive-ion-etched silicon by a novel ultrashallow depth profiling technique
Authors: Chang W. H. , Huang L. J. , Lau W. M. , Abraham T. , King M.
Published: July 2002

Silicon treated with reactive ion etching in a CHF3/O2 plasma has been characterized by x-ray photoelectron spectroscopy and surface charging spectroscopy, in conjunction with ozone oxidation and subsequent HF-etching for nanodepth profiling. It was found that the residual damage mainly consisted of, from the bulk to surface, 2 nm of defective silicon where the Fermi level was pinned, 0.5 nm of silicon mainly contaminated by silicon carbide, 1 nm of silicon compounds (fluorides, oxides, and carbide), and 5 nm of fluorocarbon. After the removal of this damaged region, the Fermi level became unpinned.
Distributed feedback laser amplifiers combining the functions of amplifiers and channel filters
Authors: Wang Z. , Durhuus T. , Mikkelsen B. , Stubkjaer K. E.
Published: July 2002

A dynamic model for distributed feedback amplifiers, including the mode coupled equations and the carrier rate equation, is established. The presented mode coupled equations have taken into account the interaction between fast changing optical signal and the waveguide with corrugations. By showing the possibility of amplifying 100 ps pulses without pulse broadening, we anticipate that a distributed feedback amplifier can be used as a combined amplifier and channel filter in high bit rate transmission systems.
Laser activation of diamond surface for electroless metal plating
Authors: Pimenov S. M. , Shafeev G. A. , Laptev V. A. , Loubnin E. N.
Published: July 2002

Selective area electroless nickel and copper deposition onto the surface of diamond single crystals and polycrystalline diamond films has been realized. Three methods of laser-assisted activation of diamond surface were applied: (i) prenucleation of diamond surface with a thin layer of palladium catalyst via laser-induced decomposition of a palladium acetyl-acetonate [Pd(acac)2] solid film; (ii) deposition of palladium by means of the decomposition of Pd(acac)2 dissolved in dimethylformamide; (iii) laser-induced damage of diamond surface.
Broadband femtosecond pump-probe setup operating at 1300 and 1550 nm
Authors: Mark J. , Tessler N. , Eisenstein G. , Mo/rk J.
Published: July 2002

We describe a broadband, tunable femtosecond pump-probe measurement setup operating in the 1300 and 1550 nm wavelength range. We demonstrate measurements of carrier dynamics in the barrier states of a multiple quantum well optical amplifier. The amplifier is excited (pumped) in the gain region near 1510 nm and probed, with femtosecond time resolution, in the barrier region, at 1300 nm, yielding dynamical details which cannot be observed with conventional, single- wavelength pump-probe techniques.
Direct observation of exciton localization in a GaAs/AlGaAs quantum well
Authors: Takahashi Yutaka , Kano Satoru S. , Muraki Koji , Fukatsu Susumu , Shiraki Yasuhiro , Ito Ryoichi
Published: July 2002

We present the direct observation of exciton localization in a GaAs/AlGaAs quantum well. We have observed the two-component exponential decay of photoluminescence from heavy-hole excitons when the excitation density is very low. We have confirmed by measuring the lateral spatial motion of excitons that the fast component is attributable to the radiative recombination of free excitons while the slowly decaying component is due to the localized excitons.
Impurity-mediated growth and characterization of thin pseudomorphic germanium layers in silicon
Authors: Osten H. J. , Bugiel E. , Dietrich B. , Kissinger W.
Published: July 2002

We deposited thin germanium layers (among 4 and 12 monolayers thick) in silicon with antimony-mediated molecular beam epitaxy. All layers were investigated with Raman spectroscopy, electroreflectance measurements, and transmission electron microscopy in the lattice-imaging mode. The layers are continuous, no islanding could be observed even for the 1.8-nm-thick layers. Raman spectroscopic and electroreflectance measurements indicate some relaxation of the strained Ge layers. The interface between germanium layers and silicon buffer and cap layer are not sharp; significant intermixing could be detected.
Nucleation of boron nitride on cubic boron nitride microcrystallites using chemical vapor deposition
Authors: Saitoh Hidetoshi , Hirose Takeshi , Ohtsuka Tomoo , Ichinose Yukio
Published: July 2002

BN containing both cubic and turbostratic phases were synthesized using a chemical vapor deposition apparatus having a tungsten hot filament and a rf induction coil. The films deposited on the Si substrate demonstrated infrared absorption peaks at 800, 1080, and 1380 cm−1, suggesting that the deposited films contained both cubic and turbostratic BN. Transmission electron microscopy revealed that the BN films included clusters having 200–300 nm in size. In addition, it also appeared that these clusters were composed of crystalline cubic BN. To investigate the nucleation of BN on seed crystallites, cubic BN microcrystals were scattered on the Si single crystal wafer. On these crystallites, only submicron clusters were seen. These displayed broad Raman peaks at ∼1050 and ∼1300 cm−1, which are attributable to those from cubic BN. Thus, we suggest that the nano- crystalline cubic BN grew on cubic BN seeds possibly having preferential nucleation.
{H,P}0↔{H,P}+ transitions: A new look at donor-hydrogen pairs in Si
Authors: Estreicher S. K. , Jones R.
Published: July 2002

Recent experiments have shown that reversible changes in the charge state of {H,P} pairs in silicon can be initiated by injection of holes. The reaction {H,P}0+h+→{H,P}+ is spontaneous, while the reverse {H,P}++e−→{H,P}0 is very slow. We have calculated the barriers for these two reactions and the vibrational modes of H in the two charge states. These calculations explain most of the new data and two experimentally verifiable predictions are made.
Low temperature electron cyclotron resonance plasma etching of GaAs, AlGaAs, and GaSb in Cl2/Ar
Authors: Pearton S. J. , Ren F. , Abernathy C. R.
Published: July 2002

Sidewall etching of GaAs, AlGaAs, and GaSb in electron cyclotron resonance Cl2/Ar discharges is found to be completely suppressed by cooling the semiconductor sample to −30 °C during the process. Vertical etch rates of ≳1500 Å min−1 at 1 mTorr and −50 V dc bias are obtained for all three materials under conditions where the lateral etch rates are negligible. Ex situ chemical analysis of the sidewall shows substantially increased Cl-containing residue on low temperature etched samples, which can be removed by a 5 min H2 plasma clean-up step. The exploitation of temperature to control undercutting enables use of simpler gas chemistries because there is no need to form a sidewall polymer.
Diffraction limited dry etching of GaAs at λ=130 nm
Authors: Li B. , Twesten I. , Krause H.-P. , Schwenter N.
Published: July 2002

The promising recently reported high efficiency in dry etching of GaAs with vacuum ultraviolet radiation around 130 nm could be accompanied by a deterioration of resolution due to the involved amplification processes. It is shown that this is not the case and that the spatial resolution can be exploited up to the diffraction limit.
Ion trajectory distortion and profile tilt by surface charging in plasma etching
Authors: Murakawa Shigemi , Fang Sychyi , McVittie James P.
Published: July 2002

Surface charging effects on etching profiles during silicon etching in a nonuniform plasma were investigated by scanning electron micrographs and plasma potential measurements. The distortion in ion trajectories caused by the surface charging was calculated by an ion lens simulator. A tilt in the etching profile was found in holes and trenches near a large etched area when an insulating mask such as photoresist or silicon dioxide was used. Ion trajectory calculations showed that this profile tilt was caused by the local electric field resulting from the potential difference between the charged mask surface and the electrically grounded silicon substrate. This profile result agrees well with gate oxide damage results which were also successfully explained by surface charging.
Conduction-band states of thin InAs/AlSb quantum wells
Authors: Boykin Timothy B.
Published: July 2002

We study the conduction-band states of thin InAs quantum wells confined by relatively thick AlSb barriers with a ten-band tight-binding model, considering the results in the context of recent experiments. For the 1 monolayer well structure, we find that the wave function has significant evanescent-state contributions both in the well and barriers, while we find that the wave function of the 5 monolayer device is mostly Γ-like throughout.
Large-numerical-aperture microlens fabrication by one-step etching and mass-transport smoothing
Authors: Liau Z. L. , Mull D. E. , Dennis C. L. , Williamson R. C. , Waarts R. G.
Published: July 2002

Precision f/1 microlenses have been fabricated in GaP by smoothing a multiple-mesa structure etched with a designed width and length variation. High-resolution lithography and ion-beam- assisted etching were used for mesa definition and resulted in accurate lens profiles after mass-transport smoothing at 900–1070 °C. This much simplified fabrication technique is highly promising for efficient, diffraction-limited micro-optical elements.
Selective-area room temperature visible photoluminescence from SiC/Si heterostructures
Authors: Steckl A. J. , Su J. N. , Xu J. , Li J. P. , Yuan C. , Yih P. H. , Mogul H. C.
Published: July 2002

SiC/Si heterostructures have been patterned by reactive ion etching with CHF3/O2 to produce SiC-covered and Si-exposed regions with lateral dimensions of 2.5 to ∼500 μm. The patterned samples were then anodized in HF/ethanol solutions. Short anodization times (<3 min) result in selective-area UV-induced visible photoluminescence (PL), with a peak located at 650 nm, being observed at 25 °C from only the SiC-covered regions. The emission is generated by porous Si (PoSi) selectively formed under the SiC cap and transmitted through the wide band-gap SiC layer. Longer etching times result in nonselective PL.
Surface plasmon resonance microscopy: Reconstructing a three-dimensional image
Authors: Morgan Hywel , Taylor D. Martin
Published: July 2002

A method for reconstructing three-dimensional images of thin films from surface plasmon resonance (SPR) microscopy images is described. As an example, monolayers of a lipid were deposited onto a gold substrate using Langmuir–Blodgett technology and an SPR microscope image obtained. Using data from reflectance-angle (R-θ) curves obtained in supplementary measurements, the contrast in the microscope image was used to provide thickness information. Converted to a z modulation this was used to produce a three-dimensional image of the monolayer.
Piezoelectricity and electrostriction of dye-doped polymer electrets
Authors: Winkelhahn H.-J. , Winter H. H. , Neher D.
Published: July 2002

An interferometric measurement technique is reported by which the piezoelectric and electro- strictive properties of thin films of electrets can be determined. The frozen-in polarization can be determined from the ratio between piezoelectric and electrostriction constants of the electret film. The method is applied to a poled-polymer guest-host system consisting of a polycarbonate host and 4-dimethylamino-4′-nitrostilbene dye. The frozen in polarization measured as a function of poling field agrees well with the predictions for dilute dipolar systems if an affine motion contribution is added to the established theory of the piezoelectric effect of electrets.
Preparation of epitaxial AlN films by electron cyclotron resonance plasma-assisted chemical vapor deposition on Ir- and Pt-coated sapphire substrates
Authors: Zhang Wei , Vargas Roberto , Goto Takashi , Someno Yoshihiro , Hirai Toshio
Published: July 2002

AlN epitaxial films have been fabricated on Ir- and Pt-coated α-Al2O3 substrates via electron cyclotron resonance plasma-assisted chemical vapor deposition (ECRPACVD) using an AlBr3-N2-H2-Ar gas system at substrate temperatures ranging from 500 to 700 °C. The epitaxial relationships between AlN films and substrates were determined by x-ray diffraction, x-ray pole figure, and reflection high-energy electron diffraction. The results are useful in practical applications, such as AlN/metal/α-Al2O3 structure in surface acoustic wave (SAW) devices.
Vacuum deposition of nonlinear chromophore-polymer composite thin films
Authors: Yang G.-R. , Ma X. F. , Chen W. X. , You L. , Wu P. , McDonald J. F. , Lu T.-M.
Published: July 2002

Novel nonlinear composite thin films containing 4-dialkylamino-4′-nitro-stilbene (DANS) and Teflon AF 1600 have been deposited by vacuum evaporation techniques. Pure DANS thin film, due to its centrosymmetric crystal structure, does not exhibit any electro-optic effect. However, composite thin films of DANS and Teflon AF 1600 with a DANS concentration of 5%–25% (by volume) do exhibit an electro-optic effect after poling. Their electro-optical coefficients are measured to be as large as 2.4 pm/V. X-ray diffraction shows that these composite thin films are in an amorphous state as-deposited as well as after poling. It is argued that the DANS molecules are in their molecular form embedded in the Teflon AF amorphous matrix, thereby allowing the effect of their large molecular hyperpolarizability to be detected. The characterization of the thin films using scanning electron microscopy is also presented.
Hall measurements on selectively doped InSb heterostructures grown by molecular beam epitaxy on GaAs (001)
Authors: Songpongs P. , Andersson T. G. , Ekenstedt M. J. , Söderström J. R. , Cumming M. M.
Published: July 2002

Hall measurements were made on selectively Si-doped InSb, GaSb/InSb, and GaAs/InSb heterostructures grown by molecular beam epitaxy using cracker sources. A cap layer had a pronounced influence especially on the low temperature conduction. The measurements showed an apparent increase in free carrier concentration and reduction of mobility due to compensation and/or parallel conduction. The best mobility, 38 700 cm2/V s at room temperature, was measured in a 2-μm-thick InSb layer capped with GaSb and doped with a concentration of 3×1016 cm−3 within 1000 Å from the cap interface. The variation of carrier concentration with temperature in doped samples revealed singularities at 50 and 90 K due to conduction from an unintentional p-background doping.
Atomic force microscopy study of uv-induced anisotropy in hydrogen-loaded germanosilicate fibers
Authors: Inniss D. , Zhong Q. , Vengsarkar A. M. , Reed W. A. , Kosinski S. G. , Lemaire P. J.
Published: July 2002

Thermally treated and uv-exposed hydrogen-loaded germanosilicate fibers are profiled with an atomic force microscope after cleaving the fiber in the exposed region and etching the cleaved endface in hydrofluoric acid. Thermally treated fibers etch symmetrically throughout the core region, but the uv-exposed fibers etch differently. In the uv-exposed fibers, both the etch depth and the refractive index are asymmetric. They are highest at the core-cladding interface on the side exposed to the uv radiation. We propose that a photolytic process increases the refractive index across the entire core, but the asymmetry is the result of transient heating due to uv absorption. Furthermore, we demonstrate that uniform circumferential exposure symmetrizes the etch depth and refractive index change and reduces the induced birefringence.
Chemically pumped visible-wavelength laser with high optical gain
Authors: Benard D. J. , Boehmer E.
Published: July 2002

Excitation of a mixture of FN3, B2H6, SF6, and He by a pulsed CO2 laser generates a transient gain medium capable of supporting laser oscillation at 433 nm in an optical cavity with threshold gain of 2.5%/cm.
Directional growth of copper phthalocyanine crystal by selective chemical vapor deposition method
Authors: Sekiguchi A. , Uchida T. , Sugimura H. , Shimo N. , Masuhara H.
Published: July 2002

Novel deposition behavior was observed when 1,4-dicyanobenzene was sublimed onto copper micropatterns on silicon wafer. On the patterns copper-phthalocyanine whiskers and debris of similar size were formed and preferentially oriented along or perpendicular to the copper lines. The directional growth was confirmed to have nothing to do with crystal axis of the silicon, but was considered to be due to the periodic structure of the copper lines.
Mechanical stength of Czochralski silicon crystals with carbon concentrations from 1014 to 1016 cm−3
Authors: Fukuda Tetsuo
Published: July 2002

Using Czochralski-grown silicon crystals with carbon concentrations from 1014 to 1016 cm−3, we studied the influence of oxygen precipitates on the mechanical strength of silicon crystals. Reducing carbon concentration from 1016 to 1014 cm−3 suppressed oxygen precipitation and thus, improved the strength. Carbon concentration reduction from 1015 to 1014 cm−3 did not, however, decrease oxygen precipitation as dramatically as reduction from 1016 to 1015 cm−3. Carbon impurities below 1014 cm−3 no longer affect oxygen precipitation. Therefore, we conclude that reducing carbon concentration below 1014 cm−3 no longer improves the mechanical strength of silicon crystals.
Demonstration of quantum confinement in InSb-In1−xAlxSb multiquantum wells using photoluminescence spectroscopy
Authors: Saker M. K. , Whittaker D. M. , Skolnick M. S. , McConville C. F. , Whitehouse C. R. , Barnett S. J. , Pitt A. D. , Cullis A. G. , Williams G. M.
Published: July 2002

We report the observation of quantum confinement, using photoluminescence, in InSb-In1−xAlxSb (0.08≤x≤0.23) multiquantum well samples grown by molecular beam epitaxy. A series of samples were studied with different well widths and varying concentration of aluminum in the barriers. The upshifted luminescence energies behave qualitatively as expected due to changes in confinement, and are in good quantitative agreement with calculated upshifts taking into account strain in the barriers. These results demonstrate that good quality heterostructures can be obtained in this material system and show its potential for device applications.
Intersubband hole absorption in GaAs-GaInP quantum wells grown by gas source molecular beam epitaxy
Authors: Brown G. J. , Hegde S. M. , Hoff J. , Jelen C. , Slivken S. , Michel E. , Duchemin O. , Bigan E. , Razeghi M.
Published: July 2002

P-doped GaAs-GaInP quantum wells have been grown on GaAs substrate by gas source molecular beam epitaxy. Structural quality has been evidenced by x-ray diffraction. A narrow low-temperature photoluminescence full width at half-maximum has been measured. Strong hole intersubband absorption has been observed at 9 μm, and its dependence on light polarization has been investigated.
Assessment of hot-hole-induced interface states and trapped carriers in submicron n (metal–oxide semiconductor field effect transistors) by gate-to-drain capacitance measurement
Authors: Ghodsi R. , Yeow Y. T. , Alam M. K.
Published: July 2002

Change in small-signal gate-to-drain capacitance of an n-metal–oxide semiconductor field effect transistor as a function of gate and drain voltages before and after drain avalanche hot-hole injection was used to study the nature of trapped charge. The results show the trapping of holes and generation of acceptor interface states at the top half of the silicon band gap. Comparison with the Pbo dangling bond model was made and the difference explained.
Secondary ion mass spectroscopy study of Zn or Cd implanted and rapid thermally annealed Pd/Ge contacts to p-In0.53Ga0.47As
Authors: Ressel P. , Strusny H. , Trapp M. , Kräutle H. , Fritzsche D.
Published: July 2002

Backside secondary ion mass spectroscopy is used to examine elemental redistribution in Zn or Cd implanted Pd/Ge contacts to p-InGaAs. A quaternary Pd-In-Ga-As layer is observed at annealing temperatures of 200–250 °C. At temperatures ≳250 °C, this layer disappears due to PdGe formation and InGaAs regrowth. Excess Ge diffuses to the contact interface. Cd and Zn accumulate inside the regrown InGaAs creating a thin, highly doped layer. Due to its abrupt interface and the formation of a highly doped layer beneath the contact, this implanted Pd/Ge contact scheme is a promising candidate for shallow ohmic contacts to p-InGaAs.
Spontaneous patterning in high temperature superconducting film by liquid-gas-solidification processing
Authors: Chou H. , Chow T. H. , Wang K. K. , Chau Z. M. , Chen H. S. , Fitzgerald E. A. , Hsu S. N.
Published: July 2002

Without any post physical or chemical patterning a Tl-base high temperature superconducting film has been observed to pattern spontaneously on SrTiO3 (100) by liquid-gas-solidification process. The film exhibits the morphology of a microelectric network in which the directions of growth of the crystal walls follow the directions of the SrTiO3 (100) substrate. The crystal walls consisting of Tl-1223 and Tl-1212 phases are 0.25–1 μm wide, 2 μm high, and a few millimeters long. These walls are proposed to grow from independent nucleation sites and coalescence to form semiconductive junctions. The network exhibits a superconducting transition onset at 113 K and approaches zero resistance at 95 K. Below 95 K, the resistance increases exponentially with decreasing temperature. This strongly suggests that the films form a natural superconductor/semiconductor/superconductor junction array.
Evaluation of growth temperature, refractive index, and layer thickness of thin ZnTe, MnTe, and CdTe films by in situ visible laser interferometry
Authors: Glanner G. J. , Sitter H. , Faschinger W. , Herman M. A.
Published: July 2002

The experimental procedure and the results of in situ determination of growth temperatures, refractive indices at growth temperatures, and thicknesses of ZnTe, cubic MnTe, and CdTe thin films grown by molecular beam epitaxy (MBE) are reported. Visible laser interferometry with He-Ne laser 0.6328-μm light has been applied in the performed experiments. A 290-μm-thick plane-parallel GaP wafer polished to an optical finish on both sides has been used as a growth temperature calibration standard. The exemplary substrate temperature calibration curves, as well as the data gained at dynamic thermal conditions are presented and discussed. The following numerical values concerning refractive indices n at elevated temperatures have been evaluated from experimental data for the MBE grown films: n (286 °C)ZnTe=2.51, n (175 °C)ZnTe=2.49, n(286 °C)cubic MnTe=3.26, and the extinction coefficient k (286 °C)CdTe=0.23.
Reduction of Be out-diffusion from heavily doped GaAs:Be layers by pseudomorphic InxGa1−xAs barrier layers
Authors: Zhang K. , Chen Y. C. , Singh J. , Bhattacharya P.
Published: July 2002

The effectiveness of suppressing Be out-diffusion from a Be-doped GaAs layer by strained InGaAs layers using secondary ion mass spectroscopy has been evaluated. The experimental structures consist of an 800 Å Be-doped (∼1×1019 cm−3) GaAs layer sandwiched between 80 Å InxGa1−xAs (x=0,0.1,0.25) layers. The samples were subjected to rapid thermal annealing (RTA) at 750 °C for 6 min. It is clearly observed that Be diffusion beyond the InGaAs layers is the fastest for the structure with x=0 and the slowest for the structure with x=0.25.