bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of thermophoretic protection with speed-controlled particles at 100, 50, and 25mTorr
Authors: Kim Jung Hyeun , Fissan Heinz , Asbach Christof , Yook Se-Jin , Pui David Y. H. , Orvek Kevin J.
Published: June 2006

Thermophoresis is considered as a candidate for protection of extreme ultraviolet lithography masks from particle contamination during vacuum exposures. A thermophoretic force is exerted on a particle by surrounding gas molecules within a temperature gradient. Gas molecules on the “warm side” of the particle provide more momentum than on the “cool side,” so particles move from the warm to the cool region. In this study, thermophoretic protection of a critical surface from particles injected with known initial speeds into a quiescent gas has been investigated at 100, 50, and 25mTorr. Initial particle speed was varied from 10to31m∕s depending on the gap distances (1, 2, and 3cm), particle sizes (125 and 220nm), and system pressures. A pinhole plate is used to supply speed-controlled particles with almost no accompanying gas flow. The results demonstrate that the window of protection offered by thermophoresis is very narrow for inertial particles, and that thermophoresis offers the greatest protection for low-velocity particles subject to diffusional motion in the vacuum system. Furthermore, the experimental results verify the results of an analytical model, developed by Asbach et al. [Appl. Phys. Lett. 87, 234111 (2005)]. The analytical model can be used to predict the particle stopping distance under any thermophoretic gradient.
Approach to optimizing n-SiC Ohmic contacts by replacing the original contacts with a second metal
Authors: Ervin Matthew H. , Jones Kenneth A. , Lee Unchul , Wood Mark C.
Published: June 2006

Nickel (Ni) contacts to n-type silicon carbide (n-SiC) have good electrical properties, but the physical contact, and therefore the reliability, is poor. An approach is described for using the good electrical properties of Ni Ohmic contacts, while using another metal for its superior topological, mechanical, thermal, or chemical properties for the chosen application. In the present work, we show that once the Ni contact has been annealed, forming nickel silicides, it can be etched off and replaced by a second metal chosen for its desired properties. This second metal displays an as-deposited contact resistance as low as the original annealed Ni contact, indicating that the critical feature responsible for Ohmic contact formation has not been removed when the silicide phases were etched off. Not only does this approach provide more flexibility for optimizing the contact for a given application but it also provides some insight into the Ohmic contact formation mechanism.
Calcium impurities in enhanced-depletion-width GaInNAs grown by molecular-beam epitaxy
Authors: Ptak A. J. , Friedman D. J. , Kurtz Sarah , Reedy R. C. , Young M. , Jackrel D. B. , Yuen H. B. , Bank S. R. , Wistey M. A. , Harris J. S.
Published: June 2006

Ca impurities are observed in GaInNAs grown by both molecular-beam epitaxy and metal organic chemical-vapor deposition by high-mass-resolution secondary-ion mass spectrometry measurements. The Ca appears to originate from the surface of the as-received GaAs substrates, and presumably comes from the polishing process used in substrate preparation. Ca was observed in samples grown by different growth methods and in different laboratories. No detectable Ca incorporates into epitaxial GaAs, although Ca levels as high as 1017cm−3 are observed in GaInNAs. There are indications that the Ca impurities act as shallow acceptors in GaInNAs and may, at least in part, control the background acceptor concentrations. This has implications for high-current, p-i-n GaInNAs solar cells that require very low background doping to enhance current collection.
Growth optimization of InGaAs quantum wires for infrared photodetector applications
Authors: Tsai Chiun-Lung , Xu Chaofeng , Hsieh K. C. , Cheng K. Y.
Published: June 2006

We studied the quantum wire photodetector (QRIP) structures with an InGaAs quantum wires (QWRs) active region formed by the strain-induced lateral ordering (SILO) process. The InGaAs multiple layer QWR structure maintains a small total strain due to the strain-balanced nature of the SILO process. The effects of growth temperature and layer structures on the QWR formation are studied using photoluminescence and transmission electron microscope measurements. High-resolution x-ray diffraction studies on QRIP structures consisting of 20 QWR layers confirmed the strain-balanced property of SILO-based structures.
Molecular beam epitaxy grown In1−xAlxSb∕InSb structures for infrared detectors
Authors: Klin O. , Klipstein P. C. , Jacobsohn E. , Saguy E. , Shtrichman I. , Raizman A. , Weiss E.
Published: June 2006

The core of SCD’s present day focal plane array (FPA) technology is a two-dimensional array of InSb photodiodes. It is produced by ion implantation and is attached to a silicon focal plane processor by indium bumps. We have extended this technology with In1−xAlxSb (0<x<0.03) alloys grown by molecular beam epitaxy on InSb substrates, utilizing a p-i-n structure. The advantages of the grown structures over those fabricated by implantation are already demonstrated in 320×256 element FPAs based on epitaxial InSb mesa diodes. These FPAs have dark currents at 100K comparable to those of implanted FPAs at 77K, with an operability (fraction of working diodes) in excess of 99.5%, and with a residual non-uniformity (RNU) at 100K of less than 0.03% (standard deviation/dynamic range) after a two-point non-uniformity correction (NUC). The RNU remains very low (<0.1%) even when the FPA temperature is shifted by as much as 10K from the NUC temperature. The average dark current at 100K and also the width of its distribution are further reduced by increasing the Al concentration in the FPAs by up to 3%, in accordance with the increase in the alloy energy gap. This has enabled us to achieve high quality thermal images at even higher temperatures than in the binary InSb FPAs. A key issue in achieving highly uniform FPAs is the degree of control of the InAlSb composition, misfit strain relaxation, and defect density. A series of In1−xAlxSb layers with x up to 6% was grown in order to study the effect of the growth conditions on these features. We discuss our results in terms of the misfit strain relaxation mechanisms in the In1−xAlxSb structures including dislocations, tilt, microcracks, and morphological crosshatch patterns.
Vertically aligned carbon nanotube field emission devices fabricated by furnace thermal chemical vapor deposition at atmospheric pressure
Authors: Wei S. , Kang W. P. , Davidson J. L. , Choi B. K. , Huang J. H.
Published: June 2006

Multiwalled carbon nanotubes (CNTs) grown by thermal chemical vapor deposition (CVD) in a tube furnace at atmospheric pressure are reported. The CNTs were synthesized at 750°C using C2H2 as the carbon source and a mixture of Ar∕H2 (80vol%:20vol%) as a carrier gas, with NH3 serving as a processing reagent. The catalytic properties of nickel (Ni) particles are strongly affected by the CVD process parameters and this effect is reflected in the morphologies and field emission behaviors of the as-grown CNTs. The flow rate ratio of NH3 to C2H2 is found to be critical to the formation of vertically aligned CNTs, which demonstrated better field emission characteristics than the randomly oriented nanotubes. The successful synthesis of vertically aligned CNTs at atmospheric pressure in a tube furnace is beneficial for large area mass production such as flat panel field emission displays at lower cost.
High performance self-organized InGaAs quantum dot lasers on silicon
Authors: Mi Z. , Yang J. , Bhattacharya P. , Chan P. K. L. , Pipe K. P.
Published: June 2006

We report the molecular beam epitaxial growth and characteristics of room temperature InGaAs quantum dot lasers grown directly on silicon utilizing thin (⩽2μm) GaAs buffer layers and quantum dot layers as dislocation filters. Cross-sectional transmission electron microscopy studies show that defect-free quantum dot active regions can be achieved. Room temperature photoluminescence emission from quantum dots grown on silicon is comparable, in intensity and linewidth, to that from similar dots grown on GaAs substrates. The best devices are characterized by relatively low threshold current (Jth∼1100A∕cm2), high output power (>150mW), large characteristic temperature (T0=244K), and constant output slope efficiency (⩾0.3W∕A) in the temperature range of 5–95°C.
Size evolution of site-controlled InAs quantum dots grown by molecular beam epitaxy on prepatterned GaAs substrates
Authors: Atkinson P. , Bremner S. P. , Anderson D. , Jones G. A. C. , Ritchie D. A.
Published: June 2006

Ex situ electron-beam lithography followed by conventional wet or dry etching has been used to pattern small holes of 60–150nm wide, 10–40nm deep in GaAs substrates. These holes then act as preferential nucleation sites for InAs dot growth. Preferential nucleation occurs due to a reduction in the apparent critical thickness above the pattern site, which is dependent on the dimensions of the initial pattern. We demonstrate that subsequent growth of site-controlled dots over the patterned sites varies with InAs deposition amount and growth temperature in a similar way to InAs dot growth on planar substrates. By varying temperature and either InAs deposition amount or pattern size, both the size and position of InAs quantum dots can be controlled.
In
As
∕
Ga
As
quantum-dot infrared photodetectors grown by molecular beam epitaxy
Authors: Pal D. , Walker J. , Towe E.
Published: June 2006

We have studied InAs∕GaAs quantum-dot photodetectors containing 50 periods of quantum-dot layers. Clean photoresponse spectra and a peak responsivity of about 99mA∕W are observed up to about 120K. The device structures contain no (Al, Ga)As current-blocking layers. A relatively low dark current and a high peak responsivity (0.242A∕W) are observed at 78K. These results suggest that increasing the dot density, controlling the dopant impurity concentration, and incorporating a current-blocking layer would most likely increase the operating temperature of the devices beyond 120K.
Nonstoichiometric growth and cluster formation in low temperature grown GaAsSb for terahertz-applications
Authors: Sigmund J. , Pavlidis D. , Hartnagel H. L. , Benker N. , Fuess H.
Published: June 2006

Nonstoichiometric low-temperature grown (LTG) GaAs0.6Sb0.4 is epitaxially grown by molecular beam epitaxy on a lattice mismatched Al0.77In0.23As buffer layer. Ex situ annealing leads to an increase in the wafer sheet resistivity. Values as high as 1.7×108Ω∕sq were measured. By high resolution transmission electron microscopy, clusters were observed in LTG-GaAs0.6Sb0.4 after annealing, some of them attached to dislocation lines. Moreover, in a 600°C annealed sample, the clusters have two different crystal structures and a spread in cluster size is present from an early formation state up to a diameter of 12.5nm. Hence, the strain surrounding the clusters is not uniform, which leads to an asymmetry of the x-ray diffraction (XRD) peak. In addition to an increased peak asymmetry with increasing annealing temperature, the XRD peak is shifted towards higher 2θ values, resulting in a lattice constant shift of 0.24%. This lattice constant shift is due to a strain relaxation process by forming clusters.
High performance GaAsSb∕InP double heterojunction bipolar transistors grown by gas-source molecular beam epitaxy
Authors: Wu Bing-Ruey , Chu-Kung Benjamin F. , Feng Milton , Cheng K. Y.
Published: June 2006

High quality GaAsSb∕InP double heterojunction bipolar transistor (DHBT) structures were grown using gas-source molecular beam epitaxy. The substrate temperature and V/III flux ratio were optimized to grow single phase GaAsSb base layers lattice matched to InP. The dc gain as high as 40 was obtained in 60×60μm2 GaAsSb∕InP DHBTs with a 500Å carbon doped (7×1019cm−3) GaAsSb base layer. High performance DHBT with a 250Å base layer shows a current gain cutoff frequency fT of 346GHz and maximum oscillation frequency fmax of 145GHz.
Fabrication and molecular beam epitaxy regrowth of first-order, high contrast AlGaAs∕GaAs gratings
Authors: Wang C. S. , Morrison G. B. , Skogen E. J. , Coldren L. A.
Published: June 2006

We present a fabrication technique and molecular beam epitaxy (MBE) regrowth of first-order, high contrast AlGaAs∕GaAs diffraction gratings for laser emitting at 980nm. An immersion holography technique is used to uniformly pattern first-order gratings with a pitch of 155nm. MBE is used to overgrow Al0.75Ga0.25As on etched GaAs gratings. It is found that slow growth rates with optimum arsenic overpressure are necessary to overgrow gratings with low pitting defect densities. These first-order, high contrast gratings are integrated as distributed Bragg reflectors in an edge-emitting laser structure. Single-mode emission at 1μm with a side mode suppression ratio greater than 30dB is demonstrated.
Molecular beam epitaxial growth of osmium silicides
Authors: Cottier R. J. , Amir F. Z. , Zhao W. , Hossain K. , Gorman B. P. , Golding T. D. , Anibou N. , Donner W.
Published: June 2006

Details of the molecular beam epitaxial growth of osmium silicide (OsSi2 and Os2Si3) thin films are presented. The study has been motivated by reports that OsSi2 has a band gap between 1.4–1.8eV [L. Schellenberg et al., J. Less-Common Met. 144, 341 (1988); K. Mason and G. Muller-Vogt, J. Cryst. Growth 63, 34 (1983)], and Os2Si3 has a band gap of 0.95eV [A. B. Filonov et al., Phys. Rev. B 60, 16494 (1999)] or 2.3eV [L. Schellenberget al., J. Less-Common Met. 144, 341 (1988)]. Of particular note is that the Os2Si3 band gap is predicted to be direct, and thus has significant potential optoelectronic applications. The resulting films have been analyzed using reflection high-energy electron diffraction, scanning electron microscopy, x-ray reflectivity measurements, and out-of-plane x-ray diffraction. For low Si∕Os flux ratios (∼1.5), both OsSi2 and Os2Si3 phases are observed. However, with a larger Si∕Os flux ratio (∼4) the crystalline quality is greatly increased and only a single phase Os2Si3 is observed. We present our results and discuss our observations in relation to thermodynamic considerations and growth parameters.
Study of the homoepitaxial growth of GaAs on (631) oriented substrates
Authors: Cruz-Hernández E. , Rojas-Ramírez J. S. , Vázquez-López C. , López-López M. , Pulzara-Mora A. , Méndez-García V. H.
Published: June 2006

We have studied the GaAs growth on (631) oriented substrates by molecular beam epitaxy (MBE). Different samples were prepared by varying the growth temperature and the III/V equivalent pressure ratio. We observed by atomic force microscopy a high density of hilly like features elongated towards the [−5,9,3] direction formed during the MBE growth. The growth temperature dependence of the hillock length and width follows an Arrhenius-type behavior with activation energies of 1.4 and 0.5eV, respectively. The hillock formation is discussed in terms of adatom diffusion anisotropy and diffusion barriers. Employing photoreflectance spectroscopy we found a splitting of the GaAs band gap energy transition that increases with the hillock density.
Hydrogen-plasma assisted molecular beam epitaxial growth of high-purity InAs
Authors: Chen Y. Q. , Unuvar T. , Moscicka D. , Wang W. I.
Published: June 2006

In this article we report the effect of H plasma on the purity and transport properties of molecular beam epitaxial (MBE) grown InAs, which has attracted considerable attention for high-speed and low power electronic devices in recent years. We observed that the native oxide on the InAs surface could be desorbed at temperatures as low as 300°C under H-plasma irradiation. The time required for oxide desorption increased with decreasing substrate temperature. Thick InAs was grown with H-plasma assistance on semi-insulating (SI) GaAs and on an AlAs0.16Sb0.84∕InAs insulating buffer layer to investigate the effect of H plasma on the transport properties of InAs. Significant improvement of the electron mobility was observed using H-plasma assisted growth. For 6μm InAs grown with H plasma on SI GaAs, the electron mobilities were as high as 98000cm2∕Vs at 77K and 19500cm2∕Vs at 300K, which represent the best published data for MBE grown InAs on GaAs. For thick InAs grown on AlAs0.16Sb0.84∕InAs, the electron mobilities were as high as 420000cm2∕Vs at 77K and 31000cm2∕Vs at 300K. The free carrier concentration of InAs grown with H-plasma assistance is larger than that of the sample grown without, indicating the H plasma yields a much lower compensation ratio γ(γ=(NA+ND)∕n), and moreover, the H plasma is more effective in passivating acceptors than donors in InAs. The mobility and free carrier concentration were both unchanged after thermal annealing, which are advantageous for device processing.
Optical characterization of In0.27Ga0.73Sb and InxAl1−xAsySb1−y epitaxial layers for development of 6.2-Å-based heterojunction bipolar transistors
Authors: Glaser E. R. , Magno R. , Shanabrook B. V. , Tischler J. G.
Published: June 2006

Low temperature photoluminescence (PL) has been employed to assess the crystalline quality and obtain the band gap energies of (InAs∕AlSb∕GaSb) 6.2-Å-based ternary and quaternary epitaxial layers grown by molecular beam epitaxy. These alloys are employed in low power, high frequency heterojunction bipolar transistors. Strong emission between 0.5 and 1.1eV attributed to band edge recombination was observed from In0.27Ga0.73Sb and InxAl1−xAsySb1−y layers deposited on both GaSb and GaAs substrates with the best material obtained for substrate temperatures between 350 and 400°C. The PL energies observed for the InAlAsSb epitaxial films are ∼300meV less than the band gaps predicted for this system. Most notably, a much higher bowing parameter value (∼1.8eV) is required to model the dependence of the InAlAsSb PL energies on alloy composition.
cw midinfrared “W” diode and interband cascade lasers
Authors: Canedy C. L. , Bewley W. W. , Kim C. S. , Kim M. , Lindle J. R. , Vurgaftman I. , Meyer J. R.
Published: June 2006

We studied the I-V characteristics, lasing thresholds, and wall plug efficiencies of type-II “W” mid-IR diode lasers from 16 different wafers. At T=90K, the wall plug efficiency for a 1-mm-long gain-guided device was >10% and the slope efficiency was 142mW∕A (38% external quantum efficiency). When a 22-μm-wide ridge was lithographically defined on a five-period W with ap-GaSb etch stop layer, the maximum cw operating temperature increased to 230K. We also investigated ten-stage interband cascade lasers containing W active quantum wells. While the low-temperature threshold current densities were somewhat higher than in the W diodes, at higher temperatures the pulsed thresholds were slightly lower. The threshold voltage was only ≈0.1V larger than the photon energy multiplied by the number of stages, corresponding to a voltage efficiency of >96%, while the differential series resistance-area product above threshold was as low as 0.21mΩcm2 at 100K. At T=78K, the cw slope efficiency was 0.48mW∕A (126% external quantum efficiency), and a maximum cw power of 514mW was produced by an epi-side-up-mounted 2-mm-long laser cavity with uncoated facets.
Gain saturation and carrier distribution effects in molecular beam epitaxy grown GaAsSb∕GaAs quantum well lasers
Authors: Yu S.-Q. , Jin X. , Johnson S. R. , Zhang Y.-H.
Published: June 2006

Ga As Sb ∕ Ga As quantum well (QW) lasers grown by solid source molecular beam epitaxy are fabricated into ridge lasers and tested. These devices have a lasing wavelength around 1.2μm that is substantially blueshifted relative to the electroluminescence peak. The magnitude of the blueshift increases as the cavity length is shortened, indicating that the blueshift increases with injection level. This blueshift is attributed to material gain saturation and band filling effects. The internal quantum efficiency is ∼75%, the transparency current density is ∼120A∕cm2, and the threshold characteristic temperature is ∼60K, all typical for GaAsSb∕GaAs based edge emitting lasers. The extracted gain constant is ∼800cm−1 for single QW active regions and approximately half that amount for double QWs. This discrepancy is attributed to nonuniform carrier distribution in double QW structures.
Molecular beam epitaxy grown 0.6eV n∕p∕n InPAs∕InGaAs∕InAlAs double heterostructure thermophotovoltaic devices using carbon as the p-type dopant
Authors: Wernsman Bernard , Bird Thomas , Sheldon Michael , Link Samuel , Wehrer Rebecca
Published: June 2006

Beryllium (Be) has been previously shown to be an adequate p-type dopant for molecular beam epitaxy (MBE) grown 0.6eV n∕p∕n InGaAs∕InPAs double heterostructure thermophotovoltaic (TPV) devices. However, due to environmental, safety, and health operational concerns caused by airborne exposure to Be during cleaning operations in a MBE system, carbon (C) was investigated as a p-type dopant substitute. However, due to the amphoteric nature of C, it incorporates on the group-III site in InGaAsP material with high P content, making it n type. Therefore, to grow the n∕p∕n InGaAs double heterostructure TPV device, InAlAs was developed as the back surface field (BSF). By using C as the p-type dopant and InAlAs as the BSF, MBE grown 0.6eV n∕p∕n InPAs∕InGaAs∕InAlAs double heterostructure TPV devices were successfully made. The demonstrated room temperature reverse saturation current density (j0) value from this MBE grown device was ∼9μA∕cm2. This j0 value was only three times larger than the previous best MBE grown 0.6eV n∕p∕n InGaAs∕InPAs double heterostructure TPV device using Be as the p-type dopant. Internal quantum efficiency evidence suggested that, by improving the base/BSF interface for the device having the InAlAs BSF and C p-type doping, j0 values lower than the previous best MBE grown TPV material were possible. Therefore, C was found to be a promising alternative to Be in 0.6eV n∕p∕n InPAs∕InGaAs∕InAlAs double heterostructure TPV devices.
Carbon-doped high-mobility hole gases on (001) and (110) GaAs
Authors: Gerl C. , Schmult S. , Wurstbauer U. , Tranitz H.-P. , Mitzkus C. , Wegscheider W.
Published: June 2006

Since Stormer and Tsang have introduced the two-dimensional hole gas (2DHG) in the GaAs∕AlGaAs heterosystem, the choice of suitable dopants was limited to beryllium and silicon over the last 20years. Both acceptor atoms have significant disadvantages, i.e., either high diffusion rates or a limitation to specific growth directions. Utilizing a carbon filament doping source we prepared high-quality 2DHGs in the (001) and the nonpolar (110) crystal plane with carrier mobilies beyond 106cm2∕Vs in quantum-well and single-interface structures. Low temperature magnetoresistance measurements recover a large number of fractional quantum Hall effect states and show a pronounced beating pattern from which the Rashba-induced spin splitting has been determined. In addition, 2DHGs have been grown on cleaved edges of (110) and (001) wafers with transport features in qualitative agreement with our findings on (110) substrates.
Reaction of molecular beam epitaxial grown AlN nucleation layers with SiC substrates
Authors: Hoke W. E. , Torabi A. , Hallock R. B. , Mosca J. J. , Kennedy T. D.
Published: June 2006

GaN high electron mobility transistor (HEMT) structures containing AlN nucleation layers were grown on SiC substrates by molecular beam epitaxy. Deleterious charge is observed near the GaN∕AlN interface when the AlN layer is grown using aluminum-rich growth conditions which promote AlN material quality. The unwanted charge is correlated with nondestructive mercury probe buffer leakage measurements and degraded capacitance-voltage profiles. Secondary ion mass spectrometry measurements on a HEMT structure with a thick AlN layer grown aluminum rich confirm that the unintentional dopant is silicon which rapidly migrates through the AlN layer to the GaN buffer layer. Leakage current measurements on aluminum-rich AlN layers indicate that the conduction is in the initial GaN layers near the GaN∕AlN interface. It is proposed that under aluminum-rich conditions the excess aluminum present on the growth surface in the liquid state is reacting with the substrate surface resulting in dissolved silicon that rapidly travels with the growth surface. Thermodynamic calculations and aluminum-silicon phase diagrams support this mechanism. By careful adjustment of the aluminum to nitrogen flux ratio, silicon outmigration is significantly reduced with a concomitant reduction in leakage current by four orders of magnitude.
Hydrogen limited nitrogen incorporation in III-V dilute nitrides grown by rf nitrogen plasma assisted chemical beam epitaxy
Authors: Fotkatzikis A. , Freundlich A.
Published: June 2006

We present a study on the impact of hydrogen upon the growth mode and structural and optical properties of GaAsN epilayers. Samples studied in this work were grown on (001) GaAs by radio frequency plasma assisted chemical beam epitaxy, at 445–455°C, with the epilayer thickness maintained below the critical onset for lattice relaxation. Hydrogen interaction with the nitrogen plasma source was monitored in real time using optical spectroscopy while the evolution of the growth mode was examined using reflection high-energy electron diffraction. Small quantities of hydrogen were introduced independently in the growth chamber and the increase of background H pressure was directly correlated with an increase of the 656nm line in the plasma spectrum, and altered the growth mode (e.g., 2×4–2×1 at T=455°C). X-ray diffraction analyses indicate an apparent drop in the nitrogen composition for samples fabricated with excess hydrogen. In addition, the later samples exhibit a blueshift of their band gap (beyond the one associated with the apparent composition drop) and a significant (∼20-fold) degradation of their low temperature photoluminescence signal.
Reactive ion etch damage on GaN and its recovery
Authors: Fan Qian , Chevtchenko S. , Ni Xianfeng , Cho Sang-Jun , Yun Feng , Morkoç Hadis
Published: June 2006

Surface properties of GaN subjected to reactive ion etching and their impact on device performance have been investigated by transport, optical, and surface potential measurements. Different etching conditions were studied to minimize plasma-induced damage. Higher etch rates could be obtained at high powers and low pressures, with the accompanying roughening of the surface. Surface potential for the as-grown samples was found to be in the range of 0.5–0.7V using scanning Kevin probe microscopy. However, after etching at a power level of 300W, the surface potential decreased to 0.1–0.2V. An almost linear reduction was observed with increasing power. Additionally, the intensity of the near band edge photoluminescence decreased and the free carrier density increased after etching. These results suggest that the changes in the surface potential may originate from the formation of possible nitrogen vacancies and other surface oriented defects. To recover the etched surface, N2 plasma, rapid thermal annealing, and etching in wet potassium hydroxide were performed. For each of these methods, the surface potential was found to increase by 0.1–0.3V, also the reverse leakage current in Schottky diodes, fabricated on treated samples, was reduced considerably compared with as-etched samples, which implies a partial to complete recovery from the plasma-induced damage.
Monte Carlo simulation of process parameters in electron beam lithography for thick resist patterning
Authors: Zhou Jianyun , Yang XiaoMin
Published: June 2006

To better understand the proximity effect of electron-beam lithography and its limitation on aspect ratios in a thick resist film (>1.0μm), the simulation of isolated trench patterning has been performed using the Monte Carlo simulation software SELID™. Various key process parameters, including beam energy, exposure dose, substrate, acid diffusion length, and development time have been analyzed by means of the point-spread function, secondary electron distribution, energy distributions, and developed resist profiles. Exposure dose and development time are optimized to achieve vertical sidewalls, and the acid diffusion length has been adjusted to slightly change the top and bottom dimensions of the patterned trench. The simulation results show that increasing the beam energy significantly reduces the forward proximity effect and thereby increases the trench aspect ratio. In contrast, the substrate generally has only a minor effect in terms of the resist profile because its backscattering effect covers a long range up to 10.0μm from incident point (50keV). The achievable maximum aspect ratio for a given resist thickness was found to scale approximately linearly with beam energy. The aspect ratio in a 1.0μm thick resist film increased from 3:1 to 20:1 as the beam energy was increased from 10to100keV, and from 5:1 to 10:1 for a 4.0μm resist film as the beam energy was increased from 50to100keV. Finally, experimental data using a 50keV Leica e-beam writing tool is presented, and they agree with the results from our simulations.
Visible light photocatalysis with nitrogen-doped titanium dioxide nanoparticles prepared by plasma assisted chemical vapor deposition
Authors: Buzby S. , Barakat M. A. , Lin H. , Ni C. , Rykov S. A. , Chen J. G. , Ismat Shah S.
Published: June 2006

Nitrogen-doped TiO2 nanoparticles were synthesized via plasma assisted metal organic chemical vapor deposition. Nitrogen dopant concentration was varied from 0to1.61at.%. The effect of nitrogen ion doping on visible light photocatalysis has been investigated. Samples were analyzed by various analytical techniques such as x-ray diffraction, transmission electron microscopy, x-ray photoelectron spectroscopy, and near-edge x-ray absorption fine structure. Titanium tetraisopropoxide was used as the titanium precursor, while rf-plasma-decomposed ammonia was used as the source for nitrogen doping. The N-doped TiO2 nanoparticles were deposited on stainless steel mesh under a flow of Ar and O2 gases at 600°C in a tube reactor. The photocatalytic activity of the prepared N-doped TiO2 samples was tested by the degradation of 2-chlorophenol (2-CP) in an aqueous solution using a visible lamp equipped with an UV filter. The efficiency of photocatalytic oxidation of 2-CP was measured using high performance liquid chromatography. Results obtained revealed the formation of N-doped TiO2 samples as TiO2−xNx, and a corresponding increase in the visible light photocatalytic activity.
Data processing system for maskless lithography toward 65nm node and below
Authors: Hoshino Hiromi , Machida Yasuhide
Published: June 2006

Multiple-beam and multiple-column exposure systems in maskless lithography tools are expected to significantly increase exposure throughput. However, the throughput performance obtained from a multiple-beam exposure system using vector writing did not improve as much as could be expected based on the number of beams. This is because the movement speed of a stage is determined by the maximum number of shots in each area to which multiple simultaneously emitted beams are deflected. We found that actual chips have a great variation in this number of shots, and that this variation halves the high throughput efficiency provided by multiple beams. Our proposed data processing system can provide high exposure throughput by controlling variations in the numbers of shots in the unit areas exposed to multiple beams emitted simultaneously, and suppresses these variations to an extremely low level. It succeeds in making throughput performance proportional to the number of beams by creating exposure data for the multiple-beam exposure system.
Ultrahigh-aspect-ratio SiO2 deeply etched periodic structures with smooth surfaces for photonics applications
Authors: Hosomi K. , Kikawa T. , Goto S. , Yamada H. , Katsuyama T. , Arakawa Y.
Published: June 2006

One-dimensional SiO2 deeply etched periodic structures were fabricated. The fabrication process was based on an anisotropic Si etching, followed by a direct oxidation of the etched Si structure. The obtained submicron-scale SiO2 periodic structure had an ultrahigh aspect ratio of 16 for the etched space and an etching depth of as large as 12.5μm. The etched depth was limited only by the etching mask. Therefore, increasing the mask thickness, or replacing it with a much harder mask material, should result in a much larger aspect ratio and etching depth. This structure also had an excellent vertical profile of less than 0.5° and extremely smooth surfaces of only 0.6nm rms suitable for use in various applications, particularly in photonics fields that require a broad band performance, ranging from ultraviolet to near infrared.
Growth and characterization of a high-purity ZnO nanoneedles film prepared by microwave plasma deposition
Authors: Lin Tien-Chih , Wang Chih-Yuan , Chan Lih-Hsiung , Hsiao Da-Qing , Shih Han C.
Published: June 2006

A high-density crystalline ZnO nanoneedles film (∼5μm thick) has been fabricated using a microwave plasma enhanced chemical vapor deposition apparatus. The nanostructures and properties were examined by scanning electron microscopy, high resolution transmission electron microscopy, and x-ray diffraction. The results indicated that the ZnO nanoneedle possesses a wurtzite structure (hexagonal) with lattice constants of a0=3.24Å and C0=5.19Å, and an average length up to 5μm, while the diameters of the tip and the pillar of the nanoneedle are of ∼30 and ∼300nm, respectively. The film density reaches ∼1011cm−2. The room-temperature photoluminescence spectrum reveals a strong and sharp near-UV emission band at 386nm and exhibits a very weak deep-level emission, which implies the high-purity nature of the ZnO nanoneedles film. The high specific surface of ZnO nanoneedles film has potential applications in chemical sensors while the excitation property has optoelectronic and photochemical applications.
Controlling interface reactivity and Schottky barrier height in Au∕ZnSe(001) junctions
Authors: Pelucchi E. , Kumar D. , Lazzarino M. , Rubini S. , Franciosi A.
Published: June 2006

Transport studies of patterned Au∕ZnSe(001) contacts fabricated by molecular beam epitaxy reveal substantial lateral inhomogeneities in the Schottky barrier height. The x-ray photoemission results provide evidence of chemical reactions at a number of preferential surface sites. Incorporation of ultrathin Zn interlayers between the ZnSe substrate and the Au overlayer decreases the value of the n-type Schottky barrier height from 1.62to1.05eV and eliminates all evidence of lateral inhomogeneities in the barrier height. The interlayer-induced Schottky barrier tunability is found to be primarily limited by Zn–Au alloying within the overlayer.
Nanostructure evolution of YBa2Cu3Ox thin films grown by pulsed-laser glancing-angle deposition
Authors: Wang Huan-hua , Zhao Yi-Ping
Published: June 2006

Nanostructured thin films of amorphous YBa2Cu3Ox were prepared using pulsed-laser glancing-angle deposition. Ambient oxygen pressure and laser fluence have a strong effect on the microstructure of the films. The films exhibit a structural evolution from isolated directional nanorods, through a network of vertical nanocolumns, to nanoparticles fractal with increasing ambient oxygen pressures from below 1 to above 180mtorr. The shadowing effect, surface diffusion, and flux scattering by ambient gas play main roles in determining the structural evolution.
Lithographic characterization of the flare in the Berkeley 0.3 numerical aperture extreme ultraviolet microfield optic
Authors: Cain Jason P. , Naulleau Patrick P. , Gullikson Eric M. , Spanos Costas J.
Published: June 2006

Flare remains a crucial issue for extreme ultraviolet (EUV) lithography. Achieving required flare levels demands mid-spatial-frequency surface roughness levels on the order of 1Å, which is on par with present metrology limits. Lithographic verification of predicted flare levels is thus critical to the validation of current metrology methods. In this work we present the lithographic characterization of flare in the Berkeley EUV microfield exposure tool. Experimental analysis shows good agreement between predicted and measured results. The results also show that it is essential to compensate for proximity and die-to-die effects. In an isolated microfield, flare values of 6.8% and 4.8% in 500nm and 2μm lines, respectively, have been verified.
Directed growth of horizontal silicon nanowires by laser induced decomposition of silane
Authors: Abed H. , Charrier A. , Dallaporta H. , Safarov V. , Jamgotchian H. , Tonneau D.
Published: June 2006

We present an original method to force the horizontal growth of silicon nanowires by laser assisted chemical vapor deposition of silane. The Ar+ laser beam, tightly focused on the absorbing sample, induces a local thermal horizontal gradient over the laser spot area, which determines the growth direction of the nanowires (NWs). The reaction of formation of Si NWs occurs via the vapor-liquid-solid process, when gold particles are spread on the surface to catalyze the reaction. The effect of laser power (i.e., of laser induced local temperature) and silane pressure on the morphology of the nanowires is presented.
Fabrication and characteristics of P-channel silicon-oxide-nitride-oxide-silicon flash memory device based on bulk fin shaped field effect transistor structure
Authors: Cho Il Hwan , Park Tai-Su , Choe Jeong Dong , Cho Hye Jin , Park Donggun , Shin Hyungcheol , Park Byung-Gook , Lee Jong Duk , Lee Jong-Ho
Published: June 2006

A p-channel silicon-oxide-nitride-oxide-silicon (SONOS) flash memory device based on bulk fin shaped field effect transistor (FinFET) structure was fabricated and characterized as a highly scalable device structure. Key process steps were explained in detail and electrical characteristics were measured. The threshold voltage shift (ΔVth) was checked in the proposed device with the source/drain floating and grounded. This result means that the proposed device structure can be applicable to NAND and NOR flash memories. In this structure, program/erase times can be controlled by fin body width, which is the unique parameter of FinFET structure. In the endurance test, about 1.3V of the ΔVth was kept until 104P∕Ecycles. The ΔVth of the proposed flash memory device was extrapolated to about 0.5V after 10y retention. The ΔVth with crystal orientation of the side-channel also was checked.
Ion and neutral transportation consideration in etching of thin Si3N4 in high aspect ratio structures for aspect ratio independent etching
Authors: Bai K. H. , Chi K. K. , Kim M. C.
Published: June 2006

We investigate the reactive ion etching (RIE) lag or aspect ratio dependent etching in etching of a thin Si3N4 layer in the regime of relatively low ion bombardment energy. The surface reaction is studied through the transportation of ions and radicals in high aspect ratio holes. The radical transportation is studied in the regime that the radical concentration is low and the ion flux is saturated. The key parameter for the radical transportation is the high substrate temperature, where radicals can reach the hole bottom, easily resulting in high surface coverage. On the other hand, in a regime of saturated surface coverage with abundant radicals, the ion flux is the reaction limiting parameter for the RIE lag. The comparison of RIE lag with the surface coverage shows that the transportation of depositive radicals is more sensitive to the temperature. Finally, in the range where the neutral and ion fluxes are balanced, we achieved a result of aspect ratio independent etching in a structure with an aspect ratio higher than 13:1.
dc thermal plasma synthesis and properties of zinc oxide nanorods
Authors: Liao Shih-Chieh , Lin Hsiu-Fen , Hung Sung-Wei , Hu Chen-Ti
Published: June 2006

In this research, a dc thermal plasma reactor was used to produce ZnO nanorods with a diameter of about 30nm and a length of 100–200nm. In the photocatalytic study, visible light absorption of the ZnO nanorods was achieved by doping up to a few thousands ppm of nitrogen. The nitrogen-doped ZnO nanorods under the visible light radiation exhibited excellent antimicrobial ability. UV-visible spectroscopy of the N-doped ZnO nanorods annealed in a reductive atmosphere revealed a strong absorption of near-IR light starting at around 1μm, which is attributed to the effect of plasmon resonance. Room-temperature photoluminescence spectroscopy of the N-doped ZnO nanorods showed an UV emission peak at 380nm, a green emission peak at 520nm, and a weak near-IR emission peak at 760nm. The UV emission was assigned to the near band-edge emission, while the green and the near-IR emissions corresponded to the deep-level emission from different defects. In addition, we found that photoluminescent characteristic of the ZnO nanorods depends strongly on the synthesis and annealing atmospheres. Finally, discrete UV lasing modes were observed in the random-packed ZnO nanorods at room temperature. This may be attributed to recurrent light scattering that provides coherent feedback for lasing.
Multistep fabrication of self-assembled unstrained quantum dashes
Authors: Ukhanov A. A. , Bracker A. S. , Boishin G. , Culbertson J. C.
Published: June 2006

We describe a technique for molecular-beam-epitaxy-based fabrication of unstrained quantum dashes with AlxInyGa1−x−yAs alloys lattice matched to InP substrates. Templates for lattice-matched quantum dash growth are obtained by combining molecular beam epitaxy with in situ etching by arsenic bromide. A seed layer of strained self-assembled InAs quantum dashes is converted into nanotrench templates through overgrowth followed by strain-enhanced etching. We have explored limitations on the accessible range of alloy compositions imposed by the etch process and found that strain-induced etching is limited to compounds with low Al content. Nanotrench templates can be filled with lattice-matched alloys of varied compositions to define barriers and quantum wires that could lead to optoelectronic devices in a spectral range around 1.5μm.
Development of 6.00Å graded metamorphic buffer layers and high performance In0.86Al0.14As∕In0.86Ga0.14As heterojunction bipolar transistor devices
Authors: Cavus A. , Sandhu R. , Monier C. , Cox C. , Pascua D. , Gutierrez-Aitken A. , Noori A. , Hayashi S. , Goorsky M.
Published: June 2006

In x Al 1 − x As ∕ In x Ga 1 − x As heterojunction bipolar transistors (HBTs) with lattice parameters ranging from 6.00to6.058Å employing the use of narrow band gap InxGa1−xAs base epitaxial layers toward InAs (0.86<Xln<1) allows for the development of high speed digital and mixed signal circuits to perform at half the power required for conventional group III-V-based HBT device technologies. However, one of the key challenges inhibiting the development of low power narrow band gap HBT device circuits is the absence of semi-insulating (SI) substrates with lattice parameters towards 6.058Å. Therefore, a metamorphic InxAl1−xAs (0.52<Xln<0.86) graded buffer layer (GBL) grown on InP by molecular beam epitaxy was investigated as a means to enable a SI template with a lattice parameter of 6.00Å. The metamorphic InxAl1−xAs GBL thickness is desired to be less than a micron in order for this approach to be compatible with the aggressive design rules of high-density transistor circuits. In this study, In0.86Al0.14As∕In0.86Ga0.14As double heterojunction bipolar transistor devices were grown on 0.90, 0.45, and 0.23μm thick InxAl1−xAs GBLs to assess the role of buffer layer thickness on both defect formation and device performance. The material characterization results for the 0.90 and 0.45μm thick buffer layers exhibited a crosshatch pattern with a surface rms roughness of 4nm and threading dislocation densities of ∼106cm−2. Excellent dc and rf characteristics from metamorphic HBT devices with submicron emitter widths were observed with low turn-on voltage of 0.45V, high current gain, low reverse junction leakage(<1μA), and rf peak performance in the vicinity of 150GHz. Finally, preliminary circuits (dividers and delay chains) have been designed, fabricated, and demonstrated with the 6.00Å HBT technology.
Growth mechanism and diffusion barrier property of plasma-enhanced atomic layer deposition Ti–Si–N thin films
Authors: Park Jin-Seong , Kang Sang-Won , Kim H.
Published: June 2006

Ti–Si–N thin films were deposited by plasma-enhanced atomic layer deposition from TiCl4, SiH4, and N2∕H2∕Ar plasma at 350°C. For comparison, TiN plasma-enhanced atomic layer deposition (PEALD) was also performed from TiCl4. The effects of growth parameters on film properties were studied. Especially, the changes in sequences of precursor-reactant exposure steps were found to produce large change in the growth rates and Si concentration in the films. The results are discussed based upon the molecule-surface reaction mechanisms. Also, the Cu diffusion barrier properties of the PEALD Ti–Si–N films were investigated. PEALD Ti–Si–N films have shown better diffusion barrier properties than PEALD TiN films and can be a promising candidate for future Cu interconnect technology beyond 65nm technology node.]
Oxidation of silicon nanowires
Authors: Shir D. , Liu B. Z. , Mohammad A. M. , Lew K. K. , Mohney S. E.
Published: June 2006

Silicon nanowires have received attention for nanoscale electronic devices and chemical and biological sensors. The thermal oxide grown on the silicon nanowires could be used in a variety of devices, so the oxidation of the silicon nanowires is investigated in this work. Silicon nanowires with an average radius of 37nm were grown for these experiments using the vapor-liquid-solid technique with Au to mediate the growth. Etching of the Au tips from the silicon nanowires was performed prior to oxidation to avoid local accelerated oxidation at the nanowire tip. Oxidation was performed at 700°C for 1–121h and at 650 and 750°C for 4h in O2, and the oxidized nanowires were examined by transmission electron microscopy. Depending on the conditions for oxidation, an oxide shell as thin as 6nm was observed, or the entire nanowire was oxidized. The kinetics of oxidation differ from those of a planar silicon wafer and are discussed in this work.
Interface configuration and Fermi-level pinning of fully silicided gate and high-K dielectric stack
Authors: Joo Moon Sig , Park Chang Seo , Cho Byung Jin , Balasubramanian N. , Kwong Dim-Lee
Published: June 2006

Metal-induced gap states (MIGS) theory is applied to fully silicided (FUSI) gate for the investigation of Fermi-level pinning at the interface of FUSI gate and high-K dielectrics. Using the combination of semiempirical approach and MIGS theory, it has been found that FUSI gate has effectively MSi2 configuration at the interface with gate dielectrics. The vacuum work function values of several FUSI gates have been obtained through the analysis, and it has also been found that the Fermi-level pinning behavior of FUSI gate on high-K dielectric follows the MIGS theory well. FUSI gate on high-K dielectric shows much weaker Fermi-level pinning compared with polysilicon gate on high K dielectric, which is another attractive advantage of FUSI gate process.