bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrogen redistribution in SiO2 under ion bombardment
Authors: Banerjee Indrajit , Kuzminov Dimitry
Published: July 2002

Secondary ion mass spectrometry (SIMS) and electron spectroscopy for chemical analysis were used to study SiO2/Si3N4/SiO2 (ONO) structures. The purpose was to determine if the nitrogen tail seen going into the silicon substrate was real or an artifact of ion bombardment. To determine this without an element of doubt, samples were thinned from the backside to the ONO layer and SIMS depth profiling was carried out on the exposed underside of ONO. Profiling from the backside shows there is no nitrogen tail in the silicon substrate and there is no nitride at the oxide/Si interface, as seen from front side profiling. The effects seen during profiling from the front side are due to anomalous diffusion of nitrogen caused by ion bombardment. It is believed that nitrogen–oxygen complexes are formed in the silicon substrate as a result of nitridation, and this adversely affects device performance. Though this may still be true, one needs to be cautious in interpreting SIMS and Auger depth profiles from the front side in order to corroborate the electrical results.
Scanning tunneling microscopy of InAs/GaSb superlattices: Subbands, interface roughness, and interface asymmetry
Authors: Feenstra R. M. , Collins D. A. , Ting D. Z.-Y. , Wang M. W. , McGill T. C.
Published: July 2002

Scanning tunneling microscopy and spectroscopy is used to characterize InAs/GaSb superlattices, grown by molecular-beam epitaxy. Roughness at the interfaces between InAs and GaSb layers is directly observed in the images, and a quantitative spectrum of this roughness is obtained. Electron subbands in the InAs layers are resolved in spectroscopy. Asymmetry between the interfaces of InAs grown on GaSb compared with GaSb grown on InAs is seen in voltage-dependent imaging. Detailed spectroscopic study of the interfaces reveals some subtle differences between the two in terms of their valence-band onsets and conduction-band state density. These differences are interpreted in a model in which the GaSb on InAs interface has an abrupt InSb-like structure, but at the InAs on GaSb interface some Sb grading occurs into the InAs overlayer.
Structural and electronic properties of an organic/inorganic semiconductor interface: PTCDA/GaAs(100)
Authors: Hirose Y. , Chen W. , Haskal E. I. , Forrest S. R. , Kahn A.
Published: July 2002

A study of the formation of an interface between the archetype organic semiconductor, 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA), and GaAs(100) is presented. We examine the growth of thin (few monolayers) and thick (up to 3000 Å) organic layers are examined at room and low temperature, and conclude that bonding across the PTCDA/GaAs interface is stronger than the PTCDA van der Waals intermolecular bond. Although the molecular stacking distance of 3.21 Å is clearly seen in x-ray diffraction, the films are polycrystalline, and no interface molecular ordering is detected. The interface electronic structure and the energy band lineup are studied with photoelectron spectroscopy. The highest occupied molecular orbital in PTCDA is found at 0.7 eV below the top of the GaAs valence band, in agreement with a vacuum level alignment a this interface.
Biological materials studied with dynamic force microscopy
Authors: Anselmetti D. , Dreier M. , Lüthi R. , Richmond T. , Meyer E. , Frommer J. , Güntherodt H.-J.
Published: July 2002

Biological materials such as hexagonal packed intermediate (HPI) layers, DNA, tobacco mosaic virus and collagen deposited on various substrates with noncontact dynamic force microscopy under ambient conditions were investigated. This method is highly suited for the investigation of soft organic matter where a minimized interaction between tip and sample is needed for nondestructive and reliable operation. Hence, additional anchoring of the biological specimens was no longer found to be crucial. The vertical and lateral resolution limits of this gentle method were determined to be <0.1 nm and 1–2 nm, respectively, allowing very stable and high resolution results on all investigated systems. By taking approach curves and monitoring the dynamic properties of the cantilever (resonance frequency and Q value) during the experiment, the interaction mechanism between tip and sample was found to be dominated by attractive van der Waals interaction and capillary forces. Furthermore, initial results from a HPI layer imaged with noncontact dynamic force microscopy in a water environment are presented.
Threading dislocations in GaAs grown with free sidewalls on Si mesas
Authors: Knall J. , Romano L. T. , Krusor B. S. , Biegelsen D. K. , Bringans R. D.
Published: July 2002

We have studied the mechanisms that determine the density and structure of threading dislocations (TDs) in GaAs on Si by growing GaAs films on continuous Si substrates and on 10–34-μm-wide Si mesas that provided free-sidewall growth. The effects of a soft ZnSe interlayer and of postgrowth annealing to 850 °C were also investigated. TD densities were accurately determined using large area plan-view transmission electron microscopy. Burgers vector analysis of the TDs showed that threading segments associated with both sessile 90° misfit dislocations and glissile 60° misfit dislocations were present after growth. A difference in dislocation structure between the annealed and unannealed samples was observed. It was also found that the dislocations were unaffected by proximity to free sidewalls and by the ZnSe interlayer. The results indicate that dislocation interactions during the early stages of growth determine the structure and density of TDs in as-grown films. It was also concluded that plastic relaxation of thermal mismatch strain during cooldown from the growth temperature does not strongly affect the TD density in the films. This is in contradiction to previous studies.
Deep-ultraviolet damage to fused silica
Authors: Schenker Richard , Schermerhorn Paul , Oldham W. G.
Published: July 2002

Several experiments using 213-nm radiation have been performed with the goals of characterizing and understanding better the mechanisms behind UV damage to fused silica. A novel method of monitoring compaction in real time was discovered which measures the amount which the damaged fused silica depolarizes the incident beam. Refractive index changes of less than one part in ten million were resolved. Compaction induced stress was observed to extend well beyond the irradiation site with a maximum at the edge of the irradiation site. Detection of compaction occurred much earlier than the detection of color center absorption when fused silica was irradiated. The rates of both compaction and of color center formation depend superlinearly on pulse energy density and can be fitted by a quadratic function, suggesting a two-photon damage process. In the same energy density range, the absorption coefficient depends linearly on energy density, from which we extract a 213-nm two-photon absorption coefficient of 5×10−4 (cm/MW). This value is a factor of 4 smaller than the value published for 193 nm [R. S. Taylor et al., Appl. Opt. 27, 3124 (1988)].
Fabrication of atomic-scale metallic microstructures by retarding-field focused ion beams
Authors: Woodham R. G. , Ahmed H.
Published: July 2002

Atomic-scale metallic microstructures have been deposited on various semiconductor substrates. A retarding-field method is used to form a low-energy, focused beam of Au ions from a liquid metal alloy source. The ions were deposited with landing energies down to 20 eV to form ultrathin films. The microstructure of the ultrathin films was found to be metallic islands, the smallest of which are 1 nm or less. The microstructure on a GaAs substrate displayed a high degree of size and spacing regularity. The technique was used as a method to fabricate nanometer-scale islands in a multiple-junction Coulomb blockade device.
Scanning tunneling microscopy study of the adsorption of C60 molecules on Si(100)-(2×1) surfaces
Authors: Chen Dong , Gallagher Mark J. , Sarid Dror
Published: July 2002

Scanning tunneling microscopy has been used to investigate the adsorption of C60 molecules on Si(100)-(2×1) surfaces at various deposition temperatures. At room temperature, submonolayers of C60 molecules experienced limited surface diffusion and randomly adsorbed to sites between dimer rows. At 650 °C, the C60 exhibited increased diffusion and preferentially adhered to step edges, and defects, or bonded to the top of the dimer rows. At low coverage, a strong interaction between the C60 and Si was evidenced by increased defect density which included the local atomic rearrangement in the vicinity of the C60 molecules. Higher coverage created a substantial concentration of defects which induced Si(100)-c(4×4) reconstruction. At 750 °C, the C60 molecules decompose and react with the Si surface forming islands of SiC and C60–Six species.
Scanning tunneling microscopy of argon-ion bombarded GaAs (001) surfaces
Authors: Ohkouchi Shunsuke , Ikoma Nobuyuki , Tanaka Ichiro
Published: July 2002

The atomic structures of argon-ion bombarded GaAs (001) surfaces were investigated using in situ scanning tunneling microscopy (STM). The experiments were conducted in an ultrahigh vacuum multichamber system equipped with a STM, a molecular beam epitaxy facility, as well as an argon-ion gun. MBE-grown GaAs surfaces were bombarded by argon ions of 500 eV at doses of ∼1013 ions cm−2, and the resulting surface structures were examined by a STM. In the STM images, most of the defects produced by the argon-ion bombardment were about 1.6 nm wide in the [110] direction. This result seems to suggest that the interaction of surfaces with argon ions during the bombardment took place in a (2×4) unit cell; that is, all of the three arsenic dimers of a (2×4) unit cell in the bombarded regions were taken away as if they comprised a single unit of interaction. The average defect density increased with increasing argon-ion dose.
Ballistic-electron emission microscopy on the Au/n-Si(111)7×7 interface
Authors: Cuberes M. T. , Bauer A. , Wen H. J. , Vandré D. , Prietsch M. , Kaindl G.
Published: July 2002

Ballistic-electron emission microscopy (BEEM), performed under ultrahigh vacuum conditions at the room-temperature-grown Au/n-Si(111)7×7 interface, allows a measurement of the BEEM current for tip biases up to ≊ 8 V without a noticeable change in ballistic transmissivity. The differences of the present results to previous reports, where either no BEEM current was observed or the transmissivity was modified when applying high tip voltages, can be explained by the absence of intermixing at the Au/Si interface. Scanning tunneling microscope images of ≊40-Å-thick Au films reveal a characteristic topography of the metal surface with ≊2.5 Å high circular terraces stacked in up to four stages.
Electrical properties of blue/green diode lasers
Authors: Fan Y. , Grillo D. C. , Ringle M. D. , Han J. , He L. , Gunshor R. L. , Salokatve A. , Jeon H. , Hovinen M. , Nurmikko A. V. , Hua G. C. , Otsuka N.
Published: July 2002

In this paper we report the implementation of low resistance ohmic contacts to p-type ZnSSe and ZnMgSSe which involves the injection of holes from heavily doped ZnTe into an adjacent alloy layer(s) via graded band gap regions. Temperature-dependent Hall effect measurements on nitrogen-doped Zn(S,Se) and (Zn,Mg)(S,Se) were performed and the activation energy of nitrogen acceptors was obtained. With the use of this graded contact, room-temperature continuous-wave laser diode operation has been achieved at a threshold voltage of 5.8 V in a ZnCdSe/ZnSSe/ZnMgSSe separate confinement heterostructure.
Effects of interface flatness and abruptness on optical and electrical characteristics of GaAs/AlGaAs quantum structures grown by metalorganic vapor phase epitaxy
Authors: Shinohara Masanori , Yokoyama Haruki , Inoue Naohisa
Published: July 2002

Heterointerface flatness and abruptness of GaAs/AlGaAs quantum wells are controlled during metalorganic vapor phase epitaxy (MOVPE). Various growth modes such as two-dimensional (2D) nucleation, step flow, and step bunching are achieved by changing the growth temperature and substrate surface misorientation angle. The degree of monolayer step smoothness and ordering are also changed. The effects of these nanometer-scale morphologies and interface abruptness on the full width at half maximum (FWHM) of 4.2-K photoluminescence spectra from quantum wells (QWs) are individually determined. The FWHM is increased in order by degraded interface abruptness, step roughness, multisteps, and 2D islands. Effective thickness variations introduced by these features are roughly ≳2.0, 1.0, 0.6, and 0.2 monolayers (ML), respectively, for 7-ML-thick QWs. Some of these effects on current–voltage characteristics of double barrier resonant tunneling diodes (DBRTDs) are also investigated. The factor most strongly affecting the characteristics of DBRTDs is step disordering, that is, a difference in step edge location between the top and the bottom surfaces of barriers. By making this difference smaller than the electron’s de Broglie wavelength using vicinal substrates, we obtain the best negative resistance characteristics ever reported for MOVPE growth.
Ge island formation on Si(111) in solid phase epitaxy studied by medium-energy ion scattering
Authors: Sumitomo K. , Nishioka T. , Ogino T.
Published: July 2002

The formation of three-dimensional Ge islands in solid phase epitaxy is studied by medium-energy ion scattering and atomic force microscopy. When a six-monolayer Ge film on a Si(111) substrate is annealed below 580 °C, many small islands of various heights below 100 Å form on the two-dimensional layer strained by lattice mismatch. After annealing at higher temperatures such as 770 °C, the islands agglomerate to form large islands higher than 100 Å with definite facets. These three-dimensional islands do not relax completely from the lattice mismatch strain; they are compressed horizontally and expanded vertically compared with the ideal Ge bulk crystal. The vertical lattice length is 2.3% longer than the in-plane length.
Magnetic funnels for projection electron lithography
Authors: Saville Gordon F. , Platzman P. M. , Ku Long-Poe
Published: July 2002

Electrons moving in inhomogeneous magnetic fields, which are slowly varying, behave like beads on a string. Because of this a converging magnetic funnel (MF) can be used to reduce an electron image in a way which is physically very different from a conventional lens. We analyze and numerically simulate the trajectories of electrons in a realizable MF. We show that such magnetic configurations are generally capable of projecting and reducing several cm2 images with features in the 0.1 μ range. Distortions are <10−6, there is good depth of focus (≥1 μm), and spot sizes (≤20 nm) are achievable.
Si1−xGex pulsed plasma etching using CHF3 and H2
Authors: Paul D. J. , Law V. J. , Jones G. A. C.
Published: July 2002

Selective reactive ion etching of Si over Si1−xGex and Si1−xGex over Si has been demonstrated by using a modulation-frequency, plasma-etch technique which employs CHF3 and H2 as the etch precursor gases. The selective etch crossover region appears at a modulation frequency of 2–3 Hz for a duty cycle of 50%. It is suggested that the etch selectivity phenomenon arises from the relative ion-assisted and purely chemical components of the radio frequency plasma and decaying plasma afterglow.
Surface preparation of ZnSe by chemical methods
Authors: Liu Lu-Min , Lindauer Greg , Alexander W. Brock , Holloway Paul H.
Published: July 2002

The effects of several chemical treatments on ZnSe surface composition and morphology have been analyzed with scanning electron microscopy and Auger electron spectroscopy. Polycrystalline bulk and thin film ZnSe heteroepitaxed onto GaAs were used. Large variations in the etching rate and surface conditions, such as roughness, contamination, oxides, and stoichiometry, have been observed with different etchants. Contamination by carbon and oxygen was present on all the treated surfaces. Surface oxides could be thinned by dipping in HF or HF/NH4Cl, which did not etch ZnSe. Methanol with 1% bromine etched ZnSe vigorously and selectively, and resulted in a rough surface. A relatively smooth ZnSe surface resulted from etching in NH4OH/H2O2, but excess Se precipitated from this solution to form whiskers. These whiskers could be removed using CS2. No excess Se was found after etching in hot NaOH but a thicker oxide and a pitted, rough surface was observed.  A two stage etch consisting of NH4OH/H2O2 followed by CS2 is recommended for a smooth, near-stoichiometric surface.
Effects of glancing-angle ion bombardment on GaAs(001)
Authors: Labanda J. G. C. , Barnett S. A. , Hultman L.
Published: July 2002

The effect of glancing-angle argon ion energy E (0.5–3.0 keV), dose D (0.3–10×1016 ions cm−2), flux J (0.6–5.9×1013 ions cm−2 s−1), impingement angle φ (6°–30°), and substrate temperature Ts (440–650 °C) on the surface morphology and crystallinity of clean and air-exposed GaAs(001) surfaces was studied. For air-exposed GaAs, the lowest roughness measured by atomic force microscopy was 0.3 nm at D=2.3×1016 ions/cm2, E=1 keV, and φ=15° for Ts=570 °C and an ≊1.5×10−5 Torr As4 overpressure. These conditions provided sufficient sputtering to remove surface contamination, as indicated by streaky, 2×4 reconstructed reflection high-energy electron diffraction patterns and C- and O-free low-energy ion scattering spectra, while avoiding ion damage as judged by cross-sectional transmission electron microscopy. Defect-free epitaxial GaAs layers were grown on the sputter-cleaned substrates. Ion bombardment of clean surfaces showed roughening at larger φ values, but smooth surfaces were maintained for φ=6°. Cross-sectional transmission electron microscopy studies of clean bombarded surfaces showed that ion damage decreased with decreasing D, E, and φ, and no damage was observed over a range of conditions. Sputter yields as a function of energy and φ are reported.
Thermal stability of MoAu and TiPtAu nonalloyed InGaAs contacts
Authors: Wakita A. S. , Moll N. , Rosner S. J. , Fischer-Colbrie A.
Published: July 2002

The thermal stability of nonalloyed Mo/Au and Ti/Pt/Au contacts on n+ InGaAs, ranging in thickness from 3 to 50 nm, was investigated for a heterojunction bipolar process. Layers of highly silicon doped InGaAs were grown on n+ GaAs by molecular beam epitaxy, without a compositionally graded layer between the InGaAs and GaAs. The as-deposited contact resistance exhibits a strong dependence on InGaAs thickness. For In0.5Ga0.5As, as the InGaAs thickness increases from 6 to 20 nm, the contact resistance decreases from 8×10−7 Ω cm2 to as low as 2×10−7 Ω cm2. Ohmic contacts with various InGaAs thicknesses, InGaAs composition, and contact metallurgies were heat treated at 300 °C for times of 2 h or more. The contact resistivity of MoAu on In0.5Ga0.5As contact layers that are thinner than 20 nm shows poor thermal stability, increasing as much as 160% for a 6 nm thick layer of InGaAs. Contacts on a pseudomorphic InxGa1−xAs layer of the same thickness, but with a lower In mole fraction of x=0.35, exhibit better thermal stability, increasing by only 15% in contact resistivity with heat treatment. Stable contacts can also be obtained by making the In0.5Ga0.5As thickness at least 20 nm. Cross-sectional transmission electron microscopy (TEM) of 20 nm InGaAs films heat treated at 300 °C for 2 h reveals a virtually unchanged Mo–InGaAs interface. TEM analysis of TiPtAu contacts shows that the Ti/InGaAs interface and the InGaAs layer thickness become increasingly nonuniform with thicker titanium layers. This physical degradation correlates to an increase in the contact resistivity. The increase in contact resistivity can be minimized by reducing the Ti thickness to 5 nm or less. For extended anneals at 300 °C for accumulated times of 397 h, MoAu on 20 nm of In0.5Ga0.5As demonstrates better stability in contact resistance than Ti (5 nm)/Pt/Au on 20 nm of In0.5Ga0.5As.
Fabrication of thickness-controlled silicon nanowires and their characteristics
Authors: Namatsu Hideo , Takahashi Yasuo , Nagase Masao , Murase Katsumi
Published: July 2002

A process for fabricating thin Si nanowires is proposed which can reduce the parasitic series resistance of the nanowire. The process includes electron cyclotron resonance plasma deposition of a SiO2 film through the openings of a patterned resist film. Since the SiO2 thickness decreases as the opening narrows, the SiO2 film can be made thinnest in the nanowire region. Therefore, during the following reactive-ion etching, the SiO2 film in this region is removed first and the Si layer is then selectively etched. A Si nanowire fabricated through this process shows quantized conductance at temperatures as high as 200 K.
Real-time extraction of growth rates from rotating substrates during molecular-beam epitaxy
Authors: Collins D. A. , Papa G. O. , McGill T. C.
Published: July 2002

We present a method for measuring molecular-beam epitaxy growth rates in near real-time on rotating substrates. This is done by digitizing a video image of the reflection high-energy electron diffraction screen, automatically tracking and measuring the specular spot width, and using numerical techniques to filter the resulting signal. The digitization and image and signal processing take approximately 0.4 s to accomplish, so this technique offers the molecular-beam epitaxy grower the ability to actively adjust growth times in order to deposit a desired layer thickness. The measurement has a demonstrated precision of approximately 2%, which is sufficient to allow active control of epilayer thickness by counting monolayers as they are deposited. When postgrowth techniques, such as frequency domain analysis, are also used, the reflection high-energy electron diffraction measurement of layer thickness on rotating substrates improves to a precision of better than 1%. Since all of the components in the system described are commercially available, duplication is straightforward.
In segregation at the growth front of the GaAs/In0.30Ga0.70As (100) heterojunction
Authors: Williams M. D. , Chiu T. H. , Storz F. G.
Published: July 2002

The strained layer In0.30Ga0.70As/GaAs (100) multiple quantum well system has attracted considerable interest as an amplifier for Er-doped optical fibers at a wavelength of 0.98 μm. In situ ultraviolet photoemission spectroscopy and reflection high energy electron diffraction have been used to study the growth front profile and pseudomorphism of single GaAs/In0.30Ga0.70As heterojunctions. These interfaces were grown by solid source molecular beam epitaxy at different substrate temperatures under As2 overpressure using interrupted and continuous growth mode techniques. The In concentration in the overlayer increases exponentially with temperature in a manner analogous to that of the diffusion constant for equilibrium growth conditions.
Issues of II–VI molecular-beam epitaxy growth toward a long lifetime blue/green laser diode
Authors: Grillo D. C. , Ringle M. D. , Hua G. C. , Han J. , Gunshor R. L. , Hovinen M. , Nurmikko A. V.
Published: July 2002

Although many advances in the field of II–VI laser diodes have been reported since the first demonstrations of II–VI lasers in the summer of 1991, several obstacles still exist along the path towards long-lived II–VI laser diodes. This article will discuss mechanisms which lead to the degradation of the pseudomorphic separate confinement heterostructure laser diodes. Point defects and stacking faults are shown to play an important role in the degradation of these laser diode structures. The importance of controlling the substrate temperature to control the strain will be shown; a method to improve substrate temperature control will be provided.
Novel GaAs photodetector with gain for long wavelength detection
Authors: Harmon E. S. , McInturff D. T. , Melloch M. R. , Woodall J. M.
Published: July 2002

A novel photodetector based upon annealed low temperature molecular beam epitaxy GaAs capable of detecting wavelengths out to 1.5 μm has been developed. The device utilizes a photoconductive detector with a high photo-generated carrier lifetime to transit time ratio in order to achieve a high internal gain. The sensitivity to illumination with photons of sub-bandgap energies is achieved due to the internal photo-emission from the semi-metallic arsenic precipitates. The device exhibits higher gains at lower input powers because the effective carrier lifetime is longer for lower input power levels. This variation in carrier lifetime can be explained in terms of the effectiveness of the arsenic precipitates as recombination centers as a function of optical power levels.
Effects of interface states on submicron GaAs metal–semiconductor field-effect transistors assessed by gate leakage current
Authors: Ahmed M. M. , Ahmed H. , Ladbrooke P. H.
Published: July 2002

The effects of the interfacial oxide layer in Schottky barrier junctions on submicron GaAs metal–semiconductor field-effect transistors (MESFETs) have been investigated. These effects include a shift in threshold voltage and compression in transconductance which can be explained by the current transport theory for the Schottky barrier with an interfacial layer. MESFETs were characterized by direct current measurements and oxide-related degradation was evaluated by measuring the gate leakage current. It has been shown that a gate-length dependent study of threshold voltage and transconductance is only possible if all the devices under consideration have identical Schottky responses. The current through a Schottky barrier appears to flow in a voltage-dependent resistor and the voltage drop across this resistor cannot be neglected when the density of states at the metal–semiconductor interface becomes prominent because it will effectively increase the threshold voltage and reduce the device gain.
Scanning tunneling microscopy induced local deposition of Si or SiHx on Si(111)-(7×7)
Authors: Rauscher H. , Memmert U. , Behm R. J.
Published: July 2002

In search for a method to produce small artificial surface structures, the scanning tunneling microscope (STM) is used for direct local deposition of Si or Si–Hx species from a SiH4 precursor gas on the Si(111)-(7×7) surface. For material deposition, the tip is brought into the field emission regime and the emitted electron beam is utilized for direct proximal probe lithography at room temperature. The SiH4 precursor is activated by electron bombardment from the STM tip with energies from 10 to 100 eV and emission currents of 30 pA up to 20 nA. This produces local accumulation of the dissociation products on the surface just below the tip. Direct writing of nanostructures with lateral dimensions down to 40 nm is accomplished. Structures with a height from ∼0.36 up to 5 nm are presented. Deposition and imaging of the cracking products are carried out with the same tip.
Fabrication of InP/InGaAs quantum wires by free Cl2
Authors: Panepucci R. , Youtsey C. , Turnbull D. A. , Gu S. Q. , Caneau C. , Bishop S. G. , Adesida I.
Published: July 2002

Free Cl2 etching of InP/In0.53Ga0.47As at high temperatures was investigated for the fabrication of nanostructures. The effects of Cl2 flow rate, mask material, and substrate temperature on the sample etch rate, surface morphology, and etch profile are described. The etch profile is found to be temperature dependent for stripes along the crystal directions studied, namely, 〈110〉, 〈11̄0〉, and 〈010〉. The profile was affected by the choice of mask material among Ti and SiO2. The etch characteristics are found to be suitable for controlled etch of quantum wires. The etch technique is compatible with in situ etch and regrowth when SiO2 is used as the etch mask, since InP does not grow on SiO2 surfaces and allows selective regrowth immediately after etching. Quantum well wires (QWWs) with widths as low as 30 nm were fabricated using electron beam lithography and free-Cl2 etching. Low temperature photoluminescence (PL) was used to characterize the QWWs. The normalized PL efficiency of narrow free-Cl2 etched QWWs was found to be higher than that of ion-assisted dry-etched wires and comparable to that of wet-etched wires.
Nanometer-scale pattern formation of GaAs by in situ electron-beam lithography using surface oxide layer as a resist film
Authors: Ishikawa Tomonori , Tanaka Nobuyuki , López Máximo , Matsuyama Isamu
Published: July 2002

We have studied the effects of the microscopic roughness of a GaAs epitaxial surface on the oxide layer, which is used as a resist-mask material in in situ electron-beam lithography. When electron beam patterning, followed by Cl2 gas etching, was carried out for an oxide-mask layer formed on a rough surface, an indented pattern edge elongated along the [11̄0] direction, typically having a size of several tens of nm, was formed. On the other hand, when we used a misoriented substrate in order to obtain a smooth epitaxial surface by introducing the so-called step-flow growth mode, the resulting pattern exhibited a sufficiently sharp edge. Based on this improvement, together with the optimized electron-beam patterning system, we successfully fabricated an ultrafine trench structure with a width as small as 20 nm.
Fabrication of microstructures for studies of electromigration in sub-0.25 μm metal interconnections
Authors: Lee K. Y. , Hu C.-K. , Shaw T. , Kuan T. S.
Published: July 2002

Electromigration test structures consisting of 0.1–0.5-μm-wide and 0.25-μm-thick Al(4%Cu) wires and W contacts have been fabricated on 70-nm-thick Si3N4 membranes using electron-beam lithography and reactive-ion etching. Observation of grain structure evolution with electromigration in these wires by transmission electron microscopy is reported. It is shown that dissolution of Al2Cu grains is accompanied by the growth in neighboring Al grains.
A study of the effect of ultrasonic agitation during development of poly(methylmethacrylate) for ultrahigh resolution electron-beam lithography
Authors: Ryan J. M. , Hoole A. C. F. , Broers A. N.
Published: July 2002

Experiments on poly(methylmethacrylate) electron resist have been performed in order to understand how ultrasonic agitation during development affects sensitivity, contrast, and resolution. A modified JEOL 4000 EX electron microscope with a beam diameter of 1 nm was used for writing the resist patterns. First, the development/exposure characteristics of the ultrasonic development process were measured using large area (2×2 μm) patterns. With a 5 s develop in a mix of 3:7 cellosolve:methanol, it was found that ultrasonic agitation increases the effective sensitivity of the resist by roughly 20% but resist contrast does not change significantly (5.7±0.5). It was also found that the sensitivity increases approximately linearly with accelerating voltage from 75 to 400 kV but contrast does not change with voltage significantly. Resolution was explored by writing fine lines at progressively increasing doses in 60 nm of poly(methylmethacrylate) and examining these lines with high resolution scanning electron microscopy. Complete development to the substrate was verified by wet etching a thin chromium layer underneath the resist. The narrowest lines that developed to the substrate had a width of about 10 nm although at this width considerable ‘‘bridging’’ of the lines was observed. We were unable with the ultrasonic agitation conditions used in our experiments to reduce the degree of bridging or the minimum linewidth.
Structure of epitaxial thin TiOx films on W(110) as studied by low energy electron diffraction and scanning tunneling microscopy
Authors: Herman G. S. , Gallagher M. C. , Joyce S. A. , Peden C. H. F.
Published: July 2002

We have studied the growth and structure of thin TiOx films on W(110) using Auger electron spectroscopy, low energy electron diffraction (LEED), and scanning tunneling microscopy (STM). The procedure used to grow these films includes the deposition of Ti metal onto the W(110) surface followed by a saturation oxygen exposure. LEED and STM reveal that several different ordered TiOx film structures can result depending upon the initial amount of Ti deposited and the final annealing temperature. Specifically, the oxidation and anneal to 1350 K of a one monolayer (ML) film of Ti resulted in the formation of a strained ML structure that has a distorted hexagonal lattice and long-range order as observed by LEED and STM. The epitaxial relationship of this 1 ML TiOx structure with the W(110) substrate is found to occur with a Nishiyama–Wassermann orientation.
Characterization of a low pressure, high ion density, plasma metal etcher
Authors: Hill Rod
Published: July 2002

As the backend device geometries shrink to near 0.5 μm, the challenges placed on plasma metal etching continue to mount. Profile control, critical dimension and etch rate microloading, selectivities to masking and substrate materials, defect densities and uniformities are being pushed to tighter limits. The typical results of the low ion density, low pressure batch systems and the low ion density, high pressure single wafer etchers cannot satisfy the demands of the 0.5 μm technologies. The very low pressure, high ion density plasma sources ostensibly offer some advantages in plasma metal etching. A transformer coupled plasma metal etcher is characterized with respect to the aforementioned process outputs. Statistically designed experimental data to optimize the selectivity to photoresist and the etch rate uniformity are presented. Additionally, in situ resist stripping in a transformer coupled plasma strip chamber is studied. Experiments designed to understand the causes of polymer residues are presented. Methods are given to eliminate polymer residues. Galvanic pitting of the AlCu layer in the vicinity of theta phase Al2Cu precipitates at grain boundaries was found to be a function of the in situ resist stripping and water rinsing conditions. The pitting was eliminated by optimizing the postetch plasma ashing and water rinsing conditions. Profile microloading and aspect ratio dependent etch effects are reported.
Combined scanning tunneling microscopy and infrared spectroscopy study of the interaction of diborane with Si(001)
Authors: Wang Yajun , Shan Jun , Hamers Robert J.
Published: July 2002

The atomic-resolution spatial analysis capability of scanning tunneling microscopy is combined with the chemical analysis capability of Fourier transform infrared spectrometry as an integrated approach for atomic scale chemical identification. This approach was tested by studying the adsorption and decomposition of diborane (B2H6) on Si(001). Diborane interacts with Si(001) to produce a metastable B2H5 species, which decomposes into stable surface BH2 units. They further decompose at elevated temperatures; the hydrogen produced can be liberated either onto the surface or into the gas phase, depending on the availability of free Si surface sites.
Sheet resistance corrections for spreading resistance ultrashallow profiling
Authors: Clarysse T. , Vandervorst W. , Pawlik M.
Published: July 2002

Carrier profiles of ultrashallow structures obtained from raw spreading resistance probe (SRP) data frequently display artifacts related to sheet resistance values which are higher than those measured by the four point probe. Furthermore, the SRP raw data may already display a substantial resistance increase while the probes are still stepping over the original polished surface as they approach the bevel edge. It can be shown that these artifacts are related to the surface damage due to the beveling procedure. Carrier and electrically active dopant profiles can in principle be corrected for this damage either by introducing a depth dependent mobility function allowing for a reduced mobility near the surface or by introducing surface states and Fermi level pinning into the calculations. Both approaches will be discussed in relation to Poisson based calculations since carrier spilling is not negligible for these structures. The surface states approach fits best the currently available data.
Friction forces on hydrogen passivated (110) silicon and silicon dioxide studied by scanning force microscopy
Authors: Scandella L. , Meyer E. , Howald L. , Lüthi R. , Guggisberg M. , Gobrecht J. , Güntherodt H. -J.
Published: July 2002

Scanning force microscopy (SFM) was used to study the surface topography and the low load, small contact area frictional behavior of hydrogen passivated (H-terminated) silicon and silicon dioxide in a dry nitrogen atmosphere. The unpassivated samples showed no significant contrast in frictional sliding of a SFM tip between the thermally grown silicon dioxide and the native silicon dioxide that typically covers exposed silicon surfaces. The H-termination of the sample surface leads to an increase in friction by a factor of 2 on silicon, whereas the friction of the silicon dioxide is not influenced. Coefficients of friction were determined by using the two-dimensional histogram technique. On SiO2 and H-terminated Si surfaces, using standard Si3N4 tips, coefficients of friction were determined to be 0.3±0.1 and 0.6±0.1, respectively.
Basic analysis of atomic-scale growth mechanisms for molecular beam epitaxy of GaAs using atomic hydrogen as a surfactant
Authors: Okada Yoshitaka , Harris James S.
Published: July 2002

A basic analysis is given to understand how a continual irradiation of atomic hydrogen (H) during molecular beam epitaxy (MBE) of GaAs could result in production of atomically smooth surfaces, abrupt heterointerfaces, and high-quality epitaxial layers as required for many applications. Some interesting results related to the atomic-scale growth mechanisms and atomic interactions are presented, and a growth model is proposed for atomic H-assisted homoepitaxial MBE of GaAs. It is thought that atomic H is an effective surfactant reducing the surface and total energy of GaAs (001), and acts to provide favorable kinetic and energetic pathways to promote an ideal layer-by-layer two-dimensional growth mode.
Dry etching of horizontal distributed Bragg reflector mirrors for waveguide lasers
Authors: Thomas S. , Pang S. W.
Published: July 2002

Distributed Bragg reflector mirrors were etched in InP and GaAs. The mirrors were patterned using electron-beam lithography and etched with an electron cyclotron resonance source. This fabrication technique has the advantage that no regrowth step is required and the length of the passive mirror region is confined to a few micrometers. The structure requires etching vertical profiles with smooth surface morphology and high selectivity to the masking material. The effects of rf power, Cl2 percentage in Ar, chamber pressure, and stage temperature were studied. Increasing the rf power from 100 to 250 W caused the InP selectivity to Ni to decrease from 147 to 55. A similar effect was observed for etching GaAs. For both InP and GaAs, a vertical profile can be obtained by reducing the Cl2 percentage in Ar and by using low chamber pressure of 1 mTorr. Increasing the Cl2 percentage, however, improves selectivity to the Ni mask. With 20% Cl2 in Ar, vertical profiles and high selectivities are obtained for both InP and GaAs. Using high temperature increases the volatility of InClx etch products and improves the selectivity of InP to Ni. For InGaAsP/InP waveguide lasers, 122 nm wide mirrors were etched in InP to a depth of 2.0 μm for maximum reflectivity at 1.55 μm. For AlGaAs/GaAs waveguide lasers, 59 nm wide mirrors were etched in GaAs to a depth of 1.5 μm. Etching of nλ/4 mirrors, where λ is the emission wavelength, was studied and the dependence of gap spacing on etch depth was measured. The variations in etch depth for different gaps were minimized by reducing the pressure.
Fabrication of nanostructures on silicon surfaces on wafer scale by controlling self-organization processes
Authors: Ogino T. , Hibino H. , Prabhakaran K.
Published: July 2002

We describe a novel route for future Si integration technology in which atomically controlled nanostructures are designed to the level of full wafers based on self-organization processes. As an example of the scenario, we present a Ge quantum dot network where individual dots interact with the neighboring dots through tunneling barriers, Schottky junctions, and so on. Ge dots are patterned on Si(111) surfaces by preferential nucleation of Ge islands at atomic steps and boundaries between reconstructed domains. It is then demonstrated that atomic step arrangement can be designed by patterning assisted control; this means that Ge quantum dot network can also be designed. Selective oxidation and silicidation in the Si/Ge systems are effectively utilized to form semiconductor/insulator/metal nanostructures from well-ordered semiconductor structures. Based on the above processes, we propose a new approach to design nanostructure integration organized on wafer scale.
Rugged surface polycrystalline silicon film deposition and its application in a stacked dynamic random access memory capacitor electrode
Authors: Ino M. , Miyano J. , Kurogi H. , Tamura H. , Nagatomo Y. , Yoshimaru M.
Published: July 2002

Rugged surface polycrystalline silicon (poly-Si) films deposited by low-pressure chemical vapor deposition have been studied and the films have been applied to a storage electrode for stacked dynamic random access memory capacitors. The surface morphology of the films was drastically affected by growth conditions and by the film thickness. However, the rugged surface poly-Si was characterized by the growth of grains that have 〈311〉 preferred orientation. The grains had grown on the amorphous Si surface just after deposition in the low-pressure chemical vapor deposition furnace. It was observed that the amorphous Si films deposited at the transition temperature between amorphous and polycrystalline Si have small crystalline particles in the films. We surmise that the nucleation sites of rugged surface poly-Si grains are small crystalline particles in amorphous Si near the surface, because the amorphous Si films deposited at high SiH4 pressure and low temperature (less than 540 °C) that have no crystalline particles in the film show no grain growth of rugged surface poly-Si. Stacked capacitors were fabricated using rugged surface poly-Si films and thin silicon nitride dielectric films. It was found that the thin poly-Si film electrode about 100 nm thick deposited at 570 °C shows 2.5 times more surface area than that of the conventional poly-Si film electrode. A rugged surface poly-Si electrode deposited under optimized growth conditions is promising for high density dynamic random access memory with stacked capacitor cells.
Photoluminescence studies on radiation enhanced diffusion of dry-etch damage in GaAs and InP materials
Authors: Chen Ching-Hui , Yu D. Ginger , Hu Evelyn L. , Petroff Pierre M.
Published: July 2002

We have investigated the radiation enhanced diffusion of ion defects during reactive ion beam etching of GaAs and InP, using the multiple quantum well (MQW) probe technique. During low energy (sub-keV) Ar+ ion exposure, illumination with light of energy above the band gap can substantially reduce the photoluminescence efficiency of MQW samples, relative to those which were not laser illuminated; the degradation of luminescence efficiency increases with the intensity of the light. Illumination with light of energy below the band gap produces a slight increase in the damage profiles. The observation of enhanced defect diffusion due to optical radiation in our studies suggests that in ion-assisted etching of semiconductors, the generation of excess electron-hole pairs and their subsequent recombination can play an important role in the propagation of defects into the substrate.
0.1 μm AlGaAs/InGaAs high electron mobility transistor fabrication by the new method of thinned resist pattern reversed by metal
Authors: Tanabe M. , Matsuno T. , Kashiwagi N. , Sakai H. , Inoue K. , Tamura A.
Published: July 2002

We have developed a novel subquarter micron gate fabrication process without any electron beam (EB) lithography techniques or phase shift (PS) methods. To fabricate a subquarter micron width mask, the process uses thinning line patterns of photoresist by O2 reactive ion etching and the reversing of that resist by a thin Al film. We applied this process to fabrication of a pseudomorphic AlGaAs/InGaAs high electron mobility transistor. The device exhibited a peak gm of 715 mS/mm, fT of 95 GHz, and fmax of 176 GHz. These results show this process to be a useful alternative to EB or PS techniques for subquarter micron gates.
Electron transport at Au/InP interface with nanoscopic exclusions
Authors: Anand S. , Carlsson S-B. , Deppert K. , Montelius L. , Samuelson L.
Published: July 2002

We present an investigation of electron transport at the Au/InP metal semiconductor (MS) interface in the presence of nanoscopic barrier inhomogeneities. In particular, we focus on the transport regime wherein the low barrier inhomogeneous regions are pinched off by the depletion potential of the surrounding higher barrier region. To realize this, we have fabricated a composite MS structure comprising of a known density of nanometer sized Ag aerosol particles on InP overlayed by a uniform Au film. Temperature dependent current–voltage (I–V) measurements were performed to characterize the electron transport at the composite MS interface. The experimental observations are explained using a simple model for the MS junction current in which the Ag/InP regions are assumed to be identical and noninteracting. Our results clearly demonstrate that the electron transport at the MS interface is significantly affected by low barrier regions even in the pinch-off regime. In addition, the influence of the particle density and the Ag/InP barrier heights on the diode characteristics is also investigated. It is suggested that Schottky barrier inhomogeneities could be the main source of the usually observed larger-than-unity ideality factors in diodes. Furthermore, our results indicate possibilities of using such composites to explore the physics and applications of nanoinjecting contacts.
Molecular-beam epitaxial growth and characterization of AlxIn1−xSb/InSb quantum well structures
Authors: Liu W. K. , Zhang Xuemei , Ma Weiluan , Winesett J. , Santos M. B.
Published: July 2002

We report the realization of two-dimensional electron systems in InSb quantum wells. AlxIn1−xSb barriers were selectively δ-doped with Si to produce electron densities between 0.9×1011 and 4×1011 cm−2 with electron mobilities as high as 97 000 cm2/V s at 4.2 K. A decrease in the electron density and an increase in the electron mobility are observed when the distance between the quantum well and the dopants is increased.
Improved luminescence quality with an asymmetric confinement potential in Si-based type-II quantum wells grown on a graded SiGe relaxed buffer
Authors: Fukatsu S. , Usami N. , Shiraki Y.
Published: July 2002

A new class of Si-based quantum confined geometry is demonstrated using a combination of oppositely strained layers grown on a step-graded relaxed SiGe buffer. The role of heterointerfaces is revealed as the controlling mechanism of the exciton localization, which results in enhanced no-phonon transition intensity.
Tensile strain relaxation in GaNxP1−x (x≤0.1) grown by chemical beam epitaxy
Authors: Li N. Y. , Wong W. S. , Tomich D. H. , Kavanagh K. L. , Tu C. W.
Published: July 2002

A study of strain relaxation in GaNxP1−x epilayers grown by chemical beam epitaxy, using a rf-plasma nitrogen radical beam source, tertiarybutylphosphine, and triethylgallium, is reported. Microcracks are observed in GaNxP1−x epilayers grown on GaP when the nitrogen composition is greater than 1.6%. Transmission electron microscopy results show that the tensile-strain relaxation in GaNxP1−x epilayers is initially relieved by microcrack formation without misfit dislocations. These microcracks penetrate through the interface, degrading the crystallinity of the GaP substrate. Microcracks formation can not be alleviated by adjusting the growth rate, growth temperature, V/III ratios, and forward plasma power, but they can be eliminated by reducing the growth area of the GaP substrate.