bluuebunny/crossref_metadata_2025 huggingface dataset:
Correct substrate temperature monitoring with infrared optical pyrometer for molecular-beam epitaxy of III–V semiconductors
Authors: Mizutani T.
Published: July 2002

Correct GaAs and InP substrate temperatures are monitored with an infrared optical pyrometer. The temperature calibration for the pyrometer is carried out with the help of an emissivity change, produced by an eutectic reaction, in the Al deposited Si substrate. It is found that large apparent temperature differences exist between n+- (or p+-) and semi-insulating GaAs and InP substrates when constant emissivity is assumed. The temperature difference is ∼60 °C at 500 °C for InP, and 10–30 °C for GaAs. The temperature differences are found to increase with increasing substrate temperature. A model calculation is given for substrate temperature monitoring with an infrared optical pyrometer. The apparent temperature difference is attributed to the presence of optical absorption mechanisms in an n+- (and p+-) substrate and its absence in a semi-insulating substrate. The limiting temperature of congruent evaporation and the native oxide evaporation temperature for GaAs are measured with an accurately calibrated infrared optical pyrometer. They are found to be 612±10 °C and ∼585 °C, respectively.
Focused ion beam induced deposition of low-resistivity gold films
Authors: Blauner Patricia G. , Butt Yousaf , Ro Jae Sang , Thompson Carl V. , Melngailis John
Published: July 2002

Focused ion beam induced deposition of metals has up to now produced films with resistivities 30–5000 times higher than bulk values for metals because of high concentrations of impurities from the precursor gas incorporated into the films. We have demonstrated for the first time deposition of submicron Au films with resistivities approaching that of the bulk metal and carbon contents of <10 at. %. These results are particularly relevant to applications in integrated circuit restructuring and x-ray lithography mask repair, where high film conductivity and purity improves interconnect quality and x-ray opacity.
Short-period gratings for long-wavelength optical devices
Authors: Andideh E. , Adesida I. , Brock T. , Caneau C. , Keramidas V.
Published: July 2002

The reactive ion etching in InGaAsP and InP have been characterized in methane-based plasma. The role of H2, He, and Ar as diluents have been investigated. Highly anisotropic short-period gratings with periods as small as 0.2 μm and with smooth etched surfaces are presented. Auger electron spectroscopy has been used to delineate a proper processing sequence to obtain etched surfaces as clean as the surface of control samples. The CH4/He gas mixture is suggested for the fabrication of gratings as a compromise for achieving good etched profiles as well as to minimize hydrogen passivation of donors in etched samples.
Study of sidewall passivation and microscopic silicon roughness phenomena in chlorine-based reactive ion etching of silicon trenches
Authors: Oehrlein G. S. , Rembetski J. F. , Payne E. H.
Published: July 2002

Sidewall passivation layers produced in the formation of Si trenches by HCl/O2/BCl3 reactive ion etching have been characterized by angle-resolved x-ray photoemission measurements and secondary electron microscopy. Electron-shading effects observed at grazing electron emission angles and electrostatic charging of insulating portions have been used to differentiate photoemission contribution from (i) the trench sidewall film (moderately insulating), (ii) the oxide mask (highly insulating), and (iii) the Si trench bottom (conductive). The sidewall passivation film for this process is found to be a silicon oxide. Only minor amounts of chlorine are incorporated in this film. The thickness of the sidewall passivation layer depends on the width of the Si trench and ranges from ≂0.1 μm for narrow trenches to ≂0.7 μm for wide Si trenches for our conditions. The Si taper formed in this trench etching process is produced by the simultaneous formation of the sidewall film which protects the underlying Si from etching. It is also shown that microscopic silicon pillars (‘‘black silicon’’ or ‘‘grass’’) form by micromasking under process conditions where large areas of unmasked silicon are exposed. The microscopic Si pillars are protected by the same sidewall passivation film as the trench sidewalls. Islands of black silicon are observed only in large open silicon areas and separated from oxide masked areas by a characteristic distance which is free of silicon pillars. This roughness-free distance is of the order of the mask thickness employed. Ion scattering from the sloped mask sidewalls and sputtering of involatile micromasking material can explain this observation. Our results are consistent with a mechanism in which the processes that cause the formation of the beneficial sidewall film also initiate and control the production of undesirable silicon roughness in large unmasked Si regions.
Characterization of ion beam deposited refractory WNx films on GaAs
Authors: Lee J. S. , Park C. S. , Kang J. Y. , Ma D. S. , Lee J. Y.
Published: July 2002

An ion beam assisted deposition (IBAD) technique has been explored for the growth of refractory W and WNx films on n-GaAs as candidate gate materials for GaAs integrated circuits. Tungsten was deposited by Ar-ion beam sputtering, and simultaneously low energy nitrogen ions were introduced directly onto the GaAs substrate, using a Kaufman-type ion gun, for nitridation of the W deposits. The deposited films were characterized by electrical resistivity measurements, x-ray diffraction, and x-ray photoelectron spectroscopy analyses. The results showed that the composition and the electrical resistivity could be controlled with the nitrogen-ion dose. Thermal stability of the WNx /GaAs interfaces was also investigated by examining Schottky diode characteristics and microstructures. The WNx contacts investigated in the composition range from x=0 to 0.47 were electrically stable up to 850 °C and showed remarkable enhancements in the Schottky barrier height through high temperature annealing. Such annealing induced barrier enhancements were attributed to the dissociation of a thin native oxide layer which was observed between the as-grown film and the GaAs substrate. Comparisons of our results with previous works on conventional sputter-deposited WNx films led to a conclusion that the IBAD technique generates much less ion damage in the substrate and the film, and therefore, is promising for growing refractory compounds on GaAs.
Distributions of growth rates on patterned surfaces measured by scanning microprobe reflection high-energy electron diffraction
Authors: Hata M. , Isu T. , Watanabe A. , Katayama Y.
Published: July 2002

Microscopic distributions of growth rates on GaAs(001) layers next to (111)A and (111)B surfaces were measured in real time during molecular beam epitaxy growth by scanning microprobe reflection high-energy electron diffraction. The increase in the growth rate on the GaAs(001) surface near the edge of (111)A surfaces is observed and the decrease in the growth rate on the GaAs(001) surface near the edge of the (111)B surfaces is found out. The exponential variation of the growth rate as a function of the distance from the edge, reflects surface diffusion of Ga atoms. The diffusion lengths along the [110] and [1̄10] directions are estimated to be about 1 and 8 μm at 560 °C, respectively.
Resist profile simulation for photoresist composition optimization
Authors: Ushirogouchi Tohru , Onishi Yasunobu , Tada Tsukasa
Published: July 2002

Monte Carlo dissolution simulation and dissolution properties related to resist composition were studied. Using these results, a composition assembling resist profile simulator (CARPS) has been developed. This simulator makes it possible to optimize the resist composition.
Imaging of silver and copper tetracyanoquinodimethane salts using a scanning tunneling microscope and an atomic force microscope
Authors: Yamaguchi S. , Viands C. A. , Potember R. S.
Published: July 2002

Silver and copper tetracyanoquinodimethane (TCNQ) salts have been imaged using a scanning tunneling microscope (STM) and an atomic force microscope. Single crystal, polycrystalline thick films, and vacuum-deposited thin films on highly oriented pyrolytic graphite molybdenum disulfide, silvered mica, and potassium chloride (KCl) were imaged in this study. Images of the AgTCNQ thin films grown on several of these substrates showed molecular-level resolution. A previously reported field-induced switching phenomenon of silver TCNQ has now been observed using a STM. These results may be the basis for developing a molecular-based information storage system.
Electrolytic scanning tunneling microscopy and point contact studies at electrochemically polished Au(111) substrates with and without Pb adsorbates
Authors: Binggeli M. , Carnal D. , Nyffenegger R. , Siegenthaler H. , Christoph R. , Rohrer H.
Published: July 2002

Electrochemically polished Au(111) substrates have been investigated by scanning tunneling microscopy in 0.5M NaClO4 in absence and presence of Pb underpotential adsorbates. The nm-scale morphology of the electropolished electrodes features densely terraced dome-shaped domains with heights up to more than 5 nm, whereas only small atomically flat surface regions of ∼5 nm width are observed. During polarization in the ideally polarizable potential range in absence of Pb adsorbates, considerable smoothening and lateral displacement of the dome-shaped domains occurs within a time scale of minutes. Extended polarization in presence of a full Pb adsorbate coverage leads to a marked increase in substrate corrugation, up to the scale of several nm. At Pb-free substrates, controlled variations of the tip-sample separation in the transition regime from tunneling to point contact exhibit a similar distance dependence of the tip current as observed in previous vacuum studies, and allow for the first time an approximate assessment of the tunneling distance range in an electrolytic system. In the case of Au tips, the transition from tunneling to point contact is observed at tunneling resistances of ∼2⋅104 Ω, in good agreement with previous vacuum results. A tunneling regime with RT<107 Ω is assigned approximately to a substrate-tip separation range <1 nm.
Comparison of CH4/H2/Ar reactive ion etching and electron cyclotron resonance plasma etching of In-based III–V alloys
Authors: Pearton S. J. , Chakrabarti U. K. , Katz A. , Perley A. P. , Hobson W. S. , Constantine C.
Published: July 2002

An electron cyclotron resonance plasma etching system with the capability of additionally radio-frequency biasing the substrate has been used to study the etching characteristics of InP, InAs, InSb, InGaAs, and AlInAs in CH4/H2 -based discharges. The etch rates of these materials increase linearly with rf power and retain smooth surface morphologies for microwave powers below 150 W. At higher microwave powers the surface becomes rough due to preferential removal of the group V species. The quality of Au Schottky diode contacts on InP degrades for high-bias etching, but the addition of PCl3 to the discharge retards this degradation by providing an overpressure of P. The room temperature photoluminescence intensity of InP is also preserved by this PCl3 addition. We obtained highly anisotropic etching of all five semiconductors over the whole pressure range investigated (1–20 mTorr). Low-bias (25–100 V) etching occurs with rates in the range 10–140 Å min−1, dependent on the particular semiconductor (InP is the fastest and AlInAs the slowest). Etch rates up to 500 Å min−1 are obtained for high-bias (≤1000 V) conditions. The use of CH3Cl in preference to CH4 in order to increase the etch rate of InGaAs and AlInAs was investigated; this appears to have few advantages since the etch rates are comparable to those with CH4/H2. The degree of polymer deposition during CH4/H2/Ar etching on the type of mask used (photoresist, W, or SiO2 ) was also studied-for short duration or low-bias etches any of these masks perform adequately, but SiO2 is a superior choice under all other conditions. Finally, the uniformity of etch depth for ECR plasma etching of 2 in. diam InP substrates was found to ±3.0% over the whole wafer and ±2.4% over a randomly chosen 1600×1600 μm2 area.
Role of atomic force in tunneling-barrier measurements
Authors: Chen C. J. , Hamers R. J.
Published: July 2002

Experimental measurements of the apparent barrier height as a function of tip-sample separation using a scanning tunneling microscope (with clean W tips and clean Si surfaces in ultra high-vacuum) show that the barrier height starts at 3.5 eV at large separations, increases to 4.8 eV at about 1.5 Å before the mechanical contact, and then drops to below 0.3 eV within a fraction of an ångström. At the distances encountered in scanning tunneling microscopy, forces between sample and tip can be significant. Using a simple model of this system including tip-sample forces leads to a calculated apparent barrier height which quantitatively reproduces the observed variation in apparent barrier height over the entire range of tip-sample separations.
Focused Ga ion beam etching characteristics of GaAs with Cl2
Authors: Komuro Masanori , Hiroshima Hiroshi
Published: July 2002

The etching characteristics of GaAs bombarded with 20 keV Ga+ ion beam during impingement of Cl2 gas flux have been investigated. At room temperature, an etch yield (the number of substrate atoms removed per ion) with showered ion beam irradiation approaches a saturated value of 101 atoms/ion with the increase in gas flux for different incident ion fluxes of the order of 1014 ions/s/cm2. A previously proposed etching model which accounted well for the experimental results for Si/Cl2 is in good agreement with the present results. Variation of etch depth computed by this model for focused ion beam raster scanning also agrees with the experimental results. However, as the substrate temperature rises up to 110 °C, the etch yield increases as opposed to the case of Si/Cl2 and the saturated etch yield becomes 430 atoms/ion. It seems that formation of several layers of chlorinated compounds might be responsible for the increase in etch yield. Finally, fabrication of multineedle field electron emitter is demonstrated.
Applications of focused ion beam technique to failure analysis of very large scale integrations: A review
Authors: Nikawa K.
Published: July 2002

Focused ion beam (FIB) technique applications to very large scale integration (VLSI) failure analysis are reviewed. Three examples of microscopic cross sectioning and in situ observation on a VLSI chip are presented. One is a cross section of an electromigration-induced open circuit. Another shows a pinhole in the SiO2 layer between the metal layer and the substrate. The third shows an open circuit, caused by process anomalies. Five preparation methods for further failure analysis are presented: cutting and connecting metal lines, making holes at insulation layer for electron beam probing, probing pad formation for mechanical and electron beam probing, microscopic cross sectioning for secondary electron miscroscopy observation, and marking for transmission electron spectroscopy observation. FIB was shown to be useful, as an aluminum microstructure observation tool, not only for qualitative observation of aluminum grains, but also for quantitative measurement of aluminum grain orientation. Each example is shown in many photographs.
A focused ion beam system with a retarding mode objective lens
Authors: Sawaragi H. , Kasahara H. , Mimura R. , Thompson W. , Shearer M. Hassel
Published: July 2002

Emerging focused ion beam application (FIB) require that the incident ion range and lateral scattering be variable. It is desirable that the energy change required to alter the ion range produce a minimal variation of the incident beam diameter and current. A new FIB system with an energy range from 5 to 70 keV has been developed to meet these requirements. In order to produce a low energy fine ion beam with a high current density we have designed a column with two objective lens elements in tandem. The first element is a conventional einzel lens while the second is a retarding mode immersion lens. This immersion lens can also be operated as a short working distance einzel lens during high energy operation. In this paper the construction of the ion optical system and its performance are discussed. Initial results from ion induced secondary electron images demonstrates 100 nm resolution and a 20 nm resolution at 69 keV.
Observation of the first-order phase transition from single to double stepped Si (001) in metalorganic chemical vapor deposition of InP on Si
Authors: Grundmann M. , Krost A. , Bimberg D.
Published: July 2002

The first-order phase transition at the Si (001) surface from single to double atomic steps as a function of temperature T and off-orientation θ of the Si (001) surface along [11̄0] is observed in a metalorganic chemical vapor deposition environment at surprisingly low temperatures. At a given temperature the surface morphology of Si is frozen in by growing InP on top of Si. The existence or the lack of antiphase domains in the InP provides the information about the presence of single or double atomic steps on the Si, respectively, in the moment of growth. Reversability and slight hysteresis of the phase transition are found. The growth parameters for obtaining antiphase domain-free InP are optimized. Residual stress, epilayer tilt, and defect distribution are discussed. The different peaks in photoluminescence spectra are identified; the assignments are confirmed by using time-delayed cathodoluminescence (CL) spectra. The lateral variation of quantum efficiency is imaged with scanning CL.
Trapping effects in HgCdTe
Authors: Nemirovsky Y. , Fastow R. , Meyassed M. , Unikovsky A.
Published: July 2002

Carrier trapping influences the performance of HgCdTe infrared detectors in the 8–12 μm range by enhancing tunneling currents, reducing excess carrier lifetimes, and increasing g–r and 1/f noise. In this work, the effects of carrier trapping on the tunneling currents in n+p diodes are calculated, and the dependence of the tunneling current on temperature, bias, doping level, and trap characteristics is illustrated. It is shown that by assuming the dominant trap energy to be at the Fermi level, the calculated tunneling currents exhibit many of the peculiar features which have been observed experimentally. The related effects that minority carrier traps have on the excess carrier lifetimes are also discussed, and a simple method of estimating many of the relevant trapping characteristics from lifetime measurements is presented.
Investigation of radical-beam ion-beam etching-induced damage in GaAs/AlGaAs quantum-well structures
Authors: Skidmore J. A. , Green D. L. , Young D. B. , Olsen J. A. , Hu E. L. , Coldren L. A. , Petroff P. M.
Published: July 2002

Dry etching-induced damage is investigated using radical-beam ion-beam etching. This technique allows the systematic study of process-induced damage over a wide range of etching rates and with varying components of physical and chemical etching. Induced damage is characterized by I-V measurements from Schottky diodes on etched surfaces and from luminescence from quantum wells situated in close proximity to etched surfaces. We have designed a novel multiple-quantum-well probe structure that also includes a 4000 Å-thick quarter-wavelength mirror stack layer to allow in situ monitoring of etch rate and etched depth. Our work examines damage as a function of ion beam voltage and beam current density, microwave power, and with and without a reactive gas. We have found that damage increases with increased ion energy and decreases with etch yield.
Low voltage backscattered electron collection for package substrates and integrated circuit inspection
Authors: Lee K. L. , Ward M.
Published: July 2002

A low voltage backscattered electron collection technique has been developed. This technique collects low energy backscattered electrons in a sequential retarding field environment. This collection approach provides most of the desirable features for insulating package substrates and passivated integrated circuit (IC) devices inspection. These features are (1) high current and resolution, (2) high detector gain at low voltage, (3) good signal immunity from sample surface charging, and (4) on-line topographical and compositional information at low voltage. In this paper, various details of the technique; such as detector arrangement, signal collection efficiency, sample charging immunity, beam current and resolution, image distortion and its comparison with conventional low voltage scanning electron microscopy inspection for insulating package substrate, and passivated IC inspection will be discussed.
Surface diffusion during molecular-beam epitaxy growth of ZnSe studied by reflection high-energy electron diffraction
Authors: Gaines J. M. , Ponzoni C. A.
Published: July 2002

We report the use of reflection high-energy electron diffraction (RHEED) oscillations to characterize surface diffusion during ZnSe crystal growth by molecular-beam epitaxy (MBE). For GaAs growth on vicinal (001) surfaces, RHEED oscillations disappear above a certain substrate temperature, indicating that the Ga diffusion length exceeds the step terrace width. However, for ZnSe, we observe RHEED oscillations over the entire range of substrate temperatures (250–400 °C) typically used during MBE growth. The diffusion length of Zn and/or Se is determined to be less than 40 Å. The slow diffusion of Zn and/or Se that we observe can explain the general difficulty in observing RHEED oscillations during ZnSe growth, and has implications for interface roughness in heterostructures containing ZnSe layers.
Effect of interface composition on the band offsets at InAs/AlSb (001) heterojunctions
Authors: Waldrop J. R. , Sullivan G. J. , Grant R. W. , Kraut E. A. , Harrison W. A.
Published: July 2002

X-ray photoemission spectroscopy has been used to directly measure the dependence of the valence band offset ΔEv on interface composition (AlAs-like versus InSb-like) for InAs/AlSb (001) heterojunctions grown by molecular-beam epitaxy. A staggered band alignment with a consistent average value of ΔEv = 0.16 eV is measured for three samples with the InSb-like interface. A difference of 0.07 eV is observed between the average ΔEv values for two AlAs-like interface samples (0.15 and 0.22 eV, respectively). The growth-to-growth variation in ΔEv value for the AlAs-like interface, and the 0.06 eV difference between the InSb-like ΔEv value and the larger AlAs-like ΔEv value are both attributed to interface composition differences. We interpret the ΔEv = 0.22 eV value as being most characteristic of the AlAs-like interface. A tight binding model calculation of the effect of local strain on InAs/AlSb band offsets is compared to experiment.
Formation and electrical effects of process induced dislocations in HgCdTe
Authors: List R. S.
Published: July 2002

This study provides quantitative assessments of both the stress levels required to form dislocations in HgCdTe and the effect of these process induced dislocations on metal–insulator semiconductor device performance. Unlike previous millimeter size stress-strain measurements, this study determined the yield stress of HgCdTe on the scale of microns by performing defect etches beneath lithographically defined, high stress films. Both the magnitude and temperature dependence of the microyield stress appear to be similar to macroyield stress values found in the literature. The ability to lithographically define dislocated regions with high stress discontinuous films was used to produce test structures with variable dislocation densities and distributions. The electrical effects of process induced dislocations in these test structures provide insight into the defect production and dark current mechanisms of dislocations. Specifically, dislocations appear to increase the donor and Hg interstitial-like concentrations in addition to the thermally activated, trap assisted tunneling. The effects of dislocations on array performance were also investigated.
Localized plasma etching for device optimization
Authors: Larson Donald R. , Veasey David L.
Published: July 2002

We have developed an unconventional approach to down-stream plasma etching: only a small area of the substrate is exposed to the low pressure, reactive gaseous environment. The remainder of the substrate is outside the miniature plasma chamber, providing physical access for probing apparatus. Etch rates of 6 μm/h were obtained. The process can be especially useful when in situ monitoring of the effects of etching is required. Using this process, we improved the responsivity of a semiconductor optical detector deposited on top of an optical waveguide. This was accomplished by monitoring the transmitted intensity of light in an integrated optical waveguide while etching a thin semiconductor film covering a small region of the waveguide.
Spatially indirect intersubband transitions of localized electrons and holes at the staggered band lineup In0.52Al0.48As/InP interface
Authors: Böhrer J. , Krost A. , Bimberg D.
Published: July 2002

The electronic and crystallographic properties of InAlAs/InP interface grown by metalorganic chemical vapor deposition are studied using double-crystal x-ray diffraction, calorimetric absorption spectroscopy (CAS), steady-state and time-resolved photoluminescence (PL), and Shubnikov–de Haas (SdH) experiments. A high crystalline quality of the interfaces is suggested by the observation of Pendellösung oscillations in the x-ray rocking curves. A two-dimensional electron gas with ns∼6×1011 cm−2 is formed at the InP side of the interface by carrier transfer from the unintentionally doped InAlAs and is directly observed by SdH. Localized hole levels are formed at the InAlAs side of the interface. Spatially indirect optical intersubband transitions between localized electron and hole levels up to n=4 are observed in CAS. The PL and CAS experiments yield an electronic subband structure which is in perfect agreement with results of self-consistent band structure calculations. The 6 K luminescence between localized electrons and holes in their respective n=1 states decays with a time constant of 3.8 ns, considerably larger than what is usually observed at type I quantum wells.
Fabrication of freestanding structures and proposed applications in tunneling sensors
Authors: Moore D. F. , Lutwyche M. I. , Hoole A. C. F.
Published: July 2002

Suspended microstructures which can be deflected electrostatically are potentially useful in sensors, especially with tunnel junction readout schemes. This article describes an integrated device geometry which compensates for the effects of thin film stress in the freestanding parts, and allows a contact to be made by laterally deflecting beams electrostatically.
Fabrication of curved mirrors for visible semiconductor lasers using electron-beam lithography and chemically assisted ion-beam etching
Authors: Unger P. , Boegli V. , Buchmann P. , Germann R.
Published: July 2002

(Al)GaInP ridge-waveguide lasers with curved dry-etched mirrors have been fabricated which operate in the visible-light regime at a wavelength of 690 nm. High-resolution electron-beam lithography is used to define the mirror shapes in a 25 nm design grid while the rest of the fabrication technology is done conventionally by optical lithography. The mirror patterns are transferred into the underlying epitaxial layers by chemically assisted ion-beam etching. The properties of the laser devices are comparable to devices with cleaved facets. Single-mode behavior is observed up to cw output power levels of 30 mW. The horizontal far-field angle of the emitted light can be influenced by varying the curvature radius of the mirror facets.
Variation of internal stresses in sputtered Ta films
Authors: Yoshihara Takuya , Suzuki Katsumi
Published: July 2002

It has been found that the stress of a sputtered Ta film gradually changes toward compression in a normal atmosphere. It was found that the cause of this Ta film stress change is quick oxygen diffusion along grain boundaries. The amount of this stress change was measured to be about ∼3×107 N/m2 when the Ta film was sputtered with Ar gas below 3.5 Pa. The stress change occurred neither in a vacuum nor in a nitrogen atmosphere, but only in an oxygen atmosphere. Once the Ta films had been annealed for 60 min at 100 °C in an oxygen atmosphere, no further stress change was observed.
Proposal for precise manipulation of C60 molecules
Authors: Viitanen Jouko
Published: July 2002

Scanning tunneling microscope has previously been used to move single atoms. This article proposes a new method for performing accurate manipulations of C60 molecules. The new method may have potential advantages over previous approaches for molecular scale operations. One advantage comes from the noncontact electrode principle that allows longer distance manipulations and low-cost construction of the manipulating device. The unique properties of C60 may also facilitate precise manipulations of thin layers, in addition to single molecule operations. Construction of a device for testing the new principle is under work.
Arsenic cluster engineering for excitonic electro-optics
Authors: Melloch M. R. , Nolte D. D. , Otsuka N. , Chang C. L. , Woodall J. M.
Published: July 2002

An unexpectedly large room-temperature electro-optic effect has been observed in Al0.25Ga0.75As containing As clusters. The room-temperature band-edge absorption of this metal–semiconductor composite exhibits a clearly defined excitonic edge. This band-edge absorption can be strongly affected by electric fields due to exciton life-time broadening; almost a 60% differential transmission was obtained for a 1 μm thick Al0.25Ga0.75As epilayer containing As clusters. This is comparable to values obtained using GaAs/AlGaAs multiple quantum well structures. The excitonic absorption is a strong function of the average As cluster spacing that is controlled with the cluster coarsening anneal temperature. This enhancement of the excitonic optical properties by embedded metallic clusters represents a fundamental departure from traditional quantum well engineering.
Single wafer process integration for submicron structures
Authors: Masnari N. A.
Published: July 2002

As semiconductor technology moves toward reduced feature size, increased device density, and larger diameter wafers, there is increasing need for reliable, economical, in situ, single-wafer processing under low-thermal budget conditions. Two promising techniques to do this are rapid thermal processing and remote plasma-enhanced chemical vapor deposition. The integration of such processing techniques together with proper surface preparation has significant potential for meeting the fabrication needs at the deep submicron level. The extension of such in situ processing to include the clustering of multiple processing tools is another step in the development of low-thermal-budget, in situ, single-wafer processing. Such cluster tools require the development of well-controlled high throughput technologies that are cost effective and compatible with high-yield manufacturing.
Applications of computational fluid dynamics for improved performance in chemical-vapor-deposition reactors
Authors: Kotecki David E. , Conti Richard A. , Barbee Steven G. , Cacouris Theodore D. , Chapple-Sokol Jonathan D. , Eschbach Rudolph J. , Wilson Donald L. , Wong Justin , Zuhoski Steven P.
Published: July 2002

Engineering models, based on computational fluid dynamics, have been developed and used to improve the performance of two metalorganic chemical-vapor-deposition reactors. Though the knowledge of the chemical reactions occurring during film deposition is incomplete, the models provide insight into the reactor’s performance and are useful in guiding reactor modifications. In one reactor, the effect of three gas injector designs on the film thickness uniformity is examined; in a second reactor, the shape and placement of a flow deflector, which redistributes the flow of gas over the wafer surface, is studied. In both cases, comparing the experimental results obtained both before and after the reactor modifications, significant improvements in film thickness uniformity were realized.
CdTe/GaAs(100) heterojunctions: Growth modification by thin silicon interface layers
Authors: Cairns J. W. , Woolf D. A. , Bennett M. R. , Williams R. H. , Ballingall R. A.
Published: July 2002

The growth of CdTe epilayers on GaAs has been explored as a potential buffer layer for the fabrication of CMT/CdTe/GaAs structures on silicon substrates. CdTe layers were deposited by molecular beam epitaxy onto GaAs(100) specimens transferred into the II–VI reactor protected by an amorphous arsenic (a-As) cap. Reflection high energy electron diffraction and double- crystal-x-ray diffraction studies show that CdTe{111} layers grow epitaxially on both As- and Ga-rich GaAs(100) surfaces. The relatively narrow x-ray linewidths associated with the layers demonstrate that the layers are of high structural quality. The detailed nature of the interface between CdTe and GaAs has been studied by x-ray photoemission spectroscopy and low energy electron diffraction. It is shown that the interface is highly reactive, leading to the formation of gallium telluride, which influences the growth orientation of the CdTe layer. In an attempt to prevent such interface chemical reactions, we have explored the use of ultrathin silicon interface layers. Thus, GaAs(100) substrates were covered with 1 ML of Si before being capped with a-As. The samples were transferred to a surface science spectrometer, where the a-As cap was removed, producing an ordered Si-(3×1)/GaAs(100) surface. The subsequent growth of CdTe on the Si/GaAs(100) samples yielded well-ordered epilayers, always displaying the (100) orientation. Possible reasons for the change in epilayer crystallographic orientation due to the presence of the Si interlayer are considered.
Dynamical transmission effects and impact ionization in hot-electron transport across NiSi2/Si(111)7×7 interfaces
Authors: Bauer A. , Ludeke R.
Published: July 2002

Impact ionization and interface transmission, two important processes in hot-electron transport in semiconductor structures, have been studied by ballistic electron emission microscopy (BEEM) at interfaces of NiSi2/n-Si(111)7×7. The analysis of BEEM spectra taken in pinholes of thin NiSi2 films allows a direct determination of the quantum yield of impact ionization in Si over a wide energy range (≳7 eV). BEEM images and spectra recorded on NiSi2 terraces show evidence for the conservation of transverse momentum and a small probability for normal interface transmission up to high energies (≊4 eV above the Fermi energy), in accordance with dynamical calculations of the transmission probabilities.
Scanning tunneling investigation of DNA structures involved in gene regulation
Authors: Pasero P. , Blettry C. , Marilley M. , Jordan B. , Granjeaud S. , Dayez M. , Humbert A.
Published: July 2002

Scanning tunneling microscopy (STM) observations made on pBR322 DNA are compared with methods known to give information on DNA intrinsic curvature: polyacrylamide gel retardation, electron microscopy and computer modeling. It is concluded that STM is a powerful method for studying DNA structural features. Moreover, it is the only method to reveal simultaneously nanometric scale detail and long-range information. Use of STM for analyzing fine DNA structural features in regions involved in gene regulation should make an important contribution to genetics.
Comparison of multipolar and magnetic mirror electron cyclotron resonance sources for CH4/H2 dry etching of III–V semiconductors
Authors: Pearton S. J. , Abernathy C. R. , Kopf R. F. , Ren F. , Hobson W. S.
Published: July 2002

The dry etching characteristics of InP and GaAs using CH4/H2 plasmas produced by two different electron cyclotron resonance (ECR) source configurations were examined in terms of surface morphology, stoichiometry, etch rate and anisotropy and finally the etch uniformity on 3″φ wafers. Both the multipolar resonant cavity ECR source and the more conventional high-profile magnetic mirror configuration produce high ion densities (∼7×1011 cm−3 at 1000 W) in 1 mTorr CH4/H2/Ar discharges, although the mirror source has slightly faster etch rates for both InP and GaAs. The etching becomes more anisotropic as the rf power to the chuck position is increased, and the rates fall for substrate temperatures below −10 °C, although the stoichiometry of the near-surface region of InP is slightly better under these conditions. The optimized etch uniformity is ≤±2% for both sources and in general is better for high rf and microwave powers. Manual tuning of the multipolar source is simpler than for the mirror source and it is a little more stable during operation, with fewer of the mode jumps observed for the mirror configuration.
Plasma immersion ion implantation for semiconductor thin film growth
Authors: Tuszewski M. , Scheuer J. T. , Campbell I. H. , Laurich B. K.
Published: July 2002

A new experiment has been constructed to explore the potential of the plasma immersion ion implantation technique for thin film growth on semiconductor substrates. The experiment consists of an inductive plasma source, an ultrahigh vacuum vessel, and a 10 kV pulse generator. The first nitrogen and oxygen plasma results obtained with the inductive source are presented and analyzed.
Magnetic insulation of secondary electrons in plasma source ion implantation
Authors: Rej D. J. , Wood B. P. , Faehl R. J. , Fleischmann H. H.
Published: July 2002

The uncontrolled loss of accelerated secondary electrons in plasma source ion implantation (PSII) can significantly reduce system efficiency and poses a potential x-ray hazard. This loss might be reduced by a magnetic field applied near the workpiece. The concept of magnetically insulated PSII is proposed, in which secondary electrons are trapped to form a virtual cathode layer near the workpiece surface where the local electric field is substantially reduced. Subsequent electrons that are emitted can then be reabsorbed by the workpiece. Estimates of anomalous electron transport from microinstabilities are made. Insight into the process is gained with multidimensional particle-in-cell simulations.
Oxidized amorphous silicon as gate insulator for silicon tips
Authors: Peters D. , Paulus I. , Stephani D.
Published: July 2002

Field emission cathode arrays of Betsui type [K. Betsui, Technical Digest of the International Vacuum of Microelectronics Conference, Nagahama, Japan, 1991 (unpublished)] need an intermediate spacer layer with excellent insulator properties, i.e., ultrahigh resistivity, high breakdown voltage, excellent adhesion both to substrate and gate layer, low roughness, low dielectric constant, and sufficient long term stability. This study reports on an investigation of various fabrication methods for this insulating film in order to optimize its properties. Silicon and some compounds (a:Si, SiO, SiO2, SiOxNy) have been deposited by e-beam or thermal evaporation and plasma enhanced chemical vapor deposition, respectively. These layers have been annealed or oxidized before deposition of the extraction gate layer. The structures have been characterized by means of capacitance measurements. The best results have been obtained with the deposition of pure silicon by e-beam evaporation followed by an oxidization process. The method described in detail results in an insulator consisting of SiO2 which exhibits excellent insulating properties (breakdown field strength 7 MV/cm). Field emission cathodes fabricated in this manner exhibit stable emission currents up to 1 μA/tip.
Observation of the relaxation processes that follow atom removal from the Au(111) surface with the scanning tunneling microscope
Authors: Hasegawa Y. , Avouris Ph.
Published: July 2002

The scanning tunneling microscope (STM) has been used to perturb distribution of surface stress, and to observe the resulting relaxation processes in a time-resolved manner. Using nanoscale manipulation with the STM, we generated a hole with a radius of about 10 Å on the 22×√3 reconstructed structure of Au(111) surface, and observed the rearrangement of the dislocation lines of the reconstructed surface as a result of the formation of the hole. The area in which the pattern of dislocation lines is affected extends to about 80 Å from the site of the hole. The large range of the perturbation is most likely due to the long-range substrate-mediated elastic interaction of the hole with domain boundaries of the reconstructed surface. We find that a structure involving a closed loop of dislocation lines is formed at the initial stage of the relaxation process.
Strain relief and ordering of (2×n)-Bi structure on Si(100)
Authors: Park Ch. , Bakhtizin R. Z. , Hashizume T. , Sakurai T.
Published: July 2002

(2×n)-Bi phases formed on the Si(100) surface are studied using scanning tunneling microscopy and low-energy electron diffraction. A series of well-ordered (2×n) superlattices with n ranging from 5 to 12 are observed, resulting from the ordering of the missing Bi-dimer rows in the (2×1) Bi overlayer. Long stripes of the (2×n) unit meshes separated by missing Bi rows with almost perfect periodicities of n are found to extend through the whole terraces. The periodicity of n in the striped (2×n) structures depends on the Bi coverage and the annealing temperature. The formation of successive phases of the (2×n) structures as a function of coverage and annealing temperatures reflects various strain relief processes in the direction of the compressed Bi-dimer rows by creating missing rows and line dislocations as well as rectangular vacancies. The remarkable long-range ordering of missing Bi rows in the compressed Bi overlayer suggests the presence of strong repulsive long-range elastic interaction among missing Bi-dimer rows.
Glow discharge processing to enhance field-emitter array performance
Authors: Schwoebel P. R. , Spindt C. A.
Published: July 2002

The current-voltage characteristics of microfabricated field emitters following inert gas ion bombardment have been investigated and correlated with changes in the electron-emission spatial distribution. The combination of glow discharge treatments in hydrogen and neon cause contaminant removal and mild emitter tip sputtering, leading to increases in the emitting area and significant improvements in the uniformity of the electron emission between tips in emitter arrays. The improved uniformity of the electron emission appears to be associated with a net smoothing of the emitter tip surfaces through the removal of field-enhancing protuberances by the inert gas ion bombardment.
Study of dislocations in ZnSe and ZnS by scanning force microscopy
Authors: Nickolayev O. , Petrenko V. F.
Published: July 2002

Images of grown-in and deformation-introduced dislocations penetrating cleaved {110} surfaces of ZnSe and ZnS were obtained by scanning force microscopy. No electrical effects associated with dislocations were found.
Deposition of single phase, homogeneous silicon oxynitride by remote plasma-enhanced chemical vapor deposition, and electrical evaluation in metal–insulator–semiconductor devices
Authors: Ma Y. , Lucovsky G.
Published: July 2002

Device-quality thin silicon oxynitride films were successfully prepared by combining remote plasma-enhanced chemical-vapor deposition and rapid thermal annealing techniques. The physical, chemical, and electrical properties of the films are determined by the relative flow rates of the N-atom and O-atom source gases, NH3 and N2O, respectively. Analysis of metal–insulator–semiconductor devices indicated the fixed charges in the dielectric (Qf) and the interface defect state densities (Dit), as determined from the analysis of conventional capacitance–voltage (C–V) measurements, were significantly reduced following post-deposition rapid thermal annealing. The approximate compositions of the films were obtained by on-line Auger electron spectroscopy, and the local bonding arrangements were determined by Fourier transform infrared spectroscopy. Correlations between the local bonding structures in the oxynitride films and the electrically active defective states at the Si–SiOyNz interface are also discussed.
Molecular beam epitaxial heterostructures in the (311)A orientation
Authors: Hsu Y. , Wang W. I. , Kuan T. S.
Published: July 2002

We observed the flat, smooth interfaces between GaAs and AlAs epilayers in GaAs/AlAs superlattices which were grown on the GaAs (311)A substrate at 600 °C by molecular beam epitaxy. Both the bright field images of the cross-section GaAs/AlAs superlattice structures along the [011̄] and [2̄33] directions by transmission electron microscopy (TEM) showed the flat, smooth interfaces between epilayers. Observation of satellite spots up to to fifth order in diffraction patterns indicates that the interfaces between GaAs and AlAs layers are sharp. These results of TEM investigation show that the GaAs (311)A surface is stable. It is clear that the recent report of the occurrence of corrugated structure, viewed along the [2̄33] direction, on a GaAs (311)A substrate is not intrinsic to the (311) surfaces.
Roughness analysis of Si/SiGe heterostructures
Authors: Feenstra R. M. , Lutz M. A. , Stern Frank , Ismail K. , Mooney P. M. , LeGoues F. K. , Stanis C. , Chu J. O. , Meyerson B. S.
Published: July 2002

Atomic force microscopy is used to measure surface morphology of modulation doped Si/SiGe heterostructures. Three components in the surface roughness are observed: μm-scale roughness arising from misfit dislocations formed to relieve strain, 1000-Å-scale roughness believed to be associated with three-dimensional growth of the electron or hole channel layers, and atomic-scale roughness with wavelengths of 10–100 Å. Detailed Fourier spectra of the roughness are obtained and used as input to a scattering computation for determining mobility. The results are compared with other mobility-limiting mechanisms, including scattering from ionized impurities and from dislocations.
Arsenic cap layer desorption and the formation of GaAs(001)c(4×4) surfaces
Authors: Karpov I. , Venkateswaran N. , Bratina G. , Gladfelter W. , Franciosi A. , Sorba L.
Published: July 2002

GaAs(001)c(4×4) surfaces were obtained in the 380–450 °C temperature range by thermal desorption of As cap layers from substrates prepared by molecular beam epitaxy. Although reflection high-energy electron diffraction patterns showed little change in the temperature range explored, in situ scanning tunneling microscopy and Auger spectroscopy, complemented by ex situ atomic force microscopy, indicate that in the lower-temperature range examined up to 11%–12% of the surface may still be occupied by adsorbed As in the form of wires and particles preferentially oriented along 〈100〉 directions.
Growth of InAsSb quantum wells for long-wavelength (∼4 μm) lasers
Authors: Turner G. W. , Choi H. K. , Le H. Q.
Published: July 2002

Molecular-beam epitaxy (MBE) has been employed for the growth of quantum-well laser structures grown on GaSb substrates. These lasers consist of compressively strained InAsSb wells, tensile-strained InAlAsSb barriers, and lattice-matched AlAsSb cladding layers. A broad-stripe diode laser with an emission wavelength of 3.9 μm has operated cw up to 123 K, with a characteristic temperature T0 of 30 K. Optical pumping of this laser structure has provided pulsed operation up to 162 K, with a peak output power of up to ∼0.6 W at 110 K. Emission wavelengths as long as 4.5 μm have been obtained in other laser structures with InAlAs barriers. In this article we present the key issues regarding the MBE growth of long-wavelength strained quantum-well lasers on GaSb, including shutter sequencing for interface control, analysis of characterization data, and laser results, with a comparison to double-heterostructure devices.