bluuebunny/crossref_metadata_2025 huggingface dataset:
Full-wafer technology for large-scale laser processing and testing
Authors: Voegeli O. , Benedict M. K. , Bona G. L. , Buchmann P. , Cahoon N. , Dätwyler K. , Dietrich H. P. , Moser A. , Sasso G. , Seitz H. K. , Vettiger P. , Webb D. J. , Wolf P.
Published: July 2002

A new approach for large-scale semiconductor laser fabrication is presented. In this ‘‘full-wafer processing and testing’’ concept, the mirrors are fabricated, not by cleaving the wafer but by forming them by means of a chemically assisted ion beam etching process. This allows for on-wafer mirror passivation and testing of the finished devices. Full-wafer technology changes the traditional way of discrete device fabrication and testing to a method more akin to today’s very large-scale integrated (VLSI) technology. Consequently, it provides similar advantages in cost and throughput. Additionally, it allows other electrical and electro-optical device components to be monolithically integrated on the wafer. Currently, we are routinely fabricating AlGaAs/GaAs diode lasers with a single quantum well graded index separate confinement heterostructure (SQW-GRINSCH)-type ridge structure using full-wafer technology. Such lasers exhibit excellent beam properties in single mode up to at least 50 mW output power. Their functional characteristics are indistinguishable from comparable lasers with cleaved facets obtained from the same wafer for comparison purposes. This result reflects the high quality of the etched mirrors. Typically, their surface roughness is less than 200 Å, with mirror reflectivities of about 30% and losses due to mirror scattering below 2%. Having functional parts on the uncleaved wafer allows automated full-wafer testing that encompasses wafer characterization and part screening. This not only eliminates part handling, with its associated yield loss, it also permits a much expanded scope of testing in a fraction of the time previously required.
Influence of silicon nitride deposition conditions on the electrical properties of oxide-nitride (ON) dielectrics on smooth and as-deposited rugged polycrystalline silicon
Authors: Chan Hiang C. , Mathews Viju K. , Turner Charles , Fazan Pierre C.
Published: July 2002

The effect of Si3N4 deposition conditions on the electrical properties of ON dielectric films on smooth and as-deposited rugged polycrystalline silicon is investigated. The results show that the leakage current, dielectric breakdown strengths, and the charge trapping characteristics of ON dielectric films are influenced by the Si3N4 deposition conditions. Larger capacitance increases on rugged electrodes, lower leakage currents, higher breakdown fields, and lower electron trapping rates are observed for ON dielectric films fabricated with low NH3:SiH2Cl2 gas ratio and deposited at higher temperature. These films are also expected to have a thicker bottom oxide due to the poor oxidation resistant characteristic of the thin nitride layer deposited at high temperature.
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u two-dimensional electron gas fabrication by focused Si ion beam implantation and molecular beam epitaxy overgrowth
Authors: Arimoto H. , Kawano A. , Kitada H. , Endoh A. , Fujii T.
Published: July 2002

We have demonstrated the possibility of in situ two-dimensional electron gas (2DEG) fabrication in GaAs/AlGaAs heterostructures, using focused ion beam implanter and molecular beam epitaxy (FIBI-MBE) crystal growth system. 2DEGs are formed in a GaAs channel layer which is overgrown on an AlGaAs electron supply layer implanted selectively with Si-FIBs. Implanted Si atoms are activated by rapid thermal annealing (RTA). We confirmed 2DEG formation by Shubnikov–de Haas oscillation. We clarified the influence of ion implantation damage on the quality of overgrown epilayers and obtained an extremely high 2DEG mobility of 32 000 cm2/V s at 77 K and 48 000 cm2/V s at 20 K. We also discussed possible quantum-size doping by direct FIB implantation, considering the lateral scattering of incident Si ions in the substrate.
Electron microscopy study of microvoid generation in molecular-beam epitaxy-grown silicon
Authors: Perovic D. D. , Weatherly G. C. , Noël J.-P. , Houghton D. C.
Published: July 2002

In a study of (100)Si growth by molecular-beam epitaxy, we have observed an interesting phenomenon associated with the breakdown of (100)-oriented growth at low temperatures (<∼400 °C). Electron microscope imaging revealed that the (100) surface no longer remains planar but develops a series of cusps with {111} oriented facets. At the base of each cusp a small (∼3 nm) cylindrically shaped defect region is formed, but this is morphologically unstable and breaks down to form a linear array of spherical defects trailing behind the growing interface, aligned parallel to the growth direction. The similarities observed between these structures and those found in the unidirectional solidification of rod eutectoids or monotectoids are striking, although the scale of the microstructure in the present case is much smaller. From a series of electron microscopy experiments using both cross-sectional and plan-view specimen geometries it has been found that the cylindrical–spherical defects are microvoid regions. Furthermore, the microvoid defect structure was found to be stable as the epitaxial Si matrix transformed to the polycrystalline and amorphous states beyond an epitaxial critical thickness.
Au and Al Schottky barrier formation on GaAs (100) surfaces prepared by thermal desorption of a protective arsenic coating
Authors: Spindt C. J. , Yamada M. , Meissner P. L. , Miyano K. E. , Herrera A. , Spicer W. E. , Arko A. J.
Published: July 2002

Soft x-ray photoemission spectroscopy has been used to investigate the initial stages of Schottky barrier formation on GaAs (100) surfaces prepared by the thermal desorption of an As cap. This work was motivated by a previous study [Brillson et al., J. Vac. Sci. Technol. B 6, 1263 (1988)] of identically grown and capped samples which reported ‘‘unpinned’’ Schottky barrier formation, with barrier heights falling over a wide range (0.75 eV) of energies. This large energy range is a striking result, as a considerable number of prior studies on both (110) and (100) surfaces have found that all metals will pin in a narrow (0.25 eV) range near midgap. Since Au and Al are the extremes of the larger 0.75 eV span of Schottky barriers, we have studied the deposition of these two metals. We found that the barrier height measurements on the low doped n-type samples used in this work and in the paper referenced above are affected by photovoltaic effects, even at room temperature. These photovoltaic effects cause shifts in the band bending, which are an artifact of the measurement. We also performed measurements on more heavily doped samples, and the photovoltaic effects were removed. In addition, we point out that Au–Ga alloying makes the case of Au potentially misleading. With the photovoltaic effects removed, and the Au–Ga alloying carefully accounted for, we found that the barriers heights for Au and Al differ by only 0.25 eV.
Modeling of shot noise in x-ray photoresist exposure
Authors: Turner S. , Babcock C. , Cerrina F.
Published: July 2002

New photoresist technologies yielding higher resist sensitivities together with the greater photon energies inherent in x-ray lithography put lithography systems closer and closer to the shot noise limit. Thus there is a need to address the effects of shot noise on resist exposure. We will present the description of a stochastic model, and its implementation in a simulator, which emulates the exposure process by effecting what amounts to a photon-by-photon treatment of the problem, thereby taking into account the effects of shot noise. The model starts with an aerial image, computed using a deterministic model based on Fresnel diffraction, interprets it as the probability density function (pdf) for the distribution of the photons. The stochasticity of the process is taken into account by randomly generating a finite number of events (photons) whose distribution follows the pdf. The penetration depths are stochastically predicted according to the appropriate distribution. At the point predicted, the incident energy is redistributed according to a point spread function or a full Monte Carlo method. The superposition of all of the photons provides us with the latent image. The dissolution process is then modeled using a stochastic cell dissolution model. We will present results of practical importance for chemically amplified resist systems and correlate the results with observations made in the laboratory.
The influence of surfactants on growth modes in molecular-beam epitaxy: The growth of germanium layers on Si(100)
Authors: Osten H. J. , Lippert G. , Klatt J.
Published: July 2002

Up to 30 nm thick Ge layers were grown on Si(100) by using Sb as a surfactant and were investigated by reflection high-energy electron diffraction, x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, transmission electron microscopy, and confocal laserscan microscopy. The introduction of a surfactant alters the growth mode drastically from a three-dimensional clustering mechanism to a two-dimensional layer-by-layer growth. Smooth and strained Ge layers, with a thickness much larger then the critical thickness for commensurate growth, are achievable. The antimony monolayer mainly segregates on top of the grown germanium layer.
Fabrication of lateral superlattices using multilayer resist techniques
Authors: Chang H. , Nummila K. , Grundbacher R. , Adesida I. , Leburton J.-P. , Hess K.
Published: July 2002

A procedure utilizing multilayer resist systems has been developed for the fabrication of artificial lateral surface superlattices (LSSLs) and other structures involving multiple point contacts and split gates. Two electron beam exposures are performed with the first exposure properly adjusted to result in a development down to the surface of the bottom resist layer with suitable undercut profile in the top resist layers. Electron beam exposure of arbitrary geometries at high resolution is then performed on the bottom layer through the opening in the top layers. After metal lift-off, all these geometries are connected together via an airbridge network. The fabrication of field-effect devices with split gates and LSSL gates in GaAs/AlGaAs modulation-doped heterolayers are demonstrated. These devices exhibit quantum conductance at 1.8 K.
Acid-diffusion effect on nanofabrication in chemical amplification resist
Authors: Yoshimura Toshiyuki , Nakayama Yoshinori , Okazaki Shinji
Published: July 2002

Acid-diffusion effect on nanometer pattern fabrication in a chemical amplification resist, SAL601 (Shipley Co.), is investigated with a finely focused electron beam. During postexposure bake (PEB), acid generated by the electron beam exposure diffuses and is assumed to cause pattern size changes. A scanning electron microscope, S-900 (Hitachi), which has a beam diameter of approximately 2 nm at 5 kV, is used to make latent images of nanometer isolated lines in a resist film. After electron beam exposure, the resist films with a thickness of 20 nm are baked in different conditions before development. The measured linewidths are found to be proportional to the square root of the PEB time. According to a simple acid diffusion model, this can be explained by the diffusion of generated acid during PEB. A minimum feature size of a 20 nm isolated line is obtained by adjusting the PEB conditions. It is therefore important to control the PEB conditions to suppress the acid diffusion for the critical dimension control of nanofabrication when using chemical amplification resist systems. Fine edge roughness is also observed in the delineated patterns. This is thought to originate from the distribution of diffused acid or from the random distribution of the base polymer with finite molecular sizes.
Accuracy of proximity correction in electron lithography after development
Authors: Aristov V. V. , Gaifullin B. N. , Svintsov A. A. , Zaitsev S. I. , Raith H. F. , Jede R.
Published: July 2002

The established methods after Parikh [M. Parikh, IBM J. Res. Dev. 24, 438 (1980)] allow a dose correction using the ‘‘Two Gaussian Model’’ by considering the parameters α, β, and η. A guaranteed accuracy after development cannot be given for these methods because the development process, depending on resist type, thickness and contrast, is not taken into account. In order to calculate a final guaranteed accuracy considering α, β, η, and the full resist development process, we did a calculation in following steps. First, we calculated the proximity correction just for backscattered electrons by the method of ‘‘simple compensation’’ [V. V. Aristov, A. A. Svintsov, and S. I. Zaitsev, Microelectron. Eng. 11, 641 (1989)]. In the second step, we simulated the proximity effect after development (modeling) with the before corrected dose distribution, but now considering all parameters: α, β, η, thickness H, and contrast γ of positive resist. This leads to a guaranteed accuracy δ (maximum structure deviation) for a given design rule L using the correction method of simple compensation. This guaranteed accuracy can be expressed in dimensionless coordinates δ/α=f(L/α,H/α,η,γ). So the accuracy of the electron lithography in this approach is determined by the beam size, characterized by α. Simple compensation results in the accuracy equal to a fraction of α. A better proximity correction below the guaranteed accuracy is possible by using simple compensation in iteration and by correcting for α inside a small structure frame.
Growth of Ga1−xInxAs/GaAs1−yPy multiple quantum well structures by gas source molecular beam epitaxy
Authors: Cunningham J. E. , Goossen K. , Williams M. , Jan W.
Published: July 2002

We examine growth of Ga1−xInxAs/GaAs1−yPy multiple quantum well structures by gas source molecular beam epitaxy for photonic switching applications at 1.06 μm. For appropriate x and y values these structures can be grown pseudomorphically at the GaAs lattice constant. Such structures show good morphology, room-temperature photoluminescence and sharp excitonic absorption edges near 1.06 μm.
Investigation of molecular-beam epitaxially grown InAs/(In,Ga)Sb strained-layer superlattices
Authors: Golding T. D. , Shih H. D. , Zborowski J. T. , Fan W. C. , Horton C. C. , Chow P. C. , Vigliante A. , Covington B. C. , Chi A. , Anthony J. M. , Schaake H. F.
Published: July 2002

We report on an investigation into the molecular-beam epitaxial growth and characterization of InAs/InxGa1−xSb (0≤x≤0.4) heterojunctions and strained-layer superlattices (SLS) for long-wavelength infrared detector applications. All structures have been grown on GaSb(100) substrates with period thicknesses of the SLS in the range 25–180 Å. Interface properties of single heterojunction structures have been characterized by x-ray photoelectron spectroscopy and secondary-ion mass spectroscopy depth profiles, and structural properties of the SLS have been assessed by transmission electron microscopy and x-ray diffraction analysis. For growth at an optimal temperature (390 °C) the SLS are of high structural quality, with no evidence of compound formation at either (GaSb/InAs, InAs/GaSb) interface, or of post-growth interdiffusion. However, significant levels of As (7%) are found to be present in nominally grown InxGa1−xSb layers, resulting from incorporation from background. Fourier transform infrared absorption spectra of SLS samples have shown absorption thresholds out to 19 μm.
Defects in strained In0.2Ga0.8As/GaAs multiple quantum wells on patterned and unpatterned substrates: A near-infrared cathodoluminescence study
Authors: Rich D. H. , Rajkumar K. C. , Chen Li , Madhukar A. , George T. , Maserjian J. , Grunthaner F. J. , Larsson A.
Published: July 2002

The spatial distribution of the long-wavelength luminescence in thick In0.2Ga0.8As/GaAs multiple quantum wells (MQWs) grown on patterned and unpatterned substrates has been investigated using cathodoluminescence (CL) imaging and spectroscopy. By spatially correlating the luminescence arising from the MQW exciton recombination (λ≊950 nm) with the longer wavelength (1000≲λ≲1200 nm) luminescence arising from the defect-induced recombination, we demonstrate that it is possible to determine the regions of highest film quality in both the mesa and valley regions for growth on patterned GaAs substrates. The present approach enables a judicious determination of the optimal regions to be used for active pixels in InGaAs/GaAs devices. For growth on unpatterned substrates, the CL spectra show defect-induced broad bands between 1000≲λ≲1600 nm. These bands exhibit spatial variations which correlate with the dark line defects (DLDs) observed in the λ=950 nm exciton luminescence imaging. Transmission electron microscopy showed that [110]-oriented misfit dislocations occur primarily at the substrate-to-MQW interface. The large spatial variation of the luminescence intensities indicates that the DLDs observed in CL images are caused by the presence of nonradiative recombination centers occurring in the MQW region located above the interface dislocations. This study provides new information describing the origin and nature of DLDs and differs from previous models, which have regarded the electronic nature of dislocation cores as the primary mechanism for inducing DLD radiative contrast in luminescence imaging of strained InGaAs/GaAs.
Band-edge exciton luminescence from Si/strained Si1−xGex/Si structures
Authors: Sturm J. C. , Xiao X. , Schwartz P. V. , Liu C. W. , Lenchyshyn L. C. , Thewalt M. L. W.
Published: July 2002

Well-resolved band-edge exciton photoluminescence has been observed in strained Si1−xGex layers grown on Si(100) by rapid thermal chemical vapor deposition. The luminescence is due to shallow-impurity bound excitons at low temperatures (under 20 K) and is an excellent probe of quantum confinement effects in narrow quantum wells. At higher temperatures, the luminescence is due to free excitons or electron hole plasmas, depending on the pump power. Experiments with single and multiple quantum well structures indicate that most of the Si1−xGex luminescence is from carriers which were generated in the silicon substrate and subsequently were trapped in the quantum wells.
Vacuum ultraviolet photoelectron spectroscopy study of the interaction of molecular sulfur with the GaAs(100) surface
Authors: Roberts L. , Hughes G. , Fennema B. , Carbery M.
Published: July 2002

The surface chemistry resulting from the interaction of molecular sulfur with the clean GaAs(100) surface has been studied using surface-sensitive synchrotron radiation photoemission spectroscopy. Clean GaAs(100) surfaces were obtained by the thermal decapping of a protective As overlayer deposited on a molecular-beam-epitaxy-grown GaAs epilayer. Molecular sulfur S2 was generated by the electrochemical decomposition of Ag2S in ultrahigh vacuum. The intensity of the chemically shifted components on both As and Ga 3d core levels has been found to critically depend on the As-to-Ga ratio in the topmost atomic layer of the clean decapped surface. This As-to-Ga surface ratio can be selectively altered by annealing the surface at different temperatures during the decapping procedure. Experiments have been carried out on both the Ga- and As-rich surfaces and it has been found that the magnitude of the chemical shifts can also appear to depend on the precise surface composition. For the exposure times investigated in this study, the sulfur treatment results in the GaAs surface being terminated in a monolayer of sulfur bonded to both Ga and As surface atoms.
Si(111)/FeSi2 heterostructures: Formation and properties of the low temperature metallic (γ) and semiconducting (β) disilicide phases
Authors: Moritz H. , Rösen B. , Popović S. , Rizzi A. , Lüth H.
Published: July 2002

Very thin layers (<100 Å) of FeSi2 have been grown on Si(111) by solid phase epitaxy (SPE) under ultrahigh vacuum conditions. Two different phases for the iron disilicide layers, γ- and β-FeSi2, can be obtained, depending on the initial Fe coverage, by annealing at temperatures below 600 °C. For low coverages (∼3 Å Fe) the metallic cubic γ silicide phase is obtained, while for higher Fe coverages (∼ 20 Å) the semiconducting orthorhombic β phase is grown. A quantitative Auger analysis shows how the Fe initial coverage dependence can be related to the RT formation of an intermixed FeSi2-like layer at the interface. The electronic properties and annealing behavior of these ultrathin silicide layers on Si(111) have been studied in situ by high resolution electron energy loss spectroscopy and ultraviolet photoemission spectroscopy. Due to the very small thickness of the metastable γ phase as grown by SPE, no direct phase transformation to the β phase could be observed by thermal treatment.
Dimer formation on (001) GaAs under organometallic chemical vapor deposition growth conditions
Authors: Kamiya Itaru , Aspnes D. E. , Tanaka H. , Florez L. T. , Harbison J. P. , Bhat R.
Published: July 2002

We report the first evidence of dimer formation on semiconductor surfaces under atmospheric pressure (AP) conditions. We successfully employ reflectance-difference spectroscopy to link structures of well-defined (001) GaAs surfaces prepared in ultrahigh vacuum (UHV) by molecular-beam epitaxy with structures of (001) GaAs surfaces prepared in AP by organometallic chemical vapor deposition (OMCVD). These measurements reveal that surface reconstructions also occur under AP-OMCVD conditions, forming structures similar, possibly identical, to the (4×2), (2×4), c(4×4), and disordered c(4×4), that occur in UHV. Our results provide a justification for applying the results of UHV studies of these surfaces to non-UHV environments and yield new insights on the mechanisms and kinetics of non-UHV growth.
Properties of (211)B HgTe–CdTe superlattices grown by photon assisted molecular-beam epitaxy
Authors: Harris K. A. , Yanka R. W. , Mohnkern L. M. , Reisinger A. R. , Myers T. H. , Yang Z. , Yu Z. , Hwang S. , Schetzina J. F.
Published: July 2002

The results of detailed optical, electrical, and structural studies performed on a series of (211)B oriented HgTe–CdTe superlattices grown by photon assisted molecular-beam epitaxy are reported. Higher order optical transitions in infrared (IR) photoluminescence (PL) spectra were observed for the first time in HgTe–CdTe superlattices. Low residual carrier concentrations were measured in undoped superlattices. Acceptor-bound excitonic transitions were observed in IR PL spectra of an arsenic doped superlattice for the first time. Excess carrier lifetimes of several hundred nanoseconds were measured, approaching that observed in the corresponding alloy. These results represent significant improvement in the electrical quality of HgTe–CdTe superlattices, and is another step towards the realization of a superlattice-based IR device technology.
p-type doping of metalorganic chemical vapor deposition-grown HgCdTe by arsenic and antimony
Authors: Edwall D. D. , Bubulac L. O. , Gertner E. R.
Published: July 2002

Extensive data are presented on the arsenic doping characteristics of Hg1−xCdxTe layers grown by metalorganic chemical vapor deposition using the dopant source tertiarybutylarsine (TBAs). The incorporation of arsenic in the layer is proportional to the II–VI alkyl ratio during TBAs injection. High arsenic concentrations significantly increase the layer dislocation density. Acceptor activation efficiency (taken to be the 77 K carrier concentration divided by the layer arsenic concentration) is ∼50% for a wide range of conditions, but decreases for arsenic concentrations approaching 1018 cm−3. For arsenic concentrations below low-1017 cm−3, the 77 K carrier concentration is stable even for sample annealing at 400 °C on the Te-rich side of the phase boundary. 77 K hole mobility strongly depends on composition x. Variable temperature Hall effect measurements show that one layer exhibits the expected carrier freeze-out with an ionization energy of 4.8 meV, but three other layers exhibit a much smaller degree of freeze-out. Preliminary results using the dopant source triisopropylantimony are also presented.
Fabrication of 50 nm line-and-space x-ray masks in thick Au using a 50 keV electron beam system
Authors: Chu W. , Smith Henry I. , Rishton S. A. , Kern D. P. , Schattenburg M. L.
Published: July 2002

Using a 50 keV, fine diameter electron beam lithography system, and a substrate consisting of a 10 nm-thick gold plating base on a 1 μm-thick, 2 cm-diam SiNx x-ray mask membrane, we have successfully exposed interdigitated electrode patterns for quantum-effect devices having lines and spaces of 50 nm. The resist is a single layer of polymethyl methacrylate (PMMA), 496 K molecular weight, 250 nm thick. That such fine features are achievable in a single layer of thick resist is attributed to: (1) reduced backscattering from the very thin plating base (10 nm Au versus the standard 30 nm) and thin substrate (1 μm-thick SiNx); (2) a well focused beam; (3) proximity-effect correction; and (4) precise exposure and development control. Once developed and ‘‘de-scummed,’’ 200 nm-thick gold is electroplated into the PMMA mold, yielding high contrast (∼12 dB) x-ray masks suitable for the CuL lines at 1.3 nm. To avoid problems of distortion and peeling of the 50 nm-wide lines, the plating was done under current–density and pH conditions that produce zero stress. The x-ray masks were replicated onto substrates and ‘‘daughter’’ x-ray mask membranes and electroplated, yielding ‘‘polarity reversal.’’ These polarity reversed masks, with 50 nm line-and-space features, can then be exposed onto device substrates using either contact or proximity x-ray lithography. This overall process takes advantage of the best aspects of electron-beam and x-ray nanolithographies, i.e., the capabilities of the former to create patterns of arbitrary geometry, and the robustness and high process latitude of the latter.
Effects of Si on electromigration of Al–Cu–Si/TiN layered metallization
Authors: Koubuchi Yasushi , Ishida Shin-ichi , Sahara Masashi , Tanigaki Yukio , Kato Tokio , Onuki Jin , Suwa Motoo
Published: July 2002

This work investigates electromigration (EM) in Al-1 wt %Si, Al-1 wt %Si-0.5 wt % Cu and Al-0.5 wt % Cu films with TiN barrier metals. The EM resistance of the Al-0.5 wt % Cu layered metallization was found to be higher than that of the Al-1 wt % Si-0.5 wt % Cu layered metallization. The electromigration test results show that the reaction between Al films and underlying TiN layer degrades the electromigration performance of the Al-1 wt % Si, Al-1 wt % Si-0.5 wt % Cu films. The reaction kinetics between Al alloys and TiN layers was studied by transmission electron microscopy and by investigating the resistance rise mechanism. Si was found to enhance thin intermetallic compound formation between the Al alloys and TiN on samples annealed at 450 °C.
Noncontact, 1 °C resolution temperature measurement by projection moiré interferometry
Authors: Zaidi Saleem H. , Brueck S. R. J. , McNeil J. R.
Published: July 2002

A rapid, inexpensive temperature measurement scheme, applicable across a broad temperature range, based on noncontact measurement of the expansion of a grating structure on the surface of interest is demonstrated. A simple projection moiré technique is used to remotely determine the grating periodicity and, hence, the temperature. An optical Fourier transform technique is introduced to simplify the analysis. A sensitivity of ±0.5 °C for a grating length of 6 mm in a Si wafer around room temperature is demonstrated.
Spin–disorder scattering in europium-doped indium antimonide thin films
Authors: Morelli D. T. , Partin D. L. , Heremans J. , Thrush C. M.
Published: July 2002

We have studied the low temperature magnetoresistance of In1−xEuxSb for a range of europium concentrations. We find that the addition of the rare earth element reduces the carrier mobility substantially and alters dramatically the character of the magnetoresistance. In particular, we observe negative magnetoresistance for 0.012<x<0.05. We attribute this to a predominance of scattering of the conduction electrons by the magnetic spins of the europium atoms, a scattering process which becomes less effective as the spins align with the magnetic field. For the most lightly doped sample, the magnetoresistance becomes positive at high fields, indicating complete saturation of the spin alignment and appearance of normal (classical) magnetoresistance. In addition, for samples not too heavily doped with europium, the magnetoresistance for very low fields (less than 0.5 T) is small and positive before reaching a maximum and evolving into a negative magnetoresistance. This behavior, similar to that seen in EuSe, is thought to be due to a redistribution of the conduction electrons in the spin–split electronic energy levels.
Continuous wave laser induced chemical reactions with integrated circuits
Authors: Auvert Geoffroy
Published: July 2002

Interaction of a focused continuous wave laser beam with integrated circuits leads to various chemical reactions according to the nature of the irradiated interface and to the surrounding atmosphere. Silicon, tungsten, and nickel were locally deposited using silane, tungsten fluoride, or nickel carbonyl, respectively. The kinetics of these chemical reactions have been investigated and compared to the results of an appropriate kinetic model for surface reactions. Various chemical reactions for surface etching have also been investigated, such as etching of aluminum or silicon dioxide which occur at high temperature. Cutting interconnections, etching insulator layers, or depositing new chemical connections are the main applications of the laser–gas–surface chemical interaction, which is being more and more widely used for micron size features.
Photoionization of sputtered neutrals for reliable and sensitive depth profiles
Authors: Becker C. H. , MacKay S. G. , Welkie D. G.
Published: July 2002

Two relatively new methods of sensitive and quantitative depth profiling are described. They both rely on efficient photoionization of sputtered neutral atoms and molecules, followed by mass spectrometry. This is in contrast to the commonly used technique of secondary ion mass spectrometry (SIMS) where only the charged sputtered particles are observed. The prime reason for examining the neutral sputtered component is that it typically represents the overwhelming majority of the sputtered flux, and therefore this decoupling of sputtering and ionization can readily result in a much more quantitative and sensitive measure. The two methods that probe the neutral component are distinguished by whether selective or nonselective photoionization is used. These two approaches are discussed briefly and some examples of the nonselective approach (surface analysis by laser ionization, SALI) are shown along with comparisons to SIMS. These examples demonstrate a substantial reduction of matrix effects for SALI at buried interfaces and at surfaces of ultrashallow implants.
Molecular-beam epitaxy growth of GaAs/Ca0.5Sr0.5F2/GaAs multilayer structure
Authors: Young K. , Kahn A. , Horng S. , Phillips Julia M.
Published: July 2002

Epitaxial GaAs/Ca0.5Sr0.5F2(1800 Å)/GaAs heterostructures have been grown by molecular-beam epitaxy on (100), (111)A, (511)A, (511)B, (711)A, and (711)B GaAs substrates. We used reflective high-energy electron diffraction, Auger electron spectroscopy, low-energy electron diffraction, Rutherford backscattering (RBS), scanning electron microscopy, and Raman scattering to study the surface morphology, crystallinity, and chemical composition of these films. On the (100) orientation, the top GaAs had a flat microstructure; the surface crystallinity improved with increased thickness from 500 Å to 1 μm, but the size of grains due to antiphase disorder also increased with thickness. On the (111)A orientation, the GaAs formed (100)-facets to lower the surface free energy. The surface morphology and near-surface crystallinity improved with increased thickness. The top GaAs films from (511)A and (511)B substrates showed the best near-surface crystallinities from RBS, electron channeling pattern, and Raman scattering experiments. The properties of top GaAs on (711)A and (711)B substrates were not as good as those from (511)s, but better than those from (100) and (111)A.
Accurate determination of misfit strain, layer thickness, and critical layer thickness in ultrathin buried strained InGaAs/GaAs layer by x-ray diffraction
Authors: Chen Y. C. , Bhattacharya P. K. , Singh J.
Published: July 2002

We have analyzed data obtained from double-crystal x-ray rocking curve measurements to determine the lattice constants, strain relaxation, thickness, and critical thickness of a thin InxGa1−xAs layer embedded in GaAs. The use of a very wide x-ray scan angle (∼2.0°) allows the simultaneous determination of buried layer thickness and strain with greater accuracy. The critical thicknesses so obtained for buried InGaAs layers are smaller than that predicted by the energy balance model and larger than that predicted by the force balance model.
Fabrication of silicon nanostructures with electron-beam lithography using AlN as a dry-etch durable resist
Authors: Tada Tetsuya , Kanayama Toshihiko
Published: July 2002

Radio-frequency-sputtered AlN acts as a negative-type electron- and ion-beam resist with high-resolution and high dry-etch durability. Fine structures of silicon (30–50 nm wide) with high-aspect ratio (≳10) have been fabricated using the AlN resist with electron-beam lithography and succeeding low-temperature dry etching with SF6 at −130 °C. They were thermally oxidized at 800 °C to reduce the size further. Structures less than 20 nm have been obtained.
Three-dimensional simulations of quantum transport in semiconductor nanostructures
Authors: Ting D. Z.-Y. , Kirby S. K. , McGill T. C.
Published: July 2002

We introduce the planar supercell method as a means for treating three-dimensional quantum transport in mesoscopic tunnel structures. Our model treats potential variations along the growth direction as well as the lateral directions. The flexibility of the method allows us to examine a variety of physical phenomena relevant to quantum transport, including alloy disorder, interface roughness, defect impurities, and zero-dimensional, one-dimensional, and two-dimensional quantum confinement, in a variety of device geometries ranging from double barrier heterostructures to quantum wire electron waveguides. Using this method, we have studied the transport properties of double barrier heterostructures with alloy barriers, including the effect of clustering in the alloy layers. We have also examined interface roughness in double barrier structures, and analyzed k∥ scattering and lateral localization. In addition, we have studied the transport properties of a quantum wire electron waveguide, and explored its sensitivity to the geometry of waveguide openings.
Ohmic contact to p-Zn(S,Se) using a pseudograded Zn(Te,Se) structure
Authors: Fan Y. , Han J. , He L. , Saraie J. , Gunshor R. L. , Hagerott M. , Jeon H. , Nurmikko A. V. , Hua G. C. , Otsuka N.
Published: July 2002

A low-resistance quasiohmic contact to p-Zn(S,Se) is described which involves the injection of holes from heavily doped p-ZnTe into ZnSe via a Zn(Te,Se) pseudograded band gap region. The specific contact resistance is measured to be in the range of 1.2–2.1×10−3 Ω cm2. The graded heterostructure contact scheme allows temperature-dependent Hall measurements of p-ZnSe, and also has been incorporated as an effective injector of holes for a Zn(S,Se)-based diode laser and light emitting devices, demonstrating the usefulness of the new contact scheme at high current densities.
Effects of low energy ion exposure on modulation-doped GaAs heterostructures
Authors: Li F. , Spencer G. F. , Wang T. , Andrews C. C. , Kirk W. P.
Published: July 2002

In order to determine the electrical isolation mechanism of low energy ions impinging on GaAs heterostructures, a systematic magnetotransport study was performed on the two-dimensional electron gas (2DEG) of a GaAs modulation doped heterostructure. Sample devices were bombarded with 150 eV Ar+ ions while the room temperature resistances were measured in situ. The effectiveness of photoresist as a masking material was tested. Magnetotransport measurements were carried out in a dark condition at 4.2 K, and the resistance, mobility, and carrier density of the 2DEG were monitored as functions of the ion exposure time. The isolation results are consistent with a screening model for the 2DEG electrons. In this model, the onset of electrical isolation is due to the breakdown of the screening because milling of the surface results in depletion of the 2DEG carriers. At present, no additional effects of the low energy ions, such as material damage from ion penetration, have been confirmed
Diffraction gratings for measuring slow mode surface plasmon polaritons
Authors: Tiberio R. C. , Pugh G. M. , Sjodin T. , Reed B. W. , Sparks P. D.
Published: July 2002

Electron beam lithography and reactive ion etching were used to fabricate diffraction gratings with periods between 70 and 110 nm. The gratings were formed in a thermally grown SiO2 layer and used as substrates for aluminum–aluminum oxide–gold tunnel junctions. The light emission from the tunnel junctions under direct-current bias conditions is due to the scattering of the surface plasmon polaritons (SPPs). In particular, by isolating the scattering of the slow mode SPP off the gratings the dispersion relation of the slow mode was determined.
Molecular-beam epitaxial growth surface roughening kinetics of Ge (001): A theoretical study
Authors: Venkatasubramanian R. , Dorsey Donald L.
Published: July 2002

A stochastic model for the molecular-beam epitaxial (MBE) growth of Ge is developed based on the master equation approach with solid-on-solid restriction and quasichemical approximation. The surface kinetic processes included are adsorption, evaporation, and intralayer and interlayer surface migrations. The growth rate, the time averaged intensity of reflection high-energy electron diffraction (RHEED) (using kinematical theory of electron diffraction) were obtained for the MBE growth of Ge with the temperature in the range 423—698 K and a flux of 1 Å/s. The growth rate was observed to be 1 Å/s implying unity sticking coefficient. The time averaged surface roughness and isolated terrace adatom concentration which are good indicators of the average surface roughness, are found to be independent of the substrate temperature below 473 K and above 648 K. In the intermediate temperature range, the isolated terrace adatom concentration and the surface roughness decrease with increasing temperature. The kinetic roughening temperature above which a smooth surface remains smooth, is identified from the temperature dependence of the time averaged surface roughness, terrace adatom concentration, and the RHEED intensity, as 648 K. The temperature dependence of the time averaged RHEED intensity and the kinetic roughening temperature obtained from this study compare favorably with experimental results. The phenomenon of kinetic surface roughening is explained in terms of competition between the incorporation of Ge atoms on the surface, which is a surface roughening process and the migration of Ge atoms to energetically favorable island edge sites which is a surface smoothing process.
Observation of a 1.2 eV defect photoluminescence peak in heavily planar-doped n-type GaAs grown by molecular- beam epitaxy
Authors: Sadwick L. P. , Reihlen E. H. , Jaw D. H. , Hwu R. J. , Streit D. C.
Published: July 2002

In this work, the results of a study on the 10 K and room temperature photoluminescence (PL) response of single and multiple silicon planar- (also known as delta) doped GaAs are reported. These PL results were compared to the PL results from a comprehensive set of 24 uniformly silicon-doped n-type samples with nominal doping levels from 1015 to 1019 cm−3. The silicon planar-doped GaAs samples consisted of a set of seven samples and were grown in sequential order so as to minimize any systematic variations or errors. All of the planar-doped samples were cladded with AlGaAs to increase the PL efficiency. For all cases investigated, both the free carrier density and Hall mobility monotonically decrease as the nominal effective doping increases. Strong peak broadening and shifting was observed indicative of the Moss–Burstein effect in both the uniformly and planar-doped samples having an effective nominal volume doping density in the range of 1018 cm−3 or higher. The most striking feature observed in the PL spectra of the high integrated sheet charge density planar doped samples was a strong peak which occurred at a photon energy of ∼1.2 eV. Also this 1.2 eV peak was observed in all uniformly doped samples which had a nominal doping density greater than ∼6×1018 cm−3.
Deep level transient spectroscopy and admittance spectroscopy of Si1−xGex/Si grown by gas-source molecular-beam epitaxy
Authors: Li S. H. , Smith S. R. , Bhattacharya P. K. , Chung S. W. , Mitchel W. C.
Published: July 2002

Deep levels and measured band discontinuities in Si/SiGe heterostructures grown by gas-source molecular-beam epitaxy have been identified. Hole traps in the p-type, undoped, single layers of Si1−xGex (0.05≤x≤0.26) have activation energies ranging from 0.029 to 0.45 eV and capture cross sections (σ∞) ranging from 10−9 to 10−20 cm2. Possible origins of these centers are discussed. It is found from admittance spectroscopy measurements that the band discontinuity is almost entirely in the valence band for 0<x≤0.1.
Molecular-beam epitaxy growth of semiconductor heterostructure optical converter lasers using the InGaAs/AlGaAs materials system
Authors: Goodhue W. D. , Le H. Q. , Cecca S. Di
Published: July 2002

Optically pumped semiconductor heterostructures offer a new way to fabricate lasers and amplifiers having high output powers and efficiencies together with low output beam divergences, beam aspect ratios, and thresholds. High-power diode-pumped InGaAs/GaAs/AlGaAs semiconductor heterostructure optical converter (SHOC) lasers have been operated at output powers as high as 1.7 W continuous wave with an output beam divergence as low as ∼11° by ∼3° at the half-power points. The molecular-beam epitaxy grown 12–20-μm-thick InGaAs/GaAs/AlGaAs heterostructures forming the SHOC laser cavities consist of distributed gain media over dielectric mirror stacks. Although the present devices have been optimized for efficient transverse pumping using external linear diode-laser arrays, designs that monolithically incorporate the pump with the SHOC structure are also feasible.
Molecular-beam epitaxial growth of InSb on GaAs and Si for infrared detector applications
Authors: Li L. K. , Hsu Y. , Wang W. I.
Published: July 2002

InSb epitaxial films were grown on GaAs and Si substrates by molecular-beam epitaxy using an intermediate AlSb buffer layer. The use of an AlSb intermediate buffer layer greatly facilitates the overgrowth of InSb on significantly lattice-mismatched foreign substrates, such as GaAs and Si. Hall mobility, x-ray rocking curve, and infrared absorption measurements were performed to characterize the samples. Using a 300 nm AlSb buffer layer, 3 μm thick InSb films on GaAs and Si substrates with room-temperature electron mobilities as high as 55 000 cm2 V−1 s−1 were routinely achieved. X-ray rocking curve linewidths of 199 arcsec for InSb on GaAs and 230 arcsec for InSb on Si have been achieved, which represent the best results to date. Our results indicate that AlSb is a very effective buffer layer for InSb devices grown on GaAs and Si substrates.
Ge segregation during the growth of a SiGe buried layer by molecular beam epitaxy
Authors: Godbey D. J. , Ancona M. G.
Published: July 2002

The germanium concentration profile of thin Si/SiGe heterostructures grown at 500 °C using elemental source molecular beam epitaxy were measured by x-ray photoelectron spectroscopy. The primary finding from these measurements is that there are significant segregation effects in these commonly grown structures which affect both the ‘‘leading’’ and ‘‘trailing’’ interfaces. Kinetic simulations derived from the measurements indicate that upon opening of the germanium shutter for the deposition of a Si0.7Ge0.3 layer, the surface monolayer must be built up to a germanium composition of greater than 96% before the composition of the deposited alloy layer is equal to the flux composition. This buildup causes a germanium depletion at the leading interface. Upon termination of the germanium flux, incorporation of the germanium rich monolayer into the growing silicon cap layer causes a corresponding degradation of the trailing interface.
Characteristics of in situ Cl2 etched/regrown GaAs/GaAs interfaces
Authors: Mui D. S. L. , Strand T. A. , Thibeault B. J. , Coldren L. A. , Petroff P. M. , Hu E. L.
Published: July 2002

In situ etch and regrowth experiments on GaAs have been performed. The etching and electrical characteristics of the regrown interface of two different etching methods have been studied. The etching was carried out either by uncracked Cl2 chemical gas etching (CGE) at 300 °C or ion beam assisted etching (IBAE) using Cl2 gas and an argon ion beam. Reflection high-energy electron deflection (RHEED) patterns of IBAE surfaces are streaky indicating that the surfaces are smooth. On the other hand, CGE surfaces exhibit spotty RHEED which is a result of the crystallographic etching nature of CGE at low etching temperatures. The electrical properties of planar p-type etched/regrown samples are studied by deep level transient spectroscopy and capacitance–voltage. CGE samples exhibit a discrete trap level located at 0.52 eV above the valence band maximum (VBM), while IBAE samples display two discrete trap levels at 0.72 and 0.98 eV above VBM.
Reproducible growth and application of AlAs/GaAs double barrier resonant tunneling diodes
Authors: Mars D. E. , Yang L. , Tan M. R. T. , Rosner S. J.
Published: July 2002

More than 15 AlAs/GaAs double barrier resonant tunneling diode wafers of nominally identical structure were grown and excellent reproducibility in the I–V characteristics was found. The peak current density varied by less than 10% within a wafer and less than 20% from wafer to wafer. A variation of 20% in the peak current density corresponds to an average variation of 0.3 monolayers in the thickness of the AlAs barriers. An internal switching time of 6 ps was measured using electro-optic sampling and a circuit using these devices operated at more than 50 GHz.
Determination of molecular beam epitaxial growth parameters by ellipsometry
Authors: Droopad R. , Kuo C. H. , Anand S. , Choi K. Y. , Maracas G. N.
Published: July 2002

The use of ellipsometry as an alternative technique for in situ determination of molecular beam epitaxial growth parameters has been demonstrated. Epitaxial growth has been monitored in real time using three discrete wavelengths to extract growth rates and alloy composition. The effect of substrate rotation on the measured growth rates has also been determined by this technique. From measurements of the GaAs growth rates versus substrate temperature, a value of 4.68±0.12 eV for the activation energy for Ga desorption during GaAs growth was obtained. This agrees with values obtained by other measurement techniques.
Thin film materials for the preparation of attenuating phase shift masks
Authors: Shih K. K. , Dove D. B.
Published: July 2002

There is considerable interest in the use of phase shift masks as a route to extend the resolution, contrast, and depth-of-focus of lithographic tools beyond what is achievable with the normal chrome mask technology. In the attenuating phase shift mask, the chrome layer is replaced with a slightly transparent layer and the mask is etched so that light through the layer is 180° out of phase with light through clear regions. Thus, optical interference occurs which has the effect of increasing contrast at edges and of improving depth-of-focus. In this article, experiments of thin film materials designed to provide both the desired 180° phase shift and optical absorption in a single layer are described.