bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanometer lithography for III–V semiconductor wires using chloromethylated poly-α-methylstyrene resist
Authors: Maile B. E. , Forchel A. , Germann R. , Menschig A. , Meier H. P. , Grützmacher D.
Published: July 2002

Chloromethylated poly-α-methylstyrene negative resist was investigated for its suitability in the fabrication of nanometer structures for optical studies. Investigating the photoluminescence efficiency of etched GaAs/AlGaAs wires we find a steep decrease with decreasing wire width, whereas for InGaAs/InP the decrease is much smaller. The difference in the behavior of the material systems can be explained by the effectiveness of surface recombination.
High-resolution fabrication process for silicon ion masks
Authors: Fong F-O. , Sen S. , Stumbo D. P. , Wolfe J. C. , Randall John N.
Published: July 2002

A process is described for fabricating silicon masks for ion beam lithography. Masks have been fabricated with 0.02-μm features in 1.5-μm-thick silicon membranes.
Defect study in GaAs bombarded by low-energy focused ion beams
Authors: Gamo Kenji , Miyake Hideto , Yuba Yoshihiko , Namba Susumu , Kasahara H. , Sawaragi H. , Aihara Ruso
Published: July 2002

GaAs was exposed to focused Ga+ beams at various beam energies ranging from 100 eV to 150 keV to investigate properties of defects induced by low-energy focused ion beams. Defect concentration and distribution profiles were measured by the deep-level transient spectroscopy technique. It was found that the defect concentration is greatly reduced for irradiation at a beam energy below 1 keV. Defects were observed even at a depth of ≥1500 Å, which is far beyond the ion range (∼15 Å) for 1-keV Ga+ . This indicates that the defect is induced by diffusion and trapping of mobile primary defects. It was also found that the defects induced by the low-energy irradiation are easily annealed out at 600 °C, while the defects induced by the high-energy irradiation still exist after annealing at 850 °C.
A new approach to simulating the operation of liquid metal ion sources
Authors: Zheng Cui , Linsu Tong
Published: July 2002

In order to simulate the electrically driven motion of conducting fluid occurring in the operation of liquid metal ion sources (LMIS’s), an equation system of electrohydrodynamics (EHD) has been set up, which includes gravity, viscosity, electrical stress, and surface tension. A set of numerical methods has been developed to compute the EHD equations. By means of a special technique, the MAC (marker and cell) method, the emitter shape of LMIS can be dynamically described without any assumptions. With the help of the numerical methods, a cylindrical fluid motion driven by electrical force and the liquid metal flow on a needle apex have been calculated. The results have thrown new light on the physical understanding of LMIS operation.
Fabrication and transport characteristics of semiconductor wire and ring structures
Authors: Ishibashi K. , Takagaki Y. , Gamo K. , Namba S. , Takaoka S. , Murase K. , Ishida S. , Aoyagi Y.
Published: July 2002

We have fabricated narrow wires and small rings from GaAs/AlGaAs double heterostructures by using electron beam lithography and dry etching techniques. We describe the nature of universal conductance fluctuations in a single wire and the magnetoresistance oscillations with a period of-h/e in a ring structure. It is experimentally shown that (i) from a single wire experiment, electrons with energies differing by the correlation energy Ecorr, have quite different magnetoresistance patterns, and (ii) from a ring experiment, the large aspect ratio (diameter/width) is important to obtain well-defined oscillations.
A new formation process of anodizable structures of n, n+, and n− silicon for the production of silicon-on-insulator structures
Authors: Tu Xiang-Zheng
Published: July 2002

A new formation process of anodizable structures of n, n+, and n− silicon for the production of silicon-on-insulator (SOI) structures is described. In this process, proton implantation is employed to produce a high donor concentration layer near the surface of n-type silicon substrates, and nitrogen ion implantation is employed to define highly resistive islands in the high donor concentration layer. The anodization of silicon in HF solution to form porous silicon and the consequent oxidization of the porous silicon to form silicon dioxide is restricted to the high donor concentration regions. It is demonstrated that silicon islands with a width of 50 μm and a thickness of 0.55 μm are successfully isolated by an oxidized-porous-silicon layer with a thickness of 2.25 μm.
Localized ion beam induced deposition of Al-containing layers
Authors: Rüdenauer F. G. , Steiger W. , Schrottmayer D.
Published: July 2002

A simplified model is developed for localized ion beam induced metal deposition from metal-containing gases. The model takes into account simultaneous deposition and resputtering of deposited material and is based on two parameters, i.e., deposition cross section and sputtering yield of the deposit. Numerical values of these parameters are determined from experimental measurements of layer thickness under different deposition conditions for the case of deposition of Al-containing layers by 3.5–10 keV Ar bombardment in a trimethyl-aluminum (TMA) atmosphere. The knowledge of these parameter values allows one to predict deposition rates for given experimental conditions (current density, gas pressure, and beam energy).
Ion-bombardment-enhanced plasma etching of tungsten with NF3/O2
Authors: Greene W. M. , Hess D. W. , Oldham W. G.
Published: July 2002

Ions and neutrals sampled from a NF3/O2 etching plasma were observed by a quadrupole mass spectrometer and cylindrical mirror ion energy analyzer to investigate ion-bombardment-enhanced etching of tungsten. Dc biasing of a 13.56 MHz, 2.7 Pa, 1.24 W/cm2 , 3/1 NF3/O2 glow discharge raised the average ion energy bombarding the grounded electrode from 35 to 172 eV concurrent with an increase in the ion current by a factor of 3. Total conversion of NF3 to N2 and F2 occurred under these conditions yielding a typical etch rate of polycrystalline tungsten of 150 nm/min. The primary ion observed was WF+5. The WF6 etch product concentration was independent of ion energy, but correlated strongly with ion current. The results support a damage-induced chemical reaction as the enhancement mechanism.
Properties of strained layer InxAl1−xAs/InP heterostructures
Authors: Chu P. , Wieder H. H.
Published: July 2002

X-ray diffraction and photoluminescence measurements were made on InxAl1−xAs layers grown by molecular-beam epitaxy whose lattice constants are matched, in tension, or in compression, relative to their (100)-oriented InP substrates. Using a linear interpolation between the InAs and AlAs elastic stiffness coefficients, hydrostatic pressure coefficients, and shear deformation potentials, the strain-dependent fundamental band gaps were calculated and shown to be in good agreement with the experimentally measured data within the pseudomorphic limit. The calculated composition-dependent critical thickness for the onset of plastic deformation of these layers is shown to be in better agreement with the energy balance model of People and Bean than the mechanical equilibrium model of Matthews and Blakeslee.
Simulation of GaAs cluster formation on GaAs(001̄), AlAs(001̄), Si(001), and As1/Si(001) surfaces
Authors: Choi D. K. , Koch S. M. , Takai T. , Halicioglu T. , Tiller W. A.
Published: July 2002

Recently developed semiempirical potential energy functions for the Ga–As–Si and Ga–As–Al systems have been applied here to determine the excess formation energy for GaAs clusters on GaAs(001̄), AlAs(001̄), Si(001), and one atomic layer As-covered Si(001) substrates as a function of cluster size and cluster shape by the Monte Carlo technique. Pyramidal type ledges on the GaAs clusters are found to be the favored ledge for the first three layers while an inverted-pyramidal type ledge is also favored in certain cases for the As1/Si(001) substrate. Cluster formation at ledges is compared with cluster formation on a flat terrace for the Si(001) and the As1/Si(001) substrates.
Molecular-beam epitaxy and deposition of high-T
c superconductors
Authors: Hellman E. S. , Schlom D. G. , Missert N. , Char K. , Harris J. S. , Beasley M. R. , Kapitulnik A. , Geballe T. H. , Eckstein J. N. , Weng S.-L. , Webb C.
Published: July 2002

We have grown thin, highly oriented, polycrystalline DyBa2Cu3O7−x films using molecular-beam epitaxy (MBE) techniques that show the onset of superconductivity at temperatures above 90 K and complete transitions at temperatures as high as 87 K. These films have critical current densities as high as 5×105 A/cm2 at 4.2 K. Films were grown in a modified Varian 360 MBE machine using effusion sources containing the metal constituents, along with a gaseous oxygen source. The early stages of deposition were monitored with reflection high-energy electron diffraction (RHEED). The best films were obtained on SrTiO3 substrates at substrate temperatures of 600–750 °C. At these temperatures, the initial stage of growth is dominated by epitaxy of copper islands. At lower temperatures, the growth is amorphous, while at higher temperatures, copper may not be incorporated into the film. Copper incorporation is also affected by oxygen flux. In all cases, the films are semiconducting or insulating as grown, and become superconducting only after high-temperature oxygen anneals. We comment on the prospects for obtaining true epitaxy superconducting phase in situ.
Molecular-beam epitaxial growth mechanisms on the GaAs(100) surface
Authors: Harbison James P. , Farrell Helen H.
Published: July 2002

We propose a mechanism for molecular-beam epitaxial growth on GaAs(100) and other III–V(100) surfaces which includes a detailed description of the changes in surface reconstructions throughout the growth cycle. We have previously used the electronic stability criterion which requires all arsenic dangling bonds to be filled and all gallium dangling bonds to be empty to successfully predict static surface reconstructions of III–V surfaces. In the work presented here, we use these same criteria to predict electronically stable intermediates during the growth cycle which are characterized by surface dimers and dimer vacancies. The resulting model proposes specific reconstructed electronically stable intermediates during the complete growth cycle. The model explains the retention of the (2×4) overall reconstruction throughout the cycle, provides at least one mechanism for the cyclical roughness variations observed via reflection high-energy electron diffraction oscillations, and pinpoints certain rate limiting configurations in the process which should lead to further fruitful experimental investigations.
Mass spectrometry during molecular-beam epitaxy: An alternative to reflection high-energy electron diffraction
Authors: SpringThorpe A. J. , Mandeville P.
Published: July 2002

A quadrupole mass spectrometer has been positioned in a commercial molecular-beam epitaxy system so that the desorption of atomic and molecular species, from GaAs substrates, can be monitored at various stages in the growth process. The sharply peaked Ga2O154 thermal desorption spectrum, from the surface oxides, is found to provide a useful temperature calibration, and its width is a measure of the substrate temperature distribution. Gallium desorption from GaAs surfaces, as a function of temperature, can be used to calculate growth rate curves, whereas the desorption flux from GaAlAs surfaces enables the alloy composition to be determined directly. Interfacial transients between layers can be monitored, and results are described which suggest that GaAs/AlAs interfaces are not atomically abrupt. Unlike the reflection high-energy electron diffraction technique, these measurements can all be carried out on rotating, large size, substrates.
Direct determination of Al content in molecular-beam epitaxially grown AlxGa1−xAs (0≤x≤1) by nuclear resonant reaction analysis and x-ray rocking curve techniques
Authors: Xiong Fulin , Tombrello T. A. , Chen H. Z. , Morkoç H. , Yariv A.
Published: July 2002

The techniques of nuclear resonant reaction analysis (NRRA) using 27Al(p,γ)28Si and x-ray rocking curve (XRC) based on double-crystal diffractometry have been utilized to determine directly the Al concentration and its depth distribution in molecular-beam epitaxially (MBE) grown AlxGa1−xAs /GaAs heterojunctions. Combination of these two methods has revealed a linear relationship between the Al mole fraction and the lattice strain. This can eliminate the need for assuming that Vegard’s law holds and that extrapolated elastic coefficients are accurate. The result supports that both of these two techniques provide an accurate determination of the absolute Al content and crystalline quality in AlxGa1−xAs /GaAs throughout the entire composition range (0≤x≤1) as well as profiling the Al distribution. In addition, significant depth fluctuations in the Al mole fraction in some samples have been probed by the NRRA technique as well as by the XRC. The result suggests that a reliable and accurate measurement must be undertaken to ensure the control of the required Al distribution, which is necessary for the high performance of many devices.
Growth of GaAs, AlGaAs, and InGaAs on (111)B GaAs by molecular-beam epitaxy
Authors: Elcess K. , Liévin J.-L. , Fonstad C. G.
Published: July 2002

The growth by molecular-beam epitaxy of high-quality epitaxial layers of GaAs, AlGaAs, and InGaAs on GaAs substrates oriented normal to the [111] direction is reported. The (111)B surface of GaAs is found, in contrast to the (001) surface, to be extremely fragile after the desorption of its oxide. Surface roughening occurs within seconds of oxide desorption unless growth is initiated promptly. Reflection high-energy electron diffraction studies also reveal several structural transformations occurring on the surface of the substrate. The reconstructions are sensitive to the temperature and to the arsenic flux. Temperature and flux ranges leading to two-dimensional, monolayer growth are delineated, and this information is used to grow superlattices and quantum wells with smooth interfaces. Both unstrained lattice-matched and strained pseudomorphic layers have been grown.
Surface science studies of semiconductor growth processes
Authors: Buhaenko D. S. , Francis S. M. , Goulding P. A. , Pemble M. E.
Published: July 2002

A new approach to the study of semiconductor growth mechanisms is described which utilizes surface science and related photon-based techniques. It is possible to study growth processes over the pressure range 5×10−11 to 103 mbar through the use of an isolatable atmospheric pressure reactor described briefly. As an illustration of the potential of the surface science approach, the effectiveness of the reducing hydrogen atmosphere employed in the pregrowth bake of a GaAs (100) metal-organic vapor phase epitaxy (MOVPE) substrate in removing surface carbon and oxygen is determined using Auger electron spectroscopy. It is shown that at a pressure of 0.5 mbar of H2, temperatures as low as 600 K are sufficient to remove the surface carbon and oxygen contamination present on the substrate following wet chemical etching and heating in ultrahigh vacuum. This result implies that the conventional MOVPE sample bake at high temperatures (>850 K), in H2 and AsH3 is not necessary to produce clean substrates. Following the H2 treatment the GaAs(100) surface gives rise to a (1×1) low-energy electron diffraction pattern suggesting that it has been stabilized towards reconstruction via hydrogen chemisorption.
Ion beam assisted chemical etching of Si by SF6
Authors: Affolter K.
Published: July 2002

Ar+ ions of 0.5 to 2 keV from a broad-beam Kaufman ion source have been used to induce chemical etching of Si by SF6 effusing from a gas dispensing ring placed near the Si surface. Etch rates have been measured as a function of sample temperature, SF6 flux, and ion energy. As the Si temperature is reduced below 120 K the Si yield per Ar+ ion rises to reach a maximum enhancement of about 8–10 just below 100 K, compared to pure physical sputtering. The results suggest that the dominant effect of the sample temperature is to control the fluorine supply via the evaporation rate of physisorbed SF6 molecules. This etching process has been applied to produce micron-sized, blazed gratings in Si, using Al as a hard mask. Blaze angles up to 70° have been produced by tilting the sample with respect to the ion beam.
Pilot production of half-micron x-ray masks
Authors: Hughes Gregory , Doyle Gary , Foss Gordon , Gorbachenko Nick
Published: July 2002

The key specifications for 0.5-μ x-ray mask have been achieved in a pilot production operation. A poly(butene-1-sulfane) (PBS), Cr patterning process has been used as the top layers of a trilevel stencil in which to plate the opaque gold absorber. The following specifications were exceeded: registration <0.08 μ (3 σ), linewidth control <0.06 μ (3 σ), and defect density <20/cm2.
The electrical characteristics of metal/SiO2/InSb capacitor fabricated by photoenhanced chemical vapor deposition
Authors: Sun Tai-Ping , Lee Si-Chen , Yang Sheng-Jenn
Published: July 2002

The AuCr/SiO2/InSb metal–oxide semiconductor capacitor was fabricated using photo-enhanced chemical vapor deposition. The SiO2 layer with a thickness of 1000 Å was deposited on InSb substrate at 200 °C. The electrical and structural properties were analyzed by capacitance–voltage and Auger electron spectroscopy, respectively. The high-frequency (1-MHz) capacitance–voltage measurements were usually performed after positive or negative bias-temperature stressing. Both the flatband voltage shift and the change of hysteresis of capacitance–voltage curve indicate the existence of enormous negative mobile charges in the bulk SiO2. These negative charges can move in SiO2 freely even in the room temperature. Auger depth profile reveals that these negative mobile charges are metallic indium and antimony ions.
Surface photoprocesses in laser-assisted etching and film growth
Authors: Houle F. A.
Published: July 2002

Photochemical etching and deposition systems involve a range of laser-induced and spontaneous processes occurring on rough, chemically heterogeneous surfaces. As such, they present an interesting opportunity for extending our understanding of surface photophysical and photochemical phenomena. In this article results of recent experiments investigating the effect of illumination on adsorption, dissociation, and desorption in such systems are described. Studies carried out under realistic film deposition and etching conditions are compared to studies of submonolayer assemblies on clean crystalline surfaces.
Temporal and spectral dependences of the anisotropic dielectric responses of singular and vicinal (001) GaAs surfaces during interrupted molecular-beam epitaxy growth
Authors: Aspnes D. E. , Studna A. A. , Florez L. T. , Chang Y. C. , Harbison J. P. , Kelly M. K. , Farrell H. H.
Published: July 2002

We determine the temporal evolution of the real and imaginary parts of the anisotropic components of the surface dielectric responses Δ(εd) of singular and vicinal GaAs surfaces on interruption of the As flux during otherwise normal growth by molecular-beam epitaxy (MBE). The measurement of dielectric, rather than simply reflectance, anisotropies is made possible by a new, essentially strain-free quartz window that not only extends our spectral range but also allows relative phases as well as amplitudes to be measured for near-normal incidence reflectances along [110] and [1̄10]. Data are obtained in 0.1-eV increments from 1.5 to 5.5 eV for a singular (001) surface and for vicinal surfaces 6° off (001) toward (111)A and (111)B, respectively. The observed temporal evolutions are approximately piecewise linear or exponential, indicating that each surface passes through several distinct phases before arriving at its final Ga-stabilized condition. Nearly exponential initial transients with time constants of <1 s are interpreted as evaporation of excess As present during growth. A supersaturation phase transition is observed for the vicinal surface 6° off (001) toward (111)A. Spectra constructed from these transients show optical structures at 1.8–1.9. 2.5, and 4.1 eV that, because they are already well developed at 1 s, can be related to the initial As excess. The change in Δ(εd) that occurs between 2 and 5 s for the singular surface is similar to the Δ(εd) spectrum of Ga–Ga dimers, which is calculated here in a tight-binding approximation.
Photoluminescence in strained-layer quantum wells
Authors: Wang T. Y. , Lin Z. H. , Stringfellow G. B. , Taylor P. C.
Published: July 2002

Photoluminescence and thermally modulated photoluminescence have been employed in thin single quantum wells in the InP/Ga1−x Inx As/InP system (0≤x≤1). The potential use of these methods to estimate conduction and valence-band offsets in strained-layer heterostructures is discussed.
Vacancy first and second neighbor hopping at a compound semiconductor interface: Insights from computer simulation
Authors: Van Vechten J. A. , Schmid U.
Published: July 2002

We have now demonstrated that the ratio of the activation enthalpies for nearest neighbor hopping of the two types of vacancy in InP are in the 4 to 1 ratio of the masses of the atoms that hop and are in good agreement with the values predicted by the ballistic model (BM), which identifies the activation enthalpy as a kinetic energy. A consequence is that relatively light atoms should hop to second neighbor vacancy sites as easily as heavy atoms hop to nearest neighbor vacancies, and do so without the complication of forming or annihilating antisites. For example, in GaAs B, C, N, Al, Si, and P are predicted to hop to second neighbor sites as easily as As hops to a first neighbor site. Of course, they hop to nearest neighbor sites even more readily. The import of this on the array of point defects predicted to occur as a heterojunction anneals is rather complex. Experiment supports our contention of complexity. For example, in As rich, n-type AlGaAs Mei et al. report D(Al)∝n1  exp(−2.9 eV/kT) if the doping is with Te but D(Al) ∝n3  exp(−4 eV/kT) if the doping is with Si, where n is the free electron density. We have studied the Al diffusion in AlGaAs with the aid of a microcomputer simulation that works out the complex consequences of one’s assumptions re thermochemical parameters at the atomic level. Our previously published BM assumptions lead to the conclusion that Si promotes the conversion of Ga vacancies to trivacancies while Te does not; they also identify 2.9 eV as the sum of the Ga second-neighbor hopping enthalpy and the enthalpy of formation of single negative Ga vacancy in n-type GaAs and identify 4 eV as the sum of the enthalpy of formation of the trivacancy plus its nearest neighbor hopping energy in GaAs. The simulation also finds that Al by itself converts As vacancies to trivacancies plus metal antisite. It shows the trivacancies to diffuse very rapidly and to entrain Al.

We propose that the cation sublattice dominance of Si induced host interdiffusion follows from this entrainment. We also suggest these complexes are related to DX and account for the anomalous variation of the parameters of that defect with Al concentration. Except for the assumption that the hopping kinetic energy be proportional to the mass of the hopping atom, the conclusions stated above are insensitive to the precise values of atomic level parameters assumed. Quantities such as activation energies for macroscopic diffusion are sensitive to the precise values and some of these are either poorly determined or controversial. More simulation than we have accomplished to date is required to establish the relation between precise atomic level values and observable macroscopic quantities.
Ultraviolet photoemission studies of GaAs(100) surfaces chemically stabilized by H2S treatments
Authors: Tiedje T. , Colbow K. M. , Rogers D. , Fu Z. , Eberhardt W.
Published: July 2002

We report photoemission studies of GaAs(100) surfaces treated with H2S. Our high-resolution core level photoemission data show that these surfaces are completely terminated by a GaSx species and the treated surface is stable in air or water. Thus a H2S treatment might result in better device quality surfaces and interfaces than the surfaces prepared by recently proposed chemical treatments involving Na2S or (NH4)2S.
Reduction of GaAs metal–semiconductor field effect transistor sidegating by ultraviolet/ozone cleanup prior to molecular-beam epitaxial growth
Authors: Hitchens W. R. , Brunemeier P. E. , Dobkin D. M.
Published: July 2002

This work demonstrates that UV-ozone cleaning of substrates prior to molecular-beam epitaxial growth, which has been shown by other workers to remove carbon contamination, is effective in suppressing sidegating problems otherwise encountered in GaAs metal–semiconductor field effect transistors fabricated on the epitaxial layers.
Rapid thermal processing of silicon dioxide films in metal–oxide semiconductor capacitors: High-temperature SiO2 decomposition at the SiO2–Si interfaces in inert ambient
Authors: Xie Joseph Z. , Kauget Harvey , Murarka Shyam P.
Published: July 2002

Polycrystalline silicon–silicon dioxide–silicon capacitors were annealed in argon and argon containing oxygen ambients in a rapid thermal annealer. Capacitance–voltage (C–V) characteristics were determined before and after anneal as a function of annealing time at 1100 and 1200 °C. C–V characteristics of the capacitors annealed in argon degraded with increased annealing time and temperature. At 1100 °C oxide capacitance decreased and oxide leakage occurred. At 1200 °C the annealing resulted in catastrophe, capacitance decreased by more than factor of ten. Careful examination of the thin oxide layer, after selective removal of the polysilicon film, showed holes in the oxide, hole density increasing with time and temperature. On the other hand, C–V characteristics of capacitors, annealed in argon containing oxygen, had no significant change after anneal at 1100 °C. Also defect density was extremely low. The C–V characteristics of capacitors annealed in pure argon can be recovered by the anneal in oxygen ambient. Thermal oxide films on silicon wafers were annealed in argon at high temperatures. Formation and lateral growth of physical holes in the oxide layer was found. The linear relation between the size of hole and annealing time was verified. Results are discussed in terms of thermodynamic stability of silicon dioxide on silicon in inert and oxidizing mediums.
Dimer and tetramer formation in an AsH3 cracker studied by calibrated quadrupole mass spectrometry
Authors: Lohe C. , Kohl C. D.
Published: July 2002

The reaction of AsH3 in a gas source with a tungsten filament (W-GS) was studied. The reaction products were detected by a quadrupole mass spectrometer and measured as a function of filament temperature and feed pressure. The mass dependence of the transmission of the quadrupole system was optimized and calibrated using a mixture of five noble gases. The results were corrected for ionization efficiency and cracking pattern. Background and noise effects were reduced by beam modulation. Conditions for buildup of an arsenic deposit within the gas source are discussed. Maximum As2 and As4 production was observed at 800 and 630 °C, respectively. The gas source which decomposes the hydride at a tungsten wire is compared with a second one which decomposes the hydride at a tantalum wire (Ta-GS). Operating conditions that yield predominantly arsenic dimers are achieved only with the tungsten wire source. Chemical reasons are discussed to explain the higher dimer yield of the tungsten source.
I
n s
i
t
u infrared spectroscopy of molecular-beam epitaxy grown GaAs
Authors: Sadwick Larry P. , Wang Kang L. , Joseph David L. , Hicks Robert F.
Published: July 2002

Infrared spectroscopy of adsorbed molecules has been used to characterize semiconductor surfaces before, during, and after molecular-beam epitaxy growth. The technique relies on the principle of multiple internal reflections to enhance the weak response arising from the molecules adsorbed onto the semiconductor surface or trapped within the film. The resulting IR spectrum due to the adsorbed molecules provides detailed information about the chemical and physical structural bonding properties both within the epitaxial layer and at the semiconductor–vacuum interface. The experimental setup is compatible with UHV requirements and has been utilized in the pressure range from atmospheric down to the low-10−10 Torr level.
Molecular-beam epitaxial growth and characterization of InSb on Si
Authors: Chyi J.-I. , Biswas D. , Iyer S. V. , Kumar N. S. , Morkoç H. , Bean R. , Zanio K. , Grober R. , Drew D.
Published: July 2002

InSb layers have been epitaxially grown on Si substrates by molecular-beam epitaxy. Room-temperature electron mobilities are 48 000 and 39 000 cm2/V s for 3.2-μm-thick InSb with and without GaAs buffers, respectively. The corresponding carrier concentrations are 2.2 ×1016 and 2.7 ×1016 cm−3. A sample with an 8-μm thickness has room-temperature mobilities as high as 55 000 cm2/V s with carrier concentrations of ∼2.0 ×1016 cm−3. A sharp band-edge transmission spectrum is observed at room temperature for the 8-μm layer. The photoluminescence spectrum of a 3.2-μm InSb layer grown directly on Si shows a linewidth of 50 meV.
Resonant tunneling of holes through silicon barriers
Authors: Gennser Ulf , Kesan V. P. , Iyer S. S. , Bucelot T. J. , Yang E. S.
Published: July 2002

We have investigated molecular-beam epitaxy (MBE) grown Si/SiGe hole resonant tunneling devices (RTDs) consisting of an unstrained Si0.5Ge0.5 quantum well between two strained Si barriers. A peak current density of 104 A/cm2 and a peak-to-valley current ratio of 1.5:1 at 77 K and 2:1 at 4 K has been obtained. Using magnetotunneling measurements at 4 K, two resonances, corresponding to tunneling through the heavy hole and light hole states, have been identified with a light hole-to-heavy hole effective mass ratio of 3.2, suggesting that the hole band structure in the Si/Si0.5Ge0.5 double barrier system is silicon-like. We have examined devices with the same quantum well structure, but with different spacer thicknesses (90–360 Å) to study the influence of doping profile on the peak-to-valley current ratio and peak voltage position. Using these measurements, we have extracted the electric field across the quantum well for the different devices. These electric field values suggest that holes are exiting the quantum well at their saturation velocity of ∼107 cm/s.
High-temperature growth of Si-doped AlGaAs by molecular-beam epitaxy
Authors: Saito Junji , Kondo Kazuo
Published: July 2002

We studied the growth rate, AlAs mole fraction, surface morphology, and electrical properties of Si-doped AlxGa1−xAs (0≤x≤0.3) layers grown by molecular-beam epitaxy at substrate temperatures from 620 to 770 °C. From the dependence of the growth rates and the AlAs mole fraction on the substrate temperature, we showed that the equilibrium partial pressure of Ga, Al, and As molecules at the growth surface governs the growth rates and the AlAs mole fraction of the epitaxial layers grown at these temperatures. This paper also deals with the growth mechanism of the smooth surface morphology of AlxGa1−xAs grown between 700 and 750 °C using the bonding energy of Al–As and Ga–As. Above 700 °C, the free electron concentration and the mobility of the Si-doped AlxGa1−xAs epitaxial layers were reduced. In particular, the electron concentration and the mobility of AlxGa1−xAs were significantly decreased by intervalley scattering because of incremented AlAs mole fraction. Secondary ion mass spectroscopy showed us that carbon incorporation into the AlxGa1−xAs increased with substrate temperature. We discuss the substrate temperature dependence of mobility and concentration of a two-dimensional electron gas in selectively doped GaAs/N-AlxGa1−xAs heterostructures at 77 K.
A novel electron-beam exposure technique for 0.1-μm T-shaped gate fabrication
Authors: Samoto N. , Makino Y. , Onda K. , Mizuki E. , Itoh T.
Published: July 2002

This article reports on a novel fabrication technique for T-shaped short gates using double-layer electron-beam(EB) resist system, which provides uniform gate length across 2-in. wafers. In the proposed novel fabrication technique, a 1-μm PMMA(I)/0.25-μm PMMA(II) (HI/LOW MW) double-layer resist system is adopted to fabricate T-shaped gates. To avoid the influence of scattered electrons, the bottom PMMA(II) resist is EB-exposed through the top opening with an acceleration of 50 or 25 kV and a single-path line dose of 0.8–2.0 nC/cm. The top opening has been formed with a 25-kV Gaussian electron beam at a 120 μC/cm2 dosage. The developed technique has accomplished T-shaped gates with 70-nm minimum footprint and 0.1–0.2-μm T-shaped gates, whose yield is over 80% on wafers.
The structure of the ZnSe(100)c(2×2) surface
Authors: Farrell H. H. , Tamargo M. C. , Shibli S. M. , Chang Yeh
Published: July 2002

We have investigated the structure and composition of the ZnSe(100)c(2×2)–Zn surface. Contrary to prior assumptions, this surface is not terminated with Zn dimers, but, rather with a half monolayer of Zn atoms. This new structure markedly changes our understanding of the growth interface and should lead to better heteroepitaxial growth on this and similar surfaces.
High-efficiency GaAs solar cells grown by molecular-beam epitaxy
Authors: Melloch M. R. , Tobin S. P. , Stellwag T. B. , Bajgar C. , Keshavarzi A. , Lundstrom M. S. , Emery K.
Published: July 2002

Previously, solar cells fabricated from molecular-beam epitaxually (MBE)-grown material have been inferior in performance to those fabricated from metalorganic chemical vapor deposited (MOCVD) material. We have obtained 1-sun air mass (AM) 1.5 efficiencies of 23.8% for 0.25 cm2 GaAs solar cells fabricated on MBE-grown material. This is the first solar cell fabricated on MBE material which is of comparable performance to solar cells fabricated on MOCVD material. Details of the MBE system preparation and film growth procedure along with a detailed evaluation of the solar cells will be presented.
Exposure characteristics of high-resolution negative resists
Authors: Chiong Kaolin Grace , Wind Shalom , Seeger David
Published: July 2002

Positive and negative resist systems are both essential in the microfabrication of experimental devices. While numerous positive resists have been shown to have high-resolution, negative resists were considered to have poor contrast and resolution. In this paper, the electron-beam exposure characteristics of several negative resist systems including epoxy novolac-type systems [K. J. Stewart, M. Hatzakis, J. M. Shaw, and D. E. Seeger, J. Vac. Sci. Technol. B 7, 1734 (1989); M. Hatzakis, K. Stewart, J. Shaw, and S. Rishton, Microelectron. Eng. 11, 487 (1990)] and two selected vendor resist systems have been investigated. These resist exposure characteristics are related to resist resolution, image profile, edge acuity, and process latitude. The sensitivity of various resists to slight exposures which may be caused by electron scattering in electron-beam lithography or mask diffraction in optical or x-ray lithography varies from resist to resist. The resist system that is least sensitive to these slight exposure effects offers the highest resolution. High-resolution images down to 0.25-μm lines and spaces were delineated only in resist systems with a gamma value higher than 2.5. Resist images of 50 nm dimensions in 0.4-μm-thick resist films have been obtained from the epoxy novolac system with vertical sidewalls and good edge acuity. In addition, results of high-voltage electron-beam exposures showed that residues between small shapes are substantially reduced. Similarly, cleanly resolved features were obtained when a high-contrast mask is used in x-ray synchrotron exposures.
A 100-nm patterned x-ray mask technology based on amorphous SiC membranes
Authors: Haghiri-Gosnet A. M. , Rousseaux F. , Kebabi B. , Ladan F. R. , Mayeux C. , Madouri A. , Decanini D. , Bourneix J. , Carcenac F. , Launois H. , Wisniewski B. , Gat E. , Durand J.
Published: July 2002

A mask technology based on amorphous SiC membranes and stress minimized W and Au absorbers has been developed to reach 100-nm critical linewidth pattern. Using low temperature techniques, plasma-enhanced chemical vapor deposition and rf triode sputtering, very smooth large membranes (45×45 mm2 with a surface roughness <5 nm) have been produced. Two absorber technologies have been developed: gold electroplating in a cyanide bath and tungsten rf sputtering with subsequent dry etching. Induced film stresses were investigated as a function of the absorber microstructure and minimized by a fine adjustment of the deposition parameters. With a new process, based on a single patterned resist layer, we succeeded in transfering patterns with linewidth down to 100 nm. To demonstrate the dimensional quality of the x-ray masks, x-ray exposures have been performed under synchrotron radiation at Super-ACO:150-nm-wide line and 450-nm-wide space gratings have been obtained in 1.7-μm-thick PMMA resist by contact printing. This faithfully replicates the mask patterns.
Lithography with a 50 KV e beam and a vacuum scanning tunneling microscope in a polydiacetylene negative resist
Authors: Dobisz E. A. , Marrian C. R. K. , Colton R. J.
Published: July 2002

We present complementary studies of high (50 KeV) and low (5 eV) energy e-beam lithography in a polydiacetylene negative resist. A 50 KV probe of 1/e radius 8.3 nm defined a minimum continuous linewidth of ≊80 nm, with a dose of 1.7 nC/cm. The scanning tunneling microscope (STM) can image and lithographically pattern the resist in situ. Comparison of STM images of undeveloped lines to micrographs of developed lines show little difference in size. Lines 55 nm wide were produced by a 5 V probe with a line dose of 2000 nC/cm. The latent images of the 5 V defined lines and the 50 KV defined lines both appear as depressions in the resist. The minimum feature sizes cannot be explained by the probe diameters, electron scattering, or resist swelling in the developer. The possible effect of resist chemistry on the minimum feature size is discussed.
Imaging of bromo- and hydrogen-terminated azobenzene derivatives by scanning tunneling microscopy
Authors: Sano M. , Kunitake T.
Published: July 2002

Two groups of azobenzene derivatives, one with a hydrogen (H) terminated alkyl chain and another with a bromine (Br) terminated chain, adsorbed on graphite in the crystalline state were imaged by scanning-tunneling microscopy. A head-to-tail configuration was seen in the Br-terminated compounds, while some of the H-terminated derivatives showed a head-to-head configuration. These images reflect the strong interaction of hydrogen atoms of alkyl chain with the hexagon center of graphite lattice, resulting in an epitaxial crystal rather than simply an adsorbed thin film. For both compounds, lower limits of tunneling impedance were determined for stable molecular imaging. Due to the crystalline state of both compounds under observation, it was found that by lowering the impedance below the threshold value molecules are irreversibly removed from a small area around the tunneling region.
Long range modulation of the charge density wave structure in 1T–TaS2 studied by scanning tunneling microscopy
Authors: Slough C. G. , McNairy W. W. , Wang Chen , Coleman R. V.
Published: July 2002

The charge density wave (CDW) structure in 1T–TaS2 has been studied at room temperature using scanning tunneling microscopy. The CDW amplitude shows a continuous long range modulation of ∼6 CDW wavelengths giving rise to a two dimensional pattern of domain-like regions rotated with respect to the CDW superlattice.
Electron-beam-induced resist and aluminum formation
Authors: Ishibashi Akira , Funato Kenji , Mori Yoshifumi
Published: July 2002

We have grown electron-beam-induced resist and aluminum from alkyl naphthalene and trimethyl aluminum, respectively. The growth mechanism of the electron-beam-induced materials has been suggested to be bridge-formation by the physically adsorbed molecules of the sources. We believe that the bridge-formation is driven by direct interaction with electrons, not by diffusive processes such as local heating and catalytic reactions. The observed growth rate is consistent with the one calculated from the heat of physical adsorption. The method is of potential interest for stereo-resist and also for selective atomic layer epitaxy.
Alloyed contacts to susceptor rapid thermal annealed Si-implanted InP
Authors: Katz A. , Pearton S. J.
Published: July 2002

The performance of AuGe contacts to n-type InP layers, formed by implantation of Si into semi-insulating InP substrates and activated by rapid thermal annealing within an enclosed SiC-coated graphite susceptor (700 °C, 10 s) was studied. These contacts were purely ohmic with the lowest contact resistivity value of 1×10−7 Ω cm2 which was measured at the contact to 3×1018 cm−3 Si-doped InP substrate after rapid thermal processing at 375 °C for 30 s.
A combined Rutherford backscattering and Auger electron spectroscopy analysis of Ni/Au/Te ohmic contacts to n-GaAs
Authors: Wuyts K. , Watté J. , Silverans R. E. , Bender H. , Van Hove M. , Van Rossum M.
Published: July 2002

Rutherford backscattering spectrometry and Auger electron spectroscopy are combined to study the interdiffusion behavior in alloyed Ni/Au/Te/Ni/GaAs ohmic contacts. The data are correlated to the results of electrical measurements to allow for a discrimination between the different ohmic contact models. Good ohmic behavior is found to coincide with the presence of a thin (≂200 Å) Te-rich (5–10 at. %) layer in the substrate surface layers. This result and the diffusion data on nonohmic behaving contacts can most consistently be interpreted in the frame of the graded crystalline and/or amorphous heterojunction model.
Focused ion beam induced deposition of tungsten on vertical sidewalls
Authors: Stewart D. K. , Morgan J. A. , Ward B.
Published: July 2002

We have observed focused ion beam (FIB) induced deposition of tungsten on vertical sidewalls. This phenomenon allows high aspect ratio structures such as deep holes to fill with greater efficiency than expected from yields measured when the ion beam is at normal incidence to the surface. However we have also observed indirect deposition on vertical sidewalls which face a clear defect (an area which is missing x-ray absorber) on an x-ray mask that had to be repaired by depositing x-ray absorbing material. Since tungsten is used for both IC microstructuring and x-ray mask repair, deposition on vertical sidewalls can be exploited for certain repair processes on these structures. However we also propose ways of reducing the effect when deposition distorts facing vertical sidewalls on x-ray masks.
Interdiffusion of GaAs/GaAlAs quantum wells enhanced by low energy gallium focused ion beam implantation
Authors: Assayag G. Ben , Vieu C. , Gierak J. , Planel R. , Schneider M. , Marzin J. Y.
Published: July 2002

The mixing of GaAs/GaAlAs quantum wells by low energy gallium focused ion beam implantation and thermal annealing, was characterized by low-temperature photoluminescence spectroscopy. The depth extension of the induced disordering as well as the lateral resolution of interdiffused lines generated by line-and-space scan of the ion beam, was evaluated. On a multiple quantum well structure, no significant channeling of the ions, impinging on the target normally to the surface, could be evidenced, and the mixing was found to affect only the first quantum well located near the surface. On the other hand, the width of the interdiffused region observed laterally to the implanted lines is much larger than the spot diameter of the ion beam. It is concluded that the defects which activate the Ga–Al exchange at the interfaces, diffuse more rapidly in the aluminum rich layers. The influence of a rapid thermal annealing and the aluminum content in the barriers, on the lateral selectivity of the induced disordering is discussed.
Disordering of InGaAs/InP superlattice and fabrication of quantum wires by focused Ga ion beam
Authors: Yu S. J. , Asahi H. , Takizawa J. , Asami K. , Emura S. , Gonda S. , Kubo H. , Hamaguchi C. , Hirayama Y.
Published: July 2002

The disordering and compositional change of the InGaAs/InP superlattice by the Ga ion beam was investigated, and using the effect, quantum wires were fabricated by focused Ga ion beam. The analysis of Raman scattering shows that in the implanted region intermixing, i.e., alloying takes place in such a way that the intermixed In1−xGaxAsyP1−y alloy has the compositions of alloy with the lattice constant nearly equal to that of InP, although at higher doses the compositions x and y become smaller due to larger interdiffusion. Focused Ga ion beam of 100 kV was irradiated in lines onto InP (350 Å)/InGaAs (50 Å)/InP (500 Å) single quantum well at doses of 1×1013 –1×1014 cm−2. Implanted samples were annealed at 650–670 °C for 60 min. The photoluminescence measurements at 30 K for wires with various widths show that with decreasing wire width the luminescence peak energy increases nearly following the change of the quantum levels in the potential well calculated by taking into account lateral straggling of implanted Ga ions. The implanted and alloyed regions are confirmed to act as potential barriers by which carriers are confined.
Role of electric fields in enhancing the doping of semiconductors during epitaxial growth
Authors: Rajakarunanayake Y.
Published: July 2002

A novel technique is described to enhance the doping in semiconductors by the application of external electric fields during crystal growth. We show that this technique can enhance the doping efficiency, and suppress self-compensation processes in novel growth techniques such as molecular-beam epitaxy (MBE). An obvious application of this technique is to enhance the doping of wide band gap II–VI semiconductors, where doping in both n- and p-types is usually not possible to achieve because of extensive self-compensation. The physics of the electric field assisted doping process can be described in two parts. First, the external electric field produces a change in the band bending at the growth surface and alters the carrier concentrations near the surface region. This influences doping near the surface region. Second, this enhanced surface doping concentration can be kinetically buried by low temperature growth processes. In our calculations, the dopants are modeled as charged, mobile species that are free to diffuse and drift under electric fields. In the case of MBE growth, we solve for the equilibrium of these species in a moving coordinate frame that travels with the growth front. We have specifically applied our analysis to Li donors in n-type ZnTe. Our results indicate that excellent improvements in the doping concentrations could be obtained under normal MBE growth conditions, with the application of substantial electric fields. We expect that our analysis, and the proposed electric field assisted doping technique will play an important role in the effort to overcome compensation, and achieve selective doping in wide band gap II–VI semiconductors.
Phase stability versus the lattice mismatch of (100)Co1−xGax thin films on (100)GaAs
Authors: Baugh Delroy A. , Talin A. Alec , Williams R. Stanley , Kuo Tsung-Chia , Wang Kang L.
Published: July 2002

Thin films of the intermetallic compound Co1−xGax, which has a broad homogeneity range and a continuously variable lattice constant, were grown on the (100)GaAs surface by molecular beam epitaxy. The stoichiometry of the films and the cleanliness of the substrates were determined in situ by Auger electron spectroscopy. The identity and orientation of the phases present in the films were determined ex situ by x-ray diffraction (XRD). The films were annealed to various temperatures in N2 and reexamined by XRD to detect any chemical interactions between the Co1−xGax and GaAs. Films of Co1−xGax deposited with a 2% lattice mismatch (x=0.5) reacted with the substrate to produce CoGa3 at 600 °C, whereas films with no detectable mismatch (x=0.61) did not react until they had been heated to 800 °C.