bluuebunny/crossref_metadata_2025 huggingface dataset:
Valence-band offset and interface chemistry of CdS/InP(110)
Authors: Wilke W. G. , Seedorf R. , Horn K.
Published: July 2002

The CdS/InP(110) heterojunction, which is one example of a lattice matched combination among the junctions between II–VI and III–V compound semiconductors, was studied on molecular-beam epitaxy grown samples on cleaved as well as ion bombarded and annealed InP(110) surfaces. The junctions were characterized by core and valence photoemission using synchrotron radiation, Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED). Deposition of CdS on cleaved InP(110) surfaces led to layers which exhibited good laminar growth, and gave sharp LEED patterns with fairly low background, with a periodicity of the InP(110) substrate lattice, demonstrating that CdS was grown in the metastable zinc-blende conformation. On InP surfaces cleaned by ion bombardment and annealing, however, growth of crystalline CdS could not be achieved. From the evaluation of band bending upon CdS growth on the basis of core level, line-shape deconvolution, and the changes in the valence-band emission, we have derived a valence-band offset in this system of −0.77±0.1 eV; this means that this heterojunction is of the straddling type, in disagreement with previous data from C–V measurements which indicated a staggered lineup. We compare our result for the band lineup with current theoretical models.
Adsorption of chlorine and oxygen on cleaved InAs(110) surfaces: Raman spectroscopy, photoemission spectroscopy, and Kelvin probe measurements
Authors: Smit K. , Koenders L. , Mönch W.
Published: July 2002

The interaction of Cl2 and of O2 molecules with cleaved InAs(110) surfaces was investigated at room temperature. Ultraviolet photoemission spectroscopy, a Kelvin probe, and electric-field-induced Raman spectroscopy were used to determine both the changes of surface band bending and of the ionization energy as a function of exposure to the molecules mentioned. Chlorine as well as oxygen are inducing depletion (inversion) and accumulation layers on samples doped p- and n-type, respectively. The Fermi level becomes finally pinned at 0.52 eV above the valence-band top for both adsorbates. This behavior indicates the presence of adsorbate-induced surface states of donor type at this energy position. With chlorine, an intermediate pinning position at 0.48 eV above the valence-band maximum, which is below the branch point of the virtual gap states of the complex InAs band structure, is observed. This result suggests that chlorine induces surface states of acceptor character on InAs(110) surfaces as is observed with GaAs(110) as well as InP(110) surfaces. Electric-field-induced Raman scattering has proven to be a very valuable tool for studies of accumulation layers.
Layer by layer growth of FeAl on InP(100) substrates
Authors: Wowchak A. M. , Kuznia J. N. , Cohen P. I.
Published: July 2002

Thin films of FexAly have been grown by molecular-beam epitaxy on InP(100) substrates. Before growth of the epitaxial intermetallic alloy a 0.2-μm InAlAs buffer and a ten-layer AlAs diffusion barrier were deposited. Initial films were grown at 200 °C and were stable up to at least 600 °C. Upon the initiation of growth the reflection high-energy electron diffraction intensity was observed to decrease slowly and then exhibited oscillations corresponding to layer-by-layer growth. There was a short incubation period before the onset of the intensity oscillations that depended upon the ratio of the Fe and Al fluxes. The shape of the specular beam was measured versus incident angle and indicates that the surface is nearly as smooth as the starting AlAs surface. Upon heating to 550 °C the beams became sharper yet. Growth on the annealed surface at 200 °C gave intensity oscillations that were an order of magnitude stronger. Initial attempts to grow epitaxial AlAs on top of the FeAl layer showed three-dimensional island growth.
Engineering lateral quantum interference devices using electron beam lithography and molecular beam epitaxy
Authors: Allee D. R. , Chou S. Y. , Harris J. S. , Pease R. F. W.
Published: July 2002

Various new lateral quantum interference devices (QIDs) have been facbricated using high resolution electron beam lithography and molecular beam epitaxy. These QIDs utilize various nanometer scale electrodes to introduce electrostatic potential barriers in the electron gas at an AlGaAs/GaAs heterojunction. At low temperatures, as the electron mean free path approaches the dimensions of the gate electrode, quantum interference of the electron wave with the barriers and wells creates quasibound states that result in conductance oscillations as the gate voltage is scanned. High resolution electron beam lithography is used to define the nanometer gates, readily allowing the definition and alignment of different electrodes on the same wafer. A planar implantation isolation step is used to facilitate the liftoff of the Ti/Au gates patterned in polymethyl methacrylate (PMMA). Several novel QIDs will be described; emphasis will be on a new lateral double barrier resonant tunneling diode formed by two 80 nm gates separated by 100 nm. At 4.2 K, structure in the drain current is seen as the gate voltage is scanned for drain voltages less than 5 mV.
Molecular-beam epitaxy of InSb/CdTe heterostructures
Authors: Glenn J. L. , O Sungki , Kolodziejski L. A. , Gunshor R. L. , Kobayashi M. , Li D. , Otsuka N. , Haggerott M. , Pelekanos N. , Nurmikko A. V.
Published: July 2002

We report the growth by molecular-beam epitaxy of CdTe/InSb double heterostructures and multiple quantum wells on InSb and CdTe substrates. For the double heterostructures, InSb and CdTe layers were grown in separate chambers connected via an ultrahigh vacuum transfer module. Here, antimony originated from a compound InSb source oven. For multiple quantum wells, InSb and CdTe layers were grown in a single InSb/CdTe epitaxy chamber, where antimony was derived from an antimony cracking furnace. Infrared photoluminescence from InSb double heterostructures has shown the existence of recombination features which are similar to that of the bulk. Multiple quantum well structures have been examined by transmission electron microscopy. Raman spectroscopy has also been used to examine the interfacial and in-layer nature of InSb/CdTe heterostructures.
Electrical and optical characterization of molecular-beam epitaxy grown Ga-doped ZnSe.
Authors: Vaziri M. , Reifenberger R. , Gunshor R. L. , Kolodziejski L. A. , Venkatesan S. , Pierret R. F.
Published: July 2002

Epitaxial undoped and Ga-doped ZnSe have been grown on (100) GaAs substrates by molecular-beam expitaxy (MBE). The optical and electrical properties of these films have been characterized using standard photoluminescence, deep-level transient spectroscopy, and transport techniques. For a Zn-to-Se flux ratio of one, the undoped samples exhibit high resistivities; their photoluminescence spectra show a dominant free exciton band-edge emission. Under the same growth conditions, low-resistivity Ga-doped samples have been produced. The photoluminescence spectra for the doped samples are dominated by bound exciton emission related to the Ga donors (I2 at 2.795 eV). The deep-level transient spectroscopy studies show two prominent defect levels at energies of 0.26 and 0.34 eV below the conduction band. Electron transport measurements show that a lightly doped sample having a room-temperature carrier concentration of 8.0×1014 cm−3 exhibits a peak mobility of 7900 cm2/V s at 50 K.
Optical and structural properties of molecular-beam epitaxial GaAs on sapphire
Authors: Chin Albert , Bhattacharya Pallab , Chang Kevin H. , Biswas Dipankar
Published: July 2002

We have evaluated the structural and optical properties of GaAs grown by molecular-beam epitaxy on (0001) and (011̄2)-oriented sapphire substrates for possible direct deposition on sapphire optical fibers and optoelectronic device applications. X-ray diffraction studies and cross-sectional transmission electron microscopy measurements show that the GaAs films are single-crystal and have a (111) orientation for both substrate orientations. Both x-ray and temperature-dependent photoluminescence measurements indicate that the quality of the GaAs films is better for the (011̄2) sapphire orientation. The best results are produced when growth is initiated at a very slow rate (∼0.1 μm/h) and low temperature (∼400 °C) followed by growth parameters for normal homoepitaxial GaAs (1 μm/h, 560–600 °C). The incorporation of a graded band gap strained layer in InGaAs/GaAs superlattice near the sapphire–GaAs interface also improves the optical quality of the GaAs films. Low-temperature photoluminescence spectra is dominated by a peak at 1.49–1.495 eV, with a best linewidth of 26.9 meV, which we believe is due to an integration of several impurity and defect related bound exciton transitions. A peak to lower energies by ∼60 meV is thought to be due to acceptorlike impurity defect complexes. Post growth short term halogen lamp annealing marginally improves the overall luminescence intensity of the samples. A linewidth of 20 meV is measured for a (80 Å) GaAs/(120 Å) Al0.3 Ga0.7 As multiquantum grown on sapphire. From this initial study it is apparent that device-quality single-crystal GaAs and GaAs-related compounds can be deposited directly on sapphire substrates by molecular beam epitaxy, using special growth techniques.
Growth condition studies of pseudomorphic InGaAs/GaAs strained layer structures and InGaAs/AlGaAs high electron mobility transistor layer properties
Authors: Weng Shang-Lin , Webb C. , Eckstein J. N.
Published: July 2002

We use reflection high-energy electron diffraction (RHEED) oscillations to study the growth condition dependence of the growth of pseudomorphic InGaAs layers on GaAs, as well as van der Pauw/Hall measurements to evaluate the growth parameter dependence of the electrical properties of InGaAs/AlGaAs high electron mobility transistor structures. We present our conclusions regarding growth conditions for which smooth RHEED oscillations can be obtained, and the parameters for which optimal electrical properties can be reached.
The electrical properties of molecular-beam epitaxy grown InxGa1−xAs on GaAs
Authors: Kim T. S. , Shih H. D. , Anthony J. M. , Duncan W. M. , Farrington D. L. , Keenan J. A. , Moore T. M.
Published: July 2002

The electrical properties of relatively thick (∼1 μm) InxGa1−xAs (0.08≤x≤0.17) layers grown by molecular-beam epitaxy on nonlattice-matched GaAs substrates are studied. It is found that InxGa1−xAs layers with low-field mobilities comparable, if not better, to those of GaAs can be grown despite the relatively large lattice mismatch. The InxGa1−xAs layers with the graded buffers show marginally higher mobilities than those with the abrupt buffers. It is also found that the layers grown on misoriented substrates have higher mobilities than those grown on exactly oriented substrates. The surface morphology and buffer quality are, however, better on exactly oriented substrates. The threading-dislocation density is lower with graded buffers (and lower growth temperature) than with abrupt buffers (and higher growth temperature), but the effect of the substrate orientation on the threading dislocation density is not clear. The background doping level is higher with the abrupt buffer and higher InAs mole fractions.
The effect of inhibited growth kinetics on GaInAs and AlInAs alloy and interface quality
Authors: Brown A. S. , Delaney M. J. , Singh J.
Published: July 2002

Ga0.47In0.53As and Al0.48In0.52As alloys, lattice matched to InP substrates, are typically grown under conditions (low substrate temperature and high V/III flux ratios) which limit cation surface mobilities. For the (Al,Ga)As system, the growth of material with low-defect density and good microscopic surface morphology is dependent on highly mobile cations which can reach kink sites on the growing surface. In the (Al,In,Ga)As system, other factors such as the miscibility gap in the AlInAs phase diagram and the volatility of InAs component dominate the growth condition requirements. In order to determine the role kinetic limitations play in reducing the quality of GaInAs and AlInAs under ‘‘normal’’ molecular beam epitaxy growth conditions, epitaxial layers were grown at extremely low substrate temperatures and high V/III ratios to examine the sensitivity of materials properties to these growth conditions.
Reduction and origin of electron and hole traps in GaAs grown by molecular-beam epitaxy
Authors: Chand Naresh , Sergent A. M. , van der Ziel J. P. , Lang D. V.
Published: July 2002

Deep-level transient spectroscopy (DLTS) is shown to be a simple and powerful diagnostic tool for monitoring the cleanliness of a molecular-beam epitaxy (MBE) system and for determining optimum growth conditions. GaAs, grown by MBE under ideal conditions, is essentially free from electron and hole traps, and any contamination introduced by impurities in the sources, or resulting from substandard growth conditions, is reflected by the presence of traps as detected by DLTS. We find that the origin of dominant MBE-GaAs hole traps and electron traps M1, M3, and M4 is the complexing of unknown chemical impurities and defects in the crystal. Impure arsenic is the major source of such chemical impurities, although these impurities can originate from other sources as well, such as the molybdenum substrate holding blocks. These chemical impurities do not appear to be the shallow donors or acceptors. Electron traps M5–M8 are due to crystal defects.
Magnetron ion etching with CF4 based plasmas: Effects of magnetic field on plasma chemistry
Authors: Bright A. A. , Kaushik S.
Published: July 2002

Etching plasmas based on CF4 have been studied in a magnetron ion etching (MIE) system. Optical emission and mass spectra were measured as a function of applied power, pressure, and gas composition. Electrical probes were used to measure the plasma floating potential and the dc self-bias of the rf electrode. The magnetic field has an effect not only on the physics of the plasma (ion density, plasma impedance, etc.) but also on the chemistry. Two regimes of operation are found to exist. Under typical high-power MIE operating conditions, the species present in the plasma tend to be more highly dissociated than in a conventional reactive ion etching (RIE) plasma. As a consequence, the tendency for C–F polymer to form on etched Si surfaces is suppressed and selective etching of SiO2 over Si does not occur. At lower powers, the plasma characteristics and etching response revert back to RIE-like behavior as the degree of dissociation decreases. The implications for etching processes are discussed.
Generation of low-energy neutral beams and radiation damage of SiO2/Si by neutral bombardment
Authors: Mizutani Tatsumi , Nishimatsu Shigeru
Published: July 2002

In order to apply to neutral beam etching, several hundred eV neutral beams have been generated by charge exchange reaction using a magneto-microwave plasma ion source. The charge exchange cross sections for Ar+ and Kr+ are unexpectedly small, whereas the cross section for Ne+ of 300 eV is 1.7×10−15 cm2 in good agreement with published results. The small cross sections for Ar+ and Kr+ in the present experiments are explained in terms of a nonresonant charge exchange scheme. The capacitance–voltage (C–V) measurements show that the radiation damage to SiO2/Si by Ne0 neutral beam bombardment is much less than those by Ne+ ion beam and by vacuum ultraviolet photons. Consequently, the neutral beam process is a promising method for charge-free and low-damage surface processes.
A comparative study of growth of ZnSe films on GaAs by conventional molecular-beam epitaxy and migration enhanced epitaxy
Authors: Lilja Jarmo , Keskinen Jari , Hovinen Minna , Pessa Markus
Published: July 2002

Growth of high-quality ZnSe films on GaAs(100) substrates by conventional molecular-beam epitaxy (MBE) and migration enhanced epitaxy (MEE) have been examined. We have found a self-regulatory MEE process in the temperature range between 350 and 400 °C where a complete monolayer of ZnSe was achieved per three operational cycles of Zn+Sen. Thin films (<1 μm) grown by self-regulatory MEE exhibited much higher structural perfection than MBE thin ZnSe films grown under closely identical conditions. The explanation for these structural differences must lie in details of how initial nucleation takes place in MBE and MEE. For thicker films (≂2 μm) no significant differences in structural or electrical properties were found for the two methods.
A transmission electron microscopic study of the topography of clean Si(111) surfaces
Authors: Tung R. T. , Schrey F. , Eaglesham D. J.
Published: July 2002

Steps on Si(111) surfaces are shown to be preserved at the interfaces of epitaxial silicide layers grown at room temperature. Symmetry requires the formation of a dislocation at every step of this (type B) interface. This has enabled the examination, by transmission electron microscopy, of the topography of large areas of the Si surface after various treatments. Silicon molecular-beam epitaxy (MBE) is shown to occur via step-flow mechanism at high temperatures, and through nucleation and growth of islands on the terraces at low growth temperatures. These observations point to the importance of including nucleation mechanism into existing theories, especially at high supersaturation. A change of step character from 〈112̄〉to 〈∼(11) 2〉 at the initial stage of MBE is observed and is attributed to the stabilities of the two types of steps in relationship to the 7×7 structure. Preliminary results on vicinal Si(111) surfaces are also presented.
Laser induced fluorescence study of CF radicals in CF4/O2 plasmas
Authors: Hansen S. G. , Luckman G. , Nieman George C. , Colson Steven D.
Published: July 2002

Laser induced fluorescence is used to monitor CF radicals in both a 13.56 MHz CF4 processing plasma and a pulsed dc discharge. The axial spatial variation of CF shows a drop near added silver and copper substrates, a local maximum at polymer surfaces, and a flat approach to aluminum, SiO2 , and silicon. The same behavior was previously observed with CF2 and it is argued that the CF profile reflects its formation by electron impact on CF2 rather than its heterogeneous reactivity. As oxygen is added to a CF4 discharge, [CF] drops off faster than [CF2 ]. The voltage dependence of the CF decay rate in a pulsed discharge suggests CF oxidation involves molecular rather than atomic oxygen.
Elimination of gallium-source related oval defects in molecular-beam epitaxy of GaAs
Authors: Chand Naresh
Published: July 2002

By evaporating gallium from a pBN crucible which was previously used for evaporation of Al, ‘‘Ga-spitting’’ and formation of Ga-cell related oval defects have been eliminated in molecular-beam epitaxy (MBE) of GaAs. MGE-GaAs layers as thick as 20 μm were totally free from the Ga-cell related oval defects. Remaining oval defects were those related to particulates and substrate contamination and their densities were 100 and 500 cm−2 on 5 and 20-μm thick layers of GaAs on GaAs substrates. However, these particulates related oval defects were hardly seen on up to 4-μm thick GaAs layers grown on Si substrates. Aluminum wets and reacts with the pBN crucible when heated up to 1300 °C during evaporation of Al. Condensed gallium near the orifice wets the such aluminum treated pBN surface and is not expected to spontaneously flow to the Ga charge in the form of droplets. As a result, Ga spitting does not occur and related oval defects do not form.
The role of heat transfer during reactive-ion etching of polymer films
Authors: Dems B. C. , Rodriguez F.
Published: July 2002

A study of the kinetics of O2 and Ar reactive-ion etching (RIE) of organic polymer films and an analysis of substrate heat transfer was carried out. Radiative heat transfer played a significant role in determining the substrate temperature profile during RIE. At the relatively low pressure of 5 mTorr, where anisotropic etch profiles are typically achieved, radiative heat transfer accounted for nearly 85% of the total energy (heat) flux away from the substrate. RIE processing time (substrate temperature) drastically affected the RIE rate of chain-scissioning polymers, which included poly(methyl methacrylate) and poly(α-methylstyrene), while processing time had absolutely no effect on etch rates of cross-linking polymers. To confirm the role of radiative heat transfer during RIE, the underside of a silicon wafer was painted black, which increased the total radiative surface emittance and lowered the steady-state substrate temperature for a given set of RIE conditions. Ultimate etch rates of poly(methyl methacrylate) were measurably lower for films on the black-silicon substrates. Thermal bonding alleviated substrate heating and greatly improved etch rate control.
Stress migration resistance and contact characterization of Al–Pd–Si interconnects for very large scale integrations
Authors: Koubuchi Y. , Onuki J. , Suwa M. , Fukada S. , Moribe S. , Tanigaki Y.
Published: July 2002

Stress-induced migration resistance and contacts to silicon of Al–0.3%Pd–1%Si interconnections for submicron process integrated circuit devices have been investigated and compared to Al–0.5%Cu–1%Si. Using creep tests, Pd has been found to be an excellent additional element to Al for reducing grain boundary diffusion. Palladium improved the stress-induced migration resistance and reduced void and hillock formation in Al–Si conductors. Aluminum palladium precipitates in Al–Pd–Si alloys were found to be formed at higher temperatures than aluminum copper compounds and may be the reason for the improvements. The contact resistance of Al–Pd–Si was found to be similar to that of Al–Cu–Si. The reliability and yield data from 1.2 μm ROM test devices using Al–Pd–Si conductors is better than that of Al–Cu–Si conductors.
A proposed quantum wire structure: An ‘‘accumulation wire’’ at crossing heterointerfaces
Authors: Harbury Henry , Porod Wolfgang
Published: July 2002

We demonstrate that a quasi-one-dimensional quantum wire can, in principle, be produced at the crossing point of heterointerfaces. We show that the intersection of two accumulation layers, which are formed along separate heterointerfaces, realizes an ‘‘accumulation wire.’’ Our theoretical analysis yields potential distributions which possess confined electronic states in the vicinity of the point of intersection. In our design, confinement in the quantum wire is solely provided by the inherent electric fields associated with heterointerfaces without the need for additional lithography. In other words, our proposal of the quantum wire compares to previous designs in the same manner in which a quasi-two-dimensional (2D) system in an accumulation (or inversion) layer compares to a quasi-2D system in a quantum well.
Formation of device quality Si/SiO2 interfaces at low substrate temperatures by remote plasma enhanced chemical vapor deposition of SiO2
Authors: Lucovsky G. , Kim S. S. , Fitch J. T.
Published: July 2002

We discuss the factors that contribute to the formation of device quality Si/SiO2 interfaces using the low temperature process of remote plasma enhanced chemical vapor deposition (PECVD) to deposit the SiO2 thin films. This includes identification of: (i) the ex situ and in situ processes required for surface preparation prior to film deposition; (ii) the factors that define the range of substrate temperatures for thin film deposition; and (iii) the factors that are important in post-deposition annealing of Si/SiO2 interfaces. The low temperature limit for SiO2 deposition by remote PECVD derives from increased SiOH incorporation, whereas the high temperature and thickness limitations derive from subcutaneous surface reactions in which the Si substrate can be oxidized via process gas/substrate reactions during the deposition process.
Repair of transparent defects on photomasks by laser-induced metal deposition from an aqueous solution
Authors: Jacobs Jan W. M. , Nillesen Chris J. C. M.
Published: July 2002

This paper describes a newly developed technique for repairing transparent defects on photomasks. After the uniform application of a thin transparent TiO2 film on the entire mask, a noble metal is photodeposited locally on the mask from an aqueous plating solution. The rate of photodeposition, and thereby, the structure and adherence of the deposited metal, depend on the preparation conditions of the TiO2 film, the composition of the plating solution and the incident light flux. These parameters can be selected in such a way that opaque metal metal pads can be deposited in sufficiently short illumination times (∼5 s). By means of laser projection through a variable rectangular aperture, it is possible to deposit rectangular metal pads with micron-sized dimensions and sharp edges and corners in a controlled and reproducible way. Since deposition is induced photochemically, thermal broadening of the deposit does not occur. It is shown that the repair process meets the requirements with respect to spot definition, photolithography, mask cleaning, and laser trimming.
Etching procedures of GaAs: Cathodoluminescence study of the induced damages and of the recovering techniques
Authors: Papadopoulo A. C. , Dubon-Chevallier C. , Bresse J. F. , Duchenois A. M. , Heliot F.
Published: July 2002

Effects of ion-beam and chemical etching on the optical properties of GaAs were studied by means of cathodoluminescence. An important degradation of the radiative properties is observed at the surface as well as in depth. This degradation is not removed by the ohmic contact annealing process at 450 °C. In the case of chemical etching, a complex behavior of the luminescence properties after annealing is indicative of surface-states modifications. To optimize the etching procedure, we defined a process combining an ion-beam etching at 250 eV and a short-duration chemical etching.
Deposition of oxide films by metal-organic molecular-beam epitaxy
Authors: Bade J. P. , Baker E. A. , Kingon A. I. , Davis R. F. , Bachmann K. J.
Published: July 2002

Molecular-beam epitaxy (MBE) has been used in tandem with a unique class of metallo-organic precursors to deposit thin films of Cu, Y2O3, and BaF2 on (100) MgO substrates. The temperatures of deposition were 400, 500, and 625 °C. It was found that the presence of an activated oxygen species, such as ozone, was required to obtain a film product. The influence of oxidizing environment and substrate temperature on precursor decomposition and deposition yield are described.
Aerial image formation in synchrotron-radiation-based x-ray lithography: The whole picture
Authors: Guo J. Z. Y. , Chen G. , White V. , Anderson P. , Cerrina F.
Published: July 2002

The problem of the image formation in a proximity x-ray lithography (XRL) system has been addressed several times in the past, while a full description of the system has never been implemented for the case of a synchrotron radiation source. It is then necessary to (a) define exactly the properties of source, optical system and mask on the image and (b) correlate the different terms into a common ground. We first discuss the degree of coherence of the synchrotron source in term of the the broadband soft x-ray spectrum and of the partial degree of coherence of the source (finite size) on the linewidth control and the processing latitude (broadening). The effect of the optical system is fully taken into account. We propose a new image calculation method based on fast Fourier transform. On the basis of the result of the aerial image calculation, we discuss the possibility of using a uniform bias on the mask pattern to improve linewidth control in the submicrometer feature range. The result shows that for printing 0.25-μm features, the synchrotron-radiation-based XRL is an ideal tool when the gap is set correctly and that typical wafer topography can be handled without any problem.
A simple model of the chemically assisted ion beam etching yield of GaAs with Cl2 at medium current densities
Authors: Davis Robert J. , Wolf Edward D.
Published: July 2002

We present a simple analysis of the chemically assisted ion beam etching (CAIBE) yield of a solid under exposure to an ion beam and flux of molecular chlorine, using a mass-balance approach. In this model, dichloride species formed by the dissociative chemisorption of physisorbed chlorine are removed by collisional cascade mechanisms. We show that the energy and ion flux dependences of the yield deviate from expected forms depending primarily on the surface chemisorption rate and the surface flux ratio, but even in this simple model there are reasons why the latter might not be a good parameter for the comparison of experimental data. The model describes the important features of the etch rates of GaAs in chlorine and low-energy (500–1250 eV, 0.05–0.35 mA/cm2) Ar+, including a changing energy dependence of the yield with chlorine partial pressure.
Carbon doping of GaP, GaInP, and AlInP in metalorganic molecular beam epitaxy using methyl and ethyl precursors
Authors: de Lyon T. J. , Woodall J. M. , Kirchner P. D. , McInturff D. T. , Scilla G. J. , Cardone F.
Published: July 2002

The group III precursors trimethylgallium (TMG), triethylgallium (TEG), trimethylaluminum (TMA), and triethylaluminum (TEA) have been investigated as intrinsic carbon doping sources for epilayers of GaP, Ga0.51In0.49P, and Al0.51In0.49P grown by metalorganic molecular-beam epitaxy (MOMBE) using thermally cracked phosphine (PH3). Carbon incorporation in these films has been evaluated with calibrated secondary ion mass spectrometry (SIMS), Hall effect measurements, and capacitance-voltage (C–V) profiling. The carbon doping properties of TMG and TEG in GaP growth are compared with those observed in MOMBE growth of GaAs. Hole concentrations in excess of 1×1020 cm−3 have been measured in films of GaP grown with TMG/PH3, which is far above that achievable in GaAs grown with TMG/AsH3 under similar growth conditions. Neither TMG nor TEG result in p-type conductivity in films of Ga0.51In0.49P. At a growth temperature of 500 °C, SIMS measurements indicate that the carbon incorporation is inversely related to the In content of the films, with the carbon concentration falling by 1 decade for every 1.5% increase of InP mole fraction above 5%. Al0.51In0.49P films are generally highly resistive when grown with either TMA or TEA, despite incorporated atomic carbon concentrations in excess of 1×1019 cm−3. These results indicate that while carbon doping with methyl and ethyl precursors is readily extensible to GaP, carbon is not at present a useful dopant species for the MOMBE growth of In-containing III–V phosphides due to incorporation limitations and poorly understood compensation mechanisms.
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u stress monitoring and deposition of zero-stress W for x-ray masks
Authors: Ku Y.-C. , Ng Lee-Peng , Carpenter Roger , Lu Kenneth , Smith Henry I. , Haas L. E. , Plotnik I.
Published: July 2002

We have developed and tested a computer-controlled system for monitoring in situ the stress of tungsten sputter deposited onto x-ray mask membranes. This system allows us to achieve zero stress (i.e., <5×107 dyn/cm2) tungsten. The stress is monitored via the resonant frequency of the x-ray mask membrane which changes during deposition due to W stress, mass loading, and temperature rise. Differences in W stress give rise to differences in curvatures of the plot of resonant frequency versus W thickness. This effect can be used to ensure that a film will have stress below 1×108 dyn/cm2 and can also be the basis of an automated closed-loop, in situ stress control system.
Theoretical model for scanning electron microscopy through thin film windows
Authors: Green E. D. , Kino G. S.
Published: July 2002

We have developed a model for electron beam scattering in a thin film window atmospheric scanning electron microscope (SEM). The model is accurate for plural scattering, which covers film thicknesses up to 100 μm and window to sample spacings to 20 μm, for energies above 20 keV. We demonstrate experimental verification of our model for energies from 20 to 50 keV and film thicknesses from 30 to 100 nm.
Cleaning of Si(001) surfaces studied by optical second-harmonic generation and x-ray photoelectron spectroscopy
Authors: Hollering R. W. J. , Dijkkamp D. , Lindelauf H. W. L. , van der Heide P. A. M.
Published: July 2002

Optical second-harmonic generation (SHG) data are presented on the cleaning of Si(001) surfaces covered with thin (20–40 Å) oxide layers. The removal of an oxide layer by annealing, results in the formation of a 2×1 reconstructed surface and a concurrent increase in second-harmonic intensity of nearly two orders of magnitude. A comparable signal increase is observed in the transition from an unreconstructed passivated Si(001) surface, produced by etching, to a clean 2×1 reconstructed surface. It is concluded that SHG is very sensitive to the presence of surface states on the 2×1 reconstructed Si(001) surface.
Mechanisms of incorporation of donor and acceptor dopants in (Hg,Cd)Te alloys
Authors: Vydyanath H. R.
Published: July 2002

The usefulness of the quasichemical approach in predicting the defect structure of undoped and doped (Hg,Cd)Te crystals is emphasized. To begin with, the defect structure of undoped (Hg,Cd)Te crystals is established along with mass action constants for the intrinsic excitation process and the formation of the dominant native acceptor defects. Subsequently, the defect structures of donor doped and acceptor doped (Hg,Cd)Te crystals are established. With the values of the mass action constants established for the undoped crystals along with those for the doped crystals, the concentrations of defects present at the high temperature are calculated along with the carrier concentrations expected in the cooled crystals. The results of the carrier concentration calculations are compared with the experimental values to verify the validity of the incorporation mechanisms established for the doped crystals.
The effect of growth orientation on the morphology, composition, and growth rate of mercury cadmium telluride layers grown by metalorganic vapor phase epitaxy
Authors: Cinader G. , Raizman A. , Sher A.
Published: July 2002

We have measured the growth rate dependence of CdTe and HgTe layers in the growth surface direction. The growth mechanism of HgTe and CdTe were concluded to be heterogeneous, surface kinetic limited. The morphology of CdTe and mercury cadmium telluride interdiffusion multilayer process layers is found to be strongly effected by the large anisotropy of the CdTe growth rate. The best morphologies were found to be on surfaces having directions of maximum CdTe growth rates, with respect to surfaces of other crystallographic directions. A model for hillocks formation is given, based on the CdTe growth rate anisotropy. The different nature of twins stacking faults in (111)A and (111)B layers is explained by the different morphologies of these layers.
Studies of β-SiC (001) and (111) surfaces by scanning tunneling microscopy
Authors: Chang C. S. , Zheng N. J. , Tsong I. S. T. , Wang Y. C. , Davis R. F.
Published: July 2002

Scanning tunneling microscopy is used to study β-SiC (001) and (111) surfaces. The (001) surfaces of β-SiC were grown on Si(001) substrates while the (111) surfaces were grown on α-SiC{0001} substrates, both by chemical vapor deposition. The surface morphology for the β-SiC(001) surface grown on Si(001), the β-SiC(111) surface grown on Si-terminated α-SiC(0001), and the β-SiC(111) surface grown on C-terminated α-SiC(0001̄) are compared. Atomically resolved images of the c(2×2) and (3×2) reconstructions of the β-SiC(001) surface and the honeycomblike reconstruction on the β-SiC(111) surface are presented.
Observation of crystal dislocations in GaAs
Authors: Cox G. , Szynka D. , Poppe U. , Graf K. H. , Urban K. , Kisielowski-Kemmerich C. , Krüger J. , Alexander H.
Published: July 2002

Scanning tunneling microscopy was used to study the penetration of bulk dislocations on a {110} n-GaAs cleavage plane under ultrahigh vacuum conditions. Perfect and partial dislocations were imaged with atomic resolution for the As sublattice. From the atomically resolved images the Burgers vector and the slip plane of the dislocations can be directly determined. During the experiment the dislocations were found to be mobile over nanometer distances. No band bending was found around the dislocation cores, indicating that they are essentially electrically neutral in n-GaAs.
Scanning tunneling microscopy/scanning tunneling spectroscopy simulation of Si(111)√3×√3-B surface
Authors: Tsukada Masaru , Kobayashi Katsuyoshi , Shima Nobuyuki , Isshiki Nobuyuki
Published: July 2002

Mechanism of the negative differential resistance (NDR) observed in the scanning tunneling spectroscopy of the Si(111)√3×√3-B surface is discussed based on the simulation with the first-principles electronic states calculation. The NDR is reproduced by the W10[111] tip model, but not by the W14[110] and Pt10[111] models. The presence of the localized dangling bond state near EF for the surface in conjunction with a single tunnel active orbital at the tip apex causes the NDR.
The continuous wave laser-induced dry etching of GaAs and related substrates in a dimethylzinc ambient
Authors: Licata Thomas J. , Scarmozzino Robert
Published: July 2002

A laser-induced dry etching process based on the generation of reactive species from the pyrolytic decomposition of selected metal alkyls is presented. Specifically, a focused, 514 nm cw laser to locally heat the surface of a GaAs sample in a dimethylzinc (DMZn) ambient is used. The DMZn dissociates pyrolytically at the hot surface, yielding reactive species that locally etch the GaAs. We have studied the process by characterizing etch rates in terms of laser dwell time, laser-induced temperature, and DMZn pressure. Further, we have investigated the thermal dependence of the process, and have determined the boundaries of the parameter space for the successful avoidance of competing processes. Based on our experimental results and those of previous workers, we speculate that reactive methyl groups produced in the pyrolytic decomposition of DMZn react with the GaAs surface to produce volatile alkylated by-products. Finally, the process to allow for the direct writing of surface-relief features having smooth walls and submicron to micron-scale depths have been optimized, which are potentially useful as electronic or optoelectronic device components. To demonstrate the utility of the etching process, riblike waveguiding structures in GaAs/Al0.3Ga0.7As multilayer substrates have been fabricated.
Surface Fermi level engineering: Or there is more to Schottky barriers than just making diodes and field effect transistor gates
Authors: Freeouf J. L. , Warren A. C. , Kirchner P. D. , Woodall J. M. , Melloch M. R.
Published: July 2002

Surface scientists argue about the fundamental nature of Schottky barriers, or more precisely what determines the location of the Fermi level at semiconductor surfaces and interfaces. Electrical and materials engineers worry about how to make Schottky barrier diodes and gates to field effect transistors and the control of barrier heights. There is some interesting middle ground in which the location of the surface and interface Fermi level can, for example, determine semiconductor doping characteristics during crystal growth. In keeping with the trendy fashion of the 80’s to invent ‘‘catchy phrases’’ to describe marginally important new fields, we dub this middle ground as ‘‘surface Fermi level engineering.’’ Within the framework of this concept, we will discuss several interesting and well known examples of doping characteristics which are still somewhat mysterious. Specifically, we will address the following questions: (1) why is Ge doped GaAs p type when grown from Ga melts but n type when grown from Au melts? (2) why is low resistivity p type ZnSe, AlAs, and AlGaInP hard to make, and more importantly, how can we fix this problem? In addition we will describe how this concept relates to the electronic properties of a new type of GaAs, GaAs:As, which contains a high density of As precipitates.
Observation of a (2×8) surface reconstruction on Si1−xGex alloys grown on (100) Si by molecular-beam epitaxy
Authors: Croke E. T. , Hauenstein R. J. , Fu T. C. , McGill T. C.
Published: July 2002

We present evidence supporting the formation of a new, (2×8) surface reconstruction on Si1−xGex alloys grown on (100) Si substrates by molecular-beam epitaxy. Surfaces of Si1−xGex alloys were studied using reflection high-energy electron diffraction (RHEED) and low-energy electron diffraction (LEED) techniques. RHEED patterns from samples with Ge concentrations, x, falling within the range 0.10–0.30 and grown at temperatures between 350 and 550 °C, exhibit n/8 fractional-order diffraction streaks in addition to the normal (2×1) pattern seen on (100) Si. The presence of fractional-order diffracted beams is indicative of an eight-fold-periodic modulation in electron scattering factor across the alloy surface. LEED patterns from surfaces of samples grown under similar conditions are entirely consistent with these results. In addition, the LEED patterns support the conclusion that the modulation is occurring in the direction of the dimer chains of a (2×1) reconstruction. We have examined the thermal stability of the (2×8) reconstruction and have found that it reverts to (2×1) after annealing to 700 °C and reappears after the sample temperature is allowed to cool below 600 °C. Such behavior suggests that the reconstruction is a stable, ordered phase for which the pair-correlation function of surface Ge atoms exhibits an eightfold periodicity in the ‘‘1’’ direction of a Si-like (2×1) reconstruction. We also present a simulation in the kinematic approximation, confirming the validity of our interpretation of these findings.
Quantum devices using SiGe/Si heterostructures
Authors: Karunasiri R. P. G. , Wang K. L.
Published: July 2002

Strained-layer Si1−xGex/Si heterostructures have created a great deal of interest due to the potential of integration with the conventional silicon very large scale integrated technology. With the current advances in silicon molecular beam epitaxy (Si-MBE) and other low-temperature epitaxial techniques, many Si1−xGex/Si heterojunction devices have been realized. For example, among those realized are avalanche photodiodes, modulation-doped field-effect transistors, heterojunction bipolar transistors, and more recently, resonant tunneling structures, hot-carrier transistors, and quantum well metal-oxide-semiconductor field-effect transistors. In this paper, several quantum size effects in strained Si1−xGex layers and their potential in device applications will be reviewed. Among those to be discussed are resonant tunneling, miniband transport, and intersubband absorption in Si1−xGex/Si superlattice structures, optical properties of monolayer SimGen superlattices, and observation of large Stark effect associated with interband transition between quantized states in Si1−xGex/Si quantum well structures.
Magneto-optical transitions between subbands with different quantum numbers in narrow gap HgTe–CdTe superlattices
Authors: Luo H. , Yang G. L. , Furdyna J. K. , Ram-Mohan L. R.
Published: July 2002

Magneto-optical transitions induced by the coupling between the conduction and the valence bands through the momentum matrix element, and by the coupling terms between light and heavy holes resulting from an applied magnetic field are studied theoretically in narrow gap HgTe–CdTe superlattices. Selection rules and transition probabilities for the above transitions are presented and compared with allowed transitions. The numerical results for the transition probabilities show that some of the interband transitions with ΔN=±1 are significant and have to be considered in the studies of interband magneto-optical spectra of narrow gap superlattices.
Structural characterization of the (111) surfaces of CdZnTe and HgCdTe epilayers by x-ray photoelectron diffraction
Authors: Seelmann-Eggebert M. , Richter H. J.
Published: July 2002

HgCdTe epilayers and lattice matched CdZnTe (111) substrates have been investigated by x-ray photoelectron diffraction to characterize their surface structure in regard to termination, reconstruction and relaxation as well as in regard to degradations. Well-ordered CdZnTe surfaces of stoichiometric composition were realized by Ar ion sputtering, while sputter cleaning of the HgCdTe epilayers led to a significant increase of the CdTe mole fraction in the surface region. However, the crystallinity of the HgCdTe surfaces is found to be maintained in spite of their compositional degradation. Ordered and nondegraded HgCdTe(111) surfaces are obtained by electrochemical etching. The examined (111)A and (111)B surfaces can be easily differentiated since their photoelectron diffraction patterns indicates a surprisingly perfect termination. Evidence for any reconstruction or relaxation of the investigated (111) surfaces of CdZnTe and HgCdTe is not found.
Electron optical properties and aberrations of a miniaturized electron beam system
Authors: Ximen Jiye , Ximen Hongyu , Zhou Li
Published: July 2002

Based on dimensional analysis, a configuration of a microlens system for focusing an electron beam can be obtained by the dimensional scaling down from a conventional lens. An electrostatic microlens system consisting of two planar microsize apertures has been investigated. For this microlens, the spherical and chromatical aberrations, the astigmatism due to elliptic distortion, and the displacement due to misalignment have been calculated in detail. The resolution has been derived by a general formula, and thus has been evaluated numerically. The computational results have shown that the miniaturized microlens system proposed in the present article possesses remarkably small aberrations and ultrahigh resolution in the low voltage operation, and will be likely applicable for some practical uses.
New in situ electron beam patterning process for GaAs using an electron-cyclotron-resonance plasma-oxidized mask and Cl2 gas etching
Authors: Takado N. , Kohmoto S. , Sugimoto Y. , Ozaki M. , Sugimoto M. , Asakawa K.
Published: July 2002

A new electron beam (EB) patterning process capable of resistless nanofabrication for GaAs has been developed using enclosed continuous-vacuum processes. These processes are surface oxidation by electron cyclotron resonance (ECR) O2 plasma, oxidized-surface modification by EB irradiation, and subsequent etching by Cl2 gas. The time and oxygen gas pressure required for the oxidation are greatly reduced, compared to other oxidation methods, by using ECR plasma to form an oxide mask for Cl2 gas etching. The plasma-oxidized mask without EB irradiation cannot be removed by Cl2 gas etching even for 4 h at a sample temperature of 100 °C. In spite of its resistance to Cl2 gas etching, the mask can be easily removed by thermal treatment of the sample at about 620 °C in an As atmosphere.
Molecular-beam epitaxially grown Si/GaAs interfaces: Delta-doping, Si on GaAs, and GaAs on Si
Authors: Crook G. E. , Brandt O. , Tapfer L. , Ploog K.
Published: July 2002

Silicon layers with thicknesses covering the range from delta-doping densities to relaxed Si have been embedded in GaAs using molecular-beam epitaxy. The Si thickness for which the onset of relaxation of the Si layer occurred was found to be about 12 Å by analysis of double-crystal x-ray diffraction and Hall effect measurements. Reflection high-energy electron diffraction observations indicate the presence of GaAs at the surface of Si-on-GaAs layers. The orientation of the (2×4) reconstruction for the GaAs grown on top of the Si-on-GaAs layers was always the same as that of the substrate GaAs for strained Si layers and rotated 90° from that of the substrate for relaxed Si layers. A transition Si thickness region between 13 and 15 Å was discovered for which the GaAs cap layer had a double-domain [(2×4)+(4×2)] reconstruction.