bluuebunny/crossref_metadata_2025 huggingface dataset:
The growth and properties of In-doped metalorganic vapor phase epitaxy interdiffused multilayer process (HgCd)Te
Authors: Gough J. S. , Houlton M. R. , Irvine S. J. C. , Shaw N. , Young M. L. , Astles M. G.
Published: July 2002

Indium doping of Hg1−xCdxTe layers grown by metalorganic vapor phase epitaxy using the interdiffused multilayer process has been investigated using trimethyl indium as the dopant source. The epitaxial growth was performed onto 2° off 〈100〉 CdTeSe substrates at ∼350 °C using dimethyl cadmium (DMCd) and di-isopropyl telluride as the alkyl sources. Doping in the range 1017–2×1018 cm−3 was achieved. By comparing Hall effect measurements of carrier concentration with secondary ion mass spectrometry analyses of the In concentrations in the layers, it was found that the In was only 30% active in the as-grown layers but ∼100% active after Hg-rich isothermal annealing at 250 °C for 48 h. At In concentrations greater than 2×1018 cm−3, the carrier concentration levels off, probably due to the solubility limit of In being reached. The annealed doped layers show slightly higher carrier mobilities than as-grown layers for the same carrier concentration. An apparent shift of the absorption edge to shorter wavelength with increasing donor concentration is thought to be due to the Moss–Burstein effect rather than a change in alloy composition x. A significant ‘‘memory’’ effect has been found with trimethyl In which persists for several runs and is probably due to strong adsorption onto the stainless steel surfaces in the growth system. This can be overcome by vacuum baking of the pipework. The growth of a heterostructure using In doping has shown that there is no serious diffusion problem with In under the growth conditions used.
Arsenic doping in metalorganic chemical vapor deposition Hg1−xCdxTe using tertiarybutylarsine and diethylarsine
Authors: Edwall D. D. , Chen J.-S. , Bubulac L. O.
Published: July 2002

P-type arsenic doped epitaxial layers of HgCdTe have been grown by metalorganic chemical vapor deposition using two alkyl sources, tertiarybutylarsine and diethylarsine. Data are presented on Hall characteristics and arsenic concentration profiles. High activation efficiencies and hole mobilities have been obtained over the range mid-1015 to low-1017 cm−3.
Mercury cadmium telluride junctions grown by liquid phase epitaxy
Authors: Wang C. C.
Published: July 2002

This article reports the advancement of HgCdTe epitaxial technology. Specifically, we will discuss the grown p–n junctions using liquid phase epitaxy (LPE). In our LPE approach, CdTe is used as the substrate. In the LPE technology studied, an HgCdTe active layer is first grown with a desired composition. After growth is terminated, the furnace is cooled down to room temperature. The HgCdTe layer is then characterized before reinserting into the furnace for the second layer growth. Both P-on-n and N-on-p type of heterostructures are obtained by controlling dopants in each layer properly. For the P-on-n type, the active layer is either un-doped or doped with In and the top layer is doped with column V species. For the N-on-p type, the active layer is undoped and the top layer is doped with In together with Cu. In either case, the location of the p–n junction can be well controlled.
Dislocation density reduction by thermal annealing of HgCdTe epilayers grown by molecular beam epitaxy on GaAs substrates
Authors: Arias J. M. , Zandian M. , Shin S. H. , McLevige W. V. , Pasko J. G. , DeWames R. E.
Published: July 2002

Post growth thermal annealing has been used to reduce the threading dislocation density of Hg1−xCdxTe (0.20≤x≤0.28) epilayers grown on (211)B GaAs substrates by molecular beam epitaxy. Etch pit density studies indicate an order of magnitude reduction on the surface threading dislocations after annealing at 490 °C for 30 min. The dislocation density at the HgCdTe surface on this highly mismatched system is only a factor of 2–6 times higher than the best values (1×105 cm−2 ) we have obtained using CdZnTe bulk lattice-matched substrates. The reduction of dislocations may be due to enhanced dislocation movement and their annihilation and coalescence at Hg vacancies point defect pinning centers introduced during the annealing process.
Effects of annealing on anodic oxides of GaP
Authors: Kato Y. , Geib K. M. , Gann R. G. , Brusenback P. R. , Wilmsen C. W.
Published: July 2002

The surface topography and the chemical composition of anodic oxides on GaP have been studied. The surface of the as grown anodic oxide was featureless but annealing at T≥600 °C causes the formation of hollow bumps and blisters which increase in size with temperature or duration of the anneal. The oxide composition was investigated by x-ray photoelectron spectroscopy (XPS) and was found to be a nonuniform mixture of P2O5, Ga2O3, and GaPO4. There is some evaporation of phosphorus oxide near the surface when annealed at T≥300 °C but little or none from the bulk of the oxide film.
Superstructures on graphite near platinum particles
Authors: Xhie J. , Sattler K. , Müller U. , Venkateswaran N. , Raina G.
Published: July 2002

We present STM images of 4 different superstructures on highly oriented pyrolytic graphite near adsorbed platinum particles. The patterns are independent of the size of the particles and decay within a distance of 2–5 nm into the graphite lattice. When Fourier transformed, the structures contain up to three pairs of first-order components in addition to those of graphite. They can be considered as periodic charge density modulations and described by the superposition of three standing electron density waves with different intensities and phases but with the same period of 1.5a (a, the lattice constant of graphite), rotated 30° relative to the graphite lattice.
GaAs quantum well negative differential resistance device prepared by molecular-beam epitaxy
Authors: Liu Wen-Chau , Lin Ching-Hsi , Lee Yeong-Shyang , Guo Der-Feng
Published: July 2002

A novel GaAs quantum-well (QW) negative differential resistance (NDR) device, prepared by molecular-beam epitaxy (MBE), has been fabricated and demonstrated. The S-shaped NDR characteristics is attributed mainly to the impact ionization effect. First, the theoretical analysis based on a triangular barrier model is employed to study the influence of structure parameters on the barrier height. Then, the experimental S-shaped NDR behaviors are observed and analyzed for two-terminal operation and three-terminal operation, respectively. The successful usage of three-terminal control gives flexible and wide application in switching circuits. Furthermore, the studied device exhibits a considerable reaction to illumination and temperature variation. Therefore, the studied NDR device may be used as a sensitive switch under excitation of light illumination and temperature variation.
Doping characteristics of Si into molecular-beam epitaxially grown InAlAs layers
Authors: Higuchi M. , Ishikawa T. , Imanishi K. , Kondo K.
Published: July 2002

We studied the doping characteristics of Si into molecular-beam epitaxially grown InAlAs layers for various growth conditions. The growth temperature and V/III beam flux ratio proved to play different roles in Si doping. The growth temperature affects the Si doping concentration, and the V/III flux ratio does the compensation ratio. At Ts=560 °C, a rather high temperature for the growth of InAlAs layers, the Si doping concentration reached 150% as compared with growth at Ts=500 °C. With increasing V/III flux ratio, on the other hand, electron mobility and donor concentration increased, suggesting a decreased compensation ratio. We also found a considerable number of electron trapping centers at a low-growth temperature of 400 °C.
Characteristics of W films formed by ion beam assisted deposition
Authors: Koh Y. B. , Gamo K. , Namba S.
Published: July 2002

The properties of tungsten films and W–GaAs contact characteristics formed by low energy ion beam assisted deposition (IBAD) have been investigated. For the deposition of tungsten films, low energy (0.5–4.0 keV) H2+ and Ar+ beams were irradiated in W(CO)6 ambient. The deposition rate was higher for heavier ion (Ar+) and higher ion energy because of higher energy deposition rate. The deposited films consisted of about 75% of tungsten and 11%–14% of oxygen and carbon, respectively. The resistivity of deposited films was about 600–800 μΩ cm. The damage induced during ion beam irradiation was examined by W–GaAs contact characteristics. The results suggest that it is desirable to use lighter ion and lower ion energy to reduce the damage on the substrate.
Intrinsic, heterointerface excitonic states in GaAs(n)/Al0.3Ga0.7As( p) double heterostructures
Authors: Gilliland G. D. , Wolford D. J. , Kuech T. F. , Bradley J. A.
Published: July 2002

We have used extensive photoluminescence (PL), PL time-decay measurements, and detailed quantum mechanical modeling to both interpret and quantify the electronic and optical properties of free excitons localized near heterointerfaces. Through detailed spectroscopic measure of the recombination kinetics of the recently observed H-band emission, we find this emission arises from the radiative decay of such weakly bound (≂0.5 meV) excitonic species confined to the hole-attractive quantum potentials formed at the p–n heterointerfaces. Detailed measurements in virtually ‘‘interface-free’’ double GaAs(n)/Al0.3Ga0.7As( p) heterostructures shows the effects of GaAs layer thickness upon the H-band kinetics—thus confirming quasi-2D excitons become effectively ‘‘shared’’ by both heterointerfaces for sufficiently thin GaAs layers (<0.5 μm). Moreover, we find detailed dynamics of these 2D excitons to be influenced by nonradiative interfacial recombination present in nonideal structures. Lastly, we use a novel, all-optical technique to measure the transport properties of these quasi-2D excitons, and find exceedingly long-range (>400 μm) low temperature diffusion.
Photoluminescence from epitaxial Si/Si0.95Ge0.05 heterostructures as probed by optically active deep levels
Authors: Northrop G. A. , Wolford D. J. , Iyer S. S.
Published: July 2002

A detailed study of near-gap photoluminescence (PL) from strained Si1−xGex alloy layers (x=0.01–0.05) and Si/Si0.95Ge0.05 multi-quantum-wells (MQWs) has failed to show either free- or dopant-bound excitons in as-molecular-beam-epitaxy-prepared epitaxial layers. Low-temperature PL was, however, successfully induced in these same heterostructures by the selective introduction of relatively shallow radiation-damage bound-exciton centers, I1 and G (137 and 186 meV deep, respectively). The I1 center, in particular, produced broadened spectra which are shown clearly to emanate from the epitaxial layers, with separate and distinguishable components originating from both the Si and the Si1−xGex (x=0.01–0.05) layers. This is among the first such reports of luminescence verifiably originating from within a Si/Si1−xGex multiple heterostructure. Importantly, we find that this defect-induced PL is not significantly diminished (or even significantly influenced) by the addition of multiple heterointerfaces, thus leading to the conclusion that heterointerface quality may be good. This indicates that these heterointerfaces are not the source of the competing nonradiative recombination which likely prevents the observation of near-gap PL, which is instead possibly due to bulk defects.
The role of As in molecular-beam epitaxy GaAs layers grown at low temperature
Authors: Liliental-Weber Zuzanna , Cooper Greg , Mariella Raymond , Kocot Chris
Published: July 2002

Annealed GaAs layers grown at low temperatures (180–300 °C) by molecular-beam epitaxy (MBE) were studied by transmission electron microscopy (TEM). These layers were used as buffers for a field-effect transistor (FET) device structure and effectively eliminated sidegating effects. All these layers were found to contain As precipitates. Precipitate size and separation between them differed from sample to sample. The smallest precipitates were coherent ‘‘pseudocubic.’’ Larger precipitates had hexagonal structure. The distance between precipitates was estimated to be in the range of 10–40 nm. These results are consistent with the buried Schottky model by Warren et al., although other explanations cannot be excluded at present.
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u doping of Si and Si1−xGex in ultrahigh vacuum chemical vapor deposition
Authors: Racanelli M. , Greve D. W.
Published: July 2002

We report on the growth of germanium–silicon and silicon epitaxial layers by ultrahigh vacuum/chemical vapor deposition. When an in situ clean is used, films grown at 600 °C are defect-free by planar section transmission electron microscopy and no oxygen is detectable by secondary ion mass spectroscopy at the growth interface. In situ doping has been studied using B2H6/H2 and PH3/H2 as source gases. Ge0.13Si0.87 films doped with boron up to 5×1019 cm−3 have been grown and sharp doping transitions have been obtained. Phosphorus doping concentrations in silicon are limited by a decrease in growth rate with increasing phosphorus flow rate which is attributed to phosphorus blocking of reaction sites. A model for the decrease in growth rate with PH3/H2 flow is proposed which provides a good fit to the measurements.
Silicon surface damage caused by reactive ion etching in fluorocarbon gas mixtures containing hydrogen
Authors: Norström H. , Blom H.-O. , Ostling M. , Nylandsted Larsen A. , Keinonen J. , Berg S.
Published: July 2002

For selective etching of SiO2 on silicon, gases or gas mixtures containing hydrogen are often used. Hydrogen from the glow discharge promotes the formation of a thin film polymer layer responsible for the selectivity of the etching process. The reactive ion etch (RIE) process is known to create damage in the silicon substrate. The influence of hydrogen on the damage and deactivation of dopants is investigated in the present work. The distribution of hydrogen in silicon, after different etching and annealing conditions have been studied. The influence of the RIE process on the charge carrier concentration in silicon has been investigated. Various analytical techniques like contact resistivity measurements, four point probe measurements, and Hall measurements have been used to determine the influence of the RIE process on the electrical properties of processed silicon wafers. The hydrogen profile in as-etched and post annealed wafers was determined by the 1H(15N,αγ)12C nuclear reaction. The depth of the deactivated surface layer is discussed in terms of the impinging hydrogen ion energy, i.e., the possibility of H+ ions to pick up an energy equal to the peak-to-peak voltage of the rf signal.
Electrical degradation of Al/TiW/CoSi2 shallow junctions
Authors: Eshraghi S. A. , Georgiou G. E. , Liu R. , Beairsto R. C. , Cheung K. P.
Published: July 2002

TiW barrier properties have been investigated by electrical testing of shallow CoSi2 junctions. Rutherford backscattering and Auger analyses have been used to study Al(0.5% Cu)/TiW/CoSi2/Si structure. Based on the electrical data, it was demonstrated that 900 Å of TiW will serve as a good diffusion barrier up to 475 °C/30 min. The junctions failed at 450 °C when TiW thickness was reduced to 450 Å. The electrical data show the stress of TiW film does not show any significant effects on its properties. Furthermore, shallower junctions (i.e., p+n ) are more vulnerable to barrier failure.
CXrL aligner: An experimental x-ray lithography system for quarter-micron feature devices
Authors: Chen G. , Wallace J. , Nachman R. , Wells G. , Bodoh D. , Anderson P. , Reilly M. , Cerrina F.
Published: July 2002

This article describes the CXrL aligner, an experimental x-ray proximity lithography system developed at the University of Wisconsin Center for X-Ray Lithography. The main features of the aligner are (1) exposure in an atmospheric He environment; (2) mask to wafer alignment error detection and correction during exposure; and (3) mask to wafer continuous gap setting based on capacitance gauges. The aligner consists of a three-axes two-state alignment system for continuous alignment error detection and a piezobased precision mechanical stage for alignment error correction. The wafer is held by a flat vacuum chuck and the mask is held by three vacuum suction cups located around the glass ring. Since the optical system is located outside of the synchrotron radiation path, alignment can be performed during the exposure. We have obtained a noise equivalent misalignment of 2 nm with an alignment signal response time less than 10 ms. An alignment signal repeatability (3σ) better than 0.06 μm has been achieved. In the preliminary evaluation of x-ray printed patterns, we obtained an overlay accuracy of 0.18 μm, to which the measurement error contributes most.
Synchrotron radiation stepper with new alignment system
Authors: Sato F. , Ito K. , Miyatake T. , Yamazaki K. , Hamada S. , Tomita Y.
Published: July 2002

A vertical stepper for synchrotron radiation (SR) x-ray lithography has been developed. Evaluation tests have been done with SR light from the superconducting compact synchrotron ‘‘AURORA’’ located in SHI-Tanashi Works, Tokyo. An overlay accuracy of less than 0.08 μm was obtained. A 0.2 μm line-and-space pattern was successfully resolved with a high-aspect ratio. The designed specifications have been attained. The system is ready for the future generation ultra-large-scale integration applications.
Optical detection of multibit logic signals at internal nodes in a flip-chip mounted silicon static random-access memory integrated circuit
Authors: Heinrich H. K. , Pakdaman N. , Prince J. L. , Jordy G. , Belaidi M. , Franch R. , Edelstein D. C.
Published: July 2002

We report the first optical measurements of multiple bit-pattern logic signals at internal nodes in a flip-chip mounted silicon static random-access memory integrated circuit. This probing system measures signals by interferometrically detecting the electrically induced charge-density modulation within devices and parasitic pn junctions. The optical measurements, made on an output driver circuit, compared well with those on an external high-speed oscilloscope. Measurements made at internal points generally compared well with circuit simulations. However, the bit-sense circuit measurements suggested internal logic-level problems in the circuit design.
Etch-rate characterization of irradiated SiO2 and its application in the fabrication of a T-gate structure
Authors: Hoole A. C. F. , Broers A. N.
Published: July 2002

Experiments to determine the effect of the e-beam irradiation dose on the etch rate enhancement of SiO2 in p etch have been performed. These experiments have been carried out across the dose range of 0–1.5×10−2 C/m and at various acceleration voltages in the 100–350 kV range. The results clearly show the existence of a saturation in the etch rate around a line dose of 3×10−3 C/m. The first direct observation of the resulting trench profiles in the SiO2 have been obtained. These clearly show the effect of the accelerating voltage on the minimum achievable linewidth. Preliminary results of the application of the SiO2 irradiation process to the fabrication of T-gate type structures are also shown.
Be diffusion at the emitter-base junction of graded AlInAs/GaInAs heterojunction bipolar transistors
Authors: Metzger R. A. , Hafizi M. , Wilson R. G. , Stanchina W. E. , Jensen J. F. , McCray L. G.
Published: July 2002

Compositional grading at the emitter-base junction of Npn heterojunction bipolar transistors (HBTs) has been achieved by using a nine period graded gap AlInAs/GaInAs superlattice of 300 Å thickness. The as designed 500 Å base region was doped using Be fluxes that ranged from 0.8×1012 to 1.4×1012 atoms/cm2 s. Growth over this flux range resulted in a base doping of 4.5×1019 cm−3 with the highest flux producing an additional 160 Å of Be penetration into the graded region as compared with the lowest flux. The dc and rf characteristics of the graded emitter-base HBTs are found to be tolerant to this degree of Be outdiffusion.
Wet and dry etching characteristics of Al0.5In0.5P
Authors: Lothian J. R. , Kuo J. M. , Hobson W. S. , Lane E. , Ren F. , Pearton S. J.
Published: July 2002

A selective wet chemical etching solution for removal of Al0.5In0.5P from GaAs based on HCl:H2O has been developed. Controllable etch rates from 600 Å min−1 at 1HCl:30H2O to 6000 Å min−1 at 1HCl:5H2O at 25 °C are obtained. The etch rate is thermally activated of the form R∝exp(−Ea/kT) where Ea=12.4 kCal mol−1, consistent with reaction-limited etching. Dry etch rates of AlInP in PCl3/Ar, CCl2F2/Ar, or CH4/H2/Ar electron cyclotron resonance discharges are all <300 Å min−1 for additional dc self-biases of ≤250 V. Selectivities of ≳600:1 are obtained for etching GaAs over AlInP in CCl2F2/Ar discharges for dc biases ≤150 V. The etched surface morphologies are smooth, with small quantities of Cl-containing residues remaining after PCl3/Ar exposure, and both Cl and F detectable after CCl2F2/Ar dry etching.
High performance double pulse doped pseudomorphic AlGaAs/InGaAs transistors grown by molecular-beam epitaxy
Authors: Hoke W. E. , Lyman P. S. , Labossier W. H. , Brierley S. K. , Hendriks H. T. , Shanfield S. R. , Aucoin L. M. , Kazior T. E.
Published: July 2002

Double pulse doped AlGaAs/InGaAs pseudomorphic high electron mobility transistors have been grown by molecular-beam epitaxy on GaAs substrates. Hall mobilities in excess of 7100 cm2/V s at 300 K and 25 000 cm2/V s at 77 K are obtained with a sheet density of 3×1012 cm−2. Photoluminescence measurements indicate that two electronic subbands are occupied, and the subband energies are determined. The doping pulses are resolved in secondary ion mass spectrometry measurements. Using a double recess process, transistors have been fabricated that have produced state of the art microwave performance. At 10 GHz a 1.2 mm device has simultaneously achieved a power added efficiency of 70%, output power of 0.97 W, and gain of 10 dB.
In situ spectroscopic ellipsometry studies of hydrogen ion bombardment of crystalline silicon
Authors: Hu Y. Z. , Li M. , Conrad K. , Andrews J. W. , Irene E. A. , Denker M. , Ray M. , McGuire G.
Published: July 2002

Hydrogen-bombardment induced damage in single crystal silicon as a function of the substrate temperature, ion energy, and ion dose was studied using in situ spectroscopic ellipsometry over the photon energy range 2.0–5.5 eV under high vacuum conditions. The incident hydrogen ion energies were 300 and 1000 eV, and the doses were 1015–1018 ions/cm2. In situ spectroscopic ellipsometry results showed that the damage layer thicknesses for the samples bombarded at elevated temperatures are smaller than for samples bombarded at room temperature and subsequently annealed at the same elevated temperature. The diffusion coefficient for hydrogen in silicon of 6 × 10−15 cm−2/s was obtained from the in situ spectroscopic ellipsometry data.
Techniques and applications of graded-composition InGaAlAs alloys
Authors: Vlcek James C. , Choi Woo-Young , Fonstad Clifton G.
Published: July 2002

As molecular-beam epitaxy crystal growth techniques steadily progress from the research stage into full-scale production, the need for precise control of the crystal growth process becomes increasingly important. This is particularly true for epitaxial layer structures requiring precisely controlled compositional gradients. We have developed techiques for the growth of linearly graded InGaAlAs, while precisely maintaining lattice matching to the InP substrate, such that x-ray full widths at half-maximum close to the theoretical limit have been achieved. Through the use of these techniques, heterojunction bipolar transistors and graded-index separate confinement heterostructure laser diodes have been grown, fabricated, and tested.
Enhanced etching of Si(100) by neutral chlorine beams with kinetic energies up to 6 eV
Authors: Campos Francis X. , Weaver Gabriela C. , Waltman Curtis J. , Leone Stephen R.
Published: July 2002

Enhanced etching of a room temperature Si(100) surface is observed during exposure to a neutral hyperthermal chlorine beam. Etching is monitored by mass spectrometric detection of silicon chloride products (SiClx) in the scattered flux. The etchant beam is produced by laser vaporization of cryogenic chlorine films; it consists of ≥93% molecular chlorine with a variable kinetic energy distribution depending on laser energy. The sustained etching rate, based on detection of SiCl3+, is independent of energy when the maximum Cl2 kinetic energy is less than 3 eV but increases by a factor of 3.6±1 when the maximum energy is ≊6 eV. No etch products are detected with thermal Cl2. The etching rate of the most energetic chlorine is greater than the thermal chlorine etching rate by a factor of ≥30.
20 nm linewidth platinum pattern fabrication using conformal effusive-source molecular precursor deposition and sidewall lithography
Authors: Hsu David S. Y. , Turner N. H. , Pierson K. W. , Shamamian V. A.
Published: July 2002

In a manner suitable for large-scale processing, vertical platinum structures having thicknesses (linewidths) down to 20 nm, heights up to 700 nm, an aspect ratio up to 13, and different geometric shapes have been fabricated on top of a silicon dioxide substrate by Pt deposition from the thermal decomposition of a platinum precursor molecule under gas phase collisionless conditions followed by ion-assisted etching. Scanning electron microscopy analysis shows that the structures have very small grains, high uniformity, and very sharp contours, demonstrating a high degree of conformal deposition. Scanning Auger microscopy reveals platinum only on the structures. X-ray diffraction and x-ray photoelectron spectroscopy analysis of the as-deposited platinum film show that the platinum film is polycrystalline and has no detectable impurity. Scotch tape test shows good bonding of the film. Mass spectrometric measurements suggest that substantial amounts of stable precursor fragments from partial decomposition of the parent precursor desorb from the substrate. The observed desirable film morphology and purity can be attributed to the favorable choice of template material, decomposition mechanism of the precursor, and the chemical beam conditions used.
Analysis of molecular-beam epitaxial growth of InAs on GaAs(100) by reflection anisotropy spectroscopy
Authors: Scholz S. M. , Müller A. B. , Richter W. , Zahn D. R. T. , Westwood D. I. , Woolf D. A. , Williams R. H.
Published: July 2002

The molecular-beam epitaxial growth of InAs on GaAs(100) was investigated in situ using reflection anisotropy spectroscopy (RAS) and simultaneously reflection high-energy electron diffraction. The RAS spectra of the GaAs c(4×4) and (2×4) and the InAs (4×2) and (2×4) reconstructions are reported. During InAs deposition, the RAS signal shows significant changes for InAs coverages as low as 1/6 of a monolayer. At this coverage surface reconstructions are responsible for the signal variation. For InAs coverages larger than four monolayers, the RAS signal is essentially determined by the anisotropic roughness of the three-dimensional growing surface. This is verified using a three-layer model which gives an excellent description of the experimental spectra at large coverages.
Are there Tamm-state donors at the InAs–AlSb quantum well interface?
Authors: Kroemer Herbert , Nguyen Chanh , Brar Berinder
Published: July 2002

An explanation of the temperature dependence of the electron concentration in InAs/AlSb quantum wells, along with the high electron mobilities found, calls for a model involving a high concentration of interface donors whose electron scattering cross section is much less than that of conventional point defect donors. We postulate that the interface donors are in fact not point defects, but a Tamm-state-like band of de-localized interface states not associated with defects, but with the strong discontinuity in the periodic potentials on the two sides of the interface. Heuristic arguments supporting this hypothesis are given.
Gas source iodine doping and characterization of molecular-beam epitaxially grown CdTe
Authors: Rajavel D. , Wagner B. K. , Benz R. G. , Conte A. , Maruyama K. , Summers C. J. , Benson J. D.
Published: July 2002

Investigations are reported on the gas source iodine doping of CdTe grown by molecular-beam epitaxy, utilizing ethyliodide as the dopant precursor. Structural and electrical characterizations of these layers showed them to have favorable crystalline properties and indicated that the electrical activity of iodine in CdTe was between 50% and 100%. Electron concentrations between 6×1016 and 3×1018 cm−3 were obtained and showed the highest mobilities measured in epitaxial n-type CdTe. These studies also showed that the incorporation of iodine was independent of the II/VI flux ratio and that its electrical activity was independent of both dopant concentration and II/VI flux ratio. The photoluminescence spectrum at 10 K was dominated by strong excitonic recombination bound to ionized and neutral iodine donors. These results demonstrate that iodine is a highly effective donor in CdTe.
Photoelectron holography of Si(100)-[2×1] and other surface and thin-film structures
Authors: Tonner B. P. , Zhang J. , Chen X. , Han Z.-L. , Harp G. R. , Saldin D. K.
Published: July 2002

Direct imaging of near-neighbor atomic structure in Si(100) is demonstrated using photoelectron holography with the Si 2s core level. Photoelectron diffraction studies of the initial stages of epitaxy of copper on Si(100)-[2×1] surfaces show that room-temperature deposition does not result in ordered films. Examples of quantitative photoelectron diffraction studies of epitaxial copper films show that bond-length accuracies of 0.05 Å are possible by fitting techniques.
Secondary ion mass spectrometry depth profiling of nanometer-scale p+-n junctions fabricated by Ga+ focused ion beam implantation
Authors: Novak Steven W. , Magee Charles W. , Mogul Homi C. , Steckl A. J. , Pawlik M.
Published: July 2002

We have used secondary ion mass spectrometry (SIMS) as an analytical tool to measure the depth distribution of 2–10-keV focused ion beam Ga implants into crystalline Si. Depth profiling was carried out by SIMS using 2-keV Cs+ bombardment at 60° with respect to normal and monitoring positive secondary ions. Implant ranges correlate well with those calculated by trim but are shallower by 20–25 Å; in contrast ΔRp values are identical to those calculated by trim. Rapid thermal annealing has been used to electrically activate the Ga and SRP measurements have been used to determine junction depths.
Methods for the measurement of two-dimensional doping profiles
Authors: Subrahmanyan Ravi
Published: July 2002

The problem of measuring two-dimensional (2D) diffusion profiles in silicon is a critical one. Several very different methods for 2D dopant profiling have been proposed recently, but the methods are often applied only by specialists to selected problems and wide acceptance of these methods is yet to take place. This article presents a comprehensive review of methods for the measurement of 2D dopant profiles, along with a complete bibliography. The goal is to compare the various methods on the basis of some common factors, and to begin to establish some criteria for selecting 2D dopant profiling methods. First, some issues are raised which, in addition to criteria such as resolution and sensitivity, form a basis for differentiating between various methods. The methods described in the literature to date are then classified and discussed briefly. All reported methods and their variations are at least mentioned with appropriate references. Finally, a comparison of various methods is presented, focusing on specific issues such as resolution, accuracy, complexity of sample preparation, and the complexity of equipment required for the measurement.
Reconstructed two-dimensional doping profiles from multiple one-dimensional secondary ion mass spectrometry measurements
Authors: Goodwin-Johansson Scott H. , Ray Mark , Kim Yudong , Massoud H. Z.
Published: July 2002

Two-dimensional doping profiles can be determined from multiple one-dimensional secondary ion mass spectrometry (SIMS) profiles using computed tomography techniques. The chemical nature of SIMS enables the measurement of both as-implanted and annealed profiles with this technique. Mechanical lapping was done of multiple samples to expose different faces of the substrates followed by one-dimensional SIMS measurements. Doping profiles of 0.4 μm boron junctions have been measured and reconstructed using the maximum likelihood estimation algorithm. Issues of sample alignment, SIMS depth resolution and SIMS sensitivity are discussed with respect to the application of this technique to sub 100 nm junctions.
Two-dimensional carrier profiling
Authors: Vandervorst W. , Clarysse T. , Vanhellemont J. , Romano-Rodriguez A.
Published: July 2002

Two-dimensional (2D) carrier profiling is an important aspect of the characterization of ultra-large-scale integrated devices. Through a special measurement procedure and sample preparation it has been shown that the use of spreading resistance profiling (SRP) for this application is possible with 10–20 nm spatial resolution. Extension to the quantitative determination of a three-dimensional profile appears to be possible. Higher spatial resolution has been achieved using transmission electron microscopy (TEM) based methods whereby chemical etching and electron irradiation are investigated. For these methods detection limits down to 5×1017 cm−3 have been determined. Based on the properties of SRP (sensitivity and quantification) and TEM (high spatial resolution, on-chip application) both methods are found to be highly complementary for 2D carrier profiling.
Two-dimensional p
n-junction delineation on cleaved silicon samples with an ultrahigh vacuum scanning tunneling microscope
Authors: Kordić S. , van Loenen E. J. , Walker A. J.
Published: July 2002

Two-dimensional scanning tunneling microscope (STM) measurements on cleaved interdigitated shallow pn junctions are presented. The two-dimensional part of the junction is localized to within 30 nm. The cleaving of the junctions and the STM measurements are performed in ultrahigh vacuum (UHV). STM measurements on pn junctions in air are also discussed. These measurements show that there is a relation between the magnitude of the tunneling current and the local impurity concentration of the sample. A qualitative model is presented that explains the observed effects.
Reduction of outdiffusion at the Ge/GaAs (100) interface by low temperature growth
Authors: Demirel A. L. , Strite S. , Agarwal A. , Ünlü M. S. , Morkoç H. , Rockett A.
Published: July 2002

Ga outdiffusion into Ge layers grown epitaxially by molecular beam epitaxy was observed by secondary ion mass spectroscopy, x-ray photoemission spectroscopy, capacitance–voltage, and temperature dependent Hall-effect measurements. Films were initially grown at low rates (0.03–0.04 nm/s) and low temperatures (150–300 °C) on GaAs buffer layers on GaAs (100) substrates. The temperature and rate were then increased to 500 °C and 0.1 nm/s. The amount of Ga outdiffusion was greatest for films initially grown at 300 °C. No direct evidence of As outdiffusion at any temperature or Ga outdiffusion for initiation temperatures below 300 °C was found. Hall-effect measurements showed higher hole concentrations and greater levels of compensation in films initiated at 300 °C, consistent with outdiffusion of both Ga and As at this temperature. No degradation in the electrical characteristics of Ge–GaAs diodes was observed when the initial Ge growth temperature was reduced from 300 to 200 °C.
A collector design study for GaAs/Ge/GaAs double heterojunction bipolar transistors
Authors: Strite S. , Ünlü M. S. , Demirel A. L. , Mui D. S. L. , Morkoç H.
Published: July 2002

We analyze the effect of the conduction band offset in the collector heterojunction in NpN GaAs/Ge/GaAs double heterojunction bipolar transistors (DHBT). Despite excellent diode characteristics in both the emitter-base and base-collector diodes, the GaAs/Ge/GaAs DHBTs exhibit relatively low common-emitter dc current gains and a lack of collector current saturation with increasing collector-emitter bias. Simulations indicate that this is at least in part attributable to a reduction in collection efficiency caused by the large collector-base conduction band offset (0.26 eV) between the Ge base and the GaAs collector. A modified collector design, which incorporates higher doping in the region of the GaAs conduction band spike, is proposed to decrease the width of the barrier to electrons. Simulations predict that the collection efficiency will be greatly improved with the incorporation of a modified collector.
ZnSe/ZnCdSe quantum well light emitting diodes
Authors: Tamargo M. C. , Brasil M. J. S. P. , Nahory R. E. , Martin R. J. , Farrell H. H. , Gmitter T. J. , Aspnes D. E. , Weaver A. L. , Zhang Y. , Skromme B. J.
Published: July 2002

We report the growth and operation of a ZnSe/ZnCdSe quantum well light emitting diode (LED). I–V characteristics confirm the presence of a p–n junction and are similar to those previously reported for homojunction ZnSe LEDs. The room-temperature electroluminescence spectrum exhibits strong recombination at the quantum well, demonstrating effective confinement and high-quality materials. The electroluminescence is studied as a function of temperature and operating current of the device.
Contactless electromodulation investigations of surface/interface electric fields in semiconductor microstructures
Authors: Pollak Fred H.
Published: July 2002

This article reviews some recent experiments using contactless electromodulation techniques, i.e., photoreflectance and contactless electroreflectance, to investigate the surface/interface electric fields in (a) pseudomorphic GaAlAs/InGaAs/GaAs modulation-doped quantum well structures (including the determination of the two-dimensional electron gas density) and (b) Fermi-level pinning on n- and p-type GaAs (001) surfaces. Evidence for the reduced surface state density on p-type material will be presented from both prior and new experiments.
Absorption modulation induced by electron beam excitation of strained In0.2Ga0.8As/GaAs multiple quantum wells
Authors: Rich D. H. , Rammohan K. , Tang Y. , Lin H. T. , Maserjian J. , Grunthaner F. J. , Larsson A. , Borenstain S. I.
Published: July 2002

The effects of excess carrier generation on excitonic absorption phenomena in nipi-doped In0.2Ga0.8As/GaAs multiple quantum wells (MQWs) was examined using a novel technique called electron beam-induced absorption modulation imaging. The nipi-doping induced barrier height is determined by measuring the frequency response of the absorption modulation as a function of temperature and employing a model which is based on thermal excitation of carriers in the limit of Boltzmann statistics. Spatial steps in the absorption modulation which correlate with the positions and orientation of dark line defects imaged in cathodoluminescence are observed. These results indicate the existence of defects in the MQWs which impede the ambipolar diffusive transport of the spatially separated electron-hole plasma.
Synchrotron radiation-assisted etching of Si in the presence of reactive species produced by microwave discharge
Authors: Terakado Shingo , Kitamura Osamu , Suzuki Shigeo , Tanaka Kenichiro
Published: July 2002

The photochemical etching of Si has been studied using synchrotron radiation (SR) in the presence of reactive species produced by 2.45 GHz microwave discharge in a mixture of SF6 and Ar. The effect of SR irradiation was investigated, and it was found that the SR-irradiated region was etched at a rate one order of magnitude faster than was the nonirradiated region. A clear fringe pattern appeared parallel to the edge of the replicated mask pattern on the Si surface. These fringes were interpreted as caused by the diffraction effect of the incident beam at the mask. By comparing the etched fringe pattern with the calculated one of the Fresnel diffraction, it was clarified that the etched pattern agreed with the diffraction one. That is, the spatial distribution of the photointensity was replicated on the etched surface. Therefore, it was concluded that the main effect of SR irradiation was to activate the etching reaction on the sample surface.
Characterization of silicon dioxide and phosphosilicate glass deposited films
Authors: Rojas S. , Zanotti L. , Borghesi A. , Sassella A. , Pignatel G. U.
Published: July 2002

Silicate glasses, both undoped and lightly doped with phosphorus, prepared by a low pressure plasma enhanced chemical vapor deposition (PECVD) system using tetraethylorthosilicate or silane as silicon sources and atmospheric pressure chemical vapor deposition technique using silane, were evaluated. The three analyzed phosphosilicate films were nominally 4.0 wt % doped. All the samples were deposited in the temperature range of 350–420 °C. Their main properties such as refractive index, density, wet etch rate, stress, step coverage, moisture resistance, and infrared absorption are reported. Infrared absorption measurements were performed on both as-deposited and annealed films (430 °C for 15 min in N2) to investigate the presence of water and Si–OH groups, as well as P=O and Si–O bond interactions. The P-doped films were tested as final passivation layers on 1 Mbit erasable programmable read only memory devices mounted in ceramic packages. Similar electrical results have been obtained with three different phosphosilicate glass films. However, the most reliable results after assembly and packaging were obtained for films deposited by PECVD technique using tetraethylorthosilicate as the source of silicon in the films.
Fabrication of high performance 512K static-random access memories in 0.25 μm complementary metal–oxide semiconductor technology using x-ray lithography
Authors: Viswanathan R. , Seeger D. , Bright A. , Bucelot T. , Pomerene A. , Petrillo K. , Blauner P. , Agnello P. , Warlaumont J. , Conway J. , Patel D.
Published: July 2002

Functional 512K static random access memory (SRAM) devices containing more than 3.6 million transistors have been successfully fabricated in a 0.25 μm complementary metal–oxide semiconductor technology using compact storage ring x-ray lithography. In this demonstration a comparison of critical dimension control was made between x-ray and optical (i-line and excimer laser) lithography by fabricating SRAM devices using both lithographic techniques. For the x-ray fabricated devices the channel length, a key device performance parameter, was controlled to within 0.036 μm (3σ), demonstrating the excellent process robustness, and dimensional control available from x-ray lithography. These SRAMs had excellent electrical characteristics, including cycle times of 1.8 ns and access times of 3.7 ns. The ability of the existing x-ray lithography infrastructure to produce a fully functional (‘‘perfect’’) chip has been demonstrated in a companion device fabrication program. A 512K SRAM chip of a slightly different design, with 0.35 μm minimum channel length, was fabricated with 100% bit yield using x-ray lithography. This article describes these device demonstrations, including the observed advantages of x-ray lithography, as well as the status of IBM’s x-ray lithography program and associated infrastructure.
Determination of acid diffusion rate in a chemically amplified resist with scanning tunneling microscope lithography
Authors: Perkins F. Keith , Dobisz Elizabeth A. , Marrian Christie R. K.
Published: July 2002

A scanning tunneling microscope (STM) was employed to investigate properties of the chemically amplified negative electron beam resist MICROPOSIT■ SAL-601■, from Shipley Company. The usual processing sequence of the resist includes a postexposure bake (PEB) to promote the cross-linking action of the acid catalyst. However, it has been proposed that PEB can induce thermally activated diffusion of the acid catalyst as well. Using the STM to generate a spatially localized beam of low kinetic energy electrons, we have investigated the effects of exposure dose and voltage and PEB time on linewidth in thin (50 nm) resist films. Even with no PEB, insoluble resist features were observable. Energy calculations do not support significant local heating. Therefore, cross-linking must be due to the electron exposure. Dose and PEB times under 10 min have only a small effect on linewidth. From the variation of feature size with PEB time, an upper limit to the diffusion coefficient was measured to be 0.3 nm2/s. This value is well below what has been previously reported. The process latitude of exposure with a 50 kV electron beam has also been investigated. Both dose and PEB conditions had a much larger effect on feature size for the high energy lithography.
Investigations of artificial nanostructures and lithography techniques with a scanning probe microscope
Authors: Griesinger U. A. , Kaden C. , Lichtenstein N. , Hommel J. , Lehr G. , Bergmann R. , Menschig A. , Schweizer H. , Hillmer H. , Koops H. W. P. , Kretz J. , Rudolph M.
Published: July 2002

In this article, the examination and realization of nanometer structures by an atomic force and a scanning tunneling microscope (AFM/STM) is reported. Nanometer structures [etched wires and gratings for distributed feedback (DFB) lasers] were investigated down to a width of 50 nm with respect to profile, structure height, and sidewall roughness. Special DFB gratings for fine tuning of the emission wavelength are analyzed with respect to Fourier components of the periodic structure. The use of a STM and an AFM for low voltage electron-beam lithography of artificial nanometer structures will be demonstrated.
Integrated silicon process for microdynamic vacuum field emission cathodes
Authors: Zhang Z. Lisa , MacDonald Noel C.
Published: July 2002

An integrated silicon process has been developed to produce self-aligned gated field emitters on suspended and movable single-crystal silicon beams. The field emitter fabrication process is compatible with an extended version of the single crystal reactive etching and metallization (SCREAM) process. The extended SCREAM process has been used to produce silicon stages with three-dimensional (3D) translation (x,y,z) using integrated capacitive actuators and sensors. Here, we outline the field emitter fabrication process, the extended SCREAM process, and process integration. The integrated structural scheme includes the suspended field emitters integrated with the 3D translator. Electrical isolation and metal contacts are also incorporated with multiple, suspended silicon beams to provide electrical interconnects and isolation of the integrated tips, gate electrodes, actuators, and sensors. The stage with integrated field emitters, translators, isolation, and interconnects is a new approach to the 3D precision positioning and scanning of field emitter tips or scan probes.
In situ strain measurements during the formation of palladium silicide films
Authors: Buaud P. P. , d’Heurle F. M. , Chevacharoenkul S. , Irene E. A.
Published: July 2002

The evolution of strain in the Pd–Si system during the growth of Pd2Si thin films on Si (100) substrate has been followed in situ using a double optical beam technique. As was observed for the Pt–Si system, the reaction to form Pd2Si yields a compressive intrinsic surface film stress as well as for the silicon-rich silicides as proposed by Angilello et al. [Thin Film Interfaces and Interactions, edited by J. Baglin and J. Poate (The Electrochemical Society, Pennington, NJ, 1980)]. A transmission electron microscopy analysis has revealed grain growth during the formation of Pd2Si which cannot account for the compressive film stresses. The formation of silicide at the interfaces rather than the overall change in volume agrees with the sign of the stresses formed.