bluuebunny/crossref_metadata_2025 huggingface dataset:
Minority carrier lifetime and photoluminescent response of heavily carbon-doped GaAs grown with gas source molecular-beam epitaxy using halomethane doping sources
Authors: de Lyon T. J. , Woodall J. M. , Kash J. A. , McInturff D. T. , Bates R. J. S. , Kirchner P. D. , Cardone F.
Published: July 2002

CCl4, CHCl3, and trimethylgallium have been utilized as carbon doping sources for GaAs epilayers sandwiched in isotype GaAs/Al0.33Ga0.67As heterostructures and for p-GaAs active layers in Ga0.51In0.49P/GaAs/Al0.30Ga0.70As double-heterostructure light emitting diodes (LEDs) grown by gas source molecular-beam epitaxy (MBE). Minority carrier lifetimes and photoluminescence (PL) intensities have been evaluated from time-resolved PL spectroscopy of the isotype heterostructures with GaAs active layers ranging in thickness from 0.2–1.0 μm and carbon doping from 1018 to 1020 cm−3. These results are compared to those measured in Be-doped films grown in the same MBE system and to results on Be-doped films published by others. Measurements of LED responsivity and optical modulation bandwidth are discussed for carbon doping over the same 1018–1020 cm−3 range. Although electrical 3 dB bandwidths increase with C doping and exceed 1.5 GHz at 1020 cm−3 C doping, both LED brightness and epilayer PL intensities are presently limited by the onset of nonradiative recombination for C concentrations in excess of 1019 cm−3.
Control of Be diffusion in AlInAs/GaInAs heterostructure bipolar transistors through use of low-temperature GaInAs
Authors: Metzger R. A. , Liu T. , Stanchina W. E. , Wilson R. G. , Jensen J. F. , McCray L. G. , Pierce M. W. , Kargodorian T. V. , Allen Y. K. , Lou P. F. , Mishra U. K.
Published: July 2002

Low-temperature (LT) GaInAs has been used to inhibit the diffusion of Be from the base to emitter in Npn AlInAs/GaInAs/GaInAs heterostructure bipolar transistors (HBTs) grown lattice matched to InP substrates by molecular-beam epitaxy (MBE). A series of Be planar-doped spikes (1.0–0.017 monolayers) were grown in LT GaInAs (over a temperature range of 225–445 °C as compared to normal growth at 500 °C) and it was determined by secondary-ion mass spectroscopy (SIMS) that the Be full width at half-maximum decreased by a factor of 3 for LT GaInAs grown below 350 °C. A series of LT GaInAs spacers of varying thicknesses (up to 150 Å) and Be dopings (2 × 1018–1 × 1020 cm−3) were grown at 300 °C and placed at the emitter-base junction of Npn HBTs. The optimum spacer configuration as determined by Be penetration into the AlInAs emitter, and rf performance, was with a LT GaInAs spacer of 150 Å and Be doped at 2 × 1018 cm−3 producing no observable (determined by SIMS) Be penetration into the emitter and an fmax of 73 GHz and ft of 110 GHz.
Kinetics of ideal dopant segregation in GaAs
Authors: Cunningham J. E. , Williams M. , Chiu T. , Jan W. , Storz F.
Published: July 2002

We evaluate Be and Si segregation in GaAs during growth by gas source molecular-beam epitaxy and molecular-beam epitaxy. We find that the dopant segregation lengths, when detected, are thermally activated with an energy of 0.6 eV. These kinetics are too small to be explained by classical models of dopant segregation, but instead lie close to motion energies corresponding to the elementary jumps executed by the dopant near the surface.
New low-strain II–VI superlattices: ZnTe/CdSe and ZnTe/Cd1−xMnxSe
Authors: Samarth N. , Luo H. , Pareek A. , Zhang F. C. , Dobrowolska M. , Furdyna J. K. , Chou W. C. , Petrou A. , Mahalingam K. , Otsuka N.
Published: July 2002

We have used molecular-beam epitaxy to fabricate ZnTe/Cd1−xMnxSe (0≤x≤0.30) superlattices. This is a low-strain system, with lattice mismatch ranging from 0.35% for x=0 to 1% for x=0.3. Structural and optical evaluation of these superlattices is discussed.
Deep levels and DX centers in AlxGa1−xAs/GaAs. I. Composition dependence study
Authors: Halder N. C. , Barnes D. E.
Published: July 2002

We have utilized the isothermal capacitance transient spectroscopy and modulated function waveform analysis to investigate the deep levels and DX centers in molecular beam epitaxially grown AlxGa1−xAs/GaAs Schottky diodes deposited on n+ GaAs, with Al composition ranging from x=0 to 0.5, and implanted with Si. In the concentration range x=0.19 to 0.50, two major electron trap levels (E1 and E2) were detected, which gradually changed with composition. For example, E1 changed from 0.393 to 0.339 eV and E2 changed from 0.136 to 0.287 eV. However, in pure GaAs, three major trap levels with energy E1 (hole)=0.226 eV, E2 (electron)=0.496 eV, and E3 (EL2)=0.74 eV were observed. Apparently, these levels are governed by the deep levels known as DX centers.
Deep levels and DX centers in AlxGa1−xAs/GaAs. II. Field effect deep level transient spectroscopy study
Authors: Halder N. C. , Barnes D. E.
Published: July 2002

The field effect has been investigated on the deep levels and DX centers in molecular-beam epitaxilly-grown AlxGa1−xAs on n+ GaAs for several compositions. We have measured the isothermal and isofield capacitance transients for the major energy levels with the applied potential in the range from −0.1 to −3 V. In samples with x=0.5, two electron trap levels (E1 and E2) were detected. While E1 was strongly field dependent (changed from 0.499 to 0.287 eV) E2 was practically unchanged (0.305 eV) with respect to energy, cross section, and peak broadening. Contrary to this in pure GaAs (samples x=0), we observed three energy levels, one hole trap (E1=0.239 eV), one electron trap (E2=0.512 eV), and the usual EL2 trap (E3=0.72 eV). At this composition, however, levels E1 and E2 were absent at low reverse fields (at −1 V) and EL2 remained unchanged at 0.72 eV. We have considered the recent theories of Pool–Frenkel effect and tunneling for electron–phonon interaction to interpret the results. In particular, for AlxGa1−xAs with x=0.5, the electron–phonon coupling factor (S) was found to be about 4 and the deep centers were identified as neutral to repulsive.
Focused ion beam micromachining for transmission electron microscopy specimen preparation of semiconductor laser diodes
Authors: Szot J. , Hornsey R. , Ohnishi T. , Minagawa S.
Published: July 2002

A new method based on focused ion beam micromachining of optoelectronic semiconductor microdevices for cross-sectional transmission electron microscope analyses has been developed. Electron transparent areas in excess of 200 μm2 have been fabricated. These enabled an investigation of the origins of structural defects in a prespecified submicron-sized region of GaInP/AlGaInP-based semiconductor laser diodes.
Automated control of III–V semiconductor composition and structure by spectroellipsometry
Authors: Quinn W. E. , Aspnes D. E. , Brasil M. J. S. P. , Pudensi M. A. A. , Schwarz S. A. , Tamargo M. C. , Gregory S. , Nahory R. E.
Published: July 2002

Probes that can monitor and control crystal growth in real time could significant improve sample yield and material reliability. We are developing one such probe, spectroellipsometry, for controlling growth by organometallic molecular beam epitaxy. Our system is presently capable of holding the composition of thick AlxGa(1−x)As layers constant to a precision of ±0.1%, and has been used to control growth of purposely compositionally graded structures, such as parabolic quantum wells 200 Å wide.
Characteristics of selective reactive ion etching of InGaAs/InAlAs heterostructures using HBr plasma
Authors: Agarwala Sambhu , Adesida Ilesanmi , Caneau Catherine , Bhat Rajaram
Published: July 2002

A highly selective reactive ion etching (RIE) process based on HBr plasma has been demonstrated for the removal of InGaAs on InAlAs over a wide range of plasma self-bias voltages. Etch selectivities of 160 at −100 V and 50 at higher voltages up to −300 V have been obtained. It is shown with the aid of x-ray photoelectron spectroscopy analysis that the surface residues on the etched structures can be removed by a simple treatment in dilute HCl. No incorporation of impurities from the plasma, such as hydrogen and bromine, was detected by secondary ion mass spectroscopy analysis in samples treated in RIE up to −150 V. No degradation in mobility and sheet carrier density of the two-dimensional electron gas was observed in modulation-doped InAlAs/InGaAs field-effect transistor (FET) structures, at low self-bias voltages. The dc and rf device parameters of FETs fabricated using RIE as the gate-recess process compare favorably with those of corresponding devices fabricated using a selective wet-etching process.
Chemical amplification electron beam positive resist process free from surface insoluble layer
Authors: Fujino Takeshi , Maeda Hiroshi , Kumada Teruhiko , Moriizumi Koichi , Kubota Shigeru , Koezuka Hiroshi , Morimoto Hiroaki , Watakabe Yaichiro , Tsubouchi Natfuro
Published: July 2002

This article describes a chemical amplification electron beam (EB) positive resist, and associated overcoat process with an acidic film. The EB resist consists of three components; the modified poly(p-vinylphenol), a dissolution inhibitor, and an acid generator. Polymer containing a sulfonic acid group is used as the overcoat material. A 0.16-μm lines-and-spaces pattern is successfully fabricated at 14.6 μC/cm2 using 50 keV EB. The process latitude on EB exposure for 0.3-μm lines and spaces exceeds ±10% of the standard dose. The acceptable delay time between resist coating and EB exposure exceeds 200 h, and the acceptable delay time between EB exposure and postexposure bake is as much as 38 h. The limitation of the latter delay time is not restricted by the generation of surface insoluble layer but by the acid catalyzed reaction at room temperature. It is experimentally confirmed that the acidic overcoat film is effective for both protecting a surface of EB resist against airborne contaminants and dissolving the surface insoluble layer.
Directly patterned low voltage planar tungsten lateral field emission structures
Authors: Hoole A. C. F. , Moore D. F. , Broers A. N.
Published: July 2002

Using high resolution electron beam lithography it has been possible to directly pattern planar structures which exhibit lateral conduction characteristics that are consistent with field emission. Two terminal and three terminal structures have been fabricated in a tungsten layer on an insulating substrate using a combination of an aluminum lift-off and dry etching. By careful control of the electrode spacings it has been possible to ensure that the emission occurs for voltages less than 100 V. In the three terminal structures fabricated a high proportion of the emitted current reaches the collector.
Sub-100 nm pattern formation using a novel lithography with SiNx resist by focused ion beam exposure and dry-etching development
Authors: Takahashi S. , Ohashi M. , Fukatsu S. , Shiraki Y. , Ito R.
Published: July 2002

A novel lithography applicable to in situ processing is proposed, where plasma-chemical-vapor-deposited (PCVD) SiNx is used as a resist, exposure is by Ga focused ion beam (Ga-FIB) implantation, and CF4 dry etching is used for development. The Ga-implanted SiNx film acts as a negative resist for CF4 dry-etching development when the ion dose exceeds 1016 cm−2. The imaging contrast appears to be 4.0 when the acceleration voltage in the FIB exposure is 40 kV and chemical dry-etching development is employed. Very fine resist patterns of 50 nm are obtained using the finest beam available with our FIB system in combination with anisotropic reactive ion etching development. The substrate damage due to FIB exposure is not significant thanks to the presence of the SiNx resist. GaAs substrates are successfully dry-etched with deep and anisotropic profiles using SiNx masks fabricated by this lithography method.
Plasma etching of ZnS, ZnSe, CdS, and CdTe in electron cyclotron resonance CH4/H2/Ar and H2/Ar discharges
Authors: Pearton S. J. , Ren F.
Published: July 2002

Smooth anisotropic dry etching of ZnS, ZnSe, CdS, and CdTe in electron cyclotron resonance CH4/H2/Ar discharges at low pressure (1–25 mTorr) and low direct-current (dc) bias (−100 to −250 V dc) is reported. The presence of CH4 at low flow rates is necessary to obtain the best morphologies and to retain the stoichiometry of the surfaces, although H2/Ar discharges readily etch all four materials. Increasing the microwave power into the discharge at fixed dc bias produces significant increases in the resulting etch rates, while retaining the highly anisotropic nature of the pattern transfer.
Elimination of planar faults in lattice-matched heteroepitaxial films using ion-assisted molecular-beam epitaxy
Authors: Choi C.-H. , Hultman L. , Barnett S. A.
Published: July 2002

The nucleation and defect structure of GaAs films grown on Ge(001) by molecular-beam epitaxy (MBE) and ion-assisted MBE (IAMBE) were studied using reflection high-energy electron diffraction and transmission electron microscopy. Three-dimensional (3D) islands nucleated during the initial stages of MBE growth at 580 °C, and continued growth led to nonplanar surfaces and a high density of stacking faults and twins in the films. Irradiation by 33 eV Ar ions during IAMBE growth at 580 °C suppressed 3D island nucleation, yielding relatively flat surfaces throughout growth. Antiphase domains were the only defects observed in the IAMBE films.
Blue/green light emitting diodes and laser diodes based on II–VI heterostructures grown on predeposited GaAs buffer layers
Authors: Ren J. , Eason D. B. , Lansari Y. , Yu Z. , Bowers K. A. , Boney C. , Sneed B. , Cook J. W. , Schetzina J. F. , Koch M. W. , Wicks G. W.
Published: July 2002

Blue/green light emitting diodes and laser diodes based on II–VI heterostructures have been grown on GaAs substrates with predeposited GaAs epilayers capped with As. Improved diode characteristics resulted, along with improved structural, electrical, and optical properties.
Molecular-beam epitaxy investigation of interface disorder effects in magnetic II–VI quantum wells
Authors: Hagston W. E. , Harrison P. , Hogg J. H. C. , Jackson S. , Nicholls J. E. , Stirner T. , Lunn B. , Ashenford D. E.
Published: July 2002

The present article describes the results of a combined theoretical and experimental investigation into the quality of the interfaces of II–VI quantum well structures grown by molecular-beam epitaxy (MBE). Detailed information is presented on the dilute magnetic semiconductor system CdTe/Cd1−xMnxTe in which the CdTe forms the well and the Cd1−xMnxTe forms the barrier. Structures are grown routinely in which both the photoluminescence (PL) and photoluminescence excitation (PLE) linewidths are narrow (∼1–2 meV). This is indicative of high quality material, a feature which is confirmed by the x-ray data in which Pendellösung fringes can be seen. However, in spite of this, it is found that although the same growth conditions are nominally employed quantum well structures are obtained which show either (i) different discernible structures in the PL and the PLE spectra, or (ii) marked differences in the Stokes’ shift between the PLE and PL from one sample to the next. A related feature concerns observations of an asymmetrical magnetic field splitting of the heavy-hole exciton states in the barriers.

The results of theoretical calculations of the exciton energy levels and their associated linewidths are presented. A comparison of theory with the experimental observations shows that the above effects can be accounted for in terms of interface disorder and magnetic field dependent interface potentials. Thus in case (i) above, the relative intensity of the components in the PLE is different from that in the PL. This is consistent with large island growth in the plane of the well, large here meaning that the island diameters exceed those of the exciton diameter (∼140–150 Å). Observations of a Stokes’ shift, even though the absorption and emission lines are narrow, can be accounted for theoretically if the concept of smaller scale disorder is introduced, i.e., island sizes that are small compared with the diameter of the exciton. Finally, results are presented which show a remarkable asymmetry in the Zeeman splitting of the heavy-hole exciton lines. It is shown that this can be accounted for by introducing deep, short-range interface potentials (∼1 or 2 monolayers). The latter are magnetic field dependent, the source of the asymmetry being attributed to band-gap renormalization effects. The implications of all these results for MBE growth conditions are described.
Determination of the mechanical stress in plasma enhanced chemical vapor deposited SiO2 and SiN layers
Authors: Ambrée P. , Kreller F. , Wolf R. , Wandel K.
Published: July 2002

The mechanical stress in plasma enhanced chemical vapor deposited SiO2 and SiN layers is investigated. The dielectric films are deposited on Si and GaAs substrates, respectively. A first annealing of the samples yields irreversible structural changes of the films due to a loss of water and hydrogen. The elastic constant and the thermal expansion coefficient of the densified SiO2 layers are estimated by temperature dependent curvature measurements to be Ec/(1−γc)=(1.0±0.1)×1012 dyn/cm2 and αc=(0.6±0.2)×10−6 °C−1. IR absorbance measurements show a dependence of the center frequency of the Si–O bond-stretching vibration on the total film stress. Correlating the strain deduced from this measurement with the total film stress yields an elastic constant of about Ec/(1−γc)=(3±1)×1011 dyn/cm2. The physical fundamentals of this measuring method as well as the temperature dependent measurements are discussed in detail to explain the apparent discrepancies in the estimation of the elastic constant. These considerations show that the true elastic constant of the SiO2 film can only be estimated by the temperature dependent measuring method.
Multiple-exposure interferometric lithography
Authors: Zaidi Saleem H. , Brueck S. R. J.
Published: July 2002

Interference effects between two coherent laser beams have long been used to create simple grating patterns in photoresist. With the addition of multiple exposures with variations in period, phase, and orientation, in the same level of photoresist, highly complex one- and two-dimensional patterns of potential interest for device application are demonstrated. The spatial scale of the lines forming these patterns is ∼1/4 of the writing wavelength λ (period to λ/2 and line to space ratio of 1:1) and is in the extreme submicron range, ∼0.1 μm, for readily available laser sources, such as an Ar+-ion laser operating at 364 nm. Importantly, the depth-of-focus for these pairwise exposures is unlimited on the scale of typical semiconductor device topographies and large area, uniform exposures to scales much larger than projected integrated circuit die sizes (e.g., to 30×30 cm2) are easily achieved. These patterns are closely related to moiré interference patterns; relationships are illustrated. Diffractive readout is shown to be a powerful and intuitive technique for monitoring these structures. Additional flexibility in pattern fabrication is provided with conventional lithography to define areas on a larger scale and by the use of aperture and phase masks to isolate areas. An example is the fabrication of an interdigitated structure with submicron spaces over a large area.
Method of fabrication of matrix carbon fiber field emission cathode structures for flat-panel indicators
Authors: Chakhovskoi A. G. , Sheshin E. P. , Kupryashkin A. S. , Seliverstov V. A.
Published: July 2002

A matrix carbon fiber field-emission cathode structure with isolated emitters has been developed for use in flat-panel fluorescent indicators and displays. The array is composed of singular carbon polyacrilonitril fibers, 7 μA in diameter, united into a matrix by a silicoorganic dielectric. A method of fabrication of the matrix cathode structure is discussed. Cathode matrices with the number of emitters from 10 to 32×32 and isolated connections for power supply were made. Control of the emission currents is possible both independently and by coupling the emitters as a common cathode circuit with external conductors. The distance between the emitters in the array is 1.5 or 1 mm; the matrix external sizes are 18×20 or 32×32 mm. Nominal potential for the designed cathode in a diode configuration was ∼1.5 kV. The current could be controlled in the range from 0.01 to 100 mA/emitter. Models of flat digital indicators based on the designed cathode arrays were tested.
Emission characteristics and morphology of wet etched cathodes in p-type silicon
Authors: Boswell E. C. , Wilshaw P. R.
Published: July 2002

An isotropic wet etching process was used to generate arrays of field emitting, square-based pyramidal cathodes on (001), p-type silicon wafers. Their general morphology compared well with that found by Cade et al.,1 except that for cathodes with edges oriented along 〈110〉 directions, a ridgelike apex was formed. Transmission electron microscope examination of oxidized tips confirmed that tip sharpening occurs, improving the aspect ratio and producing two sharp cusps from a ridgelike apex and a single sharpened tip from a pointed apex. A modified Philips 505 SEM was used to make electrical measurements from the arrays. Measurements could be made over the range 1–2500 V with a current sensitivity of 10−13 A, current readings being taken over 6 orders of magnitude, in a vacuum of 3×10−7 Torr. Fowler–Nordheim plots exhibited characteristics typical of p-type silicon showing a plateau region which was eliminated by coating with metal. Oxidation sharpening was shown to improve emission and the lowest voltage at which electron emission occurred from a given tip was found to decrease with emission time.
Application of an in situ hydrogen plasma to the epitaxial regrowth of InP grown by molecular beam epitaxy
Authors: Hofstra P. G. , Thompson D. A. , Robinson B. J. , Streater R. W.
Published: July 2002

The application of an in situ electron cyclotron resonance (ECR) generated H plasma to produce high quality growth interrupted interfaces on both n- and p-type InP has been investigated. The H plasma was applied to epitaxial layers as well as to surfaces that were passivated by sulfur or an UV/ozone oxide. An in situ reflection high energy electron diffraction (RHEED) and a vacuum-linked Auger spectrometer were used to determine surface characteristics. Postgrowth analysis of the interfaces was done by C–V profiling and secondary ion mass spectroscopy measurements. Results indicate that the effectiveness of the H plasma is sensitive to the magnetic field configuration of the ECR source and the gas flows in the discharge chamber. In certain configurations the plasma is effective at removing passivating layers; however, a high P2 overpressure must be maintained to compensate for excess depletion of phosphorus from the substrate. High quality interfaces were obtained on n-type material, while p-type interfaces had a defect density as low as 8×1011 cm−2..
Ballistic-electron emission microscopy at metal/GaP(110) interfaces: Electron transport and Schottky-barrier heights
Authors: Bauer A. , Cuberes M. T. , Prietsch M. , Kaindl G.
Published: July 2002

Ballistic-electron emission microscopy (BEEM) was performed for Au and Mg films on n-type GaP(110). BEEM spectra taken with tip voltages up to 6 eV reveal a strong dependence of the spectral shape on metal-film thickness and on the type of the metal. Monte Carlo simulations of the electron transport allow a quantitative description of the BEEM current, and provide information on the tunneling process, on hot-electron transport in the metal film, on transmission across the interface, and on impact ionization within the semiconductor. In addition, the simulations quantitatively account for the observed dependence of the BEEM current on topographic features. The Schottky-barrier heights were also found to increase with the thickness of the metal film, demonstrating that Schottky-barrier formation is not yet completed when the overlayer metallizes.
Studies of Si segregation in GaAs using current–voltage characteristics of quantum well infrared photodetectors
Authors: Wasilewski Z. R. , Liu H. C. , Buchanan M.
Published: July 2002

Segregation of Si in molecular beam epitaxy grown GaAs quantum wells is investigated using current–voltage characteristics (I–V) of quantum well infrared photodetectors. Theoretical modeling is used to derive the extent of segregation from the measured ratio of dark currents through the device in forward and reverse directions. The segregation length, expressed in Å per decade of concentration decay, increases from 12 to 52 Å on increasing the growth temperature from 550 to 605 °C. The character of this increase indicates that Si segregation is kinetically limited in this temperature range, but approaches thermal equilibrium above 600 °C. The effect of arsenic overpressure on the segregation length at a growth temperature of 595 °C is also studied. An increased overpressure of arsenic suppresses Si segregation for both dimeric and tetrameric forms of As. The effect of As2 is very small, with the segregation length decreasing from 52 to 48 Å on increasing the arsenic flux by a factor of eight from its nominal value. The same increase in flux gives a much stronger suppression of Si segregation if As4 is used: the segregation length decreases from 51 to 40 Å.
Ultra-shallow-doped film requirements for future technologies
Authors: El-Kareh B.
Published: July 2002

The simulation, fabrication, and characterization of ultra-shallow-doped films are critical to optimizing sub-half-micron devices. This article describes key metal–oxide–semiconductor field effect transistor elements and their impact on device performance, emphasizing the need for ultra-shallow-doped films. Methods to achieve such small geometries are discussed. Future technology trends are projected. These trends are evolving at a fast pace, requiring improved simulation tools and novel measurement methods. Simulated structures are used to define device needs for abrupt composition profiles and to highlight the stringent requirements that are imposed on film characterization and model verification.
Stability of the emission of a microtip
Authors: Py C. , Baptist R.
Published: July 2002

In order to evaluate the potential of microtips in novel electron optics applications, the emission stability of a single tip was studied. It was found that after a few hours of ‘‘self-shaping,’’ a tip may emit a very stable spot (for 700 nA of global emission, 7 min is reported without any change over 1 nA, and a couple of hours with less than ±1% change). Unfortunately, a period of instability may follow a period of stability. It was observed that the spot is composed of several subspots, each one having a much greater stability than the whole spot. These subspots are very likely to be emitted from independent nanoprotrusions or atoms, and changes in the emission occur because of motions of atoms and/or adsorption–desorption processes. It was concluded that, though the stability of an electron beam cannot be ‘‘infinite’’ as a laser beam is, very long periods of stability (hours) and high coherence of wave packets can be obtained, if work was done under very high vacuum (several 10−11 mbar) and with a unique beam emitted from a single atomic site.
Investigation of chemically assisted ion beam etching for the fabrication of vertical, ultrahigh quality facets in GaAs
Authors: Hagberg Mats , Jonsson Björn , Larsson Anders G.
Published: July 2002

Extensive theoretical and experimental investigation of the chlorine and argon chemically assisted ion beam etching process for the fabrication of vertical, ultrahigh quality facets in GaAs are reported. The dependence of etch rate and verticality of the etched profile on chlorine flow and ion flux have been studied and analytical expressions for the etch rate are presented. The analytical expressions are based on previously suggested surface-reaction models as well as on a new model where the reactions are stimulated by the incident argon ions. Using this new surface-reaction model together with ion trajectory simulations, computer programs were developed for the etch rate and etch profile which allow us to study the dependence on chlorine flow, argon ion current density, and argon ion energy. The dependence of the etch rate and the etch profile on the chlorine flow is explained by the combined effect of a saturation of the chlorine surface coverage and increased scattering of the high-energetic argon ions with increasing chlorine flow. Furthermore, the importance of the etch-mask profile as well as adequate heat sinking, for the verticality of the etched facets is demonstrated.
Damage to Si substrates during SiO2 etching: A comparison of reactive ion etching and magnetron-enhanced reactive ion etching
Authors: Gu Tieer , Ditizio R. A. , Fonash S. J. , Awadelkarim O. O. , Ruzyllo J. , Collins R. W. , Leary H. J.
Published: July 2002

The damage and contamination effects present in silicon substrates from both reactive ion etching and magnetron-enhanced reactive ion etching of SiO2 have been examined for various overetch percentages using spectroscopic ellipsometry (SE) and secondary ion mass spectroscopy (SIMS). The former method has shown that the thickness of the etch-induced heavy damage layer in silicon decreases, but its damage density increases with magnetic field. In addition, a thinner fluorocarbon residue layer was detected by both SE and SIMS on the samples etched in the presence of a magnetic field. The high temperature annealing behavior of silicon surfaces after UV/O2 removal of this polymer layer was also compared for samples etched with and without the presence of a magnetic field. Almost complete surface recovery was observed for the samples etched with the presence of a magnetic field as a result of a 15 min anneal at 600 °C.
Atomic hydrogen resist process with electron beam lithography for selective Al patterning
Authors: Masu Kazuya , Tsubouchi Kazuo
Published: July 2002

The resolution of electron beam lithography using polymer resist is limited to be 10–20 nm because of electron scattering effects and molecular size of polymerized resist. Thinning the resist thickness is a method to improve the resolution. In this article, we discuss a new atomic hydrogen resist process for area-selective Al patterning. The atomic resist is monolayer thick hydrogen terminated on a Si surface, i.e., the thickness of the resist is ultimately thin. The features are (1) patterning of the monolayer thick terminated H on the Si surface by focused electron beam exposure and (2) selective growth of Al on the remaining terminated H area by low pressure chemical vapor deposition using dimethylaluminum hydride [(CH3)2AlH] and H2. In the electron beam exposed area, the terminated H on Si is removed and the Si surface is activated. Then the activated Si surface is oxidized in nanometer thickness in a clean-room environment. The Al is selectively deposited on the remaining terminated H region. We have successfully formed the area-selective Al patterning by the atomic hydrogen resist process.
Effect of superlattices on the low-energy ion-induced damage in GaAs/Al(Ga)As structures: Channeling or diffusion?
Authors: Green D. L. , Hu E. L. , Stoffel N. G.
Published: July 2002

We have recently reported on the dramatic effect on the damage profile achieved using a ten-period lattice-matched AlAs/GaAs superlattice placed above a multiple quantum well probe. We sought to better understand the effect of the superlattice on the damage profile, whether due to gettering of defects or due to an actual modulation of the ion channeling. To examine the latter hypothesis, the schleich program simulating SCattering of Heavy, Low Energy Ions into CHannels, was modified to allow simulations of layered zincblende structures. We report here on simulations carried out using that modified program. Additionally, we have carried out a series of experiments to investigate effects that defect diffusion may be having on the damage profiles. Preliminary results from these experiments indicate gettering of defects by the superlattice. These results indicate that although deep channeling of ions along the 〈011〉 directions of our III–V structures most certainly defines the ion penetration depths and subsequent deeply generated damage, a second factor, that of diffusion of defects within these regions, may significantly affect the damage profile.
Surface structure of YBa2Cu3O7−x probed by reversed-bias scanning tunneling microscopy
Authors: Edwards H. L. , Markert J. T. , Lozanne A. L. de
Published: July 2002

We report the results of scanning tunneling microscopy studies on high-quality single crystals of YBa2Cu3O7−x (YBCO) which were cleaved along a basal plane in situ at 20 K prior to measurement. The initial results of a systematic study of the YBCO surface are presented. Reversed-bias images of the CuO chain layer reveal modulations 3.3±0.3‖b‖=1.3±0.1 nm in wavelength which change phase by 180° under bias polarity reversal along solid chains, and are invariant under bias polarity reversal at a point defect. Regions of sharp unit-cell-sized square corrugations with disordered islands are also observed. We interpret these new results in terms of our previous model [H. L. Edwards, J. T. Markert, and A. L. de Lozanne, Phys. Rev. Lett. 69, 2967 (1992)] of the cleaved YBCO surface.
Early stages of Cu growth on boron segregated Si(111) surfaces: A scanning tunneling microscopy study
Authors: Roge T. P. , Thibaudau F. , Mathiez Ph. , Dumas Ph. , Salvan F.
Published: July 2002

Out segregation of boron from the bulk of highly doped Si samples leads to surfaces which present a B–Si(111)√3×√3 R(30°) reconstruction (hereafter abbreviated B√3). Scanning tunneling microscopy investigations show that, depending on the annealing temperatures, different boron equilibrium surface concentrations are obtained in the B√3 substrates. Comparisons of Cu growth on such substrates show that copper nucleation is highly correlated to the density of dangling bonds at the surface.
Silicon tips with diamond particles on them: New field emitters?
Authors: Givargizov E. I.
Published: July 2002

A new approach to preparation of effective field emitters is proposed. The approach consists in deposition of diamond particles on high aspect ratio silicon tips. Field-emission measurements of such objects have given rather low effective work function values, from 0.3 to 1.2 eV.
Enhancement in emission current from dry-processed n-type Si field emitter arrays after tip anodization
Authors: Takai M. , Yamashita M. , Wille H. , Yura S. , Horibata S. , Ototake M.
Published: July 2002

n-type porous Si field emitter arrays (FEAs) have been fabricated by tip surface anodization to improve the emission characteristics. The gate voltage required for emission could be lowered by tip anodization and the emission current was enhanced by a factor of up to 10. Fowler-Nordheim plots for the FEAs before and after tip anodization revealed that the work function of the tips could be decreased and the emission from various FEAs with initially different characteristics could be homogeneously improved by tip surface anodization.
Filling dual damascene interconnect structures with AlCu and Cu using ionized magnetron deposition
Authors: Rossnagel S. M.
Published: July 2002

The semiconductor industry is moving toward the use of damascene processes for wiring of circuits on chips. These processes are based on the etching of vias and trenches into dielectric layers, filling these features with metal, and finally chemical–mechanical polishing, which results in a planarized, embedded feature. A two-layer feature, typically a pad or trench with a via at the bottom which connects to some underlying contact is known as ‘‘dual damascene.’’ Ionized magnetron sputter deposition has been used to successfully fill these two-layer features, both with AlCu and Cu metallurgies. This process uses conventional, commercial manufacturing-scale magnetrons in combination with a dense, inductively coupled rf discharge to ionize a large fraction of the sputtered atoms. A small electrical bias on the sample then causes the metal ions to deposit at normal incidence, which results in dense fills at moderate aspect ratios (AR = 2:1) on room temperature samples.
Extremely low resistance Au/Mn/Ni/Au ohmic contact to p-GaAs*
Authors: Thiery Jean-François , Fawaz Hussein , Leroy André , Salmer Georges
Published: July 2002

p-type alloyed ohmic contacts of Au/Mn/Ni/Au have been fabricated for application to compound semiconductor devices. Extremely low resistance contacts to 3×1019 cm−3 Be-doped p-GaAs were achieved by electron-beam evaporation and rapid thermal annealing. Contacts were thermally stable, and the contact resistance remained below 0.04 Ω mm in the temperature range from 360 to 450 °C. Annealing at 400 °C for 40 s resulted in a minimum contact resistance of 0.012 Ω mm, corresponding to a specific resistivity of 1.6×10−8 Ω cm2, which is very close to the theoretical predictions. The mechanism of formation of Au/Mn ohmic contacts was discussed, based on Auger electron spectroscopy data.
Low resistivity vertical-cavity surface emitting lasers grown by molecular- beam epitaxy using sinusoidal-composition grading in mirrors and in situ nonalloyed ohmic contacts
Authors: Hong M. , Vakhshoori D. , Mannaerts J. P. , Hsieh Y.-F.
Published: July 2002

Low resistance vertical-cavity surface emitting lasers have been grown by molecular beam epitaxy using a hybrid mirror approach. The total resistance in the range of 3–10×10−5 Ω cm2 was achieved using a combination of sinusoidal-like grading in composition at the interface of p-type distributed Bragg reflector mirrors and in situ nonalloyed ohmic contacts. Threshold current densities in the range of 1.5–3 kA/cm2 were obtained.
Growth of InGaAsSb layers in the miscibility gap: Use of very-low-energy ion irradiation to reduce alloy decomposition
Authors: Kaspi R. , Barnett S. A. , Hultman L.
Published: July 2002

Thin (∼0.2–0.5 μm), quaternary InxGa1−xAsySb1−y alloy films with compositions across the solid-phase miscibility gap were grown using ion-assisted deposition (IAD) on Si(001) and InP(001) substrates. The IAD chamber was designed to provide very-low-energy (≤30 eV), high flux (∼0.4 mA/cm2) Ar ion irradiation of the film surface during growth. Under conditions where ion irradiation effects were negligible, broadened x-ray diffraction peaks and increased surface roughness as a function of the proximity of the alloy composition to the center of the miscibility gap was observed. High-resolution cross-sectional transmission electron microscopy analysis of films, deposited nearly lattice matched on InP substrates, showed decomposition into columns elongated in the growth direction when the alloy composition was within the miscibility gap. A composition modulation wavelength of ∼7 nm was measured parallel to the film surface. The role of ion irradiation in suppressing decomposition in InGaAsSb alloy thin films deposited within the miscibility gap was investigated. Ar+ ion irradiation with a flux of ∼3×1015 cm2 s−1, and energy of 19–21 eV was found to improve both the homogeneity and electron mobility of the alloy films. This was attributed to the suppression of composition modulations by collisional mixing of the film surface during growth. Ar+ ion energies above 21 eV resulted in excessive structural damage to the films.
Novel high-yield trilayer resist process for 0.1 μm T-gate fabrication
Authors: Wakita A. S. , Su C.-Y. , Rohdin H. , Liu H.-Y. , Lee A. , Seeger J. , Robbins V. M.
Published: July 2002

By utilizing a novel ZEP/PMGI/ZEP trilayer resist process, GaInAs/AlInAs T-gate modulation-doped field effect transistors on InP with 0.1 μm gate lengths have been demonstrated. The trilayer resist requires only a single exposure. An overhang structure for liftoff, with a 0.1 μm footprint, is created by a sequence of infinitely selective developments for each layer. Linewidths as narrow as 65 nm have been obtained. Devices with a maximum current of 860 mA/mm, extrinsic transconductances of 658 mS/mm, and a current-gain-cutoff frequency ft of as high as 203 GHz have been fabricated. Yields as high as 96% and a threshold voltage uniformity of 34 mV (1 sigma) have been achieved on a 2 in. wafer.
Spectroscopic characterization of self-assembled organosilane monolayer films
Authors: Perkins F. Keith , Dobisz Elizabeth A. , Marrian Christie R. K. , Brandow Susan L.
Published: July 2002

We have used the scanning tunneling microscope (STM) to investigate self-assembled monolayer films formed from three organosilane precursors. We have studied these films in order to understand better the interaction between them and the microscope and their utility as resist materials for STM-based lithography. These films were chemisorbed onto hydrogen-passivated silicon substrates. One was studied immediately after film growth; another sample of that film, as well as the other two, were studied four weeks later. We compared topography, morphology, and site-specific current–voltage spectroscopy of the films with each other before and after patterning the films. Patterning consisted of operating the STM at tip biases expected to induce a modification of the film that inhibits an electroless metallization process we have described previously. Two films did not exhibit observable changes after operation at conditions expected to induce exposure. We attribute this to high resist sensitivity and a low voltage threshold for exposure, and thus inadvertant exposure. The film that was studied when fresh and after aging in air exhibited changes attributable to oxidation of the substrate. We conclude that the STM is interacting directly with the films and is sensitive to their chemical composition. The effects of exposure on the individual molecular precursors are slight. The molecules remain present on the surface, even though the chemical functionality is greatly modified.
Field emission from microtip test arrays using resistor stabilization
Authors: Levine J. D. , Meyer R. , Baptist R. , Felter T. E. , Talin A. A.
Published: July 2002

A lateral resistive layer which stabilizes field emission arrays also makes these devices robust. Initial activation of a microtip array after exposure to air and without bakeout can be accomplished with the sudden application of high voltage at room temperature, without fear of tip destruction. Analysis of initial activation curves of current versus time are made at various constant voltages in 11 tests. Reversible degradation and recovery of cathode emission is observed when contaminating anodes containing ITO and phosphor are replaced by a stainless steel anode. The major effect in the activation procedure is field induced desorption of a high work function adsorbate from the cathode. Analysis of the various I–V curves taken during the activation process at 55 V yields an equivalent series limiting resistance and the fraction of emitting microtips, which is 4% for a contaminating unbaked ITO anode and 10% for a stainless steel anode.
Review of focused ion beam implantation mixing for the fabrication of GaAs-based optoelectronic devices
Authors: Steckl A. J. , Chen P. , Jackson H. E. , Choo A. G. , Cao X. , Boyd J. T. , Kumar M.
Published: July 2002

The fabrication of GaAs-based optoelectronic components by the technique of focused ion beam (FIB) implantation mixing is reviewed. The basic mechanisms and practice of the FIB-induced mixing process of GaAs/AlGaAs multiple quantum well and superlattice structures are discussed. The use of the FIB mixing technique for the fabrication of optoelectronic devices (such as channel waveguides and distributed Bragg reflection distributed feedback lasers) by the single-step, maskless/resistless FIB implantation process is described and their characteristics are reviewed.
Growth of NiO(100) layers on Ag(100): Characterization by scanning tunneling microscopy
Authors: Bertrams Th. , Neddermeyer H.
Published: July 2002

We have prepared thin ordered NiO(100) films by evaporation of Ni in an O2 atmosphere onto Ag(100). The films have been analyzed by using scanning tunneling microscopy and low-energy electron diffraction. For room temperature deposition a c(1×2) Ni/O Ag structure in two orthogonal domains is obtained in the submonolayer coverage range. Annealing such a film produces regular islands with NiO(100) double layers. For higher coverage (five monolayers) a layer-by-layer-like growth mode is obtained.
New and simple method of contact processing characterization using atomic force microscopy
Authors: Mariolle D. , Lafond D. , Morand Y.
Published: July 2002

This article reports on the use of atomic force microscopy coupled with a simple wet chemical sample preparation to characterize processes involved in the realization of 0.4 μm metal on silicon contacts. Photolithography and contact etching processes both lead to high aspect ratio topography (≳4). The samples are imaged after a preparation which removes the high aspect ratio and leads to a better image. The main parameters of this new procedure are highlighted in this report, namely contact area for lithography and etching processes and silicon consumption for the etching process. The contact silicidation process is also monitored, and the electrical results are correlated with the silicide thickness formed in the contact.
Two-dimensional dopant profiling of very large scale integrated devices using selective etching and atomic force microscopy
Authors: Barrett M. , Dennis M. , Tiffin D. , Li Y. , Shih C. K.
Published: July 2002

We report a detailed mapping of a two-dimensional dopant profile on a fully processed industrial sample with large dynamic range and high spatial resolution by utilizing a dopant-selective etching process and atomic force microscopy. The experimental profiling results show excellent agreement with those obtained from spreading resistance probe and secondary ion mass spectroscopy as corroborative methods. We also discuss the most critical factors which influence the applicability, reproducibility, and reliability of this dopant selective etching method.
Process control based on quadrupole mass spectrometry
Authors: Greve D. W. , Knight T. J. , Cheng X. , Krogh B. H. , Gibson M. A. , LaBrosse J.
Published: July 2002

Real-time feedback control of semiconductor processes based on in situ sensors can complement present statistical process control techniques. In this article, we explore the potential of quadrupole mass spectrometry as an in situ sensing technique. We show that it is possible to sense the fluxes of important species in a plasma process and use these measurements to implement a multivariable control scheme. As an example, the control of hydrogen, unreacted ammonia, and direct current bias in a plasma enhanced chemical vapor deposition silicon nitride process is demonstrated.
Lithographic band gap tuning in photonic band gap crystals
Authors: Cheng C. C. , Scherer A. , Arbet-Engels V. , Yablonovitch E.
Published: July 2002

We describe the lithographic control over the spectral response of three-dimensional photonic crystals. By precise microfabrication of the geometry using a reproducible and reliable procedure consisting of electron beam lithography followed by dry etching, we have shifted the conduction band of crystals within the near-infrared. Such microfabrication has enabled us to reproducibly define photonic crystals with lattice parameters ranging from 650 to 730 nm. In GaAs semiconductor wafers, these can serve as high-reflectivity (>95%) mirrors. Here, we show the procedure used to generate these photonic crystals and describe the geometry dependence of their spectral response.