bluuebunny/crossref_metadata_2025 huggingface dataset:
Scanning tunneling microscopy study of the cleaved InSb(110) surface
Authors: Liang Yong , Packard William E. , Dow John D.
Published: July 2002

The clean InSb(110) surface was imaged in ultrahigh vacuum with scanning tunneling microscopy. A 1×1 surface structure was observed. A super-periodicity consistent with a c(4×6) reconstruction was also observed on some regions of some cleaved surfaces, and appears to be cleavage dependent. The InSb(110) surface can easily be altered by the tunneling process to produce nanoscopic dots on the surface as small as 9 Å radius.
Wide area windowless disk plasma lamp of uniform intensity for use in microelectronic film processing
Authors: Yu Z. , Sheng T. Y. , Pihlstrom B. , Luo Z. , Collins G. J.
Published: July 2002

A wide area windowless plasma disk excited by a soft vacuum electron beam provides a wide area uniform source of vacuum ultraviolet (VUV) photons as well as atomic radicals. Hydrogen and oxygen when excited by the soft vacuum electron beam, emit strong atomic resonance radiation at 121.6 and 130 nm, respectively; in fact up to 8% of the total applied discharge power is emitted as VUV photons. The spatial uniformity of the atomic VUV resonance radiation approaches 6% across a disk 19 cm in diameter. The density of atomic oxygen species generated in the plasma disk has also been experimentally determined using an established polymer film etch rate method as well as with a conventional silver thin film sensor. We employ the disk plasma in a windowless configuration to achieve lower temperature chemical vapor deposition (CVD) than conventional thermal CVD. The VUV photon flux as well as the radical and excited atomic gas species emitted from the lamp can assist dissociation of feedstock reactant gases as well as assist heterogeneous surface reactions and increase surface mobility of absorbed species allowing for lower temperature CVD. Thin films of an aluminum nitride and hydrogenated amorphous silicon have been deposited at temperature between 100–400 °C. The deposited films show improvement over other plasma and photo-assisted CVD processes in the film quality achieved, the area covered, the substrate temperature required, and the maximum deposition rates that are possible. In situ generation of arsine (AH3) and unsaturated arsenic hydrides AsHx (x≤2) have also been achieved by placing elemental arsenic in an environment rich in atomic hydrogen created from the disk–plasma source.
Fabrication of 0.25 μm surface acoustic wave devices by ion beam proximity printing
Authors: Stumbo D. P. , Sen Sudipto , Damm G. A. , Fong F-O. , Engler D. W. , Fong K-F. , Wolfe J. C. , Cho Frederick
Published: July 2002

The electrodes of surface acoustic wave (SAW) devices cannot be represented in a stencil mask as cantilevered beams because the high aspect ratio makes them unstable. Therefore a complementary exposure technique has been developed. The mask pattern is formed by segmenting the electrodes into equal length open and closed areas. The wafer is then exposed twice with an offset equal to the segment length, thus forming a continuous electrode image. This approach has two advantages: (1) the high process latitude of ion beam proximity printing (IBPP) is preserved since, in contrast to the grid-support approach, no areas are doubly exposed; and (2) only precision translation is required to register the exposures, preserving the single level nature of SAW patterns. Linewidth is shown to change by less than ±15% for ±20% changes in exposure at a 0.25 μm nominal linewidth.
Dry etch processing of GaAs/AlGaAs high electron mobility transistor structures
Authors: Pearton S. J. , Ren F. , Lothian J. R. , Fullowan T. R. , Kopf R. F. , Chakrabarti U. K. , Hui S. P. , Emerson A. B. , Kostelak R. L. , Pei S. S.
Published: July 2002

Damage introduction into GaAs/AlGaAs high electron mobility transistor (HEMT) structures during either pattern transfer or gate mesa etching steps has been characterized. For O2 reactive ion etching of the polydimethylglutarimide (PMGI) planarizing layer in a trilevel resist mask, the threshold dc bias for observable damage introduction in the AlGaAs donor layer is ∼200 V. This threshold bias for damage is a function of the PMGI overetch time and for extended times (>10 min), a decrease in saturated drain-source current (IDSS) of the HEMTs can be detected for oxygen ions accelerated through a bias of ∼150 V. The use of combined electron cyclotron resonance (ECR)/radio frequency (rf) O2 discharges enhances the PMGI etch rate without creating additional damage to the device, and 0.25-μm gate widths have been demonstrated. Gate mesa formation by etching the GaAs cap with CCl2F2/O2 or CH4/H2/Ar discharges is shown to produce damage in the underlying AlGaAs at dc negative biases of 125–150 V. In addition, substantial hydrogen passivation of the Si dopants occurs for the latter mixture. Recovery of the initial carrier concentration in the damaged HEMT occurs around 400 °C, provided the maximum dc biases were kept to ≤400 V during the dry etch step. Finally, changes in the surface chemistry of the exposed AlGaAs after various post-RIE processing steps have been monitored by x-ray photoelectron spectroscopy. Complete removal of AlF3 was obtained only after careful H2O and NH4OH:H2O rinsing, while chlorides are removed by H2O alone.
Thermal effects in high voltage e-beam lithography
Authors: van der Drift E. , Enters A. C. , Radelaar S.
Published: July 2002

Modeling of resist heating for 50- and 100-kV e-beam exposures of single layer resist on silicon wafers and quartz mask plates is reported. The resist heating from energy dissipation in both the thin resist layer itself and the underlying substrate has been taken into account. A variety of single spot exposure situations are considered to put forward the main features for minimization of thermal effects. Modeling results are compared with experimental results reported in literature. The future perspective for resist heating control in high throughput e-beam writing is illustrated with a practical example.
Chemical-vapor deposition of SiC thin films for x-ray mask applications
Authors: Fuentes Ricardo I.
Published: July 2002

In this article some of the results on growth and application of SiC thin films for x-ray mask substrates are presented. Aspects of the process that are relevant to the film’s use for x-ray masks, such as growth defects, roughness, stress, and growth rate versus gas composition, growth temperature, and flow rates are discussed. There are definite regions in composition space within which the growth rate is useful and the growth defect population is minimized. The film’s internal stress is generally tensile and increases with growth temperature, although it can be made compressive by the appropriate choice of growth parameters. The SiC film’s surface roughness also decreases with growth temperature, and growth temperature/gas composition combinations exist which yield smooth films (roughness less than 200 Å) with a desirable stress (less than 300 MPa). Our SiC films are typically 20–500 Å rough (peak-to-peak), tensile with a stress in the range of 100–500 MPa, and grow at a nominal rate of 0.8 μm/h. The films appear to be radiation hard up to incident doses of approximately 25 KJ/cm2. The chemical-vapor deposition system is a cold-wall-type with a temperature range of 1423–1673 K. The growth takes place at pressures of 100–700 Torr in a H2–C2H4–SiH4 atmosphere.
Repair of opaque defects on reflection masks for soft x-ray projection lithography
Authors: Hawryluk Andrew M. , Stewart Diane
Published: July 2002

We have developed a new technique for removing opaque defects on soft x-ray projection lithography reflection masks using ion beam etching. This technique clears the defect without damaging the multilayer mirror or introducing an absorptive element into the multilayer. Our procedure uses a thin, Si overcoat to protect the multilayers from the kinetic energy of the ion beam, reduced ion beam energy, and a Ar ion beam to avoid absorption losses. A Si ion beam could also be used in this process.
Laser plasma sources for proximity printing or projection x-ray lithography
Authors: Chaker M. , La Fontaine B. , Côté C. Y. , Kieffer J. C. , Pépin H. , Talon M. H. , Enright G. D. , Villeneuve D. M.
Published: July 2002

In this article, we present a theoretical and experimental study of the x-ray emission produced by laser plasma sources in different spectral ranges appropriate for x-ray lithography either in proximity printing (XRL) or projection (XRPL) approaches. For XRPL application, experiments using 10 ns laser pulses show that the maximum conversion efficiency in the (80–250 eV) range is attained at I=1011 W cm−2 whereas for 25 ns pulses and I≤6×1011 W cm−2, it is still increasing with laser intensity. On the other hand, higher laser intensities are required to obtain a high conversion efficiency for XRL (0.9–1.4 keV). Efficient emission peaked at 1.1 keV can be achieved for I≥1013 W cm−2 with copper targets and pulse duration shorter than 5 ns. For iron line emission (peak at 0.9 keV), the laser intensity can be lower (I=5×1012 W cm−2) and the pulse duration longer (τp=10 ns). Finally, we discuss the different approaches which may lead to the appropriate laser design.
Direct-current and radio-frequency characterization of submicron striped-channel field effect transistor structures using focused ion beam and electron-beam lithography
Authors: Hashemi M. M. , Li Y. , Kiziloglu K. , Wassermeier M. , Petroff P. M. , Mishra U. K.
Published: July 2002

Submicrometere-gate GaAs metal–semiconductor field effect transistors (MESFETs) have been fabricated using focused ion beam (FIB) and electron-beam lithography. The channels of these devices are composed of several high conductance implanted stripes of 1 μm width, connecting source to drain. These conductive stripes are formed by Si implantation using FIB and annealed for 30 s at 850 °C. The region between the conductive stripes are semi-insulating GaAs having width of ‘‘S.’’ MESFETs with stripe width of 1 μm and stripe separation of 0.1, 1, and 2 μm were fabricated and characterized. The device with 0.1 μm separation represents the control sample with a uniformly doped channel due to overlap of conductive stripes upon the postimplant annealing. Devices with higher stripe separations showed higher effective transconductance (gm), lower output conductance (go), higher breakdown (Vbr), and higher current gain cut-off frequency (fT). All transistor showed well behaved direct-current output performance with excellent pinch-off characteristics and low leakage currents as small as 50 μA for source-drain voltage of 4 V and gate bias of −9 V without any soft breakdown. Transconductance of 200 mS/mm, gate-drain breakdown voltage as high as 20 V, output conductance of 4 mS/mm, and fT of 9 GHz from a device with 0.35 μm gate length with stripe separation of 2 μm.
Micromachined electrostatic electron source
Authors: Crewe D. A. , Perng D. C. , Shoaf S. E. , Feinerman A. D.
Published: July 2002

A microfabrication technique has been developed that combines the precision of silicon micromachining and fiber optics to allow the construction of large three-dimensional structures with dimensional tolerances approaching 1 μm [A. D. Feinerman, S. E. Shoaf, and D. A. Crewe, Proceedings of the 180th Annual ECS Conference, Phoenix, AZ, October 1991 (unpublished)]. A miniature scanning electron microscope (MSEM) is being designed using this method. In this article we will present the electron optic calculations of a simple 1 kV MSEM consisting of a source, a three element electrostatic lens, deflectors, and a detector. The MSEM measures less than one cubic centimeter. There are many advantages of a MSEM. The performance of a SEM is improved as its length is reduced. [T. H. P. Chang, D. P. Kern, and L. P. Murray, J. Vac. Sci. Technol. B 8, 1698 (1990)]. The need for mechanical adjustments and motion feedthroughs is eliminated since the microscope components are prealigned to the optic axis. All components are ultrahigh vacuum compatible and can be heated to 500 °C. A small, portable electron microscope can be brought to the sample to be inspected instead of the sample being brought to the microscope. Vacuum hardware requirements are minimized. The fabrication technology is inexpensive compared to the conventional methods of electron microscope construction. Our construction method is easily extended to permit arrays of MSEMs to allow applications in high throughput e-beam lithography and wafer inspection.
Cell projection column for high speed electron-beam lithography system
Authors: Itoh H. , Todokoro H. , Sohda Y. , Nakayama Y. , Saitou N.
Published: July 2002

The cell projection column for the high throughput electron-beam lithography system (HL-800D) has been developed. This column forms a conventional variable shaped beam and five kinds of cell pattern beams with a maximum 5 μm dimension. A new in-lens three stage deflection system consisting of a magnetic and two electrostatic deflectors provides low distortion and high speed 5 mm square deflection at 50 kV. Beam shaping optics have a two stage deflector for rectangular beam sizing and cell beam selection. The settling times coincide with three stage deflection system to prevent extra overhead time. The beam shaping system has an inspection function for the cell aperture by switching the crossover focusing. Complicated deflection calibration systems are necessary to correct precisely in advance to exposure. To reduce the correction time, a simplified method which separates time dependent terms from whole correction terms, has been developed. This method decreases the total correction time and procedures, because time dependent terms generally consist of first order terms such as gain and rotation. The correction time is typically reduced to less than 1/10, if the correction term is limited to the first order term. The measured data are statistically averaged and improve the accuracy of the beam correction. Other features of the cell projection column are as follows: (1) long life LaB6 emitter, (2) automatic cell mask handling system, and (3) dry evacuation system. These items provide easy handling and high reliability of the electron beam column.
High accuracy electron-beam grating lithography for optical and optoelectronic devices
Authors: Dix C. , McKee P. F.
Published: July 2002

Much of the development of recent optoelectronic and optical devices has been undertaken using the lithographic tools designed for conventional microelectronic circuits. For the latter, the need for spatial linearity and accuracy is mainly concerned with overlay accuracy and device yield. But the characteristics of optical structures, such as gratings, can be affected by the spatial errors of the tools used to make them. The linearity of a Leica Cambridge EBMF-10.5 electron beam lithography system has been investigated with particular regard to the writing of gratings for distributed feedback lasers and optical waveguide devices. Since the gratings can be narrow, it is possible to take advantage of the lower distortions associated with scanning in a single axis. The distortion correction system has been shown to provide significant improvements in linearity even at small field sizes of around 1 mm, and an overall beam placement accuracy of 20 nm within the writing field has been demonstrated. The applications illustrated have required different approaches to calibration and writing, and have employed gratings written using both distortion corrected and uncorrected fields.
Investigation of the generation–recombination currents in HgCdTe midwavelength infrared photodiodes
Authors: Schoolar Richard , Price Stephen , Rosbeck Joseph
Published: July 2002

The I–V characteristics of HgCdTe midwavelength infrared (MWIR) double-layer heterojunction photodiodes at temperatures below 120 K are dominated by thermal generation–recombination in the depletion region. The diode R0A’s, determined from the slope of the I–V curves, are in excess of 1 × 108 Ω cm2 at 77 K when measured in the dark but are much lower when measured with ambient backgrounds. In order to better understand this phenomenon, the I–V characteristics of numerous MWIR HgCdTe photodiodes were measured as functions of background flux using a blackbody source and several narrowband spectral filters. Based on the measured R0A at 100 K in the dark, where thermal G–R currents dominate, the G–R lifetimes are approximately equal to the Auger lifetime for the minority carriers in the lightly doped n-type base layer. At backgrounds in excess of 1 × 1012 photons/cm2 s, the R0A decreases inversely with background flux. The magnitude of the effect at wavelengths much shorter than the cutoff agrees well with estimates based on the depletion modulation theory. At wavelengths very close to the cutoff, the effect is largest and agrees well with a theory based on optical generation of carriers in the depletion region. Thus, the background dependence of R0A is due to the combined effects of depletion modulation and optical generation in the depletion region.
Process optimization of 200 nm wide trenches in SiO2 using a chemically amplified acid catalyzed e-beam resist
Authors: Kocon Waldemar W. , Shacham-Diamand Y. , Frechet Jean M. J. , Fahey James
Published: July 2002

In this article we present a novel acid catalyzed chemically amplified resist and the associated silicon-dioxide etch process that was developed using that resist. The 200 nm wide and 250 nm deep trenches in the silicon dioxide are part of a multilevel fully planar metallization scheme, where copper lines are fully imbedded in the interlevel dielectric. Conventional resist materials are not sensitive enough to be used in high-throughput production and in many cases their selectivity versus silicon dioxide reactive ion etching is low. Resist materials based on acid catalyzed chemical amplification show very desirable properties with respect to their sensitivity, flexibility in design, and resolution capability. The resolution capability extends down to 200 nm for 290 nm thick resist presented in this report. Moreover, as such resists meet the requirements of deep UV, x-ray, and e-beam exposure tools, it is expected that they will replace the ‘‘standard’’ novolac resists in many applications. A process window for silicon dioxide etching using a single layer resist based on poly(4-hydroxy styrene-co-4-acetoxymethyl styrene) has been developed. Lithographic sensitivity, resolution, contrast as well as etching characteristics of this resist were evaluated. The resist demonstrated a sensitivity of 2–2.5 μC/cm2 for 50 keV e-beam exposure by the JEOL 5DIIU system. A contrast value of 5.1 was obtained using a postexposure bake of 130 °C for 2 min. The resist selectivity with respect to thermal oxide in CHF3 plasma reactive ion etching (RIE) was about 1–3. Using this resist and CHF3 RIE we were able to etch 0.25 μm deep and 0.2 μm wide trenches with vertical sidewalls in SiO2. These results showed that the resist system is very feasible for future single layer resist e-beam pattern definition, and it also has a very promising prospects for deep UV and x-ray lithographies.
0.35 μm rule device pattern fabrication using high absorption-type novolac photoresist in single layer deep ultraviolet lithography: Surface image transfer for contact hole fabrication
Authors: Tomo Y. , Kasuga T. , Saito M. , Someya A. , Tsumori T.
Published: July 2002

0.35 μm design rule device patterns were fabricated using high absorption-type positive and negative photoresist with a KrF excimer laser stepper. The main reason for using high absorption-type photoresist was to minimize the thin film interference effect caused by high reflectivity of the substrate in the deep ultraviolet region. The positive photoresist was FH-EX1 (Fuji-Hunt) and negative photoresist was SAL601. Both contain novolac resin as the base polymer. The positive photoresist was mainly used for poly-Si and W–Si layer pattern fabrication and the negative photoresist was used for the contact hole pattern fabrication. In the contact hole fabrication a surface image transfer technique was used. This technique relies on the direct transfer of the surface negative photoresist image to the insulating layer with highly anisotropic etching and is completely different from the so-called ‘‘surface imaging technique’’ using gas phase silylation and successive dry resist development (O2 reactive ion etching). Although the process was a tentative one, critical dimension controllability of this approach satisfied research and development level device fabrication requirements.
New model of polymer silylation: Application to lithography
Authors: Pierrat C.
Published: July 2002

A new model of polymer silylation is proposed. This model takes into account the reaction of the silylating agent with the hydroxyl groups of the polymer and the relaxation rate of the polymer after reaction. The diffusion coefficient of the silylating agent is supposed to be a function of the expansion of the polymer matrix. At the interface between the silylating agent and the polymer, it is assumed that sorption driven by the pressure of the silylating agent, and desorption driven by the concentration of the silylating agent can occur. The resulting differential equations are solved using a finite element technique and the influence of the main parameters, namely, the reaction rate, the relaxation rate, and the diffusion coefficients is studied.
Residue formation and elimination in chlorine-based plasma etching of Al–Si–Cu interconnections
Authors: Suzuki Teruo , Kitagawa Hideo , Yamada Katsumi , Nagoshi Masayasu
Published: July 2002

In very large scale integrated circuit technology, Al–Si–Cu alloys have been used for interconnections to improve electromigration resistance and suppress stress-induced voids. Copper addition, however, makes plasma etching difficult because of the formation of residues. We found that micromasks of Al2Cu remain on the etched surface that could cause conical residues of the aluminum alloy. In this article, the formation mechanism of the residues is presented based on structural analyses of the conical residues by transmission electron microscope/energy dispersive x-ray analysis and x-ray photoelectron spectroscopy. A multistep, sequential etching process is proposed that effectively eliminates the residues.
Modification of polymer surfaces and the fabrication of submicron-scale functionalized structures by deep-ultraviolet and electron-beam lithography
Authors: Wybourne M. N. , Wu J. C. , Yan Mingdi , Cai Sui Xiong , Keana John F. W.
Published: July 2002

A general technique to modify polymer surfaces using N-hydroxysuccinimide (NHS) functionalized perfluorophenyl azides (PFPAs) is presented. Thin polystyrene films are spin-coated with a solution containing the NHS PFPA ester and are either ultraviolet (UV) photolyzed with a dosage of 10 mJ cm−2 or exposed with a 15 kV electron beam with a dosage between 1 and 75 μC cm−2. The NHS active ester groups become covalently attached to the polymer via photogenerated or electron beam generated, highly reactive nitrene intermediates derived from the PFPA. Using this technique, it is demonstrated that well-defined surface regions can be functionalized with a minimum observable feature size of 0.5 and 0.2 μm for UV and electron-beam exposure, respectively. Through reaction of the functionalized surfaces with primary amine-containing reagents, biological molecules have been installed on the polymer and the activity of an immobilized enzyme has been measured.
Valence band structure and Mn 3d derived density of states in epitaxially grown zinc-blende MnSe
Authors: Bressler P. R. , Klöpper Th. , Gumlich H.-E.
Published: July 2002

Zinc-blende MnSe films (0–8 monolayers) were grown by molecular-beam epitaxy on ZnSe(100). Angle-resolved photoelectron spectroscopy and resonantly enhanced photoelectron spectroscopy were performed. The experimental valence band structure along Γ-X and Mn 3d-derived partial density of states (Mn 3d PDOS) were determined for the first time. The width of the valence band region was found to be 0.2 eV larger in MnSe than in ZnSe. Emission between 1 and 3.5 eV binding energy (BE) is assigned to MnSe sp-derived bands. The dispersion is weaker than in ZnSe and is related to hybridization with Mn 3d states. Emission between 4 and 5 eV, BE is ascribed to flat Mn 3d-derived bands and to high DOS emission from other regions in the Brillouin zone. Se 3d core emission shifts to 0.6±0.1 eV higher BE as a function of MnSe coverage. By analysis of the Fano-like Mn 3p–3d resonance near hν=50 eV three contributions to the Mn 3d PDOS are derived (denoted M, at 3.4 eV BE, V, at 1.1 eV BE and S, near 7 eV BE, respectively). The relative branching ratios for the latter two features to the first (V/M and S/M) grow monotonically as a function of thin MnSe coverage reaching bulk Zn1−xMnxSe values for thicker films. This behavior is likely due to strain and distortion of the tetrahedral symmetry at the interface.
Orientation dependence of normal incidence absorption in ellipsoidal-valley quantum wells
Authors: Zhang Y. , Katz J. , Wang W. I.
Published: July 2002

In this article, we present the first systematic studies of normal incidence infrared absorption from interconduction subband transitions for different orientations in ellipsoidal-valley quantum wells. Due to the effective-mass anisotropy of electrons in the ellipsoidal valleys, normal incidence absorption is allowed when the growth direction is not collinear with the principal axes of the ellipsoidal valley. From the relationships between the reciprocal effective mass tensor of the x valley and absorption coefficient, we found that in the AlAs quantum well system the absorption is near optimal for such low-index structures as [210], [320], and [113] quantum wells, contrary to the intuitive conclusion that the optimum absorption will be along [111]. For normal incidence radiation at wavelengths of 12–20 μm, peak absorption coefficients of 3000–6000 cm−1 could be obtained with well widths in the range of 30–50 Å and sheet doping concentrations of 1012 cm−2. Infrared absorption measurements were performed on samples grown on a few selected orientations including [113], [115], [111], and [100] with normal incidence radiation at wavelengths of 5–20 μm. The results showed that their absorption properties are consistent with our theoretical predictions. Long-wavelength broadband normal incidence infrared photodetectors (on [113] and [115]) were demonstrated. High infrared absorption quantum efficiency (α=2000 cm−1, η=17%), wide-band peak photoresponsivity of Rp=0.54 A/W and low dark current (ID=10−6 A at 68 K) have been achieved. These structures’ good performance make them promising for use as normal incidence infrared photodetectors.
Mask assisted off-axis illumination technique for random logic
Authors: Garofalo J. , Biddick C. J. , Kostelak R. L. , Vaidya S.
Published: July 2002

While off-axis illumination has been demonstrated to improve contrast and depth of focus for low k1, packed line–space (L/S) patterns [S. Asai, I. Hanyu, and K. Hikosaka, J. Vac. Sci. Technol. B 9, 2788 (1991); K. Kamon et al., Jpn. Appl. Phys. 30, 3021 (1991); K. Tounai et al., Proc. SPIE 1674, 753 (1992)], application of this approach to the more discordant patternings associated with random logic levels is suspect. We introduce a conventional mask ‘‘assist’’ feature technique that extends the off-axis L/S enhancements to more isolated features (both spaces and lines). It will be shown that the effective process window is substantially improved and exhibited proximity effects are mitigated for this technique. Also, a comparison to a phase-shifting mask solution for the patterning mix expected in random logic layouts is performed. Simulation results are verified on a 0.53 NA, DUV stepper.
Ridge-waveguide sidewall-grating distributed feedback structures fabricated by x-ray lithography
Authors: Wong Vincent V. , Choi Woo-Young , Carter J. M. , Fonstad C. G. , Smith Henry I. , Chung Y. , Dagli N.
Published: July 2002

A novel distributed feedback structure has been developed in which the grating is patterned onto the sidewalls of a ridge waveguide. Such a laser structure results in simplified processing in that the grating fabrication is independent of both the materials growth and the guide formation. The ridge waveguide is first formed by wet-chemical etching. Then, a poly(methylmethacrylate) grating (Λ=230 nm) is patterned onto this ridge waveguide using x-ray lithography. A Ti/Al etch mask is lifted-off to serve as a mask for subsequent reactive-ion etching. Gratings with long-range spatial-phase coherence and negligible distortion, characteristics which are necessary for accurate control of the wavelength and bandwidth, are obtained using a holographically generated x-ray mask.
Effect of Si δ doping and growth temperature on the I(V) characteristics of molecular-beam epitaxially grown GaAs/(AlGa)As resonant tunneling devices
Authors: Henini M. , Sakai J. W. , Beton P. H. , Eaves L. , Main P. C. , Hill G.
Published: July 2002

(AlGa)As–GaAs–(AlGa)As double barrier resonant tunneling diodes with different δ-doping levels in the GaAs quantum well (QW) together with undoped control samples have been investigated. A new subthreshold peak in the I(V) characteristics is observed and assigned to resonant tunneling through the bound state of a shallow donor impurity in the QW. By comparing the I(V) characteristics for wafers grown at different temperatures between 480 and 630 °C, the effects of Si segregation from contact layers into the well can be identified. This constitutes a new technique of assessment of donors which is sensitive to areal doping densities as low as 107 cm−2. The effect of low growth temperature (480 °C) and δ doping on peak/valley ratios of the resonances on the I(V) characteristic is also assessed.
Enhancement of Hall mobility in coupled δ-doped layers grown by molecular-beam epitaxy
Authors: Carns T. K. , Zheng X. , Wu B. J. , Wang K. L.
Published: July 2002

When two or more highly doped, thin (‘‘delta’’ doped) layers are placed in close proximity to one another, it is found that an enhancement of the Hall mobility occurs over that of a single delta layer as well as that of the bulk case. In Si, Hall hole mobilities of up to 2400 cm2 V−1 s−1 at 77 K have been obtained with δ layers spaced 200 Å apart compared to a mobility of 280 cm2 V−1 s−1 for the single delta layer. The conductance of the coupled δ-doped well exceeds that of comparable uniformly doped bulk layers, especially at lower temperatures. It is also found that when two Si δ-doped wells in GaAs are placed in close proximity to one another, the electron Hall mobility is enhanced two to five times over that of the single well case. These types of structures show great promise in obtaining high mobilities with high carrier densities for semiconductors grown by simple homoepitaxy.
Scanning tunneling microscopy study of molecular-beam epitaxial growth of GaAs on GaAs(001)
Authors: Sudijono J. , Johnson M. D. , Snyder C. W. , Orr B. G.
Published: July 2002

Scanning tunneling microscopy studies have been performed on GaAs(001) homoepitaxial films. By quenching the growth, we are able to image the surface as it appeared during deposition. Images from the early stage of growth show that the morphology oscillates between one with two-dimensional islands and flat terraces. It is noted that there is a correspondence between the surface step density and reflection high-energy electron diffraction specular intensity. In addition, depending upon the buffer layer preparation prior to the desired growth there is a significant difference in the surface morphology. Two processing methods are presented that produce recovered surfaces with either a high or low step density. Possible mechanism will be discussed.
Effect of structural and chemical parameters on the optical properties of highly strained AlGaAs/InGaAs/AlGaAs quantum wells
Authors: Kaviani Kian , Chen Li , Hu Kezhong , Xie Qianghua , Madhukar Anupam
Published: July 2002

The realization of high-quality AlxGa1−xAs/In0.26Ga0.74As/AlyGa1−yAs single quantum wells on GaAs(001) substrates for the entire range of Al compositions, 0≤x, y≤1.0 is being reported. The effect of replacing the AlGaAs alloy in the barriers with (AlAs)m(GaAs)n short-period superlattice is also examined and presented. The photoluminescence (PL) transition energies are calculated within a model in which the effect of strain is also included. Analysis of the PL transition energies as a function of the well width and the Al and In contents in the barriers and the well reveals that the exciton peak position is most sensitive to variation in the In content in the well. Possible causes of this variation are discussed.
Electrical characteristics of double-base Si/Si1−xGex/Si heterojunction bipolar transistors
Authors: Prinz Erwin J. , Xiao Xiaodong , Schwartz Peter V. , Sturm James C.
Published: July 2002

Recent advances in low-temperature epitaxial growth of strained, single-crystalline silicon–germanium random alloys (Si1−xGex) have introduced band gap engineering into the design of silicon-based devices. Here we describe a novel device, the double-base heterojunction bipolar transistor, which increases the functionality of a ‘‘normal’’ Si/Si1−xGex/Si heterojunction bipolar transistor by having two base contacts which can independently control the collector current. It can be used in a single-transistor NAND gate at temperatures up to 140 K, as an amplifier with digital ON/OFF control, or to increase the Early voltage (output resistance). In this article, the fabrication procedure of the device is outlined in detail, followed by complete electrical evaluation and modeling.
Field-emitter-array development for high-frequency operation
Authors: Spindt C. A. , Holland C. E. , Rosengreen A. , Brodie I.
Published: July 2002

Power amplification at high frequencies is one of many applications under investigation using vacuum microelectronics technology. The results of an ongoing program to develop a gigahertz amplifier using Spindt-type field-emitter arrays are reported. The maximum frequency at which a field-emission source in the form of a Spindt-type cathode array can be operated is determined by the capacitance of the structure and the transconductance of the array. It has been shown that by fabricating arrays with high emitter-tip packing densities and small total areas it should be possible to achieve operation in the gigahertz range. Structures having a capacitance in the range of 0.1 pF have been fabricated, and total emission currents of 25 mA with current densities of 1000 A/cm2 have been demonstrated with a 0.1 pF structure having 625 emitter tips (40 μA/tip). The transconductance under these operating conditions was 500 μs or 0.8 μS/tip. Simultaneous experiments with our standard low-frequency Spindt-type cathode geometry have shown that average emitter tip loadings of 200 μA/tip and transconductances of 5 μS/tip can be achieved. A 625-tip, 0.1-pF array with transconductance of 5 μS/tip would have a cutoff frequency of about 5 GHz. The factors determining the capacitance and transconductance of the device and methods for improving performance are discussed.
Design and technology features of heating-free magnetrons with autoemission excitation
Authors: Kopylov M. F.
Published: July 2002

Design and technology of a heating-free magnetron cathode with autoelectron and secondary electron emitters are presented. It is reported that there is a high electric field concentration on an edge of a super thin metal film. Pulsed volt–ampere characteristics of activated and deactivated emitters and their reciprocal transitions are shown. Main characteristics of heating free magnetrons with 10, 25, and 50 kW pulse output power are tabulated.
Possibility of amplification of microwaves using the negative conduction of an electron beam (polytron)
Authors: Solntsev Victor A.
Published: July 2002

The possibility to amplify waves in the waveguide or strip line penetrated by a transverse electron beam has been considered. Electrons can be emitted by FEAS or an extended thermionic cathode located along the line. The structure using FEAS is similar to the microtriode amplifier, but the input signal is supplied into the anode line instead of the cathode one. Wave amplification along the waveguide or line can be achieved due to the well-known effect of negative conduction of electron beam, used formerly in oscillating monotrons with cavities. If the transit angle of electrons drifting across the waveguide or line is 2π <θ <2.8π, the electrons at an average give the energy to the electromagnetic field, and if the current density is sufficient, it becomes possible not only to compensate losses, but to amplify the signal in the frequency band. The amplifier designed on the basis of this principle may be called a polytron. The analyses of polytron has shown that the amplification of millimetric waves is possible for the existing current densities being provided by thermionic cathodes or by FEAS. For example, minimum current densities Je,min providing the loss compensation in copper waveguide are Je,min =73 A/cm2 when λ=2 mm; Je,min =13 A/cm2 when λ=4 mm; Je,min =2.3 A/cm2 when λ=8 mm. The value of amplification depends on the difference between the working current density and the minimum one and the required distance between wide walls of the waveguide or between strip-line conductors makes up 10’s to 100’s of microns. The conducted analysis has shown the proposed principle of amplification in vacuum microelectronics to be promising.
Manufacturable vacuum field emission diodes
Authors: Weichold Mark H. , Legg James D. , Mason Mark E. , James Thomas C.
Published: July 2002

Realization of an easily manufacturable field emission device will be a key to the widespread acceptance of vacuum microelectronics technology. Many current devices under investigation work well in the laboratory but face serious manufacturing obstacles. With this in mind, a manufacturable cold field emission diode has been developed. The structure described here takes advantage of the edge emission cathodes similar to those developed by Gray et al., with the major difference being that the anode and cathode are not coplanar [H. F. Gray, Proceedings of the Third Annual IEEE Vacuum Microelectronics Conference, Monterey, CA, July 1990 (unpublished)]. The ability to easily define, nonphotolithographically, the anode-to-cathode spacing during the fabrication process allows control of the diode turn-on voltage over a wide range. Additionally, a symmetrical device geometry provides for increased field emission area. Extensive device testing has shown current–voltage characteristics that follow the Fowler–Nordheim model for cold field emission over several orders of magnitude of current. In this work, various metals have been examined for use as the cathode and their differences noted. Finally, it should be reported that the structure developed here will lend itself well to light emitting diode and triode devices.
Flat display based on the metal–insulator–metal emitter array
Authors: Troyan P. E. , Lubsanov R. B. , Vorobyev G. A. , Ghyngazov S. A. , Lakstroem I. V. , Kramor S. S.
Published: July 2002

The brightness versus voltage characteristics of the flat display based on an array of 32×16 metal–insulator–metal (MIM) emitters were studied. It was shown that about 16 gradations of brightness may be provided. The luminuous efficacy of such a display was about 0.4 lm/W. Forming microtips on the base electrodes of the MIM emitters and using a relatively thick operating dielectric (130–150 nm) enabled to obtain an increase in the value of the transmission coefficient α up to (7–8)×10−3 (which will lead to an increase in the luminous efficacy up to 1.0–1.2 lm/W) and decrease the emission variation between the emitters up to 10%. An array of 128×128 MIM emitters was developed using the above-mentioned technique.
Fabrication and characterization of lateral ‘‘cusp-edge’’ and ‘‘knife-edge’’ geometry cathodes
Authors: Kim J. M. , Carr W. N. , Zeto R. J.
Published: July 2002

Two lift-off techniques are demonstrated to form lateral field emission cathodes by shadowing a sputter deposition for tungsten composite. A current of 26 μA is observed for ‘‘knife-edge’’ cathodes of 23 μm edge length. The I–V characteristics are consistent with the Fowler–Nordheim relationship. The effect of focusing electrodes for increasing anode collection efficiency is consistent with our electron trajectory tracing simulations. The fabrication process for these devices is described in detail.
Atomic and electronic structure of B/Si(100)
Authors: Cao R. , Yang X. , Pianetta P.
Published: July 2002

The atomic and electronic structures of the B/Si(100) surface have been studied using high-resolution core level and valence band photoelectron spectroscopy as well as low energy electron diffraction. The structure models for such a surface have been proposed, which consist of boron atoms residing on the top surface adatom sites. Experimental evidence shows that this surface is not a dangling bond-free surface. Epitaxial growth of Si and Ge on this structure has been achieved at relatively low temperature, and our results indicate that boron atoms underneath the epitaxial layer act as acceptors. As a result, conversion of an n-type to p-type region takes place near the surface. Comparison of this surface with the other group-III metals on Si(100) surface has also been conducted.
Role of ionicity in the determination of surface atomic geometries: GaP, ZnS, and CuCl (110) surfaces
Authors: Klepeis J. E. , Mailhiot C. , van Schilfgaarde M. , Methfessel M.
Published: July 2002

First-principles total energy calculations were carried out in order to determine the local atomic geometry of the (110) surfaces for the isoelectronic series GaP, ZnS, and CuCl. Despite the large change in ionicity across the series (Phillips ionicities: fGaP=0.37, fZnS=0.62, and fCuCl=0.75), it was found that all three surfaces exhibit an activationless, bond-rotation relaxation with a rotation angle of ∼25° or greater. While this result is well known in the case of III–V (110) surfaces, it is in contradiction to a previous calculation which predicted that the bond-rotation angle would decrease with increasing ionicity, going to zero for CuCl. However, our results are in qualitative agreement with a recent dynamical low-energy electron diffraction analysis of the CuCl (110) surface. Despite the presence of a large-angle bond rotation for all three surfaces, the local atomic geometries depend on ionicity as follows: both the total energy gain for a given bond-rotation angle and the deviation of the surface anion from its ideal, bulk-terminated position decrease with increasing ionicity. In addition, the contraction of the top-layer anion–cation bond, relative to the bulk bond length, increases with increasing ionicity.
Scanning tunneling microscopy studies of Ge/GaAs(100) interface formation
Authors: Wang X.-S. , Self K. , Leonard D. , Bressler-Hill V. , Maboudian R. , Petroff P. M. , Weinberg W. H.
Published: July 2002

Study of the Ge/GaAs(100) interface provides important information to aid in understanding the formation of elemental-compound semiconductor heterojunctions. Using scanning tunneling microscopy and other surface sensitive probes, the Ge/GaAs(100) interface formation was investigated. On a molecular-beam epitaxially grown GaAs(100)-(2×4) substrate, submonolayer coverage of Ge atoms converts the surface into a (1×2) superstructure after annealing above 825 K. This structure can be explained by the formation of Ge–Ga dimer rows along the [01̄1] direction. On a surface with a submonolayer coverage of Ge annealed at a lower temperature, rows along the [011] direction with poor (2×1) order have been observed, which are considered to be an intermediate structure formed by Ge–As dimers. On vicinal GaAs(100) surfaces, the Ge–Ga dimer (1×2) reconstruction reduces the step-kink density.
Semiconductor heterojunctions at the Conference on the Physics and Chemistry of Semiconductor Interfaces: A device physicist’s perspective
Authors: Kroemer Herbert
Published: July 2002

After a very slow start, heterojunctions have emerged as one of the central topics of the Conference on the Physics and Chemistry of Semiconductor Interfaces. The presentation describes this emergence, starting from such items as the electron affinity rule of conduction band offsets, Dingle’s first determination of the GaAs–(Al,Ga)As band lineups, and the first lineup theories. Some of the blind alleys in this development (85:15 Rule, Common-Anion Rule, and others) are retold by one of the participants. The treatment then turns to a few of the most recent developments, such as the emerging role of ab initio computations as a quasiexperimental tool, plus a few developments this writer finds worth speculating about. The treatment is from the perspective of a device physicist, rather than a surface scientist, and some thoughts are offered on why there is not more commonality between heterojunctions and Schottky barriers.
Equilibrium gas-phase composition of cracked AsH3 and PH3
Authors: Robertson A. , Jordan A. S.
Published: July 2002

A thermodynamic analysis involving the pyrolysis products of AsH3 and PH3 has been performed. For the first time we have determined the concentration of subhydrides, (AsH, AsH2, PH, PH2) resulting from the decomposition. In the case of AsH3 and the corresponding subhydrides, we have also determined the thermodynamic properties (free-energy function, entropy, etc.) from critically assessed or estimated spectroscopic data from statistical thermodynamics. A free-energy minimization technique permitted the calculation of species concentrations that differ by orders of magnitude. The mass conservation constraints formulated here are applicable to crackers with effusive flow through an orifice as used in metalorganic molecular beam epitaxy and hydride source molecular beam epitaxy. The calculated concentrations, including the dimer/tetramer ratios, are in reasonable agreement with mass spectrometric measurements.
Carbon p+ doping of molecular-beam epitaxial GaAs films using carbon tetrabromide
Authors: Lemonias P. J. , Hoke W. E. , Weir D. G. , Hendriks H. T.
Published: July 2002

Carbon-doped GaAs films have been grown by molecular-beam epitaxy using carbon tetrabromide as the carbon source. The films were doped up to 1.3 × 1020 cm−3 with mobilities which compare favorably to beryllium-doped films. Secondary-ion mass spectrometry measurements made on these films indicate sharp transitions and negligible memory effects as well as near unity doping incorporation. Room temperature photoluminescence intensities were equivalent to comparably beryllium-doped films at 5.0 × 1019 cm−3. Photoluminescence intensities and hole concentrations were found to be dependent on both arsenic to gallium flux ratios and substrate temperature. Annealing studies on a film doped with carbon at 4.6 × 1019 cm−3 indicate good thermal stability of the carbon in the arsenic lattice site.
Characterization and improvement of the layer uniformity for large-area quantum well device arrays grown in an Intevac/Varian Gen II molecular beam epitaxy system
Authors: Svensson Stefan P. , Towner Frederick J.
Published: July 2002

The uniformity of GaAs, AlAs, and InAs grown in an Intevac/Varian Gen II molecular beam epitaxy system has been characterized using a quantum well (QW) structure and room-temperature photoluminescence (PL) evaluation. Artifacts in the measured distributions have been identified through simulations and were proposed to originate from incomplete rotation averaging during growth of the QW and/or oscillations of the Al mole fraction in the growth direction. The first effect is an actual thickness variation while the second effect leads to shifts in the PL signal that will be incorrectly interpreted as thickness variations when Schrödinger’s equation is solved for wells with symmetric potential barriers. Modeling of the flux distribution predicted that an upward tilt of the substrate away from the group III cells is beneficial. This was confirmed experimentally with the best overall uniformity achieved for a tilt of ∼9 deg.