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Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures

Issue 3 • Date May 2000

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Displaying Results 1 - 25 of 139
  • Issue Cover

    Page(s): c1
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    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
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  • Noise in scanning capacitance microscopy measurements

    Page(s): 1125 - 1133
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    Scanning capacitance microscopy (SCM) is a powerful tool for two-dimensional (2D) dopant/carrier profiling. Currently noise limits the accuracy of 2D dopant profiles obtained by SCM. In an effort to reduce noise, a systematic analysis of different SCM noise sources is provided. The main noise sources during SCM measurements are capacitance sensor noise and oxide–semiconductor surface induced noise. For adequate tip size, the dominant noise in SCM measurements is caused by variations in the quality of surface. On as-polished surfaces, nonstationary noise is observed. This noise is likely caused by the variations in the density of oxide traps. Tip induced charging of these traps and local variations or fluctuations in discharge time during SCM imaging cause the noise level and noise pattern to be different from image to image. Heat treatment under ultraviolet irradiation or in a hydrogen ambient is found to be an effective way to reduce or even eliminate this type of SCM noise. Stationary surface noise is mostly created by the variations in the oxide thickness. This type of noise correlates with topographic roughness and is very consistent during SCM measurements. By reducing the topographic roughness, the stationary surface noise may be reduced to the level of ∼10-2 of the depletion SCM signal for typical experimental conditions. It is shown that the capacitance sensor noise depends on the capacitance sensor tuning parameters and under proper conditions can be reduced to a negligible level for standard probe tips used in SCM measurements. © 2000 American Vacuum Society. View full abstract»

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  • Optical active gallium arsenide cantilever probes for combined scanning near-field optical microscopy and scanning force microscopy

    Page(s): 1134 - 1137
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    The fabrication process of a GaAs cantilever probe with an integrated vertical cavity surface emitting laser (VCSEL) for scanning near-field optical microscopy applications is described. The VCSEL illuminates an aperture in a thin Au/Ge metallization layer at the tip apex. The light emitting aperture serves as a subwavelength light source and thus can be used to reduce the lateral resolution in transmission imaging beyond the far-field diffraction limit. The light beam of the VCSEL emitted to the opposite side is exploited for the detection of the mechanical deflection of the cantilever that additionally facilitates the scanning force microscopy setup. © 2000 American Vacuum Society. View full abstract»

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  • Resolution in scanning near-field cathodoluminescence microscopy

    Page(s): 1138 - 1143
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    The lateral resolution in scanning near-field cathodoluminescence microscopy, in the case of bulk materials, is theoretically and experimentally studied. Although the theoretical resolution of near-field optical collection systems is determined by the probe size and thus should not be dependent on the energy dissipation volume in the material, it is theoretically shown that the contribution of the far-field signal caused by the radiative centers situated far from the probe can alter the resolution by adding a background noise to the near-field signal. In order to see the role of the energy dissipation volume, the electron beam accelerating voltage is varied and its influence on lateral resolution is studied in the case of a material that does not present a large energy transfer range, a fluorite doped with 0.3% europium. Cathodoluminescence images of this one confirm that the resolution is improved by working at low accelerating voltage to limit the energy dissipation volume, hence the contribution of the far-field radiative centers. On the other hand, for materials having a large energy transfer range (several micrometers) and therefore for which the far-field contribution can be strongly disturbing, the question concerning the efficiency of the near-field collection systems arises. Our experimental results on indented MgO crystal, which presents a large energy transfer range, demonstrates that near-field collection, despite the large contribution of the radiative centers situated far from the tip, gives still a better resolution than far-field collection. © 2000 American Vacuum Society. View full abstract»

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  • Imaging of soft structures: Dependence of contrast in atomic force microscopy images on the force applied by the tip

    Page(s): 1144 - 1150
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    Forces acting on atomic force microscope tips during scanning of films of ionic surfactant molecules adsorbed from aqueous solutions onto hydrophilic substrates are measured. Near critical micellar concentration images of mica substrates show aggregate regions at the interface. Force versus distance curves indicate that aggregates are the thickest adsorbed structures on the substrate. However, topographic images registered at low scanning speed (15 μm/s) show that these aggregates appear as holes, consequently observed as inverted in contrast images. In atomic force microscope imaging of soft structures such as surfactants or biological material, inverted images may be observed when the tip penetrates the scanned layers. This penetration can be adjusted by changing the force applied by the tip, which results in different images. In order to obtain the conventional atomic force microscope contrast in scanned images the applied force set point is determined by the analysis of the force versus distance curves.© 2000 American Vacuum Society. View full abstract»

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  • Study of Pb diffusion on Si(111)-(7×7) with scanning tunneling microscopy: Low coverage

    Page(s): 1151 - 1155
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    The diffusion of single Pb atoms and the formation of stable clusters containing two and three Pb atoms on a Si(111)-(7×7) reconstructed surface was studied with variable temperature scanning tunneling microscopy (STM). The numbers of single Pb atoms and Pb atoms in clusters were monitored as a function of time. A new and simple statistical model describing diffusion was developed. This model enables us to estimate the diffusion coefficient and the activation energy of diffusion. The main advantage is the avoidance of questionable counting of jump events in successive STM images. For substrate temperatures of 308, 311, and 313 K we obtained diffusion coefficients of 8.1×10-18, 1.2×10-17, and 1.9×10-17cm2 s-1, respectively, and the activation energy of diffusion equaled E=0.56±0.07 eV. The energy difference ΔE between the binding energies of single Pb atoms at faulted and unfaulted halves of the Si(111)-(7×7) unit cells was estimated to be 27±9 meV. © 2000 American Vacuum Society. View full abstract»

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  • Study on nucleation and growth of Ag nanoparticles prepared by radio-frequency sputtering on highly oriented pyrolytic graphite and amorphous carbon

    Page(s): 1156 - 1159
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    The initial growth process of silver nanoparticles on highly oriented pyrolytic graphite (HOPG) and amorphous carbon (a-C) was studied. Scanning tunneling microscopy was used for analysis of the nanoparticles formed on HOPG. Transmission electron microscopy was employed to study the growth procedure on a-C. The number densities (Dn) of silver nanoparticles on both HOPG and a-C remain constant at a very early stage, then both decrease with deposition time and have a saturated value. The Dn decrease suggests migration followed by impingement. We found evidence of migration of 5 nm particles on a-C. Interpretations are given to explain the impingement and shape change of the silver nanoparticles. © 2000 American Vacuum Society. View full abstract»

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  • Electrical testing of gold nanostructures by conducting atomic force microscopy

    Page(s): 1160 - 1170
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    We devised a method for the reliable electrical testing of nanoscale wire arrays using conducting probe atomic force microscopy (AFM) in ambient conditions. A key requirement of this approach is the formation of highly reproducible electrical contacts between the conducting tip and the sample. We discuss the basic mechanical and electrical criteria of nanocontacts and derive a force-controlled protocol for the formation of low-ohmic contacts. Tips sputter coated with platinum provided the mechanical stability for both tapping-mode imaging and the formation of low-ohmic contacts on gold samples. Nanostructures on the sample were identified by topographic imaging and subsequently probed using the AFM tip as a mobile electrode. We measured resistivities in arrays of nanowires or local potentials of wires within electrical circuits, and detected electrical failures, thermal gradients, and small geometrical variations. The ability of this instrument to address electrical characteristics with high spatial resolution makes it a powerful tool for lithography developments and on-chip monitoring of nanoscale circuits. © 2000 American Vacuum Society. View full abstract»

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  • Direct patterning of noble metal nanostructures with a scanning tunneling microscope

    Page(s): 1171 - 1176
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    We demonstrate in this article the controlled deposition of noble metal dots and lines using local chemical vapor deposition in the tip–sample gap of a scanning tunneling microscope. 3 nm diam rhodium dots have been patterned by local decomposition of an inorganic precursor, which was synthesized on purpose. Deposition is obtained on gold surfaces by applying a series of negative voltage pulses on the sample exceeding a voltage threshold of 1.9 V. The influence of kinetics parameters (pulse voltage duration and number, as well as the effect of gas pressure) are presented. In a second step, the deposition process has been applied on hydrogenated silicon (100) surfaces. These samples were previously hydrogen passivated using two different wet etching operations, leading surface dangling bonds saturated by either mono- or di-hydride bonds. The difference in the deposition processes observed in both cases is discussed. © 2000 American Vacuum Society. View full abstract»

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  • Fabrication of dissimilar metal electrodes with nanometer interelectrode distance for molecular electronic device characterization

    Page(s): 1177 - 1181
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    We report a versatile process for the fabrication of dissimilar metal electrodes with a minimum interelectrode distance of less than 6 nm using electron beam lithography and liftoff pattern transfer. This technique provides a controllable and reproducible method for creating structures suited for the electrical characterization of asymmetric molecules for molecular electronics applications. Electrode structures employing pairs of Au electrodes and non-Au electrodes were fabricated in three different patterns. Parallel electrode structures 300 μm long with interelectrode distances as low as 10 nm, 75 nm wide electrode pairs with interelectrode distances less than 6 nm, and a multiterminal electrode structure with reproducible interelectrode distances of 8 nm were realized using this technique. The processing issues associated with the fabrication of these structures are discussed along with the intended application of these devices. © 2000 American Vacuum Society. View full abstract»

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  • Ti/TiN coatings for microfabricated cantilevers used in atomic force microscopy

    Page(s): 1182 - 1186
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    We report the successful sputter coating of microfabricated silicon cantilever and tip assemblies with high-quality titanium/titanium nitride (Ti/TiN) thin films using a technique that will be available to many researchers. We demonstrate that the use of pulsed mode reactive dc magnetron sputtering, adequate thermal budget, and careful control of a titanium seed layer were the key elements for producing usable coated cantilevers. This coating material takes advantage of the excellent adhesive properties of Ti with silicon and silicon oxide and the intrinsically hard and conductive properties of TiN. Hence, these coated cantilever and tip assemblies have promising advantages over standard cantilever and tip assemblies for many demanding atomic force microscopy applications. We were able to fabricate Ti/TiN coatings with negligible stress-induced bending of the delicate cantilevers. Tests to assess the performance of the Ti/TiN coatings were done on the tip assemblies and on sputter-coated blanket films on thermally oxidized silicon to obtain a measure of the film resistivity and thickness. © 2000 American Vacuum Society. View full abstract»

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  • Nanometer-scale data storage on 3-phenyl-1-ureidonitrile thin film using scanning tunneling microscopy

    Page(s): 1187 - 1189
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    We present nanometer-scale date storage on 3-phenyl-1-ureidonitrile thin film using scanning tunneling microscopy (STM). This monomer film can become polymerized when a voltage pulse is applied between the STM tip and the substrate. The affected region changes from being electrically resistant to electrically conductive along the direction of the polymeric molecular chain. The recorded mark of the data occurs in the region, and is 0.8 nm. We have obtained recorded marks arranged regularly as 6×8 arrays. A possible chemical mechanism of this data storage would be the phase transition from the monomer state to the polymeric state. The small marks are very stable. © 2000 American Vacuum Society. View full abstract»

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  • Defect observation on a 12-in. silicon wafer using large sample atomic force microscopy

    Page(s): 1190 - 1193
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    As semiconductor devices have become more highly integrated and miniaturized, defects originating within single-crystal silicon occur more frequently. Defect observation of silicon wafer surfaces using atomic force microscopy (AFM) is an analysis technique that reduces defect density on silicon surfaces and, thereby, increases yield (Ref. ). We have developed an AFM that can directly observe the entire surface of next-trend, 12-in. wafers. We observed the defects of 12-in. Czochralski (CZ) wafers and compared the results with those of 8-in. wafers. We also observed the defects of 12-in. epitaxial Si wafers as a reference. The defects of the 12- and 8-in. CZ wafers are similar, and the 12-in. wafers display two types of defects in the silicon crystals: (1) Crystal originated particle, which is a shape surrounded by a {111} facet, and (2) dislocation loops. These defects are caused when crystals are lifted, and reflect the lifting conditions (Ref. ). Although, there were fewer defects on the epitaxial Si wafers than on the CZ wafers, defects like hillock were found on the epitaxial Si wafers. © 2000 American Vacuum Society. View full abstract»

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  • Characterization and nanometer-scale modifications of Bi2Te3 surface via atomic force microscopy

    Page(s): 1194 - 1197
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    The structure of the basal plane of a Bi2Te3 crystal surface was studied by means of the atomic force microscopy (AFM) technique. The measured heights of steps, ranging from 0.2 to 1.4 nm, were in agreement with other structural data of Bi2Te3. The images of freshly cleaved surface, obtained with atomic resolution, revealed a plane of tellurium atoms. The recorded interatomic distances of 0.42±0.02 nm were also in accordance with the structural data. We also showed that there is a possibility of surface nanostructures formation using the AFM probe, when working above force threshold value. © 2000 American Vacuum Society. View full abstract»

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  • Homoepitaxial diamond (001) thin film studied by reflection high-energy electron diffraction, contact atomic force microscopy, and scanning tunneling microscopy

    Page(s): 1198 - 1202
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    A surface of the homoepitaxial diamond (001) thin film produced by microwave plasma chemical vapor deposition was observed by reflection high-energy electron diffraction (RHEED), contact atomic force microscopy (contact-AFM) and scanning tunneling microscopy (STM) on the same sample. It was checked by the RHEED observation that most areas of the sample surface had a 2×1 or 1×2 reconstructed structure, which indicates that most areas of the surface were covered with hydrogen termination. By contact-AFM a pseudoperfect surface with rare atomic-scale defects and steps was observed. By STM, on the other hand, a 2×1/1×2 double-domain structure was observed and the surface had many steps and defects. One should be careful because a contact-AFM image does not ensure true atomic-resolution since the multitip effect is dominant. © 2000 American Vacuum Society. View full abstract»

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  • Comparison between tantalum carbosulfide and TaCl5-graphite intercalation compound by scanning tunneling microscopy

    Page(s): 1203 - 1206
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    The layered compounds of TaCl5-graphite intercalation compound, second-stage stacking sequence: C–TaCl5–C–C and tantalum carbosulfide were studied by scanning tunneling microscopy. Although both materials consist of layers the information on their content gathered by scanning tunneling microscopy is quite different for both. The second-stage TaCl5-graphite intercalation compound provides detailed information concerning the superstructure and positions of adjacent chlorine atoms at the upper graphene layer. Tantalum carbosulfide is a layered compound with a stacking sequence of S–Ta–C–Ta–S. Direct information from the first (sulfur) layer only could be obtained. Measured amplitudes are distinguishable for the sulfur layer, this may indicate the occurrence of charge density waves. © 2000 American Vacuum Society. View full abstract»

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  • High current density field emission from arrays of carbon nanotubes and diamond-clad Si tips

    Page(s): 1207 - 1211
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    Arrays of carbon nanotubes (CNT) and diamond-clad Si tips were grown by microwave plasma-enhanced chemical vapor deposition. The former ones were grown directly on prepatterned cobalt-coated silicon substrate, while the latter ones were grown on Si-tip arrays. Each array contains 50×50 emitting cells and each individual cell is 3 μm square. A maximum effective emission current density of about 17 A/cm2 (at a macroscopic field of 17.5 V/μm) has been demonstrated, while a macroscopic emission current density of 10 mA/cm2 with operating fields around 10 V/μm can be routinely achieved from an array of CNT emitters. In contrast, operating fields above 20 V/μm were needed to draw a comparable emission current density from all of the diamond-clad Si tips arrays. Emission stability test performed at 40 mA/cm2 for CNT arrays also showed little sign of degradation. Due to the high efficiency of electron emission, simple sample process, and large area growth capability, field emitter arrays based on CNT are attractive for flat panel display applications. © 2000 American Vacuum Society. View full abstract»

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  • Arrays of field emission cathode structures with sub-300 nm gates

    Page(s): 1212 - 1215
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    A novel field emission cathode process has been developed to produce cathode arrays with individual emitter structures having gates with ≪300 nm diameters. Ion tracking lithography was utilized to pattern submicron features, which can be controlled over the range 30–300 nm, and to create self-aligned and nanosized, gated emitter structures. Nanocone emitter tips were deposited into the gate structure using a variation of the Spindt process. Field emitter arrays having ∼300  nm gate diameters and an emitter density of 108/cm2 exhibited a current density of 4  mA/cm2 for a 45 V gate bias. This ion tracking lithographic approach is suitable and scalable for large flat panel video displays and appears to be commercially viable. © 2000 American Vacuum Society. View full abstract»

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  • Mapping the field-emission tunneling barrier of organic adsorbates on tungsten

    Page(s): 1216 - 1221
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    The field-emission tunneling barrier has been mapped for the doublet and quadruplet emission patterns associated with organic adsorbates on tungsten. The tunneling barrier was mapped by photometric probe-hole field-emission electron microscopy (PhotoFEEM). The adsorbates were deposited by evaporating a film of the molecule copper-phthalocyanine (CuPc) but it may be polymeric groups of CuPc or decomposition products. The tunneling barrier displays unexpected structures that are not seen in the corresponding field-emission images. Doublet patterns observed in the FEEM image can display singlet structures in the corresponding PhotoFEEM barrier maps. Similarly, quadruplet patterns in the FEEM image can display doublet structures in the PhotoFEEM barrier maps. This behavior is similar to supply limited tunneling previously observed in the field-emission barrier of a clean tungsten emitter. An analysis of deviations from purely linear Fowler–Nordheim behavior indicates that the observed structures arise from independent emitters that are spatially superimposed on the surface. © 2000 American Vacuum Society. View full abstract»

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  • Prebreakdown and breakdown investigation of needle-plane vacuum gaps in the micron/submicron regime

    Page(s): 1222 - 1226
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    This article reports investigations of insulation failure of needle-plane gaps of micrometric dimensions. Using a piezoelectric translational stage it is possible to set the gap spacing in the range between 0.1 and 40 μm with a resolution less than 0.04 μm. The prebreakdown and breakdown characteristics of the needle-plane gap were investigated as a function of the gap spacing, emitter radius, ambient pressure, and conditioning effects. The experimental results showed that the breakdown voltage of a microtip-plane gap is relatively high. For a 2 μm radius tip set at a 1 μm gap distance from a planar electrode, the breakdown voltage was about 500 V. It was found that an increase of pressure from 10-6 to 10-2Torr did not influence the value of the threshold voltage for breakdown. dc glow discharge conditioning in air at a pressure of ∼1 Torr increased the value of threshold voltage for breakdown in vacuum by about 20%–30%. The obtained prebreakdown characteristics of microtip type gaps is very important for the development of vacuum microelectronic devices; specifically, these data provide valuable insights to the practical limits to which microtip-gate gaps can be stressed in practical field emitter arrays in field emission displays. © 2000 American Vacuum Society. View full abstract»

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  • Influence of getter activation and aging in a frit-sealed field emission display panel

    Page(s): 1227 - 1231
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    A field emission display (FED) panel system was successfully built through integration of a 0.7 in diagonal Si-based Mo-tip field emitter array with 25×25 pixels, a Y2O3:Eu or ZnO:Zn phosphor screen, and vacuum sealing through an exhausting glass tube, including a getter. The panel system was driven by an external driver circuit that has a pulse width modulation driving scheme. We have tried to evaluate quantitatively the activation effect of a getter. The getter activated at a relatively low temperature was shown to act as a good in situ minipump during the life of the FED. Before character imaging, it was stabilized through tip aging by slowly increasing a pulse-mode emission current and phosphor aging by a Coulombic charging process. After aging, luminescent characteristics such as emission uniformity, charging and arcing phenomena were shown to be improved significantly. © 2000 American Vacuum Society. View full abstract»

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  • Growth of InxGa1-xAs/GaAs heterostructures using Bi as a surfactant

    Page(s): 1232 - 1236
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    The effects of a bismuth surfactant layer on the molecular beam epitaxy of GaAs and InxGa1-xAs layers on GaAs (001) were studied. The InxGa1-xAs surface reconstruction changed from arsenic stabilized 2×4 to bismuth stabilized 1×3 for high enough bismuth fluxes and low enough substrate temperatures. Maintaining a bismuth stabilized surface during InxGa1-xAs growth resulted in a larger number of reflection high-energy electron diffraction (RHEED) oscillations. RHEED patterns were also streakier after InxGa1-xAs growth with Bi. Roughness measurements using atomic force microscopy showed reduced root mean square roughness with Bi, e.g., from 3.8 to 2.8 nm, for 4 nm thick In0.3Ga0.7As layers. Simulations of x-ray diffraction results from 10 period In0.5Ga0.5As/GaAs superlattices showed that Bi reduced interface roughness from 1.1 to 0.5 nm and reduced interfacial broadening from 2.8 to 2.1 nm. The latter was attributed to reduced In segregation. InxGa1-xAs/GaAs (x=0.2–0.4) multiple quantum wells grown with Bi exhibited photoluminescence peaks that were more intense than those grown without Bi. © 2000 American Vacuum Society. View full abstract»

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  • Electrical properties and defect states in undoped high-resistivity GaN films used in high-power rectifiers

    Page(s): 1237 - 1243
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    The electrical properties and spectra of deep centers in high-resistivity undoped GaN samples used to fabricate high-power Schottky diode rectifiers with breakdown voltages exceeding 2000 V are reported. It is shown that the Fermi level in such material is pinned by defects with energy levels close to Ec-0.6 eV. Thermally stimulated current measurements revealed the presence of unidentified traps with activation energies of 0.3 and 0.7 eV. The important role of hole traps with energy levels Ev+0.3 eV and Ev+0.9 eV was confirmed by measurements of temperature quenching of photocurrent and by photoinduced transient current spectroscopy measurements. Prominent persistent photoconductivity was observed even for temperatures above 300 K. Imaging of the sample using microcathodoluminescence showed the existence of cellular nonuniformities with characteristic dimensions of the cells of about 3 μm. © 2000 American Vacuum Society. View full abstract»

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  • Elevated source drain devices using silicon selective epitaxial growth

    Page(s): 1244 - 1250
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    Elevated source drain (ESD) structure in deep submicron metal oxide semiconductor field effect transistors (MOSFETs) can help reduce parasitic series resistance and simultaneously achieve shallow contacting junctions to minimize short channel effects. A self-aligned ESD structure in conventional complimentary metal–oxide–semiconductor processing can be achieved using silicon selective epitaxial growth (SEG). A robust low thermal budget high quality SEG process using a commercial rapid thermal chemical vapor deposition reactor for ESD formation has been demonstrated. The preclean sequence prior to SEG is the key to achieve facet-free epitaxy. Low line-to-line leakage confirms the high selectivity to nitride and oxide. The growth on exposed polysilicon (poly) gates leads to gate linewidth widening and lower gate sheet resistance. ESD parametric data suggest that the well doping needs to be optimized to counter the slight increase in n+-p diode leakage. Capacitance–voltage simulations indicate that the gate to drain capacitance initially decreases and then increases with SEG thickness. © 2000 American Vacuum Society. View full abstract»

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Aims & Scope

The Journal of Vacuum Science and Technology B is devoted to reports of original research, review articles, and Critical Review articles.

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Meet Our Editors

Editor
Gary E. McGuire
International Technology Center