bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of substrate temperature in SiOxNy films deposited by electron cyclotron resonance
Authors: del Prado A. , Martı́nez F. L. , Mártil I. , González-Dı́az G. , Fernández M.
Published: July 2002

The effect of deposition temperature on the physical properties of SiOxNy films has been studied. The films have been deposited from mixtures of SiH4, O2 and N2, using the electron cyclotron resonance–chemical vapor deposition technique, with substrate temperature ranging from room temperature (50 °C) to 200 °C. When substrate temperature is increased, a slight decrease in both Si–H and N–H bond concentration is detected. A small shift (10–17 cm−1) in the dominant Fourier transform infrared (FTIR) absorption peak (Si–O/Si–N stretching band) seems to be associated with a decrease in the N–H bond concentration. This behavior is attributed to the formation of Si–N bonds at the expense of N–H bonds, with no significant change in the film composition. Full width at half maximum (FWHM) of the dominant FTIR peak decreases as temperature is increased for all the composition range, indicating an improvement in the quality of the films. Silicon oxide films (SiO2.0) deposited at 200 °C show improved properties with respect to those deposited at room temperature. FWHM decreases from 95 to 87 cm−1, and the shoulder-to-peak ratio from 0.29 to 0.22. The position of the Si-O stretching band (1071 cm−1) is unaffected. These values are very close to those obtained for thermally grown oxides, while the thermal budget of the process is significantly reduced.
In situ study of interface reactions of ion beam sputter deposited (Ba0.5Sr0.5)TiO3 films on Si, SiO2, and Ir
Authors: Gao Y. , Mueller A. H. , Irene E. A. , Auciello O. , Krauss A. , Schultz J. A.
Published: July 2002

( Ba 0.5 ,Sr 0.5 )TiO 3 (BST) thin films were deposited on MgO, Si, SiO2 and Ir surfaces by ion beam sputter deposition in oxygen at 700 °C. In situ spectroscopic ellipsometry (SE) has been used to investigate the evolution of the BST films on different surfaces during both deposition and postannealing processes. First, the optical constants of the BST films in the photon energy range of 1.5–4.5 eV were determined by SE analysis on crystallized BST films deposited on MgO single crystal substrates. The interfaces in BST/Si and BST/SiO2/Si structure were examined by SE and Auger electron spectroscopy depth profiles. Subcutaneous oxidation in the BST/Ir structure was observed by in situ SE during both ion beam sputter deposition and postdeposition annealing in oxygen at 700 °C. A study of the thermal stability of the Ir/TiN/SiO2/Si structure in oxygen at 700 °C was carried out using in situ SE. The oxidation of Ir was confirmed by x-ray diffraction. The surface composition and morphology evolution after oxidation were investigated by time of flight mass spectroscopy of recoiled ions (TOF-MSRI) and atomic force microscopy. It has been found that Ti from the underlying TiN barrier layer diffused through the Ir layer onto the surface and thereupon became oxidized. It was also shown that the surface roughness increases with increasing oxidation time. The implications of the instability of Ir/TiN/SiO2/Si structure on the performance of capacitor devices based on this substrate are discussed. It has been shown that a combination of in situ SE and TOF-MSRI provides a powerful methodology for in situ monitoring of complex oxide film growth and postannealing processes.
Characteristics of BeTe films grown by molecular beam epitaxy
Authors: Cho M. W. , Chang J. H. , Saeki S. , Wang S. Q. , Yao T.
Published: July 2002

Systematic investigations are performed on the surface morphology, structural properties, and p-type dopability of BeTe epilayers grown on GaAs (001) by molecular beam epitaxy under various growth temperatures and p(Te)/p(Be) flux ratios. A phase diagram for surface reconstruction is obtained with regard to the BEP (beam equilibrium pressure) ratio of p(Te)/p(Be) and growth temperature. Irrespective of growth temperature (300–500 °C), a surface phase transition from weak (4×1) to (2×1) reconstruction occurs near p(Te)/p(Be)∼10 as the p(Te)/p(Be) value increases. Epilayers grown at a low Te pressure of p(Te)/p(Be)⩽10 show Be droplets on the surface as observed by atomic force microscopy, which eventually leads to degraded crystallinity. It is noted that such growth features are different from conventional II–VI compounds. The differences in growth features are discussed in terms of the relationships between the equilibrium vapor pressures of the compound and constituent elements. By optimizing growth conditions, i.e., flux ratio of 15<p(Te)/p(Be)<20, epilayers with high structural quality and smooth surface are obtained. Good correlation between the surface morphology and crystallinity is found. p-type BeTe layers doped with N are grown using a radio-frequency nitrogen plasma source. The net acceptor concentration increases as the p(Te)/p(Be) flux ratio is decreased. It is shown that p-BeTe with high hole concentrations above 6×1018 cm−3 can be readily grown.
Delivery of pure ozone in ultrahigh vacuum
Authors: Zhukov V. , Popova I. , Yates J. T.
Published: July 2002

An apparatus designed to produce and deliver pure ozone to a sample inside a metal ultrahigh vacuum apparatus is described. Ozone of 96%–97% purity is prepared in a glass vacuum system and converted to a molecular beam of known flux using an all glass doser. The storage lifetime of the O3 at Torr pressure in the glass storage vacuum system (containing a small surface area of metal) has been measured, and it is shown that the rate of O3 destruction during storage is inconsequential for hours of storage.
Use of a modified paraxial formalism for particle beam dynamics: Application to liquid metal ion sources
Authors: Miskovsky N. M. , Cutler P. H. , Feuchtwang T. E.
Published: July 2002

A modified paraxial formalism has been developed and used to describe two-dimensional ion beam dynamics in liquid metal ion sources with pointed geometries. It has been shown that appreciable differences exist between first-order and modified paraxial theory in the calculation of beam dispersion. For a singly charged ion the effects of mass and initial energies on calculated trajectories in the modified theory are demonstrated. Finally, it is argued that only the modified theory can accurately describe within the paraxial approximation the ion trajectories close to the apex of needle-type liquid metal ion sources.
Above-bandgap optical anisotropies in cubic semiconductors: A visible–near ultraviolet probe of surfaces
Authors: Aspnes D. E.
Published: July 2002

I describe some results of the first systematic study of above-bandgap optical anisotropies in cubic semiconductors. The anisotropies are large, of the order of 1% of the relative reflectance differences for light polarized along orthogonal principal axes of the dielectric tensor of the anisotropic phase. Extrinsic contributions arising from anisotropic surface films, physisorbed molecules, and chemisorption-induced changes in the electronic polarizability of the outermost plane of substrate atoms are identified. The line shapes of these reflectance-difference (RD) spectra provide the first critical test of models proposed to describe intrinsic contributions to the optical anisotropies of these materials. The dominant intrinsic contribution is shown to be a surface (interface) many-body effect due to the reduced screening of the surface atoms as a result of the termination of the bulk lattice. A secondary intrinsic contribution from the influence of spatial dispersion on interband energy gaps in the one-electron band structure is also observed. The identification of the intrinsic contributions allows the surface contributions to be obtained. The results show that interface state effects in this spectral range are minimized by oxidation for (110) Si and Ge.
Kinetics of formation and properties of epitaxial CoSi2 films on Si (111)
Authors: D’Avitaya F. Arnaud , Delage S. , Rosencher E. , Derrien J.
Published: July 2002

Very thin CoSi2 films, epitaxially grown on silicon (111) surfaces, have been obtained under ultrahigh vacuum conditions by thermal reaction of Co layers deposited onto Si (111) substrates. The morphology and structural properties of the CoSi2 films depend strongly on experimental parameters such as film thickness, annealing temperature to form CoSi2, or substrate temperature during Co deposition. Usually for high-temperature formation (≥700 °C) and large thickness (≥200 Å) CoSi2 islands are observed. Below these limits the CoSi2 films display a rather smooth and homogeneous aspect. The reaction kinetics are also followed in situ monitoring the Co and Si Auger peaks versus annealing temperature. Two interfaces have been examined, namely Co–Si and Co–CoSi2. Plateaus in the Auger peak variation show the evolution of the sampled region from the Co metallic phase to successively Co2Si, CoSi, and CoSi2 phases. Finally, electrical characteristics of some nearly perfect CoSi2–Si Schottky barriers have been checked with intensity and capacitance versus voltage techniques. The deduced barrier ranges around 0.65±0.02 eV and no signal has been detected with deep-level transient spectroscopy.
Fabrication of sub-100-nm linewidth periodic structures for study of quantum effects from interference and confinement in Si inversion layers
Authors: Warren A. C. , Plotnik I. , Anderson E. H. , Schattenburg M. L. , Antoniadis D. A. , Smith Henry I.
Published: July 2002

Two new types of Si metal-oxide-semiconductor field-effect transistor (MOSFET) devices have been fabricated and tested which involve a dual gate structure, the lower one being a W grating of 0.2 μm period, 0.1 μm linewidth. These devices, the lateral surface superlattice and the quasi-one-dimensional device, explore the regime where quantum mechanical effects become important. Fabrication techniques are described and projections made with regard to lithographic techniques for future electronic systems based on sub-100 nm linewidth devices. X-ray lithography at λ∼1 nm can provide linewidth control ≲10 nm and high pixel-transfer rate. The mask-to-substrate gap is constrained by diffraction. However, with a resist of sufficiently high contrast (and low sensitivity to avoid edge raggedness) linewidths of 50 nm should be feasible in high volume production at mask–substrate gaps of a few μm.
The contrast of ion beam stencil masks
Authors: Randall J. N. , Stern L. A. , Donnelly J. P.
Published: July 2002

Masked ion beam lithography using stencil masks has demonstrated high resolution proximity printing with short exposure times. Stencil masks generally consist of a thin (∼1 μm) membrane with transmission holes etched through the entire membrane thickness. To the first order the mask contrast will be infinite if the membrane is thicker than the range of the exposing ions in the membrane. However, any ion impinging very near a transmission hole may scatter laterally into the transmission hole and escape the mask at an arbitrary angle. These scattered ions reduce the effective contrast of the mask in a manner which is pattern dependent. Grid-support stencil masks, which employ a matrix of small transmission holes instead of completely open transmission areas, are used to eliminate most of the pattern restrictions associated with stencil masks, and to improve mask stability. However, the grid significantly increases the mask area from which scattered ions may escape, and this type of mask requires a higher fluence to accomplish an exposure than simple stencil masks. Both effects will decrease the effective mask contrast. A Monte Carlo program has been developed which models ion scattering in stencil masks. The computer model predicts excellent performance from a grid-support stencil mask which has high-aspect-ratio transmission holes and has a membrane considerably thicker than the ion range.
Pressure dependence of GaAs/AlxGa1−xAs quantum-well bound states: The determination of valence-band offsets
Authors: Wolford D. J. , Kuech T. F. , Bradley J. A. , Gell M. A. , Ninno D. , Jaros M.
Published: July 2002

We report experiment and theory on the pressure dependence of quantum-well bound states formed in the GaAs/AlxGa1−xAs heterostructure system. Using MQW’s and SL’s of various barrier compositions x, we trace in photoluminescence (8 K), and in full-scale pseudopotential calculation, the pressure-induced evolution of the lowest spatially confined states within the wells. With increasing pressure Γ-confined states follow the shift to higher energies of the direct GaAs band gap. At critical pressures a crossing occurs between these Γ bound states and the barrier indirect X states. Here, Γ intensities plunge and new emission tracking the X edges appears. Confirmed in wave function calculation, these new transitions occur across the heterointerface, between X-confined electrons within the AlxGa1−xAs and Γ-confined holes within the GaAs. Arising from valence-offset-induced staggered band alignment, critical pressures for observation of these states decrease with increasing Al mole fraction. We thus obtain, with potentially meV resolution, the first direct measure of valence band offsets. For x≊0.28 and 0.70 we find ΔEV≊(0.32±0.02)ΔEΓg. Taken together, we believe these results are among the most precise and spectroscopically detailed accounts of staggered band alignment yet reported for a semiconductor interface. The optical method reported on here should apply to other interface systems. Our results also represent the first spectroscopic evidence concerning the physical properties of confined states associated with secondary (X) minima. An excellent agreement between theory and experiment is achieved.
Properties of TiSi2 as an encroachment barrier for the growth of selective tungsten on silicon
Authors: Chen S. S. , Sivaram S. , Shukla R. K.
Published: July 2002

Selective growth of chemical-vapor deposited selective tungsten, on thermally grown titanium silicide thin films, on silicon substrates, has been characterized. The nucleation of selective tungsten is found to be strongly affected by the surface chemical composition of the silicide. A thin layer of titanium nitride, formed on the silicide surface during the silicidation of sputtered titanium in nitrogen ambient, does not allow selective tungsten nucleation and has to be chemically removed to observe growth of the tungsten film. Localized titanium oxide regions on the silicide surface lead to adhesion problems between tungsten film and the silicide underlayer resulting in tungsten film blistering and bubbles formation. The regions of silicide where these bubbles form show accumulation of fluorine from the WF6 reduction at the interface. In regions of good adhesion and normal growth characteristics, no titanium oxide was found, almost all the silicide was consumed during the growth of selective tungsten and no fluorine accumulation at the interface was observed. These results indicate that it is possible to grow selective tungsten on titanium silicide barrier over silicon substrate provided that the surface of silicide is free of any titanium oxide or nitride layers. Under such conditions, the silicide layer acts as a sacrificial barrier allowing selective tungsten growth without resulting in any silicon consumption or encroachment of tungsten into the silicon substrate.
Molecular-beam epitaxial growth and characterization of strained GaInAs/AlInAs and InAs/GaAs quantum well two-dimensional electron gas field-effect transistors
Authors: Griem H. T. , Hsieh K. H. , D’Haenens I. J. , Delaney M. J. , Henige J. A. , Wicks G. W. , Brown A. S.
Published: July 2002

Defect free strained layer epitaxy opens possibilities for further improvement on the quantum well two-dimensional electron gas (TEG) structures grown using the GaInAs/AlInAs on InP materials system. Increased freedom with composition allows for optimizing certain properties of the structure, such as, the conduction edge discontinuity which controls the maximum sheet concentration (ns); and the electron effective mass which influences the speed of the structure. These enhancements can be made, respectively, by increasing the Al concentration in the AlInAs and/or by decreasing the Ga concentration in the GaInAs. The maximum amount of strain which can be incorporated into the unrelaxed material sets an upper limit on the compositional tolerances. The tolerances will be shown to be large for the AlInAs and the active TEG GaInAs region. The compositions are obtained using the intensity oscillations observed in the reflective high-energy electron diffraction (RHEED) specular beam during growth of GaAs, AlAs, and subsequently GaInAs and AlInAs on GaAs. X-ray rocking curves and photoluminescence (PL) are used to verify the calibrations for growths on InP. The dependency of the mobility on strain is shown. The maximum 300 K mobility obtained was 12 360 cm2/V s, with ns of 1.25×1012/cm2. The well thickness was 84 nm. The AlInAs and GaInAs were estimated to be +0.04 and +0.17 In mole fraction from lattice match, respectively. A mobility of 11 550 cm2/V s was obtained using a 34-nm well. InAs/GaAs superlattice quantum well TEG structures were grown and characterized. TEG field-effect transistors performance comparable to standard structures were obtained in preliminary layers. Exceptionally high Si doping levels roughly 20 times the maximum obtained with Al0.25Ga0.75As have been achieved with lattice matched AlInAs.
Structure and lateral diffusion of ohmic contacts in AlGaAs/GaAs high electron mobility transistors and GaAs devices
Authors: Langer Dietrich W. , Ezis A. , Rai A. K.
Published: July 2002

A conventional Au–Ge–Ni based metallization scheme is used to obtain low resistivity ohmic contacts (≤0.2 Ω mm) to GaAs–AlGaAs based high electron mobility transistor devices and GaAs devices. Thermal stressing reveals that contact resistance remains stable to about 250 °C. At 300 °C an accelerated resistance degradation occurs and instability sets in after 40 h. Cross-sectional electron transmission and energy dispersive x-ray analysis reveals the extent of alloying and the composition of contact region. In the unstressed samples alloying and singular protrusions extending to 0.2 μm below the crystal surface, are observed. At the edge of the contact considerable lateral (0.12–0.15 μm) and vertical protrusions are regularly observed. The extent of the vertical penetration at the contact edge implies that current flow between the alloyed region and the two-dimensional electron gas region occurs in the lateral direction. The lateral contact penetration decreases the nominal source–drain separation and has to be taken into account for accurate device modeling.
Comparison of different x-ray sources using the same printing process parameters
Authors: Cullman E. , Künneth T. , Suss Karl , Neff W. , Stephan K. H.
Published: July 2002

The x-ray printing performance of a conventional electron bombardment source , a plasma focus source, and a synchrotron radiation source are compared. The same mask, resist process, and gap between mask and wafer are employed for all sources. A step-and-repeat x-ray mask aligner holds both mask and wafer in ambient atmospere so that the radiation travels through 1 mm of air. Both point sources—a stationary W anode source, and a plasma focus source using Ne gas—emit their radiation from a 1 mm diam spot at a 40-cm distance from the mask. This geometry is chosen to allow high resolution image transfer. The BESSY electron storge ring in Berlin is used as the synchrotron radiation source providing nearly parallel exposure light. All exposure sources emit their radeation at about the same wavelength

, i.e., between 7 and 12 Å. Differences in imaging quality and exposure times will be discussed based on prints typically performed at a 40-μm gap in poly(methylisopropylphenylketone) (PMMA). The masks employed use a 1 μm gold absorber pattern on a silicon wafer thinned to 2-μm thickness. In future x-ray technology, the choice of the source may be related to the application. Depending heavily on throughput considerations all three sources might have a place in this promising technique.
Electron beam probing system with ultrahigh time resolution
Authors: Ozaki K. , Ito A. , Goto Y. , Furukawa Y. , Inagaki T.
Published: July 2002

We have developed an electron beam (EB) probing system with an ultrahigh time resolution of 10 ps. To achieve this, the distortion of the rise/fall time of the observed waveform must be less than 10 ps and the resolution of the time scale must be 10 ps. In the newly developed system, the distortion is less than 10 ps for rise/fall times of more than 100 ps. This was achieved by using trough-type traveling-wave deflectors and low jitter circuits for EB pulse generation. The 10 ps time scale resolution was achieved by using an EB pulse phase shifter with electrical correction. The EB probing system can be applied to the internal diagnosis of very high speed ICs, such as GaAs ICs.
Formation and properties of rapid thermally annealed TiSi2 on lightly doped and heavily implanted silicon
Authors: Shenai K. , Piacente P. A. , Lewis N. , Smith G. A. , McConnell M. D. , Baliga B. J.
Published: July 2002

Detailed material and electrical characteristics of rapid thermally annealed (RTA) TiSi2 on doped silicon are presented using transmission electron microscopy, Rutherford backscattering spectrometry, secondary ion mass spectrometry (SIMS), Auger analysis, and four-point probe measurements. TiSi2 films with varying sheet resistances were formed on lightly doped and heavily arsenic and phosphorus implanted 〈100〉 silicon by rf sputtering titanium and forming the silicide using two-step flash anneals at different temperatures. It is shown that the silicide sheet resistance is a sensitive function of the silicon surface condition prior to titanium sputtering; in particular, silicide films formed on heavily implanted silicon had significantly higher sheet resistance compared to films formed under identical conditions on lightly doped prime silicon. The higher silicide sheet resistance resulted because of the surface damage created during arsenic and phosphorus implantation and higher silicon dopant concentration. The RTA silicide films showed excellent film properties across 4-in.-diam wafers with good thickness uniformity and minimal sheet resistance variations compared to furnace annealed samples. Detailed SIMS and Auger analyses showed minimal film contamination and negligible dopant redistribution for RTA silicided wafers.
Radical beam/ion beam etching of GaAs
Authors: Skidmore J. A. , Coldren L. A. , Hu E. L. , Merz J. L. , Asakawa K.
Published: July 2002

A novel combined radical beam and ion beam etching (RBIBE) technique that uses a microwave-excited radical beam combined with an Ar+ ion beam has been developed for smooth, low damage, and rapid etching of GaAs structures. Separate control of both argon ion (Ar+) energy and/or current and chlorine radical (Cl*) beam flux density has enabled us to realize highly chemically enhanced GaAs etching. This RBIBE technique differs qualitatively from and offers greater flexibility than reactive ion etching (RIE), ion beam assisted etching (IBAE), where the reactive etch gas is not plasma excited, or reactive ion beam etching (RIBE), where independent control of radical and ion beam flux is difficult. Our work examines etch rate as a function of flow rate, temperature, microwave power, and ion beam current. The etch rate and reactive sputter yield are typically eight times greater with the microwave plasma on (RBIBE) than with the plasma off (IBAE). With RBIBE, high etch rates (2.5 μm/min) have been realized at room temperature and for low ion energies (200 eV). Optical emission spectroscopy is used to correlate the etch rate with the concentration of chlorine radicals in the microwave cavity. The reactive sputter yield and degree of anisotropy can be varied over a wide range by varying the microwave power level and the ion beam current density. We demonstrate that this etching technique should be capable of producing smooth, low-damage structures for applications in optoelectronics.
Molecular-beam epitaxial growth and exciton lifetime studies of lattice-matched and coherently strained quantum wells
Authors: Chen Y. , Oh J. , Singh J. , Bhattacharya P. K.
Published: July 2002

We have made temperature-dependent photoluminescence and absorption measurements of the dominant excitonic transitions in high-quality lattice-matched and strained single and multiple quantum well systems grown by molecular-beam epitaxy. GaAs/AlGaAs, InGaAs/InAlAs, and InGaAs/GaAs single quantum wells grown under the optimal conditions exhibit liquid helium photoluminescence linewidths (HWHM) equal to 0.39, 3.2, and 2.7 meV, respectively. GaAs/AlGaAs multiple quantum wells of well size 60, 96, and 200 Å exhibit low-temperature linewidth (HWHM) of 1.3, 1.6, and 2.2 meV, respectively. Strained InGaAs/AlGaAs multiple quantum wells (120 Å) have 3.5 meV HWHM linewidth. These excitonic linewidths are among the smallest reported for each system. The excitonic peaks are clearly present in all material systems up to 300 K. The finite exciton linewidth at the lowest temperature is attributed to inhomogeneous broadening due to interface roughness and well size fluctuations, while the temperature broadening results from homogeneous interactions of excitons with both acoustic and optical phonons. Based on this assumption we have calculated the homogeneous part of the linewidth and consequently the exciton lifetime at higher temperatures by careful fitting of experimental data with Gaussian and Lorentzian line shapes. The results are interpreted in terms of exciton–phonon interactions.
Evaluation of polycrystalline silicon membranes on fused silica for x-ray lithography masks
Authors: Trimble L. E. , Celler G. K.
Published: July 2002

Single crystalline Si films, heavily doped with boron for etch selectivity and often counterdoped with Ge to reduce stresses, are now commonly used as membranes in x-ray masks. We have investigated preparation and properties of much simpler membrane structures, consisting of undoped polycrystalline Si films deposited either on oxidized Si wafers or on fused silica substrates. The latter case is particularly simple since concentrated HF that is used for etching the fused silica substrate, does not attack Si. Therefore, after coating both sides of a fused silica substrate with polycrystalline Si, a window is opened in Si on one side by simple lithography, and the wafer is immersed in HF to complete the process. Stress of the membranes can be tuned by adjusting deposition conditions, annealing temperature, and choice of high temperature glass instead of silica for the substrate. Data from three polycrystalline membranes indicate a higher fracture strength and a larger effective elastic modulus than in equivalent single crystalline Si structures. However, optical transparency is lower because of light scattering by grain boundaries.
Coverage dependence of Schottky barrier formation
Authors: Klepeis John E. , Harrison Walter A.
Published: July 2002

When the metal coverage at the surface of a semiconductor is sufficiently small so that there are isolated metal adatoms and therefore localized states, there is a distinction between the energy (0,+) to remove an electron from a neutral adatom and the energy (−,0) to add an electron to a neutral adatom. The acceptor level (−,0) is higher in energy than the donor level (0,+) by an energy U*, just as in the free atom, but here U* is modified by the presence of the surface. For these isolated metal adatoms, the donor level (0,+) frequently lies in the semiconductor gap with the acceptor level (−,0) coming in the conduction band. This circumstance leads to an asymmetry between the low-coverage band bending for n-type semiconductors versus that for p-type. As the number of adatoms is increased, the (0,+) and (−,0) levels shift relative to the semiconductor bands at the surface. These shifts can be understood in terms of the polar bonds between the metal adatoms and the semiconductor surface atoms. At sufficiently large metal coverages the wavefunctions of adjacent metal adatoms overlap and the discrete levels broaden into bands. Eventually the donor and acceptor bands overlap and the asymmetry between n-type and p-type band bending disappears. This picture is modified if the metal adatoms are clustered rather than uniformly distributed.
Molecular-beam epitaxial growth of NiAl on GaAs(001)
Authors: Chambers S. A.
Published: July 2002

High-quality, single-crystal overlayers of NiAl that create a Schottky barrier height of 0.90 eV have been grown on semi-insulating GaAs(001) by molecular-beam epitaxy and characterized by high-energy resolution x-ray photoelectron spectroscopy, low-energy electron diffraction, and high-energy x-ray photoelectron diffraction. Thin Al interlayers were grown between the NiAl and the substrate in order to test the possibility that an ultrathin AlxGa1−xAs layer of higher band gap than the substrate forms at the interface and is the cause of the high barrier height. It has been found that such a layer does indeed form when the Al prelayer is deposited near room temperature and annealed at 500 °C, or if the deposition is carried out at a substrate temperature of 500 °C. Moreover, the presence of this prelayer correlates with the appearance of a high barrier height at the interface. Virtually identical results are obtained when layers of Ni and Al are deposited sequentially at room temperature and then annealed at 500 °C to alloy and recrystallize the metal. The realization of a 0.9-eV barrier height occurs independently of the removal of any excess As from the interface, which according to the advanced unified defect model, is thought to cause the high barrier height by virtue of a change in the balance of antisite defects.
Compound magnetic and electrostatic lenses for low-voltage applications
Authors: Frosien J. , Plies E. , Anger K.
Published: July 2002

We report on three compound magnetic and electrostatic lenses for low-voltage applications: an immersion condenser lens, a compound spectrometer objective lens for electron beam testing, and an objective lens for a low-voltage scanning electron microscope (SEM). A common characteristic of all lenses is the electrostatic retarding field in front of an intermediate, or the final crossover image. This keeps electron energy high as long as possible and results in a reduced Coulomb interaction and low aberration constants. In the case of the objective lens for low-voltage microscopy, we have calculated 3.7 mm for the spherical and 1.8 mm for the chromatic aberration constant at a beam energy of 500 eV and a working distance of 4 mm. With such a lens, which allows tilting even of large specimens, a resolution of 11 nm should be obtained.
The effect of aluminum masks on the plasma etch rates of polysilicon and silicon nitride
Authors: Grynkewich Gregory W. , Fedynyshyn Theodore H. , Dumas Richard H.
Published: July 2002

Plasma etch rates of both aluminum and photoresist masked polysilicon and silicon nitride are reported. Both thermally grown and plasma deposited substrates of both films were studied. It is shown that all aluminum masked substrates except thermal nitride exhibit enhanced etch rates relative to photoresist masked samples. Aluminum masked thermal nitride etches more slowly than does photoresist masked. These results are shown to be consistent with a metal catalyzed surface reaction which generates additional fluorine radicals at the surface of the wafer.
Characterization of high purity GaAs films grown by molecular-beam epitaxy from a solid As cracker
Authors: Chow Robert , Fernandez Rouel , Atchley David , Chan Kam , Bliss David
Published: July 2002

Two series of high-quality, unintentionally doped GaAs films were grown to evaluate a solid As cracker source with a graphite crucible. In the first series, material properties comparisons were made between a film grown with the As cracker in the dimer mode, a film from the same cracker source but in the tetramer mode, and lastly, a film from a conventional As cell. The film grown with the dimers had a n-type unintentional background doping level of 5×1014 cm−3 and a 104 000 cm2/V s mobility at 77 K. The films grown with As tetramers gave low p-type unintentional background doping levels of less than 1.1×1014 cm−3, respectively. Photoluminescence spectra taken of these films at 4 K showed various excitonic transitions and comparable C incorporation. In the second series, films grown at As2/Ga incorporation rate ratios of 1.1, 1.5, and 2.0 had layers that were p-type, resistive, and n type, respectively. Samples taken from the film grown at the 2.0 ratio had 77 K mobilities as high as 195 000 cm2/V s, with a corresponding net carrier concentration of 3.8×1014 cm−3. These mobility values are the highest reported for GaAs grown with a solid As dimer source. Results from a variable temperature van der Pauw measurements of another sample cut from this film gave a donor ionization energy of 2.6 meV.
Growth of wide band gap polycrystalline semi-insulating polycrystalline silicon
Authors: Sands David , Brunson Kevin M. , Spink D. M. , Thomas Clive B. , McNeill D. , McDonald A. A. , Jennings S. , Rosser P. J.
Published: July 2002

Semi-insulating polycrystalline silicon (SIPOS) films have been grown by low-pressure chemical vapor deposition at 590 °C rather than the conventional 650 °C. Three compositions have been achieved; 6.1 at. % of oxygen, 17.7 at. % oxygen, and 26.4 at. % oxygen with 15.3 at. % hydrogen. Films of the first two compositions are amorphous as grown and have properties very similar to known properties of SIPOS. In the last composition, wherein hydrogen is incorporated, the film is polycrystalline as grown with an optical band gap of 2.1 eV, and it has some properties similar to more conventional SIPOS containing 51 at. % oxygen—49 at. % silicon which has been annealed at 900 °C. Upon implantation with a dose of 2×1016 P atoms/cm2 followed by annealing at 1150 °C, conductivities of 5×102 (Ω cm)−1 are possible.
High repetition rate electron beam chopping system for electron beam testing at microwave frequencies
Authors: Thong J. T. L. , Breton B. C. , Nixon W. C.
Published: July 2002

A new beam deflection-chopping system has been developed which circumvents the limitation of electron pulse generation at maximum repetition rates of a few GHz with low energy beams using conventional deflection-chopping techniques. In an electron-optical arrangement involving two sets of orthogonal deflectors placed above and below a multislot chopping aperture immersed in a magnetic lens field, electron pulses are generated at regular deflection phase increments as the beam, scanned in a circle, traverses the radial slots. This results in beam pulse generation at a frequency which is the product of the deflection frequency and the number of slots. By changing the deflection amplitude, the beam transmission ratio can be altered, shorter electron pulses being generated at larger amplitudes. Time-resolved electron pulse measurements demonstrate pulse production at frequencies of up to 64 GHz while 18 GHz waveforms on a coplanar waveguide have been measured with an electron-beam testing system incorporating this beam chopper. The system’s electron-optical performance and issues concerning the integration of the beam chopper into a testing system are discussed.
Reactive ion etching of indium compounds using iodine containing plasmas
Authors: Flanders D. C. , Pressman L. D. , Pinelli G.
Published: July 2002

A reactive ion etching process and system using iodine containing plasmas for etching InP, InGaAs, and InGaAsP is described. A special system was constructed to deliver iodine to an etching chamber and trap the iodine to prevent damage to the pumping system. Etch rates and profiles were determined using both large area and grating test patterns with linewidths as small as 20 nm. Using mixtures of Ar:I2 and H2 :HI:CH4 at a substrate temperature of 100 °C, lines 20 nm wide and 1 μm deep with vertical sidewalls were etched in InP at a rate of 200 nm/min using a Ni mask. The use of this etching technique in the fabrication of highly reliable InGaAsP distributed feedback lasers with a unique structure is also described.
Stress in silicon dioxide films deposited using chemical vapor deposition techniques and the effect of annealing on these stresses
Authors: Bhushan Bharat , Murarka S. P. , Gerlach Jeff
Published: July 2002

Using an in situ stress measurement technique that measures stress as a function of annealing temperature, instabilities in mechanical stress induced by heat treatment in a variety of doped/undoped SiO2 films deposited by atmospheric-pressure chemical vapor deposition (APCVD), low-pressure chemical vapor deposition (LPCVD), and plasma-enhanced chemical vapor deposition (PECVD) techniques have been investigated. A large hysteresis in mechanical stress, caused by first heat treatment to which the as-deposited films are subjected, has been observed in films deposited by APCVD/LPCVD techniques. No such hysteresis is observed in films deposited by PECVD technique. Hysteresis in APCVD/LPCVD films is found to vanish once the films are heat treated at or above 800 °C. Stress behavior of heat treated (≥800 °C) films is found to resemble that of thermally grown SiO2 films and can be described by simple elastic theory. During the first annealing cycle, APCVD/LPCVD films have been found to develop stress levels as large as an order of magnitude higher than their as-deposited stress value. Maximum stress developed in the film during heat treatment and the temperature TR at which maximum stress occurs have been found to be dependent on phosphorous content in the film. For heat treatment below this temperature TR, the stress on cooling becomes significantly larger than the as-deposited stress. The results are discussed in terms of oxide densification, the presence of hydrogenous species, and phosphorous.
Morphological study of Ag, In, Sb, and Bi overlayers on GaAs(100)
Authors: Spindt C. J. , Cao R. , Miyano K. E. , Lindau I. , Spicer W. E. , Pao Y.-C.
Published: July 2002

We have used ultraviolet photoemission spectroscopy to study the morphology of the nonreactive materials In, Ag, Sb, and Bi deposited on the GaAs(100) surface. The attenuation of the substrate core levels and the electronic structure of the overlayers yield information on the growth modes and others properties of these interfaces. We find that in all cases the behavior is significantly different from the growth on the more heavily studied (110) surface. In the case of In, we observe isolated In atoms in between large clusters, while on the (110) surface, only strong clustering is observed. Ag forms a larger number of small clusters compared to the (110) surface. This indicates that the mobility of small Ag clusters is lower, and/or the number of nucleation sites is greater on our (100) surfaces. Both Sb and Bi grow in more laminar modes, as opposed to the Stranski–Krastanov mode observed on (110). The Sb film is found to be closer to perfectly laminar. After annealing at 250 °C for 10 min, the Bi film is found to cluster heavily except for a strongly bound single layer. In addition, the resulting Sb thin film is semiconducting up to a thickness of about 100 Å, while the Bi film appears to be semimetallic even at relatively low coverages. We find that the clean surface Fermi level is roughly 0.5 eV from the valence band maximum. However, we will concentrate on the growth mode of the overlayer. Band bending issues will be discussed elsewhere.
Characterization of InGaAs surface passivation structure having an ultrathin Si interface control layer
Authors: Hasegawa Hideki , Akazawa Masamichi , Ishii Hirotatsu , Uraie Atsuhiro , Iwadate Hirokake , Ohue Eiji
Published: July 2002

A recently proposed passivation structure of In0.53Ga0.47As surface is characterized by x-ray photoelectron spectroscopy (XPS), capacitance–voltage, and deep-level transient spectroscopy measurements. It uses an ultrathin molecular beam epitaxy Si interface control layer (ICL) and a photochemical vapor deposition (CVD) SiO2 outer insulator. XPS study indicates that growth of Si ICL is coherent and two-dimensional up to about 10 Å beyond which clustering is initiated, and that it is effective in preventing the InGaAs layer from selective oxidation of Ga during photo-CVD SiO2 deposition. C–V and deep level transient spectroscopy (DLTS) measurements give Nss distributions of very different shapes, the latter exhibiting two distinct peaks, which may be erroneously interpreted as defect levels. Suppression of selective oxidation of InGaAs does not alter the shapes of these distributions, although it reduces the magnitude. The results are explained by the disorder-induced gap state model rather than the defect model or the effective work function model.
Effects of rapid thermal annealing on InP layers grown on GaAs substrates by gas-source molecular beam epitaxy
Authors: Riesz Ferenc , Rakennus Keijo , Hakkarainen Tuula , Pessa Markus
Published: July 2002

InP layers were grown on (100) GaAs substrates by gas-source molecular beam epitaxy and then were annealed by the rapid thermal annealing (RTA) method. The effects of annealing time and temperature on crystalline structure were studied by double-crystal x-ray diffraction. Significant improvement in crystalline quality was observed, due to RTA. The smallest linewidth was 315 s of arc for the 2-μm-thick layers upon annealing at 940 °C for 10 s. Using lower temperatures and longer annealing times, the linewidths remained broader but the loss of phosphorus was reduced.
Uncooled 10.6 μm mercury manganese telluride photoelectromagnetic infrared detectors
Authors: Becla P. , Grudzien N. , Piotrowski J.
Published: July 2002

Photoelectromagnetic PEM detectors for 10.6 μm utilizing Hg1−xMnxTe alloys have been designed and fabricated. Numerical and experimental analysis of the PEM effect has been performed. The normalized responsivity Rv detectivity D* and time constant τ were calculated using Lile’s generalized theory of the PEM effect. The responsivity (Rv=0.1 V/W) and detectivity (D*=1.2×107 cm Hz1/2 W−1 ) were achieved with p-type of Hg1−xMnxTe having the composition x∼0.08 and acceptor concentration ND of about 2×1017 cm−3. The experimental values of Rr and D* are a factor of 3 below the calculated values.
Specific atom imaging, nanoprocessing, and electrical nanoanalysis with scanning tunneling microscopy
Authors: Kazmerski Lawrence L.
Published: July 2002

Scanning tunneling microscopy is used to provide integrated imaging, processing and electrical characterization on the nanoscale level for the same defect region in CuInSe2. The use of coordinated electronic and photon biasing is demonstrated to provide specific atomic imaging for covalently bonded semiconductors. The high-resolution conditions of the instrument provide for nanoprocessing with passivation of defects using oxygen. The same regions are analyzed for minority-carrier losses by a nanoscale electron-beam induced current technique.
Beyond Tersoff and Hamann: A generalized expression for the tunneling current
Authors: Sacks W. , Noguera C.
Published: July 2002

We present an analytical method for treating the tunneling current between a probe tip and a sample in scanning tunneling microscopy (STM). The choice of a highly idealized tip permits a direct calculation of the tunnel current without resorting to perturbation theory (Bardeen approximation). In our model, the tip is a semi-infinite chain of spherical potential wells oriented orthogonal to the sample surface. The sample surface, however, is arbitrary. The wavefunction for the entire system is obtained by a matching procedure, from which the total current is determined. For small bias voltage the result is comparable in simplicity with that of Tersoff and Hamann [Phys. Rev. B 31, 805 (1985)]. We find that the tunnel conductance is proportional to the local density of states (LDOS) of the surface, but renormalized to include multiple reflections to all orders: σ∝ρL(r0,EF)/D, where D depends on both the tip and sample electronic structure, and the tip position r0. As the tip-surface separation increases D approaches unity, and we recover the result of TH. We find that D can be smaller or greater than unity, leading to a relative reduction or enhancement of the current. This effect which can be significant, both in the interpretation of STM images and in related spectroscopies, depends on the particular surface electronic structure.
Fractal characterization of gold deposits by scanning tunneling microscopy
Authors: Gómez-Rodríguez J. M. , Baró A. M. , Salvarezza R. C.
Published: July 2002

We have used scanning tunneling microscopy (STM) to investigate the fractal character of gold deposits grown by electroreduction of hydrous oxide layers. We have been able to precisely measure the fractal dimension (D′) of several samples grown under different conditions by processing three-dimensional STM images. Lake patterns were generated by computer simulating the filling with ‘‘water’’ up to a given level of the surface topography. Lake perimeter (L) versus area (A) relationships could be established leading to a fractal description (L∝AD′/2) of the sample surface.
Dose-rate effects in focused-ion-beam implantation of Si into GaAs
Authors: Lezec Henri J. , Musil Christian R. , Melngailis John , Mahoney Leonard J. , Woodhouse John D.
Published: July 2002

Ion current densities in focused-ion-beam (FIB) implantations are several orders of magnitude greater than those of conventional broad-beam implantations. The corresponding increase in dose rate during implantation is shown to affect parameters of interest in device fabrication. FIB and broad-beam Si implants into GaAs at energies from 70 to 280 keV and at doses from 3×1012 to 1014 cm−2 are characterized using secondary ion mass spectroscopy (SIMS) and Hall-effect measurements. Reduced straggle, decreased activation, and modified carrier profiles are observed for FIB implants, particularly at higher energies and doses. These effects are attributed to dose-rate-dependent lattice damage.
I
n s
i
t
u strain measurements during the formation of platinum silicide films
Authors: Buaud P. P. , d’Heurle F. M. , Irene E. A. , Patnaik B. K. , Parikh N. R.
Published: July 2002

Using an in situ double optical beam technique, the evolution of the strain for the Pt–Si system was followed before, during, and after reaction. During initial heating and prior to reaction only a compressive thermal stress is observed whereupon reaction to form Pt2Si yields a compressive intrinsic stress. The mechanism for stress buildup and relaxation is elucidated and shown to be related to the relative motion of Pt and Si atoms during the respective processes.
Schottky barrier heights for GaAs diodes fabricated at low temperatures
Authors: Wilks S. P. , Morris J. I. , Woolf D. A. , Williams R. H.
Published: July 2002

High-quality Schottky diodes have been fabricated by depositing several metals onto atomically clean molecular-beam epitaxy grown surfaces of GaAs(100) displaying (4×6) and c(4×4) reconstructed forms. Diodes have been made at temperatures of 80, 200, and 300 K and the barrier heights investigated by the current-voltage method at these temperatures and following temperature cycles. In all cases investigated, the Schottky barrier heights are large and similar to those for the same metals on GaAs (110) surfaces. These results are in complete contrast with those recently reported where soft x-ray photoemission and internal photoemission data for metals on GaAs (100) surfaces were interpreted in terms of the Schottky model.