bluuebunny/crossref_metadata_2025 huggingface dataset:
Quasiperiodic microfacets on the surface of AlGaAs/GaAs quantum well structures grown by molecular beam epitaxy on (311)A high-index substrates
Authors: Freire S. L. S. , Cury L. A. , Matinaga F. M. , Valadares E. C. , Moreira M. V. B. , de Oliveira A. G. , Alves A. R. , Vilela J. M. C. , Andrade M. S. , Lima T. M. , Sluss J. A.
Published: July 2002

Standard molecular beam epitaxy is used to demonstrate the growth feasibility and reproducibility on the formation of microfacet array on the top surface of higher-index (311)A quantum well structures. The quasiperiodic microfacet array was characterized by atomic force microscopy and was observed to be along the [2̄33] direction, whereas for the (100) reference sample the microscopic surface morphology presented the terraces formation. We have used photoluminescence to characterize the optical properties of the samples. The observed redshift of the luminescence from the (311)A sample, in relation to the (100) reference sample, was correlated with the existence of a lateral confinement potential induced by the period of faceting in this structure. The comparative analysis based on photoluminescence measurements have also shown the higher quality and the lower impurity incorporation for the (311)A oriented samples.
Investigation of face-centered-cubic Fe thin films using wedged samples
Authors: Kawakami R. K. , Escorcia-Aparicio Ernesto J. , Qiu Z. Q.
Published: July 2002

The structural and magnetic properties of metastable face-centered-cubic (fcc) Fe thin films on fcc Co(100) substrate were studied using wedged samples. fcc Co(100) was chosen for the substrate because it is structurally very similar to Cu(100) but is ferromagnetic at room temperature. Reflection high energy electron diffraction and low energy electron diffraction characterizations confirm that epitaxially grown (MBE) Fe on Co(100) is structurally very similar to Fe on Cu(100): face-centered-tetragonal (fct) for dFe<6 ML, fcc for 6 ML<dFe<11 ML, bcc for dFe≳11 ML. In situ surface magneto-optic Kerr effect measurements show that at room temperature the fct and bcc regions are ferromagnetic, while the fcc region is nonferromagnetic with some magnetic live layers. All magnetizations are in-plane. Oxygen absorption experiments suggest that these live layers are at the Fe/Co interface. Low temperature growth Fe/Co(100) shows a Kerr signal that increases linearly with dFe and suggests that the magnetic moments for fcc Fe and bcc Fe are the same. To further study the magnetic properties of the nonferromagnetic ‘‘fcc’’ phase, we used metastable fcc Fe as a spacer layer between two Co layers. The Co/fcc Fe/Co on Cu(100) sandwiches exhibit ferromagnetic coupling, strong antiferromagnetic coupling (AFC) and weak AFC. An oscillation in the strong AFC was found by artificially lengthening the thickness range of the nonferromagnetic fcc phase.
Heavy Be doping of GaP and InxGa1−xP
Authors: Tagare M. V. , Chin T. P. , Woodall J. M.
Published: July 2002

Very high p-type doping is achieved in GaP and InxGa1−xP with Be in solid source molecular beam epitaxy equipped with a valved phosphorus cracker. Dependence of hole concentration on the growth temperature and on the Be flux during growth is studied for GaP. The hole concentration peaks at 3×1019 cm−3 for normal temperature (600 °C) growth. It is slightly higher at a lower growth temperature of 400 °C for the same Be flux. A higher hole concentration (5×1019 cm−3) is obtained by giving a high temperature rapid thermal anneal to this sample. A hole concentration of 2×1019 cm−3 is achieved in In0.49Ga0.51P by using a lower temperature growth (350 °C). To our knowledge, this is the highest reported hole concentration for any p-type dopant in In0.49Ga0.51P.
InGaP/GaAs/InGaP double-heterojunction bipolar transistors grown by solid-source molecular-beam epitaxy with a valved phosphorus cracker
Authors: Chin T. P. , Chang J. C. P. , Woodall J. M. , Chen W. L. , Haddad G. I.
Published: July 2002

The growth and device characterization of an InGaP/GaAs double-heterojunction bipolar transistor is reported, the device is grown in a solid source molecular beam epitaxy system equipped with a valved phosphorus cracker. Various designs of base–collector (B–C) junction are used to eliminate the current blocking effect caused by the conduction band discontinuity. The results show that a chirped superlattice with a delta-doping layer at the B–C junction has the best dc characteristics. Both dc and microwave results of these devices are comparable to those obtained with other advanced growth techniques.
B/Si(100) surface: Atomic structure and epitaxial Si overgrowth
Authors: Zhang Z. , Kulakov M. A. , Bullemer B. , Eisele I. , Zotov A. V.
Published: July 2002

A boron-accumulated Si(100) surface with boron coverage up to 0.1 monolayer has been prepared by high-temperature annealing of B-doped Si samples. Scanning tunneling microscopy has been used to monitor the transformation in surface morphology and surface atomic structure induced by boron surface accumulation. The specific boron-induced surface features have been elucidated and a model of their atomic structure has been proposed. On the boron-accumulated surface epitaxial Si films with a thickness of 0.1–3.0 monolayers have been grown using solid phase epitaxy and molecular beam epitaxy. The results show that under appropriate growth conditions B surface segregation can be suppressed even on the atomic scale. The effect of boron induced features on the growth process has been discussed.
Use of maximum entropy deconvolution for the study of silicon delta layers in GaAs
Authors: Cooke G. A. , Dowsett M. G. , Allen P. N. , Collins R. , Miethe K.
Published: July 2002

Semiconductor layer structures with sharply changing concentration, and more especially delta-doped (single atomic plane) structures, provide an ideal environment for the study of the more subtle mass transport phenomena such as concentration-dependent diffusion and localized mixing caused by ion bombardment. However, to be able to extract meaningful parameters from such experiments, accurate depth profiles must be obtained with extremely high depth resolution and good sensitivity. Secondary ion mass spectrometry (SIMS) provides one of the most sensitive methods for acquiring such profiles. To obtain high depth resolution, a number of criteria must be satisfied, not the least of which is the reduction of redistribution by the probe; thus it is essential to employ a low energy primary beam. It is also vital that the crater floor recedes parallel to the original surface of the specimen. This necessitates accurate scanning of a stable ion beam, so as to ensure a constant flux across the entire sampled area.

If this is not the case, depth resolution will degrade as a function of depth, and important information will be lost. However, even if probes of the order of 1–2 keV are used, together with a precision scan system, beam-induced redistribution is still a significant limit to the sharpness of the recorded profiles. To further improve upon the data, the effects of the analysis must be removed from the profile. In this article we demonstrate the use of the maximum entropy deconvolution technique, applying it to a SIMS depth profile of a multilayer silicon in gallium arsenide structure containing alternating layers of high and low areal density. The important issue of data validity is discussed and the deconvolved results are used to calculate a diffusion constant for the denser layers, the less dense layers show no diffusion at the growth temperature of 450 °C.
Characterization of Si/Si1−yCy superlattices grown by surfactant assisted molecular beam epitaxy
Authors: Pettersson P. O. , Ahn C. C. , McGill T. C. , Croke E. T. , Hunter A. T.
Published: July 2002

Si/Si0.97C0.03 superlattices grown on Si(001) substrates by Sb surfactant assisted molecular beam epitaxy are characterized by in situ reflection high energy electron diffraction (RHEED), atomic force microscopy, transmission electron microscopy (TEM), and high resolution x-ray diffraction. The RHEED shows that, in the absence of Sb, the growth front roughens during Si0.97C0.03 growth and smooths during subsequent Si growth. In contrast, when Sb is present, the growth front remains smooth throughout the growth. This observation is confirmed by cross-sectional TEM, which reveals that for samples grown without the use of Sb, the Si/Si0.97C0.03 interfaces (Si0.97C0.03 on Si) are much more abrupt than the Si0.97C0.03/Si interfaces. In the case of Sb assisted growth, there is no observable difference in abruptness between the two types of interfaces. Atomic force microscopy micrographs of the Si0.97C0.03 surface reveal features that could be the source of the roughness observed by RHEED and TEM.
Reflection anisotropy spectroscopy, surface photovoltage spectroscopy, and contactless electroreflectance investigation of the InP/In0.53Ga0.47As(001) heterojunction system
Authors: Leibovitch M. , Ram P. , Malikova L. , Pollak Fred H. , Freeouf J. L. , Kronik L. , Mishori B. , Shapira Yoram , Clawson A. R. , Hanson C. M.
Published: July 2002

Using the optical methods of reflection anisotropy spectroscopy, surface photovoltage spectroscopy, and contactless electroreflectance, we have conducted an ex situ investigation of (a) the InP/In0.53Ga0.47As(001) heterojunction interface as a function of InP overlayer thickness (50–1000 nm) and (b) the surfaces of n- and p-doped In0.53Ga0.47As(001). All samples were fabricated by organometallic vapor phase epitaxy. The results from these optical probes make it possible to form a comprehensive quantitative picture of the InP/InGaAs heterojunction, including conduction and valence band offsets of 275 and 325 meV, respectively, as well as the (001) surface of InGaAs (surface Fermi level=200 mV from the conduction band edge).
Characterization of mixed miscible and nonmiscible phospholipid Langmuir–Blodgett films by atomic force microscopy
Authors: Solletti J. M. , Botreau M. , Sommer F. , Duc Tran Minh , Celio M. R.
Published: July 2002

Langmuir–Blodgett (LB) phospholipid films have proved to be efficient models for biological membranes. In order to acquire a better knowledge of the structure of these membranes, LB films of a mixture of miscible and nonmiscible phospholipids were studied by atomic force microscopy (AFM). Mixtures of various compositions were deposited on mica and graphite substrates at various pressures. AFM images showed two coexisting domains corresponding to the nonmiscible (DPPE-DOPE) phospholipids with difference in height of about 0.5 nm due to the structural differences between the two phospholipids. The area ratios between the two types of domains, measured on AFM images, were consistent with the molar fraction and area per molecule at the surface pressure during deposition. We have also reported on the topography of multilayers of nonmiscible mixtures. In conclusion, AFM allowed us to have a better insight into deposition mechanisms and the properties of binary mixtures of phospholipids LB films.
Atomic scale roughness of GaAs(001)2×4 surfaces
Authors: Fan Y. , Karpov I. , Bratina G. , Sorba L. , Gladfelter W. , Franciosi A.
Published: July 2002

The atomic structure and atomic scale roughness of GaAs(001)2×4 surfaces fabricated by molecular beam epitaxy was examined by scanning tunneling and atomic force microscopy. In particular, the size and spatial distribution of atomic steps at the surface was quantitatively determined as a function of annealing time and annealing temperature. Two different parameters are required to fully describe the surface roughness. In general, we found that prolonged annealing under vacuum of surfaces produced by thermal desorption of As cap layers is sufficient to reduce the surface roughness to that typical of as-grown surfaces.
Variable low-temperature scanning tunneling microscopy study of Si(001): Nature of the 2×1→c(2×4) phase transition
Authors: Smith A. R. , Men F. K. , Chao K.-J. , Shih C. K.
Published: July 2002

We have studied the Si(001) surface from 120 K to room temperature using a variable low-temperature scanning tunneling microscope. Complementary investigations were carried out on two distinctly different types of surfaces: first, the normal 2×1 surface and second, the 2×n (4<n<12) surface. For the 2×1 surface, the defects are scattered randomly. By plotting out the fraction of buckled dimers as a function of temperature, we find a slow transition from predominantly c(2×4) at low temperature to mostly 2×1 at room temperature for a defect concentration of about 8.5%. For the 2×n surface, the much larger number of surface vacancies form long-range ordered chains, dividing the surface into many short dimer segments. These dimer segments predominantly appear to be unbuckled at room temperature. Upon cooling to 190 K, we observe very little change in the amount of buckling. The implications of this result are discussed.
Spatial variations in luminescence and carrier relaxation in molecular beam epitaxial grown (InP)2/(GaP)2 quantum wires
Authors: Tang Y. , Rich D. H. , Moy A. M. , Cheng K. Y.
Published: July 2002

Phase separation in III–V semiconductors has led to a unique method for fabricating quantum wires via a strain induced lateral ordering process. Quantum wire (QWR) arrays were formed during the gas source molecular beam epitaxial (MBE) growth of (InP)2/(GaP)2 bilayer superlattices (BSLs) and were studied by time-resolved and linearly polarized cathodoluminescence. Nonlinear optical properties, such as phase-space filling effects, were observed to be indicative of the QWR nature of the samples. Samples prepared by gas source MBE were found to have a greater uniformity, smaller QWRs, and higher optical quality in comparison to those obtained by metal–organic chemical vapor deposition. Misfit dislocations also formed in one of the BSL samples, indicating a partial strain relaxation at the GaAs/InGaP and BSL/InGaP interfaces. The carrier relaxation, transport, and collection in the QWRs were studied with time-resolved cathodoluminescence.
Plasma-assisted formation of low defect density SiC–SiO2 interfaces
Authors: Gölz A. , Lucovsky G. , Koh K. , Wolfe D. , Niimi H. , Kurz H.
Published: July 2002

The initial stages of SiC–SiO2 interface formation by low temperature (300 °C) remote plasma assisted oxidation (RPAO) on flat and vicinal 6H SiC(0001) wafers with Si faces have been studied by on-line Auger electron spectroscopy (AES). Changes in AES spectral features associated with Si–C and Si–O bonds are readily evident as oxidation progresses; however, there are no detectable AES features that can be attributed to C–O bonds. Initial oxidation rates as determined from AES data are greater for vicinal wafers than for flat wafers paralleling results for RPAO oxidation of Si. Devices fabricated on vicinal SiC wafers require an 1150 °C anneal in an H2 containing ambient to reduce defect densities from the 1013 to 1011 cm−2 range, consistent with termination of C atom step edge dangling bonds by H atoms. Devices prepared by thermal oxidation also require a 1150 °C anneal in H2 even though silicon oxycarbide regions with C–O bonds are formed in a transition region at the SiC–SiO2 interfaces.
Local interface composition and extended defect density in ZnSe/GaAs(001) and ZnSe/In0.04Ga0.96As(001) heterojunctions
Authors: Heun S. , Paggel J. J. , Sorba L. , Rubini S. , Franciosi A. , Bonard J.-M. , Ganière J.-D.
Published: July 2002

We have recently shown that in II–VI/III–V heterojunctions and related devices fabricated by molecular beam epitaxy, the II/VI flux ratio employed during the early stages of II–VI growth can be used to control the local interface composition and the band alignment. Here we demonstrate that the local interface composition in pseudomorphic, strained ZnSe/GaAs(001) heterostructures as well as lattice-matched ZnSe/In0.04Ga0.96As(001) heterostructures also have a dramatic effect on the nucleation of native stacking fault defects. Such extended defects have been associated with the early degradation of blue-green lasers. We found, in particular, that Se-rich interfaces consistently exhibited a density of Shockley stacking fault pairs below our detection limit and three to four orders of magnitude lower than those encountered at interfaces fabricated in Zn-rich conditions.
Nanometer table-top proximity x-ray lithography with liquid-target laser-plasma source
Authors: Malmqvist L. , Bogdanov A. L. , Montelius L. , Hertz H. M.
Published: July 2002

A compact laser-plasma proximity x-ray lithography system suitable for laboratory-scale low-volume nanometer patterning is presented. The laser-plasma source, which is based on a fluorocarbon liquid-jet target, generates high-brightness λ=1.2–1.7 nm x-ray emission with only negligible debris production. The Au/SiNx x-ray mask is fabricated by employing ion milling and a high-contrast e-beam resist. With SAL-601 chemically enhanced resist we demonstrate fabrication of high-aspect-ratio, sub-100 nm structures. The exposure time is currently 20 min using a compact 10 Hz, λ=532 nm, 70 mJ/pulse mode-locked Nd:YAG laser. However, the regenerative liquid-jet target is designed for operation with future, e.g., 1000 Hz, lasers resulting in projected exposure times of ∼10 s.
Influences of the [(Ba,Sr)TiO3]-modified RuO2 interface on the dielectric constant and current–voltage characteristics
Authors: Jeon Min-Seok , Choi Duck-Kyun
Published: July 2002

The electrical properties of (Ba,Sr)-TiO3 (BST) thin films on modified RuO2electrodes were investigated. The surfaces of rf magnetron sputtered RuO2 electrode were modified by rf plasma etching,O2 annealing, and overlayer coating of Pt. BST thin films were deposited on the various electrodes at identical conditions. There was no significant influence of the surface roughness on the phase formation and columnar, hillock-free, and dense BST films were obtained in all cases. BST films on different electrodes showed analogous dielectric constant when the effective electrode area was considered in calculation. But the roughened surface having large charge accumulation area is advantageous for carrying larger charge storage capacity. The leakage current of the BST film on RuO2 electrode without any modification at 1.5 V was 5.06×10−5 and it increased to 7.92×10−5 and 1.07×10−4 A/cm2 for the BST films on annealedRuO2and rf plasma etched RuO2, respectively. The BST film on Pt/RuO2/SiO2/Si showed the lowest leakage current of 9.64×10−7 A/cm2. The Schottky barrier height acquired from the temperature dependence of I–V characteristics turned out to be 0.94, 0.79, 0.72, and 1.65 eV for the interface between the BST film and the RuO2 reference, rf plasma etched RuO2, annealedRuO2, and Pt(50 nm)/RuO2.
Effect of etch holes on the mechanical properties of polysilicon
Authors: Sharpe William N. , Vaidyanathan Ranji , Yuan Bin , Bao Gang , Edwards Richard L.
Published: July 2002

For large movable parts in the microelectromechanical systems, etch holes are needed to facilitate the releasing process. These etch holes obviously weaken the structure and affect its mechanical properties. New techniques and structures have been developed to measure the mechanical properties of very thin microelectromechanical systems (MEMS) materials. A dog-bone shaped tensile specimen is imposed with a uniaxial stress field and strain is directly measured on the specimen with the interferometric strain/displacement gage. This testing approach has been used to study the effect of etch holes on the mechanical properties of polysilicon thin film. The material is phosphorus doped, low pressure chemical vapor deposited polysilicon deposited at MCNC the multi-user MEMS processes. The specimen is 3.5 μm thick and 0.6 mm wide at its narrowest point. The etch holes are about 5 μm in diameter and 30 μm apart. Compared with the mechanical properties of the specimens without etch holes, the tensile strength has dropped by 50% and the Young’s modulus decreases only about 18% due to the existence of the etch holes. Finite element modeling is applied to the specimens with etch holes and in agreement with the test results.
Determination of trace metallic impurities on 200-mm silicon wafers by time-of-flight secondary-ion-mass spectroscopy
Authors: Chu Paul K. , Schueler Bruno W. , Reich Fraser , Lindley Patricia M.
Published: July 2002

Surface contamination on silicon wafers is an important issue in integrated circuit fabrication. The concentration of many surface metallic impurities is below the detection limit of total reflection x-ray fluorescence (TXRF). Vapor phase decomposition—atomic absorption spectroscopy (VPD-AAS) cannot reveal the lateral distribution of these impurities even though the detection limits can be as low as 107 atoms/cm2. The time-of-flight secondary-ion-mass spectroscopy (TOF-SIMS) technique can deliver sensitivity close to that by VPD-AAS for many metallic impurities. For example, the detection limits of Fe, Al, Na, and K are 6×108, 3×108, 7×107, and 3×107 atoms/cm2, respectively. In addition, this technique can disclose the lateral distribution of the impurities as well as information on organic contaminants. This article addresses some of the latest development of TOF-SIMS in the determination of surface impurities of 200-mm silicon wafers. When choosing conditions such that the analysis is integrated throughout the native oxide layer, good quantitative correlation with TXRF and VPD-AAS data can be achieved.
Factors affecting two-dimensional dopant profiles obtained by transmission electron microscopy of etched p-n junctions in Si
Authors: Neogi Suneeta S. , Venables David , Na Zhiyong , Maher Dennis M.
Published: July 2002

Transmission electron microscopy (TEM) was used to characterize image contrast obtained from doping-dependent etching of p-n junctions in silicon. The local variations in crystal thickness give rise to the appearance of thickness fringes which may be interpreted as two-dimensional iso-concentration contours that map the dopant distribution. The samples used for the study consisted of solid source diffusions of boron into substrates of varying resistivities of both n- and p-type. The factors which affect the interpretation of dopant profiles obtained from selective chemical etching of cross section TEM samples is addressed. One-dimensional chemical dopant concentration data were derived from secondary ion mass spectroscopy and one-dimensional carrier concentration data were derived from spreading resistance profiling.
Gated Si field emitter array prepared by using anodization
Authors: Higa Katsuya , Nishii Kiyoaki , Asano Tanemasa
Published: July 2002

High aspect-ratio gated field emitter arrays have been fabricated using silicon tip prepared by the anodization of a silicon wafer with periodic n/p junctions. The tips were formed by the preferential growth of porous silicon in p-type material and were transferred to a separate silicon substrate by direct bonding. Gate electrodes were then formed by depositing a WSi2 film over the tips, and apertures were subsequently created by etching with an argon milling process. The resulting gated tip arrays demonstrated field emission, although higher than usual gate voltages were required.
Field emission characteristics of defective diamond films
Authors: Park Kyung Ho , Lee Soonil , Song Kug-Hyun , Park Jung Il , Park Kwang Ja , Han Seok-Yoon , Na Seong Jun , Lee Nam-Yang , Koh Ken Ha
Published: July 2002

We have studied the field emission characteristics of defective diamond films grown by microwave plasma enhanced chemical vapor deposition. X-ray diffraction, Raman spectroscopy, scanning electron microscopy, atomic force microscopy, and the reflectance measurements have revealed the poor crystal quality and/or small grain sizes of the diamond phase and the inclusion of the non-diamond carbon phases in these films. The degrees of the film defectiveness have been found to depend on the methane concentration. Current-versus-voltage measurements have demonstrated that the defective diamond films have good electron emission characteristics, and, moreover, that the emission characteristics depend on the methane concentration. The observed correlation between the degrees of film defectiveness and the emission characteristics strongly suggests the defect-related electron-emission mechanism. In this study, the lower limits of the field emission current densities, estimated by averaging the total measured emission currents over the entire sample areas, of 1 μA/cm2 and 1 mA/cm2 have been measured at electric fields as low as 4.5 and 7.6 V/μm, respectively. We have also examined the reproducibility, the uniformity, and the stability of emission currents.
Emission characteristics of ZrN thin film field emitter array fabricated by ion beam assisted deposition technique
Authors: Nagao M. , Fujimori Y. , Gotoh Y. , Tsuji H. , Ishikawa J.
Published: July 2002

ZrN thin film field emitter arrays were fabricated by the ion beam assisted deposition technique. The work function of ZrN is controlled by the selection of the deposition parameters. We investigated the relationship between the work function and the emission stability, and the influence of the ambient gas on the emission stability by introducing the gases of N2 and O2 into the measurement chamber. It was found that the emission stability depended on the work function: the emitters with a lower work function were more stable than those with a higher work function. The dependence is explained qualitatively by the analysis of the Fowler–Nordheim equation. Emission noise increased with the increase of the ambient gas pressure. However, difference in the increase of noise between N2 gas and O2 gas was seen. O2 gas severely affected the emission stability of the ZrN emitter.
Nanostructured integrated electron source
Authors: Schoessler C. , Koops H. W. P.
Published: July 2002

Additive nanolithography with electron-beam induced deposition is applied to generate a nanostructured integrated field emission electron source. The source is built into a lithographically fabricated pattern of connecting lines on a chip. Current stabilizing resistors are integrated in to the connecting lines with the deposition technique. Field emission microscope investigation of deposited supertips proves that a confined emission is delivered from conducting tips into a beam divergence angle of ±7°. The reduced brightness of the deposited supertips is evaluated. A tenfold higher reduced brightness is observed if compared to conventional Schottky field emitters.
Si growth on partially relaxed Ge islands
Authors: Sutter P. , Mateeva E. , Lagally M. G.
Published: July 2002

We use low-energy electron microscopy (LEEM) to study Si growth on {105} faceted Ge islands on Si (100). A quantitative analysis of LEEM growth sequences suggests, that for low Si coverage no growth occurs at the island apex, and that adatoms in the apex region are collected onto the {105} side facets. This “partial wetting” growth mode leads to a characteristic formation of a large (100) plane bounding the top of the islands. We find Ge surface segregation on the {105} facets to play an important role in the overgrowth process: Ge/Si intermixing leads to a stabilization of the facet structure over a large range of Si coverage and results in a shape of buried islands mapping their morphology during overgrowth: a truncated pyramid, bounded on top by a (100) plane.
State of the art of 3C-SiC/silicon on insulators
Authors: Camassel J.
Published: July 2002

The state of the art of 3C-SiC deposited on various silicon on insulator substrates is reviewed and the result of structural (x-ray and transmission electron microscope) properties as well as micro-Raman, infrared, and electrical examinations is compared with 3C-SiC/Si. It is shown that in order to fully optimize this novel material system one has to call at the same time for a better thermal stability of the current oxides and for an optimized elastic compliance of the buried layer system silicon/silicon dioxide. A proper way seems to lower the standard SiC deposition temperature.
Modification of quantum dot properties via surface exchange and annealing: Substrate temperature effects
Authors: Shen Jeng-Jung , Brown April S. , Metzger Robert A. , Sievers Barry , Bottomley Lawrence , Eckert Patrick , Carter W. Brent
Published: July 2002

Increasingly, self-assembled quantum dots produced by the Stranski–Krastanov growth mode during molecular beam epitaxy are being used for both photonic and electronic devices. In order to fully realize the potential of these nanostructures, control of both the quantum dot size and the density distributions is very important. In addition, the ability to tune the confined energy states will enhance the ability to exploit these nanostructures. Herein, we report on the structural modifications induced by annealing dots under dissimilar anion fluxes. Such strain and chemical tuning enabled by annealing can be used as a means of further controlling quantum dots properties.
Damage-free cleaning of Si(001) using glancing-angle ion bombardment
Authors: Labanda Jose Gregorio C. , Barnett Scott A. , Hultman L.
Published: July 2002

The effects of glancing-angle argon ion bombardment on air-contaminated Si(001) surfaces were studied. Bombarding at substrate temperature Ts=730 °C, impingement angle φ=3–15° relative to the surface plane, ion energy E=1 keV and dose D=3×1015 ions cm−2 gave high-quality reflection high energy electron diffraction (RHEED) patterns and contaminant-free surfaces as observed by ion scattering spectroscopy. Atomic force microscopy images showed roughness value ⩽0.5 nm under these conditions, but the roughness increased and RHEED patterns became spotty for higher doses or energies. Secco etching of samples bombarded at Ts=730 °C showed etch pits with a density of 106–107 cm−2 that increased with increasing D and E. Room-temperature bombardment with E=1 keV, D=3×1015 ions cm−2 and φ=3°, followed by a 730 °C anneal, yielded a lowest roughness value of 0.2 nm. Secco etching showed no resolvable pits, indicating a dislocation density <4×104 cm−2.
Evidence of depth and lateral diffusion of defects during focused ion beam implantation
Authors: Vieu C. , Gierak J. , Schneider M. , Ben Assayag G. , Marzin J. Y.
Published: July 2002

We have investigated the evolution of the photoluminescence intensity of different GaAs/GaAlAs quantum wells to probe the defect penetration during focused ion beam implantation at various sample temperatures. By implanting homogeneous areas, it was possible to evaluate the depth extension of the ion-induced damage, while by localizing the implantation at a submicrometric length scale, it was also possible to quantify the lateral damage extension. Both the depth and lateral damage extensions are found to be reduced when the sample temperature is changed from 300 to 80 K. This result is used to demonstrate that a fast diffusion of nonequilibrium defects is taking place in the irradiated sample. It is found that this diffusion is highly anisotropic with a lateral diffusion length ten times higher than the depth one, suggesting that the defects easily diffuse in the GaAlAs barrier layers. The results are interpreted as a manifestation of a radiation enhanced diffusion mechanism. The advantage of using low temperature irradiations to better localize the injected defects by focused ion beam is highlighted, specially for quantum nanostructure fabrication.
Heterointerface dipoles: Applications to (a) Si–SiO2, (b) nitrided Si–N–SiO2, and (c) SiC–SiO2 interfaces
Authors: Lucovsky G. , Yang H. , Massoud H. Z.
Published: July 2002

This article identifies procedures to calculate charge-transfer dipoles at semiconductor–dielectric interfaces, focusing primarily on the Si–SiO2 system. Since SiO2 is more polar than Si, there is a transfer of electrons from Si to SiO2 to balance the difference in chemical potentials creating a dipole localized at the semiconductor–dielectric interface. This dipole increases the conduction-band offset energy difference between Si and SiO2, and therefore, has important effects on interface electrical and optical properties. Empirical chemistry and ab initio methods have been applied to molecular clusters which emulate the interface bonding, and have been used to calculate interfacial charge transfer at (i) abrupt Si–SiO2 interfaces and (ii) nitrided Si–N–SiO2 interfaces. Additional calculations have applied to determine the average dipoles at Si–SiO2 interfaces with suboxide bonding in excess of the monolayer level required to form an ideal interface. The calculations support experimental data that indicate that the effective conduction-band offset energies at nitrided Si–N–SiO2 interfaces and at interfaces with minimized suboxide bonding are essentially the same. Finally, the calculations have been extended to SiC–SiO2 interfaces to illustrate the effects of changing from a homopolar to a more ionic or heteropolar semiconductor.
Influence of carbon on the electrical properties of W/SiGeC-p/Si(100)-p Schottky diodes
Authors: Serpentini M. , Brémond G. , Aubry-Fortuna V. , Meyer F. , Mamor M.
Published: July 2002

In this work, the electrical influence of carbon on W/SiGeC-p/Si(100)-p Schottky diodes is investigated. Analyzed samples consist of fully strained SiGe and SiGeC layers grown by room temperature chemical vapor deposition, deep level transient spectroscopy, (DLTS), I–V, C–V, and secondary ion mass spectroscopy measurements have been carried out. These experiments have shown that carbon incorporation leads to a full depletion of the epitaxial layer. In order to explain this phenomenon, we propose two assumptions: (1) electrical compensation of the active dopant due to a bulk defect, (2) important charge trapping mechanism at the interfaces. Three groups of defects have been detected by DLTS. Their binding energies are respectively 0.21, 0.36 and 0.62 eV above the valence band. Considering the possible origin of these defects, the hypothesises proposed before are discussed.
Dry etching of copper film with hexafluoroacetylacetone via oxidation process
Authors: Kang Sang-Woo , Kim Hyo-Uk , Rhee Shi-Woo
Published: July 2002

Dry etching of Cu film was achieved via oxidation process using oxidizing agents such as O2 plasma, O3, or O3 plasma, followed by the removal process of the copper oxides (CuOx) by reaction with hexafluoroacetylacetone [H(hfac)] to form volatile copper compound, [bis-hexafluoroacetylacetonate: Cu(hfac)2] and H2O. The etching rate was increased with the increase of etchant [H(hfac) and O3] flow rate, plasma power, and substrate temperature. Oxygen radical concentration is the highest in the plasma generated with ozone, which leads to the highest etching rate up to 1400 Å/min. The etch rate dependence on the substrate temperature showed the activation energy of about 7 kcal/mol and gas phase transport seems to be the rate controlling step.
B implantation in 6H–SiC: Lattice damage recovery and implant activation upon high-temperature annealing
Authors: Valcheva E. , Paskova T. , Ivanov I. G. , Yakimova R. , Wahab Q. , Savage S. , Nordell N. , Harris C. I.
Published: July 2002

Implantation of B into n-type 6H–SiC has been investigated. B ion implantation was performed in n-type 6H–SiC single crystals at room temperature and 500 °C. The implanted specimens were annealed at 1700 °C in SiH4 atmosphere. Lattice damage induced by implantation and its recovery was characterized by Raman scattering. The net boron concentration and the amount of damage created were predicted by TRIM simulations. The redistribution of the implanted atoms during high-temperature annealing was obtained by simulation of the diffusion process. Capacitance–voltage characteristics of Ni/6H–SiC Schottky barrier were numerically simulated assuming different boron incorporation lattice sites. The degree of p-type activation of B ions after annealing at 1700 °C was estimated to be in the range of 8%–15%. A compensation ratio of about 48% was determined. The conductivity type was not converted from n to p type. The comparison between the experimentally obtained dopant concentrations and those predicted by simulations shows that the concentration of the electrically active acceptors is affected by outdiffusion of B due to the high annealing temperature of 1700 °C. Reduced damage compared with other ions implantation was observed. Recrystallization of the implanted material and absence of amorphous phases were detected after high-temperature annealing.
GaP(001) and InP(001): Reflectance anisotropy and surface geometry
Authors: Esser N. , Schmidt W. G. , Bernholc J. , Frisch A. M. , Vogt P. , Zorn M. , Pristovsek M. , Richter W. , Bechstedt F. , Hannappel Th. , Visbeck S.
Published: July 2002

We have investigated the optical anisotropy of GaP(001) and InP(001) surfaces. The samples were prepared by homoepitaxial metalorganic vapor phase epitaxy growth and either directly transferred into ultrahigh vacuum (UHV) or in situ capped and, after transfer, decapped in UHV by thermal desorption of a P/As capping layer. Symmetry, composition, and surface optical anisotropy were characterized by low-energy electron diffraction, Auger electron spectroscopy, and reflectance anisotropy spectroscopy. We observe (2×1)/(2×2)-like reconstructions for the very P-rich and (2×4) reconstructions for the more cation-rich surfaces. No (4×2) reconstruction could be prepared, independent of the preparation method. A comparison of the reflectance anisotropy between GaP(001) and InP(001) surfaces shows similar line shapes for the very cation-rich (2×4) surfaces. For less cation-rich surfaces, however, we observe distinct differences between the spectra of the two systems. In both cases, different line shapes in the reflection anisotropy spectra occur for the (2×4) periodicity, suggesting the existence of different (2×4) geometries. The experimental results are discussed on the background of atomic structures, total energies and reflectance anisotropy spectra obtained ab initio from density-functional theory local-density approximation calculations.
Constraint theory and defect densities at (nanometer SiO2-based dielectric)/Si interfaces
Authors: Phillips J. C.
Published: July 2002

Native SiO2 passivating films grown thermally on flat Si(100) surfaces exhibit many ideal properties that justify regarding them as well-defined (albeit noncrystalline) phases with a continuous and almost defect-free interface with the Si substrate in spite of a large difference in density. Global constraint theory explains this remarkable situation without recourse to elaborate mathematical or geometrical local models, and it correctly predicts the scaling dependence of defect densities in films doped with N and H with essentially no adjustable parameters.
Comparison of nanomachined III–V semiconductor substrates
Authors: Grazulis L. , Kelly D. L. , Walker D. E. , Tomich D. H. , Eyink K. G. , Lampert W. V.
Published: July 2002

Emerging device applications demand surface features on the order of hundreds of angstroms. Nanolithography by machining with a diamond tip is proposed as a means to reproducibly pattern semiconductor surfaces on this scale. This technique has already been shown to produce controlled features with depths down to 10 Å on GaAs [S. H. Goss et al., J. Vac. Sci. Technol. B 16, 1439 (1998)]. In this technique, a diamond tip is scanned along the sample surface with a constant force to produce the desired features. In this article we show the observed quality and reproducibility achieved by this technique in the patterning of several semiconductor substrates. The substrates patterned and examined include GaAs, GaSb, GaP, and InP. The samples were machined at a series of loads ranging from 9.8 to 196 μN. After machining they were cleaned with an appropriate solvent and supercritical CO2 to remove debris caused by the machining. The resulting patterned surfaces were characterized with an atomic force microscope. Lateral resolutions as good as 100 Å were successfully achieved illustrating the ability of this technique to achieve the dimensions required to form quantum dots. Line profiles indicated cut depths ranging from 5 to 500 Å. A near linear trend was observed in the depth of cut versus applied force over the investigated range for most of the substrates. The exact slope and intercepts were material dependent.
Image formation in extreme ultraviolet lithography and numerical aperture effects
Authors: Bollepalli Srinivas B. , Khan M. , Cerrina Franco
Published: July 2002

The problem of image formation in extreme ultraviolet lithography from the mask to the wafer is studied by physical modeling along with computer simulations. The reflective properties of multilayer mirrors and some of the demands that they impose upon the optical system design for accurate replication of mask patterns is discussed. Numerical aperture size effects in relation to the critical dimension at the wafer is presented along with several illustrative examples.
Fabrication techniques for grating-based optical devices
Authors: Lim Michael H. , Murphy T. E. , Ferrera J. , Damask J. N. , Smith Henry I.
Published: July 2002

We describe a novel, versatile process for fabricating integrated Bragg-grating devices. Our process addresses many of the critical challenges presented by such devices, including period selection, alignment, spatial coherence, and nanolithography. Using a combination of e-beam, x-ray, optical, and interference lithographies, we have successfully employed this process to construct 244 nm period, quarter-wave-shifted Bragg gratings on top of 1-μm-tall waveguide structures in InP.
Influence of growth temperature of InAsP/InP strained multiple quantum wells grown by metalorganic chemical vapor deposition
Authors: Lee Chong-Yi , Shiao Hung-Pin , Wu Meng-Chyi , Chen Chyuan-Wei
Published: July 2002

In this article, we report the influence of growth temperature on the luminescent and structural properties of InAsyP1−y/InP strained multiple quantum wells (SMQWs) and strained single quantum wells (SSQWs) grown by metalorganic chemical vapor deposition (MOCVD). The strained quantum wells are characterized by high-resolution transmission electron microscope (TEM), photoluminescence (PL), and double-crystal x-ray diffraction (DC-XRD). An AsH3/(AsH3+PH3) gas flow ratio of 0.50% and 1.48% at 580 and 650 °C growth temperatures, respectively, will result in an InAsP layer with y=0.3 solid composition. The experimental PL emission energies at 10 K at different well thicknesses for the InAsyP1−y/InP SSQWs grown at 580 and 650 °C are in well agreement with the trend of the calculated curves. The TEM lattice image of an InAsP/InP SSQW grown at 580 °C on the order of two monolayers has been demonstrated. The InAsP/InP SSQW structure grown at 580 °C appears to be extremely abrupt, uniform, free of misfit dislocations, and narrow PL linewidth. Besides, the growth of InAsP/InP SMQWs at 580 °C maintains its structural integrity throughout the deposition sequence with smooth interface and well-defined periodicity. However, the InAsP/InP SSQWs or SMQWs exhibit an adverse property at 650 °C growth temperature. From the above results, the lower growth temperature is necessary for the InAsP/InP SMQW growth by MOCVD.
Evaluating probes for “electrical” atomic force microscopy
Authors: Trenkler T. , Hantschel T. , Stephenson R. , De Wolf P. , Vandervorst W. , Hellemans L. , Malavé A. , Büchel D. , Oesterschulze E. , Kulisch W. , Niedermann P. , Sulzbach T. , Ohlsson O.
Published: July 2002

The availability of very sharp, wear-proof, electrically conductive probes is one crucial issue for conductive atomic force microscopy (AFM) techniques such as scanning capacitance microscopy, scanning spreading resistance microscopy, and nanopotentiometry. The purpose of this systematic study is to give an overview of the existing probes and to evaluate their performance for the electrical techniques with emphasis on applications on Si at high contact forces. The suitability of the characterized probes has been demonstrated by applying conductive AFM techniques to test structures and state-of-the-art semiconductor devices. Two classes of probes were examined geometrically and electrically: Si sensors with a conductive coating and integrated pyramidal tips made of metal or diamond. Structural information about the conductive materials was obtained by electron microscopy and other analytical tools. Swift and nondestructive procedures to characterize the geometrical and electrical properties of the probes prior to the actual AFM experiment have been developed. Existing contact models have been used to explain variations in the electrical performance of the conductive probes.
Improvement of AlAs–GaAs interface roughness grown with high As overpressures
Authors: Wohlert D. E. , Chang K. L. , Lin H. C. , Hsieh K. C. , Cheng K. Y.
Published: July 2002

The interface when switching from AlAs to GaAs during solid source molecular-beam epitaxial growth is investigated. The growth conditions for the AlAs layers were kept constant except for the As overpressure. Using a valved As cracker cell, we varied the V/III flux ratio from ∼5.0 to ∼25.0. Cross-sectional transmission electron microscopy, photoluminescence spectroscopy, and reflectivity measurements from distributed Bragg reflectors indicate that the material quality tends to improve with increasing dimeric As overpressure. Using secondary ion mass spectroscopy, it is shown that the rough interfaces are due to oxygen accumulation at the AlAs growth front. It is believed that arsenic forms an oxide with the oxygen on the AlAs surface, which is subsequently desorbed away at typical growth temperatures. For samples grown at higher overpressures, there is more arsenic present to remove the oxygen thereby resulting in a smoother interface
Optical Control of Electrons During Electron Transfer
Authors: Martini Ignacio B. , Barthel Erik R. , Schwartz Benjamin J.
Published: July 2002

The dynamics of electron transfer reactions in solution can be controlled with the use of a sequence of femtosecond laser pulses. In the charge transfer to solvent (CTTS) reaction of sodide (Na
−
) in tetrahydrofuran, an initial light pulse launched the CTTS reaction, ejecting an electron into either an immediate or a solvent-separated Na
0
:solvated electron contact pair. A second pulse was used to excite the electrons in the contact pairs, and a third pulse monitored the amount of Na
−
produced through the back electron transfer. Excitation of the electrons in immediate contact pairs shut off the back electron transfer, whereas excitation of the electrons in solvent-separated pairs both enhanced and hindered the back electron transfer.
Time-Resolved Measurement of Dissipation-Induced Decoherence in a Josephson Junction
Authors: Han Siyuan , Yu Yang , Chu Xi , Chu Shih-I , Wang Zhen
Published: July 2002

We determined the dissipation-induced decoherence time (DIDT) of a superconducting Josephson tunnel junction by time-resolved measurements of its escape dynamics. Double-exponential behavior of the time-dependent escape probability was observed, suggesting the occurrence of a two-level decay-tunneling process in which energy relaxation from the excited to the ground level significantly affects the escape dynamics of the system. The observation of temporal double-exponential dependence enables direct measurements of the DIDT, a property critical to the study of quantum dynamics and the realization of macroscopic quantum coherence and quantum computing. We found that the DIDT was τ
d
> 11 μs at
T
= 0.55 K, demonstrating good prospects for implementing quantum computing with Josephson devices.
The 110% Solution
Authors: Voss David
Published: July 2002

In a Nota Bene item, Voss discusses results recently reported in
Physical Review Letters
in which lasers were used to initiate crystallization of a supersaturated solution. Earlier such observations were the results of photochemical changes, but the latest findings indicate a purely nonchemical, photophysical alignment and clustering of molecules as the trigger.