bluuebunny/crossref_metadata_2025 huggingface dataset:
Translationally hot neutrals in etching discharges
Authors: Sommerer Timothy J. , Kushner Mark J.
Published: July 2002

The presence and influence of translationally energetic ions in low-pressure etching discharges is well known. Neutral atoms and molecules, though known to be chemically reactive, are not generally considered to be otherwise activated in these plasmas. Neutral species may, however, become translationally hot through either charge exchange collisions or by dissociative excitation caused by electron impact. These species are important in etching discharges because they may bring an isotropic source of activation energy to the substrate which may compromise anisotropic etching mechanisms. In this paper we present a theoretical study of the sources and effects of translationally hot neutral atoms and molecules in CF4 etching plasmas. We find that ballistically hot F atoms comprise a significant fraction of the radical flux striking the substrate at pressures of <100 mTorr. In CF4 plasmas, the maximum flux of translationally hot F incident on the substrate of a parallel-plate rf etching discharge occurs between 10 and 100 mTorr. At these pressures the hot atom and ion fluxes to the substrate are comparable. The effects of translationally hot species on gas-phase plasma chemistry and surface reactions are discussed.
A non-Fickian diffusion equation
Authors: Das Amal K.
Published: July 2002

A non-Fickian diffusion equation, which differs from the usual (Fickian) diffusion equation by having an additional, second-order derivative term in time, is considered to describe the dynamics of a Brownian particle. Some useful perspectives on this generalized diffusion equation are presented, particularly with respect to the effect of a potential field. Two quantities of physical interest, namely the mean square displacement and the particle flux at an absorbing boundary, are considered in the process of a comparative study of the two diffusion equations. We also discuss the applicability of the non-Fickian diffusion equation to some systems of physical and practical interest.
Low-temperature C-V characteristics of Si-doped Al0.3Ga0.7As and normal n-GaAs/N-Al0.3Ga0.7As isotype heterojunctions grown via molecular beam epitaxy
Authors: Kim Dojin , Madhukar Anupam
Published: July 2002

C-V measurements on normal isotype GaAs/Al0.3Ga0.7As heterojunctions grown via molecular beam epitaxy were undertaken in the temperature ranges between 300 and 4.2 K. For temperatures ≤100 K, we found a persistent conductivity effect due to the field emitted and then capture delayed electrons in the Si-doped Al0.3Ga0.7As layer. These capture-delayed free carriers lead to apparent increase of the base doping in the AlGaAs and consequent reappearance of the valley in the concentration-versus-distance profiles of the heterojunctions at temperatures ≤100 K. The resultant temperature dependence of the calculated conduction-band offsets and the interface-state densities were found to be an artefact. Apparent shifting of the heterointerface positions observed in inverted heterojunctions was not observed in the normal GaAs/AlGaAs heterojunctions. The normal heterostructure enabled us to distinguish and determine the concentration of each deep donor level.
Ferromagnetic and antiferromagnetic exchange coupling in ultrathin Fe(001)/Pd(001)/Fe(001) structures
Authors: Celinski Z. , Heinrich B. , Cochran J. F.
Published: July 2002

A new phase of fcc Pd with an expanded lattice (5%) was grown on Fe(001). This structure is maintained up to 12 monolayers (ML) of Pd and then it undergoes a complex lattice reconstruction. Ultrathin Fe/Pd, Pd/Fe bilayers, and Fe/Pd/Fe trilayers with Pd thicknesses between 4 and 18 ML were studied using ferromagnetic resonance and Brillouin light scattering. The metallic Pd and particularly its lattice-expanded structure is believed to have a strong tendency to become ferromagnetic. This tendency was observed in Fe/Pd/Fe trilayers with Pd thicknesses less than 6 ML. The exchange coupling remains ferromagnetic up to 12 ML of Pd and then it changes to a weak antiferromagnetic coupling. The exchange coupling in the ferromagnetic region exhibits a distinct oscillatory behavior superimposed on a decreasing background.
Inspection of transparent polymers by photothermal detection of ultraviolet-laser generated thermal waves
Authors: Eickmeier Achim , Bahners Thomas , Schollmeyer Eckhard
Published: July 2002

The concept of photothermal wave imaging has been adapted to the nondestructive inspection of transparent polymeric samples by specific generation of thermal waves. Utilization of light sources according to the absorption properties of the material secured pure surface heating which is necessary for sensible measurements. Thickness profiles of thin films made of poly(ethylene terephthalate), which are transparent in the visible spectrum, could be measured using a pulsed KrF laser. Examples for the nondestructive inspection of complex textile samples such as coated fabrics are presented.The photothermal analysis (PTA) of optically generated thermal waves is a powerful tool for nondestructive, contactless inspection and evaluation of intrinsic properties of a sample.1,2 The method has been used for the observation of dynamic processes in adhesives, for the inspection of coatings on metal and of carbon fiber composites. A modulated light source, e.g., a chopped HeNe- or Ar+ laser, is used for local, modulated heating at the sample’s surface resulting in a time- and space-dependent temperature modulation which propagates through the material. In the case of a homogeneous layer heated only in a small volume at the surface the solution of the heat diffusion equation gives a heavily damped thermal wave T(x,y,z;t). In a one-dimensional model3 only the direction z perpendicular to the surface is considered and we obtain
Ga adatom incorporation kinetics at steps on vicinal GaAs (001) surfaces during growth of GaAs by molecular beam epitaxy
Authors: Shitara T. , Zhang J. , Neave J. H. , Joyce B. A.
Published: July 2002

We have systematically examined the transition from two-dimensional nucleation to step-flow growth on variously misoriented vicinal GaAs (001) surfaces during molecular beam epitaxy using reflection high-energy electron diffraction (RHEED). The time to the first maximum of the RHEED intensity oscillations is gradually delayed as the growth mode transition temperature is approached from below as the result of an increasing number of adatoms being incorporated at steps. Detailed analysis of this delay has shown that the incorporation rate is independent of the Ga flux, but it is strongly dependent on the direction of misorientation. This means that step edges do not act as perfect sinks for adatoms, but that detachment can occur relatively easily. The energy barrier for incorporation is considerably higher for Ga- than As-terminated steps, which strongly suggests that the anisotropic growth mode transition on GaAs (001) stems mainly from the different step structures rather than anisotropic Ga adatom migration.
Nondestructive determination of damage depth profiles in ion-implanted semiconductors by spectroscopic ellipsometry using different optical models
Authors: Fried M. , Lohner T. , Aarnink W. A. M. , Hanekamp L. J. , van Silfhout A.
Published: July 2002

A several-parameter fitting of spectroscopic ellipsometry data is developed to characterize near-surface layers in semiconductors damaged by implantation. The damage depth profiles are described by either rectangular, trapezoid-type, or coupled half-Gaussian (realistic) optical models. The rectangular model has three parameters: the average damage level, the effective thickness of the implanted layer, and the thickness of the native oxide. The trapezoid-type model is enhanced with a fourth parameter, the width of the amorphous/crystalline interface. The realistic optical model consists of a stack of layers with fixed and equal thicknesses. The damage levels are determined by a depth profile function (presently coupled half-Gaussians). Five parameters are used: the position of the maximum, the height, and two standard deviations of the profile, plus the thickness of the native oxide. The complex refractive index of each layer is calculated from the actual damage level by the Bruggeman effective medium approximation. The optical models were tested on Ge-implanted silicon samples and cross checked with high-depth-resolution Rutherford backscattering spectrometry and channeling.
Exchange effect in coupled one-dimensional electron-gas systems
Authors: Wu Zhiqiang , Ruden P. Paul
Published: July 2002

An exchange effect in one-dimensional quantum-wire electron-gas systems is investigated. The theoretical study presented shows that the electron population of a symmetrical structure consisting of two parallel quantum wires in close proximity may exhibit bistability with all electrons contained in one of the quantum wires. Compared to a similar effect in a two-dimensional system reported earlier, the excitation energy associated with the transfer of one electron is found to be much larger. For certain configurations, this energy can be as large as ∼50 meV. The theory predicts the exchange-induced bistability to exist in realistic configurations, and it may possibly be used in practical electronic devices such as memory elements.
Experimental investigation and simulation of Sb diffusion in Si
Authors: Solmi S. , Baruffaldi F. , Derdour M.
Published: July 2002

An extensive investigation on the diffusion and precipitation of Sb implanted in Si has been carried out. The rapid epitaxial regrowth of the amorphous layer produced by the incident ions brings Sb atoms into a substitutional position up to a concentration threshold of about 3.5 × 1020 cm−3. This high supersaturation (the solubility of Sb in Si is about 2 × 1019 cm−3 at 1000 °C) and the low value of the surface free energy facilitate the nucleation of precipitates, which form and grow in concomitance with the diffusion during the annealing. The kinetics of the precipitation has been investigated at 800, 900, and 1000 °C with isothermal treatments ranging between 3 min and 341 h. The experimental data have been compared with the results of a simulation program that takes into account the precipitation phenomena. Good agreement has been obtained for all the investigated experimental conditions both for total and carrier distributions. The model represents a significant improvement of the simulation of Sb diffusion in silicon; in fact, the more commonly used process codes are inadequate to correctly foresee the dopant distribution in supersaturated conditions.
Defect-induced redistribution of Fe- or Ti-implanted and annealed GaAs, InAs, GaP, and InP
Authors: Ullrich H. , Knecht A. , Bimberg D. , Kräutle H. , Schlaak W.
Published: July 2002

The structural properties of GaAs, InAs, GaP, and InP implanted by Fe or Ti at 150 keV/400 keV and doses of 1012–1×1015 cm−2 and the depth distribution of the implants are comparatively studied before and after annealing with and without a Si3N4 cap. Results of Rutherford backscattering, x-ray double-crystal diffractometry, and secondary-ion mass spectroscopy experiments are presented. Fe redistributes strongly in all materials upon annealing, Ti does not redistribute at all. The driving force of redistribution of Fe is not classical diffusion but reaction with implantation-induced defects and stoichiometric imbalances. The actual defect chemistry of the as-implanted arsenides is found to be fundamentally different from the as-implanted phosphides since in the latter case the mass ratio of the constituents is much larger and the specific energy for amorphization is much lower. Consequently, redistribution of Fe in the phosphides and the arsenides differs qualitatively from each other.
Complete characterization of transport parameters in semiconductor substrates through lateral bipolar transistor measurements
Authors: Misiakos Konstantinos , Tsoi Elisabeth , Neugroschel Arnost
Published: July 2002

A method is proposed for a thorough characterization of semiconductor substrates in terms of transport and recombination parameters. The method is based on exploiting the fundamentally simple geometry of a lateral bipolar transistor in low injection. Accurate two-dimensional numerical solutions of the continuity equation show how the collector current depends on geometry elements and recombination parameters. In addition to the steady-state analysis, the frequency dependence of the collector current was determined for a more direct assessment of the bulk and surface recombination. The theoretical results were experimentally demonstrated by measuring the surface recombination velocity and bulk lifetime in a silicon wafer.
Silicon dioxide films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition
Authors: Andosca R. G. , Varhue W. J. , Adams E.
Published: July 2002

Thin films of silicon dioxide were deposited at low substrate temperatures (<375 °C) using electron cyclotron resonance plasma enhanced chemical vapor deposition. The deposition parameters studied included substrate temperature and radio frequency substrate bias. The deposited material was compared to thermally grown SiO2, through its etch rate in a buffered hydrofluoric solution, index of refraction, Fourier transform infrared spectroscopy, and Rutherford backscattering spectrometry. Through the application of rf substrate bias the deposited material properties approached that of thermally grown oxide. The feed to the substrate chamber was 40 sccm of a 2.0% silane in He. The large quantity of He in the chamber is credited with making the material more thermal-like.
Deposition of hydrogenated amorphous silicon by an inductively coupled glow discharge reactor with shield electrodes
Authors: Yokota Katsuhiro , Takada Manabu , Ohno Yoshikazu , Katayama Saichi
Published: July 2002

A plasma was produced using an inductively coupled glow discharge method in which electrodes connected to earth were located in the neighborhood of both sides of the rf working coil. The plasma did not vary according to the position of the substrates. The deposition rate and the electrical property of grown hydrogenated amorphous silicon (a-Si:H) films, however, depended on the position of the substrate. This was due to the fact that the concentration of H varied much more with position than the concentration of a-Si:H film precursors as the large H flux removes Si atoms from the a-Si:H film surface [F. J. Kampas, J. Appl. Phys. 53, 6408 (1982)].
Effects of abrupt and graded a-Si:C:H/a-Si:H interface on internal properties and external characteristics of p-i-n a-Si:H solar cells
Authors: Smole F. , Furlan J.
Published: July 2002

Using a computer simulation, the effects of abrupt and graded a-Si:C:H/a-Si:H interfaces on the performance of a-Si:H p-i-n solar cells are discussed. It is shown that structures with graded heterojunction transitions possess much lower recombination near the junction and a higher accelerating built-in electric field in the i layer, both of which increase the open-circuit voltage and improve the solar cell fill factor.
Raman investigation with excitation of various wavelength lasers on porous silicon
Authors: Zhang Shu-Lin , Hou Yongtian , Ho Kuok-San , Qian Bidong , Cai Shengmin
Published: July 2002

By varying the incident laser wavelength, the intrinsic Raman spectrum of porous silicon formed on nondegenerate p-type silicon is identified and used to determine the dependence of the average pore size and porosity on the depth of the porous silicon layer. It is found that with increasing layer depth, the average pore size and porosity decreases, which is contrary to that of porous silicon formed on degenerate n-type silicon. This may indicate a different formation mechanism for these two types of porous silicon.
A surface kinetics model for the growth of Si1−xGex films from SiH4/GeH4 mixtures
Authors: Russell N. M. , Breiland W. G.
Published: July 2002

A model has been developed that semiquantitatively describes the kinetics of Si1−xGex alloy deposition over a wide range of temperatures in the absence of gas-phase chemistry. The salient feature of the model is that the kinetics of germane and silane deposition are treated as parallel processes, each with an adsorption step in series with a hydrogen desorption step. The two processes are coupled by competition for sites in the adsorption process, and fast equilibration between silicon and germanium hydride on the surface. The model is fit to, and compared with, data available in the recent literature.
The effects of ion implantation on the interdiffusion coefficients in InxGa1−xAs/GaAs quantum well structures
Authors: Bradley I. V. , Gillin W. P. , Homewood K. P. , Webb R. P.
Published: July 2002

Photoluminescence coupled with repetitive thermal annealing has been used to determine the diffusion coefficients for intermixing in InxGa1−xAs/GaAs quantum wells and to study the subsequent effects of ion implantation on the intermixing. It is shown that following ion implantation there is a very fast interdiffusion process, which is independent of the implanted ion and that is thought to be due to the rapid diffusion of interstitials created during the implantation. Following this rapid process, it was found that neither gallium nor krypton ions had any effect on the subsequent interdiffusion coefficient. Following arsenic implantation in addition to the initial damage related process, an enhanced region of interdiffusion was observed with a diffusion coefficient that was an order of magnitude greater than that of an unimplanted control wafer. This enhanced process is thought to be due to the creation of group III vacancies by the arsenic atoms moving onto group V lattice sites. This fast process was present until the structure had broadened by about 75 Å when the diffusion coefficient returned to the unimplanted control value. The activation energy for the interdiffusion was measured over the temperature range 1050–750°C and a value of 3.7±0.1 eV was measured. This was found to be independent of the implanted ion.
Hydrogen diffusion and acceptor passivation in p-type GaAs
Authors: Rahbi R. , Pajot B. , Chevallier J. , Marbeuf A. , Logan R. C. , Gavand M.
Published: July 2002

Deuterium diffusion profiles in GaAs doped with different acceptors of group II (Mg,Zn,Cd) or group IV (C,Ge) have similar characteristics even though the neutralization of acceptors measured at 300 K is not always efficient. Conductivity and Hall measurements have been used to study the electrical characteristics of hydrogenated p-type GaAs epilayers. The temperature dependence of the free-carrier concentration and hole mobility before and after hydrogenation shows that the neutralization of acceptors by atomic hydrogen leads to the elimination of the shallow acceptor states. Infrared-absorption lines associated with hydrogen-acceptor complexes are observed for all acceptors except magnesium. It is established that the microscopic structure of hydrogen-acceptor complexes depends on the acceptor site in the lattice.
MeV energy Fe and Co implants to obtain buried high resistance layers and to compensate donor implant tails in InP
Authors: Vellanki Jayadev , Nadella Ravi K. , Rao Mulpuri V. , Holland O. W. , Simons David S. , Chi Peter H.
Published: July 2002

High-energy Fe and Co implantations were performed into InP:Sn at room temperature and 200 °C in the energy range 0.34–5.0 MeV. Range statistics were calculated for these ions in the above energy range. For the room-temperature implants, implant redistribution peaks around 0.8Rp and Rp+ΔRp, and both in- and out-diffusion of the implant are observed in the secondary-ion-mass-spectroscopy profiles of the annealed samples. The implant redistribution present in the room-temperature implants is much different than in elevated-temperature implants. For buried (high-energy) implants, much of the implant diffusion is eliminated if the implants are performed at 200 °C. For 200 °C implants, the yield of the Rutherford backscattering spectra on the annealed samples is close to that of a virgin sample. The MeV energy Fe and Co implantations at 200 °C are useful to obtain thermally stable, buried, and high-resistance layers of good crystalline quality in n-type InP and for the compensation of the tail of the buried n-type implant. However, due to the low solubility of Fe and Co in InP, the implants of these species are useful only to compensate n-type carriers with concentrations below 1017 cm−3.
The effect of excitons on apparent band gap narrowing and transport in semiconductors
Authors: Kane D. E. , Swanson R. M.
Published: July 2002

The interactions between electrons and holes are known to alter the energy levels in semiconductors. At high carrier densities, these interactions produce extended states that can be described by a carrier-induced band gap narrowing. Below the Mott density, this description is no longer valid and electron-hole interactions produce localized excitonic states. Excitons in Si have been thoroughly studied at low temperatures but they are usually ignored in semiconductor device operation. We have performed an analysis of the thermodynamics of excitons in Si below the Mott transition and find that the presence of excitons is expected to be significant at certain carrier densities, especially at 77 K. The electrical properties of semiconductors containing excitons are described and contrasted with the situation above the Mott transition where the conventional rigid band gap narrowing of extended states is valid. There are two key results. First, excitons mimic a rigid band gap narrowing in that they lead to an increase in the carrier density at a given voltage level. This occurs because as electrons occupy the excitonic states, the total electron density increases without increasing the density of electrons in the extended conduction band states. Second, excitons affect device transport and the result is different from the rigid band gap narrowing case. Since excitons can be mobile, they can contribute to diffusion. Because they are neutral, however, they cannot contribute to drift currents. In the extreme limit that all the carriers exist as excitons, there will be a finite ambipolar diffusion constant, but the conductivity mobility will drop to zero. Such an outcome is not possible within the framework of conventional device modeling. The necessary modifications are discussed.
Temperature dependence of the 90° coupling in Fe/Al/Fe(001) magnetic trilayers
Authors: Filipkowski M. E. , Gutierrez C. J. , Krebs J. J. , Prinz G. A.
Published: July 2002

The temperature dependence of the unusual magnetic 90° coupling in epitaxial Fe/Al/Fe(001) trilayers has been determined. For specific values of applied field and temperature, in-plane anisotropy and the interlayer coupling drive abrupt first-order changes in the temperature-dependent moment of these trilayers. The occurrence of such a first-order transition can be used to determine the value of the interlayer coupling constant, JQ, at the transition temperature. We show that Fe/Al/Fe(001) trilayers also exhibit distinct second-order transitions in the temperature-dependent moment, and that the occurrence of a second-order transition can similarly be used to specify JQ(T). A comparison is made of the values of JQ(T) determined by these two approaches, and the dependence of JQ on T is analyzed.
keV x-ray production using 50 mJ KrF laser produced plasmas at 1 and 100 ps
Authors: Broughton J. N. , Fedosejevs R.
Published: July 2002

The emission of 800–1400 eV x rays from plasmas produced by KrF discharge laser pulses with durations in the range of 1 and 100 ps with energies up to 50 mJ has been studied using various metal targets. The emission spectra, angular distribution, and x-ray conversion efficiencies into 2π Sr have been measured in vacuum. Peak conversion efficiencies of 10%–13% were obtained for Fe, Co, Ni, Cu, and Zn when a 90 ps, 50 mJ pulse was used. A 2 ps, 40 mJ pulse yielded efficiencies of 8%–10% with plasma reflectivity accounting for the reduction in conversion efficiency. An 850 fs, 35 mJ pulse gave reduced yields of 4% for Cu. In a background gas of 1 atm helium a reduction of conversion efficiency by 15% was observed for 90 ps pulses.
Measurement of stress and relaxation in Si1−xGex layers by Raman line shift and x-ray diffraction
Authors: Dietrich B. , Bugiel E. , Klatt J. , Lippert G. , Morgenstern T. , Osten H. J. , Zaumseil P.
Published: July 2002

Epitaxial Si1−xGex layers, grown by molecular beam epitaxy (MBE) and by chemical vapor deposition (CVD) on Si(001) substrates, with thicknesses between 20 and 50 nm and Ge contents from 4% to 23% were investigated by micro Raman backscattering, x-ray double crystal diffractometry, and transmission electron microscopy. A quite simple phenomenological model was developed to derive the Raman shift of the Si–Si mode as a function of the germanium content for the two limiting cases, the pseudomorphically strained layer, and the alloy-like stress-free layer. A measure for the degree of relaxation can be obtained from the measured Raman shift and from the independently determined germanium content, using the results of the model. The degree of relaxation was determined for a number of CVD- and MBE-grown Si1−xGex layers. The as-grown pseudomorphic layers relax partially after annealing at 900 °C. The Raman scattering allows the monitoring of the development of relaxation during the semiconductor device processing.
Implantation-enhanced interdiffusion of CdTe-ZnTe heterostructures
Authors: Hamoudi A. , Ligeon E. , Cibert J. , Dang Le Si , Tatarenko S. , Feuillet G. , Jouneau P. H. , Pautrat J. L. , Saminadayar K.
Published: July 2002

Implantation-enhanced interdiffusion of CdTe-ZnTe strained heterostructures is studied by photoluminescence, channeling, transmission electron microscopy, and secondary-ion-mass spectrometry. In the tellurides, implantation defects significantly diffuse and anneal out during implantation, so that only residual extended defects are found, at depths several times greater than the implantation projected range Rp. As a result, interdiffusion is achieved during the implantation, and not during the subsequent annealing which only serves to eliminate the residual defects, thereby restoring the optical properties of the heterostructures. Evidence has been found for trapping of residual defects at the interfaces, perhaps due to strain, and of slower diffusion in multiple quantum wells than in bulk material. These interface-trapped defects are quite hard to anneal out, so that single quantum wells exhibit poor optical properties after implantation and annealing, while multiple quantum wells give rise to nice photoluminescence spectra with sharp blue-shifted lines and appear as promising candidates to realize lateral confinement.
Defects in MeV Si-implanted Si probed with positrons
Authors: Nielsen Bent , Holland O. W. , Leung T. C. , Lynn K. G.
Published: July 2002

Vacancy-type defects produced by implantation of MeV doses of Si ions (1011–1015 atoms/cm2) at room temperature have been probed using depth-resolved positron annihilation spectroscopy. The defect (divacancy) concentration increases linearly with dose for low doses (<1012 Si/cm2). In situ isochronal annealing was followed for oxygen-containing Si (10 ppm) and oxygen-‘‘free’’ Si implanted to doses (5×1012 and 5×1014 Si/cm2). Two main annealing stages were observed at the same temperatures in the studied samples in spite of significant differences in doses and oxygen content. In the first stage (∼200 °C) a significant fraction of divacancies was observed to form large vacancy clusters. These clusters were removed in the second stage (∼675 °C) after which the oxygen-free samples returned to pre-irradiation conditions, whereas oxygen-defect complexes were formed in the oxygen-containing samples.
Evidence of silicon interdiffusion in selectively doped GaAs-AlAs superlattices by Hall measurements
Authors: Sellitto P. , Jeanjean P. , Sicart J. , Robert J. L. , Planel R.
Published: July 2002

Hall and photo-Hall measurements have been performed on GaAs-AlAs short-period superlattices selectively doped with silicon. The dopant was introduced selectively in either the GaAs or AlAs layers or at the interface. A superlattice doped uniformly in both layers was investigated for comparison. The electrical properties were controlled by DX deep donors lying in the gap of the superlattice. Hall data are interpreted with a model taking into account the existence of two DX deep donors and a shallow donor both related to the silicon impurity. It is found that the silicon donor state in AlAs lies 60 meV below the silicon donor state in GaAs. The ionization energies of the DX states in GaAs and AlAs are computed to account for the experimental results. Interpretation of Hall data in selectively doped samples needs to assume segregation of silicon atoms during epitaxy.
Investigation of time-dependent resonant interband tunneling
Authors: Wang Jian , Wang Yongjiang , Guo Hong
Published: July 2002

We present a time-dependent calculation of InAs/AlSb/GaSb/AlSb/InAs and InAs/GaSb/InAs resonant interband tunneling structures. We follow the propagation of electron wave packets through the systems and determine the temporal behavior of the device operation by calculating various time scales. We compare these time scales with the lifetime of the corresponding quasi-bound state computed from both the static transmission curve and the exact solution of the quasi-bound state.
Nucleation of dislocations in SiGe layers grown on (001)Si
Authors: Mooney P. M. , LeGoues F. K. , Tersoff J. , Chu J. O.
Published: July 2002

A comprehensive x-ray-diffraction study of the variation of the tilt angle between a Si1−xGex layer and the (001) Si substrate is presented. Such measurements provide the basis of a new method for determining the nucleation activation energy of misfit dislocations. A detailed model, independent of the particular relaxation mechanism, is derived which relates the tilt angle to the nucleation activation energy on the different slip systems and to the density of misfit dislocations. The model has been applied to the modified Frank–Read mechanism observed in graded samples. Relaxation occurs in such samples for strain in the range 0.002≤ε≤0.006 with an activation energy of about 4 eV. The critical thickness for growth of a strained layer is shown to be smaller when the substrate is miscut than when it is well oriented.
Trap generation at Si/SiO2 interface in submicrometer metal-oxide-semiconductor transistors by 4.9 eV ultraviolet irradiation
Authors: Ling C. H.
Published: July 2002

Subfemtofarad changes are reported in the gate-to-drain capacitance of submicrometer metal-oxide-semiconductor transistors subjected to 4.9 eV (253.7 nm) ultraviolet irradiation. The observation is attributed to trap generation at Si/SiO2 interface, proposed to be due to the breaking of Si—H bonds.
Time-resolved investigations of excitonic recombination in highly strained InAs/Al0.48In0.52As quantum wells
Authors: Daiminger F. , Dite A. F. , Tourníe E. , Ploog K. , Forchel A.
Published: July 2002

We have investigated the exciton dynamics in strained InAs/Al0.48In0.52As quantum wells with well thicknesses of 2, 4, and 5 monolayers by time-resolved photoluminescence spectroscopy. Temperature-dependent measurements of the decay time reveal a significant drop of the decay time above a critical temperature which depends on the well width. The simultaneous measurement of the decay time and the integrated photoluminescence intensity enables us to estimate the radiative time constant. As can be shown from the temperature dependence of the decay time nonradiative processes become more and more important at higher temperatures. The strong increase of the radiative lifetime at higher temperatures is attributed to a thermal ionization of the excitons.
High field effective linewidth and eddy current losses in moderate conductivity single crystal Zn-Y hexagonal ferrite at 10–35 GHz
Authors: Truedson John R. , Kabos Pavel , McKinstry Kevin D. , Patton Carl E.
Published: July 2002

The microwave losses associated with the extreme high field tail region of the ferromagnetic resonance (FMR) absorption curve for 0.08- to 1.38-mm-thick c-plane circular disks of single crystal Zn-Y hexagonal ferrite materials with planar anisotropy were investigated at 10, 19.3, and 35.3 GHz, with the static external magnetic field applied in plane. Analysis of the data in terms of magnetic losses only gave anomalous high field effective linewidth ΔHF results; this ΔHF showed a substantial increase with the field, changed with both disk thickness and radius, and was higher for an out-of-plane microwave field direction than for an in-plane direction. This linewidth did scale with the square of the disk thickness, one indication of predominant eddy current losses. The data were then analyzed in terms of eddy current losses, based on the assumption of an insulator FMR response and a high field eddy current loss absorption tail driven by that response. The predictions of the model were in good agreement with the data. Fits to the data gave reasonable and consistent values of the microwave conductivity which ranged from 0.03 to 0.05 Ω−1 cm−1 at 10 GHz to 0.06–0.07 Ω−1 cm−1 at 35 GHz, relative to a measured dc conductivity of 0.02–0.03 Ω−1 cm−1.
Hydrogen concentration and mass density of diamondlike carbon films obtained by x-ray and neutron reflectivity
Authors: Findeisen E. , Feidenhans’l R. , Vigild M. E. , Clausen K. N. , Hansen J. Bindslev , Bentzon M. D. , Goff J. P.
Published: July 2002

Specular reflectivity of neutrons and x rays can be used to determine the scattering length density profile of a material perpendicular to its surface. We have applied these techniques to study amorphous, diamondlike, hydrocarbon films. By the combination of these two techniques we obtain not only the mass density, but also the concentration of hydrogen, which varies in our case between 0 and 30 at. %. This method is a new and nondestructive way to determine the concentration of hydrogen within an error of less than 2 at. % in samples with sharp interfaces. It is especially suited for diamondlike carbon films.
Proper interpretation of photoconductive decay transients in semiconductors having finite surface recombination velocity
Authors: Derhacobian N. , Walton J. T. , Luke P. N. , Wong Y. K. , Rossington C. S.
Published: July 2002

The influence of finite surface recombination velocity on the proper interpretation of photoconductive decay (PCD) transients in semiconductors is discussed. The limitations of simple analytical equations which relate the observed effective lifetime to the material parameters are considered. It is shown that, under most circumstances, the correct application of the appropriate analytical expression requires some prior knowledge of the material parameters under investigation. Several methods are proposed to extract useful information from PCD experiments. Finally, the practicality of these methods is investigated by measuring the effective lifetimes of high-purity germanium and float-zone silicon using a noncontact PCD technique.
Aluminum gettering of cobalt in silicon
Authors: Apel M. , Hanke I. , Schindler R. , Schröter W.
Published: July 2002

We investigated the gettering effect of an evaporated aluminum layer on single crystalline and cast multicrystalline silicon doped with radioactive cobalt-57 by means of radiotracer methods and Mössbauer spectroscopy. We present evidence that aluminum gettering works at high temperatures and transfers the cobalt atoms from the Si bulk to the liquid Al-Si phase. Presumably Al gettering can be explained as a segregation induced process caused by a higher solubility of the metallic impurity in the liquid Al-Si phase compared with that in solid silicon.
Electrical properties of contact etched p-Si: A comparison between magnetically enhanced and conventional reactive ion etching
Authors: Awadelkarim O. O. , Mikulan P. I. , Gu T. , Reinhardt K. A. , Chan Y. D.
Published: July 2002

We report the results of a comparative study of the damage induced in boron-doped Si by contact etching. The two approaches compared are conventional reactive ion etching and magnetically enhanced reactive ion etching (MERIE). The two structure-chemistry combinations used are SiO2/Si with CHF3/O2 plasmas, and bare Si wafers with CHF3/Ar plasmas. The damage examined in the Si substrates of both structures is that of electronic states in the band gap, the permeation into Si of hydrogen, and the deactivation of boron acceptors. These types of damage are explored by means of deep level transient spectroscopy and capacitance-voltage measurements on Ti/Si Schottky diodes fabricated on the etched substrate surfaces. The gap states induced by these contact etches are ascribed to interstitial-atom-related defects which are proposed to be formed as a result of interactions involving self interstitials. During etching these defects are observed to be both generated by the etching process itself as well as electrically passivated by permeating hydrogen. The hydrogen permeation of the substrate, monitored via acceptor deactivation, is seen to be enhanced for MERIE with increasing magnetic field intensities.
Velocity surface measurements for ZnO films over {001}-cut GaAs
Authors: Kim Yoonkee , Hunt William D. , Liu Yongsheng , Jen Cheng-Kuei
Published: July 2002

A potential application for a piezoelectric film deposited on a GaAs substrate is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the filmed structure is critical for the optimum design of such devices. In this article, the measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metallized ZnO/SiO2 or Si3N4/GaAs {001}-cut samples are reported using two different techniques: (1) knife-edge laser probe, (2) line-focus-beam scanning acoustic microscope. Comparisons, such as measurement accuracy and tradeoffs, between the former (dry) and the latter (wet) method are given. It is found that near the 〈110〉 propagation direction the autocollimating SAW property of the bare GaAs changes into a noncollimating one for the layered structure, but a reversed phenomenon exists near the 〈100〉 direction. The passivation layer of SiO2 or Si3N4 (<0.2 μm thick) and the metallization layer change the relative velocity but do not significantly affect the velocity surface. On the other hand, the passivation layer reduces the propagation loss by 0.5–1.3 dB/μs at 240 MHz depending upon the ZnO film thickness. Our SAW propagation measurements agree well with theoretical calculations. We have also obtained the anisotropy factors for samples with ZnO films of 1.6, 2.8, and 4.0 μm thickness. Comparisons concerning the piezoelectric coupling and acoustic loss between dc triode and rf magnetron sputtered ZnO films are provided.
Defect ordering in epitaxial α-GaN(0001)
Authors: Xiao H. Z. , Lee N.-E. , Powell R. C. , Ma Z. , Chou L. J. , Allen L. H. , Greene J. E. , Rockett A.
Published: July 2002

The microstructure of nominally undoped epitaxial wurtzite-structure α-GaN films, grown by gas-source molecular-beam epitaxy, plasma-assisted molecular-beam epitaxy, and metalorganic chemical-vapor deposition, has been investigated by transmission electron microscopy (TEM) and high-resolution TEM. The results show that undoped α-GaN films have an ordered point-defect structure. A model of this defect-ordered microstructure, based upon a comparison between experimental results and computer simulations, is proposed.
New rare-earth intermetallic phases R3(Fe,M)29Xn: (R=Ce, Pr, Nd, Sm, Gd; M=Ti, V, Cr, Mn; and X=H, N, C) (invited)
Authors: Cadogan J. M. , Li Hong-Shuo , Margarian A. , Dunlop J. B. , Ryan D. H. , Collocott S. J. , Davis R. L.
Published: July 2002

New rare-earth (R), iron-rich ternary intermetallic compounds of the form R3(Fe,M)29 with the monoclinic Nd3(Fe,Ti)29 structure (space group P21/c, ♯14, Z=2) have recently been shown to form with R=Ce, Nd, Pr, Sm, and Gd, and M=Ti, V, Cr, and Mn. This novel structure is derived from the alternate stacking of Th2Zn17 and ThMn12-type segments and contains two R sites and fifteen Fe(M) sites. Reported Curie temperatures of the 3:29 compounds range from 296 K (R=Ce, M=Cr) to 524 K (R=Sm, M=V). The 3:29 compounds all show improved magnetic properties after interstitial modification with H or N; in particular, room-temperature coercivity has been reported in Sm3(Fe,Ti)29N5, making this compound a candidate for possible permanent-magnet applications. In this article we will review the work carried out to date on the 3:29 compounds.
Structural and magnetic properties of R3(Fe,T)29 compounds
Authors: Fuerst C. D. , Pinkerton F. E. , Herbst J. F.
Published: July 2002

We report the formation of several members of the recently discovered class of R3(Fe,T)29 compounds and some of their intrinsic properties. Focusing on materials with T=Ti and Cr, we have prepared R3(Fe,Ti)29 (R=Ce, Pr, Nd, Sm) and R3(Fe,Cr)29 (R=Ce, Nd, Sm) compounds which all feature the novel monoclinic crystal structure first established for Nd3(Fe,Ti)29. In each of the Ti- and Cr-containing groups the Ce member has the smallest magnetization, Curie temperature, and unit cell, suggesting that the Ce ion is tetravalent, or nearly so, in this family of materials. We observed no evidence of R3(Fe,Ti)29 phase formation for R=Y, Gd, Dy, and Er. Our magnetization measurements indicate that only Nd3(Fe,Ti)29 and Nd3(Fe,Cr)29 exhibit spin reorientations, at temperatures of 235 and 145 K, respectively.
Nitrogen effects on thermal donor and shallow thermal donor in silicon
Authors: Yang Deren , Que Duanlin , Sumino Koji
Published: July 2002

Nitrogen effects on thermal donors and shallow thermal donors in nitrogen-doped silicon have been investigated by means of the far infrared technique at low temperature (8 K). It is evident that nitrogen can suppress the formation of the thermal donor in silicon annealed at 450 °C. Nitrogen atoms are combined with oxygen atoms to produce the oxygen-nitrogen complexes related with the shallow thermal donors. It is believed that nitrogen interacts with the oxygen atoms to form oxygen-nitrogen complexes so as to reduce the thermal donors.
Oxidation of Cu and Cu3Ge thin films
Authors: Liou H. K. , Huang J. S. , Tu K. N.
Published: July 2002

We have studied the oxidation kinetics of Cu and Cu3Ge thin films in air using in situ resistivity measurement and x-ray photoelectron spectroscopy. Thin films of Cu oxidize in air around 250 °C to form CuO with an activation energy of 0.74 eV. In contrast to Cu, thin films of Cu3Ge oxidize only above 450 °C. The excellent oxidation resistance of Cu3Ge is due to the thin GeO2 layer which protects Cu3Ge from oxidation below 450 °C. Above 510 °C, GeO2 evaporates and the oxidation protection is lost. Besides the excellent oxidation resistance and low resistivity, we also found Cu3Ge to have a better adhesion to SiO2 than Cu. It has the potential to be used as an adhesion layer and passivation layer in Cu metallization.
Measurement of the GaAs/AlAs valence-band offset from a single quantum well near the Γ-X crossover
Authors: Yeh C. N. , McNeil L. E. , Blue L. J. , Daniels-Race T.
Published: July 2002

An iterative procedure which utilizes the type-I and type-II transitions of a GaAs/AlAs single quantum well is used to determine the GaAs/AlAs valence-band offset. The iteration is based on the fact that the confinement energy is not sensitive to the change of the barrier potential. It has the advantage that knowledge of the thickness of the quantum well is not necessary to determine the valence-band offset. Both the type-I and type-II transitions can be observed in the low-temperature photoluminescence spectrum if the GaAs is thin enough so that the lowest-energy level of the electron in the GaAs well is higher than the X-conduction-band minimum of the adjacent AlAs. We illustrate this procedure with a 35 Å GaAs/AlAs single quantum well, and the valence-band offset is found to be 36% of the Γ-gap difference.
A study of interlayer coupling in Co/Cu multilayers
Authors: Jin Q. Y. , Zhai H. R. , Xu Y. B. , Zhai Y. , Lu M. , Zhou S. M. , Payson J. S. , Dunifer G. L. , Naik R. , Auner G. W.
Published: July 2002

Co(22 Å)/Cu multilayers with Cu thicknesses varying from 6 to 40 Å are studied by vibrating-sample magnetometry and ferromagnetic-resonance spectroscopy (FMR). The magnetization was found to increase with decreasing Cu thickness, whereas the linewidth of the uniform mode of the FMR was found to decrease. This is attributed to the spin polarization of the Cu layers due to interlayer coupling and its effect on the lowered dimensionality of the Co layers. We also observed a peak on the high-field side of the uniform FMR mode, which we attribute to antiparallel coupling of adjacent ferromagnetic layers producing an ‘‘optical’’ mode.
Atomic scale etching processes of n-Si(111) in NH4F solutions: In situ scanning tunneling microscopy
Authors: Kaji Kazutoshi , Yau Shueh-Lin , Itaya Kingo
Published: July 2002

In situ scanning tunneling microscopy (STM) was employed to examine the electrochemical etching process of an n-Si(111) electrode in dilute NH4F solutions under potential control. Time-dependent STM images have revealed prominent effects of microscopic structures of Si on the rate of its dissolution. Multiple hydrogen-terminated Si atoms at the kink and step sites were eroded more rapidly than the monohydride Si step. This presumably resulted from the difference in reactivity of these hydrogen-terminated Si species. It is demonstrated that the density of kinks plays a main role in controlling the etching rate of Si. In the absence of kinks, not only the monohydride but also the dihydride steps were found to be stable. The etching rate of the monohydride step is substantially increased from a negligible value to 15 nm/min by the introduction of kink sites. The average etching rate for a dihydride step was 32 nm/min. Overall, the difference in the reactivity guides the dissolution of Si in a layer-by-layer fashion.
Dielectric tensor characterization and evaluation of several magneto-optical recording media
Authors: Fu Hong , Yan Zheng , Lee Seh Kwang , Mansuripur M.
Published: July 2002

We attempt to establish a dielectric tensor database for magneto-optical (MO) thin film materials with potential application for blue recording. For this purpose a method is developed for measuring the dielectric tensor of the MO layer within a multilayered stack. It uses a combination of ellipsometric, reflection/transmission, and polar MO Kerr effect measurements, and employs the MULTILAYER computer program to analyze the data. Using this approach we have measured the dielectric tensor for thin films of BiDy3(FeGa)5O12 garnet, MnBi, multilayered Co/Pt, amorphous TbFeCoTa, and fcc cobalt in the wavelength range of 400–780 nm. The dielectric tensor for the Heusler alloy films of PtMnSb, which is available from the published literature, is also presented for the sake of completeness. These materials are then evaluated based on the intrinsic MO figure of merit defined by FOM≡‖εxy‖/(2 Im εxx), where εxx and εxy are the diagonal and off-diagonal elements of the dielectric tensor of the MO material. In the blue–green regime of 400–550 nm, the relationship of the derived FOMs is as follows: FOMMnBi(≊0.027–0.045) ≊ FOMGarnet (≊0.023–0.032) ≳ FOMPtMnSb(≊0.015–0.026) ≳ FOMCo/Pt(≊0.013–0.015) ≊ FOMCo(fcc) (≊0.011–0.016) ≳ FOMTbFeCoTa (≊0.009–0.011).
Diamond-like carbon films deposited by laser ablation using frozen acetylene targets
Authors: Hanabusa Mitsugu , Tsujihara Kiyohito
Published: July 2002

A new laser ablation method based on frozen gas targets was tested by depositing carbon films. The source gas was acetylene. With an ArF laser at a power density of 9×108 W/cm2 the deposition rate varied from 17 nm/min at room temperature to 13 nm/min at a substrate temperature of 300 °C. The films showed the broad Raman peak at 1540 cm−1 characteristic of diamond-like carbon films. A KrF laser produced the diamond-like carbon films at substrate temperatures above 200 °C. Particles were absent in the films if the power density was not excessively high. Energetic species ejected from frozen acetylene improved the adherence of the films to quartz substrates.