bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical activation and local structure of Se atoms in ion-implanted indium phosphide
Authors: Yu Kin Man , Chan Ning , Hsu Leonardo
Published: July 2002

The solid phase regrowth, dopant activation, and local environments of Se-implanted InP are investigated with ion-beam techniques and extended x-ray-absorption fine structure spectroscopy. We find that the local Se–In structure is already established in the as-implanted amorphous InP although the Se atoms have a lower average coordination number (∼3.5) and no long-range order. After high-temperature rapid thermal annealing (950 °C, 5 s), the amorphous InP regrows, becoming a single crystal with the Se atoms bonded to four In neighbors; however, only ∼50% of the Se becomes electrically active. Part of the Se precipitates in the form of an In–Se phase, another part is compensated by defects which are not totally removed by annealing. The Se—In bond distance for a Se on a P site is 4.5% longer than the matrix In—P bond length, introducing large strains in the crystal. The solid solubility of Se in InP is estimated from our results to be ≊8.7×1019/cm3 while the electron concentration saturates at 5.4×1019/cm3. Se atoms in InP regrown at lower temperatures in a furnace are only ∼7% electrically active and are found to have different local environments (higher coordination number and shorter bond distance) than those in the InP perfectly regrown at higher temperature.
Effects of gas ratio on electrical properties of electron-cyclotron-resonance nitride films grown at room temperature
Authors: Chang Kow-Ming , Tsai Jung-Yu , Li Chii-Horng , Yeh Ta-Hsun , Wang Shih-Wei , Yang Ji-Yi
Published: July 2002

The effects on the electrical properties of electron-cyclotron-resonance (ECR) nitride films grown at room temperature with different SiH4/N2 gas ratios from 7 sccm/43 sccm to 2 sccm/48 sccm are systematically investigated. Superior properties of the films with low bulk trap density 8×1017 cm−3, small trap cross section, high breakdown strength 12.12 MV/cm, and near-stoichiometric refractive index 2.0 are obtained when the gas ratio SiH4/N2 is 5 sccm/45 sccm, the microwave power is 210 W, and the chamber pressure is 0.5 mTorr. With the microwave power, total gas flow rate, and total pressure unchanged, the decrease in SiH4/N2 ratio lower than 5/45 results in larger trap density and some lower breakdown strength. On the other side, increasing SiH4/N2 ratio results in higher hydrogen content, lower breakdown strength, and films which are easily degraded during consecutive voltage sweep. High microwave power will eliminate the weak bonds and strengthen the electrical stability of the high SiH4/N2 ratio film.
Low Schottky barrier height contacts to n-CdTe using rare-earth metals
Authors: Cunff D. Brun-Le , Daudin B.
Published: July 2002

Low-resistance contacts on n-type CdTe have been produced by molecular-beam epitaxy using metallic rare earths (europium, samarium, and neodymium). The metallic europium and neodymium epitaxy is achieved via an interfacial layer about 3 nm thick which results from the strong reactivity between the rare-earth metal and the tellurium semiconductor anion. For the two-dimensional growth of europium the interfacial layer is deliberately formed with samarium or neodymium, whereas for neodymium epitaxial growth the interfacial layer is formed with neodymium. Schottky barrier heights of the different heterostructures are determined by current–voltage characteristics and the specific contact resistance is measured using the transmission line model. The best results are obtained for neodymium/n-CdTe heterostructures with a specific contact resistance of 8×10−4 Ω cm2 for a doping level of 4×1017 cm−3. The Schottky barrier heights have been determined to be about 0.35±0.05 eV for the various rare-earth/n-CdTe heterostructures. The temperature and the doping level dependence of the current–voltage characteristics suggests furthermore that a dipolar layer is present at the interface.
Effect of deformation on the temperature dependence of the resistivity of palladium–molybdenum and palladium–tungsten alloys
Authors: Lang C. I. , Doyle R. A.
Published: July 2002

We have measured the temperature dependence of the resistivity of alloys of the palladium–molybdenum and palladium–tungsten systems between 10 and 300 K. These alloys exhibit a decrease in electrical resistivity after deformation, contrary to the expected increase due to increased scattering from dislocations. It is shown that these changes are associated with significant alterations in electronic structure brought about by changes in atomic configuration in the lattice.
Angular distributions of electrons transmitted ballistically through tapered constrictions
Authors: Hornsey R. I.
Published: July 2002

Monte Carlo simulation results are presented for the angular distributions of electrons which have been transmitted ballistically through constrictions with a variety of geometries and specularity coefficients. The behaviors of parallel, convergent, and divergent constrictions and their combinations are discussed with reference to existing experimental results and previous theoretical studies. Maximum divergence angles are well described by the analytic adiabatic approximation only for very small taper angles (<10°). Investigation of these simple geometries offers useful insights into the behavior of the more complex structures found experimentally.
A statistical mechanics approach to digital image processing: Image enhancement
Authors: Aldave-Matar R. , Ley-Koo M.
Published: July 2002

An algorithm for the enhancement of digital images is described. The algorithm is based upon the analogy that may exist between the description of a macroscopic system composed of many particles, and a digital image composed of many pixels. The analogy assumes that the intensity in a digital image fluctuates, so that the algorithm takes into account that fluctuations must decrease to a minimum in such a way that an enhanced image may be thought of as an image in an equilibrium state, leading to a quantitative criterion to stop the enhancement process. This may be taken as the starting point of a computer aided vision system, the next step being the image segmentation leading to the identification of the various patterns forming the image and which is described in a forthcoming paper.
Cross section measurements of the 1H(3He,1H)3He reaction at 20° and 30° between 1.9 and 3.0 MeV
Authors: Terwagne G. , Ross G. G. , Leblanc L.
Published: July 2002

The cross sections of the 1H(3He,1H)3He reaction have been measured at two different angles (20° and 30°) for 3He particles incident energies between 1.9 and 3.0 MeV. This reaction offers an alternative to the classical 1H(4He,1H)4He elastic recoil reaction and can be more attractive because 3He incident particles induce nuclear reactions on light elements such as 12C, 14N, or 16O. The new technique has been applied to silicon implanted with low energy hydrogen as well as a CxHy/Cu/CuxHy/Si specimen. For this multilayer, carbon, hydrogen, and carbon can be analyzed together using three different charge particle detectors.
Phase transformation in amorphous silicon under excimer laser annealing studied by Raman spectroscopy and mobility measurements
Authors: Inushima Takashi , Kusumoto Naoto , Kubo Nobuo , Zhang Hong-Yong , Yamazaki Shumpei
Published: July 2002

The transformation of silicon from an amorphous phase to a polycrystalline phase by excimer laser annealing was investigated by means of Raman spectroscopy and electron mobility measurements. It was shown that the phase transformation was mainly governed by the energy density of the laser, and that when the density was high enough to evaporate the surface layer of the amorphous silicon, a latent state of the multiple irradiated sample was formed, where the Raman intensity exceeded that of the bulk crystal silicon and the electron mobility of the film became very high. This observation was explained by the pyramidal grain growth structure of the crystalline silicon. The amorphous component at the grain boundary was also observed in measured Raman spectra and it was shown that the presence of this phase had a significant influence on reducing the field effect mobility.
High-resolution x-ray-diffraction analysis of epitaxially grown yttrium iron garnet films on gadolinium gallium garnet
Authors: Dimer M. , Gerdau E. , Rüffer R. , Rüter H. D. , Sturhahn W.
Published: July 2002

X-ray-diffraction analysis was applied to determine the lattice strain and degree of crystalline perfection of yttrium iron garnet (YIG) films on [100]- and [111]-oriented gadolinium gallium garnet (GGG) substrates. Rocking curves were measured with a high-resolution x-ray diffractometer in which a four-reflection monochromator in a (+,−,−,+) setting produces a beam with a very small angular divergence (2.3 μrad, Mo Kα1) and energy bandwidth (about 80 meV). Therefore a series of different reflections of intrinsic angular width could be obtained from the same crystalline layer system. The dynamical diffraction theory was used to compute the rocking curves. A simple recursion formula allowed a computer simulation of the measured reflectivity. The fit to the measured rocking curves for each reflection resulted in the probable change of the lattice constant with depth. It was possible to successfully fit the rocking curves of four different reflections of one YIG/GGG crystal with only one strain profile. The changing of the lattice constant gives an insight into the crystal growth and could be important for improving the process.
Diffusion at the Al/Al oxide interface during electromigration in wide lines
Authors: Augur R. A. , Wolters R. A. M. , Schmidt W. , Dirks A. G. , Kordić S.
Published: July 2002

Significant large-scale modification of the surface of Al–Si conductors was observed, due to electromigration in wide lines and under low stress conditions. After electromigration stressing the Al layers showed local thickness variations, i.e., damage by thinning. The mechanism underlying this damage causes substantial metal transport. Nevertheless, damage by thinning has received little attention in the past. Thinning was observed: (1) in a number of different alloys (Al–Si, Al–Cu, Al–Si–V, and Al–Si–V–Pd), (2) with a number of different underlayers [SiO2, W–Ti (no vacuum break after Al deposition) and W–Ti (oxidized surface before Al deposition)], (3) over an extended temperature range, (4) over a range of current density, and (5) in structures with and without passivation. The results show that thinning is a general phenomenon. An activation energy of approximately 0.5 eV was determined for the temperature dependence of a combined mechanism of concurrent thinning plus voiding in Al99Si1. Several alternatives are examined to explain the observations, namely mass movement along dislocations, Al bulk diffusion, and diffusion at the interface between the Al and its oxide. It is shown that diffusion at the Al/Al oxide interface most probably plays an important role in the damage mechanism, even under stress conditions where grain boundary diffusion is traditionally thought to dominate. Results also showed that alloying of Al with Pd can reduce the effects of damage by thinning.
Chemical interaction of Si, Ti, and Mo with graphite surfaces
Authors: Roth J. , Graupner H. , Withrow S. P. , Zehner D. , Zuhr R. A.
Published: July 2002

The interaction of Si, Ti, and Mo atoms with pyrolytic graphite substrates has been studied for evaporated layers of about 100 nm and implanted ions with mean ranges between 2 and 4 nm. In the temperature range from room temperature to 1800 K the thermal diffusion of carbon into the evaporated layers has been studied by Rutherford backscattering spectroscopy while the temperature dependence of the carbide formation has been studied by x-ray photoelectron spectroscopy. For all three systems stable carbidic phases are predicted by equilibrium phase diagrams. For Ti the formation of TiC is already observed after room temperature implantation, while for Mo annealing to 1200 K is necessary for Mo2C formation. In the case of Si oxygen contamination due to the air transfer after implantation resulted in a mixed SiOxCy phase which only transformed into a SiC phase at temperatures above 900 K, where the oxygen was released. The temperature range of stability of the carbidic layers was found to be correlated to the melting temperature of the metal–carbide eutectic. Above this temperature the metal atoms rapidly dissolve in the graphite lattice.
Electrical and optical properties of infrared photodiodes using the InAs/Ga1−xInxSb superlattice in heterojunctions with GaSb
Authors: Johnson J. L. , Samoska L. A. , Gossard A. C. , Merz J. L. , Jack M. D. , Chapman G. R. , Baumgratz B. A. , Kosai K. , Johnson S. M.
Published: July 2002

The InAs/Ga1−xInxSb strained-layer superlattice (SLS) holds promise as an alternative III–V semiconductor system for long wavelength infrared detectors. In this article, we present the first investigation, to the best of our knowledge, of heterojunction photodiodes using this new material. The devices were grown by molecular beam epitaxy on GaSb substrates, and are comprised of a 38 Å InAs/16 Å Ga0.64In0.36Sb SLS used in double heterojunctions with GaSb contact layers. The structures were designed to optimize the quantum efficiency while minimizing transport barriers at the heterointerfaces. The photodiodes are assessed through the correlation of their performance with the SLS material quality and the detector design. X-ray diffraction, absorption, and Hall measurements are used to determine the SLS material properties. The electrical and optical properties of the photodiodes are determined using current–voltage and spectral responsivity measurements. At 78 K, these devices exhibit rectifying electrical behavior and photoresponse out to a wavelength of 10.6 μm corresponding to the SLS energy gap. The responsivity and resistance in these thin-layered (0.75 μm), unpassivated photodiodes result in a detectivity of 1×1010 cm √Hz/W at 8.8 μm and 78 K. Based upon the performance of these devices, we conclude that high-sensitivity operation of long-wavelength photovoltaic detectors at temperatures well in excess of conventional III–V band gap-engineered systems, and potentially in excess of HgCdTe, is feasible using this material system.
Filling the carbon nanocages
Authors: Seraphin Supapan , Zhou Dan , Jiao Jun
Published: July 2002

Twenty elements were codeposited with carbon in an arc discharge between graphite electrodes. The majority of them were evaporated from composite anodes that contained the elements or their oxides stuffed into central bores in the graphite rods. The deposits, found in the soot at the reactor walls or as slag at the cathode, were characterized using scanning and transmission electron microscopy, electron energy loss spectroscopy, and x-ray diffraction. The products fall into four categories: (1) elements that can be encapsulated in the form of their carbides (B, V, Cr, Mn, Y, Zr, Nb, Mo); (2) elements that are not encapsulated but tolerate the formation of graphitic carbon cages (Cu, Zn, Pd, Ag, Pt); (3) elements that form stable carbides, competing with and pre-empting the carbon supply for the graphitic cage formation (Al, Si, Ti, W); and (4) the iron-group metals (Fe, Co, Ni) that stimulate the formation of single-walled tubes and strings of nanobeads in the conventional arc discharge condition, and produce the nanometer-size carbon-coated ferromagnetic particles in a modified arc discharge in which metals are in molten form in graphite crucible anodes exposed to a helium jet stream. The criterion determining the formation according to one of the four categories is discussed on the basis of this extended study. It is apparent that the physical properties such as vapor pressure, melting and boiling points, the completeness of the electronic shells of the elements, or their heat of carbide formation are not sufficient to explain the selectivity of the encapsulation without exceptions. A hypothesis is advanced that emphasizes the existence of the carbide, interfacial compatibility with the graphitic network, as well as the transport and supply parameters in the reaction space.
Solid-state dye lasers based on modified rhodamine 6G dyes copolymerized with methacrylic monomers
Authors: Costela A. , Garcia-Moreno I. , Figuera J. M. , Amat-Guerri F. , Mallavia R. , Santa-Maria M. D. , Sastre R.
Published: July 2002

Modified rhodamine 6G molecules with polymerizable double bonds have been copolymerized with methacrylic monomers and the resulting polymers have been pumped at 337 nm with a N2 laser in a transversal configuration. The preparation of these new materials is described in detail and their lasing properties are evaluated. Important increases in photostability, with lasing efficiencies similar to those found for the parent dye rhodamine 6G in ethanol solution, have been obtained for some of these materials. Lifetimes (measured as an 80% efficiency drop) in excess of 20 000 shots at repetition rates of 2 Hz have been demonstrated. Strong dependence on pump repetition rate was observed. Possible mechanisms and processes responsible for the behavior of these materials are discussed. By using a rotating system where the sample is scanned in a continuous way, the laser output remained stable, with no sign of degradation, after 500 000 shots.
Kerr rotation enhancement and correlation between perpendicular anisotropy and Kerr effect in PtCu(Al,Ag)/Co multilayers
Authors: Wang Y. J. , Guo Z. H. , Zhu D. K. , Shang C. H.
Published: July 2002

The effects of doping Cu, Al, and Ag in Pt spacer layers on the perpendicular anisotropy Ku and the polar Kerr rotation Θk in the wavelength range of 400–800 nm have been investigated for sputtered 0.8 nm Pt/0.3 nm Co multilayers. Ku and Θk measured below 633 nm decrease with the increase of the concentrations of Cu, Al, and Ag in the Pt spacer layers. It is found that the variation of Ku and Θk with the doping concentrations follows a quadratic equation of Ku=aΘ2k+b (a, b are constants here). This suggests that both Ku and Θk originate from a common micromechanism, i.e., spin-orbit coupling. An obvious enhancement in the peak of the polar Kerr rotation appears at 770 nm for Cu and Ag dopings and at 680 nm for Al doping. Moreover, the polar Kerr rotation Θk* at this enhanced peak shows an oscillation behavior with the increasing doping concentrations in the Pt spacer layers.
Raman spectroscopic study of surface layer in fluorine-implanted Si
Authors: Park Yong-Jik , Mo Yujun , Kim Jong-Jean
Published: July 2002

Raman scattering application was introduced to directly probe the depth profile of structural changes in a very thin surface layer of F+-implanted Si by use of a single Ar+ laser (488 nm) excitation. The results of Raman scattering and sheet resistance measurement showed an unusual annealing behavior of the F+-implanted Si:In the range of annealing temperature Ta from 200 °C to 400 °C, disordering was observed to increase with increasing Ta but a stronger trend of ordering with Ta increasing further above 400 °C. This abnormal behavior could be explained as due to competition between the ordering effect of thermal annealing with increasing Ta and the disordering effect of the implanted fluorine ions randomly breaking the Si–Si crystal bonds in the surface diffusion layer.
Prediction of low dose-rate effects in power metal oxide semiconductor field effect transistors based on isochronal annealing measurements
Authors: Dusseau L. , Randolph T. L. , Schrimpf R. D. , Galloway K. F. , Saigné F. , Fesquet J. , Gasiot J. , Ecoffet R.
Published: July 2002

A method for predicting the long term behavior of semiconductor devices in the low dose-rate ionizing-radiation space environment is presented. The operating conditions related to this environment are briefly reviewed. The new method consists of three major steps. The first step is the determination of the trap characteristics using the experimental recording of an isochronal annealing curve. The second step is the prediction of the isothermal annealing behavior deduced from the experimentally deduced trap characteristics. This approach makes it possible to avoid time-consuming isothermal measurements. As trapping and detrapping processes are independent, combining both processes by convolution, the last step, allows prediction of low dose-rate effects. Up to now, this accelerated characterization method has not been applied to electronic devices. An experimental application of the model to predict the long term behavior of a typical metal oxide semiconductor field effect transistor is given and the results, as well as the validity and the limitations of the model, are discussed.
Characterization of heterojunction devices constructed by amorphous diamondlike films on silicon
Authors: Konofaos N. , Thomas C. B.
Published: July 2002

The electronic properties of amorphous diamondlike carbon (DLC) films on silicon were examined for their capability for application to electronic devices. Metal-insulator-semiconductor (MIS) diodes and p-n heterojunction devices were created and characterized. The films used were grown using rf plasma assisted CVD of methane. They were grown on n-type silicon (100) wafers. Their structural composition was identified by Raman spectroscopy, ellipsometry, and x rays. They showed an insulating behavior and they were suitable for the creation of MIS devices. They showed extremely low internal conductivity due to defect currents. This conductivity showed a behavior of the form I∼T1/4. Then the density of trapping states at the silicon/carbon interface was measured using the conductance technique. The aim of investigating the nature and behavior of these states was to determine the magnitude of the density of states and try to find a way to reduce it. Thus optimization of the DLC/silicon interface could be made, for future reference to the construction of heterojunction devices containing the DLC/silicon configuration. The values of the density of states were of the order of 1011–1012 cm−2 eV−1. Annealing had the effect of reducing the magnitude of the Dit. The ion implantation technique was used to transform the insulating DLC films into semiconducting by adding boron ions as dopants to achieve p-type conductivity. Thus p-n heterojunction devices were made, having silicon as one of the elements and DLC as the other element. Four different doses of boron were implanted, producing different conducting properties of the DLC films. Those devices performed like Schottky diodes for low boron doses and like p-n diodes for high doses.
Influence of fluorine in BF2+ implantation on the formation of ultrashallow and low-leakage silicon p+n junctions by 450–500 °C annealing
Authors: Nakada Akira , Kanemoto Kei , Oka Mauricio Massazumi , Tamai Yukio , Ohmi Tadahiro
Published: July 2002

The influence of fluorine upon the annealing behavior at 450–500 °C of BF2+ implanted layers on silicon wafers was investigated by measurement of the sheet resistance, the carrier profile, and the crystallinity. The junction leakage current was also measured. Approximately one order of magnitude retardation in the average regrowth rate and lower electrical activation of implanted boron were observed in BF2+ implanted layers as compared with B+ implanted preamorphized layers. However, a leakage current level as low as 1.97×10−9 A/cm2 was measured, which is about three orders of magnitude less than reported in the literature. This result was obtained in the BF2+ implanted silicon p+n junction at an annealing temperature as low as 500 °C by employing ultraclean ion implantation techniques.
Finite size effects in the static and dynamic magnetic properties of FeNi wire array structures
Authors: Ercole A. , Adeyeye A. O. , Daboo C. , Bland J. A. C. , Hasko D. G.
Published: July 2002

We report on systematic studies of both the static and dynamic properties of FeNi wire arrays on GaAs(001) substrates. The wires were between 0.4 and 10 μm wide and were separated by twice their width. The static magnetic properties were investigated using magneto optical Kerr effect magnetometry. The dynamical magnetic properties (spin-waves) were investigated by Brillouin light scattering in the Voigt geometry. With an external field applied along the hard shape axis, the saturation field was observed to increase and the spin-wave energies decreased with decreasing wire size. For fields applied along the (easy) axis of the wire, we observed an increase in the coercive field as the width of the wire is decreased. The frequency of the surface mode was found to increase with decreasing wire size while the first volume mode frequency was found to be wire size independent.
Effects of Fe doping in the colossal magnetoresistive La1−xCaxMnO3
Authors: Ahn K. H. , Wu X. W. , Liu K. , Chien C. L.
Published: July 2002

The effect of Fe doping (<20%) on the Mn site in the ferromagnetic (x=0.37) and the antiferromagnetic (x=0.53) phases of La1−xCaxMnO3 has been studied. Upon doping, no appreciable structure changes have been found in either series. However, conduction and ferromagnetism have been consistently suppressed by Fe doping. Colossal magnetoresistance has been shifted to lower temperatures, and in some cases enhanced by Fe doping. These results are not due to the strong lattice effects commonly seen in doping of the La sites. Rather, replacement of Mn3+ by Fe3+ depopulates the hopping electrons, and weakens the double exchange. The effect of Fe doping can be explained in terms of the band structure.
Temperature dependence of interlayer coupling in δ MnGa/(Ga,As,Mn)/δ MnGa trilayers
Authors: Akinaga H. , Van Roy W. , Miyanishi S. , Tanaka K.
Published: July 2002

We present the temperature dependence of the interlayer coupling, from 15 to 300 K, in ferromagnet/semiconductor/ferromagnet trilayers with the nominal structure of 10 nm δMn60Ga40/GaAs (n monolayers)/20 nm δMn54Ga46 [n=6–16 monolayers (ML) nominally] grown on (001) GaAs substrates by molecular-beam epitaxy. Since compositional analysis showed a strong diffusion of Mn into the GaAs spacer layer, we represent the trilayer structure as MnGa/(Ga,As,Mn)/MnGa. The magnetic-circular-dichroism loops showed antiferromagnetic coupling between both MnGa layers for the samples with a spacer layer from 6 to 14 ML GaAs nominally in the whole temperature range. The temperature coefficient of the coupling field was found to be positive for 6–8 ML spacers and negative for 10–14 ML spacers. We interpret these facts as the competition between two (or more) coupling mechanisms. For the sample with a 16 ML GaAs spacer layer, the interlayer coupling was antiferromagnetic below 200 K, but ferromagnetic above 200 K.
Magnetic properties of FeAlN films at elevated temperatures
Authors: Zheng P. , Bain J. A. , Kryder M. H.
Published: July 2002

FeAlN films were fabricated by reactive sputtering from an Fe alloy target in a nitrogen containing plasma. By varying the nitrogen content in the films, magnetic moment as high as 20 kG and coercivities less than 1 Oe can be achieved at room temperature. However, it has been observed that the soft properties of these films experience a reversible degradation at elevated measuring temperatures. The critical temperature, T0c, defined as the temperature at which the coercivity doubles, generally decreases as more nitrogen is incorporated into the film. T0c agrees well with the temperature where remanent squareness (Br/Bs) equals 0.83, indicating a reduced intergranular exchange coupling in films. However, T0c is far below either the reported Curie temperature of the γ′-Fe4N phase or that of the α-Fe phase, which are found in these films. It is suggested that an interfacial granular phase between the grain boundaries of α-Fe or γ′-Fe4N crystallites is responsible for the low T0c. When the temperature increases above T0c, the interfacial phase becomes paramagnetic, and the exchange interaction between crystalline grains becomes weak, thereby causing the coercivity increases.
Observation of the development of hysteretic behavior using a scanning tunneling microscope
Authors: Zasadzinski Roberta , De Wilde Yannick , Crabtree George W.
Published: July 2002

A scanning tunneling microscope was used to record tip-sample displacements inferred from the tunnel current versus applied piezoelectric voltage. This provides a means to determine the range in which the mechanical system, especially the piezoelectric element, exhibits hysteretic behavior. Graphite and gold were used as the substrate samples. With graphite, reversible behavior of the displacements is observed until 2.1 Å; beyond this point, the system exhibits persistent irreversible behavior. In the gold system, irreversible behavior appears initially at 0.8 Å, but repeated cycling extends the range of reversibility to a displacement of 3–4.8 Å. Irreversible behavior dominates beyond this tip displacement range, although the system exhibits sporadic reversible behavior even for tip excursions as large as 46 Å.
Addendum: Deep emission band at GaInP/GaAs interface
Authors: Kwok S. H. , Yu P. Y. , Uchida K. , Arai T.
Published: July 2002

We have performed high pressure photoluminescence studies of the deep emission band in GaInP/GaAs quantum well. Our results suggest that this peak is related to donor-acceptor pair transitions in the GaAs well.
High-lying thermally excited subbands of two-dimensional electron gases in GaAs/AlGaAs heterojunction for modulation-doped field-effect transistor
Authors: Chen Zhanghai , Hu C. M. , Liu P. L. , Shi G. L. , Shen S. C.
Published: July 2002

The cyclotron resonance of two-dimensional electron gases was directly measured on a modulation-doped field-effect transistor structure by the gate voltage ratio spectroscopy. The intersubband energies between the lowest subband and the subbands with quantum index up to i=5 were determined by resonant subband-Landau-level coupling (RSLC) under relatively low magnetic field. The experimental results were in good agreement with the self-consistent calculations including the depolarization shift and exciton-like effect corrections. The quantum index dependence of the level splitting due to the RSLC was discussed.
Study on magnetoresistance coercivity and aging for [FeNi/Cu/Co/Cu]N spin valve multilayered films
Authors: Fang Rui-yi , Chen Ting-yong , Yu Ying-lei , Dai Dao-sheng
Published: July 2002

Spin valve [FeNi/Cu/Co/Cu]N multilayers were prepared using the electron beam method. The influence of the thickness of magnetic and nonmagnetic layers, preparation process, and coercive force Hc on the magnetoresistance (MR) were studied. Using fairly optimum preparing technology, we prepared many samples with low center field H0 in the range of 10–20 Oe, the MR merit is larger than 0.2%/Oe, where H0 is the center magnetic field of the linear region in the MR-H curve. The variation of MR in this linear region is reversible during repeated magnetizing. The change of MR is smaller than 1% for several samples after aging for one year in a dry air chamber at room temperature. Moreover, the MR value decreases greatly when Cr or Cu is added into the Co layer, or Co layers are replaced by SmCo5 magnetic layers.
Doping effect on normal incident InGaAs/GaAs long-wavelength quantum well infrared photodetectors
Authors: Wang S. Y. , Lee C. P.
Published: July 2002

8–12 μm InGaAs/GaAs quantum well infrared photodetectors with two different well doping concentrations have been studied. The devices with and without surface gratings are compared for normal incident operation. It is found that the TE to TM absorption ratio depends on the doping density in the quantum wells. A higher doping density increases TE absorption. A detectivity about 1×1010 cm Hz1/2/W and a peak responsivity of 0.23 A/W at 9 μm have been obtained for the grating-free devices.
Influence of mobility fluctuations on random telegraph signal amplitude in n-channel metal–oxide–semiconductor field-effect transistors
Authors: Godoy A. , Gámiz F. , Palma A. , Jiménez-Tejada J. A. , Banqueri J. , López-Villanueva J. A.
Published: July 2002

The amplitude of random telegraph signals (RTS) in an n-channel metal–oxide–semiconductor field-effect transistor has been investigated. Current fluctuations originating when a single-channel electron is trapped or detrapped in the silicon dioxide have been evaluated. A simulation has been performed where the inversion-layer quantization, the dependence of the electron mobility on the transverse and longitudinal electric fields, and the influence of the oxide charges on free-carrier density and on electron mobility have been taken into account. This procedure provides the chance of studying the influence of trap depth in the oxide on the RTS amplitude. In addition, the contributions of the mobility and carrier fluctuations on the amplitude of discrete current switching have been separated, revealing the importance of each factor. Normalized mobility fluctuation has been defined and it was found that its dependence on the gate and drain voltages helped to explain the behavior of the normalized current fluctuations. Finally, the scattering coefficient was evaluated, showing good agreement with previously published data. All these results have allowed us to gain further insight into the role played by electron mobility fluctuations on random telegraph signal amplitude.
A new method to detect geometrical information by the tunneling microscope
Authors: Tasaki Shuichi , Levitan Jacob , Mygind Jesper
Published: July 2002

A new method for the detection of the geometrical information by the scanning tunneling microscope is proposed. In addition to the bias voltage, a small ac modulation is applied. The nonlinear dependence of the transmission coefficient on the applied voltage is used to generate harmonics. The ratio of the harmonics to the dc current is found to give the width between the sample and the probe, i.e., the geometrical information. This method may be useful to measure materials, where the local-spatial-density of states may change notably from place to place.
Optical parameters of pyrite thin films
Authors: de las Heras C. , Lifante G.
Published: July 2002

Optical properties of pyrite thin films obtained by iron sulfuration have been studied in samples of different iron thickness (0.12–0.5 μm) sulfurated at different temperatures in the range 620–770 K. Dispersion values of the optical absorption coefficient and refractive index for wavelengths 0.8–3.0 μm have been determined by fitting the optical transmission spectra in this range using a multivariable nonlinear program of optimization. Values of absorption background, optical energy gap, and optical film thickness have been obtained for all the samples. These values have been related to microstructural and electrical properties measured in the films. The background absorption is associated with the polycrystalline nature of the samples, as well as the presence of an interface between pyrite film and glass substrate. The optical energy-gap variation found in the samples is attributed to the difference in structure and stoichiometry in the grain and at grain boundaries, respectively.
p–n
and p–n–p junction arrays in CuInSe2 crystals: Cathodoluminescence and capacitance study
Authors: Medvedkin G. A. , Sobolev M. M. , Solovjev S. A.
Published: July 2002

Microstructures in p-CuInSe2 single crystals tailored by a strong electric field have been studied using the methods of local cathodoluminescence, electron-beam-induced current (EBIC), capacitance–voltage (C–V) characteristics, and deep-level transient spectroscopy (DLTS) spectra, and have been considered through a prism of elemental stability in the ternary compound. The shortest-wavelength cathodoluminescence radiation (ℏωm=1.023 eV) is observed from a layer of n type, the longer-wavelength radiation (ℏωm=1.01 and 0.973 eV), from p-type areas, both a p layer and the p-bulk crystal. The analysis of the spectra has allowed us to attribute experimental features to optical transitions associated with donor and acceptor levels of VCu, VSe, Cui point defects. The capacitance study by the C–V characteristics and DLTS spectra as well as the EBIC test have shown formation of diode-type or transistor-type microstructures. The |ND−NA| concentration profile, thermal activation, and emission energies of 22–25 and 170 meV, and a capture cross-section σh=2×10−19 cm2 of the deep donor level have been obtained for the microstructures. The two-stage resistive model has been considered for p–n and p–n–p junction formation.
Harnessing reverse annealing phenomenon for shallow p-n junction formation
Authors: Krasnobaev L. Y. , Cuomo J. J. , Vyletalina O. I.
Published: July 2002

Monocrystalline silicon was implanted with 60 keV fluorine and 20 keV boron ions and annealed. Carrier profile, fluorine and boron redistribution, and the parameters of p+-n junctions were investigated. In ion implanted Si two specific regions were observed in which peculiarities in carrier concentration, resistivity, and F atoms redistribution occurred. It was reasoned that the “under-surface” specific region is enriched with vacancy-type defects while the “amorphous/crystalline (a/c) interface” region is enriched with interstitial type defects. After annealing at a temperature corresponding to the reverse annealing phenomenon, boron atoms were activated in the “under-surface” and deactivated in the “a/c interface” region. The possibility of PMOS transistor fabrication with ultrashallow p+-n junction (60 nm) and low leakage current by F++B+ implantation and low temperature (600–700) °C annealing by using this phenomenon was demonstrated.
Effect of doping density on capacitance of resonant tunneling diodes
Authors: Jo J. , Alt K. , Wang K. L.
Published: July 2002

We studied capacitance and parallel resistance in resonant tunneling diodes as a function of the doping density in the emitter and the collector regions. Capacitance was obtained by analyzing resonance in the admittance measured. Our data show that the capacitance varies with the doping density, and that the capacitance is smaller than the value expected from the growth parameters. Electron density modulation exists around the barriers, and capacitance has doping density dependence as a result of the modulation.
Near-ballistic transport and current–voltage characteristics of a GaAs/AlGaAs heterojunction field effect transistor under the influence of impurity scattering
Authors: Fu Y. , Willander M.
Published: July 2002

By calculating the current–voltage relation for a quantum-size GaAs/AlGaAs heterojunction field effect transistor, we have shown that the electronic near-ballistic transport from the source to the drain is ideal only at zero source-drain bias in the absence of scattering centers. The electron transmission coefficient of the near-ballistic transport reduces following the increase of the source-drain bias so that the source-drain current is lower than the one at ideal transmission condition. The current is further reduced when impurities are introduced and the current reduction depends on the concentration and spatial configuration of impurities. Together with our early work we have shown that the ionized impurities and heterointerface roughness are two important factors in determining the ballistic transport properties in a heterojunction field effect transistor. An optimal current is reached when the AlGaAs spacer in a usual GaAs/AlGaAs heterojunction transistor is about 100 Å thick.
Kinetics and aging in atomic layer epitaxy ZnS:Mn ac thin-film electroluminescent devices
Authors: Soenen B. , Van den Bossche J. , De Visschere P.
Published: July 2002

The kinetics of the aging of atomic layer epitaxy ac thin-film electroluminescent devices was studied. In a first series of experiments, we aged devices at different temperatures from 50 to 190 °C, and measured the steady-state transferred charge versus voltage characteristics. From monitoring Q145 V, the charge transferred at 145 V, we could trace the relationship between Q145 V and the aging time. The aging process was found to be temperature dependent, and we could deduce an activation energy of 0.34 eV. In a second series of experiments, devices were aged 16 h at room temperature and subsequently heat treated at different temperatures from 250 to 450 °C. Monitoring again Q145 V, we found that the devices recover from aging following the relationship −krecot=ln[Q145 V/Q145 V(t=0)], where t is the heat treatment time. The recovery rate constant kreco was found to have an activation energy of 1.3 eV. In a last series of experiments we found the aging rate to be proportional with the transferred charge. Possibly aging is a process of defect creation at the interface near the substrate. For this creation thermal energy and the energy of the accelerated electrons are needed. The defects can be annihilated by heating the device above 350 °C.
Response to “Comment on ‘The analysis of piezoelectric/piezomagnetic composite materials containing ellipsoidal inclusions’ ” [J. Appl. Phys. 82, 5268 (1997)]
Authors: Huang Jin H. , Kuo Wen-Shyong
Published: July 2002

The approach that we have adopted is fundamentally different from Nan’s, although the numerical results of both appear to be very similar. Using this approach, the resulting properties can be expressed in a rather simple form, without the need to evaluate the intermediate terms requiring additional calculations such as Nan’s Eqs. (28) and (29) [Phys. Rev. B 50, 6082 (1994)]. For circular continuous fiber, for example, the use of our approach enables the magnetoelectric coupling coefficients to be expressed as λ̄33=[2f(1−f)e31*q31]/[(1−f)(C12−C12*−C11*)−(1+f)C11], in which all terms involved are fundamental material constants. The influence of the material constants on the coupling coefficient can be readily understood.
Resonance effects in photoluminescence from deep traps in CdSxSe1−x doped glasses
Authors: Ivanda M. , Bischof T. , Lermann G. , Materny A. , Kiefer W.
Published: July 2002

We present photoluminescence studies on CdSxSe1−x semiconductor doped glasses with gap energies ranging from about 2 to 3 eV (400–600 nm). The investigations were performed by near-resonance as well as temperature-dependent resonance Raman spectroscopy. On the basis of the strongly resonant behavior of the deep trap photoluminescence with the excitonic states of the nanocrystallites, we have demonstrated that—besides the effect of photodarkening—inconsistencies in the experimental results of semiconductor doped glasses presented in literature, could be due to changes in the electronic resonance conditions when experimental parameters are changed.
Characterization of excimer laser annealed polycrystalline Si1−xGex alloy thin films by x-ray diffraction and spectroscopic ellipsometry
Authors: Yu Guolin , Krishna Kalaga Murali , Shao Chunlin , Umeno Masayoshi , Soga Tetsuo , Watanabe Junji , Jimbo Takashi
Published: July 2002

Thin films of Si1−xGex alloys of different compositions x have been deposited, on single-crystal Si (100) surface and glass substrates, by simple ion beam sputtering, at room temperature. Crystallization of these films has been done using excimer laser annealing. Structural and optical properties of as-deposited and annealed Si1−xGex alloy films are characterized by x-ray diffraction (XRD), uv-visible spectrophotometry, spectroscopic ellipsometry (SE), and Auger electron spectroscopy (AES). The as-deposited films, both on Si and glass, have been found to be amorphous by XRD. Polycrystalline nature of laser-annealed samples has been evidenced by both x-ray and SE measurements. The results of x-ray, uv-visible, AES, and SE are compared and discussed. The poly-Si1−xGex films were oriented predominantly to (111) and the grain sizes were determined from half-width of x-ray peaks. The compositions x of Si1−xGex films have been evaluated from the SE dielectric function ε(ω) data, using the second-derivative technique, and are found to be 0.23 and 0.36 for two different compositions. A detailed analysis of ε(ω) with the effective-medium theory has demonstrated the volume fraction of crystalline Si1−xGex increases with the increasing energy of laser irradiation.
Thermoelectric amplification of phonons in cylindrical quantum well wires
Authors: Nunes O. A. C. , Agrello D. A. , Fonseca A. L. A.
Published: July 2002

The damping coefficient γq of acoustical phonons interacting with electrons confined in a cylindrical quantum well wire subjected to an external temperature gradient is calculated. The phonon amplification coefficient (γq>0) under certain conditions for material and temperature gradient is obtained. In the size quantum limit (ground state), in nondegenerate semiconductors, the amplification coefficient is found to be enhanced over its bulk value for the whole range of the radius of the wire. It is also found that phonon amplification is obtained for smaller temperature gradients as compared with their corresponding values in bulk. An application is made for AlxGa1−xAs/GaAs quantum well wires.
Growth and thermal behavior of sputtered Mo/Al2O3 multilayers
Authors: Veldkamp M. , Zabel H. , Morawe Ch.
Published: July 2002

We have examined the structure and thermal stability of Mo/Al2O3 multilayers grown on sapphire (112̄0) substrates by rf and rf-magnetron sputtering techniques. The properties of the multilayer stack have been analyzed by x-ray diffraction. A fit to the data points based on the dynamical scattering theory shows an internal oxidation of molybdenum after annealing. The multilayer system is stable up to 900 °C for 3 h. At 1000 °C, Bragg measurements show the formation of large Mo (110) crystallites, whose size exceeds one single Mo layer. Furthermore, we have performed in situ resistance measurements during the deposition of the film indicating the percolation threshold of molybdenum to be about 2.5 nm.
Theory of thermally stimulated charges in metal–oxide–semiconductor gate oxide
Authors: Cai Jin , Sah Chih-Tang
Published: July 2002

The theory of thermally stimulated charges (TSQs) due to thermal emission of trapped carriers in thin oxide film is analyzed in detail which relates TSQs to the gate voltage shifts of a metal–oxide–semiconductor transistor during an arbitrary temperature ramp. Solutions are obtained for stepped and continuous temperature ramps with a constant rate. The Simmons–Taylor formula for extracting the density of states of oxide traps is shown to be off by a numerical factor. The Lu–Sah formula used in their TSQ experiments is shown to agree with the general result of Miller–Fleetwood–McWhorter. The present TSQ theory gives a minimum full width at half maximum of 0.11 eV for the trap reported by Lu and Sah at EV+1.44 eV in thin silicon oxide films compared with their experimental 0.07 eV. The difference could be attributed to multiphonon absorption during thermal emission of the trapped oxide holes.
Effects of impurities on dielectric properties of fluorozirconate glasses at microwave frequencies
Authors: Ding X. Z. , Taijing Lu , Ong C. K. , Tan B. T. G. , Dai Yisheng
Published: July 2002

The dielectric properties of fluorozirconate glasses doped with different impurities have been investigated in the frequency region of 3.0–12.5 GHz using a microwave network analyzer. For glasses containing oxide impurities such as PbO, SiO2, and TiO2, the position of the dielectric resonance, which is observed in the pure fluoride glass, shifts to higher frequencies. Amplitudes of the resonance peaks also become much smaller. The oxide impurities are observed to exist as large numbers of tiny precipitates in the glasses. When the glasses are doped with InF3, the position of the resonance peak shifts to a higher frequency but the amplitude of the peak remains unchanged. The InF3 may be substituted for AlF3 in the glasses. A higher half-resonance width is observed in the doped fluorozirconate glasses. The changes in the dielectric properties are attributed to the different behaviors of the impurities, which affect the structural interunit vibration in the fluoride glasses.