bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of an optically pumped titanium vapor laser
Authors: Hirata K. , Yoshino S. , Ninomiya H.
Published: July 2002

Characteristics of an optically pumped titanium vapor laser have been investigated on the 3d2 4s(4P)4p 3D01−3d3(4F)4Rs 3F2 transition at 551.4 nm. An excimer laser of 14 mJ/pulse for vaporization and an N2 laser of 5 mJ/pulse for optical pumping are employed. The laser output energy is measured as a function of buffer gas pressure, delay time, output mirror reflectivity, pumping laser intensity, and vaporizing laser intensity. The possibility of lasing on the other transitions is also discussed.
The synthesis and properties of low barrier Ag-Ga intermetallic contacts to n-type GaAs
Authors: Kniffin Margaret L. , Helms C. R.
Published: July 2002

It is demonstrated that uniform silver-gallium alloy films, containing up to 30% gallium, can be controllably and reproducibly fabricated by electron-beam evaporation from a single alloy source. As expected from bulk thermodynamic arguments, these films are metallurgically stable with respect to GaAs up to their melting point. The alloying of silver with gallium results in a substantial reduction in n-type barrier height. Analogous increases in barrier height were observed for contacts to p-type material. Barrier heights as low as 0.59–0.62 eV were measured for annealed ζ-AgGa contacts to n-type material.
X-ray diffraction of multilayers with a systematic deviation of period
Authors: Gao Chen , Jiang Zuimin , Wu Zigin
Published: July 2002

The x-ray diffraction profile of multilayers with systematic deviation of period has been studied and simulated on computer. The peak shift, asymmetric peak shape, and decrease of peak intensity can be predicted. The influence is much more severe than that of random fluctuation of period.
Critical current measurements in YBa2Cu3O7−x thin film grown on LaAlO3 substrate
Authors: Qiu X. G. , Cui C. G. , Zhang Y. Z. , Li S. L. , Zhao Y. Y. , Xu P. , Li L.
Published: July 2002

The critical current density Jc(B,T) of epitaxial YBa2Cu3O7−x (YBCO) thin films on LaAlO3 was measured under different applied magnetic fields (0–7 T) with the temperature ranging from 65 to 79 K. At 65 K, the zero-field critical current density of the best film was 5.8×106 A/cm2; even at magnetic fields up to 7 T, Jc could reach as high as 1×106 A/cm2. Strong anisotropy was observed at 79 K. The anisotropy behavior diminished with the decrease of temperature. Experimental results showed that Jc was proportional to (Tc−T)3/2 ; this was in accordance with the theoretical explanation by the Josephson junction model for granular superconductors.
Characterization of the Ag/YBa2Cu3O7−x contact in thin films
Authors: Jia Q. X. , Anderson W. A. , Zheng J. P. , Zhu Y. Z. , Patel S. , Kwok H. S. , Shaw D. T.
Published: July 2002

Silver (Ag) contacts to very thin superconducting YBa2Cu3O7−x films were prepared by thermal evaporation. The nature of the Ag/YBa2Cu3O7−x contact during thermal treatment was in situ investigated by a combination of three- and four-terminal resistance measurements. The experimental results suggested that the interaction between Ag and the YBa2Cu3O7−x film began at a temperature of around 370 °C. The contact resistance measurement for different films also demonstrated that the contact property was a strong function of the film quality and surface conditions. The lack of reproducibility in forming a low-resistance contact to very thin YBa2Cu3O7−x films and the high probability of degrading the film quality after thermal treatment of the contact might be due to the excess Ag doping in YBa2Cu3O7−x. Ag island formation, as revealed by scanning electron microscopy after thermal treatment of the contact, is a limitation of Ag for use as a good contact electrode for very thin superconducting films.
Surface order transition in nematic liquid crystals induced by the flexoelectric polarization
Authors: Barbero G. , Durand G.
Published: July 2002

The influence of the flexoelectric polarization on the nematic surface energy is analyzed. It is shown that if the dielectric constant of the substrate is lower than a critical value the undistorted orientation is no more the one corresponding to lowest energy. The presence of a conducting substrate is also considered. In this case it is shown that by changing the thickness of the dielectric material deposited over the conducting material, a surface order transition is expected. Furthermore, the influence of a finite anchoring energy between nematic and substrate on the critical value of the dielectric constant is discussed.
Reactive ion etching of zinc doped InP using methane and hydrogen: Assessment of the degree and extent of changes in surface carrier concentration
Authors: Singh Jaspal
Published: July 2002

Reactive ion etching of zinc-doped InP has been assessed in terms of the degree and extent of the passivation (reduction in carrier concentration). It is found that passivation of acceptors depends on the rf power as well as etching times used. Reduction in carrier concentration as large as three orders of magnitude can be achieved by the use of powers as low as 0.5 W/cm2 for 10 min. The effect of this passivation on the characteristics of semiconductor lasers is reported.
Polydisperse analysis of small-angle intensities scattered by natural coals
Authors: Ciccariello S. , Benedetti A. , Polizzi S.
Published: July 2002

The small-angle x-ray intensities, scattered by four of the most typical natural coals, are analyzed assuming that coals behave as polydisperse distributions of cubic particles having a layered structure with an interlayer spacing partly dependent on particle sizes. The particle distributions are determined by a rather fast numerical algorithm, and in the considered momentum-transfer range, they appear independent of the interlayer spacing. The model reproduces quite well only the intensities which are neither particularly structured nor fractal at very small momentum transfers. Micropore, mesopore, and macropore relative sizes are estimated starting from the obtained particle distributions.
Hall effect of the high-T
c superconducting Bi-Sr-Ca-Cu-O thin film
Authors: Li Bing-Zong , Aiken Robert G. , Daneshvar Kasra , Kwor Richard Y. , Kalkur T. S.
Published: July 2002

The Hall effect of BiSrCaCuO thin film is studied in the temperature range of 2–300 K. In the normal state the Hall-effect data show a holelike carrier conduction and the Hall coefficient decreases slowly with increasing temperature. The hole density obtained at room temperature is 3×1021 cm−3. Near the superconducting transition temperature (TMid =83 K), the Hall coefficient shows a rapid change and drops sharply from a positive value to a negative minimum value with decreasing temperature.The possible physical meaning of the obtained results is discussed.
Dopant diffusion control in silicon using germanium
Authors: Aronowitz Sheldon
Published: July 2002

Theory and experiment reveal that germanium, in large quantities and when integrated in the crystalline silicon environment, has a long range influence on electrically active dopant species. In regions having very high concentrations of substitutional germanium, calculations predict, and experiments confirm, sharp distinctions between the diffusion pattern exhibited by n-type dopants and the diffusion pattern produced by p-type dopants. n-type dopant diffusion, whether the species occupies a substitutional site or an interstitial position, is predicted and observed to be retarded through regions of very high concentrations of germanium. On the other hand, the dual behavior pattern for p-type dopants, predicted successfully, results in diminished diffusion of interstitial dopant but enhanced diffusion when the species occupies a substitutional site.
Anomalous behavior in transport critical current density of YBa2Cu3O7−x and YBa2Cu3O7−x-Ag bulk samples
Authors: Hascicek Y. S. , Kennedy R. J. , Testardi L. R. , Niculescu H. , Gielisse P. J. , Leventouri Th.
Published: July 2002

Transport critical current density Jc versus temperature measurements on bulk YBa2Cu3O7−x and YBa2Cu3O7−x-Ag samples were carried out. An anomalous bifurcation in Jc-T curves was observed at temperatures between 55 and 88 K. The bifurcation was introduced by application of a transient pulse. The x-ray, scanning electron microscopy, and electron microprobe analysis results on these samples are presented.
Accurate methods for simulating electroreflectance and photoreflectance spectra of GaAs
Authors: Jackson P. L. , Seebauer E. G.
Published: July 2002

Various methods have been used up to now in order to simulate the effects of inhomogeneous electric fields on the modulation spectra of semiconductors. Some methods involve partitioning a layer with a continuously varying field into a series of discrete steps. We show that in the case of a wide space-charge region, solving the resulting set of reflectance equations directly can give misleading results under some conditions because of subtle numerical problems. However, a WKB approach exists that avoids these problems and can be used for GaAs under essentially all conditions. Our simulations lend support to an excitonic mechanism for spectral ‘‘rotation’’ in photoreflectance of GaAs even at room temperature.
Movement of phase boundaries of metals subjected to surface periodic energy pulses
Authors: Smurov I. Yu. , Uglov A. A. , Lashin A. M. , Matteazzi P. , Tagliaferri V. , Covelli L.
Published: July 2002

The heat phenomena including heating, melting, evaporation, cooling, and solidification are analyzed by means of mathematical modeling. Velocities and positions of phase boundaries (both evaporation and melting) are determined for different conditions of pulse-periodic energy flow irradiation of metallic materials. Heat process dynamics, determined by the shape of the single energy pulse, by the energy input per oscillation period, and by the average energy density flow, are discussed.
ZnSe/CaF2 quarter-wave Bragg reflector for the vertical-cavity surface-emitting laser
Authors: Lei C. , Rogers T. J. , Deppe D. G. , Streetman B. G.
Published: July 2002

Data are presented on an electron-beam evaporated ZnSe/CaF2 distributed Bragg reflector for use on a vertical-cavity surface-emitting laser operating at a wavelength ∼0.98 μm. Mirror characteristics are measured using optical transmission and reflectivity for quarter-wave structures with varying numbers of pairs from one to five. The optical characteristics of the ZnSe/CaF2 quarter-wave stack is compared to similar structures of electron-beam evaporated Si/SiO2 reflectors. The ZnSe/CaF2 mirror is found to be superior to the Si/SiO2 mirror in terms of both higher reflectivity and lower optical loss for all structures investigated. Comparison is also made between ZnSe/CaF2 and Si/SiO2 mirrors in the continuous-wave performance of AlAs-GaAs-InGaAs quantum-well vertical-cavity surface-emitting lasers. Superior laser performance is achieved with the ZnSe/CaF2 mirror in terms of threshold current and lasing efficiency.
Temperature dependence of width of inhomogeneously broadened spectral lines in lightly doped weakly compensated semiconductor
Authors: Gelmont Boris
Published: July 2002

The width of the spectral lines related to intraimpurity transitions in GaAs is determined by random electric fields of charged acceptors and donors. The broadening of spectral lines with the increase in temperature was interpreted as the transition from correlated distribution of electrons located on the donors to the random distribution. Baranovskii and Shklovskii [Sov. Phys. Semicond. 23, 122 (1989)] suggested that the distribution function for intermediate temperatures may be approximated in a lightly doped weakly compensated semiconductor as joint probability distribution for two independent systems. In this paper, the dependence of the line width on temperature is obtained using their approach.
Magnetic resonance and magnetization studies of natural volcanic glasses: Lipari obsidians (abstract)
Authors: Chávez-Rivas F. , Zamorano-Ulloa R. , Galland D. , Regnard J. R. , Chappert J.
Published: July 2002

Magnetic resonance spectra of Fe3+ and Mn2+ ions in natural volcanic glasses, black obsidians from Lipari (Island of Southern Italy), have been investigated at 9 (X band) and 35 GHz (Q band). The spectrum in the X band is found to exhibit at g=4.3 the classical signal of isolated Fe3+ ions.1 At g=2 it is found the superposition of a superparamagnetic signal and a ferromagnetic resonance arising from the small and not so small magnetite particles previously found.2 It was also observed at X band a granular dependence of the g=2 line shape, similar to that observed in polycrystalline powders. At Q band there were two signals, one due to iron clusters at g=2 and a weak hyperfine sextet attributed to Mn2+ free ions. The magnetization for a given temperature (from 1.75 to 20 K) and very high magnetic fields (up to 150 kOe) shows the lack of hysteresis loops and the absence of remanent magnetization, both indicative of superparamagnetism. However, the magnetization curves do not superpose to a Langevin function L[M(H/T)], which reflects the presence of inhomogeneous ferrimagnetic magnetite particles.
Magnetic properties of amorphous BiFeO3-PbZrO3 sputtered films
Authors: Rao B. Uma Maheshwar , Srinivasan G. , Babu V. Suresh , Seehra M. S.
Published: July 2002

Amorphous thin films of (1−x)BiFeO3-xPbZrO3 for x=0.1–0.9 have been prepared by the technique of rf sputtering and the effects of sputtering conditions and annealing at high temperatures on magnetic properties of such films have been studied through magnetization measurements. A sintered polycrystalline target was used to sputter 0.2–1.4-μm-thick films in oxygen, argon, and mixed oxygen and argon atmospheres onto glass and silicon substrates. As-sputtered films are x-ray amorphous and show paramagnetism at room temperature. A hard-ferromagnetlike character with remanence is observed in films annealed at temperatures Ta above 500 °C. The room-temperature magnetization increases with further increase in Ta and shows a maximum for Ta = 650 °C. A partial crystallization occurs for Ta ≳ 650 °C and is accompanied by a decrease in the magnetization. The magnetization for annealed samples shows a dependence on x, with a minimum of 0.6 emu/g for x=0.9 and a maximum of 40 emu/g for x=0.5.
Magnetic properties of CoNiPt and CoNiPd thin films
Authors: Inase T. , Kondo A.
Published: July 2002

CoNiPt and CoNiPd thin films were investigated for high-density longitudinal recording media. The samples were prepared by dc magnetron sputtering. Concentration of Pt or Pd was controlled by changing the number of Pt or Pd chips put on the Co 20 at. % Ni target. It was observed that the coercivity of the samples increased with increasing the Pt or Pd concentration. The x-ray diffraction intensity of Co(002) of the CoNiPt and CoNiPd samples also increased as Pt and Pd content increased, respectively. As a result, it was found that the coercivity increased as the intensity of Co(002) in both films increased. There was no significant difference between CoNi and CoNiPt and CoNiPd films in SEM surface micrographs. The cause of the difference in coercivity may be attributed to the difference in magnetocrystalline anisotropy of the films.
Magnetization fluctuations and characteristic lengths for sputtered CoP/Cr thin-film media
Authors: Tarnopolsky Giora J. , Bertram H. Neal , Tran Lung T.
Published: July 2002

Magnetization fluctuations of uniformly magnetized media have been measured in sputtered CoP thin films as a function of Cr underlayer thickness. Increasing underlayer thickness from 20 to 400 nm in nine steps yields decreasing magnetization fluctuation noise from 210 nm to about 25 nm, similar to the known decrease of transition noise. For virtually every disk, the noise power dependance on magnetization is well fit by the square of the magnetization versus current loop derivative, (dM/dI)2. Thus, the noise mechanism appears to be a modulation process over the entire series. Analysis of measured magnetization noise spectra yields approximate correlation lengths which decrease with increasing Cr underlayer thickness.
Giant magneto-optic rotation in amorphous uranium antimonide (invited)
Authors: Gambino R. J. , Plaskett T. S. , McGuire T. R. , McElfresh M. W.
Published: July 2002

Amorphous U-Sb alloys in the vicinity of the composition U3Sb4 have magneto-optic Faraday rotations of + 2 × 106 deg/cm. This is the highest rotation of any amorphous ferromagnetic material. These alloys also have relatively high Curie temperatures of about 140 K with magnetic moments per uranium of up to 1.4μB. These properties are unexpected since it is known from intermetallic compounds that U atoms must be isolated from each other in order to develop a magnetic moment. In a concentrated random amorphous alloy, no magnetic moment on the uranium would be expected because of the high probability of uranium near neighbors. In the U-Sb amorphous alloys, however, there appears to be chemical short-range order which tends to favor Sb nearest neighbors for uranium. The amorphous U-Sb alloys have Kerr rotations of about −3°. This value is comparable in magnitude but opposite in sign to that of the single-crystal rock salt compound USb in the visible. In these amorphous alloys the Hall angle from the spontaneous Hall effect can be as much as 17°. Similar large magneto-optic and Hall coefficients have also been found in amorphous U-Bi, U-Sb-Mn, and U-Sb-Co alloys.
Germane discharge chemistry
Authors: Doyle J. R. , Doughty D. A. , Gallagher Alan
Published: July 2002

The stable gas products of germane dissociation and subsequent radical reactions have been measured in pure germane glow discharges characteristics of the initial germane fragmentation are inferred from these data. The spatial distribution of discharge optical emission, and of film deposition on glass fibers, have also been measured. Finally, the surface reaction probability β of depositing neutral radicals has been measured to be 0.61±0.09 on the grounded electrode. Major differences between germane and silane discharges occur in all these observables. Possible explanations of these differences are given, but much less chemical data exists for germane, thereby precluding definitive judgments. A probable cause of the normally much poorer semiconductor quality of a-Ge:H films, compared to a-Si:H, is suggested. This is based on the thermodynamics of the H2 release reaction at the growing surface.
Molecular-beam epitaxial growth of InAs/GaAs superlattices on GaAs substrates and its application to a superlattice channel modulation-doped field-effect transistor
Authors: Toyoshima H. , Onda K. , Mizuki E. , Samoto N. , Kuzuhara M. , Itoh T. , Okamoto A. , Anan T. , Ichihashi T.
Published: July 2002

The molecular-beam epitaxial growth conditions for (InAs)m(GaAs)n short period superlattices (SPSs) on GaAs substrates have been optimized by monitoring reflection high-energy electron diffraction (RHEED) intensity oscillations. The RHEED oscillation measurements enable understanding InAs growth behavior on a 7% lattice-mismatch GaAs substrate. Within one monolayer InAs deposition with lower than 560 °C growth temperature can give high SPS crystalline quality. The SPS periodic structure and the monolayer InAs formation, embedded in GaAs layers, have been confirmed by x-ray diffraction and transmission electron microscopy measurements. The obtained thickness controllability for the SPSs is less than±6% for InAs and ±3% for GaAs. The electron Hall mobilities for modulation-doped structures having an (InAs)1(GaAs)n SPS as an electron channel, whose layer index of n varied from 3 to 6, have been compared with those with a pseudomorphic InGaAs random alloy channel which has the equivalent In composition. The SPS channel samples have shown up to 15% higher electron Hall mobilities than the InGaAs alloy channel samples at 77 K. A 0.2-μm-gate (InAs)1(GaAs)6 superlattice channel modulation-doped field-effect transistor (FET) has exhibited a maximum extrinsic transconductance of as high as 450 mS/mm with a 70-GHz cut-off frequency at room temperature. The best noise figure of 0.58 dB with an associated gain of 11.15 dB has been attained. The obtained device characteristics are comparable or superior to those for the corresponding InGaAs alloy channel FETs. These results demonstrate, for the first time, the (InAs)m(GaAs)n SPS potentialities as an ordered counterpart for InGaAs random alloy for high-speed device applications.
Minority-carrier lifetime in AlxGa1−xAs grown by molecular-beam epitaxy
Authors: Ahrenkiel R. K. , Keyes B. M. , Shen T. C. , Chyi J. I. , Morkoc H.
Published: July 2002

AlxGa1−xAs (x>0.30) double heterostructures are grown by molecular-beam epitaxy (MBE) and the minority-carrier lifetimes are measured by time-resolved photoluminescence. The data indicate that the minority-carrier lifetimes in high aluminum (x>0.30) AlxGa1−xAs grown by MBE are comparable to the previously published lifetimes of material grown by liquid-phase epitaxy. The lifetimes in MBE materials appear to be somewhat larger than those measured in materials grown by metalorganic chemical vapor deposition. Factors affecting AlGaAs minority-carrier lifetime, such as the growth temperature, the aluminum concentration, and the confinement layer composition will be discussed.
High-speed electron microscopy of laser-induced vaporization of thin films
Authors: Bostanjoglo O. , Kornitzky J. , Tornow R. P.
Published: July 2002

Laser-driven explosive vaporization of free germanium films was investigated with a high-speed transmission electron microscope. Double frame and streak imaging with nanoseconds exposure and sweep times were exploited to visualize the fast processes. Using focused 30-ns laser pulses of about 1 μJ and 10 MW/cm2, the films were shattered within 100–300 ns by three cooperating mechanisms: Marangoni flow, jerky boiling, and capillary forces. These effects are very different from those ablating supported films. They suggest that large temperature gradients of 1000 K/μm centered near 4000 K are generated within the laser spot, and the homogeneous nucleation theory of boiling is not applicable.
A rebound mechanism for Lomer dislocation formation in strained layer structures
Authors: Dregia S. A. , Hirth J. P.
Published: July 2002

A rebound mechanism is proposed for the formation of Lomer misfit dislocations at interfaces in strained layer structures. The model involves dislocation nucleation at a free surface, glide to the interface, reaction to form the Lomer dislocation and another nucleated dislocation, and glide of the latter to the free surface. For either a strained overgrowth layer or a layer within a multilayer structure, where another interface would replace the free surface, the process is energetically favorable once conditions favor the initial nucleation event. The mechanism is consistent with experimental observations of interface structure, including its thickness dependence, for semiconductor and metal systems.
Spectroscopic measurements of tokamak plasma ion temperature using Doppler broadening of impurity lines: Correction for chordal line-of-sight observations
Authors: Haddad E. , Bélanger C. , Gregory B. C. , Abel G. , Pacher H. D.
Published: July 2002

Tokamak ion temperatures measured using the Doppler-broadened impurity spectral line technique are usually underestimated because the line intensity is integrated along chordal lines of sight and is assumed to be the intensity at the chordal distance from the center of the plasma (radial distance). An analytical correction of the ion temperature radial profile during a series of reproducible discharges on the Tokamak de Varennes reveals a 10%–20% underestimation at the plasma center. The lines used are Ne IX (1248.2 Å) and O VII (1623.7 Å). Reconstruction of spectral line intensities and shapes using measured electron temperature and density profiles, ion density radial profiles simulated by a plasma impurity transport code, and published atomic data can verify and predict this correction.
Recording on Co/Pt magneto-optical disks using a 488-nm wavelength laser
Authors: Hashimoto S. , Maesaka A. , Ochiai Y.
Published: July 2002

Co/Pt multilayer disks with a double-layer and a quadri-layer structure were prepared on a 2 P (photopolimerized) glass substrate with 1-μm-pitched grooves. The read/write characteristics of the disks were studied using Ar gas laser at a wavelength of 488 nm. It was confirmed that very small domains 0.3 μm in length were stably recorded. The carrier-to-noise ratio was 29 and 32 dB (30 kHz BW) at a mark length of 0.3 μm for double-layer and quadri-layer disks, respectively, being larger than that measured for a TbFeCo disk because of a higher figure of merit. In higher-density recording below 0.5-μm mark length, a quadri-layer disk shows a larger recording power margin than a double-layer disk due to the smaller expansion of domain with power, originating from the sharper thermal distribution.
Deep intrinsic and photostructural defect levels in amorphous selenium films
Authors: Chand Suresh , Bhatheja R. C. , Sharma G. D. , Chandra Subhas
Published: July 2002

The thermally stimulated discharge current (TSD) behavior of native (dark rested) and irradiated amorphous selenium films (∼100 μm) has been studied in the temperature range 295–385 K. The TSD spectra of these films shows, in addition to the already reported relaxation at 310 K, a new relaxation peak in the temperature range 370–380 K. The origin of this relaxation is attributed to the trapping of charge carriers i.e., electron and holes at deep intrinsic and irradiation induced photostructural defect levels lying at ∼1.6 and 1.7 eV, respectively.
Light detection using high-T
c microstrip transmission lines as a probe of film homogeneity
Authors: Culbertson J. C. , Newman H. S. , Strom U. , Pond J. M. , Chrisey D. B. , Horwitz J. S. , Wolf S. A.
Published: July 2002

We have studied the effects of light on high-temperature superconductor microstrip transmission lines under conditions for which a bolometric photoresponse is expected. We illustrate the pitfall of comparing a spatially local property (such as microwave detected photoresponse) and a global property (such as microwave transmission), and then drawing conclusions regarding the bolometric character of the photoresponse. For low microwave powers, the photoresponse, measured as function of the position of the spot illuminated, provides a measurement of the spatial inhomogeneity of the microwave properties of the film. For microwave powers large enough to depress the critical temperature, such measurements provide information about standing waves in the microstrip.
Time evolution of the residual stress of plasma-polymerized acetylene films in various ambients
Authors: Shiosawa T. , de Moraes M. A. B. , Scarminio J.
Published: July 2002

The behavior of the residual stress with time of plasma-polymerized acetylene films in various ambients has been investigated. The plasma polymers were deposited on thin glass substrates in dc and rf discharges of acetylene. After deposition, the specimens were mounted in a chamber that could be evacuated or filled with air, oxygen, or nitrogen. Stress measurements were carried out by the bending beam method, using a He-Ne laser. A steady rise in the stress during time periods of several hours following film deposition was observed in most of the samples studied. Stress increments of more than one order of magnitude were detected in some of the films upon exposure to air. Pronounced stress increments were also observed during exposure to oxygen. Rises in the stress were detected even in a vacuum ambience. Nitrogen exposure was found to have little effect on the stress. The effect of the moisture content of air on the stress was also examined. The evolution of the stress was found to depend also on the film preparation conditions. The results strongly suggest that postplasma reactions involving active chemical species trapped in the film during deposition play an important role in the development of the stress.
Conductance technique measurements of the density of interface states between ZnS:Mn and p-silicon
Authors: Simons Andrew J. , Tayarani-Najaran Mohammed H. , Thomas Clive B.
Published: July 2002

Capacitance and conductance measurements are presented for dc-driven Au/ZnS:Mn/p-Si electroluminescence metal-insulator-semiconductor (MIS) devices, where the ZnS:Mn films are deposited by radio frequency sputtering. Stable dc operation is achieved by introducing oxygen into the film during deposition and subsequently annealing. The effect of the post-deposition annealing upon the density of states at the ZnS:Mn/p-Si interface is investigated. As deposited, the devices show unusual MIS C-V characteristics, that indicate a very high interface state density. Annealing at 700 °C, normal C-V characteristics are observed, indicating that the very high density of states is greatly reduced. For these films the conductance technique has been used to measure the density of states at the interface between the ZnS:Mn and p-Si. The statistical model is found to describe most accurately the interface state conductance response. The interface state density consists of a tail of states that varies between 3.7×1013 cm−2 eV−1 at the silicon Fermi level and 1.1×1013 cm−2 eV−1 at the silicon mid-gap. A small peak is superimposed upon this tail at (−0.16±0.01) eV below mid-gap. The tail of states is believed to be intrinsic to the ZnS:Mn/p-Si interface, but evidence suggests that the small peak is due to the presence of oxygen, which is shown by secondary-ion mass spectrometry analysis to accumulate at the interface after annealing at 700 °C. It seems likely that the very high density of interface states in as deposited devices is a consequence of a plasma damage to the silicon surface during growth, creating defects such as silicon dangling bonds. One possible explanation for the decrease in this density is that by annealing at 700 °C, oxygen in the bulk of the film diffuses to the interface, where it mops up these defects by forming compounds such as SiOx. A simpler model of interface recrystallization is also suggested. The doping density in the depletion region of the silicon is calculated as (7.5±0.5)×1014 cm−3, and the interface state capture cross section for holes is found to have mean value of approximately 10−15 cm−2.
Diffusion mechanism of chromium in GaAs
Authors: Yu S. , Tan T. Y. , Gösele U.
Published: July 2002

The diffusion of the substitutional Cr atoms (Crs) in GaAs results from the rapid migration of the interstitial atoms (Cri) and their subsequent changeover to occupy Ga sites (or vise versa), a typical substitutional-interstitial-diffusion (SID) process. There are two possible ways for the Cri-Crs changeover to occur: the kick-out mechanism in which Ga self-interstitials are involved, and the dissociative mechanism in which Ga vacancies are involved. The Crs in-diffusion profiles are of characteristic shapes indicating the dominance of the kick-out mechanism, while the Crs out-diffusion profiles are error-function shaped, indicating the dominance of the dissociative mechanism. In this study, an integrated SID mechanism, which takes into account both the kick-out and dissociative mechanisms, is used to analyze Cr diffusion results. Going beyond just qualitative consistency, the Cr in- and out-diffusion features in GaAs are explained on a quantitative basis. It is confirmed that the kick-out mechanism dominates Cr in-diffusion while the dissociative mechanism dominates Cr out-diffusion. Parameters used to fit existing experimental results provided quantitative information on the Ga self-interstitial contribution to the Ga self-diffusion coefficient. The values obtained are consistent with those obtained from a study of Zn diffusion in GaAs, and with available experimentally determined Al-Ga interdiffusion coefficients.
Co diffusion and precipitation in Si/SiGe heterostructures
Authors: Dekempeneer E. H. A. , Zalm P. C. , Vriezema C. J. , van den Heuvel R. A.
Published: July 2002

Several Si/Si1−xGex multilayer structures, grown by molecular-beam epitaxy (MBE) or synthesized by high-dose Ge implantation into Si substrates, have been implanted with Co atoms at doses of typically 1.0×1015 and 1.0×1016 ions/cm2. These samples are annealed at elevated temperatures (typically 850 °C) to study the diffusion and precipitation of the Co atoms. Depth distributions of Co atoms are measured with secondary-ion mass spectrometry. X-ray diffraction is used to measure the strain evolution of the Si/Si1−xGex MBE multilayers during processing. Channeling Rutherford backscattering spectrometry is used to study the lattice position of the Co atoms after heat treatment. Upon annealing, Co atoms are observed to diffuse out of the Si1−xGex layers. The efficiency of this outdiffusion process strongly depends on the implantation dose. The released Co atoms are gettered by the Si layers adjacent to the Si1−xGex layers and, in case of the MBE samples, at the interface between the substrate and MBE-grown bufferlayer. A physical model to explain these observations is presented.
General variational expressions for the calculation of the binding energies of anisotropic donor states in stepped quantum wells
Authors: Huo Chong-ru , Gu Ben-Yuan , Gu Lei
Published: July 2002

General variational expressions for the calculation of the binding energies of the low-lying bound states of an anisotropic donor in a quantum well (QW) are presented. To demonstrate the utilization of these expressions the binding energies of anisotropic donor states in a stepped quantum well are studied theoretically. The variations of the binding energies of the anisotropic donor states as a function of impurity position are presented for different values of the anisotropy factor γ=m*⊥■m*∥, where m*⊥ and m*∥ represent the effective electron mass perpendicular to and parallel to the z axis (perpendicular to the interfaces of the QW), respectively. The peak position of the binding energy curves shifts to the deep side of the stepped well. The smaller the γ, the larger the peak shift. The peak shift and the maximum in the binding energies are also dependent on the potential V2 of the step barrier. For the 2p0-like state the corresponding binding energy curve exhibits double peaks, different from the s- and 2p±-like states.
A model of a dc silane discharge
Authors: Koch D. J. , Hitchon W. N. G.
Published: July 2002

This paper describes a novel approach to modeling chemically active dc discharges, and its application to silane. An appropriate electric field was determined from a combination of experimental results and classical dc discharge theory. Utilizing this electric field, a kinetic description of the electron motion was used to calculate the ionization rate and the electron distribution function throughout the discharge. From the calculated rate of ionization and the assumed electric field and allowing for chemical reactions, steady-state fluxes of ions to the anode were calculated. These results compared favorably to the experimental results of Weakleim et al. [J. Vac. Sci. Technol. A 1, 29 (1987)]. A proposed model for the observed variations in the fractional ion currents is given.
A study of lattice damage in silicon induced by BF+2 ion implantation
Authors: Paek Mun Cheol , Kwon Oh Joon , Lee Jeong Yong , Im Ho Bin
Published: July 2002

Lattice damages induced by BF+2 ion implantation in single-crystalline silicon have been analyzed using secondary-ion mass spectrometry, ion channeling technique in Rutherford backscattering spectroscopy, and transmission electron microscopy. Concentration depth profiles of boron and fluorine showed the same values of projection range 400 Å at all doses for 50-keV energy. A considerable amount of damage was formed in the silicon lattice and the surface region of the substrate was amorphized when the dosage exceeded a critical value, which was determined to be 8.0 × 1014/cm2 experimental dose. The amorphized layer showed a clear boundary to the crystalline silicon, which contains severely damaged regions identified to be microamorphous clusters. He2+ ion channeling data revealed that the integrated damage in implanted layers increases linearly with dosage up to the critical dose and increases with a much smaller rate with further increase in the dosage. It is suggested that the integrated damage shows a smaller damage rate once the surface was amorphized because there can be no further increase of lattice damage in the amorphous layer. The calculated values of the integrated damage based on a model for damage formation agree well with the measured ones.
Narrow linewidth gain measurements in KrF and ArF excimer amplifiers pumped longitudinally by high-power electrons
Authors: Adams Richard G. , Dillon Maurice M.
Published: July 2002

Single-pulse KrF and ArF gain measurements have been conducted with an excimer amplifier longitudinally pumped by a high-power (∼5-MW/cm3 deposition) electron beam. This amplifier has preserved the narrow linewidth (∼10 GHz) exhibited by the probe laser beam generated by a grating-tuned, discharge pumped excimer laser. Single-pass gain was measured at 248.45 nm, the peak of the KrF laser gain profile, for a laser pulse with full width half maximum (FWHM) of 20 ns. Analysis of the gain data by a modified Rigrod steady-state formulation yielded values for the small-signal gain, the nonsaturable absorption, and saturation intensity of g0 = 12.6%/cm, α∼0.45%/cm, and Is = 4.1 MW/cm2, respectively, for a 750-Torr laser mix. The corresponding gain peak measurement for an ArF beam at 193.31 nm with FWHM of 15 ns produced g0 = 12.1%/cm, α∼0.70%/cm, and Is = 6.7 MW/cm2 for a 963-Torr laser mix with the same stopping power as the KrF mix. Measurement of gain at 193.68 nm, well away from gain peak, resulted in g0= 10.8%/cm, α∼0.70%/cm, and Is = 7.9 MW/cm2 for the same ArF mixture. Several amplified spontaneous emission and oscillator measurements have also been performed. Indications of laser gain saturation at high-power electron-beam deposition have been deduced.
Optically controlled varactor diode
Authors: Tsai Chaochieh , Campbell Joe C. , Dupuis Russell D.
Published: July 2002

We describe the design and operating characteristics of an optically controlled varactor diode. Applications include optically controlled microwave elements and detection of optical signals in lightwave receivers. The structure consists of a p-n junction formed in an epitaxial layer of InP grown by metalorganic chemical vapor deposition on a semi-insulating InP substrate. A capacitance shift as high as 1.5 pF has been achieved for a photocurrent level as low as 9 μA.
Pulsed laser stripping of polyurethane-coated wires: A comparison of KrF and CO2 lasers
Authors: Brannon James H. , Tam Andrew C. , Kurth Richard H.
Published: July 2002

Compared to mechanical, thermal, electric, or chemical means of removing plastic wire insulation, laser removal offers precision and speed without the necessity of contacting the material. Utilizing the technique of excimer laser ablation of organic polymers, it is shown that excimer laser removal of polyurethane-type wire insulation proceeds with much higher precision and cleanliness than does pulsed CO2 laser wirestripping. A reason for this difference is polyurethane’s much higher absorptivity of ultraviolet compared to infrared radiation. Scanning electron microscope photographs of both stripped wires and ablated regions on polyurethane-coated flat disks clearly show the superior quality of the excimer method. The paper concludes with a discussion of the photophysical parameters and mechanisms responsible for the large difference between excimer and CO2 stripping.
Charge trapping and interface state generation in ultrathin stacked Si3N4/SiO2 gate dielectrics
Authors: Ting W. , Ahn J. , Kwong D. L.
Published: July 2002

Charge trapping and interface state generation in ultrathin (58-Å equivalent oxide thickness) stacked Si3N4/SiO2 (NO) films prepared by rapid thermal processing have been studied. Results show that the charge trapping characteristics of stacked films is comparable to those of pure SiO2, but interface state generation, especially under positive gate polarity stressing, is significantly enhanced. The high interface state generation rate under positive gate bias in stacked NO layers is explained by enhanced hole injection from the gate due to the low hole injection barrier at the polycrystalline-Si gate/nitride interface.
Non-zone-folded transition-energy calculations for quantum-confined Stark effect in Si1−xGex/Si quantum wells
Authors: Chowdhury Andalib A. , Jung K. H. , Kwong D. L. , Maziar C. M.
Published: July 2002

We report calculated bound-state transition energies at 77 K for symmetrically strained Si1−xGex/Si quantum wells grown on (100) Si substrates. The red shift in transition energies with bias due to the quantum-confined Stark effect is also examined. Transition energies are plotted as a function of Ge concentration, quantum-well thickness, and applied electric field. The calculations are based on phenomenological deformation potential theory and the envelope function method popularized by G. Bastard [Phys. Rev. B 24, 4714 (1981)]. The results presented here are useful for the design of Si1−xGexSi optoelectronic modulators operating at 1.3 and 1.55 μm.
Recombination at GaAs surfaces and GaAs/AlGaAs interfaces probed by in situ photoluminescence
Authors: Sandroff C. J. , Turco-Sandroff F. S. , Florez L. T. , Harbison J. P.
Published: July 2002

We use in situ photoluminescence (PL) to investigate recombination at (100)GaAs surfaces and GaAs/AlGaAs interfaces in a controlled crystal growth environment. PL was monitored for different GaAs surface reconstructions, after surface chemical modification, and during early stages of AlGaAs heteroepitaxy. Depositing ∼1 ML of Se to form a (2×1) surface increased the GaAs PL intensity 200 times. Surprisingly, it required 6 ML (15 Å) of heteroepitaxial AlGaAs to achieve the same degree of surface passivation. We invoke lateral variations in interfacial AlGaAs composition to explain these results.
Magnetization curling in an infinite cylinder with a uniaxial magnetocrystalline anisotropy
Authors: Ishii Y.
Published: July 2002

The magnetization curling mode for an infinite cylinder with a uniaxial magnetocrystalline anisotropy is considered. The angular dependence of the nucleation field HN and the coercive force Hc are estimated as a function of the radius, the magnetocrystalline anisotropy, and the inclination of the axis to the applied field. It is assumed that only curling and rotation in unison occur, and that the discontinuous jump by the curling mode brings the magnetization to the lower energy state given by Stoner–Wohlfarth. With this assumption, the rotational hysteresis loss Wr and integral Rh are evaluated both for an aligned and for a random assembly of infinite cylinders.
Characterization of polymer dispersed liquid-crystal shutters by ultraviolet/visible and infrared absorption spectroscopy
Authors: West J. L. , Ondris-Crawford R.
Published: July 2002

Incorporation of dichroic dyes substantially improves the contrast of polymer dispersed liquid-crystal (PDLC) shutters. The efficiency of dichroic dyes in a PDLC shutter depends on the scattering efficiency of the film, the dichroic ratio of the dye, the order parameter of the dye in the liquid crystal, and the fraction of dye dissolved in the droplets. Ultraviolet/visible spectroscopy can be effectively used to determine the scattering efficiency of PDLC films, and the distribution of dichroic dye dissolved in the liquid-crystal droplets. To achieve high contrast the dichroic dye must be segregated in the droplet. We show that the segregation of dye in the PDLC droplets is dependent on the type of dye used and ranges from 19% to 100%. The scattering efficiency of the PDLC shutter provides insight into the effect of the dichroic dye on the contrast of the film. Production of a black PDLC shutter requires a mixture of several dichroic dyes. By careful consideration of the relative amounts of the components of the dye mixture, a black PDLC shutter can be constructed with a uniform contrast over the entire visible region. The dichroic absorption in the infrared of the liquid crystal used to make a PDLC can be analyzed in a manner analagous to the dichroic dye to determine the fraction of liquid-crystal phase separated in droplets and dissolved in the polymer binder.
Effect of laser irradiation on structural, electrical, and optical properties of p-mercury cadmium telluride
Authors: Dawar A. L. , Roy Savita , Mall R. P. , Mathur P. C.
Published: July 2002

Single crystals of p-Hc1−xCdxTe (x=0.16) were grown by the Bridgeman technique. The bulk single crystals were irradiated with laser pulse of various energy densities. A pulsed laser (Nd:YAG) capable of producing 10-ns pulses of 0.53 μm wavelength (frequency doubled) with varying energy densities (2–50 mJ/cm2) was employed. dc conductivity and Hall coefficient measurements were made on the single crystal using the Van der Pauw technique in the temperature range 77–300 K for both as-grown and laser-irradiated samples. Also the x-ray diffraction pattern and transmission measurements of the samples were taken at room temperature. Electrical studies shows that the p-mercury cadmium telluride after the laser irradiation becomes n type and optical results show that the free-carrier concentration after laser irradiation increases sharply so that there is negligibly small transmission. The x-ray studies show that single crystal p-type samples after laser irradiation undergo structural changes as well, introducing phases of CdTe, Hg, and Te in the lattice.
X-ray study of defect depth distribution in silicon wafers after heat treatment
Authors: Holý V. , Kuběna J. , Bochníček Z.
Published: July 2002

A surface defect-free denuded zone in silicon wafers has been studied by x-ray double-crystal diffractometry. On the basis of the dynamical theory of x-ray diffraction on crystals with microdefects, it has been demonstrated that the x-ray reflection curve of a crystal with a denuded zone measured in the Bragg geometry (reflection case) depends strongly on the denuded zone thickness, while that in the Laue geometry (transmission case) is practically not affected by the zone. Thus, it is possible to determine the denuded zone thickness nondestructively from the ratio of the tails of the reflection curves measured in both geometries. The thickness values obtained experimentally by this approach have been compared with those from chemical etch patterns of cleavage wafer cross sections, and a good agreement has been achieved.
Plasma-assisted decomposition of trimethylarsine
Authors: Pihlstrom B. G. , Sheng T. Y. , Yu Z. , Collins G. J.
Published: July 2002

The downstream near afterglow region of a hydrogen plasma is used to decompose and convert trimethylarsine (TMAs) into methylarsine homologs [(CH3)3−xAsHx, where x=1,2,3] including that of arsine (x=3). Approximately 30%, 17%, and 10% of the TMAs is converted into dimethylarsine (DMAs), monomethylarsine (MMAs), and arsine, respectively, while 28% remains undecomposed. Hydrogen is replaced by deuterium to isotopically verify that the origin of the arsenic hydrogenation occurring during gas conversion arises from both the plasma gas and fragmented hydrogen from the TMAs. Deuterium tagging of the MMAs, DMAs, and hydrocarbon byproducts is consistent with TMAs decomposition via plasma initiated CH3 radical removal and explains why the predominant light stable hydrocarbon produced is methane while ethane and acetylene account for the main higher hydrocarbons.