bluuebunny/crossref_metadata_2025 huggingface dataset:
Carrier capture by multiphonon emission at extrinsic deep centers induced by self-trapping in GaAs
Authors: Goto Hiroshige , Adachi Yoshio , Ikoma Toshiaki
Published: February 2003

The extent of electron-lattice coupling at neutral, extrinsic self-trapping-induced deep centers in III-V compound semiconductors is estimated by assuming deformation potential interaction in the framework of a continuum lattice model, and its delocalization around these deep centers is pointed out. A model potential which takes into account the delocalization of the coupling is proposed and a theoretical expression is derived for capture cross sections at these centers by combining the model potential with multiphonon emission carrier capture scheme. The theory successfully explained both temperature dependence and the magnitude of capture cross sections observed at three electron traps (deep centers) in GaAs. Although the magnitude of capture cross sections at two of these three electron traps seem to deviate from that predicted by Henry and Lang, the multiphonon emission carrier capture scheme is still applicable to such deep states by employing our model potential.
1/f noise in thin oxide p-channel metal–nitride–oxide–silicon transistors
Authors: Maes Herman E. , Usmani Sabir H.
Published: February 2003

The 1/f noise behavior of p-channel metal–nitride–oxide–silicon transistors is presented. Devices with different oxide thicknesses, geometries and different technological treatments were used for this study. It is shown that the noise behavior can be well explained quantitatively with the number fluctuation model developed for MOS transistors. The close correlation between the increase of the noise and of the interface state density after different levels of degradation indeed indicates that the exchange of carriers between the channel and the interface traps lies at the origin of the 1/f noise. The observed degradation in MNOS devices is consistent with a diffusion controlled model for the creation of surface traps but is found to be a saturating effect. The predictions of the mobility fluctuation model are not confirmed in our experiments.
Analysis of thermal stresses induced in silicon during xenon arc lamp flash annealing
Authors: Bentini G. G. , Correra L.
Published: February 2003

Evaluation of thermal stresses induced on silicon wafers during flash annealing with incoherent light from a xenon lamp has been performed. The thermally induced stresses have been computed taking into account that the slip planes, in 〈100〉 silicon crystal, are {111} and the slip directions in the plane are 〈110〉. The computed stresses have been compared with the yield stress of the material, to determine the threshold of damage introduction by the annealing process. For the light flash durations shorter than 500 μsec, a preheating of the sample is necessary to obtain a good annealing of a 1000 Å implanted layer without defects introduction. A relationship among flash duration, preheating temperature and flash energy density has been established allowing the identification of the best annealing conditions. The computed results have been compared with experimental annealing data obtained on 〈100〉 silicon, phosphorus implanted at 10 keV, 1.5×1015 at/cm2 and irradiated with an original flash annealing system set up in our laboratory.
On the point and line defects which are common to both degraded light emitting diodes and plastically deformed GaAs
Authors: Liliental Zuzanna
Published: February 2003

Similar dipoles with Burger’s vector b=a/2 [1̄01] (also referred to as dark line defects) were found in the active layer of degraded light emitting diodes (LED’s) and in plastically deformed GaAs. The dependence of characteristic x-ray production of electron channeling conditions has been used in an electron microscope to study point defects in the neighbourhood of these dipoles. Our results are consistent with the occurence of IAs, IAs +VGa, VGa and IGaAs in descending order of likelihood. Of these, IAs +VGa can explain the dislocation climb without any extra point defects involved in such process.
Astigmatism and spontaneous emission factor of laser diodes with parabolic gain
Authors: Mamine Takayoshi
Published: February 2003

An explicit relation between the astigmatism and the spontaneous emission factor of gain guiding lasers has been derived with the assumption that the gain profile can be approximated to be a parabola or that the lowest order mode in the cavity is approximately Gaussian. The maximum value of the spontaneous emission factor is shown to be √2 if index guiding is dominant. Beyond K=√2, where gain guiding is dominant in this region, the astigmatism decreases with the spontaneous emission factor. It is also shown that the spontaneous emission factor of the gain guiding lasers does not much exceed ten and this conclusion has been confirmed experimentally for those whose stripe widths are larger than 4 μm.
Effective p-type doping of diamond by boron ion implantation
Authors: Braunstein G. , Kalish R.
Published: February 2003

Highly conducting p-type diamond layers have been obtained by high-dose boron implantation followed by annealing (1400 °C) and subsequent removal of the graphite-like layer that is formed as a result of the heat treatment. Conductivity and Hall measurements showed transport features typical of heavily doped semiconductors. The fact that identical carbon implantations have yielded no measurable conductivity is taken as evidence that the highly conductive p-type layer obtained by boron implantation is indeed due to effective doping.
Thermal expansivity measurements below 300 K on a copper–beryllium alloy
Authors: Holtz R. L. , Swenson C. A.
Published: February 2003

High accuracy (0.1%) linear thermal expansivity results are given for a copper-1.8 wt. % beryllium alloy in both the half-hard and precipitation-hardened conditions. These results, which are of technical importance for low temperature experiments, also show a small anomaly near 25 K in the temperature dependence of the ratio of the alloy expansivity to that of copper.
A generalized approximation of the Fermi–Dirac integrals
Authors: Aymerich-Humet X. , Serra-Mestres F. , Millán J.
Published: February 2003

An analytical approximation for the Fermi–Dirac integral F j(η) for real j is proposed. This approximation works for −∞< η < ∞, with an error of 1.2% for −1/2< j < 1/2 and 0.7% for 1/2 < j < 5/2. The error increases with j for higher j values.
Niobium thin-film point-contact Josephson junction
Authors: Naito Seiichi , Higashino Yasushi , Ibuka Makoto
Published: February 2003

A stable, niobium thin-film point-contact Josephson junction can be fabricated using rf magnetron sputtering and electron beam lithography. Constant-voltage steps based on a ac Josephson effect are observed up to a voltage level of 4 mV at 4.2 K when a 9-GHz microwave signal is applied. This voltage level is the highest for any thin-film weak link except for the tunnel junction.
Reply to ‘‘Comment on ‘X-ray photoelectron spectroscopic studies of oxygen chemisorption on thick films of photoconducting cadmium sulphide’ ’’
Authors: Amalnerkar D. P. , Badrinarayanan S. , Date S. K. , Sinha A. P. B.
Published: February 2003

A thorough examination of all our experimental data revealed that the two additional photopeaks in question do not originate from indeterminate stray AlKα radiation as suggested by Lichtensteiger and Webb, but are due to sulphur-oxygen species formed on the surface of CdS thick films.
Defect states and donors in thermally annealed or post-hydrogenated chemically vapor-deposited amorphous SiNx alloy
Authors: Sasaki Goro , Fujita Shizuo , Sasaki Akio
Published: February 2003

Thermal annealing and post-hydrogenation effects on the electrical properties of chemically vapor-deposited (CVD) amorphous silicon-nitrogen (a-SiNx ) alloys are studied. Annealing of CVD a-Si and a-SiNx films causes the increases in the ESR centers, the hopping conduction, and the gap-state density evaluated by the field-effect method. The nitrogen incorporation reduces the number of ESR centers in a film. The Fermi level of CVD a-SiNx films is shifted by post-hydrogenation, which suggests that the films include donors. The ημτ products of CVD a-Si and a-SiNx films are increased by post-hydrogenation, exceeding two orders of the magnitude. Post-hydrogenated CVD a-SiNx films show larger ημτ product than post-hydrogenated CVD a-Si.
A study of Si plasma etching in CF4+O2 gas with a planar-type reactor
Authors: Kawata H. , Shibano T. , Murata K. , Nagami K.
Published: February 2003

The plasma etching of silicon has been performed on both electrodes with a conventional parallel-plate-type reactor. The optical emission intensity and the etch rate were measured as a function of O2 content in CF4 gas. These measurements were carried out both with and without silicon loading wafers on the anode. The experimental results show that the O2 contents where the etch rate and the F emission intensity show the peak value do not coincide, as was pointed out by a previous author. The relation of the F emission intensity and the etch rate on the anode is well described by the competitive mechanism between F atoms and O atoms. When the Si loading wafers are placed on the anode, the F emission intensity and the etch rate can be predicted by combining this competitive theory with a continuity equation for F atoms. On the other hand, the etching mechanism of etching on the cathode cannot be interpreted only by the competitive theory. In order to interpret it in the future, one has to take into account etching species other than F atoms and/or species assisting the etching, which have little dependence on the O2 content.
A geometric model of alternating current etching of aluminum
Authors: de Wit H. J. , Boots H. M. J.
Published: February 2003

Prolonged alternating current etching of aluminum foil, to be used as anode of electrolytic capacitors, leads ultimately to a stationary state in which the gain of area deep inside the foil is offset by loss of area at the foil surface. A model is described in which the etching process is assumed to be built up from successive removal of straight strings of cubes starting randomly on the already etched surface. This model explains the evolution of the etch structure. The relations between string length, string width, and width of the etched layer, as well as the area magnification predicted by the model, are consistent with experimental data.
A pragmatic approach to adatom-induced surface reconstruction of III-V compounds
Authors: Wood C. E. C. , Singer K. , Ohashi T. , Dawson L. R. , Noreika A. J.
Published: February 2003

Al, Ga, and In arsenides and antimonides and Al phosphide show different reconstructions for group V and group III-terminated surfaces, whereas Ga and In III phosphides typically have one dominant reconstruction. This paper reports congruent sublimation temperature Tcs determination for GaAs, InAs, the ternary AlInAs and GaInAs alloys, and AlSb and GaSb. The dominance of ‘‘phosphorus stabilized’’ (2×4) and c(2×8) reconstructions has so far inhibited us from determining Tcs for group III phosphides from RED observations. Tcs for AlAs was not found below 860 °C. Coverage of heat-cleaned substrates with a few monolayers of group III atoms at elevated temperatures prior to growth improves the surface topography to that of grown films.
Surface preparation effects on efficient indium-tin-oxide-CdTe and CdS-CdTe heterojunction solar cells
Authors: Werthen J. G. , Fahrenbruch A. L. , Bube R. H. , Zesch J. C.
Published: February 2003

The effects of CdTe surface preparation and subsequent junction formation have been investigated through characterization of ITO/CdTe and CdS/CdTe heterojunction solar cells formed by electron beam evaporation of indium-tin-oxide (ITO) and CdS onto single crystal p-type CdTe. Surfaces investigated include air-cleaved (110) surfaces, bromine-in-methanol etched (110) and (111) surfaces, and teh latter surfaces subjected to a hydrogen heat treatment. Both air-cleaved and hydrogen heat treated surfaces have a stoichiometric Cd to Te ratio. The ITO/CdTe junction formation process involves an air heat treatment, which ahs serious effects on the behavior of junctions formed on these surfaces. Etched surfaces which have a large excesss of Te, are less affected by the junction formation process and result in ITO/CdTe heterojunctions with solar efficiencies of 9% (Vsc =20 mA/cm2). Use of low-doped CdTe results in junctions characterized by considerably larger open-circuit votages (Voc =0.81 V) which are attributable to increasing diode factors caused by a shift from interfacial recombination to recombination in the depletion region. Resulting solar efficiencies reach 10.5% which is the highest value reported to date for a genuine CdTe heterojunction, CdS/CdTe heterojunctions show a strong dependence on CdTe surface condition, but less influence on the junction formation process. Solar efficiencies of 7.5% on an etched and heat treated surface are observed. All of these ITO/CdTe and CdS/CdTe heterojunctions have been stable for at least 10 months.
Barrier at the interface between amorphous silicon and transparent conducting oxides and its influence on solar cell performance
Authors: Sánchez-Sinencio F. , Williams Richard
Published: February 2003

We have found that a heterostructure made of a conductive transparent oxide (SnO2, ITO, or Pt:SiO2) and p-type or n-type or intrinsic a-Si:H shows a substantial potential barrier at the interface. This barrier is important in order to explain the behavior of Voc versus doping of the p layer in p-i-n solar cells. The barrier should also be taken into account in order to explain the poor blue response of solar cells.
Scalar transport coefficients for the hydrogen plasma in the cathode-grid region of a thyratron
Authors: Kunc J. A. , Gundersen M. A.
Published: February 2003

The scalar conductivity, electron diffusion coefficient and mobility have been calculated for a hydrogen plasma in the cathode-grid region of a hydrogen thyratron, assuming neutral pressure about 0.5 Torr, electron temperature 1 eV, electron density Ne≊1014, and electric field Ep=5–10 V/cm. The role of coulomb collisions is considered, and it is shown that coulomb collisions are important in the plasma.
Phase-slip shot noise contribution to excess noise in superconducting bolometers
Authors: Knoedler C. M.
Published: February 2003

Phase-slip shot noise caused by the current induced motion of vortices across a superconducting film can lead to excess noise in superconducting bolometers. The occurrence of this noise and its influence on the electrical noise equivalent power can be directly related to parameters such as the thermal conductance, sheet resistance, and bias current. The existence of phase slip shot noise may also explain discrepancies among previous researchers.
Parametric excitation of lower hybrid waves by helicon waves in magnetoactive semiconductors
Authors: Salimullah Md.
Published: February 2003

A theoretical investigation has been done on the parametric excitation of the electrostatic lower hybrid wave when an electromagnetic helicon wave propagates in a magnetoactive semiconductor. Fluid equations of homogeneous plasmas have been employed to find the nonlinear response of electrons. The low frequency nonlinearity arises through the ponderomotive force on electrons, whereas the high frequency nonlinearity arises through the current density associated with the scattered helicon wave. For the typical plasma parameters in n-type indium antimonide and for the considerable power density (∼7.6 kW cm−2) of the incident helicon wave, the growth rate of the parametric instability turns out to be quite large (∼108 rad s−1). The presence of the linear damping of the decay waves in the semiconductor plasma reduces the growth rate of the instability by two orders of magnitude.
Schottky barrier type diode with an electrochemically prepared copolymer having pyrrole and N-methylpyrrole units
Authors: Koezuka H. , Etoh S.
Published: February 2003

A Schottky type diode has been constructed with the electrochemically prepared copolymer having pyrrole and N-methylpyrrole units and a low work function metal (In). The heat treatment of the copolymer in air was performed in order to stabilize the electrical characteristics of the device before the deposition of a blocking electrode. The electrical properties have been investigated by means of I–V and C–V measurements. The diode quality factor and the barrier height have been obtained to be n=1.2 and ψb=0.81 V by applying a thermionic emission theory, respectively. At high current densities in the forward direction, a space-charge-limited current has been observed. This observation would be due to the charge-injection across the thin oxidized layer which would be formed during the heat treatment of the copolymer in air. Other junction parameters have been also determined by means of C–V measurements.
The electrical behavior of GaAs-insulator interfaces: A discrete energy interface state model
Authors: Kazior T. E. , Lagowski J. , Gatos H. C.
Published: February 2003

The relationship between the electrical behavior of GaAs Metal Insulator Semiconductor (MIS) structures and the high density discrete energy interface states (0.7 and 0.9 eV below the conduction band) was investigated utilizing photo- and thermal emission from the interface states in conjunction with capacitance measurements. It was found that all essential features of the anomalous behavior of GaAs MIS structures, such as the frequency dispersion and the C–V hysteresis, can be explained on the basis of nonequilibrium charging and discharging of the high density discrete energy interface states.
Generation-annealing kinetics of the interface donor states at 0.25 eV above the midgap and the turn-around phenomena on oxidized silicon during avalanche electron injection
Authors: Sah Chih-Tang , Sun Jack Yuan-Chen , Tzou Joseph Jeng-Tao
Published: February 2003

The generation and the annealing kinetics of the donorlike peaked interface density of states (DOS’s) at 0.25 eV about the midgap and the turn-around phenomenon of the flat-band voltage generated by the avalanche electron injection are reported. The generation of the peaked interface DOS follows a first-order kinetics and it anneals out at 25 C following a second-order kinetics. The devices with dry oxide show a small buildup of peaked DOS as well as a small turn-around phenomenon. However, after a deionized (DI) water rinse before gate metallization, a large buildup of peaked DOS and turn-around states were observed. After avalanche electron injection is terminated, in the devices with small peaked DOS, the midgap slowly drifts in the negative voltage direction under negative gate bias. However, in the devices with large peaked DOS, the midgap voltage slowly drifts in the positive gate voltage direction even under negative gate bias. Detailed analyses of both the generation and annealing data suggest that the peaked DOS is a donor which can account for most of the turn-around phenomenon as well as the midgap voltage instabilty phenomenon after avalanche electron injection. DI water dependence suggests that the peaked DOS and the turn-around states may be related to hydroxyl species in the oxide.
High-temperature phase transitions in pure and deuterated ammonium dihydrogen phosphate: Conductivity and dielectric measurements
Authors: Subhadra V. K. , Syamaprasad U. , Vallabhan C. P. G.
Published: February 2003

Results of axiswise measurements of the electrical conductivity (dc and ac) and dielectric constant of NH4H2PO4 confirm the occurrence of the recently suggested high-temperature phase transition in this crystal (at 133 °C). The corresponding transition in ND4D2PO4 observed here for the first time takes place at 141.5 °C. The mechanism involved in these transitions and those associated with the electrical conduction and dielectric anomalies are explained on the basis of the motional effects of the ammonium ions in these crystals. Conductivity values for deuterated crystals give direct evidence for the predominance of protonic conduction throughout the entire range of temperatures studied (30–260 °C).
Quantum efficiency of alexandrite
Authors: Shand M. L.
Published: February 2003

The first measurement of the radiative quantum efficiency (QE) of alexandrite has been determined using a photoacoustic (PA) technique which depends on the phase of the PA signal as a function of chopping frequency. The measured QE=0.95±0.05.
Low threshold photopumped AlxGa1−xAs quantum-well heterostructure lasers
Authors: Burnham R. D. , Streifer W. , Scifres D. R. , Holonyak N. , Hess K. , Camras M. D.
Published: February 2003

Data are presented on very low threshold photopumped separate-confinement quantum-well heterostructure (SC QWH) lasers grown by metalorganic chemical vapor deposition (MOCVD). An unusually thin single quantum well (size Lz≲ 60 Å) is employed in the QWH with the carriers confined (‘‘trapped’’) in the interior ‘‘cladding’’ region, which serves also as the optical waveguide. Excess carriers, which are photogenerated (or injected), are confined in the thin interior cladding region (size Lz′ ∼1000 Å) and, in this charge reservoir and waveguide region, are thermionically ‘‘emitted’’ back and forth across the well until scattered to lower energy in the well (ΔE∼ℏωLO) and collected. Continuous (cw) 300 K photopumed laser operation of these QWH’s is demonstrated for very short cavities. For one QWH wafer laser operation occurs at λ∼7730 Å with a photopumping threshold of 380 W/cm2 (Jeq ∼160 A/cm2) and for another wafer at λ∼7000 Å with threshold 103 W/cm2(Jeq∼ 410 A/cm2). The photopumped samples are as small as 20×40 μm, thus making these laser thresholds (for such short cavity lengths) a factor of 3–10 better than the lowest previously reported.
Temperature and excitation dependences of active layer photoluminescence in (Al,Ga)As laser heterostructures
Authors: Swaminathan V. , Anthony P. J. , Pawlik J. R. , Tsang W. T.
Published: February 2003

The excitation and temperature dependences of the active layer photoluminescence intensity in (Al,Ga)As laser heterostructures in the range 75–300 K are described. Of the wafers investigated, in a majority of those grown by molecular beam epitaxy and in all the wafers grown by liquid phase epitaxy, the AlxGa1−xAs (0≤x≤0.08) active layer photoluminescence intensity at any temperature increased linearly with increasing excitation intensity at high power levels (≥100 W/cm2) but decreased very rapidly with decreasing excitation intensity at lower power levels indicative of a p-n junction. Since the excitation intensity required to saturate the losses due to the p-n junction, Psat, increased with increasing temperature, the photoluminescence intensity measured at power levels (typically 1–10 W/cm21) lower than Psat decreased by a factor of 100–1000 on increasing the temperature to 300 K. In contrast, for a few wafers grown by molecular beam epitaxy, the active layer intensity varied linearly with excitation at all power levels and at any temperature suggesting the absence of a p-n junction. Consequently, the intensity for these wafers decreased by only a small factor (<10) as temperature was increased from 75 to 300 K. These wafers were of particular interest since lasers fabricated from them also exhibited reduced temperature dependence of threshold current. Examination of the wafer by secondary ion mass spectroscopy indicated that in the temperature insensitive wafers only the p-type dopant in the active layer, Be, extended for a short distance into the n-type confinement layer creating essentially an isotype structure. A first-order calculation of this structure showed also a reduced temperature dependence of the laser threshold current.
Temperature evolutions in silicon induced by a scanned cw laser, pulsed laser, or an electron beam
Authors: Ferrieu F. , Auvert G.
Published: February 2003

A self-consistent time procedure for solving a nonlinear heat diffusion equation is proposed. This paper addresses three-dimensional time dependent heat equations with nonlinear sources and diffusivity. The semianalytical model of the static regime is thereby extended to transient treatment. The advantage of this method is that it allows handling of nonlinearity in the heat diffusion equation, while keeping calculations simple. The method may be applied to either a cw laser beam or a pulsed beam. In the latter case, the method applies for any spot size, since the problem remains three-dimensional. Different deposited energy pentrations are reviewed, among them the Gaussian-shaped deposited energy corresponding to the case of the scanned electron beam. Using this method, temperatures are calculated and compared with the high speed melting isotherm for silicon under cw laser irradiation.
Matrix effect and surface oxidation in depth profiling of AlxGa1−xAs by secondary ion mass spectrometry using O+2 primary ions
Authors: Meyer Ch. , Maier M. , Bimberg D.
Published: February 2003

The dependence of the ionization probability in secondary ion mass spectrometry experiments of the dopants Be, Ge, and Sn and the matrix atoms Ga and As in AlxGa1−xAs with 0≤x≤0.83 on the matrix composition is determined using O+2 primary ions. The composition of the surface is analyzed for the first time by Auger electron spectrometry during O+2 bombardment. The ionization probability shows an approximately linear increase with increasing Al content ranging from a factor of 2.5 (for Ga+) to 7.5 (for Ge+). The variation of the ionization probability is a function of the degree of oxidation which depends on the metal-oxygen bond energy and on the availability of oxygen. The availability of oxygen is controlled by the implantation sputtering process during O+2 bombardment.
Substrate heating effects in CO2 laser annealing of ion-implanted silicon
Authors: Blomberg M. , Naukkarinen K. , Tuomi T. , Airaksinen V.-M. , Luomajärvi M. , Rauhala E.
Published: February 2003

A pulsed CO2 laser has been used for the annealing of doped ion-implanted silicon crystals. Good recrystallization was achieved for a sample with a dopant density of 7×1015 cm−3, when preheated to 850 K. Damage caused by thermal runaway however made annealing of samples with a dopant concentration of this order difficult. The effect of the strong temperature dependence of the absorption coefficient at the CO2 laser photon energy is considered. Melting model calculations give agreement with the experimental observations.
Phenomenological theory of shock-induced polarization. II. Mathematical treatment of the oscillogram
Authors: de Icaza-Herrera M.
Published: February 2003

The mathematical treatment of the theory presented in the preceding paper is detailed. Less than ten distance measurements on the oscillogram are enough to determine the dielectric properties of the shcoked medium and the polarization discontinuity across the shock front. The last one agrees approximately with Allison’s mechanical polarization, but does not depend on the dielectric properties of the shocked medium. The treatment is valid for the dipolar orientation and bond scission models of shock-induced polarization. Finally, the effect of a changing pressure profile is discussed.
Megavolt electron irradiation induced regrowth of amorphous zones in silicon
Authors: Washburn J. , Sadana D. K.
Published: February 2003

Deep buried amorphous layers were created in (100)Si by 11-MeV As implantation. The effect of 1.2-MeV electron irradiation at the upper and lower interfaces of the buried layer was investigated in thin cross-section specimens prepared for transmission electron microscopy. It was found that in partially amorphous silicon amorphous zones (≤100 Å) imbedded in crystalline matrix shrank during the irradiation. On the basis of these results and earlier published data, the mechanism of the crystal to amorphous transformation has been discussed.
Effect of magnetic field in rf sputtering on the crystal orientation and magnetic properties of Co-Cr perpendicular anisotropy films
Authors: Maeda H.
Published: February 2003

Co–23-wt. %-Cr alloy films with thicknesses of 0.3 to 2.5 μm were deposited using a conventional rf diode sputtering system when a magnetic field Hs less than 90 Oe is applied during deposition. As Hs increases, the hcp c-axis orientation normal to the film plane develops and the half-angle width of the rocking curve of the (002) line Δθ50 reaches to 3.5 deg at Hs more than 40 Oe. The development of the orientation is strongly related to the concentration of O in the films, which is lower in the films deposited in a magnetic field than those in a nonmagnetic field. The magnetic properties such as perpendicular coercive force Hc⊥ and saturation magnetization Ms strongly depend on the substrate temperature rather than Hs.
Carrier surface recombination in HgI2 photon detectors
Authors: Levi A. , Schieber M. M. , Burshtein Z.
Published: February 2003

Carrier collection efficiency versus voltage characteristics were studied in detail in HgI2 photon detectors of various thicknesses for the 5.9-keV x-ray emission of 55Fe. The results prove the important role of carrier surface recombination in limiting the carrier collection, and its consequences on the detector performances. Electron and hole surface recombination velocities in our samples were about 104 cm/sec. Hole trapping times were about 10−6 sec, while electron trapping times were much longer than ∼10−5 sec.
High pressure photoelectric studies of semiconductor-electrolyte systems
Authors: Gulino D. A. , Faulkner L. R. , Drickamer H. G.
Published: February 2003

Data are presented which show the behavior of the valence and conduction band-edge energies (Ev and Ec, respectively) as a function of pressure for the n-type semiconductor electrodes TiO2, CdS, and CdSe. For TiO2, the 3 meV/kbar increase in the band-gap energy (Eg) is due entirely to an increase in Ec. For CdS, the 5.1 meV/kbar increase in Eg is the difference between the 9.5–11.5 meV/kbar increase in Ec and the (calculated) 4.5–6.5 meV/kbar increase in Ev. In the case of CdSe, both Ec and Ev move to lower energies with increasing pressure. Their behavior is complex.
Effect of reabsorbed recombination radiation on the diffusion length of minority carriers in wide-band-gap semiconductors
Authors: von Roos Oldwig
Published: February 2003

The integrodifferential equation governing the diffusion of minority carriers under the influence of both recombination by flaws and multiple photon absorption and emission via band-band transitions recently developed by the author is solved by means of a variational principle. It is shown that for bulk material the effect of the reabsorbed recombination radiation (RRR) on carrier diffusion is negligible when the average mean free path of photons is larger than the diffusion length of the carriers. In the opposite case, this is not true and the results previously obtained by a different method are recovered. Applied to GaAs, these findings signify that if the diffusion length L due to flaws or recombination centers possesses a magnitude less than 1 μm, the effect of the RRR may safely be ignored. But, on the other hand, if L is greater than 1 μm, there exists an effective diffusion length Leff always larger than L, which is engendered by the RRR and which enhances carrier transport. This enhancement becomes noticeable only at high doping levels.
Short wavelength laser calculations for electron pumping in neon-like krypton (Kr XXVII)
Authors: Feldman U. , Bhatia A. K. , Suckewer S.
Published: February 2003

We present calculations of electron impact collision strengths and spontaneous radiative decay rates for neon-like krypton (Kr XXVII) for the 2s22p6, 2s22p53s, 2s22p53p, and 2s22p53d configurations. From these atomic data the level populations as a function of the electron density were calculated at two temperatures (Te=1×107 K and Te=3×107 K). The analysis of level populations shows that a volume of krypton in which a significant number of the ions are in the Kr XXVII degree of ionization can produce a significant gain in transitions between the 2s22p53s and 2s22p53p configurations. At an electron density of 1×1019 cm−3 the plasma length has to be on the order of 1 m; at a density of 1×1021 cm−3 the length is reduced to about 0.5 cm; and at an electron density of 1×1022 cm−3 the length of the plasma is further reduced to about 1 mm.
Low-current-threshold (GaAl)As visible lasers with emission wavelengths below 750 nm
Authors: Hayakawa T. , Yamamoto S. , Hayashi H. , Miyauchi N. , Yano S. , Hijikata T.
Published: February 2003

Low-current-threshold behavior of (GaAl)As v-channeled substrate inner stripe lasers emitting below 750 nm is presented. The variation of the threshold current of these devices with the lasing wavelength agrees with that of 1/ηi calculated using the energy-band parameters where the indirect-direct crossover is assigned at the AlAs mole fraction of 0.45. cw operation was achieved at as short as 688 nm. These performances result from the improved laser properties by growing the Te-doped cladding layer on top of the active layer using the p-type GaAs as a substrate.
Evaluation of the thermal focal length produced in a repetitively pulsed solid-state laser
Authors: Jing-ya Hou
Published: February 2003

An approximate expression for the focal length of the thermal lens produced in a repetitively pulsed laser rod is presented. Numerical evaluations reveal relations between thermal focusing and the rod radius, cooling conditions, pulse repetition rate, and nonuniformity of pumping. The aberration produced under different operating conditions is also discussed. A critical rod radius is identified for which the thermal lens effect is most sensitive to cooling and nonuniformity of pumping.
Modelling of the low-pressure argon positive column
Authors: Ferreira C. M. , Ricard A.
Published: February 2003

The properties and operating characteristics of the positive column of a low-pressure positive column in argon have been investigated experimentally and theoretically. In the experiments the pressure was varied from 5×10−2 to 1 Torr, the discharge current from 0.2–20 mA, and the discharge tube was 2.6 cm inside diameter. Measurements of the axial electric field, electron density and population in 3P2 metastable states are reported for various discharge conditions. A test is made of the usefulness of a two-moment theory which is applicable in the intermediate pressure range of this work, i.e., in the transition from inertia-limited to mobility-limited flow of ions to the wall, for the prediction of the operating characteristics. For this purpose, the electron excitation and ionization rates, and transport parameters were calculated from the homogeneous Boltzmann equation. The predicted similarity laws for the positive column are in reasonable agreement with the measurements only in the lower pressure region, i.e., for a pressure-radius product less than about 0.1 Torr cm. The discrepancy between theory and experiment at the higher pressure is, presumably, the result of our failure to correct the calculated ionization rate and effective electron loss rate for the effects caused by ionization from metastables and by space-charge fields.
Evidence for a time dependent excitation process in silane radio frequency glow discharges
Authors: de Rosny Gilles , Mosburg Earl R. , Abelson John R. , Devaud Genevieve , Kerns Ralph C.
Published: February 2003

A new phenomenon in rf glow discharges has been observed, namely the existence of a strongly time dependent excitation of atomic levels. The observed excitation width of 10 ns (FHWM) is short compared to the 37-ns duration of a half-cycle of the 13.56-MHz applied rf power. This implies a similar time dependence of the density of those electrons responsible for the excitation. Moreover, the excitation propagates through the glow away from the nearer electrode. The nature of this propagation phenomenon is uncertain. These results are deduced from a time resolved study of the λ=288.2 nm emission from neutral excited silicon, Si(4s1,1P0) and λ=656.3 nm emission from H(n=3), generated within the rf silane glow discharge. The radiative lifetimes of these two states are 5.2 and 10 ns, respectively. A study of the Si to H yield ratio, together with some Langmuir probe measurements, indicates that the electrons are themalized in the glow regions.
Theory of diffusion in a polycrystalline material
Authors: Zaeschmar G.
Published: February 2003

A new approach to the general theory of diffusion in polycrystalline materials has been taken. By means of introduction of a third empirical parameter, the filling time of a grain, the mass transfer coefficient between the boundary of two media can be determined if only a typical grain dimension and the bulk diffusion constant are known. A subsequent expression for the diffusion in a finite length grain boundary permits the determination of the grain boundary diffusion constant. A stack of circular cylinders is used as a model. It permits calculation of the concentration functions for large penetration depth as well as bottom to top filling of an individual cylinder.
The nature of defect layer formation for arsenic ion implantation
Authors: Prussin S. , Margolese David I. , Tauber Richard N.
Published: February 2003

A series of {100} silicon wafers were implanted with As ions over the range of 1×1013 at. cm−2 to 1×1016 at. cm−2 with energies of 50, 100, and 190 keV, using a commercial ion implanter, the Varian 200-DF4. Two end stations were used, the Waycool which provided good contact between the wafers and a thermal sink and the Wayflow, which holds the wafers without any provision for obtaining such contact. Precise values of amorphous layer depth were obtained by a newly developed technique, using direct measurement of the depth exposed by a tapered groove. For the Waycool implanted wafers, the amorphous layer depth increased with dose. For the Wayflow wafers, the amorphous layer depth increased to a maximum and then decreased, finally disappearing at the higher doses. Combining shallow angle-lapping, etching, and profilometry, it was possible to study the submerged amorphous layers originating at the threshold dose for the 190-keV implantations. For Waycool implanted wafers, the surface crystalline layer thickness decreased and disappeared with increased dose. For Wayflow wafers, the surface crystalline layer increased with dose, meeting the crystalline substrate which grew from the opposite direction. The differences in defect structure between Waycool and Wayflow implanted wafers are attributed to the dynamic annealing which occurs during implantation. The defects remaining after a low temperature transformation anneal are correlated to dynamic annealing effects.
Nonlinear regression least-squares method for determining relaxation time spectra for processes with first-order kinetics
Authors: Cost J. R.
Published: February 2003

A simple method is shown for calculating the relaxation time spectrum which controls the rate at which a process following simple first-order kinetics takes place. The method involves unfolding a Fredholm equation of the first kind using least-squares and then using a modified nonlinear regression rather than a linear least-squares technique, thereby avoiding the highly oscillatory solutions which tend to occur with the latter with reduced mesh spacing or an increased number of bins. The validity and accuracy of the method for analyzing experimental data to reproduce various known input spectra are assessed and found to be excellent for data with no experimental error. For data with simulated experimental error with standard deviations up to σ=0.05 the method provides acceptable approximate solutions even though no exact solution is expected. Increasing the magnitude of the experimental error for a single lognormal input spectrum appears to have an increasing but nonsystematic effect upon the uncertainty of the approximate solution. Effects due to increasing the number of bins in the interval over which the spectrum is calculated are assessed and shown not to appreciably change the results, even for up to 60 bins. The methods is shown to be applicable to a wide variety of input spectra including single and double lognormal and box distributions. Importantly, in each of the cases studied the approximate solution appeared both to be unique and to converge toward the known input spectrum. Based upon this validation it is concluded that this method has applicability to a wide range of problems in which simple exponential decay is occurring with a spectrum of time constants. It may also be useful for problems with different kernals than that for first order kinetics; however, careful validation will be required.
Spall studies of differently treated 2024A1 specimens
Authors: Rosenberg Z. , Luttwak G. , Yeshurun Y. , Partom Y.
Published: February 2003

Commercial manganin stress gauges are used in planar impact experiments to determine spall strengths of variously heat-treated 2024A1 specimens. A one-dimensional Lagrangian code is used to find the best fit of calculated versus experimental stress histories by varying the spall strength in the code and using a simple threshold criterion. We found values in the range of 1.2–1.75 GPa for spall strengths of the differently treated specimens. These values are in good agreement with published data obtained by other methods. We also confirmed the spall strength values by a series of low-stress experiments resulting in only incipient spalls. A specimen of 2024T351 which was shocked perpendicular to the rolling direction has a lower spall strength (by about 0.3 GPa) than a specimen shocked along the rolling direction. This difference is very close to that predicted earlier.
Low threshold voltage ZnSe:Mn thin film electroluminescent cells prepared by molecular beam deposition
Authors: Mishima Tomoyoshi , Takahashi Kiyoshi
Published: February 2003

An Al/ZnSe:Mn/ITO dc-operated electroluminescent (EL) cell was prepared by molecular beam deposition. The threshold voltage was 6–10 V, which is the lowest value in these types of EL cells reported so far. The deposited ZnSe:Mn layer was a polycrystal with only (111) orientation and exhibited sharp x-ray diffraction and reflection high energy electron diffraction patterns which have been hardly obtained by conventional evaporation methods. This low threshold voltage EL cell has a great potential of application in panel displays because of the low cost and the large size of Indium-Tin-Oxide (ITO)-coated glass substrates.
Importance of emitter recombinations in interpretation of reverse recovery experiments at high injections
Authors: Jain S. C. , Agarwal S. K. , Harsh
Published: February 2003

At high injections, the effect of recombinations in the emitter becomes important in interpreting reverse recovery experiments. If this effect is taken into account, the observed values of ts yield considerably larger values of base lifetime than those obtained by using the simple Kingston’s theory.
Refractive index of quaternary In1−xGaxAsyP1−y lattice matched to InP
Authors: Jensen B. , Torabi A.
Published: February 2003

The refractive index of the quaternary InGaAsP lattice matched to InP at energies below the fundamental absorption is presented. The theoretical result for refractive index n is obtained from a quantum mechanical calculation of the dielectric constant of a compound semiconductor. It is given in terms of basic material parameters only, with no adjustable constants. Comparison of theory with experimental data is also discussed.
CO2 laser-induced melting of silicon
Authors: Hasselbeck M. , Kwok H. S.
Published: February 2003

CO2 laser-induced melting of heavily doped silicon (>1018 cm−3) was studied using both nanosecond and picosecond laser pulses. Evidence for melting is presented and the duration of the melting was measured at intensities below the damage threshold. Dense plasma formation was observed before melting occurred. The melt durations were considerably longer than reported previously for visible laser pulses of comparable durations, indicating a very deep (≳1 μm) molten layer had been achieved.
Laser induced copper plating
Authors: Al-Sufi A. K. , Eichler H. J. , Salk J. , Riedel H. J.
Published: February 2003

Argon laser induced plating of copper spots and lines from copper sulfate solutions on glass and phenolic resin paper has been investigated. The substrates had to be precoated with an evaporated copper film. The highest plating rates have been obtained with a small film thickness of 25 nm. Spots with a thickness up to 30 μm were plated.
Calculation of temperature profiles in radiantly heated and cooled silicon wafers
Authors: Aaron D. B. , Thomas R. E. , Wiley J. D.
Published: February 2003

Temperature gradient zone melting can be utilized to force metallic migration through a semiconducting wafer. The rate of metallic migration is dependent on the temperature profile within the wafer. Kellett’s model is applied to determine the temperature gradient within a radiantly heated wafer. This model includes the absorption and reradiation of energy along with strictly conductive heat transfer. Computer calculations based on the model show that the temperature gradient is constant inside the wafer and that it tends to zero near the wafer surfaces. This indicates that heat transfer is primarily by conduction inside the wafer and by radiation near the surface.
Polypyrrole-semiconductor Schottky barriers
Authors: Inganäs Olle , Skotheim Terje , Lundström Ingemar
Published: February 2003

Junctions between polypyrrole, a conducting polymer formed by electrooxidation, and n-type semiconductors have been studied. Cadmium sulphide and titanium dioxide were chosen as substrates as a complement to earlier studies on silicon. The junctions behave as Schottky barriers on these semiconductors. The series resistance of the polypyrrole film is large and was taken into account in the evaluation of the data. The barrier heights of the junctions are compared with those found with ordinary metals. It is deduced that the work function of polypyrrole must be close to 5 eV.
Selective surfaces of anodic copper oxide for solar collectors
Authors: Milgram Alvin A.
Published: February 2003

The hemispherical spectral reflectance and the hemispherical total emittance were measured for copper oxide films produced by anodic oxidation. The anodic copper oxide films are shown to have desirable selective surface properties for use as solar absorbers.
Rod-like defects in oxygen-rich Czochralski grown silicon
Authors: Yamamoto N. , Petroff P. M. , Patel J. R.
Published: February 2003

Rod-like defects in annealed oxygen rich silicon crystals grown by the Czochralski method were investigated by means of transmission electron microscopy. The rod-like defect has an apparent Burgers vector along 〈100〉 and gives a dipole-like contrast. The rod defect plane is 〈100〉 and its character is found to be extrinsic. The clearly resolved dipoles associated with the rod-like defect consist of perfect dislocations and are interstitial in character. The rod-like defects are tentatively attributed to some form of SiOx precipitate.
Use of a superconductive magnetic gradiometer near magnetic objects
Authors: Podney Walter , Sager Ronald
Published: February 2003

We present a technique for orienting a superconductive magnetic gradiometer, formed by two coplanar pickup loops, to suppress gradient fluctuations originating from nearby magnetic objects. We developed the technique to quiet fluctuations coming from the steel structure of an oceanographic research tower that impressed gradients of about 200 nT/m at the gradiometer. Facing the loops nearly edgewise to the tower quiets noise to the level of inherent instrument noise, ∼0.1 (pT/m)/(Hz)1/2, at frequencies from 1 to 25 Hz. It also quiets noise nearly to inherent instrument noise at frequencies from 0.1 to 10 mHz. Comparison of the empirical result with the quieting expected from a formulation of gradiometer response shows that gradient fluctuations coming from a nearby magnetic object appear to a gradiometer to come from fluctuations in location and moment of a magnetic dipole near the magnetic centroid of the object, whatever the magnetic structure of the object.