bluuebunny/crossref_metadata_2025_split huggingface dataset:
Antiphase Domain Structures of CdTe on Sapphire Substrates
Authors: Maruyama Kenji , Yoshikawa Mitsuo , Takigawa Hiroshi 
Published: March 2011

ABSTRACTAntiphase domain (APD) structures have been discovered in CdTe layers grown on (0001) sapphire substrates by MOCVD. To explain APD formation, an obstruction model based on a surface-reaction mechanism has been proposed. The proportion of one-phase domains to the total area varies with the [DETe]/[DMCd] ratio (VI/II ratio). A single-domain CdTe layer can be obtained at a VI/II ratio of 5. The APD structure shows a strong correlation with the crystallinity measured by X-ray. For a single-domain CdTe epilayer, theFWHM of the X-ray rocking curve shows 114 arc seconds and the EPD is 6×10 cm−2
Charge Carrier Recombination in Doped a-Si:H Studied by Contactless Photoconductivity Measurements
Authors: Werner A. , Kunst M. 
Published: March 2011

AbstractTransient photoconductivity measurements in a-Si:H at different n- and p-doping level point to decay kinetics which strongly depend on the doping level and excitation densities. In undoped a-Si:H excess charge carriers decay mainly by a transition between electrons and holes at their respective mobility edges. The generation of hole traps by n-doping quenches this decay channel and transitions between localized states in the bandgap play an important role in charge carrier kinetics. In p-doped material the availability of a large density of mobile holes and positively charged recombination centers increases the electron decay drastically.
Hydrogen Content and the Optical Bandgap in Amorphous Silicon
Authors: Maessen K. M. H. , Pruppers M. J. M. , Bezemer J. , Habraken F. H. P. M. , van der Weg W. F. 
Published: March 2011

AbstractThe dependence of the optical bandgap on the hydrogen concentration is measured for amorphous silicon films prepared under different glow-discharge conditions. A deviation from the usually accepted linear dependence is found for hydrogen concentrations above 12 at.‰ We find that in this concentration region an increase of hydrogen incorporated as SiH2 is responsible for this behaviour.
Exafs Study of a-Si1−xGex:H, a-Si1−x Cx:H and a-Si1−xNx:H at the Si K-Edge
Authors: Filipponi A. , Fiorini P. , Evangelisti F. , Mobilio S. 
Published: March 2011

AbstractThe structure of three series of hydrogenated amorphous Si-based alloys was studied by EXAFS at the Si K-edge. Average bond-lengths and first shell compositions were determined. It is shown that the two atomic species are randomly distributed in a-Si1−xGex:H whereas a chemical ordered composition is favored in a-Si1−xNx:H
Comparative Study of Structure and Hydrogen Incorporation in Glow Discharge a-Si:C:H and a-Si:N:H Alloys
Authors: Beyer W. , Wagner H. , Mell H. 
Published: March 2011

AbstractPlasma-deposited a-Si:C:H and a-Si:N:H alloys both show a rapidly rising hydrogen incorporation with increasing carbon or nitrogen content. For hydrogen concentrations exceeding ∼ 20 at.%, the host material starts to lose its connectiveness leading to the formation of a void structure as evidenced by hydrogen evolution and infrared absorption. Raising the substrate temperature leads to a reduction of the hydrogen concentration, to an increase of the Si-C and Si-N bond concentration and to a more compact naterial. However, for a-Si:C:H films it leads also to graphitic carbon bonds. The widening of the optical bandgap of a-Si:C:H films up to about 50 at.% of carbon is almost entirely due to the increased hydrogen incorporation whereas for a-Si:N:H films both hydrogen and nitrogen incorporation plays a role.
Substitutional and Interstitial Doping of Amorphous Silicon Nitride
Authors: Spear W. E. , Dunnett B. , Lecomber P. G. 
Published: March 2011

AbstractDoped films of amorphous silicon nitride have been prepared by the glow discharge technique over a wide range of ammonia/silane mixtures. P- and B-doped specimens were produced by admixing phosphine or diborane during deposition. Interstitial doping was attempted by Na-ion implantation, and by in-diffusion of evaporated Li. For values of the ammonia/silane volume ratio R < 10−2, the optical gap remains unchanged and all the above dopants raise the room temperature conductivity to σRT ≅ 10−2(Ω cm)−1. With increasing R the efficiency of P, B and Na doping decreases rapidly. However, incorporation of Li continues to significantly increase σRT at higher R where the optical gap approaches 5eV. Near-stoichiometric, transparent specimens have been prepared with σRT increased by up to 14 orders of magnitude by Li doping. A discussion of the doping results is given.
Dynamic Characteristics of Amorphous Silicon Thin Film Transistors
Authors: van Berkel C. , Hughes J. R. , Powell M. J. 
Published: March 2011

AbstractIn this paper we report on the dynamic characteristics of amorphous silicon thin film transistors in the time interval between ips to 1s after gate switch-on. The experimental results show a continuous change in the threshold voltage in this t'me regime. A model based on carrier thermalisation to the deep states including the spatial dependence of the thermalisation process in the band-banding region is presented to account for these results. The effect responsible for the observed time dependence of the threshold voltage is shown to be the trapping of charge in deep states in the bulk amorphous silicon away from the interface with the gate dielectric.
Properties of a-SiGe and Application to Stacked Solar Cell
Authors: Itozaki H. , Fujita N. 
Published: March 2011

AbstractDeposition technique of a-SiGe:H and its application to a stacked solar sell were investigated. Properties of a-SiGe:H were improved by a glow discharge method with a negatively biased substrate, and a mercury sensitized photo CVD under lower pressure. An a-SiGe:H single junction solar cell was improved by slight boron doping to an i layer and insertion of a buffer layer into a p/i interface. A conversion efficiency of more than 10 % was obtained by a triple stacked solar cell on a alass substrate.
Characterization of Heavily Boron-Doped a-Si:H Films Deposited at Low Substrate Temperatures
Authors: Jang Jin , Kim Sung Chul , Lee Dae Bong , Lee Choochon 
Published: March 2011

AbstractThe electrical and optical properties of heavily boron-doped hydrogenated amorphous silicon (a-Si:H) films deposited at 100°C with a gas phase doping concentration between B2H6/SiH4=0.001 and 0.1 have been investigated. The absorption edge exhibits the characteristic Urbach form and the width of exponential absorption tail, Eo, increases with increasing doping concentration. The optical gap has a linear relationship with the Eo and it is expected to be 2.20 eV when the Eo is zero. Thus, the disorder determines the optical gap directly whether the sample is doped or undoped, the hydrogen and boron in the film change the disorder. The conversion efficiency of n-i-p cell is improved by 15% if the p-layer is deposited at 100°C after preparing the n- and i-layers ∼250°C.
Changes of Drift Mobility in a-Si:H with Light Exposure and Doping
Authors: Takada J. , Fritzsche H. 
Published: March 2011

AbstractMeasurements of the drift mobility μ of photo-excited electrons in n-type hydrogenated amorphous silicon (a-Si:H) as a function of light intensity are reported. The value of μ increases as the quasi Fermi level is moved closer to the transport states in accordance with the multiple trapping theory. The drift mobility decreases with increasing doping as well as with an increase in the concentration of metastable dangling bonds defects by strong light exposures. This decrease in μ between 300 and 360K can be explained by a corresponding decrease in the microscopic mobility, by an increase in the density of tail states within 0.35eV below the electron mobility edge, or by a combination of both these effects.
Light Induced Change in a-Si:H p-i-n Solar Cells Under Various Light Soaking Conditions
Authors: Sakai H. , Ihara T. , Nabeta O. , Yoshida T. , Maruyama K. , Ichikawa Y. , Uchida Y. 
Published: March 2011

AbstractLihgt-induced change in photovoltaic performance of p-i-n solar cell was studied. The behavior of degradation of the solar cell strongly depends on the intensity and the spectrum of illumination light. The results of these light soaking tests are presented and discussed. On the basis of these results, the superiority of double-stacked a-Si/a-Si tandem solar cells is discussed.
Heterojunction Bipolar Transistors (HBT) with a-Si:H or μc-Si Emitter
Authors: Symonsj J. , Nijs J. , Vanhellemontk J. , Baerth K. , Michielg H. , Willekew G. , Vandervors W. , Mertens R. 
Published: March 2011

AbstractIn this paper phosphorous doped amorphous and microcrystalline silicon are used as emitter material for npn bipolar transistors. A heterojunction is formed between emitter and base, resulting in a higher current gain β for the same base parameters in comparison with conventional transistors. Because the amorphous silicon results in a too high emitterresistance, a compromise solution is microcrystalline silicon (μc-Si). HREM-micrographs give credit to the true heterojunction concept and show epitaxial reorganization, especially after annealing of the amorphous silicon.
The Properties of Microcrystalline and Amorphous Silicon Electron Blocking Layers in a-Si Alloy Photoreceptors
Authors: Johncock A. G. , Hudgens S. J. , Guha S. 
Published: March 2011

AbstractPositive charging amorphous silicon alloy photoreceptors require intentionally fabricated electron blocking layers at the photoreceptor/substrate interface. Thin insulating films and lightly boron doped (300ppm) a-Si alloy layers have been previously employed either singly or in multilayers as back blocking layers. We report here, for the first time, the use of thin (≈300Å) heavily doped microcrystalline (≈10 Ω−1 cm−1) Si back blocking layers [1], with enhanced photoreceptor performance. Investigation of the temperature and electric field dependence of the dark decay of photoreceptors with amorphous or microcrystalline silicon back blocking layers as a function of blocking layer thickness and boron doping is interpreted within a comprehensive model of blocking layer operation.
Application of a Low Frequency Technique to the Study of Amorphous Materials.
Authors: Pickup C. , Cochrane R. W. , Brebner J. L. , Perluzzo G. 
Published: March 2011

AbstractThe extension of a recently reported application of a dielectric spectroscopic technique on c-GaAs will be shown in the case of a-Si:H. This technique is based upon the application of a small signal a.c. voltage at several fixed frequencies using a Frequency Response Analyzer.The technique is particularly useful for applications to material study where more traditional methods (i.e. DLTS) fail to apply. Thus we can probe the nature of bulk transport processes in the most resistive of materials and also study the interface between the contact and the substrate. It therefore becomes relatively simple to distinguish Schottky or blocking contacts from Ohmic or quasi-Ohmic contacts.Typical capacitance and dielectric loss data will be presented as a function of frequency. Arrhenius plots obtained from the temperature dependence of the above parameters will show that activated processes have been observed and may be related to specific defect centres.
A Study of the State Distribution in Various a-Si:H Materials by a New Capacitance Method
Authors: Balberg I. 
Published: March 2011

AbstractA new method for the determination of the deep states density in amorphous semiconductors is presented. The method is based on the carriersemission- time dependence of the capacitance-voltage characteristics of Schottky barriers. The applicability of the method for the study of hydrogenated amorphous silicon materials is demonstrated. The pitfalls associated with trying to deduce the density of states from a single capacitance-voltage characteristic are also discussed.
Real Structure and Internal Friction of Boron Doped with Zirconium
Authors: Darsavelidze G. Sh. , Tsagareishvili G. V. , Antadze M. E. , Tsagareishvili O. A. , Khvedelidze A. G. , Tavadze F. N. 
Published: March 2011

ABSTRACTThe nature of interaction of point and linear defects in semiconductor boron doped with zirconium (∼ 1.5% at.) has been studied using electron microscope and internal friction methods. It was shown that doping with zirconium promoted the multiplication of polysynthetic twins and stacking faults. A computer simulated analysis of diffraction patterns was performed in terms of trigonal presentation. At the frequency of free torsional vibrations of ∼ 1Hz a high level of internal friction with maxima at 250, 300–320 and 380–420°C was revealed. It is supposed that the maxima are respectively due to: the twin-boundary motion accompanied by breaking of intericosahedral bonds (a); the process of ordering-disordering of atoms in the impurity atmospheres under the continuous change of the temperature and elastic fields of moving twinning dislocations in the {100} system (b); the impurity controlled twin-boundary motion in the {511} system.
Electron Deformation Density Distribution in α-Boron
Authors: Will G. , Kiefer B. , Morosin B. , Slack G. A. 
Published: March 2011

ABSTRACTThe bonding features of α-boron were studied using electron density analysis procedures. Deformation density maps and valence density were calculated and the structure analysed by so-called multipole refinements, yielding R - 0.0119. The refinement model correctly describes the bonding and results in a difference density distribution free from any meaningful residual peaks.
Epitaxy of SiC Films on Sapphire by Laser CVD
Authors: Nakamatsu Hirohide , Kawai Shichio 
Published: March 2011

ABSTRACTArF excimer laser CVD was performed in a very-low pressure reactor. C2H2 and Si2H6 were used as source gases and carrier gases were not used. Epitaxial 3C-type SiC(111) grew parallel to α-Al2O3 (0001) substrate. It had a twin structure. Mismatch between the lattice parameters was estimated to be 12%. The epitaxial growth occurred down to 980°C and the films about 0.5μm in thickness grew at 1150°C for 30 minutes. Unirradiated films were polycrystalline or spontaneously peeling-off epitaxial films, while irradiated ones were strongly adherent epitaxial films.
Inversion-Type Mos Field Effect Transistors Using CVD Grown Cubic SiC on Si
Authors: Shibahara K. , Takeuchi T. , Saitoh T. , Nishino S. , Matsunami H. 
Published: March 2011

ABSTRACTInversion-type n-channel MOSFET's of cubic-SiC were successfully fabricated. MOSFET's were fabricated on an antiphase-domains free layer grown on Si(100) by carbonization and subsequent chemical vapor deposition. Ion implantation technique was used to form source and drain of MOSFET's. A gate oxide of SiO2 was formed by thermal oxidation of SiC. Inversion mode operation was confirmed for the first time. Annealing temperature dependence of electrical characteristics of P+ and N2+ implanted layer and characteristics of p-n junction diodes fabricated using ion implantation technique were also investigated.
Anomalous Seebeck Coefficient in Boron Carbides
Authors: Aselage T. L , Emin D. , Wood C. , Mackinnon I. , Howard I. 
Published: March 2011

ABSTRACTBoron carbides exhibit an anomalously large Seebeck coefficient with a temperature coefficient that is characteristic of polaronic hopping between inequivalent sites. The inequivalence in the sites is associated with disorder in the solid. The temperature dependence of the Seebeck coefficient for materials prepared by different techniques provides insight into the nature of the disorder.
Single Crystal Epitaxial Growth of β-SiC for Device and Integrated Circuit Applications
Authors: Parsons J. D. 
Published: March 2011

ABSTRACTBeta SiC is an important semiconductor whose development has been slowed by synthesis difficulties. The physical and electronic properties which make β-SiC desirable for high speed and high power electronics are discussed, with special emphasis on field effect transistor (FET) applications. A history of synthesis efforts is presented to illuminate the obstacles encountered in the growth of semiconductor device quality P-SiC. A new approach to single crystal epitaxy of β-SiC, using TiC as a substrate, is described. The properties of TiC which make it a uniquely suitable substrate for β-SiC epitaxial growth are discussed, and procedures used to prepare TiC surfaces for β-SiC epitaxy are described. The growth process employed at our laboratory, chemical vapor deposition (CVD), is described, and experimental observations of the effects of the CVD growth environment on β-SiC epitaxial growth are presented. Based on these observations, we propose to synthesize β-SiC in a singlesource reaction, using molecules which decompose directly to SiC units. This contrasts with current approaches, which introduce Si and C separately, in molecules which must decompose and subsequently react to form SiC.
Growth of Diamond Films by Plasma CVD
Authors: Yugo Shigemi , Kimura Tadamsa , Kanai Hisayuki , Adachi Yoshio 
Published: March 2011

ABSTRACTGrowth of filmy diamond crystals has been strongly desired, and the plasma CVD is expected as one of the growth techniques which provide high quality crystalline diamond films. This study deals with the growth of uniform crystalline diamond films by means of the plasma CVD. The main stress was laid on the effects of the surface treatments of the silicon substrate and the substrate potential on composition of deposited materials as well as on the morphology of diamond crystals grown on the substrate.
A mixture of methane (1%)/hydrogen with a pressure to 400 Pa was flown at a rate of 150 cc/min and was discharged by applying 200 W, 2.45 GHz microwave power. The Si substrates were heated to 850 ° C.
Nuclei for the diamond crystal growth were preferentially generated on the defect sites caused by the surface treatments. With increasing the substrate potential in the negative direction, the growth of silicon carbide was observed to increase. When the substrate was positively biased, filmy diamond layers were found to be deposited.
Refractory Semiconductors for High Temperature Thermoelectric Energy Conversion
Authors: Wood Charles 
Published: March 2011

ABSTRACTThermoelectric energy conversion utilizing nuclear heat sources has been employed for several decades to generate power for deep space probes. In the past, lead telluride and, more recently, silicon-germanium alloys have been the prime choices as thermoelectric materials for this application. Currently, a number of refractory semiconductors are under investigation at the Jet Propulsion Laboratory in order to produce power sources of higher conversion efficiency and, thus, lower mass per unit of power output. Included amongst these materials are improved Si-Ge alloys, rare earth compounds and boron-rich borides. The criteria used to select thermoelectric materials, in general, and the above materials, in particular, will be discussed. The current state of the art and the accomplishments to date in thermoelectric materials research will be reviewed.
Bipolaron Formation in B12 and (B11C)+ Icosahedra
Authors: Howard I. A. , Beckel C. L. , Emin David 
Published: March 2011

ABSTRACTBoron carbides, B1-xCx with 0.085 ≤ × ≤ 0.200, generally contain both B12 and B11C icosahedra. However, the electronic transport with 0.1 ≤ × ≤ 0.2 is believed to occur by means of bipolaron hopping between only B11 C icosahedra [i]. We have calculated the changes in energy, atomic positlions and charge distribution when a pair of electrons is added to the isoelectronic icosahedral clusters B12 and (B11C)+. We simulate an icosahedron in a neutral lattice by bonding the icosahedral atoms to hydrogenic atoms which we constrain to be neutral. The computations are performed with a self-consistent molecular-orbital method, PRDDO.We find a total energy reduction of -3.7 eV for two electrons added to a B12 icosahedron. Of this, -2.7 eV arises from the electrons filling the icosahedron's bonding orbitals. The remaining -1.0 eV comes from the contraction of the icosahedron's radius by -0.09 Å. For two electrons added to a (B11C)+ icosahedron we find a total energy reduction of -18.2 eV. Of this, -16.5 eV arises from filling the icosahedron's bonding orbitals. The remainder arises frop a -0.09 Å contraction of the icosahedron's radius. Thus, we find (B11C) icosahedra to be strongly energetically favored over B12 icosahedra as bipolaron sites.The positive charge associated with a (B11C)+ icosahedron is distributed over the eleven boron atoms. Concomitantly, we find the added two electrons of the bipolaron to be distributed over all twelve sites of the B11C icosahedron. We find the energy difference between an electron pair added to B12 and (B11C)+ icosahedra to arise principally from the increased Coulomic attraction provided by the extra positive charge of the (B11C) icosahedron.
Synthesis of New Chalcogenide Materials. The Novel One-Dimensional Semiconductor K4 Ti3 S14
Authors: Sunshine Steven A. , Kang Doris , Ibers James A. 
Published: March 2011

ABSTRACTThe use of A2 Q/Q melts (A - alkali metal, Q - S or Se) for the synthesis of new one-dimensional solid-state materials is found to be of general utility and is illustrated here for the synthesis of K4 Ti3 SI4. Reaction of Ti metal with a K2 S/S melt at 375°C for 50 h affords K4 Ti3 SI4. The structure possesses one-dimensional chains of seven and eightcoordinate Ti atoms with each chain isolated from all others by surrounding K atoms. There are six S-S pairs (dave - 2.069(3) Å) so that the compound is one of TiIV and may be described as K4 [Ti3 (S)2 (S2)6]. Electrical conductivity measurements indicate that this material is a semiconductor.
Nature of Paramagnetic Centers in Amorphous Boron
Authors: Tsiskarishvili G. P. , Tsagareishvili G. V. , Antadze M. E. , Tavadze F. N. 
Published: March 2011

ABSTRACTAmorphous powders of boron isotopes have been studied in the temperature range 100–450 K using EPR method. It was shown that paramagnetic centers with g=2.0029 ± 0.0001 are the holes captured on trapping levels. The centers represent volume defects. On the basis of temperature dependent measurements of the concentration of paramagnetic centers and their linewidth an energetical parameter of trapping level equal to 0.11eV over valence band was defined. An observed strong narrowing of the EPR line is connected with the increase of the frequency of delocalization of electrons with temperature. The structure of powders was studied by electron microscope method. Experimental results confirm the existence of icosahedral arrangement in amorphous boron.
Microscopic Origin of the Composition-Dependent Change of the Thermal Conductivity in Boron Carbides
Authors: Emin David , Howard I. A. , Green T. A. , Beckel C. L. 
Published: March 2011

ABSTRACTLarge grain polycrystalline boron carbides have a high-temperature thermal conductivity which changes from being characteristic of a crystal to being glass-like as the carbon content is reduced from its maximal value. We relate this phenomenon, to compositional changes within the three-atom intericosahedral chains. With a reduction of the carbon concentration from its maximal concentration (20 %), a carbon atom within some of the three-atom (CBC) intericosahedral chains is replaced by a boron atom, thereby producing CBB chains. We estimate that the CBB chains are significantly softer than the CBC chains. Thus, with this reduction of carbon content the intericosahedral chains are inhomogeneously softened. This suppresses the coherent transport of heat through the chains. The remaining thermal transport occurs incoherently through vibrationally inequivalent structural units, i.e. “phonon hopping.”