bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Boron Implantation on Silicon Dioxide Passivated HgCdTe
Authors: Bowman R. C. , Marks J. , Downing R. G. , Knudsen J. F. , To G. A.
Published: March 2011

The influence of boron ion implants on the optical and physical properties of photochemically deposited SiO2 films on HgO 7 CdO 3Te and silicon has been investigated. The distributions of the boron atoms between the SiO2 film and substrate have been determined by a nondestructive neutron depth profiling method. The implants produce an apparent densification of the SiO2 films, which is accompanied by an increase in refractive index and changes in the infrared vibrational spectra for these films.
Epitaxial Semiconductor Structures for the Infrared: Where Are We Now?
Authors: Panish Morton B.
Published: March 2011

EXTENDED ABSTRACT

The use of epitaxial structures for the generation, detection, and modulation of light has had as its strongest driving force the development of fiber optic communications systems. Partly for that reason, the semiconductor materials systems that can be most readily optimized for wavelengths (800-1600nm) transmittable through state-of-the-art optical fibers, have been the most well developed. It also appears that the communications community has been most fortunate in that the semiconductor systems required, although far more difficult to deal with than Si, are relatively benign compared to those that operate at significantly shorter or longer wavelengths. Two developments that are now more than 15 years old initiated the extensive studies of compound semiconductor epitaxial structures that are now so important. These were the introduction of the heterostructure concept in the study of injection lasers and light emitting diodes (1), and the realization that lattice matched isoelectronic epitaxial layers, consisting in part of solid solutions between the binary compounds, would permit such structures to be grown.
Liquid-Phase Epitaxy of Hg1−xCdxTe from Hg Solution: A Route to Infrared Detector Structures
Authors: Tung Tse , Kalisher M. H. , Stevens A. P. , Herning P. E.
Published: March 2011

Over the past few years, liquid-phase epitaxy (LPE) has become an established growth technique for the synthesis of HgCdTe. This paper reviews one of the most successful LPE technologies developed for HgCdTe, specifically, “infinite-melt” vertical LPE (VLPE) from Hg-rich solutions.

Despite the very high Hg vapor pressure (> 10 atm) and the extremely low solubility of Cd in the Hg solution (< 10−3 mol%), this approach was believed to offer the best long-term prospect for growth of HgCdTe suitable for various device structures. Since the initial demonstration of LPE growth of HgCdTe layers from Hg solution in experiments conducted at SBRC in 1978, the VLPE technology has advanced to the point where epitaxial HgCdTe can now be grown for photoconductive (PC) and photovoltaic (PV) as well as monolithic metal-insulator-semiconductor (MIS) and high-frequency laser-detector devices with state-of-the-art performance in the entire 2–12 μm spectral region.

A historical perspective and the current status of VLPE technology are reported. Particular emphasis is placed on the important role of the ther-modynamic parameters (phase diagram) and on control of stoichiometry (defect chemistry) and impurity doping (distribution coefficient) for growth of HgCdTe layers from Hg solution. Critical material characteristics, such as transport properties, minority-carrier lifetime, morphology and crystal structure, are also discussed. Finally, a comparison with the LPE technol-ogy using Te solutions, which has been the mainstay of the remainder of the IR community, is presented.
Hg1−x−yCdxZnyTe: Growth, Properties and Potential for Infrared Detector Applications
Authors: Kaiser Debra L. , Becla Piotr
Published: March 2011

Close-spaced isothermal vapor phase epitaxy (VPE) was used to grow quaternary Hg1−x−yCdxZnyTe epillayers on Cd1−zZnzTe substrates. Composition, resistivity, and carrier concentration depth profiles were determined in the epilayers. p-n junctions were produced from material with appropriate properties using the Hg diffusion method. The junctions showed excellent I-V characteristics and high spectral detectivities.
Metallurgical Profile Modeling of Hg Corner LPE HgCdTe
Authors: Ludington Burt W.
Published: March 2011

Mercury cadmium telluride (Hg1-x Cdx Te) is an important material for infrared detector applications due to tde variable bandgap obtained through simply varying the mercury/cadmium ratio. Thus IR sensing systems with various wavelength requirements, typically from 2 to 12 μm, can potentially all be supplied by one materials technology. Bulk crystal growth technology was originally pursued for these applications. However, large, high quality crystals are difficult to grow because of the high melting point of HgCdTe and the resulting high Hg vapor pressure. Liquid phase epitaxial (LPE) growth techniques can lower the growth temperature through the use of a solvent, and allow the deposition of thin films on large foreign substrates that are grown without any Hg.
InAsSbBi and InSbBi: Potential Material Systems for Infrared Detection
Authors: Bedair S. M. , Humphreys T. P. , Chaing P. K. , Katsuyama T.
Published: March 2011

InSb1−x Bix (0.01 < × < 0.14) and InAsSbBi quaternary alloys are potentially attractive materials for the development of semiconductor infrared detectors covering the 8–14 μm range [1,2,3].

We report for the first time, MOCVD growth of InSo1−x Bix (0.01 < × < 0.14) and InAs1−x−y Sbx Biy with 0.5 < × < 0.7 and 0.01 < y < 0.04 on both GaAs and InSb substrates using AsH3, TMSb, TEI and TMBi. Electrical measurements of the undoped InSo0.99 Bi0.01 shows a background carrier concentration of approximately 1016/cm3 and a room temperature mobility of 20,215 cm2/V.sec. To-date, these are the best reported electrical measurements for this ternary alloy.

The formation of a secondary Bi phase and single crystal growth of metallic bismuth-antimony at the surface of InSo1−x Bix which results in deterioration of morphology with increasing values of x is also investigated. A wide range of analytic techniques, including SEM, EDX, electron microprobe and AES have been employed in our surface analysis.
Preparation and Applications of Lead Chalcogenide Diode Lasers
Authors: Partin Dale L.
Published: March 2011

Lead chalcogenide diode lasers are useful for spectroscopic and fiber optics applications in the mid-infrared (2.5-30 μm) wavelength range. These devices have previously required cryogenic cooling (<100 K) for CW operation. This limitation has been overcome through the use of a new, lattice-matched alloy system, Pb1-xEuxSeyTe1-y as well as the introduction of advanced, quantum well active region device structures grown by molecular beam epitaxy (MBE). Operating temperatures have been increased to 175 K CW (at 4.4 μm) and to 270 K pulsed (at 3.9 μm). Thermal leakage currents out of the device active region appear to be limiting device performance. This has led to the study of band offsets in PbEuSeTe/PbTe heterojunctions as well as to exploration of alternative high energy band gap alloys of PbTe with Ge, Yb, Ca, Sr, and Ba. The status of this work and examples of ultrahigh resolution studies done with these tunable laser sources will be included.
Epitaxial IV-VI Semiconductor Films
Authors: Chu T. K. , Martinez A.
Published: March 2011

Epitaxial films of IV-VI semiconductors and their alloys form the basis of an infrared detector technology that offers advantages in material stability as well as spectral versatility. These films are prepared by epitaxial hot-wall techniques and their material properties are essentially the same as those of bulk crystals. Because of their stability, multilayer growths of the materials can be achieved in a straight-forward manner. To date, multi-color detectors and small scale two-color detector arrays have been demonstrated successfully. A brief review of the growth method and the growth characteristics is given. Recent advances in superlattice research, especially those of interest to electro-optical devices, will be discussed. These include persistent photoconductivity and sub-bandgap optical transition.
Molecular Dynamics Studies of Semiconductor Thin Films and Interfaces
Authors: Grabow Marcia H. , Gilmer George H.
Published: March 2011

The structure and stability of thin epitaxial films have been investigated using molecular dynamics computer simulations. One issue of interest is the stability of a smooth film relative to 3-dimensional clusters. The simulation results show that the uniform film is never the lowest energy state for a system with finite misfit. However, the uniform film, produced in a layer-by-layer growth mode, can persist in a metastable state at substantial misfits, e.g. 10% at 1/2 the melting point. This is a result of the large nucleation barrier to the formation of clusters.

The second issue is the quality of the interface between the film and the substrate. At equilibrium, the critical thickness for the introduction of misfit dislocations is larger for films on the diamond cubic (100) substrate than on the (111), and differs from predictions based on continuum mechanics. We find that coherent films remain in metastable equilibrium far beyond the critical misfit calculated for full equilibrium, because a large free energy barrier inhibits the introduction of misfit dislocations.
Atomic Structures of Silicon Surfaces and Silicon-Silicide Interfaces
Authors: Liu H. M. , Tsong T. T.
Published: March 2011

Atomically resolved and well ordered field ion images of silicon surfaces have been obtained for the first time when a carefully cleaned Si tip is annealed to 700 to 800°C for several minutes. Well ordered atomic structures develop on high index planes such as the (130), (135), (124), (234), (123), (113), (115) and (320). Some of them develop the (1×1) structure while others are reconstructed. Two structures coexist for the (130) plane. Twodimensional defects can be seen and their density is surprisingly high. We have also studied formation of thin layers of silicide on silicon surfaces.
GaAs – on – Si Epitaxy: Results for Coverage of ∼ 1 Monolayer
Authors: Bringans R. D. , Olmstead M. A. , Uhrberg R. I. G. , Bachrach R. Z.
Published: March 2011

Core level spectroscopy measurements have been made on Si substrates with coverages of around one monolayer of As, Ga and GaAs. The interfaces were formed on on-axis Si(100) and Si(111) substrates using molecular beam epitaxy. Results are also presented for an arsenic monolayer on a single-domain Si(100) surface prepared by cutting the crystal off-axis by 4 degrees. The strong bonding between As monolayers and the surface of the substrate causes the GaAs to begin to form islands at average coverages of less than one monolayer. The surface between the islands is found to be terminated by a single atomic layer of As. Use of a Ga predeposition technique shows evidence of reducing the tendancy towards island formation.
Investigations of Microstructural Changes in Nickel Thin Films on Ionimplanted Silicon by Cross-Sectional Transmission Electron Microscopy with Intermittent Annealings in N2 Ambient
Authors: Lu S. W. , Nieh C. W. , Chang C. S. , Chen L. J.
Published: March 2011

The feasibility of studying dynamical changes in nickel thin films on ion-implanted silicon thin films by cross-sectional transmission electron microscopy (XTEM) with intermittent annealings in N2 ambient up to 850 °C is demonstrated. Interactions of nickel thin films with oxidation induced stacking faults, fluorine bubbles and process-induced defects in ion implanted silicon are provided as examples. The technique may be applied to clarify a number of important issues encountered in the study of the reactions and diffusion of thin films and obtain informations otherwise unattainable.
The Kinetics of Ni-Al Spinel Growth Using Rutherford Backscattering Spectroscopy
Authors: Simpson Y. Kouh , Colgan E. G. , Carter C. B.
Published: March 2011

Using a planar thin-film specimen geometry, the growth kinetics of the spinel in NiOAl2O3 system has been studied with Rutherford backscattering spectroscopy. A thin-layer of Ni film is deposited by the electron-beam deposition technique onto single-crystal alumina substrates of different orientations including, (0001), {1120}, {1102} and {1100}. The subsequent heat-treatment in air then converts the Ni to NiO, thus producing a uniform layer of NiO with good adhesion between the NiO and the alumina. The kinetics of the Ni-Al spinel growth has been found to be different for different single-crystal substrate orientations. The kinetics behavior follows a parabolic growth-rate law for each orientation but shows a different reaction-rate constant. X-ray diffraction and transmission electron microscopy have been used as complementary techniques to confirm the phases that form at each stage of the heat treatment and the corresponding microstructures of the thin-film layers respectively.
Optical and Electrical Characterizations of AlxGa1−xSb
Authors: Kitamura N. , Yamamoto H. , Higuchi K. , Maeda Y. , Usami A. , Wada T.
Published: March 2011

The LPE grown AlxGa1−xSb was investigated by means of TEM, a carrier profiler and PL. The TEM image showed the dissociated 60° dislocations and Lomer-Cottrell sessile dislocation formed by the reaction of two dissociated 60° dislocations on different {111} planes. The EPMA measurement showed that Sb concentrations at the dislocation were lower than the stoichiometric composition. The epi-layer grown at 400°C had a relatively uniform carrier concentration of ∼7×1016cm−3. The PL spectra showed five emission peaks in 0≦×≦0.29. One shallow acceptor level and two native defect levels were introduced to interpret these PL emissions. The shallow acceptor level of Ev+∼30meV may be due to the defect of VGaGaSb. The native defects introduce two levels of EΓ1 - ∼90meV and EL1 - ∼160meV. The defect levels may be related to the complex defect of the Sb vacancy.
Control of the Initial Stage of Ge Overgrowth on CaF2/Si Structures by Electron Beam Exposure
Authors: Kanemaru S. , Ishiwara H. , Furukawa S.
Published: March 2011

The initial stage of Ge overgrowth on CaF2/Si structures was controlled by electron beam (e-beam) exposure through a room-temperature-deposited thin Ge layer on CaF2. It was found that the island growth of Ge was prevented in the e-beam exposed region and the crystalline quality and the surface flat-ness of the Ge film were much improved. From several experimental results, a growth model that e-beam dissociates the surface F atoms of CaF2 and improves the wettability between Ge and CaF2 is proposed.
Surface Stress Tensor Mediation of the Ledge Nucleation/Growth Process with the Surface Reconstruction Process in GaAs
Authors: Choi D. K. , Halicioglu T. , Tiller W. A.
Published: March 2011

A new GaAs semiempirical potential energy function which utilizes both two-body and three-body contributions has been used to evaluate the surface energy and surface stress tensor for the (111) and (001)(As-terminated) surfaces as well as for ledges on the (001) surface. Both surface and ledge reconstruction patterns appear to be driven by stress tensor considerations and a long range ledge-ledge interaction arises via the stress tensor. The impact of this finding on two dimensional cluster formation and nucleation at the growing surface is very substantial.
The Role of Misfit Dislocation During Epitaxial Growth
Authors: Cherns D.
Published: March 2011

The theory of Frank and van der Merwe (FM) in 1949 showed that a minimum energy criterion could explain the pseudomorphic growth of a deposit on a substrate of different lattice spacing and the subsequent relief of strain by misfit dislocations as the deposit thickness increases. Although the “equilibrium” theory is qualitatively correct, account must be taken of actual dislocation sources, which may be complex, and which may be more or less efficient for misfit relief than predicted by the FM model. Moreover, misfit dislocation sources may determine the morphology of the growing film, the interface topology and even the atomic structure of the deposit/substrate interface. These various roles of misfit dislocations are reviewed here with examples from work on metal/metal, semiconductor/semiconductor and metal/semiconductor systems.
Theoretical Analysis of Sweep-Out Experiments in Doped Hydrogenated Amorphous Silicon Films
Authors: Silver Marvin , Branz Howard M. , Adler David
Published: March 2011

We analyze the transient response of i/n/i and i/p/i semiconductor structures in terms of space-charge-limited and emission-limited currents. In this ‘sweep-out’ experiment, an initial space-charge-limited current governed by the i-layer characteristics gives way at later times to an emission-limited current from the doped layer. The emission-limited current response can be used as a new spectroscopy for determining the electronic density of states near the mobility edge of doped semiconductors. We summarize the published experimental sweep-out data and draw conclusions about the density of electronic states of both n-type and p-type hydrogenated amorphous silicon.
Experimental Study of Sweep-Out in N-Type Hydrogenated Amorphous Silicon
Authors: Winborne G. , XU L. , Silver M. , Branz H. M.
Published: March 2011

Experimental results on the temporal response of i/n/i hydrogenated amorphous silicon structures are presented as a function of voltage. The current is initially space charge limited followed by a transition to an emission limited current. The data generally exhibits four subsequent time dependence regimes e.g. :(1) an exponential decay, (2) followed by a t−2 decay, (3) then a t−1 decay and (4) lastly a t(α−1) decay where α<1. The current versus time allows one to derive a density of states. The deduced density of states in the arsenic doped n layers displays a peak at shallow energies followed by an exponential with an energy decay constant of approximately 300°K followed by a flat region and finally followed by a slowly rising density of states. The initial Fermi level is estimated to be within the peak located less than 0.3eV from the mobility edge.
Phosphorus and Boron Doping of a-Si:H Effects of Deposition Temperature
Authors: Pruppers M. J. M. , Maessen K. H. M. , Bezemer J. , Habraken F. H. P. M. , van der Weg W. F.
Published: March 2011

Heavily phosphorus and boron doped hydrogenated amorphous silicon films were deposited in the temperature range 50 to 300 °C. Concentrations of P, B and H, IR spectra and room temperature conductivity have been measured. When the deposition temperature is raised from 50 to 300 °C the concentration of P increases, while the concentration of B decreases. The dark conductivity of both P and B doped films decreases dramatically when the deposition temperature is lowered. We interpret these results on the basis of assumptions concerning the microstructure of the deposited films, and especially the variation of this structure with deposition temperature.
Effect of Low Level Doping of Boron and Phosphorus on the Properties of Amorphous Silicon Films
Authors: Tran N. T. , Epstein K. A. , Grimmer D. P. , Vernstrom G. D.
Published: March 2011

Effect of low level doping of boron and phosphorus on the properties of amorphous silicon films (a-Si:H) was studied. Doping level of both boron and phosphorus was in the range of 1017 atoms/cm3. Apparent improvement in the stability of dark and photoconductivity of a-Si:H films upon low level doping does not result from the elimination of light-induced defects. The stability of the dark and photoconductivity upon doping is an indication of pinning of the Fermi level.
NMR Investigation of the Local Dopant-Hydrogen Configuration in Amorphous Silicon
Authors: Ready S. E. , Boyce J. B.
Published: March 2011

Hydrogen's role in the doping efficiency and long term stability of hydrogenated amorphous silicon is not well understood. The introduction of dopants has been observed to cause an increase in the deposition rate and in the formation of dangling bonds. We have performed NMR spin echo double resonance measurements on heavily doped amorphous silicon samples prepared via plasma deposition in order to ascertain the dopanthydrogen structural units. The resulting dopant concentrations were 2.0 and 0.5 at. % boron and/or phosphorus in compensated and singly doped material respectively. Our results indicate no direct dopant-hydrogen bonding in the compensated or n-type samples. However, in the p-type material the data indicate that approximately 40% of the boron atoms are directly bonded to a hydrogen.
Possible Diffusion of Molecular Hydrogen Along Microvoids in Device-Quality a-Si:H
Authors: Vanderheiden E. J. , Ohlsen W. D. , Taylor P. C.
Published: March 2011

A comparison of 1H nuclear magnetic resonance (NMR) measurements in freshly prepared a-Si:H films on substrates with those removed from the substrates shows that a large fraction of the trapped H2 molecules are released when the films are removed from the substrates. After the films on substrates have been aged for several months, an equal amount of H2 has diffused out of the film. This gradual aging appears-to stabilize after several months. Once aged, H2 can be diffused into the films by immersion in H2 gas. The diffusion time is around 2 weeks at 300 K which is much slower than in vitreous quartz or 7059 glass at the same temperature. Diffusion, which is enhanced during the aging process, could proceed via the remnant columnar structure in the film. This speculation is supported by the inability to detect, using pake-doublet experiments, significant changes in the H2 content and by the recent observation of oxygen diffusion along remnant columnar structure in device quality films.
Hydrogen Diffusion in Undoped a-Si:H
Authors: Chou S. F. , Schwarz R. , Okada Y. , SLOBODIN D. , Wagner S.
Published: March 2011

We measured the diffusion coefficient of H in a-Si:H between 36°C and 690°C via H2-evolution and the pressure rise in a closed ampoule. Our measurement temperatures reached ∼110°C above the highest T reported to date. The diffusion coefficient for unalloyed a-Si:H, DH=1.66×10−3 exp [−1.45 eV/kT] cm2 s−1, agrees with the earlier, lower-T, measurements. Between 250°C and 690°C the H-diffusion mechanism in a-Si:H appears to remain the same, with DH ranging from 10−17 cm2s−1 to 10−10cm 2s−1.
Composition Oxidation and Chemical Etching Properties of a New Amorphous Silicon-Boron Thin Film
Authors: Tong B. Y. , Wong S. K. , Yao J. , Lau W. N. , Du N. , John P. K.
Published: March 2011

When silane, with more than 0.1% of diborane in the gas mixture, are co-pyrolyzed at temperatures below 540°C, an amorphous silicon-boron alloy is formed. The composition of the solid film was determined by SINS and Auger spectroscopy. The amorphous nature of the films was established by X-ray diffraction, laser Raman spectroscopy, and TEM electron diffraction. Electrical and optical properties of this material are reported. Oxidation and chemical etching of this material were also studied.
Quantitative Measurement of Hydrogen Content in a-Si:H by Ar+ Excited Auger.
Authors: Farias M. H. , Hirata G. A. , Cota-Araiza L. , Galvan D. H. , Asomoza R.
Published: March 2011

Abstact

Hydrogenated amorphous silicon (a-Si:H) is well known by its applications for solar energy conversion devices in a large scale. Hydrogen has the capability of terminating the dangling bonds in the amorphous silicon structure and improves the optical properties for effective utilization of the solar spectrum. With this, the quantification of the hydrogen content in a-Si:H is an important task in its characterization.

Auger electron spectroscopy induced by Ar+ ion bombardment (IAES) has been shown to be sensitive to the presence of hydrogen in a-Si:H [1,2]. The Si-L 2VV peak has a distinctively new shape as compared to electron- xcited. Auger were only some slight differences can be observed [3]. contribution to the IAES to that particular peak coming from de-excitations inside and outside the solid can be identified [4].

In this work, IEAS of the Si-L23VV peak were obtained for a-Si:H prepared by glow discharge, grystalline silicon, and crystalline silicon implanted with silicon ions. The relative differences in the spectra are characterized. In particular the changes in the relative amplitudes of the so-called “bulk-like” peak to the “atomic-like” peak as a fuction of hydrogen content are obtained.
Defect Dynamics and the Properties of Amorphous Silicon – a New Perspective
Authors: Pantelides Sokrates T.
Published: March 2011

In the last twenty years, the dominant paramagnetic defect in a-Si (the D center) was believed to be threefold-coordinated Si (dangling bond) which is not mobile. Many observations, however, have not been explained in a satisfactory way. This paper summarizes recent contributions of the present author which offer a novel and systematic description of the properties of a-Si. It is shown that overcoordinazion is an essential concept and that fivefold- and threefold-coordinated Si are the primitive conjugate intrinsic defects. Overcoordination is the key to defect migration and thus to the realization of reactions between intrinsic defects, hydrogen, and impurities. Most properties of a-Si are a consequence of a small set of reactions. The available data favor the identification of the D center as fivefold-coordinated Si (floating bond). Dangling bonds are nonmagnetic and their signature is a photoluminescence peak at ∼0.9 eV.
Comparison of Properties of a-Si1−x Gex:H and a-Si1−x Gex:H:F
Authors: Mackenzie K. D. , Paul W.
Published: March 2011

The structural, electrical and optical properties of amorphous Si-Ge alloys prepared either from mixtures of hydrides or of fluorides will be compared. It will be shown that the majority of many properties studied are essentially the same, the major exceptions being the structure of thin films used for TEM investigation, and the photocurrents developed between contacts in a coplanar configuration. Possible explanations for the result of including fluorine in the preparation plasma will be discussed.
Structural, Optical, and Electrical Properties of Amorphous Hydrogenated Carbon Nitride
Authors: Han He-Xiang , Feldman Bernard J.
Published: March 2011

Amorphous hydrogenated carbon nitride thin films have been grown by plasma decomposition of a feedstock of CH4 and N2. In the films with higher nitrogen concentration, the infrared absorption spectra are dominated by NH2 modes and give strong evidence of a polymeric structure. The optical absorption and photoluminescence spectra show that nitrogen incorporation decreases the bandgap and increases the structural order of these thin films. The undoped material is an insulator with resistivities up to 1015Q cm, but when doped with iron, it becomes a p-type degenerate semiconductor.
Determination of Interface and Surface Structure During the Growth of a-Si:H-Based Heterostructures
Authors: Collins R. W. , Cavese J. M.
Published: March 2011

Ellipsometry measurements of hydrogenated amorphous silicon (a-Si:H)-based heterostructures have been used to characterize surfaces and single interfaces. From spectroscopic studies before and after plasma oxidation of a-Si:H, surface roughness on the atomic scal; (in the plane of the surface) can be distinguished from larger scale (> 100 Å) modulation. We also show how in situ studies of heterostructure preparation can be used to set deposition conditions to minimize near-interface layers owing to thickness dependent film properties. When these are eliminated, the discrepancies in the data from planar layer-bylayer growth models can be attributed to the larger scale surface and interface modulation. Finally, extensive deviations from planar growth for a-Si:H/μc-Si:H have been characterized in terms of specific heterogeneities.
a-Si:H TFT Driven Linear Image Sensor
Authors: Ito H. , Suzuki T. , Nobue M. , Nishihara Y. , Sakai Y. , Ozawa T. , Tomiyama S.
Published: March 2011

A new contact type linear image sensor, which has 8.5 inches in length and 300 dot/inch, has been developed. By using a thin film transistor (TFT) array as a switching device, it requires only one IC chip compared with 20 ICs in conventional sensor.

The new sensor integrates a-Si:H photodiode (PD) array, a-Si:H TFT array, multiplex circuits and an analog multiplexer on a single substrate. The TFT has an inverted staggered structure and amorphous silicon nitride (SiNx) is used as a gate insulator. The PD has a Cr/a-Si:H/ITQ sandwich structure and each PD is completely isolated by photolithography. In the multiplex circuits, a ground line is inserted between each signal line to reduce a capacitive coupling between them.

A new custom LSI has also been developed. It has 64-ch input terminals to detect small signal with amplification and 41-ch output terminals to control the gates of TFT array. The sensor with the new LSI has achieved 2MHz clock frequency operation and proved to be used as a high speed device.
Physics of Novel Amorphous Silicon High-Voltage Transistor
Authors: Hack M. , Tuan H. , Shaw J. , Shur M. , Yap P.
Published: March 2011

In this paper we describe the operation of a novel amorphous silicon high voltage transistor. Its attractive feature is that it can operate at source-drain voltages in excess of 400 volts but its characteristics are controlled by applying only a low bias (0-10 volts) to a gate electrode covering a small portion of the sourcedrain channel near to the source. The portion of the device over this gate electrode operates as a conventional amorphous silicon Field-Effect Transistor which injects electrons into the intrinsic amorphous silicon between this region and the drain electrode. We present experimental data showing the current-voltage characteristics of this new transistor as a function of geometry and demonstrate that the above model realistically describes its operation.
Amorphous Silicon Thin Film Transistor Array Technology: Applications in Printing and Document Scanning
Authors: Weisfield R. L. , Tuan H. C. , Fennell L. , Thompson M. J.
Published: March 2011

Amorphous silicon (a-Si:H) thin-film transistor (TFT) array technology has been developed for new applications in low-cost, high-quality electronic printing. We have fabricated page-wide arrays of low-voltage pass transistors using a-Si:H TFTs for ionographic printing, in which voltages of 0 to 15 volts applied to a line of output electrodes modulate the flow of ions charging a dielectric receptor. High-voltage a-Si:H TFTs have been used in an electrographic printer to modulate high voltages required to initiate air discharges. Combining a-Si:H photodiodes on TFT arrays, we have also designed circuits for document scanning and photosensor amplifiers. TFT performance in relation to these novel printer and sensor applications will be discussed. Issues related to process integration, circuit design, and large-area fabrication technology will be addressed.
Radiative Recombination in a-Si:H-FETs
Authors: Carius R.
Published: March 2011

We have studied the photoluminescence in the space charge region of field effect transistors (FETs) based on a-Si:H in the temperature range T>100K. The radiative recombination rate rises with increasing gate voltage (Vg >0) The increase is more pronounced at the high energy side of the photoluminescence spectrum and the relative changes increase with temperature. These results are compared to those obtained on doped a-Si:H films, where the defect photoluminescence band increases slightly with increasing doping level but the intrinsic band drops off very rapidly. The different influence of the Fermilevel shift in the doped films is explained by the increasing defect concentration which dominates the photoluminescence results. The results in the FETs are attributed solely to the changes in the occupation of the dangling bond states.
Undoped Amorphous Silicon TFTs with n-Channel OR p-Channel Device Operation for the Determination of the Gap States Distribution.
Authors: Schropp Ruud E.I. , Verwey Jan F.
Published: March 2011

Hydrogenated amorphous silicon thin-film transistors (TFTs) were made with either n-channel or p-channel device operation. Layers of undoped amorphous silicon were deposited in the same run and appropriate contact implantation techniques were used. These devices offer the possibility of investigating unipolar conduction of either electrons or holes. In this way ambiguities in the field-effect (FE) analysis of the density of states (DOS) can be avoided. We present the DOS distribution over the entire band gap region of undoped amorphous silicon deduced from a pair of transfer characteristics (one forward and one in reverse). Both types of TFTs are subject to degradation under continuous accumulation conditions. The rate of current decay under hole accumulation appears to be larger than under electron accumulation, as is expected from the width of the respective tail-states distributions. The ON/OFF current ratios obtained for the p- and n-channel devices were 105 and 107, respectively, and both devices showed good pinchoff behaviour. Therefore, these devices are in principle attractive for application in novel amorphous silicon integrated logic circuits (IC).
Progress in Tandem PV Power Modules
Authors: Gay Charles F. , Mitchell K. W.
Published: March 2011

Advances in materials research continue to push forward the performance of thin film photovoltaic technology and bring closer to reality the goal of low cost (less than $2/wattpeak selling price), high efficiency (greater than 15%) modules. A tandem module of thin film silicon:hydrogen alloy (TFS) above copper indium diselenide (CIS) promises to be a most effective approach to this goal. The performance of the high band gap TFS and low band gap CIS has been advanced in part by understanding the nature of the materials and by optimizing the processing techniques. Careful evaluation of various alternatives has led to the selection of suitable materials to serve as the transparent conductive electrodes and the transparent optical coupler between the TFS and CIS. This paper addresses the next steps in capturing efficiency improvements and characterizes probable real world performance.
Determination of the Efficiency Enhancement Due to Scattering from Rough TCO Contact for a-Si:H P-I-N Solar Cells
Authors: Walker C. , Hollingsworth R. E. , Madan A.
Published: March 2011

A-Si:H p-i-n solar cells were deposited on textured transparent conducting oxide coated glass substrates to experimentally determine the enhancement in the short circuit current density. It was found that the optical thickness can be increased by a factor from 3 to 5. These results agree reasonably well with the predictions of optical enhancement theory.
Radiation Resistance of Amorphous Silicon Alloy Photovoltaic Cells
Authors: Woodyard James R. , Hanak J. J.
Published: March 2011

The results of investigations of high energy proton radiation resistance of a-Si alloy thin film photovoltaic cells are reported. Irradiations were carried out with 200 keV and 1.00 MeV protons with fluences ranging between IEII and IEl5 cm-2. Defect generation and passivation mechanisms were studied using the AM1 conversion efficiency and isochronal anneals. It is concluded that the primary defect generation mechanism results from the knock-on of Si and Ge in the intrinsic layer of the cells. The defect passivation proceeds by the complex annealing of Si and Ge defects and not by the simple migration of hydrogen.
Effects of Silicon:Carbon P+ Layer Interfaces on Solar Cells
Authors: Jeffrey F. R. , Vernstrom G. D. , Weber M. F. , Gilbert J. R.
Published: March 2011

Results are presented showing the effects on amorphous silicon (a-Si) photovoltaic performance of the interfaces associated with a silicon carbide (a-Si:C) p+ layer. Carbon grading into the intrinsic layer from the p+ layer increases open circuit voltage (Voc) from O.7V to 0.88V. This effect is very similar to the boron profile effect reported earlier and supports the contention that Voc is being limited by an electron current at the p-i interface. The interface between the p+ a-Si:C layer and the transparent conductive oxide (TCO) is shown to be a potential source of high series resistance, with an abrupt interface showing the most serious problem. The effect is explained by electron injection from the TCO into the p+ layer being inhibited as a result of band mismatch.
Effects of Carbon Grading at the p/i Interface on the Open Circuit Voltage of p-i-n and n-i-p Amophous Silicon Solar Cells
Authors: Tran N. T. , Jeffrey F. R. , Olsen D. J.
Published: March 2011

Carbon grading in the buffer layer at the p/i interface increases the open circuit voltage of both p-i-n and n-i-p amorphous silicon solar cells. We propose that carbon grading enlarges the electric field and reduces the electron tunneling at the p/i interface.
Stability in Amorphous Silicon
Authors: Smith Z E. , Wagner S.
Published: March 2011

The experimental phenomena associated with light-induced degradation and thermal recovery of hydrogenated amorphous silicon (a-Si:H) films are reviewed, with special emphasis on the limitations of each experimental technique. When several techniques are used in concert, a fuller picture emerges. Recent experiments suggest different positions in the band-gap of the paramagnetic-associated defect states (the dangling bonds) for doped and undopedfilms; this information can be combined with conductivity, sub-bandgap optical absorption and electron spin resonance data to yield a model for the density of gap states (DOS) in a- Si:H, including how the DOS changes upon illumination and annealing.
Degradation Behavior of a-Si:H Pin Solar Cells With Intentionally O-Contaminated i-Layers
Authors: Krühler W. , Gonzel E.
Published: March 2011

The discussion about the influence of oxygen on the degradation be-havior of a-Si:H pin solar cells is now as before controversial. Therefore, we prepared a-Si:H pin solar cells having different amounts of O contami-nation in the i-layer by adding O2 gas to the silane gas during the glow-discharge deposition of the i-layer. The admixture of O2 gas was in the 0 ppm to 1000 ppm range resulting in an O concentration in the i-layer of 1.10190/cm3 to 3.1020 0/cm3 determined by SIMS measurements. Then we inves-tigated the long-term degradation behavior of these cells, exposing them for about 270 h to white light of 100 mW/cm2 intensity. During the first 20 h the cell efficiencies dropped relatively fast to about 80 % of the initial value and then more slowly to about 60 % after 270 h. The degradation of the cells may be slightly different during the first 20 h, but this has nothing to do with the O concentration. The normalized efficiency values meet all at the 60 % level after the long-term light exposure for 270 h. We there-fore conclude that the degradation behavior of pin a-Si:H solar cells after long-term exposure is not dependent on the O concentration in the range investigated. At O concentrations higher than about 5.1020 cm−3, the den-sity of states increases rapidly and the electrical properties of the solar cells deteriorate, making it difficult to clarify the true influence of oxygen on the degradation behavior.
Amorphous Silicon Alloy Punch-Through Diodes for Display Applications
Authors: den Boer W. , Guha S. , Kawasaki A. , Yaniv Z.
Published: March 2011

The current-voltage characteristics of amorphous silicon alloy n-π-n and p-i-p diodes have been investigated. These diodes show highly nonlinear conduction characteristics which are attributed to the punch-through effect. The dependence of the non-linearity on the thickness and doping of the intermediate active layer support this interpretation. An experimental 108 × 108 pixel liquid crystal display was built with punch-through diodes as pixel switches.
Transient Photoresponse of Amorphous Silicon p-i-n Diodes
Authors: Deimel P. P. , Moller G. , Baumeister K.
Published: March 2011

Amorphous silicon p-i-n diodes were illuminated with LED-generated trains of rectangular light pulses under various duty-cycle conditions. Our results indicate that such diodes are able to handle modulation rates in excess of 10MHz over a wide range of operating temperatures. Measurements of the dark I-V characteristics show that the shot-noise in properly designed junctions can be reduced to a level comparable to c-Si photodiodes.
Quantum Effect Device Using Disordered Surface in Doped Si Near the Metal-Nonmetal Transition
Authors: Ochiai Y. , Yoshizaki R. , Matsuura E.
Published: March 2011

We have observed several steps in the I-V characteristics of nonmetallic Sb doped Si near the metal-nonmetal transition. The steps appear at equal intervals in the bias voltage of the low temperature I-V curve and the intervals in the voltage are independent on magnetic field. Such strongly nonlinear conduction can be explained by neither the Joshphson junction effect nor the Stark ladder effect. We have compared it with tunneling models in order to study a new application to a current or a voltage standard using quantum effect transport.
Charge Carrier Relaxation after Subbandgap Excitation in Doped a-Si:H
Authors: Werner A. , Kunst M.
Published: March 2011

Charge carrier dynamics in doped and undoped a-Si:H after subbandgap excitation at 1064 nm was followed by transient photoconductivity experiments. The kind of optical transitions induced by 1064 nm light is strongly dependent on the position of the Fermi-level. This allows the seperation of excess electron and excess hole kinetics as in n-doped samples mainly mobile electrons and in moderately p-doped samples mainly free holes are generated by 1064 nm light. From comparison of the photoconductivity after 532 nm and 1064 nm excitation it is inferred that the rate controlling step for the electron decay is the availability of free holes.
High Deposition Rate, Thick a-Si Films for Electrophotographic Applications
Authors: Cueto J. Del , Von Roedern B. , Madan A.
Published: March 2011

The attraction for amorphous Silicon based alloys (a-Si) stems in large part from its ease in its depositing uniformly over large areas in a cost effective manner. We here at Glasstech Solar, Inc. (GSI) wish to report on the development of a-Si films for electrophotographic applications. For this specific purpose we have developed thick films (˜30–40 μm) of intrinsic a-Si deposited on TCO at deposition rates of up to 14 Å/S We tested the material for its photoconductivity and breakdown voltage, and its suitability for the application at hand with one measured parameter, the 400 volt switching time, TΔ400. Essentially the goal consisted of developing a high voltage photoconductive switch, that would swing 400 volts at the terminals in a few μsec.
Low-Carbon Boron Carbidestproduced by CVD
Authors: Campbell A. N. , Mullendore A. W. , Tallant D. R. , Wood C.
Published: March 2011

Boron carbides with low C contents were produced from BC13 and CCl4 by chemical vapor deposition at temperatures of 1020–1500°C. The deposits were found to be between B13C2 and B13 C (8.3 to 13.3 at %C) in composition by means of Auger electron spectroscopy. Raman spectroscopy demonstrates that the specimens contain very little free carbon. Further, disordering of C in the chains and icosahedra of the rhombohedral boron carbide structure for C contents of less than 20 at.% is indicated by the Raman results. Singlephase rhombohedral boron carbides with C contents as low as 12.5 at.% (≈B7C) have been produced. The most B-rich specimens, containing 8.3 at.% (B11 C) or less C, were phase separated. At least one of the phases in the phase separated specimens is tetragonal. The electrical conductivity and Hall mobility of the B11C specimen are reported.
A Comparison of Calculated and Experimental Hrtem Images for Twinned Boron Carbide
Authors: Miller Mark L. , Mackinnon Ian D. R.
Published: March 2011

High resolution TEM images of boron carbide (B13C2) have been recorded and compared with images calculated using the multislice method as implemented by M. A. O'Keefe in the SHRLI programs. Images calculated for the [010] zone, using machine parameters for the JEOL 2000FX AEM operating at 200 keV, indicate that for the structure model of Will et al., the optimum defocus image can be interpreted such that white spots correspond to B12 icosahedra for thin specimens and to low density channels through the structure adjacent to the direct inter-icosahedral bonds for specimens of intermediate thickness (-40 > t > -100 nm). With this information, and from the symmetry observed in the TEM images, it is likely that the (101) twin plane passes through the center of icosahedron located at the origin. This model was tested using the method of periodic continuation. Resulting images compare favorably with experimental images, thus supporting the structural model. The introduction of a (101) twin plane through the origin creates distortions to the icosahedral linkages as well as to the intra-icosahedral bonding. This increases the inequivalence of adjacent icosahedral sites along the twin plane, and thereby increases the likelihood of bipolaron hopping.
Heteroepitaxial Growth of Antiphase-Boundary Free Cubic Sic(100) Single Crystals on Si(100)
Authors: Shibahara Kentaro , Nishino Shigehiro , Matsunami Hiroyuki
Published: March 2011

Cubic SiC was grown on Si substrates by a combination of carbonization and consecutive chemical vapor deposition. Grown layers on the (100) and (111) substrates were single crystalline cubic SiC. Those on the (110) and (211) were poly-crystalline. A model for the mechanism of carbonization was proposed as a result of these observations. Based on this model, the origin of antiphase boundaries were made clear, and antiphase boundaries were expected to be eliminated by controlling atomic steps of the Si surface. In fact, antiphase boundaries were eliminated by introduction of off orientation of Si(lO0) substrates. The relationship between generation of antiphase boundaries and off orientation of the surface was investigated by using spherically polished Si(100) substrates. Off orientation towards (011) was found to be effective for elimination of antiphase boundaries. Off orientation except for towards (011) resulted in generation of antiphase boundaries.
Optical, Vibrational and Surface Properties of SiC
Authors: Choyke W. J.
Published: March 2011

A short historical introduction concentrates on key experimental and theoretical developments prior to the mid-seventies which form the basis of our present understanding of the semiconducting and optical properties of the polytypes of SiC. Selected research of the last decade is reviewed. Finally, we discuss our on-going surface and defect studies in both epitaxial single crystal films of 3C SiC and other hexagonal SiC polytypes.
Lattice Vibrations and Defect-Induced Vibrational Properties in Cubic SiC
Authors: Lin-Chung P. J.
Published: March 2011

A theoretical study of both the bulk phonon dispersion relations in cubic SiC and the vibrational properties induced by native defects is presented. The Keating Hamiltonian is used for the quadratic potential energy of the system, and the supercell approach is employed to treat the defect problem. The defect complexes considered are antisite defects, divacancy defects, and three different types of carbon di-interstitial defects.