bluuebunny/crossref_metadata_2025 huggingface dataset:
Amorphous Silicon Thin Film Transistors With High Electron Field Effect Mobility
Authors: Andújar J.L. , Bertrán E. , Canillas A. , Campmany J. , Cifre J.
Published: March 2011

Normal staggered hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFT) were prepared by rf plasma deposition through a three-step process. The TFTs were constituted by an a-SiN/a-Si:H structure grown on NiCr source-drain electrodes evaporated on glass substrates. The intrinsic a-Si:H active layer (Fermi level at EC-EF = 0.7 eV) was deposited from pure SiH4 rf plasma, and the insulator layer of a-SiN was grown using a high rf power plasma (200 mW/cm2) of SiH4-N2 mixture with a SiH4 fraction of 0.5 %. Ellipsometric measurements showed that a very transparent a-SiN film was grown with an abrupt interface insulator/a-Si:H. TFTs with 0.2 μm thick a-Si:H layer and 10 μm channel length have on-off current ratios of 5 104, electron field effect mobility of 1.5 cm2/V-s (dielectric constant εri ≈ 7.9), and threshold voltage around 5 V. The results are discussed in terms of low hydrogen content and low porosity of these a-SiN films prepared from silane-nitrogen.
Studies of the Stability of Amorphous Silicon Thin Film Transistors
Authors: Globus T. , Shur M. , Hack M.
Published: March 2011

Our experimental studies confirm that changes in a-Si Thin Film Transistors (TFTs) under voltage stress occur in the device channel and not in the contacts. We demonstrate that stressing an a-Si TFT not only shifts the device threshold voltage but can also changes the slope of the semilog subthreshold current dependence on the gate voltage. In addition, stressing can decrease the minimum leakage current. The creation of new localized states in the amorphous silicon under voltage stress qualitatively explains all these effects, while carrier tunneling and trapping in the gate insulator layer cannot by itself explain our data. At large negative gate voltages, the leakage current increases due to the holes injected into the channel. This hole current is also affected by voltage stress as can be predicted by the state creation mechanism.
Electron Transport Mechanisms in Nickel Schottky Barrier Contacts to Hydrogenated Amorphous Silicon
Authors: Heller D.E. , Gunes M. , Rubinelli F. , Dawson R.M. , Nag S. , Fonash S.J. , Wronski C.R.
Published: March 2011

Dark J-V characteristics of Ni Schottky diodes on a-Si:H films of various thicknesses were measured as a function of device temperature. Room-temperature photoconductivity and sub-bandgap absorption v. wavelength measurements of the intrinsic layers were also performed. Detailed numerical modelling was employed to determine the nature, density and energy distribution of sub- bandgap states. Best-fit modelling of photoconductivity, sub-bandgap absorption and dark JR-VR indicates that Nc=Nv=2.5×1020 cm-3, vR=2×106 cm/s, μn=33 cm2/V-s and μp=0.15 cm2/V-s for these films. It is found that a joint thermionic emission-drift/diffusion mechanism, as envisaged by Crowell and Sze, appears to be the most accurate picture of electron transport in Schottky diodes on intrinsic a-Si:H films.
High Performance Input Scanning Arrays Using Amorphous Silicon Photodiodesand Thin-Film Transistors
Authors: Weisfield Richard L.
Published: March 2011

The use of large area hydrogenated amorphous silicon (a-Si:H) technology has enabled compact, full page width scanners to be built inexpensively, and is now the dominant method for fabricating low-end facsimile machines. This technology has now been extended to scanners with considerably higher levels of performance. High speed, high resolution, full-width input scanning arrays have been developed using a-Si:H photodiodes and thin-film transistors (TFTs). A 12” long array has been designed to scan 3 colors at 400 spots per inch, and operates at speeds of up to 40 pages per minute, achieving a signal/noise ratio of 400:1 at intensities of 30 μWcm-2.

The color scan array is made using 3 rows of a-Si:H photodiodes, one per color, addressed by TFTs which share sets of common data lines. The data lines are arranged in a low capacitance non-crossing configuration which allows the scanner to achieve high responsivity with low crosstalk. The data lines are connected to a number of readout chips, each of which amplifies and multiplexes the photosignals onto a single video output line. Optoelectronic test results and images obtained from this device will be presented. These results indicate that high quality color images can be obtained from a-Si:H scanners, and that the present scanner is more limited by the speed of the readout chips than by the a-Si: H devices themselves.
A High Speed Contact-Type Image Sensor using Amorphous Silicon Alloy Pin Diodes
Authors: Kitamura K. , Mimura H. , Tsukada K. , Nakayama T. , Yamaguchi M. , Tawada Y.
Published: March 2011

A new A4-size contact-type image sensor with 8 elements per millimeter (1,728 elements) was developed by using amorphous silicon alloy pin photodiodes as the light receiving elements. The matrix switching method is employed for signal reading. This method can read the signals from all of the 1,728 photodiodes using a 54 (54-channel input) x 32 (32.channel output) matrix switching scheme. It is advantageous in that the required input and output external circuits can be simplified. To prevent signal crosstalk between the diodes in the matrix, amorphous silicon alloy pin diodes, which are made in the same process as the photodiodes for maintaining a low cost, are connected in series to each photodiode in reverse polarity as blocking diodes.

To achieve superior signal-to-noise ratio and response at the same time, amorphous silicon alloy pin diodes are optimized to satisfy both a high photo-to-dark ratio and a high rectification ratio. The image sensor can operate at up to 2 MHz signal reading clock, maintaining a signal-to-noise ratio of over 24 dB under 0. 1–1x sec exposure.
The Role of the a-Si:H Layer in Metal / a-Si:H / Metal Memory Structures
Authors: Osborne I.S. , Hajto J. , Rose M.J. , Snell A.J. , Leœmber P.G. , Owen A.E.
Published: March 2011

In this paper we report the role of the a-Si:H on the electrical behaviour of Metal/ a-Si:H / Metal memory devices. We have investigated layers deposited at 250°C by the glow discharge method with various doping concentrations, from undoped up to 104vppm of either diborane or phosphine in silane. We have found that the a-Si:H layer affects the initial forming process and the subsequent OFF state resistance. The hydrogen contents of the films have been measured and are found to correlate, for the p-type samples, with the forming voltage.
Engineering of PECVD Systems for Macroelectronic Applications
Authors: Martins R. , Ferreira I. , Carvalho C. N. , Maçarico A. , Guimarães L.
Published: March 2011

The materials quality (uniformity and homogeneity) produced by PECVD technique depends on the plasma behaviour. Problems related to the gas dissociation ratio and powder formation are responsible for materials costs and the appearance of voids. In this paper, we present data concerning the role of the plasma and reactor design, on the deposition conditions, suggesting ways to improve them for large area device (macroelectronics) applications.
Role of Hydrogen Microstructure in Amorphous Silicon
Authors: Zafar Sufi , Schiff E. A.
Published: March 2011

A model for correlating the observed properties of hydrogenated amorphous silicon (a-Si:H) with the underlying hydrogen microstructure is reviewed. The model provides a unified description of defect equilibration, hydrogen evolution, rehydrogenation and hydrogen diffusion measurements.
Near-Surface Density of States in a-Si:H By Photoelectron Yield Spectroscopies.
Authors: Wang S.L. , Patriarca F. , Evangelisti F.
Published: March 2011

The density of occupied states was investigated in a number of intrinsic a-Si:H samples by means of photoelectron yield spectroscopy operated in the constant final state mode. Valence band edge, exponential tail and deep state distribution were analyzed and compared with the bulk density of states as determined by spectral dependence of photoconductivity. By evaporating Cs atoms on the clean surface the Fermi level position was progressively shifted toward the conduction band and the evolution of localized states was investigated. On the assumption that these near-surface states are paramagnetic centers with positive correlation energy, the results agree with the prediction of the “defect pool” model.
Detection of Atomic Order in Quasiamorphous Materials
Authors: Timsit Roland S. , Waddington W.G. , Gallerneault C.
Published: March 2011

The cross-correlation of intensity fields of different regions of an HREM micrograph can identify regions of structural order in an apparendy random matrix. This paper presents results of cross-correlations on computer-simulated HREM images of a diin Si crystallite located on a relatively thick slab of amorphous Si. These simulations confirm the efficacy of cross-correlations in retrieving atomic order from die image of an apparently amorphous material and thus confirm the interpretation of experimental results obtained earlier.
The Atomistic and Quantum Mechanical Origins of Light-Induced Defects in a-Si
Authors: Fedders P. A. , Fu Y. , Drabold D. A.
Published: March 2011

We present an atomistic and quantum mechanical model of light-induced defects (the Staebler-Wronski effect). The model is based in part on our observations of molecular dynamics simulations with an ab initio code and requires a change in the charge of a well localized state in the gap, such as a dangling bond, to nucleate the new defects. Besides the new defects, a substantial rearrangement of the supercell is observed.
Deuteron Magnetic Resonance Studies of Structure and Photo-Induced Metastable Rearrangements in Deuterated Amorphous Si, Ge and SiGe Films
Authors: Norberg R. E. , Bodart J. , Corey R. , Fedders P. A. , Paul W. , Turner W. A. , Pang D. , Wetsel A.
Published: March 2011

The spin dynamics of deuteron magnetic resonance (DMR) components have been studied in deuterated plasma-deposited thin films of a-Si, Ge and SiGe. Transient recoveries of perturbed deuteron magnetization components evolve via magnetization transport in the limit of large inhomogeneity. The evolution is well-described by an error function expression whose parameters correlate with the film photovoltaic quality as measured by the photoresponse ημτ and the photosensitivity, ΔI/Id. These relaxation results are correlated with our continuing DMR measurements of reversible metastable photo-induced rearrangements in high-quality a-Si:D,H films. These studies indicate that about 0.5% of the hydrogens interact with a light-induced defect.
Charge-Defect Thermodynamic Equilibrium and Metastable Defects in Amorphous Silicon
Authors: Fortmann C.M. , Cohen J. D.
Published: March 2011

The thermodynamic equilibrium framework first presented at the Spring ′91 MRS meeting is refined and applied. The effect of temperature on band gap is added, resulting in a larger estimate of the loss in entropy associated with dangling bond formation. The magnitude of the entropy loss is consistent with a structural rearrangement. At the temperatures of interest, dangling bond defect formation is exothermic with negative entropy and free energy changes. The thermodynamic framework was used to address some practical issues including the estimation of the saturated dangling bond density resulting from low temperature light soaking and the electronic energy levels of the various dangling bond charge states.
Observation of Metastability in Amorphous Silicon Containing 0.1 at.% Hydrogen
Authors: Branz Howard M. , Iwaniczko Eugene
Published: March 2011

We observe reversible quenched-in metastability in the dark conductivity of extremely low-H-content amorphous silicon (a-Si). The sample is sputtered, P-implanted a-Si containing 0.1 at.% of H. Except for the high value of its equilibration temperature (T*), 355° ± 20°C, this metastability is similar to that observed in doped hydrogenated a-Si (a-Si:H). The ∼10 at.% H present in a-Si:H is not essential for a-Si metastability. After hydrogenation with about 10 at.% of H, T* falls to 175° ± 10°C. We propose that higher H content reduces T* by increasing Si network flexibility.
Annealing of Metastable Recombination Centers in Hydrogenated Amorphous Silicon
Authors: Yoon Jong-Hwan , Lee Yoon-Zik
Published: March 2011

We report results on the annealing behaviors of light- and deposition-induced metastable recombination centers, as measured by steady-state photoconductivity, in undoped hydrogenated amorphous silicon. The relaxation time inferred from the stretched-exponential time law reveals a thermally activated behavior, and the activation energies are nearly identical in both (Ea=1.1eV). This value is much less than that of the light-induced darkconductivity relaxation (Ea=1.7eV) measured simultaneously with photoconductivity. While in the deposition-induced case both activation energies of dark- and photoconductivity relaxation time are identical. These results support that there is more than one kind of defect created by light exposure, and at least, as considering activation energies for annealing defects, the light-induced recombination center differ from other metastable defects.
Relation Between Defect Density and Conductivity Changes with Light-Soaking and Annealing in a-Si:H
Authors: Shimizu T. , Iwami M. , Okagawa T. , Morimoto A. , Kumeda M.
Published: March 2011

It is found in a-Si:H and N-doped a-Si:H that the ESR spin density Ns increases and saturates with light-soaking slower than the dark- and photoconductivities (αd and αp) do. In the recovery process by annealing, the change in Nsalso occurs slower than αd and αp. From the measurement of the activation energy for αd the change in αd is found to originate mainly from the movement of the Fermi level Ef. In order to elucidate the origin of different behaviors between Ns and αd or αp, the light-induced ESR and the constant photocurrent method measurements have been carried out.
Effect of Photodegradation on Transient and Steady State Forward Bias Characteristics of A a-Si:H P-I-N Diode
Authors: Amokrane R. , Vanderhaghen R. , Silver M.
Published: March 2011

We have measured dark and photocurrent under double injection. The injection gain gives information on capture rate, dos shape and recombination mechanism. Before degradation, the recombination is bimolecular, and it becomes monomolecular after degradation. We observe effects of interface change as well as thickness inhomogeneity.
Multi-Cycling of Staebler-Wronski Effect
Authors: Guangling Kong , Guosheng Sun
Published: March 2011

The effect of illumination/annealing multi-cycling treatment on the dark and photo conductivities of undoped a-Si:H film has been investigated. With the increase of cycling number the conductivities in annealed state and light-soaked state are drawn close to each other, which provides a unique irreversible effect.
The Farthest Reaches of a-Si,Ge:H,F Parameter Space… Where no One Has Gone Before
Authors: Morin P.A. , Wang N.W. , Wagner S.
Published: March 2011

We report the deposition parameters for optimized a-Si,Ge:H,F alloys in the range of optical (Taue) gap of 1.22eV to 1.65eV. These deposition parameters were optimized using the photosensitivity and initial defect density as figures of merit. We observe two distinct regimes of film growth rate, dependent on the choice of source gases. Growth from fluoride source gases results in a growth rate of less than 0.6 Ås--1. Growth from a mixture of fluorides and silane gives a range of growth rates from 2 Ås-l to 5.5Ås1. Alloys in both regimes display the low defect densities and the high photosensitivities required for devices.
Time-of-Flight Measurement on a-Ge:H and a-SiGe:H Alloys
Authors: Liu E.Z. , Pang D. , Paul W. , Chen J.H.
Published: March 2011

We report TOF measurements on high quality intrinsic a-Ge:H and a-SiGe:H films of E04=1–4.eV in temperature ranges of 200 to 280 and 230 to 300K, respectively. Complete charge collection is achieved in all measurements. For a-Ge:H films, the (μτ)e product obtained from the Hecht plot is (5±3)×10-8 cm2/V above 240K and decreases at lower temperatures. The electron transit signal is dispersive at all temperatures. The a obtained from ttV-1/αis 0.23 at 200K and approaches 1.0 at 260K. The electron drift mobility μd shows activated behavior, with an energy of 0.37±0.05eV, and has an extrapolated room temperature value of 0.03 cm2/Vs. Compared to a-Ge:H, μd of a-SiGe:H alloy samples is lower by one order of magnitude but has a similar activation energy. These results are consistent with a band tail hopping transport model.
Amorphous Ge/Si Multilayer Structures as Models for Optical Memories
Authors: Järrendahl K. , Jansson R. , Sundgren J.-E. , Arwin H.
Published: March 2011

Prototype memory cells of a proposed three-bit memory device, whose optical read-out is based on the ellipsometric principle, nas been fabricated by deposition of 5 nm layers of amorphous silicon and amorphous germanium on crystalline silicon substrates. The differences in the ellipsometric parameters of memory cells corresponding to different logical states were much larger than the instrumental resolution. The possibility to optimize with respect to photon energy and angle of incidence is demonstrated.
Non-Equilibrium Carrier Dynamics in a-Si:H/a-SiC:H Multilayers
Authors: Petrauskas M. , Kolenda J. , Galeckas A. , Schwarz R. , Wang F. , Muschik T. , Fischer T. , Weinert H.
Published: March 2011

For a series of a-Si:H/a-SiC:H quantum well structures and superlattices the diffusion coefficient for the lateral ambipolar motion of optically excited free carriers was measured using the transient grating technique. A significant dependence of the diffusion coefficient on the well layer thickness was found. With decreasing quantum well thickness the lateral mobility decreases. These observations may be explained assuming that scattering due to interface roughness is the dominant scattering process.
Metastability of Light-Induced Defects in Very Low Density of Gap States α- Si1-αCα:H Alloys
Authors: Sebastiani M. , Fiorini P. , Alvarez F. , Pozzilli F. , Pulci O. , Evangelisti F.
Published: March 2011

We have prepared silicon carbon alloys with Tauc's gap of 2.1 eV, low defect density (≃ 3–1015cm-3) and large photoconductivity (αPhoto/αdark=105 in AM 1.5 illumination). On these samples light soaking induces a large number of metastable gap defects which are annealed out at 250 °C. We have studied the kinetics of defect formation varying the duration of light exposure and the light intensity. The experimental data are consistent with a bond breaking model (conversion of tail weak bonds into dangling bonds), provided that the actual occupation of tail states is taken into account.
Improved Properties of a-SiC:H Alloys with Reduced Density of CH3 Radicals
Authors: Camargo S. S. , de Oliveira M. L. , Pasa A. A. , Gatts C.
Published: March 2011

In this paper we report on the properties of a-SiC:H alloys with reduced density of CH3 radicals obtained by hydrogen dilution of gases. A reduced density of voids, hydrogen content and density of carbon bonded hydrogen atoms, were obtained; while carbon content and density of Si-H bonds are not affected much. A reduction of the optical gap and an increase of the refractive index were observed and related to the reduced densities of CH3 groups and voids. Dark- and photo- conductivity measurements showed that a performance comparable to the best undiluted films may be easily achieved, associated with a shift of the dark Fermi level towards the conduction band.
A Thermally Stable Silicon Rich Amorphous Silicon Nitride Alloy for Electronic Device Applications
Authors: Bernstein Joseph B. , Gleason Edward F. , Wyatt Peter W.
Published: March 2011

We have developed an alloy of silicon rich amorphous silicon nitride as a linkable interlevel metal dielectric. This material is thermally stable through a heat treatment of 425°C for 30 minutes. The hydrogen content remains at approximately 21 at.%, even after this heat treatment. The breakdown potential is 1.9 × 106 V/cm at which point a metallic filament link forms between the metal contacts. The index of refraction is 2.43 and the HF permittivity is 9 Co- One important property is its ability to store polarized charge like an electret. This feature could allow it to be used in memory applications like MNOS. The alloy is also photoconductive with a response time of less than 5 μs, allowing it to be used as part of an optically sensitive circuit element.
Structural Properties of High Electronic Quality a-Si1-xCx:H by Infrared Spectroscopy
Authors: Eberhardt K. , Lotter E. , Heintze M. , Mohring H.-D. , Bauer G.H.
Published: March 2011

Infrared (ir) spectroscopy is used to investigate the structural properties of a-SiC:H in a wide compositional range and as a function of film thickness. Hydrogen content NH increases considerably with increasing carbon fraction. For low carbon alloys this is mainly due to an increase of hydrogen bonded to silicon, incorporated in a mono- or dihydride form. Above Eg=2.3eV the proportion of hydrogen incorporated in C-H bonds increases considerably. Oxidation of high C alloys is observed. Converting experimental transmission exactly into absorption data yields thickness independent NH values. It is shown that the previously reported discrepancy between the hydrogen content calculated from ir and nuclear reaction techniques is an artifact of the ir analysis.
The Impact of a Long-Ranged Random Potential on the Transport Properties of Amorphous Semiconductors
Authors: Overhof Harald
Published: March 2011

We discuss electrostatic random potentials in doped and in compensated amorphous semiconductors. These potentials are caused by the residual inhomogeneity of a random distribution of charged dopants and their compensating charges. Random potentials are also present in undoped material with negative-U defects. A high density of positive-U defects can also give rise to a random potential in undoped material.

We demonstrate with the help of detailed model calculations the effect of such random electrostatic potentials on the transport properties. For transport in extended states the random potential does not give rise to a mere shift of the mobility edge. Instead several new features are observed: the activation energy of the resulting Ohmie dc conductivity is virtually unaffected by the random potential in contrast to the activation energy of the thermoelectric power and that of the Hall effect, respectively. The Ohmie dc current changes at high fields into a superlinear current. The random potential contributes to the dispersion of the transients in time-of-flight experiments but leaves the field dependence of the TOF mobility unaltered. Comparing our results with experimental data we discuss under which circumstances the effect of random potentials can be identified.
The Study on Microstructure by NMR, FTIR, Raman, Conductivity and Optical Bandgap in Hydrogenated Amorphous Silicon Prepared by Novel Fabrication Methods
Authors: Hsu K. C. , Chang H. , Hong C. S. , Hwang H. L.
Published: March 2011

It was found that hydrogen dilution in the SiH4/H2 mixture tend to show a sharp line-shape in the NMR spectra as the substrate temperature is higher than 300 °C. The hydrogen-atom-treatment method also produces the same effect at a lower substrate temperature about 250°C. The Raman scattering spectra show that the hydrogen-atom-treatment creates the microcrystalline structure at a temperature higher than 250°C while hydrogen dilution produces mixed phases containing amorphous phase and a small quantity of micro-crystalline phase. Together with the optical bandgap narrowing, the increase of the dark conductivity and the reduction of photo-to-dark conductivity ratio, these samples indicate that with more hydrogen incorporation during deposition and plasma hydrogen treatment, these films possess a much compact structure, and the degree of crystallinity of hydrogenated silicon film was found to be systematically changed.
Simulation of the Steady-State Photocarrier Grating Method Applied to Amorphous Materials
Authors: Abel C.-D. , Bauer G. H.
Published: March 2011

General features of the steady-state photocarrier grating technique applied to amorphous semiconductors are investigated by complete numerical simulation. The results are interpreted with an analytical model which delivers a closed-form expression for β(A,E) assuming dominance of one carrier type. The variation of the electric field E instead of the grating period A is suggested as an easier and more accurate tool for the experimental technique.
Deposition Temperature and Optoelectronic Properties of a-Si:H Films
Authors: Wiatkowski C. S. , Hirsch W. , Kunst O.
Published: March 2011

In the present work the change of the opto-electronic properties of intrinsic a-Si:H films as a function of their deposition temperature is investigated by transient photoconductivity measurements with the contactless Time Resolved Microwave Conductivity (TRMC) technique. As well in-situ as ex-situ TRMC-measurements will be presented. It is concluded that the electron drift mobility for a-Si:H films deposited in the temperature range between 200° C and 300° C does not depend on the deposition temperature. For temperatures below 200° C the electron drift mobility decreases with decreasing deposition temperature. Annealing of opto-electronic properties of intrinsic a-Si:H films deposited at lower temperatures is observed.
Delayed Field Transient Photocurrent Measurements in a-Si:H
Authors: Antoniadis Homer , Schiff E. A.
Published: March 2011

We have measured the transient photocurrent in “time-of-flight” structures of a-Si:H using bias voltages applied following photocarrier generation by a laser flash. The delayed field technique appears promising both as a probe of the deep level distribution and also of photocarrier thermalization. We describe a simplified theory for the delayed field transients including the effects of the delay time and the magnitude of the applied voltage. The theory accounts for the measurements adequately.
Optical Absorption Spectra Under DC Light Bias in Undoped a-Si:H
Authors: Liu J. Z. , Conde J. P. , Lewen G. , Roca i Cabarrocas P.
Published: March 2011

Under a dc light bias, the ac constant photocurrent method (CPM) yields an anomalous subgap optical absorption over that without the bias. When the intensity of the bias is high, an absorption band appears. However, absorption measured by ac photothermal deflection spectroscopy (PDS) is much less affected by the bias. A simple model qualitatively explains the effect on the PDS spectra and suggests that the anomalous CPM absorption is an apparent one which represents a variation of the recombination lifetime.
A More Than 18% Efficiency Hit Structure a-Si/c-Si Solar Cell Using Artificially Constructed Junction (ACJ)
Authors: Kuwano Y. , Nakano S. , Tanaka M. , Takahama T. , Matsuyama T. , Isomura M. , Nakamura N. , Haku H. , Nishikuni M. , Nishiwaki H. , Tsuda S.
Published: March 2011

We have obtained the world's highest total area conversion efficiency of 11.1% for a 100cm2 integrated-type single-junction a-Si solar cell submodule. This was achieved by the development of various advanced technologies, such as a new ultra-thin i/n interface layer and a new laser patterning method using an ablation phenomenon.

To acheive further improvement in the conversion efficiency of a-Si based solar cells, we focus on polycrystalline silicon (poly-Si) thin-film for a-Si/poly-Si tandem solar cells. As far as material technology is concerned, we have used a new solid phase crystallization (SPC) method from amorphous silicon (a-Si) films deposited by plasma-CVD. The maximum mobility of 623 cm2/V.s was achieved on textured substrates at a carrier concentration of 3.0 × 1015 cm-3. This film has been applied to the active layer of poly-Si solar cells on metal substrates and a conversion efficiency of 6.2% has been obtained with poly-Si film of 12 μm thickness made by SPC at 600°C.

In the field of device technology, we have developed new artificially constructed junction (ACJ) solar cells using p-type a-Si/i-type a-Si/n-type crystalline silicon (c-Si). We call this a HIT (Heterojunction with Intrinsic Ihin-layer) structure, and we have achieved a conversion efficiency of 18.1% for this type of solar cells. This is the highest reported value for a cell with a junction fabricated at low temperature (∼ 120°C).
Experimental Characterization and Optical Modelling of Absorption and Light Trapping in a-Si:H Solar Cells on Textured Tco
Authors: Leblanc François , Perrin Jérâme , Cornil Elizabeth. , Schmitt Jacques
Published: March 2011

The quantitative description of the optical phenomena occuring in a-Si:H solar cells on textured substrates is a key issue to maximize the photovoltaic conversion efficiency. A semi-empirical numerical model is proposed taking into account the scattering induced by roughness at each interface of a multilayer structure. The scattered reflected and transmitted components are added to a classical matrix treatment of specular components. For each scattering angle, a new source beam is tracked in the subsequent layers. Light polarization and interference effects are properly taken into account and the energy deposited in each layer is derived. The model is tested on various structures and on a-Si:H p-i-n solar cells by angular-resolved reflectance and transmittance measurements and photothermal deflection spectroscopy.
Film and Solar Cell Properties of a-SiC:H Alloys
Authors: Li Yuan-Min , Catalano A. , Fieselmann B.F.
Published: March 2011

Hydrogenated amorphous silicon-carbon alloys (a-SiC:H) with 1.9–2.0 eV bandgaps have been grown by glow-discharge using methane as the source of carbon with high hydrogen dilution (CH4+H2) at various substrate temperatures. A thickness dependence of the properties of un-doped films is observed. The photo-electronic properties have been much improved in these undoped alloys compared to those of CH4 based films without H-dilution, however the CH4+H2 based boron doped a-SiC:H films show little improvement. Simple p-i-n single junction solar cells using improved wide-gap a-SiC:H Mayers, based on the CH4+H2 recipe and the novel carbon feedstock trisilylmethane (TSM), show high open circuit voltages and high fill factors. The cell stability under illumination has been tested. There is no correlation in degradation rates between the a-SiC:H cell efficiency and the photoconductivity of the corresponding i-layer films.
Effect of Boron and Phosphorus Ion Implantation on a-SixC1-x:H Thin Films
Authors: Demichelis F. , Galloni R. , Pirri C. F. , Rizzolid R. , Summonte C. , Tresso E.
Published: March 2011

Ion implantation of boron and phosphorus in device quality a-SixC1-x:H films deposited by Ultra High Vacuum Plasma Enhanced Chemical Vapor Deposition (UHV PECVD) has been performed. The effects of damage and of damage recovering after annealing were investigated by optical absorption, electrical conductivity and infrared (IR) spectroscopy measurements. It is found that samples doped by phosphorus implantation can have dark conductivities as high as those obtained on samples doped with boron, either by ion implantation or gas phase.
Transient Leakage Currents in Amorphous Silicon Thin-Film Transistors
Authors: Hack M. , Steemers H. , Weisfield R.
Published: March 2011

In this paper we present both experimental data and computer simulations of the leakage characteristics of amorphous silicon (a-Si) thin film transistors operated under time transient conditions. The transient behaviour of these devices for realistic operating conditions is often very different from their steady-state characteristics, due to the slow response of deep traps in a-Si. Our model is in good agreement with the data and realistically accounts for the time-dependent behaviour of amorphous silicon with leakage being mainly determined by a combination of fixed charge in the passivation dielectric and a distribution of surface states at the top silicon interface. We show how voltage pulses applied to the gate of a TFT affect its performance as a pixel switch in a two-dimensional array. In particular we concentrate on the effects of light and bias stressing.
Low-Resistivity Amorphous Silicon for Contacts Using Low-Temperature Rapid Thermal Annealing
Authors: Knoch Lynnita , Tam Gordon , Theodore N. David , Pennell Ron
Published: March 2011

Fabrication of SiGe heterojunction bipolar transistors (HBTs) requires a low thermal budget to avoid relaxation of the strained SiGe base layer. Ion implantation is one of the most widely used techniques to achieve contacts. However, due to thermal budget constraints, low temperature rapid thermal annealing (RTA) cycles to activate these implants are insufficient to anneal out all of the implant damage. Polysilicon contacts provide an alternative to ion implantation, but are typically annealed at high temperatures (>950°C) to achieve low sheet resistivity. In this study, amorphous silicon and polycrystalline silicon films were implanted with boron, arsenic, or phosphorus and RTA'd at temperatures from 800°C to 950°C and compared to single crystal silicon with identical implants and RTA cycles. The films were characterized using four-point probe, Hall measurements, TEM (transmission electron microscopy), and SIMS (secondary-ion mass-spectrometry). TEM analysis shows that the amorphous deposition produces larger grains upon RTA due to more rapid grain growth than the polycrystalline deposition. The sheet resistance for the amorphous deposited films is much lower than that of the polycrystalline deposition for all implant conditions. Activations of the implants indicate that the arsenic and phosphorus segregate to the grain boundaries, while the boron does not. The segregation is more significant for the polycrystalline films than for the amorphous films and can be explained by the grain boundary area. For contacts to the SiGe HBT, which requires a low thermal budget, an amorphous deposited silicon film is advantageous over a polycrystalline film at low annealing temperatures because it has lower sheet resistance, less segregation to the grain boundaries, and produces larger grains.
A New Model for Series Resistance of Amorphous Silicon Thin Film Transistor
Authors: Kim Yong S. , Park Jin S. , Lee Seong K. , Hwang Jung R. , Choi Hong S. , Choi Yearn I. , Han Min K.
Published: March 2011

We presents a new model for the series resistance of an amorphous silicon (a-Si) thin film transistor (TFT) with an inverted-staggered configuration, considering the current spreading under the source and the drain contacts as well as the space charge limited current. The calculated results of our model have been in good agreements with the measured data over a wide range of applied voltage, gate-to-source and gate-to-drain overlap length, channel length, and operating temperature. Our model shows that the relative contribution of the series resistances to the current-voltage (I-V) characteristics of the a-Si TFT in the linear regime is more significant at low drain and high gate voltages, for short channel and small overlap length, and at low operating temperature, which has been verified successfully by the experimental measurements.
A New Narrow Width Effect in Amorphous Silicon Thin Film Transistors
Authors: Martin Russel A.
Published: March 2011

A new narrow width effect is described for a-Si thin film transistor, TFT, having the inverted staggered structure with source and drain contacts overlapping the edge of the island passivation nitride. In this structure, where the source and drain contacts overlap the edge of the island they contact the a-Si and make a segment of channel effectively shorter. The edges thereby contribute a greater amount to the total drive current, and as width decreases, that fraction increases; what is therefore seen is a channel length effect masquerading as a width effect.

The results of measurements down to a width of 3um are given and the effective region of enhanced current is estimated. A SPICE model is presented that allows a simple representation of this effect.
Ion Channeling and Spectroscopic Ellipsometry Examinations of Thin-Film SiO2 /EPI-Si(001) Structures
Authors: Fiory A. T. , Roy P. K. , Jellison G. E.
Published: March 2011

Rutherford backscattering ion-channeling spectrometry (RBS) and 2-channel spectroscopic polarization modulation ellipsometry (2-C SPME) were combined in a study of 3- to 16-nm SiO2 films to discern possible differences between conventional MOS oxides, modified surface preparation, and stacked-oxide processes which combine chemical vapor deposition with furnace oxidation. An excess silicon scattering is observed by RBS, which suggests atomic displacements associated with interfacial roughness and strain in the crystalline Si. Ellipsometry observes an increase in refractive index with decreasing film thickness, which is consistent with interfacial roughness or Si strain. The various preparation methods for device-quality MOS oxides yielded essentially equivalent results and film densities close to bulk, fused SiO2.
VPD/SIMS Measurement of Surface Al on Silicon Substrates
Authors: Chia V.K.F. , Odom R.W. , Bleiler R.J. , Sams D.B. , Hockett R.S.
Published: March 2011

An experimental protocol using secondary ion mass spectrometry to measure Al in vapor phase decomposition (VPD) solutions has been developed to achieve a detection limit of 108 atoms/cm2. The analytical technique is called VPD/SIMS. The procedure utilizes sample preparation techniques developed for microvolume SIMS. Preliminary SIMS analysis of simulated VPD solutions consisting of dilute HF indicate that a theoretical detection limit of 5.7×105 Al atoms/cm2 is possible from a 6″ wafer.
Kinetics of UV/O2 Cleaning and Surface Passivation: Experiments and Modeling
Authors: Bedge Satish , McFadyen Joseph , Lamb H. Henry
Published: March 2011

Removal of adsorbed organic contaminants from Si surfaces by reaction with molecular O3 and photo-generated atomic oxygen species in a UHV-compatible photochemical reactor was investigated. Treatment of contaminated wafers with externally generated O3 at 25°C was effective in removing adsorbed organics, but surface cleaning rates were enhanced by simultaneous 254-nm UV irradiation of the reactor contents. In situ photo-generation of O3 and atomic oxygen species by 185- and 254-nm irradiation of O2 gave comparable results. A simplified gas-phase kinetics model describing O3 generation by a low-pressure Hg lamp was developed and used to gain insight into the effects of relative humidity and O2 partial pressure on steady-state O3 concentrations.
Surface Stability and Flow Characteristics of BPSG Film by N2O Plasma Treatment
Authors: Kim C.G. , Lee H.S. , Ahn Y.C. , Chung U.I. , Lee J.K. , Lee J.G.
Published: March 2011

BPSG films show good flow characteristics with the increase of boron and phosphorus concentration. As–deposited BPSG films with high boron and phosphorus concentration, however, have a dopant instability which results in film bursts, cracks, and precipitates, due to water absorption. Elimination of dopant instabilities of BPSG films by N2O plasma treatment is investigated. Film structure, composition and flow properties are evaluated by FT-IR, SIMS, and SEM, respectively. Dopant stability is examined after H2SO4 boiling. After H2SO4 boiling without N2O plasma treatment, BPSG films with high boron and phosphorus concentration show poor flow characteristics. Boron and phosphorus are leached out of the BPSG films by reaction with absorbed water during the H2SO4 boil. N2O plasma treatment results in a thin surface layer composed of Si-O-B bonds. These bonds do not dissolve in water. It is proposed that the thin layer consisting of Si-O-B bonds prevents the penetration of water into BPSG film during H2SO4 boiling.
Detection of Thin Interfacial Layers by Picosecond Ultrasonics
Authors: Tas G. , Stoner R. J. , Maris H. J. , Rubloff G. W. , Oehrlein G. S. , Halbout J. M.
Published: March 2011

We report on experiments in which the picosecond ultrasonics technique is used to detect the existence of thin layers of CFx at the interface between a metal film (Al) and a silicon substrate. Acoustic vibrations are excited in the metal film when a picosecond light pulse is absorbed. The thickness of the CFx can be estimated from the rate at which these vibrations are damped out via transmission of sound into the silicon substrate through the CFx layer. We show that thin CFx layers can also be detected via their effect on the rate at which heat flows from the metal to the silicon.
The Wet Etching of CdZnTe Substrates for OMVPE Growth
Authors: Chan T.W. , Bao X.J. , Oh I.H. , Sides P.J. , Ko E.I.
Published: March 2011

The etching of CdZnTe substrates by bromine-methanol solutions was studied by chemi-mechanical polishing. Over a bromine concentration of 0.5 to 3.5 volume percent, the etch rates varied linearly with bromine concentration, were independent of substrate orientation, and, within experimental uncertainties, were identical to those for the etching of CdTe. The etched samples were used as substrates for the organometallic vapor phase epitaxy (OMVPE) growth of CdTe in an impinging jet reactor. The bromine concentration used in etching did not affect the growth rate or the morphology of the deposited CdTe films, but a higher defect density was found for the film grown on a substrate with the orange-peel structure.
Improvement in the Activation Efficiency of Implanted Si in GaAs using Oxygen Plasma Pretreatment
Authors: Cho Jaeshin , Pawlowicz Leszek M. , Saha Naresh C.
Published: March 2011

We have investigated the effect of GaAs surface conditions prior to plasma enhanced chemical vapor deposition of a silicon nitride cap on the activation efficiency of implanted Si in GaAs. The oxygen plasma treatment improved the activation efficiency of implanted Si by ∼35% over (1:10) NH4OH:H2O treatment. X-ray photoelectron spectroscopy (XPS) analysis of the oxygen plasma treated GaAs surface indicated the formation of ∼25Å thick oxide layer consisting of Ga2O3, As2O3, As2O5 and elemental As. During the activation anneal, the arsenic-containing oxides react with the GaAs substrate to form Ga2O3 and elemental As. The presence of excess As between the GaAs and the nitride cap film increases the probability that the implanted Si incorporates in the Ga sites over the As sites, and thereby improves the activation efficiency. This surface-related mechanism suggests that the variation in activation efficiency is mostly attributed to variation in surface conditions, and may explain the wide variety of reported values of activation efficiency.
Vapor Phase Cleaning of Silicon Wafers
Authors: Deal Bruce E. , Helms C. Robert
Published: March 2011

Vapor phase cleaning of silicon wafers is reviewed. Particular emphasis is placed on oxide etching and removal, including the mechanisms involved in vapor HF etching of silicon oxides. Other items discussed include native oxide formation, impurity removal, and device applications. Future directions involving other chemistries and integrated processing are summarized.
The Effect of Dopant Concentration on the Native Oxide Growth on Silicon Wafer Surface
Authors: Ishimaru Y. , Yoshiki M. , Hatanaka T.
Published: March 2011

The effects of dopant type and dopant concentration on the native oxide growth in air on the silicon surface were investigated. The oxide thickness was measured by X-ray photoelectron spectrometry (XPS). The oxide was thicker on n-type Si than on p-type Si in early oxidation. The oxide increased linearly with the dopant concentration. This enhancement of oxidation was assumed to be caused by vacancies near the surface in the silicon bulk.
Porous Amorphous Si Formation by the Etching of Single Crystal Si Substrates
Authors: George T. , Vasquez R. P. , Kim S. S. , Fathauer R.W. , Pike W. T.
Published: March 2011

The nature of light-emitting porous Si layers produced by non-anodic stain etching of p-type (100) Si substrates is studied. The layers were characterized by transmission electron microscopy as being amorphous in nature. X-ray photoelectron spectroscopy and electron spin resonance measurements show these layers to be composed mainly of a-Si. The formation mechanism of the a-Si is explored using by stain etching SiGe ‘marker’ layers within epitaxially grown Si films and by high temperature annealing. These experiments provide strong evidence for a spontaneous crystalline-amorphous phase transformation during the etching process.
Si MBE on H-Passivated Si(100)
Authors: Eaglesham D.J. , Unterwald F.C. , Luftman H.
Published: March 2011

The use of H-passivation as an initial surface for Si MBE or CVD is becoming more widespread. The H-terminated Si(100) surface is prepared using the spin-etch, vapour-cleaning with HF, or an HF dip, as the final pre-clean before sample loading. The hydrogen is then desorbed in-situ prior to deposition, typically at ≈650 °C. We have shown that deposition directly onto these surfaces leads to epitaxy at substantially lower temperatures (≈350°C). In order to understand how epitaxy occurs far below the hydrogen desorption temperature we have investigated growth on clean Si(100) during deliberate dosing with deuterium in this temperature regime. Since the final coverage observed in SIMS is always far lower than the total dose, we conclude that deposition of Si induces desorption of H, as opposed to simple H segregation.
Photoemission Study of the Si, Ge Epitaxial Growth Process Using Surfactants
Authors: Yang Xiaoyu , Cao Renyu , Terry Jeff , Pianetia Piero
Published: March 2011

Heteroepitaxial growth of Ge on Si(100) and Si on Ge(100) surfaces with Sb as a surfactant has been investigated by in situ high resolution photoemission and low energy electron diffraction (LEED). Our results show that an ordered monolayer of Sb atoms saturate the surface dangling bonds and consequently lower the surface free energy. Deposition of Ge or Si on the Sb/Si(100) or Sb/Ge(100) surfaces either at room temperature, followed by mild annealing or deposition at elevated temperature, result in an epitaxial layer of Ge or Si on the substrate, respectively. We provide clear experimental evidence that the deposited Ge or Si atoms changes position with the surface Sb atoms in this process. Ge or Si atoms occupy the epitaxial sites previously occupied by the Sb atoms. The Sb atoms in turn segregate to the surface and form a new ordered layer. The Bi-assisted growth process is also discussed.
Optimization of SI-Wafer Cleaning and the use of Buffer-Layers for Epitaxial Growth of Sige-Layers by VLPCVD at T = 650 C
Authors: Caymax Matty R. , Poortmans J. , Ammel A. Van , Vandervorst W. , Vanhellemont J. , Nijs J.
Published: March 2011

For low-temperature epi-growth in UHV-CVD-systems, the pre-epi, ex-situ cleaning of Si-wafers is known to be very critical. Various ways of etching the chemical oxide-layer after RCA-cleaning have been analysed by SIMS-measurements of the interfacial C, 0 and Bcontamination. Layer growth was performed at 650 C under a flow of 20 sccm of silane at 0.26 Pa. The best results (C and 0 below 2 % of a monolayer, and no detectable amounts of B) were obtained with “dry” etch-procedures, i.e. in which no water-rinse was applied after a normal 2 % HF-dip, or where 1F-vapour was used instead. Growth of Si1-xGex-layers with x < 0.1 succeeds quite well on such prepared substrates; for x between 0.1 and 0.25, we have found the use of a thin, pure Si-buffer layer (150 Å) to be indispensable. For x > 0.25, the growing layer can become quite rough, although this varies in time.