bluuebunny/crossref_metadata_2025 huggingface dataset:
An Investigation of the Behaviour of a-Si:H Thin Film Transistors Fabricated With Different Proximity Recovery Layer Doping Levels
Authors: Willums M.F. , Lecomber P.G. , Hack M.
Published: March 2011

Experiments have been carried out on inverted staggered amorphous silicon (a-Si:H) thin film transistors (TFTs). Depending on the voltage stressing conditions the electronic characteristics of these devices tend to shift with time [1]. To slow these changes down, and to speed up the recovery of the TFT, a lightly doped compensation or proximity recovery layer (PRL) has been placed in close proximity to the active layer of the undoped a-Si:H [2]. The effects of varying the dopant concentrations in the PRL have been studied by comparing the PRL TFTs with conventional control TFTs containing no PRL.
High Electric Field Amorphous Silicon Structures : Application to Particle Detection
Authors: Equer B. , Chevrier J.B.
Published: March 2011

Thin-film ionizing radiation detectors prepared from amorphous semiconductors are receiving a growing interest. To reach ultimate sensitivity, single particle detection is needed. Amorphous silicon detectors operated in this mode require a high polarization to overcome the limitations due to the low electron and hole effective mobilities and to charge trapping. In this review, we summarize results obtained on charged particle detection (electrons, protons and alphas) with special emphasis on the electron-hole pair generation and collection mechanisms. We report a study on the role of p-doped layers in obtaining high breakdown voltages (more than 7 × 105V/cm). Physical mechanisms underlying leakage current injection and generation are discussed.
Aspects of Non-Volatility in a-Si:H Memory Devices
Authors: Rose M.J. , Snell A.J. , Lecomber P.G. , Hajto J. , Fitzgerald A.G. , Owen A.E.
Published: March 2011

ABSTRACT.: a-Si:H p+-n-i devices, after a once only forming process, switch between two distinct states, both of which are memory states, and are electrically programmable with pulses in the nanosecond range with at least a 1 million cycle endurance. They are known to be non-volatile memory states which persist for long periods. This paper examines the nature of this non-volatility by looking at the effects of time, temperature, bias and radiation. It is found that these digital memory states persist with no change in state for at least four years under zero bias, and that they can withstand high temperatures both under bias and at zero bias. This and a resistance to radiation and a space environment shows that a mechanism of charge storage is unlikely and that they may have applications in hostile environments. The reason for such stability is unclear, but may be associated with the incorporation and distribution of metal in the filamentary region.
Crystallization Kinetics of Hydrogenated Amorphous Silicon During Pulsed Excimer Laser Annealing
Authors: Ready S. E. , Roh J. H. , Boyce J. B. , Anderson G. B.
Published: March 2011

Explosive crystallization of amorphous silicon (a-Si) during pulsed laser annealing occurs at an intermediate laser energy fluence above the threshold for surface melting. Mediated by a molten silicon layer which is undercooled with respect to crystalline silicon and above the melting point of a-Si, the crystallization interface drives down into the sample, sustaining itself due to the difference in the latent heats of the crystalline and amorphous silicon. Explosive crystallization has been the subject of numerous studies which have for the most part been restricted to ion implanted amorphized layers in silicon bulk samples. In this study we examine the crystallization kinetics of vapor deposited thin films of hydrogenated a-Si for films of differing hydrogen content and substrate temperature. We reevaluate current models of interface and nucleation kinetics qualitatively in light of these results. The fundamental physical mechanisms in these non-equilibrium phase transitions during pulsed laser annealing are discussed.
Thin Film on Asic - A Novel Concept for Intelligent Image Sensors
Authors: Fischer H. , Schulte J. , Giehl J. , Böhm M. , Schmitt J. P. M.
Published: March 2011

Two different pixel detectors have been fabricated, each of them consisting of an a-Si:H based photodiode layer on top of a crystalline silicon integrated circuit. Both sensors are arranged in a matrix and addressed columnwise, providing parallel readout of the matrix rows or optional random access. One sensor is an a-Si:H detector / x-Si switching transistor combination with 256 × 256 pixels and a pixel size of 100μm × 100μm. The signal transport in the array is examined, demonstrating its capability of very fast information readout. The second sensor, which consists of an array of 32 × 32 pixels on a 5μm PMOS ASIC, performs digital contour extraction. Experimental data on the performance of the intelligent array are also reported.
Comparison of Computer Simulations with Measurements From a-Si:H Imaging Arrays.
Authors: Yorkston J. , Antonuk L.E. , Seraji N. , Boudry J. , Huanga W. , Morton E.J. , Street R.A.
Published: March 2011

The design and characterization of flat panel a-Si:H arrays for imaging applications in radiotherapy and diagnostic radiology has already begun. Future improvements in design and performance will be heavily reliant on the results of computer simulations capable of accurately predicting the behavior of the arrays in a variety of operating conditions. These results will allow the design of new arrays to be optimized for the particular application before they are committed to fabrication. This paper outlines the results of an investigation into the effects of varying a number of array parameters and operating conditions using a simulation code which models the operation of a-Si:H devices. The results are compared with actual measurements from arrays fabricated at Xerox PARC.
Charge-Sensitive Poly-Silicon TFT Amplifiers for a-Si:H Pixel Particle Detectors
Authors: Cho G. , Perez-Mendez V. , Hack M. , Lewis A.
Published: March 2011

Prototype charge-sensitive poly-Si TFT amplifiers have been made for the amplification of signals (from an a-Si:H pixel diode used as an ionizing particle detector). They consist of a charge-sensitive gain stage, a voltage gain stage and a source follower output stage. The gain-bandwidth product of the amplifier is ∼ 300 MHz. When the amplifier is connected to a pixel detector of 0.2 pF, it gives a charge-to-voltage gain of ∼ 0.02 mV/electrons with a pulse rise time less than 100 nsec. An equivalent noise charge of the front-end TFT is ∼ 1000 electrons for a shaping time of 1 μsec.
Effect of Annealing on Undoped a-Si:H Films Prepared by Mercury-Sensitized Photochemical Vapor Deposition
Authors: Niiyama T. , Nozaki H.
Published: March 2011

The effects of annealing on undoped a-Si:H films were studied. Films of a-Si:H were prepared by mercury-sensitized photochemical vapor deposition, and were annealed immediately. The hydrogen configuration was altered in the annealing process below 200°C, although films were prepared at a substrate temperature of 230°C. At the same time, electron drift mobility greatly increased. These observations indicate a reduction in the number of tail states in the a-Si:H band-gap. Thus the annealing below the substrate temperature clearly influences not only the bonded-hydrogen atoms but also the Si-Si network in the films to some extent.
A Particular Photo-CVD Apparatus for Hydrogenated Amorphous Silicon Deposition
Authors: Manfredotti C. , Fizzotti F. , Osenga C. , Boero M. , Rigato V. , Quaranta A.
Published: March 2011

A new PHOTO-CVD apparatus has been built in order to deposit a – Si : H films and other kinds of amorphous thin films by a technique which is both simple and versatile. This apparatus is composed of three chambers connected together: a load-lock chamber, a process chamber and a third chamber for in-situ analysis of deposited films. A peculiarity of the lamp, a dielectric discharge lamp which can work with noble gases like Xe or Kr, is that it can be completely dismounted without breaking the vacuum in order to clean the optical MgF2 window. By this method, the deposition chamber can be kept in very clean conditions. In this apparatus, we started to deposit a – SixC1−x: H of very good quality, taking their thickness into account. These films have been completely characterized by chemical (RBS, ERDA) and optical (PDS) methods. Their quality can be compared with quality of a – Si : H samples of the same thickness obtained by PECVD.
Effects of Hydrogen Plasma Treatment on Hydrogenated Amorphous Silicon
Authors: Lee J.-K. , Schiff E. A.
Published: March 2011

We have studied the effects of hydrogen plasma treatments of a-Si:H at elevated temperatures using conductivity, photoconductivity, and spin density measurements. Effects were measured as a function of temperature and of treatment time; control specimens were subjected to comparable treatments without the plasma. In no case did plasma treatment improve the specimen photoconductivity over the as-deposited state. At treatment temperatures (230 °C < T < 460 °C) plasma treatment reduced the photoconductivity below that of the control specimen. This effect may be evidence for plasma-assisted dehydro-genation of the specimen. The defect structural equilibration determined by hydrogen chemical potential depending on temperature and hydrogen plasma is also addressed.
Configurational Relaxation of the D Defect in Hydrogenated Amorphous Silicon as a Function of Fermi Energy
Authors: Leen Thomas M. , Rasmussen Randall J. , Cohen J. David
Published: March 2011

By using light soaking and partial dark annealing to vary the Fermi level in n-type a-Si:H, we have examined the thermal emission of electrons from the dangling bond (D) defect. We find optical evidence for a change in the configuration of the D defect when EF = Ec-0.55±0.08eV. We find that the relaxation rate increases with temperature and increases as EF is brought closer to Ec. Voltage-pulse photocapacitance and depletion-width-modulated ESR show emission is predominantly from D° defects for short emission times and short filling pulse widths. With longer emission times and longer filling pulse widths, emission from D-dominates. We also find that the charge emission transient fits a universal scaling law under a variety of pulsing conditions, temperatures, and anneal states.
Optical Properties and Structure of Microcrystalline Silicon
Authors: Nguyen Hien V. , An Ilsin , Li Youming , Wronski C.R. , Collins R.W.
Published: March 2011

The optical properties of thin film microcrystalline silicon (μc-Si:H) prepared by plasma-enhanced chemical vapor deposition (PECVD) have been studied by real time spectroscopie ellipsometry in the nucleation regime as isolated crystalline particles increase in size. A simple geometric model of nucleation allows us to remove the dominant effect of voids and extract the dielectric functions of the crystallites themselves. We find that the results can be understood in terms of a classical size effect whereby limitations on the electron mean free path by scattering at crystallite surfaces control the absorption onset from 2.0 to 3.0 eV. Finally, we describe how well-ordered, continuous 15 Å c-Si films can be prepared on metal substrates.
Origin of Surface Defects in a-Si:H Films
Authors: Yan H. , Morimoto A. , Kumeda M. , Shimizu T. , Yonezawa Y.
Published: March 2011

Surface oxidation and surface defect creation processes in a-Si:H films have been studied in detail by means of electron spin resonance(ESR) and X-ray photoelectron spectroscopy(XPS). It is found that Si dangling bonds created by the surface oxidation distribute far wider than the thickness of the SiO2 layer. These defects are also found to be removed out by annealing at around 100°C. These defects are proposed to be created by a stress in a-Si:H induced by the surface oxidation. Moreover, the presence of the surface defects unrelated to oxidation is shown for the first time by the present experiment. The origin of these defects, however, are not clear at present.
A Multiple Quantum NMR (MQNMR) Study of Hydrogen Microstructure in Boron Doped a-Si:H
Authors: Mitra S. , Levy D. H. , Gleason K. K. , Jia H. , Shinar J.
Published: March 2011

An IR and multiple quantum NMR (MQNMR) study of hydrogen microstructure in three boron doped a-Si:H is discussed. The total Si-bonded H content of all films was 6.5 ± 1.0 at.% as determined by the 640 cm-1 IR wagging mode, but their boron content, which was determined by secondary ion mass spectrometry, ranged from 0.02 to 0.3 at. %. The number of correlated hydrogen, as measured at a preparation time of 600 μSwas found to be more weakly dependent on the boron content than previously observed in phosphorous-doped glow-discharge films. Upon annealing at 220 °C the MQNMR spectrum show a moderate increase in the number of correlated hydrogen in all three samples.
Small Angle X-Ray Scattering (Saxs) and IR Study of Microvoid Dynamics in Annealed RF Sputter-Deposited A-SI:H
Authors: Jia H. , Shinar J. , Chen Y. , Williamson D. L.
Published: March 2011

A SAXS and IR study of microvoid distribution and dynamics in a-Si:H deposited by rf sputtering at 200 – 600 W on nominally unheated substrates is described and discussed. The 640 cm-1 band of the 200 W film yielded a total Si-bonded H content CH=21 at. %; the 840 – 890 cm-1 band yielded a dihydride content CH2 3.4 at. %. The SAXS measurements yielded a microvoid volume fraction vf=8.2 vol.%, and tilting SAXS data indicated elongated voids consistent with a columnar microstructure. In the other films, 9<CH<12 at. % and CH2 was negligible, vf was -2 vol. %. Annealing from 250°C to 310°C for 6 hrs resulted basically in no changes of CH and vf. However CH decreased and vf increased significantly after annealing at 350°C and above. The results showed a strong correlation between the IR determined CH and CH2 and the SAXS determined vf.
Dipolar Measurements of Hydrogen in Amorphous Silicon
Authors: Hari P. , Taylor P.C. , Street R.A.
Published: March 2011

The dipolar interaction of hydrogen (∼ 10 at. %) in boron-doped amorphous silicon has been studied using the Jeener-Broekaert pulse sequence. The sample was prepared on an Al foil substrate at a temperature of 230°C using a standard glow discharge system (operating at 1 W rf power). The diborane/silane ration was 10-4. The same sample was removed from the Al substrate using dilute hydrochloric acid. The Jeener-Broekaert pulse sequence consists of three pulses: π/2|x′ – τ1 – π/4|y′ – τ2 – π/4|y′ – echo. We measured T1D, the dipolar spin lattice relaxation time, for τ1 = 82 μs, τ1 = 100 μs and τ1 = 50 μs at 299°K. The value of τ1D was found to be independent of τ1. At 335°K we found τ1D to be much longer than at room temperature. The values of τ1D at 299 K, 314 K and 335 K are, respectively, 0.7 ms, 1.2 ms and 1.8 ms. From the data we estimate an activation energy for microscopic motion to be ∼ 0.2 eV.
Surface and Bulk GAP States Distributions in Amorphous Silicon Films as Obtained by Optical Methods
Authors: Amato G. , Benedetto G. , Boarino L. , Giorgis F. , Spagnolo R.
Published: March 2011

The aim of this work is to achieve detailed information about surface and bulk density of states in device quality a-Si:H films by means of deconvolution of PDS spectra. Unambiguous deconvolution of the spectra has been performed by calculating the first derivative vs. energy of the absorption coefficient of the samples. The results are compared with those obtained by means of the integration rule. Calculations of the density of states carried out on samples having different thickness suggest that the defect distribution differs from surface to bulk. The surface defect peaks are found to lie closer to the corresponding mobility edges, with respect to the bulk defect peaks: these results agree well with those obtained by means of other techniques, like total yield spectroscopy and can be explained in terms of a defect pool model.

The present deconvolution procedure when applied to samples having different thickness provides new results about the film's homogeneity in terms of deep defect and valence tail states.
Enhanced Hydrogen Diffusion Under Illumination in Hydrogenated Amorphous Silicon
Authors: Santos P.V. , Johnson N.M. , Street R.A.
Published: March 2011

We provide experimental evidence for the fact that hydrogen diffusion in hydroge-nated amorphous silicon is controlled by the concentration of electronic carriers. It is experimentally demonstrated that the hydrogen diffusion coefficient (a) is enhanced if the carrier population is increased by illumination and (b) is strongly suppressed if carriers are extracted from the diffusion region by the application of an electric field.
Study of Short-Range Motion of Atomic Hydrogen in Amorphous Silicon by Neutron Reflectometry
Authors: Dozier W. D. , Herwig K. W. , Shinar R. , Jia H. , Shinar J.
Published: March 2011

Preliminary results of neutron reflectometry (NR) measurements on if sputter-deposited a-Si:H/a-Si:D bilayers indicate that this technique may be used to monitor H and D motions over distances of ≈ 10 to 200 Å with a nominal resolution of 5 – 10 Å. In studying rf sputter-deposited thin films containing a high density of microvoids annealed at 270 C, we found that the hydrogen diffused a distance of only ≈ 100 Å. Further annealing at 270 and 280 C produced no additional motion. This result is consistent with a model of this system in which the hydrogen is trapped in microvoids after moving a relatively short distance.
Concentration-Dependent Hydrogen Diffusivity in a-Si:H
Authors: Santos Paulo V. , Jackson Warren B.
Published: March 2011

We present experimental evidence for an enhancement in hydrogen diffusivity in a-Si:H with hydrogen concentration. The concentration dependence is attributed to the saturation of the density of hydrogen traps consisting of Si-H bonds with increasing hydrogen concentration. As a consequence, hydrogen lifetime in mobile interstitial and/or bond-center sites is enhanced. The saturation occurs when the rate of trap filling by hydrogen injection from the plasma exceeds the rate of trap creation.
Kinetics of Growth and Recovery of Light-Induced Defects Under High-Intensity Illumination
Authors: Isomura Masao , Wagner Sigurd
Published: March 2011

We report a study of the rates of generation and of annealing of the light-induced defects in hydrogenated amorphous silicon (a-Si:H). The rates of generation are found to be sensitive to temperature when the light intensity is high. This increased sensitivity to temperature at high rates suggests that a temperature-activated process such as hydrogen motion controls the rates of generation more when they are high. The rate of annealing at 130°C is strongly accelerated by illumination, and depends strongly on the light intensity. This may be explained by the diffusion of hydrogen, accelerated by excess carriers.
Toward the Elimination of Light-Induced Degradation of Amorphous Si by Fluorine Incorporation
Authors: Deng X. , Mytilineou E. , Young R. T. , Ovshinsky S. R.
Published: March 2011

We report on evidence that fluorine, properly incorporated into a-Si, replaces weakly bonded hydrogen and improves the material stability under light soaking. Our fluorinated amorphous silicon (a-Si:H:F) is made by if glow discharge at high deposition temperatures up to 430 C from a gas mixture of SiH4 or Si2H6 and F2. These a-Si:H:F films show much lower density of states in the light soaking saturated state than device quality a-Si:H prepared in the same deposition system. It is evident from our results that fluorine incorporated into the network at such high deposition temperature makes for a new configuration which minimizes dangling bonds and other defects.
The Vibrational Spectrum of a-SiC:H Films in the 500 cm-1 to 9000 cm-1 Range by Ftir Transmission and Photothermal Deflection Spectroscopy
Authors: Lotter E. , Bauer G.H.
Published: March 2011

Applying PDS in the energy range from 3000 to 9000 cm-1 considerably improves the sensitivity of vibrational spectroscopy of thin films. In a-SiC:H we have found a large number of absorption features not seen before, which give new insight in structural and compositional properties of these alloys.

In a-SiC:H, in addition to the fundamental and the first and second overtone of C-H stretching modes, O-H vibrations occur at 3500 cm-1 and allow a very sensitive detection of chemical degradation of films due to in-diffusion of water. Combined excitation of C-H stretching and C-H wagging or bending modes give rise to a modified interpretation of the origin of the C-H related absorption features observed in methane based a-SiC:H. The induced absorption of molecular hydrogen together with a band at 7000 cm-1, which results from a combined excitation of C-H bonds and H2 molecules colliding with the C-H, indicates that the amount of H2 increases with C alloying. The C-H + H2 combination mode is very strong compared to the corresponding Si-H + H2 peak observed in pure a-Si:H and signalizes mat a considerable amount of the molecular hydrogen enclosed in voids, containing CH3 or CH2 groups.
Anomalous Carbon Interdiffusion in a-Si:H/a-SiC:H Multilayers
Authors: Schwarz R. , Fischer T. , Hanesch P. , Lanz J. , Schirmacher W. , Kolodzey J. , Zorn G. , Goebel H.
Published: March 2011

The interdiffusion of carbon in a-Si:H and a-Si1-xCx:H multilayers is measured by analyzing the time evolution of the X-ray diffraction from the superlattices. A time dependent diffusivity D(t)which follows a power law is found. The theoretical analysis shows that such a time dependence, referred to as “dispersive” or “anomalous” diffusion and studied for hydrogen diffusion in the literature, is fundamentally related to the amorphous structure of the material.
Optoelectronic Properties of Plasma CVD a-Si:H Modified by Filament-Generated Atomic H
Authors: Li Y.M. , An I. , Gunes M. , Dawson R.M. , Collins R.W. , Wronski C.R.
Published: March 2011

We have studied a-Si:H prepared by alternating plasma deposition with atomic H treatments performed with a heated W filament. Real time spectroscopie ellipsometry provides the evolution of film thickness, optical gap, and a measure of the fraction of Si-Si bonds broken in the near-surface (200 Å) during H-exposure of single films. This information guided us to the desired parameters for the H-treatments. Here, we concentrate on a weak hydrogenation regime characterized by minimal etching, a higher H content by 2 at.%, and a larger optical gap by 0.02 eV for the growth/hydrogenation structures in comparison to continuously deposited control samples. This new material has shown an improvement in the defect density in the light-soaked state in comparison to the control samples. This may result from stabilization of the Si structure due to an increase in the H chemical potential in the a-Si:H.
A New Method of Depositing Amorphous Hydrogenated Silicon Carbide with Low Ir-Detected Microstructure
Authors: Lu Hsueh Yi , Petrich Mark A.
Published: March 2011

We report a new method of depositing amorphous hydrogenated silicon carbide thin films with low IR-detected microstructure in a plasma-enhanced chemical vapor deposition reactor. Films prepared at various conditions are studied with Fourier-transform infrared absorption. Their optical band gaps and photoconductivities are also measured. The amount of microstructure can be controlled by adjusting the powered-electrode potential during deposition, and the microstructural changes are reflected in the film properties. By applying an external dc voltage to the rf-excited powered electrode, we can shift the optimal deposition temperature from 250 °C to as low as 100 °C. We find that films deposited at positive powered-electrode potential and low substrate temperature exhibit less microstructure, wider optical band gaps, and faster deposition rates than films deposited at conventional conditions.
Review of the Simulation of Transient Experiments on Amorphous Silicon Hydride
Authors: Shapiro Finley R.
Published: March 2011

The transient characteristics of amorphous silicon hydride (a-Si:H) devices are of great importance as a means of studying the fundamental electrical and photo-electrical processes in the material. To assist in the interpretation of these experiments, several groups have performed simulations to understand better the meaning of transient waveforms. Simulations begin with hypotheses of how the processes of interest affect each other and affect the measured quantity, and then calculate an expected experimental result. Transient experiments on a-Si:H have been simulated by a variety of techniques, including the Monte Carlo, Laplace transform, and time integration methods. Of these methods, time integration is the most powerful but also the most demanding on computer capabilities. Fortunately, recent advances in computer technology have brought the simulation of transient experiments on a-Si:H by time integration within the capabilities of advanced personal computers.
The Spectral Dependence of the Non-Radiative Efficiency in Hydrogenated Amorphous Silicon
Authors: Fan J. , Kakalios J.
Published: March 2011

The room temperature non-radiative efficiency, defined as the ratio of the heat released per absorbed photon for doped and undoped hydrogenated amorphous silicon (a-Si:H) has been measured using photo-pyroelectric spectroscopy (PPES) for photon energies ranging from 2.5 to 1.6 eV. There is a fairly sharp minimum in the non-radiative efficiency when the a-Si:H is illuminated with near bandgap photons. We describe a model wherein this minimum arises from the variation in the amount of heat generated by free carrier thermalization as the incident photon energy is varied, and report measurements of the excitation kinetics of the non-radiative efficiency which support this proposal.
An Assessment of the Light Modulated Photocurrent Method in the Study of the Density of Gap States in Hydrogenated Amorphous Silicon
Authors: Zhong Fan , David Cohen J.
Published: March 2011

We have applied the modulated photocurrent (MPC) method over a wide range of frequencies (5Hz-100kHz) and temperatures (120K-380K) to assess its ability to accurately deduce the mobility gap distribution in a-Si:H. We have also investigated the effects of moving both the Fermi level within some samples (by light soaking and partial annealing) and the quasi-Fermi level (by applying the bias light) to observe how such changes influence the deduced density of states (DOS). We then compared the MPC results directly with the DOS determined by junction capacitance measurements in the same sample devices. We have determined general conditions under which, we believe, the MPC results provide an accurate picture of the gap state distribution. However, we found that under other conditions, the appearance of the deep defect peaks and other features do not represent the actual defect distribution but, rather, are artifacts due to recombination processes.
Electron and Hole Transport in a-SiH at High Field and Low Temperature
Authors: Nebel C. E. , Street R. A.
Published: March 2011

Low temperature, high field properties of electron and hole transport are investigated by time-of-flight (TOF), steady-state and transient space charge limited current (SCLC) experiments on intrinsic a-Si:H. Charge collection and TOF experiments performed at T= 80 K reveal hole μτ-products of = 8 × 10-10 cm2/V and hole mobilities μ ≤ 9×10-3 cm2/Vs. The field effect on hole thermalization is demonstrated by evaluation of the post transit current decay. SCLC experiments on p+ -i-n+ (electron transport) and p + -i-n+ (hole transport) configurations are introduced and interpreted in terms of field enhanced conductivity and mobility. The experiments demonstrate the overwhelming field effect on carrier hopping in the band tail regions of a-Si:H. Considerably higher fields have to be applied in the case of hole transport than electron transport to achieve comparable conductivities; this is discussed on the basis of the different tail state distributions and localization lengths.
Transient Forward Bias Response of Amorphous Silicon P-I-N Diodes
Authors: Street R. A. , Hack M.
Published: March 2011

When a forward bias is applied to an amorphous silicon p-i-n diode, there is a delay in the onset of the current. We present experimental data and numerical calculations, showing that the effect is due to trapped space charge which inhibits the onset of a double injection current. The dependence of the delay time on defect density, bias, illumination and the location of the defects is examined.
Reverse Recovery and Decay of Stored Excess Carriers in a-SI:HP-I-N Diode
Authors: Han Daxing , Wang Keda , Silver Marvin
Published: March 2011

Carrier transport properties, including mobility and carrier lifetimes, or the mobility-lifetime-product, are important parameters for the understanding of the electronic properties of amorphous silicon devices. We have attempted to study these parameters by the junction recovery method which is useful in crystal p-i-n devices, and by the decay of the forward and reverse bias current with varying periods of zero bias delays after removal of the forward bias. We found that the current decay by the standard reverse bias recovery is much faster than that due to the decay under zero bias. In this paper we present our experimental results. We conclude that the true decay of the stored charged due to forward bias is much longer and consequently, the stored charge is much larger than that suggested by standard reverse recovery experiments.
Room Temperature Recovery of Light Induced Degradation in A-SI:H Solar Cells
Authors: Fischer D. , Pellaton N. , Keppner H. , Shah A. , Fortmann C. M.
Published: March 2011

High intensity light-soaking and post-degradation room temperature recovery of single junction a-Si:H solar cells were investigated. After high intensity short term light-soaking, it was found that the degraded state was itself not stable. In the dark, fast degraded samples improved with time, even at room temperature. Two different sets of samples showed recovery rates in the range of 1 % gain of relative efficiency per hour. Recovery kinetics were the same in the dark and under low intensity carrier generation. Continued high intensity light soaking resulted in a steady decrease of the recovery rate with time. To explain this behavior, we suggest the presence of a non-electronic, slow process related to lattice reconfigurations that lock-in the light-induced defect states.
Quantum Efficiency of Textured a-Si:H P-I-N Solar Cells After High Intensity Light-Soaking
Authors: Li X. R. , Wagner S. , Bennett M. , Fonash S. J.
Published: March 2011

We studied the effect of high-intensity light-soaking on the quantum efficiency spectrum of textured a-Si:H solar cells. We report experimental results on the time, temperature, and soaking light intensity dependence of the quantum efficiency (QE) measured in short circuit. Under 3Wcm-2 of white light the QE saturates after 30 minutes. The QE decays little in the blue and strongly in the red. The higher the temperature of saturation, the smaller the decay of the QE.
Evaluation of the Dice Method as A Tool For Amorphous Silicon Solar Cell Optimization
Authors: Von Der Linden M. B. , Schropp R. E. I. , Stammeijer J. G. F. , Van Der Weg W. F.
Published: March 2011

Information about the spatial collection efficiency in a-Si:H solar cells is obtained from the Dynamic Inner Collection Efficiency (DICE) technique. With this non-destructive method single junction solar cells with efficiencies up to 10 % have been analysed under operating conditions. The influence of i-layer deposition parameters, such as the temperature and deposition time, on the spatial collection efficiency have been investigated. Deposition parameters for the i-layer have a large influence on the collection from the first 100 nm from the p+/i-interface. A higher i-layer deposition temperature or a longer deposition time results in a higher internal collection efficiency at a depth of 70 nm into the i-layer. Also results of DICE experiments on various textured TCO substrates are presented.
Kink Effect in Short Channel a-Si:H Thin-Film Transistors
Authors: Fortunato G. , Mariucci L. , Mattacchini A. , Pecora A.
Published: March 2011

An avalanche increase of the drain current for high source-drain voltage (commonly called “kink effect”) has been observed for the first time in short-channel amorphous silicon thin-film transistors, fabricated using electron-beam lithography. This effect, caused by generation mechanisms at the drain junction, has been shown to be not only field but also temperature enhanced. The Frenkel-Poole mechanism is proposed in order to explain the data.
HF/Ethanol Preoxidation Silicon Cleaning: Analysis of the Silicon Surface and of the Ultra-Thin Oxide Layer
Authors: Garrido B. , Gessinn F. , Prom J.L. , Morante J.R. , Samitier J. , Sarrabayrouse G.
Published: March 2011

The HF/Ethanol cleaning treatment is analyzed in comparison to the HF/H 20 one. The surface analysis is made on <100> silicon wafers with sacrificial oxide layer and silicon wafers with different crystallographic orientation without sacrificial layer. The results deduced from Atomic Force Microscopy, X-ray Photoelectron Spectroscopy and ellipsometry, show that siliconfluorine bonds are related with reactive sites. The structure of the thermally thin oxide layer grown after both cleanings has been analyzed and the electrical measurements show better performance for the HF/Ethanol cleaning.
Surface Cleaning and Passivation for the Growth of Si/Oxide/Si Structures
Authors: Wang Kun—Chih , Hwang Huey—Liang , Kung Chung—Yuan , Yew Tri—Rung
Published: March 2011

This paper presents the results of surface cleaning and passivation of Si and oxide surfaces for the growth of Si/oxide/Si structures. Silicon surfaces are cleaned by the spin—etch process prior to the growth of silicon oxide. A silicon layer is then deposited after subsequent surface cleaning and chemical treatment on the surface of oxide/Si. Both the oxide and the silicon layers are grown in a plasma enhanced chemical vapor deposition system. The interface structure between layers of deposited Si/oxide/Si are observed by cross—section transmission electron microscopy (XTEM).
KOH-ETCH Related Defects on Processed Silicon Wafers
Authors: Kassel Laurent E.
Published: March 2011

KOH, an anisotropic etchant of monocrystalline Si, may cause roughness and defects whose shapes are related to crystallographic orientations. This paper studies the effect of processing steps on the formation of geometric etch defects. Implantation, thermal treatment, epitaxial growth or photoresist were not the source of such defects. In the scope of this study, only unwanted damage caused geometric etch defects. This makes the observation of the wafer after KOH etch a good indicator of the quality of previous steps.
Photo-Excited Cleaning of Silicon with Chlorine and Fluorine
Authors: Ito T. , Sugino R. , Sato Y. , Okuno M. , Osawa A. , Aoyama T. , Yamazaki T. , Arimoto Y.
Published: March 2011

Chlorine radicals generated with UV irradiation are effectively used to remove residual metal contaminants after vatious LSI processes. Aluminum, iron, and copper atoms are effectively removed as volatile chloride species from silicon surfaces. The mechanism has been studied using silicon wafers intentionally contaminated with those metal ions. Contaminants are involved in native oxides as metal oxides or hydroxides. Chlorine radicals penetrate the native oxides and attack those oxides or hydroxides vaporizing metal chlorides. The cleaning process is accompanied with slight etching of silicon surfaces to a depth as thin as a few nm. However, this is not essential because the substrate temperature is more important than the etching depth. Alkaline metals are also removed from the surfaces to the level as small as the detection limit of atomic absorption spectroscopy. We believe that those are removed through a lift-off process. The, wixture of fluorine and hydrogen gases removes a native oxide of silicon under UV irradiation. Hydrogen fluoride radicals react with native oxide resulting in hydrogen termination on silicon dangling bonds. These cleaning processes are advantageous for low temperature silicon epitaxy, reliable contact formation, and thin gate oxide growth.
Plasma-Surface Interaction Limits for Remote H-Plasma Cleaning of Si(100)
Authors: Schneider T.P. , Bernhard B.L. , Chen Y.L. , Nemanich R.J.
Published: March 2011

An investigation of the parameters in H-plasma cleaning influencing H-diffusion and surface etching is described. The Si surface and subsurface regions were characterized with Raman spectroscopy and high resolution transmission electron microscopy (HRTEM), and the plasma parameters were monitored with a double Langmuir probe and optical emission spectroscopy. The parameters varied in the rf plasma cleaning were the substrate temperature, the rf power, and the plasma exposure time. It was found that low pressure and low power H-plasma exposure was effective in terms of cleaning the surface. In the 300°C, 20 Watts, 2 min. H-plasma exposure case, the Raman spectra indicated that there was no detectable H incorporation into the Si bulk and HRTEM showed no obvious defect microstructure in the near surface region and that the surface was smooth. In contrast, in the 150°C, 50 Watts, 60 min. H-plasma exposure case, HRTEM indicated that H-induced platelet defects formed in the Si(100) subsurface region and that the surface morphology was rough. Raman scattering revealed Si-H features at ∼2100 cm−1.
Double Beam Photoconductivity Modulation System and its Application to the Characterization of a Process of Photoresist Removal
Authors: Usami A. , Fujiwara H. , Nakai T. , Matsuki K. , Takeuchi T. , Wada T.
Published: March 2011

A laser/microwave method using two lasers of different wavelengths for carrier injection is proposed to evaluate near surface regions. These lasers are a He-Ne (wavelength=633nm, penetration depth=∼3μm) and a YAG lasers (wavelength=1060nm, penetration depth=∼500μm). Using a microwave probe, the amount of injected excess carriers can be detected. The carrier concentration is mainly dependent on the condition of the surface when carriers are excited by the He-Ne laser. It is mainly dependent on the condition of the bulk region when carriers are excited by YAG laser. We refer to microwave intensities detected by the He-Ne and the YAG lasers as the surface-recombination-velocity-related microwave intensity (SRMI) and bulkrelated microwave intensity (BRMI), respectively. We refer to the difference between SRMI and BRMI as relative SRMI (R-SRNI), which is closely related to the condition of surface and surface active region. We evaluate the near surface regions of the samples after plasma and wet etching for removing the photoresist layer. And we evaluate the near surface regions of the samples after a heat treatment which is done to recover the damage introduced by plasma etching. It is found that the R-SRMI method is better suited to near surface region evaluation than conventional lifetime measurements.
Sulfidation and Post-Sulfidatton Reactions on Gallium Arsenide
Authors: Yota J. , Burrows V. A.
Published: March 2011

Chemical treatment of GaAs with sulfur-containing compounds has been shown to improve GaAs surface electronic properties. There is still considerable controversy, however, regarding the chemical nature of the surface film which results from the sulfidation, and of the basis of the electronic improvement and of the decay in the improved electronic properties with time. We have investigated the surface chemistry of the chemical sulfidation treatment of GaAs with Na2S.9H2O and (NH4)2S. Using surface infrared reflection spectroscopy (SIRS) and x-ray photoelectron spectroscopy (XPS), we have studied the GaAs surface and its behavior with time after such treatments. Results show that both of these sulfidation treatments removed the chemical oxide of GaAs, leaving behind a thin film on the surface. XPS results show that the Ga-O and As-O peaks were removed after treatment and that As-S and no Ga-S peaks were formed. Infrared results show that the film deposited after Na2S.9H2O treatment slowly reacted in air to form sodium carbonate and rhombic sulfur. In addition, this film contains compounds with sulfur-oxygen bonds, which most likely were arsenic sulfate, sulfite, and thiosulfate salts. The film deposited on the (NH4)2Streated GaAs surface was identified as ammonium thiosulfate and slowly decomposed with time. Rinsing with water removed the thin film formed after either sulfidation treatment.
The Passivation of Gallium Arsenide Surfaces with Selenium from Gaseous Sources
Authors: Gu G. Y. , Ogryzlo E. A. , Wong P. C. , Mitchell K. A. R.
Published: March 2011

Two techniques were used to apply a thin layer of selenium to GaAs (100) surfaces: (a) the thermal decomposition of hydrogen selenide at 120°C, and (b) the deposition of gaseous selenium formed in the reaction of hydrogen atoms with H2Se. Angle dependent XPS measurements show that AsxSey, but not GaxSey, forms on the surface in both cases. This work therefore establishes a surface behavior for selenium on GaAs(100) which contrasts with that described earlier for sulfur on this surface.
S-Passivated InP Surfaces Prepared by (NH4)2S Treatments
Authors: Tao Y. , Yelon A. , Sacher E. , Lu Z.H. , Graham M.J.
Published: March 2011

S-terminated InP(100) surfaces which are chemically clean and stable were obtained by sulfide solution treatments. X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) were used to investigate the thermal and chemical stability of the surfaces. Schottky diodes based on S-passivated InP(100) wafers were used as test devices tostudy the surface electrical properties.
Science Issues Related to Wafer Cleaning in Silicon Technology
Authors: Liehr M.
Published: March 2011

This paper highlights a number of basic science issues related to wafer cleaning in silicon technology. Particle removal techniques, metal contamination, surface passivation, and integrated processing are used as key examples of areas of active research related to wafer cleaning. It is highlighted that wafer cleaning plays a far more significant role in device processing than just for contamination removal. However, even contamination removal faces formidable challenges such as the determination of safe contamination limits and the detection of trace amounts of contamination, all of which go well beyond the traditional realm of contamination control.
SHG(Second Harmonic Generation) in Reflection from GaAs Surfaces during Sulfur Passivation and Photochemical Washing Processes
Authors: Yamada Chikashi , Kimura Takahiro , Fuqua Peter
Published: March 2011

A passivation processes using Na2S and photochemical washing of GaAs (100) surfaces was studied in real time by a second-harmonic generation (SHG) technique. The intensities of surface-specific SHG signals were compared with those of photoluminescence (PL) signals. We found a remarkable similarity between the SHG and PL intensity changes during these processes. A band-bending model due to Fermi-level pinning at the surface has been applied in order to account for both the SHG and the PL intensity changes.
Texturing of InP Surfaces for Device Applications
Authors: Bailey Sheila G. , Fatemi Navid S. , Landis Geoffrey A.
Published: March 2011

A unique process for texturing InP (100) wafers by anisotropic etching has been developed. The process produces irregular V-grooves on the surface, which reduce the surface reflectivity. The process does not require photolithography or masking. The etching characteristics depend on doping, with etching tending to proceed more rapidly on the more heavily doped samples. Reduced reflectivity surfaces formed using this process can be applied to solar cells, photodetectors, and other optoelectronic devices.
Etching of Silicon (111) and (100) Surfaces in HF Solutions: H-Termination, Atomic Structure and Overall Morphology
Authors: Chabal Y. J.
Published: March 2011

HF etches silicon oxide, removes metal impurities and completely terminates the silicon surface with hydrogen. The H-passivated Si surfaces are stable, but can be slowly and selectively etched in buffered HF solutions or in hot water, changing the initial morphology of the interface. Si(111) surfaces flatten, forming large, ideally H-terminated (111) planes. Si(100) surfaces roughen, ultimately developing H-terminated (111) facets.
First-Principles Investigations of Hydrogen and Fluorine on Silicon Surfaces
Authors: Walle Chris G. Van De
Published: March 2011

State-of-the-art first-principles calculations allow detailed studies of the mechanisms by which hydrogen and fluorine interact with silicon. The results for hydrogen are presented in the form of an energy diagram which includes many different configurations. The theoretical values allow a discussion of issues such as hydrogen solubility, and desorption from a Si surface. For fluorine, we investigate the behavior as an interstitial impurity in the bulk, as well as Si-F interactions at or near the surface. A study of the insertion of F atoms into Si-Si bonds elucidates the microscopic mechanisms of etching, and the dependence of etch rate on doping. Thermodynamic aspects of HF etching are briefly discussed.
Scanning Tunneling Microscopy of HF-Controlled Si(111) Surfaces
Authors: Tokumoto Hiroshi , Morita Yukinori , Miki Kazushi
Published: March 2011

Scanning tunneling microscopy (STM) was made in order to examine the surface structure and roughness in an atomic scale. The surfaces were prepared by several ways: NH4F (pH = 8) dipping just after RCA cleaning or after keeping in dry air for a few weeks; dipping into NH4F (pH = 8) solution or dipping into solutions with pH=10 just after boiling in HNO3. The STM images clearly showed that the surface structure and roughness are dependent on the sample treatments. The smooth surfaces with less defects were obtained for surfaces prepared by removing the HNO3-oxidized layer by NH4F (pH = 8) dipping.
Surface Conditioning Issues Related to Patiterning and Etching
Authors: Fonash S.J. , Ditizio R.A. , Gu T. , Mikulan P.I. , Awadelkarim O.O. , Collins R.W. , Rembetski J.F. , Reinhardt K.A. , Chan Y.D.
Published: March 2011

Surface conditioning issues arising from pattern transfer utilizing plasma etching are discussed. Two situations are considered: one in which an oxide on a silicon substrate is exposed to a plasma etching environment and one in which a silicon substrate is exposed to a plasma etching environment. Both situations can lead to the need for surface conditioning and, in some cases, even 950°C, 30 min. furnace anneals or 1050°C, 26 sec. rapid thermal anneals can fail to restore surface and near-surface properties.
Silicon Surface Morphology and the Reaction of Silicon with Oxygen
Authors: Ross Frances M. , Gibson J. Murray
Published: March 2011

We discuss the measurement of the morphology of exposed surfaces and buried interfaces using plan view transmission electron microscopy techniques. We have observed the evolution of the silicon/oxide interface during both oxidation and oxygen etching of the Si (111) surface. We describe the interface morphology, the mechanisms of these oxidation reactions and the implications of these results for the processing of silicon surfaces.
Preliminary Post-Emplacement Safety Analysis of the Subseabed Disposal of High-Level Radioactive Waste
Authors: Kaplan Maureen F. , Koplik Charles M.
Published: March 2011

The radiological hazard from the disposal of high-level nuclear waste deep within the ocean sediments is evaluated, on a preliminary basis, for locations in the central North Pacific and in the northwestern Atlantic. Radionuclide transport in the sediment and water column and by marine organisms is considered. Peak doses to an individual are approximately five orders of magnitude below background levels for both places. Sensitivity analyses for several imporLant aspects of the post-emplacement systems model are described.