bluuebunny/crossref_metadata_2025_split huggingface dataset:
High-Bandgap a-SI:H Deposited by Concentric-Electrode rf Glow Discharge
Authors: Conde J.P. , Lau F. , Chu V. , Chan K. K. , Blum J.M. , Arienzo M. 
Published: March 2011

ABSTRACTHydrogenated amorphous silicon (a-Si:H) with Tauc's optical bandgap (Eopt) between 1.7 and 2.1 eV was deposited at room-temperature by concentric-electrode plasma-enhanced chemical vapor deposition (CE-PECVD). The variation of Eopt was achieved by varying the flow of silane, without hydrogen dilution. The increase in Eopt results from an increase in the hydrogen concentration in the film from 7 to 15%. The photoconductivity shows a monotonie decrease with increasing Eopt and is 10'-7 Scnr-1 for the 2.1 eV sample. The Urbach energy (Eu) is observed to increase sharply with increasing Eopt, while the subgap defect (Ns) density remains approximately constant.
Comparative Study of the Optical and Vibrational Properties of a-SiNx:H Films Prepared from SiH4-N2 and SiH4-NH3 Gas Mixtures by rf Plasma
Authors: Campmany J. , Bertran E. , Andújar J.L. , Canillas A. , López-Villegas J. M. , Morante J.R. 
Published: March 2011

ABSTRACTThe properties of amorphous silicon nitride films (a-SiNx:H) prepared by PECVD from SiH4-NH3 and SiH4-N2 gas mixtures have been determined by spectroscopie ellipsometry and FTIR spectroscopy as a function of the nitrogen concentration measured by XPS. The films are transparent for silane ratios [SiH4]/([SiH4] + [NH3]) < 20% and [SiH4]/([SiH4] + [N,]) < 1.5%. The refractive index shows a wide range of progressive variation from 3.2 for high silane concentrations to 1.8 for low silane concentrations. The hydrogen content of the low-absorbing films has much lower values for those obtained by SiH4 + N2 plasma than for those obtained by SiH4 + NH3 plasma. The results are discussed in terms of growth models of PECVD a-SiNx:H films from SiH4-NH3 and SiH4-N2 mixtures.
Investigation of Hydrogen and Nitrogen Thermal Stability in PECVD a-Sinx:H.
Authors: Fitzner M. , Abelson J.R. , Kanicki J. 
Published: March 2011

ABSTRACTWe study the high temperature (≤1300°C) thermal evolution from hydrogenated amorphous silicon nitride (a-SiNx:H) films prepared by plasma enhanced chemical vapor deposition. Two principle peaks are found, one at 525–750°C associated with hydrogen release, and one at ≥950°C from hydrogen and nitrogen release. In nitrogen-rich films (x>4/3), the low temperature (525°C) peak intensity is smaller compared to silicon-rich films (x≤4/3), implying that hydrogen is more thermally stable in N-rich films. Helium dilution during film growth further reduces the low temperature peak intensity, producing the most thermally stable N-rich material, with the onset of hydrogen evolution occurring at ∼600°C. For a nitrogen-rich film, high temperature hydrogen evolution began at ∼900°C and was accompanied by nitrogen evolution starting at ∼950°C. UV-illumination of N-rich samples prior to thermal evolution produced no observable changes in the evolution spectra.
Percolation Behaviour in the Electrical Characteristics of Hydrogenated Amorphous Silicon Nitride Films.
Authors: López-Villegas J.M. , Garrido B. , Benrakkad M.S. , Samitier J. , Bertran E. , Canillas A. , Morante J.R. 
Published: March 2011

ABSTRACTThe electro-optical properties of hydrogenated amorphous silicon nitride films (a-SiNx:H) prepared by rf glow discharge of SiH4 and N2 have been determined as a function of the silicon content in the alloy. The stoichiometry and structure of the layers have been studied by ellipsometry, infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Two different electrical behaviours have been found. The samples with x>0.8 show conductivity based on the Frenkel-Poole mechanism, while the samples with x<0.8 show quasi-ohmic conductivity. Both kinds of conduction and the transition between them are analyzed in the framework of the percolation theory. In this context, the correlation between the stoichiometry and structure of the layers with their electrical behaviour indicate that the transition from the Frenkel-Poole to the quasi-ohmic conduction is a consequence of the formation of conducting paths as the percolation threshold of Si-Si bonds is reached.
Photoluminescence in Nitrogen-Rich a-SiNx:H
Authors: Chen D. , Viner J.M. , Taylor P.C. , Kanicki J. 
Published: March 2011

ABSTRACTWe report the measurement of photoluminescence (PL) from nitrogen-rich hydrogenated amorphous silicon nitride (a-SiN1.6:H) films. Excitation at 4.8 eV gives a PL spectrum of approximately Gaussian lineshape centered at 2.9 eV with a full width at half maximum of 1.4 eV. The PL intensity at 2.9 eV fatigues under continuous 4.8 eV excitation, but may be restored by thermal annealing or photobleaching with light of energy ≥ 2 eV. For emission at 2.9 eV, the PL excitation spectrum in the range 3.0 to 5.2 eV follows the a-SiN1.6:H film optical absorption edge at low energy and then decreases with a maximum at approximately 5.4 eV. The PL results are discussed within the framework of a negative effective electron-electron correlation energy (negative Ueff) for the dominant defect (silicon atom bonded to three nitrogen atoms).
Simulation of Steady State and Transient Phenomena in a-Si:H Pin Structures and Films
Authors: Brüggemann Rudi , Main Charles , Bauer Gottfried H. 
Published: March 2011

ABSTRACTIn this paper we report on a range of simulation studies. The transient photocur-rent decay after switching off of steady illumination is investigated and we show that the protracted decay in undegraded pin-solar cells is a hole current. In degraded pin samples a change of sign in the photocurrent during the decay is observed by simulation (as is experimentally) which is attributed to an electron diffusion current in reverse direction. We study the distribution of defects according to the defect pool model in a pin structure. The varying dangling bond density with position of the Fermi level leads to large inhomogeneities in defect density across the i-layer in thermal equilibrium leading to increased band bending and giving increased recombination close to the interfaces under illumination. As a demonstration of another application of the simulation method we show how the quasi-steady state is established in the steady state photocarrier grating experiment in lock-in technique.
Photomking Determination of Mobility and Lifetime in Intrinsic a-Si:H
Authors: Tang Yi , Braunstein R. , Roedern Bolko Von 
Published: March 2011

ABSTRACTA photomixing technique was employed to determine the lifetime and the mobility in intrinsic a-Si:H, by measuring the power of the beat frequency in conjunction with the dc. photocurrent. Both the mobility and lifetime were found to decrease continuously following the light-soaking process, which indicates the existence of long-range potential fluctuations and a change in the recombination processes due to light-soaking. For the first time, evidence is provided that degradation is accompanied by loss of mobility, a fact that is neglected in all prevailing models for the Staebler-Wronski effect. Intrinsic a-Si:H samples produced by glow-discharge deposition and the hot wire technique were employed in this work.
Experimental Determination of the Dark Fermi Level in Hydrogenated Amorphous Silicon.
Authors: Dawson R.M. , Nag S. , Gunes M. , Wronski C.R. , Bennett M. , Li Y.M. 
Published: March 2011

ABSTRACTThe position of the dark fermi level in hydrogenated amorphous silicon (a-Si:H) is important in determining its electrical properties and is a key parameter in the detailed modelling of materials and devices. The activation energies of conductivities have been investigated on intrinsic a-Si:H films from various laboratories where the slopes of the Arrhenius plots have ranged from 0.27 eV to 0.87 eV. In many cases, marked differences are found between the results obtained from two and four probe measurements, highlighting the importance of the four probe configuration. Results are presented which help to explain the scatter in the measured activation energies between intrinsic films of a-Si:H. Differences in the activation energies are discussed in terms of current limiting processes which act in series with the material bulk resistance. It will be shown that the conductivity of the film and the contact are key factors in assessing whether the position of the fermi level can be accurately determined from a two contact measurement.
Transient Versus Steady State Measurements on the Transport Properties of a-SI:H Films
Authors: Vieira M. , Martins R. , Fortunato E. , Soares F. , Guimarães L. 
Published: March 2011

ABSTRACTTransient and steady-state measurements of the ambipolar diffusion length (L*) in undoped a-Si:H films have been carried out through Flying Spot Technique (FST) and Spectral Photovoltage Technique (SPT) using either Schottky or pin structures. The FST is based on the photovoltage response of a monochromatic light that moves with a constant velocity in the interface direction, while in SPT the optical excitation is achieved by changing the absorption coefficient of the incident light and so, the light depth penetration. In FST the additional photo-effect due to the light spot movement allows to infer separately L* and the effective lifetime, (τ*) while in SPT the curve shape of the spectral response allows to estimate the interface behavior and L*. The obtained results reveal that the transient measurement is useful for determining the transport properties of the bulk while the steady technique seems to be more useful to infer the role of the interface on device performances. Limitations of the above techniques will also be reported.
Subband Recombination in a-Si:H
Authors: Gu S.Q. , Taylor P.C. 
Published: March 2011

ABSTRACTPhotoluminescence (PL) in a-Si:H has been studied as a function of excitation energy from above the gap down to well below the gap. Although the width of the PL peak shows no strong dependence on the excitation energy at low temperatures, the low energy tail of bandtail PL exhibits an approximately exponential drop with decreasing energy, I ≈ exp(hν/δE), where δE increases with decreasing excitation energy for excitation energy below about 1.65 eV. This behavior is attributed to the slow downward hopping of holes in the valence band tail that are generated below a thermalization threshold at low temperatures.
Free Carrier Lifetime in a-Si,Ge:H Alloys
Authors: Young D.A. , Fauchek P.M. , Liu Y.M. , Nighan W.L. , Fortmann C.M. 
Published: March 2011

ABSTRACTThe lifetime of carriers injected optically in the extended states of amorphous silicon-germanium alloys has been measured by time-resolved pump and probe optical techniques using either a femtosecond dye laser or a picosecond free electron laser. When Ninj > 1018 cm-3, the lifetime of the carriers is in the picosecond time domain. Our results are comparable to what we have observed previously in a-Si:H and very recently in a-Si,C:H. There are two lifetime regimes: at high densities, the recombination is bimolecular and nonradiative, whereas at lower densities, the recombination tends to be monomolecular but still nonradiative. The origin of these lifetimes is discussed.
Characterization of Arsenic-Implanted Amorphous Silicon
Authors: Knoch Lynnita , Theodore N. David , Tam Gordon , Pennell Ron 
Published: March 2011

ABSTRACTIn this study, amorphous silicon and polycrystalline silicon films were implanted with arsenic and subjected to varied low temperature (<900°C) anneal conditions and characterized using TEM. The microstructure is of interest for later correlation with electrical measurements. The amorphous deposition produces larger, more irregular grains with more strain than does the polysilicon deposition for a single-step rapid thermal anneal (RTA) cycle. This can be explained by the number of critical nucleii and the rate of grain growth. The sheet resistivity, as measured by four-point probe, correlates to the deposition conditions. A two-stage anneal makes the grains less irregular by reducing the roughness of the grains and decreasing the strain in the grains. For a given deposition condition, the final microstructure is most strongly influenced by the first anneal. The second anneal produces no clear change in grain size. 800°C anneals result in larger grains than 900°C anneals. This is explained by the presence of less critical nucleii for 800°C anneals. In comparing short and long durations of RTA, the short duration produced slightly larger grains than the long duration RTA due to greater nucleation in the longer RTA wafers. In the case of RTA versus furnace anneals, RTA produces larger, more irregular grains, with more strain in the grains. A model in terms of the size of critical nucleii is used to explain the difference.
Tunneling Spectroscopy of Amorphous Semiconductors
Authors: Wen J. , Kakalios J. 
Published: March 2011

ABSTRACTThe tunneling transmission coefficient as calculated by the WKB and the multi-potential approximation (MPA) is compared for tunneling through an a-Si:H/a-SiNx:H double barrier structures. The MPA method leads to shifts in the location of the quantum well states, which complicates the interpretation of quantum size effects in amorphous silicon multilayers. Experimental studies of tunneling currents through a-Si:H/a-SiNx:H single barrier structures are presented. At low temperatures the conductance data resembles tunneling data for metal/insulator/metal structures with an asymmetric barrier, while at room temperature a pronounced peak is observed in the conductance-volatge characteristics.
Improvement in Wide-Gap A-SI:H For High-Efficiency Solar Cells
Authors: Tsuge Sadaji , Hishikawa Yoshihiro , Okamoto Shingo , Sasaki Manabu , Tsuda Shinya , Nakano Shoichi , Kuwano Yukinori 
Published: March 2011

ABSTRACTA hydrogen-plasma treatment has been used for the first time to fabricate wide-gap, high-quality a-Si:H films. The hydrogen content (CH) of a-Si:H films substantially increases by the hydrogen-plasma treatment after deposition, without deteriorating the opto-electric properties of the films. The photoconductivity (σph) of ≥ 10-5 ο-1 cm-1, photosensitivity ( σ ph/σ d) of > 106 and SiH2/SiH of <0.2 are achieved for a film with CH of ∼25 atomic >%. The optical gap of the film is > 1.70 eV by the (α h ν )1/3 plot, and is >2 eV by the Tauc's plot. The open circuit voltage of a-Si solar cells exceeds 1 V conserving the fill factor of > 0.7 when the wide-gap a∼Si:H films are used as the i-layer, which proves the wide band gap and low defect density.
Electron Transport in a-Si1-xGex:H Solar Cells
Authors: Wang Qi , Antoniadis Homer , Schiff E. A. , Guha S. 
Published: March 2011

ABSTRACTWe report a study of the correlation between solar cell parameters and electron transport parameters in a series of a-Si1-xGex:H alloys with bandgaps spanning the range 1.42 – 1.72 eV. Fill factors and open circuit voltages were measured in p-i-n solar cells with 0.32 μm thick i-layers. The electron drift mobility and deep-trapping mobility-lifetime product were measured using transient photocurrent techniques on p-i-n cells with thicker i-layers. The open circuit voltage tracked the bandgap accurately. Both the electron drift mobility and the deep-trapping mobility lifetime product correlated reasonably well with the fill factor measured with illumination absorbed near the p-i interface. We present a discussion of the relationship of the fill factor to these transport parameters.
Kinetics of Light-Induced Degradation of a-Si:H Solar Cells Compared to I-Layer Films
Authors: Li X.R. , Wagner S. , Bennett M. , Fonash S. 
Published: March 2011

ABSTRACTWe report the CPM defect density of a-Si:H material and the performance characteristics of pin solar cells during high-intensity light-soaking. In one group of experiments we compared the effects of soaking with monochromatic light from a Kr+ laser to white light from a Xe arc lamp. The effects are identical for the same electron-hole pair generation rate. In a second group of experiments we light-soaked at the two different temperatures of 50°C and 90°C. At 90°C the defect density saturates at a lower value than at 50°C, and correspondingly the cell performance parameters saturate at higher values.
Effect of Interface and Surface on the Performance of a-Si:H TFTs
Authors: Jang Jin , Jung Moon Youn , Yoo Sun Sung , Song Hyon Kyun , Jun Jung Mok 
Published: March 2011

ABSTRACTWe have studied the effects of interface and surface on the performance of hydrogenated amorphous silicon(a-Si:H) thin film transistors. The effects of rf power, the buffer layer between the gate insulator and a-Si:H, and the surface oxidation on the performance on the a-Si:H TFTs have been investigated. By introducing suitable buffer layer, we can increase the mobility up to 2.1 cm2/Vs. The surface oxidation gives rise to the electron accumulation near the surface.
Work Function Difference Between N-Type μc-Si Gate Electrodes Deposited by Remote Pecvd and P-Type c-Si Substrates in Mos Capacitors
Authors: Lee D.R. , Lucovsky G. 
Published: March 2011

ABSTRACTWe have used remote PECVD to deposit highly-doped μc-Si films for use as gate electrodes in MOS capacitors. The flatband voltages of capacitors with different oxide thicknesses have been measured by high-frequency capacitance-voltage and have been used to determine the work function difference between an n-type μc-Si electrode and a p-type c-Si substrate. This value for ϕμs is discussed in terms of a band diagram for the stacked-gate MOS device, and is compared to the expected value.
An Investigation of a-Si:H Thin Film Transistors by A Comparison of Transient Measurements and Numerical Simulations.
Authors: Willums M.F. , Hack M. , Lecomber P.G. , Shaw J. 
Published: March 2011

ABSTRACTTransient measurements of the source-drain current ISD of amorphous silicon (a-Si:H) thin film transistors are compared with the results of two dimensional simulations. In particular, we have investigated the effect of different amorphous silicon layer thicknesses on the transient response. It is found that the dynamic response of a transistor with 0.4 μm a-Si:H is significantly slower than that of a device with only 0.06 μm of a-Si:H.
Cleaning Procedures for UHV Cluster-tool MOS Fabrication
Authors: Sofield C J , Murrell M P , Sugden S , Heyns M , Verhaverbeke S , Welland M E , Golan B , Barnes J 
Published: March 2011

ABSTRACTWe have investigated the effect on a silicon surface of both wet chemical and cluster-tool UV/ozone cleaning, prior to UHV processing to fabricate MOS test structures. The physical and chemical condition of the Si surface has been examined by Scanning Tunnelling and Atomic Force Microscopy (STM, AFM) and Medium Energy Ion Scattering (MEIS). After MOS fabrication some of the structures were examined by Cross-sectional Transmission Electron Microscopy (TEM). The electrical performance of the MOS test sets were characterized by breakdown voltage measurements.We have found correlations between the electrical performance of the MOS devices, the structure of the Si surface prior to oxidation, and the details of the UHV fabrication technique. In particular any MOS device fabricated on a Si surface thermally cleaned in UHV prior to oxidation has a poor breakdown strength. We have found that this is the result of the formation of silicon carbide on the Si surface at high temperature and the subsequent local disruption of the oxidation step of MOS fabrication by the SiC. A UHV cleaning procedure has been developed to avoid this C contamination problem.
Chemical Structure of Native Oxide Grown on Hydrogenterminated Silicon Surfaces
Authors: Takakura M. , Yasaka T. , Miyazaki S. , Hirose M. 
Published: March 2011

ABSTRACTChemical bonding features and suboxide compositions in native oxide grown on chemically-cleaned hydrogen-terminated Si(100) surfaces stored in pure water have been studied by using surface sensitive infrared spectroscopy and x-ray photoelectron spectroscopy. The LO phonon peak for the native oxide is located at 1210cm−1, which is shifted to a significantly lower wavenumber side than the ultrathin thermal oxide peak at 1250cm−1. This is because an appreciable amount of SiHx bonds are incorporated in the native oxide/Si interface and such hydrogen termination in the network dramatically reduces strained bonds in the interface. Very weak Si2+ suboxide signal from the oxide grown in pure water is also explained by the incorporated SiHx bonds which interrupt the Si2+ suboxide formation in the interface.
Pre-oxidation Silicon Cleaning and its Relation to MOS Reliability and Process-Induced Damage
Authors: Kasi S. R. , Rubloff G. W. , Cohen S. A. , Hsia L. C. 
Published: March 2011

ABSTRACTMaterial and device reliability issues play a critical role in the choice of materials and processing options for ULSI technology and manufacturing. Recently, chemical surface treatments (e.g., fluorine incorporation, nitridation) have been shown to benefit MOSFET gate dielectric reliability. This paper describes the impact of different pre-oxidation chemical surface treatments on the reliability characteristics of MOS structures by using a combination of x-ray irradiation and electrical stress-induced charge injection techniques. X-ray irradiation at 1-2 keV increases oxide-trapped charge and the density of interface states substantially (80-800X), but these changes depend significantly on the chemistry of pre-oxidation cleaning. Furthermore, the specific surface treatment strongly affects subsequent device reliability; MOS degradation is up to 5X lower when fluorine-based surface pre-cleaning is used.
Spectroscopic Ellipsometric Analysis of Surface and Subsurface Damage in Chemical-Mechanical Polished Semiconductors
Authors: Xiong Yi-Ming , Snyder Paul G. 
Published: March 2011

ABSTRACTSpectroscopic ellipsometry (SE), with the added capability of variable angle of incidence, is a sensitive technique for nondestructive surface and interface analysis. In this work, we demonstrate the application of this technique to the quantitative characterization of surface and subsurface damage in Si and GaAs, induced by conventional chemical-mechanical polishing. We show that the optimum selection of angle of incidence and spectral range is of crucial importance for detecting and evaluating surface and subsurface quality. To adequately describe the measured SE data, a two-layer model (i.e. oxide overlayer/subsurface damage layer/substrate) was found to be necessary. In this model, the oxide overlayer and subsurface damage layer were each modeled as a simple physical mixture of the chosen constituents, using the Bruggeman effective medium approximation. SE analysis clearly indicated the presence of surface microscopic roughness and subsurface damage for all the samples investigated. Typical results for thickness were 2 to 3 nm of surface overlayer, and 15 to 40 nm of damage beneath it, containing about 1 ∼ 2% volume fraction of either oxide or voids. As verification, atomic force microscopy (for surface characterization) and wet chemical oxide stripping (for subsurface analysis) were used to substantiate the SE results.
In Situ Control of Native Oxide Growth for Semiconductor Processes
Authors: Morita Mizuho , Ohmi Tadahiro 
Published: March 2011

ABSTRACTIn situ control methods of native oxide growth on Si surfaces at room temperature and during the temperature ramp-up are proposed for metal/Si contact formation, lowtemperature Si epitaxy, and very-thin thermal oxide film formation, based on analyses of factors dominating the oxide growth. Low-resistance W/Si contacts are formed by N2 gas sealed processing of HF cleaning right before W chemical vapor deposition(CVD). Highquality epitaxial Si films are grown at a low temperature of 550°C using Si2H6 molecular flow pre-showering to suppress the oxide growth caused by water or oxygen in a CVD reactor. Very thin gate oxide films with high insulating performance are realized by the preoxidation step at 300°C to form one-molecular-layer oxide for passivation and by the subsequent temperature ramp-up step in ultraclean Ar gas to prevent oxide growth and an increase of surface microroughness before the thermal oxidation step.