bluuebunny/crossref_metadata_2025 huggingface dataset:
Variation of Bandgap in Nanocrystalline Silicon as Monitored by Subgap Photoluminescence
Authors: Kalkan A. Kaan , Bae Sanghoon , Cheng Shangcong , Wang Yaozu , Fonash Stephen J.
Published: April 2011

Infrared PL from νc-Si and nc-Si thin films is a potential spectroscopic tool for sensitive diagnostics of structure and defects. Bhat et al. have shown that the dominant PL band found in νc-Si centered at 0.9 eV cannot be assigned to the amorphous phase, as the energeticaly similar defect band found in a-Si:H (i.e., at 0.9 eV) shows a different temperature dependence and is much broader (i.e., FWHM of 0.15 eV compared to 0.35 eV) [1]. Recently, Carius et al. have observed a gradual lower energy shift of the 0.9 eV PL down to 0.82 eV for nc-Si as the plasma deposition excitation frequency is increased with a corresponding decrease in FWHM from 0.15 0.12 eV, respectively [2]. However, a lower energy shift in optical absorption was not observed, nor did they look for a correlation with the variation of any other physical property. Here, we report a broader range of energy variation for PL from our ECR-PECVD deposited nc-Si films accompanied with an energy shift in optical absorption and variation in dark conductivity and crystallite size. It has been argued that this PL peak in question could arise from the radiative transitions between bandtail states as in the case of ∼1.3 eV PL in a-Si:H or it may be associated with structural defects [2,3]. Our observations support both possibilities.
X-Ray Sensing Properties of a Lead Oxide Photoconductor Combined With an Amorphous Silicon Tft Array
Authors: Brauers A. , Conrads N. , Frings G. , Schiebel U. , Powell M.J. , Glasse C.
Published: April 2011

We present first results on the performance of flat dynamic x-ray detectors (FDXD) based on arrays of amorphous silicon thin film transistors (TFT) with charge storage capacitances and lead oxide as x-ray photoconductor. In order to increase the “active area” of every pixel, the layout of the array has been made in a multilevel arrangement, where the charge collecting electrode is separated from the underlying electronics by a thick insulating layer. This allows for a geometrical overlap of the pixel electrodes and TFTs. PbO has been chosen as the x-ray sensing material due to its very high x-ray sensitivity. The relevant detector properties of evaporated PbO layers are described along with results obtained on first FDXD devices with PbO.
First Monolithic Tandem Photovoltaic-Powered Electrochromic Smart Window
Authors: Gao W. , Lee S.H. , Xu Y. , Morrison S. , Benson D.K. , Branz H.M.
Published: April 2011

We report on the first monolithic, amorphous-silicon-based, photovoltaic-powered electrochromic window coating. The coating employs a wide bandgap a-Sil-xCx:H n-i-p photovoltaic (PV) cell as a semitransparent power supply, and a LiyWO3/LiAlF4/V205 electrochromic (EC) device as an optical-transmittance modulator. The EC device is deposited directly on top of a PV device that coats a glass substrate.

The a-Sil-xCx:H PV cell has a Tauc gap of 2.2 eV and a transmittance of 60 to 80% over a large portion of the visible light spectrum. We reduced the thickness of the device to about 600 Å while maintaining a 1-sun open-circuit voltage of 0.9 V and short-circuit current of 2 mA/cm2.

Our prototype 16 cm2 PV/EC device modulates the transmittance by more than 60% over a large portion of the visible spectrum. The coloring and bleaching times of the electrochromic device are approximately 1 minute under normal operating conditions (±1 volt).
Band-Offset Determination for Intrinsic a-Si/ p+μc-Si or Intrinsic a-Si/n+νc-Si Heterostructure
Authors: Zhu Hong , Fonash Stephen J
Published: April 2011

The conduction band ΔEcand valance band ΔEv, off-sets at interfaces are critical parameters for device simulation. With the transport simulation code AMPS we demonstrate the possibility of using an analysis of the far forward I-V characteristics versus temperature for i- layer /n+or i-layer /p+hetero structures to obtain ΔEcor AE., respectively. For example, if one wants to extract AE, from experimental data for the interface a-Si/uc n+Si interface, we show this can be done using a metal/intrinsic a-Si:H/uc n+Si structure. With proper choice of the metal, the hole barrier height at the metal can be made large enough that the far forward current is only carried by electrons. We have found that, with the proper choice of structure thickness this far forward current can be controlled by ΔEcand not by space charge limited current. Unlike the work of Arnold et al [1], we have found that the choice of structure thickness is critical. In this case of an a-Si/uc n+structure this far forward current is actually controlled by ΔEC+ΔVnwhere ΔVnis the activation energy in the n+uc-Si layer. Since ΔVncan typically be ∼ 0.05eV in uc-Si, we see that ΔEcis essentially controlling this far forward current. To demonstrate the approach for the case of an a-Si/uc n+Si interface we consider different i-layer thicknesses.
Plasma Deposition of Silicon Clusters: A Way to Produce Silicon Thin Films With Medium-Range Order ?
Authors: Cabarrocas P. Roca i
Published: April 2011

The growth of hydrogenated amorphous silicon films is often explained by the arrival of SiHx radicals on the substrate and the subsequent cross-linking reactions leading to an homogeneous material which can be described by a continuous random network. Here we summarize our recent Work on a new class of silicon thin films produced under plasma conditions where silicon clusters and radicals contribute to the deposition. The main aspects are: i) silicon clusters with sizes of the order of 1-5 nm are easily formed in silane plasmas; ii) these silicon clusters can contribute to the deposition and lead to the formation of films with medium-range order (“polymorphous silicon”); iii) despite their heterogeneity, the films have improved transport properties and stability with respect to a-Si:H. The excellent transport properties are confirmed by the achievement of stable single junction p-i-n solar cells with efficiencies close to 10 %.
Investigation of the Electronic Transport in Pin Solar Cells Based on Microcrystalline Silicon by 2D Numerical Modeling
Authors: Zimmer J. , Stiebig H. , Wagner H.
Published: April 2011

We investigated the transport and recombination behavior of pin solar cells based on micro- crystalline silicon (μc-Si:H). A comparison of experimental and simulated data of the dark I/V- curves, the I/V-behavior under AM1.5 illumination as well as the quantum efficiency reveals an enhanced defect density in μc-Si:H compared to c-Si which could be located as defect rich grain boundaries around the crystallites. Further, in case there is amorphous phase in the material, the distribution of a-Si:H around the crystallites is unlikely, since the electronic transport properties are disturbed, whereas an arrangement in the shape of extended areas does not affect the transport behavior significantly due to occurrence of percolation.
Small-Signal Admittance of Forward-Biased a-Si:H p+-i-n+ Diodes by Time Domain Analysis
Authors: Lemmi F. , Johnson N. M.
Published: April 2011

In order to study the observed frequency variation of small-signal admittance of forward- biased amorphous silicon (a-Si:H) p-i-n diodes, we performed time-resolved measurements of currents induced by application of a small voltage step superimposed on a constant DC bias. The small amplitude ensures a linear behavior of the system under study. The transient current response includes all the details necessary to explain the stationary response to small sine-wave excitation. Details are obtained through a Fourier transform of the transient current. The real and imaginary parts of the resulting complex current are related to the capacitance and conductance spectra. This approach can explain phenomena taking place in the stationary regime such as negative capacitance values measured at low frequencies.

In the frequency domain, measured capacitances do show negative values, as well as a clear dependence on the applied forward bias voltage. Namely, higher voltages extend the region in which the phenomenon occurs to higher frequencies of the probe signal. In the time domain, all measured transient currents exhibit common features such as an initial decay after the displacement current and, for higher DC biases, a gradual increase. A physical explanation of the current transient is proposed which accounts for the dependence on applied DC bias. A mathematical model is used to show how a delayed increase in the current leads to a modulation of the capacitance and conductance in the frequency domain, the two being related to each other. This finally allows the comprehension of the observed frequency domain behavior.
Investigation of a-Si:H PH(1)N Color Detector Operation
Authors: Topiĉ M. , Smole F. , Furlan J.
Published: April 2011

Using numerical simulator, the operational principle of two-terminal a-Si:H based three-color detectors with the multi-layer multi-bandgap PIN or PIIiN structure is investigated. Two different approaches, which lead to bias-controlled three-color detection, are described and evaluated in terms of spectral response, rejection ratio, color suppression, illumination intensity and bias-light. For both PIIN and PIIN structure, bias-light dependence and intensity dependence is investigated. Numerical simulation results showed strong negative correlation between color separation and bias-light sensitivity. The importance of the transparent conducting oxide for the three-color detection limits is demonstrated.
Enhanced Crystallinity of Microcrystalline Silicon Thin Films Using Deuterium in Reactive Magnetron Sputter Deposition at 230°C
Authors: Gerbi J. E. , Voyles P. , Gibson J. M. , Abelson O J. R.
Published: April 2011

We analyze the formation kinetics and microstructure of hydrogenated vs. deuterated microcrystalline (μc-Si:H or D) thin films using real-time spectroscopic ellipsometry, post- deposition thermal hydrogen evolution, and TEM. The films are deposited by reactive magnetron sputtering of a silicon target in Ar (1.65 mT) with added partial pressures of H2or D2(0-5.5mT) on Coming 7059 glass substrates at 230°C. Amorphous films are deposited when PH2=0. When hydrogen is added to the chamber, the reactive magnetron sputtering process generates a flux of fast neutral H which promotes stc-Si growth. The substitution of D for H varies the kinetics of hydrogen reflection from the target and implantation into the growing film. We analyze the amorphous to microcrystalline transition as a function of the isotope (H2or D2) and pressure used in the deposition process. We find that the films enter the microcrystalline regime at lower D2pressures than H2pressures. Furthermore, the <ε2> data determined by ellipsometry have a different shape for deuterated films, compared to hydrogenated films at similar growth pressures. This indicates changes in band structure which we interpret as evidence for enhanced crystallinity.
Influence of Plasma Chemistry on the Properties of Amorphous (Si,Ge) Alloy Devices
Authors: Dalal Vikram L. , Maxson Tim , Haroon Sohail
Published: April 2011

We report on the growth and properties of a-(Si,Ge):H films and p-i-n solar cell devices prepared using a remote, low pressure ECR plasma deposition technique. The films and devices were prepared using either He or H2 as the diluent gas. The plasma conditions were controlled so as to induce significant ion bombardment during growth. We find that there is a dramatic influence of plasma chemistry on the growth and properties of a-(Si,Ge):H films and devices. In particular, with hydrogen as the diluent gas, changing the pressure in the reactor dramatically changes both the Germanium incorporation in the film, and the electronic properties. Lower pressures lead to less Ge being incorporated, and higher mobility-lifetime product for holes for a given Tauc gap, as well as better p-i-n devices. In contrast, changing the pressure when He is the diluent gas does not produce such large changes. We speculate that the changes in device and film properties are due to the influence of ion bombardment on growth chemistry, and that both efficient energy and momentum transfer to the growing surface are necessary to achieve the best devices. The differences between He and hydrogen may simply be due to the fact that He plasma is much more energetic than a comparable hydrogen plasma, and there is more efficient momentum transfer when He is used as compared to when hydrogen is used. We have also produced very good single junction a-(Si,Ge) devices using the ECR technique.
Silicon Clathrates: Synthesis and Characterization
Authors: Ramachandran Ganesh K. , Diefenbacher Jason , Sankey Otio F. , Sharma Renu , Marzke Robert F. , O'keeffe Michael , Gryko Jan , Mcmillan Paul F.
Published: April 2011

Two types of silicon clathrates, NaxSi136 (0≤ × ≤ 24) and Na8Si46 and a mixed clathrate (Na,Ba)Si46 were synthesized and characterized by X-ray diffraction, 23Na NMR and high resolution TEM. Systematic changes in X-ray diffraction intensities enabled the sodium content and site occupancy in the NaxSi136 series to be followed and then refined by Rietveld profile analysis. 23Na NMR spectra of Na8Si46 and NaxSi136 samples reveals two peaks with large paramagnetic shifts (1600-2000 ppm) for each phase, associated with the presence of Na atoms in two different environments. High resolution electron microscopy reveals the clathrate structures of these samples, and allows classes of defects to be characterized.
In-Situ Study of the Optoelectronic Properties of Very thin P-TYPE μc-Si:H Films and the Potential Profile at the p-(μc-Si:H)/i-(a-Si:H) Interface
Authors: Hamma S. , Cabarrocas P. Rocai
Published: April 2011

In-situ UV-visible ellipsometry and Kelvin probe measurements were performed to study the growth of boron-doped microcrystalline silicon (μc-Si:H) thin films and the band profiling at the p- (μc-Si:H)/i-(a-Si:H) interface. The in-situ UV-visible spectroscopic ellipsometry measurements, combined with dark conductivity measurements, performed at different stages of the growth show that p-type μc-Si:H formation can be achieved for a film thickness below 10 nm. These analyses also reveal that both the optical absorption, and the dark conductivity do not change significantly for a crystalline volume fraction above 50%. Moreover, the contact potential as measured by in- situ Kelvin probe shows a saturation just after the percolation threshold. These results indicate that highly crystallized doped layers are not necessary in device applications. From the Kelvin probe measurements, the potential profile through the p-(μc-Si:H)/ i-(a-Si:H) interface was measured. The microcrystalline silicon p-layers were successfully incorporated in single junction solar cells.
Scanning Tunnelling Microscopy Study of the Growth Mechanism for Hydrogenated Amorphous Silicon Produced by Plasma Enhanced Chemical Vapour Deposition
Authors: Flewitt A.J. , Milne W.I. , Robertson J. , Stephenson A.W. , Welland M.E.
Published: April 2011

Thin films of hydrogenated amorphous silicon (a-Si:H) have been deposited by plasma-enhanced chemical vapour deposition (PECVD), and the resulting topography measured in-situ on a nanometre scale using a scanning tunnelling microscope (STM). An island structure is observed on the surface of device quality a-Si:H, which can be quantitatively analysed using a one dimensional Fourier transform of the topography. Results suggest that deposition is limited by the creation of dangling bonds on the a-Si:H surface and not by the surface transport of SiH 3 radicals at the deposition temperature (598 K). Island nucleation takes place through the abstraction of hydrogen atoms from the a-Si:H surface by plasma etching and the subsequent attachment of an SiH 3 radicals to the available sites. A thermally activated hydrogen effusion process around the edge of each island, where the step edge causes a high local hydrogen concentration, then creates further dangling bonds which allow the islands to grow. A simulation has been constructed, which confirms this two stage mechanism.
Changes in Short- and Medium-Range Order in a-Si:H Induced by Light-Soaking, Pseudodoping and Doping With Boron
Authors: Golikova O.A. , Kazanin M.M. , Kudoyarova V.Kh. , Adriaenssens G.J. , Eliat A.
Published: April 2011

A study of a-Si:H structure on the scales of short- and medium- range order has been carried out by the Raman spectroscopy method. Undoped a-Si:H films were deposited by the conventional rf- PECVD with some special variations in the process conditions ( pseudodoping technique); doping with boron was performed from a gas phase as well as by ion implantation. Changes in short- and medium- range order induced by light-soaking, pseudodoping and doping with boron were determined and compared.
INTERFACE CHARACTERISATION AND INTERNAL ELECTRIC FIELD EVALUATION OF a-Si:H PIN SOLAR CELL BY VARIABLE ENERGY POSITRON ANNIHILATION SPECTROSCOPY
Authors: Zou X. , Chan Y. C. , Webb D. P. , Lam Y. W. , Chan F. Y. M. , Lin S. H. , Hu Y. F. , Beling C. D. , Fung S.
Published: April 2011

By means of the slow positron beam Doppler-broadening technique, the depth profile of microvoids across a p-i-n double junction solar cell has been resolved. VEPFIT fitting results indicate an approximately uniform density of the defects throughout the solar cell, but with an enhanced concentration at all of the interfaces possibly due to network mismatch. In order to evaluate the internal electric field, Variable Energy Positron Annihilation Spectroscopy (VEPAS) measurements have been performed on a single junction pin solar cell at different biases. The internal electric field effect on positrons has also been examined in terms of the bias dependence of positron drift in a-Si:H single junction pin solar cell.
Photoinduced Structural Changes in Hydrogenated Amorphous Silicon
Authors: Shimizu K. , Tabuchi T. , Hattori K. , Kida H. , Okamoto H.
Published: April 2011

Polarized electroabsorption method has been used to study photo-induced structural changes in hydrogenated amorphous silicon. The field-modulated absorption signal consists of two components, one of which is the true polarization-dependent electroabsorption serving as an indicator of the structural disorder, and the other is the thermoabsorption resulted from the temperature modulation due to Joule heating. The thermoabsorption component has removed from the observed field-modulated absorption signal to make an accurate and reliable evaluation of structural disorder by phase-separation procedure. As a result, about 15-25 % of the observed signal arises from the thermoabsorption effect for the Tauc gap region. Nevertheless, any essential alteration is not needed for our previous PEA results. The internal stress as well as density have been measured to provide another evidences for the photo-induced structural change. It is found that amorphous silicon film expands and the density tends to decrease upon light-exposure, the temporal behaviors of which coincide with that of the PEA ratio factor indicating disorderness of the amorphous network structure. The results permit us to conclude that a large scaled change in the amorphous network structure occurs under light-exposure, which might proceed the light-induced creation of metastable dangling bond defects.
Low Defect Density Microcrystalline-Si Deposited by the Hot Wire Technique
Authors: Mahan A. H. , Vanecek M. , Poruba A. , Vorlicek V. , Crandall R. S. , Williamson D. L.
Published: April 2011

The optical and electronic properties of a series of microcrystalline silicon (μ-Si) films, deposited by the hot wire (HW) technique, are reported. Preliminary results suggest, using moderate H2 /SiH4 dilution ratios and substrate temperatures (320°C), high filament temperatures, and no H gas purifier, that the subgap absorption for these films, measured using the constant photocurrent (CPM) method, can be as low as that obtained for films deposited by the very high frequency glow discharge (VHF-GD) technique. The film dark conductivities of the HW samples, ranging as low as 2.0 × 10−8 (ohm cm)−1, lend further credance to these low defect values. At the same time, the optical absorption in the region > 1.6 eV is higher than that previously observed for the VHF-GD deposited samples. The present results, discussed in the context of the film microcrystalline fraction, suggest that there is no unique, good quality, low defect density μ-Si material, and that different deposition techniques can be used to successfully deposit device quality gc-Si. We also present optical and structural data for films deposited at lower substrate temperatures and higher deposition rates, and suggest combinations of deposition parameters to be used that may further improve the electronic properties of these films.
The Effect of Hydrogen Dilution on Hot-Wire Thin-Film Transistors
Authors: Conde J.P. , Silva H. , Chu V.
Published: April 2011

Bottom-gate thin film transistors (TFT) were fabricated with amorphous and microcrystalline silicon active layers deposited by hot-wire (HW) chemical vapor deposition using different levels of hydrogen dilution. As the hydrogen dilution was increased above 80%, the active layer made a transition from amorphous to microcrystalline. This transition resulted in an increase of the TFT off-current and in an increase of the TFT subthreshold slope. The TFT on- current and the TFT mobility remained at levels comparable to those of the a-Si:H HW TFTs. A comparison is made between TFTs with amorphous and microcrystalline silicon active layers prepared both by rf glow discharge and HW. HW TFTs with an active layer consisting of a thin layer deposited with high hydrogen dilution underlying a thicker amorphous silicon layer are also compared to TFTs with an active layer of the same total active layer thickness consisting only of the high hydrogen dilution film.
Structural Characterization and Crystallization Process of Nanostructured Silicon Thin Films Produced in Low-Pressure Silane Plasma
Authors: Viera G. , Cabarrocas Proca i , Costa J. , Martínez S. , Bertran E.
Published: April 2011

Nanostructured silicon thin films (ns-Si:H), consisting of a two-phase mixture of amorphous and ordered material, were obtained by plasma-enhanced chemical vapor deposition (PECVD) under a wide range of plasma conditions. The key to embedding Si-ordered particles in the amorphous Si matrix was the formation of silicon clusters in the gas phase (diameter < 2nm) under conditions of plasma polymerization, and their incorporation into the growing films. The crystallization induced by thermal annealing in these nanostructured films can be attained faster than in conventional a-Si:H thin films, because the silicon-ordered particles cause a heterogeneous nucleation process in which they act as seeds for crystallization. In this work, we present a detailed structural characterization by using electron and X-ray diffraction patterns and Raman spectroscopy. The crystallization dynamics were studied in-situ by Raman spectroscopy.
Raman and Spectroscopic Ellipsometry Studies of P-Doped Poly-Si
Authors: Zollner Stefan , Liu Ran , Christiansen Jim , Chen Wei , Monarch Kathy , Lee Tan-Chen , Singh Rana , Yater Jane , Paulson Wayne M. , Feng Chris
Published: April 2011

Phosphorus-doped poly-Si films were studied with Raman spectroscopy and spectroscopic ellipsometry. We determine strain and grain size and compare with a structural analysis using plan-view transmission electron microscopy and atomic force microscopy. We analyze the derivatives of our ellipsometry data (peak shifts and broadenings) using analytical lineshapes, which are affected by grain size, film thickness, doping, and inhomogeneity, but only minimally by macroscopic biaxial strain.
Facetting Growth of Low Temperature Polycrystalline Silicon by Ecr-Cvd with Hydrogen Dilution Method
Authors: Hsiao H.-L. , Yang A.-B. , Hwang H.-L.
Published: April 2011

The polycrystalline silicon films with grain size of 1 μ m have been successful deposited on glass substrates using ECR-CVD with hydrogen dilution method at 250°C and without any thermal annealing. The deposited poly-Si films exhibit severe “hill and valley” surface roughness and facets structures. The X-ray diffraction spectra show that the dominant crystal textures are <220> and <111> orientations. The leaf-like two-fold symmetrical grain shape and the corresponding crystallography diffraction pattern indicate the orientation of largest grain is <110>. The dark field TEM image also shows the upside octahedral facets shape. Considering the effect of orientation on deposition rate and symmetry, the possible facets orientation should be <311>. Moreover, the grain sizes of poly-Si thin films deposited on bare Si wafer and on oxidized Si substrates or glass are almost the same. The facetting and textural structures can be attributed to the surface free energy change induced by the adatom quasi-liquid layer which is composed by the radicals and energetic atomic hydrogen. This adatom quasi-liquid layer would dramatically change the surface diffusion processes of adsorbed precursors and surface free energy of low index planes. Therefore, the SiHn radicals and SinHm molecular precursors with enhanced surface mobility would relax to their stable sites and form the crystalline silicon clusters.
Material Issues in the Commercialization of Amorphous Silicon Alloy Thin-Film Photovoltaic Technology
Authors: Guha S. , Yang J. , Banerjee A. , Sugiyama S.
Published: April 2011

Two significant developments took place in 1997 in the field of amorphous silicon alloy photovoltaic technology. First, a world record stable cell efficiency of 13% was demonstrated using a spectral-splitting, triple-junction structure. Second, a triple-junction photovoltaic manufacturing facility of an annual capacity of 5 MW was commissioned. In order to make the transition from R&D to production, critical material issues and deposition methods which ensure the lowest module cost per delivered watt needed to be evaluated. In this paper, we discuss some of these issues with special reference to the cell materials.
Low-Temperature, High-Quality Silicon Dioxide Thin Films Deposited Using Tetramethylsilane (TMS)
Authors: Reber D. M. , Fonash S. J.
Published: April 2011

Silicon dioxide thin films have been deposited at temperatures from 40°C to 250°C by plasma enhanced chemical vapor deposition (PECVD) using tetramethylsilane (TMS) as the silicon containing precursor. The properties of the PECVD TMS oxides (PETMS-Oxs) were analyzed with Fourier Transform Infrared (FTIR) transmission spectroscopy, BOE and P-etch rates and both current-voltage (I-V) and capacitance-voltage (C-V) electrical characterization. At both 130 °C and 250 °C, deposition conditions were identified which formed high quality as-deposited oxide films. Under the best conditions, unannealed Al/PETMS-Ox/c-Si capacitor structures displayed flat band voltages of Vfb = -2.5 V and breakdown fields (Vbd) in excess of 8 MV/cm. These PETMS-Ox films also show low leakage current densities <10-9 A/cm2 which can be maintained up to fields in excess of 4.5 MV/cm. The PETMS oxide electrical quality and process simplicity combine to make a very attractive oxide deposition technology for low temperature, large area applications.
a-Si:H Thin-Film Transistors on Rollable 25-µ;m Thick Steel Foil
Authors: Ma E.Y. , Wagner S.
Published: April 2011

We report the first amorphous silicon thin film transistors (TFTs) on flexible, ultra-thin substrates of 25 µm thick stainless steel foil. The transistors remain operational under convex or concave bending down to 2.5 mm radius of curvature. Taking advantage of the flexibility and resiliency of these devices, we have successfully fabricated TFTs using only xerographic toner masks printed directly on to the steel substrate and using mechanical alignment in the laser printer to obtain the necessary overlay accuracy. The goal of our work is to develop a foldable active-matrix transistor backplane, at low cost and high throughput, for use in highly rugged and portable applications such as foldable intelligent maps. Our results suggest that such foldable backplane circuits are feasible.
Low-Temperature Floating Plasma Oxidation of Poly-SiGe
Authors: Fan Zhineng , Zhao Gang , Chu Paul K. , Jin Zhonghe , Kwok Hoi S. , Wong Man
Published: April 2011

Abstractor

Low temperature oxidation is an essential process for thin-film transistors (TFT) used in active-matrix liquid crystal displays (AMLCD). However, low temperature oxidation gives rise to defects at SiO2/poly-SiGe interfaces. We have recently developed a novel plasma oxidation method for poly-SiGe materials. The poly-SiGe wafers are soaked in 0.1 Torr pure oxygen RF (Radio Frequency) plasma and isolated. That is, the sample voltage is the same as the sheath potential of the floating wall, which is always negative since electrons move faster than ions.The defects caused by ion impact can therefore be reduced. No heating is applied during oxidation, as the sample is heated slightly by the plasma. Under our conditions, the temperature is below 100°C even after oxidation for two hours. Depth profiles are acquired by AES and the oxide/substrate interface is examined by XPS. NMOS devices fabricated using this gate oxide show good characteristics.
Effect of Ni and Al on the Low-Temperature Field Aided Lateral Crystallization (FALC)
Authors: Park Sang-Hyun , Jun Seung-Ik , Lee Chan-Jae , Yang Yong-Ho , Choi Duck-Kyun
Published: April 2011

There have been many reports on the low temperature crystallization of amorphous silicon films by introducing a trace amount of metal impurity for low temperature poly-Si TFTs applications. MIC (Metal Induced Crystallization) uses various metals, to lower crystallization temperature. In this study, a new crystallization method called FALC (Field Aided Lateral Crystallization) in which an electric field is applied during the crystallization was explored. Among possible alloying elements with Si, Ni and Al were selected to compare the effects of these impurities on the FALC.

A trace of Ni lowered the crystallization temperature of a-Si down to 5001C and induced lateral crystal growth along the electric field into the metal free region. But Al exhibited no such effect. A new crystallization method, FALC, showed considerably enhanced speed of lateral crystallization and a strong preferred orientation in crystallized Si-films.
High Sensitivity Polymer Photosensors for Image Sensing Applications
Authors: Yu Gang , Wang Jian , McElvain Jon , Heeger Alan J.
Published: April 2011

Conjugated polymers and polymer blends were developed for photosensing applications. Large size photosensors fabricated in ITO/polymer/metal configuration show high photosensitivity, 0.1-0.4 A/Watt in visible and near UV, as good as that made with inorganic semiconductors. The processability of the polymeric materials allows these photosensors be made in large size, onto substrates in desire shape, or even in flexible form, hybridized or integrated with optical devices or electronic devices. Large area, full-color, digital image sensing is demonstrated using photodiode arrays made from semiconducting polymers. The photodiode arrays, fabricated by casting the semiconducting polymer from solution at room temperature, have high photosensitivity, low dark current and large dynamic range. Photo-detection with desired spectral response or multi-band selection are also demonstrated.
Production of Strontium Sulfide Coatings by Metal Organic Chemical Vapor Deposition
Authors: Moss T.S. , Dye R.C. , Tuenge R.T.
Published: April 2011

This work was focused on the MOCVD of the cerium-doped strontium sulfide (SrS:Ce) phosphor for use in thin film electroluminescent displays (TFELs). Following previous research on a small scale reactor, a feasibility scale-up using a commercially available reactor enlarged the size of the deposition area to a 4” diameter wafer or a 2” by 2” glass slide. Films were deposited from the reaction of Sr(thd)2, Ce(thd)4, and H2S at 450 °C and 5 torr. This system employed a liquid delivery system for the accurate and repeatable delivery of the metal organic reagents. The deposition from this reactor was shown to be crystalline-as-deposited SrS with a (200) orientation, possibly a result of the thin nature of the coating and the involvement of (200) grains in the initial nucleation process. The wafers showed good uniformity, but had some thickness variation near the outer radius of the wafer resulting from the addition of H2S from the outside edge. There were eighteen total deposition experiments, of which nine were characterized for EL performance. The highest brightness observed was 5 fL. The samples were exceedingly thin as a result of the fifteen fold increase in the surface area between the deposition reactors. Increasing the sample thickness to 7,000 Å or higher will dramatically increase the brightness of the emission.
Hybrid Amorphous and Polycrystalline Silicon Devices for Large-Area Electronics
Authors: Mei P. , Boyce J. B. , Fork D. K. , Anderson G. , Ho J. , Lu J.
Published: April 2011

Distinct features of amorphous and polycrystalline silicon are attractive for large-area electronics. These features can be utilized in a hybrid structure which consists of both amorphous and polycrystalline silicon materials. For example, an extension of active matrix technology is the integration of peripheral drivers for the improvement of reliability, cost reduction and compactness of the packaging for large-area electronics. This goal can be approached by a combination of amorphous silicon pixel switches and polysilicon drivers. A monolithic fabrication process has been developed based on a simple modification of the amorphous silicon transistor process which uses selective area laser crystallization. This approach allows us to share many of the process steps involved in making both the amorphous and polysilicon devices. Another example of the hybrid device structure is a self-aligned amorphous silicon thin film transistor with polysilicon source and drain contacts. The advantages of the self-aligned transistor are reduction of the parasitic capacitance and scaling down of the device dimension. With a selective laser doping technique, self-aligned and short-channel amorphous silicon thin film transistors have been demonstrated.
Enhanced Luminescence Properties of Pulsed Laser-Deposited Eu:Y2O3 Thin Film Phosphors Using Diamond Buffer Layer
Authors: Cho K.G. , Kumar D. , Lee D.G. , Holloway P.H. , Singh R.K.
Published: April 2011

Europium-activated yttrium oxide (Eu:Y2O3) phosphor films have been grown in-situ on (100) bare silicon and diamond-coated silicon substrates using a pulsed laser deposition technique. Diamond-coated silicon substrates were prepared by hot filament chemical vapor deposition on (100) silicon wafer. Measurements of photoluminescence and cathodoluminescence properties of Eu:Y2O3 films showed that the films grown on diamond-coated silicon substrates are brighter than the films grown on bare silicon substrates. The improved brightness of the Eu:Y2O3 films on diamond-coated silicon substrates is attributed to reduced internal reflection and enhanced scattering of incident beam with lattice. These effects are primarily brought about by the presence of a rough diamond buffer layer between the phosphor film and substrate. Oxygen environment during deposition is necessary for better crystallinity but excess oxygenation of the Eu:Y2O3 films during cooling degrades the brightness of the films.
Passivation of Poly-Si Thin-Film Transistors With Ion-Implanted Deuterium
Authors: Wang Albert W. , Saraswat Krishna C.
Published: April 2011

A comparison of ion-implanted deuterium and ion implanted hydrogen for passivation of grain boundary states in poly-Si thin film transistors (TFTs) is presented for the first time. Gate-drain bias stressing was carried out after anneals at 350 °C, 400 °C, and 450 °C. Under stress, deuterated TFTs are more resistant to bias stress than hydrogenated TFTs in terms of most PMOS performance parameters and NMOS leakage current, but are markedly less resistant to NMOS threshold degradation. While still showing promise, these results are not as impressive as those shown for hot carrier degradation in very large scale integration (VLSI) MOS devices. After 350 °C activation anneal, deuterium is less effective than hydrogen at initial device passivation, probably as a result of excessive implant damage. After anneals at 400 or 450 °C, deuterium becomes more effective at passivation than hydrogen, possibly due to differences in diffusion between hydrogen and deuterium.
Chimney-Shaped and Plateau-Shaped Gate Electrode Field Emission Arrays
Authors: Tarntair F. G. , Wang C. C. , Hong W. K. , Huang H. K. , Cheng H. C.
Published: April 2011

A triode structure of chimney-shaped field emitter arrays is proposed in this article. This triode structure includes the chimney-shaped emitter, thermal oxidation dioxide, and the plateau-shaped singlecrystalline silicon gate electrode. For the application of the matrix-addressable and large area flat panel display, the uniform structure of the emitters and the yield become critical manufacturing issues when attempting to control nano-meter size features. The uniformity and yield of the chimney-shaped emitters are very well controlled. The nano-sized gate-to-emitter separations can be created by the changing thickness of the insulator. The uniformity of the insulator and emitter material can be controlled within 3% which can be obtained by most large area thin film deposition tools, not by photolithography.
UHV STM of Cesium on Oxygenated Epitaxial Diamond (100) Films
Authors: Stallcup R.E. , Perez J.M.
Published: April 2011

The effects of Cs on oxygenated epitaxial diamond (100) films are studied using ultrahigh vacuum (UHV) scanning tunneling microscopy (STM). The epitaxial diamond (100) films are grown on synthetic diamond substrates using chemical vapor deposition and are boron doped. Before Cs deposition and oxygenation, UHV STM imaging of the epitaxial (100) films reveals a (2×l) dimer reconstruction. After Cs deposition and oxygenation, steps with relatively smooth surfaces are observed using positive tip voltages. Using negative tip voltages, many round bright structures approximately 20 Å in diameter are observed on the surface. We propose that these bright structures are Cs atoms or clusters of Cs atoms. Since these structures are only observed for negative tip voltages, they have a large number of empty states. Our observations are compared with recent theoretical predictions for Cs adsorbed on oxygenated diamond (100).
Field Emission Properties of Ion Beam Synthesized SiC/Si Heterostructures by MEVVA Implantation
Authors: Chen Dihu , Wong S. P. , Cheung W.Y. , Luo E.Z. , Wu W. , Xu J.B. , Wilson I.H. , Kwok R.W.M.
Published: April 2011

Planar SiC/Si heterostructures were formed by high dose carbon implantation using a metal vapor vacuum arc ion source. The variations of the field emission properties with the implant dose and annealing conditions were studied. A remarkably low turn-on field of IV/μm was observed from a sample implanted at 35 keV to a dose of 1.0×1018 cm−2 with subsequent annealing in nitrogen at 1200°C for 2h. The chemical composition depth profiles were determined from x-ray photoelectron spectroscopy and the surface morphology was observed by atomic force microscopy. The formation of a thin surface stoichiometric SiC layer and the formation of densely distributed small protrusions on the surface are believed to be the two factors responsible for the efficient electron field emission.
Theoretical Analysis of Fowler Nordheim Parameterization and RLC Characteristics for Ring Cathode Field Emitter Arrays for Next Generation RF Amplifiers
Authors: Jensen K. L.
Published: April 2011

Of all applications for which field emitter arrays (FEAs) are being designed, RF vacuum microelectronics is the most technically challenging application. The current density is typically three orders of magnitude larger than that required for displays (which require < 0.1 A/cm2). Due to their high current density capabilities and instant turn-on, FEAs may be a promising alternative to thermionic emitters for use in Inductive Output Amplifiers (IOAs). An analytical model of a field emitter is used to estimate Fowler Nordheim A and B parameters, effective resistance and capacitance of the array under several GHz modulation, signal propogation lengths, total current and current density, and effects of emitter non-uniformity on the basis of array geometry and materials. Estimates of inductance, resistance, and capacitance are made to estimate the drive power required to produce a bunched electron beam for Inductive Output Amplifier applications. An electronic efficiency of 32% with 15 dB gain may be possible from an array producing 260 mA peak, 71 mA average, current at 10 GHz using a TWT helix 1.51 cm long.
Nanoporous Silica For Low K Dielectrics
Authors: Ramos T. , Rhoderick K. , Roth R. , Brungardt L. , Wallace S. , Drage J. , Dunne J. , Endisch D. , Katsanes R. , Viemes N. , Smith D. M.
Published: April 2011

As integrated circuit sizes decrease below 0.25 microns, device performance will no longer improve at the same rate as for past generations because of RC interconnect delay which becomes significant as compared to the intrinsic gate delay. Parallel approaches to address this are to use a lower resistance metal (i.e., copper instead of aluminum) and to use a dielectric material with a dielectric constant significantly below that of dense silica (∼4). Recently, considerable progress has been made in development of thin films of nanoporous silica for these applications. Advantages include high thermal stability, small pore size, similarity to conventional spin-on deposition processes and spin-on glass precursors and final material (silica). The dielectric constant of nanoporous silica can be tailored between ∼1 and 3 which allows its’ implementation at multiple technology nodes in integrated circuit manufacture.

Recent development efforts have been focused on; 1) simpler and more reproducible deposition processes, 2) a more complete understanding of processing-property relationships for this material, 3) scale-up of manufacturing to yield a range of precursor products with stability for at least six months and very high purity, and 4) working with customers to integrate this material into both aluminum/gapfill and copper/damascene process flows. This paper targets several specific issues related to nanoporous silica use including water adsorption, pore size distribution control, processing at commercially viable throughputs, and obtaining thickness and dielectric uniformity across 200 mm wafers and wafer to wafer.
Dielectric Anisotropy of Organic Interlayer Dielectrics Confined in Submicron
Authors: Cho T. H. , Todd E. Ryan , Ho Paul S.
Published: April 2011

Dielectric anisotropy was studied using two fluorinated polymers(fluorinated polyirnide and fluorinated poly(aryl ether)), which are promising candidate as interlayer dielectrics(LLD). From the measurement of the optical anisotropy, the fluorinated polyimide has larger birefringence than fluorinated poly(aryl ether) because the fluorinated polyimide is a rigid rod-like polymer, while the fluorinated poly(arly ether) has an ether linkage to allow the flexibility. The large optical birefringence in the fluorinated polyimide may indicate the large dielectric anisotropy. The dielectric anisotropy of more flexible fluorinated poly(arly ether) was very similar to the expected anisotropy from optical birefringence, but the fluorinated polyimide with rigid rod-like chains has much smaller dielectric anisotropy than expected in the spin-coated film. From the FTLR spectra of the rigid rod-like polymer, the olecular orientation of the rod-like polymer confined in the submicron gaps is shown to be different from that of the blanket film spin-coated on the substrate. This change of the molecular orientation in the confined submicron gap is responsible for the change of the dielectric anisotropy.
A Novel Method to Determine The Mechanical Properties of Ultra-Thin Films.
Authors: White C. C. , Wu W. L.
Published: April 2011

Recent experimental results based on x-ray reflectivity[1, 2], and ellipsometry[3] have demonstrated that physical properties of polymer films thinner than one micron may deviate significantly from bulk values[4]. The mechanical properties of the ultra-thin films (sub-micron) are experimentally difficult to determine with precision. The quartz crystal microbalance is an established technique for measuring properties of polymer thin films of a few microns thick. [5–7] Recently this quartz crystal microbalance technique has been modified for measuring the mechanical properties of sub-micron polymer films with high precision. The details and preliminary results from this recently modified quartz crystal microbalance technique will be presented.
Process Integration issues for Interlevel Dielectric Materials for Sub-quarter Micron Silicon Integrated Circuits
Authors: Parihar Vijay , Singh R.
Published: April 2011

The continued miniaturization towards sub-quarter micron feature size mandates the search for low dielectric constant interlayer dielectric materials. A large number of materials and processing techniques has been suggested, but so far none of the proposed dielectric materials as well as processing techniques have been integrated into standard integrated circuit processing. In this paper, a new approach has been formulated for integration of low-k dielectric materials for future integrated circuits.
Electron Beam Processing for Spin-on Polymers and its Applications to Back-End-of-Line (BEOL) Integration
Authors: Yang J. J. , Gill J. , Kennedy J. , Wang S.-Q. , Forester L. , Ross M.
Published: April 2011

The versatility of e-beam processing provides the capability of tailoring the properties of spin-on polymers. Using different e-beam processing schemes, one can obtain a variety of films such as a homogeneous film with modified properties from the original, a film with variable properties as a function of depth, or a film having two distinct layers. In this paper, we demonstrated how to utilize this advantage of e-beam process to facilitate integration of spin-on polymers in the back-end-of-line manufacturing.
Low-Dielectric Constant SiO(F,C) Films for ULSI Interconnections Prepared by CF4 Plasma Ion Implantation
Authors: Zhou Yuanzhong , Qin Shu , Chan Chung , Chu Paul K.
Published: April 2011

Plasma ion implantation (PII) doping technique has been utilized to prepare a new lowdielectric constant (low k) material SiO(F,C). Fluorine and carbon were implanted into SiO2 films by CF4 PII using an ICP plasma reactor. The effective dielectric constant of the films was significantly reduced after PH doping. An analysis of a double layer model indicated that a high quality dielectric layer with a dielectric constant down to 2.8 can be achieved by an optimized PII process. Contrasting to other conventional low-k material techniques, PII process also improved bulk resistivity and electrical field breakdown strength. The improvement possibly resulted from adding carbon into the films. The etching effect of CF4 PII could be beneficial to planarization and gap filling of dielectric interlayer.