bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectral Response and Loss Mechanisms in Amorphous Silicon Solar Cells Determined by Photothermal Deflection Spectroscopy
Authors: Höhne N. , Carius R. , Wagner H.
Published: April 2011

A new method to analyse the optical and thermal losses in amorphous silicon solar cells is presented. It is demonstrated that PDS measurements can provide important information on the losses that limit the performance of such cells. The major advantage of the method presented is the ability to determine parameters which are not accessible by other methods, i.e. the reflection, absorption without carrier separation, thermalization and losses in p- and n-layer, field losses, recombination and electrical gain of the solar cell under operating conditions. The method can be applied to thin film solar cells of all kinds complementary to DSR which can also be measured in the same set-up. Eliminating some experimental difficulties could lead to a new comprehensive and complementary characterisation method of solar cells of all kinds.
a-Si:H Thin Film Transistors on Rollable 25-μM 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.
Thin Film Poly-Si Solar Cell on Glass Substrate Fabricated at Low Temperature
Authors: Yamamoto Kenji , Yoshimi Masashi , Suzuki Takayuki , Tawada Yuko , Okamoto Yoshifumi , Nakajima Akihiko
Published: April 2011

The performances of thin film poly-Si solar cells with a thickness of less than 5 μm on a glass substrate have been investigated. The cell of glass / back reflector / n-i-p type Si / ITO is well characterized by the structure of naturally _surface texture and enhanced absorption with a back reflector (STAR), where the active i-type poly-Si layer was fabricated by plasma chemical vapor deposition (CVD) at low temperature. The cell with a thickness of 2.0 μm demonstrated an intrinsic efficiency of 10.7% (aperture 10.1%), the open circuit voltage of 0.539 V and the short current density of 25.8 mA/cm2 as independently confirmed by Japan Quality Assurance. The optical confinement effect explains the excellent spectral response at long wavelength for our cells through the PCID analysis. The higher sensitivity at long-wavelength of our cell appeared in quantum efficiency curves is well correlated to the result of reflectance measurement. The efficiency of 9.3% cell with a thickness of 1.5 pm was proved to be entirely stable with respect to the lightsoaking. Based on the result of various evaluation of diffusion length, it is postulated that the low temperature poly-Si prepared by plasma CVD gives a device quality of poly-Si film.
Optical Properties Of Si Nanocrystals Formed In Si02 By Ion Implantation
Authors: White C. W. , Withrow S. P. , Meldrum A. , Budai J. D. , Hembree D. M. , Zhu J. G. , Henderson D. O. , Prawerttt S.
Published: April 2011

Si nanocrystals formed in SiO2 by high-dose ion implantation and annealing give rise to strong optical absorption and intense photoluminescence (PL). The dose dependence of optical absorption provides evidence for size-dependent quantum confinement in the Si nanocrystals. PL peak energies are nearly independent of dose suggesting that surface or interface states play an important role in PL. Estimates of absorption bandgaps in the nanocrystals are given.
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. , Hack M. , Lujan R.
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 shortchannel amorphous silicon thin film transistors have been demonstrated.
Transistors with a Profiled Active Layer Made by Hot-Wire Cvd
Authors: Meiling H. , Brockhoff A.M. , Rath J.K. , Schropp R.E.I.
Published: April 2011

In order to obtain stable thin-film silicon devices we are conducting research on the implementation of hot-wire CVD amorphous and polycrystalline silicon in thin-film transistors, TFFs. We present results on TFTs with a profiled active layer (deposited at ≥9 Å/s), and correlate the electrical properties with the structure of the silicon matrix at the insulator/semiconductor interface, as determined with cross-sectional transmission electron microscopy. Devices prepared with an appropriate H2 dilution of SiH4 show cone-shaped crystalline inclusions. These crystals start at the interface in some cases, and in others exhibit an 80nm incubation layer prior to nucleation. The crystals in the TFTs with the incubation layer are not cone-shaped, but are rounded off. The hot-wire CVD deposited devices exhibit a high fieldeffect mobility up to 1.5 cm2V−1s−l. Also, these devices have superior stability upon continuous gate bias stress, as compared to conventional glow-discharge α-Si:H TFTs. We ascribe this to a combination of enhanced structural order of the silicon and a low hydrogen content.
Guide for Low-Temperature and High-Rate Deposition of Device Quality Poly-Silicon Films By Cat-Cvd Method
Authors: Heya Akira , Nakata Kazuhisa , Izumi Akira , Matsumura Hideki
Published: April 2011

Polycrystalline silicon (poly-Si) films are obtained at temperatures lower than 400°C by catalytic chemical vapor deposition (Catalytic CVD = Cat-CVD) method, often called hot-wire CVD method. Structural properties of the Cat-CVD poly-Si films, deposited with various gas pressures, are studied by Raman scattering spectroscopy and X-ray diffraction technique. It is found that there are two recipes for obtaining device quality poly-Si films, that is, such poly-Si films are obtained at low gas pressure around 1 mTorr or less as already reported, and also at high gas pressure around 0.1 to 1 Torr. It is also found that, in addition to catalyzer temperature, the gas pressure is a key factors to obtain device quality poly-Si films at high deposition rates.
Recent Progress of Low Temperature Poly Si Tft Technology
Authors: Yoneda Kiyoshi
Published: April 2011

Since being introduced to the production line in 1996, replacing the first generation a-Si TFT line, low-temperature poly-Si production technology aimed at manufacturing small and medium size LCD products has improved steadily corresponding to customers' requirements for rapid growth of the DVC and DSC markets. In the future, this production technology must progress to actual industry technology levels in order to cope with production applied not only to large size displays, which have a major market share in the present display market, but also to a large glass substrate, which effectively cuts the cost of products, although improvement of production yield and productivity in terms of pursuing cost reduction must be proceeded.

This paper has described existing problems of inherent low-temperature poly-Si TFT processes and their relating additional processes in present production methods. We have also discussed updating production technologies. To cope with production for a large size display, it is necessary to establish fabrication technology of higher performance TFTs with electron mobility larger than 200cm2/V·s. We believe that one key technology is to fabricate a large-scale and highly-uniform recrystallized poly-Si film with smooth surface morphology as well as precisely-controlled grain size in production. To cope with production using a large glass substrate, it is essential to develop ELA equipment with laser power greater than 200W.
Fluorinated Silicon Nitride Film Deposited at Low Temperatures from SiH4-SiF4-NH3
Authors: Park Y.-B. , Rhee S. , Choi J.-H. , Kimb C.-W. , Suok J.H.
Published: April 2011

The effect of SiF4 addition on the deposition characteristics and film property has been studied for the improvement of long term stability of the SiNx:F film in TFT applications. During the deposition with SiF4 addition, atomic hydrogen species in the gas phase significantly decreased. A detailed bonding configuration of fluorine and hydrogen was investigated by XPS and FT-IR. Optical band gap increases with the increment of fluorine concentration in the film. High compressible stress turned to low tensile stress with increasing SiF4 flow rate. The breakdown strength and barrier height for the conduction of trapped electron were improved by SiF4 addition even in Si-rich SiNx:H films due to the stable Si-F bond formation.
The Structural Evolution of A-SI:H Films Prepared by Pulse Rf Power Modulation with Hydrogen and Helium Dilution
Authors: Jiang Yeu-Long , Lee Min-Chang , Chen Shieng-Huai
Published: April 2011

A-Si:H films were deposited in a PECVD system using 5k to 5 Hz and 25 to 75% duty cycle square-wave pulse modulation RF power and with 80% hydrogen or 80% helium dilution. The transmission and the microstructure of the hydrogen bonding configuration were measured using NIR-VIS-UV and FTIR spectrometers. The powder formation in the reactor chamber was low for a deposition rate less than 5.87 nm/min and was completely suppressed by the 500 Hz pulse RF power with a duty cycle less than 33.3%. The low microstructure R ratio is the result of the reduction of the polymization reaction in the plasma for a low deposition process. A R ratio less than 14% could be obtained using 500 Hz with a duty cycle less than 33.3% for helium dilution or using 5k to 50 Hz with a duty cycle less than 50% for hydrogen dilution. The refractive index of the films is high for the films with low R ratio. The more compact and higher quality films exhibit greater SiH bonding configurations in the a-Si:H films.
High Deposition Rate Amorphous Silicon Solar Cells and Thin Film Transistors Using the Pulsed Plasma Pecvd Technique
Authors: Morrison Scott , Xi Jianping , Madan Arun
Published: April 2011

The pulsed plasma technique has been shown to increase the deposition rate without an increase in the particulate count in the plasma which is an important factor determining the yield of commercial products such as active matrix displays. In this paper, we report the deposition of amorphous silicon at deposition rates of up to 15 Å/sec, using a modulation frequency in the range of 1-100kHz. These materials have been incorporated into a simple p/i/n solar cell and thin film transistor (TFT) configurations. We report on the effect of the conversion efficiency as a function of the modulation frequency, which in turn is related to the deposition rate. We also report on the TFT performance with modulation frequency and compare the results with devices made under the conventional continuous wave PECVD plasma at 13.56MHz.
Molecular Hydrogen in Hot-Wire Hydrogenated Amorphous Silicon
Authors: Liu Xiao. , Iwaniczko E. , Pohl R.O. , Crandall R.S.
Published: April 2011

We have studied the elastic properties of hydrogenated amorphous silicon (a-Si:H) prepared by hot wire chemical-vapor deposition (HWCVD). With 1 at.% H, this material has been found to be the only amorphous solid which has a low-temperature internal friction more than two orders of magnitude smaller than all other amorphous solids studied to date, as reported recently. As the hydrogen concentration increases above 1 at.%, a broad relaxation peak in internal friction around 5 K is observed. Even more striking is an extremely narrow peak in internal friction accompanied by a discontinuous change in the sound velocity at 13.8 K, which coincides with the triple point temperature of molecular hydrogen. Evidences are provided to show that this anomaly is caused by bulk molecular hydrogen which undergoes a liquid-solid phase transition. This is the first observation for the existence of bulk H2 in HWCVD a-Si:H.
Hydrogen'S Effect on Stability of Undoped A-Si:H Under Light Soaking
Authors: Golikova O.A. , Kazanin M.M. , Kuznetsov A.N. , Kudoyarova V.Kh. , Adriaenssens G.J. , Grevendonk W. , Eliat A.
Published: April 2011

Light-soaking kinetics of photoconductivity at room temperature for undoped a-Si:H films deposited by rf-plasma enhanced chemical vapor deposition and by dc-magnetron assisted decomposition at T8 = 300 and 350°C have been investigated. The rate of degradation has been expressed by the value of exponent of the power law: σph∼t−y. The hydrogen content in the films, the type of Si-H bonds and their contribution as well as the Fermi level position were controlled by changes in the deposition conditions. Hydrogen's effect on the y value was shown for the different cases. The films, having γ=0, were identified.
Electron and Hole Transient Currents in Hydrogenated Amorphous Silicon and Some Alloys Measured by The Photoconductive Time-of-Flight Technique
Authors: Eliat Astrid , Adriaenssens Guy , Yan Baojie
Published: April 2011

A series of pure hydrogenated amorphous silicon (a-Si:H) samples as well as carbon (aSi:C:H) and sulfur alloys (a-Si:S:H) were investigated by means of the photoconductive time-of-flight technique. Drift moblility (µd) measurements reveal a fast decrease of the electron µd upon C or S addition, while the hole µd does not change significantly. Contrary to the electron transients, hole transient currents do not show the typical space-charge-limited (SCL) features, even for high light intensities where these features are normally seen. SCL features are observed to disappear for electron transients as well in the a-Si:H alloys with increasing alloy content. Above results are all explained starting from the a-Si:H density of states (DOS) model where the valence band (VB) tail is much broader than the conduction band (CB) tail. Introducing additional disorder by alloying broadens both the VB and the CB tails while the relative increase of the CB tail is much greater than that of the VB tail.
Microscopic Nature of Nature Light Induced Defects
Authors: Biswas R. , Pana B. C.
Published: April 2011

Molecular dynamics simulations find light-induced metastable defects to be silicon dangling bonds accompanied by (Si-H)2 defect complexes that have two Si-H bonds. These complexes are formed by pairs of hydrogen breaking a silicon bond. This supports the model of Branz. These defects are the analogue of the H2* defect in c-Si and their energy correlates with the bond-angle strain. Several features of annealing including E-field induced effects are well accounted for by the (Si-H)2 defect.
Concentration Dependence of Hydrogen Diffusion in Hydrogenated Silicon
Authors: Beyer W. , Zastrow U.
Published: April 2011

The concentration dependence of hydrogen diffusion was studied in hydrogenated crystalline and amorphous silicon prepared by hydrogen implantation into crystalline Si wafers and into amorphous silicon of low hydrogen concentration. The results are compared with data for plasma-grown a-Si:H and µc-Si:H films. The increase of the diffusion coefficient with rising hydrogen concentration in a-Si:H is explained by an (equilibrium) energy band model of hydrogen diffusion whereas the decrease of the diffusion coefficient in c-Si:H is explained by a trapping model. The different behavior is attributed to a greater flexibility of the amorphous Si network compared to the crystalline Si lattice which is also visible in a difference in hydrogen-related microstructure formation.
Degradation Kinetics of Hydrogenated Amorphous Silicon: The Effect of Embedded Microcrystallites
Authors: Lubianiker Yoram , Cohen J. David , Jin Hyun-Chul , Abelson John R.
Published: April 2011

We have studied the degradation kinetics of undoped a-Si:H films which contain a significant fraction of silicon microcrystallites. The degradation rate is found to be exceptionally slow in the first stage of degradation, then the defect density follows the “normal” t1/3rate and finally saturates. We present a model which relates this abnormal kinetics to the microcrystallites which are embedded in the amorphous matrix.
Analysis of Drain Currents During Switching off a-Si:H Based Thin Film Transistors
Authors: Lemmi F. , Street R. A.
Published: April 2011

We present measurements and analysis of a-Si:H thin film transistor (TFT) transients when the gate voltage switches the device from a conducting to a non-conducting state. The drain current transient has been monitored in the medium-long (Ims-100s) time range and exhibits a power law decay extending to at least 10 seconds. The decay has been studied over a range of drain voltages and gate off-state voltages. Measured data show that the gate off-state can help to obtain a low drain leakage current at long times when high drain voltages are being used.

However, the decay at low drain voltages shows little sensitivity to different gate off-state voltages. An analytical model is developed, based on the relaxation of the Fermi level toward mid-gap in a spatially uniform TFT channel. The model shows how deep defects are responsible for the current decay slope at long times, while shallower states determine the slope in the short time range. An energy-independent defect density would produce a 1/t slope for the current decay. Shallow states and deep states affect in opposite ways the slope since their density is energydependent in opposite ways as Fermi level moves deeper into the band-gap. Furthermore, long decay times are associated with a wider depletion region in the channel and increase the total number of defect states involved. A steeper decay than 1/t is expected and observed for shorttime ranges, while a more gradual (about 1/t1/2) one corresponds to long time measurements. The implications of the transient decay for the performance of active matrix arrays will be discussed.
Paramagnetic Defects in Undoped Microcrystalline Silicon Deposited by the Hot-Wire Technique
Authors: Kanschat P. , Lips K. , Brüggemann R. , Hierzenberger A. , Sieber I. , Fuhs W.
Published: April 2011

We report on a study of ESR and conductivity on a series of hot-wire CVD microcrystalline silicon samples prepared with different hydrogen dilution of silane. We observe two different types of dangling bond defects in ESR in different microscopic environments. One type of defect is located at outer surfaces accessible to oxygen and/or chemicals, the other is located at inner boundaries presumably at columnar structures. We correlate changes of the defect density induced by either annealing, exposure to air or wet-chemical treatment with the morphology and electronic properties of the films. We find that annealing at 200 °C induces irreversible changes in donor concentration as monitored by an ESR signal at g = 1.9981±3.
Excitation Intensity Dependence of Light-Induced Electron Spin Resonance in Hydrogenated Amorphous Silicon Films
Authors: Yan Baojie , Taylor P. C.
Published: April 2011

Light-induced electron spin resonance in a-Si:H films was measured using second harmonic detection over a wide range of excitation intensities. Second harmonic detection results in an undifferentiated absorption lineshape that saturates much less easily with increasing microwave power. The ratio of the spin densities of the broad line to the narrow line is approximately 3 at a generation rate of 1019 cm−3s−1, and this ratio increases only slightly with decreasing excitation intensity. The kinetics of the LESR after the light is turned on or off show dispersive behavior. The dispersive response of the LESR is related to the dispersive transport of carriers at low temperature. A model that assumes a bimolecular recombination fits the experimental results reasonably well.
Changes in the Medium Range Order of α-Si:H Thin Films Observed by Variable Coherence Tem
Authors: Gibson J. M. , Treacy M. M. J. , Voyles P. M. , Abelson J. R. , Jin H.-C.
Published: April 2011

We have investigated the structure of a-Si:H thin films using variable coherence transmission electron microscopy. Variable coherence is a new microscopy technique that is sensitive to higher-order atomic position correlations. We observe changes in the structure of α-Si:H with increasing hydrogen content and with light soaking. Based on these observations we conclude that a less ordered form of α-Si:H is more structurally stable than a more ordered form. This may have implications for understanding the Staebler-Wronski effect.
Real Time Spectroscopic Ellipsometry Studies of the Solid Phase Crystallization of Amorphous Silicon
Authors: Fujiwara H. , Koh Joohyun , Lee Yeeheng , Wronski C. R. , Collins R. W.
Published: April 2011

We have introduced real time spectroscopic ellipsometry (RTSE) for characterization of the solid phase crystallization (SPC) of intrinsic and n-type amorphous silicon (a-Si:H) thin films. RTSE has several advantages in the study and design of SPC processes for thin film transistor and solar cell fabrication. These include the capability of obtaining (i) calibration data that yield the near surface temperature of the film during processing, (ii) the volume fraction of the crystalline Si component of the film continuously versus time during SPC, and (iii) a measurement of the grain size and quality of the final polycrystalline Si film. For the thin layers studied here (∼150-1000 Å), we demonstrate excellent fitting of the SPC dynamics to the Avrami-Johnson-Mehl theory for random nucleation and two-dimensional crystallite growth. For a-Si:H n-layers, the crystallization time over the range from 565 to 645°C appears to be weakly activated with an energy of 0.6 eV.
Thermochemistry of Silicon Lpcvd Revisited with Kinetic Data
Authors: Vahlas Constantin , Blanquet Elisabeth
Published: April 2011

Partial equilibrium calculations simulating the kinetically controlled low pressure chemical vapor deposition of silicon from silane are presented. Firstly, the sticking coefficient of each reactive species (σ) is evaluated by means of homogeneous calculations in the gas phase. Then, in a series of heterogeneous calculations, the influence of σ on the formation of the film is considered a) by reducing the quantities of the reactive species in the input gas, and b) by modifying their thermodynamic data. The obtained composition of the gas phase is used to estimate its supersaturation and the driving force for the deposition of silicon. The results are correlated with the morphology of the films deposited in equivalent conditions and, in view of this correlation, the validity of the presented approach is discussed.
µc-Si:H Thin-Film Devices for Optical Image Recognition
Authors: Maçarico A. , Fernandes M. , Martins J. , Vieira M.
Published: April 2011

A study of an image detector based on µc-Si:H p-i-n structures is presented. The photodetector has a TCO/µc-p-i-n Si:H configuration with two coplanar metallic contacts and a transverse one.

We used a strong spatially fixed light pattern with different intensities to simulate the images and a weak moving light beam to sweep the device in the lateral direction, for its recognition. The sensor surface was scanned row by row and a signal processing procedure was applied to the data after each sweep. It was found that the induced transverse and lateral photovoltages are sensitive to the position and intensity of the image. Through a readout analysis it was possible to recognise, in a continuous way, the image position and relative intensity. The image resolution as a function of the pattern width and intensity is also analysed

A small signal circuit modelling and a simulation consistent with the experimental data are presented and explained. Preliminary tests show that the detector can be used as a two-dimensional image sensor.
Reaction Processes for Low Temperature (<150°C) Plasma Enhanced Deposition of Hydrogenated Amorphous Silicon Thin-Film Transistors on Transparent Plastic Substrates
Authors: Parsons Gregory N. , Yang Chien-Sheng , Klein Tonya M. , Smith Laura
Published: April 2011

This article presents mechanisms for low temperature (<150°C) rf plasma enhanced chemical vapor deposition of silicon and silicon nitride thin films that lead to sufficient electronic quality for thin film transistor (TFT) fabrication and operation. For silicon deposition, hydrogen abstraction and etching, and silicon disproportionation reactions are identified that can lead to optimized hydrogen concentration and bonding environments at <150°C. Nitrogen dilution of SiH4/NH3 mixtures during silicon nitride deposition at low temperatures helps promote N-H bonding, leading to reduced charge trapping. Good quality amorphous silicon TFT's fabricated with a maximum processing temperature of 110 °C are demonstrated on flexible transparent plastic substrates. Transistors formed with the same process on glass and plastic show linear mobilities of 0.33 and 0.12 cm2/Vs, respectively, with ION/IOFF ratios > 106.
Relationship of Field Emission Characteristics on Process Gas Nitrogen Content in Nitrogen Doped Diamond Films
Authors: Sowers A.T. , Ward B.L. , Nemanich R.J.
Published: April 2011

This study explores the field emission properties of nitrogen doped diamond grown by microwave plasma CVD. Several diamond samples were grown on silicon under varying conditions. With certain process parameters, films can be grown which exhibit photoluminescence bands at 1.945eV and 2.154eV that are attributed to single substitutional nitrogen. Field emission characteristics were measured in ultrahigh vacuum with a position variable anode. For samples grown with gas phase [N]/[C] ratios less than 16, damage from micro-arcs occurred during the field emission measurements. Samples grown at higher [N]/[C] content could be measured without damage. These measurements indicate relatively high threshold fields (>100V/µm) for electron emission. From the data, two possible field emission mechanisms are presented. Conducting defect states in the bandgap of diamond may provide a source of electrons to the emitting diamond surface.
Systematic Study of Transparent Conductors in the (Zinc, Gallium)-Indium-Tin Oxide Systems
Authors: Palmer George B. , Poeppelmeier Kenneth R. , Edwards Doreen D. , Mason Thomas O.
Published: April 2011

Bulk samples of transparent conducting oxides (TCOs) in the Zn-In-Sn and Ga-In-Sn oxide systems were prepared by solid state processing. Phase relations and physical properties were determined and the results compared to similar measurements on thin film materials.
Transistors With a Profiled Active Layer Made by Hot-Wire CVD
Authors: Meiling H. , Brockhoff A.M. , Rath J.K. , Schropp R.E.I.
Published: April 2011

In order to obtain stable thin-film silicon devices we are conducting research on the implementation of hot-wire CVD amorphous and polycrystalline silicon in thin-film transistors, TFTs. We present results on TFTs with a profiled active layer (deposited at ≥9 Å/s), and correlate the electrical properties with the structure of the silicon matrix at the insulator/semiconductor interface, as determined with cross-sectional transmission electron microscopy. Devices prepared with an appropriate H2 dilution of SiH4 show cone-shaped crystalline inclusions. These crystals start at the interface in some cases, and in others exhibit an 80nm incubation layer prior to nucleation. The crystals in the TFrs with the incubation layer are not cone-shaped, but are rounded off. The hot-wire CVD deposited devices exhibit a high field-effect mobility up to 1.5 cm2V−1s−1. Also, these devices have superior stability upon continuous gate bias stress, as compared to conventional glow-discharge a-Si:H TFTs. We ascribe this to a combination of enhanced structural order of the silicon and a low hydrogen content.
Characterization of Transparent Conductors in Indium Zinc Oxide and Their Application to Thin-Film Transistor Liquid-Crystal Displays
Authors: Takatsuji H. , Hiromori T. , Tsujimoto K. , Tsuji S. , Kurodac K. , Sakac H.
Published: April 2011

Investigation of the properties of indium zinc oxide (IZO) thin films sputter-deposited on LCD-grade glass substrate showed that the resistivity of an IZO film decreases markedly as the substrate temperature is increased from room-temperature to 120°C. This phenomenon can be attributed to the growth of In-Zn intermetallic compounds in the amorphous region as a result of annealing. The compound growth was observed by plan-view transmission electron microscopy.

Although the transmittance and resistivity of IZO are inferior to those of indium-tin oxide, these disadvantages do not present any difficulties in the practical use of IZO for designing TFT-LCDs. Since IZO is an amorphous material, we propose a five-mask process with this characteristic.
Co-Optimization of Si Thin-Film Deposition and Excimer Laser Anneal Processes for Fabrication of High-Performance p-Si TFTs
Authors: Voutsas A.T. , Marmorstein A. , Solanki R.
Published: April 2011

In this work we have co-optimized the deposition and excimer laser crystallization processes for formation of high quality, low-temperature, p-Si films (LPS). We have found that the post-ELA polysilicon structure is very sensitive to deposition process adjustments, collectively expressed by the deposition rate. At low rates the PECVD Si-film is deposited in the microcrystalline phase (µc-Si). Comparing µc-Si and a-Si film precursors, we have shown that at equivalent annealing conditions (laser energy density) polysilicon films obtained from µc-Si precursor demonstrate improved crystallinity (grain size, defect density). Polysilicon thin film transistors (p-Si TFTs) have been fabricated and characterized using this material and compared to our standard process. We have found that the performance of µc-Si precursor exceeds by 20-50% that of a-Si precursor. Use of µc-Si precursor may also have important implications in reducing substrate damage during ELA process and for widening the ELA process window.
a-Si:H TFTs Made on Polyimide Foil by PE-CVD at 150°C
Authors: Gleskova H. , Wagner S. , Suo Z.
Published: April 2011

We have fabricated high-performance amorphous silicon thin-film transistors (a-Si:H TFTs) on 2 mil. (51 µm) thick polyimide foil substrates. The TFT structure was deposited by r.f.-excited plasma enhanced chemical vapor deposition (PECVD). All TFT layers, including the gate silicon nitride, the undoped, and the n+ amorphous silicon were deposited at a substrate temperature of 150°C. The transistors have inverted-staggered back-channel etch structure. The TFT off-current is ∼ 10−12 A, the on-off current ratio is > 107, the threshold voltage is 3.5 V, the sub-threshold slope is ∼ 0.5V/decade, and the linear-regime mobility is ∼ 0.5 cm2V−1s−1. We compare the mechanical behavior of a thin film on a stiff and on a compliant substrate. The thin film stress can be reduced to one half by changing from a stiff to a compliant substrate. A new equation is developed for the radius of curvature of thin films on compliant substrates.
Structural Investigations of Laser-Crystallized Hydrogenated Amorphous Silicon
Authors: Toet D. , Smith P.M. , Sigmon T.W. , Qiu R. , Takehara T. , Sun S. , Tsai C.C. , Harshbarger W.R.
Published: April 2011

We investigated the structure of hydrogenated amorphous silicon, thin films crystallized by short pulses from a XeCl excimer laser at fluences for which total melting of the films occurs. Atomic force microscopy revealed that films prepared using optimized process conditions, leading to hydrogen contents ≤ 5 at.%, are smoother after laser crystallization than those prepared by laser-dehydrogenation. The roughness of the laser-crystallized films increases with their thickness, and can be reduced by multiple exposure. A better smoothing is obtained by partially remelting the films after the first irradiation. Transmission electron microscopy shows that the grains in the laser-crystallized films have sizes that are comparable to the film thickness.
Carbon Nanotube-Based Vacuum Microelectronic Gated Cathode
Authors: Xu Xueping , Brandes George R.
Published: April 2011

A vacuum microelectronic device containing carbon nanotube electron field-emitters was developed and tested. The gated cathode was fabricated using conventional microelectronics fabrication techniques and a final, self-aligned, in situ carbon nanotube growth step. To our knowledge, this is the first vacuum microelectronics device with carbon nanotube field-emitters grown in situ with a catalytic growth process. The turn-on voltage of the cathode was less than 20 volts and the emission current density at 50 volts was as high as 9 mA-cm−2. The fabrication process, device performance, manufacturing issues and cathode applications will be discussed.
Quasi-Ballistic Stable Electron Emission from Porous Silicon Cold Cathodes
Authors: Sheng X. , Koshida N.
Published: April 2011

Based on the previously-reported porosity multilayer technique, cold electron emission properties of porous silicon (PS) electroluminescent diodes with a structure of Au/PS/n-type Si are further improved by introducing a graded-band multilayer structure. It is shown that electrons are quasiballisticly emitted from PS diodes owing to a significantly reduced electron scattering in PS layer. As a result, the emission current shows a fluctuation-free behavior. These observations are very important for both understanding the electron transport in PS and developing high performance electron emitters in application to vacuum microelectronic technology.
A Novel Lateral Field Emission Triode for Microwave Application
Authors: Park C-M , Lim M-S , Han M-K , Choi Y-I
Published: April 2011

We propose a novel lateral field emission triode, which does not require any additional vacuum sealing process and exhibits superb field emitter triode performance. The purpose of this paper is to compare titanium polycide tip with polycrystalline silicon tip. A new experimental results of the device, such as variation of tip material, device stability experiment, measurement of the novel device in vacuum chamber in order to verify the proposed vacuum sealing process, and transconductance characteristics at each current level.

The minimum turn-on anode to cathode voltage of titanium polycide tip is considerably decreased compared with polysilicon tip. The anode current measured in 10−8 Torr vacuum chamber is similar to the anode current measured in atmospheric pressure, which shows that the proposed vacuum sealing process is reliable. The stable current of 300μΑ is maintained during 60 h.
Emitting Carbon Thin Films and Their Characterizations
Authors: Tolt Z. Li , Fink R. L. , Yaniv Zvi
Published: April 2011

Carbon thin film cathodes have been produced with an emission site density of 2 × 105/cm2 and with current density higher than 40 mA/cm2at 10 V/μm extraction field. Characterization of the film bonding structure by UV Raman spectroscopy and emission sites by Atomic Force Microscopy (AFM) are presented and discussed in detail. A hypothesis of the nature of emission sites in these films is proposed in accordance with the analyses.
Characterizaton of Pecvd Fluorinated Silicon Oxides and Stabilization of Interaction with Metals
Authors: Kim Sarah E. , Steinbruichel Christoph , Kumar Atul , Bakhru H.
Published: April 2011

Fluorinated silicon oxide films were prepared in a plasma enhanced chemical vapor deposition reactor using TEOS, O2, and either C2F6 or NF3. Properties such as deposition rate, film refractive index, dielectric constant, density, and fluorine concentration were investigated as a function of experimental conditions. Based on nuclear reaction analysis (NRA) and Fourier Transform Infrared (FTIR) measurements, no single linear relationship was found between fluorine concentration or film density and dielectric constant. Special attention was paid to the interaction of fluorine with metals. NRA and X-ray photoelectron spectroscopy (XPS) depth profiles showed that fluorine diffuses rapidly through aluminum and piles up at the free surface. The effect of various plasma treatments was investigated to passivate the surface of fluorinated silicon oxide. CF4 - O2 plasma treatment of the fluorinated oxide before aluminum deposition produced significant improvement in inhibiting fluorine diffusion into aluminum without increasing the dielectric constant.
Porous Silica Xerogel Processing And Integration For Ulsi Applications
Authors: Jin Changming , List Scott , Zielinski Eden
Published: April 2011

With a tunable ultra low dielectric constant, porous silica xerogel is an attractive dielectric material for ULSI interconnect applications and is potentially extendable to multiple future technology nodes. Porous silica xerogel films have been processed and integrated into device test structures as ultra low k intermetal dielectrics. A fully automated thin film deposition process is recently developed and gives high throughput and good repeatability. A surface modification technique is used to make the films hydrophobic. The film dielectric constant is measured to be less than 2, depending on porosity. Because of the small pore sizes, the films display high dielectric break down strength. With proper shrinkage control, porous silica xerogel shows excellent gapfill capabilities. Integration of the porous silica xerogel material into CMP planarized double level metal (DLM) test structures with both Al and W plugs in a gapfill scheme is successful. Porous silica xerogel structures provide 14% and 35% total capacitance reduction compared to structures with hydrogen silsesquioxane (HSQ) and high density plasma (HDP) oxide respectively. Reliability and current leakage data of porous silica xerogel are comparable to that of HSQ. Feasibility of integrating porous silica xerogel into Cu damascene structures is also demonstrated. Cu/xerogel damascene structures exhibit improvements in both resistance and capacitance compared with convention Al/Oxide gapfill structures.
High-Density Plasma Etching of Low Dielectric Constant Materials
Authors: Standaert T. E. F. M. , Matsuo P. J. , Allen S. D. , Oehrlein G. S. , Dalton T. J. , Lu T.-M. , Gutmann R.
Published: April 2011

The patterning of several novel low dielectric constant (K) materials has been studied in a high-density plasma (HDP) tool. Recent results obtained on oxide-like materials, such as fluorinated oxide, hydrogen silsesquioxane (HSQ), and methyl silsesquioxane (MSQ), are reviewed. These materials can be successfully patterned using a fluorocarbon etching chemistry. The etching is in this case controlled by a thin fluorocarbon film at the surface. The patterning of polymer dielectrics can be performed in an oxygen etching chemistry. As an example, the patterning of Parylene-N in an oxygen chemistry is discussed. In this case, the ion and the oxygen radical flux need to be properly controlled to obtain a directional etching process. After the dielectric etch, either in a fluorocarbon or oxygen based chemistry, fluorocarbons and oxygen contamination remain at the exposed metal surfaces. We recently demonstrated how a plasma treatment following the dielectric etch reduces these contaminants. The results of this treatment on copper surfaces and the resulting modification to the dielectric are reviewed.
Influence of Moisture-Uptake on Mechanical Properties of Polymers Used in Microelectronics
Authors: Buchhold R. , Nakladal A. , Gerlach G. , Sahre K. , Eichhorn K.-J. , Herold M. , Gauglitz G.
Published: April 2011

Polymers are currently considered as a possible alternative to silicon dioxide in the fabrication of interlevel dielectrics. To penetrate mainstream semiconductor device fabrication polymers have to meet a number of requirements regarding their long-term stability. One aspect is the mechanical stability of integrated polymer films under changing climatic conditions. In the present work, the impact of ambient moisture on the mechanical properties of thin polymer films (PI, BCB, and PFCB) was investigated. The sorption of water molecules in these materials typically causes an anisotropic volume expansion, resulting in increased mechanical film stress if the film is physically constrained by adjacent inorganic structures. Especially polyimides show both considerable moisture uptake and large changes in the mechanical film stress, while BCB and PFCB are virtually insensitive to ambient moisture. In the paper, experimental data (water uptake, in-plane swelling, out-of-plane swelling) are presented and discussed in detail.
High Temperature Stable Titanium Carbide Ohmic and Schottky Contacts to SiC
Authors: Zetterling C.-M. , östling M. , Norin L. , Jansson U.
Published: April 2011

Epitaxial titanium carbide is investigated as a low resistivity, high temperature stable Ohmic and Schottky contact to 4H and 6H SiC. The titanium carbide films were deposited at 500°C using co-evaporation of titanium (e-beam) and C60(Knudsen cell) in a UHV system. Schottky diodes and TLM structures were fabricated on low and high doped SiC material respectively. The samples were annealed at 700 °C in a vacuum furnace, and electrical measurements were performed up to 300 °C.
Low Temperature Chemical Vapor Deposition Of 3C-SiC On 6H-SiC – An X-Ray Triple Crystal Diffractometry And X-Ray Topography Study
Authors: Chaudhur J. , Ignatiev K. , Edgar J. H. , Xie Z. Y. , Gao Y.
Published: April 2011

Highly perfect 3C-SiC thin films, on 6H-SiC deposited by the chemical vapor deposition at low temperature with various Cl/Si, H/Si and C/Si ratios were characterized by x-ray high resolution triple crystal diffractometry and double crystal topographic methods. The films were epitaxial with a low defect density present (mostly in the range of 107/cm2). X-ray topography revealed stacking faults, low angle grain boundaries, dislocations and inversion double positioning boundaries present in the film and substrate.
Low Frequency Noise In n-Type Gallium Nitride
Authors: Dyakonova N. , Levinshtein M. , Contreras S. , Knap W. , Beaumont B. , Gibart P.
Published: April 2011

Low frequency noise has been investigated in hexagonal n-type GaN with equilibrium electron concentration n ∼ 1017 cm−3 at T=300 K. The frequency and temperature dependencies of the spectral density of the current noise, SI, have been studied in the frequency range f from 20 Hz to 20 kHz. Over the whole temperature range from T=80K to 400K the SI(f) dependence is very close to 1/f. The value of the Hooge constant, α, is very large: α ∼ 5 – 7 and is found to be temperature independent. The effects of illumination on the low frequency noise in GaN are studied for the first time. The noise is unaffected by illumination with photon energy Eph < Eg, while band-to band illumination (Eph∼Eg ) influences the low frequency noise, increasing the noise at higher temperatures, and decreasing it at lower temperatures.
Effect Of No On The Electrical Characteristics Of SiO2 Grown On P-Type 4H SiC
Authors: Li H. F. , Dimitrijev S. , Harrison H. B. , Sweatman D. , Tanner P.
Published: April 2011

In this paper the effect of NO nitridation on the electrical characteristics of the oxides grown on p-type 4H SiC has been investigated. The results show that NO nitrided oxide has a lower interfacial trap density and a lower net oxide charge compared to N2 annealed oxides.
Reactive Ion Etching of Boron Nitride and Gallium Nitride Materials in C12/Ar and BCl3/Cl2/Ar Chemistries
Authors: Medelci N. , Tempez A. , Kim E. , Badi N. , Starikov D. , Berichev I. , Bensaoula A.
Published: April 2011

Boron nitride (BN) and gallium nitride (GaN) are known as superior semiconductor materials for high power and high temperature applications. Undoped BN layers grown using ion beam and electron cyclotron resonance (ECR) assisted physical deposition on conductive GaN films have demonstrated good insulating properties. These films are thus good candidates as thin insulating layers in high temperature GaN-based device structures such as MIS diodes and MISFETs due to their close thermal expansion coefficient. In order to address the device processing issue, reactive ion etching (RIE) tests were performed on these films. Using Cl2/Ar chemistry, etch rates up to 600 Å/min were measured. These rates were found to increase linearly with increasing rf power and Cl2 flow rate. GaN layers grown by gas source MBE were also dry etched, resulting in smooth sidewalls. Etch rates up to 1,400 Å/min were achieved at 200 W rf power (-280 V d.c. bias) in a BCl3/Cl2/Ar chemistry; this is the highest RIE rate reported up to now for GaN. Using Cl2/Ar and BCl3/Cl2/Ar for BN and GaN respectively, etch selectivities in excess of 5:1 can be obtained. Finally, preliminary Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) results on residue deposition and surface composition changes as a function of the different etch conditions are presented.
GaN Materials for High Power Microwave Amplifiers
Authors: Eastman Lester F. , chu Kenneth , smart Joseph , Shealy J. Richard
Published: April 2011

The key parameters of GaN for use in microwave power amplifiers are presented. The electron-scattering effect of dislocations are presented for 2 DEG in HEMT devices. The use of the piezoelectric effect in designing Aly Ga1-yN/GaN HEMT structures is reviewed for a range of y.Short-gate device fabrication methods, and the device characterization, are presented. Maximum frequency of oscillation for .15 μm gates reached 140 GHz, while .3 μm gate power amplifiers reached 74% power-added efficiency at 3 GHz.
Bulk Breakdown in AlGaN/GaN HFETs
Authors: Gradinaru G. , Kao N. C. , Gaska R. , Yang J. , Chen Q. , Khan M. A. , Sudarshan T. S.
Published: April 2011

A significant source current generated by a carrier multiplication process is observed at large drain voltages in the subthreshold regime, along with simultaneous increase of the gate current and light emission signal. Provided no on-surface premature breakdown takes place, a bulk channel avalanche breakdown process is proposed as the dominant breakdown mechanism for a large range of gate-to-source dc voltages. This process in the GaN channel is responsible for the excess source and drain currents, light emission, and excess gate current beyond its normal value measured in a gate-to-drain diode configuration. The role of the gate bias in controlling the channel vs. the gate breakdown mechanisms is described.