bluuebunny/crossref_metadata_2025 huggingface dataset:
Annealing Kinetics of Amorphous Silicon Alloy Solar Cells Made at Various Deposition Rates
Authors: Yana Baojie , Yanga Jeffrey , Lord Kenneth , Guha Subhendu
Published: April 2011

A systematic study has been made of the annealing kinetics of amorphous silicon (a-Si) alloy solar cells. The cells were deposited at various rates using H2 dilution with radio frequency (RF) and modified very high frequency (MVHF) glow discharge. In order to minimize the effect of annealing during light soaking, the solar cells were degraded under 30 suns at room temperature to quickly reach their saturated states. The samples were then annealed at an elevated temperature. The J-V characteristics were recorded as a function of annealing time. The correlation of solar cell performance and defect density in the intrinsic layer was obtained by computer simulation. Finally, the annealing activation energy distribution (Ea) was deduced by fitting the experimental data to a theoretical model. The results show that the RF low rate solar cell with high H2 dilution has the lowest Ea and the narrowest distribution, while the RF cell with no H2 dilution has the highest Ea and the broadest distribution. The MVHF cell made at 8Å/s withhigh H2 dilution shows a lower Ea and a narrower distribution than the RF cell made at 3 Å/s, despite the higher rate. We conclude that different annealing kinetics plays an important role in determining the stabilized performance of a-Si alloy solar cells.
OPTICAL EMISSION SPECTROSCOPY OF GERMANE PLASMA PRODUCED IN AN ECR REACTOR
Authors: deFreese Matt , Dalal Vikram L. , Falter Julie
Published: April 2011

Plasma deposition using silane and germane is extensively used for depositing amorphous (Si,Ge) films and devices, and has the potential of also being used for making crystalline films. In this paper, we report results on the electrical and optical characterization of germane plasmas using a Langmuir probe set-up and optical emission spectroscopy. The plasma studied was an electron-cyclotron-resonance plasma. For the first time ever, we have detected the characteristic 246 nm GeH emission peak in the plasma. The GeH emission peak is suppressed significantly when small quantities of hydrogen are added as a diluent gas. We have also studied the effect of adding a voltage bias to the substrate on the plasma properties. We find that adding voltage bias does not simply change the effective ion energy impinging on the substrate, as is usually assumed, but also changes all the plasma properties, including the density of neutral, excited H radicals arriving at the growing surface.
Some Considerations Relating to Growth Chemistry of Amorphous SI and (SI,GE) Films and Devices
Authors: Dalal Vikram L.
Published: April 2011

Recent experiments suggest that the chemistry responsible for the growth of amorphous and microcrystalline Si and (Si,Ge) alloys is more complicated than suggested by the standard model of growth. In particular, unexpected phenomena related to the density of ion flux, magnitude of ion energy and the presence of inert gas ions in the discharge suggest that both inert and reactive ion flux profoundly influence the growth of amorphous and microcrystalline films and devices. The influence of the ion flux is particularly important in understanding the growth of high quality a-(Si,Ge):H films. By carefully controlling this flux, we can change significantly the H bonding environment in a-(Si,Ge):H and produce high quality materials and devices. These observations suggest that the standard model of growth, which postulates that the growth is primarily limited by surface diffusion of radicals, and that H is eliminated by spontaneous bond breaking between neighboring Si-H bonds and formation of H2 molecule, does not describe the actual growth chemistry very well. Rather, the growth is limited by both surface diffusion of radicals and more fundamentally, by how rapidly H desorbs from surface and subsurface bonds. Ion induced desorption of excess H is shown to be very important in controlling the growth of both a-Si and a-(Si,Ge):H.
Electrical Properties and Defect States of Laser Crystallized Polycrystalline Silicon Films
Authors: Watanabe Tadashi , Andoh Nobuyuki , Sameshima Toshiyuki
Published: April 2011

In this paper, changes in electrical properties of laser crystallized silicon films doped with 8.5×1017-cm−3-phosphorus atoms as a function of laser shot number are investigated. The samples are treated with plasma hydrogenation for 30 sec at 130 Pa at 250 °C and additional H2O vapor heat treatment at 260 °C for 3 hours with 1.3 MPa. The electrical conductivity at room temperature become about 10−6∼10−-5 S/cm as laser shot number increases from 1 to 100. After hydrogenation and additional H2O vapor heat treatment, electrical conductivity remarkably increases to 100∼101S/cm. At laser irradiation of 20 or 50 shots after both treatments, the density of defect at deep level states and tail states are determined 1.15×1017 cm−3 and 5.7×1017cm−3 using an analysis program. Potential barrier height at grain boundary is 0.048 eV. The effective carrier density and carrier mobility are markedly increased up to1017cm−3 and 209 cm2/Vs by hydrogenation and additional H2O vapor heat treatment.
Hydrogen Concentration Analysis in Pecvd and Rtcvd Silicon Nitride Thin Films and It's Impact on Device Performance
Authors: Wang C. Y. , Lim E. H. , Liu H. , Sudijono J. L. , Ang T. C. , Vassiliev V. Y. , Zheng J. Z.
Published: April 2011

In this paper the impact of the ESL (Etch Stop layer) nitride on the device performance especially the threshold voltage (Vt) has been studied. From SIMS analysis, it is found that different nitride gives different H concentration, [H] in the Gate oxide area, the higher [H] in the nitride film, the higher H in the Gate Oxide area and the lower the threshold voltage. It is also found that using TiSi instead of CoSi can help to stop the H from diffusing into Gate Oxide/channel area, resulting in a smaller threshold voltage drift for the device employed TiSi. Study to control the [H] in the nitride film is also carried out. In this paper, RBS, HFS and FTIR are used to analyze the composition changes of the SiN films prepared using Plasma enhanced Chemical Vapor deposition (PECVD), Rapid Thermal Chemical Vapor Deposition (RTCVD) with different process parameters. Gas flow ratio, RF power and temperature are found to be the key factors that affect the composition and the H concentration in the film. It is found that the nearer the SiN composition to stoichiometric Si3N4, the lower the [H] in SiN film because there is no excess silicon or nitrogen to be bonded with H. However the lowest [H] in the SiN film is limited by temperature. The higher the process temperature the lower the [H] can be obtained in the SiN film and the nearer the composition to stoichiometric Si3N4.
Current Transport Mechanisms in CuIn1−xGaxSe2 and CIS Thin-Film Solar Cells on Flexible Stainless Steel Substrates
Authors: Naik Gaurav A. , Anderson Wayne A.
Published: April 2011

Copper indium gallium selenide (CIGS) solar cells on thin film stainless steel substrates were evaluated by current-voltage-temperature (IVT) from 150K-350K to determine current transport mechanisms. Both dark and photo data at reverse and low forward voltages exhibited tunneling-like behavior. At intermediate forward voltages, diffusion or thermionic emission are suggested by an ideality factor close to 1.0. At higher currents and voltages there is a trend towards recombination or space change limited behavior.
Investigation of the Trapping Mechanism for Transient Current-Voltage Behavior In CIGSS-Based Solar Cells
Authors: Johnson Pamela K. , Sites James R. , Tarrant Dale E.
Published: April 2011

Some thin-film CIS photovoltaic devices exhibit reversible transient behavior in their electrical properties induced by modestly elevated (70 - 100 °C) temperatures. This paper evaluates changes due to light exposure, thermal exposure, and applied bias in cells fabricated by Siemens Solar Industries (SSI). When a constant bias was maintained across cells subjected to elevated temperatures in the dark, and subsequent moderate- temperature light exposure, there was little reversible transient behavior. When the bias was cycled between zero and open-circuit voltage (VOC), independent of illumination, the fill factor (FF) decreased for zero bias and increased at VOC. Hence, it is the bias rather than photon absorption that drives the transient current-voltage behavior in these cells. Investigations of the relationship between trapping mechanisms and transient behavior using the frequency and temperature dependence of capacitance showed clear cyclic behavior in the trap-response frequency. Trap density profiles were found to be relatively independent of measurement temperature, and the total trap density varied only slightly with the bias cycle.
ERDA analysis of ZnSx(OH)y thin films obtained by chemical bath deposition
Authors: Neve Sven , Bohne Wolfgang , Röhrich Jörg , Scheer Roland
Published: April 2011

Thin films of Zn-compounds grown in a chemical bath have been studied by Elastic Recoil Detection Analysis (ERDA). The bath contained zinc acetate, thiourea and complexing agents such as ammonia and hydrazine. Large amounts of hydrogen and oxygen are detected within all samples. A strong effect of the pH of the solution is revealed: At high pH (>11.5) mainly ZnS growth takes place, while at lower pH Zn(OH)2 is the dominant product. Hence the pH of the solution can be used to adjust the film stoichiometry. Deposition of Zn-compound films is possible without ammonia in the solution while presence of hydroxide ions and hydrazine species is necessary. It is proposed that film formation takes place via a complex combining hydrazine and hydroxide ligands.
Micron-Resolution Photocurrent of CdTe Solar Cells Using Multiple Wavelengths
Authors: Hiltner Jason F. , Sites James R.
Published: April 2011

An apparatus developed recently at Colorado State University utilizes a diffractionlimited optics system and a high-resolution translation system to measure the laser-induced photocurrent at resolutions of 1 μm and equivalent incident laser intensities of 1 sun (100 mW/cm2). Multiple lasers in the 635-830 nm range can be easily selected by changing the fiberoptic connectors. The spot profile and location are unchanged when different lasers are selected. In addition, a laser temperature tuned through the 825-857 nm range allows measurement of local variations in the quantum efficiency near the CdTe band gap, which track intermixing of CdS/CdTe. This capability extends the previous analysis, which includes the separation of series resistance and shunting effects. The effect of post-deposition processing and elevated temperature stress on local variations in electrical and optical parameters, especially using the near-bandgap wavelengths, are examined using a series of samples fabricated at NREL.
Chemical Vapor Deposition of Titania/Silica and Zirconia Films
Authors: Gladfelter Wayne L. , Smith Ryan C. , Burleson David , Taylor Charles J. , Roberts Jeffrey T. , Campbell Stephen A. , Hoilien Noel , Tiner Mike , Hegde Rama , Hobbs Christopher
Published: April 2011

Amorphous thin films of composition TixSi1−xO2 have been grown by low pressure chemical vapor deposition on silicon (100) substrates using Si(OEt)4 and either Ti(OiPr)4 or anhydrous Ti(NO3)4 as the sources of SiO2 and TiO2, respectively. The substrate temperature was varied between 300 and 535°C, and the precursor flow rates ranged from 5 to 100 sccm. Under these conditions growth rates ranging from 0.6 to 90.0 nm/min were observed. Films were amorphous to X-rays as deposited and SEM micrographs showed smooth, featureless film surfaces. Cross-sectional TEM showed no compositional inhomogeneity. RBS revealed that x (from the formula TixSi1−xO2) was dependent upon the choice of TiO2 precursor. For films grown using TTIP-TEOS x could be varied by systematic variation of the flow of N2 through the precursor vessels or the deposition temperature. For the case of TN-TEOS x remained close to 0.5. The results suggested the existence of a specific chemical reaction between TN and TEOS prior to film deposition.

The CVD of zirconium dioxide (ZrO2) films from zirconium tetra-tert-butoxide {Zr[OC(CH3)3]4} is also described. The films, which were deposited on Si(100), were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), ellipsometry, X-ray diffraction (XRD), and Rutherford backscattering spectroscopy (RBS). Deposition was studied between ∼380 and 825 °C, and at precursor pressures between 4 × 10−5 and 1 × 10−4 Torr. The kinetics for steady-state growth were studied as functions of temperature and precursor pressure. Results were fit to a two-step kinetic model involving reversible precursor adsorption followed by irreversible decomposition to ZrO2.
Transistors Built With ZrO2 And HfO2 Deposited From Nitratos
Authors: Campbell Stephen A. , Hoilien Noel , Ma Tiezhong , Chen Fang , Smith Ryan , Gladfelter Wayne
Published: April 2011

The electrical performance of transistors built using thin films of the column IVB metal oxides ZrO2 and HfO2 deposited from their respective anhydrous metal nitrate precursors is presented. In contrast to earlier work on TiO2, which is thermodynamically unstable on silicon, ZrO2 and HfO2 form well-defined oxynitride interfacial layers and have a good interface with silicon with much less fixed charge. The inversion layer mobility for an HfO2 / SiOxNy / Si stack is comparable to that of a conventional SiOxNy/Si interface.
Comparison of Conductance and Capacitance techniques for Measurement of Interface States in Thin Oxides
Authors: Higman T. K.
Published: April 2011

Current trends in integrated circuit processing project gate insulators with oxide equivalent thicknesses of 1.5 to 1.0 nm. Gate oxides in this thickness range have oxide capacitances of 1 to 5 μF/cm2. When oxide capacitances are this large, traditional high-frequency capacitance-voltage techniques for measuring interface states can be inaccurate. We show that a combination of high and low frequency capacitance-voltage data, along with frequency dependent conductance methods, produce more accurate results.
Dual Work Function CMOS Gate Technology Based on Metal Interdiffusion
Authors: Polishchuk Igor , Ranade Pushkar , King Tsu-Jae , Hu Chenming
Published: April 2011

In this paper we propose a new metal-gate CMOS technology that uses a combination of two metals to achieve a low threshold voltage for both n- and p-MOSFET's. One of the gate electrodes is formed by metal interdiffusion so that no metal has to be etched away from the gate dielectric surface. Consequently, this process does not compromise the integrity and electrical reliability of the gate dielectric. This new technology is demonstrated for the Ti-Ni metal combination that produces gate electrodes with 3.9 eV and 5.3 eV work functions for n-MOS and p-MOS devices respectively.
Effects of a Ta Interlayer on the Titanium Silicide Reaction: C40 Formation and Higher Scalability of the TiSi2 Process.
Authors: La Via F. , Privitera S. , Mammoliti F. , Grimaldi M.G.
Published: April 2011

When a Ta layer is deposited at the Si/Ti interface a new phase has been detected, i.e. theTiSi2C40. The C40-C54 transformation kinetics and the film morphology are consistent with an increase of the nucleation density with respect to the C49-C54 transition. The activation energies for the nucleation rate (4.2±0.3 eV) and the growth velocity (4.0±0.4 eV) have been obtained from the in situ sheet resistance and the Transmission Electron Microscopy results. These results show that the process with a Ta layer at the Ti/Si interface has a greater scalability with respect to the standard TiSi2 process.
Increased Thermal Stability of Co-silicide Using Co-Ta Alloy Films
Authors: Kim Min-Joo , Choi Hyo-Jick , Ko Dae-Hong , Ku Ja-Hum , Choi Siyoung , Fujihara Kazuyuki , Kang Ho-Kyu , Lee Hoo-Jeung
Published: April 2011

The silicidation reactions and thermal stability of Co silicide formed from Co-Ta/Si systems have been investigated. In case of Co-Ta alloy process, the formation of low resistive CoSi2phase is delayed to about 660°C, as compared to conventional Co/Si system. Moreover, the presence of Ta in Co-Ta alloy films reduces the silicidation reaction rate, resulting in the strong preferential orientation in CoSi2 films. Upon high temperature post annealing in the furnace, the sheet resistance of Co-silicide formed from Co/Si systems increases significantly, while that of Co-Ta/Si systems maintains low. This is due to the formation of TaSi2 at the grain boundaries and surface of Co-silicide films, which prevents the grain boundary migration thereby slowing the agglomeration. Therefore, from our research, increased thermal stability of Co-silicide films was successfully obtained from Co-Ta alloy process.
Detecting Impurities in the Ultra Thin Silicon Oxide Layer By Hg-Schottky Capacitance–Voltage (CV) Method
Authors: Liu D. , Wang Q. , Paravi H. , Drobny V. , Moquin J.
Published: April 2011

Detecting impurities or contaminations in the ultra thin silicon oxide layer is one of the most serious challenges in wafer processing as device is scaled down toward deep sub-micron. These impurities or contaminations will create charge traps in the oxide layer and degrade gate oxide integrity (GOI). The MOS Capacitance-Voltage method which has been used to study the electrical charges in relative thicker oxide layer (> 5 nm) cannot detect, however, these contaminations related charges in the ultra thin silicon oxide layer. In this article, a new method has been developed to determine the electrical charges associated with the contaminations in an ultra thin oxide layer using Hg-Schottky capacitance-voltage method. The oxide layers of 1.2 nm in thickness with and without Cu-contamination have been tested with this new method. The results show that the new method can be used to qualitatively identify the electrical charges trapped in the ultra thin silicon oxide layer and the trapping levels associated with the contamination. The interactions among sub-stochiometric oxide structure and electron traps introduced by the metal impurities have been discussed.
Dislocation Locking by Intrinsic Point Defects in Silicon
Authors: Peidous Igor V. , Loiko Konstantin V. , Simpson Dale A. , La Tony , Frensley William R.
Published: April 2011

Dislocation pileups with abnormally weak inter-dislocation repulsion have been observed in locally oxidized silicon structures. To verify if this could be attributed to elastic interaction of dislocations with intrinsic point defects, distributions of self-interstitials in dislocation stress fields have been studied using theoretical calculations and computer simulations. According to the obtained results, self-interstitials can form atmospheres about dislocations causing dislocation stress reduction and therefore screening of dislocations from interaction with external stresses. This may represent an additional mechanism of dislocation locking in silicon alternative to oxygen pinning.
Modeling of Dislocations in an Epitaxial Island Structure
Authors: Liu X. H. , Ross F. M. , Schwarz K. W.
Published: April 2011

We present calculations of dislocations in CoSi2 islands grown by reactive epitaxy on a Si(111) substrate. The stress fields due to the lattice mismatch are calculated with standard FEM techniques, and are converted into a structured, multi-level and multi-grid stress table that is imported into the PARANOID code to study the dislocation dynamics. Single and multiple dislocations in the island have been simulated, and the predicted patterns are strikingly similar to those observed experimentally. By looking at the growth behavior of very small loops we also find that dislocation-loop nucleation becomes easier as the islands become larger, and that thick islands are dislocated at smaller sizes than thin ones. These results are also in good agreement with experimental observations. We conclude that current modeling techniques are sufficient to treat this type of problem at a useful level of accuracy.
Blistering on Silicon Surface Caused by Gettering of Hydrogen on Post-Implantation Defects
Authors: Usenko A.Y. , Carr W.N.
Published: April 2011

A well-known process for thinning of silicon by slicing submicron-thick crystalline films from substrates uses direct implantation of protons. In this paper we describe a different way of delivering hydrogen to a cleavage plane. In our process a defect-rich buried layer is first formed with ion implantation. Defects in the as-implanted silicon work as traps for hydrogen. Next monatomic hydrogen is delivered to the trap layer by electrolytic charging. To check sliceability, the samples were annealed and blistering was observed. Evidence of blistering is a sign of potential cleavage. The electrolytic charging was performed using a simple two-electrode cell. The front side of the as-implanted silicon wafer was exposed to an electrolyte. The backside of the wafer was contacted with an aluminum layer and connected to a current source. The acidic electrolyte was buffered with ethylene glycol. Buffering was used to suppress bubbling on the wafer surface and to improve the uniformity of charging. To increase charging current the wafer was illuminated with visible light. A graphite rod was used as the positive electrode in the cell. A few Coulombs per square centimeter of the wafer were passed through the cell during the hydrogenation process. The depth of blisters is about 1/2 of projection range of the implanted ions. It means that the hydrogen platelets are formed in the region of maximum of vacancy- enriched post-implantation defects. This process of electrolytic hydrogen charging may be used in future to manufacture silicon-on-insulator wafers with very thin top silicon layer. Thin SOI offers important advantages in the production of substrates for mainstream CMOS integrated circuit manufacturing.
Ultrathin Slices of Ferroelectric Domain-Patterned Lithium Niobate by Crystal Ion Slicing
Authors: Scrymgeour David A. , Gopalan Venkat , Haynes Tony E. , Levy Miguel
Published: April 2011

We report the successful fabrication of 6 µm thick slices from a ferroelectric domain micro-engineered LiNbO3 wafer device using the crystal ion slicing technique. The device was created by micropatterning ferroelectric domains in a bulk 0.3 mm thick wafer of z-cut LiNbO3, followed by ion-implanting with 3.8 MeV He+ ions to a fluence 5 × 10+16 ions/cm2 to create a damage layer at a well defined depth from the surface. Etching away this damaged layer in dilute hydrofluoric acid results in a liftoff of the top slice in which the ferroelectric domain patterns are left intact. The influence of annealing conditions on liftoff time and depth of etch lines was studied. Helium-Neon laser light was successfully coupled into the device. Due to unintentional breakage of the polished input and output faces, the electro-optic scanning performance has not been characterized so far.
Very Low Temperature E-gun Evaporated Gate Oxide of TFTs on Plastic Substrates
Authors: Kim Cheon-Hong , Jung Sang-Hoon , Han Min-Koo
Published: April 2011

A high-quality silicon dioxide (SiO2) suitable for a gate oxide on plastic substrates is successfully deposited by e-gun evaporation at room temperature. The e-gun evaporated oxide film is free from troublesome hydrogen atoms and high-energy ion damage, which ensures good electrical characteristics. N2O/N2 plasma post-treatment was effective to reduce the flat band voltage and leakage current of the evaporated oxides due to the passivation of high-energy nitrogen and oxygen radicals. In the SiO2 film treated by N2O/N2 plasma for 1 minute, the flat band voltage has been reduced from −2.5V to about −0.5V and the leakage current has been decreased by more than one order. Our experimental results show that very low temperature SiO2 film suitable for a gate insulator of TFTs on the plastic substrates has been successfully obtained by the e-gun evaporation and N2O/N2 plasma post-treatment.
Fabrication and Characterization of Poly-Si Schottky-Barrier Thin-Film Transistors
Authors: Lin Horng-Chih , Huang Tiao-Yuan , Yeh Kuan-Lin , Huang Rou-Gu , Wang Meng-Fan
Published: April 2011

Poly-Si Schottky-barrier thin-film transistors (SB-TFTs) were fabricated and characterized. In this study, SB-TFTs were first fabricated by using a conventional sidewall spacer to isolate the gate and S/D regions during salicidation. However, it was found that these SB-TFTs depict very poor on/off current ratio (<103) as well as severe GIDL (gate-induced drain leakage)-like leakage current. To overcome these shortcomings, a novel SB-TFT structure is also fabricated in this study to improve the device performance. The new device consists of a field-induced-drain region (FID), which is an offset drain region controlled by a metal field-plate lying on top of the passivation oxide. The FID region is sandwiched between the silicided drain and the active channel region. Carrier types and the conductivity of the transistor are controlled by the metal field-plate. Since the metal field plate is formed simultaneously with the regular metal patterning, no additional processing steps are required. Our results show that the new device can significantly improve the on/off current ratio to over 106 for both p- and n-channel operations, while effectively eliminating the GIDL-like leakage.
Large Area Mems: Materials Issues and Applications
Authors: Daniel J.H. , Street R.A. , Teepe M. , Ready S.E. , Ho J. , Wang Y. , Rodkin A. , Alimonda A. , Apte R.B. , Goredema A. , Boils-Boissier D.C. , Kazmaier P.M.
Published: April 2011

Conventional MEMS devices are based on silicon micro-machining and their maximum size is limited by the wafer. In contrast, we are exploring micro-machining for large area applications on substrates such as glass using polymeric materials. Our research is focused on the photopolymer SU-8, and we apply the MEMS fabrication technology to large area image sensors and displays. There are many challenges concerning the materials and processes, since large area compatibility is essential and integration with large area electronics may be required. The adhesion of SU-8 to the underlying layers as well as stress in the SU-8 are important issues and surface treatments have been investigated. Two applications of SU-8 MEMS are discussed to illustrate large area applications:. First, in the fabrication of an X-ray imager, high aspect ratio SU-8 walls form a micro-patterned phosphor screen to increase the image resolution. Second, a similar approach of patterning SU-8 into arrays of micro-cells is applied to an electrophoretic display.
Effect of a-SiC:H Film Composition on the Performance of Large Area Optical Sensors
Authors: Louro P. , Vygranenko Yu. , Fernandes M. , Vieira M. , Schubert M.
Published: April 2011

A series of large area single layers and heterojunction cells in the assembly glass/ZnO:Al/p (SixC1-x:H)/i (Si:H)/n (SixC1-x:H)/Al (0<x<1) were produced by PE-CVD at low temperature. Junction properties, carrier transport and photogeneration are investigated from dark and illuminated current-voltage and capacitance-voltage characteristics. For the heterojunction cells Atypical J-V characteristics under different illumination conditions are observed leading to poor fill factors. High serial resistances around 106 Ω are also measured. These experimental results were used as a basis for the numerical simulation of the energy band diagram, and the electrical field distribution of the whole structures. Further comparison with the sensor performance gave satisfactory agreement.

Results show that the conduction band offset is the most limiting parameter for the optimal collection of the photogenerated carriers. As the optical gap increases and the conductivity of the doped layers decreases, the transport mechanism changes from a drift to a diffusion-limited process.
Characteristics of Large-Area Plasma Enhanced Chemical Vapor Deposited TEOS Oxide with Various Short-Time Plasma Treatments
Authors: Chang Ting-Kuo , Lin Ching-Wei , Tseng Chang-Ho , Cheng Huang-Chung , Peng Yuan-Ching , Wang Wen-Tung
Published: April 2011

In this work, high quality silicon dioxide (SiO2) films were prepared by large-area plasmaenhanced chemical vapor deposition (LA-PECVD) using tetraethylorthosilicate(TEOS)-oxygen based chemistry. The effects of various short-time plasma treatments on these as-deposited TEOS oxide were also investigated. Different plasma treatments such as O2, N2O, and NH3 were used in our experiments. Electrical characteristics were exploited to examine the effects of plasma treatments. It was shown that after N2O, and NH3 plasma treatments, the electrical strength of oxide was enhanced. Besides, NH3 plasma treatment exhibited the highest enhancement efficiency. O2- plasma treatment, however, showed some harmful effects on the electrical properties of the TEOS oxide. The reliability tests including charge to breakdown (Qbd) and bias temperature stress (BTS) were also analyzed in these samples. Although better pre-stress characteristics were observed in those samples treated by NH3-plasma, samples with N2O plasma treatment showed superior stress endurance. Consequently, N2O plasma treatment seems to be the best candidate for future TFTs under the consideration of long-term reliability.
UV-Optics for Excimer Laser based Crystallization Processes
Authors: Kahlert H.-J. , Simon Frank , Burghardt Berthold
Published: April 2011

Laser based crystallization of thin amorphous films on glass substrates have entered into industrial applications since several years. The excimer laser based process provides a low temperature procedure to obtain polycrystalline silicon films on flat panel display substrates to fabricate thin film transistors (TFT's).

The key to this application is a uniform illumination of the. Line Beam systems provide up to 365mm long homogeneous exposure fields operated with up to 300 W average power 308nm excimer lasers. The paper covers a technical overview of Line Beam Optics layout, recent developments and results.

Further high resolution optics are described and discussed for sequential lateral solidification (SLS) (1,2,3) processes. The SLS application has demonstrated to efficiently produce directionally solidified microstructures or even grain-boundary –free regions on Si-films. Diffraction limited resolution in the range of several micrometers and high optical throughput are important parameters to this application.

General considerations are presented to describe technical limits which compromise laser beam related coherence effects, optimum uniform illumination, adequate resolution and depth of focus and optical efficiency for the practical application.
Capacitance-Voltage (C-V) Hysteresis in the Metal-Oxide-Semiconductor Capacitor with Si Nanocrystals Deposited by the Gas Evaporation Technique
Authors: Mishra Puspashree , Nozaki Shinji , Sakura Ryuta , Morisaki Hiroshi , Ono Hiroshi , Uchida Kazuo
Published: April 2011

Capacitance-Voltage (C-V) hysteresis was observed in the Metal-Oxide-Semiconductor (MOS) capacitor with silicon nanocrystals. The MOS capacitor was fabricated by thermal oxidation of Si nanocrystals, which were deposited on an ultra-thin thermal oxide grown previously on a p-type Si substrate. The Si nanocrystals were deposited by the gas evaporation technique with a supersonic jet nozzle. The size uniformity and the crystallinity of the Si nanocrystals are found to be better than those fabricated by the conventional gas evaporation technique. The C-V hysteresis in the MOS capacitor is attributed to electron charging and discharging of the nanocrystals by direct tunneling though the ultra-thin oxide between the nanocrystals and the substrate. The flat-band voltage shift observed during the C-V measurement depends on the size and density of the nanocrystals and also on the magnitude of the positive gate bias for charging. The retention characteristic is also discussed.
The Characterization of Initial Growth of Polycrystalline Silicon Germanium Films on Zirconium Oxide
Authors: Kim Dong-Won , Prins Freek , Ko Kil-Soo , Lee C. H. , Kwong Dim-Lee , Banerjee Sanjay
Published: April 2011

In this study, the initial growth characteristics of a SiGe film realized by ultrahigh-vacuum chemical vapor deposition (UHV CVD) using GeH4 and Si2H6 on high-K gate oxide, ZrO2, has been investigated in the temperature range from 475°C to 550°C. The influence of surface reactions on growth characteristics such as the incubation of growth, roughness of the SiGe layer, and the interface reaction of the SiGe film with ZrO2were studied using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). From our analysis we conclude that ZrO2 reacts with Si and forms zirconium silicide in the temperature range between 500°C and 550°C. The surface roughness of amorphous SiGe layers increase from 0.5nm to 1.5nm by increasing Ge content from 0.1 to 0.3. A further increase of surface roughness is observed from less than 1nm to 5nm as SiGe layer transitions from an amorphous to a poly crystalline layer.
Influence of Mg on Resistivity, Adhesion, Agglomeration of Ag(Mg)/SiO2/Si Multilayers
Authors: Kang Bongjoo , Yang Heejung , Hong Sungjin , Ko Yeonkyu , Jeong Chang-Oh , Lee Jaegab
Published: April 2011

The effect of Mg in Ag(Mg)/SiO2/Si multilayers on adhesion, agglomeration, and resistivity after annealing in vacuum at 200 to 500 have been investigated. The annealing of Ag(Mg)/SiO2/Si multilayers produced surface and interfacial MgO layers, resulting in MgO/Ag(Mg)/MgO/SiO2/Si structure. The presence of surface MgO provided the passivation against air, thus leading to the significantly enhanced resistance to agglomeration. In addition, the resistivity of Ag(Mg) film decreased by lowering Mg content and increasing the annealing temperature as well. Furthermore, Ag adhesion to SiO2 was improved due to the formation of the interfacial MgO layer resulting from the reaction of segregated Mg with SiO2. Also, the negligible solubility of Si in Ag prevented the dissolution of free silicon produced from the reaction, Mg + SiO2 = MgO + Si, which was in contrast with the dissolution of a significant amount of silicon released from the SiO2 substrate in Cu(Mg)/SiO2/Si multilayers after annealing at high temperature, e.g., 400. The dissolved Si in Cu caused the rapid increase in resistivity in Cu(Mg)/SiO2/Si.
Fabrication of MEMS Tonpilz Transducers
Authors: Zhou Q. F. , Wang L.-P. , Gerber G. , Meyer R. , Tol D. Van , Tadigadapa S. , Hughes W. J. , Trolier-McKinstry S.
Published: April 2011

Tonpilz transducers consist of a heavy tail mass, a piezoelectric spring, and a light head mass. Miniaturized tonpilz transducers are potentially interesting for the 10 to100 MHz frequency range in imaging transducers due to their high efficiency and output capabilities. Piezoelectric thin films can be used as the active element in the construction of miniaturized tonpilz structures. A 4-10 νm film is necessary for the mass-spring-mass system to resonate at these high frequencies. In this work, fabrication and characterization of lead zirconate titanate (PZT) thick films on conductive oxide LaNiO3 (LNO) coated silicon on insulator (SOI) substrates will be reported for this application. First, conductive LNO thin films, approximately 300 nm in thickness, were grown on SOI substrates by a metal-organic decomposition (MOD) method. The room temperature resistivity of the LNO was 6.5×10-4 ωcm. Randomly oriented PZT (52/48) films up to 7 νm thick were then deposited using a sol-gel process on the LNO coated SOI substrates. 20 mol.% excess lead was added to the solutions to compensate for lead volatilization during film heat treatments. PZT films with LNO bottom electrodes showed good dielectric and ferroelectric properties. The dielectric permittivity (at 1 kHz) was over 1000. The remanent polarization of PZT films was larger than 26 νC/cm2. The e31,f coefficient of PZT thick films was larger than –6.5 C/m2 when poled at -75 kV/cm for 15 minutes. A silver layer approximately 40 νm thick was screen- printed onto the PZT film to form the tail mass of the tonpilz structure. Elements were diced and the bulk silicon was removed by dry and wet-etching methods to leave the p-type silicon layer as tonpilz head mass. Fabrication of MEMS tonpilz microstructures will also be presented.
Mechanical Properties of 0.1 Micron Thick Simox Film Measured Using on-Chip Tensile Test System
Authors: Amano J. , Ando T. , Shikida M. , Sato K. , Tsuchiya T.
Published: April 2011

We evaluated the mechanical properties of a very thin single-crystal-silicon film 140 nm thick fabricated from a SIMOX wafer using an on-chip tensile testing method. The silicon specimen oriented in the <110> direction was integrated with a loading mechanism on the same chip, which was fabricated in three etching steps. The strain in the film was measured using a newly developed tensile testing system having a two-field-of-view microscope that allowed us to observe the elongation of the specimen directly. The measured fracture strain was distributed in the range of 2.4-3.2%, which is narrower than the range of 1.3-3.5% for a thicker 5-νm film.
Fabrication by Inclined-Substrate Deposition of Biaxially Textured Buffer Layer for Coated Conductors
Authors: Balachandran U. , Ma B. , Li M. , Koritala R. E. , Fisher B. L. , Erck R. A. , Dorris S. E.
Published: April 2011

Inclined substrate deposition (ISD) offers the potential for rapid production of high-quality biaxially textured buffer layers suitable for YBCO-coated conductors. We have grown biaxially textured MgO films by ISD at deposition rates of 20–100 Å/sec. Columnar grain structures with a roof-tile-shaped surface were observed in the ISD-MgO films. X-ray pole figure analysis revealed that the (002) planes of the ISD-MgO films are titled at an angle from the substrate normal. A small phi-scan full-width at half maximum (FWHM) of ≈9° was observed on MgO films deposited at an inclination angle of 55°. YBCO films were also grown on ISD-MgO-buffered Hastelloy C276 substrates by pulsed laser deposition. We obtained a critical current density of ≈2 × 105 A/cm2 at 77 K in self-field on 0.5-μm-thick, 0.5-cm-wide, 1-cm-long samples. This work has demonstrated that biaxially textured ISD MgO buffer layers deposited on metal substrates are promising candidates for fabrication of high-quality YBCO-coated conductors.
Single Buffer Layer Technology for YBCO Coated Conductors
Authors: Paranthaman M. Parans , Aytug T. , Zhai H. Y. , Sathyamurthy S. , Christen H. M. , Martin P. M. , Christen D. K. , Erickson R. E. , Thomas C. L.
Published: April 2011

In an effort to develop alternative single buffer layer technology for YBa2Cu3O7-δ (YBCO) coated conductors, we have investigated LaMnO3 (LMO) as a potential buffer layer. High-quality LMO films were grown directly on biaxially textured Ni and Ni-W (3%) substrates using rf magnetron sputtering. YBCO films were then grown on LMO buffers using pulsed laser deposition. Detailed X-ray studies have shown that both YBCO and LMO layers were grown with a single epitaxial orientation. Rutherford backscattering spectroscopy (RBS) analyses have indicated the ratio of La to Mn ratio is 1:1. SEM micrographs indicated that 3000-Å-thick LMO films on biaxially textured Ni (100) substrates were dense, continuous and crack-free. A high Jc of over 1 MA/cm2 at 77 K and self-field was obtained on YBCO films grown on LMO-buffered Ni or Ni-W substrates. We have identified LaMnO3 as a good diffusion barrier layer for Ni and it also provides a good template for growing high current density YBCO films.
Initial Assessment of the Thermoelectric Properties for the Mixed System K2−xRbxBi8Se13
Authors: Ireland John R. , Kyratsi Theodora , Kanatzidis Mercouri G. , Kannewurf C. R.
Published: April 2011

In previous studies we have investigated the thermoelectric properties of undoped and doped compositions of β-K2Bi8Se13. The attempt to substitute Rb for K resulted in a different structure type, but with potentially useful thermal properties. In this paper the results of measuring the thermoelectric properties of small crystalline samples for K2−xRbxBi8Se13 solid solutions are reported for the compositional ranges with 0 ≤ × ≤ 1 and with 1.8 ≤ × ≤ 2. The presence of rubidium provides a significant improvement in the thermopower but has much less of an effect on the electrical conductivity. The combined results are reflected in the power factor behavior as a function of temperature.
Commercial Apparatus for Measuring Thermal Transport Properties from 1.9 to 390 Kelvin
Authors: Dilley N.R. , Black R.C. , Montes L. , Wilson A. , Simmonds M.B.
Published: April 2011

We have developed an instrument which simultaneously measures the thermal conductivity κ, Seebeck coefficient α, and electrical resistivity ρ of a sample, thereby determining the thermoelectric figure of merit Z = α2/(κρ). A Quantum Design Physical Property Measurement System (PPMS) provides the temperature control from 1.9 - 390 K and applied magnetic fields of up to 14 tesla. Two small probes mounted along the sample each contain thin film Cernox chip thermometers as well as electrical contacts to monitor the temperature and voltage drops across the sample. A third probe attached to the end of the sample provides a heater and current source to stimulate the sample both thermally and electrically. The sample's response to cyclic heat pulses is analyzed in real time using DSP techniques. A nonlinear least-squares fit is used, employing a two time-constant model to determine both the thermal conductivity and the Seebeck coefficient for the material. Data acquisition using these ac techniques are expedited since we can sweep both temperature and field during a measurement. Adaptive algorithms continually adjust the thermal and electrical stimuli applied to the sample, optimizing the speed and accuracy of the measurement. We present results from some of the materials measured so far, including thermal conductivity standards and Pb in the superconducting state.
Pressure Effect of Seebeck Coeffcient for Zinc Doped Tin Clathrates
Authors: Chen F. , Stokes K. L. , Nolas G. S.
Published: April 2011

We measured the temperature dependence of electrical resistance (R) and thermopower (S) of Cs8Zn4Sn42 under high pressure up to 1.2 GPa. Both R and ∣S∣ at room temperature increased with pressure. We observed gap widening, irreversible ∣S∣ increasing under high pressure, which were similar to the behaviors of Cs8Sn44. However, the relaxation e.ect of R for Cs8Zn4Sn42 was negligible in contrast with that of Cs8Sn44. We found that the power factor S2σ (σ: electrical conductivity) near room temperature decreased linearly with pressure. The results suggest that the defects in different forms played an important role in transport properties for tin clathrates under high pressure.
High Cooling Power Density of SiGe/Si Superlattice Microcoolers
Authors: Zeng Gehong , Fan Xiaofeng , LaBounty Chris , Bowers John E. , Croke Edward , Christofferson James , Vashaee Daryoosh , Zhang Yan , Shakouri Ali
Published: April 2011

Fabrication and characterization of SiGe/Si superlattice microcoolers integrated with thin film resistors are described. Superlattice structures were used to enhance the device performance by reducing the thermal conductivity, and by providing selective emission of hot carriers through thermionic emission. Thin film metal resistors were integrated on top of the cooler devices and they were used as heat load for cooling power density measurement. Various device sizes were characterized. Net cooling over 4.1 K and a cooling power density of 598 W/cm2 for 40 × 40 μm2 devices were measured at room temperature.
When Does a Crystal Conduct Heat Like a Glass?
Authors: Sales B. C. , Chakoumakos B. C. , Keppens V. , Jin R. , Mandrus D. , Thompson J. R.
Published: April 2011

Semiconducting crystalline materials that are poor conductors of heat are important as thermoelectric materials and for technological applications involving thermal management. In the present article neutron scattering, electrical and thermal transport, heat capacity, magnetic and acoustic measurements are reported on single crystals of three semiconductors with the type I clathrate structure: Ba8Ga16Ge30, Sr8Ga16Ge30 and Eu8Ga16Ge30. Taken together these measurements suggest specific structural features that result in a crystal with the lowest possible thermal conductivity, namely that of a glass with the same chemical composition. Weakly bound atoms that rattle within oversized atomic cages in a crystal result in a low thermal conductivity, but the present data show that both rattling atoms and tunneling states are necessary to produce a true glass-like thermal conductivity.
Structure and Thermoelectric Properties of New Layered Compounds in the Quaternary System Cs-Pb-Bi-Te
Authors: Hsu Kuei-Fang , Chung Duck-Young , Lal Sangeeta , Hogan Tim , Kanatzidis Mercouri G.
Published: April 2011

By introducing of various equivalents of PbTe into the layered framework of CsBi4Te6, the four new compounds CsPbBi3Te6 (1), CsPb2Bi3Te7 (2), CsPb3Bi3Te8 (3) and CsPb4Bi3Te9 (4), were discovered. The compounds adopt layered structures built up of anionic slabs of progressively increasing thickness. The [PbmBi3Te5+m]- (m = 1, 2, 3, 4) slabs in the four structures can be viewed as fragments excised from the PbTe-type structures with 4-, 5-, 6- and 7-monolayers, respectively. As prepared, these materials are off-stoichiometric and n-type conductors. We present preliminary results of the crystal structures and thermoelectric properties of these materials and classify them as members of the new homologous series CsPbmBi3Te5+m (m = 1 to 4).
The Fabrication and Thermoelectric Properties of Amorphous Si-Ge-Au Bulk Samples
Authors: Lee Sang Min , Okamoto Yoichi , Kawahara Oshio , Morimoto Jun
Published: April 2011

The amorphous Si-Ge-Au bulk samples were fabricated with using the melt spinning method for the practical power supply or cooling devices. X-ray diffraction results showed that our samples were amorphous and the thermoelectric properties were measured by DC method. Although the electrical resistivity of the bulk sample was higher than that of the amorphous thin film, the thermoelectric power of the bulk sample was larger. The thermal conductivity of the amorphous Si-Ge-Au bulk sample was almost the same to the conventional crystalline Si-Ge bulk value. Consequently, non-dimensional figure of merit ZT is around 2 (at 600 K, • •=6.5 10λ-1V/K, • =1.9 10 ohm-m, • •= 6 W/mK) that is about ten times higher than the conventional crystalline Si-Ge bulk value.
Instrumented-Indentation for Mechanical Characterization of Boron Carbide Nano-Composite Coatings
Authors: Walter Mark , Nekkanty Srikant , Cooke Elizabeth , Doll Gary
Published: April 2011

Boron carbide (BC) is well known as a coating material that is important for a wide range of technological applications. The applicability of boron carbide stems from the fact that it is a very hard material with high lubricity, high elastic modulus, low specific gravity, and good chemical stability. Disadvantages, however, include extreme brittleness and sometimes poor adhesion. Recently, a reactive sputtering involving boron carbide targets and hydrocarbon gases has been used to produce novel nano-composite boron carbide thin films comprised of BC nano-crystals embedded in a matrix of hydrogenated amorphous carbon (DLC). The microstructure of these thin films is similar to that of other metal carbide/DLC nano-composite films. The present paper discusses the results of Vickers indentation experiments carried out on four different samples of boron carbide/DLC coatings that were sputtered deposited onto 52100 steel disks. The four different samples resulted from four different levels of hydrocarbon gas flow during processing. Acoustic emission data was recorded simultaneously with the indentation experiments. The indentations and the associated crack patterns were observed using scanning electron microscopy.