bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of the Substrate/Film Interface in GaN Films by Image Depth Profiling Secondary Ion Mass Spectrometry (Sims)
Authors: Mitha Salman , Clark-Phelps Robert , Erickson Jon W. , Gao Y. , Kim Wook , Morkoç Hadis
Published: April 2011

Epitaxial GaN films are normally grown on substrates, such as sapphire, that are not an exact lattice match for GaN. Thus during the early stages of film growth, defects may be introduced in the film. These defects can lead to islanding and form voids or other defects just above the interface. These defects produce nonuniformity in the films and affect the quality of the final film. SIMS depth profiling is a widely used to characterize GaN films. The normal SIMS depth profiles provide chemical and depth information but do not provide any lateral information. We show that image depth profiling with SIMS is a technique that can be used to identify the defects and also chemically identify other interface features with lateral dimensions down to 1 μm.
Tem/Hrem Analysis of Defects in GaN Epitaxial Layers Grown by MOVPE on SiC and Sapphire
Authors: Ruvimov S. , Liliental-Weber Z. , Dieker C. , Washburn J. , Koike M. , Amano H. , Akasaki I.
Published: April 2011

High resolution electron microscopy has been applied to study the structure of epitaxial GaN layers grown by MOVPE on SiC and sapphire substrates. Defects in GaN were systematically studied for undoped, and Si- and Mg-doped samples. For both substrates, the Si-doping was found to decrease the dislocation density at the layer surface, while Mg-doping increased it. The density of nanopipes increased with both types of doping. Cracking of GaN layers was observed for SiC substrates. Crack formation was not detected in layers grown on sapphire. Mechanisms of defect generation are discussed in relation to the initial growth stages, the effect of doping, and the type of substrate.
Characterisation of AlxGa1-xN Films Prepared by Plasma Induced Molecular Beam Epitaxy on C-Plane Sapphire
Authors: Angerer H. , Ambacher O. , Stutzmann M. , Metzger T. , Höpler R. , Born E. , Bergmaier A. , Dollinger G.
Published: April 2011

AlxGa1-xN films were grown on c-plane sapphire by plasma induced molecular beam epitaxy with 0 ≤ x ≤ 1. The composition and purity of the AlxGa1-xN layers was determined by elastic recoil detection analysis with a relative error of 5% for the Al content. Both X-ray diffraction and atomic force microscopy indicate only a slight decrease in epitaxial quality of the AlxGa1-xN films with increasing Al content up to x = 0.65. X-ray diffraction is used to separate the effects of thermally induced biaxial compressive stress and the alloy composition on the shift of interplanar spacings by measuring both lattice constants. The deviation of the c/a ratio from that of fully relaxed films is a quantitative measure of the biaxial compressive stress leading to a distortion of the unit cell. Values up to 0.5 GPa were observed. By the method proposed, the determination of alloy composition can be corrected for this effect. The results obtained by this method are in very good agreement with the elastic recoil detection measurements substantiating the validity of Vegard's law. These results, compared with optical measurements, indicate that the bowing parameter of the optical bandgap is 1.3 eV within the experimental error.
The Atomic Structure of the {1010} Inversion Domains in GaN/Sapphire Layers
Authors: Potin V. , Ruterana P. , Nouet G. , Salvador A. , Morkoç H.
Published: April 2011

Nanometric inversion domains in GaN/Al2O3 layers have been investigated using HREM. They were found to be limited by {1010} planes and to cross the entire epitaxial layer. It has been possible, using extensive image simulation and matching to discriminate between possible atomic models for the boundary plane. It is shown that the inversion domain boundaries correspond to a Holt type model containing wrong bonds (Ga-Ga, N-N), and in that plane, each atom exhibits two such bonds. This probably can explain the small size of the domains (5–20 nm).
Etch Characteristics of GaN Using Inductively Coupled Cl2/HBr and Cl2/Ar Plasmas
Authors: Kim H. S. , Lee Y. J. , Lee Y. H. , Lee J. W. , Yoo M. C. , Kim T. I. , Yeom G. Y.
Published: April 2011

To fabricate GaN-based optoelectronic devices successfully, a reproducible etch process with high etch rates, vertical etch profile, and damage-free surface is required. In this study, GaN etching was performed using planar inductively coupled plasmas and the effects of process parameters such as inductive power, bias voltage, pressures and, gas combination on the characteristics of the plasmas were studied using Langmuir probe, optical emission spectroscope (OES), and quadrupole mass spectrometer (QMS). Gas combinations of Cl2/Ar and Cl2/HBr were used to etch GaN. GaN etch rates increased with the increase of chlorine radical and ion energy (bias voltage), and the etch rates close to 4000 Å/min could be obtained without substrate heating over 100 °C. The addition of HBr and Ar (more than 20%) generally reduced GaN etch rates. In our experimental condition, it appears that the chemical reaction between Cl and Ga in GaN affects more significantly to GaN etching compared to physical sputtering, and it was partially confirmed by the data measured by Langmuir probe and OES. Angle resolved XP S data showed the variation of surface Ga/N ratio depending on the process parameters, which influence the formation of low resistance ohmic contact.
Electron Field Emission from Aluminum Nitride
Authors: Malta D. P. , Fountain G. G. , Posthill J. B. , Humphreys T. P. , Pettenkofer C. , Markunas R. J.
Published: April 2011

AlN has been identified as a candidate material for cold cathode field emitters due to its purported negative electron affinity (NEA) surface. Recent studies by our group on AlN(0001) using angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) and scanning electron microscopy (SEM) have indicated that AlN(0001) is a positive electron affinity surface. We have also investigated electron field emission behavior of AlN and pure Al films grown on Si. AlN and Al films were grown by molecular beam epitaxy (MBE) and transported via an ultra-high vacuum (UHV) integrated processing system (IPS) to an electron emission measurement system (EEMS). The reference Al film on Si showed characteristic Fowler-Nordheim behavior with a turn-on field of 120V/μm (defined at 10μA-cm-2) and ∼100μA-cm-2 emission at 140V/μm. The AlN film also showed Fowler-Nordheim behavior with a turn-on field of 60V/μm and ∼10mA-cm-2 at 100V/μm. Air exposure of the AlN film caused a shift in turn-on to 90V/μm and ∼0.1mA-cm-2 at 100V/μm. The I-V behavior of the AlN film is consistent with the ARUPS results on a different AlN sample - both indicating a positive electron affinity AlN surface.
MOCVD Growth of High Output Power Ingan Multiple Quantum Well Light Emitting Diode
Authors: Kozodoy P. , Abare A. , Sink R. K. , Mack M. , Keller S. , DenBaars S. P. , Mishra U. K. , Steigerwald D.
Published: April 2011

The MOCVD growth of InGaN / GaN multiple quantum well (MQW) structures for optoelectronic applications has been investigated. The structural and optical properties of the layers have been characterized by x-ray diffraction and photoluminescence. The effect of barrier and well dimensions on the optical properties have been examined; highest emission intensity and narrowest linewidth were obtained with thin wells (20–30 Å) and thick barriers (greater than 50 Å). By incorporating an MQW structure as the active region in a GaN p-n diode, high-brightness light emitting diodes (LEDs) have been produced. Under a forward current of 20 raA, these devices emit 2.2 mW of power corresponding to an external quantum efficiency of 4.5%. The emission spectrum peaks at 445 nm and exhibits a narrow linewidth of 28 nm. Under pulsed high current conditions, output power as high as 53 mW was realized and the peak emission wavelength shifted to 430 nm.
Growth of GaN Thin Films on Sapphire Substrate by Low Pressure MOCVD
Authors: Ishida M. , Hashimoto T. , Takayama T. , Imafuji O. , Yuri M. , Yoshikawa A. , Itoh K. , Terakoshi Y. , Sugino T. , Shirafuji J.
Published: April 2011

High quality GaN films are grown on sapphire(0001) substrates by low pressure MOCVD using TMG and NH3 as source materials. Effects of surface nitridation and buffer layer thickness on the quality of over-grown GaN films are investigated. It is revealed by atomic force microscope (AFM) observations that surface roughness of the annealed buffer layers strongly depends on the nitridation time. Dislocation density and surface morphology of the high temperature GaN layer depend on the buffer layer thickness. It is found that sufficient surface nitridation of sapphire makes the buffer layer just prior to the high temperature growth very smooth, which is essential to obtain flat thick-GaN on it. It is also found that thickness of the buffer layer largely influences the dislocation density in the over-grown thick GaN. In order to obtain good surface morphology and low dislocation density at the same time, both nitridation time and buffer layer thickness must be optimized.
Comparison of SiH4 and Si2H6 RTCVD Kinetics using in-situ Spectroscopic Ellipsometry
Authors: Hu Y. Z. , Tay S. P. , Wasserman Y. , Zhao C. Y. , Irene E. A.
Published: April 2011

A comparison of SiH4 and Si2H6 chemical vapor deposition kinetics was performed in a rapid thermal processing (RTP) system at temperatures between 600 and 800 °C and reactant gas pressures between 1 and 25 mTorr. Quantitative assessment of the nucleation parameters and the microstructures of the deposited polycrystalline Si (poly-Si) films on SiO2 have been determined using in situ real time single wavelength and spectroscopie ellipsometry. In addition to ellipsometry, atomic force microscopy and cross-sectional transmission electron microscopy were used ex situ to observe the nucleation stage and the microstructures of the poly-Si films. In the present study we compare the nucleation, poly-Si film microstructure and surface roughness using SiH4 and Si2H6 in the RTP system and show that under the same processing conditions the saturation nuclei density (1010 cm−2) for Si2H6 is about 6 times higher than that for SiH4 and the poly-Si films from Si2H6 are smoother and have better columnar structure than those from SiH4.

A particularly important parameter for selective epitaxial depositions is the time for nuclei to form, i.e. the incubation time. An operational incubation time were determined from the real time ellipsometric measurements and confirmed by AFM. The incubation times for using SiH4 and Si2H6 are different, but they show similar activation energies of about Einc = 1 eV in the 600–800 °C range. A formula of incubation time tinc was obtained and expressed.
Study of Repeatability, Relative Accuracy and Lifetime of Thermocouple Instrumented Calibration Wafers for RTP
Authors: Vandenabeele Peter , Renken Wayne
Published: April 2011

An RTP system with accurate lamp power control was used to study the repeatability of Sens Array type “1530” and “1501” thermocouple (TC) wafers. The drift of the “1530” wafers was measured over 200 heating cycles of 20 seconds at 1050 °C and 1150 °C. Over the 200 cycles at 1150 °C, a drift between -0.5 and +1.0 °C was found. Over the 1050 °C cycles a larger drift between +1.0 °C and +2.0 °C was found, possibly caused by the formation of “haze” over the wafer that changed the optical properties of the wafer. Experiments were conducted for the effect of unloading/loading of the wafer in the oven. An instability of maximum ±0.4 °C was found for “1530”, caused by the unloading/loading. The relative accuracy of “1530” from one thermocouple to another shows a typical variation of ±1.0 °C or smaller. The older technology TC wafers (1501), showed considerably higher instability upon wafer unloading/loading and higher TC to TC variations (± 5 °C). The useful lifetime of a TC wafer is at least 50 to 200 heating cycles.
The Influence of Facility Conditions on A ±0.25 °C Repeatability Lamp Voltage Controlled RTP System
Authors: Vandenabeele Peter , Renken Wayne
Published: April 2011

The influence of cooling air and cooling water parameters on the wafer temperature was studied in an RTP system with lamp power control. With a cool down time of 150 seconds between consecutive heating cycles, the wafer temperature in a 1050 °C process was highly sensitive to cooling air flow. With a cool down time of 330 seconds the sensitivity dropped a factor of 5. This was explained through the effect of radiative heat transfer from the quartz to the wafer at higher quartz temperatures (>200 °C). Other factors are variations in the water flow through the oven walls and the repeatability of wafer positioning.
Characterization of Oxide Etching and Wafer Cleaning using Vapor-Phase Anhydrous HF and Ozone
Authors: Froeschle Barbara , Deutschmann Lutz , Bauer Anton J. , Burte Edmund P.
Published: April 2011

A cleaning process using anhydrous HF (AHF)/methanol and ozone is carried out in a STEAG-AST Vapor Phase Cleaning module (VPC). This module is integrated in a state-of-the-art cluster tool also consisting of a STEAG-AST Rapid Thermal Oxidation module (RTO). The dependence of AHF vapor phase etch rate of thermally grown silicon dioxide on different process parameters, such as etch time, AHF-flow, and temperature is evaluated. The optimized etch process is found to be at a temperature of 40°C and at a pressure of 50 mbar for this VPC module. Using the above etch parameters various combinations of vapor phase surface preparation chemistries combining AHF etching and ozone/UV cleaning are evaluated.

To demonstrate the feasibility of this cluster tool for advanced gate dielectric formation, 4.0 nm thin oxide is grown directly after the cleaning in the RTO module without breaking the vacuum. Time dependent dielectric breakdown results for oxides pre-oxidation-cleaned in AHF, and in AHF followed by ozone are compared to a reference sample without any dry pre-oxidation cleaning. It can be shown, that the cleaning in AHF with a subsequent ozone step at 200°C under UV light leads to improved breakdown characteristics compared to AHF/methanol cleanings without such subsequent ozone/UV step or conventional wet cleaning using HF-Dip.
An Interactive System for Wafer Emissivity Estimation as Determined in an RTP Chamber
Authors: Fulco Maurizio , Russo Onofrio L. , Belikov Sergey , Kosonocky Walter
Published: April 2011

We demonstrate an interactive software system in which the emissivity of wafers can be estimated in situ using different models. The system allows the data taker to introduce a choice of design parameters necessary for the control of temperature uniformity. The objective of the interactive system is to obtain a better estimation of the wavelength dependent emissivity by using existing data such as integrated emissivity, for example, as input information. Results for some of the models are presented and compared to show differences in the models chosen. The principle advantage offered by the system are the likely prospects of a realistic improvement and confident assessment for real time temperature measurement and control in an RTP environment.
Deep Level Investigation in Si-GaAs by Rapid Thermal Annealing
Authors: Zhouying Zhao , Fengmai Wu , Ningsheng Li
Published: April 2011

Deep levels in undoped LEC semi-insulating (SI) GaAs have been investigated by rapid thermal annealing (RTA). The GaAs wafers were annealed for 10 sec in N2 atmosphere at temperatures ranging from 500 to 800 °C. Using photo-induced current transient spectroscopy (PITS) and Hall measurement, we have investigated the behavior of various deep levels as a function of RTA temperature and the phenomenon of thermal conversion. The change and even conversion in resistivity is related not only to decrease of the EL2 and EL6 defects, but also to shallow acceptor caused by arsenic-escaping in the surface of the wafer. Choosing proper RTA temperaturte will improve the electrical properties of SI-GaAs after RTA.
Growth and Nitridation of Silicon-Dioxide Films on Silicon-Carbide
Authors: Sweatman Denis , Dimitrijev Sima , Li Hui-Feng , Tanner Philip , Barry Harrison H.
Published: April 2011

Silicon-carbide offers great potential as a wide bandgap semiconductor for electronic applications. A good quality oxide dielectric will allow MOS device fabrication and in particular N-channel mosfets for their higher electron mobility. To date oxides on N-type silicon-carbide (nitrogen doped) have exhibited excellent characteristics while on P-type (aluminium or boron doped) the characteristics are poor. This paper presents results for the oxidation and subsequent nitridation of N and P-type silicon-carbide. It illustrates the role that nitrogen at the interface has in improving the trap densities and that nitric oxide provides the nitrogen well. Nitrous oxide, previously used to nitride silicon dioxide on silicon, is shown to substantially deteriorate the interface density of states for both N and P-type substrates.
Emissivity-Independent Rapid Thermal Processing using Radiation Shields
Authors: Timans P. J. , Morishige R. N. , Wasserman Y.
Published: April 2011

Simple rapid thermal processing (RTP) system configurations, in which the wafer temperature is controlled by a pyrometer viewing the wafer's backside, are vulnerable to changes in the spectral emissivity of this surface. One method for emissivity-independent temperature control is to use an opaque plate beneath the wafer as a radiation shield, which masks the wafer's backside from the heating lamps and provides a target whose temperature can be monitored easily by a pyrometer or a thermocouple. Experimental studies of the dynamic temperature responses of the wafer and the shield are in good agreement with predictions from a theoretical model based on a simple analysis of radiation heat transfer in the system. For the set of wafers studied here, pyrometer control of the shield temperature gave a spread of wafer temperatures of 4°C, as compared to a range of 160°C when the shield was not used. The radiation shield was also shown to give RTP process results which are immune to changes in wafer backside coatings.
Temperature Dependent Emissivity of Multilayers on Silicon
Authors: Abedrabbo S. , Ravindra N. M. , Chen W. , Rajasekhar V. , Golota T. , Gokce O. H. , Fiory A. T. , Nguyenphu B. , Nanda A. , Speranza T. , Maszara W. , Williamson G.
Published: April 2011

The spectral transmittance, reflectance and emittance of silicon related materials and structures are measured simultaneously utilizing a spectral emissometer operating at near- and mid-IR spectral range and temperature range of 300 to 1500K. Several kinds of samples have been considered here: a) SiO2/Si with oxide in the thickness range of 653–5124A, b) SiO2/Si/ SiO2 with oxide thickness of 5000A on both front and back sides c)Multi-layers of SiO2/Si/ SiO2/poly-Si, with backside oxide of 1600A and 250A, respectively and d) separation by implantation of oxygen (SIMOX), with embedded oxide thickness of 4000A. An extensive analysis has been performed to interpret and compare the results obtained from these measurements.

Concerning the SiO2/Si, we find that the experimental results are in accord with the sinusoidal relation of emissivity as a function of the silicon oxide thickness and hence the Applied Materials model. Experimental results on SiO2/Si/SiO2 are also presented here. For the multi-layers of SiO2/Si/SiO2/poly-Si, it is interesting to note that for temperatures above 600°C, the emissivity is independent of temperature and wavelength for the backside oxide thickness of 1600 and 250A. SIMOX measurements are presented as well. The Fiory model has been utilized extensively to investigate the high temperature emissivity data. The applications and limitations of this model are discussed.
Measurement of the Effective Mass of Transparent Conducting films of Cadmium Tin Oxide
Authors: Mulligan W. P. , Coutts T. J.
Published: April 2011

We have prepared transparent conducting films of cadmium stannate (Cd2SnO4 with resistivity as low as 1.5×10-4 Ω cm. The resistivity of these films is low because of their surprisingly high mobility (60 cm2 V-1 sec-1) at high carrier concentration (7×1020cm-3). We conducted an investigation to determine whether the high mobility is due to unusually low carrier effective mass or to a long carrier relaxation time. The conductivity effective mass and relaxation time were estimated by Drude free-electron modeling of reflectance and transmittance spectroscopie measurements. The Drude model appears to represent the behavior of cadmium tin oxide very well. The optical effective mass of the electrons in cadmium stannate is about 0.35 mo, which is similar to that of other transparent conducting oxides. By varying the doping level, we were able to fabricate films with various levels of degeneracy, but these showed no significant difference in effective mass.

We were also able to determine the carrier effective mass and the relaxation time by measuring four separate electron transport coefficients: conductivity, Hall, Seebeck, and transverse Nernst-Ettingshausen (Nernst). The Fermi level was found to vary from 0.31 to 0.83 eV above the conduction band minimum, and the conduction band was very close to parabolic in this range, with m* ∼ 0.33 mo, in good agreement with the optical result. We conclude that the effective mass of electrons in cadmium stannate is similar to electrons in other transparent conducting oxides and that high mobility results from a relatively long carrier relaxation time.
Hot-Wire Hydrogen Passivation of Polycrystalline Silicon TFT's
Authors: Beldi N. , Le Bihan F. , Kis-Sion K. , Sarret M. , Mohammed-Brahim T. , Raoult F. , Rogel R. , Guillet J. , Bouree J. E.
Published: April 2011

Polysilicon N-channel TFT have been hydrogenated using the H2 dissociation on a hot tungsten filament. A post-annealing realized at the optimal temperature of 300°C is necessary to obtain interesting electrical TFT characteristics. Different TFT's sizes and geometries have been processed. The analysis of their characteristics shows that hydrogen preferentially diffuses through silicon oxide layer. The enhancement of the current in the ON-state shows that hydrogen atoms have passivated silicon oxide gate / polysilicon interface traps. The important reduction of the dependency of the OFF-state current with the reverse gate voltage shows that hydrogen atoms have passivated grain boundary traps near the interface in the channel region and in the drain sheet resistance region then reducing the trapped carrier emission.
Analytical Treatment of Field-Effect Conduction in Polysilicon thin film Transistors
Authors: Eccleston W.
Published: April 2011

The drift of electrons in the channels of Thin Film Transistors is analysed for discrete grains separated by grain boundaries containing amorphous silicon. The model provides the relationship channel mobility and grain size. The relationship between drain current and the terminal voltages is also predicted. The model relates to normal high current region of transistor operation.
Performance of thin film Transistors on Unhydrogenated In-Situ Doped Polysilicon films Obtained by Solid Phase Crystallization
Authors: Mourgues K. , Raoult F. , Pichon L. , Mohammed-Brahim T. , Briand D. , Bonnaud O.
Published: April 2011

Low Temperature Unhydrogenated in-situ doped polysilicon Thin Film Transistors (LTUTFT) are made through two types of four-mask aluminium gate process. Silicon layers are elaborated by a Low Pressure Chemical Vapor Deposition (LPCVD) method and crystallized by a thermal annealing. Source and drain regions are in-situ doped. An Atmospheric Pressure Chemical Vapor Deposition (APCVD) silicon dioxide ensures the gate insulation. Two structures A and B are fabricated, the difference is that for sample B the undoped/doped polysilicon layer interface is suppressed.

The structure of the polysilicon films is studied using Transmission Electron Microscopy (TEM) and Current-Voltage characteristics of both types of TFTs indicate electrical quality of the polysilicon films.

The best electrical properties are obtained with the B type TFTs: a low threshold voltage (VT=1.2V), a low subthreshold slope (0.7 V/dec), a high On/Off state current ratio (107) for a drain voltage VDS= 1V, and a very high field effect mobility (≥100 cm2 /Vs). It is worth to notice that these good results are obtained without hydrogenation.
Enhancement of On/Off Current Ratio of Poly-Silicon TFT by Selective Laser-Induced Crystallization of Active Layer
Authors: Jeon Jae-Hong , Park Cheol-Min , Choi Hong-Seok , Kim Cheon-Hong , Han Min-Koo
Published: April 2011

We have proposed the new poly-Si TFT which reduces the leakage current effectively by employing highly resistive a-Si region in the channel. The active layer of proposed device is crystallized selectively by employing excimer laser annealing while the both sides of channel near the source/drain are not recrystallized and remained as a-Si. Unlikely LDD or offset structure, the a-Si region which is designed to reduce the leakage current acts as the conduction channel of carriers under the ON state, so that the ON current is decreased very little. The selectively crystallized active layer can be fabricated by irradiating the excimer laser through ITO film of which transmittance at the wave length of laser is selectively adjusted. In the course of fabricating the proposed device, any additional photo masking step is not necessary and misalign problem is eliminated. The experimental results show that the ON/OFF current ratio of proposed poly-Si TFT is 106 while that of conventional one is 105.
Performance Study of 4-Inch Full Color Field Emission Display Devices
Authors: Kim J. M. , Hong J. P. , Park N. S. , Jung J. E. , Jin Y. W. , Ryu Y. S. , Kim J. W. , Choi J. H. , Kang J. H. , Jang J. E. , Gofinkel B. I. , Roussina E. V.
Published: April 2011

We present performance results of 4-inch full-color field emission display (FED) devices which are constructed by using Spindt type arrays with 80,000,000 Mo-metal tips, spacers, uniquely-developed low voltage color phosphors. Spindt type microtips with less than 1.1 urn in hole size are fabricated using a total internal reflection (TIR) holographic lithograpy method. Each color phosphor is electrophoretically deposited on the ITO line. The spacer which is screen-printed is characterized by a 3-dimentional surface analysis system. Electron emission pattern and luminance test of each pixel without cross talk are analyzed under different gate voltages. In addition, the total pressure and residual gas distributions inside the panel are investigated at various gap sizes between the cathode and anode plates.
Flexible, Lightweight Steel-Foil Substrates For a-Si:H Thin-Film Transistors
Authors: Theiss S. D. , Wu C. C. , Lu M. , Sturm J. C. , Wagner S.
Published: April 2011

For many flat panel display applications, traditional glass substrates for the TFT backplane are not sufficiently rugged. Therefore, we have begun to explore the use of steel foils as TFT substrates for emissive or reflective displays. We report the fabrication of high quality a-Si:H TFTs on lightweight, flexible 75 μm thick stainless steel foils. The electrical characteristics of the TFTs were good and were not significantly affected by either dropping over 15 meters to a concrete floor or being bent to a radius of curvature of 8.25 cm for a period of over 400 hours. Typical device characteristics were: ION/IOFF > 107, IOFF ∼ 1012 A, VT ∼ 3.2 V, and μEFF ∼ 0.9 cm2/Vs. We also discuss our recent work on the successful integration of organic light-emitting diodes (OLEDs) with TFTs on steel substrates, resulting in a new form of emissive display.
Band Model for Electron Emission from Diamond and Diamond-Like Carbon
Authors: Robertson J
Published: April 2011

The band diagram is constructed for diamond on metal and diamond-like carbon on metal emitters, from data for electron affinities, Schottky barrier heights or band offsets. For diamond, there is a large offset for the conduction band at the back-contact, causing this to be the dominant barrier for emission. Nitrogen and perhaps grain boundaries reduce this barrier by forming a depletion layer of ionised donors, which narrows the tunnelling distance. In DLC, there is little conduction band offset at the back-contact, and the dominant barrier is at the surface. Nitrogen now lowers the emission barrier by raising the bulk Fermi level and lowering the work function. Unresolved problems are also pointed out.
Sputter Deposition of Nanocones for Field Emission
Authors: Jankowski Alan F. , Hayes Jeffrey P.
Published: April 2011

Deposition into micron-sized holes is known to produce cone shapes as supported on substrates. Potential uses for the cones include field-forming devices as field ionizers and field emission cathodes. The application of such devices include flat panel displays and flash x-ray tubes. Process iterations to closely space arrays of sharp cones have been extensively documented during the past two decades using the physical vapor deposition method of evaporation. Sputter deposition is well known as a method to fill holes and trenches but has only recently been demonstrated as an alternative method to produce field emission cathodes. In a further reduction in size, we have been successful in demonstrating the ability to deposit a cone shape into a cavity with a 300nm diameter hole. Through comparison to the results of electron-beam evaporative deposition, a sputter deposited nanocone appears to be suitable for use as a field emission cathode.
Microstructure and Luminescence Properties of ZnS:Cu Powders and Electroluminescent Lamps
Authors: Sangaletti Luigi , Depero Laura E. , Allieri Brigida , Antonini Livio , Fantini Roberto , Bettinelli Marco
Published: April 2011

We report on a microscopy and diffraction study of commercially available Cu-doped ZnS powders, along with an optical spectroscopy study of electroluminescent lamps fabricated with these powders. The results allowed us to identify a correlation between the microstructure and the optical properties (i.e. photoluminescence) of the ZnS powders. It is found that the best powders for EL lamps are those displaying a prevalent cubic, i.e. zincblend, structure, while the poor performances of the mixed phase (cubic + hexagonal) are tentatively ascribed to the quenching of luminescence due to defects (stacking faults) introduced into the cubic structure and resulting in a considerable amount of hexagonal phase, as detected by XRD. The mostly cubic powders have been selected to realize EL lamps. The optical properties of these lamps have been investigated by photoluminescence and electroluminescence spectroscopies with the aim to identify the degradation mechanisms leading to a decrease of brightness. The quenching of electroluminescence is primarily ascribed to a deterioration of the electrical contacts. However, the reduced brightness in photoluminescence spectra seems to indicate that additional quenching of luminescence is induced by transformations at the emitting layer of the lamps. This degradation is tentatively ascribed to the presence of voids in the emitting layer, which might induce, acting as traps for moisture, transformations in the optical and electrical properties of the transparent electrode (ITO).
Blue Electroluminescent Devices Fabricated from Silicon and Germanium Nanocrystals
Authors: Delgado Gildardo R. , Lee Howard W. H. , Pakbaz Khashayar
Published: April 2011

Blue electroluminescent (EL) devices were fabricated with Si nanocrystals produced by ultrasonic fracturing of porous silicon (PSi) as well as silicon and germanium nanocrystals synthesized through a control chemical reaction. The active EL material consists of Si and Ge nanocrystals embedded in various host matrices such as polyvinylcarbazole (PVK), polymethylmethacrylate (PMMA), silica sol-gels and other organic polymers and small organic molecules. Several device configurations were used to induce EL processes that rely on radiative electron-hole recombination within the nanocrystals. We report on the optical and electrical properties of these devices. Applications for these EL devices include highly efficient light emitting devices. The cost and ease of processing of these material systems make them potentially ideal for flat panel display applications.
Full-color Thin Film ZnGa2O4 Phosphors by Ion Implantation
Authors: Kalkhoran N. M. , Trivedi D. A. , Halverson W. D. , Vernon S. M.
Published: April 2011

Full-color cathodoluminescence (CL) characteristics of ion implanted ZnGa2O4 thin film phosphors deposited by rf sputtering have been investigated. High brightness red (R) and green (G) CL was obtained from Eu and Mn-implanted ions, respectively. Blue (B) emission has been achieved by Ce ion implantation or from high temperature annealed, self-activated films. RGB emissions of ion implanted ZnGa2O4 thin film phosphors are well saturated and enclose a larger area surrounding the central “white” zone of CIE chromaticity chart than standard CRT phosphors. Luminescence efficiency enhancements of up to 40% have been achieved through surface texturing of the substrate prior to phosphor deposition. First demonstration of bright luminescence in ion implanted ZnGa2O4 films on flexible polyimide substrates is reported.
The Application of Poly(Phenylene) Type Polymers and Oligomers in Electroluminescent Color Displays
Authors: Tasch S. , Brandstätter C. , Graupner W. , Hampel S. , Hochfilzer C. , List J. W. E. , Meghdadi F. , Leising G. , Schlichting P. , Rohr U. , Geerts Y. , Scherf U. , Müllen K.
Published: April 2011

Due to their high photoluminescence efficiency (>30%), high environmental stability and the good charge transport properties the derivatives of poly(paraphenylene) (PPP), as the laddertype PPP (LPPP) and the oligomer hexaphenyl, are very suitable materials to realise efficient, stable, large area blue organic light-emitting diodes (OLEDs). The emission of blue OLEDs can be efficiently converted into all other emission colors either by an external color conversion technique (ECCT) or an internal color conversion technique (ICCT) and hence are very interesting for a number of display applications:

Firstly, we demonstrate the realisation of efficient red-green-blue (RGB) emission colors (representing the RGB-pixels in a multicolor display) by an external CCT. In this case the blue EL device is covered with highly fluorescenct dye/matrix layers, which are excited by the blue emission and emit photoluminescence light in a lower energetic range.

Secondly, a new method for producing efficient white light-emitting polymer diodes (which are interesting for e.g. backlight sources in liquid crystal displays) based on a blend of two polymers is presented: a blue light-emitting m-LPPP and a red-orange emitter poly(perylene-co-diethynylbenzene) (PPDB). The red-orange emission is created within the EL device (ICCT) by an excitation energy transfer from m-LPPP into the energetically lower lying states of PPDB. This internal excitation energy transfer is very efficient, so that only a concentration of 0.05 weight % PPDB in the polymer blend is required in order to obtain white light emission.
Spray-Deposited Metal Oxide Films with Various Properties for Micro- and Optoelectronic Applications: Growth and Characterization
Authors: Malik A. , Séco A. , Nunes R. , Vieira M. , Fortunato E. , Martins R.
Published: April 2011

This work reports the structure and electro-optical characteristics of different metal oxide films obtained by spray pyrolysis on heated glass substrates, aiming their application in optoelectronic devices. The results show that this technique leads to thin films with properties ranging from dielectric to degenerate semiconductors, offering the following advantages: simplicity, low cost, high productivity and the possibility of covering large areas, highly important for large area device applications.
Phase Equilibria and Properties of Transparent Conductors in the Indium-Tin-Zinc Oxide System
Authors: Palmer George B. , Poeppelmeier Kenneth R. , Edwards Doreen D. , Moriga Toshihiro , Mason Thomas O. , Schindler Jon L. , Kannewurf Carl R.
Published: April 2011

Solid state bulk processing techniques were used to synthesize various transparent conducting oxides (TCO's) with In, Zn, and Sn cations. Optical and electronic properties of resultant phase-pure TCO's were compared to each other and to bulk samples of Sn-doped In2O3 (ITO). Reduction and heat treatment showed significant effects on optical and electronic performance, indicating optimization of processing conditions will be required for industrial applications.

Comparison of optical and electronic properties in the series of compounds: ZnkIn2O3+k, k = 3,4,5,7,11 revealed trends correlated with the materials’ internal structure. These layered compounds showed improvement of optical properties at higher Zn contents and improvement in conductivity at higher In contents. The trends suggest these materials may be useful for applications where tradeoffs between conductivity and transparency are acceptable.
Measurement of Strain Associated with Defects in SiTiO3 Bicrystals using Near-Field Scanning Optical Microscopy
Authors: McDaniel E. B. , Hsu J. W. P.
Published: April 2011

We incorporate a polarization modulation technique in a near-field scanning optical microscope (NSOM) for quantitative polarimetry studies at the nanometer scale. Using this technique, we map out stress-induced birefringence associated with submicron defects at the fusion boundaries of SiTiO3 bicrystals. The strain fields surrounding these defects are larger than the defect sizes and show complex spiral shapes that break the reflection symmetry of the bicrystal boundary.
Effects of Lattice Distortion, Polaron Conduction and Double-Exchange Interaction on the Physical Properties of Magnetoresistive Manganites and Cobaltites
Authors: Yeh N.-C. , Vasquez R. P. , Wei J. Y. T. , Fu C-C. , Beach G. , Huynh J. , Samoilov A. V. , BoriS A. V. , Kovaleva N. N. , Bazhenov A. V.
Published: April 2011

The relevance of lattice distortion, polaron conduction, and double-exchange interaction to the occurrence of colossal magnetoresistance (CMR) is investigated by comparing the physical properties of magnetoresistive manganites and cobaltites. The samples studied in this work include epitaxial films and ceramics of manganites with both A- and B-site substitution, (La0.7Ca0.3MnO3, LaMn0.7 Ni0.3O3, LaMnO.5Ni0.5O3), as well as epitaxial films and ceramics of cobaltites (La0.5Ca0.5CoO3). The structural, chemical, electrical transport, magnetic, optical properties and tunneling spectroscopy are studied. Based on our experimental results, we conclude that both double-exchange interaction and strong electron-phonon coupling due to the Jahn-Teller effect are essential to the occurrence of CMR.
Growth and Magnetic Structure of La0.67Sr0.33MnO3 Films
Authors: Brown G. W. , Jia Q. X. , Peterson E. J. , Hristova D. K. , Hundley M. F. , Thompson J. D. , Maggiore C. J. , Tesmer J. , Hawley M. E.
Published: April 2011

Growth of LaMnO3 films that exhibit colossal magnetoresistance (CMR) has concentrated heavily on Ca doped materials. However, since the 33% Sr doped films are ferromagnetic at room temperature, they are ideal candidates for dual growth-magnetic structure studies using scanned probe techniques. In this study, interest was focused on the relations between growth/processing parameters, film morphology, and electronic/magnetic properties. In addition, films were grown on both LaA1O3 (LAO) and SrTiO3 (STO) to examine the results of stress induced by different substrate mismatches. La0.67Sr0.33MnO3 (LSMO) was grown using pulsed laser deposition (PLD) at temperatures between 500 °C and 800 °C. The film microstructure, crystallinity, and magnetic and electrical properties were characterized by room temperature scanning tunneling microscopy (STM), atomic force microscopy (AFM), magnetic force microscopy (MFM), x-ray diffraction, and temperature dependent transport and magnetization measurements. The growth trends follow those previously reported for Ca doped films. Grains increase in size with increasing temperature and coalesce into extended layers after annealing. Although topographic contributions complicate interpretation of some MFM data, local magnetic structure observed here is generally associated with film defects.
MBE-Growth of Iron and Iron Oxide Thin Films on MgO(1OO), Using NO2, NO, and N2O as Oxidising Agents
Authors: Voogt F. C. , Hibma T. , Smulders P.J.M. , Iesen L. , Fujii T.
Published: April 2011

We have made a study of the use of NO2 as the source of oxygen in the MBE-growth of iron oxides thin films. It is found that NO2 is a much more efficient oxidising agent than molecular O2. As indicated by Mössbauer spectroscopy, performed on 57Fe probe layers, NO2 is not only capable of forming stoichiometric magnetite Fe3O41 but also all non-stoichiometric Fe3-δO4 phases. Even the metastable maghemite phase γ-Fe2O3 (Fe3-δO4 with δ=1/3) can be formed. All iron oxides grow layer-by-layer-like, as indicated by strong RHEED intensity oscillations. When small doses of NO2 are used, new wustite Fe3-xO and Fe3O4 phases are formed. In contrast to the Fe3-δO4 films, these phases have nitrogen incorporated into the crystal lattice. Similar compounds are obtained when NO is used as the source of oxygen. The use of N2O does not lead to the formation of iron oxides. It does, however, alter the growth mode of Fe on MgO(100). Whereas Fe deposited under UHV conditions forms 3D islands, the N2O acts as a surfactant and induces 2D layer-by-layer growth.
Characterization of Off-Axis Sputtered La0.67Ca0.33MnO3 Films and La0.67Ca0.33MnO3/YBa2Cu3O7-δ Bilayers
Authors: Broussard P. R. , Cestone V. C. , Qadri S. B.
Published: April 2011

Thin films of the colossal magnetoresistive material La0.67Ca0.33MnO3 (LCMO) have been grown by off-axis sputtering from a single target of the LCMO material onto various substrates and studied by electrical transport, x-ray diffraction, scanning electron microscopy and atomic force microscopy. The LCMO films typically grow with the (002) direction oriented normal to the film. We find magnetoresistances at 6 T of ≈ 90%. We observe a scaling between the temperature of the resistivity peak (Tp) and the relative change in resistivity between room temperature and the resistance peak for Tp varying from 90 to 270 K. This scaling is consistent with an activated resistivity above the peak, with an activation temperature of ≈ 940 K. Films of LCMO grown on cubic zirconia exhibit an upturn in resistivity at low temperatures. Bilayers of LCMO and the superconductor YBa2Cu3O7-δ have been grown and compared to see the effects of having either the magnetic or superconducting layer first in the sequence.
Magnetoresisnve La-Sr-Mn-O Powders and Films by Daas Technique
Authors: Yang S. , Lin C.-T. , Rogacki K. , Dabrowski B. M. , Adams P. M. , Speckman D. M.
Published: April 2011

Magnetic perovskites of the general form La1-xSrxMnO3 have successfully been synthesized using deposition by aqueous acetate solution (DAAS). This novel technique, which has the potential for depositing large area min films with high throughput and low cost, involves the preparation of an aqueous metal acetate precursor solution, drying the solution to generate a glassy gel, consolidating the gel, and then firing it for short periods of time (<2hrs) to produce crystalline lanthanum strontium manganate (LSMO). The DAAS method has been used to prepare both powders and thin films of LSMO. Powder samples of La0.83Sr0.17MnO3 annealed for 100 minutes at 1200°C were high purity, single phase, and exhibited excellent electrical and magnetic characteristics. Thin films of La0.7Sr0.17MnO3 deposited onto both sapphire and strontium titanate substrates and annealed at 900°C were also found to be crystalline, and substrate choice was found to influence thin film crystal structure. These films exhibited sharp metal-insulator transitions, and in the case of LSMO films on strontium titanate, magnetoresistance was observed at the unusually high temperature of ∼360K.
High Quality Epitaxial V2O3 Thin Films: A Material for Infrared Switching Devices?
Authors: Schuler H. , Grigoriev S. , Horn S.
Published: April 2011

The compound V20O13 undergoes a metal-insulator-transition (MIT) at T=150K with an optical gap in the insulating phase of ∼0.6eV. Therefore epitaxial films of V2O3 are of interest for infrared (IR) applications. We present the results of a systematic study of the growth conditions of such films utilizing electronic transport and infrared transmission measurements in addition to studies of crystal and microstructure.

Epitaxial V2O3 thin films were grown in a reactive oxygen atmosphere on c-axis oriented sapphire substrates by electron beam evaporation. While V2O3 single crystals show a MIT in a narrow temperature range ΔT < 1K, the MIT broadened in epitaxial thin films due to defects and stress induced by the film-substrate interaction.

In our study we defined the quality of the films by the width ΔT of the transition and the change of resistivity p and IR transmission at the MIT. We found the most important growth parameter to be the growth temperature. Only in a narrow region around 600°C the growth of high quality films was observed. The optical constants of such films were determined from IR transmission measurements in combination with an oscillator fit method. While the spectra in both the metallic and the insulting phase are dominated by d-d-transitions for photon energies above leV, in the IR region (λ > 2μm) a high transmission contrast between the two phases was almost independent of the wavelength. This behavior suggests e.g. applications as a non mechanical IR shutter or as switchable interference filter in the IR regime.
Origin of the (110) Orientation of Y2O3 and CeO2 Epitaxial Films Grown on (100) Silicon
Authors: Goettler R. L. , Maria J. P. , Schlom D. G.
Published: April 2011

A perplexing issue in the growth of epitaxial oxide films on (100) silicon is the observed (110) orientation of yttria (Y2O3) and ceria (CeO2) despite the (100) orientation having a lower lattice mismatch. As expected, yttria-stabilized zirconia (YSZ) grows with the (100) orientation, yet it has a worse lattice match than both Y2O3(100) and CeO2(100) with silicon (100). The orientations observed would be expected if an epitaxial metal suicide layer forms initially during growth, before the oxidizing ambient is introduced. Calculation of the ensuing lattice mismatch between the oxide and suicide layer and multiplicity (σoxide) of the near coincident-site lattice for the oxide lattice shows that the (110) orientation is better lattice-matched than the (100) orientation for both Y2O3 (+2.3% × -2.4%, σoxide= 2, vs. -2.4% × +3.5%, σoxide = 4) and CeO2 (+1.8% × -4.0%, σoxide = 5, vs. 1.9% × 1.9%, σoxide= 5) and that for YSZ, (100) is better lattice matched than (110) (-0.8% × -1.6%, σoxide = 1, vs. -1.1 % × +4.8%, σoxide = 3). In each case, the in-plane orientation yielding the lowest mismatch with the suicide layer is consistent with the in-plane orientation observed between the oxide film and silicon substrate. Furthermore, the commonly observed rotational twinning in the oxide film can be accounted for by the expected orthogonal domain multipositioning in both the suicide and oxide layers. In CeO2, multipositioning allows two equally matched sets of orthogonal domains. One set consists of the two experimentally observed orientations (related by a 90° rotation). The other set is rotated 37° from the commonly observed orientations. Only the set with orientations aligned to the surface steps of Si(100) is observed, indicating the likely influence of graphoepitaxy in selecting between the two degenerate sets of orientations. When grown on Pt(100), Y2O3 grows with predominantly the (100) orientation and no (110) orientation, suggesting that without suicide formation, Y2O3 will grow with the expected well matched (100) orientation even when polar interfaces are involved.