bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiative and Non-Radiative Processes for the light Emission from Porous Silicon
Authors: Vial J. C. , Bsiesy A. , Fishman G. , Gaspard F. , Herino R. , Ligeon M. , Muller F. , Romestain R. , Macfarlane R. M.
Published: March 2011

Highly porous silicon, well passivated via an anodic oxidation process, is a stable and efficient visible light emitter showing a 3% photoluminescence efficiency at room temperature. Luminescence decay times are on the order of 100 μs at room temperature and 10 ms at low temperature. Above room temperature the de-excitation is dominated by non-radiative processes well describe by a tunnelling escape of carriers from confined regions. The “anomalous” luminescence behaviour showing a dramatic increase of the lifetimes upon cooling associated with a decrease of the intensity is explained by the temperature dependence of the effective radiative recombination rates due to a population redistribution among two excited states with very different radiative relaxation rates.
Metastability of Luminescent Porous Silicon
Authors: Mtyazaki S. , Sakamoto K. , Shiba K. , Hirose M.
Published: March 2011

Photoluminescence from l–3μm thick porous Si layers prepared by anodization of p-type c-Si wafers and subsequent chemical etching exhibits an anomalous temperature dependence and light-induced degradation. The luminescence intensity is almost quenched at temperatures below 30K and recovered by laser irradiation at 48K. This quenching phenomenon is not observed for PS thicker than 10μm. The luminescence fatigue is partially recovered by annealing at 150°C for 5min during which no further oxidation takes place. These observations are interpreted in terms of the structural metastability of hydrogen-terminated porous Si.
Properties of Porous Silicon with Photoluminescence Enhanced by a Remote-Plasma Treatment
Authors: Xiao Y. , Heben M. J. , Pankove J. I. , Tsuo Y. S.
Published: March 2011

We have developed remote-plasma and argon-ion laser-illumination treatments that enhance and stabilize the photoluminescent emission from porous Si (PS) that was electrochemically etched and thermally annealed. Infrared absorption spectroscopy revealed that the bonded oxygen content in the film was increased and the density of surface silicon dihydride bonds was reduced by these processing steps. The photoluminescence (PL) intensity of the treated films was initially about 15 times higher than that of the as—etched films, and increased further with the time of laser irradiation in air until a steady—state intensity was reached. The emission from the treated samples increases with decreasing temperature to a maximum intensity at about 100 K. Below 100 K, the photoluminescence intensity of the treated PS samples remains constant with decreasing temperature down to 7.7 K, whereas the as—etched samples, as well as siloxene, show a rapid decrease in photoluminescence intensity with decreasing temperature in this temperature range. Electron spin resonance data show that dangling bond densities in annealed PS films are reduced by the remote-plasma treatment.
Optical Studies of Electroluminescent Structures from Porous Silicon
Authors: Harvey J. F. , Lux R. A. , Morton D. C. , McLane G. F. , Tsu R.
Published: March 2011

Two components of the electroluminescence (EL) from porous silicon light emitting diode (LED) devices have been observed. A slower component and a faster component have been identified. The slower component has a spectral peak shifted to the red from the corresponding photoluminescence (PL) spectrum. The faster component has a spectral peak well in the infrared (IR). Optical and electrical measurements of these two components are discussed. The temperature dependence of the two EL components are presented and contrasted. Our measurements demonstrate that the two EL components and the PL result from recombination in different parts of the porous silicon structure. As the temperature is reduced below room temperature the slower EL exhibits a decrease in intensity at relatively high temperatures, suggesting a freeze out of electrical carriers due to quantum confinement, resulting in a much reduced electrical excitation of the EL.
Study on the Photoconductive Effect from a P/N Junction Structure Incorporated with Porous Silicon
Authors: Yeh C. C. , Hsu Klaus Y.J. , Chen P. C. , Hwang H. L.
Published: March 2011

We utilized the conventional planar fabrication technique and the electrochemical etching method to prepare porous Si layers in the p-type region of a p/n junction, which could make the study on the transverse transport property of this material possible. The junctions were fabricated by low energy ion-implantation, with porous Si formed perpendicular to the junction and between two metal contacts. This structure confines currents to the direction parallel to the surface. Distinct features on current-voltage (I-V) curves has been observed.
Photovoltaic Device Applications of Porous Silicon
Authors: Tsuo Y. S. , Heben M. J. , Wu X. , Xiao Y. , Moore C. A. , Verlinden P. , Deb S. K.
Published: March 2011

We report on the results of our investigation of using porous Si to enhance the performance of crystalline silicon photovoltaic solar cells. Possible approaches include using the porous Si for (1) surface texturing to enhance light trapping, (2) front or back surface fields because of its wider bandgap, and (3) photon color conversion of blue light to longer wavelengths that have higher quantum efficiency in a Si solar cell. In our surface texturing study, a porous-Si-covered single-crystal Si wafer showed an integrated reflectance of only 1.4% at 500-nm wavelength compared to about 40% for a polished Si surface. For our solar cell study, we used a point-contact cell structure with diffused p+ and n+ point contacts on the back of the cell. This cell structure allows us to form the porous Si on the front surface after both the junction formation and the evaporation and alloying of metal contacts.
Theory of Electronic, Optical and Transport Properties in Silicon Quantum Wires
Authors: Sanders G. D. , Stanton C. J. , Chang Y. C.
Published: March 2011

Recent observation of efficient luminescence in porous silicon has stimulated interest in the electronic and optical properties of Si quantum wires [1,2,3]. If silicon becomes a material suitable for optical applications, techniques for fabricating silicon wires reliably and uniformly will be needed. Once this is achieved, there will be interest not only in optical properties of silicon wires but also transport properties. For instance, to determine the properties of a hypothetical Si LED, one needs to know about both transport and optical properties.

In this paper, we present theoretical studies of electronic, optical and transpon properties of silicon quantum wires ranging in size from 7.7Ä to 31Ä. The electronic and optical properties are treated in an empirical tight-binding approach with excitonic effects included in the effective mass approximation. Carrier transport is treated in a Boltzmann transport framework with nonpolar deformation potential acoustic phonon scattering being the dominant scattering mechanism.
The Physics of Plasma Deposition of Microcrystalline Silicon
Authors: Drevillon B. , Solomon I. , Fang M.
Published: March 2011

The growth of microcrystalline silicon (μc-Si), deposited by a succession of silane and hydrogen plasmas, is investigated in situ by ellipsometry in the visible and near UV-range. It is found that the amorphous tissue is more affected by the hydrogen etching than the crystallites. The model of “selective etching” emerges from these measurements. Although this model is compatible with the “partial chemical equilibrium” of Vep̌ek, it is somewhat more general and explains the porous nature of the (μc-Si) as well as the many atomic layers deposition-etching sequences.
Xps Studies of Hydrogen and Oxygen Bondinguy Configurations in Hydrogenated Microcrystalline Silicon Materials Produced by Neutron Irradiation
Authors: Koo Y. C. , Weatherly G. C. , Sodhi R. , Thorpet S. J. , Austt K. T.
Published: March 2011

The bonding of Si atoms in μc-Si:H thin films has been investigated using X-ray photoelectron spectroscopy (XPS) in conjunction with infra-red spectroscopy (IR), secondary ion mass spectroscopy (SIMS) and analytical electron microscopy (TEM/EDX/EELS) data. By using a-Si:H and single crystal silicon as reference samples, structural and hydrogen effects could be assessed, since both a-Si:H and μc-Si:H have a similar concentration of hydrogen based on the N15 hydrogen profiling data, but different structures. On the other hand, single crystal silicon and μc-Si:H both have a diamond cubic structure based on electron diffraction data, but single crystal silicon contains little or no hydrogen except adsorbed at the surface. Based on the XPS and IR data, charge transfer of the Si2p core level towards a deep lying level was observed in the μc-Si:H material. IR measurements snowed a large amount of hydrogen was located in the grain boundaries. The charge transfer is mainly due to a change in the hydrogen bonding configuration. A well bonded oxide is formed in the μc-Si:H material near the surface with an almost complete absence of the Si3+ intermediate oxide state. The presence of a large amount of hydrogen (25 at.%) even at a high volume fraction (70%) of μc-phase may limit the oxidation and promote better oxide formation. The variation of the quality of the oxide/μc interface could be a possible explanation for the different photoluminescence observed by various groups for porous μc-Si material.
Enhanced Conductivity in n-Type Microcrystalline Silicon
Authors: Dlrani E. A. T. , de Andrade A. M. , Pereyra I.
Published: March 2011

Phosphorus doped μc-Sl:H films have been prepared in a PECVD system from SiH4 + PH3 + H2 gaseous mixtures. The films are obtained as a result of the competition between two simultaneously occuring processes: a deposition one and an etching one due to the high concentration of hydrogen in the plasma. This competition process favours the growth of films with crystalline structure.

Highly conductive μc-Si:H layers, in the range of 20 ∼ 30 S.cm-1, were obtained for samples in the range of 70 to 85 nm thick. From Raman Dispersion Spectroscopy and X-Ray Diffraction measurements, evidences of the dominant role of the crystalline phase in the charge transport mechanisms are shown.

Through Infrared Spectroscopy measurements it was possible to obtain the concentration of the SiHn groups on the μc-Si:H n+ structure and to Infer their role on the electrical properties of the films.
A new thin film Growth/Regrowth Process Design and Experimental Comparisons with Molecular Dynamic Analyses
Authors: Okada Takako K. , Kambayashi Shigeru , Yabuki Moto , Tsunashima Yoshitaka , Mirata Yuichi , Onga Shinji
Published: March 2011

A new concept of thin film growth/regrowth process design taking atomic motions into account using molecular dynamics is proposed. In the system, a modified many-body Tersoff-type interatomic potential for silicon has been adopted. The mathematical derivation of higher order derivatives was rigorously treated. Among many applications, the solid phase growth process was studied. It has been found from simulation studies that the solid phase growth of crystalline silicon proceeded along the [110] direction layer by layer. Furthermore, it has been obtained that all the atoms are activated in an extremely thin amorphous silicon film. Based on simulated results, an experiment using an extremely thin amorphous silicon film was carried out. It has been found that the perfect spherical silicon crystals with a uniform size and spacing can be grown from a thin amorphous silicon film.
Layered Poly/Amorphous Silicon Deposition Process for Improved Silicide Integrity
Authors: Roy P. K. , Nanda A. K. , Taylor J. A.
Published: March 2011

This work describes an elegant way to control suicide integrity and the quality of the silicide/polySi or amorphous (α) Si interface by a multilayered deposition process. Structurally superior polySi/or-Si layer resulting from this process allows one to reduce the stack height of the polySi/α-Si layer without compromising suicide integrity and silicide/Si interfacial qualities.

Impact of layering during polySi/α-Si deposition on the suicided structure were evaluated from XRD, RBS, cross-sectional TEM, sheet resistance, and SIMS analysis.
High Substrate Temperature (420 °C) Excimer Laser Crystallization of Hydrogenated Amorphous Silicon
Authors: Carluccio R. , Pecora A. , Fortunato G. , Stoemenos J. , Economou N.
Published: March 2011

Excimer laser crystallization of hydrogenated amorphous silicon has been investigated as a function of substrate temperature. At low substrate temperatures hydrogen out-diffusion strongly influences the film morphology, while at 420 °C homogeneous recrystallized films are obtained, as a result of the reduced solidification velocity. This process has been successfully tested by fabricating with the recrystalllized material thin-film transistors according to the bottom-gate configuration.
Control of Polysilicon Emitter Bipolar Transistor Characteristics by Rapid Thermal or Furnace Anneal of the Polysilicon/Silicon Interface
Authors: Bhattacharya S. , Lobo M. , Jung L. , Banerjee S. , Reuss R. , Batra S. , Park K. , Hu G.
Published: March 2011

In this paper we report on the ability of rapid thermal annealing (1050C, 45s) and furnace annealing (900C, 30min) to partially break up the interfacial oxide in bipolar transistors with different oxide thicknesses at the polysilicon/silicon interface. We have obtained the different oxide thicknesses either by performing different ex situ cleans (RCA clean or RCA clean + HF dip) before Low Pressure Chemical Vapor Deposition (LPCVD) of polysilicon, or by using a cluster tool for polysilicon deposition with the ability to perform an in situ clean and then allowing the growth of different oxide thicknesses at the interface prior to polysilicon deposition. For the in situ cleaned devices, it is observed that after the interface anneal, the current gain increases with increasing oxide thicknesses, but with little penalty in terms of higher emitter resistance, Re. This indicates that by controllably increasing the interfacial oxide thickness and by subsequent annealing to partially break up the interfacial oxide, higher current gains can be obtained with little sacrifice in terms of higher Re.
I-V Characteristics and Interface Properties of Al-Si(P) Contacts by the Krf Excimer Laser Induced Recrystallization
Authors: Sohn K. , Lee H. , Hensley D. A.
Published: March 2011

Al was deposited on the both sides of p-type Si by the sputtering, and the pulsed KrF excimer laser was irradiated on the one side and both sides of Al dot contacts. Due to the thin-high doping recrystallized layer, the transitions from the Schottky diodes to the ohmic contacts via backward diodes were observed in I-V measurement. Good N-shape negative resistances and notches were observed in the diodes, and ohmic contacts. Possible interpretations of the orgin of these phenomena are discussed. And, the simple model of the effective barrier height reduction under the thermionic field emission was developed using WKB approximation, and tunneling theory. By the depth Auger analysis, Al, and Si profiles near Al-Si interface after the laser irradiation were observed.
A Selective Growth of GaAs Microcrystals Grown on Se-Terminated GaAlAs Surface for the Quantum well Box Structure
Authors: Chikyow Toyohiro , Koguchi Nobuyuki
Published: March 2011

A selective growth of GaAs microcrystals was demonstrated on a Se-terminated GaAlAs surface. Ga molecules were supplied to the Se-terminated GaAlAs surface at first. The surface consisted of Ga droplets and bared Se-terminated GaAlAs surface. After the following As molecule supply to the surface, a selective GaAs microcrystal growth from Ga droplets was observed. The cross sectional investigations by the high resolution electron microscope revealed epitaxial growth of GaAs microcrystals with (111) facets and a possibility of (GaAl)2Se3, layer formation at the GaAs/Se-terminated GaAlAs interface.
Microcavity Effects in The Luminescence of GaAs Microcrystals
Authors: Juen S. , Lamprecht K. F. , Rodrigues R. , Höpfel R. A.
Published: March 2011

Experimental photoluminescence spectra of GaAs microcrystals show pronounced variations compared to the luminescence of bulk GaAs. The observed spectra are explained by spectral enhancement and inhibition of spontaneous emission in a three-dimensional optical resonator formed by a dielectrically confined semiconductor microcrystal. The crystals were produced by pulverization of bulk GaAs, size-separated by sedimentation techniques, and characterized by transmission electron microscopy, electron diffraction and x-ray diffraction.
Investigation of Misfit Dislocation Configurations in Mbe-Grown InGaAs Layers on Misaligned GaAs (001) Substrates
Authors: Werner P. , Zakharov N. D. , Chen Y. , Liliental-Weber Z. , Washburn J. , Klem J. F. , Tsao J. Y.
Published: March 2011

The configurations of misfit dislocations in In0.2Ga0.8As/GaAs(001) hetero structures grown on slightly misoriented substrates was investigated by transmission electron microscopy (TEM). Layers 6 nm, 20 nm and 40 nm thick were grown by MBE. The substrate was tilted in [110], [110], [120], [210] and [010] directions at angles between 0° and 10°. Only in the 40 nm thick layers networks of 60° and 90° dislocations were formed. Misfit dislocations were found at the interface in <110> directions. In the substrate tilting range between 0° and 4° the changes in dislocation density can be explained by the different

character of α and β dislocations. For a substrate tilting above 6° the different dislocation sets show an increased anisotropy. The misfit dislocations at the interface were decorated by In atoms. The influence of three-dimensional crystal growth on increasing surface roughness is discussed.
Preparation and Characterization of Group 12 Thiolate Complexes and Evaluation of Their Potential as Precursors for II-VI Semiconductors
Authors: Rees William S. , Kräutern Gertrud , Goedken Virgil L.
Published: March 2011

We have prepared compounds having the general formula M(SR)2 (M = Zn, Cd; R = i-Pr, t-Bu, Bz) and Hg(SR)CI (R = i-Pr, Bz) and investigated their use as potential sources in the preparation of metal sulfides from molecular precursors. Selected examples of the prepared compounds have been studied by single crystal x-ray diffraction. Decomposition has been carried out both in the solid state and by heating a suspension of a metal thiolate in a high boiling hydrocarbon. The decomposition products have been studied by GC/MS (liquids) and XRD (solids).
Stress Compensation Techniques in Thin Layers Applied to Silicon Micromachining
Authors: Lang W. , Mük G. , Rose E. , Bausells J. , Kühl K. , Moldovan N. , Suski J.
Published: March 2011

Stress in thin films is one of the mayor technological problems of silicon micromachining. Therefore stress reduction by a compensation method increases the technological use of a material. Three methods to obtain stress free films are investigated:

1. Stress in SiO2 and Si3N4 can be compensated by ion implantation.

2. Sandwich layers of SiO2 and Si3N4 can be made internally stress compensated by variation of the thickness ratio.

3. Polysilicon is stress reduced by appropriate doping and annealing.

The film stress is evaluated by the measurement of the bending of the substrate. Examples of processed membranes, bridges and cantilevers made of stress compensated films are given.
Interface and Bulk Traps in Oxide-Nitride Stacked Films
Authors: Martin Ferran , Aymerich Xavier
Published: March 2011

A new technique for the characterization of nitride electron traps responsible for the memory action of MNOS devices is proposed. It is assumed a uniform density of traps in the nitride bulk and an excess of interface traps which is described according to an exponential decreasing distribution. We have modelled the discharge of MNOS devices induced by the application of low positive gate voltages in samples previously charged up toits maximum level of trap occupancy. Since the discharge rate is necessarily dependent on the trapped charge distribution, it is possible to infer the spatial profile of traps by comparing the results obtained by computer simulation of the model to those obtained from field assisted discharge experiences in MNOS samples.
Electrical Properties of Oxide-Nitride-Oxide, Ono, Heterostructures Fabricated by Low Temperature Remote PECVD
Authors: Ma Y. , Yasuda T. , Chen Y. L. , Lucovsky G. , Maher D. M.
Published: March 2011

Oxide-Nitride-Oxide, ONO, heterostructures, fabricated by low-temperature, 300°C, Remote Plasma Enhanced Chemical Vapor Deposition, have been used as gate dielectrics in metal insulator semiconductor devices. Analysis of C-V data for this devices indicates that higher levels of fixed charge are associated with the internal dielectric interfaces. A high-temperature, ̃900°C, Rapid Thermal Annealing, RTA, step has been inserted into the process sequence for fabricating ultra-thin, 4.7 nm SiO2 equivalent, device-quality ONO dielectric layers. The electrical properties of these ONO dielectrics, including the Si/SiO2 interfacial trap density, the flat band voltage, the charge to breakdown and the reliability under electron injection are comparable to those of high temperature, thermally-grown oxides.
Comparative Study of Simultaneous Implant Activation and Borophosphosilicate Glass (BPSG) Reflow During Rapid Thermal Processing (RTP) and Furnace Annealing on Complex Topographies
Authors: Thakur Randhir P. S. , Ward Valerie , Martin Annette
Published: March 2011

Borophosphosilicate glass (BPSG) is an essential insulating material used to modify thecomplex topography of highly dense, next generation dynamic random access memory (DRAM)devices. The shallow junctions in 16 and 64 Meg DRAMs can only be maintained by severely restricting the time, temperature, and atmosphere of all thermal process steps following the junction implant.

In this paper we present the results of rapid thermal process (RTP) assisted reflow of BPSG over complex topographies and compare the results of RTP to furnace reflow in both dry and wet ambients. We also compare the out-diffusion of boron and phosphorous from BPSG films during the RTP and furnace reflow. We found an optimum RTP cycle that completely removes voids in the vicinity of overhang geometries and provides sufficient activation of the underlying dopants (as compared to a furnace reflow and activation cycle). In this study we used the results of boron and phosphorous profile redistribution, underlying dopant activation, and the amount of reflow to compare RTP and furnace processing techniques.
Defect Reduction in Semiconductor Manufacturing a Case Study of BPO4 Elimination in BPSG Films
Authors: Wilson Jim , Stephens Tony
Published: March 2011

This paper explains the analysis and elimination of BPO4 crystal formation in an Atmospheric Pressure Chemical Vapor Deposition BPSG film. Film deposition and furnace anneal/flow parameters were studied using full factorial techniques, with anneal/flow parameters having the most significant effect. It was learned that BPO4 crystals could be readily induced by performing the anneal/flow process in a POCl3/O2 ambient. Most testing was done in a POCl3/O2 ambient and inferences made concerning the standard anneal ambient.

BPO4 formation is primarily dependent on thermal processing during anneal toprovide the activation energy necessary to initiate crystal growth. Other factors include 02:Hydride ratio during film deposition, phosphorous concentration in the deposited film, deposition temperature, and anneal/flow ambient. No tested level of these secondary factors completely eliminated crystal formation.

The growth of BPO4 crystals can be eliminated by controlling the thermal environment ofthe anneal/flow step. The primary means employed was to increase the rate of heat dissipation by doubling the spacing between wafers. An alternative method involves utilization of reduced anneal/flow furnace temperatures.
Measurements of Hydrogen Redistribution in Hot Electron Injection of Mos Capacitors
Authors: Marwick A. D. , Buchanan D. A. , Dimaria D. J. , Saunders Phil
Published: March 2011

Redistribution of hydrogen caused by hot electron injection has been studied in large Al-gate capacitors using internal photemission followed by hydrogen depth profiling with the 15 N nuclear reaction. A large peak of hydrogen (∼ 1015 at /cm2) at the Al/SiO2 interface due to a hydrated layer on the surface of the SiO2 was found to act as a source of hydrogen during the photoinjection. A small fraction of the hydrogen released from this peak was found to be re-trapped near the Si/;SiO2 interface if a field of >1 MV/cm was applied to the SiO2 during the injection. Up to 2 × 1014 atoms/cm2 of hydrogen were found to be trapped at this interface for injected fluences up to 5 C/cm2. These results are discussed in terms of current models of interface state generation involving hydrogen.
Densification and Crystallization of Amorphous SiO2 by Neutral Beam Bombardment
Authors: Mizutani Tatsumi
Published: March 2011

Amorphous SiO2 films formed by thermal oxidation of silicon have been bombarded by low-energy (350 — 400 eV) ion beam and neutral beam of inert atoms. The modified SiO2 layers have been characterized by Auger electron spectroscopy (AES), Rutherford backscattering spectroscopy (RBS) and reflection high energy electron diffraction (RHEED). It is shown that neutral beam bombardment does not cause preferential sputtering of oxygenfrom SiO2, whereas ion beam of the same energy causes significant preferential sputtering. For neutral bombardment, densification and crystallization of SiO2 have been observed. The formation of α-cristobalite and α-quartz from amorphous SiO2 has been observed for high dose bombardments (>1017neutrals/cm2). These densification and crystallization phenomena can be attributed to high temperature and high pressure local spot formation upon the incidence of energetic neutral atoms. For ion beam bombardments, these densification and crystallization phenomena have not been observed.
Low-Temperature Chemical-Vapor-Deposition of Silicon-Nitride from Tetra-Silane and Hydrogen Azide
Authors: Ishihara Ryoichi , Kanoh Hiroshi , Uchida Yasutaka , Sugiura Osamu , Matsumura Masakiyo
Published: March 2011

Silicon nitride films have been successfully deposited at a temperature as low as 300°C by chemical-vapor-deposition using tctra-silane (Si4 H10) and hydrogen azidc (HN3). Atomic ratio (N/Si) of the film deposited at 400°C was 1.47, i.e., the film was N-rich. Total hydrogen content was about 25atomic%. The breakdown-field strength was 6.5MV/cm at leakage-current density of 1μA/cm2, and the low-field resistivity was more than 1015 Ωcm. Similar electrical characteristics were obtained from films deposited at a temperature range between 300°C and 500°C. Amorphous silicon thin-film transistors equipped with this film as the gate dielectric showed good transfer characteristics.
Amorphous Silicon Thin Film Transistors Produced by Atmospheric Pressure CVD
Authors: Ann Byung Chul , Kim Jeong Hyun , Hong Chan Hee , Kim Woo Yeol , Kim Kwang Nam , Kang Hee Kyung , Jang Jin
Published: March 2011

We have studied the preparation and device application of a-Si by atmospheric pressure CVD using disilane. The deposition rate of a-Si increases with the partial pressure of disilane and with the total pressure. The deposition rate of APCVD a-Si is, therefore, very high compared with LPCVD. The photosensitivity of APCVD a-Si is 104 at 100mW/cm2. We have made an inverse staggered type a-Si TFT using SiO2 as a gate insulator. The on/off current ratio and field effect mobility are 105 and 0.19cm2/Vs, respectively.
The Effects of Light and Electrical Stress on Asymmetric a-Si TFT
Authors: Oh C. H. , Chung I. J. , Kim W. Y. , Hwang J. R. , Lee S. K. , Kim Y. S. , Park J. S. , Han M. K.
Published: March 2011

The asymmetric amorphous silicon thin film transistors are fabricated and exposed to various stress environments. A visible light illumination of 200,000 Ix and gate bias of 30 V are applied to both asymmetric and widely used symmetric a-Si TFT's. It is observed that the leakage current of asymmetric structure, where only one electrode is fully overlapped by gate electrode, is much less than that of symmetric one. The visible light illumination as well as gate bias stress do not degrade the leakage current of the asymmetric a-Si TFT's, while the leakage current in die symmetric TFT's are increased considerably due to the stress. Also, the degree of degradation in the threshold voltage, the field effect mobility and the subthreshold slope of asymmetric TFT's are relatively much less than that of conventional symmetric TFT's.
Compound Sidewall Spacer Technology for Submicron Mosfet
Authors: Roy P. K. , Kook T. , Kizilyalli I. C. , Nanda A. K.
Published: March 2011

This work describes process development of various kinds of compound sidewall spacer in submicron CMOS technology to improve gate oxide (GOX) leakage characteristics. This is attained by minimizing the impact of gate-level defects (GLDs) caused by in-process particle incorporation. Transistor characteristics did not suffer from this new sidewall spacer process.
Crystallization Behavior in Precursor-Modified Sol-Gel Lead
Authors: Powders Titanate , Shie Wei-Heng , Lu Qing , Shih Wan Y.
Published: March 2011

The molecular structure of precursors in sol-gel processing of PbTiO3 is modified via β-diketone substitution for the isopropyl groups of titanium isopropoxide. Crystallite size and crystallization behavior are studied using x-ray diffractometry and differential thermal analysis. The crystallite size decreases with increasing amount of β-diketone substitution. Whereas the weight percent of crystalline phase first decreases and then increases with increasing β-diketone substitution. Our results indicate that the β-diketone substitution reduces the size of the structural units in the gel network resulting in smaller crystallite size and more nucleation sites in the powders produced.
Dependence of the Growth of Al2O3 Films on the Growth Conditions in the ALE-Like Process
Authors: Fan Jia-Fa , Toyoda Koichi
Published: March 2011

Effects of the growth conditions on the growth and the quality of thin films of Al2O3 were investigated in the ALE-like process. It has been found that the growth rate remains nearly independent of the growth conditions when the pulse heights are 80–120 mTorr and 20–160 mTorr for H2O2 and TMA respectively, the pulse duration longer than 0.3 s, the base pressure below 1 mTorr, and the growth temperature higher than 150°C. Also, we found that the density, the chemical bonding strength, and the electrical properties improved markedly with raising the growth temperature although the growth rate remained nearly constant. In addition, area-selective growth and partly polycrystalline films were favorably obtained by using pulsed molecular beams of TMA and H2O2 in the growth.
On the Formation of Ultrathin Simox Structures by Low Energy Implantation
Authors: Namavar F. , Buchanan B. , Kalkhoran N. M.
Published: March 2011

Silicon-on-insulator (SOI) wafers made by standard energy (150–200 keV) Separation by IMplantation of Oxygen (SIMOX) processes have shown great promise for meeting the needs of radiation-hard microelectronics. However, if SIMOX material is to become a competitive substrate material for manufacturing commercial integrated circuits, the cost of the SIMOX wafers must be greatly reduced. The low energy SIMOX (LES) process accomplishes the needed reduction in cost by producing ultrathin layers which require much lower ion doses. These ultrathin layers are necessary for the next generation of commercial ultra high density CMOS integrated circuits, and must be of very high quality to be utilized for commercial applications. In this paper we discuss characterization of ultrathin LES structures.
GaAs Surface Stabilization by Vacuum Anneal with SiO
Authors: Gerardi G. J. , Rong F. C. , Poindexter E. H. , Harmatz M. , Shen H. , Warren W. L.
Published: March 2011

We find a significant alteration of the surface properties of SI- GaAs as a result of a thermal treatment with SiO under vacuum. Low temperature photoluminescence measurements reveal a tenfold increase in emissions attributed to free or donor bound excitons and the exciton bound to a silicon acceptor. A paramagnetic center is also generated as a result of this treatment. The EPR signal has a g-value of 2.0017 and a linewidth of 0.1 mT. The enhanced photoluminescence and the EPR signal are both quenched by a short exposure to hydrogen plasma at room temperature. Chemical and spectroscopic evidence indicates that the resonance is due to a silicon related center near the GaAs surface. The surface stabilization is attributed to a reaction or incorporation of SiO with the arsenic depleted GaAs surface.
Photoionization and Photofragmentation of BxNy Clusters Produced by Photoablation of Boron Nitride Followed by Supersonic Expansion Cooling
Authors: Roland Paul A. , La Placa Sam J. , Wynne James J.
Published: March 2011

Photoablation of isotopically pure boron metal and hexagonal boron nitride with a 532 nm laser, followed by supersonic expansion cooling, produces a variety of Bx, and BxNy, clusters, which are detected by photoionization of the neutral clusters with a 194 nm laser, followed by time-of-flight (TOF) mass spectrometry. Under certain experimental conditions, the mass spectrum derived from boron nitride shows resolved peaks corresponding to the clusters Bx+1Ny+. Under different experimental conditions, the mass spectrum shows an unresolved region corresponding to clusters ranging from atomic mass unit 100–1000 as well as resolved peaks, corresponding to Bx+ clusters for x = 2 − 100. These resolved peaks grow with increasing photoionization fluence, while the envelope of the unresolved region changes shape and grows with a diminished dependence on fluence. These data are interpreted as evidence that the unresolved clusters are being photofragmented as well as photoionizated by the 194 nm radiation, and the products of such photofragmentation are the aforementioned Bx+ clusters.
Excimer Laser Induced Mechanical and Electrical Nanostructures in Polymers
Authors: Phillips H. M. , Callahan D. L. , Le blanc S. P. , Ball Z. , Sauerbrey R.
Published: March 2011

Periodic line structures with periods ranging from 166 nm to 950 nm have been produced in polyimide by direct ablation with a KrF (248 nm) laser using holographic techniques. Taking advantage of the large nonlinearity in the laser ablation process, linewidths ranging from 30 nm to several hundred nanometers could be obtained. These techniques were combined with the ability to induce electrical conductivity in polyimide to produce an array of 500 nm wide electrically conducting wires. The conductivity of these wires was similar to that found in macroscopic regions of laser induced conductivity.
Profiling of Hydrogen in Zirconium Surfaces by Laser Ablation with Resonance Ionization
Authors: Bickel G.A. , Mcrae G.A. , Green L.W.
Published: March 2011

Elemental distributions in the bulk and metal oxide surface layers of zirconium alloys play key roles in the fracture toughness of the alloys. In particular, localized hydrogen build-up leads to hydride formation and delayed hydride cracking. Parts per million levels of H in Zr have been detected using the 1.06 μm or 355 nm output of a Nd:YAG laser for ablation followed by 2+1 resonance ionization detection of H and D. Analysis of the ablation plume has shown that it consists predominately of atomic species in thermal equilibrium between 2000 and 3600°C. Ablation of thin foils has shown that the ablation rate is on the order of mono-layers per shot and increases exponentially with increasing fluence. Laser ablation depth profiling results of H distributions in an anodically grown oxide film compare qualitatively with nuclear-reaction-analysis profiling of the same sample.
Selective Epitaxy as a Chemistry Free Route for Ybco Thin Film Patterning
Authors: Habermeier Hanns-Ulrich , Elkin Bentsian , Beddies Gunter , Leibold Bernd
Published: March 2011

Two different routes for micropatterning of YBCO thin films by selective epitaxy are presented; both methods are based on the intermixing of YBCO with silicon at the growth temperature for ( 001 ) as well as ( hk0 ) YBCO thin film epitaxy. One method ( I ) uses a pre-patterned yttria stabilized zirconia [ YSZ ] thin film epitaxially grown on a silicon single crystal giving rise to the epitaxy of c-axis oriented YBCO on YSZ whereas intermixing yields a nonsuperconducting Si-Y-Ba--Cu-O phase elsewhere. The other method (II ) uses SrTiO3 substrates suitable for ( 103 ) as well as ( 110 ) YBCO epitaxy coated with a pre-patterned amorphous silicon layer prior to YBCO deposition. Both techniques are chemistry free routes for YBCO thin film patterningand pave the way for superconductor/semiconductor hybride device fabrication ( route I ) as well as basic investigations of the anisotropic electronic and optical properties of YBCO ( route II ).
Controlling of Microstructure Generation by Direct Holographic Etching of Semiconductor Substrates
Authors: Toyoda K. , Kumagai H. , Ezaki M. , Obara M.
Published: March 2011

Controlling of microstructure generation was investigated in laser etching of n-GaAs. For single-beam etching and holographic etching with high ratios of average spacing of holographic grating to average spacing of microstructures (Λh/Λr), ripple structures were fabricated. Especially in p-polarization, spatial fluctuation was greater than that in s-polarization. This might occur because phase distortion inherent in the laser beam cannot be eliminated by the p-polarization beam irradiation. For holographic etching with small Λh/Λr ratios, ripple structures were changed into grating structures because these grating structures might be generated in phase with holographic gratings.
Laser Induced Damage Threshold Measurements at the Microscopic Level
Authors: Zwan Allen D. , Miller David R.
Published: March 2011

We have (tudied the laser damage threshold to silver films (500Å - 1000Å) grown on single crystal silicon <100>, in a newly developed laser damage UHV system at pressures of 10−1 torr. A 1.06μm Nd:Glass laser is used to damage the mirror surfaces in 1-on-1 pulse studies. In-situ damage characterization includes Auger, reflectivity of the primary beam, diffuse scattering of a helium-neon laser, and mass spectrometry detection of desorbed surface species. External characterization includes optical microscopy and SEM. All in-situ damage probes are well correlated and baseline damage occurs at fluences near 3.4 MW/cm2. Time-of-flight to the mass spectrometer shows ejected particles with energies in the 5 to 10 eV range indicating a plasma damage mechanism. Prior to typical thermally induced damage the external microscopy shows well defined precursor morphology changes which appear as feather-like microstructure at the submicron level.
Hyperthermal CI Atom Beam Produced by Laser Vaporization of Cryogenic ICI Films
Authors: Weaver Gabriela C. , Campos Francis X. , Leone Stephen R.
Published: March 2011

A source of energetic, neutral Cl atoms is produced by laser vaporization of cryogenic ICI films using either the 532 nm or 266 nm output of a pulsed Nd:YAG laser. The pulsed Cl mean kinetic energy can be tuned from 0.4 eV to 3.4 eV by varying the laser repetition rate or the rate of deposition of the ICl film. Also present in the beam are ICI, I, I2, and Cl2 The heavier species all have lower velocities than the Cl atoms, and this difference in velocities can be accentuated by vaporizing thinner films. Using a mechanical velocity chopper, the fastest part of the beam can be selected, which consists of > 90% Cl atoms. Results suggest that the vaporization process involves a directed mass flow in which the heavier molecules are propelled to higher velocities by the faster Cl atom flux. The atom source may be used for selective etching studies.
Excimer Laser Induced Deposition of Bisrcacuo Htsc Thin Films and Buffer Layers -Depth Profiling by SNMS
Authors: Lqrenz M. , Hochmuth H. , Börner H. , Unger K.
Published: March 2011

Secondary Neutrals Mass Spectrometry SNMS was used to investigate interdiffusion processes in laser deposited BiSrCaCuO HTSC thin films on various substrate materials. The in-situ deposition of epitaxial Bi2Sr2Ca1Cu2O8+x films requires a substrate temperature just below the decomposition temperature of the 2212 -phase of BiSrCaCuO. This high substrate temperature of about 850°C seems to be the reason for interdiffusion processes of BiSrCaCuO films and MgO(100), YSZ(100) and Si(100) with YSZ or SrTiO3 buffer layers as substrate materials. Therefore, Tc(R=0) of BiSrCaCuO films on silicon with buffer layer is not higher than 70 K at present. SNMS depth profiling gives a more detailed insight into interdiffusion phenomena than other analytical techniques.
Biaxially-Textured YBa2Cu3O7–x Thin Film Growth on Polycrystalline and Amorphous Substrates Using Ion Assisted Laser Deposition of Yttria-Stabilized Zirconia Intermediate Layers
Authors: Reade R. P. , Berdahl P. , Russo R. E. , Garrison S. M.
Published: March 2011

The growth of (001)-textured, biaxially-aligned yttria-stabilized zirconia (YSZ) intermediate layers on amorphous or randomly-oriented polycrystalline substrates is desirable for subsequent YBa2Cu3O7–x (YBCO) c-axis thin film growth. Laser deposition of YSZ on polycrystalline metal substrates (Haynes Alloy #230) in 1.0 millitorr oxygen at 70°C produces partial (001) texture but no alignment of in-plane axes. Highly-textured biaxially-aligned layers are obtained by using an ion beam to assist growth. Similar layers are obtained on amorphous silica and polycrystalline alumina substrates. The effects of ion-beam parameters including incident angle, source gas, and beam voltage and current are presented. Highly c-axis-oriented, biaxiallyaligned YBCO thin films have been deposited in situ on these YSZ layers, with Tc(R=0) ∼ 92K and Jc(77K) = 6 × 105 A/cm2. Angular magnetoresistance data shows a dip in resistance with magnetic field normal to the film, in contrast to films grown epitaxially on single crystal substrates, which have maximum resistance with field normal.
Preparation and Growth of Pb2Sr2Y0.5Ca0.5Cu3O8+δ Thin Film Superconductors
Authors: Naqvi S.H.H. , Vickers M. , Tarling S. , Barnes P. , Boyd I.W.
Published: March 2011

The lead based superconductor Pb2Sr2Y0.5Ca0.5Cu3O8+δ is a most complex material. If any oxygen is present in the PbO-CuOδ-PbO sandwich layer (i.e. if δ>0) the superconductivity deteriorates. This is also a most difficult material to grow not only because of the large number of cation stoichiometries which have to be precisely balanced but also because of the tendency for multiple phases to form. Pulsed laser deposition (PLD) has been applied to prepare thin films of the 2213-phase on MgO (100) single crystal substrates at low temperature (300°C) in low oxidizing atmospheres. A basic set of ex-situ growth conditions has been determined which produce for the first time good quality films of this material as characterized by DC resistivity using the Van der Pauw method, as well as EDX and XRD. The layers are reasonably c-axis oriented and display a superconducting onset transition temperature of 79K and zero resistance at 65K after subsequent annealing in a nitrogen ambient.
Growth of (110) Oriented YBa2Cu3O7−δ Films by Laser Ablation
Authors: Chen Neng Y. , Rietveld G. , Lander L.W. , Matijasevic V.C. , Hadley P. , Mooij J.E.
Published: March 2011

Several attempts have been made by different groups to grow (110) YBa2Cu3O7−δ thin films on (110) substrates. In most of the cases, both (103) and (110) orientations of YBa2Cu3O7−δ have been found in the film. The substrate temperature during deposition is one of the major factors that determines the crystal orientation of the YBa2Cu3O7−δ. In our experiment, effort is made to examine the influence of the initial substrate temperature from 595 °C to 660 °C on the relative amount of (110) and (103) oriented grains. The orientations are determined by x-ray analysis with a Weissenberg camera. The amount of (103) oriented YBa2Cu3O7−δ is reduced systematically with decreasing substrate temperature. At the lowest deposition temperatures we find only (110) oriented growth.
Laser Ablation Deposited YBa2Cu3Ox, Thin Films on YSZ/Si(100)
Authors: Sánchez F. , Varela M. , Queralt X. , Aguiar R. , Morenza J.L.
Published: March 2011

Superconducting YBa2Cu3Ox (YBCO) thin films have been deposited on Si(100) substrates with yttria-stabilized zirconia (YSZ) buffer layers by laser ablation. Buffers have been obtained by laser ablation as well. The films have been characterized by scanning electron microscopy, x-ray diffractometry, secondary ion mass spectrometry, and four-contact electrical resistivity measurements. Secondary ion mass spectrometry results indicate very low interdiffusion between Si, YSZ and YBCO. The best YBCO films are textured with c axis perpendicular to the substrate and their resistance shows a normal state metallic behavior with zero resistance at temperatures higher than 80 K. The properties of YBCO films have been related with the substrate temperature and oxygen partial pressure during deposition.
Photodesorption Dynamics in Threshold-Fluence UV Laser Induced Surface-Decomposition of Bi2Sr2CaCu2O8
Authors: Wiedeman Lawrence , Helvajian Henry
Published: March 2011

In this article, we review experimental measurements taken in our laboratory for the low-fluence UV pulsed laser photodecomposition of the perovskite ceramic Bi2Sr2CaCu2O8. We present the measured photoejected product kinetic energy (KE) distributions, including that for the ion and the neutral, the atomic and polyatomic species. For the specific case of the neutral species desorption, we present new experimental results that elucidate the change in the photophysical desorption process as a function of the incident laser fluence. The results show the transition from the electronic-induced desorption to thermal evaporation as the laser fluence is increased. The KE distribution data suggests that for low-fluence laser excitation, the primary photodesorption process is two-hole localization at a binding site followed by coulomb repulsion. A fraction of the escaping ions acquire the full coulomb KE (e2/ro; ro internuclear distance). The neutral species acquire a partial fraction of the available KE (i.e., the KE gained prior to the neutralization). The appearance of polyatomic species desorption is explained via the spectator-stripping model.
Titanium Oxynitride Thin Film Deposition by Pulsed Laser Ablation of Titanium Targets in Nitrogen
Authors: Craciun V. , Craciun D. , Amirhaghi S. , Vickers M. , Tarling S. , Barnes P. , Boyd I. W.
Published: March 2011

Reactive pulsed laser deposition of titanium targets in a nitrogen atmosphere has been used to deposit thin titanium oxynitride films on Si substrates. The gold coloured layers exhibited a smooth, featureless surface and good chemical resistance in HF-HNO3 mixtures. The films had a high oxygen content which was responsible for relatively high electrical resistivity, measured to be 200–600 μΩ cm. This new method can easily be applied to the growth of other important nitrides such as ZrN, WN, HfN or the deposition of multilayer structures such as TiN/Ti on a variety of substrates.