bluuebunny/crossref_metadata_2025 huggingface dataset:
Instability of Threshold Voltage of Flexible Single-Crystal Si TFTs
Authors: Pang Huiqing , Yuan Hao-Chih , Lagally Max , Celler G. , Ma Zhenqiang
Published: April 2007

N-type, top gate, single-crystal Si thin-film transistors (TFTs) using evaporated silicon monoxide (SiO) as the gate dielectric layer are fabricated on flexible plastic substrate. The threshold voltage (VT) instability of the device is studied by applying high gate voltages. VT shift to higher values under positive gate bias stress is observed. The logarithmic dependence of VT shift on time indicates that electrons are injected and trapped in the SiO layer from Si channel. The subthreshold swing degradation is also found after the stress, suggesting the generation of interface states at Si/SiO surface. However, under negative gate stress, VT firstly decreases and then increases after longer stress time. This is believed to be the combined effects of both holes injection from Si substrate and electrons emission from metal gate, for which the latter become dominant under a long- term stress.
Electronic and Thermal Properties of Silicon Nanowires
Authors: Ramayya Edwin B. , Vasileska Dragica , Goodnick Stephen , Knezevic Irena
Published: April 2007

Electron mobility and thermal conductivity of silicon nanowires (SiNWs) of different cross sections were calculated by including scattering of electrons due to confined acoustic phonons, optical phonons, and surface roughness. A reduction in the acoustic phonon group velocity due to the spatial confinement in SiNWs is found to result in lower electron mobility and thermal conductivity compared to the bulk phonon approximation. Among the square SiNWs considered, a SiNW of cross section 6 nm x 6 nm was found to have the highest electron mobility due to the interplay of volume inversion and subband modulation.
Analysis of PD SOI pMOSFET Device Performance Enhancement due to Direct-Tunneling Current in the Partial n+ Poly Gate
Authors: Guegan Georges , Pretet Jeremy , Gwoziecki Romain , Gonnard Olivier , Gouget Gilles , Touret Patricia , Raynaud Christine , Deleonibus Simon
Published: April 2007

In this paper, we investigate and analyze the impact of the body potential on the performance enhancement of BC pMOSFET when the body contact is floating. Many geometries and layouts of PD SOI pMOSFET with 1.6 nm physical gate oxide have been compared. The body potential is mainly controlled by direct tunneling mechanism due to ECB current from the partial n+ poly- gate into the conduction band of the n type silicon substrate. Narrow device and H gate layout provide the highest Ion gain.
Low Temperature Properties of Multi-Independent-Gate FET (MIGFET) Operating in Single-Gate and Double-Gate Modes
Authors: Na Kyoung-Il , Eminente S. , Cristoloveanu S. , Mathew L. , Vandooren Anne , Bae Y-H , Lee J-H
Published: April 2007

We investigated the temperature dependence of the electrical properties of the MIGFETs, such as the drain current, the transconductance, the threshold voltage, the subthreshold slope and the field effect mobility. Devices with a gate length of 30 nm, a gate width of 30 nm and a silicon fin height of 100 nm were characterized at a temperature range between 77 K and room temperature. The MIGFETs were operated and compared in double- gate (DG) and single-gate (SG) modes in order to reveal the coupling effects between the various gates. The subthreshold slope in SG mode improves with decreasing temperature, but remains far from the ideal value measured in DG mode. The variations of the transconductance and mobility as a function of temperature are explained by strong coupling and series resistance effects. In DG mode, the mobility is highly improved due to volume inversion and reduced surface roughness scattering.
Assessment of the CBR Quantum Transport Simulator on Experimentally Fabricated Nano-FinFET
Authors: Khan Hasanur , Mamaluy Denis , Vasileska Dragica
Published: April 2007

We have utilized fully self-consistent quantum mechanical simulator based on Contact Block Reduction (CBR) method, to simulate experimentally fabricated 10nm FinFET device. A series of simulations have been performed with varying S/D extension length and doping profile to match the experimental data. The simulation results have been found to be in good agreement with the experimental data in the subthreshold regime. Small signal analysis has been performed to extract device capacitances and to compare the intrinsic propagation delay to that of the experimental device.
SOI Metrology and Characterization in Modern Wafer Production
Authors: Kononchuk Oleg , Brunier F. , Kennard M.
Published: April 2007

Overview of characterization techniques used for process control and process development in modern SOI wafer manufacturing is presented. Examples of electrical characterization using Psi-MOSFET, SOI layer structural defect characterization, stress measurements in sSOI wafers are given. Advantages and limitations of the techniques are discussed.
Investigation of Apertureless NSOM for Measurement of Stress in Strained Silicon
Authors: McDonough Colin , Atesang Jacob , Wang Yunfei , Geer Robert
Published: April 2007

Strain in blanket and patterned silicon-on-insulator (SOI) structures have been investigated via apertureless near-field scanning Raman spectroscopy, specifically, to investigate the efficacy of so-called tip-enhanced Raman scattering (TERS) for Si strain characterization and metrology for integrated circuit (IC) devices. The current study compares TERS generation using Ag-coated W tips in a 45o incident beam, fixed-tip geometry and Ag-coated SiO2 capillary tips in a normal incident, scanning-tip geometry. The latter demonstrates superior performance and is used in a differential scheme to investigate strain profiles in patterned SOI structures. Specifically, a blanket device layer with an engineered strain of 0.075%, is patterned to form arrays of isolated mesa structures (2 μm diameter). These mesa structures exhibit a stress relaxation of 117 MPa over a region extending ~ 200 nm from the island edge.
X-ray Absorption Spectroscopy of Strained-Si Nanomembranes
Authors: Euaruksakul Chanan , Li Zhiwei , Savage Donald , Lagally Max
Published: April 2007

We use x-ray absorption (XAS) total electron yield measurements to investigate strain-induced splitting of the conduction band minimum in very thin Si layers and membranes. We use synchro-tron generated X rays with variable energy to excite electrons from the 2p core level of strained Si to empty electronic states in the conduction band minima. The Auger electrons emitted in the re-laxation process make the method extremely surface sensitive and reflect the position and density of states of the conduction band. We determine these parameters for elastically strained Si nanomembranes and strained-Si-on-insulator. We demonstrate sig-nificant lateral nonuniformity in the strain in strained-Si-on-insulator, while the strain is uniform on strain sharing nanomem-branes. LEEM measurements support this conclusion.
Comparison of Different Etching Techniques in Order to Reveal Dislocations in Thick Ge Layers
Authors: Abbadie Alexandra , Hartmann Jean-Michel , Deguet Chrystel , Sanchez Loic , Brunier F. , Letertre F
Published: April 2007

For the first time, we have evidenced a real correlation between 3 techniques used for defect delineation on Ge layers. Possible and different mechanisms of preferential etching will be also discussed. In the present paper we studied, namely, Cr- free wet-etching solution, gas phase HCl etching and Secco solution. Using optical microscope in the Nomarski contrast and AFM, we have studied the dislocations density and etch pits shape as a function of the etched thicknesses. Datas were compared with plan view TEM. Values close to 1E07cm-2 have been obtained in both cases, confirming the ability of the Cr-free solution to reveal dislocations. Similar values have been obtained on such thick Leti Ge layers after some Secco etch. The EPD values found using Secco are in good agreement with the ones found after HCl and Cr-free etches.
Mobility Characterization by Magnetoresistance in Ultra Thin SOI Ring-FETs
Authors: Chandrasekhar Rao Turumella V. , Cristoloveanu S. , Antoszewski Jarek , Nguyen Tuan , Hovel Harry , Gentil Pierre , Faraone Lorenzo
Published: April 2007

We report a novel use of magneto-resistance (MR) to estimate carrier mobility in ultra-thin virgin SOI wafers. Measurements were made in pseudo-MOSFET configuration with electrical contacts in Corbino geometry and substrate biasing. The use of high magnetic fields enabled accurate extraction of electron mobility as a function of gate voltage (effective field) and film thickness. The MR mobility values are large and correlate well with the field-effect mobility determined in pseudo- MOSFETs at zero magnetic field.
Mixed Orientation Si-Si Interfaces by Hydrophilic Bonding and High Temperature Oxide Dissolution: Wafer Fabrication Technique and Device Applications
Authors: Saenger Katherine L. , de Souza Joel P. , Fogel Keith E. , Ott John A. , Reznicek Alexander , Yin Haizhou , Sung Chun-Yung , Sadana Devendra K.
Published: April 2007

In this paper we describe a quasi-hydrophobic bonding method in which ultrathin (<1-2 nm) oxide present on wafer surfaces during bonding is removed after bonding by a high-temperature oxide dissolution anneal to leave the desired direct Si-to-Si contact at the bonded interface. We will show that the direct- silicon-bonded (DSB) interfaces produced by this method are clean enough to allow implementation of a recently described amorphization/templated recrystallization technique for changing the orientation of selected DSB layer regions from their original orientation to the orientation of the underlying handle wafer, and then discuss some of the mechanisms and integration challenges associated with wafer and device fabrication by these techniques.
Fabrication of SOI MOSFET by Separation by Bonding Silicon Islands (SBSI) Method
Authors: Kanemoto Kei , Oka Hideaki , Hisamatsu Hirokazu , Matsuzawa Yusuke , Kitano Yoji , Hara Toshiki , Hoshina Masaki , Ohmi Shun-Ichiro , Kato Juri
Published: April 2007

Local SOI MOSFETs were fabricated in the designed area on a Si bulk substrate using the separation by bonding silicon islands (SBSI) method. We describe the key fabrication process technology and show the electrical characteristics. The SBSI method consists of three key technologies: epitaxial growth of SiGe having high germanium concentration, lateral selective etching of SiGe, and bonding of buried oxides (BOX) grown in the gap. Epitaxial growth of 30 nm-thick Si0.63Ge0.37 without crystalline defects was achieved by reducing the growth temperature to as low as 450 ºC. The Si/Si0.63Ge0.37 structure allowed lateral etching of Si0.63Ge0.37 with a length of 1 mm in 2 minutes and with negligible etching of Si in a solution of hydrofluoric acid and nitric acid. Fabricated MOSFETs showed excellent characteristics, which were comparable to those of SOI wafers, although a small gap still remained in the BOX.
A Novel Method to Fabricate Multiple-layer SOI -- Single-Crystal Si Nanomembrane Transfer and Stacking
Authors: Peng Weina , Roberts Michelle , Nordberg Eric , Flack Frank , Colavita Paula , Hamers Robert , Savage Donald , Lagally Max , Eriksson Mark
Published: April 2007

Multiple-layer SOI, in which there are multiple device layers per unit area, is of great interest because it potentially enables fully 3D integration. It also offers the prospect of more complete integration between optics and microelectronics than is possible with purely 2D structures. Here we present a technique for transfer and stacking of multiple single crystal Si nanomembranes with intervening oxide layers, enabling fabrication of multiple-layer SOI. We explain how to overcome transfer challenges, the most important of which is unintentional bonding of nanomembranes to their host substrate during lift-off. We examine the surface roughness of the membranes using atomic force microscopy (AFM). Intriguingly, the intermediate spin-on-glass layers used in this work are rougher than the silicon layers above and below, indicating that membrane transfer can ameliorate roughness introduced by such layers. We have used this process to create multilayer Si/SiO2 heterostructures, i.e., multiple-layer SOI. These structures naturally function as Bragg reflectors, and thus their optical reflectivity can be used as a measure of structure quality. The reflectivity of one, two, and three membrane structures has been measured, and reflectivity above 99% has been achieved for three-layer samples.
Advanced Heterostructure Si-InSb on Insulator Formed by Bonding of Hydrogen Transferred Si Layer and Implanted SiO2 Film
Authors: Popov Vladimir P. , Tyschenko Ida , Cherkov Elexander , Pokhil G P. , Fridman V M. , Voelskow M
Published: April 2007

Using bulk silicon may be limited for 22 nm technological node due to silicon mobility limitation. New type of substrates needs for further scaling in CMOS microelectronics. We speculate that this new type of materials can be semiconductor heterostructure on insulator (HOI) compatible with current silicon planar CMOS technology. In this work an effect of interface mediated endotaxial (IME) growth of thin InSb film at Si/SiO2 bonded interface was experimentally observed and investigated for the first time. Joint semiconductor material stack obtained by hydrogen transfer of one layer material (silicon) and endotaxially grown second one (indium antimonide) placed initially into amorphous silicon dioxide film is presented. Thermodynamic, kinetic and lattice mismatch parameter influences on IME process are considered.
Atomic-Scale Simulations of Electron Mobilities in Ultrathin SOI MOSFETs
Authors: Pantelides Sokrates T. , Hadjisavvas George , Evans Matthew H , Tsetseris Leonidas , Caussanel Matthieu , Schrimpf Ronald D
Published: April 2007

Carrier mobilities in metal-oxide-semiconductor field-effect transistors (MOSFETs) are conventionally modeled in a semi-classical approximation, i.e., particles are treated as classical parti-cles with a suitable effective mass or with a kinetic energy given by the crystalline energy bands. Here we review a recent method based on atomic-scale models of the Si-SiO2 interface. Carriers are described by wave functions and scattering potentials are con-structed by parameter-free quantum-mechanical calculations. The effect of primitive atomic-scale roughness (Si-Si bonds on the ox-ide side and Si-O-Si bonds on the Si side of the interface) in ultra-thin SOI MOSFETs has been investigated. It is shown that this mechanism naturally accounts for strain-induced enhancement in a quantitative way. In addition, the method has been used to deter-mine the impact of stray Hf atoms in the SiO2 interlayer in alter-nate-dielectric Si-SiO2-HfO2 structures. Finally, some features of the method are compared with the density gradient method.
A Comprehensive Study of the Corner Effects in Pi-Gate SOI MOSFETs
Authors: Ruiz Francisco G. , Godoy Andres , Gamiz F. , Sampedro Carlos , Donetti Luca
Published: April 2007

In this work, a simulation-based study of the Pi-Gate SOI MOSFETs was carried out, using a 2D self-consistent Schrödinger-Poisson solver. Corner effects have been studied as a function of different parameters such as the doping density, silicon fin dimensions, corner rounding and gate oxide thickness.
Significance of Gate Underlap Architecture in FinFETs for Low-Voltage Analog/RF Applications
Authors: Kranti Abhinav , Armstrong G. Alastair
Published: April 2007

In the present work, we analyze the enormous potential of source/drain extension (SDE) region engineering in FinFETs for Ultra Low-Voltage analog/rf applications. We show that SDE region design can simultaneously improve two key analog figures of merit (FOM) - intrinsic dc gain (AVO) and cut-off frequency (fT) for 60 nm FinFETs operated at low drive current (Ids = 5 µA/µm). The results are analyzed in terms of spacer-to- gradient ratio, a new design parameter for devices with non- abrupt source/drain regions. The present work provides new opportunities for realizing future ultra low-voltage/low-power analog/rf design with nanoscale SDE engineered FinFETs.
Non-Vertical Sidewall Angle Influence on Triple-Gate FinFETs Corner Effects
Authors: Giacomini Renato , Martino Joao Antonio A.
Published: April 2007

Some fabricated FinFET devices present width variations along the vertical direction due to fabrication process limitations. These variations lead to non-rectangular cross-section shapes. One of the most frequent shapes is the trapezoidal (plane and inclined sidewalls). Another identified phenomenon in multiple- gate devices such as FinFETs is the corner effect, which occurs due to the overlapping of the influences of two gate planes near the device corners. This paper addresses the variation of the corner effect as a function of the sidewall inclination angle, through 3-D numeric simulation. A set of devices of several inclination angles and body doping levels were simulated. The corner effect depends on the inclination angle, specially for higher doping levels.
Improved Manufacturability of AlGaAs/GaAs Pnp Heterojunction Bipolar Transistors
Authors: Clevenger Jascinda B. , Patrizi Gary , Peterson Tracy , Cich Michael , Baca Albert , Klem John , Plut Thomas , Fortune Torben , Hightower Michael , Torres David , Hawkins Samuel , Sullivan Charles
Published: April 2007

Specially designed Pnp heterojunction bipolar transistors (HBT's) in the AlGaAs/GaAs material system can offer improved radiation response over commercially-available silicon bipolar junction transistors (BJT's). To be a viable alternative to the silicon Pnp BJT, improvements to the manufacturability of the HBT were required. Utilization of a Pd/Ge/Au non-spiking ohmic contact to the base and implementation of a PECVD silicon nitride hard mask for wet etch control were the primary developments that led to a more reliable fabrication process. The implementation of the silicon nitride hard mask and the subsequent process improvements increased the average electrical yield from 43% to 90%.
The Anomalous Electrical Performance of Bonded n-GaAs Wafers
Authors: Ouyang Hao , Chiou Hsiao-Hao , Liu Chia-Cheng , Cheng Ji-Hao , Wu Yewchung Sermon
Published: April 2007

Electrical performance was found to be closely related to the variation of nanosized interface morphology. This work investigated in detail the microstructural development of in- and anti-phase bonded interfaces for n-type (100) GaAs wafers treated at 500, 600, 700 and 850 oC. The interfacial energy of anti-phase bonding is higher than that of in-phase bonding based on the first-principles calculations. The higher interface energy tends to stabilize the interfacial oxide layer. The continuous interfacial oxide layer observed below 700 oC behaves to deteriorate the electrical property due to its insulating property. However, the existence of nanoscaled oxide at anti-phase bonded interfaces can improve the electrical conductivity at 700 oC. The reason will be discussed based on the analysis of autocorrelation function from HRTEM (high-resolution transmission electron microscope) and energy dispersive x-ray spectroscopy.
Annealing Effects of Diluted GaAs Nitride and Bismide on Photoluminescence
Authors: Yoshimoto Masahiro , Feng Gan , Oe Kunishige
Published: April 2007

Effects of the post-growth thermal anneal on the optical properties of GaNAsBi were systematically investigated. By the addition of Bi into diluted GaAs nitride alloy to form quaternary GaNAsBi alloy, the optical property of the diluted GaAs nitride alloy is improved which is confirmed by the photoluminescence (PL) emission from as-grown GaNAsBi samples at room temperature. The PL intensity of GaNAsBi is remarkably improved by post-growth thermal annealing process. By comparing the results of PL intensities of GaAs0.978Bi0.022, GaN0.01As0.99, and GaN0.01As0.968 Bi0.022, the improvement in PL intensity of GaN0.01As0.968Bi0.022 by anneal can be attributed to an inherited nature of GaNAs. Incorporation of Bi may suppress the blue shift induced by N incorporation. Based on results of X-ray diffraction, the blue shift is probably caused by a microscale reorganization of N and Bi mainly inside the epilayers with keeping the average N and Bi concentrations constant.
Study on ICP Dry Etching Technology for Nanostructure Photonic Device Fabrication
Authors: Sun Changzheng , Wang Jian , Hao Zhibiao , Xiong Bing , Luo Y.
Published: April 2007

In this talk, we study the application of inductively coupled plasma (ICP) dry etching for the fabrication of photonic devices with nanostructures. The gas mixture and etching conditions are optimized to ensure high anisotropy and smooth surface morphology.
Comparison of E-beam and Sputter-Deposited ITO Films for 1.55 um Metal-Semiconductor-Metal Photo-Detector Applications
Authors: Jang Soohwan , Kang Byoung Sam , Ren Fan , Emanetoglu N W. , Shen H , Chang W H. , Gila Brent , Hlad M , Pearton Steve
Published: April 2007

The optical and electrical properties and surface morphology of sputtered, e-beam deposited and composite e- beam/sputtered ITO films for Metal-Semiconductor-Metal (MSM) photo-detector applications were compared. The resistivity of sputtered ITO was almost two-orders of magnitude less than that of e-beam deposited ITO, while the resistivity of the composite films was only 15% higher than that of sputtered films. The transmittance at 1.55 μm of sputtered and composite ITO films was 83% and 77% respectively, which was much higher than the value of 13% for the e-beam deposited ITO. The composition of ITO films for both deposition techniques was very similar, as determined from with Auger Electron Spectroscopy surface scans and depth profiles. The sputtered films showed much smoother surfaces and smaller grain size. InGaAs Based MSM devices with ITO fingers have been fabricated and showed higher photo response than that of MSM devices with conventional Ti/Au fingers.
Polycrystalline Silicon Carbide Film Depositon Using Monomethylsilane and Hydrogen Chloride Gases
Authors: Habuka Hitoshi , Watanabe Mayuka , Nishida Mikiya , Sekiguchi Takashi
Published: April 2007

A polycrystalline silicon carbide film is formed on a silicon surface by atmospheric pressure chemical vapor deposition using monomethylsilane gas and hydrogen chloride gas in ambient hydrogen. The film deposition is performed near 1000 K. The excess amount of silicon on the film surface is reduced using the hydrogen chloride gas. Although the film deposition stops immediately, a further deposition is enabled using baking step at 1273 K in ambient hydrogen.
Amorphous Si-Solar Cell Assisted Hydrogen Production by Photocleavage of Water in Carbon Modified (CM)-n-TiO2/Pt Photoelectrochemical Cell
Authors: Xu Chengkun , Ingler William B. , Shaban Yasser A. , Alam Maksudul , Khan Shahed
Published: April 2007

Carbon modified (CM)-n-TiO2 was used as the photoanode in CM-n- TiO2/Pt photoelectrochemical cell (PEC), to split water and an amorphous (a)-Si triple junction solar cell was used to supply an extra photovoltage. Hydrogen production rate in terms of cell photocurrent density in CM-n-TiO2/Pt PEC was measured. Also, the effects of solar cell parameters on the PEC cell photocurrent density were investigated. It was found that under assistance of the photovoltage from the a-Si solar cell, the CM-n-TiO2/Pt PEC generated significantly increased photocurrent density (5.3 mA/cm2) compared to that by undoped n-TiO2/Pt PEC (1.0 mA/cm2). The photoresponse of CM-n-TiO2/Pt PEC was found to be limited due to low short circuit photocurrent density generated at a-Si solar cell even though it supplied needed extra photovoltage for water splitting.
Visible Light Active Carbon Modified (CM)-p-WO3 Thin Film Electrodes for Photosplitting of Water
Authors: Shaban Yasser A. , Khan Shahed
Published: April 2007

Carbon modified p-type tungsten oxide (CM-p-WO3) photoelectrodes were synthesized by flame oxidation of tungsten metal sheets (Alfa Co. 0.25 mm thick) at several temperatures for different lengths of time. The photocatalytic activity of CM-p-WO3 was evaluated by measuring the rate of water splitting reaction to hydrogen and oxygen, which is proportional to photocurrent density, jp. Carbon modified tungsten oxide photoelectrodes exhibited p-type photoresponse in acidic medium of 0.5 M H2SO4. The highest photocurrent density of 2.08 mA cm-2 was observed under illumination intensity of 80 mW cm-2 from a 150 Watt (Kratos Model LH 150/1) Xenon arc lamp at an optimal thermal oxidation temperature of 900 {degree sign}C for15 min at applied potential of -0.4 V vs Eaoc. These CM-p-WO3 photoelectrodes were found to generate highest photoconversion efficiency of 2.16 % for photosplitting of water.
ZnO Nanostructures and Device Applications
Authors: Chen Lih J. , Chang Y.C. , He J.H.
Published: April 2007

ZnO is undoubtedly the most versatile binary compound that exhibits a wide variety of morphological features. It has also been shown to be applicable to a vast range of optoelectronics and electronics devices. In this paper, two examples of recent progresses in the investigations of ZnO nanostructures and device applications are reported. Tapered ZnO nanorod, herein called nanoneedle, arrays have been grown on ZnO-coated silicon substrate by a hydrothermal downward growth process. Piezo-diodes are used as an example for device applications.
Wide Bandgap Semiconductor Nanowires for Sensing Applications
Authors: Pearton Steve , Norton David , Ren Fan , Tien Li-Chia , Kang Byoung Sam , Chi G
Published: April 2007

Wide bandgap semiconductor nanowires are attractive for a variety of sensing purposes because of their excellent stability, large surface area, pizeo-electric nature and ability to be integrated with on-chip wireless communication systems. In this brief review, we will discuss progress in these nanowires for sensing applications.
Low Temperature (< 100{degree sign}C) Patterned Growth of ZnO Nanorod Arrays on Si
Authors: Kang Byoung Sam , Pearton Steve , Ren Fan
Published: April 2007

Micro-patterned growth of ZnO nanorod arrays on silicon substrates using a low temperature aqueous method is demonstrated. ZnO nanocrystals were used as seeds for producing well-aligned, wurtzite ZnO nanorod arrays with spin coating. The shape of the ZnO nanorods was sensitive to the orientation of substrate as well as the molar composition of the chemical precursors. X-ray diffraction (XRD) was used to investigate the effect of the substrate orientation on the crystal structure of the patterned grown ZnO nanorod arrays, showing that growth on (100) Si was faster than on (111)Si, with the nanorods growing preferentially in the <001> direction. Photoluminescence (PL) of the patterned ZnO nanorod arrays showed good optical quality with near band-edge emission at 3.24 eV, showing the promise of this approach for micro-patterned optical device applications using low temperature synthesis and the conventional lithography.
Enhanced Carrier Transportation on Passivated Gallium Nitride Single Nanowire Field-Effect Transistor
Authors: Yu Jeng Wei , Wu Han Min , Peng Lung Han
Published: April 2007

We reported on the enhanced carrier transportation in gallium nitride (GaN) single nanowire field-effect transistor (FET) with top gate structure. The GaN nanowires were synthesized by a selective-site growth mechanism using vapor-liquid-solid (VLS) method on a silicon-dioxide (SiO2) capped p-type silicon substrate. The GaN nanowires were characterized with a length of 20000nm and ~80nm diameter as observed by scanning electron microscope. Data from the electrical characterization revealed a twenty-fold increase of the saturation current on the SiO2 passivated GaN single nanowire FETs compared the ones without SiO2 layer. We ascribed this observation to the suppression of the surface states density of GaN nanowires by the oxide layer.
Fabrication and Characterization of InGaN-Based Green Resonant Cavity Light-Emitting Diodes Using H+ Ion-Implantation
Authors: Horng Ray-Hua , Huang Shih Yung , Kuo Hao-Chung , Wuu Dong Sing
Published: April 2007

InGaN-based green resonant-cavity light-emitting diodes (RCLEDs) have been fabricated using hydrogen ion-implantation and laser lift-off techniques. The RCLED structure consisted of an InGaN/GaN multiple-quantum-well active layer between top (5-pairs) and bottom (7.5-pairs) dielectric TiO2/SiO2 distributed Bragg reflectors with optical reflectances of 85% and 99.9%, respectively. The insulating layers of the RCLEDs were formed by either hydrogen ion implanted layers of 1x1014 ions/cm2 or SiO2 films, respectively. The corresponding forward turn-on voltages for a 0.6 KA/cm2 dc injection current density were about 4.58 and 4.55 V, respectively. The light output intensity of the RCLEDs with H+ implantation is higher by a factor of 1.4 compared with the SiO2 structure at a current density of 0.6 KA/cm2. The RCLEDs with H+ implantation have superior directionality compared to the RCLEDs without H+ implantation.
Nitride-based Ohmic and Schottky Contacts to GaN
Authors: Voss Lars F. , Stafford Luc , Wright Jonathan , Gila Brent , Abernathy Cammy R. , Pearton Steve , Ren Fan , Kravchenko Ivan I.
Published: April 2007

Ohmic and Schottky contact formation on n-GaN using ZrN, TiN and TaN-based metallization schemes was studied. For GaN layers with an electron concentration of ~3×1017 cm-3, the minimum specific contact resistance achieved is 6x10-5 Ω cm2 for Ti/Al/TiN/Ti/Au after annealing at 800{degree sign}C. The specific contact resistance was found to strongly depend on the doping level, suggesting that tunneling is the dominant mechanism of current flow. TiN/Pt/Au and ZrN/Pt/Au metallurgies exhibited rectifying behavior up to 900{degree sign}C anneal, the maximum barrier height being ~0.85 eV for ZrN/Pt/Au after 750{degree sign}C anneal. While this value is comparable to that of standard Ni/Au and Pt/Au rectifying contacts on the same n-GaN layer, the nitride-based metallization schemes show considerable smoother surface morphologies, even after annealing in the 750-900{degree sign}C range.
InN/InAlN Multiple Quantum Well Nanocolumns Grown on (111) Si Substrates by RF-Plasma Assisted Molecular Beam Epitaxy
Authors: Kishino Katsumi , Kamimura Jumpei , Kikuchi Akihiko , Holmström Petter
Published: April 2007

High In content InxAl1-xN nanocolumns were successfully self- assembled on Si (111) substrates under nitrogen-rich conditions, by rf-plasma assisted molecular beam epitaxy. The InAlN nano-columns (XIn=0.87) were grown at 416 oC, and the room tempera-ture (RT) PL full-width-at-half-maximum (FWHM) was relatively broad at 164 meV. When the AlInN nanocolumns of 1.48mm wavelength (XIn=0.92) were grown at a higher temperature of 463 oC but increasing the V/III ratio, however the RT-PL- FWHM be-came narrower to be 106 meV. InN/In0.77Al0.23N multiple quantum well (MQW) structures of 100 wells were integrated into InAlN nanocolumns, where three such samples with the different InN well widths of 3, 2 and 1 nm were grown. The RT-PL peak wave-length shifted from 1.53 to 1.2 um depending on the well layer thickness. The quantum confinement shift is theoretically analyzed.
Comparison of Optical Characteristics of Three-Terminal Dual-Emitter Phototransistor and Three-Terminal Heterojunction Phototransistor
Authors: Chen Wei-Tien , Chen Hong-Rung , Hsu Meng-Kai , Chiu Shao-Yen , Lour Wen S.
Published: April 2007

Dual-emitter heterojunction phototransistors (DEPT) with an voltage-biased emitter is compared with the conventional heterojunction phototransistor with a voltage-biased emitter. There are four (three) operating regions in the photocurrent- voltage characteristics of the DEPT (HPT): negative-saturation, negative-tuning, positive-tuning, and positive-saturation (cutoff, positive-tuning, and positive-saturation) regions. The obtained optical gains are only 0.784~1.64 with a gain-tuning efficiency of 4.4 V-1 for the HPT while those are in the range of 12.9 ~ 32.3 with the maximum gain-tuning efficiency of 43.4 V-1 for the DEPT. The power- and voltage-tunable optical gains are both expected for the DEPT. However, the conventional HPT exhibits only voltage-tunable characteristics. DEPTs with different emitter area ratio are also discussed. The maximum gain-tuning efficiency is 75.3 for the DEPT with emitter area ratio of 8:1 under optical power of 0.423 μW. The obtained results introduce the potential of employing the DEPT for low- power optical detection.
Characteristics of a Four-Terminal Dual-Emitter Heterojunction Phototransistor with a Base Current Bias
Authors: Chen Wei-Tien , Chen Hon-Rung , Hsu Meng-Kai , Chiu Shao-Yen , Lour Wen S.
Published: April 2007

This paper reports on a four-terminal dual-emitter heterojunction phototransistor (4T-DEPT) with a base biased by current source in comparison with a three-terminal dual-emitter heterojunction photoreansistor (3T-DEPT) without the additional current bias. While only voltage can be used to tune the optical performance of the 3T-DEPT, two kinds of operation modes, voltage- (VE21) and current- (IBdc) control modes, are considered for the 4T-DEPT. In addition to the power- and voltage-tunable optical gains, current-tunable one is also available in the 4T-DEPT operation. When the 4T-DEPT operates under the incident optical power (Pin) of 0.423 μW, it shows the maximum current-dependent gain-tuning efficiency of 62.66 μA-1 at VE21 = 0.06 V and IBdc = 0.001 μA. However, it is only 45.03 V-1 for the maximum voltage-dependent gain-tuning efficiency at VE21 = 0.06 V and IBdc = 0.25 μA.
Thermally Stable Novel Metal Contacts on Bulk, Single-Crystal n-type ZnO
Authors: Wright Jonathan , Khanna R. , Voss Lars F. , Stafford Luc , Gila Brent , Norton David , Pearton Steve , Ren Fan , Kravchenko Ivan I.
Published: April 2007

The contact characteristics on bulk single-crystal n-type ZnO of TiB2/Pt/Au, ZrB2/Pt/Au and Ir/Au metallization schemes deposited by sputtering are reported as a function of annealing temperature in the range 200-1000{degree sign}C (N2 ambient). Boride contacts exhibited Ohmic behavior with minimum specific contact resistance between 10-3 and 10-5 Ωcm2 after a 700{degree sign}C or above anneal. The contacts transition to rectifying behavior after annealing above 900{degree sign}C, coincident with a degraded surface morphology. Ir contacts exhibit higher thermal stability than both Boride contacts investigated, exhibiting a minimum specific contact resistance of 3.6x10-6 Ωcm2 after annealing at 1000{degree sign}C. Ir contacts showed very little change in resistance after extended aging (30 days) at 350{degree sign}C.
Effects of Laser Sources on the Reverse-Bias Leakages of Laser Lift-Off GaN-Based LEDs
Authors: Wu Yewchung S. , Cheng Ji-Hao , Ouyanga Hao
Published: April 2007

The KrF pulsed excimer laser (248 nm) and the frequency- tripled Nd YAG laser (355nm) were used to separate GaN thin films from sapphire substrates. The effect of these two laser sources on the reverse-bias leakages of InGaN-GaN light- emitting diodes (LEDs) were studied.
In-situ Observation of Pore Formation and Photoelectrochemical Etching in n-InP
Authors: Lynch Robert P. , Dornhege Monika , Sánchez Bodega Pablo , Rotermund Harm Hinrich , Buckley D. N.
Published: April 2007

Electrochemical etching of semiconductors under anodic conditions can lead to the growth of pores under conditions both of darkness and of illumination. In previous work our group has developed a new technique which uses contrast enhanced microscopy to image full electrode surfaces simultaneously with electrochemical control of the potential at the electrode-electrolyte interface. In this paper, we present results obtained using the technique to monitor in situ the InP-electrolyte interface during linear potential sweeps (LPSs) and also to investigate selective photo- electrochemical etching.
Nanoporous Domains in n-InP Anodized in KOH
Authors: Lynch Robert P. , O'Dwyer C. , Sutton David , Newcomb Simon B. , Buckley D. N.
Published: April 2007

A model of porous structure growth in semiconductors based on propagation of pores along the <111>A directions has been developed. The model predicts that pores originating at a surface pit lead to porous domains with a truncated tetrahedral shape. SEM and TEM were used to examine cross- sections of n-InP electrodes in the early stages of anodization in aqueous KOH and showed that pores propagate along the <111>A directions. Domain outlines observed in both TEM and SEM images are in excellent agreement with the model. The model is further supported by plan-view TEM and surface SEM images. Quantitative measurements of aspect ratios of the observed domains are in excellent agreement with the predicted values.
Smoothening the Pores Walls in Macroporous n-Si
Authors: Foca Eugen , Carstensen Juergen , Leisner Malte , Ossei-Wusu Emmanuel , Riemenschneider Oliver , Foell Helmut
Published: April 2007

Our work reports on the etching of very smooth pores in n-Si with backside illumination. From the point of view of the so- called current burst model we explain the origin of the roughness on macropore walls. By trying different types of electrolytes at very low or moderate pH, electrolytes with very small dissolution rates of SiO2, or etching at very low temperatures, we show that the roughness of the walls can be controlled. Finally we propose to use a viscous electrolyte which lead to a roughness of only 9 nm on a 800 x 800 nm2 area which is a factor 5 smaller than the roughness observed for aqueous electrolytes.
FFT Photo Impedance Characterization of Semiconductors for Solar Application
Authors: Keipert Sinje , Carstensen Juergen , Foell Helmut
Published: April 2007

Based on FFT impedance spectroscopy, a fast technique for characterizing relevant properties of semiconductors for solar cell application has been developed. FFT impedance is a fast and reliable method for linear response measurements of, e.g. various electrochemical reaction systems in a wide frequency range (1) based on current or voltage modulation. In this approach a modulated front side illumination as perturbation was used to measure the frequency dependent photo response (2) of photoactive electrochemical half-cells as well as complete solar cells. The possibility of investigating experimental systems that show a (reasonable) parameter drift and to be able to recognize non-linear behavior by analyzing the response spectra makes FFT impedance technique an interesting tool for evaluating solar materials.
Impact of the Alcohol-Containing Electrolytes on the Macropores Etching in n-Si
Authors: Foca Eugen , Riemenschneider Oliver , Lage Enno , Leisner Malte , Carstensen Juergen , Foell Helmut
Published: April 2007

We present an analysis of the macropore growth conditions in n- Si for electrolytes containing different alcohols: methanol, ethanol and 2-propanol. The voltamograms for all types of electrolytes are measured for different illumination intensities. The typical features of the pores obtained are for the same etching conditions are also shown and discussed, in particular the pore diameter, depth and volume. The results show that the alcohols wet the electrode surface very well, which leads to more homogenous etching. For some applications, one of the most important features of pores is the smoothness of the pore walls. The results obtained in this study highlight the role of alcohols on the dissolution kinetics of the SiO2, which has a direct impact on the pore growth process and on the pore wall smoothness.
Electrochemical Deposition and Characterization of ZnO Nanowire Arrays with Tailored Dimensions
Authors: Levy-Clement Claude , Elias Jamil , Tena-Zaera Ramon , Mora-Sero Ivan , Luo Yan , Bisquert Juan
Published: April 2007

A systematic study of the deposition of single crystal ZnO nanowire arrays from the oxygen electroreduction was performed. The influence of deposition parameters such as the concentrations of zinc precursor (ZnCl2) and supporting electrolyte (KCl) on the formation of ZnO nanowire arrays, as well as on the dimensions of the nanowires was analyzed. Mean nanowire diameters from 25 to 80 nm were obtained by only modifying the [ZnCl2], while high [KCl] allowed to reach diameters as high as 300 nm. The influence of [KCl] on the donor density determined from electrochemical impedance spectroscopy of ZnO nanowires was also shown. Carrier densities from 1017 to 1020 cm-3 were obtained depending on the deposition and annealing conditions. The results show that electrodeposition is a cost-effective technique which allows not only to grow ZnO single crystal nanowire arrays with tailored dimensions, but also to act on their electrical properties in a controlled way.
Growth by Electrochemistry of Zinc Oxide Films with Controlled (nano)Structure and Properties
Authors: Pauporte Thierry , Lincot Daniel
Published: April 2007

Electrodeposition is a versatile method for the preparation of ZnO films with controlled nanostructures and properties. In the present paper we describe two approaches for the preparation of ZnO hybrid films with red/green adjustable luminescence. ZnO is imparted with luminescence properties by bipyridine (dcbpy)- lanthanide complexes. In the first route, ZnO/ dcbpy hybrid films are prepared and subsequently chelated with Ln3+ ions (with Ln being Eu or Tb) to form the luminescent complex. In the second proposed route, highly porous ZnO matrices are prepared by electrodeposition with help of eosin Y molecules. The matrices are loaded with in- situ assembled Ln3+:dcbpy luminescent complexes. In both cases, the ligand is anchored to ZnO by its carboxylic acid groups. The film emission and excitation characteristics show UV absorption by the ligand bipyridine group and an efficient energy transfer to Ln3+.
The Role of the Surface Chemistry on the Evolution of Kinetic of Hole Injection by Fe(CN)6
3- at n- InP
Authors: Etcheberry A. , Simon Nathalie , Gérard Isabelle
Published: April 2007

Study of InP in Fe(CN)63- solution at pH9 are presented. Modifications of cyclic voltammograms are observed and correlated to presence of thin InP oxide that change the capability of the electronic transfer through the interface.
Quantitative Infrared Investigation of the Acido-Basic Equilibrium at a Carboxy-Terminated Silicon Surface
Authors: Aureau Damien , Gouget-Laemmel Anne Chantal , Henry de Villeneuve Catherine , Moraillon Anne , Ozanam François , Allongue Philippe , Chazalviel Jean-Noel
Published: April 2007

Silicon surfaces grafted with mixed alkyl/carboxylic acid monolayers have been investigated by in-situ quantitative infrared spectroscopy at the contact with electrolytes of various pH. Ionization of the carboxy groups is found to start around pH 6 and to extend over a wide pH range. Ionization is not complete even at pH 11. These observations point to the importance of the interactions between surface charges. This effect may be accounted for by a simple model taking into account the change in the Helmholtz potential associated with the surface charge. However, the agreement is only qualitative, which indicates that the surface charge is screened more efficiently than expected, possibly due to ion penetration between the carboxy groups.
Passivation of Si(100) Surface by S from a Solution and its Effect on Schottky Barrier Height
Authors: Ali Muhammad Y. , Tao Meng
Published: April 2007

A wet-chemical process has been developed to passivate the Si (100) surface with S in an aqueous solution. The solution contains an etchant for SiO2, ammonium hydroxide [NH4OH], and a passivant, ammonium sulfide [(NH4)2S]. The compatibility of the etchant with the passivant allows SiO2, native or thermal, to be removed in-situ. A fresh and clean Si(100) surface is exposed right before the surface is passivated by S. To monitor the passivation quality, Schottky barrier heights of Al and Ni on S-passivated n-type and p-type Si(100) have been measured. Due to the passivation of dangling bonds by S, surface states are reduced to a great extent and Schottky barrier heights of Al and Ni on Si(100) show a greater sensitivity to their respective work functions. Our experimental results also reveal that surface states dominate over surface dipole in controlling the Schottky barrier height in these metal-Si systems.
Wet Chemical Etching of Wide Bandgap Semiconductors- GaN, ZnO and SiC
Authors: Pearton Steve , Lim W , Ren Fan , Norton David
Published: April 2007

Wide bandgap semiconductors have many properties that make them attractive for high power, high temperature device applications. In this paper we review wet etching of three important materials, namely ZnO, GaN and SiC. While ZnO is readily etched in many acid solutions including HNO3/HCl and HF/HNO3, and in the nonacid acetyleacetone, the group III nitrides and SiC are very difficult to wet etch and generally dry etching is used. Various etchants for GaN and SiC have been investigated, including aqueous mineral acid and base solutions, and molten salts. Wet etches have a variety of applications to wide bandgap semiconductor technology, including defect decoration, polarity and polytype (for SiC) identification by producing characteristic pits or hillocks, and device fabrication on smooth surfaces. Electrochemical etching is successful at room temperature in some situations for GaN and SiC. In addition, photo-assisted wet etching produces similar rates independent of crystal polarity.
Photoelectrochemistry and Etching of SiC: a Comparison with Si
Authors: Kelly John , van Dorp Dennis , Weyher Jan
Published: April 2007

The anodic electrochemistry and etching of the group IV compound semiconductor SiC was studied in both KOH and acidic fluoride solutions. The results for p-type and n-type electrodes are compared with those obtained for the group IV elemental semiconductor Si. We point out a number of interesting applications of this work for SiC device technology.
Photo-Dynamics of AlxGa1-xAs Heterostructure Dissolution: Experiments and Applications
Authors: Yi Eun-Hyeong , Parker Michael
Published: April 2007

We present the effects of the photo-assisted (532 nm) semiconductor dissolution on sidewall profile and etch rate for two different types of GaAs/AlGaAs laser heterostructure and two different etch masks. The experiments show that the photo-assisted dissolution characteristics (dissolution rate and side angle profile) strongly depend on the sample layer structure and mask conductivity. The experiments apply optical interference and photoluminescence techniques to determine the surface and photo-carrier dynamics. The research evaluates the application of photo-assisted semiconductor etching to the fabrication of III-V devices using 532 nm coherent illumination. The technique successfully produces vertical sidewalls and on-demand etch-stop layers in laser heterostructure using Sulfuric acid (H2SO4): Hydrogen peroxide (H2O2): DI water (H2O) etch system.
Deposition and Characterization of Copper Chalcopyrite Based Solar Cells using Electrochemical Techniques
Authors: Dale Phillip , Samantilleke Anura , Zoppi Guillaume , Forbes Ian , Roncallo Scilla , Peter Laurence
Published: April 2007

Cu(In,Ga)Se2 films were electrodeposited on molybdenum substrates from a single pH buffered bath and annealed in a reducing selenium atmosphere. The opto-electronic properties of the films were characterized using a potentiostatically- controlled three electrode setup and an electrolyte contact. Pulsed illumination was used to determine the carrier type and the speed of photoresponse. Chopped monochromatic illumination was used to measure photocurrent spectra. The electrodeposited copper chalcopyrite films were compared with films prepared by sputtering and spraying techniques.