bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of transparent conductive oxide materials for improved back reflector performance for amorphous silicon based solar cells
Authors: Jones Scott J. , Tsu David , Liu Tongyu , Steele Jeff , Capangpangan Rey , Izu Masat
Published: April 2011

A new back reflector comprised of an Al/(multi-layered stack)/ZnO structure is being developed to replace Al/ZnO used in manufacturing and boost conversion efficiencies with improved back reflector performance. Use of the multi-layered stack should lead to improved reflectivity which will in turn improve solar cell currents and efficiencies. The results from studies of different transparent conductive oxides (TCOs) which comprise the multi-layered stack are reported with emphasis on ZnO alloys. Alloying with Si or MgF2 and using moderately high substrate temperatures, TCOs with low indices of refraction between 1.6 and 1.7 have been fabricated. The Si, Mg and F contents for these alloys were near 14, 12 and 33 at.%. Structural analysis demonstrates that alloys with MgF2 have smother surfaces and finer morphologies than those for ZnO. The expected high values for multi-layered structures with these alloys have yet to be achieved but this is likely due to properties of layers in the structure other than the ZnO alloys which have yet to be fully optimized.
Transient and modulated photoconductivity in microcrystalline silicon
Authors: Brüggemann R. , Longeaud C. , Kleider J.P.
Published: April 2011

We report on transient and modulated photoconductivity experiments with undoped michrystalline silicon in which access to density-of-states information is limited because the Fermi level results in occupancy of localised states in the energy range which is scanned. Simulation results show that a defect peak will be masked if most of the distribution is occupied because of the Fermi level position and the density-of-states determined from the experimental data is not an image of the true distribution. Another difficulty with obtaining reliable density-of-states distributions in microcrystalline silicon is the metastability of samples with respect ot adsorption of gases. If dark-conductivity changes are large upon heat treatment in vacuum, the modulated and transient photocurrent response are also affected to a large degree and the density-of-states profiles apart form being influenced by the Fermi level position thus also depend on the thermal history of the sample.
Enhanced Boron Diffusion in Amorphous Silicon
Authors: Jacques J.M. , Burbure N. , Jones K.S. , Law M.E. , Robertson L.S. , Downey D.F. , Rubin L.M. , Bennett J. , Beebe M. , Klimov M.
Published: April 2011

In prior works, we demonstrated the phenomenon of fluorine-enhanced boron diffusion within self-amorphized silicon. Present studies address the process dependencies of low temperature boron motion within ion implanted materials utilizing a germanium amorphization. Silicon wafers were preamorphized with either 60 keV or 80 keV Ge+ at a dose of 1×1015 atoms/cm2. Subsequent 500 eV, 1×1015 atoms/cm211B+ implants, as well as 6 keV F+ implants with doses ranging from 1×1014 atoms/cm2 to 5×1015 atoms/cm2 were also done. Furnace anneals were conducted at 550°C for 10 minutes under an inert N2 ambient. Secondary Ion Mass Spectroscopy (SIMS) was utilized to characterize the occurrence of boron diffusion within amorphous silicon at room temperature, as well as during the Solid Phase Epitaxial Regrowth (SPER) process. Amorphous layer depths were verified through Cross-Sectional Transmission Electron Microscopy (XTEM) and Variable Angle Spectroscopic Ellipsometry (VASE). Boron motion within as-implanted samples is observed at fluorine concentrations greater than 1×1020 atoms/cm3. The magnitude of the boron motion scales with increasing fluorine dose and concentration. During the initial stages of SPER, boron was observed to diffuse irrespective of the co-implanted fluorine dose. Fluorine enhanced diffusion at room temperature does not appear to follow the same process as the enhanced diffusion observed during the regrowth process.
Advanced Thermal Processing of Semiconductor Materials by Flash Lamp Annealing
Authors: Skorupa W. , Panknin D. , Voelskow M. , Anwand W. ,   The European FLASiC Consortium, Gebel T. , Yankov R. A. , Paul Silke , Lerch Wilfried
Published: April 2011

The use of flash lamp annealing for processing semiconductor materials is outlined. Specific applications include ultra-shallow junction formation and heteroepitaxial growth of improved quality thin films of cubic silicon carbide. It is demonstrated that flash lamp annealing holds great promise as a technique for fabricating novel devices.
The Effect of Oxide Trenches on Defect Formation and Evolution in Ion-Implanted Silicon
Authors: Burbure Nina , Jones Kevin S.
Published: April 2011

Pattern induced defects during advanced CMOS processing can lead to lower quality devices with high leakage currents. Within this study, the effects of oxide trenches on implant related defect formation and evolution in silicon patterned wafers is examined. Oxide filled trenches approximately 4000Å deep were patterned into 300 mm <100> silicon wafers. Patterning was followed by ion implantation of Si+ at energies ranging from 10 to 80 keV. Samples were amorphized with doses of 1×1015 atoms/cm2, 5×1015 atoms/cm2, and 1×1016 atoms/cm2. Two independent repeating structures were studied. The first structure is comprised of silicon oxide filled trench lines, 3.7μm wide spaced 12.5μm apart, while the second structure contains silicon squares, 0.6μm on a side, surrounded by a silicon oxide filled trench. Cross- sectional and planar view transmission electron microscopy (TEM) samples were used to examine the defect morphology after annealing at temperatures ranging from 700°C to 950°C and at times between 1 second and 1 minute. Following complete regrowth, an array of defects was observed to form near the surface at the silicon/silicon oxide interface. These trench edge defects appeared to nucleate at the amorphous-crystalline interface for all energies and doses studied. Upon a spike anneal at 700°C, it was observed that regrowth of the amorphous layer had completed except in the region near the trench edge. Thus, it is believed that this defect results from the pinning of the amorphous-crystalline interface along the trench edge during solid phase epitaxial regrowth (SPER).
Influence of Atomic Hydrogen on Nickel Silicide Formation
Authors: Vengurlekar A. , Balasubramanian Satheesh , Ashok S. , Theodore N. D. , Chi D.Z.
Published: April 2011

Nickel monosilicide (NiSi) is a leading contender to replace the currently used class of silicides for contacts to the source, drain and gate regions in Complimentary Metal-Oxide- Semiconductor (CMOS) circuits. In this work, the effect of substrate hydrogenation by a hydrogen plasma treatment prior to nickel deposition and silicidation was studied. The sheet resistance of the silicide film shows a significant decrease under hydrogenation of the Si substrate prior to Ni evaporation/anneal for projected silicidation temperatures below 600°C. Correspondingly, the Si region near the interface is decorated with defects. At higher silicidation temperatures, the sheet resistance rises along with greater in-diffusion of Ni into the hydrogenated Si samples. Secondary Ion Mass Spectrometry, Transmission Electron Microscopy and Hall effect measurements are used to characterize the samples.
Behavior of Si Interstitials and Boron-Interstitial Pairs at the Si/SiO2 Interface
Authors: Kirichenko Taras A. , Yu Decai , Banerjee Sanjay K. , Hwang Gyeong S.
Published: April 2011

Using density functional theory calculations within the generalized gradient approximation, we have investigated the structure, energetics, bonding, and diffusion behavior of Si interstitials and boron-interstitial pairs at the Si/SiO2 interface. We find that interstitials are significantly stabilized at the Si/SiO2 interface and prefer to reside on the SiO2 side rather than the Si side. Due to the interstitial stabilization, boron-interstitial pairs are likely to be easily dissociated in the vicinity of the Si/SiO2 interface. This study provides valuable insight into interstitial annihilation and boron precipitation at the interface.
Role of C and Ge in the electrical activation of In implanted in Silicon
Authors: Scalese S. , Privitera V. , Italia M. , Magna A. La , Alippi P. , Renna L.
Published: April 2011

An experimental study on In implantation in Si was performed, considering some factors that affect its electrical activation. One of the critical issues concerning In is represented by its outdiffusion, during the post-implantation annealing, a limiting factor to get active In concentration suitable for applications in microelectronics. The use of different thermal processes was evaluated, aimed to achieve a reduction of the outdiffusion and an increase of the electrical activation of In in silicon. The influence of the substrate purity on the electrical activation was shown to be of great importance: in particular, it was shown that C., present in the silicon substrate as a contaminant or as a co-implanted species, has a key-role in the electrical activation and diffusion of In in silicon. Furthermore, for the first time at our knowledge, the behaviour of In implanted in Si1−xGex layers grown by CVD on Si wafers was investigated, for Ge concentration of 0.5% and 1%. An enhancement in the electrical activation was observed with increasing the Ge content in the alloy.
The Effect of Environmental Chemistry on the Pb Assisted Stress Corrosion Cracking Susceptibility of Mill-Annealed Alloy 22 and GTAW Weldments
Authors: Csontos Aladar A. , Pan Yi-Ming , Dunn Darrell S. , Yang Leitai , Cragnolino Gustavo A.
Published: April 2011

The susceptibility of mill-annealed (MA) and gas tungsten arc welded (GTAW) Alloy 22 to Pb-assisted stress corrosion cracking (PbSCC) was evaluated in supersaturated PbCl2 and Pb(NO3)2 solutions. The solution chemistries and pH were varied to evaluate the effects of specific Pb-bearing species on the SCC resistance of GTAW Alloy 22 double U-bend samples. Anodic polarization tests in acidic and basic supersaturated Pb(NO3)2 solutions indicated that the passive current densities generally increased with applied potential. These results were then compared to previous anodic polarizations results for supersaturated acidic PbCl2 solutions. Constant deformation SCC tests indicate that MA and GTAW Alloy 22 were resistant to PbSCC in supersaturated PbCl2 (16,000ppm Pb, 95°C, pH 0.5, and Eapplied = -100, -50, 0, and 50mVSCE) and Pb(NO3)2 (16,000ppm Pb, 95°C, pH 3.9 and 10.7 and Eapplied = 50 and 140mVSCE, respectively). The overall results from this PbSCC investigation suggest that MA and GTAW Alloy 22 are resistant to SCC in supersaturated PbCl2 and Pb(NO3)2 solutions at 95°C. Provided that these high Pb concentrations are not attainable in the anticipated repository environments, Alloy 22 is unlikely to be susceptible to SCC by the presence of Pb.
Process-Oriented Stress Modeling and Stress Evolution During Cu/Low-K BEOL Processing
Authors: Zhai Charlie Jun , Besser Paul R. , Feustel Frank
Published: April 2011

The damascene fabrication method and the introduction of low-K dielectrics present a host of reliability challenges to Cu interconnects and fundamentally change the mechanical stress state of Cu lines. In order to capture the effect of individual process steps on the stress evolution in the BEoL (Back End of Line), a process-oriented finite element modeling (FEM) approach was developed. In this model, the complete stress history at any step of BEoL can be simulated as a dual damascene Cu structure is fabricated. The inputs to the model include the temperature profile during each process step and materials constants. The modeling results are verified in two ways: through wafer-curvature measurement during multiple film deposition processes and with X-Ray diffraction to measure the mechanical stress state of the Cu interconnect lines fabricated using 0.13um CMOS technology. The Cu line stress evolution is simulated during the process of multi-step processing for a dual damascene Cu/low-K structure. It is shown that the in-plane stress of Cu lines is nearly independent of subsequent processes, while the out-of-plane stress increases considerably with the subsequent process steps.
Thermal Conductivity of Carbon Nanotube Composite Films
Authors: Ngo Quoc , Cruden Brett A. , Cassell Alan M. , Walker Megan D. , Ye Qi , Koehne Jessica E. , Meyyappan M. , Li Jun , Yang Cary Y.
Published: April 2011

State-of-the-art ICs for microprocessors routinely dissipate power densities on the order of 50 W/cm2. This large power is due to the localized heating of ICs operating at high frequencies, and must be managed for future high-frequency microelectronic applications. Our approach involves finding new and efficient thermally conductive materials. Exploiting carbon nanotube (CNT) films and composites for their superior axial thermal conductance properties has the potential for such an application requiring efficient heat transfer. In this work, we present thermal contact resistance measurement results for CNT and CNT-Cu composite films. It is shown that Cu-filled CNT arrays enhance thermal conductance when compared to as-grown CNT arrays. Furthermore, the CNT-Cu composite material provides a mechanically robust alternative to current IC packaging technology.
Fundamental Limits for 3D Wafer-to-Wafer Alignment Accuracy
Authors: Wimplinger M. , Lu J.-Q. , Yu J. , Kwon Y. , Matthias T. , Cale T.S. , Gutmann R.J.
Published: April 2011

Wafer-level three-dimensional (3D) integration as an emerging architecture for future chips offers high interconnect performance by reducing delays of global interconnects and high functionality with heterogeneous integration of materials, devices, and signals. Various 3D technology platforms have been investigated, with different combinations of alternative alignment, bonding, thinning and inter-wafer interconnection technologies. Precise alignment on the wafer level is one of the key challenges affecting the performance of the 3D interconnects. After a brief overview of the wafer-level 3D technology platforms, this paper focuses on waferto-wafer alignment fundamentals. Various alignment methods are reviewed. A higher emphasis lies on the analysis of the alignment accuracy. In addition to the alignment accuracy achieved prior to bonding, the impacts of wafer bonding and subsequent wafer thinning will be discussed.
Modification of Nanoporous Silica Structures by Fluorocarbon Plasma Treatment
Authors: Cho Woojin , Saxena Ravi , Rodriguez Oscar , Achanta Ravi , Ojha Manas , Plawsky Joel L. , Gill William. N. , Baklanov Mikhail R.
Published: April 2011

Polymerization occurring during fluorocarbon plasma treatment as a potential method for pore sealing was investigated. CHF3 was used as a reactant gas to expedite the rate of polymerization due to the presence of hydrogen and the low C/F ratio. The reactor pressure was varied from 30mTorr to 90mTorr to change the number of neutrals that act as the polymerizing species. The films were exposed to the plasma for times of 1min, 3min, and 5 min to observe the penetration depth of neutrals and the thickness of modified layer as a function of time. Dielectric constants were measured before and after plasma treatment. The film morphology was investigated by scanning electron microscopy before and after plasma treatment and a featureless surface morphology was observed at 90mTorr on a 56% porosity film. After plasma treatment, the average pore neck size decreases which may help reduce metal precursor penetration during metallization.
Silver Metallization with Reactively Sputtered TiN Diffusion Barrier Films
Authors: Gao L. , Gstöttner J. , Emling R. , Linsmeier Ch. , Balden M. , Wiltner A. , Hansch W. , Schmitt-Landsiedel D.
Published: April 2011

The physical and electrical properties as well as thermal stability of reactively sputtered titanium nitride (TiN) film serving as a diffusion barrier was studied for silver (Ag) metallization. The thermal stability of Ag/TiN metallizations on Si with 12-nm-thick TiN barriers, as-deposited and after annealing at 300-650°C in N2/H2 for 30 min, was investigated with sheet resistance measurement, X-ray diffraction, focused ion beam-scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. According to electrical measurement no change of sheet resistance was found after annealing at 600°C, but an abrupt rise appeared at 650°C annealing. There are two causes by which the Ag/TiN/Si structure became degraded. One is agglomeration of the silver layer, and the other is oxidation and diffusion which are also associated problems during thermal annealing.
Fabrication and Photoelectrical Characteristics of Polymer-Organic-Blend Photodetectors
Authors: Qi Difei , Varahramyan Kody , Selmic Sandra
Published: April 2011

Polymer optoelectronics and microelectronics have been recognized as next generation technologies. One of the widely investigated materials for photodiode, LED and solar cell applications is the insoluble conjugated polymer poly(p-phenylene vinylene) or PPV. In this paper we present experimental results of a blended polymer-organic compound photodiode. This diode is based on a soluble derivative of PPV, poly(2-methoxy-5- (2,9-ethyl-hexyloxy)-1,4- phenylene vinylene) or MEH-PPV, and the organic material ethyl viologen dibromide or EVD. In making the photodiodes, solutions of MEH-PPV and EVD were spin-coated on indium tin oxide coated glass substrates. The thicknesses of these polymer-organic thin films were approximately 190 nm. An aluminum cathode was deposited by thermal evaporation. These devices were illuminated under monochromatic light in UV and visible range wavelengths. These thin polymer-organic blend photodiodes have shown an eight-fold increase in responsivity and quantum efficiency compared to pure MEH-PPV photodiode devices. The increase in photoconductivity of blended MEH-PPV:EVD photodiodes may be due to charge transfer by EVD dication. The results from this work clearly demonstrate the application of the reported approach for the realization of polymer photodiodes with increased photoconductivity characteristics.
A-Si Amoled Display Backplanes on Flexible Substrates
Authors: Nathan A. , Striakhilev D. , Servati P. , Sakariya K. , Sazonov A. , Alexander S. , Tao S. , Lee C.-H. , Kumar A. , Sambandan S. , Jafarabadiashtiani S. , Vygranenko Y. , Chan I.W.
Published: April 2011

In view of its maturity and low-cost, the amorphous silicon (a-Si) technology is an attractive candidate for active matrix organic light emitting diode (AMOLED) display backplanes on flexible substrates. However, the a-Si material comes with significant intrinsic shortcomings related to speed (mobility) and stability of operation, requiring novel threshold-voltage-shift (ΔVT) compensated thin-film transistor (TFT) pixel circuits and architectures to enable stable OLED operation. But given the dramatic progress in efficiency of OLED materials over recent years, the drive current requirement has been significantly lowered, thus relaxing the constraints on a-Si TFTs. For compatibility to plastic substrates, the a-Si TFT process temperature must be reduced from the conventional 300°C to ∼150°C or below, which tends to compromise the integrity of thin- film materials and device performance. Hence, optimizing the TFT process for high device performance with limited thermal budget is a necessary step towards flexible AMOLEDs with a-Si backplanes. This paper reviews the design and process challenges, and specifically examines the performance of TFTs and ΔVT-compensated integrated pixel driver circuits on plastic substrates with respect to current driving ability and long term stability. More importantly, lifetime tests of circuit degradation behaviour over extended time periods demonstrate highly stable drive currents and its ability to meet commercial standards.
Stability of Organic Thin Film Transistors
Authors: Han Jeong In , Kim Yong Hoon , Park Sung Kyu , Moon Dae Gyu , Kim Won Keun
Published: April 2011

The stability of organic thin film transistors (OTFTs) has become one of the most vital issues in this area of research. In this report, we investigated the stability of rubber stamp printed OTFTs. The electrical properties such as saturation field effect mobility, threshold voltage and on/off current ratio change significantly in ambient air condition. In order to analyze the degradation of the device, transistors were measured in vacuum, dry N2 and air environment as a function of time. In vacuum and dry N2 atmosphere, saturation field effect mobility and threshold voltage variations are relatively small compared to those measured in ambient condition.

To realize an air stable device, we applied a passivation layer which protects the device from oxygen or water molecules which is believed to be the source of the degradation. With the passivation layer, the threshold voltage shift was reduced suggesting that a proper passivation layer is a prerequisite in organic-based electronics.
Polycrystalline Germanium and Silicon-Germanium Alloys on Plastic for Realization of Thin-Film Transistors
Authors: Hekmatshoar B. , Shahrjerdi D. , Mohajerzadeh S. , Khakifirooz A. , Robertson M. , Asl E.
Published: April 2011

Device-quality polycrystalline Ge layers have been grown on flexible poly-ethylene terephthalate (PET) substrates by means of stress-assisted Cu-induced crystallization at temperatures as low as 130°C and employed for fabrication of depletion-mode poly-Ge thin-film transistors (TFTs). These TFTs show an ON/OFF ratio of 104and an effective hole mobility of 110 cm2/Vs. The stress-assisted crystallization technique has been extended to crystallize SiGe alloys at low temperatures for possible fabrication of poly-SiGe TFTs on plastic. As a result, poly-Ge seeded poly-crystalline SiGe layers with 40% Si content are grown at a low annealing temperature of 180°C in the presence of 0.05% equivalent compressive strain.
The Electronic Circuit Composition and Structure of String for a Novel Braid Electronics-Systems by Kumihimo Structure
Authors: Kuniyoshi Shigekazu , Tanaka Kuniaki
Published: April 2011

The new integrated circuit concept that forms electronic equipment by the textile structure using the flexible fiber that has equipped the field effect transistor, the light emitting diode, the wiring pattern, etc. was proposed [1,2]. In this report, the structure of the filamentous body as a basic structure of the kumihimo with various electronic functions was examined. There are many kinds of one in the kumihimo by the number and how to unite the plaited thread used. Although such a highly efficient kumihimo-structure electronic integrated circuit can be realized using kumihimo with much thread, it becomes that much complicated. In order to simplify an argument here, square-type kumihimo that uses eight plaited threads is employed, and a basic logical circuit composition and the element arrangement on plaited thread are examined. Eight plaited-threads are divided into two groups that have four threads respectively, and they exist in the plane that intersected perpendicularly mutually. However, kumihimo is a 1-dimensional system fundamentally, it can be extended in the length direction if necessary, and it is considered that a quite complicated function is also realizable for a circuit with few input and output. Here, plaited thread that belongs to one group for convenience will be called warp and the other group will be called woof. The circuit composition and a concrete structure of threads for kumihimo are discussed.
Excimer Laser Crystallization of Sputter Deposited a-Si Films on Flexible Substrates
Authors: Kim Yong Hoon , Park Sung Kyu , Moon Dae Gyu , Kim Won Keun , Han Jeong In
Published: April 2011

In this report, excimer laser annealed polycrystalline silicon (poly-Si) films on flexible polymer substrates are investigated. The amorphous silicon (a-Si) films were first deposited on polycarbonate (PC) and polyethersulfone (PES) substrates by radio-frequency (RF) magnetron sputter and sequentially annealed by XeCl excimer laser annealing system (λ = 308 nm). The argon concentration of a-Si films which was estimated by Rutherford Backscattering Spectrometry (RBS) was found to be dependent on the dynamic pressure during the deposition process and the sputtering gas. Typically, the argon concentration of a-Si film was 1 ∼ 2% when the film was deposited using argon gas at 6 mTorr. After the annealing process, the average grain size of the poly-Si film annealed with laser energy density of 289 mJ/cm2was 400 nm estimated from transmission electron microscope (TEM) investigations.
Failure Modes and Grain-Boundary Effects in Polycrystalline Materials
Authors: Zikry M. A. , Ashmawi W. M.
Published: April 2011

Dislocation-density based multiple-slip constitutive formulations and specialized computational schemes are introduced to account for large-strain ductile failure modes in polycrystalline aggregates. Furthermore, new kinematically based interfacial grain-boundary regions and formulations are introduced to account for dislocation-density transmission, absorption, and pile-ups that may occur due to grain-boundary misorientations and void interactions.
Oxygen-Induced Dynamic Embrittlement in Nickel-Base Superalloys
Authors: McMahon C. J. , Kane W. M.
Published: April 2011

The phenomenon of dynamic embrittlement involves the stress-induced diffusion of a surface- adsorbed embrittling element into grain boundaries, leading to time-dependent decohesion along these boundaries. Here, the state of our understanding of this generic type of brittle fracture is reviewed, with the focus on cracking of nickel-base superalloys caused by oxygen, including recent and new results on cracking in bicrystals, thermo-mechanical processing to reduce the susceptibility to dynamic embrittlement, and quench cracking.
Distribution of Grain Boundary Planes at Coincident Site Lattice Misorientations
Authors: Rohrer Gregory S. , El-Dasher Bassem S. , Miller Herbert M. , Rollett Anthony D. , Saylor David M.
Published: April 2011

The grain boundary plane distributions in MgO, SrTiO3, MgAl2O4, and Al are compared at lattice misorientations with a coincident site density of greater than or equal to 1/9. In most situations, the most frequently adopted grain boundary orientation is a habit plane of low index and low surface energy that depends on the particular material. Cases where the most common boundary orientation is a plane of high planar coincident site density instead of a characteristic habit plane are rare. In fact, in most cases, the distributions of grain boundary planes at misorientations with high lattice coincidence are not substantially different from the distributions at other, more general misorientations. The results indicate that a model for grain boundary energy and structure based on grain surface relationships is more appropriate than the widely accepted models based on lattice orientation relationships.
Thermal Stability of InGaAs Quantum Dots Under Large Temperature Transients
Authors: Rangarajan R. , Elarde V. C. , Coleman J. J.
Published: April 2011

We report here studies of the thermal stability of InGaAs quantum dots that have been subjected to various thermal treatments. Atomic force microscopy and photoluminescence spectroscopy are used to analyze the effects of the thermal treatments. In this paper we present data that demonstrates a remarkable improvement in the thermal stability of quantum dots that were rapidly cooled down to room temperature following the growth of a GaAs capping layer. The observed thermal behavior is attributed to metastable states formed during post growth thermal cycle.
Spectroscopic analysis of external stresses in semiconductor quantum-well materials
Authors: Tomm Jens W. , Biermann Mark L. , Passmore B. S. , Manasreh M. O. , Gerhardt A. , Tien Tran Q.
Published: April 2011

We present an approach for spectroscopic strain analysis in semiconductor quantum-well devices. This approach is applicable to all types of semiconductor materials, and to spectroscopic techniques which employ the electronic band-structure of the material, such as photoluminescence, photoreflection, photocurrent, and transmittance. The approach is based on two components, namely the theoretical calculation of the strain-sensitivity of the spectral positions of the relevant quantum-confined optical transitions within a particular quantum-well, and the spatially resolved measurement of a substantial part of the optical transition sequence within the quantum-well. The primary experimental technique applied in our approach is photocurrent spectroscopy. InAlGaAs/GaAlAs/GaAs, high-power lasers serve as the model species.
ZnO Spintronics and Nanowire Devices
Authors: Norton David P. , Heo Young-Woo , Tien L C , Ivill M P , Li Y , Kang B S , Ren Fan , Kelly J , Hebard A F , Pearton Stephen
Published: April 2011

ZnO is a very promising material for spintronics applications, with many groups reporting room temperature ferromagnetism in films doped with transition metals during growth or by ion implantation. In films doped with Mn during PLD, we find an inverse correlation between magnetization and electron density as controlled by Sn doping. The saturation magnetization and coercivity of the implanted single-phase films were both strong functions of the initial anneal temperature, suggesting that carrier concentration alone cannot account for the magnetic properties of ZnO:Mn and factors such as crystalline quality and residual defects play a role. Plausible mechanisms for the ferromagnetism include the bound magnetic polaron model or exchange is mediated by carriers in a spin-split impurity band derived from extended donor orbitals. We will also review progress in ZnO nanowires. The large surface area of nanorods makes them attractive for gas and chemical sensing, and the ability to control their nucleation sites makes them candidates for micro-lasers or memory arrays. Single ZnO nanowire depletion-mode metal-oxide semiconductor field effect transistors exhibit good saturation behavior, threshold voltage of ∼-3V and a maximum transconductance of 0.3 mS/mm. Under UV illumination, the drain-source current increased by approximately a factor of 5 and the maximum transconductance was ∼ 5 mS/mm. The channel mobility is estimated to be ∼3 cm2 /V.s, comparable to that for thin film ZnO enhancement mode MOSFETs and the on/off ratio was ∼25 in the dark and ∼125 under UV illumination. Pt Schottky diodes exhibit excellent ideality factors of 1.1 at 25 °C, very low reverse currents and a strong photoresponse, with only a minor component with long decay times thought to originate from surface states. In the temperature range from 25–150 °C, the resistivity of nanorods treated in H2 at 400 °C prior to measurement showed an activation energy of 0.089 eV and was insensitive to the ambient used. By contrast, the conductivity of nanorods not treated in H2 was sensitive to trace concentrations of gases in the measurement ambient even at room temperature, demonstrating their potential as gas sensors. We have also made sensitive pH sensors using single ZnO nanowires.
Electrical and Optical Properties of n-type and p-type ZnO
Authors: Look D. C. , Claflin B.
Published: April 2011

In recent years, ZnO has been proposed for new electronic and optoelectronic devices, such as transparent transistors and UV light-emitting diodes (LEDs). The LED application will require both n-type and p-type ZnO, but the latter is difficult to produce, and progress in this area will require a detailed knowledge of the various impurities and defects that affect the electrical and optical properties. The dominant donors in as-grown ZnO are usually thought to be interstitial H and substitutional AlZn, with activation energies of about 40 and 65 meV, respectively. However, interstitial Zn and its associated complexes may also contribute free electrons. The dominant acceptor, at least in vapor-phase-grown material, is the Zn vacancy; however, substitutional NO is also present, although sometimes passivated by H. To produce p-type ZnO, it is necessary to dope with acceptor-type impurities, and some success has been achieved with N, P, As, and Sb. However, only N has been proven to have simple substitutional character (NO), and more complicated acceptor structures, such as AsZn-2VZn, have been proposed for some of the other group V elements. Both homostructural and heterostructural UV LEDs have been fabricated, although not of high luminescent power so far. The main objective of this paper is to review the Hall-effect and photoluminescence results on n-type and p-type ZnO.
Growth and Crystal Structure of Alq3 Single Crystals. A new structure showing π–π and CH-π interactions.
Authors: Rashid Ali N. , Craig Donald C.
Published: April 2011

Tris-(8-hydroxyquinoline) aluminum III (Alq3) is a stable metal chelate that has received a great deal of attention over the past years due to its use in the fabrication of organic light emitting diodes (OLED).[1,2] Despite all the interest in this remarkable material very little information on its' solid-state properties and packing exists. Nearly all of the available information comes from studies that have been carried out on vacuum deposited thin films.[1]
Transport Properties of Polycrystalline SiGe Thin Films Grown on SiO2
Authors: Mitsui Minoru , Arimoto Keisuke , Yamanaka Junji , Nakagawa Kiyokazu , Sawano Kentarou , Shiraki Yasuhiro
Published: April 2011

Transport properties of polycrystalline Si1−xGex (x = 0, 30, 50 and 70) thin films on SiO2 were studied by Hall measurements and transport properties of the TFTs fabricated on the films were characterized. Si1−xGex films were p-type in spite of non-doping. Room temperature hole densities of Si1−xGex films increased from 5 × 1013 to 5 × 1016 cm−3 as Ge concentration increased from 30 % to 70 %. The acceptor levels in Si1−xGex were located at 0.43, 0.40 and 0.34 eV for x=0.3, 0.5 and 0.7 from valence band, respectively. The high leakage current of SiGe-TFTs was observed and drain current could not be turned off even when the high gate voltage was applied. The acceptor density increased with increasing annealing temperature from 700 °C to 800 °C. The leakage currents were independent of the annealing temperature and is thought to originate from Ge-related defects in grain boundaries.
Structural Defects related issues of GaN-based Laser Diodes
Authors: Tomiya Shigetaka , Takeya Motonobu , Goto Shu , Ikeda Masao
Published: April 2011

Structural defects affecting the lifetime of GaN-based laser diodes (LDs) on epitaxial lateral overgrown (ELO) GaN layers have been investigated. Almost all of the threading dislocations that appeared in the wing regions have edge character, whereas the dislocations at the coalescence boundaries have both edge character and mixed character. The origins of the threading dislocations in the wing regions are the lateral extension of dislocations from the seed regions that contingently bend upwards to the epi-surface. Thus, edge dislocations are most considerable threading dislocations in GaN-based LDs on ELO GaN layers, since the laser stripes are fabricated in the wing regions. In the degraded LDs, neither dislocation multiplication from the threading dislocations nor any structural changes of the threading dislocations were observed. This indicates that degradation is not caused by dislocation multiplication at the active layers, which is usually observed in LDs featuring zincblende-based structures. Although the threading dislocations in the LD stripes do not multiply during device operation, our degradation experiments revealed that the lifetime of the GaN-based LDs depends on the dislocation density. The degradation rate was almost proportional to the square root of the aging time. Our results indicate that degradation is governed by a diffusion process, and a detailed degradation mechanism is proposed.
A Nucleation Study of GaN Multifunctional Nanostructures
Authors: Shalini Gupta , Hun Kang , Martin Strassburg , Ali Asghar , Jayantha Senawiratne , Nikolaus Dietz , Ian T. Ferguson
Published: April 2011

This paper reports the Metal Organic Chemical Vapor Deposition (MOCVD) growth of GaN nanostructures. The use of MOCVD allows the direct integration of these nanostructures into pre-existing device technology. The formation of GaN nanostructures grown on AlN epitaxial layers were studied as a function of growth temperature, growth rate, V-III ratio and the amount of deposited material. A wide range of temperatures from 800 °C to 1100 °C and V-III ratios from 30 to 3500 were applied to determine the optimal growth conditions for nucleation studies in a modified production reactor. Small GaN nanostructures with lateral dimensions below 50 nm and low aspect ratios were obtained using relatively low temperatures of 815 °C and extreme metal-rich growth conditions. Island densities up to 1010cm−2were achieved using silane as an anti-surfactant to increase the available nucleation sites. Manganese has been incorporated into these nanostructures to enhance the multifunctional ferromagnetic properties of GaMnN.
GaN Quantum Dots Grown at High Temperatures by Molecular Beam Epitaxy
Authors: Xu Tao , Williams Adrian , Thomidis Christos , Moustakas Theodore D. , Zhou Lin , Smith David J.
Published: April 2011

In this paper we report the growth by MBE of GaN quantum dot superlattices (QDSLs) with AlN barriers on (0001) sapphire substrates at relatively high temperatures (770 °C) by the modified Stranski-Krastanov method. TEM studies indicate that the GaN QDs are truncated pyramids. We find that the height distribution of the dots depends strongly on the number of GaN monolayer coverage on the top of AlN. Specifically, we find that the height distribution consists of two Gaussian distributions (bimodal) for coverage of 3 and 4 MLs, and becomes single Gaussian distribution for 5 and 6 MLs of coverage. Furthermore, we find that the density of quantum dots increases with the degree of coverage and saturates at 2×1011 dots/cm2. The number of stacks in the superlattice structure was also found to lead to bimodal height distribution of the QDs. Ordering of the quantum dots was accomplished by thermal annealing of the sapphire substrates at 1400 °C prior to the growth of GaN QDs. The annealing process reveals the vicinal steps due to the miscut of the substrates and the GaN QDs were found to line up along those steps. Photoluminescence studies show a broad luminescence spectrum centered at 3 eV which is red shifted with respect to that of bulk GaN and is consistent with internal fields due to polarization (Quantum Confined Stark Effect). Furthermore, we find that the luminescence intensity increases with the number of stacks in the superlattice structure due to higher spatial density of QDs.
Fabrication and characterization of UV Schottky detectors by using a freestanding GaN substrate
Authors: Shibata Yasuhiro , Motogaito Atsushi , Miyake Hideto , Hiramatsu Kazumasa , Ohuchi Youichiro , Okagawa Hiroaki , Tadatomo Kazuyuki , Nomura Tatsuya , Hamamura Yutaka , Fukui Kazutoshi
Published: April 2011

GaN ultraviolet (UV) detectors were fabricated on a freestanding GaN substrate with low dislocation density. The resulting dark current density was below 1 nA/cm-2 at -8 V reverse bias, which was about 3 orders of magnitude lower than that of a similar detector made on a sapphire substrate. Moreover, the ideality factor was nearer to unity than the device on a sapphire substrate. In addition, by comparing the GaN-based device to a commonly used Si photodetector, we found that the GaN device had a lower signal-to-noise ratio and greater temperature stability. Therefore, we found a drastic reduction of dark current by using GaN freestanding substrates and so the GaN substrate produced a more effective detector than the sapphire substrate.
Structural properties of Eu doped GaN and its relation with luminescence properties
Authors: Bang Hyungjin , Maruyama Takahiro , Naritsuka Shigeya , Akimoto Katsuhiro
Published: April 2011

The Structural properties of Europium (Eu) doped GaN and its relation with optical properties were studied. Concentration quenching of the intensity of the Eu related luminescence observed when Eu concentration exceeds 3 at.%. In situ reflection high-energy electron diffraction (RHEED), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were carried out to study this luminescence quenching and it was discovered that there is close relationship between the luminescence intensity at 622 nm and structural properties. The cause of the concentration quenching is likely related to the polycrystalline growth as well as to the EuN formation.
MBE Growth and Characterization of Device-Quality Thick InN Epilayers; Comparison between N-polarity and In-polarity Growth Processes
Authors: Yoshikawa Akihiko , Ishitani Yoshihiro , Che Song-Bek , Xu Ke , Wang Xinqiang , Yoshitani Masayoshi , Terashima Wataru , Hashimoto Naoki
Published: April 2011

Epitaxy of InN films with N-polarity and In-polarity was investigated by RF-MBE with several in-situ monitoring/controlling systems. It was found that the epitaxy temperature for N-polarity growth could be as high as 600 °C and this was about 100 deg higher than that for In-polarity case. This temperature difference in two polarities drastically affected not only the growth behaviors but also the properties of InN epilayers, i.e. N-polarity growth was preferable in both view-points. The step-flow-like surface morphology was achieved for the InN films grown with N-polarity at 580 °C. The FWHMs of X-ray rocking curves for InN (002) and (102) of 5–8 μm-thick InN films grown in N-polarity were about 200–350 and 650–950 arcsec, respectively. The highest Hall mobility was above 2000 cm2/V·s with a background carrier concentration of 1–2×1018 cm−3 at room temperature. For both polarity films, N-rich condition was necessary for the stable InN growth to obtain 5–8 μm-thick InN films.
Effects of the Nitridation Process of (0001) Sapphire on Crystalline Quality of InN Grown by RF-MBE
Authors: Muto Daisuke , Yoneda Ryotaro , Naoi Hiroyuki , Kurouchi Masahito , Araki Tsutomu , Nanishi Yasushi
Published: April 2011

The effects of the nitridation process of (0001) sapphire on crystalline quality of InN were clearly demonstrated. The InN films were grown on NFM (nitrogen flux modulation) HT-InN or LT-InN buffer layers, which had been deposited on nitridated sapphire substrates. We found that low-temperature nitridation of sapphire is effective in improving the tilt distribution of InN films. Whereas the twist distribution remained narrow and almost constant, independent of nitridation conditions, when LT-InN buffer layers were used. The XRC-FWHM value of 54 arcsec for (0002) InN, the lowest reported to date, was achieved by using the LT-InN buffer layer and sapphire nitridation at 300°C for 3 hours.
Carbon-related Deep States in Compensated n-type and Semi-Insulating GaN:C and their Influence on Yellow Luminescence
Authors: Armstrong A. , Green D. , Arehart A. R. , Mishra U. K. , Speck J. S. , Ringel S. A.
Published: April 2011

The physical origin of the yellow luminescence in MBE-grown GaN co-doped with C and Si was investigated. Deep level optical spectroscopy (DLOS), deep level transient spectroscopy (DLTS), and photoluminescence (PL) were used to study the deep level spectrum as a function of C incorporation. In the absence of C co-doping, samples were n-type and demonstrated a weak yellow luminescence band, likely related to VGa. For increasing C co-doping, samples became semi-insulating concurrent with increased intensity of the yellow luminescence and the concentration of C-related deep acceptors. The DLOS results were used to develop a configuration-coordinate model for a C-related deep level with optical ionization energy of 3.0 eV and Franck-Condon shift of 0.4 eV that is consistent with the observed yellow luminescence and DLTS results. From these findings, a general model for independent mechanisms of the yellow luminescence related to VGa for n-type GaN and C for n-type and semi-insulating GaN:C:Si is discussed.
The Ga-Nitride/air Two-Dimensional Photonic Quasi-crystals Fabricated on GaN-based Light Emitters
Authors: Zhang Bei , Zhang ZhenSheng , Xu Jun , Wang Qi , Yang ZhiJian , Chen WeiHua , Hu XiaoDong , Qin ZhiXin , Zhang GuoYi , Yu DaPeng
Published: April 2011

The two-dimensional (2D) Ga-nitride/air photonic quasi-crystals (PQC) were successfully fabricated by the technique of focused Ga ion beam (FIB) milling on GaN based epitaxial wafers. The effects of the PQC on the current injected edge emitting GaN-based light emitters were investigated. The quasi-crystal structures studied in this work are based on square-triangular tiling with 8-fold or 12-fold symmetry. The air hole diameter in the different PQC patterns was varied from 95nm up to 1200nm, the filling factor of air hole was in the range of 10% to 50% and the depth of the hole was 90nm to 370nm, respectively. Among these, the nearest center-to-center distance of the holes and/or the lattice constant was reached to be 170nm. The photonic quasi-crystals on the GaN-based light emitters demonstrated a two to three factor of magnitude enhancement of surface extractive emission. The blocking of the propagation of planar-guided modes by the photonic quasi-crystals was observed. By comparison of symmetry effect among the triangular lattice PC and PQCs, it was found that the GaN-based photonic quasi-crystal (PQC) with 12-fold symmetry provided a much favorable enhancement of the extractive light emission over that of triangle lattice PC and 8-fold symmetric PQC as well.
Aquamarine Luminescence Band in Undoped GaN
Authors: Reshchikov M. A. , He L. , Molnar R. J. , Park S. S. , Lee K. Y. , Morkoç H.
Published: April 2011

We report a new defect-related photoluminescence (PL) band peaking at 2.56 eV at 15 K in undoped GaN layers grown by molecular beam epitaxy (MBE) on GaN templates. The maximum of the aquamarine luminescence (AL) band shifts to higher energies by about 100 meV with increasing temperature from 15 to 300 K. In spite of the fact that the shape and the peak position of the AL band are close to the characteristics of the green luminescence band in a freestanding GaN template, we were able to delineate these two bands for their markedly different behavior with temperature and excitation intensity. The origin of defect responsible for this PL band remains unknown.
Luminescence of Rare Earth Doped Si/Al/SiO2 Co-Sputtered Films
Authors: Rozo C. , Fonseca L. F. , Resto O. , Weisz S. Z.
Published: April 2011

Er3+, and Nd3+ doped Si/Al/SiO2 and thin films have been prepared by rf co-sputtering. Some of these films were annealed to 700°C. Erbium doped Si/Al/SiO2 films were prepared with two different sputtering configurations: one configuration with a large quantity of Al and a second configuration with a smaller quantity of Al. The configuration with large quantity of Al shows a diminished luminescence at 1.53 μm, but this emission is increased by substrate heating. The configuration with smaller quantity of Al shows emission at 1.525 μm similar in intensity to the Er-doped Si/SiO2. The spectral shape for the 4I13/2→4I15/2 emission is broader than for an analogous Er3+ doped Si/SiO2. The smaller quantity of Al configuration increases the solubility of Nd3+ (and luminescence for high Nd3+ concentration) in Si/SiO2 films and changes the spectral shape of the 4F3/2 emission with respect to the Nd3+ doped Si/SiO2 films.
Formation of Hydrogen-passivated Silicon Nanochains by Pulsed Laser Ablation without Thermal Annealing
Authors: Inada Mitsuru , Umezu Ikurou , Tanaka Shukichi , Mashiko Shinro , Sugimura Akira
Published: April 2011

Hydrogen-passivated silicon nanochains were synthesized by pulsed laser ablation of silicon target in hydrogen gas atmosphere at room temperature. When the hydrogen gas pressure was higher than 670Pa, nanochains, which have crystalline silicon core, were formed. Transmission electron microscopy showed the silicon nanochains consist of connections of silicon nanocrystals with mean diameter of 4.6 nm. It is of great interest that the silicon nanochain has crystalline structure without any intentional annealing process. Optical properties of the hydrogen-passivated silicon nanochains were presented.