bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient Photoconductivity of a-Si:H at Low Temperatures Induced by Bandgap Light
Authors: Heck S. , Stradins P. , Fritzsche H.
Published: April 2011

The rise and decay of the photoconductivity σp of intrinsic and strongly p-type hydrogenated amorphous silicon (a-Si:H) samples was studied as a function of photocarrier generation rate G between 4.2K and 300K. In intrinsic samples the temperature regime T<60K of energy-loss hopping is clearly distinguishable from T>80K where thermal re-excitation of photocarriers is possible. For the p-type sample the temperature dividing the two regimes is near 170K. In intrinsic samples the rise of σp is faster when residual photocarriers exist from previous light exposures than when the samples are in the electronic dark equilibrium. This indicates that geminate recombination decreases with increasing photocarrier concentration. In the p-type sample we observe an up to 20 percent overshoot in the rise of σp before σp settles down to its steady state value. This overshoot increases with G. We interpret the overshoot as an interplay of two recombination channels with different time scales.
Amorphous Silicon TFTS and Flat Panel Displays
Authors: Tsukada T.
Published: April 2011

The current status and next-generation technologies for liquid-crystal displays based on amorphous silicon TFTs are described. Panel size, resolution, design rule, and viewing angle are discussed from the standpoint of panel performance, productivity, and product application. The material properties for future TFT/LCDs are specified based on the discussions of design rule.
Modulated Hall-Effect Techniques for the Study of Transport Properties of Microcrystalline Silicon with Different Grain Sizes
Authors: Hapke P. , Backhausen U. , Carius R. , Finger F. , Ray S.
Published: April 2011

Highly doped μc-Si:H samples with a wide range of crystalline volume fractions and grain sizes have been investigated by Hall-effect experiments. We present an experimental set-up with a current modulation technique and a 6-pole contact geometry which allows the measurement of the Hall-effect on highly doped μc-Si:H down to 10K. The experimental results exhibit a clear correlation between the mobility μ and the grain size δ. Further, the results show that the transport in μc-Si:H can not be described by thermal emission over grain boundaries alone, additional transport paths, e.g. tunneling processes through the barriers have to be taken into account.
Measured and Simulated Temperature Dependence of A-Si:H Solar Cell Parameters
Authors: Stiebig H. , Eickhoff Th. , Zimmer J. , Beneking C. , Wagner H.
Published: April 2011

In contrast to the successful application of analytic equations to the current-voltage behaviour of crystalline silicon solar cells in the dark and under AM 1.5 illumination, the description of a-Si:H solar cells parameters requires device modelling concepts taking the full set of semiconductor equations into account. This in particular holds for the explanation of the temperature dependence (225-400K) of experimentally determined a-Si:H p-i-n solar cell parameters. Device modelling calculations show that the observed decrease of the short circuit current at AM 1.5 with lower T is much more effected by the additional charge trapped in the tail states and recharging of defect states than by the broadening of the gap. The induced electric field distortion blocks the extraction of photo generated holes. The open circuit voltage Voc increases with lower T which is caused by the same trapping effect.
Lead Sulphide Quantum-Sized Particles With Absorption Band Onset in the Near Infra Red
Authors: Bhat J.C. , Krishnakumar T. , Nayak R.R. , Salata O.V. , Hutchison J.L. , Dobson P.J.
Published: April 2011

Lead sulphide nanoparticles were prepared by colloidal techniques and subsequently deposited onto glass slides as uniform, dry films. In so doing, the effective bandgap of the semiconductor was increased from that of the bulk material by the quantum size effect. By varying the growth conditions, it was possible to change the mean particle size from 3nm to 7nm. This size variation was accompanied by (i) a variation in the absorption band onset of the material from 0.7μm to 1.3μm and (ii) a change in its colour from red to greyish-brown. No excitonic features were observed. TEM showed that the shape of the particles, as well as their size, was dependent on the growth conditions. Cubic and rod-like particles were grown in aqueous solution. Spherical particles preferable for optoelectronic devices were grown in methanolic/aqueous and aqueous solutions. However, these spherical particles were not as reproducible as the cubic ones.
Strain Effects on Optical Gain Properties of GaN/AlGaN Quantum Well Lasers
Authors: Suzuki M. , Uenoyama T.
Published: April 2011

Subband structures and optical gains of the strained wurtzite GaN/AlGaN quantum well lasers are theoretically investigated on the basis of k.p theory. First-principles calculations are used for deriving the unknown physical parameters, such as deformation potentials. Neither compressive nor tensile biaxial strains are so effective on the reduction of the threshold carrier density. It is also found that the uniaxial strain in the c-plane is one of the preferable approaches for the efficient improvement of the laser performance.
Comparison of N- And P-Type Ingaas/Inp Quantum Well Infrared Photodetectors
Authors: Sengupta D.K. , Malin J.I. , Jackson S.L. , Fang W. , Wu W. , Kuo H.C. , Rowe C. , Chuang S.L. , Hsieh K.C. , Tucker J.R. , Lyding J. W. , Feng M. , Stillman G.E. , Liu H.C.
Published: April 2011

Over an order of magnitude reduction in dark current was observed for gas-source molecular beam epitaxially (GSMBE) grown, lattice-matched n- and p-type InGaAs/InP quantum-well infrared photodetectors (QWIPs). Peak spectral response at 8.93 and 4.55 μm for n- and p-type QWIPs, respectively, open the possibility of dual-band monolithic integration under identical GSMBE growth conditions.
Ecr Etching of GaP, GaAs, InP, and InGaAs in Cl2/Ar, Cl2/N2, BCl3/Ar, and BCl3/N2
Authors: Shul R. J. , Baca A. G. , Rieger D. J. , Hou H. , Pearton S. J. , Ren F.
Published: April 2011

Electron cyclotron resonance (ECR) etching of GaP, GaAs, InP, and InGaAs are reported as a function of percent chlorine-containing gas for Cl2/Ar, Cl2/N2, BCl3/Ar, and BCl3/N2 plasma chemistries. GaAs and GaP etch rates were faster than InP and InGaAs, independent of plasma chemistry due to the low volatility of the InClx, etch products. GaAs and GaP etch rates increased as %Cl2 was increased for Cl2/Ar and Cl2/N2 plasmas. The GaAs and GaP etch rates were much slower in BCl3-based plasmas due to lower concentrations of reactive Cl, however enhanced etch rates were observed in BCl3/N2 at 75% BCl3. Smooth etched surfaces were obtained over a wide range of plasma chemistries.
Oxygen-Related Defects in High Purity Movpe Aigaas
Authors: Ryan J.M. , Kuech T.F. , Bray K.L.
Published: April 2011

The near-infrared photoluminescence of high purity, nominally undoped MOVPE AlGaAs was investigated as a function of growth temperature, aluminum content and hydrostatic pressure. Two PL bands, observed at ˜1.1 eV and ˜0.8 eV independent of aluminum content, were attributed to oxygen-related defects based on the correlation of emission intensity and oxygen concentration. Hydrostatic pressure experiments, along with the measurement temperature dependence, suggest that the ˜0.8 eV band is due to emission from an oxygen-related mid-gap level to a shallow acceptor or the valence band, depending on temperature. A tentative defect model based on the off-center OA, defect in bulk GaAs and variations in the number of nearest neighbor aluminum atoms is proposed to explain the two PL bands and the dependence of their relative intensity on aluminum content.
Growth and Characterization of GaAs Epitaxial Layers by MOCVD
Authors: Hudait Mantu Kumar , Modak Prasanta , Krupanidhi S.B.
Published: April 2011

technique, on both semi-insulating and semi-conducting CraAs substrates with (100) orientation, offset by 2° towards (110) direction. Systematic variation of As/Ga was performed to gain an understanding of growth process, type of formation and other related physical properties. The films were characterized by using the variety of techniques, such as SEM, EDAX, HRTEM, XRD, and PL. Optical and electrical properties of undoped CyaAs epilayers are presented with reference to the growth conditions and AsH3/TMGa ratio. Photoluminescence measurements of GaAs epilayers were recorded at 4.2K and shows the emission of free exciton and confirmed their high purity. The dominant residual impurities in GaAs are presented by using PL. Finally, electrochemical depth profiling exhibited almost homogeneous background carrier distribution and excellent abruptness between the thin GaAs epilayer and substrate.
Atomic Force Microscope Chemically Induced Direct Processing
Authors: Shimbo B. N. , Komarov S. , Vartanian B. J. , Okada Y. , Harris J. S.
Published: April 2011

Interest in room-temperature operable quantum effect devices has created a need for simple and inexpensive nanofabrication techniques. By applying a bias to a conductive AFM tip, we have succeeded in fabricating narrow (˜30 nm) oxide lines on a variety of metal and III-V semiconductor substrates. The effects of different drawing parameters such as tip bias, translation speed, ambient atmosphere, and substrate doping on line quality were explored.
Analysis of Radiative Recombination and Optical Gain in Gallium Nitride-Based Heterostructures
Authors: Eliseev Petr G. , Smagley Vladimir A. , Osiński Marek
Published: April 2011

Threshold current density in GaN-based UV double-heterostructure lasers is predicted in the range of 2- 4 kA/cm2 using theoretical calculation of optimized heterostructure for various types of devices. Freecarrier (FC) and Coulomb-enhancement (CE) models are compared. Results are given for different combinations of effective masses. The minimum threshold current is not strongly influenced by the choice of effective masses. The FC model predicts lower than CE threshold in edge-emitting lasers, whereas the CE model predicts lower than EC threshold in thin VCSEL devices.
Selective Oxidation of Buried Aigaas for Fabrication of Vertical-Cavity Lasers
Authors: Choquette Kent D. , Geib K. M. , Chui H. C. , Hou H. Q. , Hull Robert
Published: April 2011

We discuss the selective conversion of buried layers of AlGaAs to a stable oxide and the implementation of this oxide into high performance vertical-cavity surface emitting lasers (VCSELs). The rate of lateral oxidation is shown to be linear with an Arrhenius temperature dependence. The measured activation energies vary with Al composition, providing a high degree of oxidation selectivity between AIGaAs alloys. Thus buried oxide layers can be selectively fabricated within the VCSEL through small compositional variations in the AlGaAs layers. The oxidation of AlGaAs alloys, as opposed to AlAs, is found to provide robust processing of reliable lasers. The insulating and low refractive index oxide provides enhanced electrical and optical confinement for ultralow threshold currents in oxide-apertured VCSELs.
Rutherford Backscattering and Photoluminescence Studies of Erbium Implanted GaAs
Authors: Daly S. E. , Henry M. O. , Alves E. , Soares J. C. , Gwilliam R. , Sealy B. J. , Freitag K , Vianden R. , Stievenard D.
Published: April 2011

The results of parallel RBS and photoluminescence studies of erbium implanted GaAs are presented. Low dose implantations do not produce any significant PL signals, and the dose must be in the range le14 to le15 /cm2 in order that Er related emission dominates in the PL spectrum. A comprehensive analysis of the effects of coimplantation with oxygen on the Er luminescence is reported and the data are compared to those of GaAs:Er and AIGaAs:Er samples grown by MBE. The evidence indicates that, at high doses, ErAs precipitates are formed unless oxygen is co-implanted, and that the Er atoms which produce the luminescence occupy substitutional Ga sites.
The Possible Mechanism of Excitation of the f - f Emission from Er-O Clusters in Silicon
Authors: Masterov V. F. , Gerchikov L. G.
Published: April 2011

The Er2O3 quantum dot (cluster) with dimensions about 1.2nm in silicon is discussed as the possible source of the Er related emission in Si:Er,O, excited by photogenerated carriers or in a light-emitting diodes (LED) at forward bias. This quantum dot is represented as a spherical quantum well 0.9eV in depth. The electron level with energy about 0.15eV below the bottom of the silicon conduction band plays role of an electron trap. The trapped electron interacts with a hole in valence band of silicon forming “indirect” exciton bonded to quantum well. The energy is transferred to f - shell of erbium by the Auger electron - hole recombination.
Photo- and Electroluminescence Study of Excitation Mechanism of Er Luminescence in a-Si:ff(Er)
Authors: Yassievich I. N. , Gusev O. B. , Bresler M. S. , Fuhs W. , Kuznetsov A. N. , Masterov V. F. , Terukov E. I. , Zakharchenya B. P.
Published: April 2011

Photo- and electroluminescence were studied in erbium-doped amorphous hydrogenated silicon films. A mechanism of excitation of erbium ions by defect-related Auger process is proposed which permits to explain consistently the whole set of our experimental results.
Increased Refractive Indices in Rare Earth Doped InP and In0.53 Ga0.47 as Thin Films
Authors: Stadler B. J. H. , Lorenzo J. P.
Published: April 2011

Rare earth (Gd, Eu, Er) doped InGaAs and InP layers were grown by liquid phase epitaxy (LPE). The refractive index of these layers was observed to increase with the addition of the rare earth ions. The observed increase could not be explained by changes in host composition as typically calculated from changes in lattice parameter. In fact, the refractive index was seen to increase (∼0.25) by an order of magnitude more than would be expected by the change in the lattice parameter (∼0.02). The increased refractive indices of InP layers due to Er-doping enabled waveguiding. These findings suggest that optically active waveguide devices can be fabricated from semiconducting hosts by simple rare earth doping.
Optical Centers Related to Laser-Doped Erbium in Silicon
Authors: Nakashima K. , Eryu O. , Iioka O. , Minami H , Watanabe M.
Published: April 2011

Excimer laser irradiation has been applied to dope erbium ions in silicon. Er-doping is realized with both processes of the Er-diffusion in the melted region and the subsequent solid solidification. Er atoms at the maximum concentration of 1021 cm3 are doped in the region of 150 nm thickness without significant defect formation and amorphization. Stable Er-optical centers, emitting well known series of luminescence lines near 1.54 jim, are formed after short term heat treatments at a relatively low temperature. Optical centers are distributed in proportional to the total Er concentration in the doped region. Oxygen atoms are found to play critical roles for stabilizing Er-optical centers and for rearranging the surroundings of Er ions. Modified bonding states of O and Er other than those in SiO2 or Er2O3 are formed in the Er doped region during both doping and annealing processes.
Silicon Carbide Cvd Approaches Industrial Needs
Authors: Rupp R. , Lanig P. , Völkl J. , Stephani D.
Published: April 2011

In this paper an overview is given on the current state of epitaxial growth of SiC with special regard to our work at SIEMENS CRD. Problems concerning impurity incorporation and ways to achieve background doping levels as low as 1014 cm−3 are discussed as well as the influence of high speed wafer rotation on the gas flow in our reactor and related effects on uniformity in thickness and doping. Precise control of the C/Si ratio in the gas phase, which is easily achieved in the described reactor, and the use of reduced pressure lead to a good control of dopant incorporation over more than 3 orders of magnitude while maintaining smooth surface morphology even at growth rates higher than 5 μm/h. Doping variations <±8 % across 30 mm wafers can routinely be obtained. The quality of the egilayers is proven by electrical breakdown fields as high as 2*106 V/cm at NA−ND=5* 10−15 cm−and an electron mobility greater than 700 cm2 /Vs at 300 K (4H-SiC).

Finally it is demonstrated that the gas composition at the end of the epitaxial growth process is an important step in order to get oxygen resistant surface properties for subsequent device processing.
The Impact of Pregrowth Conditions and Substrate Polytype on SiC Epitaxial Layer Morphology
Authors: Burk A. A. , Rowland L. B. , Augustine G. , Hobgood H. M. , Hopkins R. H.
Published: April 2011

4H and 6H-SiC epitaxial layers exhibit characteristic morphological defects caused by process and substrate interferences with the a-axis directed step-flow growth. 4H-SiC is shown to typically exhibit worse morphology than 6H-SiC for a given off-axis orientation. SiC epitaxial layer defects are significantly reduced by the optimization of growth conditions and substrate surface preparation. The remaining highly variable defects are shown to emanate from the substrate surface with densities of ≥1000 cm−2
Seeding With a Diamond Suspension for Growth of Smooth Polycrystalline Diamond Surfaces
Authors: Omer I. St. , Stacy T. , Charlson E. M. , Charlson E. J.
Published: April 2011

A number of techniques have been used to smooth polycrystalline diamond films. Recent work in substrate seeding with nanocrystalline diamond powder, alone or in a carrier fluid, has shown that diamond seeding improves nucleation density and reduces diamond surface roughness. In this work, silicon substrates were seeded using a commercially available waterbased 0.1 micrometer diamond polishing suspension. Growth was achieved using conventional hot-filament chemical vapor deposition (HFCVD). Films were characterized using optical microscopy, scanning electron microscopy (SEM), x-ray diffraction (XRD), and surface profilometry. The resulting diamond films exhibited well-faceted crystals, small grain size and minimal surface roughness. Additionally, the silicon substrate was chemically etched in order to permit examination of the backside of the diamond film. Results show that the diamond surface at the silicon-diamond interface is ultra-smooth. Comparison of the backside of these surfaces with those prepared using conventional diamond grit abrasion indicates that a significant improvement in surface quality is achieved using this diamond seeding technique.
SiC Semiconductor Applications - An Air Force Perspective
Authors: Rea L. S.
Published: April 2011

The Department of Defense (DoD) is investing in the development of Silicon Carbide (SiC) for a wide range of applications. Over the past year, SiC technology has demonstrated excellent device performance results for power devices, high temperature electronic devices and microwave devices. The materials growth and processing technology for SiC is now at a level of sufficient maturity to support substantial device development efforts. While there is still considerable materials and device research required for SiC to achieve it's full potential, the fundamental technology has been proven for several critical applications. A perspective on some Air Force device performance requirements will be presented. The status of SiC materials development, material limits to advances in device performance and issues relating to supporting technology will also be discussed.
X-Ray Diffraction Analysis Of Strain And Mosaic Structure In (001) Oriented Homoepitaxial Diamond Films
Authors: Alexander W. Brock , Pehrsson Pehr E. , Black David , Butler James E.
Published: April 2011

Homoepitaxial diamond films were grown on (001) oriented high pressure, high temperature type lb diamond by microwave plasma-assisted chemical vapor deposition to thicknesses of 27–48 μm. Substrates were polished off-axis 5.5° ±0.5° in the [100] direction prior to film deposition. Some of the diamond films developed tensile stress sufficiently large to result in cracking on { 111 } cleavage planes, while other films exhibited compressive stress. The strain and mosaic structure were measured with seven crystal x-ray diffraction. This characterization tool allowed the separation of misorientation effects from those of lattice parameter variation. Films exhibited smaller (˜88 ppm) and larger (˜27 ppm) perpendicular lattice parameters relative to the HPHT substrates. A cross-sectional approach for probing strain in diamond films with micro-Raman analysis was used to show stress distributions (˜100–300 MPa) through the thickness of the film.
Investigation of an NEA Diamond Vacuum Microtriode Array
Authors: Hatfield C. W. , Bilbro G. L. , Morris A. S. , Baumann P. K. , Ward B. L. , Nemanich R. J.
Published: April 2011

The properties and characteristics of vacuum microtriodes based on NEA diamond surfaces were modelled. Specifically, an NEA diamond vacuum microtriode array was investigated using electrical measurements, electron optics software, and microwave circuit simulation. Data for emission current versus applied voltage for various anode-to-cathode distances for diamond NEA surfaces was analyzed and various parameters were extracted. Electron optics software was used to determine Fowler-Nordheim and space-charge-limited DC I-V characteristics for each microtriode. Microwave circuit simulation was done to determine the behavior of arrays of these vacuum microtriodes in an RF amplifier circuit.
Growth and Characterization of AlGaN/GaN Heterostructures with Multiple Quantum Wells by PAMBE
Authors: Shim K. H. , Myoung J. M. , Gluschenkov O. V. , Kim C. , Kim K. , Yoo M. C. , Kim S. , Turnbull D. A. , Bishop S. G.
Published: April 2011

AlGaN/GaN heterostructures with multiple quantum wells were grown by plasmaassisted molecular beam epitaxy (PAMBE). Structural and optical properties of the heterostructures were analyzed using x-ray diffraction, cathodoldminescence, and photoluminescence. Interband transitions were clearly observed in the GaN quantum wells at both room- and liquid-helium temperatures. The efficiency of the interband recombination due to the confinement effect was greatly enhanced in the thinner quantum wells. The functional dependence of the interband peaks on the well thickness is shown to be in good agreement with the calculated positions of the quantized levels in the wells.
Deposition Of Adherent Diamond Films On Sapphire Substrates
Authors: Gilbert Donald R. , Singh Rajiv K.
Published: April 2011

Sapphire is an important material for infrared-transmission applications and SOI device structures. The use of diamond as a protective coating for sapphire is a desirable, yet elusive process. The primary obstacle to the successful deposition of diamond on sapphire is the large mismatch in thermal expansion characteristics between the two materials. To overcome this problem, we have used a low temperature deposition process involving an electron cyclotron resonance (ECR) assisted plasma CVD system. Continuous, adherent diamond films have been deposited over 1 to 2 cm2 areas. These films have been characterized for structural quality using Raman spectroscopy and x-ray diffraction.
ESR and LESR Studies in CVD Diamond
Authors: Graeff C. F. O. , Rohrer E. , Nebel C. E. , Stutzmann M. , GUttler H. , Zachai R.
Published: April 2011

CVD diamond films with nitrogen content varying from 10 ppm to 132 ppm have been studied by electron spin resonance (ESR), light-induced ESR (LESR) as well as spin-dependent conductivity (SDC). Two characteristic signals have been observed. A carbon-related defect line with g = 2.0029 ± 0.0002 and width 4 ± 1 G, is observed in ESR, LESR and SDC. The intensity of this line measured by ESR increases linearly with nitrogen content. For low-defect-density samples, or after illuminating the high-defect-density samples with UV light, a second signal is observed both in ESR and LESR, but not in SDC, with a central line at g = 2.0024 ± 0.001 and width 0.2 ± 0.1 G and related hyperfine satellites ≈30 G away from the central line. This line is assigned to isolated substitutional nitrogen, the so-called P1 center. The density of N-related paramagnetic states is strongly affected by illumination and heat treatments. Spin-dependent conductivity measurements show that the dark conductivity at room temperature in CVD-diamond is dominated by hopping at the g = 2.0029 defects.
Characterization of Deep Level Defects in 4h and 6H SIC Via DLTS, SIMS And MEV E-Beam Irradiation
Authors: Doyle J. P. , Aboelfotoh M. O. , Linnarsson M. K. , Svensson B. G. , Schöner A. , Nordell N. , Harris C. , Lindström J. L. , Janzén E. , Hemrnmingsson C.
Published: April 2011

Electrically active defects in both 4H and 6H polytypes of SiC have been observed through the use of deep level transient spectroscopy (DLTS). Schottky contacts were grown by vapor phase epitaxy (VPE) with doping concentrations, the epitaxial layer having a doping concentration in the range of 1014 cm−3 to 1017cm−3. Numerous levels have been found in the as-grown n-type 6H-SiC samples and secondary ion mass spectrometry (SIMS) and MeV electron irradiation have been employed to corrrelate the defect levels to impurities or structural defects. In contrast, only a single level is observed in the as-grown 4H-SiC samples.
Morphology of Optically Transparent Cubic Silicon Carbide Prepared by Chemical Vapor Deposition
Authors: Russell Michael W. , Freitas Jaime A. , Butler James E.
Published: April 2011

Crystals of cubic silicon carbide (3C-SiC) were grown in an RF-induction furnace on graphite substrates by atmospheric pressure chemical vapor deposition (APCVD) from a single precursor, methyltrichlorosilane (MTS) in hydrogen. The deposits were characterized by micro-Raman spectroscopy, x-ray diffraction, and atomic force and scanning electron microscopies. Above ˜1600°C preferential 〈110〉 growth directions were identified for the majority of the crystals. At intermediate deposition temperatures (1600–1700°C) the dominant morphology consisted of yellow prismatic crystals heavily twinned along {111 }and {111} At substrate temperatures exceeding ˜1750°C hexagonally-shaped {1111} oriented 3C-SiC platelets were formed with alternating {001 }/{ 101} edges. The dependence of nucleation density, film morphology and film orientation on deposition conditions will be discussed with emphasis on the growth of high quality single crystals of 3C-SiC.
Dopant incorporation efficiencies of SiC crystals grown on {1100}-face
Authors: Sugiyama Naohiro , Okamoto Atsuto , Tani Toshihiko , Kamiya Nobuo
Published: April 2011

The dopant incorporation efficiencies of SiC bulk single crystals were investigated by the measurement of optical absorption coefficients and chemical analysis by Glow Discharge Mass Spectroscopy. The SiC crystals were grown on the seed with the {1100} face by a sublimation method. The grown ingot consisted of approximately three parts, which were the regions grown with the {1100} face (I), the {110n} face (II) and the {110n} face (III) as a growing front. The nitrogen concentrations in these parts were in the order of II>I>III. The wafers exhibited the color distributions in the c-plane due to the difference of the growing facet. The nitrogen incorporation efficiencies were discussed in terms of atomic structure on the surface. The aluminum concentration in the crystal grown on a {1100}-faced seed was in the medium between those in crystals grown on Si-face and C-face. On the other hand, the boron concentration was similar to that of Si-face grown crystal, and higher than that of C-face grown crystal.
Activation of Acceptors in Mg-Doped, p-Type GaN
Authors: Götz W. , Johnson N. M. , Walker J. , Bour D. P.
Published: April 2011

The activation of acceptors was investigated for Mg-doped, heteroepitaxial layers of GaN grown by metalorganic chemical vapor deposition. After growth the samples were exposed to isochronal rapid thermal anneals in the temperature range from 500°C to 775°C. The samples were studied by variable temperature Hall effect measurements and photoluminescence (PL) spectroscopy in the as-grown condition and after each temperature step. The thermal treatment leads to the formation of acceptors which are characterized by an activation energy for ionization in the range between 165 meV and 182 meV. These acceptors are attributed to Mg atoms substituting for Ga in the GaN lattice. The experimental results for the acceptor activation are consistent with the dissociation of electrically inactive acceptor-hydrogen complexes. The reversibility of this process is investigated by the exposure of the activated, p-type GaN samples to atomic hydrogen in a remote-plasma hydrogenation system at 600°C and reactivating at 850°C.
Role Of Hydrogen And Hydrogen Complexes In Doping Of Gan
Authors: Neugebauer Jörg , Van de wallei Chris G.
Published: April 2011

We have calculated electronic structure, energetics and migration for hydrogen and hydrogen complexes in GaN employing state-of-the-art first-principles calculations. Using these results in combination with previous detailed investigations about native defects we have calculated the concentration of hydrogen and dopants for different growth conditions. Our results reveal a fundamental difference in the behavior of hydrogen in p-type and n-type material. In particular, we explain why hydrogen has little effect on donor impurities and why H concentrations are low in n-type GaN. We discuss why hydrogen is beneficial for acceptor incorporation in GaN, and identify the limitations of this process.
Electronic Structure of Beryllium, Magnesium and Silicon Impurity in Cubic Gallium Nitride
Authors: Gubanov V. A. , Pentaleri E. , Fong C. Y. , Klein B. M.
Published: April 2011

Beryllium (Be), magnesium (Mg) and silicon (Si) impurities in zinc-blende galliumnitride (c-GaN) are investigated by the tight binding-linear combination muffin-tin orbitals (TBLMTO) method using a 64-atom supercell. Be and Mg impurities at a Ga site, respectively induce partially empty acceptor-like bands at the valence band edge, which result in p-type conductivity of doped c-GaN. Si impurity in the Ga sublattice creates a partially occupied impurity subband overlapping with the conduction band edge and is responsible for the measured n-type conductivity. The impurity levels of a Si at a N site are located deep in the gap and do not influence much the conductivity of c-GaN. The shell-projected, total and partial densities of states and the charge density maps are used to elucidate the energy and spatial localizations of the impurity states
Formation and High Frequency CV-Measurements of Aluminum / Aluminum Nitride / 6H Silicon Carbide Structures
Authors: Zetterling C. -M. , Wongchotigul K. , Spencer M. G. , Harris C. I. , Wong S. S. , Östling M.
Published: April 2011

Undoped single crystalline aluminum nitride films were grown by metal organic chemical vapor deposition (MOCVD) at 1200 °C. The precursors used were trimethylaluminium (TMA) and ammonia (NH3) in a hydrogen carrier flow, at a pressure of 10 Torr. Silicon carbide substrates of the 4H or the 6H polytype with an epilayer on the silicon face, were used to grow the 200 nm thick A1N films. Aluminum was evaporated and subsequently patterned to form MIS capacitors for high frequency (400 kHz) capacitance voltage measurements at room temperature. It was possible to measure the structure and characterize accumulation, depletion and deep depletion. However, it was not possible to invert the low doped SiC epilayer at room temperature. From an independent optical thickness measurement the relative dielectric constant of aluminum nitride was calculated to be 8.4. The films were stressed up to 50 Volts (2.5 MV/cm) without breakdown or excessive leakage currents. These results indicate the possibility to replace silicon dioxide with aluminum nitride in SiC field effect transistors.
Radiative Recombination Rates in GaN, InN, AlN and their Solid Solutions
Authors: Dmitriev A. V. , Oruzheinikov A. L.
Published: April 2011

The radiative recombination rates have been calculated for the first time in the wide band gap wurtzite semiconductors GaN, InN and AIN and their solid solutions GaxAl1−xN and InxAl1−xN on the base of existing data on the energy band structure and optical absorption in these materials. We calculated the interband matrix elements for the direct optical transitions between the conductivity band and the valence one using the experimental photon energy dependence of the absorption coefficient near the band edge. In our calculations we assumed that the material parameters of the solid solutions (the interband matrix element, carrier effective masses and so on) could be obtained by a linear interpolation between their values in the alloy components. The temperature dependence of the energy gap was taken in the form proposed by Varshni. The calculations of the radiative recombination rates were performed in the wide range of temperature and alloy compositions.
High-Temperature Switching Characteristics of 6H-SiC Thyristor
Authors: Xie K. , Flemish J. R. , Burke T. , Buchwald W. R. , Zhao J. H.
Published: April 2011

A 280 V 6H-SiC thyristor has been fabricated and characterized. The switching characteristics of the SiC thyristor were investigated over a temperature range from 23 °C to 400 °C, with a switched current density of 4900 A/cm2 being observed under pulse bias condition. The thyristor has shown a dV/dt of 400 V/ms. Both the turn-on time and turn-off time increase significantly at 400 °C. The thyristor forward breakover voltage decreases by only 5% when the operating temperature is increased from 23 °C to 400 °C.
Low Temperature Polysilicon Materials and Devices
Authors: Pribat D. , Legagneux P. , Plais F. , Reita C. , Petinot F. , Huet O.
Published: April 2011

In this paper, we essentially discuss the material aspects of low temperature (≤ 600 °C) polysilicon technologies. Emphasis is put on the properties of polysilicon films, depending on the way they are obtained. Solid phase crystallisation as well as pulsed laser crystallisation processes are presented in some detail, together with thin film transistor characteristics. Although not yet stabilised and despite uniformity and reproducibility problems, laser crystallisation will probably end up being the technology of choice for the manufacture of large area electronics products, because it allows the fabrication of devices exhibiting superior properties, with a reduced thermal budget.
Surface Roughness of Silicon-Nitride Gate Insulators Deposited in a 40-MHZ Glow Discharge
Authors: Meiling H. , Grotenhuis E. Ten , Weg W. F. van der , Hautala J. J. , Westendorp J. F. M.
Published: April 2011

The surface morphology of 40-MHz PECVD SiNx films is investigated. We report on the correlation between the deposition conditions, bulk properties, and surface roughness of these TFT insulators. The roughness is measured with atomic-force microscopy, AFM. A link will be presented between the AFM properties and the effects of hydrogen dilution during deposition: gas composition and rf-power-density (P) dependences will be discussed. An increase of the surface roughness to 3.7 nm is observed upon H2 dilution and P increase, ascribed to enhanced ion bombardment of the surface during growth.
A New Electrically Reversible Depassivation/Passivation Mechanism in Polycrystalline Silicon
Authors: Suntharalingam Vyshnavi , Fonash Stephen J.
Published: April 2011

An electrically reversible depassivation/passivation phenomenon, recently found for hydrogen passivated polysilicon [1] is further explored in this report. This reversible effect is seen in both ECR and RE hydrogen passivated n-channel thin film transistors (TFTs) but is not seen in the corresponding hydrogen passivated pchannel TFrs, nor is it seen in either n- or p-channel TETs before hydrogenation. This phenomenon has been observed when room temperature bias stressing TFTs fabricated on solid phase or laser crystallized polysilicon films on quartz substrates [1]. A model involving hydrogen release or capture at defects, positively charged hydrogen motion in device electric fields, and subsequent hydrogen capture at other defects has been proposed. This phenomenon has significant implications for polycrystalline silicon TFT’ design and operation. By extension, it also offers significant insight into the stability problems of hydrogenated amorphous silicon.
Atomic-Ratio effect of transition layer for linear mobility in poly-Si TFTs
Authors: Jung M. Y. , Jung Y. H. , Bae S. S. , Seo S. M. , Moon D. G. , Lee G. H. , Soh H. S.
Published: April 2011

Poly-Si TFTs with high field effect mobility are fabricated by using PECVD SiO2layer deposited with a new method: two-step (graded) oxide deposition. To adjust stoichiometry of the poly-Si/oxide interface and the bulk oxide layer, the double layer oxide films were deposited. The oxide films near the interface were deposited with high N2O/SiH4gas ratio to obtain the stoichiometric layer for good matching between poly-Si and SiO2. The remaining bulk oxide films were deposited with low N2O/SiH4gas ratio. The composition of the bulk oxide film was measured by using ESCA and the interface layer was analized with ESR. The poly-Si TFT with the double layer gate oxide resulted to the better performance than conventional TFT wth single layer gate oxde.
Effect of annealing ambient on performance and reliability of low pressure chemical vapor deposited oxides for thin film transistors
Authors: Bhat N. , Wang A. , Saraswat K. C.
Published: April 2011

The performance and reliability of low pressure chemical vapor deposited (LPCVD) oxides subjected to oxidizing, inert and nitriding annealing ambients is characterized both at low temperature (600°C) and high temperature (950°C). The oxidizing ambient results in worse initial interface state density and charge to break down. We attribute this to the interfacial stress developed during the oxidation, due to the volume mismatch between Si and SiO2. The C-V measurements on poly-Si substrate capacitors and the charge pumping measurements on poly-Si thin film transistors (TFTs) indicate lower trap density for inert and nitriding ambients. The TFTs with inert anneal exhibit lower bias temperature instability compared to oxidizing ambient.
Development Of Organic Photoresist For Color Filter Black Matrix
Authors: Kim C. W. , Rho S. G. , Jung D. K. , Jeong E. J. , Kim S. Y. , Yang H. G.
Published: April 2011

Normal CrOx/Cr type color filter black matrix requires multi-layer sputtering and photo/etch processes which cause several problems such as particles generation, high production cost, and environmental issues. Various kinds of materials are being reviewed to substitute the existing Cr base materials. Especially carbon based organic type and pigment type photo-sensitive materials are actively under development. Our researches are focused on the characterization of material properties, color filter manufacturing techniques which are optimized for liquid crystal process, and the display quality of newly developed materials. Carbon based organic photoresist has excellent optical, material, and process properties which can be used for TFT-LCD color filter products. 14.2″ VGA panel is fabricated by using this organic black matrix technique. It is expected that this technique will lead the color filter production market.
Nanostructure and Electrical Properties of Anodized Al Gate Insulators for Thin-Film Transistors
Authors: Arai Toshiaki , Hiromasu Yasunobu , Tsuji Satoshi
Published: April 2011

A novel anodic oxidation method for aluminum thin-film on the glass substrate is proposed for the fabrication of a gate insulator in thin-film transistor (TFT). A proposed rear-positioned cathode makes for much more smooth surface with an average surface roughness of under 4 nm in comparison with conventional cathode positions. The anodic oxidation conditions were comprehensively investigated. The current density, ethylene glycol concentration, and cathode position were chosen as the elements of anodic oxidation condition matrix, and all these conditions affected the film formation. The surface morphology and nanostructure of the anodized films were characterized with an atomic force microscopy (AFM) and cross-sectional transmission electron microscopy (TEM). Films formed at higher ethylene glycol concentrations of over 50% and higher current densities of over 0.9 mA/cm2 exhibited higher breakdown electric fields of over 7 MV/cm, and lower leakage currents. These films had relatively smooth surfaces and took on the shapes of the underlying aluminum. In contrast, films formed at lower ethylene glycol concentrations of under 50% and lower current densities of under 0.9 mA/cm2 had rough surfaces and microvoids. A high concentration of ethylene glycol increases the cost of mass production, however, the proposed rear-positioned cathode method can be achieved even when the concentration of ethylene glycol is under 50%.
Emission Characteristics of Arrays of Diamondcoated Silicon Tips
Authors: Ohlberg Douglas A.A. , Talin Alec A. , Felter Thomas E. , Givargizov E. I.
Published: April 2011

The electron emission behavior of diamond-coated silicon whisker arrays was examined with a point-probe scanner and compared with the behavior of uncoated silicon whiskers as well as with diamond crystallites on a flat Si surface. Emission in all cases was inhomogeneous, and the emission site density was less than the whisker density. Both the diamond-coated and uncoated whiskers displayed a distribution of turn-on fields which peaked at around 10 V/µ, but the uncoated whiskers were observed to burn out if emission outputs exceeded 0.3 µA.
Phosphor Synthesis Routes and their Effect on the Performance of Garnet Phosphors At Low-Voltages
Authors: Shea L. E. , McKittrick J. , Phillips M. L. F.
Published: April 2011

Garnet phosphors have potential for use in field emission displays (FEDs). Greenemitting Gd3Ga5O12:Tb (GGG:Tb) and Y3A15012:Tb (YAG:Tb) are possible alternatives to ZnO:Zn, because of their excellent resistance to burn, low-voltage efficiency, (3.5 Im/W from GGG:Tb at 800 V), and saturation resistance at high power densities. Hydrothermal and combustion synthesis techniques were employed to improve the low-voltage efficiency of YAG:Tb, and Y3Ga5O12:Tb (YGG:Tb). Synthetic technique did not affect low-voltage (100–1000 V) efficiency, but affected the particle size, morphology, and burn resistance. The small particle size phosphors obtained via hydrothermal (<1 µm) and combustion reactions (<1 µm) would benefit projection TV, high-definition TV (HDTV), and heads-up displays (HUDs), where smaller pixel sizes are required for high resolution.
Characterization of Y2SiO5:Ce, YAG:Tb AND YAG:Eu RGB Phosphor Triplet for Field Emission Display Application
Authors: Chakhovskoi A. G , Malinowski M. E , Talin A. A , Felter T. E , Trujillo J. T. , HUNT C. E. , Stewart K. D.
Published: April 2011

The spectral response and outgassing characteristics of the three new, low-voltage phosphors combustion synthesized and electrophoretically deposited for application in field-emission flatpanel displays, are presented. The phosphors, forming a candidate Red-Blue-Green (RGB) triplet are YAG:Eu, YAG:Tb and Y2SiO5:Ce. These cathodoluminescent materials are tested with electron-beam excitation at currents up to 50 x03BC;A within the 200-2000V (eg. "low-voltage") and 3000-8000V (eg. "medium voltage") ranges. The spectral coordinates, as compared with industrially-manufactured P22 phosphors in low voltage operation, are reasonable; however, there is considerable difference in the green coordinates, and the red and green materials show significant satellite intensities. Phosphor outgassing, as a function of time, is measured by a residual gas analyzer at fixed 50 gA beam current in the low-voltage range. We find that after two hours of excitation, levels of outgassed CO, CO2 and H2 stabilize to low values.
Nature of the Green Luminescent Center in Zinc Oxide
Authors: Vanheusden K. , Warren W. L. , Seager C. H. , Tallant D. R. , Caruso J. , Hampden-Smith M. J. , Kodas T. T.
Published: April 2011

We apply a number of complementary characterization techniques including electron paramagnetic resonance, optical absorption, and photoluminescence spectroscopies to characterize a wide range of different ZnO phosphor powders. We generally observe a good correlation between the 510-nm green emission intensity and the density of paramagnetic isolated oxygen vacancies. In addition, both quantities are found to peak at a free-carrier concentration ne, of about 1.4 × 1018 cm-3. We also find that the green emission intensity can be strongly influenced by free-carrier depletion at the particle surface, especially for small particles and/or low doping. Our data suggest that the green PL in ZnO phosphors is due to the recombination of electrons in singly occupied oxygen vacancies with photoexcited holes in the valence band.
Photoluminescence Properties Of δ-Doped ZnS:Mn Grown By Metal-Organic Molecular Beam Epitaxy
Authors: Park W. , Tran T. K. , Tong W. , Kyi M. M. , Schön S. , Wagner B. K. , Summers C. J.
Published: April 2011

A detailed study is reported of the optical properties of homogeneously and δ-doped ZnS:Mn thin films grown by metal-organic molecular beam epitaxy. Fine structure in the Mn luminescence was observed at low Mn concentrations. The energy of the zero-phonon 4T1→6A1, transition of the Mn ion was determined to be 2.215eV, and the phonon energies associated with the transition to be 10meV and 37meV for the TA and TO phonons, respectively. It was found that the PL intensity depended on the Mn concentration and the δ-doped ZnS:Mn showed much brighter luminescence than the homogeneously doped samples with comparable Mn concentrations. For homogeneously doped ZnS:Mn with low Mn concentrations, the temperature dependence of the linewidth and the peak position was well described by the configuration coordinate model. For δ-doped ZnS:Mn, the antiferromagnetic interaction between Mn ions was invoked to explain the low temperature behavior. The luminescence lifetime measurements suggested that the δ-doping technique resulted in better incorporation of Mn ions in the ZnS host and less defect formation.
An Amorphous Silicon Thin Film Transistor Fabricated at 125°C by dc Reactive Magnetron Sputtering
Authors: McCormick C. S. , Webe C. E. , Abelson J. R.
Published: April 2011

We deposit hydrogenated amorphous silicon-based thin film transistors using dc reactive magnetron sputtering at a substrate temperature of 125°C, which is low enough to allow the use of plastic substrates. We characterize the structural properties of the a-Si:H channel and a-SiNx:H dielectric layers using infra-red absorption, thermal hydrogen evolution, and refractive index measurements, and evaluate the electrical quality using capacitance-voltage and leakage current measurements. Inverted staggered thin film transistors made with these layers exhibit a field effect mobility of 0.3 cm2/V-s, a Ion/Ioff ratio of 5 × 105, a sub-threshold slope of 0.8 V/decade, and a threshold voltage of 3 V.
Improved a-Si:H TFT Performance Using a-SixN1-x / a-SixC1-x Stack Dielectrics
Authors: Lavareda G. , Fortunato E. , Carvalho C. Nunes , Martins R.
Published: April 2011

In this paper we present a study on the electrical characteristics (conductivity, σ and relative dielectric constant, εr,.) of amorphous silicon nitride (a-SixN1-x) and carbide (a-SixC1-x) films deposited by PECVD, used as dielectric materials in TFT devices, aiming to select the most adequate alloy that lead to improve device performances. Besides that, double stack a-SixN1-x/a-SixC1-x structures were developed and applied as dielectric layers on TFTs, whose performances show to be superior to those ones using single silicon nitride or silicon carbide as dielectric.