bluuebunny/crossref_metadata_2025_split huggingface dataset:
Change in The Spectral Shape of the Subgap Absorption in a-SI:H by Photodegradation at 4.2K and its Relation to the Mobility-Lifetime Product
Authors: Stradins P. , Fritzsche H. 
Published: April 2011

ABSTRACTWe have observed a pronounced change in the shape of subgap absorption spectrum α(hν) of a-Si:H due to photodegradation at T=4.2K, in contrast to light exposure at T=300K. During the 4.2K exposure, α(hν) at 1.1≤(h‥)≤1.6eV increases with time as (α(t)-α(0)) ∝t0.3. However, for hν≤1eV the absorption α(hν) stays constant or decreases with exposure at 4.2K. Subsequent anneal causes the subgap absorption at the higher photon energies to decrease monotonically while a (hν ≤ 1.1 eV) increases first and goes through a maximum at T≈350K. This unexpected increase in a(hν) during annealing occurs at the anneal temperatures where the degraded mobility-lifetime product recovers. We suggest that the nonmonotonic recovery of a (hν≤ 1.1eV) during annealing is associated with preferential anneal of deeper defects or with structural relaxations around the defects during anneal causing a shift in their energy levels.
Via-Hole Addressed TFT and Process for Large-Area A-Si:H Electronics
Authors: Gleskova H. , Wagneri S. , Shen D. S. 
Published: April 2011

ABSTRACTWe demonstrate a new technology for RC gate delay reduction, by fabricating an array of amorphous silicon thin-film transistors (a-Si:H TFTs) on a thin glass substrate provided with via holes. All gates are connected through via holes to a metal line that is run on the back side of the substrate. We opened via holes with a diameter of 35 to 50 μm in 50 μm glass foil. For the first time, all TFT pattern definition steps used a process which employs electrophotographic toner masks.
Amorphous Silicon Photodiodes for Replacing Degenerated Photoreceptors in the Human Eye
Authors: Schubert M. B. , Hierzenberger A. , Baumung V. , Wanka H. N. , Nisch W. , Stelzle M. , Zrenner E. 
Published: April 2011

ABSTRACTAn ambitious neurotechnology program has been started in Germany in 1995, in the long run aiming at the realization of visual prostheses for blind people. A broad technological approach has been chosen which besides crystalline silicon microelectronics also involves amorphous silicon photodiodes for subretinal implantation, because thin film technology may be able to offer better solutions to some of the complex problems. Special topics we report on here include the development of low temperature deposition techniques for enabling the use of flexible plastic or bio-degradable substrate foils, the study of protective and bio-compatible coatings, as well as novel contacting and energy supply schemes. The key issue for stimulating retina cells by the use of technically generated photocurrents is an optimum capacitive coupling to these cells. For this purpose we study several contact layers (p-doped a-Si:H, microcrystalline Si, metal-induced crystallization) which provide high perpendicular but at the same time low lateral conductivity, thereby greatly reducing parasitic losses to the surrounding tissue. The photovoltaic mode of operation of the implanted photodiodes may be limited due to shortcomings in the charge transfer to the nerve cells, in which case additional infrared energy has to be coupled into the devices. Local light-induced stimulation can then be realised by using an a-Si:H i-layer as a photoresistor on top of the IR-sensitive solar cell.
Hydrogenated Amorphous Silicon Photoresists for Hgcdte Patterning
Authors: Hollingsworth R. E. , DeHart C. , Wang Li , Dinan J. H. , Johnson J. N. 
Published: April 2011

ABSTRACTA process to use a hydrogenated amorphous silicon (a-Si:H) film as a dry photoresist mask for plasma etching of HgCdTe has been demonstrated. The a-Si:H films were deposited using standard plasma enhanced chemical vapor deposition with pure silane as the source gas. X-ray photoelectron spectra show that virtually no oxide grows on the surface of an a-Si:H film after 3 hours in air, indicating that it is hydrogen passivated. Ultraviolet light frees hydrogen from the surface and enhances the oxide growth rate. A pattern of 60 micron square pixels was transferred from a contact mask to the surface of an a-Si:H film by ultraviolet enhanced oxidation in air. For the conditions used, the oxide thickness was 0.5–1.0 nm. Hydrogen plasmas were used to develop this pattern by removing the unexposed regions of the film. A hydrogen plasma etch selectivity between oxide and a-Si:H of greater than 500:1 allows patterns as thick as 700 nm to be generated with this very thin oxide. These patterns were transferred into HgCdTe by etching in an electron cyclotron resonance plasma. An etch selectivity between a-Si:H and HgCdTe of greater than 4:1 was observed after etching 2500 nm into the HgCdTe. All of the steps are compatible with processing in vacuum.
Light Induced Effects in A-Si:H Films Alloyed with Sulfur
Authors: Yoon Jong-Hwan , Taylor P. C. , Yan Baojie , Lee Czang-Ho 
Published: April 2011

ABSTRACTLight-induced effects are studied in hydrogenated amorphous silicon-sulfur alloys (a-SiSx:H) and compared to those that exist in a-Si:H. The a-SiSx:H films were grown by decomposition of pre-mixtures of SiH4 and H2 S. The light-induced effects were monitored using electrical (dark conductivity and photoconductivity, including the constant photocurrent method [CPM]) and optical (photoluminescence) measurements and electron spin resonance. It is found that sulfur alloying results in a significant reduction in the degradation in the dark- and photo-conductivity. For ana-SiSx:H film grown with a gas mixture of H2 S/SiH4= 0.02, there is an increase of over an order of magnitude in the dark conductivity and a small decrease in the photoconductivity after 50 hours of light soaking. The subgap deep defect density as measured by CPM increases with illumination time, following a stretched exponential to saturation. The saturated defect density is an order of magnitude higher than that observed in the annealed state.
Control of Valence States by a Codoping Method in P-Type GaN Materials
Authors: Yamamoto T. , Katayama-Yoshtoa H. 
Published: April 2011

ABSTRACTWe propose a new valence control method, the “codoping method (using both n- and p-type dopants at the same time)”, for the fabrication of low-resistivity p-type GaN crystals based on the ab-initio electronic band structure calculations. We have clarified that while doping of acceptor dopants, BeGa and MgGa, leads to destabilization of the ionic charge distributions in p-type GaN crystals, doping of Sica or ON give rise to p-type doped GaN with high doping levels due to a large decrease in the Madelung energy. The codoping of the n- and p-type dopants (the ratio of their concentrations is 1:2) leads to stabilization of the ionic charge distribution inp-type GaN crystals due to a decrease in the Madelung energy, to result in an increase in the net carrier densities.
Polar-Twinned Defects in LiGaO2 Substrates Lattice Matched with GaN
Authors: Ishii Takao , Tazoh Yasuo , Miyazawa Shintaro 
Published: April 2011

ABSTRACTWe investigated the Czochralski growth of LiGaO2 single crystal for use as a substrates for the epitaxial growth of hexagonal GaN. Crossed lines were observed in mechano-chemically polished {001} wafers sliced from a (001) axis boule. Chemical etching revealed that there exists a difference in chemical stability between two domains separated by a crossed line. Since LiGaO2 single crystal is polar along the c-axis, the formation of multi-domain structure is due to the polarity inversion of the c-axis, that is, polar twinned defects. We found that the GaN thin film on the (001) substrate with a multi-domain structure peeled off and that this is closely related with multi-polarity of substrate.
Substrate Effects on the Growth of InN
Authors: Donovan S. M. , MacKenzie J. D. , Abernathy C. R. , Pearton S. J. , Holloway P. , Ren F. , Zavada J. M. , Chai B. 
Published: April 2011

ABSTRACTAuger electron spectroscopy was used to examine the nitridation behavior of GaAs, sapphire and lithium aluminate (LAO) substrates exposed to an RF nitrogen plasma. No evidence of nitridation was found for the sapphire and LAO substrates. GaAs substrates did show evidence of nitridation which led to smooth InN surface morphology without the need for a low temperature buffer. Comparable InN films were obtained on sapphire and LAO substrates when a low temperature AlN buffer was used. Hall measurements indicate background carrier concentrations are relatively insensitive to substrate type, though mobilities decreased as surface morphology was improved.
Initial Stages of MOCVD Growth of Gallium Nitride Using a Multi-Step Growth Approach
Authors: Kobayashi J. T. , Kobayashi N. P. , Dapkus P. D. , Zhang X. , Rich D. H. 
Published: April 2011

ABSTRACTA multilayer buffer layer approach to GaN growth has been developed in which the thermal desorption and mass transport of low temperature buffer layer are minimized by deposition of successive layers at increased temperatures. High quality GaN with featureless surface morphology has been grown on (0001) sapphire substrate by metalorganic chemical vapor deposition using this multilayer buffer layer approach. The lateral growth and coalescence of truncated 3D islands (TTIs) nucleated on low temperature buffer layers at the initial stage of overlayer growth is affected by the thickness of the final buffer layer on which nucleation of TTIs takes place. The effect of the thickness of this buffer layer on the quality of GaN is studied by using scanning electron microscopy, van der Pauw geometry Hall measurements and cathodoluminescence and an optimum value of 400Å is obtained.
Mechanical Properties of Gallium Nitride and Related Materials
Authors: Drory M. D. 
Published: April 2011

ABSTRACTBasic mechanical properties, such as hardness and fracture toughness are examined for GaN and related materials. The mechanical properties are explored by indentation with a diamond (Vickers) pyramid under less than 20N load. Testing on bulk single crystal GaN indicated hardness and fracture toughness similar to GaP, but with much greater values than GaAs. Data for compound semiconductors are compared with values of a number of substrate materials. The following materials are examined in bulk form: AlN, Al2O3 (sapphire), Al2O3-TiC (ALTIC), GaAs, GaN, GaP, Ge, Si, SiC, ZnS, and ZnSe.
Resonant Raman Scattering in GaN/Al0.15 Ga0.85N and InyGa1-yN/GaN/AlxGa1-xN Heterostructures
Authors: Behr D. , Niebuhr R. , Obloh H. , Wagner J. , Bachem K. H. , Kaufmann U. 
Published: April 2011

ABSTRACTWe report on resonant Raman scattering in Al0.15Ga0.85N/GaN single quantum wells (QWs) and AlxGa1-xN/GaN/lnyGa1-yN heterostructures. By choosing appropriate excitation conditions we could probe selectively the GaN quantum well or the Al0.15Ga0.85N barrier of Al0.15Ga0.85N/GaN single quantum wells. For the InxGa1-xN material system a linear frequency shift of the E2- and A1(LO) phonon mode to lower frequencies was found with increasing In content. The shift was determined to -0.79cm-1 per % In content for the A,(LO) phonon frequency. Resonant excitation of AlxGa1-xN/GaN/InyGa1-YN heterostructures enabled us to detect phonon signals from the InxGa1-xN layer in the heterostructure and to determine its In content.
Electron-Phonon Scattering in Very High Electric Fields
Authors: Ridley B. K. 
Published: April 2011

ABSTRACTLarge-bandgap materials can support very high electric fields (>lMV/cm) without breaking down. The possibility then exists for an electron in a conduction band to become quasi-localized in Wannier-Stark states, a possibility that depends on the scattering rate being less than the Bloch oscillation frequency. If this condition is met the scattering rate itself is affected and the description of transport must be changed from the usual model in which the electron is assumed to be virtually free. Here, we examine the feasibility of obtaining this condition in GaN using a simple three-dimensional tight-binding model for the bandstructure and taking the dominant scattering mechanism to be the polar and non-polar interaction with optical phonons and short-wavelength acoustic phonons.
Optical-Gain Measurements on GaN and Alx Ga1-xN Heterostructures
Authors: Eckey L. , Holst J. , Kutzer V. , Hoffmann A. , Broser I. , Ambacher O. , Stutzmann M. , Amano H. , Akasaki I. 
Published: April 2011

ABSTRACTOptical gain processes in thin GaN and AlGaN are compared by means of gain spectroscopy using the stripe length method and high-excitation photoluminescence, both performed at various densities and temperatures. We find that inelastic excitonic scattering processes and biexciton decay are important at low temperatures and low excitation densities Both materials are similar in that increasing the excitation density results in gain spectra dominated by the electron-hole plasma and phonon-assisted band-to-band recombination. These also prevail at high temperatures.
Hrem and CBED Studies of Polarity of Nitride Layers with Prismatic Defects Grown Over SiC
Authors: Vermaut P. , Ruterana P. , Nouet G. , Salvador A. , Morkog H. 
Published: April 2011

ABSTRACTThe polarity of GaN films and their AlN buffer layer grown on (0001)si 6H-SiC by an electron cyclotron resonance plasma enhanced molecular beam epitaxy has been investigated by convergent beam electron diffraction (CBED) and high resolution electron microscopy (HREM). The experimental results are in good agreement with the simulations and allow to determine that the free surfaces of the GaN and AlN layers are Ga and Al-terminated respectively. Moreover, (1210) prismatic planar defects observed in the AlN layers have been identified as stacking faults and observations in different areas of the specimens have shown that the layers are unipolar.
Valence Band Physics in Wurtzite GaN
Authors: Azuhata T. , Sota T. , Chichibu S. , Kuramata A. , Horino K. , Yamaguchi M. , Yagi T. , Nakamura S. 
Published: April 2011

ABSTRACTWe present a summary of recent progress towards the understanding of the valence-band physics in wurtzite GaN. Systematic studies have been performed on the strain dependence of the free exciton resonance energies by photoreflectance measurements using well-characterized samples. Analyzing the experimental data with the Hamiltonian appropriate for the valence bands, the values have been determined of the crystal field splitting, the spin-orbit splitting, the shear deformation potential constants, and the energy gap in the unstrained crystal. Discussions are given on the strain dependence of the energy gaps, of the effective masses, and of the binding energies for the free exciton ground states as well as on the valence band parameters. Using the obtained values and the generalized Elliott formula, the fundamental optical absorption spectra obtained experimentally were analyzed. The values of the elastic stiffness constants, which play a crucial role to determine the shear deformation potential constants, are also given.
Electrical and Optical Properties of InGaN/AlGaN Double Heterostructure Blue Light-Emitting Diodes
Authors: Yang K. , Shi H. T. , Shen B. , Zhang R. , Chen Z. Z. , Chen P. , Zheng Y. D. 
Published: April 2011

ABSTRACTIn this paper, we studied the electrical and optical characteristics of Nichia double heterostructure blue light-emitting diodes, with In0.06Ga0.94N:Zn, Si active layer, at 77 and 300 K. Measurement of the forward bias current-voltage behavior of the device demonstrates a departure from the Shockley model of p-n diodes, and it is observed that the dominant mechanism of carrier transport across the junction is associated with carrier tunneling. Electroluminescence experiments of the devices were performed. We obtained an emission peak located at 2.80 eV, and a relatively weaker short-wavelength peak of 3.2 eV. A significant blue shifts of the optical emission peak which is consistent with the tunneling character of electrical characteristics was observed. Furthermore, we studied the properties of electroluminescence under various pulsed currents, and a degradation in I-V characteristics and a low resistance ohmic short were observed.
Effect of Hydrogen Chloride on the Capacitance-Voltage Characteristics of MOCVD-Grown AlN/6H-SiC Mis Structures
Authors: Tin C. C. , Gichuhi A. , Bozack M. J. , Shannon C. G. , Teh C. K. 
Published: April 2011

ABSTRACTAluminum nitride (AlN) is a promising material as gate insulator for 6H-SiC metal-insulator-semiconductor (MlS)-based devices. Using metalorganic chemical vapor deposition (MOCVD)-grown AlN, we have recently fabricated Au/AlN/6H-SiC MIS structures with different AlN/6H-SiC interfacial characteristics depending on the AlN growth procedures. We have also found that the use of hydrogen chloride gas is effective in improving the capacitance-voltage characteristics of the AlN/6H-SiC structure. The reason for such improvement is not well understood and several possible mechanisms for such improvement include factors such as substrate surface morphology and surface contaminants. In this paper, we will examine the relationship between surface morphology of the substrates and the capacitance-voltage characteristics of Au/AlN/6H-SiC structures.
Theory of Gain in Group-HI Nitride Lasers
Authors: Chow W. W. , Wright A. F. , Girndt A. , Jahnke F. , Koch S. W. 
Published: April 2011

ABSTRACTA microscopic theory of gain in a group-III nitride quantum well laser is presented. The approach, which treats carrier correlations at the level of quantum kinetic theory, gives a consistent account of plasma and excitonic effects in an inhomogeneously broadened system.
Growth and Characterization of Thermal Oxides on Gallium Nitride
Authors: Wolter Scott D. , Mohney Suzanne E. , Venugopalan Hari , Waltemyer Debra L. , Luther Brian P. 
Published: April 2011

ABSTRACTLittle information is available about the thermal oxidation of GaN. Since GaN is of interest for high temperature electronics, knowledge of the stability of GaN in potentially oxidizing environments would be useful. Furthermore, evaluation of the characteristics of the thermal oxide will provide information needed for assessing the potential of this oxide in processing or device applications.In this study, thick GaN epilayers and GaN powders were exposed to dry air at 450°C, 750°C, 900°C, 925°C, 950°C, and 1000°C for periods of 1 to 25 hours. Following oxidation, the epilayers were analyzed by x-ray photoelectron spectroscopy and glancing incidence x-ray diffraction, and the powders were analyzed by conventional x-ray diffraction. For both the GaN films and powders, significant oxidation was observed at 900°C, and the oxide was identified as monoclinic β-Ga2O3. Oxidation in dry air resulted in roughening of the oxide/GaN interface and oxide surface. In the temperature range 900°C to 1000°C, linear kinetics were observed for times up to 10 hours indicating an interfacial reaction mechanism as the rate limiting step for oxidation. An apparent activation energy of ∼72 kcal/mole was determined for this process.
Surface Preparation and Growth Condition Dependence of Cubic GaN Layer on (001) GaAs by Hydride Vapor Phase Epitaxy
Authors: Tsuchiya H. , Sunaba K. , Yonemura S. , Suemasu T. , Hasegawa F. 
Published: April 2011

ABSTRACTGaN buffer layers and thick GaN layers were grown on (001) GaAs substrates by hydride vapor phase epitaxy. The ratio of cubic to hexagonal components in the grown layer was estimated from the ratio of the integrated X-ray diffraction intensities of the cubic (002) plane and hexagonal (1011) planes measured by w scan. The optimum growth conditions were thermal cleaning at 600°C, growth temperature of 500°C and thickness of 30 nm for the buffer layer, and the Will ratio of 300 for thick GaN growth at 800°C. Cubic component in the layer grown with those conditions was more than 85% and strong cubic photoluminescence emission was observed at 377 nm (3.28 eV).
MBE-Growth of Strain Engineered GaN Thin Films Utilizing a Surfactant
Authors: Klockenbrink R. , Kim Y. , Leung M. S.H. , Kisielowski C. , Krüger J. , Sudhir G. S. , Rubin M. , Weber E. R. 
Published: April 2011

ABSTRACTGaN films were grown on sapphire substrates at temperatures below 725 °C utilizing a Constricted Glow Discharge plasma source. A three dimensional growth mode is observed at such low growth temperatures resulting in films that are composed of individual but oriented grains. The strain that originates from the growth on the lattice mismatched substrate with a different thermal expansion coefficient is utilized to influence the thin film growth. The strain can be largely altered by the growth of suitable buffer layers. Thereby, optical and structural film properties can be engineered. It is argued that the surface diffusion of Ga ad-atoms is affected by engineering the strain. Alternatively, surface diffusion can be influenced by surfactants. It is demonstrated that the use of bismuth as a surfactant allows to modify the surface morphology of the GaN films that reflects the size of the grains in the films. The results suggest that a substantial increase of the oriented grain sizes in the films is possible while maintaining a low growth temperature.
Quasi-Thermodynamic Analysis of Metalorganic Vapor Phase Epitaxy of GaN
Authors: Duan Shukun , Lu Dacheng 
Published: April 2011

ABSTRACTA thermodynamic analysis of GaN grown by MOVPE has been proposed based on quasi-thermodynamic equilibrium established on the solid-vapor interface. Phase diagrams for the MOVPE growth of GaN using TEGa and NH3 has been calculated. The phase diagram is consists of four phases regions: the region for single condensed phase of GaN, the region for double condensed phase of GaN (s) +Ga(l), the etching region with Ga droplets and the etching region without Ga droplets. The effect of growth temperature, reactor pressure, content of carrier gas, deposition ratio of NH3 and V/III ratio upon growth of GaN using MOVPE has been studied.
Modeling and Model Validation for RTP Design
Authors: Fordham M. , Pan M. , Hu J. , Sorrell F. Y. 
Published: April 2011

ABSTRACTSpectral and spectral band irradiance sensors are developed to measure the spatial heat flux distribution from a rapid thermal processor (RTP) lamp bank. They are used in conjunction with a Sensarray thermocouple wafer to evaluate the thermal uniformity of one axially symmetric lamp bank from a 3 zone RTP system. Measured performance of the lamp bank differs sharply from predictions obtained using a numerical ray trace model. Discrepancies between experimental measurements and model results are resolved by blackening a beveled (focusing) surface introduced to shield process lamp bases from overheating. Further modeling confirms that the bevel causes undesirable focusing of lamp radiation on the planar wafer surface. The shape of the focused component of the irradiance profile is highly dependent on the lamp radiance spatial distribution assumed in the model.
Integrated Rapid Thermal CVD Processing Solutions for 0.18–0.25μm Technologies
Authors: Gilboa H. , Gilboa Y. E. , Atzmon Z. , Levy S. , Spilberg H. , Bransky E. , Doitel Z. , Thakur R.P.S. , Weimer R. A. , Deboer S. , Pan J. 
Published: April 2011

ABSTRACTThe evolution of integrated single-wafer processing for high-temperature applications in the front end of the line (FEOL) occurred with the advancements in single-wafer rapid thermal processing and its acceptance as a manufacturing technology. The Integra RTCVD cluster tool for high-temperature applications features wafer cleaning, rapid thermal processing and single wafer chemical vapor deposition steps. The paper presents integrated vapor phase clean and RTCVD applications for FLASH memory gate stack and DRAM cell.