bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intrinsic Mobility Limits of a Two-Dimensional Electron Gas in AlGaN/GaN Heterostructures
Authors: Walukiewicz W. , Hsu L. , Redwing J. M. 
Published: April 2011

ABSTRACTWe present the results of a theoretical study of the 2D electron gas mobility at a AlxGa1−xN/GaN heterointerface. All standard mechanisms, including scattering by acoustic and optical phonons, and remote and background (residual) impurities have been included in our calculation of theoretical mobility limits in a AlxGa1−xN/GaN structure. Comparison of calculations with experimental mobilities obtained from high quality MOCVD grown Al0.15Ga0.85N/GaN heterostructures shows that the low temperature mobility in these samples is dominated by scattering from ionized impurities, with a smaller contribution from acoustic phonons.
Observation of a Two-Dimensional Electron Gas in the AlGaN/GaN on SiC Substrates
Authors: Chi G. C. , Lin C. F. , Cheng H. C. , Huang J. A. , Feng M. S. , Guo J. D. 
Published: April 2011

ABSTRACTGaN/Al0.08 Ga0.92 N heterostructure has been grown on(0001) 6H-SiC substrates using low pressure metalorganic chemical vapor deposition(LP-MOCVD). Triethylgallium (TEGa), trimethylaluminum(TMA) and ammonia(NH3) were used as the Ga, Al and N sources, respectively. The carrier gas is hydrogen(H2)and the growth pressure is kept at 76 torr. Five pairs of GaN/Al0.08 Ga0.92N(100Å/100Å)were used as buffer layer, then follow by an 1.3 μ m GaN film. The 500Å AlGaN bulk structure was grown on the GaN and Finally an 100Å GaN cap layer to prevent the oxidation of AlGaN layer. The full width half maxima(FWHM) of x-ray peak is 115 arc second for the thick layer of GaN (1.3 μ m), this value is smaller than we reported for the GaN on sapphire substrate (It was about 300 arc second). The Hall mobility and sheet carrier concentration are 887 cm2/Vs, 1.0 × 1016cm-2 at 300K and 4661 cm2/Vs, 7.2 × 1012cm-2 at 77K. This high electron mobility is an indication of a two-dimensional electron gas(2DEG) formed at the GaN/AlGaN interface.
Coexistence of Shallow and Localized Donor Centers in Bulk GaN Crystals Studied by High-Pressure Raman Spectroscopy
Authors: Perlin P. , Suski T. , Polian A. , Chervin J. C. , Knap W. , Camassel J. , Grzegory I. , Porowski S. , Erickson J. W. 
Published: April 2011

ABSTRACTCharacter of the metal-insulator transition which occurs at about 23 GPa in bulk GaN crystals has been studied by means of high pressure Raman spectroscopy. The related freeze-out of electrons is caused by the localized donor state formed by most likely oxygen and emerging at high pressures to the band gap of GaN. As a result, the electron concentration drops from its initial value of 5.1019 cm-3 to about 3. 1018 cm-3. These remaining electrons originate likely from another donor center with effective mass character, probably carbon. The obtained results raise a question whether the nitrogen vacancy is abundant enough to be observed in bulk GaN crystals.
Magnetic Resonance Studies of GaN-Based Single- Quantum Well LEDs
Authors: Carlos W. E. , Glaser E. R. , Kennedy T. A. , Nakamura Shuji 
Published: April 2011

ABSTRACTWe report electrically-detected magnetic resonance (EDMR) and electroluminescence-detected magnetic resonance (ELDMR) results on InGaN/AJGaN single-quantum-well light emitting diodes. The dominant feature detected by either technique is a broad resonance (ΔB ≈ 13 mT) at g ≈ 2.01 which is enhanced by high current stressing. Our ELDMR measurements show that, depending on bias, this defect is predominately associated with either an increase or a decrease in electroluminescence at resonance while our EDMR measurements show that this resonance is associated with an increase in current at resonance before stressing and a decrease after stressing. We suggest that this is associated with a nonradiative recombination path, in parallel with the radiative recombination path and with recombination in the depletion region of a contact. A second resonance, more prominent before stressing, with g ≈ 1.99 and ΔB ∽ 7 mT is very similar to the deep donor trap, previously observed in double heterostructure diodes and is associated with a decrease in both the current and electroluminescence at resonance.
Structural and Optical Properties of AlGaN/GaN Quantum-Well Structures Grown by MOCVD on Sapphire
Authors: Niebuhr R. , Bachem K. H. , Behr D. , Hoffmann C. , Kaufmann U. , Lu Y. , Santic B. , Wagner J. , Arlery M. , Rouviere J. L. , Jürgensen H. 
Published: April 2011

ABSTRACTAlGaN/GaN single quantum wells (QW) have been grown on 2” sapphire substrates (c-plane) by metal-organic chemical vapor deposition (MOCVD). The well width was varied between 20 and 40 Å for barriers containing 4 % and 16 % of aluminium. Cathodoluminescence (CL) and Photoluminescence (PL) spectra of the samples show, as expected, a shift of the quantum well emission to higher energies with decreasing well width, whereas the barrier luminescence stays at constant energy. Examination of the QWs by resonant Raman spectroscopy tuned to the gap of the well, clearly shows the GaN A1(LO) phonon besides the AlGaN A1(LO) phonon from the barrier. For a well width of 20 Å we observe a shift of the A1(LO) GaN phonon indicating a certain degree of intermixing at the GaN/AlGaN interface. Atomic Force Microscopy (AFM) reveals that the layers are growing in a 2-dimensional step flow growth mode with step heights of 3 and 6 Å corresponding to mono- and biatomic steps. High Resolution Transmission Electron Microscopy (HRTEM) micrographs of the 40 Å well show a very low interface roughness of 1–2 atomic layers.
Bulk and Surface Electronic Structure of GaN Measured Using Angle-Resolved Photoemission, Soft X-ray Emission and Soft X-ray Absorption
Authors: Smith Kevin E. , Dhesi Sarnjeet S , Duda Laurent-C. , Stagarescu Cristian B , Guo J. H. , Nordgren Joseph , Singh Raj , Moustakas Theodore D 
Published: April 2011

ABSTRACTThe electronic structure of thin film wurtzite GaN has been studied using a combination of angle resolved photoemission, soft x-ray absorption and soft x-ray emission spectroscopies. We have measured the bulk valence and conduction band partial density of states by recording Ga L- and N K- x-ray emission and absorption spectra. We compare the x-ray spectra to a recent ab initio calculation and find good overall agreement. The x-ray emission spectra reveal that the top of the valence band is dominated by N 2p states, while the x-ray absorption spectra show the bottom of the conduction band as a mixture of Ga 4s and N 2p states, again in good agreement with theory. However, due to strong dipole selection rules we can also identify weak hybridization between Ga 4s- and N 2p-states in the valence band. Furthermore, a component to the N K-emission appears at approximately 19.5 eV below the valence band maximum and can be identified as due to hybridization between N 2p and Ga 3d states. We report preliminary results of a study of the full dispersion of the bulk valence band states along high symmetry directions of the bulk Brillouin zone as measured using angle resolved photoemission. Finally, we tentatively identify a non-dispersive state at the top of the valence band in parts of the Brillouin zone as a surface state.
Polycrystalline Silicon Grown on Porous Silicon-on-Insulator Substrates
Authors: Hsu Klaus Y.J. , Lee C. H. , Yeh C. C. 
Published: April 2011

AbstractInexpensive full-wafer SOI substrates are appealing for various applications such as ULSI. As an attempt to achieve this goal, low-temperature deposition of silicon on novel porous Si-on-insulator (PSOI) substrates was performed in this work. The bottom insulator was obtained by anodically oxidizing a pre-formed porous silicon film in HCl solution. The thickness, uniformity and quality of the resulted bottom oxide layer as well as the residual porous silicon layer above were well-controlled. Low-temperature PECVD growth of silicon on the PSOI wafer was conducted by using the residual porous silicon as the seed. Cross-sectional TEM pictures and electron diffraction patterns showed that poly-Si films were formed on PSOI substrates under the conditions of 98% hydrogen dilution ratio, 20 Watts RF power, and 300°C substrate temperature. Further thermal annealing at 1050°C for 30 minutes significantly enhanced the crystallinity of the deposited films. Combined with the excellent insulation ability of the bottom oxide, the technique is suitable for future inexpensive full-wafer SOI fabrication.
Phosphorus Doping of Boron Carbon Alloys
Authors: Hwang Seong-Don , Dowben P. A. , Cheeseman A. , Spencer J. T. , Mcilroy D. N. 
Published: April 2011

AbstractPhosphorus doped boron carbon alloy films were made by chemical vapor deposition from a single source compound, dimeric chloro-phospha(III) carburane ((C2B10H10)2(PCl)2). Phosphorus doped B5C materials exhibit increases in the band gap from 0.9 eV to 2.6 eV.
Photoluminescence Characteristics of HF-Treated Silicon Nanocrystals
Authors: Nozaki S. , Sato S. , Ono H. , Morisaki H. 
Published: April 2011

AbstractSi nanocrystals were deposited in a helium atmosphere by the gas-evaporation technique. Their average size is 3.5 nm, much smaller than those of the Si nanocrystals deposited in an argon atmosphere. The PL spectra of the as-deposited and the HF-treated Si nanocrystals were compared. A great increase in the PL intensity of the HF-treated Si nanocrystals is attributed to the hydrogen passivation of Si surface dangling bonds. A good correlation between the amount of Si-O bonds and the PL intensity suggests that the oxygen-passivation of dangling bonds is required for the red-band PL. The PL spectra of the HF-treated Si nanocrystals resemble those of porous Si and clearly indicate that the HF-treated Si nanocrystals well simulate the porous Si.
Visible Luminescence in Si/SiO2 Superlattices
Authors: Lockwood D. J. , Baribeau J.-M. , Grant P. D. , Labbé H. J. , Lu Z. H. , Stapledon J. , Sullivan B. T. 
Published: April 2011

AbstractAmorphous Si/SiO2 superlattices with periodicities from 2 to 5 nm have been grown on (100) Si wafers by several different techniques: molecular beam epitaxy, magnetron sputtering, and plasma enhanced chemical vapor deposition (PECVD). With the first two methods little or no hydrogen was incorporated during growth and visible photoluminescence (PL) was obtained at wavelengths from 520 to 800 nm. The shift in the PL peak position with Si layer thickness is consistent with quantum confined emission. Annealing the sputtered superlattices at temperatures up to 1100°C produced a very bright red PL that is similar in intensity to that found in porous Si. The PL was also considerably enhanced by deposition on aluminum-coated glass substrates. For large numbers of periods (e.g., 425) the PL was strongly modulated in intensity owing to optical interference within the superlattice. Similar quantum-confined PL was also observed in the PECVD grown superlattices, where the amorphous Si layers were heavily hydrogenated. The blue-red cathodoluminescence observed from sputtered superlattices is due primarily to defects in the SiO2 layers.
Possible Mechanism of the 30–100 Picoseconds Fast and Efficient Photoluminescence From nc-Si/a-SiO2Doped with Transition Metals
Authors: Veprek S. , Wirschem Th. , Dian J. , Perná S. , Merica R. , Veprek-Heijman M. G. J. , Perina V. , Fuss M. , Lin X. 
Published: April 2011

AbstractThe nc-Si/a-SiO2composite thin films doped with tungsten show very fast and efficient photoluminescence (PL). In order to obtain insight into the PL mechanism we have performed a comparative study with other metals. The results lend support to the suggested mechanism which includes the photogeneration of charge carriers due to efficient absorption of the excitation UV light in the silicon nanocrystals followed by energy transfer to the Wn+radiative center from which the light emission occurs.
Growth of Germanium on Porous Silicon (001)
Authors: Thompson W. H. , Yamani Z. , Nayfeh H. M. , Hasan M.-A. , Greene J. E. , Nayfeh M. H. 
Published: April 2011

AbstractThe surface morphology of Ge grown on Si (001) and porous Si(001) by molecular beam epitaxy at 380 °C is examined using atomic force microscopy (AFM). For layer thicknesses of 30 nm, the surface shows islanding while still maintaining some of the underlying roughness of the surface of porous Si. For thicknesses in the 100 nm range, the surface roughness is not visible, but the islanding persists. Unlike the case of silicon where islands tend to merge and nearly disappear as the thickness of the deposited layer rises, we observe on the porous layer the persistence of the islands with no merging even for macroscopic thicknesses as large as 0.73 microns.
The Fabrication of Semiconductor Nanostructure Arrays on a Silicon Substrate Using an Anodized Aluminum Template
Authors: McGinnis S. P. , Cleary J. N. , Das B. 
Published: April 2011

AbstractWe have developed a nanogrowth technology for the fabrication of periodic arrays of semiconductor nanostructures on silicon that is currently being investigated for silicon based x-ray detectors. The semiconductor nanostructures are formed by chemical synthesis in pores of a template created by the anodization of aluminum on a silicon substrate. The use of the silicon substrate allows greater control over the aluminum thin film properties, better in situ monitoring of the pore formation process, and the direct integration of nanostructure arrays with conventional silicon technology.
Electronic Structure of O-D Exciton Ground State in CdSe Nanocrystals
Authors: Chamarro M. , Dib M. , Gourdon C. , Lavallard P. , Lublinskaya O. , Ekimov A. I. 
Published: April 2011

AbstractWe present results on photoluminescence excitation spectra (PLE) of wurtzite CdSe nanocrystals (NCs) embedded in a glass with effective radii in the range 15–35 Å. Information on the near band-gap absorption of an assembly of NCs is obtained by selecting a narrow energy range in the inhomogeneously broadened photoluminescence band. The size and shape dependence of the lowest exciton states are calculated for slightly non-spherical wurtzite NCs. The experimental results are in good agreement with the theoretical predictions when both shape and size dispersions are taken into account.
Formation of Buried Porous Silicon Structure by Hydrogen Plasma Immersion Ion Implantation
Authors: Fan Z. , Chu Paul K. , Lu X. , Iyer S. S. K. , Cheung N. W. 
Published: April 2011

AbstractPlasma Immersion Ion Implantation (PIII) excels in several areas over conventional ion implantation, for example, higher dose, shorter implantation time, and lower overall cost. The technique can be used to fabricate buried porous silicon. In our experiment, hydrogen is implanted into Si by PIII at 5–30kV to form underlying porous silicon (PS) which emits light at an energy higher than the Si bandgap. The optical properties of the PS samples as measured by photoluminescence are quite good. The PHI technique therefore offers an alternative means to fabricate buried porous silicon structures which can potentially be used to fabricate optoelectronic devices in silicon.
Atomic and Electronic Properties of Small Hydrogenated Silicon Clusters: Si6H2m and Si6H+2m+1
Authors: Miyazaki Takehide , Stich Ivan , Uda Tsuyoshi , Terakura Kiyoyuki 
Published: April 2011

AbstractThe atomic and electronic structures of Si6H2m and Si6H+2m+1 clusters have been investigated in the framework of density-functional theory. For both neutral and ionized clusters we found the structure to belong to one of four distinct structural families. A molecular-orbital picture of hydrogenation is presented. From the calculated formation energies of these clusters, we infer the relative stability of the different structural families discussed.
Anisotropy of the Porous Silicon Photoluminescence
Authors: Polisski G. , Averboukh B. , Kovalev D. , Koch F. 
Published: April 2011

AbstractPolarization memory effect in the porous Si photoluminescence is studied. The anisotropy of the linear polarization degree is found in the samples etched with polarized light-assistance. The effect is explained by the anisotropie in plane distribution of the elongated Si crystallites. Under resonant optical excitation four-fold anisotropy of the photoluminescence polarization, linked to the crystalline axes of the bulk Si substrate, is observed.
Integrating Bipolar Junction Transistors with Silicon-Based Light-Emitting Devices
Authors: Hirschman K. D. , Tsybeskov L. , Duttagupta S. P. , Fauchet P. M. 
Published: April 2011

AbstractSilicon-based optoelectronic devices enable the realization of optoelectronic systems that are compatible with integrated circuit manufacturing technology. This work reports on silicon-based visible light-emitting devices (LEDs) that have been successfully integrated into a standard bipolar fabrication sequence. The basic LED structure consists of a 0.5–1.0μm thick silicon-rich silicon oxide (SRSO) active light-emitting layer formed on a p-type silicon wafer by partial oxidation of porous silicon (PSi), with an n+ doped polysilicon cathode. The LEDs exhibit bright electroluminescence (EL) with a spectral peak between 1.75 and 1.90e. The LEDs are connected in a common-emitter configuration to integrated vertical pnp bipolar driver transistors. This is the first demonstration of an all-silicon visible light emitter / bipolar transistor optoelectronic integrated circuit. The LED device fabrication, process integration, and optoelectronic device characteristics are discussed.
Optical and Electrical Properties of Undoped Microcrystalline Silicon Deposited by the VHF-GD with Different Dilutions of Silane in Hydrogen
Authors: Beck N. , Orres P. , Fric J. , Remeš Z. , Poruba A. , Stuchlíková HA , Fejfar A. , Wyrsch N. , Vaněček M. , Kočka J. , Shah A. 
Published: April 2011

AbstractWe show that the optical and electrical properties of microcrystalline silicon (μc-Si:H) deposited by the VHF-GD technique at 110 MHz can considerably be tuned by changing the dilution ratio of silane to hydrogen.With increasing silane dilution we observe enhanced optical absorption for energies below 2 eV due to the transition of the material from amorphous / microcrystalline mixture to a pure microcrystalline phase. Simultaneously, the light scattering and the defect absorption increases. Strong dilution also promotes the incorporation of impurities into the material, leading to a pronounced extrinsic behaviour as seen from the decrease of the activiation energy of the electrical conductivity.The electrical properties were investigated in the dark by the Time of Flight technique. We measured drift mobilities at room temperature which slightly increase with dilution, reaching values of 3 cm2/Vs for electrons and 1.2 cm2/Vs for holes. The ratio between electron and hole drift mobilities is found to be around 2 for all samples studied, similar to that of crystalline silicon.Furthermore, post-transient Time of Flight measurements revealed detrimental electron deep traps in low dilution material.
Enlarged Parameter Space by Use of VHF-GD for Deposition of Thin <p> Type μc-Si:H Films
Authors: Torres P. , Meier J. , Flückiger R. , Keppner H. , Shah A. 
Published: April 2011

AbstractIn this paper new results on thin p - type μc-Si:H films deposited at low temperatures of 170 °C by the Very High Frequency - Glow Discharge technique (VHF-GD) are presented. The “tolerated” amount of diborane added in the gas phase ratio as well as the influence of three different plasma excitation frequencies (70, 100 and 130 MHz) in obtaining high electrical conductivity are investigated. The goal is to optimise very thin (< 400 Å) and hence optically transparent films by maintaining high conductivities for the application as window layers of solar cells.
Influence of hydrogen incorporation into Silicon on the room-temperature photoluminescence
Authors: Rappich J. , Dittrich Th. , Timoshenko Y. , Beckers I. , Fuhs W. 
Published: April 2011

AbstractWe investigated the possibility to use the photoluminescence (PL) emission at room temperature for the characterization of grain boundary and surface passivation of μc-Si and single crystalline silicon. The PL-spectra of c-Si and μc-Si taken at 300 K consist of an emission band around 1.1 and 1 eV, respectively. Measuring the PL intensity we study the influence of electrochemical and plasma passivation by hydrogen. We compare the behavior of the films to that of Si crystals. In this case the PL intensity is high for a well H-terminated c-Si surface and decreases during cathodic polarization (hydrogen evolution) which points to the formation of additional non-radiative recombination centers. Whereas the PL intensity of the as prepared μc-Si films is unchanged, that of the annealed films increases during hydrogen evolution indicating the electrochemical passivation of defects on grain boundaries.
Pulsed ESR Study of the Conduction Electron Spin Center in μc-Si:H
Authors: Zhou Jiang-Huai , Yamasaki Satoshi , Isoya Junichi , Ikuta Kazuyuki , Kondo Michio , Matsuda Akihisa , Tanaka Kazunobu 
Published: April 2011

AbstractThe spin-lattice relaxation times (T1) of conduction electron (CE) and dangling bond (DB) centers in μc-Si:H have been directly measured using the 3-pulse inversion recovery method. For both CE and DB, the inversion recovery curve follows a stretched exponential form. T1 of DB is about twice the T1 of CE, however the temperature dependence of T1 seems to be the same for both CE and DB and can be approximated by T−4 While the DB echo decay is modulated by both 29Si and 1H nuclei, we found no modulation of the CE echo decay by the H nucleus, indicating that CE centers are located in H-depleted phases in μc-Si:H. The modulation results are direct evidence that CE centers are located in the crystalline grains and DB centers in the amorphous phases.
The Effect of Film Thickness and Pulse Duration Variation in Excimer Laser Crystallization of Thin Si Films
Authors: Leonard J. P. , Bessette M. A. , Gupta V. V. , Im James S. 
Published: April 2011

AbstractRecognizing that the processing window in conventional excimer laser crystallization corresponds mainly to the partial melting regime, and that this can be properly simulated using a one-dimensional model, we investigate numerically the melting and solidification of thin silicon films on SiO2. Here a portion of the silicon film is melted and subsequent vertical solidification is initiated from the lower interface bounding the unmelted region. Upper and lower energy density limits for this regime are calculated for crystal silicon films of thickness 10 to 300 nm, and for pulse duration ranging from 10 to 200 ns. These calculations show that increasing pulse duration requires proportionally more incident energy density to partially melt the film, while decreasing film thickness reduces the range of energy densities over which partial melting can occur. The results are explained in terms of characteristic thermal diffusion distances and the enthalpy change associated with melting. In view of the results we discuss optimization of the conventional excimer laser crystallization and the avoidance of complete melting during the process.
Crystallization of Si(1-yCy Films by Excimer Laser Annealing: Characterization of the Microstructure of the Films
Authors: Boher P. , Stehle M. , Stehle J. L. , Fogarassy E. , Grob J. J. , Grob A. , Muller D. 
Published: April 2011

AbstractEpitaxial Si(1-y)Cy substitutional alloy layers are prepared on monocrystalline silicon substrates by carbon multiple energy ion implantation followed by XeCl excimer laser annealing on large surfaces. Structural analysis of the films before and after laser annealing are made very precisely using spectroscopie ellipsometry (SE), x-ray diffraction (XRD) and Rutherford backscattering (RBS) techniques. We show that annealing energy densities higher than 2J/cm2 result in monocrystalline epitaxial layers with low quantity of defects. The lattice contraction due to the carbon inclusion increases with the implanted C concentration up to about 1.1%. For higher values a more complex behaviour is observed with partial (or total) relaxation of the layer and/or carbide formation‥