Buffer Layer (buffer + layer)

Distribution by Scientific Domains

Kinds of Buffer Layer

  • aln buffer layer
  • gan buffer layer


  • Selected Abstracts


    Transparent Inverted Organic Light-Emitting Diodes with a Tungsten Oxide Buffer Layer,

    ADVANCED MATERIALS, Issue 20 2008
    Jens Meyer
    Highly efficient transparent OLEDs are demonstrated. A novel WO3 buffer layer protects the organics during the sputter deposition of the top ITO electrode. L,J,V and SIMS analysis yield optimized devices with a 60,nm thick WO3 layer. Very high efficiencies of 38 cdA,1 and 30 lm W,1 at 100,cd m,2 are obtained. At the same time the transmittance throughout the visible part of the spectrum exceeds 75%. [source]


    Metalorganic Chemical Vapor Deposition Growth of a GaN Epilayer on an Annealed GaN Buffer Layer

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003
    F. Degave
    Abstract We investigated the growth of an epitaxial layer deposited on an annealed buffer layer using transmission electron microscopy. It is shown that crystalline quality of the epitaxial layer depends on the annealing conditions of the buffer layer. Dislocations and formation of V-shaped defects are observed and may originate from the structure and morphology of the buffer layer. [source]


    Self-Organized Buffer Layers in Organic Solar Cells

    ADVANCED MATERIALS, Issue 12 2008
    Qingshuo Wei
    No abstract is available for this article. [source]


    Fabrication of Long Lengths of Epitaxial Buffer Layers on Biaxially Textured Nickel Substrates Using a Continuous Reel-to-Reel Dip-Coating Unit

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2001
    M. Parans Paranthaman
    A low-cost, nonvacuum, solution precursor route has been developed to produce epitaxial oxide buffer layers of Eu2O3 or La2Zr2O7 on biaxially textured Ni (100) tapes. A reel-to-reel continuous dip-coating unit consisting of a constant-tension tape transport system attached to a controlled atmosphere furnace was fabricated. Nickel tapes were pulled through a 2-methoxyethanol solution of europium methoxyethoxide/acetate or lanthanum zirconium methoxyethoxide. The double-sided dip-coated tapes were then annealed in a preheated furnace at 1000,1100C with a high flow rate of Ar/H2 (4%) gas. The dip-coated buffers were dense, continuous, crack-free, and epitaxial with a single cube texture. A critical current (Jc) of >1 MA/cm2 at 77 K and self-field was obtained for YBa2Cu3O7-, (YBCO) films with a layer sequence of YBCO (ex situ BaF2 process)/CeO2 (sputtered)/YSZ (sputtered)/Eu2O3 (dip-coated)/nickel. We have produced 1,2 m lengths of epitaxial buffer layers on textured nickel substrates using a nonvacuum process for the first time. [source]


    Homoepitaxy of ZnTe on (100) oriented substrates: Technology issues and MOVPE growth aspects

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 10-11 2005
    M. Traversa
    Abstract The metalorganic vapour phase epitaxy of ZnTe on single crystal (100)ZnTe:P wafers is reported. The technological steps to prepare a substrate surface suitable for the high quality homoepitaxy of ZnTe are identified and optimised in terms of structural and morphological properties of overgrown epilayers. Removal of ,7 m of material from the ZnTe:P wafers by chemical etching in 1% Br2 -methanol solution proved necessary to achieve a sufficiently smooth and homogeneous surface; in-situ H2 heat treatment of the wafers at 350C immediately before growth ensures optimal desorption of residual oxides, allowing epilayer crystalline quality comparable to the substrate. However, the structure of epilayers degrades for growth temperatures (TG) above 350 C due to the occurrence of stacking faults (SFs) within ,200-300 nm from the epilayer-substrate interface. Accordingly, the epilayer band-edge luminescence vanishes below 350 nm, indicating a worsening of the material radiative efficiency in very thin epilayers. The epilayer surface morphology is the result of a complex interplay between SF nucleation and Te:Zn ad-atom stoichiometry during growth. Almost featureless morphologies are obtained for growth at 350 C, i.e. under nearly stoichiometric surface conditions. Pyramid-like hillocks develop instead for TG , 360 C, corresponding to Te-rich surface conditions, their density rapidly increasing up to around 9 106 cm,2 at TG = 400 C. Hillocks occur in close pairs on the epilayer surface, their nucleation being strongly reduced if a thin ZnTe buffer layer is grown at low (325 C) temperature, i.e. if SFs do not occur at the epilayer-substrate interface. This demonstrates that hillocks form as a result of three-dimensional growth around partial dislocations pairs bounding SFs, the phenomenon being driven by Te ad-atoms experiencing a Schwoebel potential barrier at the surface step edges around the dislocations. ( 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Fabrication and Electrochemical Properties of Epitaxial Samarium-Doped Ceria Films on SrTiO3 -Buffered MgO Substrates

    ADVANCED FUNCTIONAL MATERIALS, Issue 11 2009
    Simone Sanna
    Abstract Thin films of samarium-oxide-doped (20,mol%) ceria (SDC) are grown by pulsed-laser deposition (PLD) on (001) MgO single-crystal substrates. SrTiO3 (STO) prepared by PLD is used as a buffer layer on the MgO substrates to enable epitaxial growth of the fluorite-structured SDC film; the STO layer provides a proper crystalline match between SDC and MgO, resulting in highly crystalline, epitaxial SDC films grown in the (001) orientation. Film conductivity is evaluated by electrochemical impedance spectroscopy measurements, which are performed at various temperatures (400,775,C) in a wide range of oxygen partial pressure (pO2) values (10,25,1,atm) in order to separate ionic and electronic conductivity contributions. At 700,C, SDC/STO films on (100) MgO exhibit a dominant ionic conductivity of about 7,,10,2,S cm,1, down to pO2 values of about 10,15,atm. The absence of grain boundaries make the SDC/STO/MgO heterostructures stable to oxidation-reduction cycles at high temperatures, in contrast to that observed for the more disordered SDC/STO films, which degraded after hydrogen exposure. [source]


    Interface Modification to Improve Hole-Injection Properties in Organic Electronic Devices,

    ADVANCED FUNCTIONAL MATERIALS, Issue 8 2006
    A. Choulis
    Abstract The performance of organic electronic devices is often limited by injection. In this paper, improvement of hole injection in organic electronic devices by conditioning of the interface between the hole-conducting layer (buffer layer) and the active organic semiconductor layer is demonstrated. The conditioning is performed by spin-coating poly(9,9-dioctyl-fluorene- co - N - (4-butylphenyl)-diphenylamine) (TFB) on top of the poly(3,4-ethylene dioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) buffer layer, followed by an organic solvent wash, which results in a TFB residue on the surface of the PEDOT:PSS. Changes in the hole-injection energy barriers, bulk charge-transport properties, and current,voltage characteristics observed in a representative PFO-based (PFO: poly(9,9-dioctylfluorene)) diode suggest that conditioning of PEDOT:PSS surface with TFB creates a stepped electronic profile that dramatically improves the hole-injection properties of organic electronic devices. [source]


    Long-Lifetime Polymer Light-Emitting Electrochemical Cells Fabricated with Crosslinked Hole-Transport Layers

    ADVANCED MATERIALS, Issue 19 2009
    Yan Shao
    By inserting a crosslinkable hole-transport layer as the buffer layer between the single-phase polymer active layer and the anode of this new type of polymer light-emitting electrochemical cells (PLECs), the interface properties are improved and the PLECs can be operated with enhanced stability. [source]


    Octree-based reasonable-quality hexahedral mesh generation using a new set of refinement templates

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 13 2009
    Yasushi Ito
    Abstract An octree-based mesh generation method is proposed to create reasonable-quality, geometry-adapted unstructured hexahedral meshes automatically from triangulated surface models without any sharp geometrical features. A new, easy-to-implement, easy-to-understand set of refinement templates is developed to perform local mesh refinement efficiently even for concave refinement domains without creating hanging nodes. A buffer layer is inserted on an octree core mesh to improve the mesh quality significantly. Laplacian-like smoothing, angle-based smoothing and local optimization-based untangling methods are used with certain restrictions to further improve the mesh quality. Several examples are shown to demonstrate the capability of our hexahedral mesh generation method for complex geometries. Copyright 2008 John Wiley & Sons, Ltd. [source]


    Transparent Inverted Organic Light-Emitting Diodes with a Tungsten Oxide Buffer Layer,

    ADVANCED MATERIALS, Issue 20 2008
    Jens Meyer
    Highly efficient transparent OLEDs are demonstrated. A novel WO3 buffer layer protects the organics during the sputter deposition of the top ITO electrode. L,J,V and SIMS analysis yield optimized devices with a 60,nm thick WO3 layer. Very high efficiencies of 38 cdA,1 and 30 lm W,1 at 100,cd m,2 are obtained. At the same time the transmittance throughout the visible part of the spectrum exceeds 75%. [source]


    Analysis of the near-wall behaviour of some self-adaptive subgrid-scale models in finite-differenced simulations of channel flow

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10 2002
    P. Sagaut
    Abstract Self-adaptive subgrid-scale models are proposed and assessed. They are based on the use of the Germano,Lilly dynamic procedure and the use of a selection function. These models, which do not incorporate any information related to the location of the solid walls, are well suited for the simulation of turbulent flows in complex geometries. Their reliability, when used together with a second-order non-dissipative numerical method, is assessed on the plane channel configuration for two values of the Reynolds number (Re, = 180 and 395) for two grid resolutions. The selection function approach for deriving self-adaptive subgrid models is found to yield results very similar to those obtained using a dynamic model, without requiring any numerical stabilization procedure. The use of the selection function is shown to be the only one which is able to capture the backscatter process in the buffer layer, while producing a strictly positive subgrid viscosity. This is demonstrated to be linked to the capability of the selection function to permit a decorrelation between the mean strain and the fluctuations of the subgrid stresses. That point is illustrated thanks to the introduction of a new decomposition of the fluctuating strain subgrid dissipation. Copyright 2002 John Wiley & Sons, Ltd. [source]


    High Tunability of Highly (100)-Oriented Lead Zirconate Titanium Thin Films

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2008
    Jiagang Wu
    Highly (100)-oriented Pb(Zr0.20Ti0.80)O3 (PZT) thin films for electrically tunable applications were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by RF magnetron sputtering with a PbOx buffer layer. The dielectric properties of PZT films were investigated. These results indicated that the applied electric field and measured frequency strongly affected the films' tunability. The PZT films exhibited good dielectric tunability (69.3%) as measured at 1 kHz and 18 V. The related physics mechanism for enhanced tunability was also discussed. The enhanced tunability is attributed to the (100) orientation of PZT films and is a result of the biaxial tensile stress making the polar axis oriented in plane. [source]


    Surface morphology of highly mismatched InSb films grown on GaAs substrates by molecular beam epitaxy

    PHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 2 2007
    Min Xiong
    Abstract InSb films on GaAs(001) substrates with and without GaAs buffer layer have been grown by molecular beam epitaxy. Rather than surface undulations, aligned ripples and pyramidal hillocks along the orthogonal ,110, directions were observed on the surface of InSb films. Both the preferential growth and the termination of ripples were proved to be related to strain-driven mass transport. A model was proposed to elucidate the formation of the hillocks, which are more efficient to relax strain than ripples. Due to the strain relaxation through hillocks with small bases predominantly, the surfaces of the InSb films grown without a GaAs buffer layer are smoother than those of films grown with a GaAs buffer layer. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Optimization of homoepitaxially grown AlGaN/GaN heterostructures

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2010
    J. A. Grenko
    Abstract We report on the growth of Al0.25Ga0.75N/GaN heterostructures on low dislocation density semi-insulating c -axis GaN substrates by metalorganic vapor phase epitaxy (MOVPE). A room temperature (RT) Hall mobility (RT) up to 2065,cm2,V,1,s,1 at sheet density (ns) of 8.25,,1012,cm,2 has been measured. This work compliments prior studies in which we observed a buffer-induced modulation of the RT two-dimensional electron gas (2DEG) ns and RT by varying the GaN buffer layer thickness. Here, we focus on the optimization of the heterostructure 2DEG properties by elimination of silicon doping in the Al0.25Ga0.75N barrier and unintentional Al in the not-intentionally doped (n.i.d.) GaN buffer layer. The 15% improvement in RT and ns relative to previous results is consistent with those predicted by Poisson solver calculations. Use of thick GaN buffers has minimized the theoretical mobility reduction based on intersubband scattering and has enabled us to determine the 2DEG sheet density associated with the polarization field () to be ,5,,1012,cm,2. [source]


    Electrochemical preparation of MoO3 buffer layer deposited onto the anode in organic solar cells

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2010
    M. Gacitua
    Abstract In this work the authors have studied the advantages of using electrochemically deposited molybdenum oxide as a buffer layer in an organic bilayer heterojunction solar cell arrangement. Furthermore, it has been probed that electrochemistry provides an alternative low cost, reproducible and less laborious method to prepare thin layered deposits. The precursor solution is composed by a concentrated molybdic acid solution in a sulphuric media in order to ensure the obtainment of low reduced molybdenum species. Therefore, by means of potentiostatic techniques, ITO/molybdenum oxide transparent anodes were tested for the photovoltaic device showing improved surface properties. XDR and AFM techniques were used to characterize the morphology of the deposits. The films with optimum thickness (5,nm) are amorphous. XPS analysis indicates that the best results in solar cell performance are in hand with a heterogeneous composition of the molybdenum oxide film presenting MoV and MoVI as predominant species. The MoO3 films deposited by cyclic voltammetry are not as homogeneous as those deposited by potentiostatic technique and only MoVI species are present. These differences may justify the different behaviour of the solar cells using these different buffer layers. Only buffer layers deposited by potentiostatic technique allow improving the cells performances in the same way than those achieved by evaporation. [source]


    Characterization of deep levels at GaAs/GaAs and GaAs/InAs interfaces grown by MBE-interrupted growth technique

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2007
    M. Kaniewska
    Abstract In order to find the origin of crystalline defects occurring in the preparation of InAs/GaAs quantum dots (QDs), their appearance was tracked through three different sample types designed as Schottky diodes. Specimens with a GaAs cap layer on a GaAs buffer layer as well as with an InAs wetting layer without QDs were grown by molecular beam epitaxy (MBE) using the interrupted growth technique. Deep level transient spectroscopy (DLTS) was used for comparison with structures containing InAs QDs. It was found that two main levels with thermal activation energies of 0.14,0.16 eV and 0.46,0.52 eV from the conduction band edge, respectively, are grown-in defects, which are characteristic of the growth interrupted interface occuring under an excess of As. Both these levels together with an additional level at 0.10,0.12 eV found in the InAs wetting layer structures were also present in those with QDs, probably resulting from strain or In penetration. All three defects were agglomerated close to the interface created by the interrupted growth. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    340,350 nm GaN-free UV-LEDs

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003
    T. Nishida
    Abstract Light extraction from AlGaN-based ultraviolet light emitting diodes (UV-LEDs) is described. The device structure is free from a GaN binary layer for the suppression of the reabsorption of the UV emission in the GaN layer. The UV extraction becomes six times higher when compared with that of the normal structure consisting of a GaN buffer layer. The highest external quantum efficiencies of 350- and 340-nm LEDs are 2.2 and 1.7%, respectively. The maximum output powers are 8.6 and 5.5 mW at injection currents of less than 150 mA. We also investigated the potential of combining the 350-nm UV-LED with a mixture of plural fluorescence materials for the application field of lighting. This combination can provide ideal lighting equipment that offers high colour rendering, steady colour, and no glare even with changes of intensity and illumination angle. ( 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Growth of GaN quantum dots on nonpolar A -plane SiC by molecular-beam epitaxy

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2006
    S. Founta
    Abstract We report on A -plane GaN quantum dots in AlN, grown on A -plane 6H SiC substrates by plasma-assisted molecular-beam epitaxy. AFM imaging revealed a strong alignment of the dots along the [100] direction that we correlated with the anisotropic morphology of the AlN buffer layer. A vertical correlation of these dots was evidenced by high resolution transmission electron microscopy on superlattice samples with an AlN spacer thickness of 5 nm. Time-resolved spectroscopy performed on both C -plane and A -plane samples revealed much shorter radiative lifetimes for the A -plane dots, indicating a strong reduction of the internal electric field with respect to the one present in their C -plane counterparts. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Buffer-trap and surface-state effects on gate lag in AlGaN/GaN HEMTs

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010
    Kazushige Horio
    Abstract Two-dimensional simulation of turn-on characteristics of Al-GaN/GaN HEMTs is performed in which both buffer traps and surface states are considered. It is studied how the so-called gate lag is affected by these factors. It is shown that gate lag due to buffer traps can occur because in the off state where the gate voltage is negative, electrons are injected into the buffer layer and captured by the traps, leading to more negatively charged buffer layer. It is also shown that gate lag due to an electron-trap-type surface state can occur only when electron's gate tunneling is considered ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Structural and optical characterization of (11-22) semipolar GaN on m -plane sapphire without low temperature buffer layer

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010
    Sung-Nam Lee
    Abstract We reported the high quality semipolar (11-22) GaN grown on m-sapphire by using the novel two-step growth method without low temperature GaN or AlN buffer layer. It is found that macroscopic surface morphology of semipolar GaN epilayer was very smooth, while microscopic surface structure was arrowhead-like surface structure toward the direction of [1-21-1]. Anisotropic crystal properties of semipolar GaN/m-sapphire were also observed by two incident directions of X-ray beam. Therefore, we suggested that the anisotropic crystal properties and arrow-head like surface structure would be caused by heteroepitaxial crystallograhpic difference between semipolar GaN and m-sapphire. Additionally, photoluminescence (PL) measurements showed the strong bandedge emission of n-type semipolar GaN without yellow luminescence ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Monolithically integrated UV/IR-photodetectors based on an AlN/GaN-based superlattice grown on an AlGaN buffer layer

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
    Daniel Hofstetter
    Abstract In this article, we demonstrate closely spaced, monolithically integrated photodetectors in two largely different wavelength ranges. The epitaxial structure of the devices was grown by plasma-assisted molecular-beam epitaxy on an AlN-on-sapphire template; it consists of a Si-doped AlGaN thin film, and a nearly strain compensated 40 period AlN/GaN superlattice with 1.0 nm thick GaN quantum wells and 2.0 nm thick AlN barriers. The entire structure is covered with an AlGaN cap layer. The superlattice acts as active region for the infrared detector, while the AlGaN buffer layer serves as active area for the ultraviolet detector. While the photovoltaic near-infrared detector has a center wavelength of 1.37 ,m, the photoconductive ultraviolet detector has a long wavelength cutoff at 250 nm. The two detectors could be operated up to room temperature with reasonable sensitivities. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Off-state breakdown in InAlN/AlN/GaN high electron mobility transistors

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
    J. Kuzmik
    Abstract Unpassivated InAlN/AlN/GaN high electron mobility transistors off-state breakdown is analyzed for different gate-to-drain distances. The breakdown voltage linearly increases with the gate to drain distance reaching 350 V for a 10 ,m contact separation; the sub-threshold leakage current is < 10,5 A/mm. Similar breakdown voltages and leakage current are obtained on GaN buffer for two Ohmic contacts if their distance is the same. It is suggested that the breakdown is governed by injection/avalanche processes in the GaN buffer layer and is basically not affected by InAlN barrier. Our conclusions are further supported by measuring all currents in the three-terminal configuration of the transistors before and during the breakdown and by using a drain current injection technique. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Reduction of buffer-related current collapse in field-plate AlGaN/GaN HEMTs

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
    Atsushi Nakajima
    Abstract Two-dimensional transient analyses of field-plate AlGaN/GaN HEMTs are performed in which a deep donor and a deep acceptor are considered in a semi-insulating buffer layer, and quasi-pulsed current-voltage curves are derived from them. It is studied how the existence of field plate affects buffer-related drain lag, gate lag and current collapse. It is shown that the drain lag is reduced by introducing a field plate, because electron injection into the buffer layer is weakened by it, and the trapping effects are reduced. It is also shown that the current collapse and gate lag are reduced in the field-plate structure. The dependence on SiN passivation layer thickness is also studied, suggesting that there is an optimum thickness of SiN layer to minimize the buffer-related current collapse and drain lag in AlGaN/GaN HEMTs. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    High power AlGaN/GaN HFETs on 4 inch Si substrates

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
    Nariaki Ikeda
    Abstract In this paper, we successfully demonstrate an AlGaN/GaN HFET with a high breakdown voltage on 4-inch Si substrates. In order to obtain the high breakdown voltage and to improve the crystalline quality of GaN layers, a thick GaN epitaxial layer including a buffer layer was grown. The breakdown voltage and the maximum drain current were achieved to be over 1.3 kV and 120 A, respectively. Furthermore, the suppression of a current collapse phenomenon was examined. The on-resistance was not significantly increased up to a high drain off-bias-stress of 900 V. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Photoluminescence and time-resolved photoluminescence in Cu(In,Ga)Se2 thin films and solar cells

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2009
    Sho Shirakata
    Abstract Photoluminescence (PL) and time-resolved PL (TR-PL) studies have been carried out on Cu(In,Ga)Se2 (CIGS) thin films and solar cells (ZnO/CdS/CIGS) to study the recombination of the photo-excited carriers. The CIGS solar cells exhibited intense near-band-edge (NBE) PL compared with the CIGS films by two orders of magnitude. PL decay time of the cell is strongly dependent on the repetition frequency of the excitation light. PL decay time of the cell is longer than that of the corresponding CIGS thin film. The chemical bath deposition of the CdS buffer layer on CIGS leads to changes in PL intensity, defect-related PL and the PL decay time. They are discussed with relation to the substitution of Cd atom at the Cu site at the Cu-deficient surface of CIGS thin film. Under the open circuit condition, NBE-PL is stronger and the decay time is longer compared with those under the short circuit condition. PL of the cell under the load was examined, and PL intensity and PL decay time are related to the photovoltage during PL measurements. Low temperature PL suggests that the Cd diffusion during the CBD process is pronounced for low Ga content CIGS. The authors demonstrate the effectiveness of PL as a powerful non-destructive device and photovoltaic characterization methods of CIGS solar cells. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Possible anomalous Hall effect of Be/Si pair delta-doped GaAs structures

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2008
    J. P. Noh
    Abstract Beryllium/Silicon pair delta-doped GaAs structures grown by molecular-beam epitaxy exhibit Hall resistance which has highly nonlinear dependence on the applied magnetic field. The dependence of the occurrence of the nonlinear Hall resistance on the sample structure is investigated. A significantly large increase in the non-linearity and magnitude of the Hall resistance is observed from a sample structure whose buffer layer is grown under the low As flux and thick buffer layer condition. The non-linearity of the Hall resistance is found to depend on a single parameter B /T, where B and T are the magnetic field and temperature, respectively. From another sample structure in which an AlGaAs barrier with a single Be delta-doped layer is placed near the Be/Si pair delta-doped layer, a similar nonlinear Hall resistance is observed. On the basis of these results, it is suggested that the anomalous Hall effect results from interplay between itinerant holes in the valence band and localized spins in the delta-doped layer in these structures. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Trap states in n-GaN grown on AlN/sapphire template by MOVPE

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2008
    T. Ito
    Abstract Using epitaxial AlN/sapphire templates, high crystalline quality GaN films are grown on them by metal organic chemical vapour deposition. The electron traps behaviour of these GaN films were observed by deep level transient spectroscopy (DLTS). Four distinct trap levels were ob-served in both n-GaN grown on AlN/sapphire template and on conventional low temperature buffer layer (LT-BL)/sapphire. The magnitude the of the DLTS signal E1 and E2 were almost same. It suggests that E1 is not only associate with dislocation density but also other defect. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Properties of Ga2O3 -based (Inx Ga1,x)2O3 alloy thin films grown by molecular beam epitaxy

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2008
    Takayoshi Oshima
    Abstract A series of Ga2O3 -based (Inx Ga1,x)2O3 alloy thin films have been grown on c-plane sapphire substrates with a thin Ga2O3 buffer layer by plasma-assisted molecular beam epitaxy. At growth temperatures of 700 C and higher, even with a slight inclusion of In2O3 to Ga2O3, for example, the film of (In0.08Ga0.92)2O3, exhibited a rough surface and degraded transmission spectrum resulting from phase separation of In2O3. Due to low temperature growth at 600 C, however, the phase separation was suppressed for the In composition up to 35%, which was confirmed by X-ray diffraction measurement, and the films exhibited high transmittance over 85% with sharp absorption edges. The bandgap could be tuned form 5.0 to 4.0 eV. The results encourage the application of (Inx Ga1,x)2O3 thin films in short-wavelength optical devices. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    PI3D processing of DLC coatings for different applications

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2008
    S. A. Nikiforov
    Abstract DLC (a -C:H) and Si-DLC coatings have been deposited on various materials (steel, aluminium, silicon, glass, polymers) using a 1-m3 interior-antenna ICP PI3D facility with HMDSO and toluene as precursors. For conformal treatment of 3-D workpiececs, a low-voltage (0.5 - 1) kV, high repetition rate (up to 70 kHz) pulsing was applied. However, DLC formation on dielectric substrates was performed at higher (2 - 10) kV voltage using short (1 - 1.5) ,s pulses to minimize surface charging. Coating adhesion was achieved by formation of multi layer structure comprising Si-containing buffer layer, transient layer, DLC layer with gradually increasing hardness, and top hard DLC. Film hardness was (5 - 20) GPa, and the deposition rate (4 - 0.5) ,m/h. DLC surface roughness was (0.7 - 60) nm and water contact angle 70 - 110 depending on process parameters which implies various applications. Batch processing of sliding parts, cutting tools, glass moulds was performed. Double-side DLC coating on polymer web eliminated its rolling up due to the coating stress. With novel ICP antenna the DLC processing is promising for large-scale nano pattern transfer technology. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Low on-resistance of GaN p-i-n vertical conducting diodes grown on 4H-SiC substrates

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007
    Atsushi Nishikawa
    Abstract We investigated the resistance of conductive AlGaN buffer layers and the current-voltage characteristics of GaN p-i-n vertical conducting diodes on n -type 4H-SiC substrates grown by low-pressure metalorganic vapor-phase epitaxy. High Si doping of the AlGaN buffer layer at the AlGaN/SiC interface produces ohmic current-voltage characteristics in spite of the large band offset between AlGaN and 4H-SiC. Owing to the optimization of the AlGaN buffer layer, a low on-resistance (Ron) of 1.12 m, cm2 with high breakdown voltage (VB) of 300 V is obtained for a GaN p-i-n vertical conducting diode on a 4H-SiC substrate, leading to the figure of merit (VB2/Ron) of 80 MW/cm2, which is larger than that for the diode with the same structure on a 6H-SiC substrate (62 MW/cm2). This result indicates that 4H-SiC is preferable for fabricating GaN-based electronic devices with a low on-resistance and high breakdown voltage. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]