Kinds Of Buffer Layers Research Articles

Ultrathin buffer layer at organic/organic interface for managing the recombination profile in organic light‐emitting diodes: Metal versus dielectric buffer

ABSTRACTWe report on the utilization of an ultrathin buffer layer at the organic/organic (O/O) interface to enhance device efficiency in organic light‐emitting diodes. Two different kinds of buffer layers are examined: metal and dielectric. It is shown that employment of an ultrathin Ag layer with a thickness of 1–2 nm enhances the device performance, while a MgF2 dielectric buffer cannot affect the device properties considerably. In particular, the turn‐on voltage of the device with an appropriate buffer layer is reduced about 3 V, its current efficiency increases by a factor of more than three, and the power efficiency increases by a factor of more than five in comparison to the control device when a Ag buffer layer is introduced at the O/O interface. By employment of the buffer layer at the interface, an accumulation of current carriers appears within the device that redistribute the recombination profile toward the interior part of the emissive layer. Also, morphological examinations reveal that distinguishable phase segregation occurs in the blend of the hole‐transport layer. In particular, the polymer component remains at the surface and facilitates the hole transport into the successive layers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43894.

Photovoltaic Properties of Solar Cells Based on Poly(methyl phenyl silane) and C60

Photovoltaic (PV) devices using blend films of poly(methyl phenyl silane) (PMPS) and fullerene (C60) are fabricated, and the effects of various technical parameters during device fabrication on the PV characteristics under AM 1.5G simulated solar light illumination of 100 mW/cm2 intensity are investigated. The PV performance of the devices depends on the mixing ratio of PMPS:C60, the kind of buffer layer, the thickness of the buffer layer, and the thermal annealing temperature of the devices. The devices optimized for the mixing ratio, kind of buffer layer, and thermal annealing temperature exhibit a short-circuit current density (JSC) of 2.26 mA/cm2, an open circuit voltage (VOC) of 0.71 V, a fill factor (FF) of 0.35, and a power conversion efficiency (PCE) of 0.57%.

High indium content InGaAs photodetector: with InGaAs or InAlAs graded buffer layers

High indium content In0.78Ga0.22As photodetector structures have been grown on InP substrates with InxGa1-xAs or InxAl1-xAs graded buffer layers wherein x changed continuously by gas source molecular beam epitaxy.Their characteristics were investigated by atomic force microscope,x-ray diffraction,transmission electron microscopy and photoluminescence.The differences between samples with the two kinds of buffer layers were studied.Results show that moderate surface morphology can be obtained with either InxGa1-xAs or InxAl1-xAs buffer layers.Larger residual strain is present in the photodetector structure with InxGa1-xAs buffer layer.On the other hand,superior optical characteristics have been observed for the photodetector structure with InxAl1-xAs buffer layer.

Crystallization of sputtered amorphous silicon induced by silver–copper alloy with high crystalline volumeratio

Silver–copper alloy-induced crystallization of sputtered a-Si has been studied. In this alloy, Cu acts as a catalyst to accelerate the crystallization, while Ag acts as a new kind of buffer layer, different from Al 2O 3 and Si 3N 4, to obtain well-crystallized poly-Si films with short annealing time and free of post-treatment for ohmic contact. When the Cu content is limited to below 30%, Ag can effectively slow down the diffusion of Cu into Si and decrease the Cu–silicide nuclei density to improve the crystalline volume ratio from 80% to over 90%. A 1:4 ratio of Cu to Ag yields the best result. The crystalline volume ratio and Hall mobility reach nearly 100% and 29.4 cm 2/V s, respectively. This high quality poly-Si film demonstrates a promising application in solarcells.

Performance analysis of copper–indium–gallium–diselenide (CIGS) solar cells with various buffer layers by SCAPS

In copper–indium–gallium–diselenide (CIGS) based solar cells, various replacements for conventional cadmium sulfide (CdS) buffer layer, such as ZnO, ZnS (O,OH), ZnSe, InS and Zn 1− x Mg x O based buffer layers have been studied by solar cell capacitance simulator (SCAPS) in terms of layer thickness, absorber layer band gap and operating temperature to find out the optimum choice. An efficiency of 21.32% (with Voc of 0.78 V, Jsc of 33.5 mA/cm 2 and fill factor of 0.82) has been achieved with CdS based buffer layer as the reference case. It is also found that the high efficiency CIGS cells have the absorber thickness between 2 μm and 3 μm. It is also revealed that the optimum thickness of buffer layer is within the range of 40–50 nm. From the study with different kinds of buffer layers, cells with ZnO buffer layer produce the best efficiency of 21.16% among others. However, the ZnO buffer layer based cells show a temperature gradient of −0.32%/K, whereas ZnS and ZnSe buffer layer based cells show −0.27%/K proving it much stable in higher operating temperature. All these simulation results give some important indication to lead to higher efficiency of CIGS solar cells for feasible fabrication.

MOVPE growth of InN buffer layers on sapphire

We report on the MOCVD growth of InN buffer layers on sapphire substrate for InN growth. The approach used assumes that an optimized InN buffer layer has to exhibit at least the same crystalline quality and sapphire surface coverage than the GaN buffer layers allowing to grow high crystalline quality GaN on sapphire. The buffer layers were characterized by AFM and GID measurements. Sapphire nitridation was investigated: it has a strong influence on in-plane crystalline quality. Two kinds of buffer layers were optimized according to the GaN buffer layer specifications: one of them only presented In droplets at its surface. It was shown that the small amount of In droplets increases the adatoms mobility of the main layer overgrown, leading to a 25% decrease of its in-plane mosaicity, compared to InN films directly grown on sapphire. To achieve a same improvement on InN buffer layer free of In droplets, the InN main layer growth temperature had to be increased from 550 °C. to 600 °C.

CHEMICAL SOLUTION DEPOSITION AND ELECTRICAL PROPERTIES OF (100)-PREDOMINANT BaTiO3 THICKER FILMS

ABSTRACT Lead-free piezoelectric films with thickness larger than 1 μm integrated on silicon substrate have been receiving considerable attention for environmental concern and potential applications in micro-electro-mechanical systems. By chemical solution deposition, it is possible to process (100)-predominant 1 μm BaTiO3 films on LaNiO3/Pt/TiO x /SiO2/Si substrates by using the same thinner high crystallinity columnar films as buffer layers. We point out that this kind of buffer layer on the surface of LaNiO3/Pt electrode is effective to enhance the crystallinity and orientation degree of the BaTiO3 films. The 1 μm BaTiO3 films showed good dielectric and insulative characteristic against applied field. Also, the (100)-predominant 1 μm BaTiO3 films have excellent piezoelectric properties, piezoelectric coefficients d 33 higher than 50 pm/V have been detected by the atomic force microscope on the bare films, which is comparable to that of Pb(Zr,Ti)O3 films. These results indicate that the highly (100)-oriented BaTiO3should be a promising candidate as the lead-free piezoelectric films for micro-electro-mechanical systems applications.

Misfit Dislocations in SiGe/Si Heterostructures: Nucleation - Propagation - Multiplication

We present experimental data on the effect of low-temperature buffer layers on the dislocation structure formation in SiGe/Si strained-layer heterostructures under thermal annealing. Specific subjects include mechanisms of misfit dislocation nucleation, propagation and multiplication as well as the role of intrinsic point defects in these processes. Samples with lowtemperature Si (400°C) and SiGe (250°C) buffer layers were grown by MBE. In general, the processes of MD generation occur similarly in the heterostructures studied independently of the alloy composition (Ge content: 0.15, 0.30) and kind of buffer layer. Intrinsic point defects related to the low-temperature epitaxial growth influence mainly the rate of misfit dislocation nucleation.

Thermally induced strain relaxation in SiGe/Si heterostructures with low‐temperature buffer layers

Processes of misfit dislocation (MD) nucleation and multiplication in SiGe/Si strained-layer heterostructures under thermal annealing were studied. Specific subjects include the kinetics of dislocation network formation in heterostructures with low-temperature (LT) buffer layers and mechanisms of dislocation nucleation. Samples with LT-Si (400 oC) and LT-SiGe (250 oC) buffer layers were grown by MBE. In general, the processes of MD generation occur similarly in the heterostructures studied independently of the alloy composition (Ge content: 0.15, 0.30) and kind of buffer layer. Intrinsic point defects related to the LT epitaxial growth influence mainly the rate of MD nucleation. We suggest a new mechanism of MD generation which includes a nucleation of incipient dislocation loops at heterogeneous sources within SiGe epitaxial layer and formation of spiral sources at threading V-shaped dislocation half-loops. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Epitaxial growth of europium on (1 1 0)Nb and (0 0 0 1)Y

A detailed structural analysis of the epitaxial growth of europium using in situ reflection high-energy electron diffraction has been performed for two kinds of buffer layers with different symmetry: (1 1 0)niobium (Nb) and (0 0 0 1)yttrium (Y). Moreover, by varying the preparation conditions of the (1 1 0)Nb layer we get either a reconstructed or an unreconstructed Nb surface, which turns out to have a strong influence on the Eu growth: the reconstructed (1 1 0)Nb surface favours the stabilisation of an Eu hexagonal surface structure, as well as the (0 0 0 1)Y buffer, whereas a pure unreconstructed (1 1 0)Nb surface enables the growth of single crystalline bcc (1 1 0)Eu films. With increasing Eu thickness, the relaxation of the metastable Eu hexagonal surface obtained on (0 0 0 1)Y or on reconstructed (1 1 0)Nb gives rise to a multidomain structure that drastically depends on the nature of the underlying buffer layer.

A simple and new 45° homo-biepitaxial Y 1Ba 2Cu 3O y junction on yttrium-stabilized zirconia substrates

We have developed a new bi-epitaxial structure, namely YBCO (780°C)/YBCO (600°C)/YSZ (in-plane rotation 45°) and YBCO (780°C)/YSZ (in-plane rotation 0°) boundary. In comparison to the YBCO/CeO 2/YSZ/MgO (in-plane rotation 45°) and YBCO/MgO (in-plane rotation 0°) boundary previously developed in our laboratory, the new preparation is much simpler and has many advantages. For one, this method avoids the difficulty of lattice mismatch between the pure YBCO film and the MgO substrate. A clean 45° rotation can be achieved without growing different kinds of buffer layers. Furthermore, the first YBCO layer can be used as an endpoint indication during dry etching for device fabrication. Most importantly, the I–V curves taken at low temperatures show the RSJ behavior, with a high J C value (∼10 5 A/cm 2) and I C R N product (∼1 mV) at 4.2 K.

Epitaxial-strain-stabilized ordering inAu1−xNixalloy thin films grown by MBE

The influence of the epitaxial strain on the structural evolution with temperature of AuNi metastable alloys thin films is investigated. Samples with different initial configurations (codeposited ${\mathrm{Au}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}$ solid solutions and artificially layered structures) were grown by molecular-beam epitaxy on different (001)-oriented buffer layers (Au, Pt, and Pd). The epitaxial strain was varied by changing (i) the Ni content of the AuNi layer for a given kind of buffer layer, (ii) the nature of the buffer layer for a fixed Ni content, and (iii) the AuNi layer thickness for a fixed Ni content and buffer layer. The structural evolution upon annealing in the 180--300 \ifmmode^\circ\else\textdegree\fi{}C temperature range was studied by in situ temperature x-ray diffraction as well as high-resolution electron microscopy. It is shown that a modulated structure develops along the growth direction of the AuNi layer, when the temperature reaches 200--240 \ifmmode^\circ\else\textdegree\fi{}C, provided that the residual strain is high enough (>2%). This structure consists of a periodic stacking of 1 Ni-rich plane and 2 or 3 Au-rich planes, depending on the Ni content. The results are explained in terms of a strain-stabilized ordering effect, as supported by energetic calculations based on semiempirical interatomic potentials within the tight-binding scheme.

A study of initial growth mechanism of c-GaN on GaAs(1 0 0) by molecular beam epitaxy

The surface morphology of several kinds of buffer layers, nitrided GaAs(100), low-temperature GaN, GaAs buffer layer, and GaAlAs buffer layer, is investigated for growing c-GaN using GaAs(100) by molecular beam epitaxy. The possibility of an epitaxial GaAlAs buffer layer for growing high-quality c-GaN on GaAs(100) is considered. A c-GaN film with a few h-GaN imperfections is successfully grown on a GaAs buffer layer, and the occurrence of h-GaN is drastically reduced by introducing an epitaxial GaAs buffer layer.

Evaluation of buffer layers for hot filament chemical vapor deposition diamond films on silicon substrates

Deposition of high-quality diamond films on technology important substrates such as semiconductor silicon is a difficult problem due to inherent interdiffusion problems between substrates and diamond overlayers. To overcome this difficulty the concept of the buffer layer has been utilized and good quality diamond films have been deposited on Si (100) substrates with different kinds of buffer layers. Aluminum nitride (AlN), titanium nitride (TiN), carbon nitride (CN x), and tungsten carbide (WC) as buffer layers have been studied for diamond nucleation enhancement. Scratching the silicon substrate surface with a diamond paste has also been investigated for diamond nucleation enhancement on Si (100) substrates. The deposited diamond films have been characterized with Raman spectroscopy, and scanning electronic microscopy (SEM) techniques. This study shows that the use of a buffer layer is very effective in enhancing the nucleation rate of diamond films. Finite-volume based computational fluid dynamics has been used to model flow, transport, gas-phase, and surface chemical reactions.

Structural and hardness studies of CN X /TiN composite coatings on Si (100) substrates by laser ablation method

CN x /TiN composite coatings were deposited on Si (100) substrates using the pulsed laser deposition (PLD) method. Previous results showed that a seed of titanium nitride (TiN) layer between silicon substrates and a top layer of carbon nitride increased the hardness and modulus values of overall composite coatings (Ref 1). This paper describes the same approach to growing carbon nitride composite coatings with varying thicknesses of different kinds of buffer layers and carbon nitride films on Si (100) substrates at different temperatures and pressures. Preliminary results showed the presence of carbon nitride films by the Fourier transform infrared spectroscopy (FTIR) method. The mechanical properties of the films were characterized using the nanoindentation technique. The crystallographic properties of the films were characterized using the x-ray diffractometer method.

Improvement of the crystallinity of a GaAs epitaxial film grown on a Si substrate using a Si/SiGe/Ge buffer layer

Double-crystal X-ray diffraction (DCXD), photoluminescence (PL), and Raman spectroscopy measurements on GaAs/Si heterostructures grown with various kinds of buffer layers by molecular beam epitaxy were performed in order to characterize the crystallinity of the samples. The strain and dislocation density of the GaAs epitaxial layer determined from the DCXD curve for the GaAs/Si/SiGe/Si heterostructure are 3.90×10 −3 and 6.99×10 6 cm] −3, respectively, and the full width at half maximum (FWHM) of the GaAs epitaxial layer for the heterostructures is 405 arcsec. The results of the PL spectrum for GaAs/Si with a Si/SiGe buffer showed that the FWHM of the band-to-band luminescence is only 5.4 meV. The ratio of the peak intensity of the longitudinal optical phonon to that of the transverse optical phonon for GaAs/Si with a Si/SiGe/Ge buffer increased dramatically in comparison with the corresponding rates for the GaAs/Si with Ge and SiGe/Ge buffers. These results indicate that the crystallinity of the GaAs epilayer was remarkably improved using a Si/SiGe/Ge buffer, and a strong binding energy of the SiSi bond in the top Si buffer layer reduced the formation of the dislocation in the GaAs active layer.

Comparative study of amorphous and crystalline buffer layers in MBE growth of GaAs on Si

The crystal quality and the annealing effect of the GaAs buffer layers grown on a (111)Si substrate were studied to find the best growth condition for two-step heteroepitaxial growth of GaAs on Si. Two kinds of buffer layers, one amorphous and the other crystalline, were grown at 100 and 350°C, respectively. The thickness of both kinds of buffer layers were varied from 25 to 200 Å. The difference in annealing behavior was studied by an in-situ RHEED technique. The amorphous buffer layer showed the presence of a much smaller number of plane defects than the crystalline buffer layer. It was found that there is a fundamental difference in the entering process of the dislocation between these two buffer layers. An X-ray diffraction study shows that the optimum thickness of the buffer layer resulting in the best epitaxial growth quality was 50–150 Å.

Light-induced degradation of differently prepared heterojunction in a-SI pin solar cells

The influence of incorporating a buffer layer adjacent to the p-SiC/i-Si heterojunction and of light-induced degradation on the performance of a-Si:H pin solar cells was investigated. For characterization we employ stationary (spectral response) as well as transient (delayed-field time of flight) photocurrent measurements. Out of different kinds of buffer layers a relatively slowly deposited undoped carbon rich layer seems to be best suited. This kind of buffer improves the solar cell performance as well as the electron lifetime at the p/i-junction. However, the introduction of a buffer layer leads to a stronger light degradation. We give evidence that this is primarily due to a lower stability of the p/i-interface and not of the bulk region.