Morphology Of Buffer Layer Research Articles

The Effect of AlN Buffer Layer Morphology on the Structural Quality of a Semipolar GaN Layer Grown on a Si(001) Substrate, According to Transmission Electron Microscopy Data

The Effect of AlN Buffer Layer Morphology on the Structural Quality of a Semipolar GaN Layer Grown on a Si(001) Substrate, According to Transmission Electron Microscopy Data

Определение толщины зародышевого слоя AlN, сформированного на поверхности Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-(0001) в процессе нитридизации, методами РФЭС и ИК-спектроскопии

The effect of different degrees of the sapphire surface nitridation process completion on the AlN buffer layer morphology has been studied. It was found that ~85% completion of the AlN crystalline phase formation promotes the growth of a two dimensional AlN buffer layer with a smooth surface morphology, regardless of the substrate temperature and ammonia flux. In contrast, during the AlN nucleation layer formation as a result of weak or excessive sapphire nitridation, a polycrystalline or three-dimensional AlN structures with a high density of inversion domains, respectively, were formed. Using independent methods of X-ray photoelectron spectroscopy and infrared spectroscopy of surface polaritons, the thickness of the AlN nucleation layer was determined at ~85% degree of the nitridation process completion, which amounted to ~1 monolayer.

The effect of AlN buffer layer morphology on the structural quality of a semipolar GaN layer grown on a Si(001) substrate, according to transmission electron microscopy data

Structural features of the interface between a semipolar gallium nitride layer and buffer layer of aluminum nitride grown on a SiC/Si(001) template misoriented by an angle of 7 were studied by high-resolution transmission electron microscopy. The effect of interface morphology on the structural quality of the gallium nitride layer was revealed: faceted structure of the buffer layer surface reduces the threading dislocations density. Keywords: semipolar GaN, transmission electron microscopy, dislocation, Si(001) substrate

Determination of the AlN nucleation layer thickness formed on the Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-(0001) surface during nitridation process by XPS and IR spectroscopy

The effect of different degrees of the sapphire surface nitridation process completion on the AlN buffer layer morphology has been studied. It was found that ~85% completion of the AlN crystalline phase formation promotes the growth of a two dimensional AlN buffer layer with a smooth surface morphology, regardless of the substrate temperature and ammonia flux. In contrast, during the AlN nucleation layer formation as a result of weak or excessive sapphire nitridation, a polycrystalline or three-dimensional AlN structures with a high density of inversion domains, respectively, were formed. Using independent methods of X-ray photoelectron spectroscopy and infrared spectroscopy of surface polaritons, the thickness of the AlN nucleation layer was determined at ~85% degree of the nitridation process completion, which amounted to ~1 monolayer. Keywords: ammonia molecular beam epitaxy, AlN, sapphire, reflection high-energy electron diffraction, nitridation, inversion domains, X-ray photoelectron spectroscopy, surface polaritons.

Growth of high quality InSb thin films on GaAs substrates by molecular beam epitaxy method with AlInSb/GaSb as compound buffer layers* *Project supported by the National Natural Science Foundation of China (Grant Nos. 61774130, 11474248, 61790581, and 51973070), the Ph. D. Program Foundation of the Ministry of Education of China (Grant No. 20105303120002), and the National Key Technology Research and

A series of InSb thin films were grown on GaAs substrates by molecular beam epitaxy (MBE). GaSb/AlInSb is used as a compound buffer layer to release the strain caused by the lattice mismatch between the substrate and the epitaxial layer, so as to reduce the system defects. At the same time, the influence of different interface structures of AlInSb on the surface morphology of buffer layer is explored. The propagation mechanism of defects with the growth of buffer layer is compared and analyzed. The relationship between the quality of InSb thin films and the structure of buffer layer is summarized. Finally, the growth of high quality InSb thin films is realized.

The facile modification of PEDOT:PSS buffer layer by polyethyleneglycol and their effects on inverted perovskite solar cell

The effect of polyethyleneglycol-200 (PEG-200) post-treatment on common commercial PEDOT:PSS buffer layer for perovskite solar cell has been carefully investigated. Through facile annealing post-treatment of PEG/PEDOT:PSS film at 120 °C for 10 min, the conversion efficiency of the cells can be enhanced 7.5% (11.68% to 12.56%) compared to the traditional inverted perovskite solar cell, with the improvement of both short-circuit current density and fill factor. Our results indicate that the treatment by PEG on PEDOT:PSS film is an effective way to improve perovskite solar cell efficiency. In addition, it reveals that the PEG-200 can greatly enhance not only the conductivity but also improve the buffer layer morphology or PEDOT:PSS polymer chain packing. Furthermore, the devices impedance spectroscopy reveals that the PEG post treatment would decrease Rct drastically, suggesting the improvement of contact interface between PEDOT:PSS and perovskite layer.

Microstructural and optical properties of GaN buffer layers grown on graphene

A conventional two-step growth process is still the state-of-the-art technology for the epitaxy of GaN, even if graphene is used as a substrate. Low-temperature buffer layers play a decisive role in forming a continuous film. In this work, the informative characterization of low-temperature (550 °C) GaN buffer layers grown on graphene by hydride vapor phase epitaxy (HVPE) was performed. High-density and sixfold-symmetry structures of GaN nucleation sites formed the primary morphology of buffer layers. The E2 (high) Raman shift of GaN buffer layers on graphene was 568 cm−1, illustrating that GaN was free of stress. We also captured nonfocusing photoluminescence (PL) spectra and observed the high intensity of near-band-edge emission of wurtzite GaN and the absence of yellow luminescence in the visible band. Thermally induced quantum effects could be found in low-temperature PL. The elementary and detailed characterizations offer referenced values for the growth of GaN films on graphene.

Improving the Brightness and Reliability of InGaN/GaN Near Ultraviolet Light-Emitting Diodes by Controlling the Morphology of the GaN Buffer Layer

A facile method for fabricating near ultraviolet light-emitting diodes (NUV LEDs) with better crystal quality and enhanced light emission is demonstrated by tuning total working pressure to modify the morphology of the buffer layer. With the conditions favoring the transition from 2-D to 3-D island growth in the GaN buffer layer, the crystal quality of the epitaxial GaN film is improved, leading to a decrease in the full-width at half-maximum of the (1 0 2) peak in $X$ -ray rocking curve measurement from 293 (arcsec) to 230 (arcsec). Scanning electron microscopy images imply the morphology of GaN grain boundaries at the buffer stage is different. The transmission electron microscopy analysis shows the edge dislocation can be bended due to the controlled morphology of buffer layer, leading to a better crystal quality of the GaN epitaxial film. Therefore, the reverse current is reduced with the reverse bias of $ - \hbox{40 V}$ . Moreover, the output power in lamp-formed NUV LEDs at a driving current of 20 mA can be enhanced by about 12%.

Influences of annealing temperature and thickness on ZnS buffer layers for inverted hybrid solar cells

In this study, the photovoltaic performances of inverted type hybrid solar cells fabricated using zinc sulfide (ZnS) as a buffer layer and blend of P3HT(poly(3-hexyl)thiophene), PCBM([6,6]-phenylC61 butyric acidmethylester) as a photoactive layer were reported. ZnS thin films were prepared by spray pyrolysis method at fixed substrate temperature. The effects of annealing under ambient conditions at different temperatures on the optical and structure properties of ZnS films were investigated. When the annealing temperatures of ZnS films were increased from 200 to 500°C, the power conversion efficiency of the inverted type hybrid solar cells was significantly enhanced by improving crystallite and morphology of buffer layer. The effect of ZnS film thickness on photovoltaic parameters of the inverted devices was also investigated.

Effects of morphology of buffer layers on ZnO/sapphire heteroepitaxial growth by RF magnetron sputtering

ABSTRACTEffects of surface morphology of buffer layers on ZnO/sapphire heteroepitaxial growth have been investigated by means of “nitrogen mediated crystallization (NMC) method”, where the crystal nucleation and growth are controlled by absorbed nitrogen atoms. We found a strong correlation between the height distribution profile of NMC-ZnO buffer layers and the crystal quality of ZnO films. On the buffer layer with a sharp peak in height distribution, a single-crystalline ZnO film with atomically-flat surface was grown. Our results indicate that homogeneous and high-density nucleation at the initial growth stages is critical in heteroepitaxy of ZnO on lattice mismatched substrates.

The influence of buffer layer coalescence on stress evolution in GaN grown on ion implanted AlN/Si(111) substrates

The effect of AlN buffer layer morphology on the evolution of growth stress in GaN epilayers deposited by metalorganic chemical vapor deposition on N+ ion-implanted AlN/Si(111) substrates was investigated. AlN buffer layers were grown using either a continuous or pulsed source flow process which altered the grain size and extent of coalescence of the films. In situ stress measurements revealed that substrate implantation reduced the initial compressive stress in the GaN epilayers likely due to a decoupling of the AlN lattice from the underlying crystalline Si substrate. The buffer layer morphology was found to significantly alter the influence of ion-implantation on the film properties. GaN epilayers grown on ion-implanted AlN/Si(111) substrates prepared with the pulsed conditions exhibited a 63% decrease in threading dislocation (TD) density compared to unimplanted substrates. In addition, these films were observed to grow under a low overall stress compared to the other samples which exhibited a more typical compressive to tensile stress transition during growth. The low overall growth stress of the GaN grown on the implanted pulsed AlN/Si(111) was explained in terms of a reduced strain gradient from dislocation inclination.

Growth and properties of ZnO films on polymeric substrate by spray pyrolysis method

The growth of ZnO layers deposited by spray pyrolysis on polymeric substrate was studied. Zinc acetate precursor solution was sprayed onto preheated polyimide (PI) and glass reference substrates at 380°C. The structural, morphological, optical and electrical properties of the layers were measured by X-ray diffraction, scanning electron microscopy, optical spectroscopy and van der Pauw and Hall method. ZnO:In layers could be grown on PI when deposited onto undoped ZnO layer acting as a buffer layer on PI. Independent of the substrate type, the ZnO/ZnO:In bilayer showed a mixed morphology from smooth canvas-like surface to large scrolled belt grains dependent on buffer layer morphology. Due to the formation of scrolled belts, the ZnO:In layer shows no preferential orientation, yet the preferred orientation of the ZnO buffer crystallites is (100) plane parallel to the substrate. The bilayers deposited on PI exhibit high light scattering capability (haze factor of 85–95% in the spectral region of 350–1500nm). The resistivity of the ZnO:In film in bilayer on PI is 4.4×10−2Ωcm mainly due to low carrier mobility of 1.5cm2/Vs, the carrier concentration is 1020cm−3.

Morphology and domain wall propagation in Au/Co/Au deposited on different substrates

We present a study of the substrate influence on the buffer layer morphology, on the static magnetic properties and especially on the magnetization reversal dynamics in 1nm thick cobalt layer of Au/Co/Au system. In all films the cobalt layer exhibits perpendicular magnetic anisotropy. The magnetization reversal process has been investigated by polar magnetooptic Kerr effect (PMOKE). It was found that magnetization reverses by domain wall propagation. A simplified form of the Fatuzzo–Labrune model was used to interpret the magnetization reversal. Correlation between magnetic and morphologic results is discussed.

The Influence of Surface Morphology of Buffer Layer on the Critical Current Density in YBCO Coated Conductors

1 μm-thickYBa2Cu3O7-δ(YBCO) films were grown on the Y2O3/yttria stabilized zirconia (YSZ)/CeO2buffer layers with different surface morphologies using direct-current sputtering. The critical current density (Jc) value of YBCO was 1.1 MA/cm2when the root mean square surface roughness (Rrms) of the buffer layer was 2.5 nm. As theRrmsof the buffer layer increased to 15 nm, theJcdecreased to 0.3 MA/cm2. X-ray diffraction and scanning electron microscopy showed the strong relevance of the evolution of the structure and surface morphologies of YBCO films with the buffer layer of differentRrms. A model was proposed to explain the influence of surface morphology on the superconducting properties of YBCO films.

The surface morphological evolution of ultrathin SiC buffer layer grown on Si (100) substrate by atmospheric pressure chemical vapor deposition

Abstract

Effects of the Morphology of a ZnO Buffer Layer on the Photovoltaic Performance of Inverted Polymer Solar Cells

AbstractThe influences of morphology and thickness of zinc oxide (ZnO) buffer layers on the performance of inverted polymer solar cells are investigated. ZnO buffer layers with different morphology and thickness varying from several nanometers to ≈55 nm are fabricated by adjusting the concentration of the precursor sol. The ZnO buffer layers with nearly same surface quality but with thickness varying from ≈7 to ≈65 nm are also fabricated by spinning coating for comparison. The photovoltaic performance is found to be strongly dependent on ZnO surface quality and less dependent on the thickness. The use of dense and homogenous ZnO buffer layers enhances the fill factor and short‐circuit current of inverted solar cell without sacrificing the open‐circuit voltage of device due to an improvement in the contact between the ZnO buffer layer and the photoactive layer. Inverted devices with a dense and homogenous ZnO buffer layer derived from 0.1 M sol exhibit an overall conversion efficiency of 3.3% which is a 32% increase compared to devices with a rough ZnO buffer layer made from 1 M sol, which exhibited a power conversion efficiency of 2.5%. The results indicate that the efficiency of inverted polymer solar cells can be significantly influenced by the morphology of the buffer layer.

Influence of Morphology and Texture of CeO2 on YBa2Cu3O7 (YBCO) Growth and BaCeO3 Formation in Solution‐Derived Synthesis

AbstractWhen working with chemical solution deposition techniques, one of the main issues for optimal performance of CeO2 buffer layers in coated conductors is the insufficient chemical stability of the CeO2 layer during YBa2Cu3O7 (YBCO) thermal processing. This work focusses on the morphology and nanostructure in thin CeO2 films prepared by means of a novel aqueous synthesis route and incorporated into a Ni–W/La2Zr2O7/CeO2/YBa2Cu3O7‐coated conductor. Optimization of precursor chemistry and thermal processing led to a reduction in barium cerate formation. In a new precursor design, iminodiacetic acid was used as a stabilizing ligand, which resulted in an improved morphology of the buffer layer. A shelf life of more than 6 months was established by using a metal‐to‐ligand ratio of 1 to 5. During thermal processing, a combination of a slow calcination ramp with a high sintering ramp, short sintering dwell time and a low oxygen partial pressure during the synthesis resulted in a root mean square roughness below 3 nm for AFM analysis, a [111] to [002] ratio of 1 to 90 in X‐ray diffraction and well‐defined patterns in reflection high‐energy electron diffraction (RHEED) analysis of the CeO2 surface. Trifluoroacetate‐YBCO was deposited on top of the CeO2 buffer layer. Cross‐section analysis with a focussed ion beam allowed us to correlate the morphology and nanostructure of the CeO2 buffer layer with the formation of BaCeO3 and the appearance of voids and secondary phases throughout the YBa2Cu3O7 layer.

Stable organic solar cells employing MoO 3-doped copper phthalocyanine as buffer layer

A stable organic solar cell with structure of ITO/buffer/donor/acceptor/cathode is presented. A thin layer (5 nm) of MoO 3-doped CuPc is adopted as the buffer in CuPc/C 60 organic heterojunction photovoltaic (PV) solar cells, resulting in two times longer lifetime. The surface morphology of buffer layer plays a decisive role in improving the stability.

Influence of Buffer Layer Surface Morphology on YBCO Critical Current Density Deposited on NiW Tapes

YBCO thin films were grown on NiW tapes under continuous moving deposition process. All of YBCO layer, buffer layer, and cap layer were deposited in a compact reel-to-reel pulsed laser deposition system. Since high critical current density is the most important and effective factor to improve performance/price ratio of coated conductor for large scale applications, we focused our research work on enhancing critical current density of YBCO layers on NiW substrates. It was found that superconducting transport properties of YBCO layers were dependent on not only in-plane texture but also surface morphology of buffer layers, especially surface structure and large particles along grain boundary in NiW substrates. High quality YBCO layers with >; 4.0 × 106 A/cm2 (at 77 K, in zero magnetic field) were fabricated on cap layers with nano-scale surface roughness.

30 mm wide process of GdBCO PLD/clad-type textured metal substrates

Gd1Ba2Cu3Ox (GdBCO) coated conductors using bi-axially textured clad-type substrates have been developed for high temperatures superconducting (HTS) power cables. In this project, large amount of coated conductors (CCs) are necessary for the several tests of basic properties of HTS power cables and the fabrication of a 15m long 3-in-one HTS model cable. In order to ensure an adequate amount and properties of coated conductors, the stable manufacturing technology and the high production rate at each process are required.In this report, we have newly installed a high power laser of 300W for the PLD system, resulting in improvement of the manufacturing stability and the deposition rate for GdBCO film. In addition, we have optimized target–substrate distance in PLD process, and the uniformity of Ic distribution across 30mm wide tapes were remarkably improved. Furthermore, the surface morphology of buffer layers were enhanced by optimizing the deposition condition using electron beam (EB) evaporation method, and the maximum Ic value for a short sample has achieved 497A/cm at 77K in the self-field. Based on these progresses, we are currently developing the stable manufacturing process for long CCs with over 400A/cm.