Role Of Buffer Layer Research Articles

The Role of Buffer Layer on the Performance and Uniformity Improvement of Long-Length HTS YBa2Cu3O7−x Tapes Derived by MOD

The Role of Buffer Layer on the Performance and Uniformity Improvement of Long-Length HTS YBa2Cu3O7−x Tapes Derived by MOD

Role of Buffer Layer and Building Unit in the Monolayer CrI3 Growth: A First-Principles Perspective.

CrI3, a two-dimensional layered material, has recently attracted a lot of research interest due to its exotic magnetic property. However, the synthesis of a CrI3 monolayer (ML) by vapor-phase deposition has not been achieved by current experimental endeavors, which require a better understanding of the vapor-phase growth mechanism involved. In this study, we theoretically simulate the growth of the CrI3 ML on the Si(111) surface by using a first-principles calculation. Our key finding is that an iodine buffer layer on the Si surface is crucial to the formation of the CrI3 ML by stabilizing the precursor and also reacting with the precursor. Moreover, our simulation reveals that the CrI2 cluster as the growth building unit, which can be formed by controlling the chemical potential of the I source, is preferred for the formation of CrI3 ML. We think that our work will provide insightful guidance for the experimental synthesis of CrI3 ML in the future.

An over 18%-efficient completely buffer-free Cu(In,Ga)Se2 solar cell

In this letter, an independently certified photovoltaic efficiency of 18.4% demonstrated from a completely buffer-layer-free Cu(In,Ga)Se2 (CIGS) solar cell is reported. A Si-doped CIGS thin film was used as the photoabsorber layer and a conductive B-doped ZnO (BZO) front electrode layer was directly deposited on the CIGS layer. Metastable acceptor activation by heat-light soaking treatment was performed to maximize the efficiency. The results presented here are expected to serve as a benchmark for simplified-structure CIGS devices as well as a reference for discussions on the role of buffer layers used in conventional CIGS solar cells.

Photocurrent Enhancement of CdSe Quantum-Dot Sensitized Solar Cells Incorporating Single-Walled Carbon Nanotubes.

We demonstrate quantum-dot sensitized solar cells (QDSSCs) which have colloidal CdSe quantum dots (TOPO-CdSe) as a sensitizer onto mesoporous TiO2 photoanodes. CdS quantum-dot (QD) layer plays a role of buffer layer for direct adsorption of TOPO-CdSe. We incorporate single-walled carbon nanotubes with TiO2 photoanode of our QDSSCs to facilitate efficient charge transfer. Shortcircuit current densities (Jsc) of our QDSSCs are enhanced while other parameters are maintained. Furthermore, we apply inert N2 pressure onto our sensitized photoanodes and observe 44% of Jsc enhancement with respect to pristine sample. Consequently, light-harvesting efficiency of our QDSSCs are increased. Significant series resistance reduction is observed from electrochemical impedance spectroscopy, indicating better interface contact between TiO2 photoanode and TOPOCdSe QD sensitizer are achieved.

Study of Carbon Thin Film Deposition on Various Buffer Layer as Characterized by X-Ray Diffraction and Raman Spectroscopy

Westudy the structural characteristic of carbon based thin filmprepared by DC unbalanced magnetron sputtering technique on different buffer layer such as γ-Al2O3, SnO2, and Cu. Sputtering parameters of carbon thin film were maintained identical for each buffer layer. Fe-doped carbon pellet and Argon gas have been used as sputtering target and to generate the sputtering plasma, respectively. The roles of buffer layer for the quality of carbon-based thin film have been investigated by X-ray diffraction and Raman spectroscopy analysis. Raman spectra indicatethe formation of agoodquality carbon thin film with crystal-like structure on γ-Al2O3and Cu buffer layer, in contrast to the SnO2buffer layer case. Furthermore Raman spectra confirm thehoneycomb structure with fewer defects in γ-Al2O3 indicating that it is more suitable buffer layer than the other. We argue that γ-Al2O3 buffer layerprovide a good nucleation site and promote a better atomic arrangement for carbon atoms to form a few layergraphene-like structure. The atomic geometry of γ-Al2O3 supports the hexagonal atomic configurationfor carbon atom inthe formation of a few layers graphene. This study mightgive a new approach for the carbon based deposition towards the devices application.

The role of buffer layer between TCO and p-layer in improving series resistance and carrier recombination of a-Si:H solar cells

The properties of the window layer and transparent conducting oxide (TCO)/p interface in silicon based thin-film solar cells are important factors in determining the cell efficiency. As the potential barrier got larger at the interface, the transmission of photo-generated holes were impeded and the recombination of photo-generated electrons diffusing back toward the TCO interface were enhanced leading to a deterioration of the fill factor. In this paper different p-layers were studied. It was found that using p-type hydrogenated amorphous silicon oxide (a-SiOx:H) layer as the window layer along with a 5nm buffer layer which reduced the barrier at the fluorine doped tin oxide (SnO2:F) TCO/p-layer interface, improved the cell efficiency. a-SiOx:H was used as the buffer layer. With the buffer layer between TCO and p-type a-SiOx:H, the potential barrier dropped from 0.506eV to 0.472eV. This lowered barrier results in increased short circuit current density (Jsc) and fill factor (FF). With the buffer layer, Jsc increased from 11.9mA/cm2 to 13.35mA/cm2 and FF increased from 73.22% to 74.91%.

The role of buffer layers in polymer solar cells

The present review rationalizes the information spread in the literature concerning the use and role of buffer layers in polymer solar cells. Usual device structures include buffer layers, both at the anode and at the cathode interface, mainly to favour charge collection and extraction, but also to improve the device’s overall performance. Buffer layers are actually essential for achieving highly efficient polymer solar cells and can no more be considered as “optional”, thus the need and importance of understanding their properties and role. The aim of this review is to give the reader an overview of this topic and to provide a practical and useful tool for the daily activities of researchers in the field of polymer photovoltaics.

Role of buffer layer in electronic structures of iron phthalocyanine molecules on Au(111)

We investigate the electronic structures of one and two monolayer iron phthalocyanine (FePc) molecules on Au(111) surfaces. The first monolayer FePc is lying flat on the Au(111) substrate, and the second monolayer FePc is tilted at ∼15° relative to the substrate plane along the nearest neighbour [101] direction with a lobe downward to the central hole of the unit cell in the first layer. The structural information obtained by first-principles calculations is in agreement with the experiment results. Furthermore, it is demonstrated that the electronic structures of FePc molecules in one-monolayer FePc/Au(111) system are perturbed significantly, while the electronic structures of FePc molecules in the second monolayer in two-monolayer FePc/Au(111) system remain almost unchanged due to the screening of the buffer layer on Au(111).

Phonon transport in atomic chains coupled by thermal contacts: The role of buffer layer

In this work, ballistic phonon transport in atomic chain nanostructures is investigated by atomic nonequilibrium Green’s functions and embedded atom method. Bond length and strength modification in atomic chain (low-dimensional structure) was taken into consideration by using bond-order-length-strength correlation premise. We especially focus on the contact interface effects on phonon transmission and thermal conductance. It is found that the contact interfaces between an atomic chain and contact reservoir, i.e., neck region or buffer layers, play an important role in phonon transport. The more buffer layers the less thermal conductance.

Electrodeposition of ZnO nanowires with controlled dimensions for photovoltaic applications: Role of buffer layer

The role of a ZnO buffer layer on the electrodeposition of ZnO nanowire arrays was analyzed. ZnO buffer layers were deposited on conducting glass substrates by spray pyrolysis and electrodeposition. The electrodeposited ZnO buffer layer resulted in a collection of open-packed small grains (∼ 20 nm), while the sprayed layers were comprised of close-packed grains with size in the range of 15–100 nm. The ZnO nanowire arrays electrodeposited on ZnO buffer layers exhibited increased nanowire density (by factors of 6× and 3×, for electrodeposited and sprayed buffer layers, respectively) compared to arrays deposited directly on naked substrates, demonstrating that ZnO nanocrystalline layers can be used to increase nucleation sites for nanowire growth. On the other hand, nanowire diameters were tailored from 45 to 160 nm as a function of the size of the grains in the buffer layer. The influence of crystallographic orientation of the buffer layer was also analyzed.

PZT thick films for sensor and actuator applications

PZT thick films with thicknesses between 5 and 150 μm are of great interest for microsystems applications where direct coating onto microelectronic substrates and high electromechanical performance are required. Dense PZT thick films have been obtained by combining a PZT-PMN powder with a low melting point glass and the eutectic forming oxides Bi 2O 3 and ZnO. Densification is due to transient liquid phase formation with additional incorporation of cations into the growing PZT grains during sintering. PZT thick films prepared by this method show excellent dielectric, ferroelectric and piezoelectric properties. They have been applied on various substrates, like Al 2O 3, ZrO 2, Low Temperature Cofired Ceramics (LTCC) and silicon wafers which are basis materials for microsystems technology. The influence of the substrate material on the PZT thick film properties and the role of buffer layers will be discussed.

Self-assembled InAs quantum dots grown on InP (3 1 1)B substrates: Role of buffer layer and amount of InAs deposited

The formation of InAs quantum dots by Stransky–Krastanow method on (3 1 1)B InP substrates has been studied. On Al 0.48In 0.52As alloy lattice matched on InP, large changes of the quantum dot structural characteristics have been observed as a function of the amount of InAs deposited and of the arsenic pressure during the InAs quantum dot formation. Small quantum dots (minimum diameter=20 nm) in very high density (1.3×10 11 quantum dots per cm 2) have been achieved in optimized growth conditions. These results are interpreted from the strong strain field interaction through the substrate at high density and from the InAs surface energy evolutions with the Arsenic pressure. The effect on quantum dot characteristics of the arsenic pressure during the growth of Al 0.48In 0.52As buffer layers has also been investigated. Despite the importance of this parameter on the Al 0.48In 0.52As clustering, weak changes have been observed.

Effect of buffer layers on the property of Pb(Zr,Ti)O3–Pb(Mn,W,Sb,Nb)O3 thin films grown by pulsed laser deposition

New ferroelectric Pb(Zr,Ti)O 3 –Pb(Mn,W,Sb,Nb)O 3 (PZT–PMWSN) thin film has been deposited on a Pt/Ti/SiO 2 /Si substrate by pulsed laser deposition. Buffer layer was adopted between film and substrate to improve the ferroelectric properties of PZT–PMWSN films. Effect of a Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) and (Pb 0.72 La 0.28 )Ti 0.93 O 3 (PLT) buffer layers on the stabilization of perovskite phase and the suppression of pyrochlore phase has been examined. Role of buffer layers was investigated depending on different types of buffer layer and thickness. The PZT–PMWSN thin films with buffer layer have higher remnant polarization and switching polarization values by suppressing pyrochlore phase formation. The remnant polarization, saturation polarization, coercive field and relative dielectric constant of 10-nm-thick PLT buffered PZT–PMWSN thin film with no pyrochlore phase were observed to be about 18.523 μC/cm 2 , 47.538 μC/cm 2 , 63.901 kV/cm and 854, respectively.

Role of buffer layer on the performances of amorphous silicon solar cells with incorporated nanoparticles produced by plasma enhanced chemical vapor deposition at 27.12 MHz

The aim of this paper is to present results concerning the role of the buffer layer on pin devices, deposited in a single chamber for plasma enhanced chemical vapor deposition, using high hydrogen dilution and pressures at 27.12 MHz. By doing so, we allow the incorporation of nanoparticles into the i-layer, during plasma process. The results show solar cells with 8.8% efficiency with a collection efficiency of 95% in the blue region of the spectra. Apart from that, the results from impedance spectroscopy, imaginary impedance vs. real impedance, show difference of a semicircle radius as function of sample temperatures, which could be explained by total device series resistance variation.

Growth and structural properties of thick InAs films on GaAs with low-pressure metalorganic vapor phase epitaxy

High quality InAs films are grown on GaAs (0 0 1) substrates by low-pressure metalorganic vapor phase epitaxy. It is found that the combination of InAs buffer grown under low temperature and InAs epilayer grown under high temperature is essential to obtain high quality InAs films. The role of buffer layer is discussed. AFM observation on thick InAs film surface shows that step-flow growth mode takes place. The crystalline quality of InAs is characterized by transmission electron microscopy and X-ray diffraction. The crystalline quality improves with increase in film thickness. Residual strain due to thermal mismatch between InAs layers and GaAs substrates is investigated with X-ray diffraction.

In-Situ Rheed Observation of Mocvd-Gan Film Growth

AbstractWe developed the MOCVD apparatus equipped with RHEED system, which enable us to observe in-situ and real time RHEED for GaN film growth in ~100mTorr of pressure. We attempted to grow GaN film with this MOCVD chamber in 100mTorr. The in-situ RHEED was subsequently observed along the film deposition process in order to understand both the role of buffer layer and the mechanism of GaN film growth by MOCVD on highly lattice-mismatched substrate like sapphire. The results indicate that oxygen removed from the sapphire surface was observed during its cleaning in H2 flow at 1100°C. The dependence of re-crystallization and evaporation of the buffer layer on the annealing ambient was also detected. Although the nitrogen was slightly deficient, HT-GaN film with smooth surface was obtained in 100mTorr by adding H2 gas and reducing total flow rate. In preliminary deposition, the RHEED oscillation-like was observed in MOCVD-GaN growth. Thus, our developing deposition system has a potential to understand the growth mechanism with atomic level.

Hysteresis caused by defects in buffer layer of metal-ferroelectric-insulator-semiconductor (MFIS) devices

We have investigated the roles of buffer layer in the Pt/SBT-Y2O3/p-Si (MFIS) capacitors. We found that the insertion of Y2O3 buffer layer prevents the charge injection from the Si substrate to ferroelectric layer. However, negative charges with the effective density of 3.21×1012/cm2 were generated due to the additional process step for Y2O3 deposition. We suggested that the asymmetrical increase of a memory window is due to the domain pinning caused by negative charges in buffer layer. In addition, we reported that the mobile positive charges in ferroelectric layer can induce the shift of the hysteresis loops depending on the gate-bias polarity and a ramp rate during the capacitance-voltage (C-V) measurement. Since Y2O3 buffer layer minimize the charge injection, the shift of the hysteresis loops was asymmetrical.

Fabrication and Properties of Epitaxial Buffer Layers on Nonmagnetic Textured Ni Based Alloy Substrates

Biaxially aligned YBCO thick films on oxide buffered metallic substrates is a promising route toward the fabrication of superconducting tapes operating at liquid nitrogen temperature. The role of buffer layer is to reduce the lattice mismatch between the substrate and the YBCO film, to adapt the thermal expansion coefficient, to hamper the diffusion of Ni in YBCO film and to prevent the oxidation of the metallic substrate surface. This paper presents a study regarding CeO 2 buffer layer deposition on a new nonmagnetic (001)[100] textured Ni-V alloy substrates. The deposition of CeO 2 was performed by both pulsed laser ablation and e-beam evaporation techniques. The θ-2θ X-ray diffraction pattern mainly exhibits the (00l) peaks of CeO 2, indicating that the films are epitaxially grown with the c axis perpendicular to the substrate. Rocking curved through the CeO 2 (002) peak have a FWHM of about 6°. The SEM studies have shown that the surface is smooth, continuos and free of cracks. Texture analysis reveals a good in-plane orientation for the ablated CeO 2 film, whereas the electron beam evaporated CeO 2 shows two textures in the growth plane. Further efforts are focused on the deposition of YBCO thick film on the as buffered nonmagnetic metallic substrate.

Fabrication of YMnO3 Thin Films on Si Substrates by a Pulsed Laser Deposition Method

We have proposed ReMnO3 (Re: Rare earth elements) films for metal-ferroelectric-semiconductor field effect transistor-(MFSFET) type ferroelectric random access memories (Ferroelectric RAMs). For this kind of application, since ReMnO3 films must be fabricated directly on Si substrates, this wrote focuses on the fabrication of YMnO3 films on Si substrates with and without buffer layers. Although only amorphous YMnO3 films are obtained without buffer layers, crystalline films are obtained using Y–Mn–O buffer layers deposited without introducing oxygen. YMnO3 films can be epitaxially grown on the top of epitaxial Y2O3 on (111)Si. For both crystalline YMnO3 films, although hysteresis behavior in D-E measurement is observed, remanent polarizations are quite small. The role of buffer layers on the thin film growth of YMnO3 on (111)Si is discussed.

The role of buffer layer in strontium bismuth tantalate based ferroelectric gate mos structures for non-volatile non destructive read out memory applications

Metal Ferroelectric Insulator Semiconductor (MFIS) structure has been fabricated with strontium bismuth tantalate (SBT) as the ferroelectric thin film and zirconium oxide (ZrO2) as the insulating buffer layer. SBT film was deposited by spin-on metal organic deposition (MOD) technique. ZrO2 film was deposited by electron beam evaporation. The capacitance versus voltage characteristics(C-V) of the MFIS structure shows hysteresis and the direction of hysteresis corresponds to ferroelectric polarization. The C-V characteristics of MFIS structure shows memory window of 1.8 volts for a write/erase voltage of 9V at a sweep rate of 1 sec/1.8V. In order to understand the role of coercive voltage on the memory window in MFIS structures, C-V characteristics metal-ferroelectric-metal (MFM) structures with various SBT film thickness’ were also studied.