MgO Buffer Layer Research Articles

An Impressive Open-Circuit Voltage of 1.223V and High Humidity Stability of Perovskite Solar Cells with MgO Buffer Layer Deposited by Low-Temperature Atomic Layer Deposition.

The performance of perovskite solar cells has been continuously improving. However, humidity stability has become a key problem that hinders its promotion in the process of commercialization. A buffer layer deposited by atomic layer deposition is a very helpful method to solve this problem. In this work, MgO film is deposited between Spiro-OMeTAD and electrode by low-temperature atomic layer deposition at 80°C, which resists the erosion of water vapor, inhibits the migration of electrode metal ions and the decomposition products of perovskite, then finally improves the stability of the device. At the same time, the MgO buffer layer can passivate the defects of porous Spiro, thus enhancing carrier transport efficiency and device performance. The Cs0.05(FAPbI3)0.85(MAPbBr3)0.15 perovskite device with a MgO buffer layer has displayed PCE of 22.74%, also with a high Voc of 1.223V which is an excellent performance in devices with same perovskite component. Moreover, the device with a MgO buffer layer can maintain 80% of the initial efficiency after 7200h of storage at 35% relative humidity under room temperature. This is a major achievement for humidity stability in the world, providing more ideas for further improving the stability of perovskite devices.

Fabrication of ZnO/CuBr1-x I x microstructural transparent solar cells with buffer layer

Transparent solar cells (TSCs) are invisible, landscape-harmonized power generation devices that can be installed on a large number of surfaces. Herein, ZnO/CuBr1-x I x (CuBrI) microstructural TSCs with ZnO nanorods (NR) were fabricated via a solution process; the ZnO NRs were used to decrease carrier loss. A ZnO or MgO buffer layer (BL) was introduced between ZnO and CuBrI to improve the open circuit voltage (V OC). The BLs significantly improved the V OC by reducing the leakage current. Moreover, owing to the suppression of carrier recombination near the p-n junction interface, the short circuit current density (J SC) of the TSC with MgO BL increased, and the V OC improved further. The TSC with MgO BL exhibited the highest power density of 7.3 nW cm−2 with a V OC of 42 mV, J SC of 0.64 μA cm−2, fill factor of 26.7%, and transmittance of over 70% across a wavelength range greater than 500 nm.

Interfacial DMI in Fe/Pt thin films grown on different buffer layers

We study the interfacial Dzyaloshinskii–Moriya interactions (i-DMI) of Fe/Pt bilayers grown on Si substrates with MgO, SiO2, or Ta each as a buffer layer on the basis of wave-vector-resolved Brillouin light scattering (BLS) measurement. The obtained i-DMI energy values for Fe/Pt on MgO, Ta, and SiO2 buffer layers are 0.359, 0.321, and 0.274 mJ/m2, respectively. The large i-DMI value observed in Fe/Pt system on the MgO buffer layer can be attributed to the good interfacial quality and the Rshaba effect at the MgO/Fe interface. Moreover, the MgO/Fe/Pt system, benefiting from better sample quality, exhibits a lower damping factor. Furthermore, layer-resolved first-principles calculations are carried out to gain a more in-depth understanding of the origin of the i-DMI in the Fe/Pt system. The results indicate that in the Fe(110)/Pt(111) system, the substantial DMI energy between Fe spins at the interface is related to a significant change in spin–orbit coupling (SOC) energy in the neighboring Pt layer. In contrast, for the MgO(002)/Fe(002) system, both the DMI and its related SOC energy are concentrated at the interfacial Fe layer. Our investigation will provide a valuable insight into the spintronic community in exploring novel devices with chirality dependence.

Epitaxial growth and electric control of magnetic behaviors in exchange biased IrMn/FeGa/MgO/PMN-PT heterostructures

We grew exchange biased (001)-textured IrMn/epitaxial FeGa bilayers on ferroelectric PMN-PT(001) substrate with assistance of an MgO buffer layer and investigated the electric control of magnetic behaviors. The as-grown sample exhibits square, asymmetrically shaped, and two-step loops at different magnetic field orientations due to the combined effect of the intrinsic magnetocrystalline anisotropy and the collinear uniaxial and unidirectional magnetic anisotropies, which can be interpreted by the magnetization reversal of domain wall nucleation. After polarized by an electric field, another kind of asymmetrically shape loops with three steps in the descending and two steps in the ascending branch is additionally observed because the uniaxial magnetic anisotropy is greatly enhanced and becomes perpendicular to the exchange bias. The angular dependent magnetic behavior suggests the exchange bias is slightly rotated by the electrically induced strain. The electric field dependence of coercive field and uniaxial magnetic anisotropy exhibit an asymmetrical butterfly-like shape, indicating a strain-mediated magnetoelectric coupling with a net 109° polarization switching of PMN-PT.

Strains in Fe/Cr/Fe trilayers and (Fe/Cr)5/Fe multilayers epitaxied on MgO and MgO/SrTiO3

Fe/Cr/Fe trilayers and multilayers are prepared as model systems designed to furnish simple data comparable with calculation results for diffusion properties in nuclear materials. Their structure (epitaxy, residual strains and dislocations) is characterized in detail. The film structure (strain and stress) is shown to be different on MgO20nm/SrTiO3 and MgO substrates due to the residual strain in the MgO buffer layer on SrTiO3. Superlattices with high crystalline quality are prepared, with Fe and Cr in coherent epitaxy. In-plane residual strain in Fe is +0.45(13)% on MgO substrates and decreases from 1.70(9)% to 0.47(2)% when increasing the thickness of the trilayers on MgO/SrTiO3 substrates. These strains enhance the contrast between Fe and Cr, opening the way to future kinetics studies using x-ray diffraction in this system, which is far more efficient (non-destructive and rapid) than high resolution transmission electron microscopy with electron energy loss spectroscopy or atom probe tomography.

Tunable magnetic anisotropy of antiferromagnetic NiO in (Fe)/NiO/MgO/Cr/MgO(001) epitaxial multilayers

We report on the magnetic properties of antiferromagnetic NiO(001) thin films in epitaxially grown NiO/MgO(dMgO)/Cr/MgO(001) system for different thicknesses of MgO, dMgO. Results of X-ray Magnetic Linear Dichroism show that together with an increase of dMgO, rotation of NiO spins from in-plane towards out-of-plane direction occurs. Furthermore, we investigated how the proximity of Fe modifies the magnetic state of NiO in Fe/NiO/MgO(dMgO)/Cr/MgO(001). We proved the existence of a multidomain state in NiO as a result of competition between the ferromagnet/antiferromagnet exchange coupling and strain exerted on the NiO by the MgO buffer layer.

Controlling the Magneto-Optical Response in Ultrathin Films of EuO1-x via Interface Engineering with Ferroelectric BaTi2O5.

Utilizing pulsed laser deposition, a film of EuO1-x was deposited onto a Si(001) substrate with MgO buffer and compared to the same heterostructure with an additional BaTi2O5 thin film on top of the EuO1-x surface. X-ray diffraction (XRD) indicates the films crystallize into a preferred EuO(111) orientation; it also reveals the clear presence of EuSi2, which suggests Si or Eu diffuses across the MgO buffer layer. EuO1-x films exhibit a ferromagnetic (FM) signature and temperature-dependent exchange bias, indicated by MOKE measurements, suggesting the presence of a magnetic order well above the EuO Curie temperature with possible origins in charge carrier density near the interface. In comparison, an antiferromagnetic character persists well above the EuO Curie temperature of 69 K and the enhanced Curie temperature of 150 K for BaTi2O5 films grown on the EuO1-x films. The antiferromagnetic behavior is not seen in thicker EuO1-x thin films when integrated with other ferroelectric (FE) phases of the BaO-TiO2 system, suggesting an origin in the perturbed charge population at the BaTi2O5/EuO1-x interface.

Optimized Tunability of Barium Strontium Titanate Thin Films onto Different Plates with Proper Buffer Layers

Misfit strain, polarization, permittivity, and tunability of Ba x Sr1−x TiO3 (BST) thin films on various substrates with varied buffer layers are calculated by a modified thermodynamic model. The lattice parameters of the LaAlO3 (LAO), CaTiO3 (CT), BaZr0.25Ti0.75O3 (BZT), and MgO buffer layers grow consecutively as does the thermal expansion coefficient (TEC) of the Si, Ti, Ni, and stainless steel (SS) substrates. When the TEC of substrates is bigger (such as Ni, SS) than that of the films, introducing buffer layers with larger lattice parameters (such as BZT, MgO) can improve the permittivity and tunability. Conversely, inserting buffer layers with smaller lattice parameters (such as LAO, CT) can enhance the dielectric response when the TEC of substrates is smaller (such as Si, Ti) than that of the films. The relationship between the TEC of substrate and the lattice parameter of buffer layer is primarily linear for achieving high tunability. According to several references, introducing LaNiO3 buffer layers can significantly increase the tunability of BST solid solutions prepared on Si‐based substrates, which is in line with the estimated rule. This law offers a guide for choosing the best substrate and buffer layer when producing BST films with strong dielectric response.

Biaxially textured MgO buffer layer on flexible metal template for coated conductor

Biaxially textured MgO buffer layer on flexible metal template for coated conductor

Epitaxial integration of a perpendicularly magnetized ferrimagnetic metal on a ferroelectric oxide for electric-field control

Ferrimagnets, which contain the advantages of both ferromagnets (detectable moments) and antiferromagnets (ultrafast spin dynamics), have recently attracted great attention. Here we report the optimization of epitaxial growth of a tetragonal perpendicularly magnetized ferrimagnet Mn2Ga on MgO. Electrical transport, magnetic properties and the anomalous Hall effect (AHE) were systematically studied. Furthermore, we successfully integrated high-quality epitaxial ferrimagnetic Mn2Ga thin films onto ferroelectric PMN-PT single crystals with a MgO buffer layer. It was found that the AHE of such a ferrimagnet can be effectively modulated by a small electric field over a large temperature range in a nonvolatile manner. This work thus demonstrates the great potential of ferrimagnets for developing high-density and low-power spintronic devices.

Atomic-Scale Insights on Large-Misfit Heterointerfaces in LSMO/MgO/c-Al2O3

Understanding the interfaces in heterostructures at an atomic scale is crucial in enabling the possibility to manipulate underlying functional properties in correlated materials. This work presents a detailed study on the atomic structures of heterogeneous interfaces in La0.7Sr0.3MnO3 (LSMO) film grown epitaxially on c-Al2O3 (0001) with a buffer layer of MgO. Using aberration-corrected scanning transmission electron microscopy, we detected nucleation of periodic misfit dislocations at the interfaces of the large misfit systems of LSMO/MgO and MgO/c-Al2O3 following the domain matching epitaxy paradigm. It was experimentally observed that the dislocations terminate with 4/5 lattice planes at the LSMO/MgO interface and with 12/13 lattice planes at the MgO/c-Al2O3 interface. This is consistent with theoretical predictions. Using the atomic-resolution image data analysis approach to generate atomic bond length maps, we investigated the atomic displacement in the LSMO/MgO and MgO/c-Al2O3 systems. Minimal presence of residual strain was shown at the respective interface due to strain relaxation following misfit dislocation formation. Further, based on electron energy-loss spectroscopy analysis, we confirmed an interfacial interdiffusion within two monolayers at both LSMO/MgO and MgO/c-Al2O3 interfaces. In essence, misfit dislocation configurations of the LSMO/MgO/c-Al2O3 system have been thoroughly investigated to understand atomic-scale insights on atomic structure and interfacial chemistry in these large misfit systems.

Tunnel magnetoresistance in magnetic tunnel junctions with FeAlSi electrode

(001)-oriented FeAlSi polycrystalline thin films with a flat surface and B2-ordered structure were grown on thermally oxidized SiO2 substrates using MgO buffer layers. The FeAlSi thin films composition-adjusted to the Sendust alloy exhibited a low coercivity (Hc) after the annealing process. We utilized these films as bottom electrodes of magnetic tunnel junctions (MTJs) and characterized their tunnel magnetoresistance (TMR) effect. The TMR effect was 35.9% at room temperature. In addition, the TMR ratio increased to 51.0% when a thin CoFeB layer was inserted into the FeAlSi/MgO interface, without degrading the small switching field of the FeAlSi electrode. These MTJs with a small switching field and relatively high TMR ratio using the FeAlSi electrode are promising for highly sensitive MTJ-based magnetic sensor devices.

The atomic ordering dependence of magnetic and magneto-transport properties for polycrystalline Fe3Si films

This work intended to give a comprehensive overview of the atomic ordering dependence of magnetic and magneto-transport properties for polycrystalline Fe3Si films on Si(111) substrates by inserting the MgO buffer layer between them. X-ray diffraction results display that the single phase polycrystalline Fe3Si film fulfilling fundamental reflections, B2-Fe3Si film and D03-Fe3Si film are acquired. Scanning electron microscopy images present the distribution of the particles dispersed and embedded in the films, resulting in rough surface. The Ms value increases and Hc value decreases with the improvement of structural and chemical order. The highly ordered D03-Fe3Si film has the highest Ms value of 610~657 emu cm−3, and the lowest Hc value of 81~93 Oe. Fe3Si films characterize metallic behavior and the resistivity declines with the improvement of atomic ordering. The phonon contribution governs the resistivity in the high temperature range and the electron–electron scattering and anomalous single magnon scattering mechanisms are available at the low temperature region of ~30 K~100 K and below ~30 K, respectively. The analysis of anomalous Hall effect demonstrates that Berry curvature dominates the anomalous Hall effect via a proper scaling law. The enhancement of intrinsic anomalous Hall effect contribution is due to the impact of the improvement of structural and chemical order on the band structure/Berry curvature modifications, accordingly affecting the intensity of spin–orbit coupling, whereas the extrinsic contributions behave in opposite manner.

Electric control of magnetic properties in epitaxially grown FeRh/MgO/PMN-PT heterostructures

We epitaxially grew the metamagnetic FeRh films on ferroelectric PMN-PT(001) substrates and investigated the electric control of magnetic properties. An MgO buffer layer is inserted to reduce the considerably large lattice mismatch of 5.44% between FeRh and PMN-PT, leading to a nice epitaxial growth with a relationship of FeRh[110](001)||MgO[100](001)||PMN-PT[100](001). The as-grown FeRh film shows a typical antiferromagnetic-to-ferromagnetic phase transition by means of varying the temperature. Because a growth-induced uniaxial magnetic anisotropy is superimposed on the in-plane four-fold magnetocrystalline anisotropy, the epitaxial FeRh film displays different kinds of multi-step hysteresis loops at various field orientations. An electric field applied on the PMN-PT substrate can remarkably increase the coercivity of FeRh film, which presents a butterfly type shape, indicating a strain-mediated magnetoelectric coupling. Because of the inhibitory effect of the remnant compressive strain on the phase transition, the critical transition temperature and the magnetization are obviously enhanced and reduced, respectively, after removing the electric effect.

Characteristics of MgIn2O4 Thin Film Transistors Enhanced by Introducing an MgO Buffer Layer

In this work, an MgIn2O4 (MIO) thin film transistor (TFT) with a bottom gate structure was fabricated. The MIO channel layer was deposited by RF sputtering using a single MgIn2O4 target. The performance of MIO TFT was highly related to oxygen vacancies. As-deposited MIO TFT showed a low field-effect mobility due to doping of Mg. An MgO buffer layer was introduced to enhance the mobility of MIO TFT due to improvement of the interface with the channel layer. In addition, oxygen vacancies in the MIO channel were suppressed because of oxygen diffusion from the buffer layer. MIO TFT with a 5 nm MgO buffer layer showed an on/off current ratio of 9.68 × 103, a field-effect mobility of 4.81 cm2/V∙s, which was increased more than an order of magnitude compared with the device without a buffer layer, a threshold voltage of 2.01 V, and a subthreshold swing of 0.76 V/decade, which was improved more than 20% compared with the as-deposited one.

Giant Faraday rotation of cobalt ferrite thin films deposited on silicon substrates for silicon photonic nonreciprocal device applications

In this study, crystalline cobalt ferrite thin films with large Faraday rotation (FR) coefficient were deposited on silicon by radiofrequency magnetron sputtering. An (100)-oriented MgO buffer layer was employed to solve the film/substrate discrepancy. A giant FR coefficient of 25 600 deg cm−1 was achieved for a cobalt ferrite film deposited at a substrate temperature (ST) of 600 °C. Moreover, the magnetic easy axis of the films switched from in-plane (IP) to out-of-plane orientation with increasing ST. This switching in the easy axis could be attributed to induced IP stress in the films with high deposition temperatures.

Stabilization of ε−Fe2O3 epitaxial layer on MgO(111)/GaN via an intermediate γ -phase

In the present study we have demonstrated epitaxial stabilization of the metastable magnetically-hard $\varepsilon$-Fe$_2$O$_3$ phase on top of a thin MgO(111) buffer layer grown onto the GaN (0001) surface. The primary purpose to introduce a 4\,nm-thick buffer layer of MgO in between Fe$_2$O$_3$ and GaN was to stop thermal migration of Ga into the iron oxide layer. Though such migration and successive formation of the orthorhombic GaFeO$_3$ was supposed earlier to be a potential trigger of the nucleation of the isostructural $\varepsilon$-Fe$_2$O$_3$, the present work demonstrates that the growth of single crystalline uniform films of epsilon ferrite by pulsed laser deposition is possible even on the MgO capped GaN. The structural properties of the 60\,nm thick Fe$_2$O$_3$ layer on MgO / GaN were probed by electron and x-ray diffraction, both suggesting that the growth of $\varepsilon$-Fe$_2$O$_3$ is preceded by formation of a thin layer of $\gamma$-Fe$_2$O$_3$. The presence of the magnetically hard epsilon ferrite was independently confirmed by temperature dependent magnetometry measurements. The depth-resolved x-ray and polarized neutron reflectometry reveal that the 10\,nm iron oxide layer at the interface has a lower density and a higher magnetization than the main volume of the $\varepsilon$-Fe$_2$O$_3$ film. The density and magnetic moment depth profiles derived from fitting the reflectometry data are in a good agreement with the presence of the magnetically degraded $\gamma$-Fe$_2$O$_3$ transition layer between MgO and $\varepsilon$-Fe$_2$O$_3$. The natural occurrence of the interface between magnetoelectric $\varepsilon$- and spin caloritronic $\gamma$- iron oxide phases can enable further opportunities to design novel all-oxide-on-semiconductor devices.

Advance in Long-Length REBCO Coated Conductors Prepared by Reel-to-Reel Metalorganic Solution and Ion-Beam-Assisted Deposition

In the present work, we report our recent efforts to improve the homogeneity of MgO buffer layers and superconducting YBa 2 Cu 3 O 7-δ coated tapes prepared by ion-beam-assisted deposition and metalorganic solution deposition (MOD), respectively. Based on previous research results involving fluorine, a reduced atmospheric pressure is used for the MOD technique to improve the in-plane texture and suppress microcracks in the film, and then more than 500 m of MOD-coated superconducting tape is manufactured, exhibiting an excellent biaxial texture and superconducting performance. The full width at half maximum values for both in-plane and out-of-plane textured films are as low as 3° based on X-ray diffraction (XRD) measurements. The superconducting current-carrying capacities for 12-mm tapes are approximately 450-520 and 450-500 A for the 100-m level and 500-m level (77 K, self-field), respectively. The current-carrying capacities were measured by both reel-to-reel transport and an inductive system, and the results demonstrated that the cost-effective MOD technique is very promising for long-length high-quality coated conductors.

Crystallization of Atomic Layer Deposited MgO Thin Filmsas a Buffer Layer for Rocksalt Beo Film Growth

Rocksalt structure beryllium oxide (BeO) thin film has been highlighted as an exceptional high-k dielectric material for various semiconductor device application because it can have a very high-k value of > 200 and high band gap of ~ 10 eV simultaneously. However, this was an only theoretical expectation based on the first-principles calculation. Also, the stable crystal structure of BeO is wurtzite at normal thermal Atomic Layer Deposition (ALD) processing conditions of which k-value is only ~8, whereas the rocksalt structure BeO could be stabilized only under an extremely high-pressure condition (> 100 GPa). Therefore, it is expected that the usual ALD process of BeO film may result in the wurtzite structure film. Considering the interfacial tensile strain offered by the larger MgO lattice parameter with a cubic-based rocksalt crystal structure, which is 4.21 Å while BeO lattice parameter is 2.70 Å for hexagonal-based wurtzite crystal structure and 3.62 Å for cubic-based rocksalt crystal structure, the adoption of cubic-based MgO as a buffer layer may enable the transition of BeO crystal structure from wurtzite to quasi-rocksalt. This work reported the optimization of both Thermal and Plasma-Enhanced ALD (TALD, and PEALD) process and post-annealing conditions of MgO and their influences on the crystallization properties of BeO on top of the MgO buffer layer, observed by X-Ray Diffraction (Figure 1 (a), (b)), Transmission Electron Microscope Selected Area Diffraction. Moreover, the electronic properties of MgO and BeO thin films, especially leakage current and dielectric constant, were verified through the measurement of Metal-Insulator-Metal (MIM) device (Figure 1 (c)). This work, thus, attempted to grow MgO film by TALD, and PEALD as a buffer layer for the rocksalt BeO film growth. Although the growth of the BeO film on top of the rocksalt MgO film is ongoing project, this work can provide a fundamental step toward the final goal of rocksalt BeO film growth by an ALD method. Figure 1

Surface polarity control in ZnO films deposited by pulsed laser deposition

We demonstrate a simple and inexpensive method of surface polarity control of ZnO grown by pulsed laser deposition (PLD). The polarity control is achieved in a straightforward way by changing the thickness of MgO buffer layer. The Zn- and O-polar ZnO films possess very distinct growth rate, electron concentration and mobility as well as different defect structures. These different structural and electronic properties result in significant differences in surface reactivity and device performance. For example, Pd Schottky diodes fabricated onto the O-polar ZnO film exhibit lower barrier height and ideality factor compared with the equivalent Zn-polar devices, while methylammonium lead iodide perovskite films are readily formed on O-terminated and rapidly decompose on Zn-terminated surfaces. This can be attributed to higher photocatalytic activity of Zn-terminated surface, as well as higher surface coverage of adsorbed hydroxyl groups. Consequently, our results indicate that polarity engineering to obtain favorable O-terminated surface can result in improved performance of ZnO-containing optoelectronic devices, while Zn-terminated surfaces could be of interest for photocatalytic and sensing applications.