Showing papers on "Pulsed laser deposition published in 2019"
TL;DR: A survey of the various material schemes and device structures that have been explored in the quest toward developing light-emitting diodes (LEDs) based on zinc oxide (ZnO) and related II-oxide semiconductors can be found in this paper.
Abstract: This paper presents a compact survey of the various material schemes and device structures that have been explored in the quest toward developing light-emitting diodes (LEDs) based on zinc oxide (ZnO) and related II-oxide semiconductors. Both homojunction and heterojunction devices have been surveyed. Material for fabricating these devices has been grown with a number of different techniques, such as pulsed laser deposition, molecular beam epitaxy, metal-organic chemical vapor deposition, and atomic layer epitaxy. This review also features a self-contained introduction to materials science and device processing technologies that are relevant for fabricating ZnO LEDs. These topics include dry and wet etching, contact formation, and optical doping of ZnO. Due to the overwhelming importance of p-type doping of ZnO for making electronic and optoelectronic devices, a separate short section on electrical doping of ZnO is also included. The rest of this paper describes several different attempts at making blue- and ultraviolet-emitting ZnO LEDs. These include simple pn-junction devices as well as more complicated heterostructure devices incorporating charge carrier barriers and quantum wells.
129 citations
TL;DR: It is demonstrated that the reversible modulation of SCO phase transforms the brownmillerite SrCoO2.5 and perovskite Sr coO3−δ, through controlling the insertion and extraction of oxygen ions with electrolyte gating, providing an alternative avenue for future neuromorphic devices via electrolyte‐gated transistors with oxygen ions.
Abstract: Artificial synaptic devices are the essential hardware of neuromorphic computing systems, which can simultaneously perform signal processing and information storage between two neighboring artificial neurons. Emerging electrolyte-gated transistors have attracted much attention for efficient synaptic emulation by using an addition gate terminal. Here, an electrolyte-gated synaptic device based on the SrCoOx (SCO) films is proposed. It is demonstrated that the reversible modulation of SCO phase transforms the brownmillerite SrCoO2.5 and perovskite SrCoO3−δ, through controlling the insertion and extraction of oxygen ions with electrolyte gating. Nonvolatile multilevel conduction states can be realized in the SCO films following this route. The synaptic functions such as the long-term potentiation and depression of synaptic weight, spike-timing-dependent plasticity, as well as spiking logic operations in the device are successfully mimicked. These results provide an alternative avenue for future neuromorphic devices via electrolyte-gated transistors with oxygen ions.
94 citations
TL;DR: In this paper, a large-energy passively Q-switched erbium-doped fiber laser was successfully used for demonstrating a large energy passively Qswitched fiber laser, where Bi2Se3 nanosheets were fabricated by a catalyst-free chemical vapor deposition method.
Abstract: In our work, Bi2Se3 was successfully used for demonstrating a large-energy passively Q-switched erbium-doped fiber laser. Bi2Se3 nanosheets were fabricated by a catalyst-free chemical vapor deposition method. Based on a pyrolysis tape transfer method, the Bi2Se3 thin film on the SiO2 substrate was transferred to the end of the optical connector for constructing the fiber-integrated saturable absorber. The saturation intensity and modulation depth of the Bi2Se3 saturable absorber were 81.1 MW/cm2 and 15.7%, respectively. A stable Q-switched operation at 1549.99 nm with a maximum average output power of 23.61 mW was achieved. The minimum pulse duration and the largest pulse energy were 1.34 μs and 224.5 nJ, respectively. In comparison with previous works, the single pulse energy (224.5 nJ) obtained in our experiment was improved significantly. Our experimental results fully proved that CVD-Bi2Se3 has good performance in obtaining large energy pulse operations and will promote the applications of 2D CVD-materials in the field of pulse laser.
89 citations
TL;DR: In this article, the structural quality of the orthorhombic Ga2O3 thin film was studied based on the growth parameters employing X-ray diffraction 2θ-ω scans, rocking curves, ϕ scans, and reciprocal space maps.
Abstract: High-quality Ga2O3 thin films in the orthorhombic κ-phase are grown by pulsed-laser deposition using a tin containing target on c-sapphire, MgO(111), SrTiO3(111), and yttria-stabilized ZrO2(111) substrates. The structural quality of the layers is studied based on the growth parameters employing X-ray diffraction 2θ-ω scans, rocking curves, ϕ scans, and reciprocal space maps. Our layers exhibit superior crystalline properties in comparison to thin films deposited in the monoclinic β-phase at nominally identical growth parameters. Furthermore, the surface morphology is significantly improved and the root-mean-squared roughness of the layers was as low as ≈0.5 nm, on par with homoepitaxial β-Ga2O3 thin films in the literature. The orthorhombic structure of the thin films was evidenced, and the epitaxial relationships were determined for each kind of the substrate. A tin-enriched surface layer on our thin films measured by depth-resolved photoelectron spectroscopy suggests surfactant-mediated epitaxy as a possible growth mechanism. Thin films in the κ-phase are a promising alternative for β-Ga2O3 layers in electronic and optoelectronic device applications.High-quality Ga2O3 thin films in the orthorhombic κ-phase are grown by pulsed-laser deposition using a tin containing target on c-sapphire, MgO(111), SrTiO3(111), and yttria-stabilized ZrO2(111) substrates. The structural quality of the layers is studied based on the growth parameters employing X-ray diffraction 2θ-ω scans, rocking curves, ϕ scans, and reciprocal space maps. Our layers exhibit superior crystalline properties in comparison to thin films deposited in the monoclinic β-phase at nominally identical growth parameters. Furthermore, the surface morphology is significantly improved and the root-mean-squared roughness of the layers was as low as ≈0.5 nm, on par with homoepitaxial β-Ga2O3 thin films in the literature. The orthorhombic structure of the thin films was evidenced, and the epitaxial relationships were determined for each kind of the substrate. A tin-enriched surface layer on our thin films measured by depth-resolved photoelectron spectroscopy suggests surfactant-mediated epitaxy as a pos...
87 citations
01 Mar 2019
73 citations
TL;DR: In this article, a highly sensitive and selective nanostructured triethylamine (TEA) gas sensor is fabricated successfully by designing semiconductor heterostructures consisting of ZnO nanorods and α-Fe2O3 nanoparticles.
Abstract: Chemiresistive gas sensor with high sensitivity, selectivity and fast response for specific target gas has many applications from environmental monitor to internet of things. Herein, a highly sensitive and selective nanostructured triethylamine (TEA) gas sensor is fabricated successfully by designing semiconductor heterostructures consisting of ZnO nanorods and α-Fe2O3 nanoparticles. ZnO nanorods grow directly on flat Al2O3 electrodes and α-Fe2O3 nanoparticles are deposited onto ZnO nanorods by pulsed laser deposition (PLD). Such α-Fe2O3/ZnO sensor has larger specific surface area (20.79 m2/g), adsorbs more oxygen ions and exhibits higher response (63 to 50 ppm TEA), lower detection concentration (˜1 ppm), and shorter response time (4 s), which are all much better than the controlled ZnO nanorods sensor. Besides the interface depletion layer at the α-Fe2O3/ZnO interface, we find that the surface depletion layer due to oxygen absorption is also very important for the sensor performance. Moreover, more surface adsorbed oxygen in the α-Fe2O3/ZnO sensor is proved by both XPS analysis and density functional theory (DFT) simulation, which highlights the significance of gas sensing mechanism study for such composite heterojunction structure.
72 citations
TL;DR: In this article, an ultralow dark current solar-blind photodetector based on β-Ga2O3/4H-SiC heterojunction is generated by depositing a thin film on n-type 4HSiC substrates using Pulse Laser Deposition method.
72 citations
TL;DR: This work investigates the thin-film growth of a heterostructure stack comprised of n-type β-Ga2O3 and p-type cubic NiO layers grown consecutively on c-plane sapphire using pulsed laser deposition, as well as the fabrication of solar-blind ultraviolet-C photodetectors based on the resulting p-n junction heterodiodes.
Abstract: In recent years, β-Ga2O3/NiO heterojunction diodes have been studied, but reports in the literature lack an investigation of an epitaxial growth process of high-quality single-crystalline β-Ga2O3/NiO thin films via electron microscopy analysis and the fabrication and characterization of an optoelectronic device based on the resulting heterojunction stack. This work investigates the thin-film growth of a heterostructure stack comprising n-type β-Ga2O3 and p-type cubic NiO layers grown consecutively on c-plane sapphire using pulsed laser deposition, as well as the fabrication of solar-blind ultraviolet-C photodetectors based on the resulting p-n junction heterodiodes. Several characterization techniques were employed to investigate the heterostructure, including X-ray crystallography, ion beam analysis, and high-resolution electron microscopy imaging. X-ray diffraction analysis confirmed the single-crystalline nature of the grown monoclinic and cubic (201) β-Ga2O3 and (111) NiO films, respectively, whereas electron microscopy analysis confirmed the sharp layer transitions and high interface qualities in the NiO/β-Ga2O3/sapphire double-heterostructure stack. The photodetectors exhibited a peak spectral responsivity of 415 mA/W at 7 V reverse-bias voltage for a 260 nm incident-light wavelength and 46.5 pW/μm2 illuminating power density. Furthermore, we also determined the band offset parameters at the thermodynamically stable heterointerface between NiO and β-Ga2O3 using high-resolution X-ray photoelectron spectroscopy. The valence and conduction band offsets values were found to be 1.15 ± 0.10 and 0.19 ± 0.10 eV, respectively, with a type-I energy band alignment.
70 citations
TL;DR: In this paper, various PVD techniques, such as pulsed laser deposition (PLD), evaporation decomposition (ED), and sputtering, are examined with respect to their conditions for VO2 fabrication, film quality and the strategies for film improvements.
Abstract: Smart windows are defined by their ability to regulate incoming solar radiation in order to reduce the energy consumption of buildings by modulating the heat intake. Vanadium dioxide (VO2) is one of the most promising potential candidates for smart window materials due to its ability to reversibly transit from monoclinic VO2 (M) to rutile VO2 (R) at near room temperature. As a result of this transition, the infrared radiation (IR) transparent VO2 (M) abruptly becomes IR opaque, effectively regulating the heat intake by solar radiation. Despite their promising potential, VO2-based smart windows have various significant intrinsic limitations: a high transition temperature (τC) of 68 °C; low luminous transmission (Tlum) of around 40% and low solar modulation (ΔTsol) of less than 25%. Currently, various methods have been used to fabricate VO2 thin films in an attempt to improve their intrinsic properties. One of those methods is physical vapour deposition (PVD). In this paper, various PVD techniques, such as pulsed laser deposition (PLD), evaporation decomposition (ED) and sputtering, are examined with respect to their conditions for VO2 fabrication, film quality and the strategies for film improvements. Lastly, some challenges and opportunities for further studies into VO2-based smart windows are discussed.
69 citations
14 Jan 2019
TL;DR: The metastable orthorhombic phase of hafnia is generally obtained in polycrystalline films, whereas in epitaxial films, its formation has been much less investigated as mentioned in this paper.
Abstract: The metastable orthorhombic phase of hafnia is generally obtained in polycrystalline films, whereas in epitaxial films, its formation has been much less investigated. We have grown Hf0.5Zr0.5O2 fil...
68 citations
TL;DR: Wang et al. as mentioned in this paper introduced sulfur vacancy on MoS2 nanolayer (MoS2−x) by a pulsed laser deposition (PLD) process, which can trap electrons and improve the electrons mobility.
TL;DR: In this paper, high-quality (-201)-oriented β-Ga2O3 thin films were epitaxially grown on c-sapphire substrates by pulsed laser deposition (PLD) at various substrate temperatures using a β-GA 2O3 ceramic target.
TL;DR: In this article, the effect of point defects such as vacancies and interstitials on the work function of β-Ga2O3 thin films grown by pulsed laser deposition was investigated.
TL;DR: The studies have shown that in the case of thin polymer coatings deposited by physical methods, the application for chemical structure evaluation of complementary techniques, with different surface sensitivity, together with the use of surface topography imaging, provide unique insight into the film morphology.
Abstract: Two methods—attenuated total reflection Fourier infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS)—have been used to analyze the chemical structure of polytetrafluorethylene (PTFE) thin coatings deposited by pulsed laser (PLD) and pulsed electron beam (PED) ablations. The volume of the analyzed materials is significantly different in these techniques which can be of great importance in the characterization of highly heterogeneous thin films. Optical microscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM) have been additionally used to examine the coating surface morphology. The studies have shown that in the case of thin polymer coatings deposited by physical methods, the application for chemical structure evaluation of complementary techniques, with different surface sensitivity, together with the use of surface topography imaging, provide unique insight into the film morphology. The results can provide information contributing to an in-depth understanding of the deposition mechanism of polymer coatings.
TL;DR: In this paper, a series of gallium oxide (Ga2O3) ultrathin films grown on sapphire with different growth temperatures were analyzed via X-ray absorption spectroscopy.
TL;DR: It is demonstrated that the multistaggered gap of multi‐T MDs/p‐Si improves the PEC performance significantly more than the homo‐TMDs/P‐Si and bare p‐Si by effective charge transfer.
Abstract: To date, the in situ fabrication of the large-scale van der Waals multi-heterojunction transition metal dichalcogenides (multi-TMDs) is significantly challenging using conventional deposition methods. In this study, vertically stacked centimeter-scale multi-TMD (MoS2/WS2/WSe2 and MoS2/WSe2) thin films are successfully fabricated via sequential pulsed laser deposition (PLD), which is an in situ growth process. The fabricated MoS2/WS2/WSe2 thin film on p-type silicon (p-Si) substrate is designed to form multistaggered gaps (type-II band structure) with p-Si, and this film exhibits excellent spatial and thickness uniformity, which is verified by Raman spectroscopy. Among various application fields, MoS2/WS2/WSe2 is applied to the thin-film catalyst of a p-Si photocathode, to effectively transfer the photogenerated electrons from p-Si to the electrolyte in the photo-electrochemical (PEC) hydrogen evolution. From a comparison between the PEC performances of the homostructure TMDs (homo-TMDs)/p-Si and multi-TMDs/p-Si, it is demonstrated that the multistaggered gap of multi-TMDs/p-Si improves the PEC performance significantly more than the homo-TMDs/p-Si and bare p-Si by effective charge transfer. The new in situ growth process for the fabrication of multi-TMD thin films offers a novel and innovative method for the application of multi-TMD thin films to various fields.
TL;DR: In this paper, the structural change in Li/Li3PO4/LiCoO2 during battery operation was investigated using in situ Raman spectroscopy, where Raman measurements were performed from the front side of the cell beside the lithium anode through the solid electrolyte and from the backside of a cell below the lithium aode through a transparent electrode.
TL;DR: In this article, a multilayer-type TiO2/Au/TiO2 nanocomposites have been prepared as photoanode thin films by pulsed laser deposition (PLD).
12 Feb 2019
TL;DR: Single-layer MoS2 is synthesized on Au(111) by pulsed laser deposition, showing the potentialities of this technique in the synthesis of high-quality 2D materials films.
Abstract: Molybdenum disulphide (MoS2) is a promising material for heterogeneous catalysis and novel two-dimensional (2D) optoelectronic devices. In this work, we synthesized single-layer (SL) MoS2 structures on Au(111) by pulsed laser deposition (PLD) under ultra-high vacuum (UHV) conditions. By controlling the PLD process, we were able to tune the sample morphology from low-coverage SL nanocrystals to large-area SL films uniformly wetting the whole substrate surface. We investigated the obtained MoS2 structures at the nanometer and atomic scales by means of in situ scanning tunneling microscopy/spectroscopy (STM/STS) measurements, to study the interaction between SL MoS2 and Au(111)—which for example influences MoS2 lattice orientation—the structure of point defects and the formation of in-plane MoS2/Au heterojunctions. Raman spectroscopy, performed ex situ on large-area SL MoS2, revealed significant modifications of the in-plane E12g and out-of-plane A1g vibrational modes, possibly related to strain and doping effects. Charge transfer between SL MoS2 and Au is also likely responsible for the total suppression of excitonic emission, observed by photoluminescence (PL) spectroscopy.
TL;DR: In this paper, a self-powered photodetector based on n-ZnO/CsPbBr3/p-GaN heterojunction exhibited a high peak responsivity of 44.53 mA/W and detectivity of 2.03✕1012
TL;DR: In this paper, high-level crystalline Ni1-xRuxO films have been prepared via a pulsed laser deposition technique using a Q-switching Nd:YAG laser.
TL;DR: In this paper, a review of recent progress made regarding investigations on electronic structure, stoichiometry, crystal structures, synthesis and applications of transition metal nitrides (TTMNs) is presented.
TL;DR: In this paper, the structure, optical and morphological properties of the prepared samples are studied by measuring the transmittance bands by using Fourier Transform Infrared Spectroscopy (FT-IR) and Scanning Electron Microscope.
TL;DR: In this article, the X-ray diffraction pattern suggested that the major crystal phase consists of orthorhombic/tetragonal phases with a small amount of monoclinic phase even for the 930-nm-thick film despite its thickness.
Abstract: Ferroelectricity has been demonstrated in polycrystalline 7%Y-doped HfO2 (YHO7) films with thicknesses ranging from 10 to 930 nm, which were grown on (111)Pt/TiOx/SiO2/(001)Si substrates by pulsed laser deposition at room temperature and subsequent annealing at 1000 °C. The X-ray diffraction pattern suggested that the major crystal phase consists of orthorhombic/tetragonal phases with a small amount of monoclinic phase even for the 930-nm-thick film despite its thickness. Moreover, the hysteresis loops associated with the ferroelectric orthorhombic phase were clearly observed for all samples including even the 930-nm-thick film. The remnant polarization (Pr) and the coercive field (Ec) are 14–17 μC/cm2 and 1300–1600 kV/cm, respectively, at max applied electric fields of ∼4000 kV/cm for all YHO7 films within the present study. These results indicate that the ferroelectric structure and properties of YHO7 films are insensitive to the film thickness.
TL;DR: In this paper, the effect of film thickness on structural, surface morphology and optical properties of ZnO thin films grown by pulsed laser deposition (PLD) method was investigated.
Abstract: In this paper, we investigated the effect of film thickness on structural, surface morphology and optical properties of ZnO thin films grown by pulsed laser deposition (PLD) method. Thickness of the films was varied by keeping all other PLD parameters same to investigate thickness dependence on the structural and optical properties of ZnO thin films. The prepared thin films have been characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), UV- visible (Uv–Vis) and photoluminescence (PL) spectroscopy. XRD confirms the formation of crystalline c-axis orientated hexagonal wurtzite structure of ZnO thin films. AFM depicts that roughness and grain size of the ZnO films increase with increase in the films thickness. The direct optical band gap of the ZnO films calculated using Tauc's plot increase from 3.28 eV to 3.34 eV as the thickness of the films varies from 55 nm to 220 nm. The high quality c-axis orientated ZnO thin films with minimum strain and tuneable optical properties could be used as a transparent conducting oxide (TCO) for optoelectronic applications.
TL;DR: In this article, flux pinning properties of BHO-doped EuBa2Cu3Ox (EuBCO, Eu = Europium) coated conductors were investigated in detail.
Abstract: REBa2Cu3Ox (REBCO, RE = rare earth) coated conductors (CCs) are promising as superconducting wires for high-field magnets because of their high in-field critical current density (Jc) performance and high tensile tolerance. Fujikura, Ltd., has been developing BaHfO3 (BHO)-doped EuBa2Cu3Ox (EuBCO, Eu = Europium) CCs using a hot-wall-type pulsed-laser deposition (PLD) in order to further improve the in-field performance. Although a high deposition rate in the PLD process is necessary for mass production, it has been found that the in-field performance greatly differ depending on the deposition rate. In this study, flux pinning properties of BHO-doped EuBCO CCs fabricated with different deposition rates by the hot-wall PLD on IBAD substrates were investigated in detail. From the scaling characteristics of the flux-pinning force density (Fp) curve, the BHO precipitates in a fast deposition rate REBCO film appeared to behave like random pinning centers, which was almost consistent with a result of transmission electron microscope observation. On the other hand, from a decrease of anisotropy in the magnetic field angle dependence of Jc, it was also confirmed that BHO precipitates were not completely random pinning centers, that is, it has some kind of anisotropy. Considering the critical current value per production time, it was also found that the fast deposition rate is advantageous since the REBCO layer could be thicker.
TL;DR: In this article, a photoresponsivity of 1.96 A W−1 is achieved in monolayer MoS2 samples under illumination with a wavelength of 300 nm.
Abstract: Due to the layered structure and thickness-dependent bandgap of MoS2, it is intriguing to investigate the layer-dependent performance of MoS2 based photodetectors. In this work, centimeter-scale layered MoS2 films with different layer numbers are achieved by using pulsed laser deposition by controlling the number of laser pulses. The measurement of transport characteristics in the dark indicates a Schottky barrier contact formed at the Au/MoS2 interface. The obtained metal–semiconductor–metal MoS2 based photodetectors present a UV-to-NIR photoresponse with high stability. When the thickness of the film is decreased, the photoresponse of the MoS2 photodetectors gradually increases from multilayer to bilayer, and more importantly, a notable enhancement in the photoresponse for the monolayer can be observed. In particular, a photoresponsivity of 1.96 A W−1 is achieved in monolayer MoS2 samples under illumination with a wavelength of 300 nm. The physical mechanism responsible for the observation is discussed based on the layer dependent Schottky barrier variation and the indirect-to-direct energy band transition in MoS2. Our work provides an insight into layer-dependent optical behavior in MoS2 films, which should be helpful for developing further large-scale photosensing applications in the atomic limit.
TL;DR: The successful growth of layered ZrTe2 thin film by pulsed-laser deposition and the experimental results of its magnetotransport properties are reported, which provide insights into further investigations and potential applications of this layered topological material system.
Abstract: ZrTe2 is a candidate topological material from the layered two-dimensional transition-metal dichalcogenide family, and thus the material may show exotic electrical transport properties and may be p...
TL;DR: In this article, a-SiOx was scavenged via in situ scavenging of the native aSiOx under ballistic conditions, which enabled the direct epitaxy of polar phases on Si using pulsed laser deposition.
Abstract: Ultra-thin Hf1-xZrxO2 films have attracted tremendous interest owing to their Si-compatible ferroelectricity arising from polar polymorphs. While these phases have been grown on Si as polycrystalline films, epitaxial growth was only achieved on non-Si substrates. Here we report direct epitaxy of polar phases on Si using pulsed laser deposition enabled via in situ scavenging of the native a-SiOx under ballistic conditions. On Si (111), polar rhombohedral (r)-phase and bulk monoclinic (m-) phase coexist, with the volume of the former increasing with increasing Zr concentration. R-phase is stabilized in the regions with a direct connection between the substrate and the film through the compressive strain provided by an interfacial crystalline c-SiO2 layer., The film relaxes to a bulk m-phase in regions where a-SiOx regrows. On Si (100), we observe polar orthorhombic o-phase coexisting with m-phase, stabilized by inhomogeneous strains at the intersection of monoclinic domains. This work provides fundamental insight into the conditions that lead to the preferential stabilization of r-, o- and m-phases.