Liquid Phase Epitaxy Research Articles

Bias-free spin-wave propagation in a micrometer-thick ferrimagnetic film with perpendicular magnetic anisotropy

The isotropic transmission of magnetostatic forward volume spin waves in magnetic films with perpendicular magnetic anisotropy (PMA) is shown to be useful in the implementation of magnon-based micro-conduits. However, to our knowledge, non-magnetic-bias-field spin-wave propagation in a PMA magnetic insulator has not been achieved yet, which constrains the development of magnonic information devices and systems. Herein, we demonstrate a robust, bias-free spin-wave transmission in an 18.5-μm-thick bismuth-doped thulium iron garnet film with PMA. This ferrimagnetic film grown by liquid phase epitaxy exhibits high quality in both its crystal structure and its chemical composition and displays a large PMA field of ∼173 mT. The bias-free and reciprocal propagation of spin waves is demonstrated by all-electrical spectroscopy and provides a group velocity of 4.90 km s−1 and a decay length of 20.5 µm at zero magnetic field. Direct imaging of the remnant state indicates that the bias-free spin waves propagate along the oppositely oriented stripe domains with Bloch-type walls, which are formed by in-plane pre-magnetization. Our work contributes to the construction of isotropic charge-free micro-circuits with high levels of integration and nonvolatility.

Strain induced anisotropy in liquid phase epitaxy grown nickel ferrite on magnesium gallate substrates

This work focuses on the nature of magnetic anisotropy in 2.5–16 micron thick films of nickel ferrite (NFO) grown by liquid phase epitaxy (LPE). The technique, ideal for rapid growth of epitaxial oxide films, was utilized for films on (100) and (110) substrates of magnesium gallate (MGO). The motivation was to investigate the dependence of the growth induced anisotropy field on film thickness since submicron films of NFO were reported to show a very high anisotropy. The films grown at 850–875 C and subsequently annealed at 1000 C were found to be epitaxial, with the out-of-plane lattice constant showing unanticipated decrease with increasing film thickness and the estimated in-plane lattice constant increasing with the film thickness. The uniaxial anisotropy field Hσ, estimated from X-ray diffraction data, ranged from 2.8–7.7 kOe with the films on (100) MGO having a higher Hσ value than for the films on (110) MGO. Ferromagnetic resonance (FMR) measurements for in-plane and out-of-plane static magnetic field were utilized to determine both the magnetocrystalline the anisotropy field H4 and the uniaxial anisotropy field Ha. Values of H4 range from −0.24 to −0.86 kOe. The uniaxial anisotropy field Ha was an order of magnitude smaller than Hσ and it decreased with increasing film thickness for NFO films on (100) MGO, but Ha increased with film thickness for films on (110) MGO substrates. These observations indicate that the origin of the induced anisotropy could be attributed to several factors including (i) strain due to mismatch in the film-substrate lattice constants, (ii) possible variations in the bond lengths and bond angles in NFO during the growth process, and (iii) the strain arising from mismatch in the thermal expansion coefficients of the film and the substrate due to the high growth and annealing temperatures involved in the LPE technique. The LPE films of NFO on MGO substrates studied in this work are of interest for use in high frequency devices.

In-plane current induced nonlinear magnetoelectric effects in single crystal films of barium hexaferrite

This report is on the observation and analysis of nonlinear magnetoelectric effects (NLME) for in-plane currents perpendicularly to the hexagonal axis in single crystals and liquid phase epitaxy grown thin films of barium hexaferrite. Measurements involved tuning of ferromagnetic resonance (FMR) at 56–58 GHz in the multidomain and single domain states in the ferrite by applying a current. Data on the shift in the resonance frequency with input electric power was utilized to estimate the variations in the magnetic parameter that showed a linear dependence on the input electric power. The NLME tensor coefficients were determined form the estimated changes in the magnetization and uniaxial anisotropy field. The estimated NLME coefficients for in-plane currents are shown to be much higher than for currents flowing along the hexagonal axis. Although the frequency shift of FMR was higher for the single domain resonance, the multi-domain configuration is preferable for device applications since it eliminates the need for a large bias magnetic field. Thus, multidomain resonance with current in the basal plane is favorable for use in electrically tunable miniature, ferrite microwave signal processing devices requiring low operating power.

In-band pumped Tm,Ho:LiYF4 waveguide laser.

A 4.5 at.% Tm, 0.5 at.% Ho:LiYF4 planar waveguide (thickness: 25 μm) grown by Liquid Phase Epitaxy is in-band pumped by a Raman fiber laser at 1679 nm (the 3H6 → 3F4 Tm3+ transition). A continuous-wave waveguide laser generates a maximum output power of 540 mW at 2051nm with a slope efficiency of 32.6%, a laser threshold of 337 mW and a linear laser polarization (π). This represents the highest output power extracted from any Tm,Ho waveguide laser. No parasitic Tm3+ colasing is observed. The waveguide propagation losses are determined to be as low as 0.19 dB/cm.

Macro- and atomic-scale observations of a one-dimensional heterojunction in a nickel and palladium nanowire complex

The creation of low-dimensional heterostructures for intelligent devices is a challenging research topic; however, macro- and atomic-scale connections in one-dimensional (1D) electronic systems have not been achieved yet. Herein, we synthesize a heterostructure comprising a 1D Mott insulator [Ni(chxn)2Br]Br2 (1; chxn = 1R-2R-diaminocyclohexane) and a 1D Peierls or charge-density-wave insulator [Pd(chxn)2Br]Br2 (2) using stepwise electrochemical growth. It can be considered as the first example of electrochemical liquid-phase epitaxy applied to molecular-based heterostructures with a macroscopic scale. Moreover, atomic-resolution scanning tunneling microscopy images reveal a modulation of the electronic state in the heterojunction region with a length of five metal atoms (~ 2.5 nm), that is a direct evidence for the atomic-scale connection of 1 and 2. This is the first time that the heterojunction in the 1D chains has been shown and examined experimentally at macro- and atomic-scale. This study thus serves as proof of concept for heterojunctions in 1D electronic systems.

Effect of growth temperature on nitrogen incorporation into GaAsN during liquid-phase epitaxy

We studied the growth temperature effect on nitrogen incorporation into GaAsN layers grown by liquid-phase epitaxy (LPE). The growth of dilute nitrides at nearly equilibrium conditions during LPE presents several major challenges: low solubility of nitrogen in Ga-melt, small incorporation efficiency in the solid and high volatility of nitrogen. GaAsN layers are grown from three different initial epitaxy temperatures: 580 °C, 680 °C and 780° C using GaN powder in the melt as a source of nitrogen. The N content in GaAsN is estimated from X-ray diffraction curves applying Vegard’s law. The local microstructure and surface morphology of the grown layers are studied by Fourier-transform infrared spectroscopy and atomic force microscopy measurements, respectively. The absorption edge and the composition dependence of the effective band gap are determined by employing optical transmission and surface photovoltage spectroscopies.

Plasma-assisted vapor liquid phase epitaxial growth of dilute GaSbxN1−x and GaBiyN1−y alloys: Confirmation of band gap reduction discontinuity

Single crystal quality films of dilute $\mathrm{Ga}{\mathrm{Sb}}_{x}{\mathrm{N}}_{1\ensuremath{-}x}$ and $\mathrm{Ga}{\mathrm{Bi}}_{y}{\mathrm{N}}_{1\ensuremath{-}y}$ alloys were synthesized through a plasma-assisted vapor liquid phase epitaxy technique in which nitrogen radicals, antimony, and bismuth species diffuse through molten gallium and form alloys at the substrate. Incorporation fractions $x$ up to 0.009 (three samples), and $y$ up to 0.011 (two samples) were achieved. Morphology and photoluminescence characteristics as well as x-ray spectra were evaluated confirming the alloys possess gallium nitride wurtzite structure but with a slightly higher lattice parameter as determined with differences of hundredths of degrees in the diffraction peak position of plane (002). UV-Vis spectrometry measurements of the alloys also resemble those of pure gallium nitride, indicating dilute anion substitution at the levels reported in this study are not sufficient to promote significant changes in the band gap versus host material, gallium nitride. First-principles density functional theory incorporating the local-density approximation/generalize gradient approximation+U formalism also reveals that relatively small concentration of Sb impurities is not sufficient to achieve a significant narrowing of gallium nitride band gap.

Investigation of the Interface of Y3Fe5O12/Gd3Ga5O12 Structure Obtained by the Liquid Phase Epitaxy

AbstractThe changes in the optical, structural, mechanical properties, and chemical composition of Y3Fe5O12/Gd3Ga5O12 (YIG/GGG) single crystal structures grown by liquid phase epitaxy, particularly at the interface between the film (Y3Fe5O12) and the substrate (Gd3Ga5O12), are studied. Different complementary techniques, including optical microscopy, local spectrophotometry, electron probe microanalysis, micro‐Raman spectroscopy, and nanohardness analysis are used. The main finding of the study is an experimental approach, in which the probe of the measuring device (light beam, electron beam, nanoindenter) is directed to the surface of the studied sample in a direction perpendicular to the direction of structure growth, and the surface is scanned along this direction. It allows to obtain the profiles of changes in refractive properties, nanohardness, optical absorption, chemical composition, and intensity of phonon spectrum bands at the transition from the GGG to YIG. It is established that the lengths of the scanning intervals, at which the changes of various properties of a specimen occur, differ significantly. The obtained results are affected by the size of the probes and by the sensitivities of both the particular measuring method and the particular physical property of the material to changes in the chemical composition and crystalline structure of the sample.

A study on the growth process for liquid phase epitaxy of GaN crystal using Na–Li–Ca flux

The liquid epitaxial growth process on the HVPE-GaN seed of GaN crystal was investigated using the Na–Li–Ca flux method. The phase structure and morphology of as-grown GaN crystals were characterized by X-ray diffraction (XRD) and the scanning electron microscope (SEM), respectively. Under the growth time of 70h, a large area of dissolution morphology could be observed accompanied by a decrease in the thickness of the HVPE-GaN seed. At the bottom of the crucible, the thinning of the seed crystal thickness was the most obvious. For the growth time of 150h, there were two kinds of appearances along the height direction, presenting gathered ridges in the upper part and cellular organizations in the middle and bottom parts. For 420h, the as-grown crystal presented a typical hexagonal layered morphology and the side face developed outward forming regular hexagonal crystallographic planes. With prolonging time from 150h to 420h, the LPE growth shifted from non-equilibrium growth mode with an unstable cellular growth surface morphology to near-equilibrium growth mode with a typical hexagonal layered growth morphology. The thickness of as-grown crystal showed a decrease trend from the gas-liquid interface to the bottom of crucible. To get near-equilibrium growth mode for the whole crystal plate in Na-flux method, the promotion of N dissolving, GaN growth unit diffusion is the key issue.

Composite Detectors Based on Single-Crystalline Films and Single Crystals of Garnet Compounds.

This manuscript summarizes recent results on the development of composite luminescent materials based on the single-crystalline films and single crystals of simple and mixed garnet compounds obtained by the liquid-phase epitaxy growth method. Such composite materials can be applied as scintillating and thermoluminescent (TL) detectors for radiation monitoring of mixed ionization fluxes, as well as scintillation screens in the microimaging techniques. The film and crystal parts of composite detectors were fabricated from efficient scintillation/TL materials based on Ce3+-, Pr3+-, and Sc3+-doped Lu3Al5O12 garnets, as well as Ce3+-doped Gd3−xAxAl5−yGayO12 mixed garnets, where A = Lu or Tb; x = 0–1; y = 2–3 with significantly different scintillation decay or positions of the main peaks in their TL glow curves. This work also summarizes the results of optical study of films, crystals, and epitaxial structures of these garnet compounds using absorption, cathodoluminescence, and photoluminescence. The scintillation and TL properties of the developed materials under α- and β-particles and γ-quanta excitations were studied as well. The most efficient variants of the composite scintillation and TL detectors for monitoring of composition of mixed beams of ionizing radiation were selected based on the results of this complex study.

Effect of Neutron Irradiation on the Spectrum of Deep-Level Defects in GaAs Grown by Liquid-Phase Epitaxy in a Hydrogen and Argon Atmosphere

Effect of Neutron Irradiation on the Spectrum of Deep-Level Defects in GaAs Grown by Liquid-Phase Epitaxy in a Hydrogen and Argon Atmosphere

Структура, морфология и фотоэлектрические свойства гетероструктуры n-GaAs--p-(GaAs)1--x(Ge2)х

The paper studies the structural properties of the thin-film (GaAs)1--х(Ge2)x solid solutions grown by liquid-phase epitaxy on single crystal GaAs substrates. The obtained epitaxial layers were 10 μm thick, had a 0.17 Ω · cm resistivity of p-type conductivity. X-ray diffraction analysis showed that the obtained films are monocrystalline with nanoinclusions with block sizes up to 49 nm, with a crystallographic orientation (100), and have a sphalerite structure of the ZnS type. Morphological studies using AFM showed that the nanocones on the surface of the epitaxial (GaAs)1--х(Ge2)x layers are due to Ge atoms in them. The analysis revealed that the diameter of the nanocones' bases is in the range from 70 to 90 nm, and the height is from 3 to 12 nm. The sizes of such nanocones, determined by the X-ray diffraction method, were close to these values. The photosensitivity spectra of these solid solutions exhibit peculiar fluctuations due to various complexes of charged atoms in them. Analysis of the photosensitivity spectrum of n-GaAs--p-(GaAs)1--х(Ge2)x heterostructures using the Wolfram Mathematics 7 program showed that the spectrum consists of three peaks due to As--Ge, Ge--Ge and Ga--Ge

Characteristics of spin-thermoelectric generators enhanced by incorporating liquid phase epitaxial Bi-substituted YIG films as a ferrimagnetic insulator

Liquid phase epitaxial (LPE) Bi-substituted YIG films exhibit a large growth-induced magnetic anisotropy (GIMA) perpendicular to the film surface. The GIMA depends on the melt composition and supercooling in the LPE growth. Our film shows a large Ku value of 0.1 × 104 J/m3 even at a Bi content, x, of 0. We assume that GIMA enhances the spin-orbital coupling (SOC) in the local d-electron spins of Fe3+, and that the SOC-enhanced thermal energy transfer from the phonon system to the spin system increases spin currents in spin-thermoelectric (STE) generation. We discuss the characteristics of STE generators on the basis of data obtained from ferromagnetic resonance measurements.

In situ observations of the dissolution of an AlN film into liquid Al using a high-temperature microscope

This report describes the implementation of an original liquid-phase epitaxy (LPE) technique using a Ga–Al solution. An N-polar AlN thin film prepared using a sapphire nitridation method was employed as the template for the LPE growth process. The growth behavior depended on attaining a competitive balance of the polarity inversion and the dissolution reaction of the AlN thin film. Therefore, to improve the overall LPE process, it was crucial to understand exactly when and how the AlN thin film dissolved in the solution. This study investigated the dissolution of the N-polar AlN thin film into liquid Al and the resulting AlN growth through in situ observation experiments. The AlN thin film dissolved at a lower temperature than the required temperature for AlN growth. On the basis of these findings, we designed an LPE growth process to obtain a homogeneous AlN layer without the dissolution of the N-polar AlN thin film. Ultimately, a homogeneous AlN layer was successfully formed on the nitrided sapphire substrate using Ga-60mol%Al at 1300 °C for 5 h.

Single- and bound-state soliton mode-locked Er-doped fiber laser based on graphene/WS2 nanocomposites saturable absorber

We report a passively mode-locked Er-doped fiber laser based on WS2, graphene, and graphene/WS2 (G/WS2) nanocomposites saturable absorber (SA), respectively. These materials were easily prepared by liquid phase epitaxy (LPE) method with isopropanol (IPA). Compared with pure graphene or pure WS2, the film of G/WS2 nanocomposites possesses low nonsaturable loss (31%) and low saturable intensity (12.78 MW/cm2), which is of benefit to achieve passive mode-locked fiber laser. Stable traditional soliton pulses were generated with central wavelength of 1566.7 nm, spectral width of 7.3 nm, pulse duration of 357 fs, and repetition rate of 22.86 MHz. Further, we present the bound-state soliton mode-locked based on G/WS2-SA with a modulation period of 4.9 nm, soliton spacing of 1.67 ps and pulse width of 353 fs. Our work extends the studies for G/WS2 nanocomposites in ultrafast photonics applications.

Effect of neutron irradiation on the spectrum of deep-level defects in GaAs grown by liquid-phase epitaxy in hydrogen or argon ambient

We present results of experimental studies of capacitance--voltage characteristics, spectra of deep-level transient spectroscopy of graded high-voltage GaAs p+-p0-i-n0 diodes fabricated by liquid-phase epitaxy at a crystallization temperature of 900oC from one solution--melt due to autodoping with background impurities, in a hydrogen or argon ambient, before and after irradiation with neutrons are presented. After neutron irradiation, deep-level transient spectroscopy spectra revealed wide zones of defect clusters with acceptor-like negatively charged traps in the n0-layer, which arise as a result of electron emission from states located above the middle of the band gap. It was found that the differences in capacitance--voltage characteristics of the structures grown in hydrogen or argon ambient after irradiation are due to different doses of irradiation of GaAs p+-p0-i-n0 structures and different degrees of compensation of shallow donor impurities by deep traps in the layers. Keywords: GaAs, neutron irradiation, capacitance spectroscopy, p0-i-n0-junction, liquid-phase epitaxy, hydrogen, argon.

Особенности перемагничивания двухслойной пленочной структуры ЖИГ/FeNi

In this work, the results of magneto-optical and magnetometric measurements carried out on YIG/FeNi film two-layer structures are presented. YIG films were grown by liquid phase epitaxy, and FeNi films were deposited using magnetron sputtering. It has been established that in the YIG/FeNi system the interlayer coupling is mainly due to the magnetostatic interaction.

Local Characterization of Ferromagnetic Resonance in Bulk and Patterned Magnetic Materials Using Scanning Microwave Microscopy

We have demonstrated the capabilities of the scanning microwave microscopy (SMM) technique for measuring ferromagnetic resonance (FMR) spectra in nanometric areas of magnetic samples. The technique is evaluated using three different samples, including a yttrium iron garnet (YIG) polycrystalline bulk sample and a thick YIG film grown by liquid phase epitaxy (LPE). Patterned permalloy (Py) micromagnetic dots have been characterized to assess the performance for imaging applications of the technique, measuring the variation of the magnetic properties of the sample along its surface. The proposed technique may pave the way for the development of high spatially resolved mapping of magnetostatic modes in different nanomagnetic and micromagnetic structures.

InGaAsP/InP photovoltaic converters for narrowband radiation

Utilizing performed research, photoelectric converters of narrow-band radiation (λ~1.0-1.3 μm) based on InGaAsP/InP heterostructures with an epitaxial p-n junction have been developed and created. Technological regimes that apply of for creating high-quality layers of quaternary InGaAsP solid solutions isoperiodic to indium phosphide in a wide range of compositions by liquid-phase epitaxy have been determined. Keywords: photovoltaic converters, narrowband radiation, InGaAsP, InP, LPE, heterostructures.

Features of remagnetization of the two-layer film structure of the YIG/FeNi

The results of magneto-optical and magnetometric measurements carried out on two-layer film structures of YIG/FeNi are presented. YIG films were grown by liquid-phase epitaxy, and FeNi films were deposited by magnetron sputtering. It has been established that an interlayer magnetic coupling takes place in the YIG/FeNi system, which is mainly due to magnetostatic interaction. Keywords: yttrium-iron-garnet, permalloy, interlayer coupling, magnetostatic and exchange interaction, magnetic domain structure.