Liquid Phase Epitaxy Research Articles

Analysis of Pristine and Tcnq-Loaded MOF FILMS By Contactless Microwave Dielectric Spectroscopy Technique

Metal-organic frameworks (MOFs) are porous and crystalline Coordination Network Compounds (CNCs), also referred to as porous coordination polymers (PCPs), which consist of inorganic metal (or metal/oxo) clusters connected by organic linkers. Surface Anchored Metal-organic-framework (SURMOF) films consist of quasi-liquid phase epitaxially grown highly ordered crystalline MOF films. For this study we used MOF Cu3(BTC)2 (BTC: benzene tricarboxylate) films, also known as HKUST-1 (Hong Kong University of Science and Technology-1), which were infiltrated with tetracyano-quinodimethane (TCNQ) guest molecules to modulate the charge transport characteristics. HKUST-1 MOF thin films have been grown using a liquid phase epitaxy (LPE) spray method in which the metal-containing solution [1 mmol Cu(OAc)2] and the linker solution [0.1 mmol BTC] are sprayed alternately on modified silicon substrates. Subsequently, the samples were immersed into an ethanoic TCNQ solution.We report on localized charge transfer processes at microwave frequencies of porous metal-organic framework (MOF) HKUST-1 Cu2(BTC)3 samples. As part of this study we will compare measurements done in the HKUST-1 pristine form of the material with open pores and HKUST-1, where the pores have been infiltrated with tetracyano-quinodimethane (TCNQ), resulting in a hybrid structure with enhanced electrical conductivity and a significant measurable effect in the microwave propagation characteristics [1]. We present data and analysis from an evaluation of pristine and loaded HKUST-1 SURMOF films using the contactless broadband microwave dielectric spectroscopy (BDS). The technique enables the accurate operando evaluation of the electrical and magnetic properties of materials without compromising the kinetic conditions of the experiment. The BDS method is uniquely suitable for investigating charge transfer reactions, regardless of the nature of the charge carriers, i.e., electrons and holes [2]. As such, these material state-sensitive parameters could be used to monitor charge transfer changes in the SURMOF and SURMOF-TCNQ hybrid analytes.[1] G. M. Espallargas and E. Coronado, “Magnetic functionalities in MOFs: from the framework to the pore”, Chem. Soc. Rev., 2018,47, 533, DOI: 10.1039/c7cs00653e[2] A. M. Wernbacher et al, Operando Electrical Conductivity and Complex Permittivity Study on Vanadia Oxidation Catalysts, J. Phys. Chem. C 2019, 123, 8005−8017, DOI: 10.1021/acs.jpcc.8b07417

Effect of the Sb content and the [formula omitted] and [formula omitted] substrates on the physical and chemical properties of InSbxAs1-x alloys for mid-infrared applications: Analysis of surface, bulk and interface

Antimonide-based family holds the potential for developing a new generation of mid-infrared applications. Here, we report on the growth of InSbxAs1-x alloys on n− and p−type GaSb(100) substrates varying the Sb mole fraction (x), using the liquid phase epitaxy (LPE) technique. We show that the ternary alloy grown on the n−type GaSb substrate presents higher crystalline quality, thermal diffusivity and interfacial thermal conductivity, as compared to the one grown on pin equation type GaSb substrates which decrease as the Sb mole fraction (x) in the layer increases. Our results demonstrate that the InSbxAs1-x/n−GaSb heterostructure reaches the thermal equilibrium faster than the InSbxAs1-x/p−GaSb structure, with lower roughness, strain, as well as a better chemical abruptness at substrate-layer interface. We also find that the growth mechanism of the InSbxAs1-x alloy is constituted by In−As and In−Sb bonds. Furthermore, the Raman scattering spectra measured at different layer depths evidence that the crystalline quality improves with depth and allow the identification of an intrinsic depletion region. Since the InSbxAs1-x alloy presents a long-range atomic order grown on both n− and p−type GaSb substrates, the phonon-plasmon coupled L− and L+ modes are observed, and from the L+ coupled mode, we obtain the intrinsic carrier concentration and its variation with the Sb mole fraction. Therefore, this work provides important guidance on the structural, thermal, and chemical properties of the surface, bulk and interface of InSbxAs1-x alloys, that should be considered to improve the performance of future devices, such as better heat dissipation.$

Current Transport and Dielectric Analysis of Ni/SiO2/P-Si Diode Prepared by Liquid Phase Epitaxy

Herein, the Ni/SiO2/p-Si MIS diode was developed via the liquid phase epitaxy (LPE) process. The structural and surface morphology were investigated by XRD and SEM techniques. The electrical study of the device, Ni/SiO2/n-Si, demonstrates a worthy rectification and the electrical parameters of the Schottky diode have computed using the I-V characterization. Different dielectric parameters as capacitance (C), permittivity (e’), dielectric loss (e”), conductance and ac conductivity (σac) were evaluated. Moreover, their relation to bias dc voltage has been examined in the frequency range 10 Hz–20 MHz, temperature 303 K to 363 K and DC bias voltage from -2 V to 2 V. Also, the variable investigated parameters were found to be dependent upon temperature, frequency and bias voltage.

Ohmic metal/Hg1-xCdxTe (x ≈ 0.3) contacts

Some technological features of p-type Hg 1-x Cd x Te (x ≈ 0.3) liquid phase epitaxy layers grown on Cd 1-y Zn y Te (y ≈ 0.04) substrates are briefly discussed. Energy dispersive analysis of mercury-cadmium-telluride (MCT) layers and metal contacts (Au(In)/Cr(Mo,Ti)) to MCT layers together with their current-voltage characteristics at T ≈ 80 and 300 K are considered. It is shown that Cr(Mo,Ti)/MCT contacts have ohmic characteristics or close to them at T ≈ 80 and 300 K for both n- and p-type MCT layers. This gives the opportunity to form ohmic contacts to n- and p-type pads in one technological cycle. The contact resistance Rc is much smaller as compared to the HgCdTe p-n junction resistance R0[ RcA (< 10–2 Ω cm2) ≪ R0A (> 103 Ω cm2), where R0 is the zero bias diode resistance at T = 80 K, and A is the MCT (x ≈ 0.3) junction area]. So, such contacts are appropriate for the fabrication of photovoltaic HgCdTe detectors.

Overview of S(T)EM electron detectors with garnet scintillators: Some potentials and limits.

The paper is focused on a complete configuration and design of a scintillation electron detector in scanning electron and/or scanning transmission electron microscopes (S(T)EM) with garnet scintillators. All processes related to the scintillator and light guide were analyzed. In more detail, excitation electron trajectories and absorbed energy distributions, efficiencies and kinetics of scintillators, as well as the influence of their anti-charging coatings and their substrates, assigned optical properties, and light guide efficiencies of different configurations were presented and discussed. The results indicate problems with low-energy detection below 1 keV when the scandium conductive coating with a thickness of only 3 nm must be used to allow electron penetration without significant losses. It was shown that the short rise and decay time and low afterglow of LuGdGaAG:Ce liquid-phase epitaxy garnet film scintillators guarantee a strong modulation transfer function of the entire imaging system resulting in a contrast transfer ability up to 0.6 lp/pixel. Small film scintillator thicknesses were found to be an advantage due to the low signal self-absorption. The optical absorption coefficients, refractive indices, and the mirror optical reflectance of materials involved in the light transport to the photomultiplier tube photocathode were investigated. The computer-optimized design SCIUNI application was used to configure the optimized light guide system. It was shown that nonoptimized edge-guided systems possess very poor light guiding efficiency as low as 1%, while even very complex optimized ones can achieve more than 20%.

Synthesis and binder-free assembly of SrFe12O19 nano-platelets for wafer-scale patterning of magnetic components

Monolithic integration of high-frequency magnetic components such as hexaferrite circulators at the wafer scale can lead to a significant improvement in radio frequency (RF) circuit performance and functionality. However, current methods to monolithically integrate hexaferrite films, such as liquid phase epitaxy, require high temperature (> 900 °C) annealing to create crystalline alignment, which is not compatible with integrated circuit process temperatures (< 350 °C) or thick patterned films (> 50 μm). In this work, we report the synthesis of pure phase, faceted, and high crystallinity hexaferrite [SrFe12O19] nano-platelets using a direct hydrothermal approach, followed by self-assembly of binder free SrFe12O19 films with high film density and high magnetic isotropy. The nano-platelets exhibit high staturation magnetization (~ 60 emu/g) and coercivity (Hc) of 815 Oe. The magnetic films exhibit dense nano-particle concentration and a magnetic squareness (Mr/Ms) of 0.7. They can be patterned using a selective assembly process through a thick photoresist mask. Thicknesses of up to 70 μm have been deposited on 4-in.-diamater wafers.

Highly Efficient Permeation and Separation of Gases with Metal-Organic Frameworks Confined in Polymeric Nanochannels.

This work demonstrates the confinement of porous metal-organic framework (HKUST-1) on the surface and walls of track-etched nanochannel in polyethylene terephthalate (np-PET) membrane using a liquid-phase epitaxy (LPE) technique. The composite membrane (HKUST-1/np-PET) exhibits defect-free MOF growth continuity, strong attachment of MOF to the support, and a high degree of flexibility. The high flexibility and the strong confinement of the MOF in composite membrane results from (i) the flexible np-PET support, (ii) coordination attachment between HKUST-1 and the support, and (iii) the growth of HKUST-1 crystal in nanoconfined geometries. The MOF has a preferred growth orientation with a window size of 3.5 Å, resulting in a clear cut-off of CO2 from natural gas and olefins. The experimental results and DFT calculations show that the restricted diffusion of gases only takes place through the nanoporous MOF confined in the np-PET substrate. This research thereby provides a new perspective to grow other porous MOFs in artificially prepared nanochannels for the realization of continuous, flexible, and defect-free membranes for various applications.

Epitaxial growth of prussian blue analogue derived NiFeP thin film for efficient electrocatalytic hydrogen evolution reaction

Hydrogen evolution reaction (HER) in water splitting plays an important role in the storage and conversion of clean energy. The development of efficient electrocatalytic materials for HER has attracted much attention in current research. In this work, a homogeneous NiFe-based prussian blue analogue (NiFe-PBA) thin film is prepared on the surface of nickel foam by liquid phase epitaxial (LPE) layer-by-layer (LBL) dipping method. Then the NiFe-PBA film reacts with PH3 produced by sodium hypophosphite to form a bimetal phosphide NiFeP film. The electrocatalytic HER properties under alkaline condition indicate that the NiFeP film only requires 99 ​mV overpotential to reach 10 ​mA ​cm−2 and the performance can be maintained for over 30 ​h without obvious degradation even at 100 ​mA ​cm−2. The results imply that the prepared NiFeP film has excellent HER performance and durable stability. This work is of great significance for the preparation of self-supporting and low-cost bimetal phosphide thin film for efficient HER.

Capacitance Spectroscopy of Heteroepitaxial AlGaAs/GaAs p–i–n Structures

The temperature dependences of the capacitance-voltage (C–V) characteristics and deep-level spectra of a graded high-voltage AlxGa1 – xAs p0–i–n0 junction grown by liquid-phase epitaxy via autodoping with background impurities are studied. Changes in the C–V characteristics at varied measurement temperature and optical illumination demonstrate that the p0-, i-, and n0-type layers in AlxGa1 – xAs under study contain bistable DX centers. Spectra furnished by deep-level transient spectroscopy (DLTS), measured at various bias voltages Vr and filling-pulse voltages Vf, show a positive DLTS peak for the n0-type layer, with a thermal activation energy of Et = 280 meV and electron-capture cross section of σn = 3.17 × 10–14 cm2, which is unusual for a majority-charge-carrier trap. This peak is attributed to the negatively charged state of the Se/Te donor impurity, which is a bistable DX center with negative correlation energy U.

TEC Colling Shortwave Infrared 320×256 focal Plane Detector

The short-wave HgCdTe thin film material was grown by liquid phase epitaxy on CdTe substrate, Adopt n on p injection bonding and function and flip-flop mixing process, With a low noise readout circuit, sealed with a high airtightness cellular-metal shell, Using a four-stage Thermo Electric Cooler (TEC),320×256 Short Wave Infrared Focal Plane Cooling Detecto r available to operate at near room temperature (210K). Its main photoelectric performance are signal-to-noise ratio greater than 400, non-uniformity equivalent to 4.69%,operability equivalent to 99.76%,frame rate equivalent to 115Hz,component weight less than 150grams.

Физико-химические основы выращивания варизонного полупроводникового Si1−xGex твердого раствора из жидкой фазы

Abstract. Single-crystal films of a graded-gap solid solution Si1-xGex (0 &lt;x &lt;1) was grown on Si substrates from limited tin, gallium solution-melt. Accordingly, liquid phase epitaxy method was applied in the process. The formation of dislocations, grown under various technological conditions, at the substrate-film interface along the growth direction of the Si1-xGex solid solution was studied. Optimal technological growth modes for obtaining crystalline perfect epitaxial layers and structures are given.

Enhanced Performance of Perovskite Single-Crystal Photodiodes by Epitaxial Hole Blocking Layer.

Introducing hole/electron transporting and blocking layers is considered to enhance the performance of electronic devices based on organic–inorganic hybrid halide perovskite single crystals (PSCs). In many photodiodes, the hole/electron transporting or blocking materials are spin-coated or thermal-evaporated on PSC to fabricate heterojunctions. However, the heterojunction interfaces due to lattice mismatch between hole/electron, transporting or blocking materials and perovskites easily form traps and cracks, which cause noise and leakage current. Besides, these low-mobility transporting layers increase the difficulty of transporting carriers generated by photons to the electrode; hence, they also increase the response time for photo detection. In the present study, MAPbCl3-MAPbBr2.5Cl0.5 heterojunction interfaces were realized by liquid-phase epitaxy, in which MAPbBr2.5Cl0.5 PSC acts as an active layer and MAPbCl3 PSC acts as a hole blocking layer (HBL). Our PIN photodiodes with epitaxial MAPbCl3 PSC as HBL show better performance in dark current, light responsivity, stability, and response time than the photodiodes with spin-coated organic PCBM as HBL. These results suggest that the heterojunction interface formed between two bulk PSCs with different halide compositions by epitaxy growth is very useful for effectively blocking the injected charges under high external electric field, which could improve the collection of photo-generated carriers and hereby enhance the detection performance of the photodiode. Furthermore, the PIN photodiodes made of PSC with epitaxial HBL show the sensitivities of 7.08 mC Gyair−1 cm−2, 4.04 mC Gyair−1 cm−2, and 2.38 mC Gyair−1 cm−2 for 40-keV, 60-keV, and 80-keV X-ray, respectively.

Deep-level defects in high-voltage AlGaAs p–i–n diodes and the effect of these defects on the temperature dependence of the minority carrier lifetime

The variation of the effective lifetime of minority carrier lifetime τeff with temperature has been studied in the temperature range 300–580 K in AlxGa1−xAs base regions of p+–p0–i–n0–n+ high-voltage GaAs–AlGaAs diodes grown by liquid-phase epitaxy. It was found by using deep level transient spectroscopy that the emission/capture of electrons and holes in AlxGa1−xAs p0–i–n0 epitaxial layers is governed by the DX− states of the DX center formed by Se/Te background impurities. The Arrhenius plots associated with the τeff were used to determine the activation energy of the hole capture to the DX− level to be Ec = 159 meV. It is shown that the thermal capture of holes to the DX− level determines the relaxation time of nonequilibrium carriers in the AlxGa1−xAs base layers as well as its temperature dependence.

Perovskite Single-Crystal Thin Film Devices Using Lithography Assisted Epitaxy

Strain engineering is an emerging technique to physically manipulate and enhance semiconductor device performance. Chen et al. recently combined strain engineering with halide perovskites, demonstrating a novel approach toward improvement in optoelectronic properties.

Channel Waveguides in Lithium Niobate and Lithium Tantalate.

Low-loss photonic waveguides in lithium niobate offer versatile functionality as nonlinear frequency converters, switches, and modulators for integrated optics. Combining the flexibility of laser processing with liquid phase epitaxy we have fabricated and characterized lithium niobate channel waveguides on lithium niobate and lithium tantalate. We used liquid phase epitaxy with K2O flux on laser-machined lithium niobate and lithium tantalate substrates. The laser-driven rapid-prototyping technique can be programmed to give machined features of various sizes, and liquid phase epitaxy produces high quality single-crystal, lithium niobate channels. The surface roughness of the lithium niobate channels on a lithium tantalate substrate was measured to be 90 nm. The lithium niobate channel waveguides exhibit propagation losses of 0.26 ± 0.04 dB/mm at a wavelength of 633 nm. Second harmonic generation at 980 nm was demonstrated using the channel waveguides, indicating that these waveguides retain their nonlinear optical properties.

Single-junction solar cells based on p-i-n GaAsSbN heterostructures grown by liquid phase epitaxy

In this paper, we present single heterojunction p-i-n GaAsSbN/GaAs solar cells grown by low-temperature liquid-phase epitaxy (LPE) – this is of interest as a component of multi-junction solar cell devices. The quaternary absorber layer was characterized by low excitation power photoluminescence to give the temperature dependence of the bandgap. This conformed to the Varshni function at low temperatures to within 10 meV, indicating relatively small alloy potential fluctuations. The absorption properties and the transport of the photogenerated carriers in the heterostructures were investigated using surface photovoltage method. A power conversion efficiency of 4.15% (AM1.5, 1000 W·m−2) was measured for p-i-n GaAsSbN/GaAs solar cells, which is comparable to the efficiency of MOCVD grown devices of this type. This is promising for the first report of LPE grown GaAsSbN/GaAs solar cells since the current record efficiency for the cells based on these compounds grown by MBE stands just at 6%. The long-wavelength photosensitivity of the cells determined from external quantum efficiency and surface photovoltage measurements was shown to be extended to 1040 nm.

THE FEATURES OF SCANNING LIQUID PHASE EPITAXY TECHNIQUE AS APPLIED TO THICK EPITAXIAL LAYERS GROWTH

Background. Growing of both thin and thick epitaxial layers is an essential part of semiconductor device technology. Liquid phase epitaxy is among well-known technological methods. There are pulse methods of liquid phase epitaxy specially developed for obtaining thin epitaxial layers. Their adaptation or modification for obtaining thick epitaxial layers is an actual issue.Objective. This work deals with the possibility of obtaining of thick epitaxial layers by extending the capabilities of scanning liquid phase epitaxy technique which also relates to pulse liquid phase growing methods.Methods. In this work we considered the influence of extra heating of the substrate on the growth of epitaxial layers when using scanning liquid phase epitaxy technique. For this purpose we carried out modelling of heat- and mass transport processes in the apparatus of scanning liquid phase epitaxy in conditions of extra heating of the substrate. To experimentally approve the validity of the model proposed we carried out the growing of Ge epitaxial layer on GaAs substrate in the above mentioned conditions.Results. The modelling showed that if the substrate was in contact with the solution-melt more than 1 second in conditions of substrate extra heating in scanning liquid phase epitaxy method, a segment of epitaxial layer dissolution appeared in plots of the grown epitaxial layer thickness against the growth time. The crystallization front temperature was lower than the initial solution-melt temperature in this case. We showed that it was connected with the magnitude of initial cooling/heating of the substrate heater. The modelling also showed that the epitaxial layer growth occurred in kind of a temperature gradient due to the extra substrate heating. Thus in a few seconds there took place the growth in the time-constant temperature gradient. Using the extra substrate heating we obtained epitaxial Ge layer on GaAs substrate from Ga-Ge solution-melt. The growth time was 60 sec. The layer thickness determined by spherical slice technique was 12.6 um.Conclusions. In this work we showed that using extra heating of the substrate’s back side there appeared the conditions for growing of thick epitaxial layers by scanning liquid phase epitaxy technique in case when the substrate temperature was lower than the solution-melt temperature. Here the growth of thick epitaxial layers took place in the condition of temperature gradient at crystallization front.

Negative resistance, capacitance in Mn/SiO2/p-Si MOS structure

In this work is that we have manufactured a new structure that had not been studied by researchers before. This structure is Mn/SiO2/Si was synthesised by liquid phase epitaxy (LPE) as a metal-oxide- semiconductor (MOS) and can be used as a tunneling diode; demonstrated from I–V measurement and negative resistance. The structure and its characterization were examined by scanning electron microscope, XRD diffraction, C-V and I–V measurements. We studied the temperature, voltage dependence of dielectric and electrical parameters of the fabricated Mn/SiO2/P-Si MOS device. I–V measurements for this structure display diode tunnel behavior with negative resistance. Parameters such as series resistance (Rs), permittivity (ε′), dielectric loss (ε″), a tangent of the dielectric loss factor (tan δ), real and imaginary parts of electrical modulus (M′ and M″) and ac conductivity were examined in a temperature range of 303–393 K and frequency range (10 Hz–20 MHz) under 1 Vrms applied voltage along with dc bias range of (−2.0–2.0 V). We found that thermal reordering of the interface is a reason for a continuous density distribution of interface states with homogenous relaxation time, which in turn induced a higher sensitivity to both C and G/w response with electric field frequency. The device showed negative values for capacitance (C), dielectric loss (ε″), and dielectric loss tangent (tan δ) at all temperatures.

Механизм токопрохождения в полупроводниковых p--Si--n--(Si2)1--x(CdS)x структурах

The paper shows that it is possible to use liquid phase epitaxy to obtain single-crystal substitutional solid solution p--Si--n--(Si2)1--x(CdS)x (0 ≤ x ≤ 0,01) on silicon substrates from Sn--Si--CdS solution melt in a palladium-purified hydrogen atmosphere. The manufacturing conditions resulting in perfect epitaxial layers with mirror surfaces exhibiting the best parameters are as follows: crystallization start temperature of 1100 °С; forced cooling rate of 1 degree/min. The epitaxial films obtained feature a thickness of 20 µm and the n conductivity type, specific resistances being 0.018 Ω·cm. Investigation results concerning charge transfer mechanisms in p--Si--n--(Si2)1--x(CdS)x structures at room temperatures show that the forward current--voltage characteristic consists of several characteristic segments, and there are various mechanisms that drive charge transfer processes. At low current densities, the increase in current is due to growing concentration of injected carriers on account of simple local centres; at high densities, it is due to recombination processes in compound complexes inside which electron exchange takes place. This fact is what proves that the structure under consideration displays better rectifying properties with increasing voltage. We determined that these epitaxial films of (Si2)1--x(CdS)x (0 ≤ х ≤ 0,01) solid solutions are promising materials for high-current rectifier diodes

Two-dimensional metal (oxy)hydroxide and oxide ultrathin nanosheets via liquid phase epitaxy

Single- or few-layer transition metal (TM) (oxy)hydroxide and oxide nanosheets are promising two-dimensional (2D) nanomaterials for catalysis and energy storage owing to their plentiful active sites. Facile and scalable synthesis of these 2D ultrathin nanosheets, however, is still a great challenge. Here, we report a liquid phase epitaxy (LPE) method to synthesize single- and few-layer TM (oxy)hydroxide and oxide nanosheets (β-Ni(OH)2, δ-FeOOH, β-CoOOH, and monoclinic LixMnO2) with high-yield and rapid procedure. In the LPE synthesis, the preformed Li2O2 nanosheets with (001) exposed planes function as substrates, enabling the epitaxial growth of TM hydroxides with coherent interface. The final TM (oxy)hydroxides and oxides ultrathin nanosheets can be obtained by in situ oxidation and removal of Li2O2 with simple distilled water washing. To demonstrate their potential applications, the obtained single- and few-layer β-Ni(OH)2 ultrathin nanosheets are coupled with functionalized graphene sheets (FGS), and tested as catalysts for oxygen evolution reaction (OER) and as cathodes for alkaline Ni/Fe battery. Importantly, the single-layer β-Ni(OH)2/FGS composite electrode exhibits excellent catalytic performance for OER and superior charge storage capability for Ni/Fe battery. The present work provides new opportunity for the high-yield synthesis of 2D materials for energy-related applications and beyond.