Control of electron concentration in liquid-phase epitaxial layers of Pb1−xSnxTe by indium doping

Indium-doped n-type Pb_1?xSn_xTe, 0?x?0.2, epilayers were grown by liquid-phase epitaxy (LPE) using metal-rich solutions containing from 0.002–10 at. % indium. Doping characteristics of indium and electrical properties of the epilayers were studied by Hall and resistivity measurements at 77K. The dependence of electron concentration and mobility of the Pb_1?xSn_xTe epilayers on indium doping is given for various alloy compositions and LPE growth temperatures. Doping coefficients of ～0.05 and ～0.03 are found for PbTe and Pb_0.8Sn_0.2Te, respectively, grown at ～450°C. For medium to high indium doping, the electron concentration saturates to a constant value independent of doping and LPE growth temperature. The saturation values decrease substantially with increasing x. This work presents the first guide for producing n-type liquid-phase epitaxial Pb_1?xSn_xTe layers with controlled carrier concentration.     

Surface Tension Components Based Selection of Cosolvents for Efficient Liquid Phase Exfoliation of 2D Materials

A proper design of direct liquid phase exfoliation (LPE) for 2D materials as graphene, MoS₂, WS₂, h‐BN, Bi₂Se₃, MoSe₂, SnS₂, and TaS₂ with common cosolvents is carried out based on considering the polar and dispersive components of surface tensions of various cosolvents and 2D materials. It has been found that the exfoliation efficiency is enhanced by matching the ratio of surface tension components of cosolvents to that of the targeted 2D materials, based on which common cosolvents composed of IPA/water, THF/water, and acetone/water can be designed for sufficient LPE process. In this context, the library of low‐toxic and low‐cost solvents with low boiling points for LPE is infinitely enlarged when extending to common cosolvents. Polymer‐based composites reinforced with a series of different 2D materials are compared with each other. It is demonstrated that the incorporation of cosolvents‐exfoliated 2D materials can substantially improve the mechanical and thermal properties of polymer matrices. Typically, with the addition of 0.5 wt% of such 2D material as MoS₂ nanosheets, the tensile strength and Young's modulus increased up to 74.85% and 136.97%, respectively. The different enhancement effect of 2D materials is corresponded to the intrinsic properties and LPE capacity of 2D materials.     

Fabrication of Pb1‐xSnxTe/PbTe heterojunctions by liquid phase epitaxy

Abstract

Pb_1‐x Sn _x Te epitaxial layers were successfully grown on PbTe substrates by liquid phase epitaxy (LPE) technique. The compositions and surface morphology of the epitaxial Pb_1‐x Sn _x Te layers were controlled in the LPE growth, and p‐Pb_1‐x Sn _x Te/n‐PbTe heterodiodes with a good junction‐perfection factor were made.     

Magnetic inhomogeneities in (YSmCa)3(GeFe)5O12 and their elimination by improved growth procedures

We have found that inhomogeneities in the growth direction are a very common occurrence in LPE films of (YSmCa)₃(GeFe)₅O₁₂. These inhomogeneities, which occur over a wide range of solution compositions and growth conditions, are not detected by the usual measurements of bubble parameters. However, they can be observed in the presence of an in-plane field using a technique which we describe. Experiments using this technique indicate that there is a thin (≤ 1 μm) layer at the film/substrate interface which has magnetic properties significantly different from the rest of the film. Special growth procedures which will avoid the formation of this “interface layer” are described in detail. Comparisons between films with and without this layer show, surprisingly, that there is no direct correlation between the coercivity and the presence of this layer. However, a correlation between coercivity and samarium concentration is observed when all other growth parameters are kept as constant as possible.     

A simple reactor for growth of HgCdTe films using LPE technique

A reactor for growth of Hg_1−x Cd _x Te epilayers by liquid phase epitaxy has been designed and developed. The layers have been successfully grown using this liquid phase epitaxy (LPE) reactor.     

Reproducible garnet film preparation using fast growth rates

Large numbers of uniform defect free magnetic garnet films having essentially identical properties can be prepared from the same melt using conventional LPE dipping techniques when growth rates of 2–4 μm/min are employed. Such fast growth rates suppress compositional drift in successive films and avoid second-phase precipitation. Data is given for 40 highly perfect films (> 1 cm², 4πM_S = ～ 200 gauss) grown sequentially from the same melt. Melt composition and growth conditions necessary to achieve fast growth are discussed.     

InAsSbP/InAs heterostructures for thermophotovoltaic converters: Growth technology and properties

A liquid phase epitaxy (LPE) technique for growing indium arsenide (InAs)based narrow-bandgap semiconductor compounds for thermophotovoltaic (TPV) applications has been developed. InAs-based multicomponent solid solutions and InAs/InAsSbP heterostructures with E _g = 0.35–0.6 eV are promising materials for TPV converters that operate at an emitter temperature of 1000–2000°C. The sensitivity of new TPV elements is extended toward longer wavelengths (up to 3.8 μm), which ensures effective conversion of low-energy photons. The epitaxial films of quaternary InAsSbP solid solutions were obtained by LPE from a supercooled solution melt and by the liquid phase electroepitaxy technique with controlled doping of a growth solution from a single liquid source of components. The films have homogeneous compositions and highly perfect crystal structures. The values of reverse saturation currents in n-InAs/p-InAsSbP heterostructures are close to theoretical predictions.     

Changing planar thin film growth into self-assembled island formation by adjusting experimental conditions

Illustrated in this paper are two examples of altering planar growth into self-assembled island formation by adapting experimental conditions. Partial oxidation, undersaturated solution and high temperature change Frank-Van der Merwe (FM) growth of Al_0.3Ga_0.7As in liquid phase epitaxy (LPE) into isolated island deposition. Low growth speed, high temperature and in situ annealing in molecular beam epitaxy (MBE) cause the origination of InAs/GaAs quantum dots (QDs) to happen while the film is still below critical thickness in Stranski-Krastanow (SK) mode. Sample morphologies are characterized by scanning electron microscopy (SEM) or atomic force microscopy (AFM). It is suggested that such achievements are of value not only to fundamental researches but also to spheres of device applications as well.     

Lead incorporation in thin iron garnet films produced by LPE and chemical analysis by the radioactive tracer technique

The mode of incorporation of lead ions into Y₃Fe₅O₁₂ single crystal thin films grown by the LPE technique from lead containing fluxes has been carefully studied using radioactive tracers as the analysis technique. In particular, the variation of lead content with film thickness has been studied. It has confirmed the existence of a lead rich layer at the interface of the substrate and the film. The formation of this layer is connected with the transient period during which stable growth is established. The variation of lead with film growth rate is established. The misfit with the substrate lattice parameter has an influence on the grown film, whereas the species of the substrate does not have an effect. There is evidence that rare-earth ions enter the octahedral sites in the garnet.     

Investigations on the nucleation parameters of InGaAs grown on InP during LPE

The initial stages of LPE growth of the InGaAs ternary compound on an InP substrate were analysed using the classical heterogeneous nucleation theory, incorporating lattice mismatch between the grown alloy and the substrate. The explicit expression for the lattice mismatch induced supercooling for the growth of the chosen system was established, and it was used to evaluate the nucleation parameters. It has been proved theoretically that the nucleation barrier for the formation of InxGa_{1 –x} As on InP depends very strongly on the composition of the alloy; the condition for the growth of good quality InGaAs on InP was calculated.     

LPE growth of iron garnets containing Ge4+ and Si4+ for bubble applications

Magnetic garnet films containing Ca²⁺ plus Ge⁴⁺ and/or Si⁴⁺ are of interest for bubble device applications. Extensive property variations can be obtained in compositions having a lattice constant essentially the same as GGG and suitable films are easily grown using conventional LPE dipping techniques. Films of Y_3?xCa_xFe_5?xGe_xO₁₂, where x = 0.0 to 3.0, have been prepared on GGG substrates and have bubble diameters from sub-micron sizes to over 150 μm. Preferred device materials having moments between ～ 200 and 500 gauss with bubble diameters of ～ 1 to 6 μm have stable bubble properties from well below ?10 to at least 120°C and mobilities of ～ 2000 cm/sec/Oe. The effect of growth conditions and melt composition on bubble properties are discussed.     

Liquid-phase epitaxy of 2H-SiC film on a (0001) 4H-SiC substrate in Li-Si melt

We first applied a liquid-phase epitaxy (LPE) method to the growth of 2H-SiC to obtain an oriented 2H-SiC layer. The LPE growth was performed on a (0001) 4H-SiC substrate in a Li-Si-C melt at 850 °C. A LPE layer grew on the carbon face of the (0001) 4H-SiC substrate with the area of about 1 × 1 mm². The thickness and morphology of the LPE layer were confirmed by scanning electron microscope (SEM), and the polytype of the LPE layer was determined using a high-resolution transmission electron microscope (HR-TEM) and a Raman spectroscopy. SEM measurements revealed that the thickness of the LPE layer was 50 μm and that this layer developed with a hexagonal shape. HR-TEM observations and Raman spectral analysis showed that 2H-SiC layer grows on 4H-SiC substrate with the relationship of (0001) 2H-SiC (0001) 4H-SiC. In this study, we first succeeded to grow <0001>-axis-oriented 2H-SiC films and concluded that the LPE technique is applicable to the growth of oriented 2H-SiC films in the Li-Si melt.     

Stress-induced anisotropy in LPE grown Ni(Fe,Al)2O4 films

Preliminary results are reported about the growth of single crystal Ni(Fe,Al)₂O₄ films, grown by means of liquid phase epitaxy on (111)MgO and on (111)ZnGa₂O₄ substrates using a PbO-B₂O₃-Fe₂O₃ solvent. While films grown upon MgO show stress relief at the growth temperature, films grown upon ZnGa₂O₄ possess a tensile strain due to elastic deformation. Since λ₁₁₁ for NiFe₂O₄ is strongly negative a stress-induced uniaxial anisotropy is present in the films. Stripe domains can be observed with the Bitter technique and when a magnetic field is applied perpendicular to the plane of the film, magnetic bubbles with a diameter of ～2 μm appear. A bubble stability factor q exceeding unity is obtained. For the first time magnetic bubbles are found in LPE grown spinel ferrites.     

Epitaxial Growth of Oriented Metalloporphyrin Network Thin Film for Improved Selectivity of Volatile Organic Compounds

This study reports an oriented and homogenous cobalt‐metalloporphyrin network (PIZA‐1) thin film prepared by liquid phase epitaxial (LPE) method. The thickness of the obtained thin films can be well controlled, and their photocurrent properties can also be tuned by LPE cycles or the introduction of conductive guest molecules (tetracyanoquinodimethane and C₆₀) into the PIZA‐1 pores. The study of quartz crystal microbalance adsorption confirms that the PIZA‐1 thin film with [110]‐orientation presents much higher selectivity of benzene over toluene and p‐xylene than that of the PIZA‐1 powder with mixed orientations. These results reveal that the selective adsorption of volatile organic compounds highly depends on the growth orientations of porphyrin‐based metal‐organic framework thin films. Furthermore, the work will provide a new perspective for developing important semiconductive sensing materials with improved selectivity of guest compounds.     

Simulation studies of liquid phase epitaxial growth of In1-xGaxAsyP1-y

Liquid phase epitaxial growth of In_1-xGa_xAs_yP_1-y, a well known quaternary compound semiconductor, has been studied systematically. A numerical simulation technique has been employed to construct the concentration profiles of Ga, As, and P atoms in an In-rich melt at successive equally spaced layers in front of an InGaAsP crystal growing by LPE. The growth rate has been calculated using the concentration gradients established at the solid-liquid interface. The composition and the thickness of the grown InGaAsP solid layer have been studied as a function of growth parameters, such as cooling rate, system temperature, and growth time. It is observed that the thickness of the grown solid depends on the cooling rate, whereas the solid compositions do not show any dependence on the cooling rate. Our theoretical findings have been compared with experimentally reported values and the results are discussed in detail.     

Fabrication of multi-layer optical waveguide by LPE technique

Multi-layer structure optical waveguides, consisting of Li(Nb,Ta)O₃ and LiTaO₃ thin films, were fabricated on LiTaO₃ substrates (Z- and Y-plates) by LPE technique. Solution compositions appropriate for Li(Nb,Ta)O₃ optical waveguiding layers and LiTaO₃ cladding layers were examined from the viewpoints of lattice matching, refractive indices and saturation temperature for LPE dipping. Based on determined solutions, multi-layer film consisting of Li(Nb,Ta)O₃ and LiTaO₃ were epitaxially grown alternately onto the substrates. Optical propagation losses in Li(Nb,Ta)O₃ waveguiding layers were 0.5 ～ 0.9 dB/cm.     

LPE growth of Cd doped PbTe

Cd doped PbTe epilayers were grown on Pb_0.8Sn_0.2Te substrates by liquid phase epitaxy (LPE). The Cd behavior in the solution and the solid (substrate and epilayer) was studied. The dependence of the carrier concentration on Cd doping was investigated.     

Empirical values for growth-induced anisotropy energy coefficient for designing garnet LPE films

Growth-induced anisotropy energy coefficients and their super-cooling temperature dependence, both attributed to rare-earth ion-pairs, Kⁱ_j, and αⁱ_j, are obtained by analyzing the relationship between growth temperature dependence of uniaxial anisotropy energy, K_u, and garnet compositions. Regression processes were used for analysis. Better agreements are obtained when the newly obtained Kⁱ_j and αⁱ_j values are applied to estimate growth-induced anisotropy energy for 24 garnet compositions. The ratio of calculated growth-induced anisotropy energy values to observed values is 0.98 ± 0.12, when newly obtained Kⁱ_j and αⁱ_j values are used in place of Eschenfelder's Kⁱ_j values (0.85 ± 0.24). Appropriate melt compositions, to obtain LPE garnet films with bubble properties which meet device requirements, are easily given by computer simulation using the newly obtained values.     

Ultimate InAsSbP solid solutions for 2.6–2.8-μm LEDs

Epitaxial layers of phosphorus-rich InAs_1? y ? x Sb _y P _x solid solutions were obtained by liquid phase epitaxy (LPE). The films with x=0.32 were grown at 575 °C on isoperiodic (100)InAs substrates. It is shown that the growth of InAsSbP layers from a phosphorus-rich liquid phase is accompanied by saturation of the phosphorus content in the solid state. InAsSbP-based diode heterostructures emitting in the 2.6–2.8 μ m wavelength range were obtained, the output emission power of which is sufficient for detecting both natural and industrial gases in the atmosphere.