Growth Of Crystal Layers Research Articles

Formation and Characterization of Single Crystal Ni2MnGa Thin Films

AbstractIn this paper, molecular beam epitaxial growth of Ni2MnGa single crystal layers on GaAs (001) using a NiGa interlayer is reported. X-ray diffraction and transmission electron microscopy confirmed an epitaxial relationship of Ni2MnGa [100]“010] // GaAs [100] [010] and a tetragonal structure of the film (a = b = 5.79 Å, c = 6.07 Å). Magnetic measurements using vibrating sample and superconducting quantum interference device magnetometers revealed an in-plane magnetization of ∼200 emu/cm3at room temperature and a Curie temperature of ∼350 K. The martensitic phase transformation was observed to occur at ∼250 K

The material quality of CVD-grown SiC using different carbon precursors

We report an investigation where nine different hydrocarbons have been used as carbon precursor in the growth of 4H and 6H silicon carbide (SiC) epitaxial layers. For the various growths the C/Si ratio was varied from 2 to 6, the temperature in the range 1550–1600°C, and the growth rate was about 3–4.6 μm/h. All hydrocarbons, except methane, could be used for growth of high crystal quality epitaxial layers at low C/Si ratio and low growth rate (3 μm/h) as confirmed by the smooth morphology, and by low-temperature photoluminescence showing strong free exciton and narrow well-resolved nitrogen-bound exciton lines. Hydrogen-related lines could be observed in the spectra of epitaxial layers grown with C-precursors which have double and triple bonds in the molecule. The unintentional incorporation of p-type dopants, such as, aluminium and boron impurities is proposed to correlate to the surface roughness. Propane gave the most stable growth of the hydrocarbons as C-precursor at higher growth rate.

A Novel Technique for Ultrathin CoSi2 Layers: Oxide Mediated Epitaxy

A novel technique, oxide mediated epitaxy (OME), was recently described for the growth of single crystal CoSi2 layers on the (100), (110), and (111) surfaces of silicon. Deposition of a thin layer of cobalt (1–3 nm) onto Si surfaces covered with a thin peroxide-grown SiOx layer and annealing at 500–700° C led to the growth of essentially uniform, epitaxial CoSi2 layers. The thin SiOx layer remained largely on the surface of the OME grown CoSi2 layers as a cap. Deposition of cobalt at elevated temperature onto OME grown CoSi2 layers led to a significant re-evaporation of cobalt from the SiOx surface. Presently, the OME effect was demonstrated on heavily doped p+ and n+-Si and on narrow (0.22 µ m) Si lines. On all surfaces, thin (10–30nm), excellent quality, CoSi2 single crystal thin films were grown by repeated growth sequences involving depositions of cobalt at room temperature and anneals at 600–700° C. It was also shown that faceting at CoSi2/Si(100) interfaces could be significantly reduced by a high temperature anneal.

Microstructural characterization of YBa2Cu3O7 whiskers grown from the gas phase

The microstructures of YBCO whiskers grown by in-situ high pressure RF magnetron sputtering in Ar-O2 atmosphere on (100) MgO substrates at a temperature range of 650–720°C were characterized by transmission electron microscopy. Two characteristic, plate-like, heavily twinned crystal and whisker shapes were formed during processing; elongated-hexagonal crystals with an average aspect ratio of 2 and long rectangular whiskers with aspect ratios from 5 up to 30 (length 60 μm). The growth direction for elongated-hexagonal crystals was \({{[110]} \mathord{\left/ {\vphantom {{[110]} {[1\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{1} 0]}}} \right. \kern-\nulldelimiterspace} {[1\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{1} 0]}}\) and for rectangular whiskers a/b-axis. In both cases the plate normal was parallel to the c-axes. At the beginning of processing a non-uniform c-axis oriented layer was formed on the MgO substrate followed by the initiation and growth of elongated-hexagonal crystal layer. Thereafter rectangular whiskers started to grow on it.

The origin of melt-texture crystal growth process in a simple tube furnace

The melt-texture growth (MTG) method has been shown to be effective in fabricating high-Tcsuperconducting bulk samples with highly oriented layers of single crystals. The critical current densityJcof the typical samples are enhanced significantly. Furthermore, making use of the nonzero spatial temperature gradient at certain locations of a common tube furnace, we fabricated Y-123 bulk samples with various dopants allowingJcup to ≈3.0×104 A cm−2 in our recent investigations. We followed up our project by analyzing the relations among the crucial parameters involved in the modified version of the MTG process. These parameters include the temperature gradient, the time rate of change of temperature, the “growth front” of the crystal, etc. Our study indicates that some of the empty space regions that appear between layers are only shallow “gap lines.” True layers of single crystals do exist, and we present an explanation for the growth of crystal layers along special directions as observed.

Aluminum nitride/silicon carbide multilayer heterostructure produced by plasma-assisted, gas-source molecular beam epitaxy

Pseudomorphic structures containing β(3C)-SiC and 2H-AlN have been grown on vicinal α(6H)-SiC(0001) at 1050 °C by plasma-assisted, gas-source molecular beam epitaxy. Reflection-high energy electron diffraction and cross-sectional high-resolution transmission electron microscopy showed all layers to be monocrystalline. The AlN layers were uniform in thickness. Defects in these layers initiated at steps on the 6H-SiC film. The 3C-SiC layers contained a high density of stacking faults and microtwins caused primarily by the interfacial stresses generated by the mismatch in lattice parameters between AlN and β-SiC coupled with the very low stacking fault energy of SiC. This is the first report of the deposition of single crystal SiC/AlN/SiC thin film heterostructures on any substrate as well as the first report of the epitaxial growth of single crystal layers of binary materials with three different crystal structures.

Growth of III–V compounds by liquid phase epitaxy

In this paper, we shall review important aspects of the growth of thin single crystal layers of binary, ternary and quaternary III–V compound semiconductors by liquid phase epitaxy (LPE). The emphasis will be on materials which can be grown lattice-matched to the common substrate materials GaAs, InP and GaSb. Usefulness and limitations of the LPE technique are highlighted.

Evidence for a Grain Boundary Grooving Model of Agglomeration in Polycrystalline Tisi2 Thin Films

ABSTRACTAn equilibrium model for agglomeration based upon the mechanism of grain boundary grooving in polycrystalline thin films is suggested. It involves an energy balance between surface, interface, and grain boundary energies, and predicts parameters which will influence the onset of agglomeration. It has been determined that small grain size, low grain boundary energy, high film surface and interface energies, and growth of single crystal epitaxial layers should promote resistance to agglomeration. Polycrystalline TiSi2 thin films deposited on Si substrates have been observed using cross-section TEM. The micrographs provide evidence that, for these films, the grain boundary grooving mechanism is dominant and most of the modeling assumptions are valid.

A new technique for the growth of III-V mixed crystal layers

A new growth technique was developed as a method to obtain thick III-V mixed crystal layers applicable to substrate for opto-electronic devices. The distinctive feature is that a growth ampoule, in which a seed crystal and the alloy solution were put, was rotated at high speed, while the crystal growth was initiated by lowering the solution temperature. The occurrence of constitutional supercooling near the growth interface was avoided by agitation of the solution due to the high speed rotation, and as a result it was possible to grow InSb 1- x Bi x and In x Ga 1- x Sb mixed crystal layers of 10 to 20 mm thicknesses on InSb and GaSb seed crystals, respectively.

Investigation of crystal structure of cubic silicon carbide layers

en

Metastable (GaSb) (1−x)(Sn 2) x alloys: Crystal growth and phase stability of single crystal and polycrystalline layers

Single-phase metastable (GaSb) (1−x)(Sn 2) x alloys with x ⩽ 0.23 far exceeding the equilibrium solid solubility limit of x ⪅ 0.02 for Sn in GaSb, have been grown by rf sputter deposition. The key feature allowing the growth of single phase alloys was the use of low energy ion-bombardment-induced collisional mixing during deposition. Films grown at elevated temperatures T s on GaAs(100) substrates were found to be single crystals while polycrystalline films with very strong (220) perferred orientation and grain sizes of 20–40 nm were obtained on amorphous glass substrates. The maximum film growth temperatures T m at which single phase films could be obtained was a function of the negative substrate potential V s during deposition and the composition x. For V s = 75 V, T m ranged from 375 °C at x = 0.06 to 125 °C at x = 0.23. Crystal growth and post-annealing studies both indicated that the transformation from the single-phase metastable state to the equilibrium (GaSb + βSn) state occurs through a continuous set of metastable GaSb-rich phases and that Sn precipitates out first in the α-diamond structure and then transforms to the β-tetragonal structure. In single crystal films, the GaSb-rich phase precipitates out coherently with the alloy matrix. The activation energy for phase separation ranged from ∼ 1.4 eV for alloys with x = 0.06 to 0.9 eV at x = 0.23. A phase map for crystal growth, plotted as a function of T s and x, and an annealing transformation diagram for (GaSb) 0.86(Sn 2) 0.14 was determined.

Growth of single crystal NiSi2 layers on Si (110)

Growth of single crystal nickel silicide layers on Si (110) under ultrahigh vacuum conditions is demonstrated. Formation of thin templates followed by deposition of nickel at ∼650 °C produced NiSi2 layers with χmin=3%. Low-energy electron diffraction revealed unreconstructed silicide surfaces. Transmission electron microscopy showed the entire silicide-silicon interface to consist of {111} type inclined facets. Long and straight dislocations were observed at facet boundaries with Burgers’ vectors of 1/4 〈111〉 type. The usual 1/2 〈11̄0〉 type misfit dislocations were also found on inclined facets.

Growth of single crystal layers of AgGaS 2 by liquid phase epitaxy using halide fluxes

High quality single crystal layers of AgGaS 2, using the halides KCl and AgCl as fluxes, have been grown by liwuid phase homoepitaxy. Temperature-composition ( T- X) phase equilibria for the systems KCl-AgGaS 2 and AgCl-AgGaS 2 are presented. The KCl-AgGaS 2 T- X diagram is seen to be a simple pseudobinary eutectic system and is therefore easily applied to solution growth of AgGaS 2. The AgCl-AgGaS 2 system, however, is more complicated due to reactions between AgCl and AgGaS 2 in forming GaCl 3 and Ag 9GaS 6. The use of AgCl as a solvent in LPE is made practical by externally refluxing GaCl 3 above the melt. Optimum conditions for growth from KCl and AgCl solutions are described. Growth rates of 0.15 μm/min have been achieved using KCl solutions. The crystalline quality of the epilayers produced was substantially better than that of the substrates as inferred from X-ray rocking curves.

Liquid phase epitaxial growth of AgGaS2 using chalcogenide (sulphide) fluxes

Growth of single crystal layers of AgGaS2 by liquid phase homoepitaxy is reported for the first time. Investigation of T- X phase equilibria of several binary sulphide AgGaS2 systems indicated Sb2S3 and PbS as suitable solvents for solution growth. The phase equilibria for the systems Sb2S3AgGaS2 and PbSAgGaS2 are described and liquid epigrowth of AgGaS2 from such solutions is presented. Growth rate of AgGaS2 epilayers, under optimum conditions, from Sb2S3 solutions i 0.12 μm/min and from PbS solutions is 0.08 μm/min.

Growth from high-temperature solutions effected by chemical potential gradients

The process of crystallization from a thin solution zone under conditions whereby the driving force of growth is the difference in the chemical potentials of the substrate and source has been investigated experimentally in the Si- Al system. It has been shown that significant growth rates can be achieved in compositions with polycrystal and stressed crystal sources. This allows use of the process as the basis for crystal and epitaxial layer growth techniques. Experimental parameter dependencies support the theoretical expressions for the growth rate. The difference in the chemical potential of silicon atoms in single crystals and polycrystals has been determined. The reasons for the occurence of this difference are discussed.

Growth kinetics of dislocation-free interfaces and growth mode of thin films

The theory of layer growth of crystals is generalized to describe the growth kinetics of interfaces free of screw dislocations when the initial surface is either of the deposited material or it is a foreign substrate. The basic kinetic equations for the height h (or the thickness) of the deposit and for the transient growth rate R of the interface are formulated upon allowing for different overall kinetics of filling up the successive layers. These equations are solved in some simple cases of continuous and nucleation growth at deposition on both own and foreign substrate and expressions are found for h and R as functions of time t, the latter giving the exact steady state growth rate at t → ∞. The thermodynamics of nucleation at low supersaturations is discussed and it is shown that the differences in the kinetics of filling of the layers may result in extreme deviations of the actual cluster shape from the equilibrium one. As an application of the theory the effect of the supersaturation on the mode of thin film growth is examined. The critical supersaturation for transition from island to layer mode of growth is defined in a general form and it is demonstrated how it may be calculated in one particular case. Many of the results obtained are valid for the whole supersaturation range and for all possible transport-transfer mechanisms.

Dependence of lattice parameter on composition in substituted yttrium iron garnet epitaxial layers

The growth of single crystal layers is described for the composition Y 3− x R x Fe 5− y Ga y O 12 (R=Sm or La) on (111) Gd 3Ga 5O 12 substrates by liquid phase epitaxy. The reproducibility of the method is presented, the dependence of the distribution coefficients of the substituents on supercooling, and the relation between strain and composition of the layers are discussed. It is concluded that the formation or ordering of vacancies or interstitials, or substitution by impurities such as Pb 2+ of B 3+, have a negligible effect on the lattice constant.

The growth habits and surface structure of ice crystals

Abstract Evidence to show that the layer growth of ice crystals occurs mainly by the surface diffusion of molecules to the growing steps is presented. Measurements of the rate-of-change of separation of adjacent growth steps allow the mean migration distance x s of molecules on the basal face to be deduced; this parameter shows a remarkable variation with temperature over the range 0°C to -40°C. The six changes of ice crystal habit, which occur between 0°C and -25°C, are explained in terms of the variation of x s with temperature and the relative rates of surface diffusion on the basal and prism faces. Photographs reveal the presence of micron-size steps on the crystal surfaces and their formation is explained in terms of the bunching and amalgamation of much thinner growth layers. It is shown that if two layers are nucleated so that their initial separation is <2x s, they will close up and amalgamate to form a double step travelling at half the speed; this in turn, will be overtaken by other layers to produce eventually very slowly moving, visible steps. The rate of closing of two adjacent steps and the distance and time required for the formation of steps of a given height are calculated and found to agree quite well with observation. Hopper, skeletal and dendritic growth of ice crystals have been studied by time-lapse ciné-photography. These growth features are largely controlled by the supersaturation of the vapour. They are shown to be a consequence of nucleation of growth layers at the crystal edges and corners under high local supersaturation, unequal rates of surface diffusion on basal and prism faces, and the bunching and amalgamation of layers as they spread towards the centres of crystal faces.