Epitaxial growth of α-SiC layers by chemical vapor deposition technique

Single crystals of α-SiC were grown on α-SiC substrates at a temperature between 1570 and 1630°C with the standard gas flow rate: H₂ ～ 1 liter/min, SiCl₄ ～ 1.7 ml/min and C₃H₈ ～ 0.1 ml/min. The grown layers were transparent greenish-blue, and surfaces were mirror-like. By an X-ray back-reflection Laue pattern and a reflection electron diffraction method, the grown layer was identified as 6H-SiC, one polytype of α-SiC. Crystal growth was influenced by substrate temperature, flow rates of reaction gases and the surface polarity of the substrate. The growth rate decreased with increase of the substrate temperature in the above temperature region. A lamellar structure was observed on the (0001) Si surface and a mosaic structure was observed on the (000$\text{1}$)C surface. The mole ratios of both SiCl₄ and C₃H₈ to H₂ and that of Si to C had some influence on crystal growth. Undoped layers were n-type due to nitrogen. P-type SiC was grown by doping Al during crystal growth. Doping effects were studied by photoluminescence and electrical measurements.     

Heteroepitaxial growth of β-SiC on silicon substrate using SiCl4-C3H8-H2 system

Single crystals of β-SiC were prepared on Si substrates at a temperature around 1390°C with the standard conditions: H₂ ≈ 1 1/min, SiCl₄≈3 ml/min, C₃H₈≈1 ml/min, deposition period≈10 min. The dependences of the growth rate and the crystallinity on the substrate temperature were studied. By detailed reflection electron diffraction analyses, the crystallinity of β-SiC with 1 μm thickness was found to be better for the layer on the (100) and (110)Si substrates than for that on the (111)Si substrate. An activation energy of 25kcal/mole was obtained for the formation of β-SiC. Optimum conditions to obtain thicker β-SiC films are discussed.     

Electron microscope study of intrinsic and extrinsic stacking faults,and twins in SOS at the early stage of epitaxial growth

Fine structures of the Si films on (1$\text{1}$02) sapphire have been studied by a lattice resolution TEM. The Si was deposited by the pyrolysis of silane in H₂ at 1000°C at a growth rate of 0.1μm/min. The samples for TEM were prepared by peeling off the Si films from the substrates after HF treatment. A film having a mean thickness of 500 Å was composed of (100) and {110} domains. The volume fraction of the {110} domains was more than 50% and about constant as a function of growth time. The {110} domains contained much higher density of microtwins than the (100) domains. These microtwins had various thicknesses including one atomic layer (intrinsic stacking faults) and two atomic layers (extrinsic stacking faults). The density of the intrinsic stacking faults was higher than those of extrinsic stacking faults and other twins. The {110} and (100) islands were nucleated independently and the microtwins were also present in the islands smaller than 500 Å in diameter.     

Step bunching behaviour on the {0 0 0 1} surface of hexagonal SiC

Surface topography of the {0 0 0 1} facet plane of as-grown 6H- and 4H-SiC crystals was studied ex situ by Nomarski optical microscopy (NOM) and atomic force microscopy (AFM). The surface polarity and the polytype of grown crystals largely affect the growth surface morphology of SiC{0 0 0 1} via differences in several thermodynamic and kinetic parameters. NOM observations revealed giant steps of a few micrometers in height on the {0 0 0 1} growth facet, and it was found that a morphological transition of the growth facet occurred when the growth conditions were changed. AFM imaging of the stepped structure of SiC{0 0 0 1} detected steps of height equal to the unit c-lattice parameter (c=1.512 nm for 6H-SiC and 1.005 nm for 4H-SiC). They are fairly straight and very regularly arranged, giving rise to equidistant step trains. Upon nitrogen doping, these regular step trains on the 6H-SiC(0 0 0  )C and 4H-SiC(0 0 0  )C surfaces became unstable: the equidistant step trains were transformed into meandering macrosteps of height greater than 10 nm. In this paper, we discuss the mechanism of macrostep formation (step bunching) on the SiC{0 0 0 1} surfaces through the consideration of the interplay between step energetics (repulsive step interaction) and kinetics (asymmetric step kinetics) on the growing crystal surface and elucidate how they affect the growth surface morphology of the SiC{0 0 0 1} facet.     

Crystal growth of SnO2 by chemical transport method

Single crystals of SnO₂ were grown by the chemical transport method from the powder prepared by heating hydrous stannic oxide. The transport reactions were carried out when iodine and sulfur were simultaneously used as transporting agent, and fine crystals of a few millimeters in dimensions were grown after a ten-day transport; the transport proceeded from 1100°C (charge) to 900°C part in a silica ampoule. The crystals were identified as SnO₂ (cassiterite) by the Weissenberg method. Thermodynamic calculations led to the equilibrium $\text{SnO}{}_2\text{(s) + I}{}_2\text{(g)}\text{+}\text{1}\text{2}\text{S}{}_2\text{(g)}\text{?}\text{SnI}{}_2\text{(g) + SO}{}_2\text{(g)}$ for this transport reaction.     

Growth of ytterbium tartrate trihydrate crystals in silica and agar‐agar gels and their characterization

Single crystals of ytterbium tartrate trihydrate have been grown by gel method using silica and agar‐agar gels as media of growth. The medium of growth influences the morphology of grown crystals, silica gel yielding single and polycrystalline in the form of spherulites whereas agar‐agar gel leading to growth of single and twinned crystals. Materials grown as single crystals have been characterized by using optical and scanning electron microscopy (SEM), EDAX, XRD, FT‐IR, CHN and thermogravimetric techniques. The stoichiometry of the grown single crystals is suggested to be Yb(C₄H₄O₆) (C₄H₅O₆).3H₂O. The FT‐IR spectrum shows the presence of singly as well as doubly ionized tartrate ligands. Results of thermal analysis indicate that the material is thermally stable up to a temperature of 200 °C. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of an External Magnetic Field on Polytypism of CdI2 Crystals Grown from Solutions

The effect of growth conditions on the polytypic structure of crystals of CdI₂ was analyzed for crystallization from solutions. Three solvents were used: H₂O, 3 H₂O + 1 C₂H₅OH and 1 H₂O + 1.C₂H₅OH. Crystals were grown at two temperatures: 5 and 25°C with low and high growth rates; an external magnetic field of about 0.25 tesla was used. The effect of the above three parameters on the formation of the basic polytypes 2H and 4H and on the ordering of faults in disordered structures and polytype cells was studied by X-ray analysis of crystal surfaces. Some distinct relations between the polytypic structure of crystals of CdI₂ and the magnetic field were found.     

Growth parameters for large diameter float zone silicon crystals

Factors that directly affect the ability to grow dislocation free float zone silicon crystals up to 80 mm in diameter have been experimentally determined. The highest yield is obtained for 80 mm diameter crystals by starting with 68 mm to 74 mm diameter poly crystal rod stock. Lower transport speeds for crystal growth of (111) orientation crystals were 3 to 4 mm/min and for (100), 2 to 3 mm/min. Rotation rates of both upper and lower shafts were found to have an effect on growth at the solid-liquid interface. Rates established for lower shaft were 6 to 8 rpm for the (111) crystals and 3 to 4 rpm for (100), counter-clock-wise. Upper rotation rates were 2 rpm on (111) crystals and 3 to 5 rpm on (100), clockwise. Seed orientation, which is critical, was held to within plus or minus $\text{1}\text{2}\text{°}$ of perfect orientation. The minimum seed growth length was 50 to 70 mm. To assist in reducing the side lobes on (111) dislocation free crystals, a cooling ring with a flow or argon was used. For best (100) growth the shape of the lower side of a one turn copper rf work coil was made conical. Six to ten dislocation free crystals in each orientation group were produced using these parameters.     

Vapor phase transport and stoichiometry control of cadmium sulfo-selenide

Cadmium sulfo-selenide Cd_1+y(S_xSe_1?x) single crystals were grown by the sublimation method under controlled partial pressures of sulfur and selenium. The partial pressure control was achieved by amounts of sulfur and selenium introduced in a closed growth tube. To control the deviation from stoichiometry y for the specified compositions x, the sum of chalcogen partial pressures Pps(=p_S2+P_Se2) was regulated, holding the partial pressure ratio () constant. The comp osition x of single crystals, grown with appreciable growth rate, was found to be the same one as the source specimen but the electrical conductivity changed extremely from 1 to 10^-12 (ω cm)^-1 with increasing Pps. Hall effect and thermally stimulated current (TSC) were also measured on the high and low conductivity specimens respectively and found to depend upon the controlled Pps. From these experimental results, it was confirmed that the deviation from stoichiometry y was effectively controlled. The transport rate was also precisely measured as a function of controlled Pps.     

Effect of Mn(II) ions on the growth of ammonium oxalate monohydrate crystals from aqueous solutions: I. Growth habit and surface morphology

The effect of concentration of Mn(II) ions on the growth habit and the surface micromorphology of different as‐grown faces of ammonium oxalate monohydrate (AO) single crystals grown from aqueous solutions was studied at a constant temperature of 30 °C and predefined supersaturations up to 20%. It was observed that the growth habit and the surface morphology of the crystals strongly depend on the supersaturation used for growth and the impurity concentration in the solution. The experimental results were analysed in terms of connected nets determined from different projections of the structure of AO crystals. Analysis of the observations revealed that: (1) the directions of connected nets corresponding to basic growth units composed of single (NH₄)₂C₂O₄ · H₂O molecules are in excellent agreement with the low‐index crystallographic directions of the orientations of growth layers, (2) all faces appearing in the growth morphology of AO crystals are F faces, and (3) the {001} face growing from pure aqueous solutions is essentially a kinetically rough face but the presence of Mn(II) impurity leads to their appearance in the morphology due to increase in the strength of bonds of the connected nets composing the surface graph.     

Epitaxial relationships during the formation of three-dimensional snow dendrites

Investigations of natural polycrystalline snow crystals, especially of plane assemblage of crystals of spatial type, have disclosed a predominant misorientation of 70° in the c-axes between the main branch and the secondary branch. As the result of application of the Coincidence Site Lattice (CSL) theory to the interpretation of this misorientation, {30$\text{3}$2}/{0001}, {30$\text{3}$4}/{30$\text{3}$4} and {30$\text{3}$8}/{30$\text{3}$8} are proposed as probable boundaries having a good atomic fit and low energies. It follows from this proposition that, once an m-c-c-m type of stacking fault is induced, CSL boundaries will extend beyond the junction, giving the 70° misorientation between a deposit and a substrate.     

High-quality silicon/insulator heteroepitaxial structures formed by molecular beam epitaxy using Al2O3 and Si

Heteroepitaxial growth of γ-Al₂O₃ films on a Si substrate and the growth of Si films on the γ-Al₂O₃/Si structures by molecular beam epitaxy have been investigated. It has been found from AFM and RHEED observations that, γ-Al₂O₃ films with an atomically smooth surface with an RMS values of ∼3 Å and high crystalline quality can be grown on Si (1 1 1) substrates at substrate temperatures of 650–750°C. Al₂O₃ films grown at higher temperatures above 800°C, did not show good surface morphology due to etching of a Si surface by N₂O gas in the initial growth stage. It has also been found that it is possible to grow high-quality Si layers by the predeposition of Al layer followed by thermal treatment prior to the Si molecular beam epitaxy. Cross-sectional TEM observations have shown that the epitaxial Si had significantly improved crystalline quality and surface morphology when the Al predeposition layer thickness was 10 Å and the thermal treatment temperature was 900°C. The resulting improved crystalline quality of Si films grown on Al₂O₃ is believed to be due to the Al₂O₃ surface modification.     

Effect of an External Electric Field on Polytypic Growth of CdI2 Crystals from Solutions

The effect of an external steady electric field on polytypic growth of CdI₂ crystals was investigated. Crystals were grown at four temperatures: 5, 25, 35, and 50°C with the use of four solvents: H₂O, C₂H₅OH, 3 H₂O + 1 C₂H₅OH and 1 H₂O + 1 C₂H₅OH. The electric field of the intensity 500 to 2500 V/cm was oriented in two directions: perpendicular or parallel to the c-axis of hexagonal plates of CdI₂ crystals. The analysis of the effect of the field on polytypism of CdI₂ was based on the analysis of the structure of about 800 crystals grown in the presence of electric field and of about 1000 crystals grown in neutral conditions. It was established that the weak electric field used for crystallization of CdI₂ does not influence noticeably the relative stability of basic polytypes (2H, 4H) and of complex polytypic structures (ordered and disordered). The electric field may influence the structure of CdI₂ crystals in two ways: (i) the polytypes formed in the presence of the field have on average two times larger cells than the polytypes formed in neutral conditions, (ii) the polytypes formed in neutral conditions have usually hexagonal cells; only 6 to 30% of polytypes are of rhombohedral type. When the electric field was used the percentage of rhombohedral polytypes increased to about 65%.     

Study of amorphous Ge–SiO2–P+Si tunnel junctions

A new method to determine ac conductivity of amorphous Ge using Al-amorphous Ge–SiO₂–P⁺Si tunnel junctions is presented. Frequency dependence of ac conductivity is found to satisfy the power law in the frequency range between 1 and 50 kHz and the density of localized states at the Fermi level is estimated to be ～ 1.7 × 10²⁰ cm^?3 eV^?1 which decreases to ～ 4.5 × 10¹⁹ cm^?3 eV^?1 after annealing at 175°C.Temperature dependence of tunneling conductance of Al-amorphous Ge–SiO₂–P⁺Si junctions is appreciable only near zero bias. Zero bias conductance of the junctions obeys the $\text{T}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>4</mtext>}}$ law of Mott; the density of localized states obtained from the $\text{T}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>4</mtext>}}$ law is one order of magnitude smaller than that obtained by ac conductivity measurements, being insensitive to annealing. This behavior of the tunnel junctions differes in many respects from those of Al–Al₂O₃-amorphous Ge tunnel juntions.     

Role of halogen in low-temperature growth of polycrystalline thin films by reactive thermal CVD

Low-temperature growth of polycrystalline silicon by reactive thermal CVD, in which a set of reactive gasses are selected to promote film growth and/or crystallization at low-temperatures in thermal CVD, was studied with disilane and halogens such as fluorine and chlorine. High quality polycrystalline Si films were grown on glass substrates in Si₂H₆–F₂ system at 450 °C, while polycrystalline films were hardly deposited when Si₂H₆–Cl₂ system was adapted in the similar condition. We examined the major factors that govern the crystal growth at low-temperature by comparing the experimental results from these two systems. We suggest that the chemical processes on the growing surface in which Si-network is formed while the terminators are eliminated play a significant role for nucleation and growth in the low-temperature deposition by reactive thermal CVD.     

Growth,Structural and Microtopographical Studies of Calcium Iodate,Monohydrate Crystals Grown in Silica Gel

Single crystals of calcium iodate, monohydrate [Ca(IO₃)₂, H₂O] have been grown by gel technique. Prismatic, prismatic pyramidal, needle shaped and hopper crystals were obtained. These crystals were also grown by doping impurities such as copper and iron. Kinetics of growth parameters was investigated. Structural analysis was carried out by using X‐ray powder diffraction method. Microtopographical study of the habit faces, such as prismatic and pyramidal, of as grown crystals was carried out. Some surface structures are reported. These crystals were etched by various etchants and appropriate etchant is reported.     

Investigation on the crystal growth process of spherical Si single crystals by melting

Spherical Si single crystals with a diameter of approximately 1 mm were grown by melting for solar cell applications. The start sources were spherical Si multicrystals fabricated by a dropping method, which had various irregular shapes. Spherical Si multicrystals were melted into droplets and recrystallized on a quartz plate sample holder that was coated with Si₃N₄. It was found that a surface coating of SiO₂ layer on the start sources and oxygen atmosphere during melting and recrystallization were essential to achieve almost perfect spherical shape. Defect-free single crystalline spherical Si could be obtained at recrystallization temperature ranging from 1400 to 1330 °C, corresponding to an undercooling ranging from 14 to 84 °C, with a yield of nearly 100%. At recrystallization temperatures higher than 1380 °C, the recrystallized spherical Si crystals were almost perfect spheres, whereas small protuberances were formed when the recrystallization temperature was lower than 1360 °C. It was also found that that melting at a temperature close to the melting point of Si (at ~1414 °C), a slow cooling rate of ~1 °C/min before recrystallization and relatively fast cooling rate of ~20 °C/min after recrystallization were important for achieving high carrier lifetime. The average carrier lifetime was greatly improved from lower than 2.5 μs of start sources up to ~7.5 μs by melting at optimized conditions. The influences of residual oxygen on the carrier lifetime of recrystallized spherical Si are discussed based on the measurement results with Fourier transform infrared spectrometer.     

Bridgman and Czochralski growth of Ge?Si alloy crystals

Ge_1–xSi_x crystals were grown with the Bridgman and the Czochralski method over a wide concentration range. With the Bridgman process single crystals up to 40 at.% Si were possible. The reasons for polycrystalline growth were the permanent contact of the interface with the crucible wall in combination with curvature towards the crystal and inclusions of high Si concentration. Analysis of striations in Czochralski grown material showed that in this process the crystal does not continuously grow in one direction but consists of piece-wise grown crystals in which the composition permanently changes. According to that fact the main reason for polycrystalline growth in the Czochralski process is common due to lattice mismatch between the seed and equilibrium concentration transients in the crystal corresponding to the microscopic growth rates.     

Study of growth kinetics of ammonium oxalate monohydrate crystals from aqueous solutions

Experimental results of the dependence of linear growth rates of ammonium oxalate monohydrate [(NH₄)₂C₂O₄ · H₂O; AO] single crystals on solution supersaturation are presented. The AO crystals were grown by constant-temperature, constant-supersaturation method at 30 and 40 °C in the supersaturation range of 1–9%. It was observed that the supersaturation dependence of growth rates follows the parabolic growth law. Analysis of the supersaturation dependence of linear growth rates of AO crystals showed (1) that growth models involving surface diffusion and direct incorporation of growth units give kinetic parameters similar to those reported for other compounds grown from solutions, and (2) that the the BCF model of cooperating screw dislocations is also applicable. An inverse relationship between the estimated values of the length, L, of the line containing the dislocations and growth rate, R, and a direct relationship between L and interplanar distance, d_hkl, of the face {hkl} were found. Both these relationships are associated with the process of generation of screw dislocations in the growing layer.