Growth Of Bulk Single Crystals Research Articles

Determination of lattice polarity for growth of GaN bulk single crystals and epitaxial layers

The polarity of the lattice of bulk single GaN crystals and the polarity of homoepitaxial and heteroepitaxial-on-sapphire GaN thin films has been studied using convergent beam electron diffraction. Diffraction patterns obtained at 200 kV for the 〈1–100〉 projection of GaN were matched with calculated patterns. The lattice orientations of two commonly observed bulk single-crystal facets were identified. It is shown that the smooth facets in single crystals correspond to the (0001), Ga-terminated, lattice planes, whereas the rough facets correspond to the (0001̄), N-terminated, planes. It is also shown that metalorganic chemical vapor deposition epitaxy retains the polarity of the substrate, i.e., no inversion boundaries were observed. Heteroepitaxy on sapphire is shown to grow in the (0001), Ga-terminated orientation.

A study of sol-gel derived Sr2(AlTa)O6 by Raman spectroscopy

Among the dielectric materials of current interest the cubic ternary system Sr2(A1Ta)Q (SAT) is particularly attractive since it exhibits an excellent lattice and thermal expansion match with Y-123, Y-124, Bi2212, Bi-2223 and T1-1223 superconductors. Its low dielectric constant and low tan 5 favours its use in microwave device applications. Thin films of high To oxides deposited on SAT ceramics are chemically non-reactive at the interface between the films and the ceramic material. SAT ceramic samples were identified to have double cell cubic perovskite strucmre with lattice parameter a = 0.77805 nm and melting temperature 1900 °C [1]. Thin films of SAT and multilayers of SAT/YBCO (YBa;Cu3OT) were grown on (001) LaA103 and (001) MgO substrates by pulsed laser deposition [2]. SAT was first prepared by Brandle and Fratello [3] in a study of potential substrate materials for the growth of high temperature superconductor films. The growth of bulk single crystals has not yet been reported. In our recent work we grew single crystal fibres by a laser beam pedestal growth technique [4]. In comparison to other binary perovskite dielectrics the crystal structure of SAT is cubic. As a result, fibres having potential deleterious multiple growth orientations [1, 5, 6] are unlikely. Phase-pure Sr2(A1Ta)O6 (SAT) was prepared by the sol-gel route including Sr metal, A1 (tri-secbutoxide) and Ta(OC2H»)» as the starting organic precursors. Sol-gel processing of SAT can lead to highly phase-pm'e homogeneous powders, and these powders can offer significant advantages over conventionally processed powders. The SAT phase was formed at 1400 °C from a transparent xero-gel. Scanning electron microscope (SEM) analysis showed the particle size to be sub-micrometre -0.1/~m. Raman analysis of SAT exhibited a sharp band at 791 cm -I due to well-defined molecular vibration. Complex alkoxides were prepared by reacting Sr metal, A1 (tri-sec-butoxide) and Ta2(OC2Hs)» organic precursors. First, B-site was formed by refluxing Al(tri-sec-butoxide) and Ta(OC2H»)5 organic precursors with 2-methoxyethanol (MOE; C3H802) at 125 °C for 6 h. Finally, the Sr metal was refluxed with C3H802 and later reacted with the double alkoxide mixture of A1-Ta precursor complex sol at 125 °C for 12 h. The solution was cooled to room temperature and the pH was found to be -4.0. Later the solution was hydrolysed with H20 and C3H80 in the ratio 1:4. The solution was placed in a 60 °C oven for 4-5 h to form the gel. The schematic reaction sequence for

Growth and Properties of Bulk Single Crystals of GaN

ABSTRACTIn this paper we review recent developments in the growth of bulk GaN crystals by a high-pressure, high-temperature method. We also provide information on various physical properties of bulk GaN material. Then, some preliminary results on the homoepitaxial growth of GaN are given. In the second part of this paper we discuss the following problems: the possible origin of the large free electron concentration in undoped GaN material, the parasitic effect of yellow luminescence and the nature of Zn- and Mg-acceptors.

Bulk Processing of High-Temperature Superconducting Oxides

Recent research and development activities related to processing of bulk superconducting oxides are reviewed. Wiring techniques in bismuth and thallium systems are already fairly well developed, allowing critical current densities to meet a required value for application at liquid helium temperature when a certain magnetic field is applied. In yttrium systems, pinning centers have been successfully introduced into the material even at liquid nitrogen temperature as a result of improvements in processing. Some applications utilizing this strong pinning force have been tested. The mechanism for growth of YBa 2 Cu 3 O 7-d from the partially molten state has also gradually been clarified. In all three types of system, it is expected that superconducting wires with high critical current densities at liquid nitrogen temperature will be developed. A recently developed method for growing bulk single crystals is also mentioned briefly.

Quantitative infrared imaging for the measurement of dopant distribution in gallium arsenide

This paper discusses a quantitative infrared imaging technique for measurement of dopant distribution for n-type semiconductors such as selenium-doped GaAs. It is demonstrated that the dopant distribution for an entire axial slice may be found using this technique. The imaging apparatus consists of a uniform light source, a narrow bandpass filter, a high resolution charged coupled divice (CCD) detector, and an image processor. Neutral density filters of known transmission are used to calibrate the grey level output of the image processor to transmission. The absorption coefficient is calculated based on the transmission, reflectance and thickness of the sample. The imaging is performed at 1.05 μm. Free carrier concentration is then found from its relation to the absorption coefficient. Grey level intensity of the sample can be used as a measure of free carrier concentration. This calibration is done assuming complete ionization of free carriers and that all absorption is due to free carriers. An illustration of the dopant distribution imaged for a longitudinal slice of a Czochralski grown bulk single crystal is shown as an example of this technique and compared to theoretical results.

Effect of impurities on the processes of crystal growth

The influence of impurities inherently present in growth media and deliberately added to them on crystal growth is manifested during the process of crystallization in a number of ways. Impurities change growth rates, shape and thickness of growth layers and growth habit, and are trapped as impurity striations and large clusters of impurities and inhomogeneities. Some of these effects of impurities are reviewed for growth of bulk single crystals.

Heat transfer during GaAs growth of bulk single crystal by the liquid encapsulated vertical Bridgman technique

We developed a numerical simulator for monitoring and predicting temperature distribution including position and shape of a melt/crystal interface in the liquid encapsulated, vertical Bridgman technique in order to determine the optimum design of the growth system and growth condition for obtaining GaAs single crystals with high quality. It is pointed out that the thermal conductivity of the crucible including anisotropy significantly affects the melt/crystal interface although thickness of the crucible wall is only 1 mm. The growth condition for obtaining crystals with the flat melt/crystal interface is determined by using the simulator.

Single Crystal Growth of Cu–III–VI2 Semiconductors by THM

The traveling heater method (THM) has been applied to the single crystal growth of Cu–III–VI2 chalcopyrite semiconductors. Up to this time, bulk single crystals of CuGaS2, CuGaSe2, CuInS2 and CuInSe2 ternary compounds have been obtained by the THM technique using In solvent. The THM growth of bulk single crystals of CuGa0.6In0.4S2 quaternary alloy, which is lattice-matched to ZnS, has been investigated. By the use of In-solution zones containing 60 mol% CuGa0.37In0.63S2 solute, single crystals with a uniform composition of CuGa0.6In0.4S2 were obtained.

Growth of bulk single crystals of YBa 2Cu 3O 7−χ from a new type of crucible

YBa 2Cu 3O 7−χ single crystals with low impurity concentration and sizes up to 2x2x2 mm 3 have been grown in a new type of ceramic crucible using both spontaneous crystallization and growth of a limited number of seeds on the yttrium oxide holder. The as-grown crystals reveal a superconducting transition with T off c=89.8 K without additional annealing in oxygen.

Phase equilibria in La(Y)-Ba-Cu-O systems and growth of high-T/sub c/ superconductor bulk single crystals

The isobaric phase diagrams of BaO(La/sub 2/O/sub 3/)-CuO-CuO/sub 0.5/ systems at a partial oxygen pressure of 0.021 MPa and the phase transition BaO/sub 2/ to or from BaO at oxygen pressure up to 2.1 MPa were studied. A flux method for growing bulk single crystals of YBa/sub 2/Cu/sub 3/O/sub 7- delta /, La/sub 2/CuO/sub 4/, (LaSr)/sub 2/CuO/sub 4/, Nd/sub 2/CuO/sub 4/, and (NdCe)/sub 2/CuO/sub 4/ has been developed using a rotatable crucible which ensures separation of crystals from the melt. The effects of temperature, oxygen pressure, and heat-treatment duration on the superconducting characteristics of the crystals were studied.

Growth of bulk single crystals of organic materials for nonlinear optical devices: An overview

Highly perfect single crystals of nonlinear optical organic materials are required for use in optical devices. An overview of the bulk crystal growth of these materials by melt, vapor, and solution processes is presented. Additionally, methods that may be used to purify starting materials, detect impurities at low levels, screen materials for crystal growth, and process grown crystals are discussed.

Crystal growth problems of YBa 2Cu 3O 7−x

The problems for growth of bulk single crystals of YBa 2Cu 3O 7−x “YBCO” and of high-quality layers are: unknown phase diagrams and difficulty to obtain equilibrium data, the low thermal and chemical stabilities of YBCO, the low solubility of YBCO in the corrosive BaO CuO melts, and the twinning problem. Based on a tentative phase diagram and systematic growth experiments, conditions could be found were nearly cm-crystals of YBCO could be separated from growth solutions by decanting.

Hydrothermal crystal growth of BaPb1− xBixO3(0⩽ x⩽0.30)

BaPb 1− x Bi x O 3 (0⩽ x⩽0.30) single crystals with a very sharp transition to the superconducting state were grown hydrothermally at temperatures below 450°C. The optimum conditions to grow bulk single crystals of BaPb 1− x Bi x O 3 in KCl solution were as follows : 4.5m KCl solution as a solvent; temperatures at the dissolution zone in a gold capsule, 400–450 °C; temperature difference ▿ T, 20–30 °C; pressure, 1000 kg/cm 2. The composition of the grown crystals deviated slightly on the lean side of the Bi content from that of the original nutrient oxide particles. It was found that exact control of the composition of the grown crystals could be achieved by using calcined BaPb 1− x Bi x O 3 with an adjusted composition x of perovskite structure starting material. The superconducting transition temperature, T c, changed with the composition x. Single crystals with x = 0.24 showed a T c of 11.7 K, and a transition temperature width of 1.8 K, which is the narrowest value reported so far.

Issues in the Growth of Bulk Crystals of Infrared Materials

ABSTRACTSelected issues in the growth of bulk single crystals for applications in infrared optoelectronics are reviewed including an overview over materials choices, bulk III-V crystal growth, and the growth of II-VI, IV-VI and I-III-VI2 compounds and alloys. The most important issues are the control of purity, perfection, stoichiometry, and uniformity during crystal growth and the control of the surface properties in wafer fabrication. Specific examples are given to illustrate problems related to these issues and to discuss approaches to their solution.

Single crystal fiber drawing

In this paper a novel method of growing from the melt single crystal fibers (SCF) of congruently melting compounds is described. This SCF growth method is characterized by the absence of an interface between the melt and its vapor from the vicinity of the growth interface during the growth process, so that the surface tension of the melt plays no role in determining the periphery of the growth interface, and the shaper functions as a die. This method is distinct from previously reported SCF growth methods, and, unlike the latter, has no analogue among the established methods of bulk single crystal growth. Because of its similarity to the process of metal wire forming we call this method of SCF growth the drawing method.

Crystal growth of some rare earth and uranium intermetallics from the melt

In the scope of the interest in determining the basic magnetic and electronic properties of rare earth and uranium intermetallics (e.g. high-field magnetic behaviour, magnetostrictive and anisotropic properties, magnetization under high pressure, De Haas-Van Alphen effect, etc.), a program has been started to grow large single crystals of these materials. A modified universal arc installation was built and used for synthesis and growth of bulk single crystals of intermetallic compounds such as CeSi2, Ho2Co17, UGe2 and UPt3. Preliminary information on the formation and crystal growth of UNi2 is also given.

Growth of compound semiconductor photovoltaic materials

In this paper we review current developments in the growth of compound semiconductor bulk single crystals and epitaxial multilayers in the context of photovoltaic solar energy conversion. The emphasis is on advanced multicolor IIIȁV alloy cells and chalcogenides that are of interest as thin film photovoltaic materials, but require work on single crystals to assess ultimate performance data and limiting degradation mechanisms.

Epitaxial growth and annealing control of FMR properties of thick homogeneous Ga substituted yttrium iron garnet films

Homogeneous, 30 μm to 70 μm thick Ga substituted yttrium iron garnet films have been grown on Y or Al substituted gadolinium gallium garnet substrates having lattice parameters matched to that of the films. Resonance field and FMR linewidth measurements as a function of frequency and annealing experiments revealed that the magnetization and cubic anisotropy of the films are identical to data from flux grown bulk single crystals, the FMR losses of the films are only slightly higher. For films grown with supercooling ΔT < 50 °C a negative, growth induced, uniaxial anisotropy was found which could be removed by annealing in air at 1100 °C. A compensation of the temperature drift of the FMR frequency can be adjusted in the Ga substituted films by changing the frozen-in Ga-Fe cation distribution by annealing and quenching from different temperatures > 800 °C.

Melt and solution growth of bulk single crystals of quaternary III–V alloys: K. J. Bachmann, F. A. Thiel and H. Schreiber, Jr. Prog. Crystal Growth Charact. 2, 171 (1979)

Melt and solution growth of bulk single crystals of quaternary III–V alloys: K. J. Bachmann, F. A. Thiel and H. Schreiber, Jr. Prog. Crystal Growth Charact. 2, 171 (1979)

Melt and solution growth of bulk single crystals of quaternary III–V alloys: K. J. Bachmann, F. A. Thiel and H. Schreiber, Jr. Prog. Crystal Growth Charact.2, 171 (1979)

Melt and solution growth of bulk single crystals of quaternary III–V alloys: K. J. Bachmann, F. A. Thiel and H. Schreiber, Jr. Prog. Crystal Growth Charact.2, 171 (1979)