Aluminum Nitride Crystals Research Articles

Raman-scattering studies of aluminum nitride at high pressure.

Single crystals of aluminum nitride were studied by Raman scattering under hydrostatic pressure up to 13 GPa. Four of the six allowed modes were observed and identified. Our results under ambient conditions do not agree with already published data. The ${\mathit{A}}_{1}$(TO), ${\mathit{E}}_{2}^{(2)}$, and ${\mathit{E}}_{1}$(LO) have been followed as a function of pressure and have mode-Gr\"uneisen coefficients of 1.58, 1.26, and 0.38, respectively. These data are compared with recent data obtained on single crystals of gallium nitride.

The estimation of maximum growth rate for aluminium nitride crystals grown by direct sublimation

The largest crystals if AIN reported have been grown by direct sublimation and this paper examines each step in the sublimation process. It is shown that the large energy (9.8 eV) required for homogeneous dissociation of N 2 precludes any contribution from the transport of atomic nitrogen. The steps considered in the evaporation direction are: (1)AIN (s) → Al ads + N ads, (2) Al ads → Al (s), (3)N ads → 1 2 N 2ads → 1 2 N 2(g) or N ads → N (g) → 1 2 N 2(g). The likely rate-limiting step is identified and simple kinetic theory used to estimate the maximum possible rate of material transport in sublimation. The sticking coefficient of N 2 has been obtained from the data of Hoch and Ramakrishnan on the nitrogen exchange reaction of AIN. Choice of useful growth temperature is shown to be restricted to the range 2000–2400°C, where maximum possible growth rates range from 0.1-4 μ m s .

Ammonothermal synthesis of aluminum nitride

This paper describes and discusses the preparation of aluminium nitride by ammonothermal reaction of aluminium with ammonia using potassium amide as transporting agent. Crystals of aluminium nitride are grown in the temperature range of 500 to 600°C and at ammonia pressures of 2 kbar. KNH 2 is removed from the reaction product by extraction with liquid ammonia. Single crystals of aluminium nitride predominantely grow in the direction of the crystallographic c-axis. Dense layers of single crystals up to a thickness of 1 mm can be produced.

Synthesis of AlN Films by Chemical Vapor Deposition in AlCl<sub>3</sub>⋅NH<sub>3</sub>-H<sub>2</sub> System

Aluminium nitride (AlN) films were prepared by the chemical vapor deposition in the AlCl3⋅NH3-H2 system under an atmospheric pressure. The effects of the synthetic conditions on the deposition rate and the morphology of AlN films were discussed. The deposition rate decreased with increasing distance (X) between the upstream end of the graphite supporting Al2O3 substrates and Al2O3 substrates and with decreasing deposition temperature (Td). The effect of AlCl3⋅H3 concentration (CA) on the deposition rate was very complicated. Generally, the deposition rate increased with increasing CA but decreased between CA=2.5 and 3.4vol%. The morphology of AlN crystals in the films deposited at 800°C depended on the X value; fine (X≅1cm), columnar (X≅2cm), needle-like (X≅3cm), and then whisker-like crystals (X≅4cm). With decreasing Td or increasing CA, the smooth surface AlN films turned rough.

The K-shell cross-section for 80 kV electrons in single-crystal graphite and AlN

The K-shell cross-section sigma k( alpha ) for 80 kV electrons traversing thin single crystals of graphite and aluminium nitride is measured from electron energy-loss spectra generated within an energy-selecting electron microscope. These values, and the variation with collection semi-angle alpha , are compared with values derived from Bethe theory for an isolated atom.

Ain single crystals

Single crystals of aluminum nitride up to 1 cm long and 0.3 in diameter have been grown by a sublimation-recondensation technique at about 2250°C. The starting material is prepared by the direct reaction of aluminum and nitrogen at 1850°C. The crystals are grown at a rate of 0.03 cm/hr. in sealed tungsten crucibes in an rf heated tungsten furnace. They are amber in color and have the wurtzite structure.

Shear strength of composites based on whiskerized fibers

The elastic and strength characteristics of unidirectional carbon plastics have been studied, based on carbon fibers, whiskerized with fiber crystals of silicon nitride prepared from the gaseous phase and titanium dioxide from an aerosol. The advantages of these composites and glass textolites based on satin-type fabrics whiskerized with fiber crystals of aluminum nitride and titanium dioxide over the usual carbon and glass plastics are demonstrated.

Growth of single crystals of aluminum nitride

The growth mechanism and the growth condition of single crystals of aluminum nitride (AlN) prepared by the sublimation method are studied in relation with their morphology. The whiskers of AlN, whose growth directions are perpendicular to the (10-10) plane (a-type whiskers), the (10-11) plane (b-type whiskers) and the (0001) plane (c-type whiskers) grow through the VLS mechanism, iron acting as liquid-forming agent in the mechanism. The growth directions of whiskers depend on the growth temperature; the c-type whiskers grow above 1550°C, the a-type above 1700°C and the b-type above 1850°C. Blade-shaped crystals with large (0001) faces (a-type crystals) grow from lateral surfaces of the a-type whiskers.Prismatic crystals with large prismatic (10-10) faces (P-type crystals) and tabular crystals with large (0001) faces (T-type crystals) grow above 1900°C in the atmosphere free from iron. The P-type crystals grow in the circumstance of high purity. The T-type crystals grow in the atmosphere comprising carbon mono-oxide.Growth spirals are observed on the (0001) face of the T-type crystals. The growth steps parallel to the c-axis and a-axis observed on the (10-10) face of the P-type crystals.

A new type of twin in an ain crystal

Plate-like crystals of aluminium nitride, prepared by a sublimation method at 1800 °C, are examined by means of transmission electron microscopy. Each crystal of about 100 μm in size is divided by a twin boundary. When the crystal is thin, it is (10 1 1) plane with an angle 63° to the (1 1 00) crystal surface, but as the thickness is increased it bends and changes to (11 2 2) plane, which is perpendicular to the surface. A growth mechanism is proposed in the conjunction with the bending of the twin boundary and the morphological aspects of the crystal.

Surface structures of aluminum nitride crystals

Surface structures of aluminum nitride crystals

VLS機構による窒化アルミニウム単結晶の成長

VLS機構による窒化アルミニウム単結晶の成長

Measurements of spontaneous bending attributed to surface stresses in thin crystals in aluminium nitride

Abstract The phenomenon of spontaneous biaxial bending in thin crystals of aluminium nitride has been studied quantitatively by transmission electron microscopy. The crystals were grown from the vapour with large surfaces parallel to the basal planes, and they were free from dislocations or other visible defects. Measurements of radii of curvature R and thicknesses t, over a wide range of these variables, have shown that R∝t 2; this is in accord with the equation which is expected if bending is due to the difference in surface stresses (σB–σA) at the polar B and A surfaces. The present data give (σB–σA)=(3°63±0·15) × 103 dynes/cm for AIN. Other evidence, from experiments on the temperature dependence of the bending and on reflection electron diffraction, is given to support the belief that the elastic bending phenomenon in AIN is due to the net surface stress. The bending is clearly revealed by six-fold symmetrical patterns of intersecting bend contours; these exhibit many fringes which are attributed to ...

Space charge conduction and electrical behaviour of aluminium nitride single crystals

Hall mobility, optical absorption and thermal activation energy have been measured on single crystals of aluminium nitride grown from the vapour phase. Colourless crystals have a resistivity of about 10 12 ohm cm and behave in a strongly non-ohmic manner for large applied fields. Blue crystals have a resistivity of about 10 4 ohm cm and are p-type.

Twist and Axial Imperfections in Filamentary Crystals of Aluminum Nitride. II

Simultaneous and independent measurements have been made of the magnitude and direction of the lattice twist and of the direction of the Burgers vector of the axial dislocations in filamentary crystals of AlN, using electron microscopy and electron diffraction. The twist was revealed by extinction contours from reflecting planes with normals perpendicular to the filament axis, and measurements of the widths and separations of these contours were used to calculate the twist. Good agreement with theory was found in the case of crystals containing the simple axial dislocation, but crystals with a complicated extended axial imperfection were found not to be twisted. It is believed that the extended axial imperfection was a fault which met the surface of the crystal and which originated from an axial dislocation; the lack of twist was then due to one or more partial dislocations having left the crystal.

Axial Imperfections in Filamentary Crystals of Aluminum Nitride. I

Axial dislocations and other imperfections in single-crystal whiskers of aluminum nitride (hexagonal, wurtzite structure) have been studied by transmission electron microscopy. Axial dislocations with c Burgers vectors and faults on the (101̄0) prismatic planes having fault vectors equal to ½ c have been identified. In addition to simple axial dislocations, the variety of axial imperfections included zig-zagged dislocations and wide periodic imperfections attributed to complicated faults, clearly related to the dislocation with a c Burgers vector. One type of AlN whisker with growth direction 〈c+2a〉 always contained an axial dislocation or the related extended defect, and it is thus concluded that the growth of this type of whisker may have involved an axial dislocation.

Some Properties of Aluminum Nitride

Aluminum nitride crystals in the form of six‐sided prismatic needles, up to 0.5 mm in diameter by 30 mm long, and thin plates, 2–3 mm in diameter, have been prepared by vaporization of aluminum in a nitrogen atmosphere at temperatures ranging from about 1800° to 2000 °C, and the properties of the crystals determined. Also, an aluminum nitride body, having a density of 98% of theoretical, has been prepared by hot pressing the fine powder, and a study made of its properties.