Growth Of Nitride Crystals Research Articles

Aluminum Nitride Crystal Growth from an Al−N System at 6.0 GPa and 1800 °C

We report on hexagonal aluminum nitride (h-AlN) crystal growth in the Al−N system by means of AlN recrystallization in the field of a temperature gradient at 6 GPa and 1800 °C. A special setup for h-AlN growth using a multianvil apparatus has been developed, which allows the growth of colorless transparent h-AlN single crystals. Crystals exhibited two distinct morphological types. The first is short prismatic and platelet-like crystals with smooth faces and a size up to 0.4 mm. The second is skeleton crystals elongated along the [12̅10] direction and flattened along the (0001) plane with a size of up to 1.0 mm. Crystals have been characterized by scanning electron microscopy, Raman spectroscopy, and electron backscattered diffraction methods. The growth mechanism and main factors determining the crystal habit and growth rate in a high-pressure solution method are discussed. We also discuss the possibility of using the employed technique for cubic aluminum nitride (c-AlN) crystal growth.

Modeling of residual thermal stresses for aluminum nitride crystal growth by sublimation

Residual thermal stress distribution in AlN single crystal, grown on tungsten as a crucible material, was investigated using a numerical study. It has been demonstrated that a three-dimensional, instead of a two-dimensional, formulation predicts significantly greater values of stress. Dimensionless coordinates were used to essentially simplify the stress analysis and reduce the number of calculations. In addition, thermoelasticity approach simplifies the study of stresses for a nonstationary temperature field. The stress in the AlN film along the thickness or [0001] growth direction is essentially zero but the in-plane stress is large. The stress at the corner of the film is much higher due to stress concentration and could cause formation of microcracks. The stress in the film is tensile while that in the substrate is compressive, which causes a reversal of the stress across the interface. Separation or delamination of the film from the substrate could occur due to this reversal of the stress at the interface. The stress decreases as the thickness of the film increases or the thickness of the substrate decreases. Thus, formation of microscopic cracks in the film could be avoided by using a thinner substrate. The analysis on interaction of neighboring islands in order to simulate coalescence of island growth indicates stress concentration at the boundaries of the islands, which could produce threading dislocations and hence polycrystalline growth. The analysis of the effect of misorientation of the neighboring grains on the residual thermal stress in the film has shown that a large stress can develop at the grain boundary and can lead to grain boundary cracking.

Preparation and characterisation of tantalum carbide as an optional crucible material for bulk aluminium nitride crystal growth via physical vapour transport

AbstractThis paper reports experimental measured and calculated phase distributions of carburised Ta sheets. Electron back scatter diffraction (EBSD) maps of carburised Ta samples have shown the progress of carburisation in respect of the annealing procedure. The initial stage is characterised by grain boundary and surface carburisation at lower temperatures (T = 2000 °C). At elevated annealing temperatures (T = 2200 °C) grain boundaries play a negligible role in the transformation of Ta to TaC. Sharply bounded phase layers of TaC1–x and Ta2C are observed in this case. Fast grain coarsening below the carburisation temperature was found. A diffusion controlled phase formation model was introduced. The calculated concentrations of C are in good agreement with the measured phase widths. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The Durability of Various Crucible Materials for Aluminum Nitride Crystal Growth by Sublimation

Producing high purity aluminum nitride crystals by the sublimation-recondensation technique is difficult due to the inherently reactive crystal growth environment, normally at temperature in excess of 2100 °C. The durability of the furnace fixture materials (crucibles, retorts, etc.) at such a high temperature remains a critical problem. In the present study, the suitability of several refractory materials for AlN crystal growth is investigated, including tantalum carbide, niobium carbide, tungsten, graphite, and hot-pressed boron nitride. The thermal and chemical properties and performance of these materials in inert gas, as well as under AlN crystal growth conditions are discussed. TaC and NbC are the most stable crucible materials with very low elemental vapor pressures in the crystal growth system. Compared with refractory material coated graphite crucibles, HPBN crucible is better for AlN self-seeded growth, as crystals tend to nucleate in thin colorless platelets with low dislocation density.

Growth and Doping of GaN and AlN Single Crystals under High Nitrogen Pressure

This work describes the recent results of gallium nitride and aluminum nitride crystal growth by the High Nitrogen Pressure Solution Growth (HNPSG) method. For GaN, the growth without intentional seeding leads to the growth of hexagonal platelets of average size of 1 cm2. The seeded growth into {110} and {0001} directions also gives the promising results. The AlN growth without intentional seeding results in needle-like crystals. The influence of supersaturation on habit and morphology of both GaN and AlN crystals is discussed.

Growth of nitride crystals in a supercritical nitrogen fluid under high pressures and high temperatures yield using diamond anvil cell and YAG laser heating

Growth of nitride crystals has been tried in a supercritical nitrogen fluid at high-pressures (about 10 GPa) and high-temperatures yield using diamond anvil cell and YAG laser heating system. Colorless transparent fine crystals of GaN in the wultz-rock type structure have been grown from molten gallium and fluid nitrogen at 10 GPa and high temperatures. They have hexagonal platelet or prismatic morphology, indicating a solution growth using supercritical nitrogen fluid as solvent. The results in this study open us a new way of crystal growth of not only GaN but also various kind of nitrides in a supercritical nitrogen fluid under high-temperatures and high-pressures yield using diamond anvil cell and YAG laser heating.

Growth of nitride crystals, BN, AlN and GaN by using a Na flux

Bulk crystals of BN, AlN and GaN were grown by means of Na flux. All these crystals were grown at a temperature of 800°C and a nitrogen pressure of 100 atm, relatively lower than that required by many flux and melt growth methods. High-quality GaN single crystals as large as 0.5 mm were obtained. Furthermore, the oriented GaN crystals were obtained by means of the seeded Na flux method with the addition of oriented AlN (0001) film in the growth ambient. The nucleation of bulk GaN was spatially confined on top of the AlN film and grown with the GaN [0001] axis parallel to the AlN [0001] axis. In addition, the h-BN polycrystals were confirmed by the h-BN (0002) peak of X-ray diffraction (XRD) at 2θ=26.700. A hexagonal grain with a size as large as 2 μm was observed by scanning electron microscopy (SEM). Likewise, AlN crystals were also obtained from Al wires.