Control of AlN single crystal nucleation: An insight into the crystal growth habit in the initial stages of the physical vapor transport method

摘要

The nucleation of AlN single crystals was investigated by heterogeneous nucleation theory, and by physical vapor transport experiments on tungsten (W) and tantalum (Ta) substrates in the temperature range of 21502250 degrees C. The theoretical analysis showed that AlN nucleation readily occurred on the substrate surface where the heterogeneous nucleation energy of AlN crystal was low. The morphologies, crystal structure and chemical compositions of AlN grains were characterized using laser scanning confocal microscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction. This revealed that the nucleation density on the W substrate was higher than that on the Ta substrate, and the grains were distributed in rows along concavities on both scrubbed W and Ta substrate surfaces. It was found that at the initial stages of crystal growth, the number of nuclei and the nucleation site can be controlled by varying the substrate type and morphology which will further influence the crystal growth from nucleation point to the final crystal.