Single crystals of cubic boron nitride grown under high pressure using temperature gradient method are described. By using single crystal of diamond as a seed crystal, CBN single crystal was reproducibly grown on the diamond surface. The growth rate and its rate controlling factor are compared with those of diamond growth. Although crystals obtained by spontaneous nucleation often have poor quality including cracks and/or twining, apparently flawless crystals are occasionally obtained. This implies that there is some unknown condition to optimize the nucleation and subsequent growth process in the growth circumstance . Prospects in obtaining high-quality large CBN single crystals are, then, discussed.

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GaN single crystals with a size of 0.2-2.0 mm were prepared in a stainless-steel tube at 600 to 800℃ from Ga using a Na flux and N_2 from the thermal decomposition of sodium azide, NaN_3. The morphology of the single crystals grown in a Na flux was prismatic or platelet. The crystals were characterized by Auger electron spectroscopy (AES), energy dispersive X-ray spectroscopy (EDX) and cathodoluminescence spectroscopy. Hall measurements were carried out for platelet single crystals with a size of 0.4-0.7 mm. The polarity was determined by X-ray diffraction using X-ray anomalous dispersion.

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A bulk GaN and a 'Quasi bulk' crystal which was selectively grown on a SiO_2-patterned GaN substrate were successfully obtained by a sublimation method. The source powder used in the growth was analyzed to show that the contributing species to the growth were the compounds composed of Ga, N and H. Characterization by X-ray diffraction, transmission electron microscopy, secondary ion mass spectrometry, and so on, demonstrated that a bulk GaN was of high quality.

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Aluminum nitride single crystal is one of the promising materials for substrates of GaN-based laser diodes. However, its potential in some of this and other applications has been hampered by the lack of bulk single crystals. Growth of AlN single crystals by the sublimation method and other growth techniques has been investigated in several laboratories. We review the sublimation method for growth of AlN single crystal, prepared crystals by this technique and characterized them. The crystals are transparent and slightly yellow. They are needle-shaped with a hexagonal cross section, plate-shaped or needle-shaped with a rectangular cross section. Their widths of x-ray rocking curves is about 39 arcsec, with a full width at half-maximum, 203 arcsec and 12 arcsec, respectively. The orientation of AlN single crystal axis is sufficient for use in substrates for GaN-based diodes. The problems on the sublimation method for better and lager AlN single crystal were also reviewed.

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