Growth of Bulk GaN Sapphire Single Crystals by The Pressure-Controlled Solution Growth Method

Gallium nitride was epitaxially grown on sapphire by the vapor phase reaction of Ga-HCl-NH3-Ar system. The growth rate on sapphire is ∼12 µm/hr, which is higher than that on {0001} sapphire by a factor of ∼1.5. The crystal on sapphire has a lower carrier concentration than that of the same thickness on sapphire by a factor of ∼0.5. The lowest carrier concentration and the highest electron mobility of undoped GaN obtained in this study were 1.6×1019 cm-3 and 78 cm2/V·s, respectively, at 300 K. When heavily doped with Mg, the crystal grown changes markedly in growth morphology. The orientation relationships developed in an undoped or lightly Mg-doped state are GaN//sapphire and GaN//sapphire, and in a heavily doped state GaN//sapphire and GaN//sapphire.

Sapphire single crystal growth of GaN by the pressure-controlled solution growth (PC-SG) method has been carried out using a high-pressure furnace. We have investigated the effect of the supersaturation of nitrogen atoms (the rate of increase of nitrogen pressure) in order to grow large GaN single crystals. It was found that the rate of increase of nitrogen pressure affected the size of a GaN single crystal and its morphology. GaN single crystals with a surface area of about 120 mm2 and/or with good morphology were obtained at a rate less than 49 MPa/h. We have studied the effect of the supersaturation of nitrogen atoms on the crystallinity. The GaN single crystals obtained had the following good crystallinity: (1) the FWHM of the rocking curve was about 120 arcsec without any low-angle grain boundaries, (2) the dislocation density was estimated to be less than 105 cm−2 by TEM observations, and (3) the photoluminescence intensity of the yellowish band became very weak and the PL intensity ratio of the band-edge band to the yellowish band was greatly improved. These results clearly suggest that the rate of increase of the nitrogen pressure in the PC-SG method must be lower to grow large GaN single crystals with good crystallinity.


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