STRUCTURAL CHARACTERIZATION OF BULK GAN CRYSTALS GROWN UNDER HIGH HYDROSTATIC-PRESSURE

This paper describes TEM characterization of bulk GaN crystals grown a t 1500-1800K in the form of plates from a solution of atomic nitrogen in liquid gallium under high nitrogen pressure (up to 20 kbars). Their x-ray rocking curves for these crystals were in the range of 20-30 ar c-sec. The plate thickness along the c axis was about 100 times smalle r than the nonpolar growth directions. A substantial difference in mat erial quality was observed on the opposite sides of the plates normal to the c direction. On one side the surface was atomically flat, while on the other side the surface was rough, with pyramidal features up t o 100 nm high. The polarity of the crystals was determined using conve rgent-beam electron diffraction. The results showed that, regarding th e long bond between Ga and N along the c-axis, Ga atoms were found to be closer to the flat side of the crystal, while N atoms were found to be closer to the rough side. Near the rough side, within 1/10 to 1/4 of the plate thickness, there was a high density of planar defects (st acking faults and dislocation loops decorated by Ga/void precipitates) . A model explaining the defect information is proposed.