Bulk and homoepitaxial GaN-growth and characterisation

Gallium nitride single crystals in the form of hexagonal platelets with dimensions exceeding 1 cm are currently grown from the solution in liquid gallium, at nitrogen pressure of 12-20 kbar and at temperatures of 1400-1700 degrees C. The crystals grown without an intentional doping are always highly conductive with typical fi ee electron concentration 3-5 x 10(19) cm(-3) and resistivity of 10(-3)-10(-2) Omega cm. The electron concentration in GaN crystals can be strongly reduced by the introduction of Mg into the growth solution.The resistivity of the crystals grown from the solutions containing Mg can be as high as 10(6) Omega cm. Physical properties for the both low- and high-resistivity GaN are compared in the paper. The results of both mechanical and mechano-chemical polishing of the (0 0 0 1) surfaces of GaN are presented. In particular, it is shown that the atomically flat GaN surfaces can be achieved by mechano-chemical polishing. Homoepitaxial layers of GaN and its ternaries have been grown on the pressure-grown GaN crystal by both MOCVD and MBE. The results of optical, electrical, structural and microscopic characterization are briefly reviewed. (C) 1998 Elsevier Science B.V. All rights reserved.