MICROSTRUCTURE EVOLUTION OF GAN BUFFER LAYER ON MGAL2O4 SUBSTRATE

Microstructure of GaN buffer layer grown on (111)MgAl2O4 substrate by metalorganic vapor phase epitaxy (MOVPE) was studied by transmission e lectron microscopy (TEM). It has been observed that the early depositi on of GaN buffer layer on the substrate at a relatively low temperatur e formed a continual island-sublayer (5 nm thick) with hexagonal cryst allographic structure, and the subsequent GaN buffer deposition led to crystal columns which are composed of nano-crystal slices with mixed cubic and hexagonal phases. After high-temperature annealing, the crys tallinity of nano-crystal slices and island-sublayer in the buffer lay er have been improved. The formation of threading dislocations in the GaN him is attributed not only to the lattice mismatch of GaN/MgAl2O4 interface, but also to the stacking mismatches at the crystal column b oundaries. (C) 1998 Published by Elsevier Science B.V. All rights rese rved.