Etch pits and threading dislocations in GaN films grown by metal-organic chemical vapour deposition

High quality epitaxial GaN films on (0001) sapphire substrates were grown by a commercial metal-organic chemical vapour deposition system. The, etch pits and threading dislocations in GaN films is studied by a scanning electron microscope (SEM) and a transmission-electron microscope (TEM). The SEM images of GaN films, etched in mixed acid solution (H3PO4:H2SO4 = 1 : 3) and molten KOH exhibit notably different, etching pit densities of 5 x 10(8)/cm(2) and 4 x 10(7)/cm(2), respectively, which probably indicate that more kinds of, etching pits were revealed when, etched in mixed acid solution (H3PO4:H2SO4 = 1 : 3). Cross section TEM of GaN films with different g vectors showed the portions of different threading dislocations. Theoretical calculation indicates that the lattice and thermal expansion coefficient mismatch may be the main origins of pure edge threading dislocations.