We have grown GaN epilayers, with a thickness of 1.3-1.5 mu m, on 100 mm di
ameter Si(lll) substrates. The GaN films were grown by using buffer layers
consisting of 3C-SiC and 2H-AlN. The buffer layers had Aat surfaces without
showing any grain microstructure. The GaN films were also flat and smooth
without noticeable microcracks but had slip lines. X-ray diffraction and el
ectron diffraction analyses showed that each of the buffer layers and the G
aN film were single-crystals. The room temperature PL showed that the FWHM
was as low as 35.5 meV, the narrowest for all reported GaN/Si films grown b
y blanket MOCVD. Voids on the top of a Si substrate were generated during t
he conversion of the Si surface to 3C-SiC. The voids may facilitate the Si
top surface to act as a compliant layer to alleviate the film stresses resu
lting from mismatches in lattice parameters and thermal expansion coefficie
nts between the films and substrate. This may be the mechanism that prevent
ed films from cracking. (C) 2000 Elsevier Science Ltd. All rights reserved.