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In this thesis, we have studied the structure and defect of
GaN films grown on (0001)sapphire by transmission electron
microscope (TEM). We have grown low temperature (525 C) GaN
buffer layer on (0001) sapphire substrate then grown GaN film at
high temperature (1025 C) by low-pressure metalorganic chemical
vapor deposition (LP-MOCVD). In our LP-MOCVD system, we used
different MO source, triethylgallium (TEGa) and trimethylgallium
(TMGa) to grow GaN films. We compare the diffraction patterns
and TEM images of GaN films grown by two MO source to indicate
the buffer layer structure,the lattice parameters of GaN films,
lattice misfit between GaN and sapphire,and dislocations of GaN
films. Two types structure of LT-GaN buffer layers are formed by
two types MO source during GaN epitaxial growth. One is columnar
structure from TMGa source and the other is stacked like disc
stacked together from TEGa source. Lattice misfits of GaN/
sapphire interface based on (1 0 -1 0)GaN // (2 -1 -1
0)Sapphire and (2 -1 -1 0)GaN // (3 -3 0 0)Sapphire are about
16.1%.The lattice parameters a & c of GaN films of initial
layers are smaller than those of layers close to the surface
(final stage). From TEM images, the dislocation density of GaN
films by TEGa source is less than that by TMGa source. The
growth rate of GaN is slower which results in better
crystallization and less defect density.
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