Influence of Growth Parameters on Structural Anisotropy of Epitaxial a???plane GaN Films

We investigated the structural anisotropy of a???plane GaN films grown by using multi???buffer layer technique on (1???102) r???plane sapphire substrates. For high quality a???plane GaN films, multi???buffer layers with various growth conditions were grown by metal???organic chemical vapor deposition, and analyzed by using several measurement systems such as optical microscopy, scanning electron microscopy, high resolution x???ray diffraction. The experimental results showed that the nucleation???layer thickness and the growth temperature of three???dimensional (3D) growth layer affect significantly the crystal quality of subsequently grown a???plane GaN films. When the nucleation???layer thickness was 150 nm, nuclei were fully coalesced. From the x???ray diffraction results, it appeared that the growth temperature during 3D islands growth affects the full???width at half maximum (FWHM) values of x???ray rocking curves along c??? or m???directions. At optimized growth conditions, the omega FWHM values of (11–20) x???ray rocking curve along c??? and m???axis were 0.137° and 0.163°, respectively