Effect of sapphire nitridation on GaN by MOCVD

Defects in the film play a critical role on lifetime and efficiency of LEDs and LDs. Majority of the defects in GaN films is the threading dislocations starting from the interface between substrate and film and grow with the film to the surface. The manipulation of physical and chemical properties of the interface provides an opportunity to reduce grow-in defects. When sapphire substrate was used, defect densities could be reduced not only by the use of an optimized buffer layer but also by the nitridation of the substrate surface. Crystal qualities and optical properties of GaN could be changed by the substrate surface roughness. AFM analysis of the nitridated sapphire substrate surface led to the best nitridation condition for the GaN growth and this was confirmed by DCXRD and photoluminescence (PL) spectra. GaN depositions and nitridations were carried out in a horizontal MOCVD system using trimethylgallium and ammonia.