Pulsed laser deposition of aluminum nitride and gallium nitride thin films

Thin films of AlN and GaN were grown by pulsed laser deposition on c-plane sapphire substrates. It is demonstrated that the surface morphology and the structure of layers can actively be controlled by adjusting the nitrogen partial pressure during the growth. The observed trends in the structural quality of the thin films can be attributed to the changes in the surface diffusion of ad-atoms. The surface diffusion of ad-atoms can be influenced by the collisions between the nitrogen gas molecules and the activated atoms, which can reduce the kinetic energy of activated atoms and increase the rate of formation of immobile surface dimers. Through these nitrogen pressure-related effects, thin films with microstructure ranging from crystalline to amorphous can be produced. Our results on the growth of GaN and AlN thin films indicate that this pressure-assisted growth procedure is generally applicable to design the surface morphology of Ill-nitride thin films. A minimal surface root means square roughness of 0.7 nm for amorphous AlN is obtained, which compares well with the substrate roughness of 0.5 nm.