Control of the structure and surface morphology of gallium nitride and aluminum nitride thin films by nitrogen background pressure in pulsed laser deposition

Thin films of AlN and GaN were grown by pulsed laser deposition on c-plane sapphire substrates. It is demonstrated that the structure and surface morphology 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 adatoms. It is argued that the surface diffusion of adatoms 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. The observed similar impact of nitrogen pressure on the growth of GaN and AlN thin films indicates that a pressure assisted growth procedure is generally applicable to design the surface morphology of group III-nitride thin films. A minimal surface root mean square roughness of 0.7 nm for amorphous AlN is obtained which compares well with the substrate roughness of 0.5 nm. Rutherford backscattering spectroscopy of thin films of GaN and AlN showed a large incorporation of oxygen which was found to reduce the lattice constants of GaN and AlN.