Epitaxial Growth and Self-Organized Superlattice Structures in AlGaN Films Grown by Plasma Assisted Molecular Beam Epitaxy

Aluminum gallium nitride alloys were grown by molecular-beam epitaxy and their film composition, structure and microstructure were investigated by Rutherford backscattering spectroscopy, atomic force microscopy, x-ray diffraction, transmission electron microscopy and high resolution electron microscopy. The kinetics of growth was investigated and the results show that at the growth temperature of 750 degrees C the sticking coefficient of Ga varies monotonically from practically one to zero as the growth varies from group-III to group-V rich regime. Correspondingly, the surface morphology changes from atomically smooth in the group-III regime to relatively rough in the nitrogen rich regime. The x-ray diffraction and transmission electron microscopy studies revealed the existence of three types of spontaneously formed superlattice structures along the [0001] direction, with periodicities of two monolayers, seven monolayers and twelve monolayers.