Characterization of aluminum nitride thin films on silicon substrates grown by plasma assisted molecular beam epitaxy

The growth characteristics and microstructure of AlN thin films grown by plasma assisted molecular beam epitaxy on Si substrates were investigated by comparing structure differences between AlN/Si(100) and AlN/Si(111). A model for the growth of AlN crystals on Si(100) and Si(111) substrate is proposed and the growth behavior of AlN film on single crystalline silicon substrate has been characterized. The difference in morphologies and microstructures between AlN/Si(100) and AlN/ Si(111) can be explained by crystalline coherency at the interface between the AlN film and the Si substrate. While the c-axis direction of the wurtzite AlN [0001] on silicon substrates are the same, the coincidence of the radial direction of each of the AlN crystallites is dependent on the coherency of the interface of AlN/Si(100) and AlN/Si(111). Thus, although each AlN column on the Si(100) has a (0002) basal plane as a bottom of the column, their radial directions do not coincide and show a columnar growth. However on Si(111), each AlN column has directional coherency and therefore are able to combine together to form a single crystallite, and show epitaxial growth. The difference in surface morphology between AlN/Si(100) and AlN/Si(111) is clearly the result of the difference of the interracial structures.