Enhanced lateral growth of AlN epitaxial layer on sapphire by introducing periodically pulsed-TMGa flows

Abstract

Crystal quality improvements of AlN epilayers grown on sapphire substrates has been achieved by using periodically pulsed-trimethylgallium (TMGa) flows (PTFs) in the initial growth stage of high-temperature AlN. The 400-nm-thick AlN layer deposited with this method demonstrated atomically flat surface, and the line widths of x-ray rocking curves were 40 and 245 arcsec for (002) and (105) reflections, respectively. GaN mole fraction was measured to be less than 0.6% in the AlN layer, indicating a surfactant effect of the PTFs. A combination of experimental characterizations and density functional theory calculations unveils that the improvements are ascribed to the supplement of Ga atoms and the enhanced surface migration of Al adatoms by using the PTFs which promotes the transition of growth mode from three-dimension to two-dimension one.