Low temperature AlN buffer layers grown by plasma-assisted Molecular Beam Epitaxy (MBE) on Si (111) were found to significantly affect the subsequent growth morphology of GaN nanowires. The AlN buffer layers exhibited nanowire-like columnar protrusions with size, shape, and tilt determined by the AlN V/III flux ratio. Piezoresponse Force Microscopy and polarity-sensitive etching indicate that the AlN films and protruding columns have mixed crystallographic polarity. Low density Ga-polar nanowires could be grown on AlN buffers that were predominantly N-polar with isolated Al-polar columns, indicating a higher growth rate for Ga-polar nanowires under typical growth conditions. The nanowires were frequently observed to adopt the structural characteristics of the underlying AlN columns, including size and degree of tilt. AlN buffer layers grown using slightly N-rich conditions (V/III flux ratio = 1.0-1.3) were found to provide a favorable growth surface for low density, coalescence-free nanowires.
Citation: Applied Physics
Pub Type: Journals
Nanostructures, Molecular Beam Epitaxy, Nitrides, Semiconducting III-V Materials