Spontaneous formation of a tilted AlGaAs/GaAs superlattice during AlGaAs growth

In transmission electron microscopical (TEM) cross-sections of AlGaAs layers grown on vicinal 111✓A facets of patterned substrates, we observe a periodic structure of Ga-rich and Al-rich layers forming angles of up to 25° with the growth front. This spontaneous tilted superlattice (TSL) formation is found in layers grown by metal-organic vapor phase epitaxy using the group III precursors dimethylethylaminealane (DMEAAl) and triethylgallium (TEGa) and in samples grown by solid source MBE. We present a growth model explaining the TSL formation in terms of step bunching and adatom diffusion. The step bunches required by the model are experimentally found by atomic force microscopy as well as high resolution TEM. Finally, we introduce a Monte Carlo simulation, which is able to reproduce the main features of the spontaneously formed TSL.