Strain and morphology compliance during the intentional doping of high-Al-content AlGaN layers

This study presents analysis of the residual strain and related surface morphology of high-Al-content Al0.82Ga0.18N layers doped by silicon up to the level of 3×1019 cm-3, and delineates an interplay between thermodynamic and kinetic processes underlying the epitaxial growth of the layers. It particularly points to the development of certain facet structure (nanopipes) within the doped layers, which is apparent at the high Si doping levels. The formation of nanopipes is considered as a matter of consequence for the performance of the transport properties of the layers. It is anticipated to give rise to facets with SiN-related coverage, outcompeting the incorporation of Si at substitutional donor sites in the lattice of the Al0.82Ga0.18N layers. We do not find evidence for kinetic stabilization of preferential crystallographic facets when a dopant flow of bis(cyclopentadienyl)magnesium (Cp2Mg), instead of silane (SiH4), is implemented in the doping process.