Indium surfactant assisted molecular beam epitaxy of AlScN

The epitaxial growth of AlScN on GaN has been traditionally performed in the nitrogen-rich condition because growth in metal-rich conditions results in the formation of Al–Sc intermetallic precipitates. Nitrogen-rich growth conditions promote island formation and roughen the surface, which is typically avoided in metal-rich growth conditions. In this work, we identify a wide window of practical growth conditions for AlScN/GaN heterostructures in which the use of indium during the growth of the AlScN layers helps mimic metal-rich growth conditions while preventing the incorporation of indium into the AlScN epitaxial layer. As a result of indium acting as a surfactant, AlScN surfaces with rms roughness as low as 0.36 nm and exhibiting step morphology are observed. We find that the growth of AlScN outside this surfactant-window results in indium incorporation at low growth temperatures or pit formation at high indium fluxes. These findings provide an alternative growth technique for highly crystalline AlScN/GaN heterostructures that overcomes limitations of nitrogen-rich growth conditions by using indium as a surfactant.