Polarity control of AlN via a combination of sputtering and face-to-face annealing

Aluminum nitride (AlN) is widely utilized in optoelectronic devices. We have successfully fabricated high-quality AlN templates by combining sputtering deposition of AlN (Sp-AlN) with high-temperature face-to-face annealing (FFA). Additionally, we achieved Al-polar and N-polar FFA Sp-AlN by annealing Sp-AlN films sputtered using a sintered AlN target and an Al metal target, respectively. By controlling the polarity, we fabricated a bilayer polarity-inverted AlN structure, where the Al-polar FFA Sp-AlN serves as the lower layer and the N-polar FFA Sp-AlN as the upper layer. In this bilayer polarity-inverted FFA Sp-AlN, an inversion domain boundary (IDB) with an abrupt interface, consisting of several monolayers (ML), and an atomically smooth surface were observed. In this study, we demonstrate the fabrication of a four-layer polarity-inverted AlN structure using multiple sputtering of AlN and FFA with the polarity control method of FFA Sp-AlN. It was found that the IDB structures vary depending on the sequence of polarity inversion.