Reduction of threading dislocation densities of N-polar face-to-face annealed sputtered AlN on sapphire

Abstract N-polar face-to-face annealed sputtered AlN (FFA Sp-AlN) was fabricated by sputtering with an Al metal target and high-temperature annealing in a face-to-face configuration. The polarities of the FFA Sp-AlN samples fabricated with different sputtering targets (i.e., Al metal or sintered AlN targets) were checked by KOH etching and cross-sectional scanning transmission electron microscopy images. As a result, samples sputtered with a sintered AlN target and an Al metal target resulted in Al-polar and N-polar FFA Sp-AlN, respectively. Then, we fabricated FFA Sp-AlN with N-polar AlN on the top-most layers (N-polar FFA Sp-AlN) with different total film thicknesses. The threading dislocation densities (TDDs) of N-polar FFA Sp-AlN were estimated from the full width at half maximum values of the X-ray rocking curves. Consequently, the TDD of N-polar FFA Sp-AlN decreased with increasing AlN film thickness, which was the same trend as that of Al-polar FFA Sp-AlN. The minimum TDD of 1.7 × 108 cm-2 was obtained from N-polar FFA Sp-AlN with a total thickness of 730 nm.