Interface Properties of Al2O3/n-GaN Structures with Inductively Coupled Plasma Etching of GaN Surfaces

The effects of the Cl 2 -based inductively coupled plasma (ICP) etching of GaN on the interface properties of Al 2 O 3 /GaN structures prepared by atomic layer deposition (ALD) were investigated. We used n-GaN layers grown on freestanding n + -GaN substrates with low dislocation density. The ICP etching caused slight disorder of the chemical bonds at the GaN surface and monolayer-level interface roughness at the Al 2 O 3 /GaN interface, resulting in poor capacitance--voltage ($C$--$V$) characteristics due to high-density interface states including nitrogen-vacancy (V \text{N ) related levels. The postannealing process in N 2 at 400 °C drastically improved the $C$--$V$ characteristics, probably owing to the partial recovery of the V \text{N -related defects and the increased ordering of chemical bonds in the GaN surface region.