Reduction of interface state density at SiO 2 /InAlN interface by inserting ultrathin Al 2 O 3 and plasma oxide interlayers

SiO 2 /InAlN interfaces formed by plasma‐enhanced chemical vapor deposition were investigated. X‐ray photoelectron spectroscopy showed that the direct deposition of SiO 2 onto an InAlN surface led to the oxidation of the InAlN surface. The interface state density, D it , was on the order of 10 12  cm −2  eV −1 (5 × 10 12  cm −2  eV −1 at 0.3 eV from the conduction band edge, E c ), which indicated the possibility of improving the interface properties. Reduction of the interface state density was attempted using an Al 2 O 3 interlayer and a plasma oxide interlayer. The insertion of a 2‐nm‐thick Al 2 O 3 interlayer to prevent surface oxidation by plasma reduced D it slightly. A marked reduction in D it to less than 10 11  cm −2  eV −1 deeper than 0.3 eV from E c , however, was achieved by the intentional formation of a 1‐nm‐thick plasma oxide layer, formed by N 2 O plasma oxidation, as an interlayer between SiO 2 and InAlN.