Interface characterization of Al2O3/m-plane GaN structure

The interface properties of Al2O3/GaN structures fabricated on the homo-epitaxial m-plane GaN were investigated. An atomically flat surface with a root mean square roughness of 0.15 nm was observed for the m-plane GaN layer on a substrate inclined 5° toward the [000-1] direction. Even for the as-prepared sample, we obtained relatively low state densities of less than 3 × 1011 cm−2 eV−1 at the Al2O3/m-plane GaN interface. A possible mechanism for such low interface state densities was discussed in correlation with the Ga–N dimer on the m-plane GaN surface. The post-metallization annealing process at 300 °C realized excellent capacitance–voltage (C–V) characteristics without frequency dispersion, further lowering state densities to 1.0 × 1010 cm−2 eV−1–2.0 × 1010 cm−2 eV−1. In addition, the present Al2O3/m-plane GaN diode showed stable interface properties at high temperatures. Neither the flatband-voltage shift nor the frequency dispersion was observed in the C–V characteristics measured at 200 °C. Furthermore, current–voltage characteristics with relatively low leakage current in the order of 10−9 A/cm2 remained almost unchanged at temperatures up to 200 °C.