Interface characterization of Al2O3/m-plane GaN structure

Abstract

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.