SiO <sub>2</sub> /GaN interfaces with low defect densities and high breakdown electric fields formed by plasma-enhanced atomic layer deposition
Keito Aoshima, Noriyuki Taoka, Masahiro Horita, Jun Suda
Abstract
Abstract We present SiO 2 /GaN interfaces with a low interface state density and a high breakdown electric field. The SiO 2 films were deposited by plasma-enhanced atomic layer deposition (ALD) using bis(diethylamino)silane and O 2 plasma at 300 °C on n-type GaN (0001) homoepitaxial layers. An interface state density of less than 10 11 cm −2 eV −1 at 0.3 eV below the conduction band edge was confirmed by the conductance method. The value is much lower than those of previously reported ALD-SiO 2 /GaN interfaces (10 12 –10 13 cm −2 eV −1 ). A low fixed charge density at the SiO 2 /GaN interface of 3.7 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">×</mml:mi> </mml:math> 10 11 cm −2 and a high dielectric breakdown field of ~10 MV cm –1 were obtained. Moreover, the interface state density and current−voltage characteristics were further improved by post-deposition annealing at 400 °C in N 2 ambient. Scanning transmission electron microscopy with energy-dispersive X-ray analysis revealed the existence of a GaO x interlayer between SiO 2 and GaN. The unintentionally formed interlayer could be one of the reasons for the improvement of interface properties at ALD-SiO 2 /GaN.