Influence of oxygen-plasma treatment on AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors with HfO2 by atomic layer deposition: leakage current and density of states reduction

The electrical properties of AlGaN/GaN MOSHFETs with HfO2 prepared by atomic layer deposition with and w/o oxygen-plasma treatment (further referred to as PHf-MOS and Hf-MOS) were investigated. The sub-threshold slope of the MOSHFETs (350 and 150 mV dec−1 for Hf-MOS and PHf-MOS, respectively) were lower than that for HFET (450 mV dec−1), which also correspond with lower leakage current of the MOSHFETs (~10−8 A mm−1 at −9 V for PHf-MOS). In addition, the density of the interface states at the oxide/GaN-cap layer near the conduction band edge and mid-gap (~5 × 1012 and 2 × 1011 cm−2 eV−1, respectively) after PHf-MOS was lower than that for Hf-MOS (~3 × 1013 and 2 × 1012 cm−2 eV−1, respectively). From the x-ray photoemission spectroscopy analysis we observed a shift in the Auger Ga LMM peaks (0.6 eV) and an increase of the intensity area of the Ga–O bond in the Ga2p3 spectrum after the oxygen-plasma treatment, mainly because the GaN-cap layer was oxidized and Ga2O3 was formed.