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. (paper)