Surface band bending and band alignment of plasma enhanced atomic layer deposited dielectrics on Ga- and N-face gallium nitride

The effects of surface pretreatment, dielectric growth, and post deposition annealing on interface electronic structure and polarization charge compensation of Ga- and N-face bulk GaN were investigated. The cleaning process consisted of an ex-situ wet chemical NH₄OH treatment and an in-situ elevated temperature NH₃ plasma process to remove carbon contamination, reduce oxygen coverage, and potentially passivate N-vacancy related defects. After the cleaning process, carbon contamination decreased below the x-ray photoemission spectroscopy detection limit, and the oxygen coverage stabilized at ∼ 1 monolayer on both Ga- and N-face GaN. In addition, Ga- and N-face GaN had an upward band bending of 0.8±0.1eV and 0.6±0.1eV, respectively, which suggested the net charge of the surface states and polarization bound charge was similar on Ga- and N-face GaN. Furthermore, three dielectrics (HfO₂, Al₂O₃, and SiO₂) were prepared by plasma-enhanced atomic layer deposition on Ga- or N-face GaN and annealed in N₂ ambient to investigate the effect of the polarization charge on the interface electronic structure and band offsets. The respective valence band offsets of HfO₂, Al₂O₃, and SiO₂ with respect to Ga- and N-face GaN were 1.4±0.1, 2.0±0.1, and 3.2±0.1eV, regardless of dielectric thickness. The corresponding conduction band offsets were 1.0±0.1, 1.3±0.1, and 2.3±0.1eV, respectively. Experimental band offset results were consistent with theoretical calculations based on the charge neutrality level model. The trend of band offsets for dielectric/GaN interfaces was related to the band gap and/or the electronic part of the dielectric constant. The effect of polarization charge on band offset was apparently screened by the dielectric-GaN interface states.