Investigation and optimization of HfO2 gate dielectric on N-polar GaN: Impact of surface treatments, deposition, and annealing conditions

UV-assisted capacitance–voltage (C–V) and current–voltage (I–V) measurements were performed on ∼20 nm HfO2/GaN metal–insulator–semiconductor capacitors. The effects of surface preparation, predeposition treatment, HfO2 deposition process, and post-deposition annealing environment on interface characteristics were studied. Surface preparation by etching in diluted BHF and piranha etch prior to atomic layer deposition (ALD) suppressed the interface states compared to the baseline sample possibly due to the removal of the native oxide and impurities. UV/ozone treatment prior to HfO2 deposition reduced the interface states by one order of magnitude compared to the baseline sample possibly due to the formation of a thin Ga2O3 interlayer. In situ ALD pretreatment with tri-methyl-aluminum/N2 plasma was also found to reduce the surface states significantly compared to the baseline sample. In addition, thermal ALD improved the dielectric constant and breakdown voltage of the dielectric as compared to plasma ALD due to less surface damage. The lowest average interface trap density achieved was 1.64 × 1012 cm−2/eV with an HfO2 dielectric constant of 16 on the sample with UV/ozone and piranha treatment with in situ ALD treatment and thermal ALD deposition.