Incorporation of Al or Hf in ALD TiO 2 for Ternary Dielectric Gate Insulation of InAlN/GaN and AlGaN/GaN MISH Structure

This article investigates high dielectric constant gate insulators for GaN-based devices. Exploiting TiO 2 as a high-κ insulator typically compromises leakage current and temperature stability of the film. In this work we compare TiO 2 mixed with either Al 2 O 3 or HfO 2 to form composite films Ti-Al- O and Ti-Hf- O, respectively, deposited by Atomic Layer Deposition (ALD) on both AlGaN/GaN and InAlN/GaN substrates. We investigated the compositional effects of the ternary compounds by varying the Al or Hf concentration, and we find that leakage current is reduced with increasing Al or Hf content in the film; with a maximum Al-content of 45 %, leakage current is suppressed by about 2 orders of magnitude while for a maximum Hf-content of 31 %, leakage current is suppressed by more than 2 orders of magnitude compared to the reference TiO 2 2 sample. Although the dielectric constant is reduced with increasing Al or Hf content, it is maintaining a high value down to 49, within the investigated compositional range. Crystallization temperature of the insulators were also studied and we found that the crystallization temperature depends on both composition and the content. For a Ti-Al- O film with Al concentration of 45 %, the crystallization temperature was increased upwards of 600° C, much larger compared to that of the reference TiO 2 film. The interface trap densities of the various insulators were also studied on both AlGaN/GaN and InAlN substrates. We found a minimal trap density of for the Ti-Hf- O compound with 35 % Hf. In conclusion, our study reveals that the desired high-κ properties of TiO 2 can be adequately maintained while improving other insulator performance factors. Moreover, Ti-Hf- O compounds displayed overall better performance than the Ti-Al- O composites.