Influence of HfO2 and SiO2 interfacial layers on the characteristics of n-GaN/HfSiOx capacitors using plasma-enhanced atomic layer deposition

We investigated the growth per cycle (GPC) for SiO2 and HfO2 on n-GaN/native oxide and p-Si/SiO2 substrates by plasma-enhanced atomic layer deposition using tris(dimethylamino)silane and tetrakis(dimethylamino)hafnium precursors, respectively, and O2 plasma gases. On the basis of the estimated GPC, we also examined the characteristics of n-GaN/Hf0.57Si0.43Ox/Pt capacitors with an inserted interfacial layer (IL) such as subnanometer-thick HfO2 and SiO2. We found that the GPC for SiO2 on n-GaN/native oxide was slightly smaller than that on p-Si/SiO2, whereas the GPC for HfO2 was the same on both substrates. The GPC for ALD-SiO2 could be reasonably plotted on the basis of the relationship between the GPC and the difference in electronegativity between the metal and oxygen in the metal-O underlayers including native oxide (Ga2O3) on GaN. On the basis of the GPC on n-GaN, Hf0.57Si0.43Ox (23 nm) capacitors were fabricated without and with a HfO2-IL (0.3 and 0.5 nm) or SiO2-IL (0.3 and 0.6 nm). These capacitors exhibited similar leakage current properties and a high breakdown electric field greater than 8.3 MV cm−1. No frequency dispersion and a flatband voltage (Vfb) hysteresis smaller than 50 mV were observed for all of the capacitors. Compared with the SiO2-IL [Si-rich HfSiOx (Si: > 0.43)] capacitors, the HfO2-IL [Hf-rich HfSiOx (Hf: > 0.57)] capacitors showed a smaller interface state density [(1.2–1.7) × 1011 cm−2 eV−1 at −0.4 eV from the conduction band] and a smaller negative Vfb shift. Therefore, the Hf-rich HfSiOx (Hf: > 0.57) grown using a HfO2-IL at the n-GaN/HfSiOx interface plays a substantial role in improving the electrical properties of n-GaN/HfSiOx capacitors.