Electrical properties of the HfO₂-Al₂O₃ nanolaminates with homogeneous and graded compositions on InP

For possible application to a gate dielectric in high-performance III-V transistors, nanolaminated HfO₂-Al₂O₃ films with artificial compositional profiles were deposited on n-type InP substrates using atomic layer deposition. The films were vertically graded (HfO₂ and Al₂O₃ at the surface and interface regions, respectively) and had a homogeneous composition. To compare their electrical properties, a similar physical thickness and capacitance-equivalent thickness (CET) were maintained, and the graded structure showed an increase in the Al₂O₃ content near the high-k and InP interface region without an increase in CET, which suppresses the In incorporation at the near-interface region and reduces the density of the interface trap. However, doing so results in a degradation of the leakage current characteristics under voltage stressing when compared to homogeneously-nanolaminated films.