Band alignment of TiO₂/SiC and TiO₂/Si heterojunction interface grown by atomic layer deposition

Silicon carbide (SiC) is regarded as a promising semiconductor owing to its wide band gap and high thermal conductivity. Meanwhile, it possesses issues such as interface properties, which may affect the performance of SiC substrate power devices (e.g. MOSFET), especially when compared with similarly structured silicon appliances. Given that the development of SiC semiconductor devices has a number of commonalities with conventional silicon-based semiconductors, titanium dioxide (TiO₂), a material that has a great track record in Si-based semiconductor devices, has been chosen for investigation in this work. Although TiO₂ is not capable of being a gate dielectric alone on the SiC substrate because of its relatively narrow band gap, it can be adopted into composite or multilayer gate dielectrics to reach satisfying characteristics. As such, the interfacial state and heterostructure between TiO₂ and SiC remain worthy being researched. In the present study, the properties of atomic layer deposited (ALD) TiO₂ films on silicon substrates were compared with those on 4H-SiC substrates via x-ray photoelectron spectroscopy, atomic force microscopy, and x-ray reflectometry. It is shown that the interface state between ALD TiO₂ film and both types of substrates as-deposited have similar chemical conditions, whereby TiO₂ layer barely react with substrates, containing great amount of oxygen vacancies. According to band alignment calculations, heterostructure of both samples are type-II heterojunctions with negatively shifted conduction band. Although the large bandwidth of 4H-SiC hinders the use of TiO₂ as a gate dielectric in power devices, this structure has the potential for other semiconductor products.