Band Alignment and Charge Transfer Mechanisms in the Prediction of Advanced Gate Dielectrics for Carbon Nanotube Field-Effect Transistors

The search for novel gate dielectrics to mitigate interface state density is a pressing concern in the fabrication of high-performance carbon nanotube field-effect transistors (CNT-FETs). In this study, we investigated the feasibility of employing strontium titanate (STO) with an ultra-high dielectric constant as the gate dielectric in CNT-FETs. By combining X-ray photoelectron spectroscopy measurements with first-principles calculations, we determined the band offsets between CNT and STO, as well as between CNT and conventional gate dielectrics such as HfO2 and SiO2. The valence/conduction band offset (VBO/CBO) at the STO/CNT interface is found to be 1.1 eV/1.5 eV, which is the smallest among all studied interfaces, followed by those at HfO2/CNT interface (VBO = 1.3 eV/CBO = 3.4 eV) and SiO2/CNT interface (VBO = 3.6 eV/CBO = 4.5 eV). Moreover, charge transfer at the STO/CNT interface exhibits two orders of magnitude lower values compared to that at HfO2/CNT interface and is also significantly smaller than that at SiO2/CNT interface. This phenomenon can be ascribed to the combined effects of van der Waals forces at the STO/CNT interface and fewer dangling bonds on the STO surface. These findings suggest exceptional compatibility between STO and CNT, making STO highly suitable for high-performance CNT-FETs.