Analysis of Transport Mechanism in Superlattice FinFETs from Room Temperature to Cryogenic Temperature and Discussion on Continued Scalability Beyond 7 nm

Abstract

In this work, the transport mechanism in p-type superlattice FinFETs are investigated from room to cryogenic temperatures, and their superior performance is experimentally demonstrated compared with conventional Silicon-germanium (SiGe) and Silicon (Si) channel FinFETs. At room temperature, the superlattice structure achieves an ON-state current (ION) up to 302 μA/μm, which is attributed to a conductive two-dimensional hole gas (2DHG) formed at the Si/SiGe heterojunction. TCAD simulations reveal that the 2DHG significantly enhances volume-inversion transport. The observed temperature dependence of Gm and mobility further supports the contribution of 2DHG to ION. Further analysis with density functional theory (DFT) explains the improved subthreshold swing (SS) by comparing the interface density of states (DOS) of SiGe/HfO₂ and Si/HfO₂. The reduced interface scattering under volume-inversion and reduced lattice scattering at cryogenic temperatures make superlattice FinFETs with high ballistic rates (0.81 at 77 K), as validated by low-temperature electrical measurements. Finally, combining DFT with non-equilibrium Green’s function (NEGF) simulations, the superlattice FinFETs are shown to be one of promising candidates for sub-7-nm technology nodes.