Analysis of transport mechanisms in superlattice FinFETs from room temperature to cryogenic temperature and discussion on continued scalability beyond 7 nm

Abstract

In this work, the transport mechanisms 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 (I_ON) of up to 302 μA μm⁻¹, 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 G_m and mobility further supports the contribution of the 2DHG to I_ON. 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 the reduced lattice scattering at cryogenic temperatures enable superlattice FinFETs to achieve high ballistic rates (0.81 at 77 K), as validated by low-temperature electrical measurements. Finally, by combining DFT with non-equilibrium Green's function (NEGF) simulations, the superlattice FinFETs are shown to be some of the promising candidates for sub-7 nm technology nodes.