Theoretical Insight into Quantum Transport Via Molecular Dots in a Vertical Tunnel Transistor

We provide a theoretical insight into the quantum transport of C60 molecules in a vertical transistor. A feature of the device is that the transistor channel is composed of a double tunnel junction based on a metal-oxide-semiconductor (MOS) structure, where the molecules are isolated from each other and are then embedded as quantum dots in the insulating layer of the MOS structure. The transistor thus allows us to examine quantum transport induced by the individual molecules even in a macroscopic device. A significant finding of this study is that the tunnel transport followed an orthodox theory that is widely used for single-carrier transport. The simulated drain current–drain voltage curves and differential conductance (dId/dVd) curves well reproduced those obtained experimentally. Notably, the intervals of the dId/dVd peaks derived from the degenerate molecular orbitals coincided with the charging energy of single or a few C60 molecules. These results confirm that the transport can be interpreted as single-carrier tunneling with interplay between a Coulomb blockade and discrete molecular orbitals. Furthermore, the theoretical work revealed that the temperature dependence of the transport was intrinsic behavior caused by the quantum confinement effect in the molecules. Our findings therefore pave the way to achieving a large-scale integrated single-carrier transistor with attractive molecular functions.