Single-Charge Tunneling in Codoped Silicon Nanodevices

Abstract

Silicon (Si) nano-electronics is advancing towards the end of the Moore’s Law, as gate lengths of just a few nanometers have been already reported in state-of-the-art transistors. In the nanostructures that act as channels in transistors or depletion layers in pn diodes, the role of dopants becomes critical, since the transport properties depend on a small number of dopants and/or on their random distribution. Here, we present the possibility of single-charge tunneling in codoped Si nanodevices formed in silicon-on-insulator films, in which both phosphorus (P) donors and boron (B) acceptors are introduced intentionally. For highly doped pn diodes, we report band-to-band tunneling (BTBT) via energy states in the depletion layer. These energy states can be ascribed to quantum dots (QDs) formed by the random distribution of donors and acceptors in such a depletion layer. For nanoscale silicon-on-insulator field-effect transistors (SOI-FETs) doped heavily with P-donors and also counter-doped with B-acceptors, we report current peaks and Coulomb diamonds. These features are ascribed to single-electron tunneling (SET) via QDs in the codoped nanoscale channels. These reports provide new insights for utilizing codoped silicon nanostructures for fundamental applications, in which the interplay between donors and acceptors can enhance the functionalities of the devices.

Ab Initio Study of Donor and Acceptor Ground States in the P–B Codoped Si Nanostructures

“…Localization of carriers due to P−B codoping is also critical for band-to-band tunneling (BTBT) phenomena in Si nanodiodes. 11 BTBT transport in Si typically requires assistance of phonons for momentum conservation, but larger uncertainty in momentum can be expected due to further localization of the electron in real space. Due to the above reasons, a more fundamental study of the localization of wave functions of the dopant's ground states (GSs) in P−B codoped nanostructures is required.…”

“…Localization of carriers due to P–B codoping is also critical for band-to-band tunneling (BTBT) phenomena in Si nanodiodes . BTBT transport in Si typically requires assistance of phonons for momentum conservation, but larger uncertainty in momentum can be expected due to further localization of the electron in real space.…”