Doping engineering to enhance the performance of double-gate pMOSFETs with ultrashort gate length (5 nm)

摘要

Enhancing the performance of Si field-effect transistors with ultrashort gate length is very challenging because of the increase of the source-to-drain tunneling and other short-channel effects. Doping engineering can affect the tunneling probability by varying the energy band profile and electric field. Full quantum ballistic simulations are performed here to study the use of doping engineering as a tool to improve the electrostatic integrity in a pMOSFETs device with a double-gate structure and a gate length of 5 nm. The simulation methodology is based on nonequilibrium Green's functions, employing a six-band k center dot p Hamiltonian. The influence of the source/drain doping profile/concentration on the electric field in both the transport and confinement directions is also discussed. The trends found for the ON- to OFF-state current ratio and the switching delay differ, depending on the doping profile/concentration for high-performance and low-operating-power applications. The results of this study highlight the importance of using a Gaussian doping profile, as compared with constant doping, to improve the performance of such ultrascaled devices in terms of enhancing the subthreshold swing, reducing the drain-induced barrier lowering, and achieving low source-to-drain tunneling. The doping concentration can be optimized by controlling the source-to-drain tunneling and overcoming the source exhaustion. The selection of a certain damping factor in the Gaussian function can be used as a parameter, in addition to the peak doping concentration, to optimize the device performance.