Heat Generation Counted by Phonon Absorption and Emission in GAA FET under the Framework of Non-Equilibrium Green's Function Method

As the most promising device beyond FinFET technology, the Gate-All-Around (GAA) field effect transistor (FET) shows excellent electrical characteristics, but also suffers severe self-heating effects, which compromise the performance and reliability of the device. The commonly used Joule heat model fails to investigate the thermal properties of nanoscale devices, and a rigorous treatment of heat generation by counting phonon absorption and emission is demanded. In this paper, we build such a heat generation model for Si GAA nanowire FETs based on the Non-equilibrium Green's function (NEGF) method with the accurate electron-phonon interaction. Both the acoustic phonon scattering and the optical phonon scattering are considered under the self-consistent Born approximation. Since the simple geometry of GAA FETs, an uncoupled mode space approach is adequate and utilized, which alleviates the computation burden dramatically. The Fourier heat equation which takes proposed heat generation model as the heat source is employed in the simulation. The simulation result shows the role of phonon scattering when compared with ballistic transport. The heat source we obtained exhibits similar characteristics to that of the Joule heat model but with a much smaller magnitude. It is also observed that as the channel length decreases, the ratio of heat dissipated in the device decreases, which means that the validity of the Joule heat model becomes even weaker.