This paper reviews our previous theoretical studies and gives further insight into phonon scattering in 3D small nanotransistors using non-equilibrium Green function methodology. The focus is on very small gate-all-around nanowires with Si, GaAs or InGaAs cores. We have calculated phonon-limited mobility and transfer characteristics for a variety of cross-sections at low and high drain bias. The nanowire cross-sectional area is shown to have a significant impact on the phonon-limited mobility and on the current reduction. In a study of narrow Si nanowires we have examined the spatially resolved power dissipation and the validity of Joule's law. Our results show that only a fraction of the power is dissipated inside the drain region even for a relatively large simulated length extension (approximately 30 nm). When considering large source regions in the simulation domain, at low gate bias, a slight cooling of the source is observed. We have also studied the impact of College of Science and Engineering, University of Glasgow, Rankine Building, Oakfield Avenue, Glasgow G12 8LT, UK the real part of phonon scattering self-energy on a narrow nanowire transistor. This real part is usually neglected in nanotransistor simulation, whereas we compute its impact on current-voltage characteristic and mobility. At low gate bias, the imaginary part strongly underestimated the current and the mobility by 50 %. At high gate bias, the two mobilities are similar and the effect on the current is negligible.Keywords Silicon and III-V nanowire field effect transistors · Non-equilibrium Green's functions · Electronphonon scattering self-energies · Phonon-limited mobility · Local power dissipation

Electro-thermal simulations in ultrascaled Si and InGaAs nanowire field effect transistors have been carried out. Devices with 2.2 Â 2.2 nm 2 and 3.6 Â 3.6 nm 2 cross-sections have been investigated. All the standard phonon scattering mechanisms for Si and InGaAs such as optical, polar optical (only for InGaAs), and acoustic phonon mechanisms have been considered. The Non-Equilibrium Green's Function formalism in concomitance with a renormalised 3D heat equation has been used to investigate the effect of self-heating. In addition, locally resolved electron power dissipation and temperature profiles have been extracted. The simulations showed that the heat dissipated inside the transistor increases as the nanowire cross-section decreases. It is also demonstrated that the commonly assumed Joule-heat dissipation overestimates the power dissipated in the transistors studied. It was found that in comparison with standard scattering simulations, electrothermal simulations caused a 72% and 85% decrease in the current in 2.2 Â 2.2 nm 2 cross-section Si and InGaAs core NanoWire Field Effect Transistors , respectively, when compared with ballistic simulations. The corresponding decrease for scattering without self-heating was 45% and 70% respectively.

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Study of individual phonon scattering mechanisms and the validity of Matthiessen's rule in a gate-all-around silicon nanowire transistor J. Appl. Phys. 113, 014501 (2013); 10.1063/1.4772720Non-equilibrium Green's function analysis of cross section and channel length dependence of phonon scattering and its impact on the performance of Si nanowire field effect transistors

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