No abstract

Self-heating effects are investigated in ultrascaled gate-all-around silicon nanowire field-effect transistors (NWFETs) using a full-band and atomistic quantum transport simulator where electron and phonon transport are fully coupled. The nonequilibrium Green's function formalism is used for that purpose, within a nearest-neighbor sp 3 d 5 s * tight-binding basis for electrons and a modified valence-force-field model for phonons. Electron-phonon and phonon-electron interactions are taken into account through specific scattering self-energies treated in the self-consistent Born approximation. The electron and phonon systems are driven out of equilibrium; energy is exchanged between them while the total energy current remains conserved. This gives rise to local variations of the lattice temperature and the formation of hot spots. The resulting self-heating effects strongly increase the electron-phonon scattering strength and lead to a significant reduction of the ON-current in the considered ultrascaled Si NWFET with a diameter of 3 nm and a length of 45 nm. At the same time, the lattice temperature exhibits a maximum close to the drain contact of the transistor.

We report on in situ doping of InAs nanowires grown by metal-organic vapor-phase epitaxy without any catalyst particles. The effects of various dopant precursors (Si(2)H(6), H(2)S, DETe, CBr(4)) on the nanowire morphology and the axial and radial growth rates are investigated to select dopants that enable control of the conductivity in a broad range and that concomitantly lead to favorable nanowire growth. In addition, the resistivity of individual wires was measured for different gas-phase concentrations of the dopants selected, and the doping density and mobility were extracted. We find that by using Si(2)H(6) axially and radially uniform doping densities up to 7 × 10(19) cm(-3) can be obtained without affecting the morphology or growth rates. For sulfur-doped InAs nanowires, we find that the distribution coefficient depends on the growth conditions, making S doping more difficult to control than Si doping. Moreover, above a critical sulfur gas-phase concentration, compensation takes place, limiting the maximum doping level to 2 × 10(19) cm(-3). Finally, we extract the specific contact resistivity as a function of doping concentration for Ti and Ni contacts.

Through advanced electro-thermal simulations we demonstrate that self-heating effects play a significant role in ultrascaled nanowire field-effect transistors, that some crystal orientations are less favorable than others (⟨111⟩ for n-type applications, ⟨100⟩ for p-type ones), and that Ge might outperform Si at this scale. We further establish a relationship between the dissipated power and the electrical mobility and another one between the current reduction induced by self-heating and the phonon thermal conductivity.

Recent experimental advances have revealed that the mean free path (mfp) of phonons contributing significantly to thermal transport in crystalline semiconductors can be several microns long. Almost all of these experiments are based on bulk and thin film materials and use techniques that are not directly applicable to nanowires. By developing a process with which we could fabricate multiple electrically contacted and suspended segments on individual heavily doped smooth Silicon nanowires, we measured phonon transport across varying length scales using a DC self-heating technique. Our measurements show that diffusive thermal transport is still valid across O(100) nm length scales, supporting the diffuse nature of phonon-boundary scattering even on smooth nanowire surfaces. Our work also showcases the self-heating technique as an important alternative to the thermal bridge technique to measure phonon transport across short length scales relevant to mapping the phonon mfp spectrum in nanowires.