Abstract
A numerical framework for DC and RF small-signal simulations of nanowire transistors is presented, which is based on the self-consistent solution of the Poisson, Schrödinger, and Boltzmann transport equations and is stable for the entire range from weak to strong particle scattering. The proposed approach does not suffer from the deficiencies due to the transformation of the Boltzmann transport equation into the energy space and can handle the quasi-ballistic case. This is a key requirement for the investigation of plasma resonances and other high-mobility phenomena. The in-house solver is validated with results of a previously developed simulator based on the H-transformation for a conventional hbox{N}^+hbox{NN}^+ silicon transistor with strong scattering. Then, its results are compared with those of moments-based models and it is shown that these do not provide a satisfactory description of the electron dynamics in the quasi-ballistic transport regime. Furthermore, the internal boundary conditions of the transport models at the contacts are found to have a significant impact on plasma resonances and the physics-based thermal-bath boundary condition strongly suppresses them.
Highlights
Scientific interest in solid-state terahertz (THz) devices has increased significantly [1,2,3,4,5]
The methods developed previously for planar transistors could be applied to nanowire transistors, it is not clear whether the assumptions on which these models are based hold in the case of quasi-ballistic transport, which is a prerequisite for plasma instabilities [14]
Since the stabilization scheme based on the H-transformation for the Boltzmann transport equation (BE) fails for quasi-ballistic transport, a scheme based on the phase-space trajectories of the electrons is presented [16]
Summary
Scientific interest in solid-state terahertz (THz) devices (operating at frequencies between 300 GHz and 3 THz) has increased significantly [1,2,3,4,5]. In the case of quasi-ballistic transport the stationary drain current of a MOSFET is limited by the finite injection velocity of the electrons from the source into the channel (e.g., [17, 18]) This leads to a much more complex behavior of the source contact at high frequencies that can be described by the simple approximation made by Dyakonov and Shur and that the small-signal electron density must satisfy a Dirichlet boundary condition (D-BC) at the source side of the channel [6]. Deterministic solvers for the BE have been successfully used in the case of nanowire transistors (e.g., [20]), even including small-signal calculations [21] In these cases, a transformation from the wavenumber to energy is used, which causes trouble in the case of a 1D k-space, because the density of states diverges at zero energy.
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