Explicit screening full band quantum transport model for semiconductor nanodevices

Abstract

State of the art quantum transport models for semiconductor nanodevices attribute negative (positive) unit charges to states of the conduction (valence) band. Hybrid states that enable band-to-band tunneling are subject to interpolation that yield model dependent charge contributions. In any nanodevice structure, these models rely on device and physics specific input for the dielectric constants. This paper exemplifies the large variability of different charge interpretation models when applied to ultrathin body transistor performance predictions. To solve this modeling challenge, an electron-only band structure model is extended to atomistic quantum transport. Performance predictions of MOSFETs and tunneling FETs confirm the generality of the new model and its independence of additional screening models.

Full Band Incorporation in Ab-initio Simulations of Two-dimensional Semiconductor Based Devices

“…The disadvantage of this approach lies in the fact that it is impossible to reduce the energy window over which the Green's function must be integrated. A solution can be found by splitting the Green's function into an equilibrium part, G < eq , and a non-equilibrium part, G < neq [7], [13]. Considering again two contacts, with broadening matrices Γ 1 and Γ 2 [14], at which carriers are injected according to the Fermi-Dirac statistics f 1 and f 2 respectively,…”

“…The poles are the poles of the Fermi-Dirac statistic function f r , with E p = E fr +ik b T π(2n+1) and Res(f r , E p ) = −k B T for n ∈ N [7]. The prohibitively high computational cost of integrating a Green's function over a large energy window is attributed to the presence of many Van Hove singularities, which require many grid points to be integrated accurately.…”

“…The prohibitively high computational cost of integrating a Green's function over a large energy window is attributed to the presence of many Van Hove singularities, which require many grid points to be integrated accurately. On the complex contour, these Van Hove singularities disappear, resulting in a smooth function requiring a significantly lower number of grid points [7]. An additional benefit of (17) is that occupation of states is not governed by injection of carriers at the contacts.…”

“…Hence, (17) also allows for occupation of bound states. These are states that are not connected to the contacts, and which would thus be empty in the ECA, irrespective of their energy [7]. The occupation of these bound states in the FBA depends on the reference level E fr .…”

“…It is presently unclear whether this approach can accurately simulate the behaviour at metallic interfaces, where there is no clear conduction band or valence band. Previous work [7] has shown that a full-band approach (FBA) can be important for the correct simulation of nanodevices based on conventional 3D materials, especially at certain interfaces. In Section II, we recapitulate the NEGF formalism and discuss the two models, i.e., the ECA and FBA.…”