Quantum transport models based on NEGF and empirical pseudopotentials for accurate modeling of nanoscale electron devices

Abstract

This paper presents significant new developments concerning the full band, quantum simulation of nanostructured systems and nanoscale electron devices based on an empirical pseudopotential Hamiltonian. We demonstrate that the method is of general applicability, in fact we show results for planar, ultra-thin body FETs and also for three-dimensional, nanowire FETs, we deal with different crystal orientations and account for possible stress/strain conditions in the simulated systems. Some of the simulations reported in this paper have been made computationally viable by the substantial improvements of the numerical efficiency compared to our previous pseudopotentials based methodology.Most of the methods and algorithms discussed in this paper are not specific to an empirical pseudopotential Hamiltonian, on the contrary they can be applied also to different Hamiltonians described with a plane waves basis, which are frequently employed for ab-initio, Density Functional Theory based calculations. The application of the methodologies described in this work may thus be more far reaching than it is illustrated by the case studies explicitly addressed in the present paper.

Full-Band Quantum Transport of Heterojunction Electron Devices With Empirical Pseudopotentials

“…Here we briefly describe the full-band model employed in this work for band-structure and quantum transport calculations, which is based on the empirical pseudopotential method (EPM) [30], [31]. The general methodology has been already described in previous publications [27], [28], so that we here focus on the aspects related to the treatment of heterojunctions that have been explicitly developed for this work.…”

“…The quantum transport model used in this work relies on the Non Equilibrium Green's Function (NEGF) method formulated in a hybrid basis, xK yz , consisting of a discretized real space in the transport direction x and of plane waves in the (y,z) directions [28]. In the hybrid basis the Hamiltonian matrix inside a given semiconductor takes the block tridiagonal form…”

“…For a 2D or a 1D electron gas the Hamiltonian matrix still has the tridiagonal form in Eq. ( 2), but the size of the blocks is increased [28]. In all the calculations of this work we used N d =32, and an EPM cutoff energy E cut = 4.5 Ry corresponding to N G ≈800.…”

“…An empirical pseudopotentials method (EPM) provides an interesting compromise between accuracy and computational burden, in that it can accurately and effectively describe both bulk and nanostructured semiconductors by using only few fitting parameters [18], [19], [20], [21], [22]. Some recent papers have explored the use of the EPM for transport modelling by using either a quantum transmitting boundary method [23], [24], [25], [26], or a Non Equilibrium Green's Function (NEGF) method [27], [28], [29]. However, no attempts have been reported to our knowledge for the use of such transport methods for electron devices whose operation relies on the heterojunction of different semiconductors.…”

An innovative technique for electronic transport model of group-III nitrides

“…Ensemble Monte Carlo (EMC) technique is the best suited numerical approach for accurate solution of the Boltzmann equation (BTE) under nonlinear response conditions 12 – 14 . The aim of the present paper is to demonstrate a simple and inexpensive theoretical approach for prediction of the low and high field mobility model for binary and ternary wurtzite nitride alloys for entire concentration range.…”