Multi-Scale Simulation of Transport via a Mo/n + -GaAs Schottky Contact
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Multi-Scale Simulation of Transport via a Mo/n+-GaAs Schottky Contact Manuel Aldegunde1, Steven P. Hepplestone2, Peter V. Sushko2 and Karol Kalna1 1 Electronic Systems Design Centre, College of Engineering, Swansea University, Swansea SA2 8PP, Wales, U.K. 2 Department of Physics and Astronomy and London Centre for Nanotechnology, University College London, Gower Street, London WC1E 6BT, U.K. ABSTRACT A multi-scale modeling of electron transport via a metal-semiconductor interface is carried out by coupling ab initio calculations with three-dimensional finite element ensemble Monte Carlo simulations. The results for the Mo/GaAs (001) interface show that variations of the electronic properties with the distance from the interface have a strong impact on the transport characteristics. In particular, the calculated tunneling barrier differs dramatically from that of the ideal Schottky model of an abrupt metal-semiconductor interface. The band gap narrowing near the interface lowers resistivity by more than one order of magnitude: from 2.1×10-8 Ωcm² to 4.7×10-10 Ωcm². The dependence of the electron effective mass from the distance to the interface also plays an important role bringing resistivity to 7.9×10-10 Ωcm². INTRODUCTION Metal-semiconductor contacts are integral components of any semiconductor device. When these devices are scaled to nanometer dimensions, transport through the contacts becomes affected by their atomic structure and atomic-scale variations of their electronic properties. Here, we present a multi-scale approach, in which the results of ab initio calculations of a metalsemiconductor interface are mapped onto semi-classical transport simulations of the electronic transport characteristics, which are performed using a three-dimensional (3D) self-consistent finite element ensemble Monte Carlo method with atomic resolution. We demonstrate this approach on the example of Mo/GaAs(100) interface [1], which belongs to a broader class on Mo-on-InGaAs structures that show a particular promise as candidates for the source/drain contacts in III-V heterostructure MOSFETs for future sub-16 nm CMOS technologies [2]. COMPUTATIONAL APPROACH We use a two-level hierarchical method for predicting electrical current through a metalsemiconductor contact. The first level is based on the density functional theory (DFT) calculations, which are used to obtain the geometrical structure and electronic properties of the interface. The results of these calculations are used to define characteristic electronic structure parameters, such as effective electron mass, as functions of the distance from the interface, which then employed in semiclassical ensemble Monte Carlo transport simulations [3, 4]. In this way, we can include the essential effects of the interaction between metal and semiconductor, such as charge density redistribution, lattice distortions and band realignment, at the atomistic level in the transport simulations, thus, building a realistic physical model of transport through the interface.
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