Thermionic Field Emission Transport at Nanowire Schottky Barrier Contacts
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Thermionic Field Emission Transport at Nanowire Schottky Barrier Contacts Kan Xie1, Steven Allen Hartz1, Virginia M. Ayres1 1 Department of Electrical and Computer Engineering, Michigan State University, East Lansing, MI 48824, USA ABSTRACT The high carrier concentrations typically reported for nanowire devices indicate that when Schottky barrier transport is present, it occurs in the thermionic field emission regime with a substantial but not exclusive tunneling component. Analysis by thermionic field emission is difficult due to its multivariate nature. In recent work, we developed a mathematical stability approach that greatly simplified the evaluation of the multivariate thermionic field emission parameters. This is a general method with potentially wide applicability, requiring only the effective mass m* and relative dielectric constant εr for a given semiconductor as inputs. In the present work, we investigate the influence of the materials properties effective mass m* and relative dielectric constant εr on stability for a range of real and simulated semiconductor nanowires. A further investigation of temperature sensitivity and regime trends is presented. INTRODUCTION Semiconducting nanowires represent a new class of device building blocks with properties enhanced by their small size and their large aspect ratios. To harness their outstanding device potential, it is urgent to fully understand and to control the contacts. The high carrier concentrations typically reported for nanowire devices indicate that when Schottky barrier transport is present, it involves a significant quantum-tunneling component. This further indicates that transport through the controlling barrier occurs in the Thermionic Field Emission (TFE) transport regime, with its substantial but not exclusive tunneling component. Both the Thermionic Emission (TE: no tunneling) and Field Emission (FE: dominant tunneling, an electron transparent Ohmic contact) descriptions of Schottky barrier transport are mathematically simpler to use for fitting experimental I-V data. The Thermionic Field Emission description is difficult to use due to the multivariate nature of this model, which requires that values for the maximum barrier height qφB, free carrier concentration n, effective Richardson constant A** and temperature T be known or guessed to within an accuracy that enables convergence to the experimental data. Use of experimentally pre-determined values acquired under, e.g., TE conditions can lead to unstable fitting results. As TFE is often the correct description for nanoFET Schottky barrier transport, it is important to develop methods that increase its ease of use. In recent work 1, we developed a mathematical stability approach that greatly simplified the evaluation of the multivariate thermionic field emission parameters and enabled a first-time analysis of changes in the barrier heights, tunneling probabilities and potential drops over time for Schottky barrier transport in gallium nitride (GaN) nanoFETs in an extreme environment. Fits perfor
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