Modeling Electrostatics and Low-Field Electron Mobility of GaN FinFETs

Abstract

Gallium nitride (GaN) high electron mobility transistors (HEMTs) are currently being used for RF applications due to the intrinsically high saturation velocity and high mobility of GaN compared to both Silicon and SiC. However, GaN HEMTs suffer from a variety of issues, such as a lack of E-Mode operation and non-linearity, which impacts their widespread adoption in the RF and low-voltage switching devices. Recent advances in material processing, high aspect ratio epitaxial growth, and etching methods has led to an increased interest in 3-D GaN nanostructures such as AlGaN/GaN MIS FinFET wherein a layer of Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> surrounds the AlGaN/GaN fin. Theoretical calculations of transport properties of AlGaN/GaN FinFETs are scarce compared to those of their planar HEMT counterparts. This work employs for the first time self-consistent solution of the coupled 1-D Boltzmann – 2-D Schrödinger – 3-D Poisson problem to yield the channel electrostatics and the transport characteristics of AlGaN/GaN MIS FinFETs. The low field electron mobility in the quasi-1-D region is calculated, using 1-D ensemble Monte Carlo method, as a function of temperature and fin width. Acoustic, piezoelectric and polar optical phonon scattering, and interface roughness scattering at the AlGaN/GaN interface, are incorporated in the theoretical model. Our simulations suggest that E-mode FinFETs can be achieved in ultranarrow fin channels. As suggested experimentally, we confirm via simulation experiments that strain relaxation increases the sheet resistance of the channel.