Design and Analysis of High Mobility Enhancement-Mode 4H-SiC MOSFETs Using a Thin-SiO₂/Al₂O₃Gate-Stack

Abstract

High-performance 4H-SiC MOSFETs have been fabricated, having a peak effective mobility of 265 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> / <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}\,\cdot $ </tex-math></inline-formula> s, and a peak field effect mobility of 154 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V s, in 2- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> m gate length MOSFETs. The gate-stack was designed to minimize interface states and comprised a 0.7-nm thermally grown SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> on 4H-SiC, followed by 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> and a metal gate contact. In this way, carbon remaining following SiC oxidation is significantly reduced. A density of interface traps in the range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6 \times 10^{11} - 5 \times 10^{10}$ </tex-math></inline-formula> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> is also obtained. Temperature-dependent electrical data reveal that the high mobility results from conduction being phonon-limited, rather than Coulomb-limited. Furthermore, universal mobility in these 4H-SiC MOSFETs is shown to be up to 50% of that observed in the Si devices. Expressions for electric field-dependent contributions to mobility are presented. A steep subthreshold slope of 127 mV/decade indicates low electrical defect density. A temperature coefficient of −4.6 mV/K in threshold voltage is similar to that in the Si MOSFETs.