A Physics Based Analytical Model for the Threshold Voltage of a Normally-off AlGaN/GaN FinFET
Gallium nitride (GaN) based transistors are advantageous for high voltage power switching applications due to its superior material properties. In power switching applications normally-off transistors are preferred for their fail-safe operation at high voltages in addition to the advantages of lower power consumption and simpler drive circuits. However, planar AlGaN/GaN high-electron mobility transistors (HEMTs) are normally-on devices with negative threshold voltage due to the presence of polarization induced two-dimensional electron gas (2DEG) at the heterojunction at zero gate voltage. It has been experimentally observed that a normally-on AlGaN/GaN FinFET can be transformed into a normally-off transistor with positive threshold voltage by reducing the fin width. In this paper a physics based analytical model for the threshold voltage of a AlGaN/GaN FinFET is presented. It is seen that the strain induced in the channel region in the piezoelectric GaN layer just below the heterojunction plays an important role in determining the threshold voltage at narrow fin widths.
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