Nanowire Channel InAlN/GaN HEMTs With High Linearity of $g_{\rm m}$ and $f_{\rm T}$

Abstract

This letter reports a high linearity InAlN/GaN high-electron-mobility transistor (HEMT) with a nanowire channel structure. It is found that the increase of source access resistance with drain current severely limits the linearity of GaN HEMTs. By increasing the ratio of the source access region width to that of the channel, the transistor access region has a larger current drivability than the channel region, which enables the source access region to behave more like an ideal source. The suppression of the increase in source access resistance with current provides a flat transconductance <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(g_{\rm{m}})$</tex></formula> at high drain current even in sub-100-nm short-channel devices. In addition, the constant source resistance allows a higher effective gate voltage overdrive, which enables a higher drain current density <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$({&gt;}{\rm 3.5}~{\rm A}/{\rm mm})$</tex></formula> in the intrinsic device. The new devices also show very flat current-gain cutoff frequency <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$(f_{\rm{T}})$</tex></formula> as a function of gate voltage. These results highlight the importance of the source access region in limiting the maximum current density and the linearity of GaN HEMTs.