Impact of barrier layer thickness on DC and RF performance of AlGaN/GaN high electron mobility transistors.

This work investigates the impact of barrier layer thickness on DC and RF performance of a GaN HEMT device, targeting the low noise high gain application. An optimisation workflow based on the barrier layer thickness and Al mole fraction is presented for improving the RF metrics of a GaN HEMT. AlGaN/GaN HEMTs with a gate length of 400 nm were fabricated with 22% Al content and a barrier layer thickness of 23 and 20 nm, respectively. TCAD simulation studies were carried out for different barrier thickness and Al mole fraction in accordance with the fabricated devices. Increasing the barrier thickness increases the 2-DEG density which increases the maximum drain current and results in a negative shift in the threshold voltage. With a thin barrier layer, the AlGaN/GaN HEMTs exhibit a higher transconductance due to improved gate action. The fabricated devices were investigated with the help of small-signal equivalent circuit, which demonstrate higher capacitances associated with a thin barrier layer. Apart from DC characteristics and small-signal performance, the intrinsic gain (gm/gd ratio), noise performance, and large-signal performance of the device has been investigated which provides a great contribution in creating a design subspace for a specific application (depending on the performance requirement). A thin barrier layer improves the intrinsic gain of the GaN HEMT device by 74% due to a higher transconductance and comparatively lower output conductance values. An increase in Al mole fraction increases the transconductance but is dominated by an increase in the output conductance, which in turn reduces the intrinsic gain of the device. An in-depth analysis is presented by investigating and optimising the trade-offs with barrier layer thickness and Al mole fraction towards the noise performance of the devices at microwave C- and X-band. [ABSTRACT FROM AUTHOR]