Analytical derivation of interface state density from sub-threshold swing in AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors

We present an analytical expression of sub-threshold swing (SS) in AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs), and describe dependences of SS on structural and relevant material parameters of the MIS-HEMTs. In this work, we derived two different equations where interface states reside at the dielectric/AlGaN interface (proposed equation) and at the AlGaN/GaN interface (conventional equation), which is the customary assumption in the literature. Analysis indicates that SS calculated by using conventional equation is always higher than that calculated by using proposed equation. To confirm the validity of the proposed equation, AlGaN/GaN MIS-HEMTs with and without recess etched gate structure are fabricated and their corresponding interface state densities are derived directly from the measured SS. The MIS-HEMTs with recess show higher SS than those without recess, which is attributed to the increase of interface state density, probably due to the damage introduced during the etching process.