Demonstration of Enhancement Mode AlN/ultrathin AlGaN/GaN HEMTs Using A Selective Wet Etch Approach

A novel recessed-gate structure involving an ultrathin AlGaN barrier layer capped by an AlN layer in the source-drain access regions has been implemented to demonstrate enhancement-mode high electron mobility transistors. A wet etch process has been developed using heated photoresist developer to selectively etch the AlN for the gate recess step, bypassing plasma etching and associated issues. The etch has been proven to be selective to AlN over AlGaN and GaN. A repeatable threshold voltage of +0.21V has been demonstrated with 4 nm AlGaN barrier layer thickness.