RECESSED-GATE HIGH-ELECTRON-MOBILITY TRANSISTORS WITH DOPED BARRIERS AND ROUND GATE FOOT CORNERS

A high electron mobility transistor comprising a substrate. The substrate comprising: a buffer layer, a channel layer disposed on the buffer layer, an interlayer disposed on the channel layer, a spacer layer, and a first barrier layer between the spacer layer and a cap layer, the spacer layer is between the interlayer and the first barrier layer. The high electron mobility transistor comprises a source electrode disposed on the channel, a drain electrode disposed on the channel, and a gate electrode disposed between the source electrode and the drain electrode, the gate electrode defining a longitudinal portion extending through the capping layer, wherein a distal end of the longitudinal portion is in contact with the first barrier layer defines an external fillet between the distal end and the longitudinal portion.