Highly stable device characteristics of InP-based enhancement-mode high electron mobility transistors with two-step-recessed gates

High-performance 0.1-mu m-gate InP-based enhancement-mode high electron mob ility transistors (E-HEMTs) were fabricated using two-step-recessed-gate te chnology, where the gate recess etching is first carried out by wet-chemica l etching to removed n(+)-cap layers and then by Ar plasma etching to remov e the InP etch stopper layer. Etching selectivies for both steps are suffic ient not to degrade the uniformity of the device characteristics. The main advantage over the conventional approach for E-HEMTs, Pt-based-gate technol ogy, is the fact that the stability of the threshold voltage is improved by means of a refractory gate metal, WSiN. The change in the threshold voltag e is only 50 mV after 160-h ias and thermal stress at 195 degrees C.