Single-Step Electron Beam Evaporation for Schottky/Ohmic Drain in GaN-on-Si HEMTs Fabrication

This letter reports a novel method for fabricating Schottky/ohmic drain for GaN high electron mobility transistors (HEMTs). Without secondary photolithography or secondary metal evaporation, the Schottky/ohmic drain can be obtained by adjusting the direction of the electron beam evaporation. Besides, different metal/semiconductor interfaces can be simultaneously formed at this state, which are beneficial to enhance the shielding effect of the rough ohmic-drain metal morphology and modulate the electric field distribution on the drain side. By using Schottky/ohmic drain technology, the average breakdown voltage calculated from 50 devices each is improved from 895 V (ohmic drain device) to 1205 V for
$\text{L}_{\text {GD}} = 18\,\,\mu \text{m}$
, indicating enhanced off-state reliability characteristics for GaN HEMTs.