Improved recess‐ohmics in AlGaN/GaN high‐electron‐mobility transistors with AlN spacer layer on silicon substrate

Abstract

AbstractA systematic investigation of recess‐ohmic contact by inductively coupled plasma etching using four layers Ti/Al/Ni/Au metal on un‐doped AlGaN/GaN HEMT structure with a thin AlN spacer layer grown on silicon substrate were performed. Although the insertion of the thin AlN spacer layer effectively increases the two‐dimensional electron gas concentration and electron mobility due to the enhanced 2DEG confinement, it causes much difficulty in forming ohmic contacts. This problem has been resolved by recess‐ohmic approach prior to ohmic metalization. Improved HEMT characteristics were demonstrated by this technique. About 17.5% of increase in IDmax and 12.5% of increase in gmmax were observed by recess ohmics. This improved device performance is due to the reduction of Rc, Rd and Rs values by recess‐ohmics. From this investigation, we found that recess‐ohmics are essential to achieve high performance device characteristics in un‐doped AlGaN/GaN HEMTs with AlN spacer layer grown on Si substrate (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)