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

Abstract

A 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)

Record-low contact resistance for InAlN/AlN/GaN high electron mobility transistors on Si with non-gold metal

“…We have also achieved low R c values in AlGaN/AlN/GaN HEMTs by an optimized ohmic-recess etching process 28) . However, these techniques are more complex than our ohmic process reported in this work, which will facilitate the high-volume manufacturing process.…”

High Johnson’s figure of merit (8.32 THz·V) in 0.15-µm conventional T-gate AlGaN/GaN HEMTs on silicon

“…1) In this letter, we report further improvement of the J-FOM by scaling down the gate length (0.15 µm) and using a thin (8 nm) AlGaN barrier with an AlN spacer layer and (NH 4 ) 2 S x treatment plus SiN passivation techniques. The combination of a thin AlGaN barrier and an AlN spacer layer helps to increase the twodimensional electron gas (2DEG) mobility, 16) drain current density I D , extrinsic transconductance g m , and f T . Simultaneously, the short-channel effect (SCE) is also suppressed for the gate length of 0.15 µm.…”

Improvement of Ohmic Contact for InAlGaN/AlN/GaN HEMTs with Recess Etching

“…Furthermore, a thin AlN interlayer is deposited between InAlGaN barrier and GaN buffer to reduce alloy scattering and optimize carrier mobility. However, the AlN layer increases the potential barrier in the Ohmic region, resulting in high Ohmic contact resistance ( R cont ) and impediment of the electron transfer from the 2DEG in the channel to the source/drain electrodes . It was experimentally confirmed that by reducing the AlGaN barrier layer thickness by dry etching, low‐resistance Ohmic contacts can be obtained .…”