GaN-Based Devices for Reliable Operation at Very High Temperatures

One of the main issues for high-temperature operation of GaN- based devices is the development of reliable metal contacts. We have investigated the thermal stability and device performance of AlGaN/GaN high-electron mobility transistors (HEMTs) with both conventional (Ti/Al/Ni/Au) and Ir-based (Ti/Al/Ir/Au) Ohmic contacts. Both dc and rf measurements showed better performance with Ir-based contacts, from room temperature up to 500{degree sign}C. We also fabricated AlGaN/GaN HEMTs with Ti/Al/TiB2/Ti/Au source/drain Ohmic contacts and a variety of gate metal schemes (Pt/Au, Ni/Au, Pt/TiB2/Au or Ni/TiB2/Au) and subjected them to long-term annealing at 350{degree sign}C. By comparison with companion devices with conventional Ti/Al/Pt/Au Ohmic contacts and Pt/Au gate contacts, the HEMTs with boride- based Ohmic metal and either Pt/Au, Ni/Au or Ni/TiB2/Au gate metal showed superior stability of both source-drain current and transconductance after 25 days aging at 350{degree sign}C.