Alloyed and Non-Alloyed Ohmic Contacts for AlInAs/ InGaAs High Electron Mobility Transistors

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Abstract
AuGe/Ni/Au alloyed and WSi non-alloyed ohmic contacts are investigated for AlInAs/InGaAs high electron mobility transistors (HEMTs). For the alloyed contact, a contact resistance (R c) lower than 0.03 Ω mm is obtained at an alloy temperature of 300°C. The value of R c drastically increases with alloy temperatures above 300°C and exceeds 0.15 Ω mm at 380°C. Auger analysis and analytical cross-sectional transmission electron microscopy have revealed significant outdiffusion of In in the epitaxial layer into the top Au layer and the formation of polycrystalline GaAs in the epitaxial layer, which cause the increase of R c with alloy temperature. For the refractory WSi non-alloyed ohmic contact, R c remains lower than 0.1 Ω mm under annealing temperatures up to 380°C. The extrinsic maximum transconductance (g m) of 600 mS/mm is obtained for the HEMT device with the WSi ohmic contact.