Non-alloyed Pd/Sn and Pd/Sn/Au Ohmic Contacts for GaAs MESFETs: Technology and Performance

摘要

Non-alloyed thermally stable Pd/Sn and Pd/Sn/Au Ohmic contacts have been utilized for the fabrication of GaAs MESFETs for the first time. MESFETs with non-alloyed Pd/Ge Ohmic contacts are also investigated for comparison. All contacts were deposited using a resistance heating evaporator and were furnace annealed in a conventional graphite strip annealer. Contact resistivities, ρ_c, of the metallizations were measured utilizing the conventional transmission line model (cTLM ) method. Metallization samples were characterized utilizing scanning electron microscopy (SEM) and current-voltage (I-V) measurements. Morphological characteristics display significant impact on the edge uniformity of the contacts. The maximum amplitude of the undulation with Pd/Sn/ Au contacts is ～ 100 nm. MESFETs with Pd/Sn/Au metallizations show improved extrinsic transconductance, g_m, when compared to the MESFETs with Pd/Sn and Pd/Ge contacts. The calculated g_m for the MESFETs with Pd/Sn/ Au metallizations is more than 100 mS/mm for a gate length, L_G, of 2 μ m. Experimental results show that non- alloyed thermally stable Pd/Sn/Au Ohmic contacts appear to be promising candidates for GaAs devices.