Pd-Ge-Au based hybrid ohmic contacts to high-low doped GaAs field-effect transistor

Effects of an intermediate layer, such as Mo or Ti, have been studied for developing Pd-Ge-Au based hybrid ohmic contacts in a high-low doped GaAs metal-semiconductor field-effect transistor (MESFET). The Pd-Ge-Au contact without the intermediate layer produces an alloyed AuGe contact at a high annealing temperature above 400°C. When Mo is added between Pd/Ge and Au, nonspiking Pd/Ge contact is formed at a low annealing temperature of 300°C. The addition of Ti, however, results in an ohmic contact with a low resistance of 0.43 Ω·mm in a wide annealing temperature ranging from 340 to 420°C. Auger depth profile and X-ray diffraction results suggest that the low resistance of the Pd/Ge/Ti/Au ohmic contact is due to formation both the Pd/Ge contact and AuGe contact through the appropriate control of Au indiffusion by Ti. The MESFET with the Pd/Ge/Ti/Au contact displays good DC characteristics. This supports that the Pd/Ge/Ti/Au contact is well suitable for application to high-low doped GaAs MESFETs due to its low-resistance and wide-process-window.