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 dope d GaAs metal-semiconductor field-effect transistor (MESFET). The Pd-Ge -Au contact without the intermediate layer produces an alloyed AuGe co ntact at a high annealing temperature above 400 degrees C. When Mo is added between Pd/Ge and Au, nonspiking Pd/Ge contact is formed at a lo w annealing temperature of 300 degrees C. The addition of Ti, however, results in an ohmic contact with a low resistance of 0.43 Ohm.m in a wide annealing temperature ranging from 340 to 420 degrees C. Auger de pth profile and X-ray diffraction results suggest that the low resista nce of the Pd/Ge/Ti/Au ohmic contact is due to formation both the Pd/G e contact and AuGe contact through the appropriate control of Au indif fusion 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 s uitable for application to high-low doped GaAs MESFETs due to its low- resistance and wide-process-window.