EFFECTS OF AU OVERLAYERS ON THE ELECTRICAL AND MORPHOLOGICAL-CHARACTERISTICS OF PD SN OHMIC CONTACTS TO N-GAAS/

The effects of Au overlayers on the electrical and morphological chara cteristics of non-alloyed Pd/Sn Ohmic contacts to n-GaAs have been stu died. Surface morphology of the contacts is investigated using surface profilometry measurements and scanning electron microscopy. Contact r esistivities, rho(c), of the proposed metallizations are measured usin g the conventional transmission line model method. A lowest rho(c) of similar to 2.07 x 10(-5) Omega cm(2) is obtained with a Pd(50 nm)/Sn(1 25 nm) contact on 2 x 10(18) cm(-3) n-GaAs after annealing at 400 degr ees C for 30 min under a forming gas atmosphere. An overlayer of Au im proves both electrical and morphological characteristics of the Pd/Sn contacts. The Au overlayer also changes the optimal annealing cycles a t the lowest rho(c) points. A Pd(50 nm)/Sn(125 nm)/Au(40 nm) contact s hows a lowest rho(c) of similar to 5.10 x 10(-6) Omega cm(2) after ann ealing at 330 degrees C for 30 min. The Pd(30 nm)/Sn(150 nm)/Au(100 nm ) contact shows a lowest rho(c) of similar to 3.89 x 10(-6) Omega cm(2 ) after annealing at 330 degrees C for 30 min.