Effects of Au overlayers on the electrical and morphological characteristics of Pd/Sn ohmic contacts to n-GaAs

Abstract

The effects of Au overlayers on the electrical and morphological characteristics of non-alloyed Pd/Sn Ohmic contacts to n-GaAs have been studied. Surface morphology of the contacts is investigated using surface profilometry measurements and scanning electron microscopy. Contact resistivities, ϱ e, of the proposed metallizations are measured using the conventional transmission line model method. A lowest ϱ e of ∼ 2.07 × 10 −5 Ω cm 2 is obtained with a Pd(50nm)/Sn(125 nm) contact on 2 × 10 18 cm −3 n-GaAs after annealing at 400 °C for 30 min under a forming gas atmosphere. An overlayer of Au improves both electrical and morphological characteristics of the Pd/Sn contacts. The Au overlayer also changes the optimal annealing cycles all the lowest ϱ e points. A Pd(50 nm)/Sn(125 nm)/Au(40 nm) contact shows a lowest ϱ e of ∼ 5.10 × 10 −6 Ω cm 2 after annealing at 330 °C for 30 min. The Pd(30 nm)/Sn(150nm)/Au(100 nm) contact shows a lowest ϱ e of ∼ 3.89 × 10 −6 Ω cm 2 after annealing at 330 °C for 30 min.