Roles of top and first Ni-layers in the improvement of electrical property and surface morphology in Ni/Al/Ni/n-InP contacts

The formation of wide band gap material (AIP) in Al/n-InP contacts leads to an enhancement of Schottky barrier height (E-SBH) upon rapid thermal annealing (RTA), but the alloying reaction was irregular. The addition of 5 nm first- and/or 14 nm top-Ni layers gives an excellent improvement in the electrical uniformity as well as the surface morphology for Al/n-InP contacts. The Ni first layer provides the formation of AlP and Ni,P by the solid-phase reaction between Ni and InP at rather low temperatures (around 450°C) and results in the uniform interface. The addition of the Ni top layer further gives the interfacial uniformity thanks to prevention of irregular alloying.