LOW RESISTANCE PD/ZN/PD AU OHMIC CONTACTS TO P-TYPE GAAS

Many optoelectronic devices require contacts to p-doped epitaxial layers. To achieve low contact resistance, the semiconductor has to be doped to high levels. The p-dopants most commonly used are Be, Mg, and Zn. The contacts were formed by the sequential e-beam evaporation of 10 nm Pd, ≤5 nm Zn, 20 nm Pd and 40 nm Au layers onto a 0.2 μm thick Be-doped (5 × 1018 cm) GaAs layer grown by MBE. The minimum contact resistance of 0.04 Ω-mm (≤1 × 10-7 Ω-cm2), as measured using the transmission line method, was obtained for contacts annealed at 500° C for 30s. These are the lowest contact resistance values reported to date for alloyed contacts to p-GaAs. © 1990 The Minerals, Metals and Materials Society.