STABLE AND SHALLOW PDLN OHMIC CONTACTS TO N-GAAS

A thermally stable, low-resistance PdIn ohmic contact to n-GaAs has been developed based on the solid phase regrowth mechanism [T. Sands, E. D. Marshall, and L. C. Wang, J. Mater. Res. 3, 914 (1988)]. Rapid thermal annealing of a Pd-In/Pd metallization induces a two-stage reaction resulting in the formation of a uniform single-phase film of PdIn, an intermetallic with a melting point greater than 1200 °C. A thin (∼5 nm) layer of average composition In0.4Ga0.6 As uniformly covers the interface between the PdIn layer and the GaAs substrate. Specific contact resistivities and contact resistances of ∼1×10-6 Ω cm2 and 0.14 Ω mm, respectively, were obtained for samples annealed at temperatures in the 600-650 °C range. The addition of a thin layer of Ge (2 nm) to the first Pd layer extends the optimum annealing temperature window down to 500 °C. Specific contact resistivities remained in the low 10 -6 Ω cm2 range after subsequent annealing at 400 °C for over two days.