Ohmic contact formation mechanism of the PdGeAu system on n-type GaSb grown by molecular beam epitaxy

We have fabricated Pd/Ge/Au/Pt/Au ohmic contacts on n-type GaSb grown by molecular beam epitaxy. The annealed contacts show specific contact resistivities which are as low as 4.9×10−6 Ω−cm2 at an annealing temperature of 300 °C for 45 s. The resistivity is very sensitive to the annealing conditions and the thickness of the constituents. The surface remains smooth after annealing. Microstructure analysis with cross-sectional transmission electron microscopy and sputtered neutral mass spectrometry elucidates the solid phase reactions and interdiffusion of the constituents. The formation of a PdGe phase and the diffusion of Ge into GaSb seem to be the decisive and annealing-dependent processes leading to the ohmic behavior.