Planar Ge/Pd and alloyed Au‐Ge‐Ni ohmic contacts to n‐Al_xGa_1−xAs (0≤x≤0.3)

Specific contact resistivity ρ_c of planar Ge/Pd ohmic contacts to n‐type Al_xGa_1−xAs is measured as a function of AlAs mole fraction x and anneal temperature T_ann. The functional dependence of ρ_c on T_ann is the same for all x, decreasing to a minimum at 275–325 °C. This indicates that the ohmic contact formation mechanism is independent of x(0≤x≤0.3) as verified by MeV Rutherford backscattering spectrometry and Read camera glancing angle x‐ray diffraction. Decomposition of an epitaxial Pd‐Al_xGa_1−xAs phase is correlated with the onset of ohmic behavior and may result in a thin solid phase regrown interfacial Al_xGa_1−xAs layer. An undoped 20 nm GaAs cap layer reduces ρ_c by about one order of magnitude. Ge/Pd contacts display greater dependence of ρ_c on x and much smoother surface morphology compared with those of standard Au‐Ge‐Ni contacts on Al_xGa_1−xAs (0≤x≤0.3).