Effects of deposition sequence on electrical properties of InAs–Ni–W Ohmic contacts to n-type GaAs

The effects of the deposition sequences on the formation mechanism of the InAs–Ni–W contacts were investigated by analyzing the interfacial structure using x-ray diffraction and transmission electron microscopy and by measuring the contact resistances using a transmission line method. Ni atoms in the Ni/InAs/W contacts (where a slash sign (/) indicates the deposition sequence) diffused into the GaAs substrate during annealing at temperatures below 300°C, and formed NiAs compounds on the GaAs surface after subsequent annealing at high temperatures. In this contacts, the total InxGa1−xAs area contacting the GaAs surface was small, resulting in high contact resistances. Ni atoms in the InAs/Ni/W contacts broke the compositional stoichiometry of the InAs layer during annealing at low temperatures, and enhanced the raction between the InAs and the GaAs upon annealing at higher temperatures. In this contacts, a large area of the GaAs surface was observed to be covered by the InxGa1−xAs layers, resulting in relatively low contact resistances. The effective barrier to limit the current flow would be the barrier at the InxGa1−xAs/GaAs interface which was simulated to be 2.1×10−20 J (0.13eV) by analyzing the temperature dependence of the contact resistances.