In_xGa_1-xAs ohmic contacts to n-type GaAs prepared by sputter deposition

Abstract

Thermally stable, low contact resistance InAs/Ni/W contacts were previously prepared by sputter depositing InAs, Ni, and W targets in our laboratory. However, the optimum annealing temperature to provide low contact resistance (R_c) was high, resulting in rough contact surface. In the present experiment, the effects of the In concentrations of In_xGa_1-x As targets on the optimum annealing temperature to prepare low R_cand the surface morphology of the_xGa_1-x/ W contacts were studied. In addition, the electrical properties and the interfacial microstructure were correlated to search the optimum In concentration to provide the minimum R_c, where the interfacial microstructure was analyzed by x-ray diffraction and transmission electron microscopy and the contact resistances (R_cc) were measured by the transmission line method. The optimum annealing temperature to provide minimum R_c was reduced by 150°C by using the In_0.7Ga_0.3As targets instead of the previous targets. The contact resistance of 0.4 Ω-mm was obtained for the In_0.7Ga_0.3As/Ni/W contacts after annealing at temperatures of around 600°C. The R_c values did not deteriorate after annealing at 400°C for 2 h. Also, the surface of this contact was smooth and no evidence of In outdiffusion on the contact surface was seen. Finally, the effect of the In concentrations at the metal/GaAs interfaces on the electrical properties will be discussed.