InxGa1-xAs ohmic contacts to n-type GaAs prepared by sputter deposition
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 (Rc) was high, resulting in rough contact surface. In the present experiment, the effects of the In concentrations of InxGa1-x As targets on the optimum annealing temperature to prepare low Rcand the surface morphology of thexGa1-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 Rc, where the interfacial microstructure was analyzed by x-ray diffraction and transmission electron microscopy and the contact resistances (Rcc) were measured by the transmission line method. The optimum annealing temperature to provide minimum Rc was reduced by 150°C by using the In0.7Ga0.3As targets instead of the previous targets. The contact resistance of 0.4 Ω-mm was obtained for the In0.7Ga0.3As/Ni/W contacts after annealing at temperatures of around 600°C. The Rc 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.