Study on diffusion barriers of doping elements in SiGe alloys

Diffusion of doping elements in the sintering process of thermoelectric SiGe alloys sometimes brings a problem to their electrical properties. This becomes serious in particular when the p- and n-type materials of SiGe are sintered monolithically in one process. The diffusion of both-type dopants, B and P at the p/n interface cancels their charge carriers out, and results in (1) increase of electrical resistivities around the interface, and (2) different width of p- and n-type regions. To solve these problems, diffusion barriers made of several kinds of material has been investigated. The material used are thin sheets of Ti, Cu, and Nb, MoSi powder and mixed powders of Ni with SiGe. The characteristics of the barriers are evaluated mainly through the distributions of the resistivities in the vicinity of the interfaces for each barrier material in the SiGe alloy system. With no barrier material the resistivity at the p-n interfaces has reached ~500 mΩ·cm at maximum. Insertion of Ni powder mixed with SiGe material into the p-n junctions reduced the resistivity down to 60~90 mΩ·cm. Difference in widths of p- and n-type material region, which had differed 40% with each other for no barrier, was improved to be within 10%