Low Contact Resistivity and Interfacial Behavior of p-Type NbFeSb/Mo Thermoelectric Junction

Half-Heusler compounds are a class of promising thermoelectric (TE) materials for power generation. However, the large contact resistivity at the interface between TE legs and metal electrode of the TE device seriously hinders the full play of the material performance. Here we report an Ohmic contact for the junction of p-type Nb0.8Ti0.2FeSb and Mo electrode with a low contact resistivity of <1 μΩ cm2 due to the matching of work functions between Nb0.8Ti0.2FeSb and FeMo interlayer. The interface carrier transport is dominated by the field emission and consequently a strong tunneling electric current is obtained due to the high doping level and relatively low dielectric constant of p-type Nb0.8Ti0.2FeSb semiconductor. The interface microstructure analysis indicates that there is a FeMo alloy interlayer with a thickness of 5 μm and a mixing layer of Nb0.8Ti0.2FeSb and Nb3Ti with a thickness of 25 μm. After a long time heat treatment at 1073 K, the FeMo alloy transforms into a FeSb2 layer, while the mixing layer is occupied totally by Nb3Ti. Due to the relatively high electrical resistivity for FeSb2 phase, the increasing content of Nb3Ti and the crack at both sides of Nb3Ti interlayer, the contact resistivity rises up to 18.4 μΩ cm2 after 32 days’ aging. These results demonstrate that the applicability of low contact resistivity NbFeSb/Mo junction in high performance TE devices.