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 NbTiFeSb and Mo electrode with a low contact resistivity of <1 μΩ cm due to the matching of work functions between NbTiFeSb 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 NbTiFeSb semiconductor. The interface microstructure analysis indicates that there is a FeMo alloy interlayer with a thickness of 5 μm and a mixing layer of NbTiFeSb and NbTi with a thickness of 25 μm. After a long time heat treatment at 1073 K, the FeMo alloy transforms into a FeSb layer, while the mixing layer is occupied totally by NbTi. Due to the relatively high electrical resistivity for FeSb phase, the increasing content of NbTi and the crack at both sides of NbTi interlayer, the contact resistivity rises up to 18.4 μΩ cm after 32 days' aging. These results demonstrate that the applicability of low contact resistivity NbFeSb/Mo junction in high performance TE devices.