Low contact resistivity and long-term thermal stability of Nb_0.8Ti_0.2FeSb/Ti thermoelectric junction

Although half-Heusler compounds are quite promising for thermoelectric power generation, there is only limited research on the interfacial structure between metal electrode and half-Heusler compounds for device applications. This work reports on the characteristics of Nb_0.8Ti_0.2FeSb/Ti junction and its evolution behavior during 973 K. The Nb_0.8Ti_0.2FeSb/Ti interface consists of one Ti_0.9Fe_0.1 layer and one Fe-poor layer. There is an Ohmic contact and a low contact resistivity (0.15 μΩ cm⁻²) in this junction, on account of the matching of working functions between Nb_0.8Ti_0.2FeSb and Ti_0.9Fe_0.1 interlayer. The high doping of Ti high carrier concentration in NbFeSb matrix leads to a high carrier concentration, which results in inducing a large tunneling current at this interface. After aging treatment at 973 K, the Fe-poor layer and the Ti_0.9Fe_0.1 layer continues to expand, resulting in the increase of the thickness of the interfacial layer and the contact resistivity. The interfacial electrical is only 1.9 μΩ cm⁻² after 25 days’ aging. The thickness of the interface layer has a good linear relation with the square root of aging time, which firmly indicates that the growth of the layer is determined by mutual diffusion of Fe and Ti atoms across the interface. The low contract resistivity and long-time thermal stability demonstrate the great potential of Nb_0.8Ti_0.2FeSb/Ti thermoelectric junction in high efficiency half-Heusler TE devices.