ICT2014 Abstracts

Traditional processes of making contacts (metallization layer) onto bulk crystalline Bi₂Te₃-based materials do not work for nanostructured thermoelectric materials because of either weak bonding strength or unstable contact interface under temperature higher than 200 ^oC. Hot pressed nickel contact onto the nanostructured thermoelectric legs in a one-step process leads to strong bonding. However, such a process caused a large contact resistance in n-type Ni/Bi₂Te_2.7Se_0.3/Ni legs, although not in p-type Ni/Bi_0.4Sb_1.6Te₃/Ni legs. A systematic study was carried out to investigate the detailed reaction and diffusion at the interface of the nickel layer and n-type Bi₂Te_­3-based thermoelectric material. We found that a p-type region formed within the n-type Bi₂Te_2.7Se_0.3 during hot pressing due to Te deficiency and Ni doping, leading to the large contact resistance. The high contact resistance in Ni/Bi₂Te_2.7Se_0.3/Ni was significantly reduced by different approaches. A low contact resistance (< 1 μΩ cm²) combined with enhanced bonding strength (16 MPa) is obtained by adding a barrier layer between Ni and Bi₂Te_2.7Se_0.3 to avoid the high contact resistance at the interface region.