Enhanced thermoelectric properties of metal film on bismuth telluride-based materials

• Interface characterization of metal coated to p-type and n-type Bi2Te3 is studied.
• We examined the phase transformation of metal/Bi2Te3 based films at 200 °C.
• We studied the Seebeck coefficient of Bi2Te3 based material with a metal coating.
• The behavior of film adhesion for Co contacts is similar to Ni contacts.
• The changes in device ZT are not due to changes in contact resistance.

Diffusion barriers have a significant influence on the reliability and life time of thermoelectric modules. Although nickel is commonly used as a diffusion barrier in commercial thermoelectric modules, several studies have verified that Ni migrates to bismuth telluride-based material during high temperature cycles and causes a loss in efficacy. In this paper, the influence of metal layers coated to p-type and n-type Bi2Te3 on the interface characterization and thermoelectric property is studied using a RF magnetron sputtering. The findings from this study demonstrate the structural and thermoelectric properties of p-type and n-type Bi2Te3 coated with different metal layers. The crystalline phase and compositional change of the interface between the Bi2Te3 materials and the metal layers were determined using an X-ray diffractometer and scanning electron microscopy with energy dispersive spectroscopy. Formation of NiTe was observed in the sample of Ni/p-type Bi2Te3 based films post-annealed in an N2 atmosphere at 200 °C. In contrast, no CoxTey was formed in the sample of Co/p-type Bi2Te3 based films post-annealed at 200 °C. For as-deposited Ni/p-type and n-type Bi2Te3 based legs, the Ni slightly diffused into the Bi2Te3 based legs. A similar phenomenon also occurred in the as-deposited Co/p-type and n-type Bi2Te3 based legs. The Seebeck coefficients of the Co contacts on the Bi2Te3 based material displayed better behavior than those of the Ni contacts on the Bi2Te3 based legs. Thus Co could be a suitable diffusion barrier for bulk Bi2Te3 based material. The observed effects on the thermoelectric and structural properties of metal/Bi2Te3 based material are crucial for understanding the interface between the diffusion barrier and thermoelectric materials.