Thermoelectric properties of Ni/Ge-multilayer-laminated silicon

We investigate the thermoelectric properties of Ni/Ge-multilayer-laminated silicon thermoelectric devices based on the number of Ni/Ge layers from single layer to 50 layers. For the Ni/Ge-multilayer lamination, Ni and Ge thin layers are alternately deposited on a bulk silicon substrate using RF sputtering at room temperature. The Seebeck coefficient improves and the thermal conductivity decreases compared with the bulk silicon thermoelectric device as the number of Ni/Ge layers increases. A seven Ni/Ge-multilayer-laminated thermoelectric device indicates a Seebeck coefficient of – 260 μV/K and a thermal conductivity of 56 W/m∙K at 510 K without electrical conductivity deterioration; subsequently, a thermoelectric power factor of 5.6 mW/m∙K² and zT of 0.05 are achieved at 510 K. The improvement in the Seebeck coefficient in the multilayer devices is attributed to the electron filtering effect due to the Schottky barriers at the Ni/Ge interfaces. It is speculated that the acoustic phonon impedance mismatch at the Si(Al)/Ni interface reduces/saturates the thermal conductivity. The thermoelectric results indicate the potential of using a Ni/Ge-multilayer structure for silicon-based thermoelectric devices.