Abstract
The multilayer thermoelectric devices including Ni/200 layers of Si/Si + Sb/200 layers of Si/Si + Ge/Ni thin films were fabricated using electron beam and DC/RF magnetron sputtering deposition systems. The thickness measurements have been performed using Filmetrics UV thickness measurement system. The Au contacts at the bottom and top of the fabricated thermoelectric devices were measured as 100 nm for each side. Ni layer at the bottom is 108 nm and Ni layer at the top of the multilayer structures is 168 nm. The thickness of 200 layers of Si/Si + Ge thin film is 173 nm and the thickness of 200 layers of Si/Si + Sb thin film is 199 nm. The fabricated thermoelectric devices have total of 402 layers of thin films with the total thickness of 648 nm thickness excluding two Au contact layers. The prepared thin film devices were annealed at different temperatures for one hour to improve the thermoelectric properties. The current studied system has reached some remarkable values of Seebeck coefficients when the suitable annealing temperatures and the suitable operating temperatures of Seebeck measurement system were applied. The multilayer thin film system has reached the Seebeck coefficient of -344.8 μV/K when the annealed temperature was 100°C and the operating temperature was 320 K. One of the main problems with the thermoelectric devices is having higher temperature dissipation during the operation of the devices. Ni thin film was used in the fabrication process to remove excess of the heat as a heat sink from the thermoelectric devices. This will bring new approach for the high efficient thermoelectric devices. The goal of the manuscript is to improve the thermoelectric properties of the fabricated thin film thermoelectric devices using Ni thin films and the thermal treatment. The resistivity values decreased when the annealing temperatures increased. The highest power factor values were reached when the thermoelectric devices were annealed at 100°C. Mobility values increased when the suitable temperatures were applied for thermal treatment.
Highlights
The first important discovery relating to thermoelectricity occurred in 1823 when a German scientist, Thomas Seebeck, found that an electric current would flow continuously in a closed circuit made up of two dissimilar metals provided that the junctions of the metals were maintained at two different temperatures
Due to the motivation of success in high energy ion beam and temperature annealing on the material systems, this study aims to perform thermal annealing effects on the multilayer thin films to see how their thermoelectric properties are effected from the thermal treatment at different temperatures
A good thermoelectric material should have a Seebeck coefficient value changing between 100 and 300 μV/K; in order to achieve a few volts at the load, many thermoelectric couples need to be connected in series to make the efficient thermoelectric devices (Purhoit et al, 2016)
Summary
The first important discovery relating to thermoelectricity occurred in 1823 when a German scientist, Thomas Seebeck, found that an electric current would flow continuously in a closed circuit made up of two dissimilar metals provided that the junctions of the metals were maintained at two different temperatures. Peltier found that the use of a current at an interface between two dissimilar materials results in the absorption of heat and release of heat at the subatomic level, this is a result of the different energy levels of materials, n and p type materials (Jangonda et al, 2016). Thermoelectric materials are being used, since few decades, for heat derived electricity generation and for Peltier refrigeration. Thermoelectric materials in general, are small band gap degenerate semiconductors capable in inter-conversion of heat energy and electrical energy (Singh et al, 2016)
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