The Fabrication Of BiCuSeO-based Thin Films And Their Thermoelectric Properties

BiCuSeO-based chalcogenide is a p-type oxide semiconductor with layered tetragonal crystal structure, which shows great potential in medium/high temperature thermoelectric applications due to its intrinsically very low thermal conductivity. However, to our knowledge, most researches have been focus on the properties of the polycrystalline bulks of the BiCuSeO, and there are very few reports on thin films. Compared to the bulks, two-dimensional themoelectric thin films have been the subject of attractive studies becaused of the advantage to realized the micro- thermoelectric power generation and refrigeration, which are important for the potential application in the themoelectric devices integration field. Besides, thin films have high potential in c-axis oriented growth, the anisotropy of BiCuSeO-based materials can significantly improve their thermoelectric properties.In this work, we have prepared high quality c-axis oriented BiCuSeO thin films on commercial wafers by pulsed laser deposition?PLD? and investigated the influence of deposition conditions and chemical element doping on the microstructure and thermoelectric properties have been investigated. The main conclusions as follow:1. Epitaxial BiCuSeO thin films have been prepared by PLD and their microstructure and thermoelectric transport properties were investigated. The films obtained under the optimum deposition conditions are c-axis oriented, at room temperature, these films showed better thermoelectric properties than bulk materials.2. The single-crystal-like texture Bi_1-xPb_xCuSeO?x=0,0.04,0.06,0.08?thin films have been successfully fabricated on the SrTiO₃?001? substrates. The microstructure and high temperature thermoelectric properties versus the content of the Pb-doping also have been investigated. The result showed that the Pb-doping could effectively enhanced the electrical conductivity and the power factor increased due to the increased hole carrier concentration. A power factor of about 1.19 mWm-1 K-2 have been found for the Bi0.94Pb0.06 CuSeO single crystalline thin films at 673 K, which is about 1.5 times larger than the values of the bulks.3. The c-axis oriented Bi_1-xBa_xCuSeO?x=0,0.025,0.05,0.075,0.1? thin films have been prepares on the SrTiO₃?001? substrates. The influences of Ba-doping on the microstructure and high temperature thermoelectric properties have been investigated. The experimental result showed that the resistivity decreased by the Ba-doping compared with the pure films and the power factor improved effectively as a results. A power factor of about 1.24mWm-1K-2 has been achieved in Bi0.925Ba0.075 CuSeO thin films at 670 K,which is about 1.4 times larger than that of the bulks.4. BiCuSeO thin films have been epitaxially grown on the commercial silicon?001? wafers by PLD technique without any surface pretreatment. The experimental results showed that all the samples showed perfect crystalline structure and thermoelectric properties, which were comparabled with the single crystal samples. This work demonstrates that the BiCuSeO thin films grown on the Si substrates can play a critical role in the functional properties of the thermoelectric device.