Fabrication and thermoelectric properties of Si micro/nanobelts

Abstract

<sec>Currently, low-dimensional materials are a hot spot in the field of thermoelectric research, because the thermoelectric properties will be significantly improved after the low-dimensionalization of bulk materials. In a bulk material, its thermoelectric figure of merit <i>ZT</i> value cannot be increased by changing a single parameter, because the parameters of the material are interrelated to each other, which is not conducive to the research of internal factors and thus limiting the efficiency of thermoelectric material, but thermoelectric material on a micro-nano scale is more flexible to adjust its thermoelectric figure of merit <i>ZT</i> value. There are many different kinds of methods of implementing the low-dimensionalization of bulk materials. In this paper, size-controllable Si micro/nanobelts are prepared based on semiconductor micromachining and focused ion beam (FIB) technology, and the thermoelectric properties of Si micro/nanobelts of different sizes are comprehensively studied by the micro-suspension structure method.</sec><sec>In this experiment, we find that the conductivity of doped Si micro/nanobelt is significantly better than that of bulk Si material, that as the width of the Si micro/nanobelt decreases, the thermal conductivity of the material decreases significantly, from 148 W/(m·K) of bulk silicon to 17.75 W/(m·K) of 800 nm wide Si micro-nanobelt, that the Seebeck coefficient of the material is lower than that of the corresponding bulkmaterials. The decrease of thermal conductivity is mainly due to the boundary effect caused by the size reduction, which leads the phonon boundary scattering to increase, and thus significantly inhibiting the behavior of phonon transmission in the Si material, thereby further affecting the transmission and conversion of thermal energy in the material. At 373 K, the maximum <i>ZT</i> value of the 800 nm wide Si micro/nanobelt reaches ～0.056, which is about 6 times larger than that of bulk silicon. And as the width of the Si micronanobelt is further reduced, the thermoelectric figure of merit <i>ZT</i> value will be further improved, making Si material an effective thermoelectric material. The FIB processing technology provides a new preparation scheme for improving the thermoelectric performances of Si materials in the future, and this manufacturing technology can also be applied to the low-dimensional preparation of other materials.</sec>