A comparative study on thermoelectric properties of ZnO bulks and thin films

Abstract

Introduction: Zinc oxide (ZnO) is well-known as a promising thermoelectric material owing to its safety, inexpensiveness, and thermal stability. This research provides an overview of thermoelectric potentials, including structure, electrical conductivity, Seebeck coefficient, and power factor of pure ZnO semiconductor synthesized in bulk and thin-film forms.
 Methods: The ZnO bulk was synthesized by solid-state reaction at high temperature, while the thin film was prepared by d.c. magnetron sputtering technique. The temperature-dependent thermoelectric properties of all the samples were measured by the Seebeck LSR-3 system. The crystallographic and surface morphological information of the samples were obtained by using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM), respectively.
 Results: The XRD results confirm that both the bulk and thin-film have polycrystalline structure and characteristics of hexagonal-wurtzite ZnO. Through the FESEM observation, the bulk is well densified under high-temperature condition, while the thin-film achieve good orientation and close-packed grains. At 573 K, the obtained thermoelectric properties (electrical conductivity, Seebeck coefficient, and power factor) are respectively 352.4 S/cm, -89.5 µV/K and 282.5 µW/mK2 for the ZnO bulk; and 289 S/cm, -113.8 µV/K and 374.3 µW/mK2 for the ZnO film.
 Conclusion: The comparative study shows the good thermoelectric potential of ZnO material in both forms of bulk and thin film. Among them, the thin film has better results, especially in the Seebeck coefficient and power factor than one.

Structural, electrical and thermoelectric characterizations of bismuth-doped ZnO ceramic material

“…To consider the effect of Bi doping on the structure of ZnO, some crystallographic parameters were determined. First, the mean crystal size D is defined by Scherrer's equation 8,9 :…”

“…Therefore, the development of oxide materials is necessary to expand applications in a broad temperature range. Herein, ZnO is one of the promising oxide materials for TE modules at high temperature [7][8][9] . ZnO has some benefits, such as a wide bandgap of 3.37 eV at room temperature and the ability to easily control structural and electrical properties through doping 10 .…”

Relationship between electrical and optical characterization of Ga-doped ZnO thin films deposited by magnetron sputtering

“…According to Bragg's law, a larger 2θ angle is associated with a decrease in the interplanar spacing d (002) (as shown in Table 1), indicating the substitution of smaller-radius Ga 3+ (0.068 nm) at Zn 2+ sites (0.072 nm) 10 . In addition, the residual stress (ε) of the films can also be estimated from the 2θ position of the (002) plane, as given by ε = A(c -c o )/c o , where A = -232.8 GPa is the elastic factor of ZnO, and c and c o are the lattice constants of the investigated films and stress-free powder 11 . Both films have compressive stress due to the negative values (as shown in Table 1).…”