Enhanced thermoelectric properties of mixed zinc antimonide thin films via phase optimization

A series of Zn-Sb thin films were deposited by direct current (DC) magnetron co-sputtering through fixing the sputtering power of Zn target while varying the sputtering power of Sb target. The deposited thin films were annealed at 673 K under Ar atmosphere for 1 h. X-ray diffraction (XRD) results show that the prepared thin film gradually transforms from p phase Zn4Sb3 to ZnSb phase with increasing Sb sputtering power. It is found that the thermoelectric properties of the prepared Zn-Sb thin films are related to the phase transformation. Firstly, the carrier concentration decreases while the Hall mobility increases with increasing Sb sputtering power until 20W, and then with further increasing Sb sputtering power, the carrier concentration increases while Hall mobility decreases. The thin films prepared by the Sb sputtering power of 20W shows a mixed phase of ZnSb and Zn4Sb3 and its Seebeck coefficient has a higher value than the samples with single beta-Zn4Sb3 or ZnSb phase. Through optimizing the ratio of beta-Zn4Sb3 to ZnSb phase in the mixed Zn-Sb thin film, an enhanced power factor of 1.91 x 10(-3) Wm K-2 can be obtained with a high Seebeck coefficient of 360 mu V K-1 and a low resistivity of 6.79 x 10(-5) Q m at 573 K. X-ray photoelectron spectroscopy (XPS) was used to investigate the binding energy of Zn and Sb in the thin film with a power factor of 1.91 x 10(-3) Wm K-2 and it is suggested that the weak bonding of the thin film could be one of the reasons resulting in enhanced thermoelectric performance. (C) 2013 Elsevier B.V. All rights reserved.