Study on material properties of Sn- and Cu-doped ZnO thin films as n- and p-type thermoelectric materials based on wet solution synthesis

Sn-doped n-type and Cu-doped p-type ZnO films were fabricated by depositing solutions derrived by sol–gel route on glass substrates through dip-coating cycles. The X-ray diffractometry demonstrates the typical crystalline structure of hexagonal wurzite of ZnO. The surface morphology was made through scanning electronmicroscopy showing the density and shape of films’ grains of which size was determined between 40 and 55 µm. The results of Hall measurement indicate clearly the material nature of fabricated films at room temperature. The best electrical property of Sn-doped n-type ZnO films is corresponding to Sn content of 2 at.% with carrier concentration of 3.0 × 10¹⁸ cm⁻³. The formation of p-type ZnO thin films was elucidated by the manner of solution synthesis that glucose was added into the solube mixer of zinc acetate and copper(II) nitrate trihydrate and the way of thermal treatment for films in vacuum with pretty good hole concentration of about 10¹⁵ cm⁻³. The electrical transport properties characterizing thermoelectric (TE) behavior of all films were investigated between room temperature to 400 °C (or from 300 to 673 K). The obtained results of electrical conductivity, Seebeck coefficient and power factor revealed that Sn-doped n-type ZnO films have the quality and properties similar to Al-doped ones and Cu-doped ZnO films can be promising p-type materials for TE applications.