Optimizing the Structural, Electrical and Thermoelectric Properties of Antimony Telluride Thin Films Deposited on Aluminum Nitride-coated Stainless Steel Foil

Aziz Ahmed,Seungwoo Han

doi:10.1038/s41598-020-63954-0

Abstract

In this study, we examined the thermoelectric (TE) properties of co-evaporated p-type antimony telluride (Sb2Te3) thin films on aluminum nitride (AlN)-coated stainless steel foil substrates. We investigated the influence of composition and substrate temperature on the thin-film microstructure and transport properties, by varying the tellurium (Te) concentration in the thin films as well as the substrate temperature during deposition (room temperature (RT) and 300 °C). Thin films prepared with an RT substrate were further annealed at 264 °C to obtain crystallized thin films with high phase purity. Columnar thin films with large grains and a standard multi-oriented crystal structure were obtained when thin films were deposited on substrates heated to 300 °C. Thin films deposited at RT and subsequently annealed at 264 °C had a dense, layered microstructure, with a preferential c-axis or (00 l) texture as the compositions approached phase stoichiometry. The temperature dependence of the thermoelectric properties was measured, and variations were interpreted in terms of the deviation from stoichiometry and the obtained microstructure. A maximum power factor (PF) of 0.87 mW/m ∙ K2 was obtained for off-stoichiometric 65.0 at% Te thin film, which was the highest among the samples deposited at high substrate temperatures. A higher PF of 1.0 mW/m ∙ K2 was found for off-stoichiometric thin films with 64.5 at% Te, which was deposited at RT and subsequently annealed. The improvement of thermoelectric power in films containing excess Te could be related to energy dependent carrier scattering at the Sb2Te3/Te interface.

Highlights

Www.nature.com/scientificreports and quantum confinement effects[13,14,15,16,17,18]
aluminum nitride (AlN) thin films deposited at RT were further annealed at 300 °C for 3 hours prior to the thermoelectric thin film deposition
Series of Sb-Te thin films with different compositions were prepared at two substrate temperatures, to determine the main factors influencing the TE properties

Summary

Introduction

Www.nature.com/scientificreports and quantum confinement effects[13,14,15,16,17,18]. Hicks and Dresselhaus[15] predicted that low-dimensional nanostructuring would increase the density of states of confined carriers near the Fermi level, while simultaneously enhancing phonon scattering, thereby increasing the ZT. Several techniques have been reported for growing Sb2Te3 TE thin films, such as thermal evaporation[13,29,30,31], sputtering[26,27,28,32,33,34], flash evaporation[35], electrochemical deposition[25,36,37], pulse laser deposition[38], metal-organic chemical vapor deposition[39], and MBE9,10,40 Some of these processes tend to be complicated, time-consuming, and require expensive precursors and equipment. A major challenge, especially when depositing thin films at higher substrate temperatures, is control over the phase stoichiometry, which frequently leads to the formation of defects in the thin films[9,36] These defects significantly influence the thin-film carrier scattering mechanisms and the transport properties, so it is important to control the defect concentration for optimal device performance. The proposed method can be used to fabricate efficient Sb2Te3 thin films without any intentional doping and with the added possibility of extending the technology to include flexible TE devices

Methods

Results

Conclusion