Investigation Of Antimony Telluride Based Thin Films Prepared By Sputtering

Thermoelectric materials interconvert heat and electricity directly, which can bewidely used in the power generators and cooling devices. Sb₂Te₃based materials isone of the best thermoelectric materials at room temperature, but the figure of merits（ZT） of Sb₂Te₃is about1for decades. The nano-structured materials have a largeamount of boundaries that will strongly scatter the phonons and carries, the thermalconductivity can be decreased more significantly than the decrease of the electricconductivity of the materials, resulting in a higher ZT for thermoelectric materials. Inthis paper, Sb₂Te₃based thin films were successfully deposited by magnetronsputtering. The microstructure and morphologies of the films were characterizedusing scanning electron microscopy, energy dispersive X-ray spectroscopy and X-raydiffraction, respectively. The electrical transport properties of the thin films, in termsof resistivity and Seebeck coefficient were determined at room temperature.In this paper, firstly the influence of deposition parameters such as target power,sputtering time to the surface morphologies, micro-structure and the thermoelectricproperties of Sb₂Te₃films were investigated. The result showed that with theincrease of sputtering power, the deposition rate of the Sb₂Te₃films increased whilethe resistivity decreased, and the Seebeck coefficient of the Sb₂Te₃films increasedfirstly then decreased. With the increase of sputtering time, the resistivity of theSb₂Te₃films decreased, but the Seebeck coefficient had no significant change. Afterannealing treatment, the crystallinity of the annealed Sb₂Te₃films was enhanced,sticking to （1010） as the preferred orientation. The carrier concentration of theSb₂Te₃films decreased while the carrier mobility increased with the increase ofannealing temperature. Further, the effective mean free path of carrier increased afterannealing, but smaller than the grain size of Sb₂Te₃films. By optimizing annealingprocess, the power factor achieved to18.09μW/cm·K-2when the annealingtemperature was increased to250℃for6hours. Sb₂Te₃based alloys that doped with nano-structured materials will stronglyscatter the phonons and carries, the thermal conductivity could be decreased and theSeebeck coefficient could be increased drastically without significantly increased theresistivity. Therefore, the ternary alloys have higher thermoelectric properties thanbinary alloys. In this paper, the Bi-Sb-Te films were deposited by co-sputtering. Theresult shows that the atoms of as-deposited films had enough energy to diffuse andagglomerate during annealing treatment, resulting in the formation of Bi-Sb-Te films.When the annealing temperature achieved at250℃, the layered structure ofBi-Sb-Te films with a preferred orientation along the （00l） plane was formed. Thecarrier concentration of Bi-Sb-Te films decreased while the carrier mobilityincreased with the increase of annealing temperature. Compared to the annealedSb₂Te₃films, the Bi-Sb-Te films deposited at room temperature had poorthermoelectric properties. On the other hand, the effective mean free path of carrierwas lower and the resistivity was higher to Bi-Sb-Te films than to the Sb₂Te₃films.However, the Seebeck coefficient of annealed Bi-Sb-Te films was enhanceddrastically compared with Sb₂Te₃films. As a result, the power factor was enhancedto22.54μW/cm·K-2when the annealing temperature reached300℃for6hours.Therefore, Sb₂Te₃based alloys that doped with Bi nano-particles could enhancethermoelectric performance and thermal stability.The substrate temperature was found to have great influence on microstructureand surface morphology of Bi-Sb-Te films. The Bi-Sb-Te films with a preferredorientation of （1010） phase were formed when deposited at150℃. Compared to theas-deposited Bi-Sb-Te films, the Bi-Sb-Te films deposited on the heated substratehad larger roughness. The resistivity was lower and the Seebeck coefficient washigher to the Bi-Sb-Te films deposited on the heated substrate than that deposited atroom temperature. The power factor was enhanced to25.32μW/cm·K-2when theannealing temperature reached300℃for6hours. Therefore, appropriate substratetemperature could improve thermoelectric properties of Bi-Sb-Te films.