Raman spectroscopy was used in the optimization of the thermal co-evaporation deposition process for n-type bismuth telluride (Bi₂Te₃) thin films for thermoelectric applications. Films were deposited with good adhesion onto glass and plastic (Kapton) substrates. The influence of deposition parameters on film composition and thermoelectric properties was studied for optimal thermoelectric performance. The film chemical composition and structure was studied by Energy-Dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Rutherford Backscattering Spectroscopy, Induced X-ray Emission and Raman spectroscopy.
Seebeck coefficient (up to 250 μVK^-1), in-plane electrical resistivity (≈10 μΩm), carrier concentration (3x10¹⁹ - 20x10¹⁹ cm^-3) and Hall mobility (80 - 170 cm²V^-1s^-1) were measured at room temperature in selected Bi₂Te₃ samples.
For Raman scattering experiments both 514.5 nm and 488 nm lines of an Ar⁺ laser and 1064 nm line of an YAG:Nd laser were used for excitation. Raman spectra were obtained in a Jobin-Yvon T64000 spectrometer and from the infrared line in a Bruker RFS 100/S FT-Raman spectrometer. In all cases, Raman spectra were performed at room temperature, in a backscattering geometry with polarized incident light and without analyser.
Bulk Bi₂Te₃ is a semiconductor which at room temperature presents four Raman active modes. Three Raman active modes of Bi₂Te₃ were detected in our films. The Eg mode at a calculated low-frequency of 50.6 cm^-1 was not observed probably due to its too weak intensity.
The agreement between the Raman and XRD results in the present work for films and bulk referenced ones allows us to conclude that the system is quite stoichiometric.

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