Electrodeposition growth of multiphase metal telluride thin films: Structural, optical, electrical properties, and DFT calculations

Abstract

This study investigated the effects of applied electrodeposition potentials on the structural, optical, and electrical properties of multiphase metal telluride thin films for optoelectronic applications. The rhombohedral Sb₂Te₃, Bi₂Te₃, Al₇Te₁₀, and Bi₄Te₃ phases were identified and incorporated into thin films containing hexagonal Bi₂Te, BiTe, and monoclinic Al₂Te₃. Variations in the crystallographic parameters are attributed to recrystallization and phase transformation processes driven by the energy stored in the parent Bi₂Te₃ phase. Scanning electron microscopy (SEM) images showed a compact inner surface covered with residuals dispersed across the film surface at the applied potentials of 4 and 6 V. At an applied potential of 8 V, crack formation accompanied by a reduction in surface residuals was observed, whereas films deposited at 10 V exhibited more pronounced cracking with no noticeable residuals. Energy-dispersive X-ray spectroscopy (EDS) confirmed the presence of Al, Sb, Te, and Bi in all the deposited films, indicating the successful incorporation of binary multiphase metal chalcogenide compounds. The band gaps of the deposited films are decreased with increasing electrodeposition potential, highlighting the tunability of the electronic properties of multiphase metal telluride thin films. A significant decline in the activation energy (E_ac) was observed between 6 and 8 V, suggesting that this range is the optimal applied voltage window for device applications due to enhanced thermally activated conduction. Finally, density functional theory (DFT) calculations of the photoabsorption coefficient indicated that Bi₂Te₃ and Sb₂Te₃ exhibited higher absorption coefficients than Al₂Te₃ and Al₇Te₁₀. Among these materials, Bi₂Te₃ exhibited the strongest absorption coefficient at higher photon energies, whereas the other phases exhibited enhanced absorption in the red-light region.