Atomic/molecular layer deposition of p-type conducting copper-sulfur-organic coordination polymer thin films for thermoelectric applications

Abstract

Here we report a three-precursor atomic/molecular layer deposition (ALD/MLD) process for the fabrication of copper-based coordination polymer thin films for thermoelectric applications. This process mimics the wet chemical synthesis of poly[metal-ethenetetrathiolate] (poly[M-ETT]) polymers based on a trans-metalation reaction. In our ALD/MLD process the Cu-for-Li trans-metalation is realized upon the pulsing of the three precursors, 1,3,4,6-tetrathiapentalene-2,5-dione (TPD), lithium hexamethyldisilazide (Li-HMDS) and copper(II) acetylacetonate (Cu(acac)2), in a cyclic manner. The process yields p-type electrically conducting poly[Cu-ETT] thin films with the appreciably high growth-per-cycle (GPC) of ~11 Å/cycle at the deposition temperature of 220 °C. The targeted chemical composition was confirmed with XPS measurements which verified the Cu:S ratio at 0.246 (i.e. very close to the ideal 0.25 value). From electrical transport measurements the room-temperature resistivity and Seebeck coefficient values were determined at 0.17 Ωm and 88 μV/K, respectively.