Influence of Cu content on the phase composition and thermoelectric properties of deposited Cu-Se films

In this study, the p-type Cu-Se films with different Cu contents were prepared on SiO2/Si substrates by magnetron sputtering using targets with different atomic ratio ([Cu]/[Se]) of Cu to Se. The relation of Cu content and phase composition in Cu-Se films was systematically studied. The deposited films took place phase transformation from p-CuSe2 to p-CuSe2+gamma-CuSe, to gamma-CuSe, to gamma-CuSe+beta-Cu2-xSe, to beta-Cu2-xSe, to alpha-Cu2Se+unknown, to alpha-Cu2Se-+unknown+Cu phase with increasing [Cu]/[Se] in the deposited films from 0.49 to 5.74. At room temperature, the carrier concentration decreases in the order of the CuSe2, CuSe and beta-Cu2-xSe phase; but the carrier mobility exhibits an opposite trend. In the studied temperature range, the Seebeck coefficient and the power factor decreases in the order of beta-Cu2-xSe, CuSe2 and CuSe phase. The [Cu]/[Se] in deposited films with single beta-Cu2-xSe phase exceeds 2.0 of stoichiometric lattice and Cu-rich beta-Cu2-xSe phase films forms. The deposited Cu-rich beta-Cu2-xSe phase film with [Cu]/[Se]=2.65 has an optimum Seebeck and resistivity value, reaching a high power factor of 2.88 mW.m(-1).K-2 at RT and 5.91 mW.m(-1).K-2 at 320 degrees C. It is of the guidance meaning for the further study the thermoelectric properties of Cu-Se films in the future.