Investigation of Znl-xMgxO:A1 film by Ratio Frequency Magnetron Co-Sputtering as Transparent Conductive Oxide layer

ZnO:Al is widely used as transparent conductive oxide (TCO) layer in Cu(In,Ga)Se₂ and Cu(In,Ga)(S,Se)₂-based solar cells. To widen the bandgap energy (E_g) of TCO layer and optimize the difference of conduction band minimum between TCO and the absorbers for the enhancement of solar cell performances, Zn_1-xMg_xO:Al was systematically investigated as the alternative TCO layer. The Zn_1-xMg_xO:Al films with different [Mg]/([Mg]+[Zn]) ratios were prepared by radio frequency (RF) magnetron co-sputtering from ZnO:Al and MgO targets. It is demonstrated that Eg of Zn_1-xMg_xO:Al is increased with enhancing [Mg]/([Mg]+[Zn]), while the basic crystal structure of Zn_1-xMg_xO:Al with [Mg]/([Mg]+[Zn]) in a range of 0-0.205 is ZnO. Moreover, Zn_1-xMg_xO:Al films with small [Mg]/([Mg]+[Zn]) ratios of approximately 0.064-0.123 with low resistivity possesses the higher film quality and Hall mobility than those of ZnO:Al, while the carrier density is decreased with increasing [Mg]/([Mg]+[Zn]), which could be beneficial to lower the free carrier absorption. Consequently, Zn_1-xMg_xO:Al films are promisingly utilized as the TCO layer.