Dc and rf (reactive) magnetron sputtering of ZnO:Al films from metallic and ceramic targets: a comparative study

Aluminium-doped zinc oxide (ZnO:Al) layers, deposited by sputtering methods, are widely used as transparent and conductive electrodes, especially as window and contact layers for thin film solar cells. For magnetron sputtering deposition both methods, reactive sputtering (d.c. and r.f.) from a metallic target (Zn:Al 2wt%) as well as r.f. sputtering from ceramic targets (ZnO:Al/ZnO:Al2O3 are used. It is the aim of this paper to study the influence of the discharge parameters on the ZnO:Al film and heterojunction properties and to correlate these properties with plasma parameters and the conditions at the target surface during sputtering. R.f. sputtering from a metallic target yields ZnO:Al films with the lowest resistivity (6.4 x 10(-4)Omega.cm) and the highest optical transmisson. But with respect to all the requirements (resistivity, transmission, deposition rate and radiation damage, technological feasibility) for a technological process for thin film solar cell windows, sputtering from a metallic Zn:Al target in the d.c. mode gives the best ZnO:Al layers. (C) 1997 Elsevier Science S.A.