Transparent conducting impurity-doped ZnO thin films prepared using oxide targets sintered by millimeter-wave heating

Abstract

The preparation of transparent conducting impurity-doped ZnO thin films by both pulsed laser deposition (PLD) and magnetron sputtering deposition (MSD) using impurity-doped ZnO targets sintered with a newly developed energy saving millimeter-wave (28GHz) heating technique is described. Al-doped ZnO (AZO) and V-co-doped AZO (AZO:V) targets were prepared by sintering with various impurity contents for 30min at a temperature of approximately 1250°C in an air or Ar gas atmosphere using the millimeter-wave heating technique. The resulting resistivity and its thickness dependence obtainable in thin films prepared by PLD using millimeter-wave-sintered AZO targets were comparable to those obtained in thin films prepared by PLD using conventional furnace-sintered AZO targets; a low resistivity on the order of 3×10−4Ωcm was obtained in AZO thin films prepared with an Al content [Al∕(Al+Zn) atomic ratio] of 3.2at.% and a thickness of 100nm. In addition, the resulting resistivity and its spatial distribution on the substrate surface obtainable in thin films prepared by rf-MSD using a millimeter-wave-sintered AZO target were almost the same as those obtained in thin films prepared by rf-MSD using a conventional powder AZO target. Thin films prepared by PLD using millimeter-wave-sintered AZO:V targets exhibited an improved resistivity stability in a high humidity environment. Thin films deposited with a thickness of approximately 100nm using an AZO:V target codoped with an Al content of 4at.% and a V content [V∕(V+Zn) atomic ratio] of 0.2at.% were sufficiently stable when long-term tested in air at 90% relative humidity and 60°C.