10 16 10 17 10 18 10 19 Carrierconcentration (cm -3 ) 10 -5 10 -4 10 -3 10 -2 Oxygen Pressure (Pa) 6 10 -3 2 4 6 10 -2 2 4 6 10 -1 2 4 Saturation Magnetization ( GLYPH<s109> B /Co) M$_{s}$ XMCD x  = 0.07 x  = 0.10 Annealed Zn$_{1-}$$_{x}$Co$_{x}$O Zn polar   M$_{s}$   n O polar  M$_{s}$   n M$_{s}$ SQUID x  = 0.10 Annealed Free Up Down (a) As-grown (b) Annealed (c) Hetero 21 FIG. 7: (Color online) Schematic drawings of Co-ion distribution in Zn$_{1}$$_{−}$$_{x}$Co$_{x}$O. (a), (b) Co distribution of the as-grown and annealed homo-epitaxial Zn$_{1}$$_{−}$$_{x}$Co$_{x}$O thin films, respectively. (c) Hetero-epitaxial Zn$_{1}$$_{−}$$_{x}$Co$_{x}$O thin film. FIG. 6: (Color online) P$_{O2}$ dependences of saturation magnetization M$_{s}$ and carrier concentration n in homo-epitaxial Zn$_{1}$$_{−}$$_{x}$Co$_{x}$O thin films. The values of O- and Zn-polar Zn$_{1}$$_{−}$$_{x}$Co$_{x}$O are taken from Ref. [16]. Here, all the experimental values of the present study are plotted based on M$_{s}$ and P$_{O2}$ .