To investigate ZnO thin films, the latter were deposited using a RF sputtering system. The substrate temperature and work pressure were set at 300C and 5.2mTorr, respectively, in the sputtering process of ZnO thin films, and 5N-purity ZnO  was the target. The thickness of ZnO thin films was about 2.1μm at the time of scanning electron microscopic analysis after sputtering. Phosphorus and As were diffused, in an ampoule at below 5 x 10−7Torr, into undoped ZnO thin films sputtered by using a RF magnetron system. The doping sources of P and As were Zn3P2 and ZnAs2. The diffusion of these elements was performed at 500, 600 and 700C for 3h. Diffusion in the conductive ZnO thin films, which had n-type and p-type properties, was discovered. The ZnO thin films in this study showed not only very high carrier concentration of above 1017/cm3 but also low resistivity of below 2.0 x 10−2Ωcm.

Diffusion of Phosphorus and Arsenic using Ampoule-Tube Method on Undoped ZnO Thin Films and Electrical and Optical Properties of p-Type ZnO Thin Films. S.J.So, C.B.Park: Journal of Crystal Growth, 2005, 285[4], 606-12