Investigation of sputtering parameters in preparation of group-V doped Zno leading to P-type transparent conducting oxide thin films

Abstract

Group-V doped ZnO thin films were investigated for the sputtering parameters of p-type conductivity. Phosphorus-doped ZnO thin films obtaining from sputtering of phosphorus-doped ZnO target exhibit n-type conductivity which is a main result of substitution of phosphorus into the zinc site. Most of nitrogen-doped ZnO thin films obtaining from sputtering of pure ZnO target under a mixture of N[subscript 2] and Ar gases and from sputtering of pure Zn target under a mixture of N[subscript 2]O and Ar exhibit very high resistivity in the order of 105 [omega]cm and do not exhibit p-type conductivity. This relates to that most of nitrogen atoms cannot occupy oxygen sites and may appear as interstitial in the films. Small amount of nitrogen occupying oxygen sites and acting as acceptors cannot compensate the donors to exhibit p-type conductivity. Finally, preparation of intrinsic ZnO with the insertion of the ultra-thin Zn:N middle layer by sputtering with suitable post annealing leads to p-type ZnO films . The film crystalline structure was distributed to quasi-stable states with p-type conductivity by short-time vacuum annealing and then redistributed to stable states with n-type conductivity by long-time vacuum annealing. The temperature and time of annealing process after the end of sputtering process are the main parameters leading to p-type conductivity. This leads to the phase formation of Zn[subscript 3]N[subscript 2] and the diffusion of nitrogen and oxygen atoms.