Growth of p-type Ag-doped ZnO by rf sputter deposition

Abstract

The growth of thin films of Ag-doped zinc oxide (ZnO) (ZnO:Ag) having p-type conductivity using radio frequency (rf) magnetron co-sputter deposition without any post-deposition annealing has been investigated. The thin films of ZnO:Ag were deposited on n-type Si substrates using a composite ZnO/Ag target (97%/3%) in argon plasma at different substrate temperatures of 300 °C, 375 °C and 600 °C. The deposited films were characterized by Hall measurement, X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDAX) techniques. Hall measurements show that the films deposited at substrate temperatures of 300 °C and 375 °C were n-type ZnO films and those deposited at a substrate temperature of 600 °C were p-type ZnO ones with hole concentration in the range (1.1–4.6) × 10⁺¹⁸/cm³. For the p-type ZnO thin films, the XRD analyses indicate substitution of Ag⁺ for Zn²⁺ in the films. FE-SEM backscattered electron images show nanocrystalline surface morphology of the film. RBS and EDAX measurements show the presence of O, Zn and Ag elements in the films. The formation of p-type Ag-doped ZnO in the films deposited at 600 °C is attributed to the appropriate conditions for incorporation of Ag⁺ into Zn²⁺ sites of ZnO at elevated substrate temperatures and formation of Ag_Zn acceptors in the as-grown thin films.

Keywords:

• ZnO
• p-type
• rf sputtering
• substrate temperature
• Ag_Zn acceptors

Acknowledgements

One of the authors (V.V. Siva Kumar) acknowledges the help of Mr P.K. Kulriya for XRD measurements, Mr S.A. Khan and Mr Sunil for FE-SEM, EDAX measurements, and Mr S. Ojha and Dr K. Saravanan for RBS measurements. The DST is acknowledged for providing the XRD and FE-SEM facilities at IUAC.