Realization of phosphorus-doped p-type ZnO thin films via diffusion and thermal activation

ZnO thin films were initially deposited on a heavily phosphorus-doped Si (n⁺-Si) substrate by radio frequency magnetron sputtering. The transition from n-type ZnO to p-type one was realized by phosphorus diffusing from Si substrate to ZnO film and being thermally activated during post annealing. Crystal structures of the ZnO films were confirmed to be highly c-axis oriented wurtzite structure by X-ray diffraction experiment. Photoluminescence spectra of the ZnO films showed strong ultraviolet emissions originated from the recombination of the band-edge excitons. The composition of the films was measured by X-ray photoelectron spectroscopy, and a typical concentration of phosphorus was about 0.48% corresponding to the order of atomic density of 10¹⁹/cm³. The hole concentration of the film was + 1.28 × 10¹⁹/cm³ measured by Hall effect apparatus. Formation of the p-type ZnO films can be further confirmed by the rectifying I-V curves of p-ZnO/n⁺-Si heterojunctions.