Proton implantation effects on electrical and recombination properties of undoped ZnO

Abstract

Electrical and optical properties of undoped n-ZnO crystals implanted with 50 keV protons with doses from 5×1013 to 5×1015 cm−2 are reported. Proton implantation leads to a decrease of the carrier concentration in the near-surface region, but at the end of the proton range shallow donors are observed whose concentration tracks the implant dose and that we attribute to hydrogen donors. Three deep electron traps with apparent activation energies of 0.55, 0.75, and 0.9 eV are introduced by proton implantation. The 0.9 eV traps have been observed through the increased thermal stability of the Schottky diodes prepared on heavily implanted n-ZnO compared to unimplanted or lightly implanted samples. In addition, hole traps located 0.16 eV above the valence band edge were introduced by implantation. Proton implantation also led to the formation of persistent-photocapacitance-active defects and to considerable decrease in the intensity of the band edge luminescence and in the value of the photocurrent of the Au/n-ZnO Schottky diodes. When compared with other wide-band gap materials, such as GaN, the recombination properties of n-ZnO are shown to be more resistant to deterioration upon proton implantation.