Passivation of defects in nitrogen-doped polycrystalline Cu2O thin films by crown-ether cyanide treatment

Crown-ether cyanide treatment, which simply involves immersion in KCN solutions containing 18-crown-6 followed by rinse, is studied in relation to electrical and optical properties of nitrogen-doped, polycrystalline ${\mathrm{Cu}}_2\mathrm{O}$ thin films, and its effect is compared with that of hydrogen treatment. By the crown-ether cyanide treatment, the luminescence intensity due to the near-band-edge emission of ${\mathrm{Cu}}_2\mathrm{O}$ at around 680 nm is enhanced, and the hole density is increased from the order of ${10}^{16}$ to ${10}^{17}\hspace{0.17em}{\mathrm{cm}}^{\text{−3}},$ analogous to hydrogen treatment. The effects of the passivation by the hydrogen treatment completely disappear after annealing at 350 °C, while those of the crown-ether cyanide treatment stay unchanged after the same annealing treatment. From these results, the crown-ether cyanide treatment for polycrystalline ${\mathrm{Cu}}_2\mathrm{O}$ thin films can be concluded to be a more suitable method of passivating defects than the hydrogen treatment.