DC magnetron reactive sputtered InN thin film electrodes as photoanodes in aqueous solution. A study of as prepared and nitrogen annealed electrodes

Thin films of indium nitride, InN, were produced by reactive magnetron DC sputtering. By post treatment in dinitrogen, N 2, in the temperature range 350–500 °C a set of films gradually going from InN to indium oxide, In 2O 3 was obtained (due to dioxygen impurities in the annealing gas). Those films were characterized by X-ray diffraction, optical-, resistivity- and photoelectrochemical measurements for the aim of direct watersplitting in a photoelectrochemical cell. Surprisingly, the caused change in the film composition by annealing gave no significant change in the room temperature resistivity, but the free electron density and the optical properties were affected. In 0.1 M NaOH annealing improved the photoresponse of the thin films. A pronounced optimum was observed for films annealed at 425 °C. Even for those films the quantum efficiency was low; at most 2% of the photons at 350 nm were transformed into readable photoelectrons. The onset wavelength for photocurrent was located around 600 nm (2.1 eV), which is far off from the onset of absorption 900 nm (1.4 eV).