5:15 PM - 5:30 PM
[15p-A24-10] Impact of surface modification on photo-induced Open-Circuit-Potential (OCP) of GaN anode
Keywords:semiconductor, photocatalyst, water splitting
We propose a method for analyzing the effect of surface modification on the carrier behavior in an n-GaN anode. Open-circuit potential (OCP) was measured as a function of the irradiation intensity of Xe lamp in NaOH solution. The light intensity was varied with ND filters taking 100 mW/cm2 as the maximum. The initial and the final “dark” state was realized by measuring OCP in a light shelter. An as-grown n-GaN electrode was measured first and then its surface was oxidized with anodic current and the same measurement was repeated. The other n-GaN had its surface coated with a 20-nm-thick ITO by sputtering.
The values of OCP followed a linear relationship with the logarithm of light intensity, suggesting that both the band bending of n-GaN and the difference between the conduction-band edge and the electron Fermi level were reduced with the accumulation of photo-generated carriers in GaN. The behavior was almost independent of surface oxidation of GaN. The value of OCP in the dark drops significantly for the as-grown GaN but the surface oxidation reduced the amplitude of the OCP drop. This is probably because the surface oxidation passivated surface dangling bonds. ITO on the GaN surface completely avoided the OCP drop in the dark because of complete surface passivation with ITO. The vertical offset of OCP from the curve for the naked GaN may indicate surface potential induced by ITO. A slight reduction in the slope of OCP versus logarithm of light intensity was also brought about by ITO coating, probably owing to the reduced surface recombination by ITO coating.
Such analysis of OCP can characterize the effect of surface modification on both the density of surface recombination centers and surface potential of a semiconductor photoelectrode. Detailed comparison with current-voltage characteristics will further clarify the physics and chemistry on the surface of photoelectrodes.
The values of OCP followed a linear relationship with the logarithm of light intensity, suggesting that both the band bending of n-GaN and the difference between the conduction-band edge and the electron Fermi level were reduced with the accumulation of photo-generated carriers in GaN. The behavior was almost independent of surface oxidation of GaN. The value of OCP in the dark drops significantly for the as-grown GaN but the surface oxidation reduced the amplitude of the OCP drop. This is probably because the surface oxidation passivated surface dangling bonds. ITO on the GaN surface completely avoided the OCP drop in the dark because of complete surface passivation with ITO. The vertical offset of OCP from the curve for the naked GaN may indicate surface potential induced by ITO. A slight reduction in the slope of OCP versus logarithm of light intensity was also brought about by ITO coating, probably owing to the reduced surface recombination by ITO coating.
Such analysis of OCP can characterize the effect of surface modification on both the density of surface recombination centers and surface potential of a semiconductor photoelectrode. Detailed comparison with current-voltage characteristics will further clarify the physics and chemistry on the surface of photoelectrodes.