Effects of Ohmic Contact Formation between GaN Photocatalyst and Pt Cocatalyst (Supporting Information)

A model photocatalyst composed of n-type GaN thin film as a photocatalyst body with a comb shaped electrode composed of Pt layer or Pt/Ti bilayer on the surface was successfully prepared, and photocatalytic and electric properties are investigated. Current-voltage (I-V) curve measurements revealed the formation of Schottky contact between Pt comb and GaN, and ohmic contact between Pt/Ti comb and GaN. In the reaction tests, the GaN model photocatalyst with a Pt/Ti comb showed about three times increased hydrogen evolution rates over the photocatalyst with a solely Pt comb. Under irradiation, about 0.2 V photovoltage at Pt-GaN interface was observed, which prevents electron transfer from the GaN photocatalyst body to Pt cocatalyst, while the photovoltage was eliminated by the introduction of a Ti layer between the Pt and GaN. In-situ photoluminescence (PL) measurement in oxygen ambient confirmed smooth transfer of photoexcited electrons in GaN to Pt/Ti comb, and the degree of quenching indicates efficient charge separation at the working potential. Furthermore, the filling of mid-gap states by electrons was also observed.