Improved Hydrogen Gas Generation Rate of n-GaN Photoelectrode with SiO[sub 2] Protection Layer on the Ohmic Contacts from the Electrolyte

Abstract

Direct photoelectrolysis of water to generate hydrogen was performed using n-type GaN films with Cr/Au ohmic contacts to serve as working electrodes. To enhance the efficiency of electron collection in the GaN working electrode, meshed Cr/Au contacts with a SiO2 protection layer were immersed in the NaCl electrolyte. With an external bias of 1 V, the typical photocurrent densities (gas generation rate) of the n-GaN working electrodes with and without the immersed ohmic contact layer were approximately 19.6 (9.4) and 9.9 A/cm(2) (3.6 mL/h), respectively, which corresponded to an enhancement in the photocurrent density (gas generation rate) of around 98% (160%). The marked enhancement in the gas generation rate could be attributed to the fact that the distance between the neighbor Cr/Au ohmic contacts is small enough to reduce the recombination probability of photogenerated electrons with holes or charged defects in the GaN layer before the electrons reach the ohmic contacts. In other words, the photogenerated electrons can be effectively collected by the Cr/Au ohmic contacts and thereby reach the Pt counter electrode to lead the generation of hydrogen.