Planar GaN/Cu 2 O Microcrystal Composite Junction Photoanode for Efficient Solar Water Splitting.

Cu 2 O microcrystals are electrodeposited on an epitaxial GaN layer on a Si(111) substrate to improve the solar water splitting efficiency of a GaN photoanode. The performance of the GaN/Cu 2 O composite junction photoanode is investigated as a function of the Cu 2 O deposition amount for Cu 2 O microcrystal formation. For optimum Cu 2 O deposition amount, the photocurrent density is significantly enhanced compared to that of the bare GaN photoanode. The improved water splitting performance is attributed to the built-in electric field and band offsets of the n-GaN/p-Cu 2 O heterostructure, promoting the separation of photogenerated electrons and holes and the transport of the hole to the surface.