Photoelectrochemical hydrogen generation using graded In-content InGaN photoelectrode structures

Highlights: • High-quality of graded InGaN layers. • Investigation of the effect of the graded InGaN on the photochemical phenomena. • The graded InGaN layer is no step-like energy barrier in the conduction band. • The graded InGaN/GaN structure significantly increased photocurrent and H₂ generation. -- Abstract: We have improved the InGaN/GaN heterointerface to achieve higher energy conversion efficiency by replacing a uniform InGaN layer with a graded In-content InGaN layer. Even In_0.08Ga_0.92N/GaN heterostructure has a large conduction band offset, which is large enough to suppress the photocurrent in the photocatalytic system. The graded In-content InGaN structures were grown by metalorganic vapor-phase epitaxy by changing the TMIn flow rate gradually. X-ray reciprocal space mapping confirmed the graded structures. The graded InGaN/GaN structure significantly increased photocurrent and H₂ generation by 50% and more compared with the conventional uniform InGaN/GaN structures.