While solar cells are becoming increasingly more efficient, intermittency remains a key issue. A potential solution to this problem is the conversion of sunlight into chemical energy. Photoelectrochemical water splitting makes use of semiconducting photoelectrodes which absorb photons to generate H₂, a high-energy-density fuel, from water. III-V semiconductors are excellent materials for this purpose, as they exhibit superb optical and electrical properties. In addition, III-V semiconductors can be alloyed, allowing for band gap tunability.

In this project, the quaternary InGaAsP and ternary AlGaAs alloys are investigated. InGaAsP can be lattice-matched to either InP or GaAs, producing small or large band gaps respectively, while AlGaAs is a well-studied large band gap material with applications in a range of other optoelectronic devices, including solar cells and light-emitting diodes. These alloys are of great interest as, unlike many other material systems, their band gaps can be optimised for photoelectrochemical water splitting to yield the highest possible energy conversion efficiency.