Novel III-nitride semiconductors for solar hydrogen production

• Main Author: Benton, Jonathan
• Other Authors: Wang, Tao ; Weinstein, Julia
• Published: University of Sheffield 2014
• Subjects: 621.3
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.632586

III-nitride materials are crucially becoming the most important and promising class of semiconductors for future optoelectronic devices including solid state lighting and solar energy applications. Presently, there are still many challenges in regards to the wide scale uptake of these devices, including low efficiencies and short lifetimes. Despite the ideal properties of InGaN for water splitting, there are still very few reports utilising these semiconductors. This thesis investigates GaN and InGaN based structures for water splitting. Initially focussing on the fabrication of nanorods via the use of a self-organised nickel mask, where diameter and height of the structures have been optimised. As a result, the surface area of the device increases dramatically leading to an enhancement in photocurrent compared to as-grown planar devices. Alongside this, the fabricated nanostructures allow for an enhancement in electron-hole separation and an increase in the hydrogen generation rate. The lifetime of the fabricated devices is also discussed. Prolonged exposure of the nanostructured devices results in the degradation and etching of the InGaN material. The addition of a secondary semiconductor material, NiO, acts as a reaction site for photogenerated holes preventing the oxidation and dissolution of InGaN devices in the experimental electrolytes, increasing the device lifetime. Furthermore, a photoelectrochemical etch technique is implemented to create a porous device structure. The nanoporous network in the structure shortens the required diffusion length of the photogenerated carriers to values close to that of InGaN. An enhancement in photocurrent and hydrogen production has been observed due to the nanoporous structure.