III-V Semiconductor Nanostructures for Photoelectochemical Water Splitting




Narangari, Parvathala

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The desire for the development of renewable energy technologies is ever growing to sustain global socio-economic growth and meet future technological developments due to declining fossil fuel reserves and growing environmental concerns of their by-products. Although photovoltaics is well established as a renewable technology to generate clean energy, it is intermittent in nature and hence storing solar energy for short and long-term applications is still challenging. Hydrogen generation via photoelectrochemical (PEC) water splitting is one of the promising routes to secure a sustainable, green, storable and portable form of energy. III-V semiconductors have gained intense research interest for PEC water splitting applications owing to their outstanding properties such as variable band gaps to capture the entire solar spectrum, high absorption coefficients and high crystalline quality. In addition, nanostructures possess several essential attributes towards achieving efficient water splitting such as enhanced light absorption, reduced carrier transfer length and large surface area. This thesis report on GaN and InP nanopillar (NP) photoelectrodes fabricated using a top-down approach for PEC water splitting. This work involves the fabrication of large area GaN and InP NPs using inductively coupled plasma (ICP) etching of the respective wafers masked by a self-organized random mask technique, followed by a study of their PEC performance. NP photoelectrodes exhibited a remarkable improvement in PEC performance compared to their planar counterparts due to the enhanced absorption and increased semiconductor/electrolyte interface area. The PEC performance of the GaN NP photoanodes was shown to be influenced by doping concentration, NP dimensions such as diameter and length, and band gap engineering of the GaN NPs. The PEC performance of the InP NPs was strongly dependent on the surface damage of NPs, which was eliminated by wet treatment of the NPs in sulfur-oleylamine (S-OA) solution. Finally, long-term photo-stability was demonstrated for both NP photoelectrodes.






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