A significant enhancement in solar hydrogen generation has been achieved using a GaN-based nanorod array structure as a photoelectrode in comparison with a planar one fabricated from the same parent wafer. The nanorod array structure was formed by dry etching using a self-organised nickel nanomask. Under identical illumination conditions in hydrochloric acid solution, the photoelectrode with the nanorod array structure has demonstrated a photocurrent enhancement with a factor of 6 and an enhancement in the rate of hydrogen generation with a factor of 7. The enhancement in solar hydrogen generation is attributed to a massive improvement in light absorption area, reduced travelling distance for the migration of the photogenerated carriers to the semiconductor/electrolyte interface, and surface band bending.

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We report the fabrication of porous GaN nanostructures using UV-assisted electroless etching of bulk GaN layer grown on c-plane sapphire substrate in a solution consisting of HF : CH 3 OH : H 2 O 2. The morphology of the porous GaN nanostructures was characterized for different etching intervals using high resolution scanning electron microscopy. The geometry and size of resultant pores do not appear to be affected by the etching time; however, the pore density was augmented for longer etching time. Micro-indentation tests were carried out to quantify the indentation modulus for different porous GaN nanostructures. Our results reveal a relationship between the elastic properties and the porosity kinetics, i.e., a decrease of the elastic modulus was observed with increasing porosity. The photoluminescence (PL) and Raman measurements carried out at room temperature for the etched samples having a high degree of porosity revealed a strong enhancement in intensity. Also, the peak of the PL wavelength was shifted towards a lower energy. The high intensity of PL was correlated to an increase of scattered photons within the porous media and to the reduction of the dislocation density. V C 2012 American Institute of Physics. [http://dx.

In this report we present the fabrication of III-nitride devices with nanoporous structure used as photoelectrodes for solar water splitting. Photoelectrochemical etching in a KOH solution of the GaN and InGaN/GaN devices at different concentrations and applied voltages has been employed to fabricate both planar and nanorod devices into nanoporous structures with controllable pore sizes. Photoluminescence measurements of the GaN and InGaN/GaN multi-quantum well (MQW) with nanoporous structures have shown an increase in intensity over the un-etched samples as a result of the release of the compressive strain which nitride samples grown on sapphire suffer. An enhancement in both photocurrent and hydrogen generation has been achieved across all samples with the nanoporous structure compared to their standard counterparts. Improved carrier extraction as a result of the enhanced surface area allows for better chargetransfer between the electrode and electrolyte. The significantly enhanced incident photon conversion efficiency (IPCE) of all nanoporous devices has been obtained.

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