Significantly enhanced performance of an InGaN/GaN nanostructure based photo-electrode for solar power hydrogen generation

Abstract

A significant reduction in photo-electrochemical etching effects has been achieved on an InGaN/GaN nanorod array structure used as a photoelectrode in NaOH electrolyte by means of depositing transparent nickel oxide nano-particles on the nanorod array structure. Alongside this, the addition of the nickel oxide nano-particles has also led to an increase in photocurrent, thus, enhancing energy conversion efficiency. The enhanced performance is attributed to the discontinuities in both conduction band and valence band formed between the nickel oxide and the GaN, which promote the photo-generated electrons to move to a counter electrode and also lead to an enhanced diffusion of the photo-generated holes from the GaN into the NiO. This effect reduces the recombination of the electrons and the holes due to an increased separation between them and also significantly decreases the photo-electrochemical etching as a result of a sizeable reduction in the number of the photo-generated holes accumulated at the GaN/electrolyte interface.

Utilisation of GaN and InGaN/GaN with nanoporous structures for water splitting

“…17,[20][21][22][23][24][25] We have recently reported the utilization of selforganized nickel nanomasks to fabricate nanorod structures employed as photoelectrodes for solar power water splitting, demonstrating a significant increase in energy conversion as a result of improved optical absorption and reduced electronhole recombination. 24,26 Further improvement in performance is still necessary.…”

“…27 Initially, a 0.5 lm buffer layer of AlN was directly grown at 1200 C, followed by a 0.3 lm of undoped GaN and finally a 1.0 lm layer of silicon doped GaN with doping level of 3 Â 10 18 cm À3 , both grown at 1120 C. A standard InGaN/GaN based device epiwafer was also utilised with the structure described in previously published work. 26 A Ti/Au (20 nm/100 nm) ohmic contact was deposited via a standard thermal evaporation technique to allow the use as an electrode. All devices have a similar size at 0.5 cm 2 .…”

An In0.5Ga0.5N nanowire photoanode for harvesting deep visible light photons

“…Previous studies confirmed long-term stable water splitting on nanostructured InGaN/GaN photoanodes in 1 M NaOH electrolyte with photocurrent densities in the sub-mA/cm 2 range under AM1.5G one sun illumination. 26,51 By developing an effective protection strategy to prevent the oxidation of the underlying Si substrates, 52 InGaN nanowire photoanodes integrated on Si have the potential to enable high efficiency and highly stable solar water splitting. Moreover, heterostructures based on such superior quality InGaN nanowires also hold tremendous promise for realizing deep visible and near-infrared light emitting diodes and lasers on a Si platform for full color displays and on-chip optical communications.…”

“…22,[27][28][29][30] Efforts in enhancing the indium incorporation lead to the formation of extensive defects and dislocations, due to the large difference (∼11%) in lattice constants between InN and GaN. [31][32][33][34] Recently, significantly enhanced photocatalytic activities have been reported for InGaN nanowires, [23][24][25][26] due to the drastic reduction of defect density and the efficient charge carrier separation. The performance of such nanowire devices, however, still suffers severely from the formation of indium-rich nanoclusters, due to the solid phase miscibility gap between InN and GaN, which not only limits the absorption wavelength but also enhances carrier recombination loss.…”

“…[22][23][24][25][26] To date, however, the best reported InGaN photoelectrodes only produced photocurrent densities (J ph ) less than 3 mA/cm 2 under AM1.5G one sun illumination. 22,[27][28][29][30] Efforts in enhancing the indium incorporation lead to the formation of extensive defects and dislocations, due to the large difference (∼11%) in lattice constants between InN and GaN.…”