Nanoporous GaN for enhanced solar hydrogen production

Abstract

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.

The development and applications of nanoporous gallium nitride in optoelectronics: a review

“…Both photocurrent and hydrogen generation were enhanced for GaN with nanoporous structure. NP-GaN can be used as a substitute for noble metal cocatalyst with high cost and low abundance [118][119][120]. NP-GaN as an electrode for photodegradation and hydrogen evolution is excited by external light to form electron-hole pairs, and then the electron-hole pairs are separated to the surface of gallium nitride for redox reactions, due to the increase of surface area to volume ratio.…”

“…It is reported that the porous structure obtained by etching GaN with KOH and changing the etching parameters affected the final electrode performance [119]. With the increase of the porous structure, hydrogen production also increased.…”

Porosity Control for Plasma-Assisted Molecular Beam Epitaxy of GaN Nanowires

“…14,15 The research on NPFs is not limited to GaN: different materials such as nanoporous InGaN, 16−19 Si, 20 carbon membranes, 21 and WO 3 22 have demonstrated a great potential for photoelectrochemical water splitting 18,20,21 and photocatalytic fuel cells. 22 A vast majority of reports on the synthesis of NPFs are focused on different kind of etching of thin films or GaN− sapphire templates such as electroless etching, 3,4 electrochemical etching, 6,10,17 or high-temperature annealing. 8,9 The fabrication of ordered NPFs has been demonstrated using inductively coupled plasma (ICP) etching with an anodic alumina template as etching mask.…”

“…The attractiveness of GaN NPFs resides in their significant strain relaxation , and enhanced surface Raman scattering . Comparing with their compact counterparts, GaN NPFs have demonstrated improved properties in diverse applications such as photoelectrochemical water splitting, − supercapacitors for energy storage, , light emitting diodes (LEDs), ,,− distributed Bragg reflectors, or mechanic removal of films from the substrate. , The research on NPFs is not limited to GaN: different materials such as nanoporous InGaN, − Si, carbon membranes, and WO 3 have demonstrated a great potential for photoelectrochemical water splitting ,, and photocatalytic fuel cells …”

“…A vast majority of reports on the synthesis of NPFs are focused on different kind of etching of thin films or GaN–sapphire templates such as electroless etching, , electrochemical etching, ,, or high-temperature annealing. , The fabrication of ordered NPFs has been demonstrated using inductively coupled plasma (ICP) etching with an anodic alumina template as etching mask . However, to the best of our knowledge very few reports on the growth of GaN NPFs can be found.…”