Improved photoelectrochemical performance of GaN nanopillar photoanodes

Abstract

In this work, we report on the photoelectrochemical (PEC) investigation of n-GaN nanopillar (NP) photoanodes fabricated using metal organic chemical vapour deposition and the top-down approach. Substantial improvement in photocurrents is observed for GaN NP photoanodes compared to their planar counterparts. The role of carrier concentration and NP dimensions on the PEC performance of NP photoanodes is further elucidated. Photocurrent density is almost doubled for doped NP photoanodes whereas no improvement is noticed for undoped NP photoanodes. While the diameter of GaN NP is found to influence the onset potential, carrier concentration is found to affect both the onset and overpotential of the electrodes. Optical and electrochemical impedance spectroscopy characterisations are utilised to further explain the PEC results of NP photoanodes. Finally, improvement in the photostability of NP photoanodes with the addition of NiO as a co-catalyst is investigated.

Engineering III–V Semiconductor Nanowires for Device Applications

“…Among them, 1D NWs attracted great attention due to their excellent crystallinity, light trapping ability, direct charge transport paths, high surface to volume ratio. In particular, compound III–V semiconductor NWs, including InGa x N 1− x alloys, InP, GaP, and GaAs have been widely investigated for PEC applications.…”

“…Metal–organic chemical vapor deposition and molecular beam epitaxy are the most commonly employed for the bottom‐up growth of InGa x N 1− x NWs, in either catalyst‐assisted or self‐catalyzed routes. In top‐down approach, the NWs are formed via reactive ion etching of lithographically or randomly patterned GaN epilayers . The advantages of top‐down approach include morphology control, ease of doping, and large‐area scalability.…”

“…The advantages of top‐down approach include morphology control, ease of doping, and large‐area scalability. We investigated n‐GaN NWs as photoanodes for water oxidation fabricated using inductively coupled plasma (ICP) etching and self‐assembled Ni random mask techniques ( Figure a,b) . A photocurrent density of ≈1 mA cm −2 was realized for GaN NW photoanode, which is 100% higher in comparison to its planar counterpart (Figure d).…”

“…We further engineered the bandgap of GaN by incorporating InGaN/GaN multiple quantum wells (MQWs) toward improving the PEC performance . The introduction of InGaN/GaN MQWs into GaN extended the optical absorption of NWs into the visible region of the solar spectrum, thereby contributing to a substantial improvement in photocurrent density for InGaN/GaN MQW nanopillars …”

Reduction of threading dislocation density in top-down fabricated GaN nanocolumns via their lateral overgrowth by MOCVD

“…In general this method is less suitable for mass-production of potential devices due to (a) unavoidable variability in individual NCs dimensions, particularly, height, (b) apex tops of grown NCs (when grown Ga-polar), (c) limited achievable fill factor of their arrays, and finally (d) issues with controlling doping levels. In contrast, many of these issues may be avoided by fabricating NC arrays using "top-down" fabrication approaches [22].…”