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 charge-transfer between the electrode and electrolyte. The significantly enhanced incident photon conversion efficiency (IPCE) of all nanoporous devices has been obtained.
We have measured the pulsed light-current characteristics of a series of InGaN/GaN quantum well light-emitting diodes which were annealed post-growth at different temperatures as a function of their operating temperature. The light output at a fixed current density increases with the temperature of measurement, reaches a maximum and then decreases for all the diodes. The measurement temperature at which the maximum light output occurs and the magnitude of the light output depend on the post-growth thermal anneal temperature. The thermal anneal temperature is thought to affect the acceptor concentration in the p-doped cap layer, which also changes the carrier mobility. A simulation, incorporating carrier leakage, is used to reproduce the experimental behavior where the acceptor concentration is changed to represent the effects of the different anneal temperatures.