Passivation of Surface States of AlGaN Nanowires Using H₃PO₄ Treatment To Enhance the Performance of UV-LEDs and Photoanodes

Surface states serve as additional charge-carrier-trapping centers and create an energy barrier at the semiconductor–electrolyte interface. This in turn may severely reduce the internal quantum efficiency of Al x Ga 1– x N nanowire ultraviolet light-emitting diodes (UV-LEDs) and solar-to-hydrogen energy conversion efficiency of photoelectrodes used in photoelectrochemical water splitting applications. These states also cause Fermi-level pinning and band bending, leading to Shockley–Read–Hall nonradiative recombination. Hence, surface states need to be passivated. In the present study, we used phosphoric acid to passivate the surface states in AlGaN nanowires. The internal quantum efficiency of the near-band-edge emission peak of the chemically treated nanowires was 7%, whereas that of the as-grown nanowires was 3%. Suppression of the oxide layers was achieved, as indicated by the reduced intensity of the O 1s peak. The higher carrier lifetime of 3.2 ns of the treated nanowires compared to the lifetime of 2.6 ns of the as-grown nanowires’ directly evidenced passivation of the surface states. Crystallinity loss at the nanowire edges was caused by strain relaxation, resulting in broadening of the A 1 (LO) AlGaN phonon mode. The experiments and findings could be useful in the fabrication of UV-LEDs and photoelectrodes with improved performance for water splitting applications.