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

Abstract

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.

AlGaN nanowire deep ultraviolet light emitting diodes with graphene electrode

“…spectra scan of binding energy (BE) obtained for three regions on the device, at a pass energy of 200 eV. All regions of the device show the expected characteristic peaks of Ga 3d, Al 2p, N 1s, O 1s and C 1s [58], [92], [93].…”

Recent Progress on Aluminum Gallium Nitride Deep Ultraviolet Lasers by Molecular Beam Epitaxy

“…(KOH) solution and phosphoric acid (H 3 PO 4 ); and both chemicals have been found to be able to reduce the adverse effects of the surface defects/states in AlGaN nanowires. [208][209][210] Moreover, the electrically injected AlGaN nanowire DUV lasers discussed in Section 4 are random lasers, i.e., the cavity cannot be controlled precisely. For real-world applications, a controlled cavity is necessary.…”

Study on the Influence of KOH Wet Treatment on Red μLEDs

“…Sun et al studied that tetramethylammonium hydroxide (TMAH) wet treatment optimized the micro trench at the bottom corner of the mesa sidewall [20]. Mahitosh et al improved the internal quantum efficiency of the near-band-edge emission peak from 3% to 7% through phosphoric acid [21]. The other type of treatment is conducted by dielectric materials passivation, which includes but is not limited to SiO 2 , SiNx, and Al 2 O 3 [17].…”