Surface-Passivated AlGaN Nanowires for Enhanced Luminescence of Ultraviolet Light Emitting Diodes

Abstract

Spontaneously-grown, self-aligned AlGaN nanowire ultraviolet light emitting diodes still suffer from low efficiency partially because of the strong surface recombination caused by surface states, i.e., oxidized surface and high density surface states. Several surface passivation methods have been introduced to reduce surface non-radiative recombination by using complex and toxic chemicals. Here, we present an effective method to suppress such undesirable surface recombination of the AlGaN nanowires via diluted potassium hydroxide (KOH) solution; a commonly used chemical process in semiconductor fabrication which is barely used as surface passivation solution in self-assembled nitride-based nanowires. The transmission electron microscopy investigation on the samples reveals almost intact nanowire structures after the passivation process. We demonstrated an approximately 49.7% enhancement in the ultraviolet light output power after 30-s KOH treatment on AlGaN nanowires grown on titanium-coated silicon substrates. We attribute such a remarkable enhancement to the removal of the surface

AlGaN Nanowires for Ultraviolet Light-Emitting: Recent Progress, Challenges, and Prospects

“…The early efforts of growing AlGaN nanowires using such large-scale epitaxy tools can be dated back to around 2000, when AlGaN nanowires with low Al contents were first investigated by MBE [46,47]. These early efforts were followed by tremendous efforts from a large number of groups who have been working on the epitaxial growth of AlGaN nanowires (primarily by MBE) [25,28,[48][49][50][51][52][53][54]. In these studies, the AlGaN nanowires are typically spontaneously formed on 2-inch or 3-inch Si substrates under the nitrogen rich conditions, with the help of GaN nanowire template.…”

“…Due to different chemical potentials on the nanowire top surface and the sidewall, the impinged atoms diffuse at the substrate surface and then migrate to the nanowire top, promoting a spontaneous vertical growth. Furthermore, for GaN nanowires grown by MBE, lattice registration (a requirement for the growth of epi-layers) is not needed [57], which enables the formation of an AlGaN nanowire segment on a wide range of substrates [27][28][29].…”

“…Over the past few years, various metal foils (e.g., Ti, Ta) [27,91] and metal-coated substrates (e.g., Al, Pt, Ti, Mo) [28,29,[92][93][94][95][96][97] have been investigated for the growth of AlGaN nanowire UV LED structures, motivated by the excellent physical properties of metals, including thermal and electrical conductivity, light reflection, as well as flexibility. In addition, by coating a metal layer to Si substrate one can also reduce the formation of SiN x .…”

Unleashing the potential of molecular beam epitaxy grown AlGaN-based ultraviolet-spectrum nanowires devices

“…A fabricated device after such treatment showed improvement in the turn-on voltage, reduction in contact resistivity, and ∼50% enhancement in output power. 47 Other than passivating the surface states by employing chemical treatments or depositing dielectric materials, researchers achieved in situ passivation by spontaneously growing shell layers around semiconductor NWs, in general. For example, AlGaAs shells were intentionally grown around GaAs NWs to prevent subsequent oxidation upon exposure to the atmosphere, without which recombination velocities would increase and PL emission would reduce.…”

Time–Energy Quantum Uncertainty: Quantifying the Effectiveness of Surface Defect Passivation Protocols for Low-Dimensional Semiconductors

“…Owing to the higher surface-area-to-volume ratios in lower-dimensional semiconductor structures and the subsequent induction of forbidden energy-band transitions caused by surface trap states, 13 14 and is commonly used in semiconductor chip fabrication. 15,16 Yet, the aforementioned reports lack discussions of physical insights into the extent of the goodness of nanowire surface passivation through quantum mechanical descriptions and criteria that set theoretical bounds.…”