Optical properties of functionalized GaN nanowires

Abstract

The evolution of the optical properties of GaN nanowires (NWs) with respect to a sequence of surface functionalization processes is reported; from pristine hydroxylated to finally, 3-mercaptopropyltrimethoxysilane (MPTMS) functionalized GaN NWs. Photoluminescence, Raman, stationary, and time-resolved photoluminescence measurements were applied to investigate the GaN NWs with different surface conditions. A documented surface passivation effect of the GaN NWs induced by the MPTMS functionalization is determined based on our characterization results. A hypothesis associated with the surface band bending and the defect levels near the band edges is proposed to explain the observed experimental results.

Effect of etching with cysteamine assisted phosphoric acid on gallium nitride surface oxide formation

“…55,56 In addition, the PL spectra of both types of samples also demonstrated yellow band emissions (not shown), which are characteristic for the presence of point defect related deep levels in the bandgap in this material. 5,21,57,58 …”

“…The concentration of cysteamine on the sample surface was determined to be low enough to avoid photon adsorption that has been seen with other surface modifications. 21 What does change is the temperature of phosphoric acid required to maximize photoluminescence in the different types of samples. It has been shown that etching increased the photoluminescence as the surface roughness increases the critical angle for photon escape; 13,14 however, there is an upper limit as over etching can produce light scattering and device degradation.…”

“…Alternatively, the surface can be etched (via heated KOH [13][14][15] or phosphoric/sulfuric 14,16 acid) or coated with thiols, 17 or other molecules. [18][19][20][21][22][23] The etching and surface functionalization routes provide convenient ways to modify GaN surface properties without the need for intensive doping strategies that predominantly rely on hazardous chemicals. 12,24 Etching adds the ability to alter both the surface morphology as well as composition through the formation of pitting structures, which cannot be accomplished by only chemi-or physisorbing compounds on the surface.…”

Enhanced Optoelectronic Performance of a Passivated Nanowire‐Based Device: Key Information from Real‐Space Imaging Using 4D Electron Microscopy

“…In InGaN, one of the most important semiconductor NW systems currently in use, nonradiative Shockley–Read–Hall (SRH) recombination at the surface defect states may arise from the presence of Ga/In dangling bonds, nitrogen vacancies, and/or incorporated oxygen . The presence of surface states may pin the Fermi level at the surface, causing band bending that decreases the density of free electrons toward the surface . Both of these effects significantly reduce the carrier density and, subsequently, the efficiency of the device.…”

“…Different techniques have been employed to passivate surface states, including growing large bandgap AlGaN shells and treating the surface with sulfur‐containing compounds, such as (3‐mercaptopropyl)trimethoxysilane or (NH 4 ) 2 S . Very recently, Zhao et al reported the use of octadecylthiol (ODT) to efficiently passivate the surface dangling bonds and weaken the band bending of an InGaN/GaN quantum‐disk (Qdisk)‐in‐nanowire LED, significantly enhancing the steady‐state photoluminescence (PL) efficiency and external quantum efficiency (EQE) .…”