Plasma-induced enhancement of UV photoluminescence in ZnO nanowires

Abstract

The photoluminescence emission of ZnO nanowires was modified by means of plasma etching, inducing a strong increase in the Near Band Edge emission (NBE) in the UV region (3.26 eV). In contrast, annealing treatment at 600 degrees C quenched the NBE peak. This opens the possibility to modify the emission properties of ZnO nanowires by means of surface treatment, and is of great importance in view of the application of ZnO as an emitting material. ZnO nanowires were prepared by the vapour phase growth technique in a tubular furnace. Morphological and structural characterization was carried out by scanning and transmission electron microscopy, showing no modifications to the morphology and crystalline arrangements after plasma etching. The nanowires are single crystalline with a high aspect ratio and diameters in the 50-100 nm range. The optical properties of the ZnO nanowires were studied by continuous wave photoluminescence (PL). Ar and O-2 plasma etching treatment caused modification of the PL spectrum, inducing a strong enhancement of the NBE peak, and an increased ratio of NBE over Deep Level Emission (DLE), thus indicating a better sample quality after the treatment. The effect of the Ar treatment is higher than the effect of O-2 treatment, since the ratio of NBE : DLE obtained for O-2 plasma etching is smaller than the ratio observed for Ar. Conversely, annealing at 600 degrees C in an O-2 or Ar atmosphere induced the quenching of the NBE and an increase of the DLE in the PL spectrum of the ZnO nanowires. The variations in the spectroscopic features are discussed in terms of hydrogen diffusion and the passivation of states responsible for non-radiative recombination

Arrays of nanorods composed of ZnO nanodots exhibiting enhanced UV emission and stability

“…48,49 The UV emission from the bare ZnO NRs grown in the present work is already rather strong, and the maximum UV emission enhancement achieved using either of 4 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 2012…”

Orange/Red Photoluminescence Enhancement Upon SF6 Plasma Treatment of Vertically Aligned ZnO Nanorods

“…The effect of Ar/SF 6 plasma treatment for ~20 min should be further investigated for shorter time intervals in order to establish any concrete surface chemistry–PL properties correlation. There are conflicting reports on the relative decrease, increase or no change in the relative intensities of the NBE (UV) or DLE (visible range) peaks, with the reported findings depending on several factors including ZnO morphology, plasma composition, plasma treatment time, that in turn, influence the defect types and concentration on ZnO surface besides attachment of hydroxyl groups [30,31,32,33,52,53].…”

“…On the other hand, Prucnal et al [31] noticed an increase in the PL intensities for both UV (near-band-edge or NBE) and visible range (deep level emission or DLE) upon SF 6 plasma treatment of the ZnO films for 125 s. Treatment of the ZnO nanorods with hydrogen or oxygen plasma has been found to reduce V O concentration and increase O i concentration, respectively, with subsequent intensity changes in the PL spectra [32]. Yet, another study of the Ar plasma treatment of the ZnO nanowires revealed intensity enhancement of the NBE emission over DLE [33]. Although there are several reports on processing or plasma-induced surface modification of ZnO thin films and nanostructures, the relative enhancement in the visible emission (DLE) still needs to be further explored.…”

Oxygen plasma assisted enhanced photoresponse of ZnO nanowires fabricated by catalyst-free chemical vapor deposition

“…Plasma treatment is one of the most effective methods for surface modication of semiconductor materials in both types of thin lms and nanowires. [11][12][13][14][15][16]40 In this study, oxygen plasma was employed to modify the surface of the ZnO NW-based IDA-PDs. By comparison, the performance of the IDA-PDs treated by oxygen plasma for 10 minutes showed great improvement.…”