Tuning of deep level emission in highly oriented electrodeposited ZnO nanorods by post growth annealing treatments

Abstract

Highly dense and c-axis oriented zinc oxide (ZnO) nanorods with hexagonal wurtzite facets were deposited on fluorine doped tin oxide coated glass substrates by a simple and cost-effective electrodeposition method at low bath temperature (80 °C). The as-grown samples were then annealed at various temperatures (TA = 100–500 °C) in different environments (e.g., zinc, oxygen, air, and vacuum) to understand their photoluminescence (PL) behavior in the ultra-violet (UV) and the visible regions. The PL results revealed that the as-deposited ZnO nanorods consisted of oxygen vacancy (VO), zinc interstitial (Zni), and oxygen interstitial (Oi) defects and these can be reduced significantly by annealing in different environments at optimal annealing temperatures. However, the intensity of deep level emission increased for TA greater than the optimized values for the respective environments due to the introduction of various defect centers. For example, for TA ≥ 450 °C in the oxygen and air environments, the density of Oi defects increased, whereas, the green emission associated with VO is dominant in the vacuum annealed (TA = 500 °C) ZnO nanorods. The UV peak red shifted after the post-growth annealing treatments in all the environments and the vacuum annealed sample exhibited highest UV peak intensity. The observations from the PL data are supported by the micro-Raman spectroscopy. The present study gives new insight into the origin of different defects that exist in the electrodeposited ZnO nanorods and how these defects can be precisely controlled in order to get the desired emissions for the opto-electronic applications.

Mapping the structural, electrical, and optical properties of hydrothermally grown phosphorus-doped ZnO nanorods for optoelectronic device applications

“…Indeed, there are more parameters to consider in designing the light-emitting devices yet, in other words, the parameters to tailor DLE emission wavelength. Simimol et al [43] and other literature indicate that the ZnO nanorods upon annealing changes the emission wavelength and hence can serve the purpose of tuning the emission spectrum. In that case, the persistent DLE emission wavelength of phosphorus-doped ZnO nanorods as per carrier concentration enables designing the light-emitting device rather straightforward; we have only one parameter (annealing) to consider in tailoring emission wavelength, and another one (phosphorus concentration or NH 4 H 2 (PO 4 ) 2 M ratio) in electrical carrier injection, separately.…”

Surface Passivated Zinc Oxide (ZnO) Nanorods by Atomic Layer Deposition of Ultrathin ZnO Layers for Energy Device Applications

“…Different approaches including heat treatment, , plasma treatment (nitrogen, hydrogen, oxygen, Argon), , laser treatment, water or hydrogen peroxide treatment, , metal shielding, and Al 2 O 3 , TiO 2 coatings , have been well-adapted to eradicate the surface states of ZnO nanostructures. Though the quality of ZnO nanostructures is significantly enhanced, the structures get disturbed or contaminated to a certain extent either in the form of chemical impurities, the formation of interfaces, or surface morphology due to the usage of heterogeneous materials and lattice-mismatch between ZnO nanostructures and passivated material.…”

Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods

“…[1][2][3][4] The room temperature luminescence of ZnO nanostructures is commonly characterized by two main bands, a sharp UV near-band-edge emission (NBE) centered at around 380 nm and the above mentioned broad deep-level emission (DLE) which literally covers the region between 400 nm and up to 750 nm. [5][6][7][8][9][10][11][12][13][14][15] According to the peak position, the broad emission band is likely to be composed of different sub-bands since it is known that there is a green emission band (500-550 nm), which is often attributed to oxygen and zinc vacancies (V O , V Zn ), 1,[11][12][13][14]16,17 in addition to the yellow and orange-red bands. The yellow emission band (550-600 nm) and red emission band (620-750 nm) are commonly attributed the presence of OH groups and to the oxygen interstitials (O i ) present on the surface of the ZnO NRs.…”