Characteristics of point defects in the green luminescence from Zn- and O-rich ZnO

Abstract

Cathodoluminescence spectra have been measured to determine the characteristics of ubiquitous green luminescence (GL) in nonstoichiometric zinc oxide (ZnO). Zn-and O-rich ZnO were found to exhibit characteristic emissions at 2.53 eV [full width at half-maximum (FWHM) 340 meV] and 2.30 eV (FWHM 450 meV), respectively. Hydrogen was used to probe the physical nature of GL centers. The Zn-rich GL is enhanced upon H incorporation, whereas the O-rich GL is completely quenched as its underlying acceptor-like V Zn centers are passivated by H. The GL emission bands each exhibit remarkably different excitation-power dependencies. The Zn-rich GL follows a close to linear relationship with excitation power, while the O-rich GL exhibits a square-root dependence. Calculations based on bimolecular recombination equations show the defect concentration in Zn-rich ZnO is three orders of magnitude greater than that in O-rich ZnO, indicating V O is more readily formed than V Zn in thermochemical treatments of ZnO.

Observation of whispering gallery modes from hexagonal ZnO microdisks using cathodoluminescence spectroscopy

“…The chemical origin of this green emission is still not well understood, even though green luminescence is attributed to intrinsic defects such as oxygen vacancies and zinc vacancies and complexes or extrinsic impurities, such as Cu. 23,24 As can be seen in Figure 3(b), the luminescence intensity of the green emission is significantly stronger near the boundary of the microdisk, likely to be enhanced by the total internal reflection of light within the microdisk. Such an enhancement is often associated with the presence of WGMs, as discussed below.…”

Molecular nitrogen acceptors in ZnO nanowires induced by nitrogen plasma annealing

“…The trend of P 1 has no association with the DAP emission, while P 3 can be ruled out since the substitution of N atom, which contains three more valence electrons than Zn, would cause N Zn or its complex to act as a donor [12]. The increase in the I(3.232 eV)/I(LO) ratio is not exactly proportional to the change of P 2 intensity since the intensities of the signature CL peaks are dependent on the capture cross section and concentration of all radiative and nonradiative recombination centers as well as the excitation conditions due to saturation effects [15]. It is noteworthy that the P 3 donor increases slightly in concentration with plasma time and could act as a compensation center in N-doped nanowires.…”

“…Using this synthesis technique, the nanowire morphology and their defect chemistry could be controlled by varying the growth temperature (700-900°C) in combination with the flow rate of oxygen carrier gas. To enhance nitrogen incorporation by vacancy doping [10], nanowires were grown under Zn-rich conditions, which led to an intense defect emission band peaking at 2.47 eV, attributable to V O [15]. Nitrogen doping was achieved by annealing nanowires at 300°C in nitrogen plasma with 230 V cathode bias.…”

Influence of anneal atmosphere on ZnO-nanorod photoluminescent and morphological properties with self-powered photodetector performance

“…The assignment of the green emission to a particular defect structure is a complex task, as a number of defects have previously been assigned to this emission. [29][30][31] Correlations between the green luminescence and oxygen vacancies (V O ) are frequently cited, which were based on V O being assigned to the g $1.96 line in EPR measurements. 55 This has since been shown to be due to shallow donors or conduction band electrons.…”

“…This DLE emission has been employed in visible light-emitting diodes 26,27 and photodetectors. 28 However, the origins of DLE are far from certain; green emission (2.4-2.5 eV), in particular, has been debated extensively for over 30 yr; [29][30][31][32] red emission (1.5-2.0 eV) is often assigned to a number of surface-related defects, 33 whereas yellow/orange (2.1-2.2 eV) emission is linked to oxygen interstitials 34,35 or extrinsic Li impurities. 16 Thermal annealing is often used to remove impurities and structural defects from the crystal lattice.…”