Cathodoluminescence study of ZnO wafers cut from hydrothermal crystals

Abstract

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Spectral behavior of the emission around 3.31eV (A-line) from ZnO nanocrystals

“…As has been reported [15], under high power UV-laser excitation the ZnO nanocrystals located in the top layers can be heated up to about 40 K, while the temperature of the cold finger of the cryostat remains at 10 K. Thus, assignment of the A-line exactly to the first LO phonon replica of free excitons or to excitons bound at structural defects may depend on not only morphology of ZnO but also measurement conditions. The obtained results are partially supported by the CL measurements, which show that the A-line is composed of two overlapped bands related to point defects and the first LO phonon replica of the free exciton [22]. Nevertheless, additional experiments are necessary for understanding the origin of the A-line emission in detail.…”

Characterization of polishing induced defects and hydrofluoric acid passivation effect in ZnO

“…20 Both CL and PL research on ZnO demonstrated that mechanical polishing leads to surface and near surface damage, which decreases near band edge (NBE) luminescence efficiency, and forms non-radiative recombination centers (NRRCs) and intrinsic defects such as zinc vacancy (V Zn ) and zinc interstitial (Zn i ). [10][11][12][13][14][15][16][17] PAS studies also show creation of dislocations and vacancy defects in the near and sub-surface region after polishing. 19 Recent DLTS measurements show that mechanical polishing introduced two defect levels at 1.0 and 1.2 eV below the conduction band edge E C whose densities subsequent hydrofluoric acid (HF) etching reduced substantially while restoring bulk carrier densities.…”

“…Previous research also showed the soft nature of ZnO, [8][9][10] which significantly affects the wafer handling, processing, and manufacture of ZnO-based devices. Polishing induced damage has been investigated by cathodoluminescence (CL), [9][10][11][12][13][14][15] photoluminescence (PL), 16,17 ion channeling, 18 positron annihilation spectroscopy (PAS), 19 and deep level transient spectroscopy (DLTS). 20 Both CL and PL research on ZnO demonstrated that mechanical polishing leads to surface and near surface damage, which decreases near band edge (NBE) luminescence efficiency, and forms non-radiative recombination centers (NRRCs) and intrinsic defects such as zinc vacancy (V Zn ) and zinc interstitial (Zn i ).…”

Influence of metal organic chemical vapour deposition growth conditions on vibrational and luminescent properties of ZnO nanorods

“…It is worth to remark that the 3.31 eV band and its phonon replicas present a high intensity, which suggests a lower concentration of defects. 49 Furthermore, the intensity of the DLE luminescence is much lower than the NBE luminescence, showing a very significant reduction in comparison with the DLE luminescence from ZnO nanorods grown on bare c-sapphire. In addition, this band denotes a shift towards high energies, from red to the yellow spectral range ($2.24 eV).…”