Zinc vacancies in the heteroepitaxy of ZnO on sapphire: Influence of the substrate orientation and layer thickness

Nitrogen and vacancy clusters in ZnO

“…Earlier studies on ZnO show that defects related to single Zn vacancies are the main defects observed with positron annihilation spectroscopy. This is seen in both undoped and Al/Ga-doped thin films 21,[26][27][28] as well as in studies in bulk crystals. [10][11][12]22,25 Clusters of vacancies in ZnO have been observed mainly in implantation studies 4,23,[29][30][31][32][33][34][35][36][37][38] and also after heavy irradiation.…”

Changing vacancy balance in ZnO by tuning synthesis between zinc/oxygen lean conditions

“…We characterized the Doppler spectra by conventional line shape parameters representing the fractions of annihilations with low-momentum ͑S͒ and highmomentum ͑W͒ electrons. 8 Figure 1 shows a typical example of the PAS results in MOVPE-ZnO, while the data obtained in the bulk ZnO reference are shown for comparison. The reference sample contains only two annihilation states-surface and lattice ͓see open squares following a linear trend in Fig.…”

“…1͑a͒ and 1͑b͔͒ are used in further analysis. 8 Figure 2 is a W-S plot containing characteristic ͑S, W͒ values of the MOVPE-ZnO films grown at different temperatures. In addition, reference parameters corresponding to the ZnO lattice and V Zn ͑Ref.…”

“…6 A method providing direct means of vacancy-type defect identification in semiconductors and ZnO in particular is positron annihilation spectroscopy ͑PAS͒. 7 To date PAS studies have mostly addressed defect formation in bulk ZnO with only a few reports on MOVPE-ZnO films, 8,9 partly because of a lack of high quality material until recently and also more complicated interpretation of the annihilation data in thin films. On the other hand, vacancy-type defects in ZnO thin films have been extensively studied using photoluminescence ͑PL͒, 10 although the exact correlation of deep-level emission ͑DLE͒ peaks with specific intrinsic defects still remains a matter of ongoing discussions.…”

Positron annihilation studies of defects and fine size effects in nanocrystalline nickel oxide

“…It is to be noted that the thermalised positrons can diffuse through the material over distances typically of the order of a few tens of nanometers in oxide semiconductors, and hence, a fraction of positrons can always traverse through the material to the surfaces of the crystallites if the latter are of diameters less than the thermal diffusion length of positrons. [29,30] In the context of positron annihilation from the defects within the nanoparticles, it should be pointed out that the charge state of the vacancy cluster is a decisive factor, which needs to be discussed here. A cationic monovacancy, resulting due to the absence of a Ni 2þ ion and denoted as V Ni , is negatively charged and hence can attract positrons to it.…”