Photoluminescence study of basal plane stacking faults in ZnO nanowires

We have investigated the photoluminescence (PL) of ZnO nanowires (NWs) containing a high density (~1×106 cm-1) of basal plane stacking faults (BSFs). It was observed that the BSFs result in a specific PL peak at ~3.329 eV along with a donor bound excitonic emission (DoX) peak at 5 K. The observed BSF-related emission is of excitonic type and possesses longer PL lifetime than DoX (~360 ps vs. ~70 ps). Via comparison of the microstructural and the PL properties of the ZnO NWs, it is shown that the observed BSF-related emission is due to the formation of crystal phase quantum wells (QWs). This is explained by the fact that BSF in wurtzite (WZ) ZnO is the thinnest segment of zinc blende (ZB) phase ZnO inserted in the WZ matrix, resulting in band alignment of type II due to the conduction and valence band offsets of ZB with respect to WZ ZnO. The mechanism of the BSF related PL is suggested to be an indirect exciton transitions due to the recombination of electrons confined in the ZB QWs to holes in the WZ barriers localized near the BSFs. © 2013 Elsevier B.V. All rights reserved

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The local features of light emission from ZnO microrods were studied: it is revealed that ZnO luminescence spectra are significantly influenced by the crystal morphology. It is shown that the near and edge ultraviolet emission occurs primarily from the top (0001) planes of ZnO microrods; while the defect related visible emission was found to occur dominantly from the side facets. The room temperature cathodoluminescence analysis revealed that visible emission consists of a few overlapping peaks, arising due to recombination on common points and surface defects (Zni, Vo, Vo 0 /Vo * * , Vo ** and surface defects.). While at low temperature, only the luminescence due to neutral donor bound exciton (D 0 X) emission is observed. The data obtained suggest that the light emission spectra of ZnO material of diverse morphology can not be directly compared, although some common spectral features are present

Complementary study of the photoluminescence and electrical properties of ZnO films grown on 4H-SiC substrates

We have studied the photoluminescence and electrical properties of ZnO films grown epitaxially by atmospheric pressure MOCVD on 4H-SiC substrates. The dominating D°X line on the low temperature PL spectrum is attributed to the emission of an exciton bound to the neutral donor. The intensity of this line correlates with the electrical properties of the films: the decrease of D°X intensity occurs simultaneously with the increase of the carrier׳s mobility. This we explain as donor activation providing free electrons to the conduction band. Based on the comparison of the calculated value of donor binding energy, the literature data and complementary SIMS analysis a suggested donor impurity is aluminum (Al). The exciton localization energy is 16.3 meV, and agrees well with localization energy of 15.3 meV for Al impurity reported by other authors (e.g. Ref. [33]). The thermal activation energy ED=22 meV, determined from the Hall data and is in agreement with the optical activation energy ~20 meV, which is derived from the temperature-dependent PL study. The calculated value of the donor binding energy of 54.3 eV is in agreement with the ionization energy of 53 meV mentioned in earlier reports for Al in ZnO films. Our results prove that the commonly observed line at ~3.3599 eV on low temperature PL spectra of ZnO is a neutral donor bound exciton emission due to the Al impurity