abstract
The existence of extended defects (i.e., dislocations) in inorganic semiconductors, such as GaN or ZnO, responsible for broad emission peaks in photoluminescence analysis remains unresolved. The possible assignments of these luminescence bands are still matter of discussion. In this study, two different zinc oxide samples, grown under different oxygen partial pressures and substrate temperatures, are presented. Epitaxial and structural properties were analysed by means of X-ray diffraction and transmission electron microscopy techniques. They confirm that the layers are single-phase with a good crystalline quality. Nevertheless, a different density of threading dislocations, with a higher contribution of edge dislocations, was found. Photoluminescence spectroscopy has been used to investigate the optical properties. The steady state luminescence spectra performed at 14K evidenced the donor bound exciton recombination and deep green and red emission bands. The red band with a maximum at 1.78 eV was found to be stronger in the sample grown at lower oxygen pressure which also shows higher density of threading dislocations. From the temperature and excitation density dependence of the red band, a donor acceptor pair recombination model was proposed, where hydrogen and zinc vacancies are strong candidates for the donor and acceptor species, respectively.
keywords
MOLECULAR-BEAM EPITAXY; THREADING DISLOCATIONS; STACKING-FAULTS; THIN-FILMS; SI 111; PHOTOLUMINESCENCE; EMISSION; GAN; TRANSITIONS; DEPENDENCE
subject category
Science & Technology - Other Topics; Materials Science
authors
Felix, R; Peres, M; Magalhaes, S; Correia, MR; Lourenco, A; Monteiro, T; Garcia, R; Morales, FM
our authors
Armando António Cardoso Dos Santos Lourenço
Assistant Professor
Marco António Batista Peres
PhD Studentacknowledgements
This work was partially supported by Junta de Andalucia (Spain) with EU-FEDER cofinancing (PAI group TEP-120 and Project P09-TEP-5403). This work is funded by FEDER funds through the COMPETE 2020 Programme and National Funds through FCT-Portuguese Foundation for Science and Technology under Project UID/CTM/50025/2013. Besides, the authors acknowledge FCT for the funding through PTDC/CTM-NAN/2156/2012 and RECI/FIS-NAN/0183/2012 (FCOMP-01-0124-FEDER-027494) and SFRH/BD/45774/2008 projects from Portugal. The EU COST MP0805 is also acknowledged. In addition, thinning methods to produce electron transparency were performed in the Laboratory for Sample Preparations, and TEM analyses were carried out at the Division of Electron Microscopy, both at the UCA central facilities (SC-ICYT).