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Pressure dependence of the optical properties of wurtzite and rock‐salt Zn 1– x Co x O thin films
Author(s) -
Sans J. A.,
Segura A.,
SánchezRoyo J. F.,
FerrerRoca Ch.,
Guillotel E.
Publication year - 2007
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.200672567
Subject(s) - wurtzite crystal structure , absorption edge , phase transition , analytical chemistry (journal) , absorption spectroscopy , metastability , absorption (acoustics) , thin film , phase (matter) , crystal (programming language) , materials science , pulsed laser deposition , chemistry , band gap , crystallography , condensed matter physics , zinc , optics , nanotechnology , metallurgy , optoelectronics , physics , organic chemistry , chromatography , computer science , composite material , programming language
In this paper we investigate the electronic structure of Zn 1– x Co x O by means of optical absorption measurements under pressure. Thin films of Zn 1– x Co x O with different Co content (from 1 to 30%) were prepared by pulsed laser deposition on mica substrates. Absorption spectra exhibit three main features that are clearly correlated to the Co content in the films: (i) absorption peaks in the infrared associated to crystal‐field‐split internal transitions in the Co 3d shell, with very small pressure coefficients due to their atomic character; (ii) a broad absorption band below the fundamental edge associated to charge transfer transitions, that exhibit relatively large pressure coefficients, indicating that the Co 3d final states must be strongly hybridized to the conduction band; and (iii) a blue‐shifted fundamental absorption edge associated to band to band transitions with a pressure coefficient close to that of pure ZnO. In the up‐stroke the transition pressure from wurtzite to rock‐salt phase decrease almost linearly as the Co increases, from 9.5 GPa in pure ZnO to about 6.5 GPa for x = 30%. In the down‐stroke pressure we observe a similar behavior, yielding a metastable rock‐salt phase at room pressure, after a pressure cycle up to 15 GPa. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)