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(a)–(e): ERD depth profiles of Zn, Mg (continuous lines), and O (short-dashed line) of the Zn1– x Mg x O thin films investigated in this work. The long-dashed lines represent linear fits to the Zn and Mg profiles. The vertical short-dashed line marks the interface between epitaxial film and sapphire substrate. (f)–(j): The corresponding PL spectra (continuous lines) and absorption spectra (open circles) recorded at T = 4.2 K. For the absorption measurements also the cumulative fitting curve according to Ref. 18 is shown.
(a) PL (continuous line) and absorption (open circles) spectra of a Zn0.89Mg0.11O epitaxial film measured at T = 4.2 K. The position of the PL zero phonon line (ZPL) and of the one phonon sideband (1 LO) are indicated. Also shown is the cumulative fit (solid line) to the absorption spectrum according to Ref. 18 and the individual contributions (dashed curves) from discrete exciton states (DES), their phonon complexes (EPCs) and from the exciton continuum. A and B excitons cannot be spectrally separated due to the alloy broadening, and therefore are subsumed into a single absorption line . (b) Stokes shift (circles) and extracted broadening parameter Γ (triangles) as a function of the Mg concentration x. The open symbols correspond to the thick film.
Dependence of the PL peak energy at 4.2 K and bandgap as determined by absorption measurements at 4.2 K and at RT on the Mg content.
Reciprocal space maps of the 205 reflex of Zn1– x Mg x O thin films investigated in the present work. The crosses mark the center position of the 205 reflexes from which the a- and c-lattice parameters are extracted (also indicated in the graphs).
Dependence of the a- and c-lattice parameters on the Mg concentration x. The long-dashed straight lines illustrate the variation of the lattice parameters for relaxed growth according to Ref. 8 . The solid line in (a) represents a quadratic fit to the data. The solid line in (b) is calculated using the expression for the effective Poisson ratio in Eq. (2) . The open symbols represent the lattice parameters of the film.
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