a b s t r a c tZnO is an efficient luminescent material in the UV-range~3.4 eV with a wide range of applications in optical technologies. Sputtering is a cost-effective and relatively straightforward growth technique for ZnO films; however, most as-grown films are observed to contain intrinsic defects which can significantly diminish the desirable UV-emission. In this research the defect dynamics and optical properties of ZnO sputtered films were studied via post-growth annealing in Ar or O 2 ambient, with X-ray diffraction (XRD), imaging, transmission and Urbach analysis, Raman scattering, and photoluminescence (PL). The imaging, XRD, Raman and Urbach analyses indicate significant improvement in crystal morphology and band-edge characteristics upon annealing, which is nearly independent of the annealing environment. The native defects specific to the as-grown films, which were analyzed via PL, are assigned to Zn i related centers that luminesce at 2.8 eV. Their presence is attributed to the nature of the sputtering growth technique, which supports Zn-rich growth conditions. After annealing, in either environment the 2.8 eV center diminished accompanied by morphology improvement, and the desirable UV-PL significantly increased. The O 2 ambient was found to introduce nominal O i centers while the Ar ambient was found to be the ideal environment for the enhancement of the UV-light emission: an enhancement of~40 times was achieved. The increase in the UV-PL is attributed to the reduction of Zn i -related defects, the presence of which in ZnO provides a competing route to the UV emission. Also, the effect of the annealing was to decrease the compressive stress in the films. Finally, the dominant UV-PL at the cold temperature regime is attributed to luminescent centers not associated with the usual excitons of ZnO, but rather to structural defects.

The MgxZn1−xO alloy system is emerging as an environmentally friendly choice in ultraviolet lighting and sensor technologies. Knowledge of defects which impact their optical and material properties is a key issue for utilization of these alloys in various technologies. The impact of phase segregation, structural imperfections, and alloy inhomogeneities on the phonon dynamics and electronic states of MgxZn1−xO thin films were studied via selective resonant Raman scattering (SRRS) and Urbach analyses, respectively. A series of samples with Mg composition from 0–68% were grown using a sputtering technique, and the optical gaps were found to span a wide UV range of 3.2–5.8 eV. The extent of the inherent phase segregation was determined via SRRS using two UV-laser lines to achieve resonance with the differing optical gaps of the embedded cubic and wurtzite structural domains. The occurrence of Raman scattering from cubic structures is discussed in terms of relaxation of the selection rules due to symmetry breaking by atomic substitutions. The Raman linewidth and Urbach energy behavior indicate the phase segregation region occurs in the range of 47–66% Mg. Below the phase segregation, the longitudinal optical phonons are found to follow the model of one-mode behavior. The phonon decay model of Balkanski et al. indicates that the major contributor to Raman linewidth arises from the temperature-independent term attributed to structural defects and alloy inhomogeneity, while the contribution from anharmonic decay is relatively small. Moreover, a good correlation between Urbach energy and Raman linewidth was found, implying that the underlying crystal dynamics affecting the phonons also affect the electronic states. Furthermore, for alloys with low Mg composition structural defects are dominant in determining the alloy properties, while at higher compositions alloy inhomogeneity cannot be neglected.

The issue of phase segregation, inherent to the MgZnO alloy system, was investigated via selective resonant Raman scattering. We demonstrate that it is a highly sensitive technique for the detection of embedded structural inhomogeneities. MgZnO thin-films with bandgaps that span the UV-range of 3.2–5.7 eV were realized. Under resonant conditions facilitated via different laser excitation energies, the LO-phonon behavior indicated that the phase segregation is in the range of 35%–65% Mg, in which domains of hexagonal-wurtzite and cubic-NaCl structures coexist. The scattering of the forbidden LO-mode of the cubic phase is discussed in terms of inversion-symmetry relaxation due to alloying.

MgZnO is emerging as a vital semiconductoralloy system with desirable optical properties that can span a large range of the UV spectrum. Due to its benign chemical character, MgZnO is considered to be an environmentally friendly material. This paper presents studies on annealing as a useful and straightforward approach for the enhancement of the optical and crystal quality of Mg 0.17 Zn 0.83 O nanocrystalline films grown via DC sputtering. The alloys were studied via several imaging and optical techniques. It was found that high-temperature annealing, *900°C, in Argon atmosphere, significantly improves the solubility of the alloy. This temperature range is consistent with the thermal diffusion temperature of Mg needed for the creation of a soluble alloy. Moreover, the annealing process was found to minimize the undesirable visible luminescence, attributed to Mg and Zn interstitials, while significantly enhancing the bandgap sharpness and the efficiency of the UV-luminescence at *3.5 eV. The analysis indicated that these optical attributes were achieved due to the combined effects of good solubility, an improved morphology, and a reduction of native defects. The annealing was also proven to be beneficial for the reduction of the compressive stress in the alloy: a relaxation *1.8 GPa was calculated via Raman scattering. The inherent stress was inferred to originate mainly from the granular morphology of the alloys.

ZnO is emerging as one of the materials of choice for UV applications. It has a deep excitonic energy level and a direct bandgap of ~3.4 eV. Alloying ZnO with certain atomic constituents adds new optical and electronic functionalities to ZnO. This paper presents research onMgxZn1−xOandZnS1−xOxnanocrystalline flexible films, which enable tunable optical properties in the deep-UV and in the visible range. The ZnO andMg0.3Zn0.7Ofilms were found to have bandgaps at 3.35 and 4.02 eV, respectively. The photoluminescence of theMg0.3Zn0.7Oexhibited a bandedge emission at 3.95 eV, and at lower energy 3.38 eV due to the limited solubility inherent to these alloys.ZnS0.76O0.24andZnS0.16O0.84were found to have bandgaps at 3.21 and 2.65 eV, respectively. The effect of nitrogen doping onZnS0.16O0.84is discussed in terms of the highly lattice mismatched nature of these alloys and the resulting valence-band modification.