I. V. Markevich

ZnO films were grown on p-type Si substrates by radio-frequency magnetron sputtering of ZnO target in pure argon or mixed argon-oxygen plasma and were investigated using atomic force microscopy, spectroscopic ellipsometry, Fourier-transformed infrared spectroscopy and electrical methods. It was observed that the films grown in argon plasma had large surface roughness which increases with the rise of deposition time. The lateral size of ZnO columns showed similar dependence on deposition parameters as the roughness. Contrary to this, the films produced in argon-oxygen plasma were found to be smoother and denser having thinner ZnO columns. These films also demonstrated an abrupt absorption band-gap edge that is the evidence of better crystalline quality of these films (the lower number of native point and elongated defects). Plasmon-phonon interaction in ZnO films as well as the effect of the plasmon system of Si substrate on this interaction was considered. The theoretical approach used for the fitting of specular infrared reflection spectra allowed determining concentration and mobility of free carriers as well as conductivity of ZnO films. It was found that the films grown in pure argon plasma demonstrated a higher concentration and a smaller mobility of free carriers in the comparison with the corresponding parameters of the films grown in argon-oxygen mixed plasma. The direct resistivity measurements show the essentially higher values compared with the values estimated from IR reflection spectra. The possible reasons of this difference are discussed. The utility of infrared reflection spectroscopy for the non-destructive analysis of electro-physical properties of polycrystalline films was shown.

ZnO ceramics undoped and doped with manganese are investigated. The Mn content NMn is varied from 1019 to 1021 cm−3. The photoluminescence (PL), diffuse reflection, and photoconductivity (PC) spectra are measured. The quenching of the self-activated ZnO emission and the appearance of the light absorption and PC are observed in the same spectral region (400–600 nm) under the doping. Simultaneously, a week PL band peaked at 645 nm arose and was assigned to intra-shell transitions in Mn2+Zn centers. Based on the analysis of obtained results, the quenching effect is attributed to the re-absorption of the self-activated ZnO emission by Mn ions. A scheme of electron transitions that allows an explanation of the low intensity of the Mn-related emission is proposed.

The effect of thermal annealing on the luminescence of wurtzite ZnMgO alloys in the films and ceramics produced by solid state reaction route is investigated. Formation of hexagonal ZnMgO phase is proved by X‐ray diffraction, micro‐Raman, photoluminescence (PL), and PL excitation methods. Mg starts incorporating into ZnO lattice at 700 °C, and its content increases with the increase of the annealing temperature up to 1000 °C. Nevertheless, in the PL spectra of the films annealed in air at 1000 °C, excitonic and defect‐related emissions from residual ZnO phase dominate, while those from the ZnMgO alloy are weak. The annealing in Zn vapor results in even weaker ZnMgO PL. In ceramics sintered in the air at 1000 °C, the PL from wurtzite ZnMgO phase is found to be strongly supressed on the surface and bright in the depth of a pellet. The gettering of Na, K, and Ca residual impurities at the surface of the samples under annealing is proved by Secondary ion mass spectrometry. It is proposed that degradation of ZnMgO PL in the near surface region is caused mainly by intense thermal decomposition of wurtzite ZnMgO phase accompanied by generation of non‐radiative defects.

The photoluminescence (PL) and PL excitation (PLE) spectra of undoped and thermally doped with Mn ZnS single crystals are studied. In the PL spectra, the bands caused by Mn-related and self-activated (SA) emission centers were observed. A number of narrow peaks whose intensity enhanced with increasing Mn content were found in the PLE spectra of SA emission. The same peaks were present in the PLE spectra of the Mn-related emission band. Some of these peaks were previously observed in the absorption spectra and attributed to Mn ²⁺ ions. The appearance of Mn-related peaks in the PLE spectra of SA emission is explained by excitation transfer from the Mn ²⁺ ions to SA emission centers. The conditions required for this transfer and possible mechanisms of the process are discussed.

The results of the investigations of photoluminescence (PL) in ZnO and ZnO-based composite materials are presented. The PL and PL excitation (PLE) spectra of undoped and doped with I group elements or rear earth ions ZnO polycrystalline films, ZnO, Zn_1–xMg_xO and ZnMgO–TiO₂ ceramics were studied. The structural properties of the samples were investigated with X-ray diffraction. Polycrystalline films were prepared by a screen-printing method and annealed at T_S = 500–1000 °C. The films annealed at T_S < 800 °C exhibited intense UV emission, whereas defect-related one appeared at 800 °C and enhanced with increasing T_S. Improvement of the PL and structural characteristics of ZnO films due to Li-doping were achieved. The PL bands caused by Sm and Ho ions were observed under ZnO band-to-band excitation. In the PL spectra of ZnO and Zn_1–xMg_xO ceramics, two types of PL bands were separated: i) the bands, whose spectral positions were not influenced by the Mg content (green Cu-related as well as self-activated orange and red ones); ii) the bands, spectral positions of which exhibited some blueshift with increasing Mg content (orange Li- and Ag-related and self-activated green ones). In the PL spectra of ZnMgO–TiO₂ composites, an intense red emission was found to appear in addition to the broad blue-orange band inherent in ZnMgO alloy. The red emission was ascribed to Mg₂TiO₄ inclusions in ZnMgO matrix.