Zinc oxide (ZnO) is a semiconductor that emits bright UV light, with little wasted heat. This intrinsic feature makes it a promising material for energy-efficient white lighting, nano-lasers, and other optical applications. For devices to be competitive, however, it is necessary to develop reliable p-type doping. Although substitutional nitrogen has been considered as a potential p-type dopant for ZnO, recent theoretical and experimental work suggests that nitrogen is a deep acceptor and will not lead to p-type conductivity. In nitrogen-doped samples, a red photoluminescence (PL) band is correlated with the presence of deep nitrogen acceptors. PL excitation (PLE) measurements show an absorption threshold of 2.26 eV, in good agreement with theory. The results of these studies seem to rule out group-V elements as shallow acceptors in ZnO, contradicting numerous reports in the literature. Optical studies on ZnO nanocrystals show some intriguing leads. At liquid-helium temperatures, a series of sharp IR absorption peaks arise from an unknown acceptor impurity. The data are consistent with a hydrogenic acceptor 0.46 eV above the valence band edge. While this binding energy is still too deep for many practical applications, it represents a significant improvement over the 1.4-1.5 eV binding energy for nitrogen acceptors. Nanocrystals present another twist. Due to their high surface-to-volume ratio, surface states are especially important. In our model, the 0.46 eV level is shallow with respect to the surface valence band, raising the possibility of surface hole conduction.

Nanowires with different nitrogen concentrations were grown by Metal-Organic Chemical Vapor Deposition (MOCVD) using DEZn, N2O and NH3as zinc, oxygen and nitrogen doping sources respectively. Low temperature photoluminescence, Raman spectroscopy and Transmission Electron Microscopy are combined to study the incorporation of nitrogen in the wires. The observation of donor-acceptor pair band confirms that the incorporation nitrogen in ZnO nanowires is responsible for the creation of acceptor centers. The additional peaks observed in Raman are correlated to nano-sized inter-atomic distance fluctuations observed in TEM. These domains combined with a resonance effect are probably the explanation of the huge Raman cross section observed for the impurity related peaks.

To apply thin ZnO film to photoacoustic tomography sensors, we investigated methods to improve its piezoelectricity with high optical transmittance. ZnO film was deposited by RF magnetron sputtering on a quartz substrate with various changes of the following conditions: RF sputtering power, Ar gas pressure, and substrate temperature (TSUB). The preliminary optimization of sputtering conditions is to form the ZnO film with good c-axis crystalline alignment. The results of X-ray diffraction measurement and cross-sectional observations indicated that the high-TSUB condition was preferable. This was because the desorption of Zn due to high-TSUB during the deposition process induced the formation of excellent columnar grains normal to the substrate. To enhance the piezoresponse, the substitution of Zn with different crystal-radius atoms was investigated, the aim being to increase the electrically neutral dipole moment by the partial displacement of the Zn-O bond. The transition metal V, with the potential to have the various configurations and coordination numbers, was selected as the dopant. As a result, it was confirmed that the diffraction peak from the (002) plane shifted to low angles with small degradation of the diffraction intensities.

Recently, the oxides have received attention and great interest due to their magnetic ordering above of the room temperature by doping a very low amount of transition metal ions, which are very promising for applications such as biosensing, hyperthermia, doped magnetic semiconductors with lower energy losses and rapid response at alternating-magnetic fields. In this work the magnetic interactions on Fe doped ZnO thin-films was studied. Raman spectroscopy allowed the monitoring of iron ions diffusion and demonstrated that symmetry modes are crucial for understanding of the magnetic ordering. X-ray diffraction (XRD) was used to determine the oxidation state of the iron ions and stress into ZnO lattice. MFM confirmed that magnetic moments and magnetic forces on scanned surface depend on magnetic-domain structure formation.

The effect of oxygen vacancy (VO) on the electronic and magnetic properties of ZnCoO was studied with first principle methods based on density functional theory (DFT). Calculations were performed, on a periodic 3×3×3 wurtzite supercell of ZnO which consists of 108 atoms with two Co ions substituted for two Zn atoms, using the generalized gradient approximation with Hubbard U correction method (GGA+U). We have studied the interatomic exchange interaction with and without VO for different configurations with different magnetic atom lattice arrangements. The total energies, electronic structures and magnetic moments were calculated for each configuration.

Cu-doped ZnO film in nanowire structure is synthesized by a closed space flux sublimation and periodic oxidation method at ∼300°C over Si substrate. Oxidative process controlled selfcatalytic VLS mechanism is proposed for the film growth. X-ray diffraction pattern establishes that Cu-doped ZnO nanowires retain the crystallite structure of the wurtzite ZnO. TEM studies indicate single crystal character of the Cu-doped ZnO nanowires. Optical absorption analysis of Cu-doped ZnO nanowires defines two direct energy band gaps. The low energy band gap at 3.2eV is intrinsic to the Cu-doped ZnO material. The higher energy band gap at 3.5eV is attributed to the nanosize, mediated by strong forward scattering of light from the nanowires. Sharp photoluminescence in Cu-doped ZnO corresponding to near bandgap free exciton emission is observed and a redshift of ∼0.07 eV is consistent with the effect of Cu-doping. The visible emission band in both ZnO and Cu-doped ZnO shows a broad green emission band with Cu-substitution shifting the maximum visible luminescence towards the higher energy side.

Ultraviolet photoconductivity in Copper doped ZnO (Cu:ZnO) thin films synthesized by sol-gel technique is investigated. Response characteristics of Pure ZnO thin film and Cu:ZnO thin film UV photodetector with 1.3 at. wt % Cu doping biased at 5 V for UV radiation of λ = 365 nm and intensity = 24 µwatt/cm2 has been studied. Cu:ZnO UV photodetector is found to exhibit a high photocoductive gain (K = 1.5×104) with fast recovery (T90% = 23s) in comparison to pure ZnO thin film based photodetector (K = 4.9×101 and T90% = 41s). Cu2+ ions have been substituted in ZnO lattice which has been confirmed by X-ray diffraction (XRD) and Raman spectroscopy leading to lowering of dark current (Ioff ∼ 1.44 nA). Upon UV illumination, more electron hole pairs are generated in the photodetector due to the high porosity and roughness of the surface of the film which favours adsorption of more oxygen on the surface of the photodetector. The photogenerated holes recombined with the trapped electrons, increasing the concentration of photogenerated electrons in the conduction band enhancing the photocurrent (Ion ∼ 0.02 mA) of the Cu:ZnO photodetector.

GaZnO and GaZnON thin films were deposited on both Si (100) and c-axis oriented sapphire substratesby RF co-sputtering of ZnO target and Ga2O3tablets in Ar/O2 and Ar/N2, respectively, by changing the number of Ga2O3tablets (NGa2O3) placed on the ZnO target in the range of 0 to 16.They were subsequently annealed in N2 at 800 °C and then, some of the samples formed by Ar/O2-sputtering were subjected to NH3 treatment at 650 °C for nitridation. XRD measurements revealed that the c-axis lattice parameter calculated from the ZnO (002) peak for GaZnON film son Si (100) was remarkably larger than for GaZnO films on Si (100). Moreover, ZnO (002) was observed up to NGa2O3=16 for GaZnON films formed on sapphire, while no XRD peaks were observed above NGa2O3=8 for GaZnON films on Si(100). Optical band-gap ofGaZnO and GaZnON films became wider from 3.34to 3.67 eVand from 3.21to 3.40 eV, respectively, with increasing NGa2O3 from 0 to 16. Photoluminescence spectra of GaZnO films showed band-to-band emission at 380nm, while those of GaZnON films exhibited broad and weak peaks centered at 550 nm and 647nm.

We analyze the influence of the Mg concentration on several important properties of the band structure of Zn1-xMgxO alloys in wurtzite structure using ab initio calculations. For this purpose, the band structure for finite concentrations is defined in terms of the Bloch spectral density, which can be calculated within the coherent potential approximation. We investigate the concentration dependence of the band gap and the crystal-field splitting of the valence bands. The effective electron and hole masses are determined by extending the effective mass model to finite concentrations. We compare our results with experimental results and other calculations.

ZnO has a huge potential and is already a crucial material in a range of key technologies from photovoltaics to opto and printed electronics. ZnO is being characterized by versatile metrologies to reveal electrical, optical, structural and other parameters with the aim of process optimization for best device performance. The aim of the present work is to reveal the capabilities of vacuum ultra-violet (VUV) reflectometry for the characterization of ZnO films of nominally 50 nm, doped by Ga and In. Optical metrologies have already shown to be able to sensitively measure the gap energy, the exciton strength, the density, the surface nanoroughness and a range of technologically important structural and material parameters. It has also been shown that these optical properties closely correlate with the most important electrical properties like the carrier density and hence the specific resistance of the film. We show that VUV reflectometry is a highly sensitive optical method that is capable of the characterization of crucial film properties. Our results have been cross-checked by reference methods such as ellipsometry and X-ray fluorescence.

Nanoporous ZnO films are fabricated using a two step approach: sputter deposition of porous Zn followed by an ex-situ annealing in an oxygen flow at 400°C. The created structures have a porosity of 34% enabling use in surface-based absorption sensors. The films are used in a resistance-based sensor allowing easy discrimination between liquid methanol and ethanol by resistance measurements and also in a transmission-based sensor to detect NO2, NH3 and H2 gases in concentration as low as 500 ppm.

Thin films of ZnO co-doped with lithium and phosphorus were deposited on sapphire substrates by RF magnetron sputtering. The films were sequentially deposited from ultra pure ZnO and Li3PO4 solid targets. Post deposition annealing was carried using a rapid thermal processor in O2 and N2 at temperatures ranging from 500 °C to 1000 °C for 3 min. Analyses performed using low temperature photoluminescence spectroscopy measurements reveal luminescence peaks at 3.359, 3.306, 3.245 eV for the co-doped samples. The x-ray diffraction 2θ-scans for all the films showed a single peak at about 34.4° with full width at half maximum of about 0.17°. Hall Effect measurements revealed conductivities that change from p-type to n-type over time.

Magnesium doped ZnO films were electrochemically grown on the NESA conductive glass substrate from the magnesium nitrate aqueous solution with zinc sulfate, kept at 323K and the cathodic potential of -0.9V vs. Ag/AgCl. The Mg/(Mg+Zn) atomic ratio of Zn1-xMgxO films increased with the decrease in the zinc sulfate concentration. The optical band gap energy of these Zn1-xMgxO films decreased with increasing content of zinc sulfate. Thus, the optical band gap energy and Mg/(Mg+Zn) atomic ratio of Zn1-xMgxO films would depend on the zinc sulfate concentration.

Thermal effects on the crystal structure, electrical and optical characteristics of the Al and F co-doped ZnO films (ZnO:AlF3) are discussed in the paper. The ZnO:AlF3 thin films are prepared by RF sputtering with a constant power (ZnO/AlF3=100W/75W) toward the ZnO and AlF3 targets. The substrate temperature varied from room temperature to 250 °C with a step of 50 °C during thin film deposition. The crystalline quality of the ZnO:AlF3 film improved as the substrate temperature increased, with a corresponding increase in grain size. The improvement of the film quality leads to a higher electron mobility, with electron mobility of 0.85 cm2/V-s for the film deposited at the substrate temperature of 250 °C. The doping effect of fluorine in ZnO, and hence carrier concentration, was reduced at high temperature due to the vaporization of fluorine. This led to a reduction of carrier concentration with increase of temperature from 25 to 200°C. The corresponding resistivity increased from 3.60×10−2 to 6.0×10−2 Ω-cm. While for a further increase in substrate temperature, the doping of Al to the ZnO film was increased and resulted in an increase in carrier concentration.

Based on the electron configurations of Mo and Zn, the valence electron difference between Mo6+ and Zn2+ is 4. Therefore, a small amount of Mo doping can produce sufficient free carriers to reduce the ion scattering effects. The Mo doped ZnO (MZO) thin film prepared by RF sputtering was studied in this research. Structural, electrical, and optical characteristics of the films were discussed. The MZO film shows a resistivity of 1.1 × 10-2 Ω⋅cm, a carrier concentration of 2.2 × 1021 cm-3,a mobility of 0.63 cm2/V⋅s, and average transparency of 81.0% at both the powers of 20 W to the Mo target and of 125 W to the ZnO target. The MZO film becomes a stable p-type semiconductor at high power process toward Mo target. The film preserves its p-type characteristics after exposure to air for one and a half months. The crystal structure of the p-ZnO films is amorphous with an average transparency of 34.5%.

The junction characteristics between ZnO:Ga (GZO) film and p-Si substrate are discussed in the research. For the transparent semiconductor ZnO, the element Ga is chosen to be the dopant source to produce a high quality n-type ZnO thin film. The ZnO:Ga (GZO) film shows a average transmittance is 84.7% (above 400 nm), a bandgap energy of 3.37 eV, a carrier concentration of 7.29×1013 cm−3and a resistivity of 118 Ω-cm. For the GZO/p-Si junction, it shows a junction barrier height of 0.54 eV with an ideality factor of 1.24. The capacitance-voltage measurement shows that it has a uniform reverse bias depletion layer. The Cheung function is also brought to discussion the diode characteristics.

We present an investigation of the degree of oxidization of tungsten oxide (WOx) thin films used as gate dielectric for metal-insulator-semiconductor field-effect transistors (MISFET). By means of X-ray photoelectron spectroscopy WOx thin films grown by pulsed-laser deposition at room temperature were investigated. The electrical and optical properties depend significantly on the oxygen pressure during deposition and are affected by the stoichiometric ratio of oxygen and tungsten.

Mg@ZnO thin films were prepared by DC/RF magnetron co-sputtering in (N2+O2) ambient conditions using metallic Mg and Zn targets. We present a comprehensive study of the effects of film thickness, variation of O2 content in the working gas and annealing temperature on the structural, optical and magnetic properties. The band gap energy of the films is found to increase from 4.1 to 4.24 eV with the increase of O2 partial pressures from 5 to 20 % in the working gas. The films are found to be ferromagnetic at room temperature and the saturation magnetization increases initially with the film’s thickness reaching a maximum value of 14.6 emu/cm3 and then decreases to finally become diamagnetic beyond 95 nm thickness. Intrinsic strain seems to play an important role in the observed structural and magnetic properties of the Mg@ZnO films. On annealing, the as-obtained ‘mostly amorphous’ films in the temperature range 600 to 800°C become more crystalline and consequently the saturation magnetization values reduce.

ZnO single crystal substrates grown by the hydrothermal method have been characterized by grazing incidence X-ray topography using both monochromaticand whitesynchrotron X ray beams.11$\bar 2$4 reflection wasrecorded from the (0001) wafers and the different contrast patterns produced by different threading defects were noted. To uniquely identify the Burgers vectors of these threading dislocation defects, we use raytracingsimulation to compare with observed defect contrast. Our studies showed that threading screw dislocations are not commonly observed.Most threading edge dislocationshavetheBurgers vector of1⁄3[2$\bar 1$$\bar 1$0] or1⁄3[12$\bar 2$10]and a density of 2.88×104/cm2.

Zinc oxide (ZnO) with excellent crystallinity and large electron mobility was grown on aplane (11-20) sapphire (a-Al2O3) substrates by a new chemical vapor deposition method via the reaction between dimethylzinc (DMZn) and high-energy H2O produced by a Pt-catalyzed H2-O2 reaction. The electron mobility at room temperature increased from 30 cm2/Vs to 189 cm2/Vs with increasing film thickness from 0.1 μm to approximately 3 μm. Electron mobility increased significantly with decreasing temperature to approximately 110 – 150 K, but decreased at temperatures less than 100 K for films greater than 500 nm in thickness. On the other hand, the mobility hardly changed with temperature for films lesser than 500 nm in thickness. Based on the dependence of the electrical properties on the film thickness, the ZnO films grown on a-Al2O3 substrates are considered to consist of an interfacial layer with a high defect density (degenerate layer) generated due to a large lattice mismatch between ZnO and Al2O3 substrates and an upper layer with a low defect density.