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The temperature dependences of pure strain, pure charge, and their coexisting effects are simultaneously investigated with electric fields applied at three individual positions of an unconventional SrTiO3(STO)/Fe3O4/Au/PbZr0.52Ti0.48O3(PZT) multiferroic heterostructure. As the temperature drops, for all situations, the magnetization anomalously decreases with an increment in coercivity. The phenomenon is ascribed to the Verwey transition present in the Fe3O4. However, the magnetic responses to electric field are different for the pure strain and pure charge effects. The maximum strain- and charge-mediated coupling coefficients are 10.51 and 1.26 Oe cm kV−1, respectively, both obtained near the Verwey transition temperature. The combination of the two coupling mechanisms leads to the nonequivalent shift of the Verwey transition temperature under reversed electric fields, which can be explained by their interaction. It is also found that large magnetoelectric couplings can be realized over a broad temperature range when the strain and charge effects simultaneously appear.

Temperature-dependent photoluminescence (PL) properties of ZnO/Zn0.9Mg0.1O multi-quantum wells (MQWs) grown on Si (1 1 1) substrates by pulsed laser deposition have been investigated. For MQWs with well widths of 14 and 3 nm, the predominant excitonic emission in the whole temperature range (8–300 K) is attributed to bound excitons and localized excitons, respectively. The effect of quantum confinement on enhancing the intensity of the excitonic emission is clearly observed in the MQWs with well width of 3 nm, while the effect on blue-shifting the emission energy is not distinct, most probably due to the quantum confined Stark effect. The PL peak from the barrier layers shows an 'S'-shaped shift with increasing temperature due to localization of carriers in the potential minima induced by composition and interface fluctuations. The depth of the potential well is determined to be ~15 meV.

We report on Sb-doped p-type Zn0.95Mg0.05O thin films grown by pulsed laser deposition. The Sb-doped Zn0.95Mg0.05O films show an acceptable p-type conductivity with a resistivity of 126 ohm cm, a Hall mobility of 1.71 cm(2) V-1 s(-1) and a hole concentration of 2.90 x 10(16) cm(-3) at room temperature. Secondary ion mass spectroscopy confirms that Sb has been incorporated into the Zn0.95Mg0.05O films. Guided by x-ray photoemission spectroscopy analysis and a model for large-size- mismatched group-V dopants in ZnO, an Sb-Zn-2V(Zn) complex is believed to be the most possible acceptor in the Sb-doped p-type Zn0.95Mg0.05O thin films. ispartof: Journal of Physics D, Applied Physics vol:40 issue:14 pages:4241-4244 status: published

Quasi-aligned Zn1?xMgxO nanorods have been synthesized on Si substrates by thermal evaporation. The Mg content (x) in Zn1?xMgxO nanorods was 0.23, higher than that in the source materials by a factor of about 1.9. Zn1?xMgxO (x = 0.23) nanorods showed a wurtzite ZnO structure with the c-axis constant of 0.5179?nm. The nanorods grew along the [0?0?0?1] crystal direction and had uniform and flat hexagonal planes with diameters of about 200?nm. Photoluminescence measurements revealed that the predominant ultraviolet (UV) emission of Zn1?xMgxO (x = 0.23) nanorods was centred at 3.78?eV, with a ~0.51?eV blueshift from the UV emission line (3.27?eV) of ZnO nanorods. This blueshift indicated the bandgap engineering in nanostructures of Zn1?xMgxO ternary alloys.

Li-doped p-type Zn0.95Mg0.05O thin films have been achieved on glass substrates by pulsed laser deposition. X-ray diffraction shows that all the films exhibit good crystallinity with a highly c-axis preferential orientation. The results of the Hall measurements indicate that p-type conduction in Li-doped Zn0.95Mg0.05O films is strongly dependent on the oxygen pressure. Films deposited at 5 and 25 Pa show n-type conduction. However, at the oxygen pressure of 15 and 20 Pa, the films show definitive p-type conductivity. The maximal hole concentration was found to be 1.26 × 1018 cm−3 at a working pressure of 20 Pa with a resistivity of 17.82 Ω cm and Hall mobility of 0.285 cm2 V−1 s−1. Furthermore, all the p-type Zn0.95Mg0.05O films possess high average transmittance of ~90% in the visible region and a band gap of 3.41 eV at room temperature.

Nominally undoped and N-doped ZnO thin films were grown by plasma-assisted metalorganic chemical vapour deposition. P-type conductivity was confirmed by Hall-effect measurements, not only in the N-doped but also in the nominally undoped ZnO. The zinc vacancy and extrinsic nitrogen acceptor states were identified by low-temperature photoluminescence, with the energy level located at 270 meV and 180 meV above the valence-band maximum, respectively. An evident increment in the oxygen as well as nitrogen concentration in the p-type ZnO : N layer was well confirmed by secondary ion mass spectroscopy.

Dendritic ZnMgO nanostructures were synthesized on Si(111) substrates by a catalyst-free thermal evaporation method using Zn and Mg powder as the source materials. The structural, compositional and optical properties were investigated by field emission scanning electron microscopy, x-ray diffraction, transmission electron microscopy, Raman scattering and photoluminescence. The results indicate that the incorporated Mg in the as-grown nanostructures mainly form a separated cubic MgO phase. By annealing in oxygen, hexagonal ZnMgO can be formed with the dendritic nanostructures maintained, which exhibits a blueshift of ~0.05 eV in the near band edge emission. It is possible to tune the Mg content in the nanostructures simply by varying the distance between the substrate and the source materials.

Al-doped quasi-aligned ZnO submicro-rods were prepared on heavily doped n-type Si(111) substrates by the thermal evaporation method. Electrical transport measurements indicate the Al-doped ZnO submicro-rods have better conductivity than the undoped submicro-rods. The photoluminescence excitation spectrum of the annealed sample indicates an energy level ~100 meV below the conduction band minimum, which may be due to the localized state of the Al impurity. The annealed sample exhibits a strong green emission centred at 2.45 eV that can be seen by the naked eye and an infrared emission centred at 1.10 eV. The intensity ratios of the deep-level green emission to the ultraviolet emission are 0.86 and 30 for the as-grown and annealed samples, respectively. Moreover, two emissions at 2.2 and 1.96 eV were discriminated from the PL spectrum of the as-grown Al-doped ZnO submicro-rods, which were not observed in the pure ZnO submicro-rods and the annealed Al-doped sample.

Fourier transform infrared absorption and photoluminescence (PL) spectroscopy were used to investigate the defects in a codoped ZnO : Al : N film grown on a Si (111) substrate. Two broad vibrational modes around 3000 and 3120 cm−1 were found, which may be attributed to the formation of N–H bonds in different configurations. The room temperature PL spectrum of the ZnO : Al : N film exhibited two dominant emissions centred at 3.04 and 2.77 eV. PL decay and x-ray photoelectron spectroscopy results suggested that the 3.04 eV emission is not likely due to zinc vacancy. We assumed that it might correlate with the N-related defect. The 2.77 eV emission was tentatively assigned to recombination involving an unknown deep localized defect.

Ternary ZnCdO single-crystal nanorods with a high Cd incorporation of about 16 at% were synthesized onto Au-catalyzed Si substrate using a physical vapour deposition method. Field emission scanning electron microscopy observation, x-ray diffraction analysis and Raman spectrum showed that the ZnCdO nanorods were well-aligned along the c-axis. Raman spectrum revealed that the E2 (high) mode of the ZnCdO nanorods shifted towards the higher frequency side by 5 cm−1 with respect to that of pure bulk ZnO, corresponding to biaxial compressive stress of 1.14 GPa. The near-band-edge emission of ZnCdO red-shifted to 3.04 eV due to Cd substitution. The defect-related emission exhibited anomalous phonon replicas with an energy of 102 meV, which was attributed to the disorder-activated B1 phonon mode.

Cu-doped ZnO (ZnCuO), Cu–Ga co-doped ZnO (Zn(Cu,Ga)O) and Cu–Na co-doped ZnO (Zn(Cu,Na)O) diluted magnetic semiconductor thin films have been deposited on (0 0 0 1) sapphire substrates by pulsed laser deposition. All the films have a hexagonal wurtzite ZnO structure with a high c-axis orientation. Hall-effect measurements showed that the ZnCuO film is n-type, in which the carrier concentration is greatly enhanced by the addition of Ga, while the introduction of Na resulted in p-type behaviour with a high resistivity. The magnetic hysteresis measurement indicated that the pure ZnCuO film is ferromagnetic at room temperature. Doping of Ga (n-type dopant) does not have a significant effect on the room temperature ferromagnetism. However, the room temperature ferromagnetic behaviour is destroyed by the addition of Na (p-type dopant). X-ray photoelectron spectroscopy analyses revealed that there exist more oxygen defects in the ZnCuO, Zn(Cu,Ga)O films than in the Zn(Cu,Na)O film. It was suggested that the interaction of Cu2+ with the oxygen defect in an n-type environment is responsible for the ferromagnetism observed in the ZnCuO system.

The conduction types of Na-doped ZnO films with different Na contents were investigated by repeated Hall-effect measurements and rectification behaviour of ZnO : Al/ZnO : Na homojunctions. A p-type ZnO : Na film with a resistivity of 13.8–19 Ω cm, Hall mobility of 0.12–1.42 cm2 V−1 s−1 and hole concentration of 4.78 × 1017–4.66 × 1018 cm−3 was achieved, and it was electrically stable over 9 months. The effect of the Na concentration on the conductivity of ZnO films was discussed tentatively from the results of x-ray diffraction and Hall-effect measurements as well as from the viewpoint of Madelung energy. Electroluminescence was obtained at 160 K from the optimized p–n homojunction on the silicon substrate.

ZnO/cubic (Zn, Mg)O core–shell heterostructure nanorods with wire-shaped tips have been synthesized via a catalyst-free thermal evaporation process on Si substrates. The average diameters were about 180 nm for nanorods and about 20 nm for tips. Transmission electron microscopy (TEM) investigations revealed that the tip was a single-crystalline cubic structure and grew along the [2 0 0] direction. A two-step growth process was used to synthesize the ZnO/(Zn, Mg)O heterostructure nanorods; that is, Zn and Mg powders were first evaporated at 630 °C and then the temperature was raised to 750 °C. High-resolution TEM and energy dispersive x-ray spectroscopy analysis confirmed that the product is pure ZnO at the first step. X-ray diffraction, photoluminescence and TEM results indicated that a final heterostructure nanorod consisted of a wurtzite ZnO core and a cubic (Zn, Mg)O shell. The growth temperature and process control were suggested to be responsible for the formation of heterostructure nanorods.

In the inset plot of the previously published figure 8, the horizontal scale in °C was incorrectly numbered from 250 to 450 °C, but should be corrected to range from 200 to 400 °C, as shown below. Figure 8. Spectral dependence of the transmittance of ZnO:Ga films in the wavelength range of 300--450 nm: (a) 200 °C; (b) 250 °C; (c) 300 °C; (d) 350 °C; (e) 400 °C. The inset shows the variation of optical band gap with substrate temperature for ZnO:Ga films.

Highly near-infrared (IR) reflecting and transparent conducting Ga-doped ZnO films were deposited on a glass substrate by dc reactive magnetron sputtering. The influence of substrate temperature on the structural, electrical and optical properties of the films was investigated. A lowest resistivity of 3.0 × 10−4 Ω cm was obtained at the substrate temperature of 300 °C. The average transmittance of the films is over 90% in the visible range. The IR transmission cut-off wavelength of the films shifts towards the lower wavelength with increasing electron concentration. All the films have low transmittance and high reflectance in the near-IR region. The IR reflectance of the films shows an increase with increasing electron concentration.