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A simple and efficient method to grow continuous large-area ZnO/MoS2 heterostructures is demonstrated by pulsed laser deposition. The layer number of MoS2 films is controlled by the number of laser pulses. The MoS2 film acts as a closely lattice-matched buffer layer for the subsequent ZnO growth, which improves the structural and optical quality of the ZnO film. ZnO film and multilayer MoS2 forms a type-II heterostructure, and the band offsets between them are quantitatively determined.

Solution-processable perovskites show highly emissive and good charge transport, making them attractive for low-cost light-emitting diodes (LEDs) with high energy conversion efficiencies. Despite recent advances in device efficiency, the stability of perovskite LEDs is still a major obstacle. Here, we demonstrate stable and bright perovskite LEDs with high energy conversion efficiencies by optimizing formamidinium lead iodide films. Our LEDs show an energy conversion efficiency of 10.7%, and an external quantum efficiency of 14.2% without outcoupling enhancement through controlling the concentration of the precursor solutions. The device shows low efficiency droop, i.e. 8.3% energy conversion efficiency and 14.0% external quantum efficiency at a current density of 300 mA cm−2, making the device more efficient than state-of-the-art organic and quantum-dot LEDs at high current densities. Furthermore, the half-lifetime of device with benzylamine treatment is 23.7 hr under a current density of 100 mA cm−2, comparable to the lifetime of near-infrared organic LEDs., Light-emitting diodes based on halide perovskites have made remarkable progress but their stability is the bottleneck. Here Miao et al. show 14% quantum efficiency at a current density of 300 mA cm-2 and 23.7 hr lifetime under a current density of 100 mA cm-2, making it promising for actual application.

Na-doped ZnMgO films have been deposited on quartz substrates by pulsed laser deposition and the effect of the oxygen pressure on their electrical properties investigated. The film deposited under optimal conditions exhibited p-type conductivity with representative hole concentration of 1.2 × 1015 cm−3, Hall mobility of 8.3 cm2 V−1 s−1, and resistivity of 6.7 × 102 Ω cm. Temperature-dependent Hall measurements were used to confirm the p-type conductivity and determine the Na-related acceptor level in the ZnMgO films, which was estimated to be 483 ± 21 meV. Temperature-dependent photoluminescence revealed an acceptor level of about 460 meV, close to the result determined by Hall measurements. The Na acceptor is deeper in ZnMgO than in ZnO due to the enlarged bandgap.

A facile and one-step transformation towards graphene using nickel foams as the substrate into a contact between semiconducting graphene (SG) and metal is developed for fabricating a SG/Ni Schottky junction. Graphene quantum dots were cut away via the electrochemical redox method and porous three-dimensional graphene with a bandgap was generated due to the abundant defects and dangling bonds. The constructed Schottky junction is the inner drives of accelerating charge transfer and thus results in significantly enhanced electrocatalytic effect. Bio-inspired porous graphene integrates micro-nano pores and functional groups, which greatly benefits to molecules separation and specific electrocatalysis. Macroscopic pores and numerous nanopores serve as “highways” for the rapid mass transport. Massive defects and rich dangling bonds act as “perceptrons” to reflect the charge distribution change. As a successful demonstration, the fabricated SG/Ni Schottky junction exhibits appreciable electro-oxidation towards H2O2 with an ultrahigh sensitivity of 4838 μA mM−1 cm-2 and an ultralow detection limit of 20 nM. This study puts forward an easy and practicable strategy to construct a Schottky junction, which is promisingly applied in other electrochemical research.

Zinc vacancy (V Zn ) plays key roles in the optical and electrical properties of ZnO, but its behaviors are not fully understood. Here we report the formation and abnormal photoluminescence (PL) of V Zn -related complex in Zn + -implanted ZnO single crystals. With increasing excitation density, we observed a new and gradually increased broad emission around 550 nm. The 550 nm emission is unexpectedly invisible under low power level excitation, indicating the lower priority of recombination of the related defect centers. Electron paramagnetic resonance (EPR) results suggest the formation of V Zn -Zn i complex after implantation, which is responsible for the abnormal PL properties.

We report the formation of high-quality Cs0.4MA0.6PbBr3 thin films with nearly full surface coverage and good emission properties upon the introduction of Cs+ into perovskite crystals. The Cs0.4MA0.6PbBr3 thin films were applied as emissive layers in light-emitting diodes. A maximum external quantum efficiency of ~2.0% was achieved for these green-emitting devices.

Two-dimensional (2D) perovskites are under extensive focus due to their natural multiple quantum well structures and intense excitonic luminescence. Here we provide comprehensive photoluminescence studies on solution-processed (C6H5C2H4NH3)2PbI4 crystals. The synthesized crystals exhibit three single excitonic emissions with different luminescent nature of 0D-like excitons, 2D localized excitons, and self-trapped excitons, respectively.

Compared to ZnO-based photoconductive photodetectors (PDs), photovoltaic PDs possess the advantages of easy fabrication, low dark current, high response speed and possible self-driven ability. In this paper, an ultraviolet (UV) photovoltaic photodetector based on graphene/ZnO heterostructure was fabricated and investigated. A simple surface treatment was conducted by soaking the as-grown ZnO film in H2O2 solution at room temperature. After this processing, a transition from ohmic contact to Schottky contact was observed in graphene/ZnO interface, accompanied with a high-performance photovoltaic behavior for the graphene/H2O2-treated ZnO (denoted as G/H-ZnO) heterostructure. The self-powered Schottky photodetector of G/H-ZnO exhibits a responsivity of 50 μA/W and a short rise/decay time of 32 ms at zero bias. The fast response performance benefits from the rapid separation of photogenerated carriers, which can be attributed to the synergistic effect of pyroelectric potential and built-in electric field at graphene/ZnO interface. This study provides a facile approach for the development of ZnO-based self-powered photovoltaic devices.

Photoluminescence (PL) properties of Zn0.8Mg0.2O film are investigated under high excitation and low temperature. With increasing excitation intensity, emission from the inelastic exciton-exciton scattering gradually dominates, meanwhile the bound exciton emission decreases. The exciton binding energy is estimated to be ~110–128 meV from the energy of P-band and PL thermal quenching, much higher than that of bulk ZnO. Temperature-dependent PL spectra reveal a room temperature internal quantum efficiency of 9.2% under high excitation, suggesting a high optical quality of the Zn0.8Mg0.2O film.

ZnO/ZnMgO multiple quantum wells (MQWs) were grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. Optical properties of the MQWs under high excitation were investigated by temperature- and excitation intensity-dependent photoluminescence spectroscopy. For weak confinement, increasing the excitation intensity leads to escape of excitons from the MQWs and appearance of ZnMgO barrier emission. While for better confinement, the ZnMgO barrier emission is almost independent on temperature and excitation intensity. The internal quantum efficiency of the MQWs increases monotonously with excitation intensity, reaching a highest value of 47% at room temperature, which suggests high quality of the MQWs.

In this paper, all-inorganic CsPbIBr2 thin films were annealed by a two-step temperature-control process. All-inorganic, hole-transporting-layer-free, carbon-based planar perovskite solar cells (PSCs) with these CsPbIBr2 thin films (FTO/c-TiO2/CsPbIBr2/C) were fabricated. The effect of different first-step annealing temperatures during the two-step temperature-control process (50 °C/280 °C, 80 °C/280 °C, 100 °C/280 °C, 150 °C/280 °C, 180 °C/280 °C) on the photovoltaic conversion efficiency (PCE) of PSCs was investigated for the first time. When the first-step annealing temperature was 150 °C and the second-step annealing temperature was 280 °C, the highest efficiency of 8.31% was obtained. Without encapsulation, the solar cell could retain 97% of the initial PCE, when it was stored at 80 °C and zero humidity for 8 days. For comparison, solar cells with CsPbIBr2 films annealed by a one-step temperature-control process were fabricated. The highest PCE was 4.98%. From this, we could see that there is an increase of 66.9% in PCE, through using a two-step temperature-control annealing process. And also, in order to investigate why the PSCs by a two-step temperature-control annealing process has a higher PCE, all kinds of measurements were done for the first time. According to the results of the measurements, the perovskite film annealed by a two-step temperature-control process has a bigger crystal size, fewer grain boundaries, stronger PL and UV–vis absorption intensities, longer lifetime of minority carriers, less energy loss for hole transporting.

Few-layer graphene sheets are applied as transparent electrode and current spreading layer for n-ZnO nanorod arrays/p-GaN light-emitting diodes (LEDs). The device with graphene electrode exhibits improved electroluminescence (EL) performance in EL intensity and reliability compared to the n-ZnO nanorod arrays/p-GaN LED with conventional indium-tin-oxide (ITO) electrode. The results prove that, with its superior electrical, optical and thermal properties, graphene can be an ideal candidate for transparent electrodes in nanorod arrays-based LEDs.

Heterostructured semiconductor nanostructures have provoked great interest in the areas of energy, environment and catalysis. Herein, we report a novel hierarchical Ag 3 PO 4 /TiO 2 heterostructure consisting of nearly spherical Ag 3 PO 4 particles firmly coupled on the surface of TiO 2 nanofibers (NFs). The construction of Ag 3 PO 4 /TiO 2 heterostructure with tailored morphologies, compositions and optical properties was simply achieved via a facile and green synthetic strategy involving the electrospinning and solution-based processes. Owing to the synergetic effects of the components, the resulting hybrid heterostructures exhibited much improved visible light photocatalytic performance, which could degrade the RhB dye completely in 7.5 min. In addition, the coupling of Ag 3 PO 4 particles with UV-light-sensitive TiO 2 NFs enabled full utilization of solar energy and less consumption of noble metals, significantly appealing for their practical use in new energy sources and environmental issues. The developed synthetic strategy was considered to be applicable for the rational design and construction of other heterostructured catalysts.

Cu-doped ZnO nano-films were synthesized by a hydrothermal method combined with post-annealing process. The mechanism for the formation of the nano-films can be explained by a Cu-adsorbed face-selective crystal growth inhibition mechanism. The 2 at.% Cu-doped sample behaved p-type conductivity, which can be verified by a p–n homojunction with well-defined rectifying characteristic. The origin of p-type conduction of the Cu-doped sample was studied by XPS and PL analyses. The Cu Zn +1 acceptor with the ionization energy of 326 meV should be the main reason for the p-type conductivity.

We carry out photoluminescence (PL) study on Na-doped ZnO nanorods to provide insights into the behavior of Na acceptor. We demonstrate the successful growth of Na-doped ZnO nanorods array by metalorganic chemical vapor deposition. PL analysis reveals the very low concentration of deep level defects such as oxygen vacancy. Unlike most ZnO materials, the low temperature PL of Na-doped ZnO nanorods is dominated by excitons bound to ionized donors (D+X), suggesting the formation of Na acceptors and high compensation between the donors and acceptors. The formation of Na acceptors is supported by the shift of Fermi level toward the valence band.

Non-polar ( 10 1 ¯ 0 ) ZnO thin films were epitaxially grown on m -plane sapphire substrates by plasma-assisted molecular beam epitaxy. The homobuffer thickness effect on the conduction type of undoped ZnO thin films is carefully investigated. With a relatively thicker buffer layer, weak p-type conductivity with a hole concentration of 1.6×10 16 cm −3 , a Hall mobility of 0.33 cm 2 V −1 s −1 , and a resistivity of 1.2×10 3 Ω cm are achieved for the film. By careful analysis of results from low temperature photoluminescence and transmission electron microscopy measurements, a correlation of the 3.32-eV emission to the p-type conductivity in the undoped non-polar ZnO films is revealed and discussed. The results are important to help deepen understanding of the origin of p-type behavior in ZnO-based materials.

We report the growth and characterization of single-crystalline, epitaxial Zn 0.9 Mg 0.1 O films on c-plane sapphire substrates with MgO buffer layer by plasma-assisted molecular beam epitaxy. The quality of the Zn 0.9 Mg 0.1 O epilayers is evidenced by a Hall mobility of more than 60 cm 2 V −1 s −1 at room temperature and an X-ray diffraction (XRD) rocking curve full-width at half-maximum of 47 arcsec for the (0 0 0 2) reflection. A screw dislocation density of 4 × 10 6 cm −2 is estimated by XRD. Transmission electron microscopy revealed that the thickness of the MgO buffer layer is about 3.5 nm, and a highly c -axis oriented Zn 0.9 Mg 0.1 O (0 0 0 2) reflection corresponding to the wurtzite-phase is observed. Alloying with Mg is found to widen the bandgap energy of the ZnO, and luminescence is observed at 3.502 eV at low temperature.

Non-polar Zn 1− x Cd x O thin films with different Cd content were grown on r -plane sapphire substrates by pulsed laser deposition. The effects of oxygen pressure on Cd content in the Zn 1− x Cd x O thin films are discussed. Single-phase Zn 1− x Cd x O thin films with a band gap of about 3.01 eV at room temperature are achieved by incorporating 13 at% Cd content. Based on the X-ray diffraction analysis, the Zn 1− x Cd x O films with Cd content below 7.2 at% exhibit unique non-polar 〈 11 2 ¯ 0 〉 orientation, while the films with Cd content above 7.2 at% present 〈0 0 0 1〉 and 〈 11 2 ¯ 0 〉 mixed orientations. The surface of Zn 1− x Cd x O film with pure a -plane orientation shows highly anisotropic morphology with stripes elongated along the c -axis.

The electrical and optical properties of zinc oxide (ZnO) films doped with different Na contents and grown by pulsed laser deposition were investigated. Hall measurements witnessed the conductivity conversion from n-type to p-type with targeted Na doping content increased up to more than 1%. The photoluminescence intensity first decreased as the targeted Na content increased to 1%, while non-degraded and even enhanced PL intensity was observed in p-type ZnO:Na0.02 film. This photoluminescence enhancement was ascribed to enhanced radiative recombination with more acceptor (NaZn) introduced. The band-gap shift of ZnO:Nax films was related to the variation of carrier type and concentration. Band-gap shrinkage was adopted to explain the carrier type- and concentration-dependent band-gap shift of ZnO:Nax films.

Time-resolved photoluminescence measurements were taken at various temperatures to investigate the behavior of excitons in ZnO/Zn0.9Mg0.1O multiple quantum wells (MQWs) grown on Si substrate using epitaxial Lu2O3 buffer layer by pulsed laser deposition. The temperature dependence of the radiative decay times of the emissions from both the ZnO wells and the Zn0.9Mg0.1O barriers is analyzed. The radiative lifetime of the well excitons exhibits linear dependence till room temperature, indicating that the excitons are effectively confined in the quantum wells and do not thermalize to 3D excitons. The short radiative lifetime of ~1.15 ns indicates high radiative recombination rate at room temperature. The radiative lifetime of the barrier excitons shows approximately T1/2 dependence on temperature. In combination with the spectral dependence of the PL lifetime, it indicates localization of excitons in the barrier due to compositional fluctuation. The short radiative lifetime at room temperature and the weak localization energy of ~9 meV suggest that our MQWs are of high optical quality.

Non-polar ZnO thin films were deposited on m-plane sapphire substrates by pulsed laser deposition at various temperatures from 300 to 700 °C. The effects of growth temperature on surface morphology, structural, electrical, and optical properties of the films were investigated. All the films exhibited unique m-plane orientation indicated by X-ray diffraction and transmission electron microscopy. Based on the scanning electron microscopy and atomic force microscopy, the obtained films had smooth and highly anisotropic surface, and the root mean square roughness was less than 10 nm above 500 °C. The maximum electron mobility was ∼18 cm2/V s, with resistivity of ∼0.26 Ω cm for the film grown at 700 °C. Room temperature photoluminescence of the m-plane films was also investigated.

We investigate the negative thermal quenching behavior of the 3.338 eV emission in ZnO nanorods. A correlation between the 3.338 eV and the 3.368 eV (surface exciton) emissions is determined from temperature-dependent photoluminescence. The activation energies of the 3.338 eV emission, obtained using an approximated multi-level model, indicate an trap state between the two surface exciton emissions. The present study demonstrates a nondestructive and easy method to understand the surface effects on the optical properties of semiconductor nanostructures.

ZnO based diluted magnetic semiconductor particles (ZnO:Co) have been grown using a hydrothermal method with good crystallinity. The atomic percentage of Co presented in the specimen is about 0.01. Based on the x-ray diffraction and high-resolution transition electron, Co is found to be incorporated into ZnO lattice without evidence of obvious Co precipitates. However, from photoluminescence (PL) spectra in the range of 1.94 –3.45 eV, a strong broad emission centered around 600 nm (2.07 eV) in the visible range as well as a relatively weak peak at 2.81 eV are observed, indicating the presence of Co impurities. Moreover, intrinsic emissions such as D O X suggest that at least some Co have been doped into ZnO lattice, substituting for Zn 2+ ions. The PL results further confirm the substitution of Zn 2+ ions by Co, which leads to the changes of the electronic band structures. Magnetism could be realized at room temperature for the ZnO:Co nanoparticles under our experimental conditions although with low coercivity. The field-cooled and zero-field-cooled curves can be explained as a result of competition between the ferromagnetic and the antiferromagnetic ordering in the ZnO:Co nanoparticles. Combining the results from PL and magnetism characterization, it is reasonable to think that both doped Co in the ZnO lattice and Co impurities contribute to magnetism in ZnO:Co nanoparticles at room temperature.

Li-doped ZnCoO (ZnCoO:Li) diluted magnetic semiconductor thin films were prepared on SiO 2 substrates by pulsed laser deposition. In ZnCoO:Li films, Co 2+ substituted Zn 2+ and Li occupied the interstitial sites behaving as donors. The ZnCoO:Li films are of high electron concentration in the 10 20 cm −3 order and acceptable crystal quality with a hexagonal wurtzite structure. No cluster, precipitate, or second phase was found from the X-ray diffraction pattern and Co k -edge X-ray absorption near-edge structure measurements. The sp–d exchange interactions between the band electrons and the localized d electrons of Co ions substituting Zn ions were observed. The magnetization of ZnCoO:Li film is 0.61 μB/Co, higher than that of the ZnCoO film (0.49 μB/Co). The enhanced defect density and electron concentration due to the introduced Li donors may answer for the improvement of ferromagnetism at room temperature.

We report the growth of uncommon layer-structured ZnO nanowire arrays via metal–organic chemical vapor deposition (MOCVD). The morphology, microstructure, and photoluminescence (PL) of the nanowires are investigated. The nanowires grow along the [0001] direction, with periodic zig-zag edges formed by the {1011}-type surfaces. The nanowires exhibit unique PL features. The PL spectra at low temperature are dominated by the surface exciton recombination at 3.366 eV and the controversial 3.32 eV emission. For the 3.32 eV emission, transformation from donor–acceptor pair recombination to free electron-to-acceptor transition is observed with increasing temperature. The stacking faults formed in the interface region between the layers are likely responsible for the strong emission around 3.32 eV.

ZnO:Al thin films were prepared at a low oxygen pressure between 0.02 and 0.1 Pa by pulsed laser deposition (PLD). The structure as well as their optical and electrical properties was investigated by X-ray diffraction, optical transmittance spectroscopy, and Hall measurements. The ZnO:Al films possess resistivity of the order of 10 −4 Ω cm and the optical transmittance exceeds 80% in the visible range. The highest electron concentration (1.18×10 21 cm −3 ) is achieved at a deposition pressure of 0.02 Pa and it decreases slightly with increasing oxygen pressure. The band gap is found to depend on the electron concentration.

Well-crystallized MgO nanosheets have been prepared with MgB 2 as a precursor without any catalyst via a simple chemical vapor deposition (CVD) method. The nanosheets are grown parallel to (2 0 0) plane according to the high-resolution transmission electron microscopy profiles. At the same time, MgO nanowires are formed in the different area of substrate, which is the result of the difference in local super-saturation. Consequently, we propose that the growth mechanism depends on the surface energy and the local super-saturation in the system.

A method for the synthesis of high quality indium-doped zinc oxide (In-doped ZnO) nanocrystals was developed using a one-step ester elimination reaction based on alcoholysis of metal carboxylate salts. The resulting nearly monodisperse nanocrystals are well-crystallized with typically crystal structure identical to that of wurtzite type of ZnO. Structural, optical, and elemental analyses on the products indicate the incorporation of indium into the host ZnO lattices. The individual nanocrystals with cubic structures were observed in the 5% In–ZnO reaction, due to the relatively high reactivity of indium precursors. Our study would provide further insights for the growth of doped oxide nanocrystals, and deepen the understanding of doping process in colloidal nanocrystal syntheses.

Quasi-aligned (Zn,Cd)O nanorods with highly faceted morphology were synthesized by a simple catalyst-free thermal evaporation method. The crystal structure and optical properties of the as-synthesized nanorods were thoroughly investigated. The results indicate that the (Zn,Cd)O nanorods are single crystals of wurtzite structure, having 12 side planes, namely, {0110} and {1120} planes. The presence of Cd is essential for obtaining these highly faceted nanorods. Room-temperature photoluminescence measurements indicated that the green emission of the products was attributed to both the surface-related defects and oxygen vacancies. These highly faceted nanorods possess significantly large surface-to-volume ratios and would be applicable in the fields of surface chemistry, photonics, and catalysis.

Temperature-dependent photoluminescence (PL) from two multi-quantum well (MQW) structures with different barrier widths has been systematically investigated. The PL band in the well layers is dominated by localized excitons (LE), D0X, and D0X-1LO. As the temperature increases, luminescence from the excitons localized in the well layers shows an ‘S’-shaped shift in the thin barrier MQW whereas a monotonic redshift is observed from the thick barrier MQW. Quenching of well-related emission is associated with delocalization of the excitons in the potential minima induced by interface fluctuations or alloy disorder. The activation energies correlated with depths of the local potential are deduced to be 7 and 17 meV for the thick and thin barrier MQWs, respectively.

The field-emission properties of the ZnO nanotip arrays, nanowire arrays as well as Al-doped ZnO nanowires were investigated in detail. After comparison of the different morphologies, it was found that the morphology of the nanostructure ZnO materials has played a crucial role in their field emission performances, especially the turn-on field and the emission current density. Among them, the ZnO nanotip arrays have the lower turn-on field, higher current density, which is attributed to the small emitter radius on the nanoscale and the well vertical align on the substrates. It can effectively improve the field-emission property to dope aluminium in ZnO nanowires because of the carrier concentration increasing, which results in the increase of the field enhancement factor and the reduction of the work function. The emission stability is very good from the emission persistence measurement.

Nb-doped ZnO thin films have been prepared on glass substrates by pulsed laser deposition (PLD). The effect of substrate temperature has been investigated from 100 to 500 °C by analyzing the structural, optical, and electrical properties. The Nb-doped ZnO films possessed a good crystallinity with a c-axis preferential orientation and a high transmittance (above 85%) in the visible region. The obtained film deposited at 350 °C exhibited the best electrical properties with the lowest room-temperature resistivity of around 5 × 10−4 Ω cm. Guided by x-ray photoemission spectroscopy analysis, NbZn3+ is believed to be the very possible donor in the Nb-doped ZnO films.

ZnO nanorods and nanonails have been synthesized on silicon wafers by a three-step catalyst-free thermal evaporation method in oxygen atmosphere. All the samples were hexagonal phase ZnO with highly c-axis preferential orientation. Different morphologies of ZnO nanostructures, i.e. ZnO nanorods and two kinds of nanonails, were observed at various temperature regions. Photoluminescence, transmission electron microscopy, and energy-dispersive X-ray spectroscope were employed to elucidate the reason for the formation of such different rod-like structures. The analysis results demonstrated that the caps of nanonails possess a large number of oxygen vacancies, which may play a key role in determining the formation of nanonails and the high intensity of green emission.

ZnO/MgO quasi core−shell quantum dots (QDs) were grown by a metal-organic chemical vapor deposition method on silicon substrates. The core−shell structure was well-characterized by a combination of cross-sectional transmission electron microscopy and angle-resolved X-ray photoelectron spectroscopy (XPS). Valence band XPS measurements were performed to investigate the effects of MgO shell layer on the energy band of ZnO/MgO QDs. Photoluminescence (PL) emission from the QDs showed remarkable enhancement after the growth of the MgO layer. In addition, exciton binding energy of 118 ± 5 meV in the ZnO/MgO QDs was obtained from temperature-dependent PL.

The authors report growth of stable Na-doped p-type ZnO films through pulsed laser deposition. Magnetic field dependent Hall-effect measurements demonstrate the firm p-type conductivity of the Na-doped films. The Na related acceptor level was estimated to be ∼164 meV by temperature-dependent photoluminescence and low temperature photoluminescence excitation spectra. ZnO p–n homojunction light-emitting diode consisting of Al-doped n-type ZnO and Na-doped p-type ZnO was fabricated on Si substrates. The diode showed evident rectification behavior with threshold voltage of ∼3.3 eV. The electroluminescence from the diode was observed at 110 K, consisting of three emission bands of 2.24 eV, 2.52 eV, and 3.03 eV from the radiative recombinations in the p-type layer. This work firmly demonstrates that Na could be a good dopant to create stable p-type ZnO.

a b s t r a c t A series of ZnO/Zn1 xMgxO multi-quantum wells (MQWs) were grown on Si(111) substrates by pulsed laser deposition (PLD), with different well widths and depths. Transmission electron mi- croscopy (TEM) analysis revealed that all the samples exhib- ited a good periodic structure with clear interfaces. Moreover, temperature- dependent behavior of excitonic photoluminescence (PL) was investigated in order to investigate the mechanism of the carrier dynamics. In the temperature range studied, the lumines- cence was dominated by localized exciton (LE) emission, which was significantly blueshifted with respect to the ZnO single layer, due to the well-known quantum-size effect. The blueshift values increased with elevating Mg compositions in barrier layers or de- creasing well thickness, being consistent with the calculated re- sults. The relevant activation energies were deduced, varying in a range of 6.2 to 22 meV.

Direct nitridation of B 4 C powder has been performed at temperatures ranging from 1600 to 2250 °C in a stream of nitrogen gas at ambient pressure. h-BN-like layered B 4 CN 4 powders have been prepared by nitridation of B 4 C at 1800 °C. Carbon atoms were found to be not isolated in BN layers in B 4 CN 4 . A structural model with stacked h-BN and graphite layers in a ratio 8/1 for B 4 CN 4 is excluded. The band gap of B 4 CN 4 was estimated to be 4 eV from the low-temperature PLE spectrum, which is much different from that of BC 2 N (2 eV) and that of h-BN (6 eV). The low-temperature PL spectrum of B 4 CN 4 revealed a dominant emission band at 3.55 eV.

Controllable ordered hexagonally patterned ZnO nanodots were achieved by polystyrene nanosphere lithography at room temperature. First a self-assembled monolayer of polystyrene spheres was formed as a mask. Then ZnO was deposited through the mask by e-beam vaporization. After the polystyrene spheres were etched away, ordered ZnO nanodots arrays were formed on the substrate. The obtained ZnO nanodots are of acceptable quality with high chemical purity and preferential c-axis orientation. A photoluminescence measurement shows a blue shift in free-exciton emission derived from low-dimensional quantum characteristics. The size of the nanodots can be controlled by varying the deposition time. The ZnO nanodots with growth times of 1, 2, and 3 min exhibit different free-exciton emission at 3.378, 3.356, and 3.314 eV. Therefore this is a technique with precise control of the size and geometry of the dots, which has a great promise for applications in nanoscale optoelectronic devices.

ZnMgO nanorod arrays were synthesized by metal-organic chemical vapor deposition using diethylzinc and magnesium nitrate as the precursors. No additional oxidant gas source such as O2 or N2O was used. The ZnMgO nanorods were homogeneous in composition and uniform in diameter. The blueshift of near-band-edge PL emission could be readily identified as compared with undoped ZnO nanostructures, indicating the band-gap engineering in the ZnO nanoscale system. The growth process was investigated in detail by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The possible growth mechanism was proposed. It is believed that this growth process may facilitate the homogenous distribution of Mg in the ZnMgO nanorods.

We report on Li-doped p-type Zn0.9Mg0.1O thin films grown by pulsed laser deposition. An optimal p-type conductivity is achieved at the substrate temperature of 550 °C, namely a resistivity of 45.4 Ω cm, a Hall mobility of 0.302 cm2 V−1 s−1, and a hole concentration of 4.55×1017 cm−3. Additionally, the p-type conductivity is stable over 5 months. From temperature-dependent photoluminescence, the energy level of LiZn acceptor is determined to be 167 meV above the valence band maximum.

Highly transparent conductive and near infrared (IR) reflective Gallium-doped ZnMgO (Zn{sub 1-x}Mg{sub x}O:Ga) films with Mg content from 0 to 10 at% were deposited on glass substrate by DC reactive magnetron sputtering. X-ray diffraction shows all the ZnMgO:Ga films are polycrystalline and have wurtzite structure with a preferential c-axis orientation. Hall measurements indicate that the resistivity of these films obviously increases with the Mg concentration increasing. The average transmittance of Zn{sub 1-x}Mg{sub x}O:Ga films is over 90% in the visible range. All the Zn{sub 1-x}Mg{sub x}O:Ga films have low transmittance and high reflectance in the IR region. - Graphical abstract: The figure shows transmittance and reflectance spectra of Zn{sub 1-x}Mg{sub x}O:Ga films measured in the wavelength range of 300-2500 nm. In the visible region the films are highly transparent, and their spectra are like those of dielectrics regardless of Mg content. In the IR region the films behave like metals and have high reflectance and low transmittance.

Vertically aligned aluminum-doped ZnO (AlZnO) nanorods with controllable Al concentration were grown on ZnO films through catalyst-free vapor phase deposition. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and photoluminescence were used to characterize the structural and optical properties of the obtained nanorods array. The aluminum doping concentration can be controlled simply by adjusting the distance between the source material and the substrates. Through photoluminescence measurements, we find out that the intensity of green band reduces as the aluminum doping concentration increases, and the origin of this phenomenon is discussed.

Gallium-doped zinc oxide (ZnO:Ga) transparent conductive films were deposited on glass substrate by DC reactive magnetron sputtering. The influence of sputtering power on the structural, electrical, and optical properties of ZnO:Ga films was investigated by X-ray diffraction, scanning electron microscopy (SEM), Hall measurement, and optical transmission spectroscopy. The lowest resistivity of the ZnO:Ga film is 4.48 x 10{sup -4} {omega}.cm and the average transmittance of the films is over 90% in the visible range. The obtained optical band gap of these films is much larger than of pure ZnO ({approx} 3.3 eV)

Li–N dual-doped p-type ZnO (ZnO:(Li,N)) thin films have been prepared by pulsed laser deposition. The introduction of Li and N was confirmed by secondary ion mass spectrometry measurements. The structural, electrical, and optical properties as a function of growth temperature were investigated in detail. The lowest room-temperature resistivity of 3.99 Ω cm was achieved at the optimal temperature of 450 °C, with a Hall mobility of 0.17 cm2/V s and hole concentration of 9.12 × 1018 cm−3. The ZnO:(Li,N) films exhibited good crystal quality with a complete c-axis orientation, a high transmittance (about 90%) in the visible region, and a predominant UV emission at room temperature. The two-layer-structure p-ZnO:(Li,N)/n-ZnO homojunctions were fabricated on a sapphire substrate. The current–voltage characteristics exhibited the rectifying behavior of a typical p–n junction.

Highly transparent conductive and near-infrared (IR) reflective Ga-doped ZnO films were deposited on glass substrate by DC reactive magnetron sputtering. The influence of post-annealing temperature on the structural, electrical and optical properties of the films was investigated. The lowest resistivity of 2.6 × 10−4 Ω cm was obtained at an annealing temperature of 450 °C. The films have low transmittance and high reflectance in the near-IR range. The average transmittance of the films is over 90% in the visible range.