NadopedZnOquantumdots of average size 6 nm were prepared using wet chemical route at room temperature without any capping agents and the formation of nanoparticles is confirmed by transmission electron microscope (TEM) and x‐ray diffraction (XRD) analysis. Optical band gap ofZnO:Na is found to be blue shifted with decrease in size due toquantum size effects. Incorporation ofNa inZnOquantumdots is confirmed using inductively coupled plasma atomic emission spectroscopy (ICP‐AES). Strong room temperature photoluminescent emissions in the violet region due to native defects ofZnO and yellow region resulting from substitutional incorporation ofNa in the Zn site was observed from theZnO:Naquantumdots. Both emission wavelength and integral intensity of emission in the visible region can be well controlled by adjusting the concentration of the alkaline precursor used as the dopant.Highlyluminescent bio‐friendlyNadopedZnOquantumdots can be used as fluorescent probes in biomedical applications.

p-Type ZnO microwires were first synthesized by a simple chemical vapor deposition method using Na as the dopant source.p-Type doping was confirmed by the electrical transport in single-wire field-effect transistors and low-temperature photoluminescence. The carrier mobility of the microwires was estimated to be2.1 cm² V⁻¹ S⁻¹.

Nanoscale light-emitting diodes (nanoLEDs) with colors spanning from the ultraviolet to near-infrared region of the electromagnetic spectrum were prepared using a solution-based approach in which emissive electron-doped semiconductor nanowires were assembled with nonemissive hole-doped silicon nanowires in a crossed nanowire architecture. Single- and multicolor nanoLED devices and arrays were made with colors specified in a predictable way by the bandgaps of the III–V and II–VI nanowire building blocks. The approach was extended to combine nanoscale electronic and photonic devices into integrated structures, where a nanoscale transistor was used to switch the nanoLED on and off. In addition, this approach was generalized to hybrid devices consisting of nanowire emitters assembled on lithographically patterned planar silicon structures, which could provide a route for integrating photonic devices with conventional silicon microelectronics. Lastly, nanoLEDs were used to optically excite emissive molecules and nanoclusters, and hence could enable a range of integrated sensor/detection “chips” with multiplexed analysis capabilities.

A large-area zinc oxide (ZnO) nanorod bundle array was grown on a silicon nanoporous pillar array (Si-NPA) substrate by a chemical vapor deposition method, and its field-emission properties was studied. The structural characterization disclosed that the bundles were composed of hexagonal ZnO nanorods growing alongc-axis and taking roots into the silicon pillars of Si-NPA. The average diameter and length of the ZnO nanorods were ∼145 nm and ∼10 μm, respectively. The field-emission measurements showed that the turn-on field of ZnO/Si-NPA was 4.6 V/μm with an emission current density (ECD) of 1 μA/cm², and an ECD of 420 μA/cm² was achieved at an applied field of 8.89 V/μm. The field enhancement factor was calculated to be ∼1700 based on the Fowler–Nordheim theory. According to the obtained charge coupled device (CCD) image, the density and brightness of the emission dots increased with the applied field, and the high emission dot density was attributed to the formation of a large number of ZnO nanorod emitting tips. Our results indicated that ZnO/Si-NPA might be a promising electron emission source.

We present an approach for the growth of ZnO nanowire arrays with a length of up to 30 μm on fluorine doped tin oxide substrates with a growth rate of 20 μm per hour. The growth was carried out in a vapor phase transport setup at a temperature of 600 °C. To achieve an aligned growth on fluorine doped tin oxide substrates we used wet-chemically grown nanowire arrays with typical length of 2 to 3 μm as a seeding layer. Additionally the nanowire arrays were used as electrodes for the manufacturing of dye sensitized solar cells and the best achieved efficiencies were 1.83% at 10 mW/cm² and 1.47% at 100 mW/cm².

Length control of ZnO nanowire arrays is a valuable concern for both fundamental research and future device application. In this article, vertically aligned ZnO nanowire arrays were synthesized by a seed layer catalyzed vapor phase transport method in a single experiment cycle. The length of these nanowire arrays exhibits a quasi-continuous evolution. It was found that the type and flow rate of carrier gas have a significant influence on the length modulation of ZnO arrays along the tube. A feasible route to tune the length of ZnO nanowire arrays from several micrometers to nearly 100 μm could be achieved by adjusting proper deposition position and carrier gas.

For the fabrication of ZnO NWs, we have used Si wafers as smooth surface substrates. Gold was deposited on to the substrates with an electron beam evaporator, since it is known that gold particles can serve as the catalyst to grow ZnO NWs on substrates in Vapor-Liquid-Solid (VLS) method. In the VLS method, the mixture of ZnO powder and graphite was placed at 1100 °C and the substrates were at 800 °C in a two-zone furnace. The reduction of ZnO of the source generates Zn vapor that diffuses to gold particles on Si substrates, and the oxidation of Zn-Au alloy grows ZnO crystals. The gold deposited area has ZnO crystal growth and that the gold particles play the role of nucleation sites. ZnO crystals have the dimension of a few hundred nm wide and 2-3 μm long under this particular condition. SEM, XRD, and PL have been used for characterization. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A novel thermal evaporation–deposition approach using microwave energy was employed for the fabrication of ZnO micro-and nano-structures. Batch fabrication of ZnO structures including microtubes, microrods, nanowires and nanobelts were successfully obtained with a unique source materials–substrate configuration in achieving desirable temperature profile. Zinc or zinc oxide source materials are evaporating from the high-temperature zone in an enclosure and single crystalline nano-or micro-structures are grown on the substrate materials with controllable dimensions by using appropriate processing conditions. Substrate, temperature, and catalyst showed significant impacts on the controlled growth of the ZnO nano- and micro-structures. X-ray diffraction (XRD) and scanning electron microscopy (SEM) characterizations reveal that these products are pure, structurally uniform, and single crystalline. The photoluminescence (PL) exhibits strong ultraviolet emission at room temperature, indicating potential applications for short-wave light-emitting photonic devices.

Mn doped ZnO nano- and microstructures have grown by a catalyst free evaporation-deposition method. Different morphologies such as nanowires, nanorods and stacks of nanoplates with a skewer arrangement around a central rod, have been obtained. Structural and cathodoluminescence investigations show the incorporation of Mn into the structures and the formation of a spinel phase in some areas. The influence of dopant distribution and local growth conditions on the formation of these structures, in particular of the stacks of nanoplates, has been also investigated.

A method combining laser ablation cluster formation and vapor-liquid-solid (VLS) growth was developed for the synthesis of semiconductor nanowires. In this process, laser ablation was used to prepare nanometer-diameter catalyst clusters that define the size of wires produced by VLS growth. This approach was used to prepare bulk quantities of uniform single-crystal silicon and germanium nanowires with diameters of 6 to 20 and 3 to 9 nanometers, respectively, and lengths ranging from 1 to 30 micrometers. Studies carried out with different conditions and catalyst materials confirmed the central details of the growth mechanism and suggest that well-established phase diagrams can be used to predict rationally catalyst materials and growth conditions for the preparation of nanowires.

Ultraviolet semiconductor lasers are widely used for applications in photonics, information storage, biology and medical therapeutics. Although the performance of gallium nitride ultraviolet lasers has improved significantly over the past decade, demand for lower costs, higher powers and shorter wavelengths has motivated interest in zinc oxide (ZnO), which has a wide direct bandgap and a large exciton binding energy^1,2,3,4,5,6. ZnO-based random lasing has been demonstrated with both optical and electrical pumping^7,8,9,10, but random lasers suffer from reduced output powers, unstable emission spectra and beam divergence. Here, we demonstrate electrically pumped Fabry–Perot type waveguide lasing from laser diodes that consist of Sb-doped p-type ZnO nanowires and n-type ZnO thin films. The diodes exhibit highly stable lasing at room temperature, and can be modelled with finite-difference time-domain methods.

The vapor–liquid–solid (VLS) mechanism is most widely employed to grow nanowires (NWs). The mechanism uses foreign element catalytic agent (FECA) to mediate the growth. Because of this, it is believed to be very stable with the FECA-mediated droplets not consumed even when reaction conditions change. Recent experiments however differ, which suggest that even under cleanest growth conditions, VLS mechanism may not produce long, thin, uniform, single-crystal nanowires of high purity. The present investigation has addressed various issues involving fundamentals of VLS growth. While addressing these issues, it has taken into consideration the influence of the electrical, hydrodynamic, thermodynamic, and surface tension effects on NW growth. It has found that parameters such as mesoscopic effects on nanoparticle seeds, charge distribution in FECA-induced droplets, electronegativity of the droplet with respect to those of reactive nanowire vapor species, growth temperature, and chamber pressure play important role in the VLS growth. On the basis of an in-depth analysis of various issues, a simple, novel, malleable (SNM) model has been presented for the VLS mechanism. The model appears to explain the formation and observed characteristics of a wide variety of nanowires, including elemental and compound semiconductor nanowires. Also it provides an understanding of the influence of the dynamic behavior of the droplets on the NW growth. This study finds that increase in diameter with time of the droplet of tapered nanowires results primarily from gradual incorporation of oversupplied nanowire species into the FECA-mediated droplet, which is supported by experiments. It finds also that optimum compositions of the droplet constituents are crucial for VLS nanowire growth. An approximate model presented to exemplify the parametric dependency of VLS growth provides good description of NW growth rate as a function of temperature.

The lateral density ofZnOnanowire arrays grown withpulsed laser deposition (PLD) can be tuned from 1 to 10⁻²μm⁻² by introducing aZnO nucleation layer and optimizing the distance between the substrate and the ablated target. High-density (10μm⁻²)nanowire arrays can be grown on sapphire substrates with or withoutgoldcatalysts. However, if aZnO wetting layer was adopted, the density ofZnOnanowires could be controlled with high reproducibility. The decreasinggrowth density is attributed to a competition between the two-dimensional filmepitaxy and one-dimensionalnanowiregrowth. The dependence ofnanowire density on the substrate–target distance mainly arises from the expansion dynamics of the plasma plume and the chamber geometry. Using low-densitynanowires as templates, a generalPLD route was developed to grow radialnanowire heterostructures. Here we demonstrateMgZnO/ZnO/MgZnOnanowire quantum wells andZnO/ZnO:P core–shellnanowire p–n junctions.

ZnO nanorod arrays (NRAs) with different Na contents were prepared by thermal evaporation. Sodium pyrophosphate was adopted as the Na source. The Na contents in NRAs were determined by X-ray photoelectron spectra to be 0, 6.1, and 9.4 at.%. X-ray diffraction (XRD) analyses of Na-doped ZnO NRAs were performed in experiment and by first-principle calculation with the assumption of Na substitutions. A couple of typical changes were found in XRD patterns of Na-doped ZnO. The simulation results well agreed with the experimental data, which revealed that Na mainly located at the substitutional sites in Na-doped ZnO NRAs.

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.