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We described a novel seeded synthesis of vertically aligned ZnO nanorod arrays on a DNA network surface. Zinc ions were first adsorbed onto the DNA network and then heated to yield layers of ZnO seeds. The DNA network plays an important role not only as a substrate for the adsorbing of zinc ions, but also as a fine template for density controllable synthesis of high-quality ZnO seeds. The density of ZnO seeds was controlled by the adsorption times of zinc ions. The final density of ZnO nanorods was determined mainly by that of ZnO seeds. The ZnO nanorod arrays were used as templates for making silver-coated ZnO nanocomposites, which were applied as substrates in surface-enhanced Raman scattering (SERS) measurements. Two typical probe molecules, R6G and 4-ATP were used to test the SERS activity of the ZnO/Ag composites and the results indicated good Raman activity on the substrate.

The photodegradation of 8-hydroxyquinoline aluminum (Alq 3 ) films under UV irradiation was studied by means of X-ray photoelectron spectroscopy, nano-second fluorescence spectrophotometer, and photoluminescence spectra. Degradation in photoluminescent properties was significant in an air environment. These results indicated that water and oxygen participate in the photodegradation processes of Alq 3 . Quartz glass, metal Al and Ag substrates influenced the degradation in photoluminescent properties of Alq 3 , but no changes in the absorption and PL spectra, and fluorescence decays of the irradiated Alq 3 were observed.

Metal-semiconductor-metal structured ultraviolet (UV) photodetector has been fabricated from zinc oxide films. The responsivity of the photodetector can reach 26 000 A/W at 8 V bias, which is the highest value ever reported for a semiconductor ultraviolet photodetector. The origin of the high responsivity has been attributed to the carrier-trapping process occurred in the metal-semiconductor interface, which has been confirmed by the asymmetric barrier height at the two sides of the metal-semiconductor interdigital electrodes. The results reported in this paper provide a way to high responsivity UV photodetectors, which thus may address a step toward future applications of UV photodetectors.

Lithium and nitrogen dual-doped ZnO films [ZnO:(Li, N)] with Li concentrations of 0%–11.2% were grown on sapphire by plasma-assisted molecular beam epitaxy, and a stable p-type ZnO:(Li, N) film was obtained by doping 6.1% of Li. The p-type conductivity of ZnO:(Li, N) is attributed to the formation of the Lii–NO complex, which depresses the compensation of Lii donor for LiZn acceptor and the generation of (N2)O donors. It is demonstrated that the Lii–NO complex can form an impurity band above the valance band maximum, resulting in a decrease in the ionization energy of the acceptor and an improvement in the conductivity and stability of the p-type ZnO:(Li, N).

Under the ultralow driven current of 25 μA an ultraviolet (UV)-blue electroluminescence (EL) with a weak defect-related emission could be obtained for the n type (n-) ZnO nanowires (NWs)/insulating (i-) polymer/p-type (p-) GaN light-emitting diode (LED). The i-MgO layer was also explored as a carrier blocking layer for the comparison. For the i-polymer inserted LED the EL emission peak was located at 400 nm, by analyzing the spectra it is believed that the emission includes several compound originations from both ZnO and GaN. The flexible carrier blocking layer, such as i-polymer, could effectively confine the radiative recombination zone.

The ZnO nanorods were used as a template to fabricate nickel nanoclusters by electrodeposition. The ZnO nanorod arrays act as a nano-semiconductor electrode for depositing metallic and magnetic nickel nanoclusters. The growth sites of Ni nanoclusters could be controlled by adjusting the applied potential. Under -1.15 V the Ni nanoclusters could be grown on the tips of ZnO nanorods. On increasing the potential to be more negative the ZnO nanorods were covered by Ni nanoclusters. The magnetic properties of the electrodeposited Ni nanoclusters also evolved with the applied potentials.

Stable p-type Sb-doped ZnO (ZnO:Sb) was fabricated reproducibly by sintering mixture of ZnO and Sb2O3 powders under 5 GPa at temperatures of 1100–1450 °C. The best p-type ZnO:Sb with resistivity of 1.6×10−2 Ω cm, carrier concentration of 3.3×1020 cm−3, and mobility of 12.1 cm/V s was obtained by doping 4.6 at. % Sb and sintering at 1450 °C. The p-type conduction is due to complex acceptor formed by one substitutional Sb at Zn site and two Zn vacancies. The acceptor level was measured to be 113 meV. Effect of pressure on formation and electrical properties of the p-type ZnO:Sb is discussed.

By controlling the incoming gas flow, vertically aligned ZnO nanowires and nanowalls have been successfully synthesized on a Si (100) substrate by the simple physical vapour deposition method. The growth process of the ZnO nanowalls was observed by adjusting the growth time. The probable growth mechanisms of the ZnO nanowires and nanowalls were discussed in detail. In contrast to the photoluminescence results of nanowires, an enhancement of the LO phonon signal was observed in ZnO nanowalls, which was attributed to an additional channel of electron-phonon coupling induced by the residual strains in the ZnO nanowalls during the coalescence growth process.

Temperature-dependent photoluminescence of MgZnO alloy film has been studied, and it is found that the emission intensity increases significantly at a certain temperature range and then decreases when increasing temperature further. The anomalous increase is resulted from the localized excitons in MgZnO alloy, as revealed by the enhanced second-order longitudinal optical phonon in the Raman spectrum of the MgZnO film. A schematic model was suggested to depict the carrier transportation process in the MgZnO film considering the existence of localized exciton states. The results reported in this paper indicate that localized excitons in MgZnO alloy can result in greatly enhanced emission efficiency, which is eagerly wanted for the application of ZnO-based materials in high-efficiency light-emitting devices.

In this study, we report the growth of MgxNi1?xO thin films on quartz substrates by electron beam evaporation. The absorption edge shows a blue shift from 340?nm to 260?nm with increase in the Mg content from 0.2 to 0.8. A metal?semiconductor?metal structured photodetector is fabricated from the Mg0.2Ni0.8O film. At a bias of 5?V, the dark current of the photodetector is about 70?nA. The maximum responsivity is about 147.3??A?W?1 at 320?nm. In addition, the ultraviolet (UV) (320?nm) to visible (400?nm) rejection ratio is nearly two orders of magnitude. Based on these results, it is proposed that MgxNi1?xO is a potential candidate for application in UV photodetectors.

Closely packed ZnO nanowire array was fabricated on a n-type Si (100) substrate by a magnetron cosputtering method. The ZnO nanowire/n-Si heterojunction showed good diode characteristics with rectification ratio of above 1.6×102 at 4V in the dark. Experiments demonstrated that the diode could be used to detect either visible or ultraviolet light by easily controlling the polarity of the voltage applied on the heterojunction. The spectral response of the device will be discussed in terms of the band diagrams of the heterojunction and the carrier diffusion process.

The relationship between band gap and biaxial stress in wurtzite ZnO thin films has been investigated by side-inclination x-ray diffraction technique and optical absorbance spectrum as well as ab initio calculation. The experimental result shows that differing from other semiconductor thin films with hexagonal structure, such as GaN, the band gap of ZnO thin films increases with the increase in biaxial tensile stress. For explaining the difference, ab initio calculation is performed to simulate the relationship between band gap and biaxial stress of wurtzite ZnO and GaN. The calculated result indicates that the band gap of ZnO increases under biaxial tensile stress but GaN is opposite, supporting our experimental result. The band offset calculation shows that the conduction-band minimum (CBM) and the valence-band maximum (VBM) of ZnO and GaN offset to low energy under biaxial tensile stress. The VBM offset of ZnO is larger than the CBM, responsible for the increase in band gap. The VBM offset of GaN is sm...

It has been predicted that the electronic properties of carbon nanotubes (CNTs) can be dramatically tuned by forming Si–C bonds with a silicon surface. Thus, the realization of Si–C bonds will broaden future applications of CNTs on nanodevices. In this paper, we use micro-Raman imaging and spectroscopy to investigate the interaction between individual CNTs and silicon substrate. We show that covalent bonds were formed between certain CNTs and the substrate, and visualized such Si-CNT bonds using micro-Raman imaging. Polarized Raman results further reveal that the Si–C bonds are arranged orderly along the long axis of the Si-CNT. We thus show that Raman imaging is a very useful technique to study properties of such Si-CNTs.

α- and β‐FeSe thin films were grown by metal organic chemical vapor deposition. Compared to the other parameters, the growth temperature shows decisive influence on the phase transition of the FeSe samples. In temperature-dependent electrical measurements, n-type to p-type reversion was observed for both the α- or and β‐FeSe samples. Furthermore, the p-type character of the films becomes more and more obvious with increasing the Se∕Fe atomic ratio in the samples. Ferromagnetism was observed in the α‐FeSe films although which is not supported by calculation on density of states. The ferromagnetic character shows significant dependence on Se∕Fe atomic ratio in the films and was attributed to the Fe vacancies or Fe clusters in the α‐FeSe thin films. The magnetic domain and hysteresis loop of the β‐FeSe thin films are also studied.

The excitonic optical nonlinearities in II-VI semiconductor thin films and multiple quantum wells (MQWs) are much complicated than those of GaAs MQWs because the wider band gap and smaller excitons of II-VI semiconductor materials. We report here the observations of dynamic optical bistabilities in ZnSe/ZnS MQWs at low temperature caused by excitonic optical nonlinearity.

The recombination mechanisms of nitrogen-related emissions in p-type ZnO films were investigated by photoluminescence (PL) measurements. The enhanced peak at 3.260 eV was confirmed as a donor-acceptor pair (DAP) transition and the emission around 3.310 eV was assigned to the free electron to acceptor (FA) recombination by studying the temperature evolution of DAP and FA luminescence, calculating the energy level of the corresponding nitrogen acceptor, and measuring the decay time of DAP transition. By comparing the PL spectra of the samples with various hole concentrations, it can be found that as the hole concentration increases, the DAP peak significantly dominates the spectra. In addition, the acceptor binding energy is estimated to be about 120 meV from the FA transition, which is in good agreement with the value calculated by a hydrogenic acceptor model.

ZnO p-n junction light-emitting diodes (LEDs) were fabricated on c-plane Al2O3 substrates by plasma-assisted molecular beam epitaxy. Gas mixture of N2 and O2 was used as the p-type dopant, by which the double-donor doping of N2(O) can be avoided significantly. The fabricated p-type ZnO layers have a higher hole density and carrier mobility. The LEDs showed a very good rectification characteristic with a low threshold voltage of 4.0V even at a temperature above 300K. The LEDs can even emit intensive electroluminescence in the blue-violet region at the temperature of 350K. The blue-violet emission was attributed to the donor-acceptor pair recombination at the p-type layer of the LED.

Magnetophotoluminescence properties of Zn0.88Mn0.12Se thin films grown by metal-organic chemical vapor deposition on GaAs substrates are investigated in fields up to 10 T. The linewidth of the excitonic luminescence peaks decreases with the increasing magnetic field (< 1 T), but the peak energy is almost unchanged. There is a crossover of the photoluminescence intensities between interband and bound excitonic transitions as the magnetic field is increased to about 1 T. These behaviors are interpreted by the strong tuning of the local alloy disorder potential by the applied magnetic field. In addition, the magnetic field-induced suppression of the energy transfers from excitons to Mn2+ ions is also observed.

A ZnO p-n junction light-emitting diode (LED) was fabricated on a-plane Al2O3 substrate by plasma-assisted molecular-beam epitaxy. NO plasma activated by a radio frequency atomic source was used to grow the p-type ZnO layer of the LED. The current-voltage measurements at low temperatures showed a typical diode characteristic with a threshold voltage of about 4.0V under forward bias. With increasing temperature, the rectification characteristic was degraded gradually, and faded away at room temperature. Electroluminescence band of the ZnO p-n junction LED was located at the blue-violet region and was weakened significantly with increase of temperature. This thermal quenching of the electroluminescence was attributed to the degradation of the diode characteristic with temperature.

ZnO particles embedded in SiO2 thin films were prepared by a radio-frequency magnetron sputtering technique. X-ray diffraction (XRD) and optical-absorption spectra showed that ZnO particles with hexagonal wurtzite structure had been embedded in the SiO2 matrix, and the size of ZnO particles increased with increasing annealing temperature from 773to973K. Raman-scattering and Fourier transform infrared (FTIR) spectrum measurements also confirmed the presence of ZnO particles. When the annealing temperature was lower than 973K, room-temperature photoluminescence (PL) spectra showed dominative deep-level emissions in the visible region and very weak ultraviolet emissions. As the annealing temperature increased to 973K, an emission band in the ultraviolet region besides the emissions from free and bound excitons recombination was observed in the low-temperature PL spectra. The origin of the ultraviolet emission bands was discussed with the help of temperature-dependent PL spectra. When the annealing temperature was higher than 973K, Zn2SiO4 particles were formed, as shown by XRD and FTIR results.

ZnO hexagonal prisms have been grown from poly (vinylpyrrolidone)-assisted electrochemical assembly onto p-type Si (111) substrate. These ZnO prisms arrays are highly (0002) orientated. The (0001) end facets and {1010} side facets of the hexagonal prisms are well defined. The photoluminescence (PL) spectrum of these ZnO prisms shows an intense ultraviolet near band-gap emission with a full width at half maximum of 86 meV at room temperature. The low-temperature PL spectrum is split into well-resolved free and bound exciton emission lines. The temperature dependence of the exciton emission intensities shows a nonmonotonic decaying behavior, which can be explained by the existence of interfacial states.

High quality ZnO thin films have been grown on a Si(100) substrate by plasma enhanced chemical vapor deposition using a zinc organic source [Zn(C2H5)2] and carbon dioxide (CO2) gas mixtures at the low temperature of 180 °C. The dependence of ZnO thin film quality on the gas flow rate ratio of Zn(C2H5)2 to CO2 (GFRRZC) is studied by using x-ray diffraction (XRD), optical absorption (OA) spectra, and cathodoluminescence (CL) spectra. High quality ZnO thin films with a c-axis-oriented wurtzite structure are obtained when the GFRRZC is 0.33. XRD shows that the full width at half maximum of (0002) ZnO located at 34.42° is about 0.2°. At room temperature, a pronounced free exciton absorption peak around 365 nm is clearly observed. Also, a strong free exciton emission without deep level defect emission is observed around 385 nm, and its temperature dependence is studied from the photoluminescence spectra. These observations indicate the formation of a high quality ZnO film. Additionally, nitridation of the Si su...

The optical bistability with picosecond switching time in ZnS-ZnTe/GaAs multiple quantum wells (MQWs) on reflection at room temperature has been studied for the first time. The research results indicate that the switching threshold from high to low state and contrast ratio for the optical bistability are about 1.2 MW/cm2 and 3:1, respectively. The major nonlinear mechanism for the optical bistability is due to the change of refractive index caused by the band filling effect.

The optical properties of Zn1-xCdxSe–ZnSe multiple quantum wells (MQWs) have been investigated. The MQWs samples exhibit five photoluminescence peaks under the 457.9 nm line of an Ar ion laser excitation at 77 K. Three of these bands are attributed to different exciton emission: the n=1 heavy–hole exciton transition, the n=1 light–hole exciton transition and n=1 heavy–hole exciton transition with the emission of two LO phonons. The room–temperature nanosecond switching property has also been studied in Zn1-xCdxSe–ZnSe MQWs F–P–type optical bistable device operation in reflection, in which their switching threshold and contrast ratio are about 47 kW/cm2 and 7:1, respectively. The origin of the major nonlinear mechanism for the optical switching property is due to the change of the refractive index caused by the effect of the excitonic saturating absorption effect in the ZnCdSe–ZnSe MQWs.

Excitonic optical bistability with picosecond switching time in ZnSe-CdZnSe multiple quantum wells (MQWs) optical bistable device is investigated at room temperature for the first time. The result indicates that the threshold and contrast ratio for the optical bistability in ZnSe-CdZnSe MQWs optical bistable device are about 210 kW/cm2 and 2 : 1, respectively. On the basis of the excitonic nonlinear theories, excitonic absorption and excitonic emission under different excitation intensities in the ZnSe-CdZnSe MQWs obtained here, we attribute the major nonlinear mechanism for the optical bistability in ZnSe-CdZnSe MQWs optical bistable device to the phase space filling of excitonic states and excitonic band broadening due to exciton-exciton interactions.

The electroluminescence emission spectrum of forward-biasec ZnS0.22Se0.78 MIS diodes excited by pulse current density from 30 to 300mA/mm2 have been studied at 77K. We first found the inelastic collision of two free excitons in ZnS0.22Se0.78 MIS diodes with high pulse current density. On the basis of the distribution of kinetic energy of free excitons, we discussed the line shape of 2L0 phonons. The results indicated that the effective temperature of free exciton is higher than the lattice temperature under high pulse current density, it was due to the inelastic collision of two free excitons.

Wurtzite nitrogen-doped MgZnO (MgZnO:N) films were grown on c-plane sapphire by using plasma-assisted molecular beam epitaxy with radical NO as the oxygen source and nitrogen dopant. P-type conduction of MgZnO:N was obtained by decreasing the donor defects ((N-2)O, VO, etc.) through annealing, revealing a hole concentration of 6.1 x 10(17) cm(-3) and a mobility of 6.42 cm(2)/Vs. Furthermore, as-grown p-type films with a hole concentration of 1 x 10(17) cm(-3) and a mobility of 3 cm(2)/Vs were obtained by decreasing the (N-2)O double donor defect through control of the plasma conditions. ZnMgO:N/ZnO p-n junctions were obtained by using these p-type films. Diode-like, rectifying I- V characteristics with a threshold voltage of about 5 V and a different reverse leakage current were observed at room temperature.

Poly[2-methoxy-5-(2-ethylhexyloxy-p- phenylenevinylene)]/ZnO nanorod hybrid solar cells consisting of PbS quantum dots [QDs] prepared by a chemical bath deposition method were fabricated. An optimum coating of the QDs on the ZnO nanorods could strongly improve the performance of the solar cells. A maximum power conversion efficiency of 0.42% was achieved for the PbS QDs' sensitive solar cell coated by 4 cycles, which was increased almost five times compared with the solar cell without using PbS QDs. The improved efficiency is attributed to the cascade structure formed by the PbS QD coating, which results in enhanced open-circuit voltage and exciton dissociation efficiency.