[Show abstract][Hide abstract] ABSTRACT: An ultraviolet photodetector was fabricated on MgZnO thin film grown by metal-organic chemical vapor deposition. The peak response of the device centers at 238 nm and cutoff wavelength is 253 nm. The peak responsivity is 129 mA/W at 15 V bias, and the UV/visible reject ratio is 4 orders of magnitude. Internal gain is due to the hole trapping at interface that brings low response speed. Native defects at the Au/MgZnO interface degrade the barrier effect, which caused large dark current and high visible response.
Full-text · Article · Dec 2011 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: Nickel-coated ZnO nanowires (NWs) were fabricated by electrodepositing Ni particles on ZnO NW arrays. The morphological, magnetic, and photoluminescent properties of the Ni-coated ZnO NWs were investigated. The Ni particles were deposited on the ZnO NWs’ surface along its length to form a Ni/ZnO shell-core structure. The Ni-coated ZnO NWs exhibited more isotropic characteristic than the electrodeposited Ni films owing to the isotropic sphere structure of the Ni particles. A strong ultraviolet emission can be obtained from the Ni-coated ZnO NWs, while the green emission related to surface states was quenched by the passivated layer.
No preview · Article · Nov 2010 · Physica B Condensed Matter
[Show abstract][Hide abstract] ABSTRACT: High quality ZnO films were grown on c-plane sapphire (c-Al2O3) substrates by plasma-assisted molecular beam epitaxy (P-MBE). The influence of Zn/O ratio on the epitaxial growth of ZnO is investigated. Via adjusting Zn/O ratio, structural, electrical and optical properties of the ZnO thin films are significantly improved, and the highest quality ZnO film with the full width of half maximum (FWHM) of 0.05° at the (002) peak and electron mobility of 54cm2/Vs is obtained at the Zn/O ratio of 1.03. When the Zn/O ratio is diverged from 1.03, the films exhibit rough surface with reticulated nanostructures. The formation mechanism of the ZnO nanostructure at non-stoichiometric condition is discussed. It is also found that both Zn-rich and O-rich samples show D0X emission peak located at 3.362eV in the PL-spectra. By using the photon energy of the D0X and the Haynes’ rules, the ionization energy of the donor corresponding to the D0X is calculated to be 36meV, which implies that the D0X is related to hydrogen donor.
No preview · Article · Jul 2010 · Journal of Alloys and Compounds
[Show abstract][Hide abstract] ABSTRACT: Cubic Mg(0.58)Zn(0.42)O thin films with (100) orientation were grown on cubic MgO substrates. The band gap of the alloy films corresponds to solar blind band. In the case that a MgO buffer layer was employed, the surface roughness was decreased from 38 to 1.6 nm under the same growth conditions. A metal-semiconductor-metal photodetector based on this MgZnO film was fabricated, which showed a low dark current of 0.16 pA and lower sub-bandgap photoresponse than the ones with rougher surface in our early reports.
[Show abstract][Hide abstract] ABSTRACT: The vertically aligned ZnO nanowire arrays prepared by vapor transport process can be assembled into complex micropatterns under capillary force. The deflection of the flexible ceramic nanowire is closely related to the liquid tension coefficient, mechanical and structural properties of the ZnO nanowires. The bended nanowires are adhesive together because the solid adhesion energy is sufficient to withstand the restoring elastic force of the deformed nanowires. The size of the bundling pattern can be controlled by varying the aspect ratio of the nanowire. The deflection of the ZnO nanostructure composed of a nanowire and a base is multifarious.
No preview · Article · Jun 2010 · Materials Chemistry and Physics
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: The metal-semiconductor-metal ultraviolet (UV) photodetector was fabricated on the Mg(0.47)Zn(0.53)O layer grown by radio-frequency magnetron cosputtering. The photodetector shows the peak response at 290 nm with a cutoff wavelength at 312 nm. It exhibits a very low dark current of about 3 pA at 5 V bias, and the UV-visible rejection ratio (R = 290 nm/R = 400 nm) is more than 4 orders of magnitude. The transient response for the detector was measured, and it was found that the rise time is 10 ns and the fall time is 30 ns. The reason for the short response time is related to the Schottky structure.
[Show abstract][Hide abstract] ABSTRACT: By controlling the incoming gas flow, vertically aligned ZnO nanowires and nanowalls have been successfully synthesized on a Si (1 0 0) 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.
No preview · Article · Jul 2009 · Journal of Physics D Applied Physics
[Show abstract][Hide abstract] ABSTRACT: 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 µA 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.
Preview · Article · Apr 2009 · Journal of Physics D Applied Physics
[Show abstract][Hide abstract] ABSTRACT: Un-doped ZnO and MgZnO thin films were deposited on c-plane sapphire substrates by molecular-beam epitaxy (MBE) and subsequently annealed in hydrogen ambient at 200–500 °C with a step of 100 °C. Hall-effect measurements show that annealing temperature has great effect on the electrical property of both ZnO and MgZnO films. The electron concentration of both ZnO and MgZnO films increases with annealing temperature ranging from 200 °C to 400 °C, and then decreases, which is attributed to incorporation of H into ZnO as a shallower donor during the annealing process and change of solid solubility of hydrogen in ZnO and MgZnO films with annealing temperature. The D0X emission is related to the hydrogen in MgZnO film and the donor level of the H is estimated to be 33.5 meV. It is also found that the controversial luminescence band at 3.310 eV can be formed in un-doped ZnO film upon annealing and its intensity increases with increasing annealing temperature, implying that this band may be not related to p-type doping.
[Show abstract][Hide abstract] ABSTRACT: Wurtzite (Mg0.40Zn0.60O) thin films have been grown on quartz substrates by using the radio frequency magnetron sputtering technique, and a metal−semiconductor−metal Schottky barrier photodetector has been fabricated from these films. The photodetector exhibits a peak responsivity at 276 nm and a very sharp cutoff wavelength at 295 nm corresponding to the absorption edge of the Mg0.40Zn0.60O thin film. At 2 V bias, the detectivity of the photodetector is 1.1 × 1012 (cm Hz1/2)/W at 276 nm, and the ultraviolet-to-visible rejection ratio [R(276 nm)/R(400 nm)] is about 4 orders of magnitude. The photodetector also exhibits a very low dark current of about 100 pA at 2 V bias.
[Show abstract][Hide abstract] ABSTRACT: 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 4 V 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.
No preview · Article · Oct 2008 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: In this paper, we have prepared Schottky type ZnO metal–semiconductor–metal (MSM) ultraviolet (UV) detector. The structural, electrical, and optical measurements were carried out. The detector exhibited a peak responsivity of 0.337A/W at 360nm and the dark current was about 1nA under 3V bias. An ultraviolet–visible rejection ratio was obtained about more than four orders of magnitude from the fabricated detector. The 10–90% rise and fall time were 20ns and 250ns, respectively. We proposed that the detector had shown a gain, which was attributed to the trapping of hole carriers at the semiconductor–metal interface.
No preview · Article · May 2008 · Solid-State Electronics
[Show abstract][Hide abstract] ABSTRACT: In recent years, ZnMgO semiconductor alloys, with a direct bandgap
tunable between 3.37 eV and 7.8 eV, become one of the most suitable
materials for the fabrication of ultraviolet detectors. In this paper,
we have fabricated metal-semiconductor-metal photodetectors on 1-μm
thick Zn0.8Mg0.2O films. The interdigital metal
electrodes are 500 μm long and 5 μm wide with an interelectrode
spacing 2 μm, 5 μm and 10 μm, respectively.
Zn0.8Mg0.2O films were grown on quartz by ratio
frequency magnetron sputtering at 500°C. Dark current, spectral
responsivity and pulse response were carried out for the devices with
different finger pitches. All the photodetectors showed the peak
responsivity at 330 nm and the ultraviolet-visible rejection ratio (R330
nm/R400 nm) is more than four orders of magnitude at 3 V bias. For the
device with 2 μm finger pitch, the detectivity was calculated as
4.2×1011 cm Hz1/2/W at 330 nm. Furthermore,
the transient response measurement for all devices revealed similar rise
time of 10 ns. The 90%-10% fall times are 130 ns, 170 ns and 230 ns for
the devices with different finger pitches of 2 μm, 5 μm and 10
No preview · Article · Mar 2008 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: Ni thin films were electrodeposited on n-Si (100) substrate from the electrolytes containing Ni(CH3COO)2 and CH3COONH4 at room temperature. The scanning electron microscope images of the films reveals the uniform distribution of the nickel all over the substrate surface, which illustrates that the fine Ni films on large scales could be obtained through the method of electrodeposition. Vibrating sample magnetometer measurement with the applied field parallel to the surface shows obvious hysteresis loops of the magnetic thin films. The morphology and magnetism of the Ni thin films evolves with the deposition time increasing. The effect of deposition conditions on the properties of the Ni thin films is investigated.
[Show abstract][Hide abstract] ABSTRACT: Ultrathin ZnO nanowire bundles have been synthesized on an indium-tin oxide substrate without any catalyst by using a simple thermal evaporation method, where self-organized ZnO nanowire bundles were grown on the hexagonal heads of ZnO nanocolumns. The nanowires obtained typically have diameters of 8 nm, with lengths extending to 0.25 microm. The size is the same order of magnitude as the ZnO exciton Bohr radius (aB). Room-temperature photoluminescence measurement shows a prominent peak at 374 nm (3.32 eV), which is about 100 meV blue-shifted from the bulk ZnO emission.
No preview · Article · Feb 2008 · Inorganic Chemistry
[Show abstract][Hide abstract] ABSTRACT: Nitrogen-doped ZnO thin films with different nitrogen concentrations were fabricated by plasma-assisted molecular beam epitaxy. Hall effect measurements show p-type conduction for samples with low doping concentration. In highly doped ZnO, the p-type conduction converted to high resistance or unstable p-type behavior. This result indicates that highly doped samples are heavily compensated. In the low temperature photoluminescence spectrum, a donor-acceptor pair (DAP) emission band shows a strong redshift and broadening with increasing nitrogen doping concentration. The large shift of the DAP emission is explained by the Coulomb-potential fluctuation model related to compensated semiconductors.
Full-text · Article · Dec 2007 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: Well-aligned ZnO nanorod and nanobolt arrays were synthesized on p-type Si(100) substrates by a simple physical vapor deposition method. During the growth process when the carrier gas was switched from Ar to air, the nanorods changed into nanobolts completely. The mechanism for this transformation process is discussed. The room-temperature photoluminescence spectrum of nanobolts showed a strong ultraviolet emission at 3.26 eV coupled with a weak deep level energy emission at 2.48 eV. The origin of the ultraviolet emission of nanobolts was investigated by temperature-dependent photoluminescence spectra.
No preview · Article · Oct 2007 · Crystal Growth & Design
[Show abstract][Hide abstract] ABSTRACT: ZnO nanorods of 25 nm with quite homogeneous size and shape have been fabricated by introducing ZnO sols as nucleation centers prior to the hydrothermal reaction. The samples were characterized by scanning electron microscope, transmission electron microscope, X-ray diffraction, photoluminescence and resonant Raman spectra. After ZnO sols are introduced, the width of the resulting nanorods decreases above an order of magnitude and the aspect ratio increases 5 times. The increase of the intensity ratio of ultraviolet to visible emissions in room-temperature photoluminescence spectrum and the decrease of the Raman linewidths show the improvement in the quality of ZnO nanorods. Influences of the number of seed nuclei and the aging time of ZnO sols on the morphology of ZnO nanorods are discussed.
No preview · Article · Jul 2007 · Materials Letters
[Show abstract][Hide abstract] ABSTRACT: The ZnO nanorod arrays were synthesized via a simple vapor deposition method on Si (111) substrates at a low growth temperature of 520°C. By selecting different source materials under different growth pressures, well-aligned hexagonal-shaped ZnO nanorod arrays were obtained under both conditions. X-ray diffraction (XRD) analysis confirmed the nanorods are c-axis orientated. Selected area electron diffraction (SAED) and transmission electron microscopy (TEM) analysis demonstrated the individual nanorod is single crystal. Photoluminescence (PL) analyses show the superior optical properties of the nanorod arrays.
No preview · Article · Apr 2007 · Journal of Luminescence