Dagui Chen

MgZnO-based metal-semiconductor-metal solar-blind photodetectors on ZnO substrates

Using lattice matched ZnO substrates, wurtzite single crystalline Mg0.49Zn0.51O films were obtained by reactive magnetron cosputtering method, and the heterostructures of MgZnO/ZnO were fabricated into metal-semiconductor-metal solar-blind photodetectors (SBPDs). Calculated and experimental results demonstrate that the response of the ZnO substrate can be suppressed by adopting a thick MgZnO epilayer. The SBPD with a 2 μm thick MgZnO epilayer shows a peak responsivity of 304 mA/W at 260 nm under 10 V bias, which is comparable to the highest value ever reported in MgZnO-based SBPDs. A rejection ratio (R260 nm/R365 nm) over 5×102 is also observed, indicating fully suppression of the signal from ZnO substrate.

High-responsivity solar-blind photodetector based on Mg 0.46Zn0.54O thin film

Adopting relatively high substrate temperature and low growth rate, single-phase wurtzite Mg0.46Zn0.54O film is grown on a quartz substrate by homemade magnetron sputtering. Solar-blind photodetector is fabricated based on the MgZnO film and shows a peak responsivity of 3.4 A/W at 265 nm with a cutoff wavelength of 280 nm under 10 V. As applied voltage increased to 70 V, the peak responsivity is up to 31.1 A/W corresponding to an internal gain of 148 times. The large internal gain was attributed to the trapping of photoionized holes at Ev + 282 meV deep level through deep-level transient spectral measurement.

Electron injection assisted phase transition in a nano-Au-VO2 junction

The semiconductor-metal transition of vanadium dioxide (VO2) thin films epitaxially grown on C-plane sapphire is studied by depositing Au nanoparticles onto the thermochromic films forming a metal-semiconductor contact, namely, a nano-Au-VO2 junction. It reveals that Au nanoparticles have a marked effect on the reduction in the phase transition temperature of VO2. A process of electron injection in which electrons flow from Au to VO2 due to the lower work function of the metal is believed to be the mechanism. The result may support the Mott–Hubbard phase transition model for VO2.

Tunable surface charge of ZnS:Cu nano-adsorbent induced the selective preconcentration of cationic dyes from wastewater.

A novel environmentally friendly nano-adsorbent is developed by doping Cu(+) cations into the lattice of ZnS microspheres. The adsorbent shows selective adsorbability for cationic dyes in low concentrations in wastewater. The adsorbed dye could be successfully eluted with alcohol, resulting in a 1000 fold enrichment of the dye solution.

Paramagnetic anisotropy of Co-doped ZnO single crystal

Zn0.95Co0.05O single crystal was obtained through hydrothermal crystal growth method. Extended x-ray absorption fine structure and x-ray absorption near-edge structure spectra as well as UV absorption measurements reveal that Co2+ ions have substituted Zn2+ ions and incorporated into ZnO lattice. The single crystal shows typical paramagnetic property from 2to300K. A paramagnetic anisotropy property in the crystal is found. The single ion anisotropy origin from tetrahedral coordination Co in the ZnO lattice was introduced to explain the phenomena. This work verified the paramagnetic anisotropy phenomena in ZnO–Co.

Ultraviolet-light-induced bactericidal mechanism on ZnO single crystals

By comparing the photocatalytic bactericidal effect on different crystal faces of bulk ZnO crystal, we found that an electron degradation mechanism dominates the photocatalytic processes of ZnO material.

Dependence of structural and optoelectronic properties of sputtered Mg0.50Zn0.50O films on substrate

Mg0.50Zn0.50O thin films were grown on MgO, sapphire and quartz substrates by a home-made magnetron sputtering system under the same deposition conditions. The Mg compositions in all these MgxZn1−xO films are around 50%, independent of the growth substrates. X-ray diffraction measurements reveal that the lattice structures of these Mg0.50Zn0.50O films depend on the lattice structures of growth substrates and are cubic (C), wurtzite (W) and mixed phase, respectively. Transmission spectra show that the cutoff wavelength of C-Mg0.50Zn0.50O is located in the UV-C (200–280 nm) region, while that of W-Mg0.50Zn0.50O is located in the UV-B (280–320 nm) region. Though Mg compositions of the Mg0.50Zn0.50O films are the same, the energy-band gap of the C-Mg0.50Zn0.50O film (5.1 eV) is much larger than that of the W-Mg0.50Zn0.50O film (4.3 eV) due to the different electronic structure between the cubic and wurtzite structures. Metal–semiconductor–metal structure solar-blind and visible-blind UV photodetectors were fabricated based on the C-Mg0.50Zn0.50O and W-Mg0.50Zn0.50O films, respectively.

Intrinsic magnetism of a series of Co substituted ZnO single crystals

Magnetic properties of a series of well-substituted Zn1−xCoxO (x = 0.018,0.036 and 0.05) single crystals were studied. A typical paramagnetic anisotropy property, which strengthens when x decreases, was found. A magnetization step was observed at 2 K when the magnetic field is parallel to the c axis, indicating that paramagnetic anisotropy is the origin of the strong crystal field effect on Co2+ ions in ZnO lattices. The Co2+ single-ion anisotropy parameter 2D is obtained as 7.5 K. The effective moment of Co2+ takes the values 2.7 µB, 1.82 µB, 1.49 µB when x = 0.018, 0.036 and 0.05, revealing that more antiferromagnetic coupling between Co2+ ions arises in the perfect crystal when x increases.