ZnO/diamond-like carbon (DLC) thin films are deposited by pulsed laser deposition (PLD) on Si (111) wafer. Visible room-temperature photoluminescence (PL) is observed from ZnO/DLC thin films by fluorescence spectrophotometer. The Gaussian curve fitting of PL spectra reveals that the broadband visible emission contains three components with λ=508 nm, 554 nm and 698 nm. The origin and possible mechanism of the visible PL are discussed, and they can be attributed to the PL recombination of ZnO and DLC thin films.
The n-type Nb-doped SrTiO3 with different doping concentrations were studied by first principles cal- culations. The effects of Nb concentration on the formation enthalpy, electronic structure and optical property were investigated. Results show that Nb preferentially enters the Ti site in SrTiO3, which is in good agreement with the experimental observation. The Fermi level of Nb-doped SrTiO3 moves into the bottom of the conduction band, and the system becomes an n-type semiconductor. The effect of Nb-doping concentration on the conductivity was discussed from the microscopic point of view. Furthermore, the 1.11 at% Nb-doped SrTiO3 shows strong absorp- tion in the visible light and becomes a very useful material for photo-catalytic activity. The 1.67 at% and 2.5 at% Nb-doped models will be potential transparent conductive materials.
The p-type N-doped PbTiO3 with different doping concentrations have been studied by first-principles calculations. The charge density differences, band structures, density of states and optical properties have been investigated. After an oxygen atom is substituted by a nitrogen atom in the crystals, the valance bands move to high energy levels and the Fermi energy level gets into the top of the valance bands. Results show that the values of the band gaps are decreased and the stability is weakened when the N concentration increases. The 2.5 at% N-doped PbTiO3 shows the best p-type conductivity and the visible-light absorption can be enhanced most at this doping concentration, which is necessary in semiconductors or photocatalysts.
The electronic structure and optical properties of N-doped β-Ga2O3 and N-Zn co-doped β-Ga2O3 are investigated by the first-principles calculation. In the N-Zn co-doped β-Ga2O3 system, the lattice parameters of a, b, c, V decrease and the total energy Etot,l increases in comparison with N-doped β-Ga2O3. The calculated ionization energy of N-Zn co-doped β-Ga2O3 is smaller than that of N-doped β-Ga2O3. Two shallower acceptor impurity levels are introduced in N-Zn co-doped β-Ga2O3. Compared with N-doped β-Ga2O3, the major absorption peak is red-shifted and the impurity absorption edge is blue-shifted for N-Zn co-dopedβ-Ga2O3. The results show that the N-Zn co-doped β-Ga2O3 is found to be a better method to push p-type conductivity in β-Ga2O3.
By using spin-polarized density functional theory calculations, the electron density differences, band structures and density of states of p-type N-doped PbTiO3 have been studied. In addition, the oxygen vacancy in N-doped PbTiO3 is also discussed. After the nitrogen dopant is introduced into the crystal, the N-doped PbTiO3 system is spin-polarized, the spin-down valance bands move to a high energy level and the Fermi energy level moves to the top of the valance bands, finally the band gap is narrowed. In this process, the N-doped PbTiO3 shows typical p-type semiconductor characteristics. When an oxygen vacancy and N impurity coexist in PbTiO3, there is no spin-polarized phenomenon. The conduction bands move downward and the acceptors are found to be fully compensated. The calculation results are mostly consistent with the experimental data.
Intrinsic fi-Ga203 and Zn-doped β-Ga203 films were prepared using RF magnetron sputtering. The effects of the Zn doping and thermal annealing on the structural and optical properties are investigated. In compar- ison with the intrinsic β-Ga203 films, the microstructure, optical transmittance, optical absorption, optical energy gap, and photoluminescence ofZn-doped β-Ga203 films change significantly. The post-annealed β-Ga203 films are polycrystalline. After Zn doping, the crystallization deteriorates, the optical band gap shrinks, the transmittance decreases and the UV, blue, and green emission bands are enhanced.
Zinc nitride films were prepared by RF magnetron sputtering a metallic zinc target in NH3-Ar mixture gases on glass substrate at room temperature. The effects of NH3 ratio on the structural and optical properties of the films were examined. X-ray diffraction （XRD） analysis indicates that the films are polycrystalline and have a preferred orientation of （321）. An indirect optical band gap increased from 2.33 to 2.70 eV when the NH3 ratio varied from 5% to 25%. The photoluminescence （PL） spectrum shows two emission peaks; the peak located at 437 nm is attributed to the incorporation of oxygen, and the other at 459 nm corresponds to the intrinsic emission.
