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The supercell structure of ZnO (2 × 2 × 2). The N atom is at the center of the supercell; the Al/Ga/In substitution sites are labeled as I–VII.
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N-mono doped and N-Al/Ga/In co-doped ZnO were investigated by first-principles calculations. We have studied the structural and electrical properties, the p-type conductivities and the defects formation energies of different doped structures. The results showed that the Fermi level moved downward into the valance band and showed p-type conductivity...
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This study reports on the dual-acceptor doping effects on ZnO for obtaining p-type conductivity and effectively tuning the band gap. The electronic and optical properties of undoped, mono-(N, Cu) and dual-(N-Cu) doped ZnO have been investigated using first-principles calculations based on the density functional theory (DFT) in the framework of gene...
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... Among them, U is the Coulomb potential (Hubbard), and Ud, Zn and Up, O of all systems are taken as 5.5 eV [31] and 8.00 eV [31], respectively. The U values of Al, Ga, In, and N are taken as the software default value of 0 eV, which is consistent with the calculation method in reference [32]. We use the Perdew-Burke-Ernzerhof parameterization to describe the exchange correlation function. ...
Current research on the Zn1-xMxO1-yNy (M=Ga, In) system mainly focuses on p-type property, where Ga-N or In-N has different preferred orientations for bonding. Studies on the magnetic, bandgap, and optical properties of ZnO co doped with N are also lacking. The generalized gradient approximation (GGA+U) plane wave ultrasoft pseudopotential method based on density functional theory is used to systematically investigate the effects of the magnetic, band gap, and optical properties of the system for addressing the aforementioned problems. Results show that the formation energy of the Zn1-xMxO1-yNy (M=Ga, In) system is negative, all doping is easy, and all doped systems are stable and magnetic. The magnetism comes from the double exchange effect of electron spin polarization. Research has found that the band gap in Ga-N or In-N bonding along the c-axis direction is narrower than that along the a-axis direction. In the low-energy region, the red shift of the absorption spectrum is more significant, and the absorption or reflection coefficient and the carrier polarization and activity are stronger. Especially, In-N forms bonds along the c-axis direction and is co doped with another N in ZnO, which results in the narrowest band gap and the most significant red shift in the absorption spectrum. The absorption of sunlight can also be achieved in the ultraviolet visible near-infrared region. The absorption or reflection coefficient and the carrier polarization and activity are relatively strongest. This work has certain reference value for the design and preparation of new solar cell light absorbing materials based on ZnO.
... The maximal valence band is mostly unchanged in the meantime. In comparison to undoped ZnO, nonmagnetic Zn 15 Li in O 15 has a greater band gap [52]. The improved hybrid coupling back-bond effect between Zn-4s, Zn-3p, and O-2p states at the minimal conduction band is responsible for this result, whereas the maximum valence band is essentially unaltered [53]. ...
The current study investigated the development and application of lithium (Li)-doped zinc oxide (ZnO)-impregnated polyvinyl alcohol (PVA) proton exchange membrane separator in a single chambered microbial fuel cell (MFC). Physiochemical analysis was performed via FT-IR, XRD, TEM, and AC impedance analysis to characterize thus synthesized Li-doped ZnO. PVA-ZnO-Li with 2.0% Li incorporation showed higher power generation in MFC. Using coulombic efficiency and current density, the impact of oxygen crossing on the membrane cathode assembly (MCA) area was evaluated. Different amounts of Li were incorporated into the membrane to optimize its electrochemical behavior and to increase proton conductivity while reducing biofouling. When acetate wastewater was treated in MFC using a PVA-ZnO-Li-based MCA, the maximum power density of 6.3 W/m3 was achieved. These observations strongly support our hypothesis that PVA-ZnO-Li can be an efficient and affordable separator for MFC.
... The perturbative harmonics, H3 and H5 reveal an isotropic dependence. Moreover, the band structure of ZnO around the bandgap is isotropic up to a conduction band energy of 6 eV [112,113], which explains why the polarization dependence of H7 (4.1 eV) is also isotropic. Accordingly, using higher intensities would allow detecting higher harmonic orders, and observing their anisotropic laser polarization dependence. ...
Since its first observation, a decade ago, high harmonic generation (HHG) in crystals has proved to be an efficient, controllable and compact source of coherent XUV radiation. In this thesis, we investigate HHG in 2D materials, particularly graphene, and in different semiconductor crystals mainly zinc oxide, silicon, gallium arsenide and magnesium oxide. We find that the laser properties, such as its intensity, polarization and ellipticity, and the crystal properties are interrelated. Moreover, we shed the light on the role of the linear and nonlinear propagation effects mainly the Kerr effect, upon laser interaction with the crystal, which can significantly influence the high harmonic generation efficiency. Although this presents major limitations, we show that in some cases it turns out to be an advantage. Finally, we demonstrate the manipulation of the harmonic radiation at the source of the emission by patterning nanostructures to confine and enhance nanojoule laser pulses, and generate harmonic beams carrying orbital angular momentum. Lastly, we successfully image a micrometer-sized sample by the coherent diffractive imaging (CDI) technique based on solid-state harmonics.
... The GGA + U method was used to correct the band gaps throughout the entire system. In this paper, U p,O = 7 eV [31], U d,Zn = 10 eV [31], and the U Li was the default value, consistent with the calculation method utilized in [32]. We used the Monkhorst-Pack scheme grid of 4 × 4 × 2 and 4 × 4 × 1 for the 32-atom supercell (2 × 2 × 2) and 64-atom supercell (2 × 2 × 4), respectively. ...
The effects of Zn/O vacancy (VZn/VO) and different proportions of Li/VZn on the magnetism of Li-doped ZnO are analyzed through first-principle calculation by using generalized gradient approximation+ U (GGA + U) under density functional theory. Results reveal that Li-doped ZnO with VZn can realize ferromagnetic long-range order and has a Curie temperature above room temperature. Under different proportions of Li/VZn (i.e., 1:1, 1:2, and 2:2) in ZnO (2 × 2 × 4), the doping system containing 2Li/2VZn (Zn28Li2O32) shows the greatest magnetic moment and the smallest differential charge density. These characteristics pave the way for enhancing the magnetic properties of dilute magnetic semiconductors. The oxygen atoms in Zn28Li2O32 show acceptor and donor characteristics and exist in the forms of itinerant electrons (O1−) and local electrons (O2−), which have different effects on Zn28Li2O32 magnetism. The spin-polarization double-exchange effect among the unpaired itinerant electron (O1−) orbit, local electron (O2−) orbit, and unpaired Zn-3d electron orbit is the origin of magnetism for Li-doped ZnO with VZn. By contrast, the doping systems of Li-doped ZnO with VO are nonmagnetic, rendering such systems inapplicable.
Elemental doping is an efficient strategy to modulate different properties of semiconductors. Conversion from n-type to p-type and band gap modulation of ZnO are investigated by theoretical and experimental pathways studies. The structural, electronic and optical properties of undoped, Ag and Ag-Li doped ZnO are studied in the framework of density functional theory (DFT). The value of direct band gap is found to be ~ 0.730, 0.440, 0.274, and 0.870 eV for undoped, Ag = 6.25 and 12.5% doped, and Ag= 6.25, Li=6.25% co-doped ZnO, respectively. Acceptor levels are created at the top of the valence band and above the Fermi level in Ag and Ag-Li doped ZnO which reveals that Ag and Ag-Li are promising dopants for generating p-type ZnO. Importantly, a remarkable change in photoconductivity and optical properties are observed. The surface morphology of the spray deposited Zn100-xAgxO (x=0.0 to 20%) and Zn100-x-yAgxLiyO (x=5, y=0.0 to 10%) thin films are changed with Ag and Ag-Li contents. The XRD patterns confirmed the hexagonal structure of all the deposited films. The band gap decreases from 3.27 to 3.08 eV (for Ag doped ZnO) and increases from 3.16 to 3.38 eV for Ag-Li doping ZnO, respectively. The dielectric constants and photoconductivity spectra support the formation of p-type conductivity of Zn100-xAgxO and Zn100-x-yAgxLiyO, which are in good agreement with the available theoretical and experimental reports. Thus, the studies performed in this work help us to understand the Ag and Ag-Li doping mechanism in ZnO; opening up possible directions toward the fabrication of p-type ZnO for advanced electronic and optoelectronic applications.
Iterant electrons exist in the f and d states of ZnO:Sm with point defects (VZn, Hi), which are often overlooked. Moreover, p-type ZnO is difficult to realize. To solve such problems, this study adopts the first-principles generalized gradient approximation (GGA + U) plane wave supersoft pseudopotential method to construct a ZnO:Sm system with point defects (VZn, Hi). The stability and conductivity of the doped system and the new magnetic mechanism are studied under a biaxial strain. Result shows that the Zn34SmHiO36 system has the lowest formation energy, simplest doping, lowest binding energy, and highest stability and is a relatively p-typed system when the Sm–H spacing is closer compared with the Zn34SmHiO36 systems with different Sm–H spacings. The hole conductivity of the Zn34SmHiO36-doped system in the z-axis direction is high when no external strain is applied. The result demonstrates that the Zn34SmHiO36 system is magnetic. The charge transfer from s state of single ion Sm to f and d states of Sm causes magnetism in the doped system, which differs from the traditional theory of orbital hybrid coupling and double exchange magnetic source between distinct ions. The Sm-4f and Sm-5d states in the Zn34SmHiO36 system have itinerant and local electron properties, which affect the magnetic source and p-type of the system. This work has certain reference value for the design and preparation of new ZnO magnetoelectric-integrated functional materials.
The influence of Sm doping on the physical properties of ZnO has been widely investigated. However, the potential point defects and interstitial H in the Sm-doped ZnO system and the influence of strain on the physical properties of ZnO remain poorly understood. First-principle studies on the effects of biaxial strain on the photocatalysis and magnetic mechanisms of ZnO with Sm doping and point defects (VZn, Hi) are rarely reported. In this work, a method based on first-principle plane wave super soft pseudopotential + U under the framework of density functional theory was adopted. A ZnO system with Sm doping and point defects (VZn, Hi) was constructed, and its formation energy, photocatalysis, and magnetic mechanism were studied within the strain range from −6% to 6%. Results showed that regardless of tensile/compressive strain, the formation energy increased in the doped system compared with that in the unstrained doped system. By contrast, stability was relatively decreased. Under the same strain conditions, the Zn34SmHiO36 system had relatively low formation energy and relatively good stability. In addition, interstitial H can effectively increase the separation speed of electron–hole pairs, thereby prolonging the carrier life. Redshift effect, electric dipole moment, oxidation/reduction reactions, and decisive carrier lifetime are affected by the photocatalytic performance of the actual doping system. Under −4% compressive strain, the Zn34SmHiO36 system acts as an excellent catalyst of light. Regardless of tensile/compressive strain, the Zn34SmO36 and Zn34SmHiO36 systems exhibit magnetic properties, and the interstitial H improves the magnetic properties of the doped system. This finding is consistent with the Ruderman–Kittel–Kasuya–Yosida (RKKY) magnetic theory. Under unstrained conditions, the Zn34SmHiO36 system exhibits a semi-metallic characteristic with 100% hole spin polarization. This research has application value for the design and preparation of novel dilute magnetic semiconductors with spin-hole injection source.
Fabricating p-type β-Ga2O3 with shallow acceptor levels is vital to the application of β-Ga2O3 based devices. Herein, we propose a potential approach, (electron-poor metal, N) co-doping, to effectively decrease the acceptor levels. The (electron-poor metal, N) co-doping is easier to be realized compared to the pure N doping for β-Ga2O3. Moreover, partial co-doping further shifts up the Ga–O bonding orbitals and down the dopant-O anti-bonding orbitals and the unoccupied p orbitals of N and O ions, thus the acceptor levels can be significantly decreased when the pure metal doping is replaced by the co-doping method. The acceptor levels of (Mg, N) and (Zn, N) co-doped β-Ga2O3 are as low as 0.16, and 0.01 eV, respectively. More importantly, (metal dopant with p orbitals, N) co-doping hinders the formation of O-vacancy which limits the formation of p-type β-Ga2O3. These results suggest that (metal, N) co-doping might be a potential way to achieve an effective p-type β-Ga2O3.
