Co-doping Of ZnO Research Articles

Raman investigations of Zn1−xCoxO nanocrystals: role of starting precursors on vibrational properties

AbstractThe Raman spectra of sol–gel derived Co‐doped ZnO nanoparticles (NPs) in the spectral range 100–1500 cm−1 were investigated. In the sol–gel method, three different series of Co‐doped ZnO particles, i.e. Zn1−xCoxO (x = 0.05, 0.10, 0.15, and 0.20), were obtained using three different starting precursors, viz. cobalt chloride hexahydrate, cobalt acetate tetrahydrate, and cobalt nitrate hexahydrate, respectively. It has been observed that cobalt acetate is a better precursor in comparison to cobalt chloride and cobalt nitrate to obtain single‐phase Co‐doped ZnO NPs. As for cobalt acetate‐derived NPs, no hidden secondary phase of Co3O4 was observed for the lower (x = 0.05) Co concentration. The Fröhlich interaction associated with the longitudinal modes was found to be destroyed with increasing Co concentration due to structural disorder and defects induced by the dopant. In addition to ZnO and Co3O4 vibrational modes, a few additional modes near 550 and 715 cm−1 were also observed in all cases, which could be attributed to the modes due to Co doping in ZnO. Copyright © 2011 John Wiley & Sons, Ltd.

Theory study of Ag-S codoping in ZnO

All calculations, regarding S-monodoped and Ag-S codoped ZnO, have been performed by first-principles density-functional calculations. In S-monodoped ZnO, the formation energies show that SZn and SO is easier to form in O-rich conditions while S dopant prefers to occupy the substitutional O site in Zn-rich conditions. In Ag-S codoped ZnO, the electrical structures show that 2AgZn+SO complex is better for p-type doping while 2AgZn+SZn and 2AgZn+Si complexes are not suitable for p-doping. Moreover, 2AgZn+SO complex is easier to form than the other two complexes according to the formation energy. Therefore, in 2Ag-S codoped ZnO, the Zn-rich condition is helpful to gain p-type ZnO.

Structural and optical analysis of ZnBeMgO powder and thin films

We here report the structural and optical studies of Zn 1− x− y Be x Mg y O (0 ≤ x ≤ 0.15; 0 ≤ y ≤ 0.20) powders and thin films. From the Rietveld refinement of the powder X-ray diffraction (XRD) patterns it was revealed that the value of ‘ a’ lattice parameter remains almost unchanged whereas ‘ c’ parameter reduces with Be and Mg co-doping in ZnO. The Zn-O bond length also decreases in co-doped samples. Raman studies of the pure ZnO powder showed all the characteristic peaks of the wurtzite hexagonal structure and with (Be, Mg) co-doping new modes appeared which can be attributed to arise as a result of substitution. The XRD of the films prepared from the powders using pulsed laser deposition (PLD) technique exhibited the preferential orientation and with increase in co-doping the (0 0 0 2) peak also shifts to higher 2 θ values suggesting the incorporation of Be/Mg at the Zn-site. From the UV–visible optical transmittance measurement it was noticed that the band gap of the pristine ZnO film is 3.3 eV which enhanced up to 4.51 eV for Zn 0.7Be 0.1Mg 0.2O film which lies in the solar blind region and is very useful in the realization of deep UV detectors.

P-type doping and codoping of ZnO based on nitrogen is ineffective: An ab initio clue

Whereas nitrogen is regarded as the best candidate to induce p-type doping in ZnO, the practical results are mainly negative either for monodoping or codoping. We perform first-principles calculations to investigate the p-type nature of boron and nitrogen codoped ZnO. The p-type character can be obtained with the proper BN3 substitutional clusters. We propose a mechanism that explains the difficulties to synthesize p-type ZnO samples: the formation of N2 molecules substituting oxygen, which are donors, energetically prevails over any codoping cluster. This mechanism is very general and explains the experimental instability of N-based doping and codoping versus time and temperature.

Structure, Electronic Structure, Optical, and Dehydrogenation Catalytic Study of (Zn1−zInz)(O1−xNx) Solid Solution

Indium and nitrogen codoping in ZnO leads to a solid solution of InN in ZnO with a composition of (Zn1−zInz)(O1−xNx). A simple solution combustion method has been adopted to prepare the above materials in less than 10 min with metal nitrates as the metal ion source and urea as fuel. With reference to ZnO, significant increase in lattice parameters was observed with increasing In-content. However, the In2O3 phase was observed along with InN for In content ≥10%. Optical absorption extended into the visible region, at least up to 550 nm, demonstrates an effective reduction of optical band gap due to the formation of solid solution. A new feature observed just above O 2p valence band in X-ray photoelectron spectroscopy (XPS) suggests the creation of N 2p states from InN; the N 1s core level XPS result too confirms nitride contribution. Raman spectroscopy and secondary ion mass spectrometry results show direct In−N, Zn−N, and In−N−Zn fragments in (Zn1−zInz)(O1−xNx). Catalytic activity explored for oxidation of...

A novel approach for codoping in ZnO by AlN

In the present work, we have illustrated a new idea of codoping in ZnO with AlN as codopant to achieve p-ZnO. ZnO films doped with different concentrations of AlN were grown by RF magnetron sputtering. The AlN doped ZnO (ANZO) films grown on sapphire substrate were subjected to X-ray diffraction (XRD), reflectance measurements, Hall measurements, atomic force microscopy (AFM) and energy dispersive spectroscopy (EDS) analysis. XRD analysis reveals that all films have grown in the form of hexagonal wurtzite structure with (002) preferential orientation. The FWHM of (002) peak decreases till 1 mol% of AlN and increases for further addition of AlN indicating the incorporation of more impurities (dopants). The reflectance measurements suggest that the reflectance decreases at lower concentration and increases above 1 mol% of AlN in the visible region ranging from 400 to 800 nm. Hall measurements show that all the films are n-type. The electron concentration increases initially and then decreases for further addition of AlN (>1 mol%) suggesting the incorporation of nitrogen into the film at higher concentrations of AlN. The presence of N in the films is further confirmed by EDS analysis. The rms surface roughness measured by AFM decreases exponentially with dopant concentration. The figure of merit increases upon codoping with AlN.

Competing effects of Cu ionic charge and oxygen vacancies on the ferromagnetism of (Zn,Co)O nanoparticles

We report the effects on the ferromagnetism due to co-doping of ZnO with Co and Cu inthe presence of variable numbers of oxygen vacancies. The co-doped nanoparticlesZn0.95−Co0.05CuyO (0.00≤y<0.009) were prepared via the chemical route with oxygen vacancies introduced viaannealing in a reducing atmosphere for variable amounts of time. In additionto the magnetization, the particles were characterized by x-ray diffraction(XRD), x-ray photoemission spectroscopy (XPS) and x-ray absorption nearedge spectroscopy (XANES). The Co ions were determined to be in the+2 state in a tetrahedral symmetry, with no evidence for metallic Coor Cu. However, the ionic state of Cu is found to change from+2 to+1 state with increasing Cu concentration, which appears to strongly decrease the concentration ofoxygen vacancies. It is found that the ferromagnetic moment initially increases with the additionof Cu but decreases above a typical concentration that coincides with the appearance of theCu+1 state and the decrease of O vacancy concentration. It is concluded that the effectof Cu in the very low range of concentrations, where it appears to go in asCu+2, is to stabilize ferromagnetism indirectly via generation of O vacancies. The effects of Ovacancy concentration on the ferromagnetism are interpreted in the light of the F-centerexchange (FCE) model.

Effect of Y2O3 and ZnO Co-doping on the Microstructure and Dielectric Properties of BaTiO3 Materials

Effect of Y2O3 and ZnO Co-doping on the Microstructure and Dielectric Properties of BaTiO3 Materials

Codoping in ZnO using GaN by pulsed laser deposition

We report on the codoping of Ga and N into ZnO films by pulsed laser deposition with ZnO:GaN targets of different concentrations. The effect of GaN dopant on the structural, optical and electrical properties have been investigated. The X-ray diffraction (XRD) measurements show that for the GaN concentration up to 0.8 mol%, the full width at half maximum (FWHM) of (0 0 2) peak significantly reduces and thereby improves the crystallinity of the films while for 1 mol% the FWHM increases. For the GaN-doped films, the photoluminescence (PL) spectra show only a strong near band edge (NBE) emission and the deep level emissions are almost undetectable, indicating that GaN doping considerably suppresses the defect related emissions. The glow discharge mass spectroscopy (GDMS) spectra confirm the presence of Ga and N in the grown films. Our Hall measurements show that all the GaN-doped ZnO films are n-type, indicating that N acceptors are not sufficient to compensate the donors. The carrier concentrations have been increased till 0.8 mol% of GaN and decreased for 1 mol% GaN-doped film.

Influence of ZnO + Fe 2O 3 additives on the anatase-to-rutile transformation of nanometer TiO 2 powders

Titania nanopowders with additives of ZnO + Fe 2O 3 were prepared by the sol-gel method. The influence of the additives on the anatase-to-rutile phase transformation of TiO 2 was investigated by using XRD, DSC and TEM. It was found that co-doping of ZnO + Fe 2O 3 noticeably enhanced the transformation by reducing the onset transformation temperature as well as the transformation temperature width.

Nd3+ centres induced by ZnO or MgO codoping LiNbO3

Laser spectroscopy has been applied to systematically investigate the effect of MgO or ZnO codoping on the Nd3+ centres formed in LiNbO3. Both codopant oxides produce the same effect, so two new Nd3+ centres appear in both LiNbO3(MgO):Nd and LiNbO3(ZnO):Nd crystals. These new centres correspond to a small percentage (less than 1%) of Nd3+ ions, which are displaced from Li+ sites to a new lattice site. The possible sites for these Nd3+ centres are discussed.