Ho Doping Research Articles

Single and binary rare earth REBa2Cu3O7-delta films prepared by chemical solution deposition

In the present work, a series of single and binary rare earth REBa2Cu3O7-delta(REBCO, RE=Y, Ho etc.) thin films, such as YBCO, HoBCO and Y0.7Ho0.3BCO, were prepared by TFA-MOD process. Screw-growth mode and island-like surface were clearly observed in the present samples. Good c-axis orientation and high in-plane texture were identified in the all studied samples by measuring four circle X-ray diffractions (XRD). Theta-2Theta patterns of XRD showed no extra phases other than REBCO. As for HoBCO and Y0.7Ho0.3BCO thin films, the temperature dependences of resistance were investigated in various applied magnetic fields (< 9T) Irreversibility fields (Hirr), characterised with a criteria of zero resistance in R-T curves, showed a similar superconducting behavior between single and binary REBCO, i.e. no obvious changes in performance due to Ho doping in YBCO.

The magnetothermoelectric power in the Y- and Ho-doped La 0.9Te 0.1MnO 3

We present the results of a systematic study of thermoelectric power S ( T ) at zero field and applied magnetic field in the nonmagnetic Y- and magnetic Ho-doped manganites La 0.9− x Y (Ho) x Te 0.1MnO 3 ( 0.05 ≤ x ≤ 0.15 ). For x ≤ 0.10 samples, an additional positive magnetothermoelectric power (MTEP) is induced by Y and Ho doping below Curie temperature T C besides a large negative MTEP in the vicinity of T C . The Ho-doped compounds have larger resistivity ρ and larger S compared to the Y-doped compounds in the same concentration. The magnetic disorder introduced by Ho doping can play an important role in affecting the electronic and thermal transport properties of the sample.

The effect of Ho doping on the microstructure and optical properties of Ba 0.65Sr 0.35TiO 3 thin films

Ba 0.65Sr 0.35TiO 3 (BST) thin films doped with holmium were prepared on silicon and fused quartz substrates by a modified sol–gel technique. The microstructures of BST films were characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD). The results showed that 3 mol% Ho-doped BST has the largest grain size and surface root-mean square roughness. The transmission spectra of Ho-doped BST films were measured by spectrophotometer. The refractive index and thickness of 1 mol% Ho-doped BST film was calculated using envelope method from the transmission spectra. It showed that the refractive index increased from 1.94 to 2.09 as wavelength decreased from 700 nm to 400 nm, which was smaller than pure BST thin films we have reported. The average oscillator strength and wavelength were estimated using a Sellmeir-type dispersion equation. These results show the potential of using Ho-doped BST thin films as an electro-optical novel material.

Electrical Properties of Holmium-Doped BaTiO3

The effects of Ho (holmium) doping on the electrical properties and microstructural development of (Ba1-xHox)TiO3 were investigated by means of defect chemistry on the basis of equilibrium electrical conductivity data measured at 1300°C, as a function of oxygen activity. Ho2O3 additions to BaTiO3 up to 0.3 mol% were compensated by electrons under all oxygen partial pressures and the samples exhibited a low insulating resistance at room temperature. However, at Ho>0.3 mol%, the compensation mode switched from electrons to cation vacancies in the region of high oxygen partial pressure. The solubility limit of HoBa• was confirmed to be less than 3.0 mol%. The specimens doped with Ho<0.5 mol% had a low insulating resistance and large grains, whereas high insulating resistance and fine grains were observed in the samples doped with Ho grater than 0.5 mol%.

Modification of exciton binding energy in the horizontal Bridgman–Stockbarger growth of InSe by Ho doping

Undoped InSe and Ho doped InSe single crystals with various Ho concentrations were grown by the horizontal Bridgman-Stockbarger method. The absorption measurements were carried out in the temperature range 10–320K. Exciton binding energies, steepness parameters, and Urbach energies of InSe and InSe:Ho samples were investigated as a function of temperature. Ho doping caused a shift towards longer wavelengths in the absorption edge. In general, Ho doping causes certain increases in the exciton binding energy and Urbach energy, and a decrease in the steepness parameter. An enhancement of exciton binding energy up to about 55meV is observed at 0.0025 mass ratio of Ho.

Solubility of Ho Ions in Ho and Mg Co-doped BaTiO3 Analyzed by Rietveld Method and EXAFS

Rietveld refinement and extended X-ray absorption fine structure (EXAFS) analysis on the synchrotron radiation X-ray data of BaTiO3-based shell phase powder specimens with Ho and Mg co-dopants were carried out to obtain the knowledge on the occupation site and its quantitative occupancy fraction in BaTiO3 perovskite structure. Ho ions occupied preferentially A-site in BaTiO3 and the occupation ratio was same in any doped compositions. Ho─O atomic distance in A-site is increased with increasing Ho doping in contract to that in B-site.

Optical studies of the Holmium-doped InGaAsP epilayers

Photoluminescence (PL), contactless electroreflectance (CER), and Raman scattering measurements have been used to study the structural properties of Ho-doped InGaAsP epilayers. Both the full width at half maximum (FWHM) of PL and the broadening parameter of CER are decreased as the doping amount of Ho element increases. This indicates that Ho doping greatly reduces the residual impurities and improve the quality of epilayers. The Raman spectra of Ho-doped InGaAsP epilayers are found to have asymmetric line shapes. Using a spatial correlation model, it is found the asymmetric broadening of the Raman signal is not influenced by the Ho doping. We hence conclude that the introduction of the Ho element can greatly reduce the residual impurities of LPE-grown layers, but no large amounts of Ho element are being incorporated into the epilayers during the purification. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of the electrical properties of Ho-doped InSe single crystal

Resistivity and Hall-effect measurements have been performed on Ho-doped InSe single crystal grown by the Bridman–Stockberger method. The mass ratios of Ho added to the starting melts were 25×10 −4, 25×10 −3: Ho added in order to obtain different Ho concentrations. We found the temperature dependence of the Hall mobility as μ e∼ T −1.26 for n-type InSe, μ e∼ T −0.24 for InSe:Ho 0.0025 and μ e∼ T −1.03 for InSe:Ho 0.025 samples at 140– 320 K . Impurity-energy levels calculated from ln( n/ T 3/2) vs 10 3/ T plots for InSe at 30–90 and 100– 320 K are E c −8.2 meV , and E c −36.8 meV , for InSe:Ho 0.0025 at 20–50 and 90– 320 K are E v +8.3 meV , and E c −32.2 meV , for InSe:Ho 0.025 at 30–90 and 80– 290 K are E c −8.53 meV , and E c −35 meV , respectively. The low Ho doping cleans the impurities acting as acceptors between the layers and makes the compensating impurity levels inactive. But the high Ho doping behaves as an impurity in InSe.

Persistent photoconductivity in Ho-doped InGaAsP epitaxial layers

Persistent photoconductivity (PPC) was investigated in Ho-doped InGaAsP epilayers with Ho concentrations in the range of 0–0.15 wt%. The decay behavior of PPC resembles that of Al x Ga 1− x As and can be well described by a stretch-exponential function. The temperature-dependent PPC studies show that the lattice relaxation of DX-like centers is responsible for the PPC effect. As the Ho doping increases, the decay-time constant and the electron-capture barrier were found to decrease. We suggest that the introduced Ho elements may chemically react with donor impurities, suppressing lattice relaxation and hence reducing the electron-capture barrier. Also, rare earth doping is demonstrated to be an effective method of improving the quality of InGaAsP epilayers.

Influence of holmium doping on the optical properties of quaternary InGaAsP epitaxial layers

Photoluminescence and photoconductivity measurements were used to study the influence of Ho doping on the optical properties of InGaAsP layers grown by liquid phase epitaxy (LPE). The full width at half maximum (FWHM) of the photoluminescence peak was found to decrease as the amount of Ho increases. When the amount of Ho is 0.11 wt%, the FWHM has a minimum value of 7.93 meV, about 46% lower than that of the undoped InGaAsP. The absorption tails observed in the photoconductivity were analyzed with the Urbach tail model and the Urbach energies were obtained from the fits. The Urbach energy decreases as the amount of Ho increases, indicating that Ho doping greatly reduces the amount of residual impurities in LPE-grown layers.

Photoluminescence in Ho-doped AgGaS 2 single crystals

Doping of Ho into AgGaS 2 has been carried out by the thermal diffusion of Ho element into the undoped crystal. Sharp photoluminescence (PL) lines related to the 5S 2→ 5I 8 and 5F 3→ 5I 7 transitions in the Ho 3+ ion are observed in the energy regions 2.23–2.28 and 1.85–1.93 eV, respectively. Temperature dependence and excitation wavelength dependence of the PL indicate the existence of at least four types of Ho-related luminescence centers. Moreover, it is found that PL lines from different Ho-related luminescence centers exhibit different excitation and recombination mechanisms.