Effect Of Oxygen Doping Research Articles

Influence of oxygen doping on the photoconductivity of π-conjugated molecules

The effect of oxygen doping on the photoconductivity of sexithiophene and oxotitanylphthalocyanine films on interdigitated electrodes is investigated by studying photocurrent kinetics after pulsed excitation. Photoadsorbed oxygen is found to increase the photoconductivity by forming a charge-transfer complex MO 2 with the film molecules. Encounters of excitons with MO 2 and electron transfer from the film to an excited MO 2 lead to efficient charge carrier separation. The resulting kinetics reproduce the experimental results.

Electronic structure of Hg 0.8 Pb 0.2 Ba 2 Ca 2 Cu 3 O 8+δ : the role of Pb doping, oxygen doping and high pressure

The effects of Pb doping, oxygen doping (δ = 0.1, 0.2, 0.4 and 0.5) and high pressure (4, 8, 15 and 20 GPa) on the electronic structure of Hg0.8Pb0.2Ba2Ca2Cu3O8+δ have been examined by the recursion method. Our calculations show that Pb doping only decreases the hole concentration slightly and oxygen doping increases the hole concentration monotonically and significantly as δ varies from 0 to 0.5, with each excess oxygen atom contributing about 1.7 holes to the CuO2 layers. The optimal δ is estimated to be around 0.4. The hole concentration increases initially with pressure but decreases as P > 8 GPa (i.e., dn/dP does change sign at similar 8 GPa). The suppressed Tc(P) by Pb substitution has to be described in the modified Neumeier's model.

Effect of pressure and of oxygen content on superconductivity in the cuprate HgBa 2CuO 4+δ. A quantitative analysis based on indirect-exchange pairing

A quantitative analysis is presented of experimental pressure and oxygen-doping effects on the critical temperature of HgBa 2CuO 4+δ over a wide range of δ, covering both under- and overdoped compositions, on the basis of indirect-exchange pairing between conduction electrons via oxygen anions. The results clearly show that for δ ⩽ 0.28, the oxygen doping process is not the same as cation doping in e.g. La 2− x Sr x CuO 4: part of the doped oxygen fulfills a double role as hole dopant and as Cooper pair mediator. Furthermore, adding or extracting oxygen under experimental conditions is accompanied by a redistribution of oxygen anions in the unit cell, to or from the neighborhood of the CuO 2 layer. This effect explains the surprisingly wide range of superconducting compositions (0.03 ⩽ δ ⩽ 0.40) of the system. The observed, anomalous, upward shift in thermoelectric power for δ />/ 0.28 is attributed to different sites of doped oxygen beyond that limit, affecting only hole conductivity.

Effects of oxygen doping and pressure on superconducting transition temperature in Y 0.9Ca 0.1Ba 2Cu 3O y

The dependence of the superconducting transition temperature T c on the Hall number was systematically investigated by changing the oxygen content and pressure in Y 0.9Ca 0.1Ba 2Cu 3O y. It was determined that the change in T c due to pressure, ΔT c, can be expressed by sum of two terms, (ΔT c) c and (ΔT c) p, where (ΔT c) c is the change in T c due to pressure-induced change in carrier density and (ΔT c) p is the change in T c due to pressure-enhanced electron pairing. The contribution of (ΔT c) c to ΔT c increases with decreasing oxygen content. This result is discussed in terms of whether oxygen atoms in the carrier reservoir can be easily moved by changing the temperature and/or pressure.

Excess Oxygen Doping in Single Crystals of La2-xBixCuO4+δwith or without Macroscopic Phase Separation

Systematic heat treatments have been performed using single crystals of La 2- x Bi x CuO 4+δ to study the effect of oxygen doping on the phase stability as well as the three-dimensional magnetic order. For La 2 CuO 4+δ , the analysis of magnetic susceptibility peak near the Neel temperature T N revealed that the continuous decrease of T N upon doping is terminated at 280 K. The further doping additionally induces the previously reported macroscopic phase separation accompanying an antiferromagnetic phase with T N =265 K and a superconducting one with T C ≤35 K. On the other hand, for La 2- x Bi x CuO 4+δ with x ∼0.05 no macroscopic phase separation was observed up to δ≈0.02. Upon the oxygen doping, the T N continuously decreases from 310 K to below 10 K only by the heat treatment. The scaling behavior of magnetic ssusceptibility previously studied by the powder sample of La 2- x SrxCuO 4+δ was reexamined in this system.

Electrical properties of CdTe films prepared by close-spaced sublimation with screen-printed source layers

CdTe films have been deposited by a close-spaced sublimation process with screen-printed CdTe layers as a new source. The source-layers were fabricated by screen printing and sintering slurries consisting of propylene glycol, CdCl2 and either CdTe powder or (Cd+Te) powder. When CdTe powder was used as a starting material for the source-layer, the electrical resistivity of the CdTe film deposited in O2 was about one-tenth lower than that of the film deposited in He. AES, EDS and PIXE analysis showed that the Cd content in the CdTe films deposited in O2 was smaller than that in the CdTe films deposited in He. Especially, no oxygen element was detected in the CdTe films deposited in O2. It turned out that the sublimated Cd(g) and CdTe(g) from the source-layer formed cadmium oxides in O2 and as a result the overall composition of vapor source became more Cd-deficient. The CdTe film with less Cd content increased cadmium vacancy defects (VCd2−Cl+ and VCd2−) and hole concentrations. As the Cd/Te ratio in the starting (Cd+Te) powder decreased, the resistivity of the CdTe films decreased and reached at a constant value of about 3x104 Ω⋅cm, regardless of deposition atmosphere. In addition, the resistivity decrease by O2 treatment was diminished when the Cd/Te ratio was below 0.7, where the composition of CdTe film might be limited by solid solubility (Cd0.92Te1.0). The above results indicated that the resistivity decrease of CdTe films deposited in O2 was not due to the effect of previously-known oxygen doping but due to the effect of Cd/Te compositional change.

Characteristics of oxygen over-reduced Nd1.85Ce0.15CuO4−y films

We have studied the oxygen doping effect in thin Nd1.85Ce0.15CuO4−y (NCCO) films. Contrary to the common believe that the disappearance of superconductivity in the over-reduced NCCO samples is a consequence of phase decomposition, we found that there exists an over-reduced region in which the crystallographic structure of the film remains essentially the same as in the optimum-oxygen doped region, but the film becomes insulating. Rutherford backscattering spectroscopy channeling analysis reveals that the oxygen over-reduction increases atomic distortion in the lattice. This work provides strong support to previous transport studies by Jiang et al. [Phys. Rev. Lett. 73, 1291 (1994)], which suggested the existence of both electron and hole carriers in superconducting NCCO.

Effects of oxygen doping on properties of microcrystalline silicon film grown using rapid thermal chemical vapor deposition

An oxygen doped microcrystalline silicon (μc-Si) deposition process is developed by mixing small amounts of nitrous oxide (N2O) with silane (SiH4) in a rapid thermal chemical vapor deposition (RTCVD) reactor. The effects of oxygen doping on the properties of RTCVD μc-Si films are studied. Experimental results show that the RTCVD process provides high deposition rates for μc-Si and polycrystalline silicon (polySi) films at elevated deposition temperatures and pressures. The surface roughness of the RTCVD μc-Si films can be significantly reduced compared to that of conventional LPCVD polySi films. Steep side walls can be realized due to the small grain size of the μc-Si films. The sheet resistance of BF2 doped μc-Si films is slightly higher than that of BF2 doped polySi films, whereas sheet resistances of P and As doped μc-Si films are much higher than those of the corresponding P and As doped polySi films. Measurements of the catastrophic breakdown strength of metal-oxide-semiconductor (MOS) capacitors indicate that the quality of gate electrodes fabricated using μc-Si is improved relative to that of MOS capacitors fabricated using polySi gate electrodes.

Optical study of the doping effect of oxygen in YBa2Cu3Oy and Bi2Sr2CaCu2O8+δ single crystals

The results of ellipsometric measurements of the optical properties of single crystals of YB2Cu3Oy and Bi2Sr2CaCu2- O8+δ at 0.1−5.0 eV are reported as a function of the concentration of free carriers. We showed that the main feature of the optical conductivity near 1.7 and 4.1 eV in YBa2Cu3Oy and 3.7 eV in Bi2Sr2CaCu2O8+δ and its spectral shapes are modified similarly in both systems on doping by oxygen. We found that for all superconducting crystals a band at 0.1−0.7 eV is observed. The values of plasma frequencies ωp and optical effective masses were evaluated.

Effects of oxygen on electroluminescent characteristics of ZnS:TbOF and ZnS:TmOF devices

ZnS:TbOF and ZnS:TmOF active layers for thin-film electroluminescent devices were deposited in oxygen atmosphere by an electron-beam evaporation method and the effects of oxygen in active layers on electroluminescent (EL) characteristics were studied. With increasing oxygen deposition pressures, the luminance and the luminescent decay time increased and the threshold voltage shifted to lower values in ZnS:TbOF devices, while they showed no notable variations in ZnS:TmOF devices. X-ray-diffraction studies for ZnS thin-films showed that by the deposition in oxygen atmosphere the film orientation of (111) plane, the film uniformity, and the grain size are improved. By an analysis based on the Auger electron spectroscopy spectra for ZnS thin films and EL emission spectra, it was confirmed that a small amount of oxygen is incorporated into films and suppresses the recombination related to zinc and sulfur vacancies. It was found that contrary to ZnS:TmOF devices, ZnS:TbOF devices show a change in the peak intensity of EL spectra by oxygen doping. From the experimental results, it is suggested that in ZnS:TbOF devices oxygen doping could give rise to the increase of the luminance due to a suppression of the nonradiative energy transfer via grain boundaries and/or vacancies, whereas in ZnS:TmOF devices it plays no role in such a mechanism. The effect of oxygen doping on interfaces is also discussed.

Low-Dielectric-Constant Interlayer Insulation for Multilevel Metallization

ABSTRACTSiBN ternary and SiOBN quaternary films prepared by rf-plasma and/or ECR-plasma CVD have been proposed, and this paper evaluates the relationship between film structure and dielectric constant as well as the other film properties. The SiBN films contain Si-N and B-N bonds, and the dielectric constant of the SiBN films reduces with increasing proportion of B-N bonds in the films. The SiBN films are less hygroscopic than BN films and they are therefore more stable. For the SiOBN films, the effects of oxygen doping on the dielectric constant and on breakdown strength are discussed in terms of the film composition and bonding configuration. The dielectric constant decreases with increasing oxygen atomic ratio and reaches a minimum when the amount of oxygen is equal to the amount of silicon. The effectiveness of this low-dielectric-constant material as an interlay-er is confirmed in actual VLSIs with planarized two-level metallization using the SiBN interlayer.

The effect of oxygen doping on the superconductivity of Bi 2CaSr 2Cu 2O 8+δ

Parent Bi 2CaSr 2Cu 2O 8+δ superconductor was doped with oxygen by annealing powder sample at 500 °C in the flowing oxygen atmosphere with intermittent grinding. The amount of amorphous phase and insulating layer found on the sample surface was increased with more oxygen doping. As a consequence, the sharpness and intensity of the XRD peaks were reduced, and the room temperature conductivity, T c, as well as the magnetic susceptibility were decreased.

Electronic and structural effects of oxygen doping in Bi2Sr2CaCu2Ox superconductors characterized by tunneling microscopy.

Scanning tunneling microscopy has been used to characterize the electronic and structural effects of oxygen doping in ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{\mathit{x}}$ materials. Bias-voltage-dependent images of oxygen-deficient nonsuperconducting crystals show that reversible oxygen loss leads to nonperiodic variations in the electronic states near the Fermi level (\ifmmode\pm\else\textpm\fi{}300 mV). Variations in the electronic states near the Fermi level are not observed, however, in images of superconducting samples. In addition, high-resolution images of the BiO layer of oxygen-deficient samples do not exhibit vacancies or strongly perturbed sites, but rather appear similar to images of the BiO layer of superconducting crystals. These data indicate that suppression of ${\mathit{T}}_{\mathit{c}}$ in ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{\mathit{x}}$ may not be due to oxygen loss from the BiO layer.

Plasma-Enhanced Chemical Vapor Deposition of ZrF4-Based Fluoride Glass Film and Oxygen Doping Effects on Glass Forming Ability

ABSTRACTZrF4-based binary glass film is synthesized for the first time by plasma-enhanced chemical vapor deposition (PCVD). The optical transmission spectrum is measured and the effects of oxygen doping on the glass forming ability are clarified. No absorption band caused by OH or other impurities is observed in the near IR region. Weak absorption bands attributed to defect centers are observed in the UV to visible region. The glass forming region in the ZrF4-BaF2 system is significantly improved by oxygen doping. Oxygen ions are distributed homogeneously in the fluoride glass film by PCVD and improve its stability against crystallization.

Effect of Oxygen Doping into SiBN Ternary Film

Oxygen-doped SiBN films are proposed. The effect of oxygen doping is discussed by considering the bonding configuration of oxygen atoms in SiBN films evaluated using infrared absorption spectroscopy and X-ray photoelectron spectroscopy. While SiBN film is characterized as a material with a low dielectric constant, a lower dielectric constant is obtained by oxygen doping into SiBN film in the [O]/2[Si]<1 region. In this region, oxygen atoms preferentially combine with Si atoms, and lower polarizability Si-O bonds are formed in the films in place of higher polarizability Si-N bonds. However, in the [O]/2[Si]>1 region, the dielectric constant of films increases because oxygen atoms combine with B atoms and polar B-O bonds are formed in the film. The breakdown strength of oxygen-doped SiBN films becomes higher with a decrease in the films' dielectric constant.

TbOF complex centers in ZnS thin-film electroluminescent devices

The effect of oxygen doping in ZnS:TbF thin-film electroluminescent (EL) devices has been studied. We concluded that the TbOF complex center is more efficient than the TbF complex center in ZnS thin-film EL devices. The improvement is attributed to the decreased nonradiative emission process of Tb and/or enlarged lattice distortions which generate electron-hole pairs efficiently at the Tb excitation site.

The effects of oxygen doping on copper Chevrel compounds

The Chevrel compounds Cu1.8Mo6S8−x O x have been studied, wherex=0.00, 0.05, and 0.10. In order to establish the effects of incorporating a small amount of oxygen into Cu1.8Mo6S8, we have measured lattice parameters, superconducting transition temperatureT c, and the temperature dependence of both the upper critical fieldH c2 and the magnetic susceptibility x. We show that the usual method of making this compound incorporates oxygen, and that this impurity may be removed by gettering the material with Y2S3. We observe that the substitution of oxygen for sulfur in Cu1.8Mo6S8 increasesT c and decreases the ratioc/a of the hexagonal lattice constants and x. A breakdown in the rigid-band approximation is indicated by a comparison of the relative signs of the effect onT c and that on x. In addition to these observations, we report on a correlation between hardness andT c of Cu1.8Mo6S8 and on the temperature dependence of the magnetic susceptibility of Cu3.2Mo6S8.

Electron Transport in Oxygenated Amorphous Hydrogenated Silicon Prepared by Reactive Sputtering

The effect of oxygen-doping on the electron transport in sputtered hydrogenated amorphous silicon has been studied by means of a time-of-flight technique. Incorporation of a slight amount of oxygen enhances both the mobility and the mobility-lifetime product. An electron drift mobility as high as 8×10-2cm2/V·s at room temperature with a non-dispersive character is observed. The enhancement of the electron mobility and the non-dispersive electron transport in slightly oxygen-doped films are discussed on the basis of two-fold coordinated oxygen atoms and oxygen-related donors.

Effect of oxygen impurities on properties of the ternary superconductor SnMo6S8: Extended x-ray-absorption fine-structure determination of bond distances and local-density cluster calculations.

Electronic structure calculations were performed for clusters representing the Chevrel-phase ${\mathrm{SnMo}}_{6}$${\mathrm{S}}_{8}$, with and without oxygen doping. In order to obtain the local structure around the Sn atom, extended x-ray-absorption fine-structure (EXAFS) measurements were made with synchro- tron radiation. The interatomic distances obtained experimentally were used in the calculations. The effect of oxygen doping on the M\"ossbauer isomer shift and quadrupole splitting values of $^{119}\mathrm{Sn}$ was investigated theoretically and compared with reported experimental values. The effect of oxygen substitution on the density of states at the Fermi energy of the [${\mathrm{Mo}}_{6}$${\mathrm{S}}_{8}$${]}^{2\mathrm{\ensuremath{-}}}$ cluster was also studied. The results suggest that oxygen doping does not alter significantly the electronic structure of ${\mathrm{SnMo}}_{6}$${\mathrm{S}}_{8}$.

Effect of axially coordinated pi-acid ligands on photovoltaic properties of Zn-tetraphenylporphyrin

Following our earlier observations that the well known doping effect of oxygen and water on electrical properties of porphyrin and phthalocyanine films may be attributed to a pi-acid axial interaction throughout the film in the case of PdTPP, we have compared Zn-TPP films supported on transparent n-doped SnO 2 electrodes which had been treated with several pi-acids in contact with an electrolyte to give photoelectrochemical cells. Photovoltages obtained in contact with a series of solution couples were used to obtain approximate photo flat band potentials. The doped films were examined by magnetic circular dichroism (MCD) spectroscopy so that the electronic effect of the dopant could be diagnosed. It was found that pi-acid dopants cause shifts to low energy in the band which indicates “hole stabilization” in the order pyridine < CO < triphenylarsine. The potentials of zero photopotential ‘E FB’, correlate approximately with spectral shifts. It is concluded that manipulation of axial ligand dopants is a promising method for design of metal porphyrin and perhaps phthalocyanine films with desired photovoltaic properties.