Change Of Doping Concentration Research Articles

Synthesis of yttrium doped zinc oxide nanorods for display, forensic and supercapacitor applications

Yttrium (1–7 mol %) doped Zinc Oxide (ZnO) nanoparticles (NPs) are synthesized by hydrothermal method followed by calcination. The synthesized NPs are characterized by different techniques. The Bragg reflections confirm the formation of a hexagonal wurtzite crystal structure. The crystallite size is estimated by both Scherrer’s and Williamson’s-Hall plot methods. The surface morphology is decorated with nanorods of different sizes with sharp edges. As the dopant concentration increases changes in their alignment were also observed. The direct energy band gap determined from Wood and Tauc’s relation was found to be increased from 3.183 to 3.197 eV with an increase in the dopant concentration. The photoluminescence emission spectra excited under 344 nm shows less intensity peaks in the blue and green region whereas the high-intensity peaks are observed in the red region. The concentration quenching is observed at 5 mol % yttrium concentration. This concentration quenching is caused due to dipole–dipole interaction. Further, the Commission Internationale de I’Eclairage (CIE) coordinates fall in a purplish-red region. The average Color Correlated Temperature (CCT) value of 3595 K clearly indicates that the present synthesized NPs might find an application in warm display technology as a nano phosphor material. For oxidation and redox peaks, cyclic voltammetry analysis is also carried out. Ion transport kinetics were disclosed by Electrochemical impedance spectroscopy (EIS), and super capacitance values were acquired using Galvanostatic Charge Discharge (GCD) analysis. For ZnO:Y (1–7 mol %) NPs, specific capacitance values were discovered to be in the range of 33 to 74 F/g with a change in dopant concentration. Therefore, the currently synthesized material may find use in both energy storage materials and the field of display technology and latent fingerprints (LFPs).

Concentration-dependent dielectric and electro-optical properties of composites based on nematic liquid crystals and CdS:Mn quantum dots.

Composites in a wide concentration range of 0-0.6 wt% based on a nematic liquid crystal mixture and CdS quantum dots doped with manganese ions (Mn 6%) are presented. The effect of the CdS:Mn quantum dots on the phase diagram and electronic structure of composites was studied using differential scanning calorimetry and fluorescence analysis. Nonmonotonic concentration-dependent changes in the clearing point, which correlate with the fluorescence quenching behavior of the main CdS:Mn peak, were found. Dielectric spectroscopy and electro-optic studies revealed a corresponding increase in the dielectric permittivity anisotropy and birefringence in the 0.2-0.4 wt% range, where thermodynamic changes occur. The initiating factors behind this effect are supposed to be the self-assembly of quantum dots, and the distortion of the orientation order of liquid crystal molecules at a higher mass concentration of quantum dots.

Gradient doping simulation of perovskite solar cells with CH3NH3Sn1−xPbxI3 as the absorber layer

In this study, we built a perovskite solar cells(PSCs) model with a Au/CuSCN/CH3NH3Sn1−xPbxI3/TiO2/FTO glass structure using the SCAPS program and use polynomial fitting to obtain the relationship between the conduction/valence bands of CH3NH3Sn1−xPbxI3 and the x value, which is more complex and accurate than that in any previous research. The influences of thickness, electron and hole mobilities, relative permittivity, effective conduction band density, effective valence band density, and the value of x on the solar cell performance are analyzed. Furthermore, we simulate the situation where the doping concentration changes with the absorption layer depth of the device and a special bandgap is formed. The power conversion efficiency of the device improves from 19.96% to 20.52%, with an open-circuit voltage of 0.776 V, a short-circuit current of 33.79 mA/cm2, and a filling factor of 77.39% when double gradient doping is performed. The application value of gradient doping in the device absorption layer is obtained.

An Alternate Approach to Backside Thinning: A Doping Selective Silicon Wet Etch

Backside illuminated (BSI) technologies have been commonly used in CMOS image sensors and are finding a renewed interest for images and detectors for LiDAR application that has been driven by the automotive industry. As the integration of signal processing into microelectronic detectors progresses, active area and fill factor become issues for monolithic solutions. Processing the detector and readout circuitry (ROIC) on different wafers allows for the separate optimization of cost and performance. As a result, backside thinning had become a critical step in the process flow for BSI technologies, with the backside of wafers needed to be thinned down to within microns of active area to effectively couple incident photons.Conventional approaches to backside thinning utilize the buried oxide layer of an SOI wafer, which acts as a reliable etch stop since there are both wet and dry silicon etchants with suitable selectivity to the oxide. Despite the robust method for SOI wafer thinning, there are a few key disadvantages that attract the exploration of alternative routes. For instance, SOI wafers are expensive when compared to conventional epitaxial substrates, with the price reaching up to 5 times more depending on quantities. Additionally, the crystallinity of the silicon film on SOI wafers is typically lower than that of epitaxial silicon, which can lead to a decrease in device performance. Thus, to reduce cost and improve performance, an etch process that uses standard epitaxial substrates provides a favorable alternative. However, a method that can reliably, and precisely thin epitaxial substrates is needed. A possible approach would be to exploit a difference in dopant concentration between the substrate and epitaxial silicon. Doing so would require a wet etchant with sufficient selectivity to etch one of the silicon and use the other as an etch stop. The difficulty with this approach is that a change in dopant concentration is not as chemically distinct as a change in material. As such, reliably achieving precise and uniform final silicon film thicknesses presents a challenge that requires optimization of chemistry. Moreover, for such a method to be implemented on a production scale a working understanding of chemical bath life and wafer to wafer etch repeatability over a large sample size is necessary.This study provides a comprehensive examination on the feasibility and reliability of thinning epitaxial substrates and provides an outline for the development of a wet process that rapidly etches heavily doped substrate silicon (etch rate >5 µm/min) and uses a lightly doped device silicon layer as an etch stop (etch rate <0.2 µm/min). Optimal etchant compositions are investigated to identify a suitable chemistry for the required etch rates and selectivity. Furthermore, the effect of bath life and spiking/regeneration schemes on the performance of the etchant in a in a recirculated chemistry application is then explored. After preliminary development work was completed, the chemistry was used to thin a series of epitaxial wafers to explore the wafer-to-wafer repeatability of the developed process. Acknowledgements This project has received funding from the ECSEL Joint Undertaking (JU) under grant agreement No 876659 (iRel40). The JU receives support from the European Union’s Horizon 2020 research and innovation programme and Germany, Austria, Slovakia, Sweden, Finland, Belgium, Italy, Spain, Netherlands, Slovenia, Greece, France, Turkey. Figure 1

Mg-doped tailoring of Zinc oxide for UV-photodetection application

Pristine and Mg-doped ZnO nanostructure have been synthesized by hydrothermal method, characterized by different techniques and their photo-response has been studied. The X-ray diffraction (XRD) pattern revealed that pure and doped ZnO have hexagonal wurtzite structures. For 7% and 10% Mg doping, an additional signature of MgO is observed, whereas for lesser doping no such additional peak appears in XRD pattern. The crystallite size of the doped sample varies with increasing Mg concentration. Raman spectra also revealed that the synthesized pure and doped ZnO nanoparticles have a wurtzite structure. XPS studies confirm that there is no impurity phase observed for pure and 5% Mg-doped ZnO samples. Field Emission Scanning Electron Microscopy (FESEM) reveals the particle are spherical shape having a particle size between 23 nm to 17 nm with the change of dopant concentration which is also supported by Transmission Electron Microscopy studies (∼16 nm for 5% Mg-doped ZnO). UV–Visible absorbance spectra reveal that the absorption edge is shifted to a lower wavelength after the Mg doping. From photoluminescence studies, it has been found that UV band emission appears around 369 nm and broad-spectrum in 400 nm–600 nm (visible) region. The UV photoresponse studies show that the 5% Mg-doped ZnO has a better photoresponse.

Structure and magnetodielectric properties of titanium substituted barium hexaferrites

BaFe12-xTixO19 barium hexaferrites up to x = 2.00 were synthesized by the usual ceramic technology. Crystal structure refinement was realized by Rietveld method of powder XRD at room temperature. The unit cell parameters change non-monotonically with titanium concentration. The minimum volume of ~698.75 Å3 was determined for the x = 1.00. The mechanism of nonequivalent crystallographic positions occupation with titanium cations is established. SEM investigation was shown that the obtained samples are ceramics with a tightly compacted polycrystals (>95%) and average crystallite size of ~5 μm. The Mössbauer investigation confirms such localization of Ti4+ cations. The field dependence of magnetization at 5 K and 300 K was measured and the main magnetic parameters were determined using the law of approach to saturation. These values decrease almost monotonically with increase in titanium concentration and temperature. The minimum values of these quantities of ~23.4 emu/g, ~1.9 emu/g, 1.2*106 Erg/g and ~105 Oe were fixed for the x = 2.00 at 300 K. With an increase in the doping concentration, both the magnitude of the electrical ac-resistivity and the temperature of transition to the activation type of conductivity increase non-monotonically. At x = 0.50, the lowest electrical resistivity of ρ ~5.1*103 Ohm*cm is observed at room temperature with the electrical transition temperature is Tel ~406.5 K. With an increase in frequency the ac-resistivity decreases, as the value of the band gap. The real part of the permittivity increases constantly with increasing temperature and decreases with increasing frequency for all the compositions. The temperature peak of the tg(d) loss tangent with the doping concentration changes nonmonotonically in magnitude and position. An interpretation of the magnetic and electric states of the substituted BaFe12-xTixO19 barium hexaferrite is given taking into account the mechanism of occupation nonequivalent crystallographic positions with titanium cations.

Improved High Precision Dopant/Carrier Concentration Profiling with Corona-Charge Non-Contact C-V (CnCV)

We report significant advancements in corona-based non-contact capacitance-voltage (CnCV) metrology recently developed for comprehensive C-V characterization of SiC and other wide bandgap semiconductors. The technique answers the industries needs for nondestructive, cost-effective C-V dopant monitoring for material and device development and manufacturing control. Excellent precision and matching to mercury probe CV is demonstrated for SiC, Ga2O3, GaN and AlGaN/GaN structures over a concentration range from 1014cm-3 to 2x1019cm-3. The emphasis in the present work is on improvement of CnCV in dopant depth profiling resolution and measurement throughout. This is achieved with a variable charge method that in-situ adjusts corona charging increments in response to changes in dopant concentration. Results are presented for multi-layer epitaxial SiC and for 2DEG in AlGaN/GaN HEMT structures. The latter represents an extreme case of high-low concentration profiling with a transition from 1020electrons/cm-3 in the 2D electron gas to a fully depleted well and dopant concentration in the 1015cm-3 range.

Structural modifications and extended optical properties of Ni1-xCoxWO4 nanoparticles

We studied the effect of cobalt doping on structural and optical properties of NiWO4 nanoparticles. Different compositions of cobalt-doped NiWO4 were synthesized using direct chemical precipitation method. X-ray diffraction patterns of Ni1-xCoxWO4 nanoparticles revealed variation in average crystallite size and micro-strain without any change in the standard crystal structure. Transmission electron microscopy studies showed a deviation of particles size and morphology of the samples with a change in dopant concentration. Raman and Fourier transformed infrared spectroscopy also confirmed the standard NiWO4 profiles at different doping ratios. UV-VIS-NIR spectroscopy gave the information related to the bandgap tuning with the change in dopant concentration. It is also confirmed dual direct-indirect nature of bandgap in Ni1-xCoxWO4 nanoparticles. Photoluminescence emission spectroscopic studies displayed variation in emission spectra and colour with cobalt doping.

Vanadium doped polyoxometalate: induced active sites and increased hydrogen adsorption

We analyzed the electronic and structural properties of an α-Keggin type molybdenum-based polyoxometalate (POM) [[PMo12O40]3−] and its capacity for reduction reaction via H adsorption using ab initio calculations based on density functional theory (DFT). We also determined the change in the electronic properties brought about by vanadium substitutional doping, and its effect on the capacity of POM to adsorb H atom. We found that the optimal substitutional doping of four vanadium per one unit of POM is adequate to maintain its structural stability. Furthermore, increasing dopant concentration changes charge redistribution such that it induces charge transfer to an initially less active sites for H adsorption on pristine POM. This may increase the possibility of creating active sites from an initially inert H adsorption sites and allows for a higher density of H adsorption. This phenomenon could be relevant for chemical reactions that initially requires high number of pre-adsorbed H atoms.

Synthesis, Characterization, Photocatalytic and Sensing Properties of Mn-Doped ZnO Nanoparticles.

In this paper, Mn-doped ZnO nanoparticles (0 to 10 mol% Mn) were synthesized by facile low-temperature aqueous solution process and characterized by several techniques such as field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-visible and Raman-scattering spectroscopy. The SEM studies confirmed that the synthesized nanoparticles are grown in high density and increase in Mn content was found to have a significant effect on the morphologies of ZnO nanoparticles. The XPS studies established the structural variation of the samples with the change in dopant concentration and its oxidation state. XPS probe the existence of impurity phases in the as-synthesized samples. The results indicate further that hexagonal wurtzite structure of ZnO undergoes distortion with the increase in the dopant concentration. Also, with the increase in the dopant concentration, the blue-shift was observed in the UV-vis. spectra. Photocatalytic and chemicals sensing performances of these nanomaterials have been investigated by subjecting them to photocatalytic degradation of methyl orange (MO) under UV irradiation and for the detection of picric acid (PA) in aqueous solutions. Mn doped ZnO samples were found to be more efficient in catalyzing the MO degradation than pure ZnO. 5 mol% Mn doped ZnO nanomaterials were studied to use as fluorescence sensor for the detection of PA and the observed detection limit was found to be 2.5 μM.

Competition of emission and lattice defects participating in energy transfer for ZnO:Tb/Y2O3:Eu nanocable arrays

Lattice defects participating in energy-transfer behaviour and competition of emissions for rare-earth-doped nanocable arrays are investigated in this article. ZnO:Tb3+/Y2O3:Eu3+ nanocable arrays embedded in anodized aluminium are synthesized via two-step template assembly approach. The outer diameter of the nanocable is about 61–71 nm. The core diameter is about 21–41 nm. The competition of emissions and lattice defects involving energy-transfer behaviour are found. With adjustment of the molar ratio of doping ion to host lattice cation to 0.01–0.05, the luminescence intensity increases first and then decreases because of concentration quenching. Although the chromaticity coordinates of nanocable arrays varies as doping concentration changes, they stay in the yellow region. In this process, the oxygen vacancy, interstitial zinc and interstitial oxygen serve as media in the energy-transfer process. Simultaneously, energy transfers from oxygen vacancy to Eu3+ and Tb3+ are also found, but energy transfer between Eu3+ and Tb3+ is not found. These nanocable arrays will have wide application in photoelectronic devices and luminescence materials.

Effect of co-activation on the thermoluminescence and photoluminescence properties of nano-crystalline K2Ca2(SO4)3:Eu,Cu

The effect of co-doping and change in dopant concentration on thermoluminescence (TL) properties of K2Ca2(SO4)3:Eu,Cu has been studied by varying the concentration of the two dopants europium and copper (0.05, 0.10, 0.20, 0.30 and 0.40 mol% equally divided between Eu and Cu). Chemical co-precipitation technique was used to prepare the co-doped phosphor K2Ca2(SO4)3:Eu,Cu. Using Williamson-Hall plot in the X-ray diffraction pattern of the phosphor, the size of the crystallites was estimated to be around 51.3–73.6 nm. Maximum TL sensitivity was obtained for 0.2 mol% concentration (0.1 mol% Eu and 0.1 mol% Cu). The co-doped phosphor was compared for its TL sensitivity with that of the singly doped phosphors K2Ca2(SO4)3:Eu, and K2Ca2(SO4)3:Cu and the standard TL dosimeter LIF:Mg, Ti (TLD-100). Higher TL peak intensity of co-doped phosphor compared to the singly doped phosphors K2Ca2(SO4)3:Eu and K2Ca2(SO4)3:Cu has been explained on the basis of energy transfer between the dopants. Photoluminescence studies of the co-doped and the singly doped samples confirm a positive energy transfer from Cu2+ to Eu2+. A linear TL response curve over a wide range of doses (10 Gy to 1 kGy) is a key factor that makes the present phosphor quite capable for dosimetric purposes.

Mg concentration profile and its control in the low temperature grown Mg-doped GaN epilayer

In this work, the Cp2Mg flux and growth pressure influence to Mg doping concentration and depth profiles is studied. From the SIMS measurement we found that a transition layer exists at the bottom region of the layer in which the Mg doping concentration changes gradually. The thickness of transition layer decreases with the increases of Mg doping concentration. Through analysis, we found that this is caused by Ga memory effect which the Ga atoms stay residual in MOCVD system will react with Mg source, leading a transition layer formation and improve the growth rate. And the Ga memory effect can be well suppressed by increasing Mg doping concentration and growth pressure and thus get a steep Mg doping at the bottom region of p type layer.

4H-SiC 소자의 JTE 구조 및 설계 조건 변화에 따른 항복전압 분석

Silicon Carbide(SiC) has large advantage in high temperature and high voltage applications because of its high thermal conductivity and large band gap energy. When using SiC to design power semiconductor devices, edge termination techniques have to be adjusted for its maximum breakdown voltage characteristics. Many edge termination techniques have been proposed, and the most appropriate technique for SiC device is Junction Termination Extension(JTE). In this paper, the change of breakdown voltage efficiency ratio according to the change of doping concentration and passivation oxide charge of each JTE techniques is demonstrated. As a result, the maximum breakdown voltage ratio of Single Zone JTE(SZ-JTE), Double Zone JTE(DZ-JTE), Multiple Floating Zone JTE(MFZ-JTE), and Space Modulated JTE(SM-JTE) is 98.24%, 99.02%, 98.98%, 99.22% each. MFZ-JTE has the smallest and SZ-JTE has the largest sensitivity of breakdown voltage ratios according to the change of JTE doping concentration. Additionally the degradation of breakdown voltage due to the passivation oxide charge is analyzed, and the sensitivity is largest in SZ-JTE and smallest in MFZ-JTE, too. In this paper, DZ-JTE and SM-JTE is the best efficiency JTE techniques than MFZ-JTE which needs large doping concentration in short JTE width.

Kapitza resistance at segregated boundaries in β-SiC

The impact of grain-boundary segregation on the high-temperature Kapitza resistance of doped β-SiC using non-equilibrium molecular dynamics simulation is investigated. In particular, low-angle, symmetric tilt grain boundaries are examined to assess the roles of dopant concentration and dopant/matrix interaction strength in determining the resistance. For relatively weak interaction strengths, dopant clustering predominates, and the Kapitza resistance increases significantly for small changes in dopant concentration. As the dopant/matrix interaction strength is increased, dopant layering is observed with a concomitant gradual increase in resistance with concentration. The different interaction strength regimes are investigated by mapping the spatial distribution of boundary temperatures and by quantifying the degree of spatial ordering at a boundary. It was found that dopant clustering leads to a heat flux parallel to the grain-boundary plane and to significant boundary disorder, partly explaining the observed increase in Kapitza resistance at the boundary.

Crystal lattice spacing shrinkage and band-gap narrowing phenomena in In-doped SnO2 nanoparticles

Pure and In-doped Tin Oxide (SnO2) nanoparticles with different doping concentration were prepared by hydrothermal method. The prepared samples were characterized by XRD, TEM, and UV–vis absorption spectroscopy. The crystal lattice spacing of In-doped SnO2 nanoparticles decreases compared with pure SnO2. The crystal lattice spacing ratios for (110), (101) and (211) crystal face shrinks acutely with 1.9% doping in SnO2. Crystallite size calculated by the FWHM of the first major XRD peaks (110) decreases from 3.945 to 3.281 nm as the doping concentration increases from 0 to 10%, whereas the strain increases. XRD study reveals that crystal lattice spacing of SnO2 nanoparticles shrinks due to the effect of In element doping. Optical band-gap of SnO2 nanoparticles decreases from 3.76 to 3.33 eV first, and then increases to 3.55 and 3.52 eV, respectively, as the doping concentration changes from 1.9, 3.8 to 10%. Band-gap narrowing originates from the effect of crystal lattice spacing shrinkage.

Phase, microstructure and microwave dielectric properties of Ca1−x La x Ti1−x/4O3 (x = 0–1) ceramics

La-doped CaTiO3 compounds with general formula Ca1−x La x Ti1−x/4O3 (x = 0–1) were prepared via a mixed oxide solid state sintering route. X-ray diffraction analysis revealed the formation of single phase compounds with orthorhombic (Pbnm) symmetry for x ≤ 0.25. At x ≥ 0.5, A n B n−1O3n type B-site deficient hexagonal perovskite phases formed along with minor secondary phases. The grain size and morphology and hence, the microwave dielectric properties varied substantially with change in dopant concentration (x). The optimum microwave dielectric properties (er = 45.3, Q × f o = 20506 GHz and τf = −14.8 ppm/°C) were achieved at x = 0.75.

Effect of hole mobilities through the emissive layer on space charge limited currents of phosphorescent organic light-emitting diodes

In this letter, we used space charge limited current measurements to evaluate the hole mobilities of candidate host materials with or without doped phosphorescent guests through a study of “hole only” devices. We found different impacts to hole mobility in each material when the dopant concentration changes. We postulated that the guest/host energy level matching in the light emissive layer plays an important role in the performance of organic light emitting devices. A number of white organic light emitting devices were designed to prove the supposition. Using guest/host energy level matching a device was fabricated which demonstrated higher efficiency, lower efficiency roll-off and lower driving voltage compared to a non-level-matched device.

Synthesis and Luminescence Properties of ZnO:Eu3+ Nano Crystalline via a Facile Solution Method

Different ZnO:Eu3+ nanocrystalline were obtained from a facile solution method with two different precipitators. The comparison of photoluminescence property of two different ZnO:Eu3+ nanocrystalline was performed. The XRD patterns and the PL spectra indirectly indicate that the dopant Eu3+ ions had entered into the crystal lattices of ZnO. The study on the PL spectra of the as-prepared ZnO:Eu3+ nanocrystalline shows that with the change of dopant concentration, the ratio of relative emission intensity of electric dipole transition to magnetic dipole transition changes, which fully expresses that the presence of the inversion centers is associated with the dopant concentration of Eu3+.

Competitions of magnetism and superconductivity in FeAs-based materials

Using the numerical unrestricted Hartree–Fock approach, we study the ground state of a two-orbital model describing newly discovered FeAs-based superconductors. We observe the competition of a (0, π) mode spin-density wave and the superconductivity as the doping concentration changes. There might be a small region in the electron-doping side where the magnetism and superconductivity coexist. The superconducting pairing is found to be spin singlet, orbital even, and coexisting sxy + dx2−y2 wave (even parity).