Doping Concentration Dependence Research Articles

Electron mobility of SnO2 from first principles

The transparent conducting oxide SnO2 is a wide bandgap semiconductor that is easily n-type doped and widely used in various electronic and optoelectronic applications. Experimental reports of the electron mobility of this material vary widely depending on the growth conditions and doping concentrations. In this work, we calculate the electron mobility of SnO2 from first principles to examine the temperature and doping concentration dependence and to elucidate the scattering mechanisms that limit transport. We include both electron–phonon scattering and electron-ionized impurity scattering to accurately model scattering in a doped semiconductor. We find a strongly anisotropic mobility that favors transport in the direction parallel to the c-axis. At room temperature and intrinsic carrier concentrations, the low-energy polar-optical phonon modes dominate scattering, while ionized-impurity scattering dominates above 1018 cm−3.

Sensitive Luminescence Thermometry through Excitation Intensity Ratio in Eu-Doped BaTiO3.

Optical ratiometric thermometry techniques have gained much attention in recent years due to their reliable and noncontact temperature sensing capability for industrial and biorelated applications. Herein, we exploited the temperature dependence of the absorption band of BaTiO3 (BTO) for novel excitation intensity ratio (EIR) thermometry. Photoluminescence and excitation properties of Eu3+-doped BTO powders were studied as a function of Eu3+ doping concentration. The excitation peak intensities at 397 and 468 nm, corresponding to the 7F0 → 5L6 and 5D2 transitions of Eu3+, were used as EIR parameters. The temperature dependence of the EIR can be explained by the competitive absorption between Eu3+ and the BTO host. The EIR properties were studied in relation to the doping concentration, registering a maximum relative sensitivity (Sr) of 4.89% K-1 in BTO:Eu3+ (0.5%) at 303 K. An amphoteric Eu3+ occupation mode at both Ba2+ and Ti4+ sites was found to interpret the doping concentration dependence of the Sr. The reduced Ba2+ site occupation ratio proved to be responsible for the low Sr values at high Eu3+ doping concentrations. Accordingly, an Eu3+/Ti3+ codoping method was further proposed to improve the Sr by increasing the Ba2+ site occupation ratio. Our result showed that BTO:Eu3+ (0.5%) demonstrated an enhancement of Sr from 4.89 to 6.42% K-1 at 303 K after 2% Ti3+ codoping.

Structures and Properties of High-Concentration Doped Th:CaF2 Single Crystals for Solid-State Nuclear Clock Materials.

Thorium-doped vacuum ultraviolet (VUV) transparent crystals is a promising candidate for establishing a solid-state nuclear clock. Here, we report the research results on high-concentration doping of 232Th:CaF2 single crystals. The structures, defects, and VUV transmittance performances of highly doped Th:CaF2 crystals are investigated by theoretical and experimental methods. The defect configurations formed by Th and the charge compensation mechanism (Ca vacancy or interstitial F atoms) located at its first nearest neighbor position are mainly considered and studied. The preferred defect configuration is identified according to the doping concentration dependence of structural changes caused by the defects and the formation energies of the defects at different Ca or F chemical potentials. The cultivated Th:CaF2 crystals maintain considerable high VUV transmittance levels while accommodating high doping concentrations, showcasing an exceptional comprehensive performance. The transmittances of 1-mm-thick samples with doping concentrations of 1.91 × 1020 and 2.76 × 1020 cm-3 can reach ∼62% and 53% at 150 nm, respectively. The VUV transmittance exhibits a weak negative doping concentration dependence. The system factors that may cause distortion and additional deterioration of the VUV transmittance are discussed. Balancing and controlling the impacts of various factors will be of great significance for fully exploiting the advantages of Th:CaF2 and other Th-doped crystals for a solid-state nuclear optical clock.

Doping effect on magnetic properties of high-temperature multiferroic compound YBaCuFeO5

We have investigated the impurity effects on magnetic properties for the oxygen-deficiency ordered perovskite YBaCuFeO5, which has multiferroic phenomenon at TN2 = 319 K. The measurements of the magnetic susceptibility χ have been carried out for the polycrystalline samples of YBaCu1-xMxFeO5 (M = Ni, Mn, and Zn), where the Cu2+ spins (S = 1/2) are partially substituted by the nonmagnetic and magnetic ions. From anomalies of the temperature dependence of χ, the doping concentration dependences of the magnetic transition temperatures such as TN1 and TN2, were determined. With increasing the doping concentration for YBaCu1-xMxFeO5 (M = Ni, Mn, and Zn), the value of TN1 decreases, and that of TN2 increases, and two magnetic transitions become one at x = xc. In the doping region of x > xc, the magnetic behaviors of the magnetic ions doped systems are different from that of the nonmagnetic one. In particular, we found that two magnetic transitions newly appear for the Ni- and Mn-doped systems in the region of x > xc. Based on the obtained results, we discussed the physics of impurity effects on the magnetic transitions for the high-temperature multiferroic compound YBaCuFeO5.

Dopant concentration dependence on optical and scintillation properties of Eu-doped Gd3Al2Ga3O12 single crystals

We have studied scintillation properties of Eu3+-doped Gd3Al2Ga3O12 single crystals. Gd3Al2Ga3O12 single crystals with different concentrations of Eu3+ (0.5%, 1.0%, 5.0%, 10.0%, and 15.0%) were grown using the floating-zone method. In photoluminescence (PL) and scintillation properties, the Eu-doped Gd3Al2Ga3O12 single crystals showed emission peaks and several millisecond decay times due to 4f–4f transitions of Eu3+ ions. Pulse height spectra of all the samples were investigated under γ-ray irradiation from 137Cs (662 keV). The 0.5%, 1.0%, 5.0%, and 10.0% Eu-doped samples showed full energy peaks. Among all the samples, the 5.0% Eu-doped Gd3Al2Ga3O12 single crystal showed the highest light yield of 36 000 photons MeV−1.

A peripheral modification strategy for high performance multi-resonance TADF emitters to construct sensitized OLEDs

Multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters show great application potential in high color purity and high-resolution organic light-emitting diodes (OLEDs) display. However, the high-performance narrowband MR-TADF based OLEDs are still scarce. In this work, two new MR-TADF emitters Me-PABCZ and Me-PABDPA with high photoluminescence quantum yields (PLQYs) of 94.6 % and 91.8 % respectively, are designed and synthesized by a one-shot electrophilic C–H borylation reaction. The full-width at half-maximum (FWHM) values of photoluminescence spectra in the high dispersion state of Me-PABCZ and Me-PABDPA luminogens are 22 nm and 29 nm, respectively. By coating large steric carbazole or diphenylamine units around the multi-resonance core, the intermolecular interactions are suppressed and the aggregation-induced emission quenching effect is inhibited. As a result, the TADF-sensitized TADF (TST) device utilizing Me-PABCZ as sensitizer and Me-PABDPA as emitter achieves a maximum external quantum efficiency (EQE) of 27.9 %. Such a type of light-emitting device exhibits a weak dopant concentration dependence characteristic. The incorporation of molecule conformational engineering and device structural engineering into the MR-TADF technology could usher in a new paradigm of OLEDs.

Exploring Stable and Selective Anode Materials for the Electrochemical Oxidative Coupling of Methane (EOCM): A Case Study of Doped Titanates

The development of next-generation solid oxide fuel cells (SOFCs) relies on integrating materials such as La0.6Sr0.4Co0.2Fe0.8O3- δ (LSCF), which has been lauded for its fast oxygen ion and electron conduction, along with its high oxygen reduction activity.[1] However, the use of LSCF has been plagued by 1) stability issues caused by surface Sr precipitation and 2) subsequent poisoning by Cr- or S- containing species.We have previously shown that the introduction of more oxidizable cations at the electrode surface can effectively improve both the stability and the oxygen exchange kinetics of the electrodes. However, the influence of these cations, as with many dopant infiltration studies, is currently not fully understood across all possible modes of electrode surface stabilization/activity enhancement. For example, we have recently discovered that at 800°C and under air atmospheres (i.e. at typical SOFC operational conditions), these Hf/Zr surface cation dopants are mobile and diffuse into the lattice of a porous LSCF electrode as evidenced by their vanishing x-ray photoelectron signals. This is accompanied nevertheless by a noticeable electrode stabilization, suggesting a sub-surface effect of the introduced dopants.Inspired by this, in this work our aim is to uncover the mechanism responsible for the stabilization of the surface oxygen exchange kinetics. Our approach involves dense thin film LSCF as model system to investigate the temperature-dependent physicochemical properties of these surface and sub-surface dopant cations. We fabricate LSCF thin films via pulsed laser deposition onto single crystalline substrates and then introduce our targeted cations at the surface via an aqueous solution infiltration. We characterize the electrochemical performance of the thin films by performing chronoamperometric and impedance spectroscopic measurements to discern the extent of the temporal electrode performance degradation using metrics such as area-specific resistance. In parallel, we aim to rationalize the observed electrochemical performance stabilization using complementary surface science techniques. We propose investigating the cation dissolution phenomenon through a combination of x-ray photoelectron and Auger electron spectroscopies, along with atomic force microscopy, scanning/transmission electron microscopy, scanning tunnelling microscopy and grazing incidence thin film x-ray diffraction. This study aims to reveal the influence of sub-surface more oxidizable cations on the extent of Sr segregation and highlights how two major factors contribute to the observed trends: Electrode fabrication conditions, for example the dopant concentration dependence (insufficient or excessive surface dopant concentrations has previously been shown to suppress the stabilization effect).[3]Electrode operation conditions, for example the temperature profile experienced by the cell (higher temperatures lead to dopant dissolution). [1] SP Jiang, Int. J. Hydrogen Energy 44 (14), 7448 (2019).[2] N Tsvetkov et al., Nature Mat. 15 (9), 1010 (2016).[3] N Tsvetkov et al., Faraday Disc. 182 (0), 257 (2015).

Rapid, noncontact, sensitive, and semiquantitative characterization of buffered hydrogen-fluoride-treated silicon wafer surfaces by terahertz emission spectroscopy

Advances in modern semiconductor integrated circuits have always demanded faster and more sensitive analytical methods on a large-scale wafer. The surface of wafers is fundamentally essential to start building circuits, and quantitative measures of the surface potential, defects, contamination, passivation quality, and uniformity are subject to inspection. The present study provides a new approach to access those by means of terahertz (THz) emission spectroscopy. Upon femtosecond laser illumination, THz radiation, which is sensitive to the surface electric fields of the wafer, is generated. Here, we systematically research the THz emission properties of silicon surfaces under different surface conditions, such as the initial surface with a native oxide layer, a fluorine-terminated surface, and a hydrogen-terminated surface. Meanwhile, a strong doping concentration dependence of the THz emission amplitude from the silicon surface has been revealed in different surface conditions, which implies a semiquantitative connection between the THz emission and the surface band bending with the surface dipoles. Laser-induced THz emission spectroscopy is a promising method for evaluating local surface properties on a wafer scale.

Engineering of Optical and Electrical Properties of Electrodeposited Highly Doped Al:ZnO and In:ZnO for Cost-Effective Photovoltaic Device Technology.

Resistivity and transparency of zinc-oxide layers (ZnO) for chalcopyrite photovoltaic technology applications were engineered by activation of the Burstein-Moss (BM) effect at high concentrations of aluminium (Al) and indium (In) dopant. The Al:ZnO and In:ZnO layers were processed by cost-effective, large-area, fast-rate electrochemical deposition techniques from aqueous solution of zinc nitrate (Zn(NO3)2) and dopant trichlorides, at negative electrochemical potential of EC = (-0.8)-(-1.2) V, moderate temperature of 80 °C, and solute dopant concentrations of AlCl3 and InCl3 up to 20 and 15 mM, respectively. Both Al:ZnO and In:ZnO layers were deposited on Mo/glass substrates with ZnO and ZnO/ZnSe buffers (Al:ZnO/ZnO/Mo/glass, In:ZnO/ZnO/ZnSe/Mo/glass), respectively. Based on the band-gap energy broadening of Al:ZnO and In:ZnO originated by the BM effect, maximum carrier concentrations of the order 1020 and 1021 cm-3, respectively, were determined by optical characterization techniques. The (electrical) resistivity values of Al:ZnO calculated from optical measurements were commensurate with the results of electrical measurements (10-4 Ohm·cm). In both cases (Al:ZnO and In:ZnO), calibration of carrier density in dependence of solute dopant concentration (AlCl3 and InCl3) was accomplished. The p-n junctions of Au/In:ZnO/ZnO/ZnSe/CIGS/Mo on glass substrate exhibited current-voltage (I-V) characteristics competing with those of crystalline silicon (c-Si) solar cells.

Yb- and Er concentration dependence of the upconversion luminescence of highly doped NaYF4:Yb,Er/NaYF4:Lu core/shell nanocrystals prepared by a water-free synthesis

High sensitizer and activator concentrations have been increasingly examined to improve the performance of multi-color emissive upconversion (UC) nanocrystals (UCNC) like NaYF4:Yb,Er and first strategies were reported to reduce concentration quenching in highly doped UCNC. UC luminescence (UCL) is, however, controlled not only by dopant concentration, yet by an interplay of different parameters including size, crystal and shell quality, and excitation power density (P). Thus, identifying optimum dopant concentrations requires systematic studies of UCNC designed to minimize additional quenching pathways and quantitative spectroscopy. Here, we quantify the dopant concentration dependence of the UCL quantum yield (ΦUC) of solid NaYF4:Yb,Er/NaYF4:Lu upconversion core/shell nanocrystals of varying Yb3+ and Er3+ concentrations (Yb3+ series: 20%–98% Yb3+; 2% Er3+; Er3+ series: 60% Yb3+; 2%–40% Er3+). To circumvent other luminescence quenching processes, an elaborate synthesis yielding OH-free UCNC with record ΦUC of ∼9% and ∼25 nm core particles with a thick surface shell were used. High Yb3+ concentrations barely reduce ΦUC from ∼9% (20% Yb3+) to ∼7% (98% Yb3+) for an Er3+ concentration of 2%, thereby allowing to strongly increase the particle absorption cross section and UCNC brightness. Although an increased Er3+ concentration reduces ΦUC from ∼7% (2% Er3+) to 1% (40%) for 60% Yb3+. Nevertheless, at very high P (> 1 MW/cm2) used for microscopic studies, highly Er3+-doped UCNC display a high brightness because of reduced saturation. These findings underline the importance of synthesis control and will pave the road to many fundamental studies of UC materials.

Influence of residual dopants to net doping concentration in N-type 4H-SiC films grown using high-speed wafer rotation vertical CVD method

In this study, the influence of residual dopants on the net doping concentration in n-type 4H-SiC epitaxial films grown at different N2 flow rates and C/Si ratios were investigated. By reducing the N2 flow rate, the influence of the residual donors on the net doping concentration was observed to become dominant for the films grown at low C/Si ratios and that of the residual acceptors on the net doping concentration becomes dominant for the films grown at high C/Si ratios. For the films grown at the middle C/Si ratio, an apparent proportional relation due to the compensation balance between the residual and intentional donors and the residual acceptors was observed in the N2 flow rate dependence of the net doping concentration. Furthermore, the decay curve of the net doping concentration observed in the C/Si ratio dependence is affected by the compensation balance between the intentional dopant concentration and the residual dopant concentration.

Carrier recombination in SrTiO3 single crystals: impacts of crystal faces and Nb doping

We observed the carrier recombination in SrTiO3 single crystals with several crystal faces and Nd doping concentrations using time-resolved photoluminescence and microwave photoconductivity decay methods. The shapes of the decay curves were independent of the excited carrier concentrations, and thus the carriers recombined through the Shockley–Read–Hall and surface recombination processes. From the measurements for different crystal faces, we found that, although the surface recombination is significant for the (100), (110), and (111) faces, they have similar surface recombination velocities of ∼106 cm s−1. Therefore, as photocatalysts, the shape of the materials has a minor effect on the energy conversion efficiency. Based on the dependence of the Nb doping concentration, a high doping concentration significantly enhances the carrier recombination, whereas a moderate Nb doping induces only a slight reduction in the time constants of the carrier decay. In addition, the time constant increases with temperature, and thus moderate Nb doping will have a positive effect on the energy conversion efficiency of SrTiO3 photocatalysts at high temperatures.

Application of statistical moment method to investigate mechanical properties of yttria-stabilized zirconia

The mechanical properties of yttria-stabilized zirconia (YSZ) crystal under extreme conditions are theoretically investigated using the analytic free energy formulas derived from the statistical moment method. We calculate the elastic moduli and constants under temperature up to 2100 K and pressure up to 20 GPa using Buckingham potential. The dopant concentration, temperature, and pressure dependences of the elastic moduli and constants of YSZ crystal are studied taking into account the anharmonic effects of the lattice vibrations. Our results are in reasonable agreement with previous experiments and simulations. This approach can then be developed extensively to investigate the thermodynamic and mechanical properties of the other ceramic materials used in solid oxide fuel cells.

Analysis of a SiGe Mach-Zehnder modulator for 400G data communication.

In this paper, the performance of a silicon (Si) Mach-Zehnder modulator (MZM) is enhanced by implanting germanium (Ge) on Si, forming a graded Si-Ge (SiGe) core. A process simulation study is done, and the effect of substrate temperature, implantation energy, and pre-amorphization on the Ge composition and developed in-plane stress is observed. The dependence of active dopant concentration and defect-cluster formation on the annealing conditions is discussed. A comparison of the process simulated SiGe phase shifter with a Si phase shifter shows 2.27× higher phase shift at -5V for 1550 nm wavelength of operation. A dual-arm drive with quadrature operation is investigated for both SiGe and Si MZMs. A traveling-wave electrode is used to enhance the modulation bandwidth. The SiGe MZM achieves better performance in terms of modulation bandwidth, modulation speed, fiber transmission length, energy per bit, and dispersion tolerance compared to the Si MZM. The dual-arm driven SiGe MZM can achieve 62 Gbps error-free 2 km fiber transmission with energy per bit of 1.92 pJ/bit and 3 dB bandwidth of 62.8 GHz at -2.5V bias using 3Vpp on-off keying modulation.

Electronic and thermoelectric properties of the layered Zintl phase CaIn2P2: first-principles calculations

ABSTRACT We have studied the doping concentration dependence of the thermoelectric (TE) properties for the n- and p-doped CaIn2P2 layered Zintl phase at two fixed temperatures: T = 600 and 900 K through first-principles electronic band structure calculations combined with Boltzmann's transport theory within charge-carrier relaxation time and rigid band approximations. The band structure calculated using the Tran-Blaha modified Becke–Johnson potential shows a fundamental indirect energy band gap (E g) of 1.10 eV that comes from the polyanion (In2P2)−2. CaIn2P2 exhibit a mixture of flat and dispersive energy bands in the energy window from to eV, which is a required characteristic for high electrical transport coefficients. The computed lattice thermal conductivity for CaIn2P2 is equal to at 900 K and at 1250 K. This relatively low lattice thermal conductivity of CaIn2P2 can be mainly attributed to its layered crystalline structure. The highest value of the figure of merit of CaIn2P2, viz. ZT = 0.73 (0.71), is obtained for an optimal electron (hole) concentration of () at 900 K.

TSL and OSL properties of SPS-derived CsBr transparent ceramics doped with various concentrations of Eu

We have investigated doping concentration dependence of optically-stimulated luminescence (OSL), as well as the fundamental optical and thermally-stimulated luminescence (TSL), in Eu-doped CsBr transparent ceramics. The photoluminescence, TSL and OSL showed a broad emission spectrum peaking around 440 nm, and the emission origin was the 5d-4f transitions of Eu2+. The emission peak position shifted to longer wavelength with increasing the concentrations of Eu. For OSL, the dose measurement sensitivity was confirmed to be as low as 0.01 mGy when the doping concentration of Eu was 0.3–1.0%; therefore, the optimal concentration of Eu was determined to be 0.3–1.0%.

Forward thermionic field emission transport and significant image force lowering caused by high electric field at metal/heavily-doped SiC Schottky interfaces

We investigated the doping concentration dependence of the barrier height and forward carrier transport mechanism in Ni/SiC Schottky barrier diodes (SBDs) in the wide range of 6.8 × 1015–. Forward current–voltage characteristics in heavily-doped SiC SBDs () can be well reproduced by a thermionic field emission model. The barrier height decreased with increasing doping concentration and the barrier height drop in the most heavily-doped SBD () was about 0.2 eV, which quantitatively agreed with the image force lowering of 0.18 eV caused by the high electric field.

Facile Combustion Synthesis of (Y,Pr)2O3 Red Phosphor: Study of Luminescence Dependence on Dopant Concentration and Enhancement by the Effect of Co-dopant

Abstract There occurs a great interest in explaining the dependence of dopant concentration on the luminescence efficiency of rare earth oxides. Unambiguously, this study explains that luminescence intensity increases with increase in dopant concentration only up to optimised value. The syntheses of doped and co-doped yttrium oxide (Y2O3) nanophosphors in this study were carried out by making use of combustion method. This method produces the nanophosphors that have sizes ranging between 5 and 20 nm as confirmed by transmission electron microscopy. X-ray diffraction pattern confirms that the incorporation of praseodymium oxide (Pr3+) and gadolinium oxide (Gd3+) does not cause any change in the cubic structure of Y2O3. The phase purity has been confirmed by Fourier transform infrared spectrum. Diffuse reflectance spectra reveal that the bandgap increases with increase in annealing temperature. Bandgap has been calculated by making use of the Kubelka–Munk function. Strongest emission was observed at 605 nm with 2 wt% of Pr3+ as optimised concentration. Replacement of Y3+ by Gd3+ partially enhances the 605-nm emission linearly. The [Y:Pr:Gd] exhibits luminescence intensity of 2.705 times more than that of Y:Pr nanophosphors. This is for the first time our team has made a detailed study regarding the effects of co-doping in the case of Y2O3:Pr powders. We have successfully presented the changes that happen to the particle after co-doping especially in the particle size and luminescence properties.

Carrier transport study on triphenylamine-thienothiophene-based hole transport material by MIS-CELIV method

Charge carrier mobility measurement of a promising hole transport material, 4,4′-(thieno[3,2-b]thiophene-2,5-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (TT-2,5-TPA), with a p-dopant, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) at various doping concentration, was carried out by utilizing metal–insulator–semiconductor charge extraction by the linearly increasing voltage (MIS-CELIV) method. Doping concentration dependence and temperature dependence of the hole mobility in TT-2,5-TPA thin films with LiTFSI were investigated in the MIS-CELIV measurement, and the enhancement of hole mobility and suppression of activation energy were discussed by taking the thermal activated hopping process into consideration.

Temperature and concentration dependent Judd-Ofelt analysis of Y2O3:Eu3+ and YVO4:Eu3+

Judd-Ofelt analysis has been performed from the photoluminescence emission spectra of Y2O3:Eu3+ with 3%, 1% and 0.1% doping concentration and YVO4:Eu3+ with 1% doping concentration, in temperature range from 40 °C to 460 °C. For precise calculation, an extended Sellmeier equation that accounts for the doping concentration and temperature dependence of the refractive index of Y2O3 doped with lanthanides is estimated. The temperature dependence of Ω2 and Ω4 parameters are fitted with quadratic and linear regression, respectively. Judd-Ofelt intensity parameters uniformly drop with increasing temperature, but at a different rate for different doping concentrations. From the Judd-Ofelt parameters radiative lifetimes and emission cross-sections were calculated. The cross-sections show a linear decrease with increasing temperature.