Influence Of Dopant Concentration Research Articles

Influence of Dopant Concentration on Dislocation Distributions in 150mm 4H SiC Wafers

Shifts in the spatial distribution of threading dislocations in 150 mm 4H SiC wafers were examined as a response to intentional changes in both the flow of the nitrogen source gas used to control resistivity during bulk crystal growth, and the growth rate. The density of threading edge and screw dislocations was found to be more evenly distributed in wafers produced under a high-growth rate, low-resistivity process. This result corresponded to a flattening of the resistivity distribution, and a ~34% reduction in on-and off-facet resistivity differential. The effect was attributed to regularized 4H island coalescence due to modulation of step terrace width.

Explaining the influence of dopant concentration and excitation power density on the luminescence and brightness of β-NaYF4:Yb3+,Er3+ nanoparticles: Measurements and simulations

We assessed the influence of Yb3+ and Er3+ dopant concentration on the relative spectral distribution, quantum yield (ΦUC), and decay kinetics of the upconversion luminescence (UCL) and particle brightness (BUC) for similarly sized (33 nm) oleate-capped β-NaYF4:Yb3+,Er3+ upconversion (UC) nanoparticles (UCNPs) in toluene at broadly varied excitation power densities (P). This included an Yb3+ series where the Yb3+ concentration was varied between 11%-21% for a constant Er3+ concentration of 3%, and an Er3+ series, where the Er3+ concentration was varied between 1%-4% for a constant Yb3+ concentration of 14%. The results were fitted with a coupled rate equation model utilizing the UCL data and decay kinetics of the green and red Er3+ emission and the Yb3+ luminescence at 980 nm. An increasing Yb3+ concentration favors a pronounced triphotonic population of 4F9/2 at high P by an enhanced back energy transfer (BET) from the 4G11/2 level. Simultaneously, the Yb3+-controlled UCNPs absorption cross section overcompensates for the reduction in ΦUC with increasing Yb3+ concentration at high P, resulting in an increase in BUC. Additionally, our results show that an increase in Yb3+ and a decrease in Er3+ concentration enhance the color tuning range by P. These findings will pave the road to a deeper understanding of the energy transfer processes and their contribution to efficient UCL, as well as still debated trends in green-to-red intensity ratios of UCNPs at different P.

Facile precipitation synthesis of green-emitting BaY2F8:Yb3+, Ho3+ upconverting phosphor

Abstract Monoclinic phase of BaY2F8:0.2Yb3+, xHo3+ (x = 0.005, 0.01, 0.02, 0.05 and 0.1 mol) and BaY2F8:yYb3+, 0.02Ho3+ (y = 0.01, 0.02, 0.05, 0.1 and 0.2 mol) phosphors were prepared by a facile precipitation method. Rietveld analysis was employed to carry out the structural refinement. The upconversion (UC) luminescence properties of BaY2F8:Yb3+, Ho3+ phosphor were investigated under near infra-red (NIR) excitation and the influence of dopant concentration on their spectra was also accessed. The possible UC processes and the energy transfer mechanisms between Yb3+ and Ho3+ were discussed on the basis of UC decay curves and the UC spectra obtained from a laser-pump power variation. The thermal stability of the BaY2F8:0.2Yb3+, 0.02Ho3+ phosphor was studied in the range of 30–300 °C. The color coordinates of the phosphor were located in the green region with very high color purity.

Biosynthesized Co-doped TiO2 nanoparticles based anode for lithium-ion battery application and investigating the influence of dopant concentrations on its performance

TiO2 is a good alternative anode material for lithium-ion battery application because of its incomparable high structural stability and safety during the charge/discharge cycles. However, the low intrinsic conductivity of TiO2 has been a limiting factor affecting its cycling and rate capability performance. Here in this work, we present Co-doped TiO2 nanoparticles based anode with good reversibility, cycling stability and rate capability performance for its envisaged application in lithium-ion battery. The Co-doped TiO2 nanoparticles with different Co concentrations (3%, 5%, and 7%) are synthesized using simple and economic biomediated green approach, wherein TiCl4 and Co precursors are allowed to react in Bengal gram bean extract containing biomolecules which act as natural capping agents to control the size of nanoparticles. Among the pure TiO2 and different Co-doped TiO2 samples, the 7% Co-doped TiO2 anode show the highest capacity of 167 mAh g−1 (88.3%) after 100 cycles at the 0.5C current density. The Co-doped TiO2 shows higher and stable coulombic efficiency up to 100 GCD cycles indicating good reversibility. Based on the results, it is expected that the Co-doped TiO2 nanoparticles might be contributing to the enhanced electronic conductivity providing an efficient pathway for fast electron transfer.

Upconversion luminescence and optical thermometry in Er3+/Yb3+ co-doped CeO2 for space application

The Er3+, Yb3+ co-doped cerium(IV) oxide powders were synthesized by inverted co-precipitation method and calcined at 1000 °C and 1500 °C, respectively. The influence of dopant concentration and calcination temperatures on the luminescence efficiency under excitation with 980 nm laser light was systematically investigated. The maximum intensity of upconversion luminescence (UCL) was observed for CeO2:Yb5Er2 calcined at 1000 °C and CeO2:Yb2Er0.5 calcined at 1500 °C, respectively. Luminescence intensity ratios (LIR) in two Stark sub-levels in green and red regions were used for the determination of temperature sensitivity of CeO2:Yb2Er0.5 sintered at 1500 °C for 1 h. The sensitivity increased for the investigated coupled sub-levels from 0.001 K-1 to 0.003 K-1 (green region) and from 0.0011 K-1 to 0.0025 K-1 (red region). Thus Er3+/Yb3+ doped CeO2 phosphors with high temperature stability seem to be promising materials for low temperature optical measurement under vacuum.

Influence of dopant concentration on electrical quantum transport behaviors in junctionless nanowire transistors**Project supported by the National Key Research and Development Program of China (Grant No. 2016YFA0200503), the Program for Innovative Research Team (in Science and Technology) in University of Henan Province, China (Grant No. 18IRTSTHN016), and the National Natural Science Foundation of China (Grant Nos. 61376096, 61327813, and 61404126).

We discuss the random dopant effects in long channel junctionless transistor associated with quantum confinement effects. The electrical measurement reveals the threshold voltage variability induced by the random dopant fluctuation. Quantum transport features in Hubbard systems are observed in heavily phosphorus-doped channel. We investigate the single electron transfer via donor-induced quantum dots in junctionless nanowire transistors with heavily phosphorus-doped channel, due to the formation of impurity Hubbard bands. While in the lightly doped devices, one-dimensional quantum transport is only observed at low temperature. In this sense, phonon-assisted resonant-tunneling is suppressed due to misaligned levels formed in a few isolated quantum dots at cryogenic temperature. We observe the Anderson-Mott transition from isolate electron state to impurity bands as the doping concentration is increased.

The influence of grain size and vanadium concentration on the spectroscopic properties of YAG:V3+,V5+ and YAG: V, Ln3+ (Ln3+ = Eu3+, Dy3+, Nd3+) nanocrystalline luminescent thermometers

The first demonstration of using V-based phosphor as a luminescent temperature sensor is presented. The luminescent properties of YAG:V3+, V5+ and YAG:V Ln3+ (Ln3+ = Eu3+, Nd3+ and Dy3+) nanocrystals were investigated in a wide range of temperature (–150 °C–300 °C). The influence of dopant concentration and size of the nanocrystals on the emission color output of the YAG:V3+, V5+ was analyzed. The provided analysis reveals that V3+ and V5+ are mainly localized in octahedral sites of Al3+ of core part of the nanocrystals and surface tetrahedral sites of Al3+, respectively. The emission spectra consists of two broad emission bands, attributed to the CT emission of V5+ (at 520 nm) and 3T2g → 3T1g electronic transition emission of V3+(at 820 nm). It was found that emission color output of the YAG:V3+, V5+ nanocrystals can be modulated either by the vanadium concentration or by the size of nanocrystals. Based on the V3+ to V5+ emission intensity ratio (LIR) in the temperature range from −150 °C to 300 °C self-reference thermometer was defined, which reveals 0.7%/°C of sensitivity at the physiological temperature and increases above 4% in 250–300 °C. However its usable temperature range was strongly restricted. It was showed that by the appropriate choice of lanthanide co-dopants, the temperature range in which high sensitivity can be modulated (0.4%/°C at 100 °C for YAG:V,Eu3+; 4%/°C at −150 °C for YAG:V,Dy3+; and 0.8%/°C at 300 °C for YAG:V,Nd3+).

Effects of doping concentration on structural, morphological, optical and electrical properties of tungsten doped V2O5 nanorods

Pure and tungsten-doped V2O5 (WxV2O5; x = 5%, 10% and 15%) nanorods were produced by the wet chemical method followed by annealing at 60 °C for 12 h and 600 °C for 1 h. The influence of dopant concentration on the structural, morphological, optical and electrical properties of V2O5 nanorods were investigated through XRD, SEM-EDS, TEM, PL and DC conductivity studies. XRD pattern analysis reveals that the pure and tungsten doped samples are annealed at 60 °C exhibits anorthic phase and annealed at 600 °C, the anorthic is phase disappeared and emerged as an orthorhombic phase. Also, structural analysis shows that the WxV2O5 (x = 15%) lattice is found to be secondary phase. The gradual morphological transformation of nanostructures due to the incorporation of tungsten is depicted through SEM/TEM characterizations. The relative differential structure of tungsten-doped V2O5 nanorods is promptly registered by SEM analysis. EDS result confirms the presence of tungsten and also oxygen vacancies in doped V2O5. The PL quenching was observed with doping is due to the absorption of energy from the defect emission in the V5+ lattice by W6+ ions. DC conductivity of WxV2O5 with respect to different temperatures is explained by the presence of defects. Further, the colloidal form of pure and n-WxV2O5 is used to deposit on p-Si substrate for formation of p-n junction by the nebulizer spray technique and the properties of fabricated diodes are investigated under dark and illumination conditions. Also, the Norde's method is used to evaluate the series resistance and barrier height of the Schottky contact. Further, the transient photocurrent measurements were carried out to analyze the photoresponse of the developed diodes.

Investigation of Structural, Optical, and Electrical Properties of In‐Doped SnO2 Thin Films Deposited by Spray Pyrolysis

In this work, undoped and 1–5 at.% In-doped SnO2-δ films are deposited onto glass substrates at 350 °C by spray pyrolysis technique. The influence of dopant concentration is investigated using X-ray diffraction (XRD), UV-Visible spectroscopy, and Hall Effect measurements using van der Pauw method. X-ray diffraction studies indicate that all films had preferred orientation along (200) plane and are polycrystalline with tetragonal rutile structure. The calculated average crystallite sizes increased after doping. Substitution of In into SnO2-δ thin films can be confirmed by the shifting of the peaks in the XRD patterns. Optical transmittance of the films show high average transparency ∼80–90% in the visible region. Hall measurements show that the conduction type is dependent on In content. For low-doped films (In ≤3 at.%), the films are n-type, while at higher doping concentration the films are p-type. The calculated values of the mean free path are very small compared to the average crystallite sizes calculated using XRD measurements. Therefore, we suggest that ionized and/or neutral impurity scattering are the main scattering mechanisms in these films. The above-mentioned characteristics render these In-doped SnO2 films potential candidates for their use in light-emitting diode and in optoelectronic devices, with the advantage that they are prepared by a simple and economical technique.

Influence of dopant concentration on the transparent and thermal properties of Nd2O3-doped alumina translucent ceramics

The transparent and thermal developments of high-purity Al2O3 doped with different levels of Nd2O3 were investigated. Dopant levels ranged from 500–1500 ppm (Nd/Al atomic ratio). The samples were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, transmittance spectroscopy and specific heat measurement. Results revealed that with proper Nd doped, Nd3+ ions solid dissolved in Al2O3 lattice, resulting in small and uniform grain and high bonding vibration, which was beneficial to transparent and thermal properties. With 1000 ppm Nd doped, Al2O3 translucent ceramics showed a total transmittance of 89% and thermal conductivity of 41.7 W/m/K, indicating a potential application as substrate for effective heat dissipation and multi emitting surface in LEDs module.

Characterization of n-Type and p-Type Long-Wave InAs/InAsSb Superlattices

The influence of dopant concentration on both in-plane mobility and minority carrier lifetime in long-wave infrared InAs/InAsSb superlattices (SLs) was investigated. Unintentially doped (n-type) and various concentrations of Be-doped (p-type) SLs were characterized using variable-field Hall and photoconductive decay techniques. Minority carrier lifetimes in p-type InAs/InAsSb SLs are observed to decrease with increasing carrier concentration, with the longest lifetime at 77 K determined to be 437 ns, corresponding to a measured carrier concentration of p 0 = 4.1 × 1015 cm−3. Variable-field Hall technique enabled the extraction of in-plane hole, electron, and surface electron transport properties as a function of temperature. In-plane hole mobility is not observed to change with doping level and increases with reducing temperature, reaching a maximum at the lowest temperature measured of 30 K. An activation energy of the Be-dopant is determined to be 3.5 meV from Arrhenius analysis of hole concentration. Minority carrier electrons populations are suppressed at the highest Be-doping levels, but mobility and concentration values are resolved in lower-doped samples. An average surface electron conductivity of 3.54 × 10−4 S at 30 K is determined from the analysis of p-type samples. Effects of passivation treatments on surface conductivity will be presented.

Influence of dopant concentration on the structural, optical and magnetic properties of nickel doped SnO2 nanoparticles

Nickel doped Tin oxide nanoparticles Sn1−xNixO2 (x = 0, 0.01, 0.02, 0.03, 0.04) have been prepared by microwave-assisted chemical route method. The prepared sample is annealed at 500 °C for 1 h for the formation of SnO2 phase. Structural properties investigated by XRD studies indicate the formation of tetragonal phase for the SnO2 nanoparticles, and the Ni doping does not transform the tetragonal structure of SnO2. The scanning electron microscope image shows the surface morphology of the synthesized nanopowder. Transmission electron microscope results illustrate the formation of tetragonal shaped and small sized spherical nanoparticles of diameter 11–19 nm. Photoluminescence emission measurements at room temperature exhibit that all the samples demonstrate photoluminescence in the visible region. VSM studies reveal the ferromagnetic behaviour at room temperature for our sample due to oxygen vacancy.

Thermoelectric performance in n‐type bulk silicon: The influence of dopant concentration and dopant species

Silicon (Si) has received recent interest for thermoelectric (TE) applications. For all TE materials, accurately tuning the doping concentration remains the easiest way to maximise the thermoelectric figure‐of‐merit (ZT). This study investigates the thermoelectric properties at 300 K of n‐type Si as a function of both dopant concentration (N ∼1019–1020 cm−3) and dopant species (P, As and Sb), including measurements of electrical resistivity, thermal conductivity, Seebeck coefficient and Hall mobility. All properties were found to vary as a function of both doping concentration and species, leading to impacts on the ZT. The electrical resistivity was lowest for P‐doped Si and highest in Sb‐doped Si. For the Seebeck coefficient, the situation was reversed. The thermal conductivity was lowest for Sb‐doping and highest in P‐doped Si. In all cases As‐doping was the intermediate dopant. An optimum doping concentration was realized at a value of ∼6–7 × 1019cm−3, and is similar for both As‐ and P‐doped Si. For Sb‐doping, the optimum value is likely to be similar, but the highest doping in commercially available wafers was ∼4 × 1019cm−3. At 300 K, ZT ∼0.010 is achieved for P‐doped bulk Si, however the best overall value was for As‐doped Si, at ∼0.013. For Sb doping the best value is ∼0.012, though a higher value is likely to be possible, but only if doping levels approximately double the concentrations available for this current study can be achieved in starting substrates. These results provide a useful insight for researchers who are selecting a starting substrate for top‐down nano‐structuring approaches to Si thermoelectrics, where a wafer with optimised ZT is required.

Structural and wettability investigation of titanium dioxide coating: influence of dopant concentration (Si and Sr)

In this study, different samples of Si and Sr co-doped TiO2 thin films (5 mol% Si and 5-10-15-20 mol% Sr) were prepared via simple sol–gel synthesis method by using strontium acetate as strontium precursor, tetraethoxysilane as silicon precursor, and titanium (IV) isopropoxide (TTIP) as titanium precursor. The effects of co-doping process on the structural, optical, and wettability properties of thin films were studied by X-ray diffraction (XRD), Scanning electron microscope (SEM) and contact angle measurement. XRD results showed that, the anatase phase formation was promoted by Si+4 and Sr+2 co-doped TiO2 samples at higher percentage of Sr.Accordingly, the titania thin films showed various water contact angles, the water contact angles first decreased from 55.1° to 8.1° then increased to 40.7° by changing the content of Sr dopant from 5 to15 mol% and then to 20% mol.

Spectroscopic Investigation of Up-Conversion Properties in Green Emitting BaMgF4:Yb3+,Tb3+ Phosphor.

In this work we have comprehensively studied the up-conversion (UC) properties of BaMgF4:Yb3+,Tb3+ phosphor for the first time. BaMgF4:Yb3+,Tb3+ phosphors were prepared by a simple and low cost precipitation method. To determine the influence of dopant concentration on luminescence properties, the corresponding UC luminescence spectra of BaMgF4:Yb3+,Tb3+ phosphors were studied under NIR excitation. Emission spectra under NIR excitation reveal the vital role of Tb3+ concentration in spectral tuning from the blue to green region. The UC decay curves were also studied to explore the possible energy transfer (ET) mechanisms between Yb3+ and Tb3+. The results reported here are expected to provide an approach for better understanding ET mechanisms in many Yb3+/Tb3+ codoped UC phosphors. This study will be helpful in applications where precisely defined optical transitions is an essential criterion.

Structural, optical and magnetic properties of (Ni–Mn) co-doped tin oxide nanoparticles

Nickel and manganese (Ni–Mn) co-doped with tin oxide (Sn(2–(x + y)) NixMnyO2) nanoparticles were synthesised by a sol-gel method. The influence of dopant concentration on prepared samples is investigated by different analytical techniques including X-ray diffraction (XRD), vibrating sample magnetometer, diffuse reflectance spectra, scanning electron microscope (SEM) and transmission electron microscope (TEM) to study the structural, optical and magnetic properties. The XRD study reveals that the formation of single-phase rutile tetragonal structure of all the samples and also the particle size vary from 8 to 6.5nm. The lattice constant and crystallite size are decreased as the (Ni–Mn) codoped with SnO2 and found to decrease with increasing doping concentrations. Magnetic measurements show that the (Ni–Mn)-doped SnO2 exhibit room temperature ferromagnetism. SEM and TEM are used to study the external morphology and particle size of the prepared sample.

Fabrication, optical and scintillation properties of transparent YAG:Ce ceramics

Highly transparent YAG:Ce ceramics (transmission of 72–82% for 2-mm-thick samples in 550–900 nm wavelength range) were fabricated by solid-state reactive sintering using a mixture of Ce2xY2-2xO3 (x = 0.001, 0.01, 0.03, and 0.05) and Al2O3 nanopowders synthesized by laser ablation with an additional round of pre-calcining before compaction. The synthesized YAG:Ce ceramic materials showed intense luminescence with a maximum at 525–545 nm. The measured absolute light yields of the synthesized YAG:Ce ceramics were 18–21 photon/MeV for 1–5 at.% Ce and 5 photon/MeV for 0.1 at.% Ce. The energy resolutions of the fabricated thin ceramic samples (2 mm) under 662 keV gamma ray were measured to be 10–15%. The decay curves of scintillations consisted of two components with the decay times depending on the Ce3+ concentration. The sample doped with 5 at.% of Ce exhibited the main fast component with 26 ns decay time. The measured data was compared to that of YAG:Ce and well-known CsI:Tl single crystal scintillators. The influence of dopant concentration on the optical, luminescence and scintillation properties was discussed.

Comparative study of sputter‐deposited SnO2 films doped with antimony or tantalum

AbstractSnO2 films doped with antimony or tantalum were sputter‐deposited for comparison, using an identical set of parameters. The influence of dopant concentration and choice of deposition parameters such as substrate temperature on the optoelectronic properties, especially film resistivity, were determined. Comparative analysis shows that tantalum doping yields lower film resistivity, probably due to an increased inhibiting influence of grain boundary scattering in the case of antimony doping. Sputter‐deposited tantalum‐doped films with lower than previously achieved resistivity , carrier density , and mobility are reported, while maintaining optical transmittance above 85% at a film thickness 400 nm. Ta/Sb co‐doped thin films were synthesized for the first time, achieving similar results.Comparison of resistivity values achievable by doping sputter‐deposited tin oxide films with antimony (blue) or tantalum (red) as a function of dopant concentration.

The influence of dopant concentration on temperature dependent emission spectra in LiLa1-x-yEuxTbyP4O12 nanocrystals: toward rational design of highly-sensitive luminescent nanothermometers.

Luminescence nanothermometry is gaining great interest, and different excitation and readout schemes have been sought to improve temperature sensitivity and sensing range, or to simplify the readout. Although many up-conversion based nanothermometers have been studied, Tb(3+) and Eu(3+) doped systems have not been widely considered, so far. Herein, we report the synthesis of new LiLa1-x-yEuxTbyP4O12 nanocrystals for luminescent thermal sensing; their spectroscopic properties have been investigated in a wide range of compositions and temperatures. In particular, the impact of dopant concentration on energy transfer processes (such as energy transfer, back energy transfer, energy diffusion and cross relaxation) is presented in a quantitative manner, both experimentally and theoretically, which enables the intentional optimization of the composition to find the finest balance between temperature sensitive excitation and depletion phenomena, and thus, enhance the luminescent thermometry properties. The studied thermometers can be applied in as wide a temperature range as 77-600 K, where they demonstrate sensitivity up to 1% K(-1), which is the highest among the Tb(3+) and Eu(3+) doped inorganic phosphor based materials, to date.

Ab initio calculations of doped TiO2 anatase (101) nanotubes for photocatalytical water splitting applications

TiO2 (titania) is one of the promising materials for photocatalytic applications. In this paper we report on recently obtained theoretical results for N and S doped, as well as N+S co-doped 6-layer (101) anatase nanotube (NT). First principles calculations in our study have been performed using a modified B3LYP hybrid exchange-correlation functional within density functional theory (DFT). Here we discuss the energy of defect formation mechanism and electronic band structure for nanotubes under study. We also report on influence of dopant concentration on the NT's band structure and discuss the defect–defect interactions.