Effect Of Doping Concentration Research Articles

Analytical Models for the electric field and potential of AlGaN/GaN HEMT with partial silicon doping

Here, we study the mechanism of AlGaN/GaN HEMT with the partial silicon doping in the AlGaN layer under reverse bias and propose a two-dimensional analytic model for this device. The local density of two-dimensional electron gas (2DEG) increase at the interface between the AlGaN and GaN buffer due to partial silicon positive charge. And a new electric field peak is introduced by electric field modulation effect, which makes the electric field distribution of the channel surface more uniform and increases the breakdown voltage of the device. An analytical expression for the electric field and potential distribution of the channel is obtained, based on the two-dimensional Poisson's equation with appropriate boundary conditions. With this model, we explain the effects of silicon doping concentration and doping length on channel potential and electric field distribution in detail. By comparing the results obtained by the analytical model with the simulation results of Silvaco TCAD software, the numerical results and simulation results mostly match which verifies the validity of the model and provides a reference to model other AlGaN/GaN HEMTs.

Dopant incorporation in ultrasmall quantum dots: a case study on the effect of dopant concentration on lattice and properties of SnO2 QDs

Although impurity doping of nanocrystals is essential in controlling their properties for various applications, but the doping mechanism of ultrasmall semiconductor QDs is not yet understood. In this study, the effect of concentration of Ni2+ ions on the lattice and properties of 1.4 nm SnO2 QDs, prepared via chemical-precipitation route has been studied in detail. The quantum dot lattice contracted at maximum Ni concentration of 10% due to the incorporation of Ni ions at the substitutional sites on the surface of SnO2 lattice, while it began to expand gradually as the Ni concentration was further decreased from 10 to 1%, due in part to the Ni ions located in the core of the host lattice, occupying interstitial sites between Sn and O atoms leading to the expansion of the lattice with the decrease in the amount of strain and dislocation density. High resolution transmission electron microscopy confirms the presence of such dislocations in pure and doped SnO2 QDs. Optical investigation shows that the Ni doping in SnO2 lattice leads to a blue shift in the absorption wavelength. The concentration quenching effect of the PL emission with Ni doping is explained in detail. An enhancement in the photocatalytic activity has been achieved with optimum Ni incorporation in SnO2. The work also successfully correlates photoluminescence quenching and enhanced photocatalytic activity with the defect production happened in SnO2 system on Ni doping.

Effects of La-doping on piezoelectricity properties of 0.15BiInO3-0.85PbTiO3 thin films deposited by RF magnetron sputtering method

La-doped 0.15BiInO3-0.85PbTiO3 thin films are deposited on SRO/Pt/MgO substrates by RF-magnetron sputtering method. The structures of the thin films are characterized by XRD and AFM. Meanwhile, the effects of La doping concentrations on the piezoelectricity of the films are measured. At the same time, the transverse piezoelectric coefficients of the films are simulated by COMSOL combined with CASTEP calculations. The simulated results are in agreement with the experimental data, which show that the La-doping 0.15BiInO3-0.85PbTiO3 films have optimized properties by properly controlling the La doping compositions. It is found that the effective transverse piezoelectric coefficients have a maximum of -9.35 C/m2 as 3 mol.% La-doping 0.15BiInO3-0.85PbTiO3 films.

Doping effect investigation of Li-doped CdS thin films

ABSTRACTLi-doped CdS (CdS:Li) thin films with 0, 1, 2 and 3 wt-% Li concentrations were prepared by the spray technique using a perfume atomiser. The effect of Li doping concentration on the structural, optical, electrical and magnetic properties was systematically investigated and the results are reported in this paper. Analysis of the microstructure indicates that all the films consist of a hexagonal CdS phase with a strong (0 0 2) preferential growth texture. Nanoneedles were evinced from the SEM images of the doped films. Optical studies reveal that the transparency and band gap were dependent on Li-doping content. Hall effect measurements reveal that all the doped films exhibit p-type conductivity and the resistivity values strongly depend on the occupancy of Li atoms on the substitutional and interstitial sites of the CdS lattice. Room temperature ferromagnetism was observed for the doped films.

Effect of Dopant Concentrations on Magnetic States of Ti, Mn, And Ni Doped Iii-V Zincblende Compounds

The effect of Ti, Mn, and Ni dopants concentration on various magnetic states of III-V zincblende compounds (Al1-xTx)M is presented by calculation of multiple scattering theory based on Korringa–Kohn–Rostoker coherent potential approximation (KKR-CPA), where T denotes Ti, Mn, and Ni atoms and M represents As and P atoms. The calculations reveal the phase changes in various magnetic states, which are solely controlled by dopant concentrations. The turning points of these behaviors are reported, which are responsible for the change of stable ferromagnetic (FM) state to unstable disordered local moment (DLM) state. The Curie temperature, magnetic moments, and density of states at different concentrations of the dopants are calculated and explain the concurrency with magnetic phase stability.
 Journal of Bangladesh Academy of Sciences, Vol. 42, No. 2, 177-182, 2018

Influence of rare earth material (Sm3+) doping on the properties of electrodeposited Cu2O films for optoelectronics

Herein, we report samarium (Sm) dopant concentration effect on Cu2O films characteristics prepared by electrodeposition method. XRD patterns of the films indicated that pristine and Sm:Cu2O films have polycrystalline cubic structure with (111) preferred orientation. It was seen from the SEM photographs pinhole free dense triangle shaped grains for undoped Cu2O thin films and the grain size was decreased as concentration of samarium was increased. Raman spectroscopy showed peaks at 108, 146, 217, 413 and 637 cm−1 which conformed the Cu2O phase formation and intensity of the peaks was decreased with a increase in dopant concentration. UV–Vis spectra exhibited that the absorption value of Cu2O films is increased gradually with reduction in band gap value for the increase of samarium content. Photoluminescence (PL) spectra revealed that all films display a visible light emissions and its intensity was reduced due to increase in doping concentration. Photosensitivity observation study indicated that the photocurrent of deposited Cu2O films was increased along with the increase in dopant material concentration.

Influence of Al doping on structural, luminescence and electrochemical properties of V2O5 nanostructures synthesized via non-hydrolytic sol-gel technique

Phase pure and Al3+ doped vanadium pentoxide nanostructure materials (AlxV(2-x)O5(x = 0, 0.01, 0.03 and 0.05)) have been synthesized by surfactant-free non-hydrolytic sol-gel route. The effect of dopant concentration on structural, morphological, elemental, luminescence and electrochemical properties was studied for the prepared samples. XRD analysis shows that all the samples possess orthorhombic structure in nature. HRSEM and HRTEM images of Al3+ doped V2O5 nanostructures revealed the morphology of self-assembled nanorods. The presence of elements, V, Al and O with their oxidation states was ensured by FTIR, EDXS and XPS analyses. The DRS-UV–vis and PLE spectral analyses exhibit that the optical band gap of Al:V2O5 nanostructure materials increases with increase in dopant concentration. The CV results reveal that the product has a better cyclic performance and might act as a primary cathode material for high energy density secondary lithium ion batteries.

Annealing studies of irradiated p-type sensors designed for the upgrade of ATLAS phase-II strip tracker

The upgrade of the LHC to the High Luminosity LHC will challenge the silicon strip detector performance with high fluence and long operation time. Sensors have been designed and tests on charge collection and electrical performance have been carried out in order to evaluate their behaviour. Besides that, it is important to understand and predict the long-term evolution of the sensor properties. In this work, detailed studies on the annealing behaviour of ATLAS12 strip sensors designed by the ITK Strip Sensor Working Group and irradiated from 5×1013neqcm−2 to 2×1015neqcm−2 are presented. Systematic charge collection and leakage current measurements have been carried out during the annealing process until break-down or the appearance of charge multiplication. The annealing was carried out, separating the sensors into two groups being either annealed at 23°C or 60°C. Sensors showing charge multiplication have been then kept at high voltage for a long time in order to monitor their stability. The difference in the annealing behaviour between the two temperatures has been analysed and compared to similar measurements on n-type sensors and with a theoretical model. From the impedance measurements for the samples irradiated to low fluences it was possible to extract the effective doping concentration. This was compared to similar measurements on n-type sensors and with a theoretical model.

Modulation of microstructure and magnetic properties of Sr-doped CdO films

ABSTRACTPure and Sr2+-doped CdO (SCO) thin films were deposited on glass substrates by the spray technique using perfume atomiser. The effect of Sr doping concentration on the structural, morphological, optical and magnetic properties was studied and the results obtained are reported in this paper. Pure and Sr-doped CdO thin films exhibit a strong (1 1 1) preferential growth. Nanosized grains are evinced from the TEM images for all the samples. Increased transparency and band gap bowing are observed for the doped films. All the films have an electrical resistivity in the order of 10−2 ohm cm. Photoluminescence studies confirm the presence of intrinsic defects on the films. Defects mediated ferromagnetic behaviour is observed for the doped films. The obtained results infer that Sr doping strongly influenced the physical properties of spray deposited CdO thin films.

Highly efficient infrared to visible up-conversion emission tuning from red to white in Eu/Yb co-doped NaYF4 phosphor.

Eu/Yb co-doped NaYF4 phosphors have been synthesized by the combustion method. The Eu doping was fixed and the effect of Yb doping concentration on the structural, morphological and luminescence properties has been investigated. X-ray diffraction analysis revealed that the phosphors consisted of mixed α- and β-phases, but the β-phase was dominant. All elements of the host and dopants, as well as adventitious C, were detected using X-ray photoelectron spectroscopy. The surface morphology showed a microrod-like structure with sharp hexagonal edges. Energy dispersive X-ray spectroscopy spectra proved the formation of the desired materials. The photoluminescence spectra illustrated the optical emission properties of Eu3+ in the red region when excited at 394 nm, while, under the same excitation, Yb3+ ions gave emission at 980 nm. The up-conversion (UC) emission of Eu/Yb co-doped NaYF4 produced a white color at the higher concentration of Yb excited by a 980 nm laser, which was made possible by green emission of Er contamination (from Yb source) and blue emission of Eu2+ ions. The lifetime of the Eu3+ UC luminescence at 615 nm was also affected by the Yb doping concentration. The temperature sensitivity associated with the Er3+ peaks at 520 and 542 nm was assessed as a function of temperature and the maximum of 0.0040 K-1 occurred at 463 K.

Synthesis of W‐doped TiO2 by low‐temperature hydrolysis: Effects of annealing temperature and doping content on the surface microstructure and photocatalytic activity

A series of tungsten‐doped Titania photocatalysts were synthesized using a low‐temperature method. The effects of dopant concentration and annealing temperature on the phase transitions, crystallinity, electronic, optical, and photocatalytic properties of the resulting material were studied. The X‐ray patterns revealed that the doping delays the transition of anatase to rutile to a high temperature. A new phase WyTi1‐yO2 appeared for 5.00 wt% W‐TiO2 annealed at 900 °C. Raman and diffuse reflectance UV–Vis spectroscopy showed that band gap values decreased slightly up to 700 °C. X‐ray photoelectron spectroscopy showed that surface species viz. Ti3+, Ti4+, O2−, oxygen‐vacancies, and adsorbed OH groups vary depending on the preparation conditions. The photocatalytic activity was evaluated via the degradation of methylene blue using LED white light. The degradation rate was affected by the percentage of dopants. The best photocatalytic activity was achieved with the sample labeled 5.00 wt% W‐TiO2 annealed at 700 °C.

One step rapid synthesis of mesoporous high surface area Sn1-xSbxO2: Electrochemical and scanning tunneling spectroscopic studies

High surface area nanoparticles of antimony doped tin oxide are synthesized for the first time by one step solution combustion method using tin oxalate and antimony chloride as precursors. The synthesis method is rapid and gives particles of sizes 9–13 nm. The material has a specific surface area of 84 m2/g as estimated by Brunaure-Emmett-Teller (BET) model. The structural properties, surface morphologies, electrical and electrochemical properties are studied as a function of the dopant concentration. Effect of dopant concentration on X-ray diffraction (XRD) patterns shows some noticeable changes in particle size. Solid state UV spectroscopy demonstrates that due to the antimony doping, the band gap of SnO2 decreases significantly. Scanning tunneling spectroscopy (STS) and Hall Effect measurement are employed to characterize the electrical properties. The comparative study of Sn1-xSbxO2 (0.01 ≤ x ≤ 0.05) indicates that the composition of Sn0.95Sb0.05O2 has the lowest resistance with the highest carrier concentration. Electrochemical properties of the material were analyzed by cyclic voltammetry in both acidic and neutral media showing the Sn0.95Sb0.05O2 with high electron transfer properties.

Enhanced performance of perovskite solar cells using p-type doped PFB:F4TCNQ composite as hole transport layer

Conjugated polymers have been widely used as hole transport materials (HTM) in the preparation of mesoscopic perovskite solar cells (PSCs). In this work, we employed p-type doped conducting polymer known as poly(9,9-dioctylfluorene-co-bis-N,N-(-4-butyl phenyl)-bis-N,N-phenyl-1,4-phenylenediamine) (PFB) as a hole transport material (HTM) in perovskite based solar cell. The effect of dopant concentration on the optical and electrical properties of PEB was investigated to optimize the electrical properties of the material for the best function of the solar cell. The highest power conversion efficiency of mesoscopic perovskite solar cells (PSCs), fabricated in this investigation, was found to be 14.04% which is 57% higher than that of pristine PFB hole transport layer. The UV–Vis absorption and Raman spectroscopy measurements confirm the occurrence of oxidation in a p-type doped PFB hole transport layer. This is attributed to the transfer of electrons from the highest occupied molecular orbital (HOMO) of PEB to the lowest unoccupied molecular orbital (LUMO) of F4TCNQ. The solar cells produced using p-type doped PFB:F4TCNQ composite not only improves device performances but also shows superior long-term stability. The optical, morphological and electrical properties of the doped composite PFB: F4TCNQ and newly fabricated devices are presented and discussed in this paper.

Effect of Eu doping concentration on fluorescence and magnetic resonance imaging properties of Gd2O3:Eu3+ nanoparticles used as dual-modal contrast agent

Europium-doped gadolinium oxide (Gd2O3:Eu3+) nanoparticles (NPs) with favorable properties for use in fluorescence imaging (FI) and magnetic resonance imaging (MRI) dual-modal contrast agent has attracted intense attention in biomedical applications. However, limited information is available on balancing FI and MRI by adjusting doping concentrations. In this study, Gd2O3:Eu3+ NPs with various Eu3+ doping concentrations were prepared by the facile and general technique of laser ablation in liquid (LAL). The influence of Eu3+-doping concentration on fluorescence properties and longitudinal relaxivity were investigated. The optimum Eu3+-doping concentration with both high fluorescence properties and longitudinal relaxivity was determined to be 5%. The characterization of the structure, morphology, and composition shows that these NPs possess good crystallinity and excellent dispersibility. These results show that Gd2O3:Eu3+ NPs prepared by LAL are promising candidates for highly efficient FI and MRI dual-modal contrast agents.

InGaN solar cells with regrown GaN homojunction tunnel contacts

Highly doped GaN p–n tunnel junction (TJ) contacts to InGaN solar cells are demonstrated, in which the TJs were grown by molecular beam epitaxy on top of active solar cell regions grown by metalorganic chemical vapor deposition. The effects of Si and Mg doping concentrations on solar cell characteristics are studied and used to improve turn-on voltage and series resistance. The highest doped cell with a TJ has an open-circuit voltage of 2.2 V, similar to that of the control cell fabricated using indium tin oxide (ITO), and a far less short-circuit current density loss from unwanted photogeneration in the TJ contact than in the ITO contact.

Synthesis, upconversion luminescence and optical heating of hexagonal NaGdF4:Yb3+,Er3+

An optical heater based on hexagonal NaGdF4:Yb3+/Er3+ is reported. XRD, SEM and EDS characterization results show that F−/Ln3+ can not only control the phase composition, particle size and morphology, but also affect the effective doping concentration of Yb3+ and Er3+. When F−/Ln3+ is 12/1, the strongest upconversion luminescence is obtained. Based on the luminescent temperature sensing behavior of Er3+, the photo-thermal conversion performance was investigated. The results indicate that the temperature of irradiation spot is linearly dependent on the power density, and the photo-thermal responsivity is determined to be 3.3 K·cm2/W. Also, it is found that the photo-thermal conversion efficiency can be regulated by changing the Yb3+ doping concentration. Compared with the nano-gold, copper sulfide and carbon nanotubes, the NaGdF4:Yb3+/Er3+ has the triple functions of upconversion luminescence, temperature sensing, and photo-thermal conversion, and may therefore be a promising optical heater for photo-thermal therapy of tumors.

Optimized Fabrication of TiO2 Nanotubes Array/SnO2-Sb/Fe-Doped PbO2 Electrode and Application in Electrochemical Treatment of Dye Wastewater

A TiO2 nanotubes array/SnO2-Sb/Fe-doped PbO2 electrode with high oxygen evolution potential and enhanced electrochemical oxidation performance was successfully manufactured. The surface morphology and electrochemical performance of the electrode were characterized by a field emission scanning electron microscope, linear sweep voltammetry, and electrochemical impedance spectroscopy experiments. The effect of Fe doping concentration on the electrode performance was also investigated. This study shows the doping of Fe on a PbO2 electrode improved the micro-morphology and the conductivity of the electrode. The oxygen evolution potential was also increased to 1.95 V [versus a saturated calomel electrode (SCE)] via Fe doping. The optimal condition of Fe doping concentration was 0.02 M. The optimized electrode showed that the decoloration rate and total organic carbon removal ratio of methylene blue approached 98% and 96% after 30 min of electrochemical treatment, respectively. The accelerated lifetime of the optimized Fe-doped electrode was approximately 4.3 times larger than that of the undoped PbO2 electrode. A Ti/TiO2 nanotubes array/SnO2-Sb/Fe-doped PbO2 anode shows potential application in the electrochemical treatment of organic dye wastewater.

The resistive switching characteristics of Ni-doped HfOx film and its application as a synapse

The effect of Ni doping concentration on resistive switching characteristics of Au/HfOx:Ni/Pt structure was investigated, and the 3.1% Ni-doped HfOx film was used to imitate the function of biological synapse. From the X-ray absorption near edge structure analysis, the forms and the local electronic structure of Ni atoms in the HfOx films with different Ni doping concentrations were investigated. According to the X-ray photoelectron spectroscopy analysis, the Ni doping introduced more oxygen vacancies in HfOx films. Gradual Reset process and concentrated distribution of resistive switching parameters were achieved for 3.1% Ni-doped HfOx films, which could be used to emulate the “learning” and “forgetting” function of the biological synapse. Multiple resistance levels can be observed in the continuously pulse number under identical pulse width of positive or negative voltage pulses. Moreover, the application of pulse-train operation scheme is an effective method to control analog synaptic devices during the Reset process, which can contribute to understand the nature of the conductive nano-filament evolution.

Effect of Mn doping concentration on structural, vibrational and magnetic properties of NiO nanoparticles

The Ni1−xMnxO (x = 0.00, 0.02, 0.04 and 0.06) nanoparticles were synthesized by chemical precipitation route followed by calcination at 500 °C for 4 h. The prepared samples were characterized by energy dispersive analysis of X-rays (EDAX), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and vibrating sample magnetometer (VSM). Rietveld refinement of XRD data confirms the structural phase purity and XRD patterns are well indexed to NaCl like rock salt fcc crystal structure with Fm-3m space group. The particle size of Mn doped samples is found to be less than that of pure NiO sample. However, the particle size increases slightly on increasing the Mn concentration due to surface/grain boundary diffusion. The vibrational properties of the synthesized nanoparticles were investigated by Raman and FT-IR spectroscopy. The results of room temperature magnetization (M-H) and temperature dependent magnetization (M-T) measurements are explained with a core-shell model. The synthesized nanoparticles show weak ferromagnetic and super-paramagnetic like behavior at room temperature.

Structural, electronic, magnetic, optical and optoelectronic properties of the sprayed cobalt doped ZnO nanostructured thin films

In this paper, we theoretically and experimentally investigated the structural, electronic, optical and magnetic properties of Cobalt doped ZnO. We used the the SPRAY Pyrolysis technique on preheated substrate glass. Samples were characterized using x-ray Diffraction. Optical parameters such as the optical band gap energy (Eg), the refractive index (n), the dielectric constants (ϵr, ϵi) and the optical conductivity (σ) as a function of photon energy have been investigated. As main result, 2% Co doping leads to improve the optical and optoelectronic properties of ZnO with a higher refractive index, optical conductivity and absorption near infrared region. Furthermore, we investigated the doping concentration effect on the magnetic and structural properties by first principal calculations and found a promising phase change temperature which is higher than room temperature.