Doping Methods Research Articles

Tuning Electrical and Optical Properties of MoSe2 Transistors via Elemental Doping

AbstractControlled doping of transition‐metal dichalcogenide (TMDC)‐layered materials is of great importance for practical device application. Doping of TMDCs and tuning of the bandgap properties remain challenging owing to the difficulty of breaking covalent bonds. In this work, the doping of V, Fe, and Nb atoms into MoSe2 is successfully synthesized using the chemical vapor transport method. By the absorption of V or Nb dopants, the intrinsic n‐type MoSe2 is tuned to be of p type. A p‐n diode based on a homojunction is fabricated by stacking the n‐ and p‐type MoSe2 vertically. The photoresponse range of intrinsic MoSe2 is only up to 785 nm. However, the photodetector based on the doped MoSe2 flake with V, Fe, and Nb can be used up to the near‐infrared (1550 nm) region at room temperature. Furthermore, the photoresponse wavelength of a V‐doped MoSe2 could reach up to 10 µm. The results indicate that the elemental doping methods could enrich the electrical and optical application prospects of MoSe2.

First principle study on electronic structure, elastic properties and debye temperature of pure and doped KCaF3

As a potential functional material in the perovskite family, the electronic structure, elasticity, Debye temperature and anisotropy of pure and doped KCaF3 structures are investigated based on density functional theory (DFT). The virtual crystal approximation (VCA) and supercell doping methods are employed to study the relation between the dopant amount and band gap. Results show that: (1) The pure KCaF3 is an indirect band-gap semiconductor, with Young's modulus E of 64.20 GPa and band gap of 6.151 eV; (2) Band gap of doped KCaF3 after the supercell doping decreases to 4.900 eV, with the top of valence band and the bottom of conduction band changed while the doped KCaF3 becomes a direct band gap semiconductor; (3) Based on GGA and Reuss-Voigt-Hill methods, the E values of doped KCaF3 after VCA and supercell doping are 71.48 GPa and 84.02 GPa, respectively, demonstrating that the doped structure is stiffer than undoped structure. The bulk modulus to shear modulus ratio of pure KCaF3 seems to be relatively ductile, and the universal anisotropic index shows that both pure and doped KCaF3 exhibit fairly high elastic anisotropy. This research provides theoretical guidance for the design of new ABX3-type materials with better performance.

Highly Stable Contact Doping in Organic Field Effect Transistors by Dopant-Blockade Method.

In organic device applications, a high contact resistance between metal electrodes and organic semiconductors prevents an efficient charge injection and extraction, which fundamentally limits the device performance. Recently, various contact doping methods have been reported as an effective way to resolve the contact resistance problem. However, the contact doping has not been explored extensively in organic field effect transistors (OFETs) due to dopant diffusion problem, which significantly degrades the device stability by damaging the ON/OFF switching performance. Here, the stability of a contact doping method is improved by incorporating "dopant-blockade molecules" in the poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT) film in order to suppress the diffusion of the dopant molecules. By carefully selecting the dopant-blockade molecules for effectively blocking the dopant diffusion paths, the ON/OFF ratio of PBTTT OFETs can be maintained over 2 months. This work will maximize the potential of OFETs by employing the contact doping method as a promising route toward resolving the contact resistance problem.

Promoting Fairness in Sport through Performance-enhancing Substances: An Argument for Why Sport Referees Ought to ‘Be on Drugs’

ABSTRACT The debate on the use of performance-enhancing substances or methods to improve refereeing is underdeveloped in the sport philosophical literature. This contrast with the attention scholars have devoted to the use of such substances and methods for athletic purposes. However, when considered from the perspective of fairness, this differential treatment is problematic. Since one of the main concerns with performance-enhancing drugs is their detrimental effect on fairness, the use of performance-enhancing drugs and methods to improve refereeing, given their positive effects on fairness, should have more relevance in the literature. If anti-doping advocates aim to protect and promote fairness in sport, they should consider the possibility of using performance-enhancing drugs or methods to improve refereeing. In this article, we make an argument for this possibility and critically discuss some possible objections. We conclude that referees, under certain conditions, ought to use doping substances or methods.

Highly Efficient n-Type Doping of Graphene by Vacuum Annealed Amine-Rich Macromolecules.

Flexible transparent conducting electrodes (FTCE) are an essential component of next-generation flexible optoelectronic devices. Graphene is expected to be a promising material for the FTCE, because of its high transparency, large charge carrier mobilities, and outstanding chemical and mechanical stability. However, the electrical conductivity of graphene is still not good enough to be used as the electrode of an FTCE, which hinders its practical application. In this study, graphene was heavily n-type doped while maintaining high transmittance by adsorbing amine-rich macromolecules to graphene. The n-type charge-transfer doping of graphene was maximized by increasing the density of free amine in the macromolecule through a vacuum annealing process. The graphene adsorbed with the n-type dopants was stacked twice, resulting in a graphene FTCE with a sheet resistance of 38 ohm/sq and optical transmittance of 94.1%. The figure of merit (FoM) of the graphene electrode is as high as 158, which is significantly higher than the minimum standard for commercially available transparent electrodes (FoM = 35) as well as graphene electrodes doped with previously reported chemical doping methods. Furthermore, the n-doped graphene electrodes not only show outstanding flexibility but also maintain the doping effect even in high temperature (500 K) and high vacuum (~10−6 torr) conditions. These results show that the graphene doping proposed in this study is a promising approach for graphene-based next-generation FTCEs.

Lewis acids and bases as molecular dopants for organic semiconductors

AbstractControlling the concentration of charge carriers (mobile electrons and holes) in organic semiconductors is vital to precisely controlling their electronic properties. Significant efforts have gone into understanding how molecular dopants induce charge carriers in organic semiconductors. The most widely used doping mechanisms occur via electron transfer (i.e., oxidation or reduction of the semiconductor) or via reaction with a strong Brønsted acid. Recently, strong Lewis acids have been observed to induce p‐type charge carriers in organic semiconductors with greater efficiency than classical dopants. The mechanism of Lewis‐acid doping could not easily be unified with either classical doping methods and has been under intense scrutiny over the past 5 years. Very recently, the Lewis‐acid doping effects have been shown to be due to water impurities in commercial Lewis acids forming strong Brønsted acids. This means that many studies on doping using Lewis acids may be occurring via a Brønsted‐acid doping mechanism. This recent revelation explains some observations in literature, but not all, and there are still unanswered questions. The nature of the Lewis acid and organic semiconductor can significantly impact the doping mechanism and the doping efficiency. Additionally, strong evidence for alternative doping mechanisms using Lewis acids not involving water has been shown. Lewis‐acid doping has mostly been studied as a p‐type dopant method on Lewis‐basic polymers. There is growing literature showing Lewis bases can also act as n‐type dopants, excluding Brønsted‐acid doping as a possible mechanism. In this tutorial review, we will present a brief overview on molecular doping of organic semiconductors, survey the literature on p‐type and n‐type Lewis doping, outline several proposed mechanisms, and speculate on some possible mechanisms using literature observations.

Silicon sensors for the CMS HGCAL upgrade: challenges, sensor design & electrical characterization

The CMS detector will undergo significant improvements to face the 10-fold increase in integrated luminosity of LHC, the so-called High-Luminosity LHC, scheduled to start in 2027. This will include a completely new calorimeter in the CMS endcap regions, which should be able to withstand fluences of up to 1016 neq/cm2. The new High Granularity Calorimeter (HGCAL) will have unprecedented transverse and longitudinal readout and trigger segmentation that will facilitate the particle-flow approach to reconstruct electromagnetic and hadronic particle showers and their energies. In regions of low radiation, HGCAL will be equipped with small plastic scintillator tiles as active material coupled to on-tile silicon photomultipliers. In the higher radiation zone, silicon has been chosen due to its intrinsic radiation hardness. The silicon sensors will be of hexagonal shape, with three nominal thicknesses of 120 μm, 200 μm and 300 μm, optimized for regions of different radiation levels. They will be segmented into several hundred cells with hexagonal shape of 0.5 to 1.1 cm2 in size, each of which is read out individually. A comprehensive campaign is in progress to converge on optimal sensor design choices and parameters, such as bulk doping, layouts and production methods. Results from full electrical sensor characterization are presented for different sensors, together with first results from an irradiation campaign of large-area silicon sensors.

Sequentially Processed P3HT/CN6‐CP•−NBu4+ Films: Interfacial or Bulk Doping?

AbstractDerivatives of the hexacyano‐[3]‐radialene anion radical (CN6‐CP•−) emerge as a promising new family of p‐dopants having a doping strength comparable to that of archetypical dopant 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyano‐quinodimethane (F4TCNQ). Here, mixed solution (MxS) and sequential processing (SqP) doping methods are compared by using a model semiconductor poly(3‐hexylthiophene) (P3HT) and the dopant CN6‐CP•−NBu4+ (NBu4+ = tetrabutylammonium). MxS films show a moderate yet thickness‐independent conductivity of ≈0.1 S cm−1. For the SqP case, the highest conductivity value of ≈6 S cm−1 is achieved for the thinnest (1.5–3 nm) films whereas conductivity drops two orders of magnitudes for 100 times thicker films. These results are explained in terms of an interfacial doping mechanism realized in the SqP films, where only layers close to the P3HT/dopant interface are doped efficiently, whereas internal P3HT layers remain essentially undoped. This structure is in agreement with transmission electron microscopy, atomic force microscopy, and Kelvin probe force microscopy results. The temperature‐dependent conductivity measurements reveal a lower activation energy for charge carriers in SqP samples than in MxS films (79 meV vs 110 meV), which could be a reason for their superior conductivity.

VACANCIES AS A METAL ALLOYING ELEMENT

Purpose. The study and development of methods for a new type of environmentally friendly alloying of metals with a controlled nonequilibrium concentration of vacancies. Methodology. System analysis of methods of alloying metals with a nonequilibrium concentration of vacancies and the mechanisms of the influence of this alloying on the structure and properties of metals. Results. The theoretical foundations of doping with a nonequilibrium concentration of vacancies by means of vacancy hardening, hydrostatic compression, cyclic deformation, special deformation-heat treatment according to the type of high-speed recrystallization annealing of cold-deformed metal, as well as a combination of these methods are developed. Originality. The processes that result in the interaction of vacancies with moving dislocations, which significantly changes the trajectories of the dislocations and forms a dislocation substructure with special quasi-equilibrium boundaries that are close in properties to the boundaries formed during high-temperature thermomechanical processing. Practical value. The principles of regulating the parameters of vacancy doping, ensuring its effectiveness and the controlled parameters of doping methods, are indicated.

Enormous enhancement in electrical performance of few-layered MoTe2 due to Schottky barrier reduction induced by ultraviolet ozone treatment

Doping can improve the band alignment at the metal-semiconductor interface to modify the corresponding Schottky barrier, which is crucial for the realization of high-performance logic components. Here, we systematically investigated a convenient and effective method, ultraviolet ozone treatment, for p-type doping of MoTe2 field-effect transistors to enormously enhance the corresponding electrical performance. The resulted hole concentration and mobility are near 100 times enhanced to be ~ 1.0 × 1013 cm−2 and 101.4 cm2/(V·s), respectively, and the conductivity is improved by 5 orders of magnitude. These values are comparable to the highest ones ever obtained via annealing doping or non-lithographic fabrication methods at room temperature. Compared with the pristine one, the photoresponsivity (522 mA/W) is enhanced approximately 100 times. Such excellent performances can be attributed to the sharply reduced Schottky barrier because of the surface charge transfer from MoTe2 to MoOx (x < 3), as proved by photoemission spectroscopy. Additionally, the p-doped devices exhibit excellent stability in ambient air. Our findings show significant potential in future nanoelectronic and optoelectronic applications.

Selective Epitaxial Growth of In Situ Doped SiGe on Bulk Ge for p+/n Junction Formation

Epitaxial in situ doped Si0.73Ge0.27 alloys were grown selectively on patterned bulk Ge and bulk Si wafers. Si0.73Ge0.27 layers with a surface roughness of less than 3 nm were demonstrated. Selectively grown p+Si0.73Ge0.27 layers exhibited a resistivity of 3.5 mΩcm at a dopant concentration of 2.5 × 1019 boron atoms/cm3. P+/n diodes were fabricated by selectively growing p+- Si0.73Ge0.27 on n-doped bulk Ge and n-doped Si wafers, respectively. The geometrical leakage current contribution shifts from the perimeter to the bulk as the diode sizes increase. Extracted near midgap activation energies are similar to p+/n Ge junctions formed by ion implantation. This indicates that the reverse leakage current in p+/n Ge diodes fabricated with various doping methods, could originate from the same trap-assisted mechanism. Working p+/n diodes on Ge bulk substrates displayed a reverse current density as low as 2.2·10−2 A/cm2 which was found to be comparable to other literature data. The layers developed in this work can be used as an alternative method to form p+/n junctions on Ge substrates, showing comparable junction leakage results to ion implantation approaches.

Electrospun Ag-TiO2 Nanofibers for Photocatalytic Glucose Conversion to High-Value Chemicals.

TiO2 nanofibers were fabricated by combination of sol–gel and electrospinning techniques. Ag-doped TiO2 nanofibers with different Ag contents were prepared by two different methods (in situ electrospinning or wetness impregnation of Ag on TiO2 nanofibers) and heat treated at 500 °C for 2 h under an air or N2 atmosphere. The obtained catalysts were characterized by field emission scanning electron microscopy, X-ray diffraction, photoluminescence, and N2 adsorption analyzed by the Brunauer–Emmett–Teller (BET) method. Photocatalytic glucose conversions with electrospun TiO2 and Ag-doped TiO2 nanofibers for production of high-value products were carried out. From different doping methods, the results indicated that 1 wt % Ag-TiO2 nanofibers prepared by an in situ method with calcination under N2 achieved the highest glucose conversion (85.49%). From several Ag loading contents (i.e., 0, 1, 2, and 4 wt %) in Ag-doped TiO2 nanofibers, the nanofibers exhibited different glucose conversions [in order of 2 wt % (99.65%) > 1 wt % (85.49%) > 4 wt % (77.72%) > 0 wt % (29.64%)]. Arabinose, xylitol, gluconic acid, and formic acid were found as the high-value chemicals with the photocatalytic reaction of TiO2 and Ag-doped TiO2 nanofibers under UVA irradiation. Product yields of each converted chemicals from different photocatalysts from different Ag loading contents showed relatively same trends with the glucose conversion. From all results, it can be concluded that the good characteristics of 2 wt % Ag-TiO2 nanofibers such as the smallest anatase crystallite size (8.25 nm) and the highest specific surface area (SBET = 53.69 m2/g) promoted the highest photocatalytic activity. Additionally, TiO2 and Ag-doped TiO2 nanofibers exhibited higher photocatalytic performance for glucose conversion than commercial TiO2 (P25) and synthesized TiO2 nanoparticles. Finally, Ag-doped TiO2 nanofibers showed recycling ability with high photocatalytic glucose conversion after four-time use.

Ultra-Shallow Doping of GaAs with Mg, Cr, Mn and B Using Plasma Stimulated Room-Temperature Diffusion.

It is demonstrated that Mg, Cr, Mn and B can be doped close to GaAs surface by plasma doping without external bias at room temperature (RT). The process only takes a few minutes, and impurity densities in the range of 1018-1021/cm₃ can be achieved with doping depths about twenty nanometers. The experiment results are analyzed and the physical mechanism is tentatively explained as follows: during the doping process, impurity ion implantation under plasma sheath voltage takes place, simultaneously, plasma stimulates RT diffusion of impurity atom, which plays the main role in the doping process. The enhanced RT diffusion coefficients of Mg, Cr, Mn and B in GaAs are all in the order of magnitude of 10-15 cm₂sec-1. This is reported for the first time among all kinds of plasma assisted doping methods.

Implementation and study of dopant-assisted photoionization with a miniature capillary inlet ion trap mass spectrometer.

Dopant-assisted photoionization (PI) has been widely used in the mass spectrometric analysis of volatile compounds. Exploring simple doping methods will benefit parameter optimization and promote the application of this technique. A previously built miniature ion trap mass spectrometer was used to study dopant-assisted vacuum PI. The sampling system of this device was modified to provide three inlets for the simultaneous introduction of analytes, dopants, and auxiliary air. Then, dopant solution was directly injected into the ion trap chamber through a self-aspirating capillary inlet and rapidly evaporated without heating. Various dopant solutions were prepared and switched during the experiments. When analyzing some aniline compounds, the signals of all analytes were improved by more than 10 times after the injection of 2% anisole solution as a dopant. In addition, anisole can provide analyte signals more than three times stronger than those provided by the other dopants. On the basis of the ionization energy selectivity of dopant-assisted PI, some isomers in the mass spectrometric analysis were distinguished using different additives. In general, liquid doping is as feasible and as effective as other traditional methods, and using appropriate dopants with high PI efficiency or feeding more dopants contributes to the ionization of analytes. The proposed method also offers several unique merits, such as simple operation, low consumption, and smooth switching with minimal residue.

Impact of Si(100) doping methods on TiSi2 formation in vertical and horizontal FET structure areas with increasing aspect ratio

Due to the increasing complexity of FET structures and the preferred high trench aspect ratios, demanding process challenges exist, not only in the structuring of the contact trenches, but also in the uniform doping of the diffusion area. Previous investigations have mainly analyzed the doping of horizontal contact areas. For this reason, this paper demonstrates how vertical and horizontal contact areas can be doped through the side wall at the same time. For this purpose, relationships between structural geometry and doping methods are studied in order to structure a multitude of contact trenches next to each other in a functional way, which can realize source and drain trenches. By means of an ion implanted test structure, high doping concentrations of up to 1019 cm−3 could be achieved at a depth of approx. 250 nm below the 2.5 μm deep contact trench bottom. The concentration which can be obtained by PSG diffusion decreases rapidly with increasing Si depth. For the first time, it is shown that the dopant particle concentration of ion implantation increases with trench height and proximity to the trench side wall. Accordingly, the electrical conductivity is also higher and the SR value lower. A positive effect of the near-surface doping concentrations on the subsequent C49-TiSi2 formation could be demonstrated, which enables uniform film growth. In contrast, dopant deposition generates asymmetric dopant concentrations and prevents uniform silicide formation as the aspect ratio increases, thus causing higher diffusion area resistances.

Heteroatom doping of two-dimensional materials: From graphene to chalcogenides

Abstract In recent years, research on two-dimensional (2D) materials including graphene and transition metal dichalcogenides (TMDCs), especially molybdenum and tungsten disulfides (MoS2 and WS2), has rapidly developed. In order to meet the increasing demands of using these 2D materials in fields as diverse as optoelectronics and sensing, heteroatom doping has become an effective method to tune their electronic and physico-chemical properties. This review discusses versatile doping methods applied to graphene and TMDCs, the corresponding changes to their properties, and their potential applications. Future perspectives and new emerging areas are also presented.

Quantitative Phase Analysis by X-ray Diffraction—Doping Methods and Applications

X-ray powder diffraction is an ideal technique for the quantitative analysis of a multiphase sample. The intensities of diffraction lines of a phase in a multiphase sample are proportional to the phase fraction and the quantitative analysis can be obtained if the correction for the absorption of X-rays in the sample is performed. Simple procedures of quantitative X-ray diffraction phase analysis of a multiphase sample are presented. The matrix-flushing method, with the application of reference intensities, yields the relationship between the intensity and phase fraction free from the absorption effect, thus, shunting calibration curves or internal standard procedures. Special attention is paid to the doping methods: (i) simultaneous determination of the fractions of several phases using a single doping and (ii) determination of the fraction of the dominant phase. The conditions to minimize systematic errors are discussed. The problem of overlapping of diffraction lines can be overcome by combining the doping method (i) and the individual profile fitting method, thus performing the quantitative phase analysis without the reference to structural models of particular phases. Recent suggestions in quantitative phase analysis are quoted, e.g., in study of the decomposition of supersaturated solid solutions—intermetallic alloys. Round Robin on Quantitative Phase Analysis, organized by the IUCr Commission on Powder Diffraction, is discussed shortly. The doping methods have been applied in various studies, e.g., phase transitions in titanium dioxide, biomineralization processes, and phases in intermetallic oxide systems and intermetallic alloys.

Chemical doping of organic semiconductors for thermoelectric applications.

Doping is essential to manipulate the electrical performance of both thermoelectric (TE) materials and organic semiconductors (OSCs). Although organic thermoelectric (OTE) materials have experienced a rapid development over the past decade, the chemical doping of OSCs for TE applications lags behind, which has limited further breakthroughs in this cutting-edge field. Recently, increasing efforts have been devoted to the development of energetically matched host and dopant molecules, exploring novel doping methods and revealing the doping mechanisms. This tutorial review covers the basic mechanisms, fundamental requirements, recent advances and remaining challenges of chemical doping in OSCs for TE applications. We first present the basic knowledge of the trade-off relationship in TE materials and its critical requirements for doped OSCs, followed by a brief introduction of recent advances in the molecular design of OSCs and dopants. Moreover, we provide an overview of the existing categories of doping mechanisms and methods, and more importantly, emphasize the summarized doping strategies for the state-of-the-art OTE materials. Finally, challenges and perspectives on the chemical doping of OSCs are proposed to highlight the research directions that deserve attention towards a bright future of OTE materials.

Potassium doping-induced variations in the structures and photoelectric properties of a MAPbI3 perovskite and a MAPbI3/TiO2 junction.

It has been experimentally demonstrated that mixed metallic cation modification could be an effective strategy to enhance the performance and stability of perovskite-based solar cells (PSCs). However, there is limited microscopic understanding at the atomic/molecular level of the behavior of small radius alkali metal cation doping in both perovskite materials and perovskite/TiO2 junctions. Here, we perform a first-principles density functional theory study on the doping-induced variation of the geometric and electronic structures of MAPbI3 (MA = methylammonium) and the MAPbI3/TiO2 junction. The impacts of different doping methods, and different charge states and locations of the given dopants have been investigated. At first, we theoretically confirm that the structures doped by K+ are the most thermally stable compared to the structures doped by the other charge states of K, and that K+ dopants prefer to modify the perovskite lattice interstitially and stay near the MAPbI3/TiO2 interface. Meanwhile, we find that a severe geometric deformation occurs if two doped lattices come into contact directly, indicating that the lattice may rapidly collapse from the interior if the doping concentration is too high. Additionally, we observe that K+ doped interstitially near the MAPbI3/TiO2 interface causes the intensive distortion of the surface Ti-O bonds and severe bond-length fluctuations. Consequently, this results in distorted TiO2 bands of the interfacial layer and a slight decrease of the band offset of conduction bands between two phases. This work complements experiments and provides a better microscopic understanding of the doping modification of the properties of perovskite materials and PSCs.

Влияние способов легирования на свойства элементов с аномально фотовольтаическими эффектами

This work presents general studies of the influence of doping methods on the properties of elements with anomalous photovoltaic effects and the process of doping of semi-crystalline thin CdTe films with isovalent impurities is also investigated. The process of thermal diffusion has been studied.