Common Dopants Research Articles

CMOS-compatible method for doping of buried vertical polysilicon structures by solid phase diffusion

Polysilicon receives attention nowadays as a means to incorporate 3D-structured photonic devices into silicon processes. However, doping of buried layers of a typical 3D structure has been a challenge. We present a method for doping of buried polysilicon layers by solid phase diffusion. Using an underlying silicon oxide layer as a dopant source facilitates diffusion of dopants into the bottom side of the polysilicon layer. The polysilicon is grown on top of the oxide layer, after the latter has been doped by ion implantation. Post-growth heat treatment drives in the dopant from the oxide into the polysilicon. To model the process, we studied the diffusion of the two most common silicon dopants, boron (B) and phosphorus (P), using secondary ion mass spectroscopy profiles. Our results show that shallow concentration profiles can be achieved in a buried polysilicon layer using the proposed technique. We present a quantitative 3D model for the diffusion of B and P in polysilicon, which turns the proposed method into an engineerable technique.

Enhanced organic photovoltaic properties via structural modifications in PEDOT:PSS due to graphene oxide doping

Poly(3,4-thylenedioxythiophene):poly(styrene sulfonate), PEDOT:PSS is a well-known conductive polymer for hole transport in organic devices, the properties of which can be enhanced by doping. Common dopants are metal oxides and nanoparticles. In this study, addition of graphene oxide (GO) to PEDOT:PSS as a dopant is addressed in organic photovoltaics (OPVs). With GO doping, electrical conductivity and transport properties of PEDOT:PSS increases due to structural alterations in the presence of COOH and OH functional groups in GO. These structural alterations have been revealed under detailed study of Raman spectra, X-ray photoelectron spectroscopy (XPS) analysis, Topographical and conductive Atom force microscopy (AFM/C-AFM) mapping. OPVs fabricated using PEDOT:PSS: GO (5:1) as a hole transport layer (HTL) exhibited a power conversion efficiency (PCE) of 7.68%, which was higher than the 7.01% that was obtained for the OPVs using pristine PEDOT:PSS.

Doping stability and opto‐electronic performance of chemical vapour deposited graphene on transparent flexible substrates

The primary barrier to wider commercial adoption of graphene lies in reducing the sheet resistance of the transferred material without compromising its high broad-band optical transparency, ideally through the use of novel transfer techniques and doping strategies. Here, chemical vapour deposited graphene was uniformly transferred to polymer supports by thermal and ultraviolet (UV) approaches and the time-dependent evolution of the opto-electronic performance was assessed following exposure to three kinds of common dopants. Doping with FeCl3 and SnCl2 showed minor, and notably time unstable, enhancement in the σ opt/σ dc figure of merit, while AuCl3-doping markedly reduced the sheet resistance by 91.5% to 0.29 kΩ/sq for thermally transferred samples and by 34.4% to 0.62 kΩ/sq for UV-transferred samples, offering a means of realising viable transparent flexible conductors that near the indium tin oxide benchmark.

The ionization mechanisms in direct and dopant-assisted atmospheric pressure photoionization and atmospheric pressure laser ionization.

A novel, gas-tight API interface for gas chromatography-mass spectrometry was used to study the ionization mechanism in direct and dopant-assisted atmospheric pressure photoionization (APPI) and atmospheric pressure laser ionization (APLI). Eight analytes (ethylbenzene, bromobenzene, naphthalene, anthracene, benzaldehyde, pyridine, quinolone, and acridine) with varying ionization energies (IEs) and proton affinities (PAs), and four common APPI dopants (toluene, acetone, anisole, and chlorobenzene) were chosen. All the studied compounds were ionized by direct APPI, forming mainly molecular ions. Addition of dopants suppressed the signal of the analytes with IEs above the IE of the dopant. For compounds with suitable IEs or Pas, the dopants increased the ionization efficiency as the analytes could be ionized through dopant-mediated gas-phase reactions, such as charge exchange, proton transfer, and other rather unexpected reactions, such as formation of [M + 77](+) in the presence of chlorobenzene. Experiments with deuterated toluene as the dopant verified that in case of proton transfer, the proton originated from the dopant instead of proton-bound solvent clusters, as in conventional open or non-tight APPI sources. In direct APLI using a 266 nm laser, a narrower range of compounds was ionized than in direct APPI, because of exceedingly high IEs or unfavorable two-photon absorption cross-sections. Introduction of dopants in the APLI system changed the ionization mechanism to similar dopant-mediated gas-phase reactions with the dopant as in APPI, which produced mainly ions of the same form as in APPI, and ionized a wider range of analytes than direct APLI.

Iron (III) Chloride doping of CVD graphene

Chemical doping has been shown as an effective method of reducing the sheet resistance of graphene. We present the results of our investigations into doping large area chemical vapor deposition graphene using Iron (III) Chloride (FeCl3). It is shown that evaporating FeCl3 can increase the carrier concentration of monolayer graphene to greater than 1014 cm−2 and achieve resistances as low as 72 Ω sq−1. We also evaluate other important properties of the doped graphene such as surface cleanliness, air stability, and solvent stability. Furthermore, we compare FeCl3 to three other common dopants: Gold (III) Chloride (AuCl3), Nitric Acid (HNO3), and TFSA ((CF3SO2)2NH). We show that compared to these dopants, FeCl3 can not only achieve better sheet resistance but also has other key advantages including better solvent stability.

Expanding the spectral tunability of plasmonic resonances in doped metal-oxide nanocrystals through cooperative cation-anion codoping.

We present a generalized cation-anion codoping methodology for the synthesis of monodisperse, doped metal-oxide nanocrystals (NCs) that exhibit near-infrared localized surface plasmon resonance (LSPR) with the highest reported quality factors. We demonstrate that, in addition to the use of common cation dopants, the incorporation of fluorine into the lattice as an anion dopant can further increase the free-carrier concentration within individual NCs; this supports the cooperative effects of mixed cation-anion doping in shifting the LSPR to higher energies. As a result, this method allows the LSPR of doped metal-oxide NCs to become tunable across a significantly broader wavelength range (1.5-3.3 μm), circumventing the prior limitations on the highest possible LSPR energies associated with single-element doping for a given oxide host. The strategy of cation-anion codoping can offer new possibilities for the chemical design of doped semiconductor and metal-oxide NCs with tailored LSPR characteristics.

First-Principles-Inspired Design Strategies for Graphene-Based Supercapacitor Electrodes

Using density-functional theory calculations on a variety of model surfaces, we demonstrate that the low theoretical quantum capacitance of graphene-based electrodes can be significantly improved by altering local structural and morphological features. Common point defects, dopants, strain, and surface rippling are considered, as well as differences between locally single-layer and multilayer configurations. Local curvature is particularly effective at improving quantum capacitance, as is the inclusion of certain point defects and substitutional dopants at sufficiently high concentrations. We also show that single-layer graphene exhibits poor screening behavior of the double-layer potential when compared with multilayer samples, which suggests that higher area-specific capacitance can be obtained with samples a few layers thick. Overall, our results demonstrate the viability of local structural engineering as a tool to optimize graphene derivatives for use as supercapacitor electrodes, potentially increasing their theoretical charge storage capacity by severalfold.

P-doping-free InGaN/GaN light-emitting diode driven by three-dimensional hole gas

Here, GaN/AlxGa1-xN heterostructures with a graded AlN composition, completely lacking external p-doping, are designed and grown using metal-organic-chemical-vapour deposition (MOCVD) system to realize three-dimensional hole gas (3DHG). The existence of the 3DHG is confirmed by capacitance-voltage measurements. Based on this design, a p-doping-free InGaN/GaN light-emitting diode (LED) driven by the 3DHG is proposed and grown using MOCVD. The electroluminescence, which is attributed to the radiative recombination of injected electrons and holes in InGaN/GaN quantum wells, is observed from the fabricated p-doping-free devices. These results suggest that the 3DHG can be an alternative hole source for InGaN/GaN LEDs besides common Mg dopants.

Process simulation of dopant diffusion and activation in germanium

Germanium with its high carrier mobility is currently being investigated as an alternative material to silicon for advanced MOS devices. We have reviewed the literature on n‐type and p‐type doping of germanium and established a baseline calibration for technology process simulation. Fundamental parameters for germanium point defects have been selected and extended defect evolution has been calibrated. Models and parameters for accurate simulation of ion implantation, diffusion, and activation of the most common dopants (phosphorus and arsenic for n‐type, boron for p‐type) have been defined. We discuss the current accuracy and limitations of the process calibration and specify missing experimental data needed for enhancing and broaden the simulation capabilities for germanium processing.

Influence of an electric field on photodegradation and self-healing in disperse orange 11 dye-doped PMMA thin films

The influence of an applied electric field on reversible photodegradation of disperse orange 11 (DO11) doped into PMMA is measured using digital imaging and conductivity measurements. Correlations between optical imaging, which measures photodegradation and recovery, and photoconductivity enables an association to be made between the damaged fragments and their contribution to current, thus establishing that damaged fragments are charged species, or polarizable. Hence, the decay and recovery process should be controllable with the applications of an electric field. Indeed, we find that the dye polymer system is highly sensitive to an applied electric field, which drastically affects the decay and recovery dynamics. We demonstrate accelerated recovery when one field polarity is applied during burning, and the opposite polarity is applied during recovery. This work suggests that the damage threshold can be increased through electric field conditioning; and, the results are qualitatively consistent with the domain model of Ramini[3, 4]. The observed behavior will provide useful input into better understanding the nature of the domains in the domain model, making it possible to design more robust materials using common polymers and molecular dopants.

Surface Doping for Hindrance of Crystal Growth and Structural Transformation in Semiconductor Nanocrystals

Doping can strongly influence the crystal growth of semiconductor nanocrystals. It can change the surface energy and therefore the growth directions and shape of the host nanocrystals. While doping of transition metal ions in various semiconductor host nanocrystals is widely studied for obtaining new material properties, the effect of doping on crystal growth has been less explored. Herein, we study the change in the crystal growth pattern and growth rate with doping of one of the most common dopants Mn in a ZnSe host. With the help of selective surface binding ligands, hemisphere-shaped zinc blende nanostructures are designed from ZnSe seeds and dopant Mn precursors in different amounts are introduced at different stages of the synthetic process. Monitoring the sequential product and analyzing the surface or internal locations of the dopants, the possibility of shape change has been discussed. Moreover, the mutual effects of crystal growth and doping on one another are also determined considering the progress of the reactions under different conditions. We believe that the results presented here are important for understanding the doping mechanism and its effects during crystal growth in semiconductor nanocrystals, which are not clear to date.

First principles description of the electronic properties of doped ZnO

We here review how the most common intrinsic defects and dopants modify the electronic properties of ZnO, providing novel results obtained by means of accurate first principles density functional calculations. In particular, we show that interstitial H is responsible for the residual and hardly eliminable n‐type character of real ZnO samples. We also show the effects of controlled doping with metal ions to obtain both transparent conductive oxides (Al, Ga, In) and p‐type materials (Ag). We demonstrate that Ag inclusions can be linked to the presence of deep acceptors in the host band gap that may cancel the p‐type character in Ag‐doped ZnO.

Performance of PCDTBT:PC70BM Organic Photovoltaic Cells Fabricated Using Dipolar and Common Dopants as Processing Additives

Polymer solar cells (PSCs) having donor-acceptor bulk heterojunction (BHJ) is one of the convenient solution for meeting the world's current energy demands. Herein, we report the fabrication and characterization of bulk heterojunction solar cells using the blend of PCDTBT and PC70BM in 1,2-dichlorobenzene (o-DCB) with the device structure of ITO/PEDOT:PSS/PCDTBT:PC70BM/BCP/Al. The effect of dipolar dopants such as dimethylsulfoxide (DMSO) and dimethylformamide (DMF) and common dopants such as 1,8-diiodooctane (DIO) and 1,8-octanedithiol (OT) as processing additive solvents on the performance of PCDTBT:PC70BM based BHJ solar cells were studied and compared with the device without additive in terms of current density, open-circuit voltage and power conversion efficiency (PCE). The addition of additives significantly leads to the aggregation of PCDTBT molecule, thereby controlling the morphology of PCDTBT:PC70BM films enhancing an efficient exciton dissociation and charge transport. Among the additives used the device containing DMSO showed the best performance with a PCE of 7.3%.

The influence of nitrogen vacancies on the magnetic behaviour of rare-earth nitrides

The rare-earth nitrides are ferromagnetic semiconductors with promise for spintronic devices. Their most common dopants are nitrogen vacancies (VN), with a small enough energy of formation that they exist at of order 1% in epitaxial films. Here we report preliminary investigations of their effect on the magnetic states of two of them in the series, GdN and EuN. In the former we find an enhanced Curie temperature at very high VN concentration, and the Eu2+ ions associated with VN in the latter show strong exchange with their Eu3+ neighbours that might form the basis of a diluted magnetic semiconductor.

Ionization of Doped Helium Nanodroplets: Residual Helium Attached to Diatomic Cations and Their Clusters

Electron impact ionization of helium nanodroplets containing a dopant, M, can lead to the detection of both M(+) and helium-solvated cations of the type M(+)·He(n) in the gas phase. The observation of helium-doped ions, He(n)M(+), has the potential to provide information on the aftermath of the charge transfer process that leads to ion production from the helium droplet. Here we report on helium attachment to the ions from four common diatomic dopants, M = N(2), O(2), CO, and NO. For experiments carried out with droplets with an average size of 7500 helium atoms, the monomer cations show little tendency to attach and retain helium atoms on their journey out of the droplet. By way of contrast, the corresponding cluster cations, M(n)(+), where n ≥ 2, all show a clear affinity for helium and form He(m)M(n)(+) cluster ions. The stark difference between the monomer and cluster ions is attributed to more effective cooling of the latter in the aftermath of the ionization event.

Diffusion of Al, O, Pt, Hf, and Y atoms on α-Al2O3(0001): implications for the role of alloying elements in thermal barrier coatings

We use density functional theory with periodic boundary conditions to investigate diffusion of Al, O, Pt, Hf, and Y on the α-Al2O3(0001) surface as a simple model to obtain insight into possible diffusion mechanisms occurring at alumina grain boundaries (GBs) in thermal barrier coatings (TBCs). We calculate diffusion pathways, activation energies, and diffusion constants. For the elements involved in alumina growth, we find that Al diffusion is facile and involves a simple hop from one most stable adsorption site to the next without local minima in between whereas O diffusion has a much higher barrier and has local minima along the minimum energy pathway. This trend is consistent with relative rates of diffusion at alumina GBs. Regarding common dopants in the metal (bond coat) alloy substrate from which alumina grows, we predict that Pt diffusion is facile but thermodynamically disfavored relative to Pt remaining in the bond coat alloy, while Hf and Y diffusion involve much higher barriers than Al diffusion. We use these results to rationalize some observations regarding the role of reactive elements Hf and Y as well as Pt in TBCs.

Effect of In, Sb and Ga doping on the structure and vibrational modes of hydrothermally grown ZnO nanostructures

Effect of common optoelectronic dopants like In, Sb and Ga on the structure, morphology and vibrational modes of ZnO nanostructures has been studied systematically using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. While incorporation of Ga has no strong effect on the lattice parameters and crystallinity of ZnO nanostructures, In and Sb doping introduce considerable lattice distortion. Sb doping results an anisotropic distortion along the c axis of the ZnO unit cell. Several anomalous vibrational modes are induced due to incorporation of dopants into ZnO lattice. Origins of the observed anomalous modes are discussed.

Suitability of tetrahydofuran as a dopant and the comparison to other existing dopants in dopant‐assisted atmospheric pressure photoionization mass spectrometry in support of drug discovery

In this paper, we investigated the suitability of tetrahydofuran (THF) as a dopant and compared it against other common dopants for atmospheric pressure photoionization mass spectrometry (APPI-MS). In a systematic analysis of 37 drug standards and 100 Wyeth proprietary drug candidates, THF was found to increase ionization efficiency as high as 33-fold when introduced through a syringe pump at a flow rate of 20 microL/min, and as high as 114-fold when introduced through the mobile phase at 100 microL/min. As a dopant, THF is as effective as acetone, better than anisole, and slightly less effective than toluene for the majority of the test compounds. The increase in ionization efficiency by THF was found to be compound-dependent. THF was more effective in facilitating the ionization of polar compounds than of non-polar compounds. With THF, toluene and acetone as dopants, a single type of molecular ion ([M+H](+) or M(+*)) is produced for analyte molecules. However, anisole can cause the formation of an ion cluster for polar analytes. The cluster contains [M-2H+H](+), M(+*), and [M+H](+) ions with varied ratios. This complexity may make interpretation of spectra difficult for unknown compounds when complimentary data are not available. Our findings indicate that THF is a suitable dopant in the daily usage for increasing ionization efficiency, especially when THF is used as the mobile phase or as an organic modifier in the mobile phase.

Ytterbium-Doping Related Stresses in Preforms for High-Power Fiber Lasers

Frozen-in mechanical stresses can significantly influence the optical and mechanical properties of optical fibers, especially in laser fibers for high-power operation. In the following, we will report on the polarimetric measurement of stresses induced by the spatially varying doping composition in fiber preforms. We investigated the effect of rare-earth laser ions and found that the dopant ytterbium generates higher stresses than other common dopants in lightwave technology such as phosphorus or aluminum. The stress-induced index change relevant for the guiding properties is derived from the stress data. Especially in large-mode-area laser fibers with low numerical apertures, such stresses can significantly modify the index profile and thereby influence the propagation behavior.

Development of certified reference materials of ion-implanted dopants in silicon for calibration of secondary ion mass spectrometers

Certified reference materials have been developed for calibration of the concentrations of the most common dopants used in silicon semiconductor technology—boron, arsenic, and phosphorus. These materials consist of a single dopant species that is introduced into a silicon wafer by ion implantation. The certified dose (at.∕cm2) of the dopant species is used for calibration of dopant concentration measurements with secondary ion mass spectrometers. Certification measurements were carried out by nuclear analytical methods—neutron depth profiling for boron, instrumental neutron activation analysis for arsenic, and radiochemical neutron activation analysis for phosphorus. SRM 2137 contains a B10 implant with a certified dose of (1.018×1015±0.035×1015)at.∕cm2; SRM 2134 contains a As75 implant with a certified dose of (7.330×1014±0.028×1014)at.∕cm2; SRM 2133 contains a P31 implant with a certified dose of (9.58×1014±0.16×1014)at.∕cm2. Several examples demonstrate the improved interlaboratory agreement that is achievable in the measurement of unknown dopant concentrations and implanted doses when these reference materials are used for calibration by each laboratory.