Conventional Doping Research Articles

Large specific surface area S-doped Fe–N–C electrocatalysts derived from Metal–Organic frameworks for oxygen reduction reaction

It is highly desired but challenging to develop platinum group metal-free electrocatalysts for oxygen reduction reaction (ORR), which can promote the commercialization of fuel cell technology. To achieve this target, we report a one-step doping method to prepare S-doped Fe–N–C catalysts using zeolite imidazole framework (ZIF-8) and iron (III) thiocyanate (Fe(SCN)3) as precursor. Different from conventional doping approach, i.e. physical mixing, Fe(SCN)3 is in-situ added during ZIF-8 formation which would encapsulate Fe(SCN)3 molecules inside ZIF-8 to avoid structure destruction and create potential replacement of Zn ions by Fe ions to form uniform Fe–N4 complexes. As a result, the prepared S-doped Fe–N–C catalysts own large specific surface areas with a maximum value of 1326 ​m2 ​g−1 and a dual-scale porous structure that benefits mass transport. Significantly, the composition-optimized catalyst exhibits superior ORR activity in both 0.1 ​M HClO4 electrolyte and 0.1 ​M KOH electrolyte, in which the half-wave potential reaches 0.81 ​V and 0.92 ​V (vs. RHE), respectively. Remarkable stability is also attained, which loses 2 ​mV only after 10000 potential cycles in O2-saturated 0.1 ​M HClO4 and remains almost constant in O2-saturated 0.1 ​M KOH, surpassing commercial Pt/C catalyst in both acidic and alkaline medium.

Partial Isolation Type Buried Channel Array Transistor (Pi-BCAT) for a Sub-20 nm DRAM Cell Transistor

In this paper, we propose a new buried channel array transistor structure to solve the problem of current leakage occurring in the capacitors of dynamic random-access memory (DRAM) cells. This structure has a superior off current performance compared with three previous types of structures. In particular, the proposed buried channel array transistor has a 43% lower off current than the conventional asymmetric doping structure. Here, we show the range of the effective buried insulator parameter according to the depth of the buried gate, and we effectively show the range of improvement for the off current.

Atomic layer deposition supercycle approach applied to the Al-doping of nearly saturated ZnO surfaces

Current research on transparent conductive oxides deals with the development of environmentally friendly materials having competitive electrical and optical properties. Also, the synthesis methods need to be compatible with the state-of-the-art microelectronics and miniaturization. ZnO films doped with Al (AZO) via Atomic Layer Deposition (ALD) have been subjected to thorough investigation for the latter. However, the conventional doping schemes in ALD seem to have reached their limit and alternative approaches are currently being explored. This work contributes to the improvement of the Al-doping efficiency of ZnO by the ALD supercycle approach, applying the doping-cycle on nearly saturated ZnO surfaces. The electrical (ρ = 1.3 × 10−3 Ωcm, n = 3.79 × 1020 cm−3, and μ = 12.3 cm2/Vs) and optical (%T > 75) properties demonstrated typical values obtained by others applying the supercycle methodology. However, the main finding of this work is the trend observed in the electrical and optical properties, which suggests that the Al solubility limit was not reached as a result of the interaction between the dopant agent and the nearly saturated ZnO surfaces. This is also evidence that the dopant atoms do not become inactive once the compensation effect between substitutional doping and structural defects, has been established. These results open the possibility of exploring the incorporation of more Al into the ZnO structure following and optimizing the doping scheme used here, which at the same time, promises materials that could substitute indium-tin-oxide in many optoelectronic applications, attending the well-known environmental and economic issues.

Engineering of the spin on dopant process on silicon on insulator substrate

We report on a systematic analysis of phosphorus diffusion in silicon on insulator thin film via spin-on-dopant process (SOD). This method is used to provide an impurity source for semiconductor junction fabrication. The dopant is first spread into the substrate via SOD and then diffused by a rapid thermal annealing process. The dopant concentration and electron mobility were characterized at room and low temperature by four-probe and Hall bar electrical measurements. Time-of-flight-secondary ion mass spectroscopy was performed to estimate the diffusion profile of phosphorus for different annealing treatments. We find that a high phosphorous concentration (greater than 1020 atoms cm−3) with a limited diffusion of other chemical species and allowing to tune the electrical properties via annealing at high temperature for short time. The ease of implementation of the process, the low cost of the technique, the possibility to dope selectively and the uniform doping manufactured with statistical process control show that the methodology applied is very promising as an alternative to the conventional doping methods for the implementation of optoelectronic devices.

Incorporating element doping and quantum dot embedding effects to enhance the thermoelectric properties of higher manganese silicides

Element doping and nano-inclusion embedding are effective approaches to enhance the electrical conductivities and decrease the lattice thermal conductivities of thermoelectric (TE) materials, respectively. However, the intrinsic low electrical thermal conductivities and high electrical properties are severely sacrificed, and the final figure of merit (ZT) is usually restricted. In this study, Ag doping and Pt quantum dot (QD) embedding were synchronously achieved via embedding Ag/Pt alloy QDs into the higher manganese silicides to avoid the conventional single-element doping strategy. The power factor (at 823 K) was enhanced from 1.57 × 10−3 W m−1 K−2 to 1.82 × 10−3 W m−1 K−2 (∼16%) due to the ∼18% increase in carrier concentration that was derived from the Ag doping effect. Simultaneously, the lattice thermal conductivity (at 823 K) decreased from 2.65 W m−1 K−1–1.92 W m−1 K−1 (∼28%) because of the broadband phonon scattering effect that resulted from the residual Pt QDs inclusions. Synthetically, the optimal ZT value increased by ∼52% from 0.42 to 0.64 at 823 K. This study demonstrated that incorporating metastable alloy QDs to obtain element doping and nano-inclusion embedding effects is a novel and feasible means to enhance the ZT value of HMS. This method is also possibly applicable to other alloy QD/TE composites.

Electrical doping in single walled carbon nanotube systems: A new technique

First report on electrically doped semiconducting carbon nanotube is presented using Extended Huckel Theory in combination with Non-equilibrium Green’s function formalism. The results show increase in current with the increasing electrical doping concentration. Electrical doping induces high charge concentration at small applied voltages and is far more superior because of its fault free approach overcoming the limitations of conventional doping. Furthermore, the device density of states confirms the sufficient number of peaks in the valence and conduction bands. The obtained results were compared with other theoretical results in the field in the form of a table. The results are very beneficial for the designing of high-performance CNT devices and enhancing their potential applications in the electronics industry.

Application of a negative thermal expansion oxide in SOFC cathode

To improve the performance of solid oxide fuel cells (SOFCs) at intermediate temperature, an idea of adding a negative thermal expansion (NTE) oxide into cathode is proposed. The effects of NdMnO3-δ (NM) NTE oxide addition in Ba0.5Sr0.5FeO3-δ (BSF) cathode on the performance of proton-conducting SOFCs (H-SOFCs) are studied. The 30 wt % NM addition can lead to an ideal thermal matching between BSF-NM cathode and BaZr0.1Ce0.7Y0.2O3-δ (BZCY) electrolyte, and improve the electrochemical performance of H-SOFCs significantly. At 500–750 °C, the peak power density (PPD) of H-SOFCs with BSF-NM cathode is 139–941 mW cm−2, which is apparently higher than that (73–661 mW cm−2) with BSF one. In addition, the relative increment of peak power density (PPD) increases from 42.36% at 750 °C to 90.41% at 500 °C, which is seldom obtained by conventional cathode doping. Comprehensive results of electrochemical impedance spectra, electrical conductivities, and SEM observations show that the apparent improvement of PPDs should be mainly associated with the increased three phase boundary length due to the ideal thermal matching between cathodes and electrolytes. In all, it provides a novel idea to develop intermediate and low temperature SOFCs.

Thermoelectric power factor of Ge1-xSnx thin films

The Seebeck coefficients (α) and the power factors of 100 nm-thick Ge1-xSnx films grown by magnetron sputtering were studied versus Sn composition (0.09 ≤ x ≤ 0.15) in the 220−330 K temperature range. The films present particularly high Seebeck coefficients at room temperature but as they are undoped, their power factors are too low for room temperature thermoelectric applications due to low electrical conductivity (σ). Nevertheless, as it is possibile to modify both α and σ by adjusting x, as well as employ conventional doping techniques, the IV-IV Ge1-xSnx semiconductor is shown to be extremely interesting for complementary-metal-oxide-semiconductor-compatible thermoelectric applications.

P‐170: Green Phosphorescent Organic Light‐Emitting Diodes with Ultra‐thin Undoped Emission Layer of nearly 24% External Quantum Efficiency

This paper reports the high efficiency green phosphorescent organic light‐emitting diode (OLEDs) with ultra‐thin emission layer structure. The OLEDs were fabricated without conventional and complicated doping process. The optimized OLEDs achieved the maximum external quantum efficiency of nearly 24% without conventional doping process.

Surface charge transfer doping for two-dimensional semiconductor-based electronic and optoelectronic devices

Doping of semiconductors, i.e., accurately modulating the charge carrier type and concentration in a controllable manner, is a key technology foundation for modern electronics and optoelectronics. However, the conventional doping technologies widely utilized in silicon industry, such as ion implantation and thermal diffusion, always fail when applied to two-dimensional (2D) materials with atomically-thin nature. Surface charge transfer doping (SCTD) is emerging as an effective and non-destructive doping technique to provide reliable doping capability for 2D materials, in particular 2D semiconductors. Herein, we summarize the recent advances and developments on the SCTD of 2D semiconductors and its application in electronic and optoelectronic devices. The underlying mechanism of STCD processes on 2D semiconductors is briefly introduced. Its impact on tuning the fundamental properties of various 2D systems is highlighted. We particularly emphasize on the SCTD-enabled high-performance 2D functional devices. Finally, the challenges and opportunities for the future development of SCTD are discussed.

Intermediate-level doping strategy to simultaneously optimize power factor and phonon thermal conductivity for improving thermoelectric figure of merit

The conventional doping strategy for thermoelectric materials generally focuses on a shallow donor/acceptor model with the energy level close to the band edge as for electronic devices. However, thermoelectric devices operate over a large temperature difference, and the optimal carrier concentration increases with increasing temperature. A shallow level cannot meet the requirement over a large temperature range. Here, an innovative strategy of introducing an intermediate level is proposed. Such an intermediate level introduces more carriers with increasing temperature, consistent with the trend of increasing optimal doping concentration with temperature, enabling larger power factor over a broader temperature range. Furthermore, the intermediate level typically requires more impurities, leading to increased phonon scattering. This strategy allows simultaneous optimization of carrier concentration over a wide temperature range and suppression of thermal conductivity via stronger point-defect phonon scattering. Experimental results from heavily-doped ZrCoSb employing shallow, intermediate, and deep levels successfully corroborate this strategy, where simultaneously improved power factor and figure of merit are obtained by introducing an intermediate level. Our work indicates that the performance of known thermoelectric materials should be reevaluated by introducing an intermediate level to unleash their full potential.

Anion-site-modulated thermoelectric properties in Ge2Sb2Te5-based compounds

The amalgamation of multi-subjects often elicits novel materials, new concepts and unexpected applications. Recently, Ge2Sb2Te5, as the most established phase-change material, has been found to exhibit decent thermoelectric performance in its stable, hexagonal phase. The challenge for higher figure of merit (zT) values lies in reducing the hole carrier concentration and enhancing the Seebeck coefficient, which, however, can be hardly realized by conventional doping. Here in this work, we report that the electrical properties of Ge2Sb2Te5 can be readily optimized by anion-site modulation. Specifically, Se/S substitution for Te induces stronger and more ionic bonding, lowering the hole density. Furthermore, an increase in electronic density of state is introduced by Se substitution, contributing to a large increase in Seebeck coefficient. Combined with the reduced thermal conductivity, maximum zT values above 0.7 at 800 K have been achieved in Se/S-alloyed materials, which is ~ 30% higher than that in the pristine Ge2Sb2Te5.

A high performance InGaN tunnel FET with InN interlayer and polarization-doped source and drain

An InGaN tunneling field-effect transistor (TFET) with a polarization-doped source and drain as well as an InN interlayer (PD-IL TFET) is proposed and investigated by Silvaco-Atlas simulations for the first time. This device features the graded InxGa1−xN source and drain where the ‘In’ fraction increases linearly in the source while it decreases linearly in the drain along the (0001) orientation. The unique design could realize the high PD carrier concentration in source and drain at the same time, benefiting from the nature of the polarization effect in III-Nitride materials. Thus, the random dopant fluctuations caused by conventional physical doping could be avoided effectively. Simulation results show that the PD-IL TFET with a 2 nm thick InN interlayer and ‘In’ fraction of 0.75 could achieve ON-state current (ION) of 74 μA μm−1, ION/IOFF ratio of 1013 and average subthreshold swing of as low as 1 mV dec−1. The effect of InN interlayer thickness and ‘In’ fraction of InxGa1−xN on the electrical characteristics of the PD-IL TFET are investigated and analyzed systematically. In addition, the circuit analysis and the feasible fabrication process issues of the proposed device are also presented and discussed. These results could break a new path to realize TFETs without physical doping in low power electronics applications.

Highly efficient modulation of the electronic properties of organic semiconductors by surface doping with 2D molecular crystals

Doping is a critically important strategy to modulate the properties of organic semiconductors (OSCs) to improve their optoelectrical performances. Conventional bulk doping involves the incorporation of foreign molecular species ( i.e. , dopants) into the lattice of the host OSCs, and thus disrupts the packing of the host OSCs and induces structural defects, which tends to reduce the mobility and (or) the on/off ratio in organic field-effect transistors (OFETs). In this article, we report a highly efficient and highly controllable surface doping strategy utilizing 2D molecular crystals (2DMCs) as dopants to boost the mobility and to modulate the threshold voltage of OFETs. The amount of dopants, i.e. , the thickness of the 2DMCs, is controlled at monolayer precision, enabling fine tuning of the electrical properties of the OSCs at unprecedented accuracy. As a result, a prominent increase of the average mobility from 1.31 to 4.71 cm2 V−1 s−1 and a substantial reduction of the threshold voltage from −18.5 to −1.8 V are observed. Meanwhile, high on/off ratios of up to 108 are retained.

Replacement Gate High-k/Metal Gate nMOSFETs Using a Self-Aligned Halo-Compensated Channel Implant

A device design technique for boosting output resistance (Rout) characteristics of long-channel halo-doped nMOSFETs for replacement gate (RMG) high-k/metal gate (HK/MG) devices is proposed based on numerical simulations. We show that the self-aligned halo-compensated channel implant (HCCI) that is carried out after dummy poly gate removal provides compensation for the conventional halo doping. This can be utilized to mitigate the magnitude of potential drop beyond saturation at the drain end so that the long-channel Rout can be boosted relative to the conventional halo-doped device. In addition, we achieve an improved Vt roll-off behavior, an advantage to hot carrier injection (HCI) characteristics at high voltage operation, and the lowered short-channel drain-induced barrier lowering (DIBL) and intrinsic delay via the optimization of the source/drain (S/D) doping profile. HCCI technique can be implemented using a process flow that is compatible with the RMG HK/MG system-on-chip (SoC) technology in the mass production.

Fabrication of high performance structural N-doped hierarchical porous carbon for supercapacitors

In this paper, a method to fabricate structural N-doped hierarchical porous carbon is proposed. KOH and melamine are found to have synergistically impact on the pore-creating and nitrogen-doping process. The targeted product possesses specific surface area of 2642 m2 g−1 with a highly promoted inner surface area. The specific capacitance increases from 364 to 715 F g−1 at the current density of 1 A g−1 in a two-electrode system using 6 M KOH electrolyte. It also shows the good rate capability (526 F g−1 at 100 A g−1) and cycle performance (98.28% retention after 5000 cycles at 5 A g−1). The energy density reaches 118 W h kg−1 at the power density of 200 W kg−1. The high specific capacitance is mostly derived from the electrical double-layer capacitance, which is a significant advantage compared to the conventional surface doping. The nitrogen atoms stably embedded into the carbon skeleton. N-5 hindered the energy storage process, while N-Q showed obvious impact both on the specific capacitance and cycle performance. All in all, a high-performance electrode material for supercapacitor is provided in this study and it also provides a brand-new idea for the structural doping porous carbon.

Pseudo core-shell LaCoO3@MgO perovskite oxides for high performance methane catalytic oxidation

Magnesia modified LaCoO3 was prepared by a facile one-step sol-gel method and used for removal of dilute methane. Compared with the conventional doping technique, the obtained LaCoO3@MgO-x exhibits pseudo core-shell structure and shows superior catalytic activity. The methane conversion exceeds 90% at 532 °C on LaCoO3@MgO-0.1, while only 60% of methane is conversed using the doped perovskite LaCo0.9Mg0.1O3. The high catalytic performance of LaCoO3@MgO-0.1 is mainly attributed to the adjustment of surface acid-base properties by the MgO shell structure. According to density functional theory (DFT) calculation, the methane is more likely to be adsorbed and cracked on LaCoO3@MgO-0.1. The in situ DRIFTS shows that CH3–O–CH3 intermediate specie is formed. The pseudo core-shell structure also enhances the stability and the LaCoO3@MgO-0.1 maintains high activity after working for 100 h. The above results demonstrate that surface modification by magnesia is an effective strategy for improving LaCoO3 catalytic performance.

Resonant Ta Doping for Enhanced Mobility in Transparent Conducting SnO2.

Transparent conducting oxides (TCOs) are ubiquitous in modern consumer electronics. SnO2 is an earth abundant, cheaper alternative to In2O3 as a TCO. However, its performance in terms of mobilities and conductivities lags behind that of In2O3. On the basis of the recent discovery of mobility and conductivity enhancements in In2O3 from resonant dopants, we use a combination of state-of-the-art hybrid density functional theory calculations, high resolution photoelectron spectroscopy, and semiconductor statistics modeling to understand what is the optimal dopant to maximize performance of SnO2-based TCOs. We demonstrate that Ta is the optimal dopant for high performance SnO2, as it is a resonant dopant which is readily incorporated into SnO2 with the Ta 5d states sitting ∼1.4 eV above the conduction band minimum. Experimentally, the band edge electron effective mass of Ta doped SnO2 was shown to be 0.23m0, compared to 0.29m0 seen with conventional Sb doping, explaining its ability to yield higher mobilities and conductivities.

Magnetic aging in TiO2-doped Mn-Zn ferrites

The soft magnetic properties of the sintered Mn-Zn ferrites can be stabilized versus changing temperature by addition of CoO in suitable proportion. The material benefits in this case of anisotropy compensation brought about by the Co2+ cations. However, prolonged exposure of magnetic cores to high temperatures, as likely to occur in automotive applications, can be associated with local phenomena of induced anisotropy, resulting in magnetic viscosity and aging. We show in this paper that proper addition of TiO2 in optimally CoO-doped ferrites can restrain aging and the ensuing detrimental effects on loss and permeability. We find, in particular, that on passing from conventional doping with 1000 ppm to 5000 ppm of TiO2, the deterioration of the soft magnetic properties of the ferrite following an aging treatment of 100 h at 200 °C is in good part reduced below a few hundred kHz. It is concluded that this effect chiefly relates to a correspondingly reduced value of the magnetic anisotropy induced by directional ordering at 200 °C. This beneficial effect appears to descend from hindered diffusion of the Co2+ cations by the dissolved Ti4+ cations. The induced anisotropy, however, while leading to increased hysteresis and excess losses, brings about a decrease of the total energy loss at intermediate frequencies, by modifying the distribution of the resonance frequencies and the associated damping of the rotational processes. Little to negligible effects are observed beyond a few MHz.

Growth of heavily-doped Germanium single crystals for mid-Infrared applications

Abstract In the growth of germanium (Ge) single crystals by Czochralski (Cz) method, a novel gas-phase doping procedure has been suggested to obtain heavily doped, both n-type (phosphorous) and p-type (boron) semiconducting crystals. The crystals were grown using the so-called “mini-Cz” technique and the pulled crystals are characterized for their structural and electrical properties. A narrow full width at half maximum (FWHM) of the X-ray diffraction rocking curves obtained for both symmetric (4 0 0) reflection (14 arcsec) and asymmetric (3 1 1) reflection (11 arcsec) indicate good crystalline quality. In addition, the grown crystals have a low dislocation density (etch pit density of ≈104 cm−2) without hot-zone optimization. Doping concentrations of up to 3 × 1018 cm−3 have been obtained so far, which implies that gas-phase doping is a viable route and may solve some of the conventional doping issues when using solids as dopants in the Cz melt. We also report here high doping of antimony (Sb) using a solid dopant source. Non-flat solid-liquid interface of the Sb-doped crystals during the growth process, as characterized by the typical ring structure of the growth striations, has been seen in lateral photovoltage scanning (LPS) measurements.