Increase In Carrier Density Research Articles

Influence of indium content and carrier density on spontaneous emission spectra of wurtzite InGaN/GaN quantum wires with screening effects

Spontaneous emission spectra of wurtzite (WZ) InxGa1−xN/GaN quantum wires (QWRs) with screening effects are investigated as a function of an In content and a carrier density. The screening potentials rapidly increase with increasing carrier density. However, for a given carrier density, the magnitude of the screening potential is nearly irrespective of the In content. In the case of the InGaN/GaN quantum well (QW) structures, the peak intensity gradually decreases with increasing In content owing to the increase in an internal field by piezoelectric (PZ) and spontaneous (SP) polarizations. On the other hand, the peak intensity of the InGaN/GaN QWR structure is less sensitive to an internal field and rapidly increases owing to the increase in the carrier confinement with increasing In content. However, it is reduced due to the decrease in a quasi-Fermi level separation when the In content further increases.

Temperature dependent charge transport in electrostatically doped poly[benzimidazobenzophenanthroline] thin films

AbstractCharge transport in electrostatically doped poly[benzimidazobenzophenanthroline]‐BBL thin films in a field‐effect transistor geometry were investigated in the temperature range 150 K < T < 370 K. At low temperatures activation and hopping transport mechanisms dominated, while phonon scattering dominated at high temperatures. The activation energies (EA) were found to lie in the range 140 meV < EA < 400 meV implying the existence of deep traps within the polymer bandgap of 1.8 eV. Two quasi‐linear dependencies of EA on the gate voltage (Vg) were observed with EA decreasing as Vg increased. An unexpected “metallic‐like” transport characteristic appeared for T > 335 K which depended on Vg. Enhanced electron delocalization combined with increased carrier density could be responsible for this “metallic‐like” behavior. Our results show that the existence of deep traps with multiple energy distributions, combined with increased carrier density led to the unusual temperature dependence of charge transport observed in BBL.

Influence of Na/Mg Co-Doping in Tuning Microstructure, Transport, Optical, and Magnetic Properties of TiO2 Compounds for Spintronics Applications

In recent years, researchers have been making a persistent effort to discover innovative and appropriate oxide materials that can be exploited in optoelectronics devices. The primary objective of this research is to study the effect of Na/Mg co-doping on microstructure, transport (dielectric and Hall Effect), optical and magnetic properties of Ti0.94-yNa0.06MgyO2 (y = 0–0.08) compounds that were synthesized using a solid-state route method. All the compounds have been crystallized to a single rutile phase, as reported by the XRD study. The elemental color mapping reveals that there is a consistent distribution of all of the elements across the compound. The XPS study suggests that Ti mostly resided in the Ti4+ oxidation state. The enhancement of the Mg co-doping concentration led to a decrease in the dielectric value as well as the AC conductivity of the material. In addition to this, it has been noted that these compounds have a low dielectric loss. The analyses of Nyquist plots reveal that the increase of Mg co-doping concentration led to a rise in the amount of relaxation that is non-Debye sort. This, in turn, caused a reduction in the amount of resistance exhibited by grains and grain boundaries. The Maxwell–Wagner model was used to conduct an analysis of the dielectric data, and the results indicated that the hopping of charge carriers is most likely to be responsible for the transport of electrical charges. From the optical properties’ measurement and analyses, it was noticed that the band gap had been slightly changed, but the transmittance value had increased from 81% for Ti0.94Na0.06O2 to 84% with an increase in Mg co-doping concentration. The Hall Effect analysis unequivocally pointed to the presence of p-type conductivity as well as an increased carrier density concentration. The room temperature magnetization versus field measurement indicates the ferromagnetic nature of the samples. Thus, the co-doping of Mg with Na in TiO2 leads to a narrowing of the band gap of TiO2 while tweaking the optical and transport properties. The studied materials can be utilized for spintronics and optoelectronics applications.

Ultrasensitive self-driven photoelectrochemical aptasensor for lincomycin detection based on oxygen vacancy-tunable BiOBr nanosheet coupled with dual-function of N-doped Ti3C2 quantum dots

A high-performance self-driven photoelectrochemical (PEC) platform was designed based on 0D N-doped Ti3C2 quantum dots/oxygen vacancies (OVs) engineered 2D BiOBr nanosheets (N-doped Ti3C2 QDs/BiOBr) nanocomposites for sensitive detection of lincomycin (Lin). The synergistic interplay between 0D N-doped Ti3C2 QDs and 2D BiOBr can generate the fascinating interface of chemical/electronic coupling to further boost the PEC activity, including efficient charge transfer, extended the light absorption and increased carrier density. Experimental results demonstrated that the PEC response of the prepared OV-riched N-doped Ti3C2 QDs/BiOBr van der Waals (vdW) heterostructures were 9-folds stronger than that of OV-deficient BiOBr. On the basis of the such excellent PEC performance, an ultrasensitive self-driven PEC aptasensor was developed with the assistance of Lin aptamer. The proposed sensor exhibited a wide linear response (1.0 × 10−14 mol/L ∼ 1.0 × 10−8 mol/L), a low detection limit (3.57 × 10−15 mol/L, S/N = 3), excellent selectivity and good reproducibility, which provided a promising tool to detect Lin in real samples. This work not only offered a versatile protocol for a wide variety of PEC detection, but also paved the way for the development of more efficient PEC biosensor.

(Digital Presentation) Characterization of Light Emission Properties of Impurity Doped Ge/Si Core–Shell Quantum Dots

Si–based quantum dots (QDs) have attracted much attention as an active element in Si-based optoelectronic applications because their light emission properties due to carrier confinement have potential to combine photonic processing with electronic processing on a single chip. We have focused on CVD formation and characterization of Si-QDs with Ge core and reported their photoluminescence (PL) properties attributable to type II energy-band alignment between the Ge–core and the Si-shell [1-2]. In addition, we have also demonstrated stable electroluminescence in the near–infrared region from diode structures having a 3–fold stacked Si–QDs with Ge core with an areal dot density of ~2.0×1011 cm−2 under pulsed bias applications [3]. One of the possible ways to enhance the radiative recombination rate and the improve the light emission efficiency is to reduce non–radiative centers and to increase carrier density by impurity doping into the QDs. In this work, in extending our research work to valency-controlled Si–QDs with Ge core, we have studied the effects of boron– and phosphorus–doping to the Ge core on PL properties.A highly dense layer of Si–QDs with Ge core was formed by controlling thermal decomposition of GeH4 and SiH4 alternately on thermally–grown ~2.0 nm–thick SiO2. During the Ge deposition, delta doping of boron and phosphorus atoms in QDs was carried out by pulse injection using 1% B2H6 and 1% PH3 diluted with He, respectively. No changes in dot size and areal dot density with B or P doping were confirmed by AFM topographic images. Under photoexcitation of undoped QDs with a 979–nm line from a semiconductor laser, a broad PL spectrum, which consists of four Gaussian components originating from radiative recombination through quantized states in QDs, were observed in the energy range from 0.62 to 0.85 eV even at room temperature. For the doped QDs, in addition to the four components seen in undoped QDs, relatively-narrow components peaked at ~0.64 eV and ~0.68eV were observed with B-doping and with P-doping to the Ge core, respectively. Notice that, with an increase in B2H6 pulse injection from 1 to 4 times, the integrated PL intensity was enhanced by a factor of 1.4 to 2.4 compared to that of the undoped QDs while no significant change in spectral shape was observable. This can be interpreted in terms of an increase in the number of holes with B-doping to the Ge core since the carrier recombination rates is proportional to the product of the number of electrons and holes confined in each of QDs under weak photoexcitation.AcknowledgementsThe authors wish to thank Dr. Akio Ohta for his contribution to the measurements. This work was supported in part by Grant–in–Aid for Scientific Research (A) 19H00762, 21H04559, and Fund for the Promotion of Joint Intentional Research [Fostering Joint International Research (A)] 18KK0409 of MEXT Japan.

Metal-free N-GQDs/P-g-C3N4 photocatalyst with broad-spectrum response: Enhanced exciton dissociation and charge migration for promoting H2 evolution and tetracycline degradation

Graphitic carbon nitride (g-C3N4) is a promising candidate for solving energy and environmental problems. However, narrow photoresponse range, difficult exciton dissociation, and high charge recombination rate severely restrict its activity. Herein, a novel ultrathin porous N-GQDs/P-g-C3N4 (PG-CNS) nanocomposite was fabricated by combining P-element doping, N-doped graphene quantum dots (N-GQDs) coupling, and morphology regulation strategies. The optimal sample (PG-CNS-0.2) was found to extend the photoresponse range over 780 nm due to the combination of midgap state induced by P-doping and excellent upconversion performance of N-GQDs, achieving a fuller utilization of solar energy. Photoluminescence and electrochemical tests confirmed that both exciton dissociation and charge transfer within PG-CNS-0.2 were dramatically enhanced, as reflected by a 3.0-fold increase in carrier density. This enhancement was attributed to reduced exciton binding energy resulting from P-doping, superior electron conduction ability of N-GQDs, as well as larger specific surface area and shorter migration paths provided by the 2D porous structure. Besides, the trapping experimental result indicated that targeted regulation of reactive oxygen species was achieved by changing the addition amount of N-GQDs, thereby enhancing the controllability of photocatalytic reactions. Compared with g-C3N4 nanosheets (CNS), the H2 production rate and tetracycline degradation rate of PG-CNS-0.2 under visible light were improved by 15.7 and 6.9 times, respectively. Meanwhile, the molecular oxygen activation ability of PG-CNS-0.2 was also significantly increased, as reflected by the generation of O2– and H2O2 at concentrations 2.5 and 3.5 times higher than that of CNS, respectively. This work not only comprehensively reveals the exciton and carrier behaviors in g-C3N4-based reaction systems, but also provides a new strategy for designing low-cost, environmentally friendly, and efficient broad-spectrum responsive photocatalysts.

Signature of superconducting onset in presence of large magnetoresistance in type-II Dirac semimetal candidate Ir2In8S

Since the discovery of type-II Dirac semimetal (DSM) as the potential candidate for topological superconductor, magneto-transport studies on diverse type-II DSMs have been of tremendous research interest. Here we report the structural and magneto-transport properties of type-II DSM candidate Ir2In8S under high pressure. With increasing pressure, this shows dramatic suppression of its characteristic large magneto-resistance, which is however partially regained upon release of pressure. No superconductivity has emerged with increasing pressures up to ∼20 GPa. However, in the pressure-released sample a significant resistivity drop below ∼4 K has been detected. The field dependent resistivity and dc magnetization measurements confirm this as superconducting onset. Ir2In8S thus becomes a unique system exhibiting large MR above the superconducting transition. X-ray diffraction results show that the ambient tetragonal structure (P42/mnm) remains stable up to ∼7 GPa, above which this undergoes a reversible structural transition into an orthorhombic structure (Pnnm). The observed enhanced residual resistivity and concurrent increase in carrier density of the normal metal state of the pressure-cycled sample indicate that the enhanced impurity scattering plays a significant role in the emergence of superconductivity.

Density-Dependent Effects on Pulse Compression in GaN Photodetectors Probed by Monte Carlo Studies

With increases in the demand for faster electronic switching, requirements for higher operating voltages and currents, and the need to perform under harsh environments while operating at even higher frequencies, the research focus in photoconductive semiconductor switch (PCSS) technology has shifted to wide bandgap semiconductors. Here, we examine the possibility of pulse compression in carbon-doped PCSS devices based on the negative differential mobility concept for faster operation. Monte Carlo simulations are used to build in and model various effects on electron transport including degeneracy, charge polarization, and scattering within a three-valley model fitted to bandstructure calculations. The focus is on exploring the density dependence of pulse compression. Thresholds for the biasing fields naturally emerge. Predictive analysis of the output full-width half-maximum (FWHM) current waveforms, as well as the dynamics of the internal charge cloud behavior, and occupancy of the various valleys within GaN are all obtained. Our results show that an increase in carrier density can increase pulse compression and create pulse-widths that are smaller than the FWHM of the input optical excitation. This bodes well for enhanced repetition rates. Variations produced by moving the laser spot along the GaN PCSS length are also examined. Though data for GaN are not yet available, the trends compare well qualitatively with previous reports for GaAs.

Mottness induced superfluid phase fluctuation with increased density

Recent observation of diminishing superfluid phase stiffness upon increasing carrier density in cuprate high-temperature superconductors is unexpected from the quantum density-phase conjugation of superfluidity. Here, through analytic estimation and verified via variational Monte Carlo calculation of an emergent Bose liquid, we point out that Mottness of the underlying carriers can cause a stronger phase fluctuation of the superfluid with increasing carrier density. This effect turns the expected density-increased phase stiffness into a dome shape, in good agreement with the recent observation. Specifically, the effective mass divergence due to ‘jamming’ of the low-energy bosons reproduces the observed nonlinear relation between phase stiffness and transition temperature. Our results suggest a new paradigm, in which unconventional superconductivity in some strongly correlated materials is described by physics of bosonic superfluidity, as opposed to pairing-strength limited Cooper pairing.

Unveiling the Role of the Metal Oxide/Sn Perovskite Interface Leading to Low Efficiency of Sn-Perovskite Solar Cells but Providing High Thermoelectric Properties

Tin halide perovskites (THPs) have appealing optoelectronic properties similar to lead halide perovskites (LHPs). However, THPs coated on metal oxide electrodes in normal-structure perovskite solar cells exhibit poor diode rectification, resulting in poor efficiency. This poor photoelectric performance in n–i–p-based THP solar cells is in contrast with LHP solar cells. We report that this deficient performance of THP solar cells is triggered by the defect states of the metal oxide layer. The defect states of the metal oxide can trap the electrons from the THP, leading to the prompt formation of Sn(IV), which will increase the carrier density and lead to poor photoelectric performance. This observation was supported by the ultraviolet-photoelectron spectroscopic measurements of inorganic thin films Al2O3, SnO2, TiO2, ZnO, and ZrO2. However, this self-doping phenomenon resulting in the increase in carrier density can be applied to thermoelectric studies. Using CsSnI3/ZrO2 nanocomposites as thermoelectric active layers, we report a power factor of 186.58 μW/mK2 measured at room temperature, which is better than the 148.61 μW/mK2 of the original CsSnI3 thin film.

Construction of internal electric field in imprinted poly (ionic liquid)-TiO2 composite nanoreactor for improving hole directional enrichment and selective photodegradation

In this work, imprinted poly (ionic liquid)-TiO2 composite nanoreactor (I-PIL-TiO2) was synthesized by the microwave-assisted in-situ polymerization in non-toxic aqueous phase. The S-scheme heterojunction made of I-PIL wrapping TiO2 had a tight and large interface region. According to Mott–Schottky's experiment and theoretical calculation, the obtained composite nanoreactor had improved the rapid separation and migration of carriers and increased carrier density, which was closely related to the formation of internal electric field (IEF) driven channels in the interface. The results showed that the orientation of the IEF was from TiO2 to I-PIL, so that photogenerated holes (h+) were accelerated to migrate to I-PIL through the interface channel, which was conducive to h+ directly attacking LEV. The photocatalytic activity of I-PIL-TiO2 was 1.69 times higher than that of TiO2. More interestingly, the presence of IEF increased the enrichment ability of h+ in imprinted cavities, improved the selective degradation ability of the composite nanoreactor, and maintained stable performance in the swine wastewater. After five degradation reactions, the composite still maintained good stability. This work provided a feasible way to synthesize polymer-inorganic composite photocatalytic materials with good interfacial charge transfer by simple and green method.

Carrier-induced metal-insulator transition in trirutile MgTa2O6

Materials exhibiting metal-insulator transitions (MITs) are proposed platforms for next-generation low-power electronics. Many of these materials exhibit strong coupling between the electronic and lattice degrees of freedom, which makes them ideal systems to examine the interplay between lattice dynamics, electronic structure, and magnetic order. The rutile structure, featuring edge-connected octahedral chains along its $c$ axis, permits metal-metal interactions that can induce metal-insulator transitions. Although the MITs in rutile-structured compounds have been thoroughly studied, the derivative trirutile phase, which accommodates similar metal-metal interactions, has yet to be examined in the context of MITs. Here we use density functional theory calculations to investigate a carrier-driven MIT in trirutile ${\mathrm{MgTa}}_{2}{\mathrm{O}}_{6}$, a ${d}^{0}$ insulator with a suitable axial ratio. Our calculations suggest the existence of four distinct phases in ${\mathrm{MgTa}}_{2}{\mathrm{O}}_{6}$ with increasing electron concentration: nonmagnetic insulator, ferromagnetic (FM) metal, FM half-metal, and nonmagnetic insulator. We explain how the resulting electronic phases arise from changes in atomic structure with increasing carrier density. Our results indicate that trirutile oxides may be a promising materials class for which to access and functionalize MITs.

(Invited) Physical Understanding and Prevention of Bipolar Degradation in SiC Power Devices

Through recent progress in SiC technology, 1–3 kV-class SiC power devices (field effect transistors and Schottky barrier diodes) have been commercialized, demonstrating remarkable reduction of power dissipation in various electric systems. However, “bipolar degradation” caused by forward conduction of pn junctions has not been completely solved [1]. In this paper, physical understanding and prevention of the bipolar degradation in SiC devices are reviewed.Degradation in SiC bipolar devices is caused by expansion of a single Shockley-type stacking fault (SSF) in {0001} from a basal plane dislocation (dislocations lying on a {0001} plane) through minority carrier injection and subsequent recombination [2]. The authors conducted careful observation and theoretical analyses on the shapes of expanded SSFs in SiC upon minority carrier injection, and clarified 36 different types of SSFs [3]. For fabrication of high-reliability SiC devices, any basal plane dislocations must be eliminated from a lightly-doped voltage-blocking layer, where a high density of excess carriers is injected during device operation. The authors carried out a number of SiC epitaxial growth runs by using a custom-made chemical vapor deposition system and discovered that almost all the basal plane dislocations can be converted to threading edge dislocations in the initial stage of SiC epitaxial growth (dislocation conversion occurs near the epilayer/substrate interface). The typical density of basal plane dislocations in SiC epitaxial layers was 1–10 cm-2, but the density could be reduced to 0.1 cm-2 or less by increasing the growth rate from 5 to 24 µm/h on 4 degrees off-axis SiC(0001) substrates without any conflicts in the surface morphology and doping control (see the attached image). The achieved dislocation density (< 0.1 cm-2) is low enough to fabricate 1 cm2 devices (300–400 A devices) free from the degradation phenomenon. A basal plane dislocation and a threading edge dislocation can possess the same Burgers vector, which is the reason why the dislocation conversion can take place. It is also noted that a threading edge dislocation, which runs along <0001> (perpendicular to the {0001} plane), does not affect the performance and reliability of SiC devices, at least, within operation conditions in practical applications.It has been experimentally revealed that a SSF can either expand or contract, depending on the current density and temperature. Thus, it is essential to clarify the critical condition where SSF expansion starts. The authors developed a physics-based model to calculate the effective formation energy of a SSF in SiC, taking account of the electronic energy gain by forming a SSF under minority carrier injection [4]. Here a SSF exhibits a slightly smaller bandgap than the perfect SiC and a SSF behaves like a quasi-quantum well in SiC. It can be judged that SSF expansion takes place when the effective SSF formation energy is negative, by which the free energy is lowered by SSF expansion [5].The effective SSF formation energy was calculated as a function of the injected excess carrier density at different temperatures. When the carrier density is low, the SSF formation energy is close to the value in equilibrium (4.7 mJ/m2 [6]). As the carrier density increases, the SSF formation energy turns to be negative due to the electronic energy gain, and the critical excess carrier density above which SSF expansion occurs can be determined as about 5E14 cm-3 at 300 K from this calculation. This critical carrier density gradually increases with elevating the temperature, due to the enhanced emission of electrons from an SSF and thereby a lowered energy gain. The critical carrier density was experimentally determined through observation of SSFs in fabricated SiC pn diodes operating at different current densities and temperatures. The critical carrier density experimentally determined was 4E14 cm-3 at room temperature, being a very good agreement with the theoretical prediction mentioned above. Therefore, the developed model serves as a guideline for preventing bipolar degradation. Based on these results, nearly perfect prevention of bipolar degradation can be achieved by introducing a “recombination-enhancement layer” between a voltage-blocking layer and a substrate, the detail of which shall be explained at the conference.[1] T. Kimoto and H. Watanabe, Appl. Phys. Express, 13, 120101 (2020).[2] M. Skowronski and S. Ha, J. Appl. Phys., 99, 011101 (2006).[3] A. Iijima et al., Philos. Mag., 97, 2736 (2017).[4] A. Iijima and T. Kimoto, J. Appl. Phys., 126, 105703 (2019).[5] K. Maeda et al., Mater. Sci. Forum, 725, 35 (2012).[6] K. Maeda et al., Appl. Phys. Express, 14, 044001 (2021). Figure 1

Increase in Photocurrent Density of WO3 Photoanode by Placing a Layer of an Ordered Array of Mesoporous WO3 Micropillars on Top of a WO3 Sheet Layer.

A facile stamping method was developed to assemble ordered arrays of mesoporous WO3 micropillars with uniform sizes, shapes, and lengths on F-doped tin oxide glass. Using this method, a series of WO3 heterostructural bilayer photoanodes consisting of an array of m-μm long ordered mesoporous WO3 micropillars at the top and the n-μm thick mesoporous WO3 plain sheet layer at the bottom (denoted as m/n) were prepared. Among them 2.5/7.5 displayed a steady state photocurrent density of 3.6 mA cm-2 at 1.23 V (vs RHE) under AM 1.5 (1 Sun), which is much higher than that of the plain 10-μm thick WO3 sheet (2.5 mA cm-2). This phenomenon occurs owing to the following six benefits: increases in charge carrier density, number of photogenerated electron, charge collection rate, thermodynamic feasibility for the vectorial charge transport from the outermost layer of the photoanode to the inner layer, the surface hydrophilicity, and the decrease in charge transfer resistance.

Thickness-Dependent Nonlinear Electrical Conductivity of Few-Layer Muscovite Mica

We report on the direct current (dc) current-voltage ($I$-$V$) characteristics of few-layer muscovite mica (MuM) flakes exfoliated and transferred onto $\mathrm{Si}\mathrm{O}$${}_{2}$/$\mathrm{Si}$ substrate, under different substrate dc bias voltages. Contrary to usual observations in conventional two-dimensional systems, we observe an increase in the in-plane electrical conductivity with a reducing thickness of MuM flakes. At a given voltage, the electrical conductivity of approximately five-layered MuM flake (${T}_{3}$) is 3 orders of magnitude larger than that in approximately ten-layered MuM flake (${T}_{2}$). The $I$-$V$ characteristics are used to analyze the mechanism of conduction. The model-based analysis reveals the hopping-conduction mechanism to be dominant as compared to the Poole-Frenkel effect. The thickness-dependent work function is measured using Kelvin probe force microscopy for a MuM flake on $\mathrm{Si}$ substrate. Assuming that the measured work function is correlated with the Fermi level, we report an upward movement of the Fermi level, toward the conduction band with the reducing thickness of MuM flakes, indicating an increase in the conduction-band carrier density. The observed increase in conductivity in ${T}_{3}$ when compared to ${T}_{2}$ may be attributed to surface doping due to the increased contribution from ${\mathrm{K}}^{+}$ ions and lattice relaxation. Our results show that there is a possibility of using few-layer mica as a wide-band-gap semiconductor and that it can open up different avenues for two-dimensional electronic devices.

Size-controlled quantum dots reveal the impact of intraband transitions on high-order harmonic generation in solids

Since the discovery of high-order harmonic generation (HHG) in solids, much effort has been devoted to understanding its generation mechanism and both interband and intraband transitions are known to be essential. However, intraband transitions are affected by the electronic structure of a solid, and how they contribute to nonlinear carrier generation and HHG remains an open question. Here, we use mid-infrared laser pulses to study HHG in CdSe and CdS quantum dots (QDs), where quantum confinement can be used to control the intraband transitions. We find that both the HHG intensity per excited volume and the generated carrier density increase when the average QD size is increased from about 2 nm to 3 nm. We show that the reduction of the subband gap energy in larger QDs enhances intraband transitions, and this in turn increases the rate of photocarrier injection by coupling with interband transitions, resulting in enhanced HHG.

Spin Hall effect driven by the spin magnetic moment current in Dirac materials

The spin Hall effect of a Dirac Hamiltonian system is studied using semiclassical analyses and the Kubo formula. In this system, the spin Hall conductivity is dependent on the definition of spin current. All components of the spin Hall conductivity vanish when spin current is defined as the flow of spin angular momentum. In contrast, the off-diagonal components of the spin Hall conductivity are non-zero and scale with the carrier velocity (and the effective $g$-factor) when spin current consists of the flow of spin magnetic moment. We derive analytical formula of the conductivity, carrier mobility and the spin Hall conductivity to compare with experiments. In experiments, we use Bi as a model system that can be characterized by the Dirac Hamiltonian. Te and Sn are doped into Bi to vary the electron and hole concentration, respectively. We find the spin Hall conductivity ($\sigma_\mathrm{SH}$) takes a maximum near the Dirac point and decreases with increasing carrier density ($n$). The sign of $\sigma_\mathrm{SH}$ is the same regardless of the majority carrier type. The spin Hall mobility, proportional to $\sigma_\mathrm{SH}/n$, increases with increasing carrier mobility with a scaling coefficient of $\sim$1.4. These features can be accounted for quantitatively using the derived analytical formula. The results demonstrate that the giant spin magnetic moment, with an effective $g$-factor that approaches 100, is responsible for the spin Hall effect in Bi.

CuS nanosheet-induced local hot spots on g-C3N4 boost photocatalytic hydrogen evolution

An ideal model composite made of CuS nanosheet (photothermal material) and g-C3N4 was constructed through in-situ assembly procedure, along with integration of dual photochemical effect and photothermal effect. Consequently, optimized CN/CuS composite approaches remarkable photocatalytic performance improved by 44.5 times with regarding to that of pristine CN. This superiority can be assignable to inherent characteristic of CuS as photochemical component, with improved charge separation and enriched surface active-sites. Additionally, the critical contribution of photothermal effect in boosting water photosplitting was also experimentally validated. CuS nanosheet as hot spots enables rapid temperature increment around photocatalysts under visible/near-infrared (NIR) light irradiation. The heat converted from solar is conducive to increase carrier density, accelerate carrier mobility, alleviate onset potential and facilitate surface redox kinetics, so as to promote photocatalytic activity. It is believed that synergetic incorporation of photothermal and photochemical conversion could be expanded to other photocatalytic systems towards effective solar energy conversion.

Evaluation of SERS activity for cosputtered Ag-ZnX@PS (X = O, S, Se) composites: Carrier density dependence

Ag-ZnX (X = O, S, Se) composites coated on polystyrene (PS) arrays (Ag-ZnO@PS, Ag-ZnS@PS, Ag-ZnSe@PS) were successfully fabricated by using cosputtering technology. We found that ZnX doping decreased the carrier densities of these composites compared to that of pure Ag@PS, which was due to redistribution of electrons between Ag and ZnX. Thus, the carrier density of Ag was decreased, and the surface plasmon resonance (SPR) of Ag was redshifted in the Ag-ZnX composites. As the redshift of the SPR of Ag induced a high SPR contribution to the surface-enhanced Raman scattering (SERS), the SPR and charge transfer (CT) contributions were simultaneously increased with increasing carrier density in the Ag-ZnX composites. This study opens a new path to designing metal–semiconductor composites with controllable carrier density. Regulation of the carrier density will be of great help in understanding SPR and CT contributions.

Plasmon-induced super-semiconductor at room temperature in nanostructured bimetallic arrays

Solid-state electrical conducting materials can be roughly categorized as superconductors, conductors, and semiconductors, depending on their conducting carriers, resistance, and band structures. This research reports the discovery of super-semiconductors, whose resistivity is 3–10 orders of magnitude lower than conventional semiconductors at room temperature. In addition, there is a transition from a metal state to a super-semiconducting state at near room temperatures, which is accompanied by an increase in hole carrier density and the mobility increase in electrons. For the first time, a hole-dominated carrier metal is observed in nanostructured bimetallic arrays near room temperature, and no other special conditions are required. Such a behavior is due to the generation of hot electrons and holes induced by metal plasmon resonance in the infrared range in the nanostructured bimetallic arrays. Our research empowers metals with semiconductor features and paves the way to realize ultra-low-power metal-based semiconductor devices.