Electron Carrier Concentration Research Articles

First‐Principles Study of Structural and Elastic, Electronic, and Thermoelectric Properties of PdSe2

The thermoelectric material in orthorhombic (Pbca) phase is studied with the help of density functional theory implemented in WIEN2k. The main properties of investigated are elastic, electronic, and thermoelectric properties. The anisotropy factors obtained with the elastic constants indicate that is strongly anisotropic. The Tran and Blaha‐modified Becke–Johnson exchange potential is used for bandgap calculations. The BoltzTraP code is used to find out the thermoelectric properties of . At 300 K, the maximum value of the Seebeck coefficient is 200 μV K−1 for the hole carrier concentration of 2.5 × 1019 cm−3 and is 241 μV K−1 for the electron carrier concentration of 1.2 × 1019 cm−3. The power factor (PF) and figure of merit (ZT) are calculated for different carrier concentrations and temperatures. The optimum value of ZT for bulk PdSe2 as calculated in this work is ≈0.6 for hole carrier concentration (p = 2.6 × 1020 cm−3) at 800 K, which suggests as a potential material in thermoelectric applications at higher temperatures.

Biaxial strain effects on electronic, transport, and thermoelectric properties of SnX[formula omitted] (X = Se, Te) and Janus SnSeTe 1T-monolayers

Biaxial strain in two-dimensional materials plays a crucial role in degenerating the valence and conduction bands, leading to energy dispersion in the band structure and causing changes in transport properties, such as carrier mobility, Seebeck coefficient, and electrical conductivity. Herein, we investigated the effects of biaxial strain on SnX2 (X = Se, Te) and the Janus SnSeTe 1T-monolayer using density functional theory, deformation potential, and semiclassical Boltzmann transport theory. Our findings reveal that the studied 1T-monolayers exhibit high and directionally isotropic electron mobility. Biaxial tensile strain has the effect of increasing the bandgap, predominantly reducing the effective mass of electrons while increasing that of holes. This results in an enhanced electron mobility along with a simultaneous reduction or increase in the concentration of electron carriers or holes, respectively. Especifically, in the case of the Janus SnSeTe 1T-monolayer, we observed a remarkable 68% increase in electron mobility, reaching a value of 1588 cm2V−1s−1. This increase contributes to higher thermoelectric performance due to elevated electrical conductivity and a simultaneous rise in the Seebeck coefficient when subjected to biaxial strain. Our study underscores that strain engineering is an effective strategy for achieving improved thermoelectric properties, particularly exemplified by the SnSeTe 1T-monolayer, which achieved a maximum value of 2.25 for n-type due the ultralow thermal conductivity of 0.359 Wm−1K−1 as result of strong phonon anharmonicity on acoustical and optical modes.

Realizing high conversion efficiency in all-ZrCoSb-based half-Heusler thermoelectric power generators

ZrCoSb-based thermoelectric materials exhibit promising potential for power generation applications due to their high performance in both p- and n-type constituents. In this work, a newly developed all-ZrCoSb-based module achieves a maximum conversion efficiency of ∼9.3 % at a temperature difference of 668 K. This high conversion efficiency is enabled by the enhanced average thermoelectric properties for both types of ZrCoSb-based materials via Bi alloying and Sn/Ni doping. The hole and electron carrier concentrations were tuned to match the theoretically predicted optimized values, contributing to high weight mobility and power factor. Additionally, the increased mass and strain field fluctuations enhance point defect scattering, leading to a significant reduction in the lattice thermal conductivity of ZrCoSb. Consequently, peak zT values of ∼1.2 and ∼1.0 at 973 K were respectively obtained in p-type ZrCo(Sb0.5Bi0.5)0.85Sn0.15 and n-type ZrCo0.85Ni0.15Sb0.5Bi0.5, resulting in high average zT values of ∼0.75 and ∼0.51 in the temperature of 300 to 973 K. This work underscores the significant potential of all-ZrCoSb-based half-Heuslers in waste heat recovery.

Influence of RF power in the sputter deposition of amorphous InGaZnO film on the transient drain current of amorphous InGaZnO thin-film transistors

The device electrical and transient current characteristics of the amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) are comprehensively investigated according to the radio-frequency (RF) power during the sputter-deposition of IGZO active film. The RF power dependencies of the oxygen vacancy (VO) concentration in IGZO and the surface morphology of IGZO film are analyzed through X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). According to the RF power change in the range of 100 ∼ 250 W, the optimal point in terms of threshold voltage (VT), ON current (Ion), field-effect mobility in the linear region (μFE_lin), hysteresis voltage (VHys), and the VT shift under current stress (ΔVT) is found to be 200 W. The existence of the optimal power condition originates from the RF-power dependencies of the electron carrier concentration, the density of electron traps in gate insulator (GI), and the interface trap density related to surface roughness.Furthermore, compared to the direct current (DC) current stress (CS) condition, it is found that when VGS rises rapidly, a total transient current ΔID can be decomposed into three components, i.e., ΔIOS, ΔIBOOST, ΔIDEG. While ΔIOS is attributed to the non-quasi static Fermi-level rising, ΔIBOOST and ΔIDEG result from the donor creation in IGZO and the electron trapping into GI and interface. Noticeably, the occurrence level of each component changes sensitively according to RF power.Our result suggests that the 200 W device has the least overshoot of transient current and shows the best reliability in terms of deterioration due to transient current characteristics.

All-SnTe-Based Thermoelectric Power Generation Enabled by Stepwise Optimization of n-Type SnTe.

The practical application of thermoelectric devices requires both high-performance n-type and p-type materials of the same system to avoid possible mismatches and improve device reliability. Currently, environmentally friendly SnTe thermoelectrics have witnessed extensive efforts to develop promising p-type transport, making it rather urgent to investigate the n-type counterparts with comparable performance. Herein, we develop a stepwise optimization strategy for improving the transport properties of n-type SnTe. First, we improve the n-type dopability of SnTe by PbSe alloying to narrow the band gap and obtain n-type transport in SnTe with halogen doping over the whole temperature range. Then, we introduce additional Pb atoms to compensate for the cationic vacancies in the SnTe-PbSe matrix, further enhancing the electron carrier concentration and electrical performance. Resultantly, the high-ranged thermoelectric performance of n-type SnTe is substantially optimized, achieving a peak ZT of ∼0.75 at 573 K with a high average ZT (ZTave) exceeding 0.5 from 300 to 823 K in the (SnTe0.98I0.02)0.6(Pb1.06Se)0.4 sample. Moreover, based on the performance optimization on n-type SnTe, for the first time, we fabricate an all-SnTe-based seven-pair thermoelectric device. This device can produce a maximum output power of ∼0.2 W and a conversion efficiency of ∼2.7% under a temperature difference of 350 K, demonstrating an important breakthrough for all-SnTe-based thermoelectric devices. Our research further illustrates the effectiveness and application potential of the environmentally friendly SnTe thermoelectrics for mid-temperature power generation.

High thermoelectric properties in polycrystalline SnSe materials realized by rare earth halide Co-doping

SnSe materials have garnered significant interest due to the intrinsic low thermal conductivity. However, its limited electrical conductivity hinders their practical implementation. This study achieved a high ZT value of 1.40 at 773 K in the samples of n-type polycrystalline SnSe0.95 + x wt% SmCl3 + y wt% ErCl3 (x = 0, 0.75, 1.0, 1.25, and 1.5; y = 0, 0.0675, 0.125, and 0.25) since (SmCl3, ErCl3) co-doping decoupled the electrical-thermal transport properties. First, the released electron carrier concentration due to SmCl3 doping enhanced the electrical transport properties. The SnSe0.95 + 1.25 wt% SmCl3 sample exhibited a high power factor of 563 μWm−1K−2 at 773 K. Then, the lattice thermal conductivity markedly decreased with further ErCl3 doping due to the high-density dislocations and coherent boundary, resulting in effective the phonon scattering. Additionally, the special microtopography was conducive to the decreased lattice thermal conductivity. Therefore, the SnSe0.95 + 1.25 wt% SmCl3 + 0.125 wt% ErCl3 sample achieved a low lattice thermal conductivity value of 0.28 Wm−1K−1 at 773 K. Simultaneously, the (SmCl3, ErCl3) co-doped samples maintained the electrical transport properties than the SmCl3-doped samples. Consequently, the SnSe0.95 + 1.25 wt% SmCl3 + 0.125 wt% ErCl3 sample obtained a peak ZT value of 1.40 at 773 K and a competitive average ZT value of 0.37 from 323 to 773 K, and a theoretically calculated conversion efficiency reached 7.2%, which can be applied in the deep space for power generation. This strategy can be utilized to optimize the thermoelectric performance of other thermoelectrical material systems.

Zinc-Doped BiOBr Hollow Microspheres for Enhanced Visible Light Photocatalytic Degradation of Antibiotic Residues.

Photocatalysis represents an effective technology for environmental remediation. Herein, a series of Zn-doped BiOBr hollow microspheres are synthesized via one-pot solvothermal treatment of bismuth nitrate and dodecyl ammonium bromide in ethylene glycol along with a calculated amount of zinc acetate. Whereas the materials morphology and crystal structure remain virtually unchanged upon Zn-doping, the photocatalytic performance toward the degradation of ciprofloxacin is significantly improved under visible light irradiation. This is due to the formation of a unique band structure that facilitates the separation of photogenerated electron-hole pairs, reduced electron-transfer resistance, and enhanced electron mobility and carrier concentration. The best sample consists of a Zn doping amount of 1%, which leads to a 99.2% degradation rate of ciprofloxacin under visible photoirradiation for 30 min. The resulting photocatalysts also exhibit good stability and reusability, and the degradation intermediates exhibit reduced cytotoxicity compared to ciprofloxacin. These results highlight the unique potential of BiOBr-based photocatalysts for environmental remediation.

Evolution of the Electronic Properties of SrFe1 − x − y − zAlxMnyCozO3 Solid Solutions Depending on the Composition and the Degree of Localization of Electronic States

The genesis of the electronic spectrum in SrFe1 −xAlxO3, SrFe1 −xMnxO3, SrFe1 −xCoxO3, SrFe1 − 2xAlxCoxO3, and SrFe1−y−zMnyCozO3cubic solid solutions of strontium ferrite, where0⩽x⩽0.15and0⩽y,z⩽0.125, is studied in the coherent potential approximation. The inclusion of electron correlations on 3datoms makes it possible to reproduce the experimental content tendencies in the variation of the electronic and magnetic properties. It is shown that codoping of ferrite with cobalt and aluminum effectively increases the concentration of electron carriers and their degree of localization in SrFe1 −x− 0.15AlxCo0.15O3, which is of interest in the development of oxide thermoelectrics. Due to a relatively large contribution from delocalized states at the Fermi level, SrFe1 −y−zMnyCozO3solid solutions withy=z=0.1−0.12are promising electrode materials.

In Situ Defect Engineering of Controllable Carrier Types in WSe2 for Homomaterial Inverters and Self-Powered Photodetectors.

WSe2 has a high mobility of electrons and holes, which is an ideal choice as active channels of electronics in extensive fields. However, carrier-type tunability of WSe2 still has enormous challenges, which are essential to overcome for practical applications. In this work, the direct growth of n-doped few-layer WSe2 is realized via in situ defect engineering. The n-doping of WSe2 is attributed to Se vacancies induced by the H2 flow purged in the cooling process. The electrical measurements based on field effect transistors demonstrate that the carrier type of WSe2 synthesized is successfully transferred from the conventional p-type to the rarely reported n-type. The electron carrier concentration is efficiently modulated by the concentration of H2 during the cooling process. Furthermore, homomaterial inverters and self-powered photodetectors are fabricated based on the doping-type-tunable WSe2. This work reveals a significant way to realize the controllable carrier type of two-dimensional (2D) materials, exhibiting great potential in future 2D electronics engineering.

Quantum effects on dispersion, threshold and gain characteristics of Brillouin scattered Stokes mode in ion-implanted semiconductor plasmas

Quantum effects (QEs) on the dispersion, threshold, and gain characteristics of the Brillouin scattered Stokes mode (BSSM) in ion-implanted semiconductor plasmas are analytically investigated using coupled mode theory. Taking into account that the origin of stimulated Brillouin scattering lies in nonlinear induced polarisation of the medium, expressions are derived for complex effective Brillouin susceptibility (due to electrons and implanted colloids) and consequently the threshold pump amplitude and the gain constant of BSSM. Inclusion of QEs is done via quantum correction term in the hydrodynamic model of semiconductor plasmas. QEs modify the dispersion, threshold and gain characteristics of BSSM in ion implanted semiconductor plasmas. In contrast to the threshold and gain characteristics of BSSM, which are impacted only by electrons and are unaffected by implanted charged colloids, the Brillouin susceptibility caused by implanted colloids has a significant impact on the dispersion characteristics of BSSM. Finally, an extensive numerical study of the n- InSb/CO2 laser system is performed for two different cases: (i) without QEs and (ii) with QEs. In both cases, the analysis offers two achievable resonances, at which the changes of sign as well as an enhancement of real part of effective Brillouin susceptibility and an enhancement of effective Brillouin gain constant are obtained. When QEs are included in the analysis, the entire spectrum shifts towards decreased levels of electron and colloidal carrier concentration.

Solvothermally silver doping boosting the thermoelectric performance of polycrystalline Bi2Te3

Bismuth telluride (Bi2Te3) is one of the most promising thermoelectric materials for commercial application at room temperature, but the thermoelectric performance of these materials still needs to be improved. In this study, we report a type of solvothermally Ag-doped Bi2Te3 microplate. By sintering these microplates into polycrystalline bulk materials, a high room-temperature figure of merit of 1 has been achieved. Based on comprehensive micro/nanostructural characterizations, we found that the solvothermally doped Ag in Bi2Te3 plays two main roles, namely as the dopants that effectively induce the point defects of AgBi and forming Ag2Te nanophases. AgBi can provide additional hole charge carriers, effectively adjusting the initially high electron carrier concentration in the system, while the Ag2Te nanophases effectively trigger energy filtering effect to maintain a high Seebeck coefficient, thereby contributing to a competitively high power factor of 25.5 μW cm−1 K−2 at 298 K. Simultaneously, a low thermal conductivity of 0.74 W m−1 K−1 is obtained due to the strong phonon scattering at various lattice imperfections, induced by the solvothermally Ag-doping, which include point defects, grain/phase boundaries, local lattice distortions, and dislocations. This work fills the gap in knowledge on the solvothermally Ag-doping mechanism in Bi2Te3 and provides guidance for the innovative design of high-performing inorganic thermoelectrics.

Band-structure based electrostatics model for ultra-thin-body double-gate silicon-on-insulator MOS devices

The effect of quantum confinement has become significant in terms of its impact on the scalability and electrostatics of ultra-thin-body double-gate MOSFETs. In this paper, we present a simplified model to account for the effect of quantum confinement, considering the contribution of the ground-state and the first excited state of the conduction band, on the electron carrier concentration, which when incorporated into the 1-D Poisson’s equation, enables the determination of the electrostatic potential. We establish the accuracy of the proposed model, over a wide range of process and electrical parameters, through aggressively benchmarking the electrostatics parameters obtained from the proposed model with results from the sp 3 d 5 tight-binding method (TBM), over a wide range of device temperatures. Furthermore, a simplified model for the integrated channel charge density is shown in the form of a diffusion layer charge where the thickness and potential of this layer, while being gate voltage dependent, enables the channel charge density obtained from the model to agree well with results from TBM. Through this physics based and accurate model for the integrated charge, a simplified understanding of the gate capacitance is shown as a series combination of the diffusion layer capacitance, strong-inversion capacitance and oxide capacitance, which includes the effects of structural confinement as well as charge confinement at low and high gate voltages, respectively.

An experimental and theoretical study on photoluminescence of Ce3+-doped ZnS quantum dots and their application in Aspergillus oryzae

ZnS and ZnS:3.125%Ce3+ (ZSC) quantum dots (QDs) were synthesized by a low-temperature solid-phase method. The crystal structure, photoluminescence (PL) properties of ZSC QDs, and their effects on the growth and kojic acid production of Aspergillus oryzae (A. oryzae) were investigated. It is found that both QDs have a cubic blend structure with the average particle size ranging of 2.75–6.14 nm. Ce3+ doping not only increases the band gap of ZnS QDs from 3.43 to 3.48 eV, but also increases the PL intensity by about 2.23 times, which is due to the fact that the electron carrier concentration is improved, and then the rate of radiative recombination is increased. The integral emission intensity, biomass, extracellular proteins yield, and kojic acid production of A. oryzae cultured with ZSC (ZnS) QDs are about 4.31 (3.23), 1.61 (1.20), 1.12 (1.09), and 2.99 (1.68) times higher than that of medium without QDs, respectively.

Ultra-low lattice thermal conductivity and high figure-of -merit in Cl and K co-dopped Bi2Se3 prepared by KCl flux

Bismuth telluride (Bi2Te3) is a widely used thermoelectric (TE) material in practical applications. However, it contains expensive and toxic tellurium, a promising TE material should include low-cost and non-toxic element. Bismuth selenide (Bi2Se3) is similar to Bi2Te3 in electronic and crystal structure. The electron effective mass of Bi2Se3 is smaller than that of Bi2Te3, while its electrical transport performance is inferior to that of Bi2Te3. Therefore, in this study, Cl and K co-doped Bi2Se3 thermoelectric material with high density, low thermal conductivity, and excellent thermoelectric performance was prepared using KCl as the solvent. It is found that the effective electron mass and carrier concentration of the doped sample is effectively improved, which significantly increases the doped sample's electrical transport properties and ZT value. Finally, the Bi2Se3(KCl)3.5 sample reached a maximum ZT value of 0.79 at 550 K, and the average ZT in the measured temperature range reached 0.45.

Intrinsic point defects and the n -type dopability of Bi2MoO6 with higher photocatalytic performance: A hybrid functional study

Intrinsic point defects play a vital role in regulating the electronic structure and electron carrier concentration (${n}_{0}$) of ${\mathrm{Bi}}_{2}\mathrm{Mo}{\mathrm{O}}_{6}$, which has been demonstrated as a promising photocatalyst. Unfortunately, the source of $n$-type conductivity for its intrinsic defects has proved challenging. Using first-principles hybrid density functional calculations, we investigate the formation energies and electronic structure of intrinsic point defects in ${\mathrm{Bi}}_{2}\mathrm{Mo}{\mathrm{O}}_{6}$. The self-consistent Fermi energies and equilibrium carrier and defect concentrations are calculated using the sc-fermi code based on thermodynamic simulation. It is found that the easy formation of the +2 charged O vacancy (${V}_{\mathrm{O}}^{2+}$) is responsible for its intrinsic $n$-type conductivity under Bi-rich/O-poor conditions, and thus, it can have a very high density (reaching up to ${10}^{19} \mathrm{c}{\mathrm{m}}^{\ensuremath{-}3}$), making it the dominant defect in ${\mathrm{Bi}}_{2}\mathrm{Mo}{\mathrm{O}}_{6}$. Under O-rich conditions, only adopting both ${\mathrm{D}}^{+}$ doping and quenching methods in ${\mathrm{Bi}}_{2}\mathrm{Mo}{\mathrm{O}}_{6}$ can reach a higher carrier density $(>{10}^{17}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}3})$. Moreover, under the broad range of chemical potentials of $\ensuremath{-}2.50\phantom{\rule{0.16em}{0ex}}\mathrm{eV}<\mathrm{\ensuremath{\Delta}}{\ensuremath{\mu}}_{\mathrm{Bi}}<0, \ensuremath{-}6.32\phantom{\rule{0.16em}{0ex}}\mathrm{eV}<\mathrm{\ensuremath{\Delta}}{\ensuremath{\mu}}_{\mathrm{Mo}}<\ensuremath{-}1.48\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, and $\ensuremath{-}2.19\phantom{\rule{0.16em}{0ex}}\mathrm{eV}<\mathrm{\ensuremath{\Delta}}{\ensuremath{\mu}}_{\mathrm{O}}<\ensuremath{-}0.65\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, after quenching from 700 to 300 K, ${\mathrm{Bi}}_{2}\mathrm{Mo}{\mathrm{O}}_{6}$ can be effectively donor doped without significant compensation, and ${n}_{0}$ increases as $\mathrm{\ensuremath{\Delta}}{\ensuremath{\mu}}_{\mathrm{O}}$ decreases or temperature increases. Our results can give a guide in selecting optimum growth and quenching conditions to achieve high $n$-type doping and suppress compensation.

Terahertz time-domain spectroscopic ellipsometry of metallic strontium titanate

The coexistence of the polar instability and metallic conduction has attracted much attention. Ferroelectric soft optic modes and carrier electrons were investigated in A- and B-site heterovalent doped strontium titanate SrTiO3 crystals by the terahertz time-domain spectroscopic ellipsometry. The observed real and imaginary parts of a complex dielectric constant were fitted by the damped harmonic oscillator model for the ferroelectric soft optic mode and the Drude-Smith model for carrier electrons. The observed soft mode frequency increases as the La and Nb content increases. It is found that the square of the ferroelectric soft mode frequency linearly changes to the carrier electron concentration. This fact indicates that the carrier electrons suppress the ferroelectric instability and the ferroelectric soft mode frequency increases as the carrier concentration increases.

Intrinsic properties and dopability effects on the thermoelectric performance of binary Sn chalcogenides from first principles

High-performance thermoelectric (TE) materials rely on semiconductors with suitable intrinsic properties for which carrier concentrations can be controlled and optimized. To demonstrate the insights that can be gained in computational analysis when both intrinsic properties and dopability are considered in tandem, we combine the prediction of TE quality factor (intrinsic properties) with first-principles simulations of native defects and carrier concentrations for the binary Sn chalcogenides SnS, SnSe, and SnTe. The computational predictions are compared to a comprehensive data set of previously reported TE figures-of-merit for each material, for both p-type and n-type carriers. The combined analysis reveals that dopability limits constrain the TE performance of each Sn chalcogenide in a distinct way. In SnS, TE performance for both p-type and n-type carriers is hindered by low carrier concentrations, and improved performance is possible only if higher carrier concentrations can be achieved by suitable extrinsic dopants. For SnSe, the p-type performance of the Cmcm phase appears to have reached its theoretical potential, while improvements in n-type performance may be possible through tuning of electron carrier concentrations in the Pnma phase. Meanwhile, assessment of the defect chemistry of SnTe reveals that p-type TE performance is limited by, and n-type performance is not possible due to, the material’s degenerate p-type nature. This analysis highlights the benefits of accounting for both intrinsic and extrinsic properties in a computation-guided search, an approach that can be applied across diverse sets of semiconductor materials for TE applications.

Hypersonic Shockwave Robustness in Infrared Plasmonic Doped Metal Oxide Nanocrystal Cubes: Implications for High-Speed Ballistics Transport Applications

We report that, in doped metal oxide nanocrystal cubes, the infrared plasmonic absorption optical property is robust under exposure to repeated hypersonic shockwaves at Mach 6.2. Fluorine–tin co-doped indium oxide (F,Sn:In2O3) shock-exposed nanocrystals demonstrate morphological and optical property robustness, including infrared localized surface plasmonic resonance absorption at 4164 cm–1 (2401 nm) and cubic shape retention at 14 nm in size. Surface oxidation from reduced indium to oxidated (In2O3) and hydroxylated (In-OH) indium states is observed. Yet, free electron carrier concentration at 8.18 × 1020 cm–3, estimated to be 2245 electrons per nanocrystal, is retained in the nanocrystal core at 15 shock cycles. This demonstrates preservation of the plasmonic absorption property under an extreme hypersonic shock environment. We expect that doped infrared plasmonic metal oxides can serve as a keystone for nanomaterial scientists in potential applications for high performance infrared optical filters and sensor devices in surface exposed hypersonic aerospace vehicles.

Electronic properties of van der Waals heterostructures based on F-GaN-H stacking and TMDs single layer

The self-doping effects in atomic layer semiconductor materials have shown great potential for the 2D electronics and optoelectronics devices. In this paper, using the density functional theory (DFT), nonvolatile self-doped p-n junctions are formed in GaN based heterostructures which based on the stacking of the hydro-fluorination buckled GaN monolayer (ML) and bilayer (BL) and transition metal dichalcogenides (TMDs) single layer. The electronic properties demonstrated that the space distribution of carrier, and the band structures of the heterostructures depend on the polarization of GaN. The anisotropic hole and electron carrier concentration (ch and ce) are obtained in the WS2 (MoS2)/ML, BL/WSe2, and WS2 (MoS2)/BL heterostructure systems respectively. Moreover, the nonvolatile self-doped p-n junctions are achieved in type-III TMDs/ML (BL) and (BL) ML/TMDs heterostructures with the ultrahigh hole and electron carrier concentration. The type of band structures and carrier of the TMDs/ML (BL) and (BL) ML/TMDs heterostructure systems have been modulated by the self-doped induced by the polarization of GaN, which provides a new doping strategy for 2D GaN based (or polar) materials and simplifies the device fabrication in electronic and optoelectronic field.

Y2Te3: A New n-Type Thermoelectric Material.

Rare-earth chalcogenides Re3-xCh4 (Re = La, Pr, Nd, Ch = S, Se, and Te) have been extensively studied as high-temperature thermoelectric (TE) materials owing to their low lattice thermal conductivity (κL) and tunable electron carrier concentration via cation vacancies. In this work, we introduce Y2Te3, a rare-earth chalcogenide with a rocksalt-like vacancy-ordered structure, as a promising n-type TE material. We computationally evaluate the transport properties, optimized TE performance, and doping characteristics of Y2Te3. Combined with a low κL, multiple low-lying conduction band valleys yield a high n-type TE quality factor. We find that a maximum figure of merit zT > 1 can be achieved when Y2Te3 is optimally doped to an electron concentration of 1-2 × 1020 cm-3. We use defect calculations to show that Y2Te3 is n-type dopable under Y-rich growth conditions, which suppress the formation of acceptor-like cation vacancies. Furthermore, we propose that optimal n-type doping can be achieved with halogens (Cl, Br, and I), with I being the most effective dopant. Our computational results as well as experimental results reported elsewhere motivate further optimization of Y2Te3 as an n-type TE material.