Ti掺杂LiZnAs的电子结构和磁学性能

通过采用第一性原理计算,研究Ti不同掺杂位置对LiZnAs电子结构和磁学性能的影响.在Ti原子附近,随机位置添加Li间隙原子,进而为掺杂体系引入电子载流子,研究电子载流子对掺杂体系磁稳定性的影响.结果表明:Li(ZnTi)As体系的磁性起源于p-d杂化作用,p-d杂化导致Ti-3d电子自旋极化.掺杂组态的磁矩主要由Ti原子提供,其中最近邻掺杂组态Ti提供的原子磁矩最大为1.90μ_(B).Li(ZnTi)As体系的基态为铁磁稳定,Ti离子间通过双交换作用发生铁磁耦合.Li间隙原子属于n型掺杂,为掺杂体系提供电子载流子.巡游的载流子有助于磁性离子之间的电子交换,体系的铁磁稳定性增强.

A New Lifetime Prediction Model for pMOSFETs Under V_g=V_d/2 Mode with 2.5nm Oxide

Gate current for pMOSFETs is composed of direct tunneling current,channel hot hole,electron injection current,and highly energetic hot holes by secondary impact ionization.The device degradation under V g=V d/2 is mainly caused by the injection of hot electrons by primary impact ionization and hot holes by secondary impact ionization,and the device lifetime is assumed to be inversely proportional to the hot holes,which is able to surmount Si-SiO 2 barrier and be injected into the gate oxide.A new lifetime prediction model is proposed on the basis and validated to agree well with the experiment.

Numerical Study of Optimization of Layer Thickness in Bilayer Organic Light-Emitting Diodes

A numerical model for bilayer organic light-emitting diodes (OLEDs) is developed under the basis of trapped charge limited conduction.The dependences of the current density on the layer thickness,trap properties and carrier mobility of the hole transport layer (HTL) and emission layer (EML) in bilayer OLEDs of the structure anode/HTL/EML/cathode are numerically investigated.It is found that,for given values of the total thickness of organic layers,reduced depth of trap,total density of trap,and carrier mobility of HTL as well as EML,there exists an optimal thickness ratio of HTL to EML,by which a maximal quantum efficiency can be achieved.Through optimization of the thickness ratio,an enhancement of current density and quantum efficiency of as much as two orders of magnitude can be obtained.The dependences of the optimal thickness ratio to the characteristic trap energy,total density of trap and carrier mobility are numerically analyzed.

First-principles Study on the Electronic Structure of Novel Titanium Yttrium Mixed-metal Nitride Clusterfullerene

We present a first-principles study on the geometric, vibrational and electronic properties of a novel Y-based non-scandium mixed-metal nitride clusterfullerene （TiY2N@C80）. Theoretical results indicate that the fundamental electronic properties of TiY2N@C80 are similar to that of TiSc2N@C80, but dramatically different from that of ScaN@C800 and YaN@C80 molecules. We find that the magnetism of TiY2N@C80 is quenched by carrier doping. The rotation energy barrier of the TiY2N cluster in C80 cage was obviously increased by exohedral chemical modification with pyrrolidine monoadduct.

Two—Electron Energy Spectrum in a Parabolic Quantum Dot Under a Magnetic Field

Two interacting electrons in a harmonic oscillator potential under the influence of a perpendicular homo-geneous magnetic field are considered. The energies of two-electron quantum dots with the electron-LO-phonon couplingas a function of magnetic field are calculated. Calculations are made by using the method of few-body physics withinthe effective-mass approximation. Our results show that the electron-LO-phonon coupling effect is very important insemiconductor quantum dots.

Femtosecond Time-Resolved Spectroscopic Photoemission Electron Microscopy for Probing Ultrafast Carrier Dynamics in Heterojunctions

The fast developing semiconductor industry is pushing to shrink and speed up transistors. This trend requires us to understand carrier dynamics in semiconductor heterojunctions with both high spatial and temporal resolutions. Recently, we have successfully set up a timeresolved photoemission electron microscopy (TR-PEEM), which integrates the spectroscopic technique to measure electron densities at specific energy levels in space. This instrument provides us an unprecedented access to the evolution of electrons in terms of spatial location, time resolution, and energy, representing a new type of 4D spectro-microscopy. Here in this work, we present measurements of semiconductor performance with a time resolution of 184 fs, electron kinetic energy resolution of 150 meV, and spatial resolution of about 150 nm or better. We obtained time-resolved micro-area photoelectron spectra and energy-resolved TR-PEEM images on the Pb island on Si(111). These experimental results suggest that this instrument has the potential to be a powerful tool for investigating the carrier dynamics in various heterojunctions, which will deepen our understanding of semiconductor properties in the submicron/nanometer spatial scales and ultrafast time scales.

Effect of Screw-Dislocation on Electrical Properties of Spiral-Type Bi2Se3 Nanoplates

We systematically investigated the electrical nanoplates through field effect transistor and properties of spiral-type and smooth Bi2Se3 conductive atomic force microscopy （CAFM） measurement. It is observed that both nanoplates possess high conductivity and show metallic-like behavior. Compared to the smooth nanoplate, the spiral-type one exhibits the higher carrier concentration and lower mobility. CAFM characterization reveals that the conductance at the screw-dislocation edge is even higher than that on the terrace, implying that the dislocation can supply excess carriers to compensate the low mobility and achieve high conductivity. The unique structure and electrical properties make the spiral-type Bi2 Se3 nanoplates a good candidate for catalysts and gas sensors.

A low-temperature TiO2/SnO2 electron transport layer for high-performance planar perovskite solar cells

Conventional titanium oxide(TiO2) as an electron transport layer(ETL) in hybrid organic-inorganic perovskite solar cells(PSCs) requires a sintering process at a high temperature to crystalize, which is not suitable for flexible PSCs and tandem solar cells with their low-temperatureprocessed bottom cell. Here, we introduce a low-temperature solution method to deposit a TiO2/tin oxide(SnO2) bilayer towards an efficient ETL. From the systematic measurements of optical and electronic properties, we demonstrate that the TiO2/SnO2 ETL has an enhanced charge extraction ability and a suppressed carrier recombination at the ETL/perovskite interface, both of which are beneficial to photo-generated carrier separation and transport. As a result, PSCs with TiO2/SnO2 bilayer ETLs present higher photovoltaic performance of the baseline cells compared with their TiO2 and SnO2 single-layer ETL counterparts. The champion PSC has a power conversion efficiency(PCE) of 19.11% with an open-circuit voltage(Voc)of 1.15 V, a short-circuit current density(Jsc) of 22.77 mA cm^-2,and a fill factor(FF) of 72.38%. Additionally, due to the suitable band alignment of the TiO2/SnO2 ETL in the device, a high Vocof 1.18 V is achieved. It has been proven that the TiO2/SnO2 bilayer is a promising alternative ETL for high efficiency PSCs.

Engineering of multiferroic BiFeO grain boundaries with head-to-head polarization configurations

Confined low dimensional charges with high density such as two-dimensional electron gas(2 DEG)at interfaces and charged domain walls in ferroelectrics show great potential to serve as functional elements in future nanoelectronics.However,stabilization and control of low dimensional charges is challenging,as they are usually subject to enormous depolarization fields.Here,we demonstrate a method to fabricate tunable charged interfaces with~77°,86°and 94°head-to-head polarization configurations in multiferroic Bi Fe O_(3) thin films by grain boundary engineering.The adjacent grains are cohesively bonded and the boundary is about 1 nm in width and devoid of any amorphous region.Remarkably,the polarization remains almost unchanged near the grain boundaries,indicating the polarization charges are well compensated,i.e.,there should be two-dimensional charge gas confined at grain boundaries.Adjusting the tilt angle of the grain boundaries enables tuning the angle of polarization configurations from 71°to 109°,which in turn allows the control of charge density at the grain boundaries.This general and feasible method opens new doors for the application of charged interfaces in next generation nanoelectronics.

Promising Cd-free double buffer layer in CZTSSe thin film solar cells

Zn(O,S)film is widely used as a Cd-free buffer layer for kesterite thin film solar cells due to its low-cost and eco-friendly characteristics.However,the low carrier concentration and conductivity of Zn(O,S)will deteriorate the device performance.In this work,an additional buffer layer of In2S3 is introduced to modify the properties of the Zn(O,S)layer as well as the CZTSSe layer via a post-annealing treatment.The carrier concentrations of both the Zn(O,S)and CZTSSe layers are increased,which facilitates the carrier separation and increases the open circuit voltage(VOC).It is also found that ammonia etching treatment can remove the contamination and reduce the interface defects,and there is an increase of the surface roughness of the In2S3 layer,which works as an antireflection layer.Consequently,the efficiency of the CZTSSe solar cells is improved by 24%after the annealing and etching treatments.Simulation and experimental results show that a large band offset of the In2S3 layer and defect energy levels in the Zn(O,S)layer are the main properties limiting the fill factor and efficiency of these CZTSSe devices.This study affords a new perspective for the carrier concentration enhancement of the absorber and buffer layers by In-doping,and it also indicates that In2S3/Zn(O,S)is a promising Cd-free hybrid buffer layer for high-efficiency kesterite solar cells.

Synergistic high efficiency and low energy loss of all-small-molecule organic solar cells based on benzotriazole-basedπ-bridge unit

Reducing energy loss(V_(loss))is one of the most crucial challenges in organic photovoltaic cells.The V_(loss),determined by the differences between the optical band gap(E_(g))of the active layer material and the open-circuit voltage(V_(oc))of the device,is generally alleviated by lowering the energy difference between the lowest unoccupied molecular orbital(LUMO)and highest occupied molecular orbital(HOMO)level of the donor(D)and acceptor(A).In this work,we synthesized two A-π-D-π-A-type small-molecule donors(SMDs)SM-benzotriazole(BTz)-1 and SM-BTz-2 by introducing a BTzπ-bridge unit and terminal regulation.The BTzπ-bridge unit significantly lowers the HOMO energy level of SMDs,resulting in high V_(oc)and high mobility,achieving a balance of low energy loss(<0.5 eV)and high efficiency.Ultimately,the organic solar cells based on SM-BTz-2 as the donor and Y6 as the acceptor obtain a high V_(oc)of 0.91 V,J_(sc) of 22.8 mA cm^(−2),fill factor of 68%,and power conversion efficiency(PCE)of 14.12%,which is one of the highest efficiencies based on the SMDs with triazoleπ-bridges to date.What’s more,the BTzπ-bridge unit is a potential unit that can improve mobility and reduce energy loss.

Low carrier concentration leads to high in-plane thermoelectric performance in n-type SnS crystals

As a simple binary compound, p-type SnS shows great competitiveness in thermoelectrics due to the certain appealing carrier and phonon transport behaviors, coupled with its cost-effectiveness, earth-abundance and environmental compatibility. To promote the application of low-cost thermoelectric devices, we synthesized n-type SnS crystals through bromine doping. Herein, we report a high in-plane power factor of ~28 μW cm^(-1)K^(-2), and attribute it to an outstanding in-plane carrier mobility in the crystal form and the large Seebeck coefficient benefitting from the low carrier concentration. The calculations of elastic properties show that the low lattice thermal conductivity in SnS is closely related to its strong anharmonicity. Combining the excellent electrical transport properties with low thermal conductivity, a final ZT of ~0.4 is attained at 300 K, projecting a conversion efficiency of ~5% at 873 K along the in-plane direction.

5 nm NiCoP nanoparticles coupled with g-C3N4 as high-performance photocatalyst for hydrogen evolution

Graphitic carbon nitride(g-C3N4) coupled with NiCoP nanoparticles with sizes around 5 nm have been fabricated via a controllable alcohothermal process. NiCoP is an excellent electron conductor and cocatalyst in photocatalytic reactions. The coupling between tiny NiCoP nanoparticles and g-C3N4 through in-situ fabrication strategy could be a promising way to eliminate the light screening effect, hinder the recombination of photo-induced charge carriers, and improve the charge transfer. The NiCoP/g-C3N4 nanohybrids exhibit an excellent photocatalytic activity in the hydrogen generation, with a significantly improved performance compared with original g-C3N4, CoP/g-C3N4 and Ni2P/g-C3N4, respectively. This study paves a new way to design transition metal phosphides-based photocatalysts for hydrogen production.

Exceptionally efficient deep blue anthracene-based luminogens:design,synthesis,photophysical,and electroluminescent mechanisms

Achieving high-efficiency deep blue emitter with CIE_(y)<0.06(CIE,Commission Internationale de L’Eclairage)and external quantum efficiency(EQE)>10%has been a long-standing challenge for traditional fluorescent materials in organic light-emitting diodes(OLEDs).Here,we report the rational design and synthesis of two new deep blue luminogens:4-(10-(4’-(9 H-carbazol-9-yl)-2,5-dimethyl-[1,1’-biphe nyl]-4-yl)anthracen-9-yl)benzonitrile(2 M-ph-pCzAnBzt)and 4-(10-(4-(9 H-carbazol-9-yl)-2,5-dimethyl phenyl)anthracen-9-yl)benzonitrile(2 M-pCzAnBzt).In particular,2 M-ph-pCzAnBzt produces saturated deep blue emissions in a non-doped electroluminescent device with an exceptionally high EQE of 10.44% and CIE_(x,y)(0.151,0.057).The unprecedented electroluminescent efficiency is attributed to the combined effects of higher-order reversed intersystem crossing and triplet-triplet up-conversion,which are supported by analysis of theoretical calculation,triplet sensitization experiments,as well as nanosecond transient absorption spectroscopy.This research offers a new approach to resolve the shortage of high efficiency deep blue fluorescent emitters.

The equivalent and aliovalent dopants boosting the thermoelectric properties of YbMg2Sb2

Antimony-based Zintl compounds AM2Sb2(A=Ca,Sr,Ba,Yb,Eu;M=Mg,Zn,Cd,Mn),which enable a broad range of manipulation on electrical and thermal transport properties,are considered as an important class of thermoelectric materials.Phonon and carrier transport engineering were realized in YbMg2Sb2 via equivalent and aliovalent substitution of Zn and Ag,respectively.The roomtemperature thermal conductivity reduces from 1.96 to 1.15 W m^-1 K^-1 for YbMg2-xZnxSb2 due to the mass and strain fluctuation through the formation of the absolute solid solution of YbMg2Sb2-YbZn2Sb2.Furthermore,the carrier concentration has been further optimized by Ag doping(from 0.42×10^19 to 7.72×10^19 cm^-3 at room temperature),and thus the electrical conductivity and the power factor are enhanced effectively.The integrated aspects make the dimensionless figure of merit(zT)reach 0.48 at 703 K,which is 60%higher than the pristine YbMgZnSb2 sample.

Polymer nanowire vertical transistors

By utilizing poly（3-hexylthiophene） （P3HT） polymer nanowires with diameters of -15 nm as the vertical channel material, a polymer nanowire vertical transistor has been demonstrated for the first time. The P3HT nanowires were characterized by absorption spectroscopy and scanning electron microscopy. A saturated output current was created by increasing the thickness of the polymer layers between the electrodes through several spin-coating cycles of the polymer nanowires prepared in a marginal solvent. The carrier mobility was also increased through utilization of polymer nanowires with strong interchain interactions. By introducing a small hole injection barrier between the emitter and semiconducting polymer, an on/off current ratio of 1,500 was obtained. The operating voltage is less than 2 V.

Optical and photo-carrier characterization of ultra-shallow junctions in silicon

Spectroscopic ellipsometry (SE), photocarrier radiometry (PCR) and photoluminescence (PL) techniques were employed to measure the ultra-shallow junction (USJ) wafers. These USJ wafers were prepared by As+ ion implantation at energies of 0.5-5 keV, at a dose of 1×1015 As+ /cm 2 and spike annealing. Experimentally the damaged layer of the as-implanted wafer and the recrystallization and activation of the post-annealed wafer were evaluated by SE in the spectral range from 0.27 to 20 m. The PCR amplitude decreased monotonically with the increasing implantation energy. The experimental results also showed that the PCR amplitudes of post-annealed USJ wafers were greatly enhanced, compared to the non-implanted and non-annealed substrate wafer. The PL measurements showed the enhanced PCR signals were attributed to the band-edge emissions of silicon. For explaining the PL enhancement, the electronic transport properties of USJ wafers were extracted via multi-wavelength PCR experiment and fitting. The fitted results showed the decreasing surface recombination velocity and the decreasing diffusion coefficient of the implanted layer contributed to the PCR signal enhancement with the decreasing implantation energy. SE, PCR and PL were proven to be non-destructive metrology tools for characterizing ultra-shallow junctions.

lon migration suppression mechanism via 4-sulfobenzoic acid monopotassium salt for 22.7%stable perovskite solar cells

The deep-level traps at grain boundaries(GBs)and halide ion migration are quite challenging for further enhancement of the stability and efficiency of perovskite solar cells(PSCs)as well as for the elimination of notorious hysteresis.Herein,we report a large-sized strongly coordinated organic anion GB anchoring strategy for suppressing ion migration and passivating defects in planar PSCs.The practical implementation of this strategy involves the incorporation of potassium salts containing a large-sized organic counter anion(4-sulfobenzoic acid monopotassium salt,SAMS)into the perovskite precursor.It has been found that anions within SAMS can be firmly anchored at GBs due to the strong coordination interaction between C=O and/or S=O at both ends of bulky anion and undercoordinated Pb^(2+)and/or halide vacancies,along with the hydrogen bond between–OH and formamidinium.SAMS can not only passivate shallowlevel defects but also cause more effective passivation of the deep-level defects.The GB manipulation strategy results in a reduced defect density,an increased carrier lifetime as well as suppressed ion migration,which in turn contributed to enhanced efficiency and stability of PSCs together with a thorough elimination of hysteresis.As a result,the SAMSmodified device with an outstanding fill factor of 0.84 delivers a significant improvement in efficiency(22.7%)in comparison with the control device(20.3%).The unencapsulated modified device demonstrates only little degradation after 1320 h at 60℃.

Study of photocurrent generation in InP nanowire-based p＋-i-n＋ photodetectors

We report on electrical and optical properties of p＋-i-n＋ photodetectors/solar cells based on square millimeter arrays of InP nanowires （NWs） grown on InP substrates. The study includes a sample series where the p＋-segment length was varied between 0 and 250 nm, as well as solar cells with 9.3% efficiency with similar design. The electrical data for all devices display clear rectifying behavior with an ideality factor between 1.8 and 2.5 at 300 K. From spectrally resolved photocurrent measurements, we conclude that the photocurrent generation process depends strongly on the p^-segment length. Without a p＋-segment, photogenerated carriers funneled from the substrate into the NWs contribute strongly to the photocurrent. Adding a p＋-segment decouples the substrate and shifts the depletion region, and collection of photogenerated carriers, to the NWs, in agreement with theoretical modeling. In optimized solar cells, clear spectral signatures of interband transitions in the zinc blende and wurtzite InP layers of the mixed-phase i-segments are observed. Complementary electroluminescence, transmission electron microscopy （TEM）, as well as measurements of the dependence of the photocurrent on angle of incidence and polarization, support our interpretations.

Electrical field tuning of magneto-Raman scattering in monolayer graphene

In this work, we report the electrical field tuning of magneto-phonon resonance in monolayer graphene under magnetic fields up to 9 T. It is found that the carrier concentration can drastically affect the G （E2g） phonon response to a varying magnetic field through a pronounced magneto-phonon resonance （MPR）. In charge neutral or slightly doped monolayer graphene, both the energy and the line width of the E2g phonon show clear variation with magnetic fields. This is attributed to magneto-phonon resonance between magnetoexcitations and the E2g phonons. In contrast, when the Fermi level of the monolayer graphene is far away from the Dirac point, the G band shows weak magnetic dependence and exhibits a symmetric line-shape. This suggests that the magneto-phonon coupling around 4 T has been switched off due to the Pauli blocking of the inter-Landau level excitations. Moreover, the G band asymmetry caused by Fano resonance between excitonic many-body states and the E2g phonons is observed. This work offers a way to study the magnetoexcitation phonon interaction of materials through magneto-Raman spectroscopy with an external electrical field.