We investigate the dependence of the electrical resistivity of $\sim 60 $nm thick single crystalline graphite samples on the defect concentration produced by proton irradiation at very low fluences. We show that the resistivity decreases few percent at room temperature after inducing defects at concentrations as low as $\sim 0.1 $ppm due to the increase in the carrier density, in agreement with theoretical estimates. The overall results indicate that the carrier densities measured in graphite are not intrinsic but related to defects and impurities.
We report on temperature-dependent size and anisotropy of the Fermi pockets in graphite revealed by magnetotransport measurements. The magnetoresistances obtained in fields along the c-axis obey an extended Kohler's rule, with the carrier density following prediction of a temperature-dependent Fermi energy, indicating a change in the Fermi pocket size with temperature. The angle-dependent magnetoresistivities at a given temperature exhibit a scaling behavior. The scaling factor that reflects the anisotropy of the Fermi surface is also found to vary with temperature. Our results demonstrate tha…
We use first-principles calculation within the density functional theory (DFT) to explore the electronic properties on stage-1 Li- and Li+-graphite-intercalation compounds (GIC) for different concentrations, LiCx/Li+Cx with x= 6,12,18,24,32 and 36. The essential properties, e.g. geometric structures, band structures and spatial charge distributions are determined by the hybridization of orbitals, the main focus of our works. The band structures/density of states/spatial charge distribution display that the Li-GIC possesses blue shift of fermi energy and just like metals, but the Li+-GIC still …
We report the development of graphite-based solar cells using a simple method and low cost materials. Suspension of graphite powder in mineral water was simply dropped onto the surface of fluorine-doped tin oxide glass (FTO) to form a thick film. Surprisingly, using mineral waters greatly improved the efficiency of the solar cell to reach the highest efficiency of 6.97%. Due to some minerals contained, the mineral water induced the development of fibrous structure between the graphite particles which is assumed to play a role as a bridge for the photoexcited electrons to quickly move to the el…
Graphite is a ubiquitous electrode material with particular promise for use in e.g., energy storage and desalination devices, but very little is known about the properties of the graphite-electrolyte double layer at technologically relevant concentrations. Here, the (electrified) graphite-NaCl(aq) interface was examined using constant chemical potential molecular dynamics simulations; this approach avoids ion depletion (due to surface adsorption) and maintains a constant concentration of ions beyond the surface. Specific Na+ adsorption at the graphite basal surface causes charging of the inter…
Crystal growth and electronic properties of a 3D Rashba material, BiTeI, with adjusted carrier concentrations
3D Rashba材料可以成为自旋相关新现象的主要参与者，从金属极端（非常规超导性）到传输中间体（自旋霍尔效应）再到新的绝缘变体（3D拓扑绝缘态）。作为这种3D Rashba材料的基础和应用研究的重要支柱，这项研究建立了候选化合物BiTeI的相当大的单晶的生长，并调整了载流子浓度。采用三种技术（标准垂直布里奇曼、改进的水平布里奇曼和蒸气传输），并通过所选技术成功地生长了具有从金属到绝缘的根本不同的电子状态的BiTeI晶体（> 1 * 1 * 0.2 mm 3）。通过相对论第一性原理计算，得到了BiTeI晶体中载流子浓度的三维Rashba电子态，包括费米面拓扑.
We demonstrate a mechanism for magnetoresistance oscillations in insulating states of two-dimensional (2D) materials arising from the interaction of the 2D layer and proximal graphite gates. We study a series of devices based on different two-dimensional systems, including mono- and bilayer Td-WTe2, angle-aligned MoTe2/WSe2 heterobilayers and Bernal-stacked bilayer graphene, which all share a similar graphite-gated geometry. We find that the resistivity of the 2D system generically shows quantum oscillations as a function of magnetic field corresponding to a high-density Fermi surface when the…
We investigate the high temperature thermoelectric properties of Heusler alloys Fe2-xMnxCrAl (0<x<1). Substitution of 12.5% Mn at Fe-site (x = 0.25) causes a significant increase in high temperature resistivity (\r{ho}) and an enhancement in the Seebeck coefficient (S), as compared to the parent alloy. However, as the concentration of Mn is increased above 0.25, a systematic decrement in the magnitude of both parameters is noted. These observations have been ascribed (from theoretical analysis) to a change in band gap and electronic structure of Fe2CrAl with Mn-substitution. Due to absence of …
Being used in optoelectronic devices as ultra-thin conductor-insulator junctions, detailed investigations are needed about how exactly h-BN and graphene hybridize. Here, we present a comprehensive ab initio study of hot carrier dynamics governed by electron-phonon scattering at the h-BN/graphene interface, using graphite (bulk), monolayer and bilayer graphene as benchmark materials. In contrast to monolayer graphene, all multilayer structures possess low-energy optical phonon modes that facilitate carrier thermalization. We find that the h-BN/graphene interface represents an exception with com…
We present a study of the lower critical field, \hc1, of \STO as a function of carrier concentration with the aim of quantifying the superfluid density. At low carrier concentration (i.e. the underdoped side), superfluid density and the carrier concentration in the normal state are equal within experimental margin. A significant deviation between the two numbers starts at optimal doping and gradually increases with doping. The inverse of the penetration depth and the critical temperature follow parallel evolutions as in the case of cuprate superconductors. In the overdoped regime, the zero-tem…
We report the observation of multiple phonon satellite features in ultra thin superlattices of form $n$SrIrO$_3$/$m$SrTiO$_3$ using resonant inelastic x-ray scattering. As the values of $n$ and $m$ vary the energy loss spectra show a systematic evolution in the relative intensity of the phonon satellites. Using a closed-form solution for the cross section, we extract the variation in the electron-phonon coupling strength as a function of $n$ and $m$. Combined with the negligible carrier doping into the SrTiO$_3$ layers, these results indicate that tuning of the electron-phonon coupling can be …
High quality InN nanoparticles are grown using atmospheric chemical vapour deposition technique via a self-seeded catalytic approach in the temperature range of 580 to 650 oC. In this temperature region, nucleation barrier of InN is overcome by seeding the low density In nano-particles prior to the introduction of reactive ammonia. Samples having increasing carrier density are grown with the help of increasing growth temperature to understand its role in optical phonon structure. Near resonance Raman spectra show complete different phonon pictures as compared to those for the off-resonance spe…
The present work investigates the less explored thermoelectric properties of n-type GaN semiconductors by combined both the experimental and computational tools. Seebeck coefficients of epitaxial thin films of GaN were experimentally measured in the wide temperature range from 77 K to 650 K in steps of ~10 K covering both low and high-temperature regimes as a function of carrier concentration 2 x1016, 2 x 1017, 4 x 1017 and 8 x 1017 cm-3. The measured Seebeck coefficient at room temperature was found to be highest, -374 microV/K, at the lowest concentration of 4 x 1016 cm-3 and decreases in ma…
Graphite crystals used to prepare graphene-based heterostructures are generally assumed to be defect free. We report here scanning tunneling microscopy results that show graphite commonly used to prepare graphene devices can contain a significant amount of native defects. Extensive scanning of the surface allows us to determine the concentration of native defects to be 6.6$\times$10$^8$ cm$^{-2}$. We further study the effects of these native defects on the electronic properties of Bernal-stacked bilayer graphene. We observe gate-dependent intravalley scattering and successfully compare our exp…
We address the role of Sn-substitution and Pb-vacancy (Pb-$\Box$) in regulating stability and carrier concentration of CH$_3$NH$_3$Pb$_{1-X-Y}$Sn$_X$$\Box_Y$I$_3$ perovskite using density functional theory, where the performance of the exchange-correlation functional is carefully analyzed, and validated w.r.t. available experimental results. We find the most stable configuration does not prefer any Pb at 50\% concentration of Sn. However, the Pb-$\Box$s become unfavourable above 250K due to the reduced linearity of Sn-I bonds. For n-type host the Sn substitution is more preferable than Pb-$\Bo…
We have quantified substitutional impurity concentrations in synthetic diamond crystals down to sub parts-per-billion levels. The capture lifetimes of electrons and excitons injected by photoexcitation were compared for several samples with different impurity concentrations. Based on the assessed impurity concentrations, we have determined the capture cross section of electrons to boron impurity, sA=1.3x10^-14 cm2, and that of excitons to nitrogen impurity, sD^ex=3.1x10^-14 cm2. The general tendency of the mobility values for different carrier species is successfully reproduced by including ca…
The influence of He+ ion irradiation on the transport and magnetic properties of epitaxial layers of a diluted magnetic semiconductor (DMS) (In,Fe)Sb, a two-phase (In,Fe)Sb composite and a nominally undoped InSb semiconductor has been investigated. In all layers, a conductivity type conversion from the initial n-type to the ptype has been found. The ion fluence at which the conversion occurs depends on the Fe concentration in the InSb matrix. Magnetotransport properties of the two-phase (In,Fe)Sb layer are strongly affected by ferromagnetic Fe inclusions. An influence of the number of electric…
Significant reduction of lattice thermal conductivity by electron-phonon interaction in silicon with high carrier concentrations: a first-principles study
Understanding how the complex intermolecular- and nano-structure present in organic semiconductor donor-acceptor blends impacts charge carrier motion, interactions, and recombination behavior is a critical fundamental issue with a particularly major impact on organic photovoltaic applications. In this study, kinetic Monte Carlo (KMC) simulations are used to numerically quantify the complex bimolecular charge carrier recombination behavior in idealized phase-separated blends. Recent KMC simulations have identified how the encounter-limited bimolecular recombination rate in these blends deviates…
High-entropy-alloy-type (HEA-type) compound superconductors have been drawing much attention as a new class of exotic superconductors with local structural inhomogeneity. NaCl-type (Ag,In,Sn,Pb,Bi)Te is a typical HEA-type superconductor, but the carrier doping mechanism had been unclear. In this study, we synthesized (Ag,In,Sn,Pb,Bi)Te with various In concentration using high-pressure synthesis: the studied system is (AgSnPbBi)(1-x)/4InxTe (x = 0-0.4). Single-phase samples were obtained for x = 0-0.3. A semiconductor-like temperature dependence of resistivity was observed for x = 0, while supe…
In many semiconductors, compensating defects set doping limits, decrease carrier mobility, and reduce minority carrier lifetime thus limiting their utility in devices. Native defects are responsible in many cases, but extrinsic dopants may also act as their own compensation when occupying an alternate lattice site. Suppressing the concentrations of compensating defects during processing close to thermal equilibrium is difficult because formation enthalpies are lowered as the Fermi level moves towards the majority band edge. Excess carriers, introduced for example by photogeneration, modify the…
Optimizing high-temperature electron mobility in single-crystal Bi$_2$O$_2$Se based on its unconventional dependence on concentration
University of Pardubice, Faculty of Chemical Technology（帕尔杜比采大学化学技术学院）；Institute of Physics of the Czech Academy of Sciences（捷克科学院物理研究所）；Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University（查理大学数学与物理学院凝聚态物理系）；Masaryk University, Department of Condensed Matter Physics（马萨里克大学凝聚态物理系）
Demonstration of Si-doped Al-rich thin regrown Al(Ga)N films on AlN on sapphire templates with $\gt10^{15}/cm^3$ free carrier concentration using close-coupled showerhead MOCVD reactor
Free-charge carrier parameters of n-type, p-type and compensated InN:Mg determined by Infrared Spectroscopic Ellipsometry
采用红外椭圆偏振光谱法研究了掺镁InN薄膜的自由载流子特性。比较了两组具有代表性的通过分子束外延生长的具有从$1.2\times10^{17}$ cm $^{-3}$到$8\times10^{20}$ cm $^{-3}$的Mg浓度的极性InN。P-型导电性表示的Mg浓度范围为$1\times10^{18}$ cm $^{-3}$到$9\times10^{19}$ cm $^{-3}$从纵向光学声子等离子体加宽和迁移率参数的Mg浓度的依赖性的系统调查。一个参数化的模型，占的声子-等离子体激元耦合被施加到确定的自由载流子浓度和迁移率参数的掺杂的块状InN层，以及GAN模板和未掺杂的InN缓冲层为每个样品。第二样品组中的自由载流子性质与先前报道的第一样品组的综合分析中确定的结果一致[Schöche等人，J. Appl.Phys.113，013502（2013）]。在第二组中，具有$2.3\times10^{20}$ cm $^{-3}$的Mg浓度的两个样品被识别为具有非常低的电子浓度的补偿n型InN，其适合于进一步研究通常由高电子浓度控制的本征材料性质，即使在未掺杂的InN中。补偿的n型InN样品可以清楚地从类似的等离子体频率的p型导电材料的强烈减少的声子等离子体激元展宽区分。
Majority-Carrier Mobilities in Undoped and \textit{n}-type Doped ZnO Epitaxial Layers
采用激光分子束外延技术制备了透明导电的ZnO：Ga薄膜。它们的电子性质进行了研究的温度相关的霍尔效应技术。300-K载流子浓度和迁移率分别为约$n_s \sim 10^{16}$ cm $^{-3}$和440 cm $^{2}$ /Vs。在实验的“迁移率对浓度”曲线中，观察到不寻常的现象，即，在$n_s \sim 5\times$ 10 $^{18}$ cm $^{-3}$下的迁移率显著小于在高于$\sim 10^{20}$ cm $^{-3}$的较高密度下的迁移率。几种类型的散射中心，包括电离施主和氧陷阱被认为是占所观察到的霍尔迁移率对载流子浓度的依赖性。的散射机制解释在晶粒间的势垒和带电杂质。理论计算结果与实验数据进行了比较。
