We report on molecular beam epitaxy and properties of a magnetic topological insulator, Cr doped Sb2Te3. The composition analysis reveals that Cr replaces Sb site, and x-ray diffraction confirms that single phase textured crystal structure can be obtained for (CrxSb1-x)2Te3 with x up to 0.44. Further increase in x results in phase separation or precipitates in the material. The Curie temperature TC increases with x up to 0.44, and reaches to 250 K, which is the highest TC observed till now in magnetically doped topological insulators.
Secondary Ions Mass Spectroscopy and Hall effect measurements were performed on boron doped silicon with concentration between 0.02 at.% and 12 at.%. Ultra-high boron doping was made by saturating the chemisorption sites of a Si wafer with BCl3, followed by nanosecond laser anneal (Gas Immersion Laser Doping). The boron concentration varies thus nearly linearly with the number of process repetitions. However, it is not the case for the hole concentration which tends to saturate at high boron concentration. The difference between boron and hole concentration increases as the square of boron con…
Doping is an effective way to modify the electronic property of two-dimensional (2D) materials and endow them with new functionalities. However, wide-range control of the substitutional doping concentration with large scale uniformity remains challenging in 2D materials. Here we report in-situ chemical vapor deposition growth of vanadium (V) doped monolayer molybdenum disulfide (MoS2) with widely tunable doping concentrations ranging from 0.3 to 13.1 at%. The key to regulate the doping concentration lies in the use of appropriate V precursors with different doping abilities, which also generat…
We report on the structural properties of highly B-doped silicon (> 2 at. %) realised by nanosecond laser doping. We investigate the crystalline quality, deformation and B distribution profile of the doped layer by STEM analysis followed by HAADF contrast studies and GPA, and compare the results to SIMS analyses and Hall measurements. When increasing the active B concentration above 4.3 at.%, the fully strained, perfectly crystalline, Si:B layer starts showing dislocations and stacking faults. These only disappear around 8 at.% when the Si:B layer is well accommodated to the substrate. When in…
Cu doped transparent ZnO thin films were spin coated on conductive glass substrates. The samples were subsequently annealed in air for 1 hour at 500 0C in order to form the phase of ZnO. ZnO samples were doped with different Cu molar percentages up to 5%. The impedance and photovoltaic properties of sample were measured. Photocurrent and photovoltage of doped and undoped samples were measured in KI/I2 electrolyte. Adding a trace amount of Cu improved the conducting properties of ZnO samples without changing other basic properties of ZnO. The photocurrent gradually increases with the doping con…
We study mechanisms of control of charge state and concentration of different point defects in doped insulating crystals. The approach is based on the density functional theory calculations. We apply it to the problem of obtaining of Ti-doped sapphire crystals with high figure-of-merit (FOM). The FOM of a given sample is defined as the ratio of the coefficient of absorption at the pump frequency to the coefficient of absorption at the working frequency of Ti:sapphire laser. It is believed that FOM is proportional to the ratio of the concentration of isolated Ti$^{3+}$ ions to the concentration…
Perovskite oxide based thin film gas sensors have long been considered as potential alternatives to commonly investigated binary metal oxides based sensors. BiFeO3, which is a prototype of p-type perovskite based semiconducting oxides, has recently drawn significant attention for its promising gas sensing characteristics. In the present work, the hydrogen sensing characteristics of calcium doped BiFeO3 has been reported by varying the film thickness, doping concentration, operating temperature, and test gas concentration. The films were deposited on glass substrates by sol-gel route using spin…
First-principles calculations have been performed to study the formation of defect complexes in Ti doped alpha-Al2O3 crystals. The formation energies of isolated Ti3+ and Ti4+ defects, pairs, triples and quadruples of Ti ions and Al vacancies are computed under different equilibrium conditions of Al-Ti-O related phases. Taking into account charge neutrality of the whole system we determine the equilibrium concentrations of simple and complex defects as well as the total equilibrium concentration of Ti in an alpha-Al2O3 crystal. It is shown that the equilibrium concentration of complex defects …
Dopant concentration and $α$, $β$ phase fraction is studied in doped W thin films. Oxygen doped $β$ W films are found to have 9.0~$\pm$~0.9 at.\% of oxygen as measured from \ac{SIMS}. Whereas, nitrogen doped $β$ W films have 0.15~$\pm$~0.02 at.\% of nitrogen, much lower than the theoretically predicted value of 11 at.\%. $β$-W films partially phase transform to $α$ by annealing at 175~$^{\circ}$C, up to maximum time of 72 hours. Weak dependence between dopant concentration and phase fraction is observed in the annealed films. The growth exponent of the phase transformation was calculated to be…
We demonstrate the gate-tunability of the long-range magnetic order in a p-type V-doped WSe2 monolayer using ab initio calculations. We found that at a low V-doping concentration limit, the long-range ferromagnetic order is enhanced by increasing the hole density. In contrast, the short-range antiferromagnetic order is manifested at a high electron density by full compensation of the p-type V doping concentration. The hole-mediated long-range magnetic exchange is ~70 meV, thus strongly suggesting the ferromagnetism in V-doped WSe2 at room temperature. Our findings on strong coupling between ch…
Scattering of carriers with ionized impurities governs charge transport in doped semiconductors. However, electron interactions with ionized impurities cannot be fully described with quantitative first-principles calculations, so their understanding relies primarily on simplified models. Here we show an ab initio approach to compute the interactions between electrons and ionized impurities or other charged defects. It includes the short- and long-range electron-defect (e-d) interactions on equal footing, and allows for efficient interpolation of the e-d matrix elements. We combine the e-d and …
Correlated anion and cation motion can significantly reduce the overall ion conductivity in electrolytes versus the ideal conductivity calculated based on the diffusion constants alone. Using coarse-grained molecular dynamics simulations, we calculate conductivity and the degree of uncorrelated ion motion in salt-doped homopolymers and block copolymers as a function of concentration and interaction strengths. Calculating conductivity from ion mobility under an applied electric field increases accuracy versus the typical use of fluctuation dissipation relationships in equilibrium simulations. I…
Electrical transport in C-doped GaAs nanowires: surface effects
研究了不同掺杂浓度的掺碳GaAs纳米线的电阻率和迁移率。通过比较钝化纳米线和钝化纳米线，评估了表面效应。我们直接看到了表面的影响：费米能级的钉扎和随之而来的耗尽区的存在导致迁移率增加，当掺杂浓度低于3*10^18 cm^-3时，迁移率最高可达30 cm ^2/（V*s）。电子束感应电流测量表明，少数载流子扩散路径可以高达190 nm的钝化纳米线。
Thin films of Zn2+ doped cupric oxide (CuO) were synthesized using spin coating technique starting from a solution with Cu and Zn. The speed of spin coating and time duration were varied to fabricate a film with required uniform thickness. Samples were subsequently annealed in air at different annealing temperatures to crystallize the phase of CuO. Doping concentration of Zn2+ was varied up to weight percentage of 10%. Structural properties of samples were determined using X-ray diffraction technique. Particle size, dislocation density and strain at different doping concentrations were determi…
Due to the photo-instability and hysteresis of TiO$_2$ electron transport layer (ETL) in perovskite solar cells (PSCs), novel electron transport materials are highly demanded. Here, we show ideal band alignment between La-doped BaSnO$_3$ (LBSO) and methyl ammonium (MA) lead iodide perovskite (MAPbI$_3$). The CH$_3$NH$_3$PbI$_3$/La$_x$Ba$_{(1-x)}$SnO$_3$ interface forms a stable all-perovskite heterostructure. The selective band alignment is manipulated with band gap renormalization by La-doping on the Ba site. LBSO shows high mobility, photo-stability, and structural stability, promising the n…
Alloying effects by T=Mn,Co,Ni-substitution on FeS$_2$ have been investigated using density-functional calculations. The ferromagnetic alloys Fe$_{1-x}$T$_x$S$_2$ have been investigated for concentrations $x=\frac{1}{4},\frac{1}{2},\frac{3}{4}$ together with the ground states of the pure compounds. The electronic structure is discussed with the goal to identify candidates for half metals, which are of interest for spintronics applications. We find interesting candidates at high concentration of the Mn-doped FeS$_2$ and at low concentrations for Ni-doped materials. For the Mn alloys we also not…
The tuning black phosphorene properties such as structural, electronic, transport are explored via substitutional C-doped. We employed density functional theory (DFT) calculations in combination with non-equilibrium Green's function (NEGF) for modeling the systems. Our results revealed that substitutional C-doped phosphorene are energetically favorable, and ruled by exothermic process. We also found that C-doping induces a change of the electric properties, such as a semiconductor-to-metal transition for the most lower concentration and zig-zag C-wire. Moreover, for an armchair C-wire and the …
The power factor of pure p-type ZnSb has been calculated via ab initio simulations assuming that the carrier concentrations are due to the doping effect of intrinsic zinc vacancies. With a vacancy concentration close to the experimental solubility limit we were able to perfectly reproduce the Power Factor measured in polycrystalline ZnSb samples. The methodology has then been successfully extended for predicting the effect of extrinsic doping elements on the thermoelectric properties of ZnSb. Germanium and tin seem to be promising p-type doping elements. In addition, we give, for the first tim…
Hole concentrations in doped gray α-Sn on InSb and CdTe measured with infrared ellipsometry
New Mexico State University（新墨西哥州立大学）；Charles University, Faculty of Mathematics and Physics（查理大学数学物理学院）；University of California Santa Barbara（加州大学圣塔芭芭拉分校）
We report on S-doping of ZnSb for S concentrations ranging from 0.02 at% to 2.5 at%. There are no previous reports on S-doping. ZnSb is a thermoelectric material with some advantages for the temperature range 400 K - 600 K. The solid solubility of S in ZnSb was estimated to be lower than 0.1% from observations of precipitates by scanning microscopy. Hall and Seebeck measurements were performed as a function of temperature from 6K to 623 K. The temperature dependence of the electrical properties suggests that S introduces neutral scattering centers for holes in the p-type material. An increase …
Understanding the nature of electronic effective mass in double-doped SrTiO$_{3}$
提出了一种通过双掺杂机制来调节氧化物半导体中有效质量的方法。我们证明了这一点在一个模型氧化物系统Sr $_{1-x}$ La $_x$ TiO $_{3-δ}$，在那里我们可以调整有效质量范围从6- 20 $\mathrm{m_e}$作为填充或载流子浓度和散射机制的函数，这取决于所选择的镧和氧空位浓度。使用Sr $_{1-x}$ La $_x$ TiO $_{3-δ}$的薄膜的测量的传输特性从玻尔兹曼传输方程计算有效质量值。我们的方法，这表明，有效质量随载流子浓度的降低，提供了一种手段，用于理解的性质的传输过程中的氧化物，通常具有大的有效质量和低的电子迁移率，相反的传统的高迁移率半导体。
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。
Mn2+-doped semiconductor nanocrystals with tuned location and concentration of Mn2+ ions can yield diverse coupling regimes, which can highly influence their optical properties such as emission wavelength and photoluminescence (PL) lifetime. However, investigation on the relationship between the Mn2+ concentration and the optical properties is still challenging because of the complex interactions of Mn2+ ions and the host and between the Mn2+ ions. Here, atomically flat ZnS nanoplatelets (NPLs) with uniform thickness were chosen as matrixes for Mn2+ doping. Using time-resolved (TR) PL spectros…
Room-Temperature Electron Spin Transport in a Highly Doped Si Channel
我们报告的第一个演示产生的自旋电流和自旋输运在高掺杂的Si沟道在室温下（RT）使用四端横向设备与自旋注入器和检测器组成的Fe/MgO隧道势垒。使用非局域技术产生自旋电流，并在300 K下成功地检测到自旋注入信号和Hanle型自旋进动，从而证明了自旋注入消除了伪信号。用Hanle型自旋旋进估算了自旋扩散长度为0.6 μ m，室温寿命为1.3 ns.
Hysteresis in the magneto-transport of Manganese-doped Germanium: evidence for carrier-mediated ferromagnetism
本文报道了用Mn离子注入Ge，然后用脉冲激光退火的方法制备Ge：Mn铁磁半导体。得益于短时间退火，Mn注入Ge中的空穴浓度从10 $^{18}$提高到10 $^{20}$ cm $^{-3}$以上，提高了两个数量级。可能是由于高空穴浓度，我们观察到纵向和霍尔电阻表现出与磁化相同的磁滞，这通常被认为是载流子介导的铁磁性的标志。
In this paper, a study is presented on the charge transport in n-type doped semiconductor 6H-SiC (in both transient and steady state) using a nonequilibrium quantum kinetic theory derived from the method of nonequilibrium statistical operator (NSO), which furnishes a clear description of the irreversible phenomena that occur in the evolution of the analyzed system. We obtain theoretically the dependence on the electric field (applied in the orientation perpendicular or parallel to the c-axis) of the basic macrovariables: the electron drift velocity and the nonequilibrium temperature. The peak …
The Fe-doped CuO thin films were deposited onto glass substrates by Spray pyrolysis technique. The structural, micro-structural, optical and electrical properties of the synthesized samples were investigated in details. The X-Ray diffraction (XRD), Raman and Fourier Transform Infrared (FTIR) spectroscopy, confirmed that the studied samples exhibit single phase monoclinic structure of CuO. The UV-VIS spectrophotometer mentioned that the transmittance increases to 80 % when increasing the Fe concentration. Furthermore, the band gap energy of the obtained CuO was 1.29 eV. This value was slightly …
We report the synthesis and thermoelectric transport properties of As-doped layered pnictogen oxyselenides NdO0.8F0.2Sb1-xAsxSe2 (x < 0.7), which are predicted to show high-performance thermoelectric properties based on first-principles calculation. The crystal structure of these compounds belongs to the tetragonal P4/nmm space group (No. 129) at room temperature. The lattice parameter c decreases with increasing x, while a remains almost unchanged among the samples. Despite isovalent substitution of As for Sb, electrical resistivity significantly rises with increasing x. Very low thermal cond…
We present a first-principles study of the magnetotransport phenomena in p-doped diamond via the exact solution of the linearized Boltzmann transport equation, in which the materials' parameters, including electron-phonon and phonon-phonon interactions, are obtained from density functional theory. This approach gives results in very good agreement with experimental data for Hall and drift mobilities, low- and high-field magnetoresistance and Seebeck coefficient, including the phonon-drag effect, in a range of temperatures and carrier concentrations. In particular, our results provide a detaile…
$La_xCa_{1-x}MnO_3$ (LCMO) has been studied in the framework of density functional theory (DFT) using Hubbard-U correction. We show that the formation of spin-polarons of different configurations is possible in the G-type antiferromagentic phase. We also show that the spin-polaron (SP) solutions are stabilized due to an interplay of magnetic and lattice effects at lower La concentrations and mostly due to the lattice contribution at larger concentrations. Our results indicate that the development of SPs is unfavorable in the C- and A-type antiferromagnetic phases. The theoretically obtained ma…
