Performing deep level transient spectroscopy (DLTS) on Schottky diodes, we investigated defect levels below the conduction band minima (Ec) in Czochralski (CZ) grown unintentionally-doped (UID) and vertical gradient freeze (VGF)-grown Zr-doped beta-Ga2O3 crystals. In UID crystals with an electron concentration of 10^17 cm-3, we observe levels at 0.18 eV and 0.46 eV in addition to the previously reported 0.86 (E2) and 1.03 eV (E3) levels. For 10^18 cm-3 Zr-doped Ga2O3, signatures at 0.30 eV (E15) and 0.71 eV (E16) are present. For the highest Zr doping of 5*10^18 cm-3, we observe only one signature at 0.59 eV. Electric field-enhanced emission rates are demonstrated via increasing the reverse bias during measurement. The 0.86 eV signature in the UID sample displays phonon-assisted tunneling enhanced thermal emission and is consistent with the widely reported E2 (FeGa) defect. The 0.71 eV (E16) signature in the lower-Zr-doped crystal also exhibits phonon-assisted tunneling emission enhancement. Taking into account that the high doping in the Zr-doped diodes also increases the electric field, we propose that the 0.59 eV signature in the highest Zr-doped sample likely corresponds to the 0.71 eV signature in lower-doped samples. Our analysis highlights the importance of testing for and reporting on field-enhanced emission especially the electric field present during DLTS and other characterization experiments on beta-Ga2O3 along with the standard emission energy, cross-section, and lambda-corrected trap density. This is important because of the intended use of beta-Ga2O3 in high-field devices and the many orders of magnitude of possible doping.
A new approach is developed to calculate temperature dependent Seebeck coefficient of heavily doped systems by using Boltzmann transport theory and electron density of states (DOS) obtained from density functional calculations. This approach is applied to heavily doped La:STO with DOS from tetrahedral method and Fermi energy using Fermi integrals. The calculated Seebeck coefficient agrees with the experimental data nearly quantitatively, which proved the accuracy of this approach. The influence of the Fermi energy and asymmetry of DOS on the Seebeck coefficient is analyzed.
We report the growth of electrically-resistive vanadium-doped beta-Ga2O3 single crystals via the optical floating zone technique. By carefully controlling the growth parameters V-doped crystals with very high electrical resistivity compared to the usual n-type V-doped beta-Ga2O3 (ne~10^(18)/cm^3) can be synthesized. The optical properties of such high resistive V-doped b-Ga2O3 are significantly different compared to the undoped and n-doped crystals. We study the polarization-dependent Raman spectra, polarization-dependent transmission, temperature-dependent photoluminescence in the optical wav…
We have studied the magneto-optical and magnetotrasnport properties of GaMnAs thin films with high Mn concentrations (x= 12.2 - 21.3%) grown by molecular-beam epitaxy. These heavily Mn-doped GaMnAs films were formed by decreasing the growth temperature to as low as 150-190 degree C and by reducing the film thickness to 10 nm in order to prevent precipitation of hexagonal MnAs clusters. Magnetic circular dichroism (MCD) and anomalous Hall effect measurements indicate that these GaMnAs films have the nature of intrinsic ferromagnetic semiconductors with high ferromagnetic transition temperature …
We report here an experimental and theoretical study on the magnetoresistance properties of heavily phosphorous doped germanium on the metallic side of the metal-nonmetal transition. An anomalous regime, formed by negative values of the magnetoresistance, was observed by performing low-temperature measurements and explained within the generalized Drude model, due to the many-body effects. It reveals a key mechanism behind the magnetoresistance properties at low temperatures and, therefore, constitutes a path to its manipulation in such materials of great interest in fundamental physics and tec…
Recombination of minority carriers in heavily doped n-InP wafers has been investigated using spectral and time-resolved photoluminescence at different temperatures. Studies of the transmitted luminescence were enabled by the partial transparency of the samples due to the Moss-Burstein effect. Temporal evolution of the transmitted luminescence shows virtually no effect of surface recombination but is strongly influenced by photon recycling. Temperature dependence of the decay time suggests Auger recombination as the dominant non-radiative process at room temperature. Radiative quantum efficienc…
We report evidence of a non-adiabatic Kohn anomaly in boron-doped diamond, using a joint theoretical and experimental analysis of the phonon dispersion relations. We demonstrate that standard calculations of phonons using density functional perturbation theory are unable to reproduce the dispersion relations of the high-energy phonons measured by high-resolution inelastic x-ray scattering. On the contrary, by taking into account non-adiabatic effects within a many-body field-theoretic framework, we obtain excellent agreement with our experimental data. This result indicates a breakdown of the …
We have studied magnetic properties of heavily Mn-doped [(In0.44Ga0.56)0.79Mn0.21]As thin films grown by low-temperature molecular-beam epitaxy (LT-MBE) on InP substrates. The (InGaMn)As with high Mn content (21%) was obtained by decreasing the growth temperature to 190 degC. When the thickness of the [(In0.44Ga0.56)0.79Mn0.21]As layer is equal or thinner than 10 nm, the reflection high-energy electron diffraction (RHEED) pattern and transmission electron microscopy (TEM) show no MnAs clustering, indicating that a homogeneous single crystal with good quality was grown. In the magnetic circular…
We present a study of the photoluminescence (PL) properties of heavily Be delta-doped GaAs/AlAs multiple quantum wells measured at room and liquid nitrogen temperatures. Possible mechanisms for photocarriers recombination are discussed, with a particular focus on the peculiarities of the excitonic and free carriers-acceptors PL emissions occurring below and above the Mott metal-insulator transition. Moreover, based on a simple theoretical model, it is found that the critical impurities concentration to observe the Mott transition in the MQW samples exhibiting 15 nm wells width and 5 nm-thick b…
Novel or unusual magnetism is a subject of considerable interest, particularly in metals and degenerate semiconductors. In such materials the interplay of magnetism, transport and other Fermi liquid properties can lead to fascinating physical behavior. One example is in magnetic semiconductors, where spin polarized currents may be controlled and used. We report density functional calculations predicting magnetism in doped semiconducting beta-FeSi2 and CrSi2 at relatively low doping levels particularly for n-type. In this case, there is a rapid cross-over to a half-metallic state as a function …
Currently, Fe doping in the ~10^18 cm-3 range is the most widely-available method for producing semi-insulating single crystalline beta-Ga2O3 substrates. Red luminescence features have been reported from multiple types of Ga2O3 samples including Fe-doped -Ga2O3, and attributed to Fe or N at O. Herein, however, we demonstrate that the high-intensity red luminescence from Fe-doped beta-Ga2O3 commercial substrates consisting of two sharp peaks at 689 nm and 697 nm superimposed on a broader peak centered at 710 nm originates from Cr impurities present at a concentration near 2 ppm. The red emissio…
Doping of semiconductors by impurity atoms enabled their widespread technological application in micro and opto-electronics. For colloidal semiconductor nanocrystals, an emerging family of materials where size, composition and shape-control offer widely tunable optical and electronic properties, doping has proven elusive. This arises both from the synthetic challenge of how to introduce single impurities and from a lack of fundamental understanding of this heavily doped limit under strong quantum confinement. We develop a method to dope semiconductor nanocrystals with metal impurities providin…
We present high-temperature ferromagnetism and large magnetic anisotropy in heavily Fe-doped n-type ferromagnetic semiconductor (In1-x,Fex)Sb (x = 20 - 35%) thin films grown by low-temperature molecular beam epitaxy. The (In1-x,Fex)Sb thin films with x = 20 - 35% maintain the zinc-blende crystal and band structure with single-phase ferromagnetism. The Curie temperature (TC) of (In1-x,Fex)Sb reaches 390 K at x = 35%, which is significantly higher than room temperature and the highest value so far reported in III-V based ferromagnetic semiconductors. Moreover, large coercive force (HC = 160 Oe) …
The n-type doping of Ge is a self-limiting process due to the formation of vacancy-donor complexes (DnV with n <= 4) that deactivate the donors. This work unambiguously demonstrates that the dissolution of the dominating P4V clusters in heavily phosphorus-doped Ge epilayers can be achieved by millisecond-flash lamp annealing at about 1050 K. The P4V cluster dissolution increases the carrier concentration by more than three-fold together with a suppression of phosphorus diffusion. Electrochemical capacitance-voltage measurements in conjunction with secondary ion mass spectrometry, positron anni…
Isotopic substitution of boron and carbon is applied for the identification of the vibrational modes of heavily boron-doped diamond synthesized by high-pressure high-temperature technique. None of the bands in the Raman spectra are shifting upon ^{10}B-substitution, whereas shifts to lower frequency are observed for all bands upon ^{13}C-substitution as compared to a sample with natural isotope abundancies. These isotopic substitution experiments exclude the hypothesis of boron dimer related normal modes and strongly support the assignment of the previously studied "500 cm^{-1}" and "1230 cm^{…
Heavily-doped semiconductor nanocrystals characterized by a tunable plasmonic band have been gaining increasing attention recently. Herein, we introduce this type of materials focusing on their structural and photo physical properties. Beside their continuous-wave plasmonic response, depicted both theoretically and experimentally, we also review recent results on their transient, ultrafast response. This was successfully interpreted by adapting models of the ultrafast response of gold nanoparticles.
The electrical behavior of Ni Schottky barrier formed onto heavily doped (ND>1019 cm-3) n-type phosphorous implanted silicon carbide (4H-SiC) was investigated, with a focus on the current transport mechanisms in both forward and reverse bias. The forward current-voltage characterization of Schottky diodes showed that the predominant current transport is a thermionic-field emission mechanism. On the other hand, the reverse bias characteristics could not be described by a unique mechanism. In fact, under moderate reverse bias, implantation-induced damage is responsible for the temperature increa…
A comprehensive current-voltage (I-V) characterization is performed for three different Schottky contacts; Pt, Ni and Ti, to unintentionally doped (UID) \{beta}-(Al0.19Ga0.81)2O3 grown by molecular beam epitaxy (MBE) on \{beta}-Ga2O3 for temperatures ranging between 25C -300C. Reciprocal space mapping shows the (Al0.19Ga0.81)2O3 films are strained and lattice matched to the substrate. Schottky Barrier Height (SBH), ideality factor (n), and series resistance (Rs) are extracted from the I-V characteristics for the three types of metals and temperatures. Room temperature capacitance-voltage (C-V)…
Sr$_{2}$FeMoO$_6$ is a double perovskite compound, known for its high temperature behavior. Combining different magnetic and spectroscopic tools, we show that this compound can be driven to rare example of antiferromagnetic metallic state through heavy electron doping. Considering synthesis of Sr$_{2-x}$La$_x$FeMoO$_6$ (1.0 $\le{x}\le$ 1.5) compounds, we find compelling evidences of antiferromagnetic metallic ground state for $x\ge$1.4. The local structural study on these compounds reveal unusual atomic scale phase distribution in terms of La, Fe and Sr, Mo-rich regions driven by strong La-O c…
Transition metal dichalcogenides (TMDs) display a rich variety of instabilities such as spin and charge orders, Ising superconductivity and topological properties. Their physical properties can be controlled by doping in electric double-layer field-effect transistors (FET). However, for the case of single layer NbSe$_2$, FET doping is limited to $\approx 1\times 10^{14}$ cm$^{-2}$, while a somewhat larger charge injection can be obtained via deposition of K atoms. Here, by performing ARPES, STM, quasiparticle interference measurements, and first principles calculations we show that a misfit co…
The missing hole packets near the Brillouin zone center render unique electronic structures to the heavily electron doped FeSe-based superconductors with Tc above 40 K. It challenges the existing scenario accounting for the nature of superconductivity in the iron-based family. Yet, one hurdle that has to be overcome is the materials complexity in the rather limited number of compounds. Here we report the growth of heavily electron doped Li-NH3 intercalated FeSe single crystals that are free of such complexities and allow access to the intrinsic superconducting properties. Our results show extr…
We present an experimental investigation of heavy doping-induced many-body effects such as band gap narrowing(BGN) and Fermi edge singularity(FES) in Al$_x$Ga$_{1-x}$As using photoluminescence(PL) spectroscopy. The band-to-band transition energy shifts to lower energies and FES-like feature in PL spectra grows with increasing electron concentration. We show that FES-like feature is a nonmonotonic function of temperature and excitation intensity. Our data lead us to suggest that a small concentration of nonequilibrated holes is required to enhance the FES-like feature in the PL spectra.
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…
Heavily electron-doped surfaces of Bi$_2$Se$_3$ have been studied by spin and angle resolved photoemission spectroscopy. Upon doping, electrons occupy a series of {\bf k}-split pairs of states above the topological surface state. The {\bf k}-splitting originates from the large spin-orbit coupling and results in a Rashba-type behavior, unequivocally demonstrated here via the spin analysis. The spin helicities of the lowest laying Rashba doublet and the adjacent topological surface state alternate in a left-right-left sequence. This spin configuration sets constraints to inter-band scattering ch…
As spintronic devices become more and more prevalent, the desire to find Pt free materials with large spin Hall effects is increasing. Previously it was shown that Beta W, the metastable A15 structured variant of pure W, has charge-spin conversion efficiencies on par with Pt, and it was predicted that Beta W(Ta) alloys should be even more efficient. Here we demonstrate the enhancement of the spin Hall ratio (SHR) in A15-phase Beta W films doped with Ta (W(4-x)Tax where x is between 0.28 and 0.4, deposited at room temperature using DC magnetron co-sputtering. In close agreement with theoretical…
Recent experiments reported an unusual nematic behavior of heavily hole-doped pnictides $A$Fe$_{2}$As$_{2}$, with alkali $A$ = Rb, Cs. In contrast to the $B_{2g}$ nematic order of the parent $Ae$Fe$_{2}$As$_{2}$ compounds (with alkaline earth $Ae$ = Sr, Ba), characterized by unequal nearest-neighbor Fe-Fe bonds, in the hole-doped systems nematic order is observed in the $B_{1g}$ channel, characterized by unequal next-nearest-neighbor Fe-Fe (diagonal Fe-As-Fe) bonds. In this work, using density functional theory, we attribute this behavior to the evolution of the magnetic ground state along the…
Steady-state access to intraband transitions in colloidal quantum dots (CQDs), via heavy doping, allows exploiting the electromagnetic spectrum at energies below the band gap. CQD intraband optoelectronics opens up a new path to cheap mid- and long-wavelength infrared photodetectors and light-emitting devices, which today employ mostly epitaxial materials. As a recent field of experimental research, thorough studies of the basic properties of intraband transitions in CQDs are still lacking. In this work, we investigate the size and temperature dependence of the intraband transition in heavily …
We report switching of magnetic anisotropy (MA) from in-plane to perpendicular with increasing the thickness d of a (001)-oriented ferromagnetic-semiconductor (FMS) (Ga0.7,Fe0.3)Sb layer with a high Curie temperature (Tc > 320 K), using ferromagnetic resonance at room temperature. We show that the total MA energy (E) along the [001] direction changes its sign from positive (in-plane) to negative (perpendicular) with increasing d above an effective critical value \mathrm{d}_\mathrm{C}^\mathrm{*}\ ~ 42 nm. We reveal that (Ga,Fe)Sb has two-fold symmetry in the film plane. Meanwhile, in the plane …
We performed a high energy resolution ARPES investigation of over-doped Ba0.1K0.9Fe2As2 with T_c= 9 K. The Fermi surface topology of this material is similar to that of KFe2As2 and differs from that of slightly less doped Ba0.3K0.7Fe2As2, implying that a Lifshitz transition occurred between x=0.7 and x=0.9. Albeit for a vertical node found at the tip of the emerging off-M-centered Fermi surface pocket lobes, the superconducting gap structure is similar to that of Ba0.3K0.7Fe2As2, suggesting that the paring interaction is not driven by the Fermi surface topology.
We have used neutron scattering and muon spin relaxation (muSR) to investigate the structural and magnetic properties of the beta-phase of elemental manganese doped with dilute amounts of indium. beta-Mn is an example of a topologically frustrated antiferromagnetically correlated metal - but which remains paramagnetic at all temperatures. The addition of In to beta-Mn results in a vast volume expansion of the lattice, and would therefore be expected to have a major effect on the stability and localization of the Mn moment - as observed in, for example, Ru and Al doped beta-Mn alloys. We find t…
Heavily-doped semiconductor films are very promising for application in mid-infrared plasmonic devices because the real part of their dielectric function is negative and broadly tunable in this wavelength range. In this work we investigate heavily n-type doped germanium epilayers grown on different substrates, in-situ doped in the $10^{17}$ to $10^{19}$ cm$^{-3}$ range, by infrared spectroscopy, first principle calculations, pump-probe spectroscopy and dc transport measurements to determine the relation between plasma edge and carrier density and to quantify mid-infrared plasmon losses. We dem…
We demonstrate heavy and hyper doping of ZnO by a combination of gallium (Ga) ion implantation using a focused ion beam (FIB) system and post-implantation laser annealing. Ion implantation allows for the incorporation of impurities with nearly arbitrary concentrations, and the laser-annealing process enables dopant activation close to or beyond the solid-solubility limit of Ga in ZnO. We achieved heavily doped ZnO:Ga with free-carrier concentrations of ~10^21 cm^(-3), resulting in a plasma wavelength of 1.02 um, which is substantially shorter than the telecommunication wavelength of 1.55 um. T…
Electronic and magnetic properties of the heavily H-doped LaFeAsO$_{1-x}$H$_x$ $(x\sim0.5 )$ were studied in the framework of the density functional theory combined with the dynamical mean field theory (DFT+DMFT). We found a stripe-like-ordered structure of hydrogen and oxygen atoms, as a ground state, with the same configuration as the antiferromagnetic (AF) order. The new configuration could explain the existing experimental results related to the heavily H-doped LaFeAsO$_{1-x}$H$_x$, such as an in-plane electronic anisotropy and a non-uniform magnetic behavior. A significant anisotropy was …
We present ultra-thin silicon membrane thermocouple bolometers suitable for fast and sensitive detection of low levels of thermal power and infrared radiation at room temperature. The devices are based on 40 nm-thick strain tuned single crystalline silicon membranes shaped into heater/absorber area and narrow n- and p-doped beams, which operate as the thermocouple. The electro-thermal characterization of the devices reveal noise equivalent power of 13 pW/rtHz and thermal time constant of 2.5 ms. The high sensitivity of the devices is due to the high Seebeck coefficient of 0.39 mV/K and reducti…
The paper reports on the investigations of the weak localization (WL) effects in 3D polycrystalline thin films of InSb. The films are closely compensated showing the electron concentration n>10^{16} cm^{-3} at the total concentration of the donor and acceptor type structural defects >10^{18} cm^{-3}. Unless Pb-doped, the InSb films do not show any measurable or show very small WL effect at 4.2 K. The Pb-doping to the concentration of the order of 10^{18} cm^{-3} leads to pronounced WL effects below 7 K. In particular, a clearly manifested SO scattering is observed. From the comparison of the e…
We report the effect of germanium as n-type dopant on the electrical and optical properties of AlxGa1-xN layers grown by plasma assisted molecular-beam epitaxy. The Al content has been varied from x = 0 to 0.66, confirmed by Rutherford backscattering spectrometry, and the Ge concentration was increased up to [Ge] = 1E21 cm-3. Even at these high doping levels Ge does not induce any structural degradation in AlxGa1-xN layers with x below 0.15. However, for higher Al compositions, clustering of Ge forming crystallites were observed. Hall effect measurements show a gradual decrease of the carrier …
Diamond has outstanding physical properties: the hardest known material, a wide band gap, the highest thermal conductivity, and a very high Debye temperature. In 2004, Ekimov et al. discovered that heavily boron-doped (B-doped) diamond becomes a superconductor around 4 K. Our group successfully controlled the boron concentration and synthesized homoepitaxially grown superconducting diamond films by a CVD method. By CVD method, we found that superconductivity appears when the boron concentration (nB) exceeds a metal-insulator transition concentration of 3.0x10^20 cm^-3 and its Tczero increases …
Using density functional theory calculations we investigate the electronic structure of graphene doped by deposition of foreign atoms. We demonstrate that, as the charge transfer to the graphene layer increases, the band structure of the pristine graphene sheet is substantially affected. This is particularly relevant when Ca atoms are deposed on graphene at CaC$_{6}$ stoichiometry. Similarly to what happens in superconducting graphite intercalated compounds, a Ca bands occurs at the Fermi level. Its hybridization with the C states generates a strong non-linearity in one of the $π^{*}$ bands be…
We focused on elastic properties of B- and N-doped graphene in wide range of concentrations up to 20%. The Young's, bulk and shear moduli and Poisson's ratio have been calculated by means of the density functional theory for a representative set of supercells with disordered impurity patterns including aggregates. In contrast to earlier work, it is demonstrated that doping with nitrogen even strengthens the graphene layers, whereas incorporation of boron induces large structural and morphological changes seen in simulated STM images. Young's and shear moduli increase or decrease with the dopin…
Plasmonic-cavity Modulator for the Mid-IR with a Semi-transparent and Nonlinear Heavily-doped Semiconductor Mirror
Istituto Italiano di Tecnologia（意大利理工学院）；Istituto di Fotonica e Nanotecnologie, Consiglio Nazionale delle Ricerche（国家研究委员会光子和纳米技术研究所）；University of Luxembourg（卢森堡大学）；Institute for Advanced Studies, University of Luxembourg Campus Belval（卢森堡大学贝尔瓦尔校区高等研究院）；Centre de Nanosciences et de Nanotechnologies (C2N), CNRS UMR 9001, Universit´e Paris-Saclay（巴黎萨克雷大学CNRS 9001联合实验室纳米科学与纳米技术中心）
The effects of hydrogen incorporation into beta-Ga2O3 thin films have been investigated by chemical, electrical and optical characterization techniques. Hydrogen incorporation was achieved by remote plasma doping without any structural alterations of the film; however, X-ray photoemission reveals major changes in the oxygen chemical environment. Depth-resolved cathodoluminescence (CL) reveals that the near-surface region of the H-doped Ga2O3 film exhibits a distinct red luminescence (RL) band at 1.9 eV. The emergence of the H-related RL band is accompanied by an enhancement in the electrical c…
Although Fe-based superconductors are multiorbital correlated electronic systems, previous nuclei magnetic resonance (NMR) measurement suggests that a single spin-fluid model is sufficient to describe its spin behavior. Here, we firstly observed the breakdown of single spin-fluid model in a heavily hole-doped Fe-based superconductor CsFe2As2 by site-selective NMR measurement. At high temperature regime, both of Knight shift and nuclei spin-lattice relaxation at 133Cs and 75As nuclei exhibit distinct temperature-dependent behavior, suggesting the breakdown of single spin-fluid model in CsFe2As2…
The light scattering properties of superconducting (Tc=3.8 K) heavily boron doped nanocrystalline diamond has been investigated by Raman spectroscopy using visible excitations. Fano type interference of the zone-center phonon line and the electronic continuum was identified. Lineshape analysis reveals Fano lineshapes with a significant asymmetry (q=-2). An anomalous wavelength dependence and small value of the Raman scattering amplitude is observed in agreement with previous studies.
In monolayer transition-metal dichalcogenide semiconductors, many-body correlations can manifest in optical spectra when photoexcited electron-hole pairs (excitons) are introduced into a 2D Fermi sea of mobile carriers. At low carrier densities, the formation of positively and negatively charged excitons ($X^\pm$) is well documented. However, in WSe$_2$ monolayers, an additional absorption resonance, often called $X^{-\prime}$, emerges at high electron density. Its origin is not understood. Here we investigate the $X^{-\prime}$ state via polarized absorption spectroscopy of electrostatically-g…
The n-type Ge-on-Si epitaxial material platform enables a novel paradigm for plasmonics in the mid-infrared, prompting the future development of lab-on-a-chip and subwavelength vibrational spectroscopic sensors. In order to exploit this material, through proper electrodynamic design, it is mandatory to retrieve the dielectric constants of the thin Ge epilayers with high precision due to the difference from bulk Ge crystals. Here we discuss the procedure we have employed to extract the real and imaginary part of the dielectric constants from normal incidence reflectance measurements, by combini…
We have observed the bulk Fermi surface (FS) in an overdoped ($x$=0.3) single crystal of La$_{2-x}$Sr$_x$CuO$_4$ by using Compton scattering. A two-dimensional (2D) momentum density reconstruction from measured Compton profiles yields a clear FS signature in the third Brillouin zone along [100]. The quantitative agreement between density functional theory (DFT) calculations and momentum density experiment suggests that Fermi-liquid physics is restored in the overdoped regime. In particular the predicted FS topology is found to be in good accord with the corresponding experimental data. We find…
We report high-resolution neutron scattering measurements of the low energy spin fluctuations of KFe$_{2}$As$_{2}$, the end member of the hole-doped Ba$_{1-x}$K$_x$Fe$_2$As$_2$ family with only hole pockets, above and below its superconducting transition temperature $T_c$ ($\sim$ 3.5 K). Our data reveals clear spin fluctuations at the incommensurate wave vector ($0.5\pmδ$, 0, $L$), ($δ$ = 0.2)(1-Fe unit cell), which exhibit $L$-modulation peaking at $L=0.5$. Upon cooling to the superconducting state, the incommensurate spin fluctuations gradually open a spin-gap and form a sharp spin resonance…
Large-volume deployment of Si-based Seebeck generators can be foreseen only if polycrystalline rather than single crystalline materials can be actually used. The aim of this study was therefore to verify whether polycrystalline Si films deposited on top of a SiO$_2$ insulating layer can develop interesting thermoelectric power factors. We prepared 450-nm thick heavily boron doped polysilicon layers, setting the initial boron content in the film to be in excess of the boron solubility in polycrystalline silicon at 1000 °C. Isochronal thermal annealings were then used to modify the B$_{Si}$ cont…
The design of beta-Ga2O3-based modulation doped field effect transistors (MODFETs) is discussed with a focus on the role of self-heating and resultant modification of the electron mobility profile. Temperature- and doping-dependent model of the electron mobility as well as temperature- and orientation-dependent approximations of the thermal conductivity of beta-Ga2O3 are presented. A decrease in drain current was attributed to a position-dependent mobility reduction caused by a coupled self-heating mechanism and a high electric-field mobility reduction mechanism. A simple thermal management so…
In correlated electrons system, quantum melting of electronic crystalline phase often gives rise to many novel electronic phases. In cuprates superconductors, melting the Mott insulating phase with carrier doping leads to a quantum version of liquid crystal phase, the electronic nematicity, which breaks the rotational symmetry and exhibits a tight twist with high-temperature superconductivity. Recently, the electronic nematicity has also been observed in Fe-based superconductors. However, whether it shares a similar scenario with its cuprates counterpart is still elusive. Here, by measuring nu…
We studied the relationship between the charge doping and the correlation, and its effects on the spectral function of the BaFe$_2$As$_2$ compound in the framework of the density functional theory combined with the dynamical mean field theory (DFT+DMFT). The calculated mass enhancements showed that the electronic correlation varies systematically from weak to strong when moving from the heavily electron-doped regime to the heavily hole-doped one. Since the compound has a multi-orbital nature, the correlation is orbital-dependent and it increases as hole-doping increases. The Fe-3d$_{xy}$ (xy) …
The layers of a high-temperature novel GaAs:Fe diluted magnetic semiconductor (DMS) with an average Fe content up to 20 at. % were grown on (001) i-GaAs substrates using a pulsed laser deposition in a vacuum. The transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy investigations revealed that the conductive layers obtained at 180 and 200 C are epitaxial, do not contain any second-phase inclusions, but contain the Fe-enriched columnar regions of overlapped microtwins. The TEM investigations of the non-conductive layer obtained at 250 C revealed the embedded coherent …
We uncover the origin of blue luminescence (BL) peak in Mg doped GaN thin film using a combination of experimental X-ray absorption near edge spectroscopy (XANES), first-principles calculations based on density functional theory and full multiple scattering theoretical analysis of various possible defect complexes and their XANES signatures. We demonstrate that a defect complex composed of Mg substituted at Ga site (MgGa) and Mg at interstitial site (Mgi) is primarily responsible for the observed BL by Donor-Acceptor Pair transition (DAP) associated with a deep donor state in the gap. It corre…
We find that Ag-interstitial ($Ag_I$) acts as an electron donor and plays an important role in Ag-excess doped polycrystalline PbTe thermoelectric materials. When Ag is heavily doped in PbTe, the neutral (Ag-Ag) dimer defect is formed at the Pb-site and the environment becomes Pb-rich/Te-poor condition. Then the positively ionized Ag interstitial ($Ag_I^+$) defect becomes the major defect under Pb-rich condition. Due to the small formation energy and small diffusion barrier of $Ag_I^+$, Ag can be easily dissolved into the PbTe matrix. The temperature behavior of the Ag defect formation energy …
We demonstrated experimentally a direct way to probe a hidden propensity to the formation of spin density wave (SDW) in a non-magnetic metal with strong Fermi surface nesting. Substituting Fe for a tiny amount of Cu (1%) induced an incommensurate magnetic order below 20 K in heavily-overdoped La2-xSrxCuO4 (LSCO). Elastic neutron scattering suggested that this order cannot be ascribed to the localized spins on Cu or doped Fe. Angle-resolved photoemission spectroscopy (ARPES), combined with numerical calculations, revealed a strong Fermi surface nesting inherent in the pristine LSCO that likely …
Electronic interactions associated with atomic adsorbates on transition metal dichalcogenides such as MoS2 can induce massive electronic reconstruction that results in the formation of a new type of heavily doped transition metal dichalcogenide that exhibits characteristics of a two-dimensional electron gas. The impact of quantum confinement and reduced dimensionality on the carrier dynamics in such two-dimensional systems is at present not known, but is of paramount importance if they are to find application in optoelectronic devices. Here we show by a combination of angle-resolved photoemiss…
