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Ge-doped famatinites Cu3Sb1−yGeyS4 (0 ≤ y ≤ 0.1) were prepared by mechanical alloying and hot pressing. The phase transition, microstructure, charge transport properties and thermoelectric properties were examined in accordance with the Ge content. The famatinites were maintained as a single phase with a tetragonal structure at temperatures below their melting point without secondary phases. The melting points of Cu3SbS4 and Cu3Sb0.92Ge0.08S4 were 817 and 819 K, respectively. The hot-pressed specimens exhibited high relative densities of 98.3–99.5%. The a-axis and c-axis were decreased from 0.5386 to 0.5378 nm and from 1.0744 to 1.0719 nm, respectively, by doping Sb sites with Ge. Both intrinsic and Ge-doped famatinites exhibited positive Hall and Seebeck coefficients. The carrier concentration and mobility of Cu3SbS4 were 2.2 × 1018 cm−3 and 1.6 cm2 V−1 s−1, but those of Ge-doped specimens increased to (0.4–3.3) × 1019 cm−3 and 29–71 cm2V−1 s−1, respectively. Cu3SbS4 exhibited non-degenerate semiconductor characteristics and demonstrated a dimensionless figure of merit, ZT, of 0.1 at 623 K owing to a power factor of 0.14 m Wm−1 K−2 and a thermal conductivity of 0.62 Wm−1 K−1. However, the Ge-doped specimens exhibited degenerate semiconductor behaviors, and Cu3Sb0.92Ge0.08S4 exhibited the highest ZT of 0.55 at 623 K owing to a power factor of 0.64 m W m−1 K−2 and a thermal conductivity of 0.72 Wm−1 K−1.

The modulations of electronic band structure of Hf2CO2 MXene through substitution-doping approaches (two different substitution sites, i.e., C and O sites) are theoretically studied within the first-principles density functional theory. It is found that SiC-, GeC-, BNC-, and NFO-doped Hf2CO2 nanosheets remain semiconductor properties with a wide range of band gap, while NC/O-, BO-, PO-, and FO-doped Hf2CO2 nanosheets possess to degenerate semiconductor or metallic characters. The orbital contribution analysis indicates that the p states of dopants play an important role in modulating the electronic band structures of the doped Hf2CO2 nanosheets. Furthermore, negative solution energy and binding energy of the above doped systems indicate the feasibility of the doping technique. We hope that these results can provide a theoretical basis to engineer the band gap of Hf2CO2 MXene materials and even guide these materials design and optimization in the applications of electronics.

Disorder arising from random locations of charged donors and acceptors introduces localization and diffusive motion that can lead to constructive electron interference and positive magnetoconductivity. At very low temperatures, 3D theory predicts that the magnetoconductivity is independent of temperature or material properties, as verified for many combinations of thin-films and substrates. Here, we find that this prediction is apparently violated if the film thickness d is less than about 300 nm. To investigate the origin of this apparent violation, the magnetoconductivity was measured at temperatures T = 15 – 150 K in ten, Sn-doped In2O3 films with d = 13 – 292 nm, grown by pulsed laser deposition on fused silica. We observe a very strong thickness dependence which we explain by introducing a theory that postulates a second source of disorder, namely, non-uniform interface-induced defects whose number decreases exponentially with the interface distance. This theory obeys the 3D limit for the thickest samples and yields a natural figure of merit for interface disorder. It can be applied to any degenerate semiconductor film on any semi-insulating substrate. Disorder in semiconductors may lead to quantum interference and positive magnetoconductivity, whose maximum value in 3D is independent of material properties. Here, an apparent violation of this upper bound, in Sn-doped In2O3 films on fused silica, is explained by a model that accounts for additional disorder close to the interface.

Li3Sb has two polymorphs crystallizing in a face-centered cubic cell (c-Li3Sb; BiF3 structure type; space group Fmm) and in a hexagonal unit cell (h-Li3Sb; Na3As structure type; space group P63/mmc). c-Li3Sb was predicted to be a promising thermoelectric material based on recent first-principles studies; however, the experimental transport characteristics have remained unknown so far. Herein, successful preparation of c-Li3Sb is reported by stress-induced mechanochemical synthesis (high-energy ball milling) along with its high-temperature thermoelectric properties. Hexagonal Li3Sb (h-Li3Sb) was revealed to be the stable phase at ambient conditions, while it starts unexpectedly transforming to c-Li3Sb by ball milling or under 60 MPa applied pressure at room temperature. The transport properties measurements performed on two polycrystalline specimens evidence that c-Li3Sb behaves as a p-type degenerate semiconductor due to the formation of Li vacancies. In agreement with lattice dynamics calculations, c-Li3Sb exhibits very low lattice thermal conductivity despite the lightweight of Li. A zT value of around 0.3 was obtained at 550 K. Modelling suggests that the hole concentration should be reduced through aliovalent substitutions or under Li-rich conditions for further optimization. Although the strong air sensitivity of Li3Sb makes its use in thermoelectric applications challenging, this simple superionic binary provides an attractive experimental platform to elucidate the effect of stress/pressure on phase transitions as well as that of Fermi surface complexity on thermoelectric properties.

Kesterite-structured phase have attracted considerable interest as earth-abundant photovoltaic and thermoelectric materials. For the kesterite, Cu2ZnGeSe4, we have established a direct link between anomalies in the temperature dependence of transport properties and an order-disorder transition. Powder neutron diffraction as a function of temperature, reveals an order-disorder transition at 473 K, involving disordering of copper and zinc cations over three crystallographic positions. Vacancies are simultaneously created on the copper-ion sub-lattice, indicative of the concomitant onset of copper-ion mobility. Differential scanning calorimetry data show a weak thermal signature in this temperature region, typical of a second-order phase transition, which is consistent with the absence of anomalies in the temperature dependence of the unit cell volume. The partial melting of the copper-ion sub-lattice induces a transition in the electrical-transport properties. The changes in electrical resistivity and Seebeck coefficient suggest this involves a transition from a conventional, activated semiconductor, to a degenerate semiconductor. The entry of an increasing fraction of the copper-ion sub-lattice into a liquid-like state is reflected in a reduction in thermal conductivity above 473 K. The order-disorder phase transition identified here has consequences for the performance of photovoltaic and thermoelectric devices based on kesterites.

Conductive coordination polymers (CPs) have potential in a wide range of applications because of their inherent structural and functional diversity. Three electrically conductive CPs (Cux C6 S6 , x=3, 4 or 5.5) derived from the same organic linker (benzenehexathiol) and metal node (copper(I)) were synthesized and studied. Cux C6 S6 materials are organic-inorganic hybrid copper sulfides comprising a π-π stacking structure and cooper sulfur networks. Charge-transport pathways within the network facilitate conductivity and offer control of the Fermi level through modulation of the oxidation level of the non-innocent redox-active ligand. Two Cux C6 S6 (x=4 or 5.5) CPs display high electrical conductivity and they feature a tunable structural topology and electronic structure. Cu4 C6 S6 and Cu5.5 C6 S6 act as degenerate semiconductors. Moreover, Cu5.5 C6 S6 is a p-type thermoelectric material with a ZT value of 0.12 at 390 K, which is a record-breaking performance for p-type CPs.

We present a semiconductor-based optoelectronic switch based on active modulation of surface plasmon polaritons (SPPs) at lattice-matched indium gallium arsenide (In0.53Ga0.47As) degenerately doped pn++ junctions. The experimental device, which we refer to as a surface plasmon polariton diode (SPPD), is characterized electrically and optically, showing far-field reflectivity modulation for mid-IR wavelengths. Self-consistent electro-optic multiphysics simulations of the device’s electrical and electromagnetic response have been performed to estimate bias-dependent modulation and switching times. The numerical model shows a strong agreement with the experimental results, validating the claim of excitation and modulation of SPPs at the junction, thus potentially providing a new pathway toward fast optoelectronic devices.

In this paper, we report on the transport and magnetic properties of layered oxytelluride BiCuTeO polycrystals with slight mixed valence of Cu. The temperature-dependent electrical resistivity reveals degenerate semiconductor behavior (similar to metals). Under the action of an external magnetic field, the BiCuTeO polycrystal sample exhibits unsaturated magnetic resistance (MR) of about 8% at 2 K and 9 Tesla. The Hall resistivities show nonlinear behavior, suggesting the coexistence of both electrons and holes in the sample. When the temperature is decreased to around 110 K, the dominant carriers are changed from electrons to holes from the viewpoint of electrical transport, which is supported by the calculated temperature-dependent Fermi energy. Meanwhile, at low temperatures (

International audience; S-based semiconductors are attracting attention as environmentally friendly materials for energy-conversion applications because of their structural complexity and chemical flexibility. Here, we show that the delicate interplay between the chemical composition and cationic order/disorder allows one to stabilize a new sphalerite derivative phase of cubic symmetry in the Cu-Sn-S diagram: Cu22Sn10S32. Interestingly, its crystal structure is characterized by a semiordered cationic distribution, with the Cu-Sn disorder being localized on one crystallographic site in a long-range-ordered matrix. The origin of the partial disorder and its influence on the electronic and thermal transport properties are addressed in detail using a combination of synchrotron X-ray diffraction, Mössbauer spectroscopy, transmission electron microscopy, theoretical modeling, and transport property measurements. These measurements evidence that this compound behaves as a pseudogap, degenerate p-type material with very low lattice thermal conductivity (0.5 W m-1 K-1 at 700 K). We show that localized disorder is very effective in lowering κ(L) without compromising the integrity of the conductive framework. Substituting pentavalent Sb for tetravalent Sn is exploited to lower the hole concentration and doubles the thermoelectric figure of merit ZT to 0.55 at 700 K with respect to the pristine compound. The discovery of this semiordered cubic sphalerite derivative Cu22Sn10S32 furthers the understanding of the structure-property relationships in the Cu-Sn-S system and more generally in ternary and quaternary Cu-based systems.

Various Sn-doped famatinite (Cu3Sb1−ySnyS4, 0 ≤ y ≤ 0.1) specimens were prepared by employing a mechanical alloying and hot-pressing method. The phase transitions, microstructures, and thermoelectric properties, i.e., the electrical conductivity, Seebeck coefficient, power factor, thermal conductivity, Lorenz number, and figure of merit, were examined. The famatinite phase with a tetragonal structure was stable below its melting point, as no secondary phases were present; however, it transformed to skinnerite Cu3SbS3 at higher temperatures. Sn doping reduced the melting point from 817 K (Cu3SbS4) to 815 K (Cu3Sb0.92Sn0.08S4). Hot-pressed compacts exhibited relative densities of 97.1–99.5%. Because Sn replaced at Sb sites, the a-axis slightly reduced, and the c-axis increased. Cu3SbS4 exhibited non-degenerate semiconductor behavior, and possessed a low dimensionless figure of merit (ZT) of 0.1 at 623 K; these phenomena were products of the power factor of 0.14 mW m−1 K−2 and thermal conductivity of 0.62 W m−1 K−1. Conversely, the Sn-doped specimens exhibited degenerate semiconductor characteristics. As the Sn content increased, the electrical and thermal conductivities and power factor increased, whereas the Seebeck coefficient decreased. The thermoelectric performance was significantly enhanced by Sn doping. The highest ZT (0.67 at 623 K) was obtained for Cu3Sb0.92Sn0.08S4, and it was a product of implementing a power factor of 0.94 mW m−1 K−2 and thermal conductivity of 0.86 W m−1 K−1.

Solid solutions of cadmium in niobium and NbCd2 phase are formed by magnetron sputtering and coprecipitation on substrates moving relative to the flow of Nb and Cd particles. The NbCd2 phase can be described by a tetragonal unit cell with the parameters a = 0.84357 nm, c = 0.54514 nm, and c/a = 0.6426. A very high hole concentration in NbCd2 is established by studying the coating absorption and transmission spectra corresponding to the intermetallic-compound composition near the fundamental absorption edge, determining the band gap, and measuring the carrier mobility. Such a concentration is characteristic of a strongly degenerate semiconductor or metal. The band gap is determined to be 1.26 eV. The variation in the concentration of carriers and their mobility depending on the cadmium concentration in coatings of the Nb–Cd system confirms the occurrence of the NbCd2 phase.

The amplitude modulation of weakly nonlinear electrostatic solitary waves is investigated using standard quantum hydrodynamic model with multiple scale perturbation technique by deriving a nonlinear Schrodinger equation for ultrarelativistic degenerate semiconductor quantum plasma. Due to nonlinear development of amplitude of electrostatic solitary waves, stable and unstable wave packets are generating and it is numerically analyzed that critical wave number separating stable and unstable wave packets is significantly dependent upon ultrarelativistic parameter, quantum Bohm potential, degenerate pressure, hole-electron mass ratio, and hole-electron temperature ratio. It is seen that critical wave number is varying in a different semiconductor material. Further instability growth characteristic is also examined for different semiconductors. In linear analysis, a dispersion relation has been evaluated analytically and the nature of two wave modes (slow frequency and fast frequency) is studied by varying different plasma parameters.

PbS2 and Pb0.9Ag0.1S2 were prepared through the reaction of PbS with excess sulfur (and silver) at 4 GPa and 600 °C. PbS2 crystallizes in the CuAl2 structure type, (I4/mcm (#140), a = 6.1106(5) A, c = 7.4949(6) A, Z = 4), determined by single crystal X-ray diffraction. Its structure consists of layers of [S2]2- dimers and Pb2+ in square antiprismatic coordination – a rare structure type for metal dichalcogenides. Electronic structure calculations suggest that the material should be an indirect band gap semiconductor. Consistent with the calculations, the temperature-dependent resistivity of undoped PbS2 is that of a degenerate semiconductor, while the Ag-doped material shows metallic temperature dependent resistivity down to 2 K. The materials are both diamagnetic. For the Ag-doped material, the Seebeck coefficient is small and shows nearly linear temperature-dependent behavior from 50 to 250 K.

The binary Ta–N chemical system includes several compounds with notable prospects in microelectronics, solar energy harvesting, and catalysis. Among these, metallic TaN and semiconducting Ta3N5 have garnered significant interest, in part due to their synthetic accessibility. However, tantalum sesquinitride (Ta2N3) possesses an intermediate composition and largely unknown physical properties owing to its metastable nature. Herein, Ta2N3 is directly deposited by reactive magnetron sputtering and its optoelectronic properties are characterized. Combining these results with density functional theory provides insights into the critical role of oxygen in both synthesis and electronic structure. While the inclusion of oxygen in the process gas is critical to Ta2N3 formation, the resulting oxygen incorporation in structural vacancies drastically modifies the free electron concentration in the as-grown material, thus leading to a semiconducting character with a 1.9 eV bandgap. Reducing the oxygen impurity concentration via post-synthetic ammonia annealing increases the conductivity by seven orders of magnitude and yields the metallic characteristics of a degenerate semiconductor, consistent with theoretical predictions. Thus, this inverse oxygen doping approach – by which the carrier concentration is reduced by the oxygen impurity – offers a unique opportunity to tailor the optoelectronic properties of Ta2N3 for applications ranging from photochemical energy conversion to advanced photonics., Metastable Ta2N3 with bixbyite structure is directly deposited by reactive magnetron sputtering. Concerted experimental and computational efforts reveal the crucial role of oxygen impurity in both the synthesis and in tuning the electronic structure.

International audience; Regardless of the complexity of the phase diagram of the Cu–Sn–S system, several compositions near the prototypical mohite Cu2SnS3 have arisen as potential non-toxic, earth-abundant and cost-efficient photovoltaic and thermoelectric materials. In this work, we revisited the Cu2+xSn1−xS3 system and discovered a monoclinic (C2) ordered sphalerite derivative member, Cu5Sn2S7. Using a combination of synchrotron diffraction and spectroscopy, transmission electron microscopy, precession-assisted electron diffraction tomography, Mössbauer spectroscopy, first principles calculations and transport properties measurements, we discuss the structure–thermoelectric properties relationships and clarify the interesting crystal chemistry in this system. The ternary sulfide Cu5Sn2S7 exhibits a degenerate semiconducting behavior with exceptionally high hole mobility originating from the interplay between atomic ordering and charge delocalization.

The influences of transition metals (Sc, Ti, V, Cr and Mn) doping at different distances on the stability, electronic structure, conductivity and optical properties of CdS are studied by using VASP code. The results show that the Cr-doped CdS is easy to form, followed by V, Ti, Sc and Mn. The next nearest-neighbor doping is the most stable in each transition metal-doped system. The band-gaps gradually decrease with the order of Sc, Ti, V, Cr, Mn-doping, all doped systems become the degenerate semiconductor. Doping not only enhances conductivity, but also improves photocatalytic performance, especially Mn-doped CdS has obvious improvement. The absorption intensity in the visible light range of the single-doping is more than that of two atoms doped system in different distances, of which Mn and Cr single-doping are the most prominent.

We report on the evolution of the average and depth-dependent magnetic order in thin-film samples of biaxially stressed and electron-doped EuTiO3 for samples across a doping range < 0.1 to 7.8 × 1020 cm-3. Under an applied in-plane magnetic field, the G-type antiferromagnetic ground state undergoes a continuous spin-flop phase transition into in-plane, field-polarized ferromagnetism. The critical field for ferromagnetism slightly decreases with an increasing number of free carriers, yet the field evolution of the spin-flop transition is qualitatively similar across the doping range. Unexpectedly, we observe interfacial ferromagnetism with saturated Eu2+ moments at the substrate interface at low fields preceding ferromagnetic saturation throughout the bulk of the degenerate semiconductor film. We discuss the implications of these findings for the unusual magnetotransport properties of this compound.

A semiconductor glass with superior flexibility, exceptional carrier mobility, and high room temperature thermoelectric properties., Most crystalline inorganic materials, except for metals and some layer materials, exhibit bad flexibility because of strong ionic or covalent bonds, while amorphous materials usually display poor electrical properties due to structural disorders. Here, we report the simultaneous realization of extraordinary room temperature flexibility and thermoelectric performance in Ag2Te1–xSx–based materials through amorphization. The coexistence of amorphous main phase and crystallites results in exceptional flexibility and ultralow lattice thermal conductivity. Furthermore, the flexible Ag2Te0.6S0.4 glass exhibits a degenerate semiconductor behavior with a room temperature Hall mobility of ~750 cm2 V−1 s−1 at a carrier concentration of 8.6 × 1018 cm−3, which is at least an order of magnitude higher than other amorphous materials, leading to a thermoelectric power factor also an order of magnitude higher than the best amorphous thermoelectric materials known. The in-plane prototype uni-leg thermoelectric generator made from this material demonstrates its potential for flexible thermoelectric device.

The van Roosbroeck system models current flows in (non-)degenerate semiconductor devices. Focusing on the stationary model, we compare the excess chemical potential discretization scheme, a flux approximation which is based on a modification of the drift term in the current densities, with another state-of-the-art Scharfetter–Gummel scheme, namely the diffusion-enhanced scheme. Physically, the diffusion-enhanced scheme can be interpreted as a flux approximation which modifies the thermal voltage. As a reference solution we consider an implicitly defined integral flux, using Blakemore statistics. The integral flux refers to the exact solution of a local two point boundary value problem for the continuous current density and can be interpreted as a generalized Scharfetter–Gummel scheme. All numerical discretization schemes can be used within a Voronoi finite volume method to simulate charge transport in (non-)degenerate semiconductor devices. The investigation includes the analysis of Taylor expansions, a derivation of error estimates and a visualization of errors in local flux approximations to extend previous discussions. Additionally, drift-diffusion simulations of a p–i–n device are performed.

In this work we investigate crystal structure, morphology, and composition of CuI films produced in different modes of SILAR on glass plates and on flexible poly(ethylene terephthalate) (PET) substrates in connection with their transport properties, and with electrical and thermoelectric properties as a whole. Temperature dependences of resistivity for most CuI films have the crossover from semiconducting to metallic behavior with increasing temperature. The semiconductor carrier transport occurs in CuI films through nearest neighboring hopping. Metallic transport in CuI films carried out in accordance with the ionized impurity scattering and the carrier–carrier scattering model.

Zinc oxide (ZnO) is a semiconductor with promising electrical and optical properties. Pure ZnO is an n-type degenerate semiconductor. It is almost entirely transparent in the optical region of the electromagnetic spectrum. In this work sol–gel spin-coating method was used to grow a ZnO thin film from Zinc acetate decomposition. The optical properties of the thin film were extracted and investigated. A ZnO/p-Si heterostructure solar cell was realized using this film and its performance (efficiency) was found to be quite poor. A numerical procedure is used to elucidate this poor performance. A first step is to use the extracted optical parameters in the simulation. However, these parameters did not lead to the reproduction of measured current-voltage and figures of merit of the solar cell by simulation when other parameters of ZnO are taken from literature. It was therefore considered that ZnO is similar to an amorphous semiconductor with a continuous distribution of states in its band gap. The density of states model used is composed of tail bands and Gaussian distribution deep level bands. Eventually, and by adjusting the constituents of the band gap states and by increasing the surface recombination velocity in ZnO/p-Si interface, it was possible to obtain a good agreement between simulated and measured J-V characteristics of this solar cell.

Pulsed electron beam deposition (PED) was used to grow indium oxide thin films on c-cut sapphire single crystalline substrates between room temperature and 500 °C under oxygen gas. A slight difference in oxygen pressure during the PED growth (from 2 × 10−2 to 1.3 × 10−2 mbar) has strong effects on the electrical and optical film properties. The indium oxide thin films grown in these conditions changed from a non-degenerate semiconducting behaviour (at 2 × 10−2 mbar) to a degenerate semiconductor one (at 1.3 × 10−2 mbar), with a metal-insulator transition at 149 K. This crossover from strong to weak localization, evidenced in the temperature dependent resistivity curves, may be due to the effects of a structural disorder in such films. The direct optical band gap was estimated from transmission spectra taking into account non-degenerate/degenerate behaviour.

A heterostructure promising for designing a backward diode is formed from a zinc-oxide nanorod array and a nanostructured copper-iodide film. The effect of modes of successive ionic layer adsorption and reaction (SILAR) deposition and the subsequent iodization of CuI films on smooth glass, mica, and fluorine-doped tin oxide (FTO) substrates and on the surface of electrodeposited nanostructured zinc-oxide arrays on the film structure and electrical and optical properties is investigated. A connection between the observed variations in the structure and properties of this material and intrinsic and iodination-induced point defects is established. It is found that the cause and condition for creating a backward-diode heterostructure based on a zinc-oxide nanoarray formed by pulsed electrodeposition and a copper-iodide film grown by the SILAR method is the formation of a p+-CuI degenerate semiconductor by the excessive iodination of layers of this nanostructured material through its developed surface. The n-ZnO/p+-CuI barrier heterostructure, which is fabricated for the first time, has the I–V characteristic of a backward diode, the curvature factor of which (γ = 12 V–1) confirms its high Q factor.

SnS is a promising photovoltaic semiconductor owing to its suitable band gap energy and high optical absorption coefficient for highly efficient thin film solar cells. The most significant carnage is demonstration of n-type SnS. In this study, Cl-doped n-type single crystals were grown using SnCl2 self-flux method. The obtained crystal was lamellar, with length and width of a few millimeters and thickness ranging between 28 and 39 μm. X-ray diffraction measurements revealed the single crystals had an orthorhombic unit cell. Since the ionic radii of S2– and Cl– are similar, Cl doping did not result in substantial change in lattice parameter. All the elements were homogeneously distributed on a cleaved surface; the Sn/(S + Cl) ratio was 1.00. The crystal was an n-type degenerate semiconductor with a carrier concentration of ∼3 × 1017 cm–3. Hall mobility at 300 K was 252 cm2 V–1 s–1 and reached 363 cm2 V–1 s–1 at 142 K.

We report the synthesis, characterization and thermoelectric properties of lead-free AgSnmSbSe2Tem (m = 2 and 10) systems. Powder X-ray diffraction patterns and Rietveld refinement results were consistent with phases belonging to the P m 3 ¯ m space group. The microstructures and morphologies of these systems were investigated using scanning electron microcopy (SEM) and high-resolution transmission electron microscopy (HRTEM). Parallelepiped bars for transport measurements were prepared using two methods: the classical method (CM) from melted samples and the spark plasma sintering (SPS). The AgSnmSbSe2Tem (m = 2 and 10) systems exhibited typical degenerate semiconductor behavior, with a carrier concentration of approximately +1021 cm−3. We determined that the Seebeck coefficient can be substantially increased from approximately +40 μV K−1 (CM) to +70 μV K−1 (SPS) in AgSn2SbSe2Te2 at room temperature. Consequently, the power factor (S2σ) was ∼22 μW cm−1 K−2. On the basis of the electrical and thermal transport properties, ZT values of ∼0.10 were obtained at room temperature.

There had been tremendous growth in the field of Integrated circuits (ICs) in the past fifty years. Scaling laws mandated both lateral and vertical dimensions to be reduced and a steady increase in doping densities. Most of the modern semiconductor devices have invariably heavily doped regions where Fermi-Dirac Integrals are required. Several attempts have been devoted to developing analytical approximations for Fermi-Dirac Integrals since numerical computations of Fermi-Dirac Integrals are difficult to use in semiconductor devices, although there are several highly accurate tabulated functions available. Most of these analytical expressions are not sufficiently suitable to be employed in semiconductor device applications due to their poor accuracy, the requirement of complicated calculations, and difficulties in differentiating and integrating. A new approximation has been developed for the Fermi-Dirac integrals of the order 1/2 by using Prony's method and discussed in this paper. The approximation is accurate enough (Mean Absolute Error (MAE) = 0.38%) and easy enough to be used in semiconductor device equations. The new approximation of Fermi-Dirac Integrals is applied to a more generalized Einstein Relation which is an important relation in semiconductor devices.

This work presents a study of the temperature dependence on the electronic transport properties for p-type (Bi0.5Sb1.5Te3) and n-type (Bi1.5Sb0.5Te3) pellets prepared by spark plasma sintering from ball-milled powders. Seebeck coefficient and electrical resistivity displayed a metallic behavior in both samples in the temperature range from 20 to 300 K, resembling to the carrier transport of a degenerate semiconductor. The magnitude of the Seebeck coefficient of the n-type sample was lower than that p-type sample, which was attributed to bipolar conduction. That is, in the n-type sample lie an acceptor level and a donor level, generating simultaneously electrons and holes. The donor level that promotes the n-type conductivity in Bi1.5Sb0.5Te3 could be attributed to the SbBi antisite defect as reveled by crystalline cell simulations.

P-type Bi2−xSbxTe3:Cum (x = 1.5–1.7 and m = 0.002–0.003) solid solutions were synthesized using encapsulated melting and were consolidated using hot pressing. The effects of Sb substitution and Cu doping on the charge transport and thermoelectric properties were examined. The lattice constants decreased with increasing Sb and Cu contents. As the amount of Sb substitution and Cu doping was increased, the electrical conductivity increased, and the Seebeck coefficient decreased owing to the increase in the carrier concentration. All specimens exhibited degenerate semiconductor characteristics and positive Hall and Seebeck coefficients, indicating p-type conduction. The increased Sb substitution caused a shift in the onset temperature of the intrinsic transition and bipolar conduction to higher temperatures. The electronic thermal conductivity increased with increasing Sb and Cu contents owing to the increase in the carrier concentration, while the lattice thermal conductivity slightly decreased due to alloy scattering. A maximum figure of merit, ZTmax = 1.25, was achieved at 373 K for Bi0.4Sb1.6Te3:Cu0.003.

We have fabricated bulk clathrate materials Ba8-xEuxCu6Si40 via high-temperature and high-pressure (HPHT) method, and the structure combined with thermoelectric properties were characterized in detail. Even more surprisingly, this method took just an hour to synthesize clathrates with BaSi2 and EuSi2 as starting materials. The substitution of Ba by Eu has great impact on its microstructure and inevitably alters thermoelectric properties. Temperature dependent thermoelectric parameters have been measured from 320 K to 720 K. The measurements of electrical properties showed the degenerate semiconductor behavior. A minimum thermal conductivity of 1.26 Wm−1K−1 was reached at 720 K for Ba8Cu6Si40. The multi-scale hierarchical microstructure, from atomic scale to micro scale, can effectively enhance the phonon scattering, thus reducing the lattice thermal conductivity.

The computational modeling within a density functional theory was applied for simulations of electronic spectra and calculations of structural and energy characteristics of the cubic double perovskite oxides Sr2Mg1−xNixMoO6–δ, where x = 0, 0.5, and 1. The oxygen stoichiometric molybdates are antiferromagnetic semiconductors with an energy gap near 2 eV. The energy-based arguments show that anti-site cation disorder may contribute to the structural stability of the molybdates. It is found that nickel doping is favorable for mitigated chemical expansion. The replacement of magnesium by nickel is accompanied by the contribution of Ni3d states to the valence band while leaving hybrid Mo4d-O2p states in the conduction band virtually unchanged. It is shown that the compounds under study are thermodynamically unstable in heavily reducing conditions which is confirmed by experimental results. The appearance of oxygen deficiency in Sr2Mg1−xNixMoO6–δ results in the formation of oxygen vacancy associated donor states near the bottom of the conduction band and the transition from the intrinsic to degenerate semiconductor. It is suggested that the influence of nickel dopants on the energy and density of the donor states may help to explain variations of the conducting properties with doping level.