Structure and Optical Properties of Chalcogenide Glassy As–Ge–Te Semiconductor

Semiconductors - The structure and optical properties of a chalcogenide glassy As–Ge–Te semiconductor film are studied by X-ray diffraction analysis, Raman spectroscopy, and optical...     

Study of Ge–Sb–Te and Ge–Te cocktail sources to improve an efficiency of multi-line CVD for phase change memory

In this study, we investigated a deposition of Ge–Sb–Te (GST) and Ge–Te (GT) phase change films using GST and GT cocktail sources to improve the efficiency of multi-line chemical vapor deposition (CVD). Cocktail sources were compounded with the chemical precursors Ge(NMe₂)₄, Sb(ⁱPr)₃, and Te(^tBu)₂. We controlled experimental conditions, such as deposition and source heating temperature and the number of precursors, and measured their influence using several methods of analysis. Precursor compatibility in the chemical cocktail source was pretested by thermogravimetric analysis. In various experimental conditions, film deposition behavior was observed by plane view and cross-sectional view of scanning electron microscopy and surface roughness was observed by atomic force microscopy. The grain size of the films was analyzed using the software program Image J. The crystallinity at each deposition temperature was measured by X-ray diffraction and was supported by high-resolution transmission electron microscopy. Competitive deposition of the cocktail source was observed at a low deposition temperature. The origin of this phenomenon is discussed in relation to the energy of the CVD process and a solution is proposed. We suggest that this cocktail CVD concept might be a new approach to multi-element deposition in memory processes.     

Ultrathin Conductive Interlayer with High-Density Antisite Defects for Advanced Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are promising next-generation rechargeable batteries due to thier high energy density, low cost, and environmental friendliness. However, the extremely low electrical conductivity of sulfur and the dissolution of polysulfides limit their actual electrochemical performances, especially in the case of high sulfur mass loading. Here, a new strategy based on intrinsic point defects of materials is proposed to simultaneously enhance the electrical conductivity of active material and regulate the migration of polysulfides. Taking advantage of ultrathin and lightweight Bi₂Te_2.7Se_0.3 (BTS) interlayers with high-density antisite defects on the separator surface, the Li–S battery with BTS interlayer shows a capacity of 756 mAh g⁻¹ at 2C and a low capacity decay rate of 0.1% over 300 cycles. The BTS interlayer can not only enhance the active material utilization but also improve capacity retention. The defect engineering strategy accompanied with facile method is promising for the development of advanced Li–S batteries for practical application.     

Composition effect on the structure and optical parameters of Ge–Se–Te thin films

The present work reported the influence of Ge content variation on the optical properties of Ge_xSe₅₀Te_50-x (x=0, 5, 15, 20, 35 at%). Vacuum thermal evaporation technique was employed to prepare amorphous Ge_xSe₅₀Te_50−x thin films. The stoichiometry of the chemical composition was checked by energy dispersive X-ray spectroscopy (EDX), whereas the thin films structure was determined by an X-ray diffraction and a scanning electron microscope (SEM). The optical absorption measurements were performed at room temperature in the wavelength range of 200–900 nm. Many optical constants were calculated for the studied thin films utilizing the optical absorption data. It was observed that the optical absorption mechanism follows the rule of the allowed direct transition. The optical band gap was found to increase from 2.31 to 2.60 eV as the Ge content increases from 0 to 35 at%. This result was explained in terms of the chemical bond approach.     

Structure and Optical Properties of Chalcogenide Glassy Semiconductors of the As–Ge–Se System

Semiconductors - The types of structural elements and chemical bonds forming an amorphous matrix of chalcogenide glassy semiconductors of the As–Ge–Se system and changes occurring in...     

Seebeck Effect in IV–VI Semiconductor Films and Quantum Wells

Theoretical calculations of the Seebeck coefficients of IV–VI semiconductors and quantum wells were performed, taking into account temperature-dependent band gaps, nonparabolicity, and anisotropy of effective masses in the framework of the Boltzmann equation. The Seebeck coefficient depends on both the density of states and a kinetic term determined from the balance between drift and diffusion currents. The theoretical Seebeck coefficients of PbTe and PbSe films were compared with experimental values, and excellent agreement was obtained. In lead-salt IV–VI materials with a positive temperature dependence of the band gap, the kinetic part becomes small or has a negative effect on the Seebeck coefficient. Strong enhancement of the Seebeck coefficient is expected theoretically in n-type PbTe/PbSe superlattices, resulting from the increase of the kinetic part due to the effective-mass difference between PbTe and PbSe.     

Dielectric Spectroscopy and Mechanism of the Semiconductor–Metal Phase Transition in Doped VO2:Ge and VO2:Mg Films

Semiconductors - The frequency dependences of the dissipation factor tanδ(f) and the Cole–Cole diagrams for germanium- and magnesium-doped vanadium-dioxide films in the range of...     

低损耗红外传输Ge30As10Se30Te30玻璃光纤的制造

利用改进的纯化技术和工艺技术制造Ｇｅ３０Ａｓ１０Ｓｅ３０Ｔｅ３０玻璃光纤，所制得的光纤在６．６μｍ波长的最低损耗达０．１１ｄＢ／ｍ。这是所报道的红外区任何碲（Ｔｅ）玻璃光纤的最低损耗。此外，这种光纤在５．２５￣９．５μｍ的损耗小于１ｄＢ／ｍ。     

Voltage oscillations in the case of the switching effect in thin layers of Ge–Sb–Te chalcogenides in the current mode

The I–V characteristics obtained for layers of chalcogenide vitreous semiconductor of the Ge–Sb–Te system in the current-generator mode are investigated. The instability region, i.e., the region of conductivity oscillations, observed in the case of the switching effect under conditions of a set current is revealed. The key parameters describing these oscillations and the conditions of their occurrence are investigated in detail. Analysis of the obtained data shows that, to explain the oscillations in the instability region, it is necessary to take into account an increase in the current density and the process of heat exchange between the current filament that arises in the film upon switching and the environment.     

Effect of the Samarium Impurity on the Local Structure of Se95Te5 Chalcogenide Glassy Semiconductor and Current Passage through Al–Se95Te5〈Sm〉–Te Structures

Semiconductors - The effect of samarium doping on the local structure and morphological features of the surface of a Se95Te5 chalcogenide glassy semiconductor film is investigated by X-ray...     

Giant Magnetoresistance in a Metal–Organic Semiconductor–Metal Structure

Semiconductors - The article presents the results of investigation of the giant magnetoresistance effect in a magnetic metal–organic semiconductor–non-magnetic metal structure with a...     

Structural and Dielectric Study of Thin Amorphous Layers of the Ge–Sb–Te System Prepared by RF Magnetron Sputtering

Semiconductors - The results of studying the structure and processes of dielectric relaxation in thin layers of Ge–Sb–Te are presented. The found permittivity dispersion and occurrence...     

Electron–Electron and Electron–Phonon Interactions in Graphene on a Semiconductor Substrate: Simple Estimations

The problem of epitaxial graphene formed on a semiconductor substrate is considered in the context of the extended Hubbard and Holstein–Hubbard models for electron–electron and electron–phonon interactions. The Haldane–Anderson model is chosen for the density of states of the substrate. Three regions of the phase diagram, specifically, spin- and charge-density waves and a spin- and charge-homogeneous paramagnetic state are considered. For a number of special cases used as examples, the similarities and differences of the electron states of graphene on semiconductor and metal substrates are demonstrated. It is shown that the main difference arises, if the Dirac point of graphene lies within the band gap of the semiconductor. Numerical estimations are performed for a SiC substrate.     

Achieving Superior Thermoelectric Performance in Ge4Se3Te via Symmetry Manipulation with I–V–VI2 Alloying

Although orthorhombic GeSe is predicted to have an ultrahigh figure of merit, ZT ≈ 2.5, up to now, the highest experimental value is ≈0.2 due to the low carrier concentration (n_H ≈ 10¹⁸ cm⁻³). Improving symmetry is an effective approach for enhancing the ZT of GeSe-based materials. With Te-alloying, Ge₄Se₃Te displays the two-dimensional hexagonal structure and high n_H ≈ 1.23 × 10²¹ cm⁻³. Interestingly, Ge₄Se₃Te transformed from the hexagonal into the rhombohedral phase with only ≈2% I–V–VI₂-alloying (I = Li, Na, K, Cu, Ag; V = Sb, Bi; VI = Se, Te). According to the calculated results of Ge_0.82Ag_0.09Bi_0.09Se_0.614Te_0.386 single-crystal grown via AgBiTe₂-alloying, it exhibits a higher valley degeneracy than the hexagonal Ge₄Se₃Te. For instance, AgBiTe₂-alloying induces a strong band convergence and band inversion effect, resulting in a significantly enhanced Seebeck coefficient and power factor with a similar n_H from 17 µV K⁻¹ and 0.63 µW cm⁻¹ K⁻² for pristine Ge₄Se₃Te to 124 µV K⁻¹ and 5.97 µW cm⁻¹ K⁻² for 12%AgBiTe₂-alloyed sample, respectively. Moreover, the sharply reduced phonon velocity, nano-domain wall structure, and strong anharmonicity lead to low lattice thermal conductivity. As a result, a record-high average ZT ≈0.95 over 323–773 K with an excellent ZT ≈ 1.30 is achieved at 723 K.     

Physicochemical Interactions in the GeSb2Te4–PbSb2Te4 System

Semiconductors - For the first time, the GeSb2Te4–PbSb2Te4 section of the GeTe–Sb2Te3–PbTe quasi-ternary system is investigated by complex methods of physicochemical analysis...     

MnQ2（Q=S,Se,Te）and [Mn（en）3]Te4 Structures and Their Semiconductor Properties

The solvo-thermal technique is used for the synthesis of [Mn(en)3]Te4 (I).The crystal structure has been determined by single crystal X-ray diffraction techniques.The crystal belongs to the monoclinic, space group p21/c with unit cell:a=0.8461(1),b=1.5653(2), c=1.4269(2)nm, α=90°,β=91.37(1) (3)°, γ=90°,V=1.8893(4)nm3,and Z=4.The results show that the structure contains a linear chain Zintl anion,[Te4]2-and a complex cation,[Mn(en)3]2+. Optical studies have been performed on the powder sample of I, suggesting that the compound is a semiconductor with a band gap of 0.73eV. The semiconductor properties for MnQ2(Q=S,Se,Te) and [Mn(en)3]Te4 have been discussed by molecular orbital theory.     

Ultrafast Dynamics of Photoinduced Electron–Hole Plasma in Semiconductor Nanowires

Experimental results obtained in a study of the effect of electron–hole plasma on the generation of terahertz (THz) radiation in semiconductor nanowires grown by metal-organic vapor-phase epitaxy (MOVPE) are presented. It is shown that the temporal dynamics of photoexcited charge carriers in semiconductor nanowires is determined by the transport of carriers, both electrons and holes, and by the time of capture of electrons and holes at surface levels.     

Defects Study in Hg x Cd1−x Te Infrared Photodetectors by Deep Level Transient Spectroscopy

At high temperature, infra-red focal plane arrays are limited by their performance in operability, detectivity D ^* or noise equivalent temperature difference. Trap characterization and defect studies are necessary to better understand these limitations at high temperature. In this paper, we use deep level transient spectroscopy to study electrically active defects in mercury cadmium telluride n ⁺/p diodes. The material investigated has a cut-off frequency (λ _c) of 2.5 μm at 180 K and p doping performed with mercury vacancy. Trap energy signatures as well as capture cross-section measurements are detailed. A low temperature hole trap close to midgap is observed in the range 150–200 K with an activation energy around 0.18 ± 0.025 eV. A high temperature hole trap is also observed in the range 240–300 K with an activation energy of 0.68 ± 0.06 eV. A hole capture cross-section of 10^?19 cm² is obtained for both traps. The nature of the defects and their correlation with dark current are discussed.