Electrical characteristics and memory behavior of Ge3N4GaAs MIS devices

MIS devices have been fabricated by the low temperature chemical vapor deposition of Ge₃N₄ on n-GaAs. From the current-voltage data an estimate of the Ge₃N₄ dielectric constant is made as 6.3 ± 0.2 and devices exhibit a breakdown field strength of ～ 5 × 10⁶ V/cm. Capacitance and conductance measurements have been performed to investigate the electrical characteristics of the Ge₃N₄GaAs interface. The interface properties of the devices are found to depend on the Ge₃N₄ deposition parameters. No major hysteresis is observed in the C-V plot and under large negative gate bias, the capacitance increases as the measurement frequency is lowered. Interface state distribution, evaluated from the conductance data, is found to have a minimum density of states of 2 × 10¹¹ cm^?2 eV^?1 with a distinct shoulder between 0.4 and 0.55 eV from the conduction band. This shoulder is assigned to an electron trap level and from thermally stimulated current measurements we obtained the density of traps as 3 × 10¹⁷ cm^?3.GaAs-MNOS devices have also been fabricated and their charge storage properties have been studied. Pulse voltages as large as 30–35 V are needed to write/erase the memory in the devices.     

Fast,Scalable Synthesis of Micronized Ge3N4@C with a High Tap Density for Excellent Lithium Storage

Nanostructuring has significantly contributed to alleviating the huge volume expansion problem of the Ge anodes. However, the practical use of nanostructured Ge anodes has been hindered due to several problems including a low tap density, poor scalability, and severe side reactions. Therefore, micrometer-sized Ge is desirable for practical use of Ge-based anode materials. Here, micronized Ge₃N₄ with a high tap density of 1.1 mg cm⁻² has been successfully developed via a scalable wet oxidation and a subsequent nitridation process of commercially available micrometer-sized Ge as the starting material. The micronized Ge₃N₄ shows much-suppressed volume expansion compared to micrometer-sized Ge. After the carbon coating process, a thin carbon layer (≈3 nm) is uniformly coated on the micronized Ge₃N₄, which significantly improves electrical conductivity. As a result, micronized Ge₃N₄@C shows high reversible capacity of 924 mAh g⁻¹ (2.1 mAh cm⁻²) with high mass loading of 3.5 mg cm⁻² and retains 91% of initial capacity after 300 cycles at a rate of 0.5 C. Additionally, the effectiveness of Ge₃N₄@C as practical anodes is comprehensively demonstrated for the full cell, showing stable cycle retention and especially excellent rate capability, retaining 47% of its initial capacity at 0.2 C for 12 min discharge/charge condition.     

Special features of the excitation spectra and kinetics of photoluminescence of the Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>:Er/Si structures with relaxed heterolayers

Luminescent properties of heteroepitaxial Si_{1 − x} Ge _x :Er/Si structures with relaxed heterolayers are studied. The results of combined studies of the excitation spectra and kinetics of photoluminescence (PL) are used to single out the components providing the largest contribution to the PL signal of the Si_{1 − x} Ge _x :Er/Si structures in the wavelength region of 1.54 μm. It is shown that relaxation of elastic stresses in the Si_{1 − x} Ge _x :Er heterolayer affects only slightly the kinetic characteristics of erbium luminescence and manifests itself in insignificant contribution of the defects and defect-impurity complexes to the luminescent response of the Si_{1 − x} Ge _x :Er/Si structures. In the excitation spectra of the erbium PL, special features related to the possibility of the rare-earth impurity excitation at energies lower than the band gap of the Si_{1 − x} Ge _x solid solution are revealed. It is shown that a peak the width of which depends on the band gap of the solid solution and the extent of its relaxation is observed in the excitation spectra of the erbium-related PL in the Si_{1 − x} Ge _x :Er/Si structures in the wavelength region of 1040–1050 nm. The observed specific features are accounted for by involvement of intermediate levels in the band gap of the Si_{1 − x} Ge _x :Er solid solution in the process of excitation of an Er³⁺ ion.     

An ab initio study of the structural,elastic, electronic,optical properties and phonons of the double perovskite oxides Sr2AlXO6 (X=Ta,Nb, V)

We report ab initio density functional theory calculations of the structural, elastic, electronic and optical properties of the double perovskite oxides Sr₂AlXO₆ (X=Ta, Nb, V). We have predicted a direct Г–Г band gap in Sr₂AlXO₆ (X=Ta, Nb) and an indirect Г–X band gap for Sr₂AlVO₆. The fundamental band gap increases linearly when the pressure is enhanced in the range 0–20 GPa. The frequency dependent of complex dielectric function, absorption, reflectivity and electron energy loss function were investigated in the range 0–40 eV. Features such as lattice constant, bulk modulus, elastic constants, band structure, total and local densities of states have been computed.     

Structural and Electronic Properties of Type I Clathrates M<Subscript>8</Subscript>Ga<Subscript>16</Subscript>Ge<Subscript>30</Subscript> (M = Ba,Sr, Yb) from First-Principles Calculations

In this work, the effects of filling atoms on the structural and electronic properties of type I clathrates M₈Ga₁₆Ge₃₀ (M = Ba, Sr, Yb) have been investigated by first-principles calculations. It is found that these alloys are all indirect-gap semiconductors, among which Yb₈Ga₁₆Ge₃₀ possesses the smallest band gap and the largest bulk modulus, and a unique feature of a sharp peak in the density of states (DOS) near the Fermi level, implying good potential as a thermoelectric material for band engineering. Moreover, calculations indicate direct chemical bonds between Yb and the nearest host Ga/Ge atoms, which can play an important role in the reduction of the lattice thermal conductivity via large off-center rattling of the Yb in the larger cage of the clathrate structure, suggesting that Yb₈Ga₁₆Ge₃₀ is of interest for future thermoelectric applications.     

Valence Band Studies of <Emphasis Type="Italic">p</Emphasis>- and <Emphasis Type="Italic">n</Emphasis>-Type Ba<Subscript>8</Subscript>Ga<Subscript>16</Subscript>Ge<Subscript>30</Subscript> Using High-Resolution Photoelectron Spectroscopy

The electronic states of p- and n-type Ba₈Ga₁₆Ge₃₀ (BGG) are studied by high-resolution x-ray photoelectron spectroscopy. In BGG, three bands are resolved in the valence band region. Theoretical calculations show that the three band structures in the valence band are mainly constructed by the Ge/Ga 4s and 4p wavefunctions with little contribution from Ba 5s, 5p, and 5d. The valence band around the Fermi level region of n-type BGG is sensitive to temperature, while that of p-BGG is stable when the temperature changes. The data indicate that the endohedral Ba in p- and n-type BGG rattle with different modes due to the different hybridization with the orbitals of the framework polyhedra.     

Structural,electronic and mechanical properties of RuO2 from first-principles calculations

The structural, electronic and mechanical properties of ruthenium oxide (IV) (RuO₂) in various space groups have been calculated using full-potential linear muffin-tin orbital method. The exchange and correlation potential is treated by local density approximation. The calculated ground state properties, including, lattice constants, internal parameters, bulk modulus and the pressure derivative of the bulk modulus are in good agreement with the available data. This compound is found to undergo a series of structural phase transitions under high pressure. The sequence of the structural phase transition is: rutile→marcasite→pyrite→fluorite that occurs at around 4.92, 22.9 and 100.6 GPa, respectively. The elastic constants C_ij for RuO₂ in its different structures are calculated using the total energy variation with strain technique. The polycrystalline elastic moduli, namely; shear modulus, Young's modulus, Poisson's ratio, sound velocities and Debye temperature were derived from the obtained single-crystal elastic constants. Band structure calculations show that this compound is a narrow band gap semiconductor with a gap of 0.47 eV in its fluorite structure. While for rutile, marcasite and pyrite structures, this compound exhibits metallic properties.     

A study of an Al-Ge3N4-Ge structure by the method of photo-capacitance-voltage characteristics

Results are reported of a study of a Ge-Ge₃N₄ interface by the method of capacitance-voltage characteristics, with the structure irradiated with photons of varied energy. The employed technique revealed trap levels in germanium nitride located at 0.75, 0.89, and 3.0 eV below the conduction-band bottom. A study of the current through the Ge-Ge₃N₄ structure yielded two levels in Ge₃N₄ at depths of 0.75 and 0.87 eV.     

Effects of Disordered Atoms and Nanopores on Mechanical Properties of β-Zn4Sb3: a Molecular Dynamics Study

Effects of disordered Zn atoms and nanopores on mechanical properties of β-Zn₄Sb₃ are studied by using the molecular dynamics (MD) method. Due to the influence of disordered Zn atoms in β-Zn₄Sb₃, the elastic modulus decreases from 90.85 GPa to 68.17 GPa, a decrease of 24.96%. The ultimate tensile stress decreases from 18.25 GPa to 9.96 GPa, a decrease of 45.42%. The fracture strain decreases from 32.7% to 20.8%, a decrease of 36.39%. Due to the influence of nanopores, the elastic modulus decreases with growing porosity, and the relationship between the elastic modulus and porosity leads to a scaling law. It seems that the porous radius and porous distribution are also important factors influencing the ultimate tensile stress and fracture strain, in addition to the porosity. However, our simulation results demonstrate that disordered Zn atoms and nanopores reduce the structural stability, dramatically decreasing the mechanical properties of β-Zn₄Sb₃.     

Density functional theory study of tin and titanium dioxides: Structural and mechanical properties in the tetragonal rutile phase

Structural and mechanical properties in rutile (tetragonal) phases of SnO₂ and TiO₂ are investigated by performing first-principle density functional theory (DFT) calculations. Generalized Gradient Approximation (GGA) potentials of electronic exchange and correlation part parameterized by Perdew–Burke–Ernzerhof (PBE) are used. Second order elastic stiffness constants, bulk modulus, first-derivative of bulk modulus, and pressure behavior of these mechanical properties are studied up to pressure of 10 GPa. Structural properties and elastic constants of SnO₂ and TiO₂ calculated in this study are compatible with experimental and other available theoretical studies. Electronic band gap energies of these semiconductors are also calculated. As expected, the calculated values by standard DFT calculations are underestimated in comparison to experimental values.     

Mechanical and electronic properties of Si,Ge and their alloys in P42/mnm structure

Structural, mechanical, and electronic properties of Si–Ge alloys in P4₂/mnm structure were studied using first-principles calculations by Cambridge Serial Total Energy Package (CASTEP) plane-wave code. The calculations were performed with the local density approximation and generalized gradient approximation in the form of Perdew–Burke–Ernzerhof, PBEsol. The calculated excess mixing enthalpy is positive over the entire germanium composition range. The calculated formation enthalpy shows that the Si–Ge alloys are unstable at 0 K; however, the alloys might exist at specified high temperature scale. The anisotropic calculations show that Si₁₂ in P4₂/mnm structure exhibits the greatest anisotropy in Poisson’s ratio, shear modulus, Young’s modulus and the universal elastic anisotropy index A^U, but Si₈Ge₄ has the smallest anisotropy. The electronic structure calculations reveal that Si₁₂ and Si–Ge alloys in P4₂/mnm structure are indirect band gap semiconductors, but Ge₁₂ in P4₂/mnm structure is a direct semiconductor.     

Boron Nitride Fibers Prepared from Symmetric and Asymmetric Alkylaminoborazines

The thermolysis of 2,4,6‐[(CH₃)₂N]₃B₃N₃H₃ ( 1 ), 2,4‐[(CH₃)₂N]₂‐6‐(CH₃HN)B₃N₃H₃ ( 2 ), and 2‐[(CH₃)₂N]‐4,6‐(CH₃HN)₂B₃‐N₃H₃ ( 3 ) led to polyborazines 4 , 5 , and 6 respectively. The polymers display direct B–N bonds between borazinic B₃N₃ rings and, in addition, a proportion of –N(CH₃)– bridges for 5 and 6 , as clearly underlined by ¹³C NMR spectroscopy. Melt‐spinning of these three polymeric precursors exemplified that their ease of processing increases in the order 4 < 5 < 6 . Nevertheless, polyborazine filaments could be prepared from each of them and a subsequent thermal treatment up to 1800 °C resulted in the formation of crystalline hexagonal boron nitride fibers, which were characterized by X‐ray diffraction analysis, Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy. Scanning electron microscopy (SEM) images showed that the ceramic fibers are circular and dense without major defects. The mechanical properties for 4 ‐derived fibers could not be measured because of their brittleness, whereas measurements on 5 ‐ and 6 ‐derived fibers gave tensile strength σ^R = 0.51 GPa, Young’s modulus E = 67 GPa, and σ^R = 0.69 GPa, E = 170 GPa, respectively. The improvement in mechanical properties for ceramic fibers prepared respectively from 4 , 5 , and 6 could be explained to a large extent by the improvement of the processing properties of the preceramic polymers. This evolution could be related to the increased ratio of bridging –N(CH₃)– groups between the B₃N₃ rings within the polymers 4 , 5 , and 6 and therefore to the functionalities of the starting monomers 1 , 2 , and 3 .     

Schottky barrier heights on IV-IV compound semiconductors

The variations of Schottky barrier heights on Si_1-x-y Ge_xC_y films with composition and strain have been investigated and compared to those expected for the band gap energy. The barrier on n-type does not depend on composition and strain. This independence suggests that the Fermi level at the interface between tungsten and Si_1-x-yGe_xC_y alloys (x≠0) is pinned relative to the conduction-band. For Si_1-xGe_x the barrier on p-type follows the same trends as the band gap. For the ternary alloys, the variations of the barrier on p-type seem to be too large to be only due to a variation of the band-gap. In addition, we have investigated the influence of the deposition conditions of the sputtered-W-gate on the barrier to silicon and Si_1-xGe_x. Our results show that the barrier on n-type-Si and p-type-Si_1-xGe_x-films increases when the stress retained in the W-films changes from compressive to tensile as the deposition pressure increases. The absence of change in the barrier height of W to p-type-silicon and n-type-Sij xGex-films suggests that the Fermi level at the interface with Si is pinned relative to the valence-band while it is pinned relative to the conduction when Ge is added.     

Control of interfacial properties of Pr-oxide/Ge gate stack structure by introduction of nitrogen

We have demonstrated the control of interfacial properties of Pr-oxide/Ge gate stack structure by the introduction of nitrogen. From C-V characteristics of Al/Pr-oxide/Ge₃N₄/Ge MOS capacitors, the interface state density decreases without the change of the accumulation capacitance after annealing. The TEM and TED measurements reveal that the crystallization of Pr-oxide is enhanced with annealing and the columnar structure of cubic-Pr₂O₃ is formed after annealing. From the depth profiles measured using XPS with Ar sputtering for the Pr-oxide/Ge₃N₄/Ge stack structure, the increase in the Ge component is not observed in a Pr-oxide film and near the interface between a Pr-oxide film and a Ge substrate. In addition, the N component segregates near the interface region, amorphous Pr-oxynitride (PrON) is formed at the interface. As a result, Pr-oxide/PrON/Ge stacked structure without the Ge-oxynitride interlayer is formed.     

First-principles calculations of structural,elastic, electronic and optical properties of XO (X=Ca,Sr and Ba) compounds under pressure effect

The structural, elastic, electronic and optical properties of XO (X= Ca, Sr and Ba) compounds were investigated by the density functional theory. A good agreement was found between our calculated results and the available theoretical and experimental data of the lattice constants. Young's modulus, Poisson ratio, bulk modulus, elastic constants and their pressure derivatives are also calculated. SrO and BaO compounds present a transition phase at 39.72 and 27.28 GPa. The SrO compound shows a change from direct band gap (Γ–Γ) to indirect band gap (Γ–X) at about 15 GPa. The top of the valence bands reflects the s electronic character for all structures. We investigate the effective mass of electrons as function of pressure at the Γ point for CaO, SrO and BaO compounds. Calculations of the optical spectra have been performed for the energy range 0–60 eV. The origin of the spectral peaks was interpreted based on the electronic structures. The enhancement of pressure increases the static dielectric function and refractive index of CaO, SrO and BaO.     

Influence of passivating interlayer on Ge/HfO2 and Ge/Al2O3 interface band diagrams

The energy band alignment between Ge, HfO₂ and Al₂O₃ was analyzed as influenced by passivating interlayers (ILs) of different composition (GeO₂, Ge₃N₄, Si/SiO_x). From internal photoemission and photoconductivity experiments we found no IL-sensitive dipoles at the Ge/HfO₂ interfaces, the latter being universally characterized by conduction and valence band offsets of 2.1 and 3.0 eV, respectively. However, in the case of HfO₂ growth using H₂O-based atomic layer deposition, the Ge oxide IL appears to have a narrower bandgap, 4.3 eV, than the 5.4–5.9 eV gap of bulk germania. Accordingly, formation of this IL yields significantly reduced barriers for hole and, particularly, electron injection from Ge into the insulator. Changing to a H-free process for HfO₂ and Al₂O₃ deposition suppresses the formation of the narrow-gap Ge oxide.     

Pressure‐Driven Eu2+‐Doped BaLi2Al2Si2N6: A New Color Tunable Narrow‐Band Emission Phosphor for Spectroscopy and Pressure Sensor Applications

A series of BaLi₂Al₂Si₂N₆ (BLASN): xEu²⁺ phosphors are successfully synthesized and their crystal structure and luminescence properties under varying hydrostatic pressures are reported herein. Structure variation is analyzed using in situ high‐pressure X‐ray diffraction and Rietveld refinements. Based on decay curves and Gaussian fitting of emission spectra, the presence of two photoluminescence centers is demonstrated. BaLi₂Al₂Si₂N₆: 0.01Eu²⁺ exhibits an evident peak position shift from 532 to 567 nm with an increase in pressure to ≈20 GPa. The possible factors and mechanisms for the variations are studied in detail. At a pressure of 16 GPa, BLASN: Eu²⁺ realizes a narrow yellow emission with a full width at half maximum of ≈70 nm. The addition of BLASN: Eu²⁺ (16 GPa) to the commercial white light‐emitting diodes combination consisting of an InGaN chip, β‐SiAlON: Eu²⁺, and red K₂SiF₆:Mn⁴⁺, can increase the color gamut by ≈15%, demonstrating the promising potential of pressure‐driven BLASN: Eu²⁺ for wide‐color gamut spectroscopy applications. Moreover, the emission shifts arising from pressure variation and the distinct color changes enable its potential utility as an optical pressure sensor; the material exhibits high pressure sensitivity (dλ/dP ≈ 1.58 nm GPa^?1) with the advantage of visualization.     

Determination of the Elastic Properties of Cu<Subscript>3</Subscript>Sn Through First-Principles Calculations

Nine elastic constants of single-crystal Cu₃Sn were determined from first-principles calculations to characterize its polycrystalline elastic behavior and elastic anisotropy. The ideal elastic (E = 147 GPa), shear (G = 56 GPa) and bulk modulus (K = 132 GPa), and Poisson’s ratio (v = 0.315), were determined using the Voigt–Reuss–Hill method and were very close to the range of experimental results. Cu₃Sn exhibits distinct anisotropy in Young’s modulus, with a 44 GPa difference between its maximum and minimum values, which may be partially responsible for the discrepancy in the reported experimental results.     

Electronic properties and bulk moduli of new boron nitride polymorphs, i.e., hyperdiamond B12N12 and simple cubic B24N24, B12N12 fulborenites

The energy-band structure, density of states, electron density distribution, equation of state, and bulk moduli of three boron-nitride fulborenite crystals, i.e., B₁₂N₁₂ with diamond lattice and B₂₄N₂₄, B₁₂N₁₂ with simple cubic lattice, whose sites contain fulborene B₁₂N₁₂ and B₂₄N₂₄ molecules, are calculated for the first time using the full-potential linearized augmented plane wave method. The following hyperdiamond B₁₂N₁₂ parameters were obtained: the equilibrium lattice parameter a = 1.1191 nm, the B-N bond length a _BN = 0.1405 nm, the number of atoms per unit cell Z = 192, the density ρ = 2.823 g/cm³, the bulk modulus B ₀ = 658 GPa, and the band gap ΔE _g = 3.05 eV. This is a previously unknown unique light superhard semiconductor faujasite with a recorded bulk modulus higher than that of diamond. There are reasons to assume that it is a E phase. The characteristics of B₂₄N₂₄ with simple cubic lattice are as follows: the equilibrium lattice parameter a = 0.7346 nm, the B-N bond length a _BN = 0.1521 nm, the number of atoms per unit cell Z = 48, the density ρ = 2.495 g/cm³, the bulk modulus B ₀ = 367 GPa, and the band gap ΔE _g = 3.76 eV. This material is a heteropolar semiconductor or insulator with a bulk modulus comparable with that of cubic boron nitride, as well as a new boron-nitride zeolite with channel diameter of 0.46 nm. B₁₂N₁₂ with simple cubic lattice is a molecular semimetal.