Hole Energy Research Articles

STUDY OF THERMOMETRIC MATERIAL Er1-xScxNiSb. II. EXPERIMENTAL RESULTS

STUDY OF THERMOMETRIC MATERIAL Er1-xScxNiSb. II. EXPERIMENTAL RESULTS

Nonparabolicity effects on carrier lifetimes in bulk Hg1-xCdxTe alloys and Mid-Infrared 2D Hg1-xCdxTe/CdTe Single Quantum Well Lasers

We report on a theoretical study of nonparabolicity (NP) effects on carrier lifetimes in narrow energy bandgap bulk (3D) Hg 1-x Cd x Te ternary alloys and their related 2D Hg 1-x Cd x Te/CdTe Single Quantum Well (SQW) nanostructures for Mid-infrared (MIR) Laser applications. Carrier lifetime (τ) calculations are performed within both the parabolic and the 4-band CB + HH + LH + SO nonparabolic models. We show that NP affects strongly all three main scattering processes: Auger, Schockley-Read-Hall (SRH), and radiative recombination (RR). At 300 K and in mid-Cd contents (0.4 < x < 0.6) 3D Hg 1-x Cd x Te alloys, Auger 1 is shown to be the dominant τ limiting factor. In 2D Hg 1-x Cd x Te/CdTe SQW nanostructures, we show that RR turns out to be the dominant τ limiting process. This strongly reduced influence of Auger1 process in 2D Hg 1-x Cd x Te/CdTe SQW nanostructures is the result of the strong 2D quantum confinement induced amplification of NP effects via much stronger electron (CB) and all three hole (HH, LH, SO) energy subbands interactions and mixing. As a consequence, NP effects are finally shown to significantly improve all main 2D Hg 1-x Cd x Te/CdTe SQW Laser parameters in the MIR λ range with an optimum at x = 0.45 and for wide enough QW with L z ≥ 100 Å. • Nonparabolicity effects on carrier lifetimes in Hg 1-x Cd x Te 3D and 2D MIR Lasers. • Auger scattering processes are dominant at 300 K in 3D Hg 1-x Cd x Te alloys (0.3 < x < 0.6). • Radiative recombination is dominant 300 K in 2D Hg 1-x Cd x Te/CdTe QW (x ≥ 0.40). • NP affects strongly carrier lifetimes, and consequently, all main laser parameters. • NP improves Laser emission wavelength, optical gain and threshold current densities.

Anisotropic exciton Stark shift in hemispherical quantum dots

The exciton Stark shift and polarization in hemispherical quantum dots (HQDs) each as a function of strength and orientation of applied electric field are theoretically investigated by an exact diagonalization method. A highly anisotropic Stark redshift of exciton energy is found. As the electric field is rotated from Voigt to Faraday geometry, the redshift of exciton energy monotonically decreases. This is because the asymmetric geometric shape of the hemispherical quantum dot restrains the displacement of the wave function to the higher orbital state in response to electric field along Faraday geometry. A redshift of hole energy is found all the time while a transition of electron energy from this redshift to a blueshift is found as the field is rotated from Voigt to Faraday geometry. Taking advantage of the diminishing of Stark effect along Faraday geometry, the hemispherical shapes can be used to improve significantly the radiative recombination efficiency of the polar optoelectronic devices if the strong internal polarized electric field is along Faraday geometry.

Quenching mechanisms of photon superradiance

Rapidly rotating black holes are known to develop instabilities in the presence of a sufficiently light boson, a process which becomes efficient when the boson's Compton wavelength is roughly the size of the black hole. This phenomenon known as black hole superradiance generates an exponentially growing boson cloud at the expense of the rotational energy of the black hole. For astrophysical black holes with $M\ensuremath{\sim}\mathcal{O}(10){M}_{\ensuremath{\bigodot}}$, the superradiant condition is achieved for bosons with ${m}_{b}\ensuremath{\sim}\mathcal{O}({10}^{\ensuremath{-}11})\text{ }\text{ }\mathrm{eV}$; intriguingly, photons traversing the intergalactic medium acquire an effective mass (due to their interactions with the ambient plasma) which naturally resides in this range. The implications of photon superradiance, i.e., the evolution of the superradiant photon cloud and ambient plasma in the presence of scattering and particle production processes, have yet to be thoroughly investigated. Here, we enumerate and discuss a number of different processes capable of quenching the growth of the photon cloud, including particle interactions with the ambient electrons and backreactions on the effective mass (arising e.g., from thermal effects, pair production, ionization of the local background, and modifications to the dispersion relation from strong electric fields). This work naturally serves as a guide in understanding how interactions may allow light exotic bosons to evade superradiant constraints.

Activated and Metallic Conduction in p -Type Modulation-Doped Ge - Sn Devices

$G{e}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}$ quantum wells can be incorporated into $\mathrm{Si}\text{\ensuremath{-}}\mathrm{Ge}$--based structures with low-carrier effective masses, high mobilities, and the possibility of direct band-gap devices with x \ensuremath{\sim} 0.1. However, the electrical properties of p-type $G{e}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}$ devices are dominated by a thermally activated mobility and metallic behavior. At 30 mK the transport measurements indicate localization with a mobility of $380\phantom{\rule{0.1em}{0ex}}{\mathrm{cm}}^{2}$/Vs, which is thermally activated with a temperature-independent carrier density of 4 \ifmmode\times\else\texttimes\fi{} ${10}^{11}\phantom{\rule{0.1em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$. This weakly disordered system with conductivity, \ensuremath{\sigma} \ensuremath{\sim} ${e}^{2}$/h, where e is the fundamental charge and h is Planck's constant, is a result of negatively charged ``Sn-vacancy'' complex states in the barrier layers that act as hole traps. A measured hole effective mass of 0.090 \ifmmode\pm\else\textpm\fi{} $0.005{m}_{e}$ from the Shubnikov-de Haas effect, where ${m}_{e}$ is the free electron mass shows that the valence band is heavy hole dominated and is similar to p-type $\mathrm{Ge}$ with the compressive strain playing the role of quenching the spin-orbit coupling and shifting the unoccupied light-hole states to higher hole energies. The $G{e}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}$ devices have a high quantum mobility of approximately 36 000 ${\mathrm{cm}}^{2}$/Vs that is not thermally activated. The ratio of transport-to-quantum mobility of approximately 0.01 in $G{e}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}$ devices is unusual and points to several competing scattering mechanisms in the different experimental regimes.

Emergence of new materials for exploiting highly efficient carrier multiplication in photovoltaics

In conventional solar cell semiconductor materials, the excess energy of electrons and holes beyond the bandgap is wasted as heat, because they cool down to the band edge due to phonon emission. If the excess energy is more than the bandgap, it can in principle be utilized through a process known as carrier multiplication (CM) in which a single photon generates two (or more) electron-hole pairs. In this way, CM can enhance the photocurrent of a photovoltaic device. We provide an overview of experimental and theoretical methods used to study CM. Next, we consider the effects of composition and nanostructure of materials, on the threshold photon energy and efficiency of CM. Results for percolative networks of coupled PbSe quantum dots, Sn/Pb based halide perovskites, and two-dimensional transition metal dichalcogenides such as MoTe2 are discussed. Based on our current understanding, the CM threshold can get close to the minimal value of twice the bandgap in materials where a photon induces an asymmetric electronic transition from a deeper valence band or to a higher conduction band. We then address the effects of the exciton binding energy and charge carrier mobility on the photogeneration of free charges and their extraction at external electrodes of a photovoltaic device. Finally, we discuss future directions toward the development of new materials to realize a low threshold photon energy and high efficiency of CM.

Exploring the emission mechanism of dichromatic white-light quantum-dot light-emitting diodes using wavelength-resolved transient electroluminescence analysis.

Exploring electroluminescence (EL) processes is extremely vital to fabricate efficient white-light quantum-dot light-emitting diodes (QLEDs). A model white QLED consisting of a bilayer CdSe/ZnSeS quantum-dot (QD)//CuInS2/ZnS QDs emissive layer has been used to analyze the white-light emission mechanism. In this design, the CdSe/ZnSeS QDs and CuInS2/ZnS QDs contribute to the blue and yellow emissions, respectively, in the dichromatic white QLED. Wavelength-resolved transient EL (TrEL) results demonstrate that the excitons are mainly formed on the CuInS2/ZnS QDs in the QLED operated at low biases due to the low barrier to hole injection and energy transfer from the CdSe/ZnSeS QDs to the CuInS2/ZnS QDs. Further, the TrEL decays of both white and monochromic devices reveal that the emission behavior of the white QLED is closely related to that of the monochromic device, but is minimally affected by the interactions between different emission units. The simulation results performed by the solar cell capacitance simulator model agree well with the experimental data. Our results show an insight into the EL processes in the white device QLED and demonstrate a powerful tool to investigate emission behavior of the white QLEDs.

Energy Levels in Nanowires and Nanorods with a Finite Potential Well

The energy of electrons and holes in cylindrical quantum wires with a finite potential well was calculated by two methods. An analytical expression is approximately determined that allows one to calculate the energy of electrons and holes at the first discrete level in a cylindrical quantum wire. The electron energy was calculated by two methods for cylindrical layers of different radius. In the calculations, the nonparabolicity of the electron energy spectrum is taken into account. The dependence of the effective masses of electrons and holes on the radius of a quantum wires is determined. An analysis is made of the dependence of the energy of electrons and holes on the internal and external radii, and it is determined that the energy of electrons and holes in cylindrical layers with a constant thickness weakly depends on the internal radius. The results were obtained for the InP/InAs heterostructures.

Horizon Thermodynamics in D-Dimensional f(R) Black Hole.

We consider whether the new horizon-first law works in higher-dimensional theory. We firstly obtain the general formulas to calculate the entropy and the energy of a general spherically-symmetric black hole in D-dimensional theory. For applications, we compute the entropies and the energies of some black hokes in some interesting higher-dimensional theories.

Hawking-Page phase transitions of charged AdS black holes surrounded by quintessence * *Supported by Fundamental Research Funds for the Central Universities of China (N170504015, N182410008-1)

Hawking-Page phase transitions between the thermal anti-de Sitter vacuum and charged black holes surrounded by quintessence are studied in the extended phase space. The quintessence field, with the state parameter , modifies the temperature and the Gibbs free energy of a black hole. The phase transition temperature and the Gibbs free energy are first analytically investigated for the special case of , and then, the results of numerical simulations are shown for general . The phase transition temperature increases with pressure and decreases with electric potential. In addition, significantly decreases owing to the quintessence field, which generates negative pressure around the black hole.

Thermodynamic properties of novel black hole solutions in the Einstein\u2013Born\u2013Infeld-dilaton gravity theory

The exact solutions of coupled scalar, electromagnetic and gravitational field equations have been obtained in the framework of Einstein-dilaton gravity theory which is coupled to the Born–Infeld nonlinear electrodynamics. The solutions show that Einstein–Born–Infeld-dilaton gravity theory admits three novel classes of nonlinearly charged black hole solutions with the non-flat and non-AdS asymptotic behavior. Some of the solutions, in addition to the naked singularity, extreme and two-horizon black holes, produce one- and multi-horizon black holes too. The electric charge, mass and other thermodynamic quantities of the black holes have been calculated and it has been proved that they satisfy the standard form of the thermodynamical first law. The black hole local stability has been investigated by use of the canonical ensemble method. Noting the black hole heat capacity the points of type-one and type-two phase transitions and the locally stable black holes have been identified exactly. By use of the thermodynamic geometry, and noting the divergent points of the thermodynamic metric proposed by HEPM, it has been shown that the results of this method are consistent with those of canonical ensemble method. Global stability and Hawking–Page phase transition points have been studied by use of the grand canonical ensemble method and regarding the Gibbs free energy of the black holes. By calculating the Gibbs free energies, we characterized the ranges of horizon radii in which the black holes remain globally stable or prefer the radiation phase.

First theoretical framework of Z-shaped acceptor materials with fused-chrysene core for high performance organic solar cells.

Chrysene core containing fused ring acceptor materials have remarkable efficiency for high performance organic solar cells. Therefore, present study has been carried out with the aim to design chrysene based novel Z-shaped electron acceptor molecules (Z1-Z6) from famous Z-shaped photovoltaic material FCIC (R) for organic photovoltaic applications. End-capped engineering at two electron-accepting end groups 1,1-dicyanomethylene-3-indanone of FCIC is made with highly efficient end-capped acceptor moieties and impact of end-capped modifications on structure-property relationship, photovoltaic and electronic properties of newly designed molecules (Z1-Z6) has been studied in detail through DFT and TDDFT calculations. The efficiencies of the designed molecules are evaluated through energy gaps, exciton binding energy along with transition density matrix (TDM) analysis, reorganizational energy of electron and hole, absorption maxima and open circuit voltage of investigated molecules. The designed molecules exhibit red-shift and intense absorption in near-infrared region (683-749nm) of UV-Vis-NIR absorption spectrum with narrowing of HOMO-LUMO energy gap from 2.31eV in R to 1.95 in eV in Z5. Moreover, reduction in reorganization energy of electron from 0.0071 (R) to 0.0049 (Z5), and enhancement in open circuit voltage from 1.08V in R to 1.20V in Z5 are also observed. Twisted Z-shape of designed molecules prevents self-aggregation that facilitates miscibility of donor and acceptor. Low values of binding energy, excitation energy, and reorganizational energy (electron and hole) suggest that novel designed molecules offer high charge mobilities as compared to FCIC. Our findings indicate that these novel designed molecules can display better photovoltaic parameters and are suitable candidates if used in organic solar cells.

Proton conductivity and transport number of complex perovskite barium strontium tantalate

Previously, complex perovskites barium strontium tantalate, i.e., Ba3Sr1.4T1.6O8.4 (BST40), has exhibited excellent proton conductivity due to its high basicity and oxygen vacancy concentration. Herein, we report proton conduction mechanism of BST40 using brick-layer model and defect equilibria model. Briefly, BST40 is prepared by solid-state synthesis method, resulting in hexagonal perovskite structure with space group of P63/m. Interestingly, grain interior and grain boundary thickness of BST40 are almost equal and the grain boundary conduction mainly dominates the conductivity at T > 500 °C. Total standard molar hydration enthalpy of BST40 and grain interior is found to be −79.6 kJ/mol and −101.3 kJ/mol, respectively. Activation energy for BST40, protons, oxygen-ions, and holes in oxygen-containing humid atmosphere is found to be 0.63 eV, 0.51 eV, 0.92 eV, and 1.08 eV, respectively. These values are higher than corresponding values for the grain interior. At 700 °C, proton transport number of BST40 and grain interior is found to be 0.7 and 0.72, respectively, which is significantly higher than other congeneric complex perovskite-type proton conductors. Overall, these results confirm that BST40 possesses excellent proton conductivity.

In Silico Modeling of New "Y-Series"-Based Near-Infrared Sensitive Non-Fullerene Acceptors for Efficient Organic Solar Cells.

This work was inspired by a previous report [Janjua, M. R. S. A. Inorg. Chem. 2012, 51, 11306–11314] in which the optoelectronic properties were improved with an acceptor bearing heteroaromatic rings. Herein, we have designed four novel Y-series non-fullerene acceptors (NFAs) by end-capped acceptor modifications of a recently synthesized 15% efficient Y21 molecule for better optoelectronic properties and their potential use in solar cell applications. Density functional theory (DFT) along with time-dependent density functional theory (TDDFT) at the B3LYP/6-31G(d,p) level of theory is used to calculate the band gap, exciton binding energy along with transition density matrix (TDM) analysis, reorganizational energy of electrons and holes, and absorption maxima and open-circuit voltage of investigated molecules. In addition, the PM6:YA1 complex is also studied to understand the charge shifting from the donor polymer PM6 to the NFA blend. Results of all parameters suggest that the DA’D electron-deficient core and effective end-capped acceptors in YA1–YA4 molecules form a perfect combination for effective tuning of optoelectronic properties by lowering frontier molecular orbital (FMO) energy levels, reorganization energy, and binding energy and increasing the absorption maximum and open-circuit voltage values in selected molecules (YA1–YA4). The combination of extended conjugation and excellent electron-withdrawing capability of the end-capped acceptor moiety in YA1 makes YA1 an excellent organic solar cell (OSC) candidate owing to promising photovoltaic properties including the lowest energy gap (1.924 eV), smallest electron mobility (λe = 0.0073 eV) and hole mobility (λh = 0.0083 eV), highest λmax values (783.36 nm (in gas) and 715.20 nm (in chloroform) with lowest transition energy values (Ex) of 1.58 and 1.73 eV, respectively), and fine open-circuit voltage (Voc = 1.17 V) with respect to HOMOPM6–LUMOacceptor. Moreover, selected molecules are observed to have better photovoltaic properties than Y21, thus paving the way for experimentalists to look for future developments of Y-series-based highly efficient solar cells.

Designing Star-Shaped Subphthalocyanine-Based Acceptor Materials with Promising Photovoltaic Parameters for Non-fullerene Solar Cells.

Star-shaped three-dimensional (3D) twisted configured acceptors are a type of nonfullerene acceptors (NFAs) which are getting considerable attention of chemists and physicists on account of their promising photovoltaic properties and manifestly promoted the rapid progress of organic solar cells (OSCs). This report describes the peripheral substitution of the recently reported highly efficient 3D star-shaped acceptor compound, STIC, containing a 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (IC) end-capped group and a subphthalocyanine (SubPc) core unit. The 3D star-shaped SubPc-based NFA compound STIC is peripherally substituted with well-known end-capped groups, and six new molecules (S1–S6) are quantum chemically designed and explored using density functional theory (DFT) and time-dependent DFT (TDDFT). Density of states (DOS) analysis, frontier molecular orbital (FMO) analysis, reorganization energies of electrons and holes, open-circuit voltage, transition density matrix (TDM) surface, photophysical characteristics, and charge-transfer analysis of selected molecules (S1–S6) are evaluated with the synthesized reference STIC. The designed molecules are found in the ambience of 2.52–2.27 eV with a reduction in energy gap of up to 0.19 eV compared to R values. The designed molecules S3–S6 showed a red shift in the absorption spectrum in the visible region and broader shift in the range of 605.21–669.38 nm (gas) and 624.34–698.77 (chloroform) than the R phase values of 596.73 nm (gas) and 616.92 nm (chloroform). The open-circuit voltages are found with the values larger than R values in S3–S6 (1.71–1.90 V) and comparable to R in the S1 and S2 molecules. Among all investigated molecules, S5 due to the combination of extended conjugation and electron-withdrawing capability of end-capped acceptor moiety A5 is proven as the best candidate owing to promising photovoltaic properties including the lowest band gap (2.27 eV), smallest λe = 0.00232 eV and λh = 0.00483 eV, highest λmax values of 669.38 nm (in gas) and 698.77 nm (in chloroform), and highest Voc = 1.90 V with respect to HOMOPTB7-Th–LUMOacceptor. Our results suggest that the selected molecules are fine acceptor materials and can be used as electron and/or hole transport materials with excellent photovoltaic properties for OSCs.

Consequences of thermal fluctuations of well-known black holes in modified gravity

Quantum fluctuation consequences have significant role in high-energy physics. These fluctuation often regarded as a correction of the infrared (IR) limit. Such correction contribute to the high-energy limit of thermodynamical quantities and the stability conditions of black holes. In this work, we analyze the thermal stability of black holes in the presence of thermal fluctuations. We consider AdS black hole in Born–Infeld massive gravity with non-abelian hair and the charged AdS black hole with a global monopole. We develop many thermodynamical quantities such as entropy, temperature, pressure, heat capacity of a system at constant volume and pressure, ratio between the heat capacities at constant pressure and volume, Gibbs free energy and Helmholtz free energy for both black holes. The critical behavior and phase transitions of black holes are also presented. We also observe the local and global stability of black holes in the grand canonical ensemble and canonical ensemble for the specific values of different parameters, such as, symmetry breaking parameter η, massive parameter m and non-abelian hair ν.

Horizon thermodynamics in theory * * Supported in part by Hebei Provincial Natural Science Foundation of China (A2014201068)

We investigate whether the new horizon first law still holds in theory. For this complicated theory, we first determine the entropy of a black hole by using the Wald method, and then derive the energy of the black hole by using the new horizon first law, the degenerate Legendre transformation, and the gravitational field equations. For application, we consider the quadratic-curvature gravity, and first calculate the entropy and energy of a static spherically symmetric black hole, which are in agreement with the results obtained in the literature for a Schwarzschild-(A)dS black hole.

Revisiting black hole thermodynamics in massive gravity: charged particle absorption and infalling shell of dust * * Supported by the Natural Science Foundation of China (11705161, 11675139, 11875220). Xiao-Mei Kuang is also partly Supported by Natural Science Foundation of Jiangsu Province (BK20170481) and Fok Ying Tung Education Foundation (171006). Shi-Qian Hu is also Supported by the Postgraduate Reaearch & Practice

In this study, we apply two methods to consider the variation of massive black holes in both normal and extended thermodynamic phase spaces. The first method considers a charged particle being absorbed by the black hole, whereas the second considers a shell of dust falling into it. With the former method, the first and second laws of thermodynamics are always satisfied in the normal phase space; however, in the extended phase space, the first law is satisfied but the validity of the second law of thermodynamics depends upon the model parameters. With the latter method, both laws are valid. We argue that the former method's violation of the second law of thermodynamics may be attributable to the assumption that the change of internal energy of the black hole is equal to the energy of the particle. Finally, we demonstrate that the event horizon always ensures the validity of weak cosmic censorship in both phase spaces; this means that the violation of the second law of thermodynamics, arising under the aforementioned assumption, does not affect the weak cosmic censorship conjecture. This further supports our argument that the assumption in the first method is responsible for the violation and requires deeper treatment.

Design and Performance of Charge-Plasma-Based Schottky –FET CMOS Circuit Ring Oscillator for High Density ICs

In this work, we developed and explored the CMOS circuits ring oscillator with n- and p-channel on scaled SB-FETs for low power applications. Newly, a source-side charge plasma schottky barrier (SB) SB-FETs have been acquainted as the furthermost practical at nano-meter node technology. So, it is essential to examine the electrical characteristics of SB-FETs and their performance. Initially, we have been explored the source-side charge plasma SB-FET and its electrical characteristics has been simulated in compared with conventional SB-FET. The SILVACO simulator is used to simulate the proposed and conventional SB-FETs. In this source-side charge plasma SB-FET technique has improved resolution, and deliver outstanding concert (higher Ion/Ioff ratio) than conventional device reported in this research. Moreover, the precise exploration of the on-state performance of SB-FETs is mostly resolved by the electron and hole energy band of the channel. Additional, for the first time, source-side charge plasma SB-FET-based CMOS inverter and ring oscillator circuits have been calculated by the numerical simulator. The concentrated gate capacitance also grades in compact dynamic power degeneracy of source-side charge plasma schottky barrier SB-FET CMOS circuits and ring oscillator suggest lower voltage of process with condensed power intake, and great noise protection compared with convention device.

On the distribution of fluxes of gamma-ray blazars: hints for a stochastic process?

ABSTRACT We examine a model for the observed temporal variability of powerful blazars in the γ-ray band in which the dynamics is described in terms of a stochastic differential equation, including the contribution of a deterministic drift and a stochastic term. The form of the equation is motivated by the current astrophysical framework, accepting that jets are powered through the extraction of the rotational energy of the central supermassive black hole mediated by magnetic fields supported by a so-called magnetically arrested accretion disc. We apply the model to the γ-ray light curves of several bright blazars and we infer the parameters suitable to describe them. In particular, we examine the differential distribution of fluxes (dN/dFγ) and we show that the predicted probability density function for the assumed stochastic equation naturally reproduces the observed power-law shape at large fluxes $\mathrm{ d}N/\mathrm{ d}F_{\gamma } \propto F_{\gamma }^{-\alpha }$ with α &amp;gt; 2.