Search

Description of the physical mechanism leading to laser induced thermal and electronic effects in semiconductors is crucial in both basic research and technological applications. In this paper, we present a thermal mirror technique to study the thermo-mechanical properties of semiconductors. A detailed theoretical investigation is presented, and the dominant effects are described in terms of the physical properties of the material. The effect of heat coupling between the sample and the surrounding fluid was taken into account and considerations on the time and spatial approximations to the photogenerated carriers profile were used to simplify the theoretical model. These approximations were then compared to numerical models and the results hold for high recombination rate semiconductors. Experiments were performed to validate the theoretical model, and the thermal diffusivity and photogenerated heat in the sample were determined. The values obtained for these properties were found to be in good agreement with literature. [ABSTRACT FROM AUTHOR]

We present a thermodynamically consistent theory for solvent-vapor induced spherulitic crystallization in binary thin-film blends, including those which consist of polymeric or organic small-molecule semiconductors. Under the proposed theory, spherulitic growth is interface driven, with no diffusion of any species. The thermodynamic driving force at the interface between the spherulite and amorphous phase is identified, and a kinetic relation that delivers a constant growth rate is proposed. [ABSTRACT FROM AUTHOR]

For carbon tetrachloride, a temperature Hugoniot at 7–23 GPa and a distribution of the constant-volume specific heat on the Hugoniot CV(T) at 1057–3275 K are simultaneously estimated from the Walsh–Christian (WC) equation such that the Hugoniot fits well to the existing measured data. The estimated CV(T) distribution reveals the significance of the contribution of electrons and ions to the specific heat. That is, in contrast to the almost uniform distribution of the specific heat predicted from the Debye equation, the CV(T) distribution increases significantly with an increase in the Hugoniot temperature due to thermal excitation of electrons at 1057–1500 K (7–10.1 GPa), additional activation of the dimerization reaction at 1500–2350 K (10.1–16 GPa), and also additional activation of the polymerization reaction at 2350–3275 K (16–23 GPa). As an example, evidence is presented that carbon tetrachloride is a semiconductor at 1500 K. The CV(T) distribution in each temperature range is formulated and a temperature Hugoniot is reevaluated from the WC equation using the specific heat equations formulated. It is confirmed by a good fit of the reevaluated Hugoniot to the existing measured data that the specific heat equations express the CV(T) distribution appropriately. [ABSTRACT FROM AUTHOR]

The effect of electric field on the thermal expansion of the TlGaSe2 ferroelectric-semiconductor with a layer crystalline structure has been investigated. A strong transformation of negative linear expansion coefficient in the layer plane has been observed as a result of the applied electric field. It was concluded that internal electric fields created by local polarized states in the ferroelectric- semiconductor are responsible for a negative thermal expansion and its behavior under the electric field. Predominantly, the electrostriction effect is the driving mechanism of the lattice deformation of TlGaSe2 crystals at low temperatures. [ABSTRACT FROM AUTHOR]

A physically rigorous computational algorithm is developed and applied to calculate subcontinuum thermal transport in structures containing semiconductor-gas interfaces. The solution is based on a finite volume discretization of the Boltzmann equation for gas molecules (in the gas phase) and phonons (in the semiconductor). A partial equilibrium is assumed between gas molecules and phonons at the interface of the two media, and the degree of this equilibrium is determined by the accommodation coefficients of gas molecules and phonons on either side of the interface. Energy balance is imposed to obtain a value of the interface temperature. The classic problem of temperature drop across a solid-gas interface is investigated with a simultaneous treatment of solid and gas phase properties for the first time. A range of transport regimes is studied, varying from ballistic phonon transport and free molecular flow to continuum heat transfer in both gas and solid. A reduced-order model is developed that captures the thermal resistance of the gas-solid interface. The formulation is then applied to the problem of combined gas-solid heat transfer in a two-dimensional nanoporous bed and the overall thermal resistance of the bed is characterized in terms of the governing parameters. These two examples exemplify the broad utility of the model in practical nanoscale heat transfer applications. [ABSTRACT FROM AUTHOR]

We investigate the influence of material properties of two coupled nanocavities on ballistic phonon transport in a semiconductor nanowire at low temperatures. For two identical-size nanocavities their material properties obviously affect the phonon transmission, the frequency of resonant transmission, especially the number n, and positions of the low-frequency gaps. When the two cavities are made of different materials, a new type gap appears in the spectrum. Moreover their positions depend respectively on the material parameters of each cavity. At lower temperatures, the thermal conductance can be enhanced by using different material parameters of cavities from those of the main nanowire. These results suggest new directions that can be explored for forming gaps and resonance phonons, for controlling thermal conductance at different temperature ranges in nanophononics. [ABSTRACT FROM AUTHOR]

Thermal degradation of GaAs(001) surfaces has been studied using spectroscopic ellipsometry (SE), optical microscopy, ex situ atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) techniques. The SE data suggest that thermal annealing causes no or little influence on the surface native oxide layer at temperatures T≤500 °C. Microscopic roughening starts to occur on GaAs surface at T>500 °C, giving maximum AFM roughness (rms∼14 nm) at 540 °C, and then tends to smoothened at T>540 °C (rms∼2.5 nm at 580 °C). Macroscopically roughened surfaces are observed at T>500 °C, becoming more pronounced at higher annealing temperature. The Ga droplets are also observed at T≥600 °C that lead to catastrophically damaged surfaces and make SE measurement impossible. The XPS data indicate thinning of the native GaAs oxide in the limited temperature range 450

Magnetotransport and thermal studies of Pr2/3Sr1/3MnO3 polycrystalline sintered bulk sample are reported here. The resistivity ρ(T) and thermoelectric power S(T) data show an insulator to metal (I-M) phase transition at TP≈294 K and TS≈290 K, respectively. Magnetization measurement confirms that the sample undergoes a transition from paramagnetic to ferromagnetic phase at a defined Curie temperature TC=280 K. A substantial increase in magnetoresistance from 2.5% at 280 K to 5% at 77 K has been noticed in a low magnetic field 0.15 T. Small polaron hopping model is found to be operative above the transition temperature TP, whereas electron-electron and electron-magnon scattering processes govern the low temperature metallic behavior. A detailed analysis of thermoelectric power in the ferromagnetic regime suggests that the complicated temperature dependence of S may be understood on the basis of electron-magnon scattering. A transition from decreasing high temperature thermal conductivity (due to local anharmonic distortions associated with small polarons), to an increasing thermal conductivity (due to decreasing of phonon-phonon scattering) and thereafter a peak at ∼100 K (signifying a crossover from Umklapp to defect-limited scattering) have also been noticed. Specific heat measurements depict a pronounced anomaly near the TC, indicating the magnetic ordering and magnetic inhomogeneity in the sample. [ABSTRACT FROM AUTHOR]

The thermal properties and their relationship to the charge transport properties of an electron-doped manganite La0.9Te0.1MnO3 were investigated. The resistivity and the Hall effect were measured. The magnetic-field dependence of Hall resistivity indicates that the carriers in La0.9Te0.1MnO3 are electrons. The thermopower S and thermal conductivity κ were also measured. Above the metal-insulator transition temperature TP, a significant difference between the resistivity activation energy (Eρ=128.3 meV) and the thermopower activation energy (ES=14.7 meV) was observed, implying that the conductivity of La0.9Te0.1MnO3 above TP was dominated by the small-polaron hopping. In the ferromagnetic region, it is found that S shows T3/2 dependence, suggesting that the electron-magnon scattering strongly affects the low-temperature thermopower of La0.9Te0.1MnO3. The temperature dependence of thermal conductivity, κ(T), reveals that the phonon component (κph) is the major one. Moreover, in the paramagnetic region, a positive dκ/dT is observed, i.e., dκ/dT>0, which might be related to the local anharmonic lattice distortions. [ABSTRACT FROM AUTHOR]

The charge transport properties of the low-dimensional thermoelectric materials K2Bi8-xSbxSe13 (0

In this study, the photocurrent (PC) spectroscopy of undoped p-type CIS layers has been investigated at temperatures ranging from 10 to 293 K. Three peaks, A, B, and C, corresponded to the intrinsic transition from the valence band states of Γ7(A), Γ6(B), and Γ7(C) to the conduction band state of Γ6, respectively. The crystal field splitting and the spin orbit splitting were found at 0.0059 and 0.2301 eV, respectively, and the temperature dependence of the optical band gap could be expressed by using the empirical equation Eg(T)=Eg(0)-(8.57×10-4)T2/(T+129). But the behavior of the PC was different from that generally observed in other semiconductors: the PC intensities decreased with decreasing temperature. From the relation of log Jph vs 1/T, where Jph is the PC density, the dominant level was observed at the higher temperatures. We suggest that in undoped p-type CIS layers, the trapping center limits the PC signal due to native defects and impurities with decreasing temperature. [ABSTRACT FROM AUTHOR]

Microstructural control by means of plasma treatment was performed on sintered Cr-doped β-FeSi[SUB2] in order to improve its thermoelectric properties. The micrograins were exposed to rf plasmas of germane (GeH[SUB4]) or a mixture of germane and silane (SiH[SUB4]) and were then sintered. The thermoelectric properties of the samples were investigated along with their microstructures. The results show that the plasma treatments reduced thermal conductivity and increased electrical conductivity and mobility, which led to an increase in thermoelectric figure-of-merit. In addition, the results show that the plasma treatments also formed small SiGe crystals distributed throughout the samples, removed most of the grain boundaries, and sometimes formed FeSi crystals. The relation between the changes in the thermoelectric properties and the modification of the microstructure was discussed. It was found that the microstmctural modification by the plasma treatment caused favorable changes in thermoelectric properties. [ABSTRACT FROM AUTHOR]

Presents information on a study on the consequences of disorder on the dispersion of the temperature behavior of multiple tunnel junction devices. Experimental technique; Discussion; Conclusion.

Presents information on a study which observed the abnormal variation of the band-gap energy with temperature in short-period-superlattice structures. Experimental method; results and discussion; Conclusion.

Presents information on a study on the temperature dependence of the piezoreflectance measurements of an iron-containing silicon carbon nitride crystalline film. Experimental details; Results and discussion; Conclusion.

Presents information on a study which analyzed the anisotropy of hot-electron thermal conductivity and related quantities in semiconductors. Theoretical approach; Monte Carlo procedure; Results; Conclusions.

Laser interference has been widely used to produce one-dimensional gratings and more recently has shown great potential for two-dimensional patterning. In this study, the authors examine by simulation, its application to in-situ patterning during materials growth. To understand the potential, it is important to study the surface processes resulting from the laser-matter interaction, which have a key influence on the resulting growth mechanisms. In this work, the intensity distribution and the laser-semiconductor interaction resulting from four-beam interference patterns are analysed by numerical simulations. In particular, the authors derive the time and spatially dependent thermal distribution along with the thermal-induced desorption and surface diffusion. The results provide a crucial understanding of the light-induced thermal profile and show that the surface temperature and the surface adatom kinetics can be controlled by multi-beam pulsed laser interference patterning due to photothermal reactions. The approach has potential as an in-situ technique for the fast and precise nanostructuring of semiconductor material surfaces. [ABSTRACT FROM AUTHOR]

Presents a study to calculate the critical thickness and strain relaxation in II-VI strained epilayers, and compare them with experimental values. What commercial semiconductor lasers are based upon; Importance of short-wavelength light emitting diodes; Methodology used to conduct study; Indication of findings; Discussion on results.

Presents a study to analyze wave propagation in piezoelectric layered structures with special emphasis on semiconductor layered systems. Methodology used to conduct study; Indication of findings; Discussion on results.

Analyzes the thermal properties of cadmium telluride (CdTe) semiconductors. Applications of CdTe; Description of the photoacoustic effect; Determination of the thermal wave attenuation.

We measured the dependence of the energy gap in Bridgman-grown Cd1-xMnxTe crystals, 0≤x≤0.25, on the Mn mole fraction and temperatures from 40 to 300 K. We determined the Mn mole fraction and energy gap, respectively, from electron probe microanalysis and near-infrared Fourier-transform infrared transmission spectra. The energy gap increased linearly with an increase in the Mn content in the crystal and with a decrease in temperature. We formulated new equations from these experimental results, wherein we expressed the energy gap as a function of Mn mole fraction and temperature. Also, we compare our findings with published results. [ABSTRACT FROM AUTHOR]

In this letter, we develop the theory of Hall effect driven by non-collinear magnetic textures (topological Hall effect—THE) in diluted magnetic semiconductors (DMSs). We show that a carrier spin-orbit interaction induces a chiral magnetic ordering inside a bound magnetic polaron (BMP). The inner structure of non-collinear BMP is controlled by the type of spin-orbit coupling, allowing us to create skyrmion- (Rashba) or antiskyrmion-like (Dresselhaus) configurations. The asymmetric scattering of itinerant carriers on polarons leads to the Hall response which exists in weak external magnetic fields and at low temperatures. We point out that DMS-based systems allow one to investigate experimentally the dependence of THE both on a carrier spin polarization and on a non-collinear magnetic texture shape. [ABSTRACT FROM AUTHOR]

We investigate temperature-dependent spectral linewidths of Bloch oscillations in biased semiconductor superlattices experimentally and theoretically. The spectral linewidth in a GaAs-based superlattice determined by terahertz emission spectroscopy becomes larger gradually as temperature increases from 80 to 320 K. This behavior can be quantitatively reproduced by a microscopic theory of the spectral linewidth that has been extended to treat the phonon scattering and interface roughness scattering of electrons on a Wannier-Stark ladder. A detailed comparison between the terahertz measurements and theoretical simulations reveals that the LO phonon absorption process governs the increase in the spectral linewidth with increasing temperature. [ABSTRACT FROM AUTHOR]

Purpose Thermal behavior of light-emitting diode (LED) device under different operating conditions must be known to enhance its reliability and efficiency in various applications. The purpose of this study is to report the influence of input current and ambient temperature on thermal resistance of InGaAlP low-power surface-mount device (SMD) LED.Design/methodology/approach Thermal parameters of the LED were measured using thermal transient measurement via Thermal Transient Tester (T3Ster). The experimental results were validated using computational fluid dynamics (CFD) software.Findings As input current increases from 50 to 90 mA at 25°C, the relative increase in LED package (ΔRthJS) and total thermal resistance (ΔRthJA) is about 10 and 4 per cent, respectively. In addition, at 50 mA and ambient temperature from 25 to 65°C, the ΔRthJS and ΔRthJA are roughly 28 and 22 per cent, respectively. A good agreement between simulation and experiment results of junction temperature.Originality/value Most of previous studies have focused on thermal management of high-power LEDs. There were no studies on thermal analysis of low-power SMD LED so far. This work will help in predicting the thermal performance of low-power LEDs in solid-state lighting applications. [ABSTRACT FROM AUTHOR]

In this paper, a rigorous methodology for extracting the thermal compact model parameters of packaged chips is presented. The methodology is based on using a custom-designed test chip with multiple heating and temperature sensing elements in order to predict the temperature distribution in packaged chips after packaging. The technique involves measurement of various chips with different thicknesses, different packages, and for different power dissipation scenarios through which the thermal model parameters can be extracted. The results show that ultrathin chips with a total thickness below 20~\mu \textm experience a dramatically increased temperature for localized heat dissipation. In addition to this, the measurements conducted in time domain and frequency domain show that at high enough frequencies of heat pulsing, the temperature variations become independent of the thermal boundary conditions of the chip. The measurement results are compared to the finite-element method simulation data. The simulations together with the measurement methodology serve as a technique to extract the thermal compact model parameters of packaged chips after being fabricated and packaged in an accurate and efficient way. [ABSTRACT FROM AUTHOR]

This article presents a comparative study between SiC MOSFETs and Si IGBTs regarding changes in their junction temperature in a PV inverter application. The estimation of these variations is made by introducing the current mission profiles extracted from a photovoltaic plant over one year into a calculation tool. The latter is based on a losses model and a thermal model including a coupling between them. The calculation of the losses in SiC MOSFETs in the 3rd quadrant is detailed. The results are the mission profiles of the junction temperature of semiconductors, which allow for determining and comparing the thermal constraints in SiC MOSFET and Si IGBT power modules. [ABSTRACT FROM AUTHOR]

The inability to scale supply voltage and hence reduce power consumption remains a serious challenge in modern nanotransistors. This arises primarily because the Sub-threshold Swing (SS) of the thermionic MOSFET, a measure of its switching efficiency, is restricted by the Boltzmann limit (kBT/q=60 mV/dec at 300 K). Tunneling FETs, the most promising candidates to circumvent this limit, employ band-to-band tunneling, yielding very low OFF currents and steep SS but at the expense of severely degraded ON currents. In a completely different approach, by introducing concurrent tuning of thermionic and tunneling components through metal/semiconductor Schottky junctions, we achieve an amalgamation of steep SS and high ON currents in the same device. We demonstrate sub-thermionic transport sustained up to 4 decades with SSmin~8.3 mV/dec and SSavg~37.5(25) mV/dec for 4(3) dec in few layer MoS2 dual gated FETs (planar and CMOS compatible) using tunnel injected Schottky contacts for a highly scaled drain voltage of 10 mV, the lowest for any sub-thermionic devices. Furthermore, the same devices can be tuned to operate in the thermionic regime with a field effect mobility of ~84.3 cm2 V-1 s-1. A detailed mechanism involving the independent control of the Schottky barrier height and width through efficient device architecture and material processing elucidates the functioning of these devices. The Gate Tunable Thermionic Tunnel FET can function at a supply voltage of as low as 0.5 V, reducing power consumption dramatically. [ABSTRACT FROM AUTHOR]

New benzothiadiazole derivatives, 4,7-bis(5-phenylthiophen-2-yl)benzo[c][1,2,5]thiadiazole (PT-BTD) and 4,7-bis[4-(thiophen-2-l)phenyl]benzo[c][1,2,5]thiadiazole (TP-BTD), were synthesized and characterized as small-molecule organic semiconductors for organic thin-film transistors (OTFTs) and complementary inverters. The thermal, optical, and electrochemical properties of the new compounds were fully characterized. Vacuum-deposition and solution-shearing methods were used to fabricate thin films based on these compounds. Thin films based on PTBTD exhibited p-channel characteristics with hole mobilities as high as 0.10 cm²V-1 s-1 and current on/off ratios >107 for topcontact/bottom-gate OTFT devices. With an optimized blending ratio of PT-BTD and the representative n-channel semiconductor N,N'-1H,1H-perfluorobutyl dicyanoperylenediimide, bulk heterojunction ambipolar transistors were fabricated with balanced hole and electron mobilities of 0.10 and 0.07 cm²V-1 s-1, respectively. Furthermore, a complementary-like inverter was fabricated using ambipolar thin-film transistors, which showed a high voltage gain of 84. [ABSTRACT FROM AUTHOR]

In this study, (Bi2O3)1−x−y(Sm2O3)x(CeO2)yternary system was synthesized by using solid-state reaction method. Structural, morphological, thermal and electrical properties of the samples were evaluated by means of X-ray diffraction (XRD), scanning electron microscopy, thermo gravimetry/differential thermal analyzer and four-probe method. The XRD measurement results indicated that the samples (x= 10–15,y= 5–10–15–20) had cubic δ-phase crystallographic structure. The phase stability of the samples was checked by the differential thermal analyzer measurements, which indicates most of the samples have stable δ-Bi2O3phase. The electrical conductivity measurement results showed that the electrical conductivity increased with mol% CeO2molar ratio at a fixed molar ratio of Sm2O3. The highest electrical conductivity obtained for the (Bi2O3)0.65(Sm2O3)0.15(CeO2)0.20system was 1.55 × 10−2(Ω.cm)−1at 600 °C. The activation energies were also calculated at low temperature range (350–650 °C) which vary from 1.1325 to 1.4460 eV and at high temperature (above 650 °C) which vary from 0.4813 to 1.1071 eV. [ABSTRACT FROM AUTHOR]

Modified diamond-like carbon (DLC) coatings were deposited onto 25 mm diameter 316 stainless steel discs by pulsed (direct current) hollow cathode plasma enhanced chemical vapour deposition (HC-PECVD). Multilayer films of total thickness 1–2 μm were deposited, both with and without germanium dopant. Characterisation of the coatings was performed by SEM/EDX, surface energy/contact angle analysis, and assessment of possible biofilm-inhibiting properties. Both modified DLC and germanium-doped DLC (Ge-DLC) coatings showed a significant anti-biofouling effect on P. aeruginosa , a Gram-negative bacterium. A 90% reduction in P. aeruginosa biomass was observed compared to control for both DLC and Ge-DLC, however this effect could not be attributed to germanium incorporation alone. Neither modified DLC nor Ge-DLC showed a significant inhibitory effect on S. aureus , a Gram-positive bacterium. Scanning electron microscopy of P. aeruginosa biofilms on Ge-DLC coated 316 stainless steel clearly displayed disruption of the cellular wall, as well as leakage of cellular components; this effect was not observed with modified DLC coating. This suggests that germanium-doped DLC coatings may potentially exhibit a cidal mode of action versus P. aeruginosa biofilms. [ABSTRACT FROM AUTHOR]

The thermodynamic origin of a relation between features of the phase diagrams and the electronic properties of molten semiconductors is provided. Leveraging a quantitative connection between electronic properties and entropy, a criterion is derived to establish whether a system will retain its semiconducting properties in the molten phase. It is shown that electronic entropy is critical to the thermodynamics of molten semiconductor systems, driving key features of phase diagrams including, for example, miscibility gaps. [ABSTRACT FROM AUTHOR]

The in-plane thermal conductivity of semiconductor nanofilm is difficult to be tested due to suspension problem. The thermal boundary resistance (TBR) plays a key role in semiconductor nanoscale structures and nanoscale thermal experiments. By applying alternating current and direct current currents simultaneously on the semiconducting nanofilm on highly insulated substrate, multiharmonics including $$1\upomega $$ , $$2\upomega $$ and $$3\upomega $$ signals originating from the self-heating of nanofilm are measured. The thermal boundary resistance is introduced into the heat diffusion equation in in-plane direction. The expression of temperature oscillation and theoretical analysis of heat transport process show that the in-plane thermal conductivity and TBR can be decoupled from the multiharmonics in frequency domain. Thermal analysis justifies the multiharmonics method according to the effect of in-plane thermal conductivity, TBR between nanofilm and insulated substrate, resistance coefficient of semiconductor nanofilm on temperature oscillation at low frequency. Results show the multiharmonic method sensitivity variations depending on the TBR, the in-plane thermal conductivity, and the electric current frequency. [ABSTRACT FROM AUTHOR]

Thermal transport in disordered organic semiconductors fundamentally differs from that in inorganic materials and is determined by the charge carriers and phonons in localized states. Understanding thermal transport performance of organic semiconductors is important for a fundamental description of energy flow and then a better design of organic thermoelectric devices. We present a unified theoretical model to describe the thermal transport performance of the disordered organic semiconductors based on hopping transport theory. The proposed model predicts that the contribution from phonon to the thermal conductivity is larger than that from charge carrier in the disordered organic semiconductors. Moreover, the proposed model can well interpret the thermal transport feature of the organic semiconductors by combining the disorder, temperature, and carrier concentration. Simulation results imply that thermal conductivity in the disordered organic semiconductors could be strongly affected under large electric field, high carrier and dopant concentration. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to present the results of measurements and calculations illustrating mutual thermal coupling between power Schottky diodes made of silicon carbide situated in the common case.Design/methodology/approach The idea of measurements of mutual transient thermal impedances of the investigated device is described.Findings The results of measurements of mutual transient thermal impedances between the considered diodes are shown. The experimentally verified results of calculations of the internal temperature waveforms of the considered diodes obtained with mutual thermal coupling taken into account are presented and discussed. The influence of mutual thermal coupling and a self-heating phenomenon on the internal temperature of the considered diodes is pointed out.Research limitations/implications The presented methods of measurements and calculations can be used for constructing the investigated diodes made of other semiconductor materials.Originality/value The presented results prove that mutual thermal coupling between diodes mounted in the common case must be taken into account to calculate correctly the waveforms of the device internal temperature. [ABSTRACT FROM AUTHOR]

Track radii are derived for semiconductors from a temperature distribution Θ(r) in which the width of the distribution is the only materials parameter. Analysis of track data for GeS, InP, GaAs and GaN show that the projectile velocity has no effect on track radii in semiconductors. Due to the missing velocity effect, the threshold for track formation, S et = 20 keV/nm is high in semiconducting UO 2 in the whole range of projectile velocities. This is the origin of the high radiation resistance for fission fragments. Consequences for the simulation experiments with insulating CeO 2 are discussed. It is verified that sputtering is described accurately by the Arrhenius equation for various materials including UO 2 . The ion-induced surface potential has a strong effect on the activation energy. [ABSTRACT FROM AUTHOR]

The model of the equations of generalized thermoelasticity based on the Lord–Shulman theory with one relaxation time is used to study the photothermal waves in a semiconducting medium. The exact expressions for the displacement components, temperature, carrier density, and stress components are obtained using normal mode analysis. Numerically simulated results are obtained and presented graphically for silicon to depict the effect of time parameter on the different physical quantities. [ABSTRACT FROM PUBLISHER]

A theoretical study is carried out of the possibility of effective second-harmonic generation in a metamaterial representing a structure of alternating layers of semiconductor material with intrinsic and metallic conductivity that can be grown by epitaxial methods. [ABSTRACT FROM AUTHOR]

We present structural and optical spectroscopy studies of thin films of Cu 2 ZnSnSe 4 (CZTSe) with strong copper deficiency deposited on Mo/Glass substrates and selenised at 450, 500 or 550 °C. Solar cells fabricated from these films demonstrated efficiencies up to 7.4% for selenisation at 500 °C. Structural analysis based on X-ray diffraction and Raman spectroscopy revealed the presence of SnSe 2 in the film selenised at 450 °C but not in the films selenised at higher temperatures. A progressive decrease of the Sn and Se content was observed as the selenisation temperature increased. Photoluminescence excitation was used to determine the bandgaps at 4.2 K. Detailed measurements of the temperature and excitation intensity dependencies of the photoluminescence spectra allow the recombination mechanisms of the observed emission bands to be identified as band-to-impurity and band-to-band transitions, and their evolution with selenisation temperature changes to be analysed. The strongest band-to-band transition is recorded in the PL spectra of the film selenised at 500 °C and can be observed from 6 K to room temperature. The compositional and structural changes in the films and their influence on the optoelectronic properties of CZTSe and solar cells are discussed. [ABSTRACT FROM AUTHOR]

The objective of this study is to create an ideal mixture of Acetaminophen/Curcumin leading to a new and improved semiconductor material, by a study of the electrical, thermal and optical properties. This new material will be compared with existing semiconductor technology to discuss its viability within the industry. The electrical properties were investigated using complex impedance spectroscopy and optical properties were studied by means of UV-Vis spectrophotometry. The electric conductivity σ, the dielectric constant ɛ r , the activation energy E a , the optical transmittance T and the gap energy E g have been investigated in order to characterize our organic material. The electrical conductivity of the material is approximately 10 −5 S/m at room temperature, increasing the temperature causes σ to increase exponentially to approximately 10 −4 S/m. The activation energy obtained for the material is equal to 0.49 ± 0.02 ev. The optical absorption spectra show that the investigating material has absorbance in the visible range with a maximum wavelength (λ max ) 424 nm. From analysis, the absorption spectra it was found the optical band gap equal to 2.6 ± 0.02 eV and 2.46 ± 0.02 eV for the direct and indirect transition, respectively. In general, the study shows that the developed material has characteristics of organic semiconductor material that has a promising future in the field of organic electronics and their potential applications, e.g., photovoltaic cells. [ABSTRACT FROM AUTHOR]

In the present study we explore the structural, electronic and thermoelectric properties of IV-VI semiconductors using first principle calculations based on the density functional theory. Generalized gradient approximation (GGA-PBEsol) is used as an exchange-correlation functional for the structural properties of the different crystal phases of these semiconductors. The compounds SnS, SnSe, GeS and GeSe favor orthorhombic structure, lead chalcogenides (PbS, PbSe and PbTe) are stable in the cubic rocksalt structure, while SnS 2 and SnSe 2 exist in hexagonal structure. For band structures additional to GGA, modified Becke and Johnson (mBJ) exchange potential is used. These compounds are narrow band gap semiconductors in the energy range 0.2–2.8 eV. These binary IV-VI chalcogenides have direct band gap nature in cubic crystals while indirect in the orthorhombic phases. The post-DFT (BoltzTraP) calculations are performed to estimate Seebeck coefficient, electric and thermal conductivities, power factor and figure of merit of these compounds to check their applicability in thermoelectric devices. Spin orbit coupling effect influences the electronic and thermoelectric properties of these compounds due to the large size of the constituent elements. Further, the total thermal conductivity is computed using ad-hoc calculation with the experimental results. The calculated values of figure of merit for PbS, PbSe, PbTe and SnTe are in the range 0.68–0.77 at room temperature. [ABSTRACT FROM AUTHOR]

The relationship between electrical and magnetic properties of manganites has been traced through the analysis of temperature dependence of the La 0.5 Ca 0.3 Ag 0.2 MnO 3 resistivity. The measurement of resistivity versus temperature ρ ( T ) of the sample shows a paramagnetic semiconductor-ferromagnetic metallic transition at T = T MS . The application of magnetic field increases the T MS value and reduces the resistivity of the compound. The estimated critical exponents are ( β =0.273±0.01; γ = 1.074±0.02 and α =0.456). The values of these exponents obtained from resistivity are very close to them predicted by the tri-critical mean-field model. These results are in good agreement with the analysis of critical exponents from magnetization measurements. The electrical resistivity was fitted with the phenomenological percolation model, which is based on the phase segregation of ferromagnetic metallic clusters and paramagnetic semiconductor regions. So, we found that the estimated results are in adequate accordance with experimental data. [ABSTRACT FROM AUTHOR]

In contrast with conventional thermal evaporation-based semiconducting oxide growth methods, gourd-like SiOx nanotubes (NTs) grown from Si substrates were achieved with incorporated Sn-embedded structures through the precontaminated SnO2 film surroundings. Interestingly, when Sn aggregations assembled as Sn nanoparticles were formed on the surface of the Si substrate, single gourd-like SiOx NTs were grown from the upper local region of the ternary alloy (Si-Sn-O) sphere, maintaining a one-to-one correspondent relationship between the ternary spheres and the Sn-embedded SiOx NTs. Both interfacial reaction-controlled and diffusion-controlled systems occurred stepwise at the smooth and rough surfaces, respectively. In addition, the elemental compositions and sizes of the final Sn-embedded SiOx NTs were influenced by the Sn concentration of the SnO2 film, the rate of In substitution by Sn in the supporting material In2O3, and the degree of carbothermal reduction of additional graphite powders. [ABSTRACT FROM AUTHOR]

We have performed ab-initio calculations for the structural, electronic, optical, elastic and thermal properties of the copper gallium chalcopyrite (CuGaSe 2 ). The Full Potential Linearized Augmented Plane Wave (FP-LAPW) method is used to find the equilibrium structural parameters and to compute the full elastic tensors. We have reported electronic and optical properties with the recently developed density functional of Tran and Blaha. Furthermore, optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients, optical conductivities, are calculated for photon energies up to 30 eV. The thermodynamical properties such as thermal expansion, heat capacity, Debye temperature, entropy and Grüneisen parameter, bulk modulus and hardness are calculated employing the quasi-harmonic Debye model at different temperatures (0–1200 K) and pressures (0–8 GPa) and the silent results are interpreted. To check the potentiality of CuGaSe 2 as future solar cell material, device modeling and simulation studies have been carried out with a variety of buffer layers over CuGaSe 2 absorption layer. The band diagram and J / V curves are analyzed and device performance parameters i.e. efficiency, open circuit voltage, short circuit current, quantum efficiency are calculated for CdS, ZnS and ZnSe buffer layers. Simulation results for CuGaSe 2 thin layer solar cell show the maximum efficiency (15.8%) with ZnSe as the buffer layer. Most of the investigated parameters are reported for the first time. [ABSTRACT FROM AUTHOR]

With the emergence of new power semiconductor devices and packaging technologies, the power density of the power packages or modules is increasing rapidly. Double-sided cooling power packages maximize heat dissipation by enabling heat removal from both the top and bottom sides of the module. This article compares single-sided and double-sided cooling power packaging structures to elucidate advantages and disadvantages of these packaging structures in terms of thermal and thermomechanical based on finite element simulations. Simulation results reveal that double-sided cooling power packages greatly improve their thermal performances, but they face challenges due to their high thermo-mechanical stresses. The use of a viscoelastic underfill resin and a coefficient of thermal expansion matched ceramic chip carrier in the double-sided cooling power packaging structure is shown to reduce thermo-mechanical stresses. [ABSTRACT FROM AUTHOR]

We studied the thermal and magnetic properties of a cylindrical quantum dot in the presence of external electric and magnetic fields. The energy spectrum and wave functions for the quantum dot of asymmetric confinement are obtained by solving the Schrödinger wave equation analytically. The energy levels are employed to calculate the canonical partition function, which in turn is used to obtain specific heat, entropy, magnetization, and susceptibility. These thermal and magnetic quantities are found to have direct dependence on confinement length, magnetic field, and temperature, thus the parameters of the system can be tuned to fit into more than one application. [ABSTRACT FROM AUTHOR]

InGaN light-emitting diodes (LEDs) with InGaN-GaN quantum barriers of gradually decreasing indium concentration along the growth direction are proposed to be used. In the proposed structure, simulation results show that the holes are widely distributed in the active region due to the larger hole injection/transportation efficiency by reducing the effective potential height for holes and the radiative recombination rate is efficiently improved, which leads to the significant enhancement of light-output power and internal quantum efficiency (IQE) over the conventional LED with GaN barriers. Moreover, the optical performance is further improved when the graded InGaN/GaN supperlattice (SL) is introduced between the multiple quantum wells (MQWs) and p-AlGaN electron blocking layer (EBL) in our designed LED structure, permitting more freedom for the optimization. [ABSTRACT FROM AUTHOR]

Semiconductor doping through solution-based self-assembling provides a simple, scalable, and cost-effective alternative to standard methods and additionally allows conformality on structured surfaces. Among the several solution-based deposition techniques, dip coating is the most promising. It consists in immersing the target to be doped inside a solution containing the dopant precursor. During this process, the molecule bonds to the target surface with a self-limiting process ruled by its steric properties. Successive annealing leads to layer decomposition and diffusion of dopant atoms inside the substrate. Most of the work on molecular doping lacks information on the molecule/Si interface chemical properties, on the mechanisms of the molecule evolution during the coating, and of its decomposition after the diffusion step. Moreover, it has so far been devoted to the molecules design to tune the final dopant dose and distribution. Here, the main results on the molecular doping are reviewed, and new findings on the interface characteristics, also in terms of mono- and multilayers formation are presented. A systematic study, carried out by fixing the dopant precursor and varying the coating conditions, is also reported, demonstrating that the important doping features can be controlled precisely and that uniformity can be achieved at nanometer level. [ABSTRACT FROM AUTHOR]

Point defects generated during motion of dislocations in silicon have been investigated using their reaction with gold atoms during gold in-diffusion. Deep Level Transient Spectroscopy (DLTS) measurements in n- and p-type samples have revealed that in regions with dislocation densities of 104-106 cm−2, the concentration of gold atoms is by 1.5-2 orders of magnitude higher than in the dislocation-free regions of the same samples. The increase in the gold atom concentration in the regions containing dislocations is explained by the presence of some vacancy complexes generated by dislocations moving in their slip planes. Just after dislocation motion, most of these complexes are not detectable by DLTS. They become observable in DLTS due to their reaction with gold atoms. [ABSTRACT FROM AUTHOR]

Single-layer WS2 is a direct-gap semiconductor showing strong excitonic photoluminescence features in the visible spectral range. Here, we present temperature-dependent photoluminescence measurements on mechanically exfoliated single-layer WS2, revealing the existence of neutral and charged excitons at low temperatures as well as at room temperature. By applying a gate voltage, we can electrically control the ratio of excitons and trions and assert a residual n-type doping of our samples. At high excitation densities and low temperatures, an additional peak at energies below the trion dominates the photoluminescence, which we identify as biexciton emission. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]