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A parameter study of ultrashort pulse laser‐induced modifications in the bulk of ZnS crystals is reported. Experimental results on these modifications and their dependence on the pulse energy, writing speed, and depth are presented, with an emphasis on cross‐sectional morphology and induced refractive index changes. Localized permanent material modifications have been inscribed in the bulk of the crystal using a laser with a center emission wavelength of 2.09 μm and a pulse duration of ≈4 ps. The morphology strongly depends on the laser and optical focusing parameters, in particular, on the pulse energy and processing speed, with a significant shift in depth dependence for short pulse‐to‐pulse separations. Depending on the applied pulse energy, distortions of the lateral profile of the refractive index changes appear in the form of oscillatory features in the transverse plane relative to the inducing laser beam. The true extent of the modified material is revealed by the alternating lateral profile with largest induced negative refractive index change, Δn, of −3.88 × 10−2 ± 0.18. Such parametric insight is of critical importance for the understanding and optimization of the fabrication process and for realizing compact 3D photonic devices in the bulk of materials in a reproducible manner. [ABSTRACT FROM AUTHOR]

ZnS is a II-VI semiconductor with a wide bandgap. ZnS-based nanomaterials have been produced in a variety of morphologies with unique properties and characteristic features. An extensive collection of research activities is available on various synthetic methodologies to produce such a wide variety of ZnS-based nanomaterials. In this comprehensive review, we thoroughly covered all the different synthetic techniques employed by researchers across the globe to produce zero-dimensional, one-dimensional, two-dimensional, and three-dimensional ZnS-based nanomaterials. Depending on their morphologies and properties, ZnS-based nanomaterials have found many applications, including optoelectronics, sensors, catalysts, batteries, solar cells, and biomedical fields. The properties and applications of ZnS-based nanostructures are described, and the scope of the future direction is highlighted. [ABSTRACT FROM AUTHOR]

Quantum dots (QDs) have attracted significant interest because of their tunable bandgaps, which enable numerous applications in fields such as photovoltaics, biomedicine, and materials science. This study explores various core electron treatments in the density functional theory (DFT) analysis of II-VI semiconductor quantum dots and their bulk counterparts. We compared All-electron (AE), Effective Core Potential (ECP), All-Electron Relativistic (AER), and DFT-Semicore pseudopotential (DSPP) treatments. Our findings indicate that the AE treatment aligns closely with the experimental results for smaller QDs, whereas the accuracy of DSPP increases with larger QDs. DSPP provides an optimal balance between computational efficiency and accuracy, making it suitable for studying II-VI QDs. Notably, the bandgap behavior varies, being direct for zinc and cadmium chalcogenides, whereas mercury chalcogenides are zero-gap semiconductors (semimetals). The inner bonds of the QDs exhibit an ionic character, whereas the terminal bonds display a covalent character. This study enhances our understanding of the structural and electronic properties of II-VI quantum QDs, aiding their application in various technologies. [ABSTRACT FROM AUTHOR]

The effect of pressure on the structural and electronic properties of the two binary compounds SrSe and SrTe have been investigated in the present work. The calculations were carried out with the CASTEP code which uses the density functional theory (DFT) based on the pseudopotential and plane-wave (PW-PP) method. To evaluate the exchange and correlation energy, we used the generalized gradient approximation (GGA-PBE). Our results show that, at ambient conditions, the two studied compounds are more stable in the NaCl-type phase (B1). Under the effect of pressure, the two materials undergo a phase transition to crystallize in the CsCl-like structure (B2) at pressures equal to 16 GPa and 12.33 GPa for the compounds SrSe and SrTe, respectively. Analysis of the band structure under conditions of pressure and zero temperature shows that the two compounds are indirect semiconductors. Under the effect of pressure, our calculations predict that the two compounds change electronically to become metals at pressures greater than 46 GPa for SrSe and 13 GPa for SrTe. To give a quantitative description of the variation of the structural and electronic parameters of the two structures with the pressure, we extracted the parametric functions of these parameters as a function of the pressure. Our results are presented and compared with a different experimental and theoretical works. [ABSTRACT FROM AUTHOR]

The experimental data of the temperature dependence of the electrical conductivity σ(T) and the Hall coefficient RH(T) on single crystal samples of n-type CdS reported in literature are reviewed and have been critically analysed including hopping conduction in an impurity band. It is shown that the experimental data of σ(T) and RH(T) reported in almost previous studies can be simultaneously fitted using a common set of the values of material parameters for calculating free-electron conduction, i.e. the conduction and the density-of-state effective mass of electrons, the acoustic-phonon deformation potential, the Fröhlich coupling constant and the piezoelectric coupling coefficient, whereas wide ranges of values for these material parameters had been adopted in different studies. The correct assignment of impurity conduction mechanisms in n-type CdS single crystals is presented. In addition, reasonable explanations are given for unresolved enigmas regarding impurity pairing, unexpected large Hall mobility at low temperatures, and the effect of electric field on hopping Hall mobility. [ABSTRACT FROM AUTHOR]

This paper presents a first-principles investigation of the energy bandgaps of Cd1−xZnxTe, Cd1−xZnxSe and Cd1−xZnxS semiconductor alloys in zinc-blende crystals. The theoretical analysis is based on the full-potential linearized augmented plane wave method within both generalized gradient and local density approximations. Tran–Blaha-modified Becke–Johnson exchange potential was invoked to accurately provide bandgaps and their bowing parameters. A moderate nonlinear dependence with average bowing parameters around b ~ 0.49 eV for Cd1−xZnxTe, b ~ 0.68 eV Cd1−xZnxS, and b ~ 0.63 eV for Cd1−xZnxSe was found. The origin of the nonlinearity is discussed in light of Zunger's approach to conclude that it arises mainly from volume deformation. [ABSTRACT FROM AUTHOR]

The II–VI semiconductor thin films have vast applications in optoelectronics. Cadmium telluride (CdTe) is one such material, which has proved to be useful in the fabrication of solar cells, photodetectors, etc. In the present work, CdTe thin films have been deposited on glass substrates by thermally evaporating CdTe powder under a high vacuum. The optimum film thickness for photovoltaic applications was determined by performing a detailed characterization of the films. The thermal evaporated CdTe films were found to be polycrystalline with a cubic structure. Considerable improvement in the crystallinity was observed with the increase in thickness. The lattice constant, dislocation density, strain, and stress have also been analyzed. The optical properties of the CdTe films have been observed to change with thickness. The maximum optical absorption was found in the near infrared region. The photoluminescence spectra showed a prominent peak, corresponding to the band-edge transition of the CdTe films. The electrical properties of the films were found to improve with thickness. The films yield maximum photocurrent at 820 nm. Based on the detailed characterization, the film thickness of 950 nm was found to be most suitable for photovoltaic application. [ABSTRACT FROM AUTHOR]

Flexible photodetectors exhibit many advantages such as a good bendability, foldability, and even stretchability as well as weight light, which have triggered a widely concerned in wearable electronics including wearable monitoring, wearable image sensing, self‐powered integrated electronics, etc. Recently, various II–VI semiconductor nanostructures have become promising candidates in flexible photodetectors due to their unique characteristics, such as direct bandgap semiconductors, excellent optical and electric properties, high quantum efficiency, and inherent mechanical flexibility. Herein, the most recent progress on low‐dimensional (0D, 1D, 2D, and related heterostructures) II–VI semiconductors based flexible photodetectors and their application in wearable electronic is reviewed. First, a brief introduction of the main sensing mechanisms and key figures of merits for photodetectors is presented. Then, the recent progresses on flexible photodetectors are provided, in which the functional materials synthesis methods are also discussed. More importantly, the applications of the flexible photodetectors are summarized, including wearable monitoring sensors, image sensors, and self‐powered integrated wearable electronics. Finally, the challenges and the future research direction of the flexible photodetectors are discussed, meanwhile the outlook for the development of flexible photodetectors in the future integration of wearable electronic is also provided. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (CQDs), especially core-shell QDs, have attracted dramatic interests as emerging materials in optoelectronic devices due to their size tuneable band-gap, high absorption coefficient, facile and low-cost synthesis routing, etc. However, the precise design of core/shell band engineering along with charge carrier transfer efficiency are still challenging, inevitably impacting the performance of optoelectronic devices. Herein, three different types of CdSe/CdS core-shell heterostructured QDs have been obtained via a proposed synthesis strategy of adjusting the core size but fixing the shell thickness. The performance of the core-shell QDs based self-powered photodetectors can be efficiently regulated by the optimization of synthesis strategy with the design of energy band alignment. Compared to the quasi type-II and the type-I QDs devices, the I l ight / I dark ratio of type-II heterostructure based photodetector is increased by ∼2 and ∼5 orders of magnitude, respectively. The champion device exhibits extraordinary optoelectronic performance in terms of ultrahigh light-to-dark current ratio of 105, photoresponsivity of 10.64 mA/W, at bias of 0 V, respectively. The charge carrier dynamics and transfer mechanisms of the QDs were further investigated, revealing the improved carrier separation and transportation efficiency induced by a strong build-in electric field in type-II CdSe/CdS core-shell heterostructure. This work provides a new strategy for the next-generation self-powered QDs optoelectronics enabled by the proposed synthesis approach along with the design of energy band alignment. [Display omitted] • Three-types of CdSe/CdS core-shell QDs are obtained via a novel synthesis strategy. • The Self-powered photodetectors based on core/shell QDs are demonstrated. • The performance of the devices can be regulated by band alignment engineering. • The type-II heterostructure photodetector exhibits a responsivity of 10.64 mA/W. [ABSTRACT FROM AUTHOR]

Abstract TThe electronic and optical properties of sphalerite (ZnS) are modulated by adsorbing alkali metals (Li, Na, K, Rb, Cs) and halogen (F, Cl, Br, I, At). Simulations based on density‐functional theory are used to study the electronic and optical properties of pristine sphalerite and alkali‐halogen adsorbed sphalerite structures. The results suggest that pristine sphalerite has high absorption in several portions of ultraviolet (UV) region (λ < 250 nm) and negligible absorption in the visible and IR region. The alkali‐halogen adsorbed structure of sphalerite results into red‐shift phenomenon in which an increase in absorption coefficient with wavelength is observed or spectrum shifting towards the red end is observed. Strong absorption for both alkali and halogen adsorbed nanostructures is found throughout the visible zone (~410 to 780 nm) of the spectrum. Bromine adsorbed sphalerite structure results in highest value of absorption in visible region in comparison to other alkali and halogen adsorbed structures. This shift in absorption peaks from UV region to desired visible region range is beneficial for optoelectronic applications and in fabrication of optoelectronics devices such as LED, ARC, solar cells, CRTs and sensors.

Abstract Zinc sulphide (ZnS) nanoparticles were synthesized by the coprecipitation method. The ZnS nanoparticle surface was polymerized with allyl glycidyl ether (AGE), and 3‐aminophenol was then deposited as a ligand on nanosorbent. The modified nanosorbent was investigated with Fourier transform infrared spectroscopy and thermogravimetric analysis. The particle size of the modified nanosorbent was studied with scanning electron microscopy. Some characteristic factors of the adsorption process such as pH and time were investigated for famotidine using the modified nanosorbent. The equilibrium adsorption study of famotidine by 3‐aminophenol‐grafted AGE/ZnS was analysed by adsorption isotherms of the Langmuir, Freundlich, and Temkin models. The famotidine‐releasing process was investigated in simulated biological fluids (intestinal fluid at pH of 7.4 and gastric fluid at pH of 1.2) and demonstrated 65% and 73% famotidine release during periods of 30 h (pH = 7.4) and 60 min (pH = 1.2), respectively. These results reveal the optimal performance of 3‐aminophenol‐grafted AGE/ZnS for sustained drug delivery.

Abstract The electrical and thermal characteristics of metal oxide varistor (MOV) are essential for the study of MOV performance and degradation. This paper provides a modelling method of MOV to simulate its microstructure geometry with the Voronoi network and derive the electrical functions on the grain boundaries. A series of discrete data to describe the resistance‐voltage (R–V) characteristics of MOV from experiments is applied to the proposed model. Through 8/20 μs surge current experiments, the electrical conductivity of MOV is determined to achieve the simulation of the clamping voltage. With this model, the current distribution and temperature distribution over a MOV sample are simulated and analysed by the finite element method (FEM). The simulation results show good agreement with the experimental measurement and inherent feature of MOV.

Peculiar and unique growth mechanisms involved in semiconductor nanowires (NWs) pave the way to the achievement of new crystallographic phases and remarkable material properties, and hence, studying polytypism in semiconductor NWs arouses a strong interest for the next generation of electronic and photonic applications. In this context, the growth of ZnS nanowires has been investigated, as bulk ZnS compound exhibits numerous unstable polytypes at high temperatures, but their stable occurrence is highly anticipated in a nanowire due to its special quasi-dimensional shape and growth modes. In this work, the idea is to provide a change in the growth mechanism via the physical state of catalyst droplet (liquid or solid) and hence, study the induced structural modifications in ZnS nanowires. The HRTEM images of VLS (via liquid alloyed catalyst) grown ZnS NWs show periodic stacking faults, which is precisely identified as a stacking sequence of cubic or hexagonal individual planes leading to an astonishing 15R crystal polymorph. This crystallographic phase is observed for the first time in nanowires. Contrastingly, NWs grown with VSS (via solid catalyst) show crystal polytypes of zinc blende and wurtzite. We calculate and discuss the role of cohesive energies in the formation of such ZnS polytypes. Further, we present the selection rules for the crystallization of such 15R structure in NWs and discuss the involved VLS and VSS growth mechanisms leading to the formation of different crystal phases. [ABSTRACT FROM AUTHOR]

CdTe photovoltaics has achieved one of the lowest levelized costs of electricity among all energy sources. However, for decades, carrier lifetimes have been inferior to those of other prevalent solar cell materials. This quality has inhibited common methods to improve solar cell efficiency such as back‐surface fields, electron reflectors, or bifacial solar cells. In this work, a significant increase in carrier lifetime to values exceeding 200 ns in fully functional CdTe solar cells is demonstrated. The increased lifetime is achieved by large CdSeTe grains at the absorber/emitter interface, intragrain passivation in the absorber layer, and chemical passivation by forming nanoscale oxidized tellurium species at the transparent conducting oxide interface. The carrier lifetime is correlated to the open‐circuit voltage and enables paths for back‐surface manipulation and novel cell architectures to further improve CdTe photovoltaic performance. [ABSTRACT FROM AUTHOR]