Binary Semiconductors Research Articles

Surface Chemistry of Ternary Nanocrystals: Engineering the Deposition of Conductive NaBiS2 Films

The ability to engineer the surface chemistry of complex ternary nanocrystals is critical to their successful application in photovoltaic, thermoelectric, and other energy conversion devices. For many years, several studies have shed light on the surface chemistry of unary and binary semiconductor nanocrystals as well as their surface modification with monodentate and multidentate ligands in a variety of applications. In contrast, our understanding of the surface chemistry and ligand modification of ternary and other complex multinary nanocrystals remains relatively limited. Recently, our group reported the synthesis of colloidal NaBiS2 semiconductor nanocrystals with sizes tunable between 2 and 60 nm and a light absorption edge of ca. 1.4 eV. Here, we use a combination of infrared and nuclear magnetic resonance spectroscopies to show that the as-made NaBiS2 nanocrystals are capped by oleylamine and neodecanoate ligands. We investigate biphasic liquid–liquid exchange as a means to replace these native ligands with either carboxylate-terminated lipoic acid or with small iodide ligands, leading in both cases to solubility in polar solvents, such as methanol, water, and dimethylformamide. We also investigate a layer-by-layer, biphasic solid–liquid exchange approach to prepare films of NaBiS2 nanocrystals capped with halide ligands—iodide, bromide, and chloride. Upon exchange and removal of the native ligands, we show that the resistance of NaBiS2 nanocrystal films greatly decreases, with their measured conductivity being comparable to that of films made of isostructural PbS nanocrystals, which have been used in solar cells. Lastly, we report the first solar cell device made of NaBiS2 nanocrystal films with a limited power conversion efficiency (PCE) of 0.07. Further nanostructuring and ligand optimization may enable the preparation of much more efficient energy conversion devices based on NaBiS2 as well as other nontoxic and Earth-abundant, biocompatible multinary semiconductors.

Atomic Investigation on the Facet‐Dependent Melting of Ceramic Nanostructures via In Situ Electron Irradiation

AbstractThermodynamic behavior investigations on nanomaterials are of great scientific interest and possess technological implications for advancing nanoscience and nanotechnology. However, nanoscale thermodynamic studies on ceramic semiconductors are faced with great challenges due to their thermostability, and there lacks a percipient understanding of their atomistic thermal behaviors. Here, the atomic‐scale mechanism of the melting and coalescence processes of binary semiconductors, including rutile TiO2(R) and SnSe nanostructures, via real‐time electron beam (e‐beam) irradiation is reported. Under the e‐beam, the inelastic electron‐matter interactions and the low thermal conductivity of the samples cause a local temperature increase. The in situ melting process is recorded via high‐resolution TEM imaging, which exclusively shows a specific planar melting order of the (001), (011), and (100) for TiO2(R). This measurement provides direct evidence that matches the surface energy differences predicted by existing theoretical calculations and experiments. A similar phenomenon is induced and observed on SnSe, which derives a particular melting order of (210), (211), and (002). Furthermore, the in situ melting and coalescence analysis of ultrafine TiO2(R) nanoparticles suggests surface atom transfer and recrystallization as observed. The demonstration of e‐beam directed shape formation and tailoring reveals the possibility for nano/microscale processing of ceramic nanostructures, which are otherwise considered chemically stable and mechanically robust.

On the Dopability of Semiconductors and Governing Material Properties

To be practical, semiconductors need to be doped. Sometimes, to nearly degenerate levels, e.g. in applications such as thermoelectric, transparent electronics or power electronics. However, many materials with finite band gaps are not dopable at all, while many others exhibit strong preference toward allowing either p- or n-type doping, but not both. In this work, we develop a model description of semiconductor dopability and formulate design principles in terms of governing materials properties. Our approach, which builds upon the semiconductor defect theory applied to a suitably devised (tight-binding) model system, reveals analytic relationships between intrinsic materials properties and the semiconductor dopability, and elucidates the role and the insufficiency of previously suggested descriptors such as the absolute band edge positions. We validate our model against a number of classic binary semiconductors and discuss its extension to more complex chemistries and the utility in large-scale material searches.

Improved Predictive Tools for Structural Properties of Metal-Organic Frameworks.

The accurate determination of structural parameters is necessary to understand the electronic and magnetic properties of metal–organic frameworks (MOFs) and is a first step toward accurate calculations of electronic structure and function for separations and catalysis. Theoretical structural determination of metal-organic frameworks is particularly challenging because they involve ionic, covalent, and noncovalent interactions, which must be treated in a balanced fashion. Here, we apply a diverse group of local exchange-correlation functionals (PBE, PBEsol, PBE-D2, PBE-D3, vdW-DF2, SOGGA, MN15-L, revM06-L, SCAN, and revTPSS) to a broad test set of MOFs to seek the most accurate functionals to study various structural aspects of porous solids, in particular to study lattice constants, unit cell volume, two types of pore size characteristics, bond lengths, bond angles, and torsional angles). The recently developed meta functionals revM06-L and SCAN, without adding any molecular mechanics terms, are able to predict more accurate structures than previously recommended functionals, both those without molecular mechanics terms (PBE, PBEsol, vdW-DF2, and revTPSS) and those with them (PBE-D2 and PBE-D3). To provide a broader test, these two functionals are also tested for lattice constants and band gaps of unary, binary, and ternary semiconductors.

Cytotoxicity, fluorescence tagging and gene-expression study of CuInS/ZnS QDS - meso (hydroxyphenyl) porphyrin conjugate against human monocytic leukemia cells

The toxicity of heavy metals present in binary semiconductor nanoparticles also known as quantum dots (QDs) has hindered their wide applications hence the advent of non-toxic ternary quantum dots. These new group of quantum dots have been shown to possess some therapeutic action against cancer cell lines but not significant enough to be referred to as an ideal therapeutic agent. In this report, we address this problem by conjugating red emitting CuInS/ZnS QDs to a 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin -photosensitizer for improved bioactivities. The glutathione capped CuInS/ZnS QDs were synthesized in an aqueous medium using a kitchen pressure cooker at different Cu: In ratios (1:4 and 1:8) and at varied temperatures (95 °C, 190 °C and 235 °C). Optical properties show that the as-synthesized CuInS/ZnS QDs become red-shifted compared to the core (CuInS) after passivation with emission in the red region while the cytotoxicity study revealed excellent cell viability against normal kidney fibroblasts (BHK21). The highly fluorescent, water-soluble QDs were conjugated to 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin (mTHPP) via esterification reactions at room temperature. The resultant water-soluble conjugate was then used for the cytotoxicity, fluorescent imaging and gene expression study against human monocytic leukemia cells (THP-1). Our result showed that the conjugate possessed high cytotoxicity against THP-1 cells with enhanced localized cell uptake compared to the bare QDs. In addition, the gene expression study revealed that the conjugate induced inflammation compared to the QDs as NFKB gene was over-expressed upon cell inflammation while the singlet oxygen (1O2) study showed the conjugate possessed large amount of 1O2, three times than the bare porphyrin. Thus, the as-synthesized conjugate looks promising as a therapeutic agent for cancer therapy.

Theoretical model for size, dimension and shape effect on electrical behavior of semiconductor nanomaterials

The present study is an effort to develop a simple analytical model without any adjustable parameter for observing the collective effect of size, dimension and shape on electrical susceptibility and dielectric constant of nanomaterials. The size dependence of electrical susceptibility and dielectric constant has been observed for some pure as well as binary semiconductor nanomaterials, in three different dimensions (i.e., nanoparticles, nanowires and nanofilms). It has been observed that the electrical susceptibility and dielectric constant both show reduction with the decrement in size, due to the increased surface-to-volume ratio and lower coordination number. The present study reveals that the difference between the values of electrical susceptibility of nanoparticles and nanowires (5–50%) is less in comparison with nanofilms (10–90%). This difference diminishes on moving toward the higher size range. The decrement in the value of dielectric constant with size is found, maximum for nanoparticles (10–80%) followed by nanowires (10–70%) and minimum in nanofilms (5–60%). The outcomes for the size-dependent dielectric constant have been compared with the available experimental and other theoretical data and found consistency in calculated results with experimental data. The model has been extended to investigate the cross-sectional shape effect along with size on the electrical susceptibility and dielectric constant of nanowires due to large applications by incorporating shape factor. Four different cross-sectional shapes: spherical, square, rectangular and hexagonal nanowires, have been taken for the present study. The calculated results of dielectric constant have been compared with the available experimental data, and close agreement was found. It has been observed that the electrical susceptibility and dielectric constant have the highest value for spherical cross-sectional-shaped nanowires and the lowest for rectangular cross-sectional-shaped nanowires. Deviation graphs show that the values of electrical susceptibility and dielectric constant for rectangular, square and hexagonal cross-sectional-shaped nanowires deviate from spherical nanowires as 2–14%, 2–4% and 1–2%, respectively. The present study confirms the importance of shape effect along with size and dimension for electrical properties of semiconductor nanomaterials.

Photovoltaic properties of low-damage magnetron-sputtered n-type ZnO thin film/p-type Cu2O sheet heterojunction solar cells

The photovoltaic properties of Cu2O-based heterojunction solar cells were improved using an n-type layer composed of thin films in a binary oxide semiconductor. This layer was prepared by a low-damage deposition method that applies a system for multi-chamber radio frequency (r.f.) power superimposed direct current (d.c.) magnetron sputtering. For an Al-doped ZnO (AZO)/n-ZnO/p-Cu2O heterojunction solar cell prepared using r.f. power superimposed d.c magnetron sputtering, we achieved the highest efficiency yet reported (3.22%) by optimizing sputtering conditions such as the substrate-target distance and the r.f.:d.c. power ratio. This value represents characteristics that exceed those of AZO/Cu2O solar cells having a similar structure based on r.f. power superimposed d.c magnetron sputtering.

Calculation of the effective thermal conductivity of a superlattice based on the Boltzmann transport equation using first-principle calculations

In this work, we calculate the effective thermal conductivity coefficient for a binary semiconductor heterostructure using the GaAs/AlAs superlattice as an example. Different periods of layers and different ambient temperatures are considered. At the scale under consideration, the use of models based on the Fourier law is very limited, since they do not take into account the quantum-mechanical properties of materials, which gives a strong discrepancy with experimental data. On the other hand, the use of molecular dynamics methods allows us to obtain accurate solutions, but they are significantly more demanding on computing resources and also require solving a non-trivial problem of potential selection. When considering nanostructures, good results were shown by methods based on the solution of the Boltzmann transport equation for phonons; they allow one to obtain a fairly accurate solution, while having less computational complexity than molecular dynamics methods. To calculate the thermal conductivity coefficient, a modal suppression model is used that approximates the solution of the Boltzmann transport equation for phonons. The dispersion parameters and phonon scattering parameters are obtained from first-principle calculations. The work takes into account 2-phonon (associated with isotopic disorder and barriers) and 3-phonon scattering processes. To increase the accuracy of calculations, the non-digital profile of the distribution of materials among the layers of the superlattice is taken into account. The obtained results are compared with experimental data showing good agreement.

Quantum confinement-induced enhanced nonlinearity and carrier lifetime modulation in two-dimensional tin sulfide

Abstract Two-dimensional tin sulfide (SnS), as a black phosphorus-analogue binary semiconductor, has received considerable attention in photonics and optoelectronics. Herein, the third-order nonlinearity susceptibility Im χ3 is enhanced from −(6.88 ± 0.10) × 10−14 esu to −(15.90 ± 0.27) × 10−14 esu by the size-related quantum confinement in layered SnS nanosheets. Due to the energy level alignment, a phonon-bottleneck effect is observed, which leads to a prolonged carrier lifetime. These results provide a platform for actively tuning the linear and nonlinear optics, and pave the way for designing SnS-based tunable and anisotropic optoelectronic devices.

Biomaterial supported binary semiconductor metal oxide nanocomposite for Water remediation under solar irradiation

An eco friendly biopolymer supported binary metal oxide nanocomposite was prepared by a co precipitation method and characterized by FT-IR, XRD, TGA, UV-DRS, SEM, EDAX and BET analysis. The band gap energy was found to be 2.06 eV. The prepared catalyst was employed for the photocatalytic dye degradation of model pollutant AB113 dye under solar irradiation. The catalytic efficiency of the photocatalyst was confirmed by preliminary studies, kinetics and COD. The reaction rate constant was calculated and the reaction follows first order kinetics. The prepared photocatalyst actively degraded the Acid Blue 113 (97%) dye under solar irradiation within 300 min. Therefore it will be a potential catalyst for dye degradation of the effluents discharged from the dyeing industries.

Effects of substrate temperature and SnO2 high resistive layer on Sb2Se3 thin film solar cells prepared by pulsed laser deposition

Sb2Se3, an emerging promising binary compound semiconductor, was prepared at different substrate temperatures by pulsed laser deposition for thin film solar cells for the first time. In this work, CdS and Sb2Se3 films were subsequently deposited by pulsed laser deposition to simplify the process. Film properties and device performance, closely related to the substrate temperature, were characterized by thermal gravimetric analysis, X-ray diffraction, UV–Vis–NIR spectrophotometer, scanning electron microscope, light and dark current density-voltage, external quantum efficiency and capacitance-voltage, respectively. Results indicate that Sb2Se3 solar cells film deposited at 500 °C is better, with a better efficiency of 3.58%. Furthermore, SnO2 high resistive layer was introduced into Sb2Se3 solar cell to improve the junction quality, leading to a champion device efficiency of 4.41%.

XXIV Международный симпозиум Нанофизика и наноэлектроника", Нижний Новгород, 10-13 марта 2020 г. Анализ фононных мод и электрон-фононного взаимодействия в квантово-каскадных лазерных гетероструктурах

The phonon modes of quantum cascade heterostructures based on binary and ternary semiconductor compounds are modeled. The dependences of the frequencies of the interface phonon modes of the structure on the wave vector in the plane of the layers and on the phase shift in the period of the superlattice are calculated. It was found that the range of variation of the quantum energy of the phonon modes of the GaAs/Al0.25Ga0.75As structure does not exceed 2 meV. The calculated resulting interband scattering rate in the structure, taking into account the interface and confined modes, practically does not differ from the calculations in the approximation of bulk phonons of the structure.

Nonequilibrium plasma aerotaxy of size controlled GaN nanocrystals

High quality gallium nitride (GaN) nanocrystals (NCs) are promising materials in a wide range of applications including optoelectronics, photonics and biomedical devices. Unlike II–VI semiconductors, the synthesis of free-standing GaN NCs is not well-established, and there is a need for a synthesis platform that can provide GaN NCs with tunable size and photonic properties. In this work, we present a flexible gas-phase synthesis method that can deliver crystalline, free-standing, pure GaN NCs with controlled size and narrow size distributions. The method, termed nonequilibrium plasma aerotaxy (NPA), employs an aerosol of Ga and gaseous N2 as the precursors. The term aerotaxy means growth on an unsupported surface, in this case promoted by a nonequilibrium plasma. The key to narrow size distributions is that the NPA mechanism is based upon surface growth, as opposed to coagulation mechanisms that result in broad size distributions. The NPA process converts the Ga aerosol into GaN NCs within 10–100 ms of residence time. The mechanism involves non-thermal vaporization of the source Ga aerosol, which is followed by nucleation and reaction with the excited N2 species in the plasma. Particles can be made to be either hollow or solid. Solid NCs were found to be photoluminescent. Large NCs emitted photons at a peak wavelength near the bulk band-gap transition. Tuning the size to be smaller than 7 nm average diameter led to a blue-shifted photoluminescence. Inline processing of these bare GaN NCs into porous films by supersonic impact deposition is demonstrated. Moving beyond the specific example of GaN, the NPA mechanism is general and can be extended to many other binary, ternary or doped semiconductors.

Temperature dependence of dielectric functions in Yb2O3 and Lu2O3 epitaxial thin films on sapphire (0001)

The fundamental band-gaps of Yb2O3 and Lu2O3 films on sapphire (0001) substrates grown by pulsed laser deposition have been measured by optical transmission and reflectance spectroscopies as a function of temperature. The temperature dependence of the band-gap was analyzed by a model based on phonon dispersion effects and could be explained in terms of phonon-related parameters such as the optical phonon temperature. The phonon dispersion in Yb2O3 was found to fall into material trend based on the data for a large variety of element and binary semiconductors.

Enhanced photoluminescence effects in nanostructured cubic CdS matrix doped with Cu2+ obtained by chemical Bath deposition

In the present work, we highlight the enhancements of the photoluminescent properties of the binary II-VI nanocomposite thin film semiconductor cadmium sulphide (CdS) doped with the metallic ions Cu2+ obtained by low-temperature chemical bath deposition (CBD). The doping percentage of the CdS matrix was around 1.74% determined by X-ray fluorescence spectroscopy. The most intense photo-electronic transitions of Cd 3d5/2 (404.94 eV), S 2p3/2 (161.52 eV) and Cu 2p3/2 (933.27 eV) were detected by X-ray photoelectron spectroscopy. The crystallographic study shows that the preferential growth planes are cubic (111) both in the matrix and the doped samples. HRTEM micrographs exhibit the reduction of the particle size of the CdS matrix from 5.87 to 4.76 nm in the doped sample, which confirms the quantum confinement effect. The first optical effect of the doped CdS was noticed in Raman spectroscopy by a frequency shift of the first longitudinal optical mode (1LO-CdS) from 306 to 302 cm−1, related with the shrinking of the nanoparticle, also a great improvement in the sensibility of the characterization by the surface effects of the Cu2+ metallic ion. Photoluminescence was measured in the temperature range of 258–298 K, which showed more recombination emissions of energetic excitons as consequence of the decrease in particle size and the defects created by the Cu2+ metallic ion in the doped sample in whole the range of investigated temperatures. Also the pronounced stimulation of the luminescent spectra of the semiconductor compound at room temperature.

Annealing and surface treatment effect on the optical and electrical properties of n-type CdS binary compound semiconductors

The preparation of CdS thin films were actualised with electrodeposition technique using cathodic voltage of 1200 milli – Volts (mV). The optical and electrical properties of three different classes of CdS semiconductors namely as – deposited CdS layers (AD-CdS), CdS layers heat-treated in air without any chemical treatment (HT-CdS) and CdS layers treated with CdCl2 and annealed in air (CC-CdS) have been investigated in this work. Results from optical analysis showed that AD-CdS layers have the least absorption edge and highest energy bandgap. Annealing the CdS thin films without and with CdCl2 treatment brings the energy bandgap to same value of ~2.42 eV. The main distinction between the HT- and CC-CdS layers is that the absorption edge of CC-CdS films is sharper than the HT-CdS. Results from electrical analysis revealed that the magnitude of photo-electro-chemical (PEC) cell signals which give a clue about the doping concentration of the semiconductor material is greater in CC-CdS layers than in AD- and HT-CdS layers.Keywords: AD-CdS, HT-CdS, CC-CdS, Energy Bandgap, Absorption Edge, PEC Cell Signal.

Two-dimensional Bi2S3-based all-optical photonic devices with strong nonlinearity due to spatial self-phase modulation

Abstract Bismuth sulfide (Bi2S3) is a binary chalcogenide semiconductor compound that has received much attention in optoelectronic devices because of its stratified structure. In this work we showed that the two-dimensional (2D) Bi2S3 shows strong nonlinearity using spatial self-phase modulation and that the all-optical photonic devices, e.g. the all-optical switches and all-optical diodes, have been demonstrated experimentally by observing the nonlinear behavior of the diffraction rings. In addition, an all-optical diode is designed in this work using combined structure with 2D Bi2S3/SnS2 nanosheet by taking advantage of the reverse saturated absorption of 2D SnS2 and saturated absorption of 2D Bi2S3. Nonreciprocal light propagation has been achieved with different incident wavelength and a variety of incident intensities. Those characteristics make 2D Bi2S3 a potential candidate for the next generation nonreciprocal all-optical device.

Identifying Clusters and/or Small-Size Quantum Dots in Colloidal CdSe Ensembles with Optical Spectroscopy.

It is well-known that optical absorption and photoluminescence (PL) provide information that is sensitive to the size and size distribution of colloidal binary semiconductor quantum dots (QDs). To explore the nature of reaction products, clusters, and/or small-size QDs, we show that it is important to perform as well photoluminescence excitation (PLE) spectroscopy. For two non-hot-injection reactions of cadmium oleate (Cd(OA)2) and selenium (Se) in 1-octadecene (ODE), we show that sequentially extracted products displayed a similar apparent red shift in both absorption and PL with a full width at half-maximum (fwhm) of ∼30 nm. We demonstrate that one reaction (with the presence of diphenyl phosphine (HPPh2)) produced multiple types of clusters (with slightly different optical properties) in one ensemble, while the other reaction (without HPPh2) yielded primarily small-size QDs. Our findings provide evidence for the probable existence of clusters within small-size CdSe QD products, the existence of which complicates the size determination of small-size CdSe QDs.

Influence of Different Spherical Binary Plasmonic NPs on HTM Layer in Methyl Ammonium Lead Triiodide Solar Cell

Methylammonium lead triiodide perovskite solar cells have attracted huge research interest. Its optoelectronic properties are competing with those of silicon wafers. It is a hybrid absorber with a direct band gap of about 1.53 eV with good light-absorption capability appropriate for optoelectronic applications. A typical perovskite solar cell HTML layer rarely incorporates ZnO or Cu 2 O or TiO 2 nanoparticles to increase charge carrier transport. These ZnO, Cu 2 O, TiO 2 nanoparticles can be introduced into the HTM layer to modify its PSCs efficiency and performance. These nanoparticles are direct band gap binary semiconductors with a wide band gap energy range of 2.17 eV to 3.37 eV respectively which can lead to higher transport mobility and enhanced HTM nanostructured layer. In this paper, two model solar cell having a ITO/TiO 2 /CH 3 NH 3 PbI 3 /P3HT/Ag and ITO/TiO 2 /Ag:CH 3 NH 3 PbI 3 /P3HT/Ag structures were proposed, geometrically modelled and simulated using SCAPS-1D software. Their HTM layer (composed of P3HT) was doped with ZnO, Cu 2 O, and TiO 2 nanoparticles respectively to determine their influence on PCEs of this solar cells. It was revealed that starting from undoped P3HT layer all through the Cu 2 O, ZnO to TIO 2 doped layers, efficiency reduced from 13.123 % and 9.071% respectively; fill factor (FF) also reduced from 69.4% to 48.9 % for the doped CH3NH3PbI3 perovskite solar cell while efficiency of doped CH 3 NH 3 PbI 3 perovskite solar cell reduced from 13.033 % and 9.091%, the fill factor (FF) also reduced from 66.4% to 52.9 % respectively. It was noted that the solar cell employing P3HT undoped layer had the best performance and concluded that introducing nanoparticles onto P3HT layer has a negative impact on the performance of CH3NH3PbI3 perovskite solar cell.

State-of-the-art progress in the use of ternary metal oxides as photoelectrode materials for water splitting and organic synthesis

Abstract To tackle the issue of the depletion of fossil fuels and their environmental misdeeds, photoelectrochemical (PEC) water splitting and organic synthesis have been drawing increasing attention as promising environmentally friendly approaches for the production of hydrogen fuel and organics. In the past few decades, almost all possible binary metal oxide semiconductors have been investigated as photoelectrode materials for PEC applications; however, a satisfactory photoelectrode remains elusive. As a result, ternary metal oxide semiconductors have garnered worldwide attention in recent years as potential photoelectrode materials due to their unique advantages. In this review, we firstly introduced the fundamental properties and limitations of ternary metal oxide semiconductors for PEC water splitting and organic synthesis. Then, modified strategies for the performance of ternary metal oxide photoelectrodes are highlighted. Next, recent developments in the use of ternary metal oxide semiconductors as photoelectrode materials for water splitting and organic synthesis are summarized. Finally, several perspectives are presented with respect to the future outlook of PEC water splitting and organic synthesis using ternary metal oxide photoelectrodes. This review provides a systematic overview of the developing information and a referential direction for this research field.