Tetrahedral Semiconductors Research Articles

Coloring Tetrahedral Semiconductors: Synthesis and Photoluminescence Enhancement of Ternary II-III2-VI4 Colloidal Nanocrystals.

Ternary tetrahedral II-III2-VI4 semiconductors, where II is Zn or Cd, III In or Ga, and VI S, Se, or Te, are of interest in UV radiation detectors in medicine and space physics as well as CO2 photoreduction under visible light. We synthesize colloidal II-III2-VI4 semiconductor nanocrystals from readily available precursors and ascertain their ternary nature by structural and spectroscopic methods, including 77Se solid-state NMR spectroscopy. The pyramidally shaped nanocrystals range between 2 and 12 nm and exhibit optical gaps of 2-3.9 eV. In the presence of excess anions on the particle surface, treatment with Lewis acidic, Z-type ligands results in better passivation and enhanced photoluminescence. Electronic structure calculations reveal the most stable, lowest energy polymorphs and coloring patterns. This work will pave the way toward more environmentally friendly, ternary semiconductors for optoelectronics and electrocatalysis.

Surface structure-based model to calculate thermal and optical properties in nanoscale and quantum dot semiconductors

Surface combination structure was used to design the construction of nano and quantum films, particles, and dots. The created model was applied to tetrahedral semiconductor nanoparticles and quantum dots with a successful performance. It works better than reported experimental data across the whole size range, from the bulk state to the critical size of quantum dots. The model helps to figure out the melting point that changes with the nanosize scale as applied on Si and Sn, which are simple tetrahedral semiconductors, and for CdS and CdSe, which are among II-VI group compounds. It was also used to calculate melting-related parameters such as cohesive energy, Debye temperature, vibrational entropy, and melting enthalpy. The nanosize dependence of the lattice volume and the atom's ionization energy describes the solid surface structure. From the model, an equation was obtained to calculate the energy gaps in Si, CdS, and CdSe particles that are nano- and quantum-dot-sized, and the results are compared to the experimental data that goes with these particles.

A comprehensive first-principles investigation of structural, electronic, vibrational, optical, thermodynamic and thermoelectric properties of LiZnAs

The structural, electronic, vibrational, optical, thermodynamic and thermoelectric properties of Nowotny–Juza filled tetrahedral semiconductor LiZnAs under high pressure is investigated using the plane-wave pseudo-potential approach in the frame work of density functional theory (DFT) within the generalized gradient approximation (GGA). The calculated lattice constant (a0) and bulk modulus (B0) at ambient pressure are consistent with earlier reported experiment and theoretical results. The variation in Lattice constant, Bulk modulus (B0), Young modulus (Y), Shear modulus (G), Elastic anisotropy factor (A), Poission ratio (μ), Paugh (B/G) ratio and Elastic constants with pressure is analyzed and concluded. Electronic band structure calculations reveal that with applied pressure direct band gap increases and the indirect band gap decreases. Thermodynamic properties reveals thermodynamically stability with pressurize conditions. The real and imaginary parts of the Dielectric function (ε), Refractive index (η), Extinction Coefficient (k), Optical Conductivity (s), Electron/Optical Energy Loss Function (L), Absorption Coefficient (α), Reflectivity (R) at different pressure conditions are correspondingly studied. With applied pressure the absorption spectra shows a blue shift which makes LiZnAs as potential candidates for the application of optoelectronic devices in ultraviolet frequency range. The thermoelectric properties like Seebeck coefficient (S), Electrical conductivity (σ), and Electronic thermal conductivity (k) and Power factor (PF) have been studied as a function of temperature and chemical potential. Positive value of calculated Seebeck coefficient with temperatures ensures the p-type semiconducting nature of LiZnAs. Results provides theoretical guidance for future experimental investigations and industrial applications of LiZnAs.

Thermoelectric performance of cadmium-based LiCdX (X = N, P, As, Sb and Bi)-filled tetrahedral semiconductors: applications in green energy resources

Thermoelectric performance of cadmium-based LiCdX (X = N, P, As, Sb and Bi)-filled tetrahedral semiconductors: applications in green energy resources

Lindemann’s Role of Melting, Debye Temperature, Dimensionless Mass and Bond Energies for Si-based Tetrahedral Compound Semiconductors

Lindemann’s Role of Melting, Debye Temperature, Dimensionless Mass and Bond Energies for Si-based Tetrahedral Compound Semiconductors

Design Principle for Tetrahedral Semiconductors and Their Functional Derivatives: Cation Stabilizing Charged Cluster Network

Colloidal quantum dots (QDs) of groups II-VI and III-V are key ingredients for next-generation light-emitting devices. Yet, many of them are heavy-element-containing or indirect bandgap, causing limited choice of environmental friendly efficient light-emitting materials. Herein, we resolve this issue by exploring potential derivatives of the parent semiconductors, thus expanding the material space. The key to success is the discovery of a principle for designing those materials, namely, cation stabilizing charged cluster network. Guided by this principle, three novel categories of cubic materials have been predicted, namely, porous binary compounds, I-II-VI ternary compounds, and I-II-III-V quaternary compounds. Using first-principles calculations, 65 realistic highly stable candidate materials have been theoretically screened. Their structural and compositional diversity enables a wide tunability of emitting wavelength from far-infrared to ultraviolet region. This work enriches the family of tetrahedral semiconductors and derivatives, which may be of interest for a broad field of optoelectronic applications.

A simple technique for evaluating dipole moments of Bloch states in tetrahedral semiconductors

Permanent dipole moments of electronic states in non-centrosymmetric materials play a pivotal role in many phenomena. Correctly evaluating them presents an arduous task and usually requires full knowledge of the band structure as well as understanding the intricate concepts of Berry curvature. Here, we show that in a few cases (e.g., zinc blende and wurtzite) a rather facile first-principle analytical derivation of the permanent dipole moments using L’Hôpital’s rule can be performed, and the values and dispersion of these dipoles near high symmetry points can be found using just a couple of widely available material parameters. The results will hopefully contribute to better understanding of shift currents, optical rectification, and other electro-optical phenomena.

Unique Conduction Band Minimum of Semiconductors Possessing a Zincblende-Type Framework.

Tetrahedral semiconductors such as Si adopt a diamond-type crystal structure with low packing density arising from open cavities in the crystallographic space. By taking LiAlGe as an example, we propose a zincblende-type framework as a platform for semiconductors possessing electroactive cavities. LiAlGe adopts a half-Heusler-type crystal structure including an ordered diamond-type sublattice (zincblende-type) (AlGe) and is an indirect semiconductor with a band gap of ∼0.1 eV. The conduction band minimum (CBM) is uniquely located at the cavity space surrounded by four cations (Al4) in real space. The bond ionicity and cation (Al) p orbitals located around the Fermi energy are requisite for the CBM to float in the cavity space. DFT calculations indicate the conversion of the semiconductor to a semimetallic electride under a pressure of ∼8 GPa, which is accompanied by band gap collapse due to electron transfer from valence band maximum to the cavity space. The high-pressure electride of LiAlGe formed under a very small critical pressure is derived from the presence of inherent crystallographic cavities having deep orbital levels energetically. This finding suggests the possible utilization of electroactive cavity spaces in tetrahedral semiconductors, which are widely used in modern electronic devices.

Multiferroicity and giant in-plane negative Poisson\u2019s ratio in wurtzite monolayers

Monolayers of layered materials, such as graphite and molybdenum dichalcogenides, have been the focus of materials science in the last decades. Here, we reveal benign stability and intriguing physical properties in the thinnest monolayer wurtzite (wz) semiconductors, which can be exfoliated from their bulk and stacked to reform the wz crystals. The candidate ZnX and CdX (X = S, Se, Te) monolayers possess low cleavage energy and direct bandgaps, which harbor strongly coupled ferroelectricity and ferroelasticity with low transition barriers, giant in-plane negative Poisson’s ratio, as well as giant Rashba spin splitting, enabling the co-tunability of spin splitting and auxetic magnitudes via multiferroic switching. These wz monolayers can be used as building blocks of devices structures, due to their inherent “self-healable” capacity, which offer more flexibility for semiconductor fabrication and provide a natural platform to probe the interplay of multiple physical effects, bringing light into the rich physics in tetrahedral semiconductors.

Extended-range order in tetrahedral amorphous semiconductors: The case of amorphous silicon

This paper reports the presence of extended-range ordering in the atomic pair-correlation function of amorphous silicon ($a$-Si) using ultra-large atomistic models obtained from Monte Carlo and molecular-dynamics simulations. The extended-range order manifests itself in the form of radial oscillations, on the length scale of 20-40 angstrom, which are examined by directly analyzing the radial distribution of atoms in distant coordination shells and comparing the same with those from a class of partially-ordered networks of Si atoms and disordered configurations of crystalline silicon from an information-theoretic point of view. The study suggests that the extended-range radial oscillations principally originate from the propagation of radial ordering from the first few atomic shells to a distance of up to 40 angstrom. The effect of these oscillations on the first sharp diffraction peak (FSDP) in the structure factor is addressed by obtaining a semi-analytical expression for the static structure factor of $a$-Si, and calculating an estimate of the error of the intensity of the FSDP associated with the truncation of radial information from distant shells. The results indicate that the extended-range oscillations do not have any noticeable effects on the position and intensity of the FSDP, which are primarily determined by the medium-range atomic correlations of up to a length of 20 angstrom in amorphous silicon.

Metal Halide Semiconductors beyond Lead-Based Perovskites for Promising Optoelectronic Applications.

In recent decades, metal halide semiconductors represented by lead-based halide perovskites have shown broad potential in optoelectronic applications. This family of semiconductors differs from traditional tetrahedral semiconductors in crystalline structure, chemical bonding, electronic-structure features, optoelectronic properties, as well as material fabrication method. At present, difficulties arising from both intrinsic material properties (including Pb toxicity and long-term stability) and technological aspects hinder their large-scale commercialization. In this Perspective, we focus on up-and-coming lead-free metal halide semiconductors toward high-performance optoelectronic applications. We start by outlining the advantages of metal halide semiconductors and their physical and chemical underpinnings. We then review composition and structure, electronic structure, optoelectronic properties, and device applications according to classification into three material categories, i.e., three-dimensional halide perovskites, low-dimensional perovskites and perovskite-like materials, and materials beyond perovskites. We conclude with an outlook on the challenges and opportunities of metal halide semiconductors and the future development of the field.

Electronic and optical properties of tapered tetrahedral semiconductor nanocrystals

The quantum confinement effect resulting from size reduction drastically alters the electronic structure and optical properties of optoelectronic materials. Quantum confinement in nanomaterials can be efficiently controlled by morphology variation combined characteristics of nanomaterials, such as their size, shape, and spatial organization. In this study, considering indium arsenide (InAs) in tetrahedral semiconductors as an example, we demonstrated the controllable morphology evolution of InAs nanostructures by tuning the growth conditions. We used the atomistic pseudopotential method to investigate the morphology-dependent electronic and optical properties of InAs nanostructures: tapered and uniform nanostructures, including the absorption spectra, single-particle energy levels, distribution and overlap integral of band-edge states, and exciton binding energies. Compared with uniform nanomaterials, a weaker quantum confinement effect was observed in the tapered nanomaterials, because of which tapered InAs nanostructures have a smaller bandgap, larger separation of photoinduced carriers, and smaller exciton binding energy. The absorption spectra of InAs nanostructures also exhibit strong morphology dependence. Our results indicate that morphology engineering can be exploited as a potential approach for modulating the electronic and optoelectronic properties of nanomaterials.

Direct evidence for the behaviour of single and bipolarons in chalcogenide glasses

We report direct evidence for the characteristic behavior of single and bipolarons in chalcogenide glasses by using broad band impedance spectroscopy. The measured ac conductivity, σ(f, T) of Te based glasses exhibit distinct behavior from those reported in amorphous tetrahedral semiconductors depending on the temperature and frequency. At low temperatures, the measured conductivity is exclusively due to the bipolarons between two charged defect centers. On the other hand, at high temperatures we find in addition to bipolaronic contribution, the single polaron hopping between a charged and neutral defect centers. The behavior of both types of charge carrier (single and bipolaron) shows the distinct relaxation characteristics within the measured frequency window. Remarkably, we observe existence of neutral defect centers with large concentration in tellurium-based chalcogenide glass under dark (normal) conditions revealed by the electron spin resonance (ESR) spectroscopy, which is an essential component for the single polaron hopping process. The estimated neutral defect centers from the dc conductivity measurements are in agreement with those derived from the ESR results. Further, we found that the effective correlation energy (Ueff) becomes less negative in glasses which exhibit single polaron hopping than the glasses found to exhibit typical bipolaronic conduction. The present work unequivocally demonstrates the characteristic behavior of single and bipolarons in chalcogenide glasses and its interdependence on thermal history of the glass samples.

Empirical Relation for Electronic and Optical Properties of Binary Tetrahedral Semiconductors

The concept of ionicity has been developed by Phillips and Van Vechten from the dielectric analysis of the semiconductors and insulators to evaluate various bond parameters of binary tetrahedral (AIIBVI and AIIIBV) semiconductors. In this paper, an advance hypothesis of average atomic number of the elements in a compound has been used to evaluate intrinsic electronic and optical parameters such as ionic gap (Ec), average energy gap (Eg), crystal ionicity (fi) and dielectric constant (ϵ) of binary tetrahedral semiconductors.

Optoelectronic Properties of Ternary Tetrahedral Semiconductors

The dielectric interpretation of crystal ionicity evolved by Phillips and Van Vechten (P.V.V) has been utilized to evaluate various ground state properties for broad range of semiconductors and insulators. Although, the relevance of P.V.V dielectric theory has been restricted to only simple ANB8-N structured compounds, which have a particular bond. Levine has broadened P.V.V. theory of ionicity to multiple bond and complex crystals and evaluated many bond parameters for ternary tetrahedral semiconductors. Some other researchers have extended Levine’s work with a concept of ionic charge product and nearest neighbour distance to binary and ternary tetrahedral crystals to evaluate the ground state properties. In this paper, a new hypothesis of average atomic number of the elements in a compound has been used to understand the some electronic and optical properties such as ionic gap (Ec), average energy gap (Eg), crystal ionicity (fi), electronic susceptibility (χ), and dielectric constant (ϵ) of ternary tetrahedral (AIIBIV and AIBIII) semiconductors. A reasonably acceptable agreement has been noticed between our evaluated values and other researchers reported values.

Structural and elastic properties of binary semiconductors from energy gaps

In the present work, we have calculated the structural and mechanical properties of II–VI and III–V tetrahedral semiconductors using some empirical relations. The calculated properties are then correlated with the optical energy gap of respective semiconductors. We carried out a comparative analysis between the predictions obtained from different empirical relations. An exponential relationship is proposed to obtain plasmon energy of binary tetrahedral semiconductors directly from their energy gap. The plasmon energy have been correlated with some of the semiconductor properties. The predicted values of the structural and elastic properties of the semiconductors from a recently proposed Tripathy relation are found to be compatible with those from many other established empirical formulae.

The underappreciated lone pair in halide perovskites underpins their unusual properties

Abstract

Disorder by design: A data-driven approach to amorphous semiconductors without total-energy functionals

X-ray diffraction, Amorphous silicon, Multi-objective optimization, Monte Carlo methods. This paper addresses a difficult inverse problem that involves the reconstruction of a three-dimensional model of tetrahedral amorphous semiconductors via inversion of diffraction data. By posing the material-structure determination as a multiobjective optimization program, it has been shown that the problem can be solved accurately using a few structural constraints, but no total-energy functionals/forces, which describe the local chemistry of amorphous networks. The approach yields highly realistic models of amorphous silicon, with no or only a few coordination defects (≤1%), a narrow bond-angle distribution of width 9–11.5°, and an electronic gap of 0.8–1.4 eV. These data-driven information-based models have been found to produce electronic and vibrational properties of a-Si that match accurately with experimental data and rival that of the Wooten-Winer-Weaire models. The study confirms the effectiveness of a multiobjective optimization approach to the structural determination of complex materials, and resolves a long-standing dispute concerning the uniqueness of a model of tetrahedral amorphous semiconductors obtained via inversion of diffraction data.

Accuracy of Hybrid Functionals with Non-Self-Consistent Kohn-Sham Orbitals for Predicting the Properties of Semiconductors.

Accurately modeling the electronic structure of materials is a persistent challenge to high-throughput screening. A promising means of balancing accuracy against computational cost is non-self-consistent calculations with hybrid density-functional theory, where the electronic band energies are evaluated using a hybrid functional from orbitals obtained with a less demanding (semi)local functional. We have quantified the performance of this technique for predicting the physical properties of 16 tetrahedral semiconductors with bandgaps from 0.2 to 5.5 eV. Provided the base functional predicts a nonmetallic electronic structure, bandgaps within 5% of the PBE0 and HSE06 gaps can be obtained with an order of magnitude reduction in computing time. The positions of the valence and conduction band extrema and the Fermi level are well reproduced, enabling calculation of the band dispersion, density of states, and dielectric properties using Fermi's Golden Rule. While the error in the non-self-consistent total energies is ∼50 meV atom-1, the energy-volume curves are reproduced accurately enough to obtain the equilibrium volume and bulk modulus with minimal error. We also test the dielectric-dependent scPBE0 functional and obtain bandgaps and dielectric constants to within 2.5% of the self-consistent results, which amounts to a significant improvement over self-consistent PBE0 for a similar computational cost. We identify cases where the non-self-consistent approach is expected to perform poorly and demonstrate that partial self-consistency provides a practical and efficient workaround. Finally, we perform proof-of-concept calculations on CoO and NiO to demonstrate the applicability of the technique to strongly correlated open-shell transition-metal oxides.

Passivating Detrimental DX Centers in CH3 NH3 PbI3 for Reducing Nonradiative Recombination and Elongating Carrier Lifetime.

After a period of rapid, unprecedented development, the growth in the efficiency of perovskite solar cells has recently slowed. Further improvement of cell efficiency will rely on the in-depth understanding and delicate control of defect passivation. Here, the formation mechanism of iodine vacancies (VI ), a typical deep defect in CH3 NH3 PbI3 (MAPbI3 ), is elucidated. The structural and electronic behaviors of VI are like those of a DX center, a kind of detrimental defect formed by large atomic displacement. Aided by the passivation mechanism of DX centers in tetrahedral semiconductors, it is found that the introduction of Br strengthens chemical bonds and prevents large atomic displacements during defect charging. It therefore reduces the defect states and diminishes electron-phonon coupling. Using time-domain density functional theory (DFT) combined with nonadiabatic molecular dynamics, it is found that the carrier lifetime can be enhanced from 3.2 ns in defective MAPbI3 to 19 ns in CH3 NH3 Pb(I0.96 Br0.04 )3 . This work advances our understanding of how a small amount of Br doping improves the carrier dynamics and cell performance of MAPbI3 . It may also provide a route to enhance the carrier lifetimes and efficiencies of perovskite solar cells by defect passivation.