Diamond-like Semiconductors Research Articles

A first-principles investigation on a new group of diamond-like semiconductors Cu4-II-Ge2-VI7 (II = Zn, Cd and VI = S, Se) as photovoltaic absorbers

Many diamond-like semiconductors with tetrahedral bonds, such as Si, CdTe and Cu(In,Ga)Se2, have been utilized as absorbers in photovoltaics (PV). In this work, a novel group of diamond-like compounds, namely Cu4-II-Ge2-VI7 with II = Zn/Cd and VI = S/Se, have been explored by first-principles means. From the calculations of the electronic structures and related optical properties, we have demonstrated that all these quaternaries have direct-type band structures, while their band gap energies are not suitable for PV applications. By anionic alloying, however, the width of the band gaps can be tuned to the desired energy. For example, the Cu4ZnGe2S4Se3 alloy has a suitable band gap of 1.34 eV. Our work provides the support and perspective for further experimental research on this group of semiconductors and their alloys as potential candidates in PV technologies.

Phase Equilibria in the Quasi-Ternary System Cu2Se-In2Se3-CuI and the Crystal Structure of the AIBIII2XVI3YVII Compounds, Where AI-Cu, Ag; BIII-Ga; XVI-Cl, Br, I; YVII-S, Se, Te

The quasi-ternary system Cu2Se-In2Se3-CuI has been investigated by x-ray diffraction and differential thermal analysis. The isothermal section at 770 K and the liquidus surface projection of the system have been built. For the first time, the primary crystallization regions, and the coordinates of the invariant and monovariant equilibria have been determined. In the system, the regions of the solid solutions based on the binary, ternary, and quaternary compounds have been investigated. The formation of the CuIn2Se3I quaternary compound, which melts congruently at 1213 K and has a homogeneity region of 15 and 9 mol.% CuI within the composition triangle has been established. For the first time, the crystal structures of CuGa2Te3I and AgGa2Te3Br compounds have been studied using a powder method. They crystallize in the tetragonal symmetry, Space Group I-4, a = 5.9147(4) Å, c = 11.952(2) Å for CuGa2Te3I; a = 6.2977(3) Å, c = 11.9473(7) Å for AgGa2Te3Br compound, respectively. The connection of their structures with the structures of the defective diamond-like semiconductors has been discussed.

Crystal structure, electronic structure, and optical properties of Cu4ZnGe2S7 and Cu4CdGe2S7: Polar diamond-like semiconductors exhibiting second harmonic generation

The novel I4-II-IV2-VI7 quaternary diamond-like semiconductors (DLSs), Cu4ZnGe2S7 and Cu4CdGe2S7, were prepared from the constituent elemental powders at elevated temperatures. Cu4ZnGe2S7 crystallizes in the polar, chiral space group C2 and adopts the Cu4NiSi2S7 structure-type, which can be considered a derivative of the cubic diamond structure. The cadmium analog takes on the Cu5Si2S7 structure-type, which is related to the hexagonal diamond structure, and displays polar, Cc space group symmetry. Both compounds contain [Ge2S7]6- anions created by corner-sharing GeS4 tetrahedra. The crystal structures were carefully evaluated using: 1) extended connectivity tables, 2) minimum bounding ellipsoid analysis, and 3) bond valence sum (BVS) and global instability index (G) calculations. Both compounds are thermally stable up to temperatures exceeding 950 °C and melt incongruently. As assessed using diffuse reflectance spectroscopy, Cu4ZnGe2S7 and Cu4CdGe2S7 possess optical bandgaps of 1.65 eV and 1.90 eV, respectively, which are narrower than the analogous I2-II-IV-VI4 DLSs. Electronic structure calculations show that both compounds are direct-bandgap semiconductors with significant contributions of Cu-d and S-p orbitals to the states at the top of the valence band. While Cu4CdGe2S7 displays a weak second harmonic generation (SHG) response, the second-order nonlinear optical susceptibility, χ(2), of Cu4ZnGe2S7 is 14.8 ± 1.5 pm V-1, assessed using the Kurtz-Perry powder method and an optical-grade AgGaSe2 (AGSe) reference. Both compounds exhibit laser-induced damage threshold values similar to AGSe, ∼0.1 GW cm-2, for λ = 1.064 µm using picosecond laser pulses. Most importantly, Cu4ZnGe2S7 exhibits a phase-matching behavior at λ = 3.1 µm. These results suggest that Cu4ZnGe2S7 holds potential for use in low-powered laser applications involving efficient wave mixing in the mid-IR region.

Structure and Optical Properties of LixAg1–xGaSe2 and LixAg1–xInSe2

Complete substitution of Li atoms for Ag atoms in AgGaSe2 and AgInSe2 was achieved, resulting in the solid solutions LixAg1-xGaSe2 and LixAg1-xInSe2. The detailed crystal structures were determined by single-crystal X-ray diffraction and solid-state 7Li nuclear magnetic resonance spectroscopy, which confirm that Li atoms occupy unique sites and disorder only with Ag atoms. The tetragonal CuFeS2-type structure (space group I4̅2d) was retained within the entirety of the Ga-containing solid solution LixAg1-xGaSe2, which is noteworthy because the end-member LiGaSe2 normally adopts the orthorhombic β-NaFeO2-type structure (space group Pna21). These structures are closely related, being superstructures of the cubic sphalerite and hexagonal wurtzite prototypes adopted by diamond-like semiconductors. For the In-containing solid solution LixAg1-xInSe2, the structure transforms from the tetragonal to orthorhombic forms as the Li content increases past x = 0.50. The optical band gaps increase gradually with higher Li content, from 1.8 to 3.4 eV in LixAg1-xGaSe2 and from 1.2 to 2.5 eV in LixAg1-xInSe2, enabling control to desired values, while the second harmonic generation responses become stronger or are similar to those of benchmark infrared nonlinear optical materials such as AgGaS2. All members of these solid solutions remain congruently melting at accessible temperatures between 800 and 900 °C. Electronic structure calculations support the linear trends seen in the optical band gaps and confirm the mostly ionic character present in Li-Se bonds, in contrast to the more covalent character in Ga-Se or In-Se bonds.

Dense twin and domain boundaries lead to high thermoelectric performance in Sn-doped Cu3SbS4

Exploring high-performance medium-temperature thermoelectric (TE) materials with nontoxicity and low price is of great significance for waste heat recovery. In spite of low price and nontoxicity, the poor intrinsic electrical properties of Cu3SbS4 restrict its potential commercial applications. Herein, intermediate-phase-free Cu3SbS4-based bulks were fabricated by incorporating a sulfurization process between melting and sintering, and the as-formed dense twin and domain boundaries in a Sn-doped Cu3SbS4 system can significantly enhance the electrical conductivity and retain a higher level of the Seebeck coefficient based on the energy filtering effect and band flattening and convergence. The high power factor of ∼13.6 μW cm−1 K−2 and relatively low thermal conductivity are achieved for a 1.5%Sn-doped Cu3SbS4 sample, resulting in a record zT of ∼0.76 at 623 K in Cu3SbS4-based systems. This work develops an effective pathway to synthesize intermediate-phase-free Cu3SbS4-based TE materials and provides an effective strategy for enhancing TE performance in diamond-like semiconductors by interface engineering.

Synthesis, structure, linear and nonlinear optical properties of noncentrosymmetric quaternary diamond-like semiconductors, Cu2ZnGeSe4 (CZGSe) and the novel Cu4ZnGe2Se7

In this study, two quaternary diamond-like semiconductors (DLSs) in the Cu-Zn-Ge-Se system, the known Cu2ZnGeSe4 (also referred to as CZGSe) and the new Cu4ZnGe2Se7, are compared in terms of their crystal structures, electronic structures and physicochemical properties. Both compounds were prepared by high-temperature, solid-state synthesis at 800 °C. Single crystal X-ray diffraction was used to determine the structure of Cu4ZnGe2Se7. The structures of both Cu2ZnGeSe4 and Cu4ZnGe2Se7 can be considered as derivatives of cubic diamond. Cu4ZnGe2Se7, with a reduced symmetry due to the cation ordering pattern, adopts the Cu4NiSi2S7 structure type, with space group C2. The corner-sharing tetrahedra in Cu4ZnGe2Se7 are slightly distorted because the charge for some of the S2- anions is not compensated by the first-nearest-neighbor cations. Rietveld refinements using synchrotron X-ray powder diffraction data were used to assess the phase purity of the samples and confirm the bulk structural behavior. Diffuse reflectance UV/Vis/NIR spectroscopy shows that Cu2ZnGeSe4 and Cu4ZnGe2Se7 have direct optical bandgaps of 1.38 and 0.91 eV, respectively. Electronic structure calculations implementing density functional theory confirm the direct bandgap for Cu4ZnGe2Se7, with a calculated value of 0.62 eV. Both compounds are air stable, thermally stable up to relatively high temperatures, undergo phase transitions and have wide windows of optical clarity. The Kurtz-Perry powder technique was used to determine the second harmonic generation (SHG) responses using a commercial AgGaSe2 standard. While Cu4ZnGe2Se7 displays a weak SHG response, Cu2ZnGeSe4 exhibits a response that is greater than several benchmark materials, with a large SHG coefficient, χ(2), of 43 ± 6 pm/V at λ = 2900 nm.

Structural Modulation from Cu3PS4 to Cu5Zn0.5P2S8: Single-Site Aliovalent-Substitution-Driven Second-Harmonic-Generation Enhancement.

Diamond-like (DL) chalcophosphates, which possess the merits of impressive second-harmonic-generation (SHG) responses, strong laser-induced damage thresholds, and low melting points, are highly desirable for IR nonlinear-optical (NLO) applications. Herein, a new quaternary DL chalcophosphate, Cu5Zn0.5P2S8, is successfully discovered, taking known Cu3PS4 as the template via a single-site aliovalent-substitution strategy. It crystallizes in the orthorhombic system with noncentrosymmetric space group Pmn21, and the 3D DL structure is built by corner-shared [(Cu/Zn)S4], [CuS4], and [PS4] tetrahedra. Compared with its parent Cu3PS4, Cu5Zn0.5P2S8 exhibits a good phase-matching capability and a sharply enhanced SHG effect (10Cu3PS4) benefiting from partial Zn substitution. Moreover, the structure-performance relationships have been illustrated by means of theoretical investigations. Such an aliovalent-substitution strategy based on known DL semiconductors might be widely applied for the discovery of high-performance IR NLO crystals.

Multicomponent Diamond-Like Semiconductors Based on the InBV–CdS System: Bulk and Surface Properties

Multicomponent Diamond-Like Semiconductors Based on the InBV–CdS System: Bulk and Surface Properties

Features and consistent patterns of changes in properties of the system AIIIBV - ZnTe solid solutions

By the methods developed for the InSb-ZnTe, GaSb-ZnTe systems, in the regions of mutual solubility of the initial binary compounds (InSb and ZnTe, GaSb and ZnTe), solid solutions (InSb)x(ZnTe)1-x, (GaSb)x(ZnTe)1-x have been obtained.X-ray, IR and Raman spectroscopic, electrophysical studies of the obtained solid solutions (in comparison with the initial binary compounds and among themselves) have been carried out, following the results of which the obtained solid solutions have been certified as substitutional solid solutions with a cubic sphalerite structure. The information on multicomponent diamond-like semiconductors has been expanded.The acid-base properties of the InSb-ZnTe, GaSb-ZnTe systems components surfaces, varying in composition from weak acid to weakly basic, have been studied.General and distinctive features in the “behavior” of the InSb-ZnTe, GaSb-ZnTe systems solid solutions have been revealed. The relative influence of binary components on the type of dependences “property – composition” has been demonstrated and explained.Practical recommendations have been given for the use of solid solutions with the lowest pHiso values as materials for the manufacture of sensors for main gases trace contamination.

Exploring the AgSb1−xBixI4 phase diagram: Thermochromism in layered CdCl2-type semiconductors

AgSbI4 and several AgSb1–xBixI4 compositions have been synthesized via solid state reactions. Both end members and all intermediate compositions crystallize with the CdCl2 structure type (space group ​= ​R3¯m) and a random distribution of the Ag+ and Sb3+/Bi3+ cations. Hypothetical cation ordered structures have been generated and their stabilities evaluated with density functional theory. This analysis suggests that while charge balanced layers are strongly favored, the long-range interactions that favor ordered stacking of layers are too weak to produce three-dimensional cation ordering. The colors of these materials change noticeably when heated, signaling a large thermochromic effect. For example, the band gap of AgSb0·25Bi0·75I4 changes from 1.68 ​eV ​at room temperature to 1.55 ​eV ​at 150 ​°C. This thermochromic shift in band gap is larger than comparable diamond-like semiconductors, such as CdTe. VASP calculations and molecular dynamics simulations indicate the large thermochromic effect is primarily caused by significant electron-phonon coupling.

Controlling thermoelectric transport via native defects in the diamond-like semiconductors Cu2HgGeTe4 and Hg2GeTe4

Defect analysis and phase boundary mapping of Cu2HgGeTe4 and Hg2GeTe4 reveal reciprocal doping potential despite their similar crystal structures. Measurements validate predictions of Cu2HgGeTe4 as highly degenerate and Hg2GeTe4 as an intrinsic semiconductor.

Cu4MnGe2S7 and Cu2MnGeS4: two polar thiogermanates exhibiting second harmonic generation in the infrared and structures derived from hexagonal diamond.

The new, quaternary diamond-like semiconductor (DLS) Cu4MnGe2S7 was prepared at high-temperature from a stoichiometric reaction of the elements under vacuum. Single crystal X-ray diffraction data were used to solve and refine the structure in the polar space group Cc. Cu4MnGe2S7 features [Ge2S7]6- units and adopts the Cu5Si2S7 structure type that can be considered a derivative of the hexagonal diamond structure. The DLS Cu2MnGeS4 with the wurtz-stannite structure was similarly prepared at a lower temperature. The achievement of relatively phase-pure samples, confirmed by X-ray powder diffraction data, was nontrival as differential thermal analysis shows an incongruent melting behaviour for both compounds at relatively high temperature. The dark red Cu2MnGeS4 and Cu4MnGe2S7 compounds exhibit direct optical bandgaps of 2.21 and 1.98 eV, respectively. The infrared (IR) spectra indicate potentially wide windows of optical transparency up to 25 μm for both materials. Using the Kurtz-Perry powder method, the second-order nonlinear optical susceptibility, χ(2), values for Cu2MnGeS4 and Cu4MnGe2S7 were estimated to be 16.9 ± 2.0 pm V-1 and 2.33 ± 0.86 pm V-1, respectively, by comparing with an optical-quality standard reference material, AgGaSe2 (AGSe). Cu2MnGeS4 was found to be phase matchable at λ = 3100 nm, whereas Cu4MnGe2S7 was determined to be non-phase matchable at λ = 1600 nm. The weak SHG response of Cu4MnGe2S7 precluded phase-matching studies at longer wavelengths. The laser-induced damage threshold (LIDT) for Cu2MnGeS4 was estimated to be ∼0.1 GW cm-2 at λ = 1064 nm (pulse width: τ = 30 ps), while the LIDT for Cu4MnGe2S7 could not be ascertained due to its weak response. The significant variance in NLO properties can be reasoned using the results from electronic structure calculations.

Твердые растворы гетеросистемы InSb-ZnS — первичные преобразователи полупроводниковых сенсоров

Using the specifically developed method, solid solutions of the AIIIBV (InSb), AIIBVI (ZnS) type semiconductor compounds of various composition (InSb)x (ZnS)1-x have been obtained. According to the results of the performed X-ray, micro-, electron-microscopic studies, the obtained solid solutions are certified as substitutional solid solutions with a cubic sphalerite structure, data on multicomponent diamond-like semiconductors has been enlarged. The chemical composition of the solid solutions surfaces and binary components of the InSb-ZnS system exposed in air and in high-vacuum, high-temperature conditions have been determined. According to the results of the acid-base properties studies, the surfaces of the InSb-ZnS system components exposed in the air are assigned to the weakly acidic region (pHiso<7). The views on the predominant relative contribution of Lewis acid sites and the increased activity of surfaces toward the main gases have been stated and proved. The interrelated consistent patterns of changes in the composition of bulk and surface properties have been established. The practicability of their use for a less labour consuming search for the advanced materials intended for the sensor technology has been shown. The obtained solid solutions, specifically those with the lowest pHiso, are recommended for the manufacture of the sensors for the main gases, particularly NH3, trace contamination.

Native Defect Engineering in CuInTe2

Ternary diamond-like semiconductors, such as CuInTe2, are known to exhibit promising p-type thermoelectric performance. However, the interplay between growth conditions, native defects, and thermoe...

Ab initio prediction of the elastic, electronic and optical properties of a new family of diamond-like semiconductors, Li2HgMS4 (M = Si, Ge and Sn)

We have performed comprehensive DFT-based ab initio calculations of the structural parameters, elastic constants and related properties, electronic structures and optical constants of new quaternary diamond-like compounds, Li2HgMS4 (M = Si, Ge and Sn), which are novel promising infrared nonlinear optical materials. Both the GGA-PBEsol and TB-mBJ functionals were used to describe the exchange-correlation interactions. The spin-orbit coupling was incorporated to account for relativistic effects. The optimized structural parameters, viz., lattice parameters and atomic position coordinates, are in very good agreement with the experimental counterparts. The full set of anisotropic single-crystal elastic constants were predicted through the stress-strain technique and the isotropic polycrystalline elastic moduli and related physical parameters were predicted via the Voigt–Reuss–Hill approximation. The elastic anisotropy was characterized through several different anisotropic indexes. Calculated electronic band structures and density of states diagrams show that the studied compounds are wide direct bandgap semiconductors. The calculated bandgaps, ranging from 2.65 eV (for the Sn compound) to 3.23 eV (for the Si compound), are in acceptable agreement with the available experimental counterparts. The energy-dependent anisotropic linear optical coefficients, viz., complex dielectric function, complex refractive index, reflectivity and energy-loss function, were determined and discussed.

Effect of Common-Cation CdBVI Compounds on the Properties of Solid Solutions of ZnS–CdBVI Systems

Solid solutions of ZnS–CdBVI systems (B = S, Se, Te), identified as substitutional solid solutions with the sphalerite and wurtzite structures, are prepared using a previously developed technique. Multifaceted investigation of the prepared systems includes the characterizations of their bulk—crystallographic, structural, and electrical and physical—properties; the surface properties (surface chemical composition and acid-base properties); and identification of the nature, acidity, and surface density of active (acid) sites, which enriches our knowledge of diamond-like semiconductors. The dependences of the bulk and surface properties on the system composition are established. These results can facilitate and expand the search for new materials for modern technology, including sensor devices. We discuss the prospective search for new materials on the basis of the considered systems and provide practical recommendations for sensor fabrication.

A systematic study of the negative thermal expansion in zinc-blende and diamond-like semiconductors

Upon heating, almost all zinc-blende (ZB) and diamond-like semiconductors undergo volume contraction at low temperature, i.e. negative thermal expansion (NTE), instead of commonly expected expansion. Specifically, CuCl has the largest NTE among these semiconductors with a coefficient comparable with the record value of ZrW2O8. So far, underlying physical mechanism remains ambiguous. Here, we present a systematic and quantitative study of the NTE in ZB and diamond-like semiconductors using first-principles calculations. We clarified that the material ionicity, which renders the softening of the bond-angle-bending and thus, the enhancement of excitation of the transverse acoustic (TA) phonon, is responsible for the NTE of ZB and diamond-like semiconductors. With the increase in the ionicity from the groups IV, III-V, IIB-VI to IB-VII ZB semiconductors, the coefficient of the maximum NTE increases due to the weakness in bond-rotation effect, which makes the relative motion between cation and anion transverse to the direction of the bond more feasible and the mode Grüneisen parameters of the TA modes more negative. Since CuCl has the highest ionicity among all ZB and diamond-like semiconductors, it is expected to have the largest NTE, in good agreement with the experimental observation. This understanding would be beneficial for tetrahedral materials with specific applications.

Density Functional Theory Investigations of the Optoelectronic Properties of Li2MnGeS4 and Li2CoSnS4

We are attempting to study the properties of new materials based on Diamond-like semiconductors (DLS). Due to broad collection of useful properties, DLS are exciting materials to study. The novel substances Li2MnGeS4 and Li2CoSnS4 result from using a rational and guileless design approach that leads the discovery of DLSs with wide-ranging regions of optical transparency. So here, we have analyzed their applications in atomic devices and system called “optoelectronic” using the FP-APW method and mBJ method. The band gap value for Li2MnGeS4 is 2.911[Formula: see text]eV and Li2CoSnS4 is 2.45[Formula: see text]eV. The present DLS materials confirm their semiconductor characters. The presence of iron and manganese in these compounds have generated magnetic properties that we explored by the calculation of magnetic moment and spin-densities maps.

ПРИМЕНЕНИЕ ТВЁРДЫХ РАСТВОРОВ АЛМАЗОПОДОБНЫХ ПОЛУПРОВОДНИКОВ В КАЧЕСТВЕ МАТЕРИАЛОВ ДЛЯ КОМПОНЕНТОВ «ЭЛЕКТРОННОГО НОСА»

ПРИМЕНЕНИЕ ТВЁРДЫХ РАСТВОРОВ АЛМАЗОПОДОБНЫХ ПОЛУПРОВОДНИКОВ В КАЧЕСТВЕ МАТЕРИАЛОВ ДЛЯ КОМПОНЕНТОВ «ЭЛЕКТРОННОГО НОСА»

Empirical modeling of dopability in diamond-like semiconductors

Carrier concentration optimization has been an enduring challenge when developing newly discovered semiconductors for applications (e.g., thermoelectrics, transparent conductors, photovoltaics). This barrier has been particularly pernicious in the realm of high-throughput property prediction, where the carrier concentration is often assumed to be a free parameter and the limits are not predicted due to the high computational cost. In this work, we explore the application of machine learning for high-throughput carrier concentration range prediction. Bounding the model within diamond-like semiconductors, the learning set was developed from experimental carrier concentration data on 127 compounds ranging from unary to quaternary. The data were analyzed using various statistical and machine learning methods. Accurate predictions of carrier concentration ranges in diamond-like semiconductors are made within approximately one order of magnitude on average across both p- and n-type dopability. The model fit to empirical data is analyzed to understand what drives trends in carrier concentration and compared with previous computational efforts. Finally, dopability predictions from this model are combined with high-throughput quality factor predictions to identify promising thermoelectric materials.