Semiconductor Solid Solutions Research Articles

(Invited) Photocatalytic H2 Evolution Activity of Anisotropic-Shaped ZnSe-AgInSe2 Solid Solution Quantum Dots with a Near-IR-Responsivity

Semiconductor nanocrystals, often referred to as quantum dots (QDs), exhibit unique physicochemical properties due to the quantum size effect when their size is less than 10 nm. In our previous works, we successfully synthesized Zn-Ag-In-S (ZAIS) solid solution QDs with a tunable energy gap (Eg) and then reported the photocatalytic activity for H2 evolution depending on their morphology and particle composition [1,2]. However, ZAIS QDs have limited light absorption with wavelengths less than ca. 600 nm, restricting their utilization of near-infrared light in solar light. In this study, we report the preparation of near-IR-responsive QD photocatalysts with use of Zn-Ag-In-Se (ZAISe) solid solution semiconductors. Precise controls over their morphology and particle composition enabled to vary their photocatalytic H2 evolution activity.ZAISe QDs with different compositions and particle shapes (sphere or rod) were synthesized by thermal decomposition of corresponding metal acetates and selenourea in a mixture solution of oleylamine and dodecane thiol at 250 oC. The chemical composition of QDs was controlled by varying the Zn fraction in metal precursors, ensuring nearly stoichiometric composition.The obtained QDs with a rod shape had lengths varying from ca. 10 to 100 nm, correlating with an increase in the Zn fraction. The onset wavelengths of absorption spectra of the ZAISe QDs were red-shifted from 500 nm to 900 nm with decreasing Zn fraction, indicating that the Eg of ZAISe QDs was controlled between visible and near-infrared wavelength regions.The QDs modified with dodecane thiol showed poor dispersibility in water and almost no photocatalytic activity for H2 evolution. In contrast, the surface modification of QDs with 3-mercaptopropionic acid enabled to uniformly disperse in an aqueous solution. The photocatalytic activity of ZAISe QDs was investigated for H2 evolution as a model reaction. The irradiation to ZAISe QDs in an aqueous solution containing Na2S and Na2SO3 as hole scavengers was carried out using Xe lamp light (λ> 350 nm). The H2 evolution rate exhibited a remarkable dependence on both the composition and particle shape of ZAISe QDs. The photocatalytic activity showed a tendency to increase with the enlargement of the Eg of QDs, probably due to the negative shift of conduction band minimum potential. The optimum H2 evolution activity was obtained with rod-shaped QDs having the Eg of 1.65 eV, being twice as large as that of spherical QDs with a similar Eg. This behavior can be attributed to the change of the crystal facets exposed on the QD surface. References Kameyama, T. Takahashi, T. Machida, Y. Kamiya, T. Yamamoto, S. Kuwabata, and T. Torimoto, J. Phys. Chem. C, 2015, 119, 24740-24749.Torimoto, Y. Kamiya, T. Kameyama, H. Nishi, T. Uematsu, S. Kuwabata, and T. Shibayama, ACS Appl. Mater. Interfaces 2016 , 8, 27151-27161.

Percolation phase transition, self-organization processes and thermal conductivity in PbSe1-xTex semiconductor solid solutions at small Te concentration

ABSTRACT The isotherms of the lattice thermal conductivity λ L for the PbSe1-xTex semiconductor solid solutions (х = 0–0.045) were obtained in the temperature range T = (200–600) K. The λ L(x) dependences exhibit a general trend to a decrease in λ L with increasing x, but the peaks are observed near x = 0.007, 0.015 and 0.0025 indicating the presence of phase transformations. We associated the first peak with a percolation-type phase transition to the impurity continuum and estimated the critical index for λ L within the framework of dynamic scaling theory. The second and third peaks were attributed to the self-organization processes in the PbSe1-xTex after the percolation threshold reaching. The effective cross-sections σ s for phonon scattering by impurity (Te) atoms were determined experimentally and calculated theoretically using the Klemens theory. The data obtained are another confirmation of our assumption about the presence of such percolation-type phase transition in any solid solution.

Advanced Cd1-xMnxTe:Fe2+ semiconductor crystals for IR applications: The role of the composition and sin-band redshift spectra effect

Doped semiconductor crystals of solid solution Cd1-xMnxTe:Fe2+ were grown by the high-pressure Bridgman method, covering the range of their existence as a zinc blende structure (0 < x < 0.76). The concentration of the Fe2+ impurities was approximately 10−3 wt% in all the studied samples. The structural and optical properties of the crystals were investigated, including the case of high concentrations of x > 0.4. The correlations between the composition of solid solution crystals of Cd1-xMnxTe:Fe2+, the lattice constant, the band gap, and the maxima positions of the Fe2+ active ion absorption and emission spectra were found experimentally and explained physically. A theoretical model based on the principle of compositional additivity for solid solution semiconductor materials was first used for explaining the long-wavelength sin-band linear “redshift” of absorption and emission bands in the spectra of Cd1-xMnxTe:Fe2+ crystals with increasing solid solution concentration. A new effect is discovered for the differentiated redshift of the Jahn-Teller components (bands) of the total absorption spectrum. Longwavelength absorption bands have a stronger redshift than shortwavelength absorption bands. The redshifts in the maxima of the total absorption and emission spectra have shift (slope) coefficients Kab≈1.7 nm/at.% and Kem≈6.1 nm/at.%, respectively. The obtained results can be used to predict and design laser media based on Cd1-xMnxTe:Fe2+ solid solution crystals while controlling the lasing range (for all Mn concentrations).

Modeling of the properties of the semiconductor solid solution Lu1-xVxNiSb in the presence of magnetic ordering

Modeling of the thermodynamic, structural, energetic and magnetic properties of the semiconductor solid solution Lu1-xVxNiSb was carried out under the condition of the presence of a magnetic moment on the V atoms and the occurrence of spontaneous magnetization. It is shown that the change in the unit cell parameter a(x) and the mixing enthalpy ΔHmix(х) depends little on the presence or absence of spontaneous magnetization. Modeling of the distribution of the density of electronic states DOS in the presence of a magnetic moment on V atoms revealed the splitting of energy states with spins up and down while preserving the band gap εg of Lu1-xVxNiSb. The relationship between the concentration of magnetic V atoms in Lu1-xVxNiSb and the Curie temperature ТС, when spontaneous magnetization is destroyed and the substance becomes paramagnetic, is established. The solid solution semiconductor Lu1-xVxNiSb, provided spontaneous magnetization is present, can be considered as a promising magnetocaloric.

Transport and thermoelectric properties of the Pb1-xSnxTe topological crystalline insulator in the vicinity of the band inversion

Semiconductor solid solutions Pb1-xSnxTe are well known as promising materials widely used in the IR electronics, thermoelectricity and other fields of science and technology. Recently, it has been found that these alloys in certain concentration ranges exhibit the properties characteristic of the new quantum objects of solid-state physics – topological crystalline insulators (TCIs), whose unique properties define new possibilities for practical use of these materials in spintronics, quantum computing and thermoelectricity. The fact that in Pb1-xSnxTe the band inversion near some composition xc, leads to the emergence of the TCI states stimulates a detailed study of the behavior of transport and thermoelectric properties near xc. In this work, for the Pb1-xSnxTe solid solutions in the composition range x = 0.59–0.68, we obtained the dependences of electrical conductivity, the Hall coefficient, charge carrier mobility, the Seebeck coefficient, and thermoelectric power factor on x at fixed temperatures in the interval (77–300) K. In the isotherms of all studied properties, we observed peaks at x ∼0.62 and attributed them to the band inversion and transition into the TCI state, which are accompanied by the self-organization processes in the crystal lattice.

Processes of Current Transport in p-Si-n-(Si&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;1−&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;y&lt;/sub&gt;&lt;/i&gt;&lt;sub&gt;−&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;z&lt;/sub&gt;&lt;/i&gt;(GaP)&lt;i&gt;&lt;sub&gt;y&lt;/sub&gt;&lt;/i&gt;(ZnSe)&lt;i&gt;&lt;sub&gt;z&lt;/sub&gt;&lt;/i&gt; Heterostructure Produced by Liquid Phase Epitaxy

The possibility of growing multicomponent epitaxial films of a semiconductor solid solution of molecular substitution (Si2)1−y−z(GaP)y(ZnSe)z on Si and GaP substrates by liquid-phase epitaxy is shown. The distribution profiles of the atoms of the solid solution components Ga, P, Zn, Se, and Si over the thickness of the epitaxial film have been determined. The current-voltage (I−V) characteristics of p-Si-n-(Si2)1−y−z(GaP)y(ZnSe)z heterostructures have been studied. A temperature-independent I−V characteristic has been found, the existence of which is explained on the basis of a theory considering the possibility of "blurring" of the impurity level. By comparing the theoretical and experimental results, the half-width of the blurring band for the energy levels of atoms of Si2 and GaP molecules was determined, which had values equal to 0.146 and 0.34 eV, respectively.

Modulating Composition upon the Spinodal Decay of Elastically Deformed Semiconductor Solid Solutions under Conditions of Energy Resonance

Modulating Composition upon the Spinodal Decay of Elastically Deformed Semiconductor Solid Solutions under Conditions of Energy Resonance

Narrow bandgap ferroelectric [KNbO3](1-x)-[BaCo1/2Nb1/2O3-δ]x solid solution for bulk photovoltaic cell

We report a stable bulk photovoltaic effect in [KNbO3]0.9-[BaCo1/2Nb1/2O3–δ]0.1 (KBCNO-91) solid solution as a result of the light-induced electric field in the orthorhombic phase of KBCNO. Introducing Ba2+ and Co3+ ions in the host lattice of perovskite solid solution, the bandgap can be tuned from 3.2 to 1.59 eV. A photovoltaic cell consists of a 43 nm thin KBCNO-91 perovskite oxide semiconductor sandwiched between the metal electrodes evoke open-circuit voltage (VOC) of >1.9 V, above the bandgap with short-circuit current of ∼1 nA at no external bias (0 V). The fabrication of a two-dimensional ferroelectric solid solution semiconductor with a narrow bandgap of ∼1.59 eV enables the conversion of visible photons into electrical energy in a compact electrode configuration. The device retains its stability for over one year and is expected to be a potential candidate for the next generation of photovoltaic cells.

Investigation of thermoelectric material based on Lu1-xZrxNiSb solid solution. II. Modeling of characteristics

The KKR (AkaiKKR software package) and FLAPW (Elk software package) methods were used to model the structural, thermodynamic, energetic, and electrokinetic characteristics of the Lu1-xZrxNiSb semiconductor solid solution. It is shown that defects of acceptor nature are present in the structure of LuNiSb as a result of vacancies in positions 4a and 4c of Lu and Ni atoms, respectively, which generates two acceptor levels eAVac 4a and eAVac 4c in the band gap εg. When Zr atoms are introduced into the LuNiSb structure by replacing Lu atoms in position 4a, Zr atoms also occupy vacancies in this position, which increases the lattice parameter a(x) and eliminates defects of acceptor nature and corresponding acceptor levels eAVac 4a. When the vacancies are filled, Lu atoms are displaced, which reduces the value of the unit cell parameter and generates defects of donor nature and donor levels eD4a. The Ni atoms return to position 4c, which increases the a(x) value and eliminates defects of acceptor nature and the corresponding acceptor levels eAVac 4c. At the lowest concentration of Zr atoms, the conduction type of Lu1-xZrxNiSb changes from p- to n-type. The simulation results are consistent with experimental studies of Lu1-xZrxNiSb.

Perspectives of Double Feeding of the Melt Method on the Example of the Analysis of the InAs(1-x)–GaAs(x) Solid Solution Crystals Growth

Using the example of InAs-GaAs system, the potential of double feeding of the melt method for growing single crystals of semiconductor solid solutions is shown. The concentration profiles of InAs-GaAs solid solutions crystals for certain modes of the considered method are calculated in Pfann approximation. In addition, under the same conditions, InAs-GaAs crystals were grown and their concentration profiles were determined. The results obtained give good agreement between the experimental and calculated data. It is shown that mathematical modeling of InAs-GaAs crystals growth by setting the crystallization and melt-feeding rates with constituent components makes it possible to obtain the required distribution of the main components in the direction of crystal growth, including uniform distribution, in the entire series of continuous InAs-GaAs solid solutions. The double feeding of the melt method is shown to be promising for obtaining single crystals of semiconductor solid solutions with a given concentration profile.&#x0D;

FEATURES OF THE ELECTRICAL PROPERTIES OF HETEROJUNCTIONS N-GAAS-P-(GAAS)1 - X - У(GE2)X(ZNSE)Y

The optimal technological conditions for growing multicomponent epitaxial films of solid solutions (GaAs)1 - x - y(Ge2)x(ZnSe)y with specified physical properties by liquid-phase epitaxy have been determined. It has been established that the above conditions for growing thin films from a tin solution-melt at temperature intervals of 730-630, 650-550 °С with a substrate cooling rate of 1 deg/min are the most optimal. In this case, the films had a thickness of 10 μm and p-type conductivity. For ohmic contacts to such semiconductor solid solutions, Sn, Au, In, (In-Ga) and (Ge-Ag) alloys were used. It was determined that the mobility of current carriers depends on the composition, the structural perfection of the epitaxial layers and the ionization energy of the atoms of the constituent components have values of 0.19, 0.07, 0.029 eV. It has been established that in heterostructures of the n-GaAs-p-(GaAs)1 - x - y(Ge2)x(ZnSe)y type, obtained at Т = 7500 °С, the current transmission is determined by tunneling-recombination, and in the samples obtained at Т = 7300 °С, by currents limited volume charges. It was also determined that a region with a higher resistivity is formed at the heterointerface, the thickness of which, depending on the growth conditions of thin films, is from 0.2 to 0.5 μm.

Assembling ZIF-67@Cd0.5Zn0.5S nanocomposites with an enhanced photocatalytic activity

Herein, an efficient inorganic/organic hybrid photocatalyst composed of zeolitic imidazolate framework (ZIF-67) decorated with Cd0.5Zn0.5S solid solution semiconductor was constructed. The properties of prepared ZIF-67@Cd0.5Zn0.5S nanocomposite and its components (ZIF-67 and Cd0.5Zn0.5S) were investigated using XRD, FESEM, EDX, TEM, DRS and BET methods. The photocatalytic activity of fabricated ZIF-67@Cd0.5Zn0.5S nanocomposite were measured toward removal of methyl violet (MV) dye as a simulated organic contaminant. Under visible-light and specific conditions (photocatalyst dose 1 g/l, MV dye 10 mg/l, unmodified solution pH 6.7 and reaction time 60 min.), the acquired ZIF-67@Cd0.5Zn0.5S photocatalyst showed advanced photocatalytic activity (96.6%) than Cd0.5Zn0.5S (91.1%) and ZIF-67 (82.7%). Besides, the recyclability assessment of ZIF-67@Cd0.5Zn0.5S in the degradation process showed an unimportant decrease (2.5%) after five successive cycles.

Activation conductivity and superconducting state in solid solutions (PbzSn1-z)0.8In0.2Te.

We have studied temperature (1.5 K < T < 300 K) and magnetic field H < 5 T dependences of the electrical resistivity in bulk polycrystalline samples of semiconductor solid solutions (PbzSn1-z)0.8In0.2Te with various Pb content 0.1 ≤ z ≤ 0.9. The transition to the superconducting (SC) state was observed in samples with z ≤ 0.5 at helium temperatures with the critical transition temperature increasing up to Tc = 4.1 K with an increase of the Pb content up to z = 0.5. The bulk superconductivity in solid solutions with z ≥ 0.6 was not detected at temperatures T > 1.5 K. An exponential increase of the resistivity was observed in samples (PbzSn1-z)0.8In0.2Te with z ≥ 0.5 in the temperature range 40 K < T < 120 K. Experimental data was interpreted considering a shift of the energy position of the indium impurity band EIn in the complex valence band spectrum of (PbzSn1-z)0.8In0.2Te with changing lead content z. The exponential increase of the resistivity with decreasing temperature in studied solid solutions is observed when an energy barrier Ea appears between valence band states and quasilocal impurity states of In. The energy barrier increases with an increase of the Pb content in compounds with 0.5 ≤ z ≤ 0.8 and reaches maximum value Ea = 9.7 meV in the solid solution with z = 0.8. The SC state at helium temperatures was observed in (PbzSn1-z)0.8In0.2Te at z ≤ 0.4 when there is no energy barrier between zone and impurity states (i.e. the indium impurity band is located within the valence Σ-band), or at z = 0.5 when the activation energy Еа = 0.7 meV is less than the superconducting gap ΔS. Possible reasons for a decrease in the resistivity at T < 4.2 K in non-SC samples (PbzSn1-z)0.8In0.2Te with z ≥ 0.6 are also discussed.

Investigation of thermoelectric material based on Lu1-xZrxNiSb solid solution. I. Experimental results

The effect of doping of half-Heusler phase p-LuNiSb (MgAgAs structure type) by Zr atoms on the structural, kinetic, energetic and magnetic characteristics of the semiconductor solid solution Lu1-xZrxNiSb was studied in the ranges: T = 80–400 K, x = 0–0.10. From experimental studies it has been established that doping of p-LuNiSb compound with Zr atoms simultaneously generates both structural defects of acceptor and donor nature, the concentration of which increases with increasing content of Zr atoms. It was shown that the investigated semiconductor solid solution Lu1-xZrxNiSb is a promising thermoelectric material.

Investigation of semiconductive Lu1-xScxNiSb solid solution

The electrokinetic and energetic characteristics of the semiconductor solid solution Lu 1- x Sc x NiSb were investigated in the ranges Т =80–400 K, х =0–0.10 . Samples were prepared using an electric arc furnace by direct arc melting of the constituent elements under a purified argon atmosphere (porous Ti was used as a getter). The alloys were annealed at 1 073 K for 720 hours and quenched in cold water. Phase analysis was performed using X-ray powder diffraction patterns of the synthesized samples. The elemental and phase compositions of the synthesized samples were examined by Scanning Electron Microscopy (SEM) using Tescan Vega 3 LMU scanning microscope. Microprobe analysis of the concentration of atoms on the surface of Lu 1- x Sc x NiSb samples, including x = 0–0.10, established their correspondence to the initial compositions of the alloys, and X-ray phase and structural analyzes showed no traces of extraneous phases on the diffractograms except for the main phase indexed in the MgAgAs structure type. The temperature dependencies of electrical resistivity ( r ( T )) were measured employing two-probe method on millimeter-scale, well-shaped pieces cut by spark erosion from the polycrystalline samples in the temperature range 80–400 K. Thermopower coefficient ( α ) was measured in relation to the pure copper in the temperature range 80–400 K. It has been experimentally established that in the Lu 1‑ x Sc x NiSb solid solution both structural defects of neutral and donor nature are simultaneously generated, the concentration of which increases with increasing content of Sc atoms. The observed high-temperature activation parts on the temperature dependences of the resistivity ln( ρ (1/ T )) for all Lu 1- x Sc x NiSb samples indicates the location of the Fermi level ε F in the band gap of the semiconductor, and positive values of the thermopower coefficient α ( T ) specify its position near the valence band. The main carriers of electric conductivity are free holes. From the high-temperature parts of the dependence α (1/ T ) the values of the activation energy ε 1 α are calculated, which are proportional to the amplitude of large-scale fluctuations of continuous energy bands. The calculated from the low-temperature parts values of activation energy ε 3 α are proportional to the modulation amplitude of small-scale fluctuations of strongly doped and compensated semiconductor. It was shown that the investigated semiconductor solid solution Lu 1- x Sc x NiSb is a promising thermoelectric material. Keywords : electric conductivity, thermopower coefficient, Fermi level, structural defect.

CHARACTERISTICS OF THERMOMETRIC MATERIAL Lu1-xScxNiSb

CHARACTERISTICS OF THERMOMETRIC MATERIAL Lu1-xScxNiSb

Composition modulation in the GaxIni-xPyAs1-y - InP heterostructure during spinodal decomposition under the conditions of internal energy resonance

The Cahn-Hilliard concepts are generalized and used to the description of the spinodal decomposition of A3B5 quaternary semiconductor solid solutions, when the mixing of components occurs simultaneously in the metallic and metalloid sublattices of the sphalerite structure. The resulting system of differential equations for material decomposition was used to describe the effect of composition modulation observed in the synthesis of GaxIn1-xPyAs1-y - InP heterostructures. Numerical simulation of the spinodal decomposition of the GaxIm-xPyAsuy solid solution is carried out. The intervals of the thermodynamic parameters of the technological process of the synthesis of structures, in which the effect of modulation of the composition should be manifested, are found.

Synthesizability and Properties of Metastable Semiconductors for Solar Energy Conversion

Metastable semiconductors in many chemical systems have been discovered that have desirable semiconductor properties for driving fuel-producing redox reactions from water and sunlight, such as strong visible light absorption, optimal band-edge energies, extreme defect tolerance, and enhanced carrier mobilities and charge separation. These properties are intimately related to their metastable nature, i.e., their crystalline structures and compositions lead to thermodynamic instabilities. New results will be presented that demonstrate flux-mediated synthetic routes to new metastable n-type Sn(II)-titanates and p-type Cu(I)-niobates. These semiconductors possess some the smallest known visible-light band gaps that also maintain suitable conduction and valence band energies for the photocatalytic reduction and oxidation of water to molecular hydrogen and oxygen, respectively. Their electronic structures also show advantageous features for solar energy conversion, such as small bandgaps, high band dispersion and defect tolerance. These characteristics are intimately related to their metastability and kinetic stabilization, which can be achieved via solid solutions that inhibit phase segregation. Thus, the solid-solution semiconductors Cu5(Ta1-x Nb x )11O30 and (Ba1-x Sn x )(Zr1-yTi y )O3 have been prepared using flux-mediated synthesis methods. Their band gaps, band edge energies and photocatalytic activities for the production of molecular hydrogen and molecular oxygen are found to be a sensitive function of their chemical compositions.

Field-Induced Electron Spin Resonance of Site-Selective Carrier Accumulation in Field-Effect Transistors Composed of Organic Semiconductor Solid Solutions

The formation and characterization of solid solutions with guest (or impurity) molecules are difficult to realize in crystalline organic semiconductors. Here, we demonstrate that an operando field-induced electron spin resonance (FIESR) experiment allows the site-selective analysis of accumulated charge carriers in polycrystalline organic field-effect transistors (FETs), which comprise molecular solid solutions as channel semiconductor layers. We utilize vacuum-deposited dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) thin films with various amounts of dibenzotetrathiafulvalene (DBTTF) as guest molecules. Our measurements reveal that the field-induced carriers are first trapped at guest DBTTF sites at low gate voltages and then begin to accumulate at host DNTT sites at higher gate voltages. Furthermore, we perform dispersion-corrected density-functional theory calculations to investigate the stability of the solid-solution crystals. It is shown that the DBTTF molecules can be stably incorporated by aligning molecular long axes within the crystal lattices of DNTT, the results of which agree well with the angle-dependent FIESR measurements. We demonstrate that the mobility, threshold voltage, and subthreshold swing are controlled by the concentration of guest molecules in solid-solution organic FETs.

Resonance of mixing energy and energy of elastic deformations during spinodal decomposition and the composition modulation effect in ZnхCd1-ХTe solid solutions

The Cahn-Hilliard equation is adapted to consider the spinodal decomposition of A2B6 semiconductor solid solutions. This approach is used to analyze the process of spinodal decomposition of ZnхCd1-хTe solid solution, which is accompanied by the appearance of the composition modulation effect during its low-temperature synthesis. Numerical simulations of the spinodal decomposition of the ZnхCd1-хTe solid solution are performed. It is shown that micro-variations of the material composition are related by the resonance phenomenon between the excess mixing energy and the energy of elastic strains arising in the inclusions of the new phase, which are coherently conjugated with the initial crystal lattice. It is revealed that such resonance phenomena are most intense when the conditions for the material synthesis are located in close proximity to the spinodal curves on the phase state diagram of the system.