KTa1—xNbxO3薄膜的性能研究进展

报道ＫＴａ１－ｘＮｂ２ｘＯ３薄膜的性能研究进展，详细地介绍了该薄膜的物化结构性能、电学性能和光学性能的表征方法及对表征结果的分析、解释。     

KTa1—xNbxO3薄膜的制备研究

介绍电光、热释电ＫＴａ１－ｘＮｂｘＯ３薄膜材料的制备研究进展，评述了Ｓｏｌ－Ｇｅｌ、ＰＬＤ，ＭＯＤ，ＬＰＥ和射频平面磁控溅射等技术制备ＫＴＮ薄膜的工艺特点。     

Microdeformations of the crystal lattice of PbTe1 − x Br x solid solutions

Microdeformations of the crystal lattice of PbTe_{1 ? x} Br _x solid solutions depending on the bromine content are determined by analysis of the physical broadening of X-ray reflections. It is found that they increase with the introduction of bromine from 0.188% (for undoped PbTe) to 0.283% for PbTe_{1 ? x} Br _x at x = 0.02. The microstrains remain constant with a further increase in the bromine content.     

Optical intersubband transitions in strained quantum wells utilizing In1−x GaxAs/InP solid solutions

Infrared absorption in strained p-type In_1−x Ga_xAs/InP quantum wells is investigated for both possible types of strain (tensile and compressive). It is observed that the normalincidence absorption increases considerably under compressive strain (when the ground state is a heavy-hole state) and decreases under tensile strain (when the ground state is a light-hole state). The peak absorption in the compressed quantum well can attain very large values, on the order of 5000 cm⁻¹ at a hole density ∼ 10¹² cm⁻²; this attribute makes “compressed” p-type quantum wells attractive for IR detection applications. Fiz. Tekh. Poluprovodn. 33, 83–90 (January 1999)     

Hubbard energy of two-electron tin centers in PbS1−zTez solid solutions

It is shown by Mössbauer spectroscopy of the isotope ¹¹⁹Sn that an isovalent tin impurity in PbS_1?z Te_z solid solutions is a two-electron donor with a negative correlation energy, where the energy levels associated with tin centers are situated against the background of the valence band continuum. The Hubbard energy U is estimated for impurity tin atoms in PbS_1?z Te_z (|U|>0.2 eV), which is found to be substantially higher than for analogous tin centers in PbS_1?z Se_z solid solutions (|U|=0.058 eV).     

Photoconductivity relaxation processes in Cu1−xZnxInS2 solid solutions

Photoconductivity and its relaxation in Cu_1−xZn_xIn₂S₄ alloys (x=0–16) single crystals were investigated in the temperature range 30–100 K. The long-lasting relaxation processes (τ~10³ s) and induced photoconductivity phenomena were identified. The main parameters characterizing the photoconductivity kinetic were determined. The observed phenomena were analyzed by taking into account effects of the trapping levels. It is shown that relaxation of the photoconductivity and induced photoconductivity are controlled by the multicenter recombination in which both 'fast' and 'slow' recombination centers take part.     

Hopping transport in doped (Pb0.78Sn0.22)1−x InxTe solid solutions

Transport coefficients in (Pb_0.78Sn_0.22)_1?x In_xTe solid solutions with indium content x=0.03 and 0.05 additionally doped with acceptors (Tl) or donors (Cl) have been measured and analyzed. The Seebeck coefficient S is positive for x=0.05 in the low temperature range 77–200 K; its sign changes to negative when the Tl acceptor is added. This unusual behavior of the thermoelectric power can be attributed to hopping conduction at a nonmonotonic energy dependence of the density of localized states. The density-of-states function has been determined at x=0.03 and 0.05 from experimental data on the thermopower. Theoretical estimates of the Nernst-Ettingshausen coefficient are made for x=0.03 additionally doped with Cl. The estimates are based on taking into account, along with the hopping conduction, the contribution from electrons with energies above the mobility edge and on using the critical electrical conductivity exponent obtained in the percolation theory. The activation energies characterizing the temperature dependences of conductivity and Hall and Nernst-Ettingshausen coefficients are discussed and compared.     

Magnetotransport in a semimetal channel in p-Ga1−x InxAsySb1−y /p-InAs heterostructures with various compositions of the solid solution

Magnetotransport properties of an electron channel at the heteroboundary in type II separated p-Ga_1?x In_xAs_ySb_1?y /p-InAs heterostructures grown by LPE (x=0.09–0.22) were studied in the temperature range of 77–300 K. It is shown that an electron channel, which is formed at the heteroboundary and has high mobility μ=(3–5)×10⁴ cm² V^?1 s^?1, exists throughout the whole composition range. The band diagram of the heterostructures under study is discussed, and some parameters of the electron channel are evaluated. It is found that the electron channel with high mobility persists up to room temperature. Type II GaInAsSb/p-InAs heterostructures can find application in new Hall sensor devices with an electron channel at the heteroboundary.     

Light induced metastable modification of optical properties in CH3NH3PbI3−xBrx perovskite films: Two-step mechanism

We have used photoluminescence (PL) and photomodulation (PM) spectroscopy to investigate the reversible spectral changes of PL in CH₃NH₃PbI_3−xBr_x films, where x is 1.7. In an as-prepared film, the peak of PL spectra shifts from ∼640 nm near bandedge to ∼750 nm after excitation by a continuous wave (CW) or a pulsed laser with high repetition rate, but keeps at 640 nm excited by same pulsed laser with the repetition rate smaller than 500 Hz. The PM spectroscopy also shows the formation of sub bandgap states after illumination which is responsible for the red shift of PL. The light induced modification of optical properties is reversible after keeping the film out of illumination for several hours at room temperature. We analyze the photoinduced modification to be two-steps processes: the temporary sub bandgap states were first photogenerated in perovskite film, if those states interacting with more coming photons within their lifetimes, light induced metastable states responsible for red-shift of PL will be formed. This instability reduces the electronic bandgap and generates more traps which will degrade the performance of the related photovoltaic devices.     

Photosensitivity of thin-film structures based on (CuInSe2)x(2ZnSe)1−x solid solutions

Polycrystalline (CuInSe₂)_x(2ZnSe)_1−x films (x=0.6–1.0) with p-type conductivity and a thickness of 0.5–0.9 μm were obtained by pulsed laser evaporation. It is shown that a chalcopyrite-sphalerite transition occurs in the above system for x=0.7. The obtained films were used to fabricate the photosensitive structure of the In/p-(CuInSe₂)_x(2ZnSe)_1−x and InSe(GaSe)/(CuInSe₂)_x(2ZnSe)_1−x types. Spectral dependences of photovoltaic-conversion quantum efficiency were studied, and the photosensitivity of the structures in relation to the type of energy barrier and the composition was analyzed. It is concluded that the structures under consideration can be used as broadband photovoltaic converters. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 5, 2000, pp. 576–581. Original Russian Text Copyright ? 2000 by V. Rud’, Yu. Rud’, Bekimbetov, Gremenok, Bodnar’, Rusak.     

Localization of the interband transitions in the bulk of the Brillouin zone of III–V compound crystals

The localization of the transitions in the bulk of the Brillouin zone that form the main structures in the spectra of the imaginary part of the permittivity in the range up to ~7 eV for III–V semiconductors (AlSb, GaSb, InSb, and InAs) is determined using electron density functional theory. It is established that intense transitions occur not only in the vicinity of the high-symmetry axes of the Brillouin zone, but also in some specific large volumes of the irreducible part of the Brillouin zone.     

Effect of Mn and Nb Doped BaTiO3 in the Dielectric Properties in the Ba(Mn1/2Nb1/2)xTi1−xO3

Polycrystalline samples of BaTi_1?x (Mn_0.5Nb_0.5) _x O₃ with x = 0.025, 0.05, 0.075, 0.1, 0.125, 0.15, and 0.175 have been synthesized by the high-temperature solid-state reaction technique. The effects of cationic substitution of manganese and niobium for titanium at B sites of the BaTiO₃ perovskite lattice on symmetry and dielectric properties were investigated. X-ray diffraction at room temperature and dielectric permittivity in the temperature range from 85 K to 500 K and frequency range from 100 Hz to 2 × 10⁵ Hz were studied. The evolution from a normal ferroelectric to a relaxor ferroelectric is emphasized. T _C or T _m decreases when both manganese and niobium are introduced into the lattice of BaTiO₃. High dielectric constant of around 9000 at T _C = 280 K was found for Ba Ti_0.925(Mn_0.5Nb_0.5)_0.075O₃ ceramic. A relaxor ferroelectric with ΔT _m = 60 K and $ \varepsilon_{\rm{r}}^{\prime } $ of about 3500 at 10 kHz with T _m = 150 K was found for the BaTi_0.85(Mn_0.5Nb_0.5)_0.15O₃ sample.     

Local neutrality and pinning of the chemical potential in III–V solid solutions: Interfaces and radiation effects

In the virtual crystal approximation the mole fraction (X) of the local neutrality level E _lnl: E _lnl(X)^ABC = XE _lnl ^AC + (1 - X) E _lnl ^BC - C _ABC X(1 - X has been calculated in ABC solid solutions for 18 pairs of III–V semiconductors. An interpolation formula is proposed for the nonlinear coefficient C _ABC (in eV): C _ABC= - 0.03 + 0.04|Δa| + 1.4|Δa|₂ as a function of the lattice mismatch |Δa| (in Å) for boundary compositions of the solid solutions. It is shown that the numerical values of E _lnl obtained provide good agreement with the experimental values of the heights of the Schottky barriers (F _bS) and the limiting Fermi level positions (F _lim) in irradiated III–V solid solutions.     

Efficiencies of perovskite hybrid solar cells influenced by film thickness and morphology of CH3NH3PbI3−xClx layer

Perovskite hybrid solar cells (pero-HSCs) have been intensively investigated due to their promising photovoltaic performance. However, the correlations between the efficiencies of pero-HSCs and thin film thicknesses and morphologies of CH₃NH₃PbI_3−xCl_x perovskite layers are rarely addressed. In this study, we report the correlation between the efficiencies of “planar heterojunction” (PHJ) pero-HSCs and the thin film thicknesses and morphologies of solution-processed CH₃NH₃PbI_3−xCl_x perovskite layers. Investigation of absorption spectra, X-ray diffraction patterns, atomic force microscopy and scanning electron microscopy images of CH₃NH₃PbI_3−xCl_x layers indicate that the efficiencies of PHJ pero-HSCs are dependent on the film thickness, as the thickness of CH₃NH₃PbI_3−xCl_x is less than 400 nm; whereas the efficiencies are significantly dependent on the film morphologies of CH₃NH₃PbI_3−xCl_x layers as the thickness is larger than 400 nm. Our studies provide a promising pathway for fabricating high efficiency PHJ pero-HSCs.     

GSH-assisted hydrothermal synthesis of MnxCd1−xS solid solution hollow spheres and their application in photocatalytic degradation

A series of Mn_xCd_1−xS (MCS) solid solutions hollow spheres (x=0.0, 0.20, 0.33, 0.50 and 0.67) have been synthesized with the assistance of l-Glutathione (GSH) by a simple hydrothermal route for the first time. Different characterization techniques, including X-Ray diffraction (XRD), atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller surface area (BET), UV–vis and diffuse reflectance spectra (DRS) are performed to investigate the structural and optical properties of the as-prepared samples. The experiment of rhodamine B (RhB) decoloration indicates that all the MCS samples show higher photo-catalytic activities than commercial CdS under visible light irradiation. Among them, the Mn_0.33Cd_0.67S exhibits the highest photo-catalytic activity. The superior photo-catalytic activity of MCS samples may be attributed predominantly to the synergistic effect of the appropriate band-gap structure as well as the special hollow spherical morphology which makes MCS samples have the ability to harvest exciting visible-light due to multiple scattering within the interior space. Furthermore, the Mn_0.33Cd_0.67S shows well stability, the photo-catalytic activities do not decrease significantly after six recycles. The work may open a novel strategy to fabricate multi-component chalcogenide solid solutions hollow spheres.     

Features of ecological control in nanotechnologies in view of features of Ca y La1 − y F3 − y and La x Ca1 − x F2 + x structuring

General features of ecological control in nanotechnologies were found. Based on the study of structural-morphological characteristics of nanoprecipitates with ordered structure in Ca _y La_{1 ? y} F_{3 ? y} and La _x Ca_{1 ? x} F_{2 + x} , it was shown that it is necessary to additionally control the formation of ordered states, the presence of antiphase domains, and the degree of order in ecological control of solution-based materials.

     

Improving efficiency of planar hybrid CH3NH3PbI3−xClx perovskite solar cells by isopropanol solvent treatment

Hybrid organic/inorganic perovskite planar heterojunction (PHJ) solar cells are becoming one of the most competitive emerging technologies. Here, the devices (ITO/PEDOT:PSS/CH₃NH₃PbI_3−xCl_x/PC₆₀BM/C₆₀/Al) are fabricated based on solution process. A power conversion efficiency (PCE) up to 13.1% was obtained after isopropanol (IPA) solvent treatment, which was 9% improvement than that of the original devices. Photocurrent hysteresis could be reduced to a certain extent by introducing IPA treatment. Solvent treatment can remove as-grown impurities like CH₃NH₃I and defects formed during the device fabrication. We also demonstrated the electrical and optical properties of perovskite films were improved. The addition of IPA-treated facilitates the formation of a relatively smooth PC₆₀BM films. This work provides a very simple but effective strategy to enhance the power conversion efficiency of perovskite solar cells.     

Phase formation upon the interaction of thin films in the system Yb1 − x Sm x Te-As2Te3

Phase formation upon the interaction of thin Yb_{1 ? x} Sm _x Te (x = 0.02) and As₂Te₃ films obtained through their simultaneous and successive evaporation is studied. It is shown that the Yb_{1 ? x} Sm _x As₄Te₇ phase is formed upon interaction of the thin films at a temperature of 473 K and the Yb_1?x Sm _x As₂Te₄ phase at 503 K.     

On the resonant level of chromium in the rhombohedral and cubic phases of Pb1 − x − y Ge x Cr y Te alloys

The temperature dependences of the Hall coefficient (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) in Pb_{1 ? x ? y} Ge _x Cr _y Te alloys (x = 0.03–0.08, y ≤ 0.01) are studied. An increase in the absolute value of the Hall coefficient with an increase in temperature is found. This fact is indicative of a decrease in the concentration of free electrons as a result of the motion of the resonant level of chromium stabilizing the Fermi level relative to the conduction-band bottom. The temperature dependences of the Hall coefficient, in satisfactory agreement with the experimental ones, are calculated in the context of the two-band Kane dispersion law allowing for the structural phase transition upon increasing temperature. The energy position and temperature coefficients of the motion of the resonant level of chromium relative to the middle of the band gap in the rhombohedral and cubic phases are determined.