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1.
Charge carrier traps in as-grown TlGaSeS layered single crystals were studied using thermally stimulated current measurements. The investigations were performed in temperatures ranging from 10 to 100 K. The experimental evidences were found for the presence of one shallow hole trapping center in TlGaSeS, located at 12 meV from the valence band. The trap parameters have been calculated using various methods of analysis, and these agree well with each other. Its capture cross-section and concentration have been found to be 8.9 × 10−26 cm2 and 2.0 × 1014 cm−3, respectively. Analysis of the thermally stimulated current data at different light excitation temperatures leads to a value of 19 meV/decade for the shallow hole traps distribution. 相似文献
2.
N.M. Gasanly 《Physica B: Condensed Matter》2012,407(21):4318-4322
The absorption edge of undoped Tl2Ga2S3Se crystals have been studied through transmission and reflection measurements in the wavelength range 440–1100 nm and in the temperature range 10–300 K. The absorption edge was observed to shift toward lower energy values with increasing temperature. As a result, the rate of the indirect band gap variation with temperature γ=−2.6×10−4 eV/K and the absolute zero value of the band gap energy Egi(0)=2.42 eV were obtained. 相似文献
3.
Thermoluminescence (TL) properties of Tl2Ga2S3Se layered single crystals were researched in the temperature range of 290–770 K. TL glow curve exhibited two peaks with maximum temperatures of ~373 and 478 K. Curve fitting, initial rise and peak shape methods were used to determine the activation energies of the trapping centers associated with these peaks. Applied methods were in good agreement with the energies of 780 and 950 meV. Capture cross sections and attempt-to-escape frequencies of the trapping centers were reported. An energy level diagram showing transitions in the band gap of the crystal was plotted under the light of the results of the present work and previously reported papers on photoluminescence, thermoluminescence and thermally stimulated current measurements carried out below room temperature. 相似文献
4.
Sb2O3 nanowires with diameters of ∼233 nm and microspheres assembled by these nanowires were successfully synthesized by a simple poly-(vinylpyrrolidone) (PVP) assisted hydrothermal method. The morphologies, nano/microstructures and optical properties of the as-grown nanowires and microspheres were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-vis diffuse reflection spectrum. It has been found that the experimental parameters, such as mineralizers, played crucial roles in the morphological control of Sb2O3 nanowires. The possible growth mechanism of microspheres has been proposed. 相似文献
5.
The trap levels in nominally undoped Ga3InSe4 crystals were investigated in the temperature range of 10-300 K using the thermally stimulated currents technique. The study of trap levels was accomplished by the measurements of current flowing along the c-axis of the crystal. During the experiments we utilized a constant heating rate of 0.8 K/s. Experimental evidence is found for one hole trapping center in the crystal with activation energy of 62 meV. The analysis of the experimental TSC curve gave reasonable results under the model that assumes slow retrapping. The capture cross-section of the trap was determined as 1.0×10−25 cm2 with concentration of 1.4×1017 cm−3. 相似文献
6.
B. RiscobS.K. Kushwaha Mohd. ShakirK. Nagarajan K.K. MauryaD. Haranath S.D.D. RoyG. Bhagavannarayana 《Physica B: Condensed Matter》2011,406(23):4440-4446
Single crystals of l-histidine nitrate (LHN), a recently investigated nonlinear optical material, were grown by conventional solution technique. Crystal structure and vibrational modes of the grown crystals were confirmed by powder X-ray diffractometry and FT-Raman spectrometry, respectively. Crystalline perfection of the grown crystals was evaluated by employing an in-house developed high-resolution X-ray diffractometer (HRXRD) and it was found that the grown crystals were free from structural grain boundaries and the perfection was reasonably good. However, HRXRD could reveal the fact that the crystals contain predominantly the interstitial point defects. The birefringence was measured over a range of wavelength between 5480 and 5630 Å and it was found that its value is nearly constant and 10 times higher than that of KDP. The optical band gap was found to be ∼3.73 eV. The photoluminescence excitation and emission spectra for single crystals were recorded. The SHG efficiencies of LHN samples of different particle sizes were measured by the Kurtz and Perry technique and they removed the ambiguity in the values reported differently in the literature. Dielectric properties were studied as a function of temperature over a wide range of frequency. The optical and dielectric studies along with the crystalline perfection reveal that the LHN crystal could be a good candidate for nonlinear optical devices. 相似文献
7.
Because of having similarities in many physical as well as chemical properties to those of Zn, Cu has been strategically used as an effective dopant e.g., Al, Ga, F, etc., to change the optical, electrical and the micro-structural properties of ZnO thin films for obtaining its favorable opto-electronic performance as a transparent conducting oxide suitable for devices. Present study demonstrates the growth of transparent conducting ZnO:Ga:Cu thin films, by low power RF magnetron sputtering at a low substrate temperature (100 °C). Highly crystalline ZnO:Ga:Cu film with preferred c-axis orientation has been obtained demonstrating a high magnitude of transmission ~85% in the visible range and a high electrical conductivity ~40 S cm–1, facilitated by large crystallite size (~29 nm), introducing reduced grain boundary scattering. XPS O 1S spectrum reveals the presence of a significant fraction of oxygen atoms effectively increasing the optical transparency. Incorporation of Ga and Cu ions into the ZnO matrix promotes violation of the local translational symmetry as suggested by the relaxation of Raman selection rules for the network, evident by the presence of strong (B1high–B1low) modes which are typically Raman inactive. The consequences of Cu doping has been compared with identically prepared ZnO and ZnO:Ga films. 相似文献
8.
Thermally stimulated current (TSC) measurements were carried out on as-grown n-Ga4Se3S layered crystals in the temperature range 10–300 K. The experimental data were analysed by using different heating rates, initial rise, curve fitting and isothermal decay methods. The results of the analysis showed good agreement with each other. The measurements revealed the presence of one trapping level with activation energy of 23 meV. The corresponding capture cross-section and concentration of traps were found to be 2.2 × 10?23 cm2 and 2.9 × 1011 cm?3, respectively. TSC experiments showed the presence of an exponential distribution of electron-trapping states in Ga4Se3S crystal. The variation of one order of magnitude in the trap density for every 34 meV was obtained. 相似文献
9.
Electron paramagnetic resonance (EPR) spectra of Cu2+ ion in ammonium dihydrogen phosphate are studied at liquid nitrogen temperature (77 K). Four magnetically inequivalent Cu2+ sites in the lattice are identified. The angular variation spectra of the crystal in the three orthogonal planes indicate that the paramagnetic impurity, Cu2+ enters the lattice substitutionally in place of NH4+ ions. The spin Hamiltonian parameters are determined with the fitting of spectra to rhombic symmetry crystalline field. The ground state wave function of Cu2+ ion is constructed and found to be predominantly |x2-y2〉. The cubic field parameter (Dq) and tetragonal parameters (Ds and Dt) are determined from optical spectra at room temperature. By correlating EPR and optical absorption spectra, the bonding coefficients are calculated and nature of bonding of metal ion with different ligands in the crystal is discussed. 相似文献
10.
Variable angle spectroscopic ellipsometry has been applied to characterize the optical constants of bulk Cu(In0.7Ga0.3)5Se8 and Cu(In0.4Ga0.6)5Se8 crystals grown by the Bridgman method. The spectra were measured at room temperature over the energy range 0.8-4.4 eV. Adachi’s model was used to calculate the dielectric functions as well as the spectral dependence of complex refractive index, absorption coefficient, and normal-incidence reflectivity. The calculated data are in good agreement with the experimental ones over the entire range of photon energies. The parameters such as strength, threshold energy, and broadening, corresponding to the E0, E1A, and E1B interband transitions, have been determined using the simulated annealing algorithm. 相似文献
11.
G.D. Sharma Vijay Singh Choudhary M.S. Roy 《Journal of Physics and Chemistry of Solids》2008,69(11):2639-2651
We have investigated the optical, electrical and photovoltaic properties of devices based on 1,2-diazoamino diphenyl ethane (DDE) and poly(3-phenyl hydrazone thiophene) (PPHT):DDE blend. It is observed from the J-V characteristics of the Al/DDE/ITO (ITO—indium tin oxide) device that the electron current injected from Al contact was shown to be space charge limited (SCL), indicating that Al forms nearly ohmic contact for electron injection into lowest unoccupied molecular orbital (LUMO) of DDE. The effect of thermal annealing and composition, on the optical, electrical and photovoltaic response of blend of PPHT and DDE sandwiched between a transparent ITO electrode and an Al back contact are investigated. The observed absorption quenching in the PPHT:DDE blend is attributed to the disordering of PPHT chains and charge transfer between PPHT and DDE as evidenced by FTIR spectra. The observed red shift in the absorption peak on thermal annealing is due to the improvement in the ordering and increases in conjugation length in PPHT. The observed dark current-voltage curves agree well with trap-controlled SCL transport theory. The photophysics of the blend material and influence of thermal annealing on the performance and morphology of these devices were discussed. Annealing process results in the formation of PPHT:DDE complex and increase in the ordering of polymer chain, that increases the incident photon to current efficiency (IPCE) and power conversion efficiency of the photovoltaic devices. 相似文献
12.
Pure ZnO and Mn (1%wt.) doped-ZnO nanocrystalline particles were synthesized by reverse micelle method. The structural properties of the nanoparticles were investigated by X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) techniques. UV–vis and photoluminescence (PL) spectroscopy was used for analyzing the optical properties of the nanoparticles. XRD and TEM results revealed the formation of ZnO and Mn doped-ZnO nanocrystalline particles with pure wurtzite crystal structure and average particle size of 18–21 nm. From UV–vis studies, the optical band gap energy of 3.53 and 3.58 eV obtained for ZnO and Mn doped-ZnO nanoparticles, respectively. Further optical analysis showed that the refractive index decreases from 2.35 to 1.35 with the change of wavelength. Room-temperature photoluminescence analysis of all samples showed four main emission bands including a strong UV emission band, a weak blue band, a week blue–green band, and a weak green band which indicated their high structural and optical quality. Moreover, the samples exposed to gamma rays sources of 137Cs and 60Co and their thermoluminescence properties were investigated. The thermoluminescence response of ZnO and Mn doped-ZnO nanocrystalline particles as a function of dose exhibited good linear ranges, which make them very promising detectors and dosimeters suitable for ionizing radiation. 相似文献
13.
V. Ganesh Ch. Snehalatha ReddyMohd. Shakir M.A. WahabG. Bhagavannarayana K. Kishan Rao 《Physica B: Condensed Matter》2011,406(2):259-264
〈1 1 1〉 oriented bis thiourea cadmium acetate (BTCA) crystal of diameter 15 mm and length 45 mm was grown for the first time by the unidirectional Sankaranarayanan-Ramasamy (SR) method. The conventional and SR method grown BTCA crystals were characterized by using high-resolution X-ray diffraction (HRXRD), chemical etching, Vickers microhardness, UV-vis, dielectric studies and differential scanning calorimetry. The HRXRD analysis indicates that the crystalline perfection of SR method grown crystal is good without having any low angle internal structural grain boundaries. The transmittance of SR method grown BTCA is 14% higher than that of conventional grown crystal. The dielectric constant was higher and the dielectric loss was less in SR method grown crystal. The crystals grown by SR method possess less dislocation density and higher microhardness. 相似文献
14.
A spectroscopic investigation on the effect of Ce3+ co-doping in fluoride KY3F10:Pr3+ crystals is presented. In particular spectroscopic measurements of three different samples of KY3F10 crystal doped with 0.3at% Pr3+ and co-doped with 0at%, 0.17at% and 0.3at% Ce3+ are discussed. Details on the growth of the crystals are also reported. Measurements were performed in the temperature range 10-300 K. Fluorescence and lifetime measurements have shown a cross relaxation between 3P0-1D2 levels of Pr3+ and 2F7/2-2F5/2 of Ce3+. Data exhibit that this effect is strictly related to the Cerium concentration. 相似文献
15.
Chiharu Hidaka Eri Yamagishi Takeo Takizawa 《Journal of Physics and Chemistry of Solids》2005,66(11):2058-2060
The single crystal of CaGa2S4:Eu is expected as a useful laser material with a high quantum efficiency of light emission. However, as far as our knowledge is concerned, the systematic study of the mixed compounds of Ca(1−x)EuxGa2S4 as a function of x has not been reported up to now. Here, we have first constructed the phase diagram of the CaGa2S4 and EuGa2S4 pseudo binary system, and show that it forms the solid solution. Then we have grown single crystals of these compounds. The maximum photoluminescence efficiency is achieved at x=0.25. From the three peak energies observed in the photoluminescence excitation (PLE) and absorption spectra, the 5d excited states are suggested to consist of three levels arising from the multiplets of Eu2+ ions. 相似文献
16.
Tae Ho Yeom Ae Ran Lim 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,200(2):261-266
Nuclear magnetic resonance (NMR) data and the spin–lattice relaxation times, T1, of 69Ga and 71Ga nuclei in a β-Ga2O3:Cr3+ single crystal were obtained using FT NMR spectrometry. Four sets of NMR spectra for 69Ga (I = 3/2) and 71Ga (I = 3/2) were obtained in the crystallographic planes. The 69Ga and 71Ga nuclei each had two chemically inequivalent GaI and GaII centers. Each of the 69Ga and 71Ga isotopes yielded two different central NMR resonance lines originating from GaI and GaII sites. The nuclear quadrupole coupling constants and asymmetry parameters of 69GaI, 69GaII, 71GaI, and 71GaII centers in a β-Ga2O3:Cr3+ crystal were obtained. Analysis of the EFG tensor principal axes (PAs) for Ga nuclei and the ZFS tensor PAs for the Cr3+ ion confirmed that the Cr3+ paramagnetic impurity ion substitutes for the Ga3+ ion in the oxygen octahedron. In addition, the temperature dependencies of the 69Ga and 71Ga relaxation rates were consistent with Raman processes, as T1−1 ∝ T2. Even though the Cr3+ impurities are paramagnetic, the relaxations were dominated by electric quadrupole interactions of the nuclear spins in the temperature range investigated. 相似文献
17.
A comparative study concerning the electronic structure of the Mn5+ ion in the Li3PO4, Ca2PO4Cl, Sr5(PO4)3Cl host lattices has been carried out in the framework of the exchange charge model. The crystal field parameters have been evaluated using the structural data as the only input information. The 10 K absorption spectra of the investigated compounds have been measured in order to verify the correspondence between experimental and calculated energy levels. A systematic trend of the crystal field splitting of the most intense transitions has been evidenced and discussed by considering the symmetry properties of the coordination polyhedra around Mn5+. 相似文献
18.
Algirdas Audzijonis Leonardas ŽigasRaimundas Žaltauskas Raimundas Sereika 《Journal of Physics and Chemistry of Solids》2014
SbSCl0.1I0.9 crystals were grown from the vapor phase and reflection spectra were recorded using a Fourier-transform IR spectrometer. The optical parameters and optical functions along the c axis were calculated using an improved Kramers–Kronig technique with two confining spectral limits. The reflection spectra were analyzed using the oscillator parameter fitting technique for comparison of results. The vibrational frequencies ωL and ωT were evaluated. The ferroelectric phase-transition temperature was estimated as 330 K for SbSCl0.1I0.9 from experimental reflection measurements and theoretical investigation of the potential energy of Sb atoms for B1u soft normal modes of SbSI and SbSCl0.1I0.9 crystals. 相似文献
19.
The effects of biaxial stress in ZnO:Ga thin films on different substrates, e.g., sapphire(0001), quartz, Si(001), and glass have been investigated by X-ray diffraction, atomic force microscopy, and electrical transport and ellipsometric measurements. A strong dependence of orientation, crystallite size, transport, and electronic properties upon the substrate-induced stress has been found. The structural properties indicate that a tensile stress exists in epitaxial ZnO:Ga films grown on sapphire, Si, and quartz, while a compressive stress appears in films grown on glass. The resistivity of the films decreased with increasing biaxial stress, which is inversely proportional to the product of the carrier concentration and Hall mobility. The refractive index n was found to decrease with increasing biaxial stress, while the optical band gap E0 increased with stress. These behaviors are attributed to lattice contraction and the increase in the carrier concentration that is induced by the stress. Our experimental data suggest that the mechanism of substrate-induced stress is important for understanding the properties of ZnO:Ga thin films and for the fabrication of devices which use these materials. 相似文献
20.
Zheng Wen-Chen Wu Shao-Yi Zhao Bei-JunZhu Shi-Fu 《Journal of Physics and Chemistry of Solids》2002,63(5):895-897
The substitutional sites of Co2+ ions in Co2+-doped CuG1−xAlxSe2 (including CuGaSe2 where x=0 and CuAlSe2 where x=1) semiconductors are studied by analyzing the composition x dependence of optical spectral parameters reported in the previous literature for these materials. From the studies, we suggest that Co2+ occupy I-group cation site rather than III-group cation site. The suggestion is discussed. 相似文献