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1.
A heterostructure consisting of a graded-gap p-AlxGa1?xAs layer on an n-GaAs substrate is studied in relation to its role as a photoelectric-response detector of X-ray photons and α particles. It is found that the current-power sensitivity of the detector is as high as 0.13 A/W and the voltage-power sensitivity exceeds 106 V/W. The effect of preliminary irradiation with 5.48-MeV α particles (241Am) on the detector’s sensitivity is studied. It is established that the detector’s sensitivity is reduced by a factor of 1.5–2 after irradiation with α particles at a dose of 5 × 109 cm?2. A further increase in the radiation dose to 4 × 1010 cm?2 does not affect the detector’s sensitivity.  相似文献   

2.
Electronic and optical properties are obtained with the increase in indium alloy content (x) in a Ga1-xInxN/Al0.2Ga0.8N quantum dot. The barrier height with the different In alloy contents is applied to acquire the confinement potentials. The results are obtained taking into consideration geometrical confinement effect. The optical absorption coefficient with the photon energy is observed in a Ga1-xInxN/Al0.2Ga0.8N quantum dot. The optical output with the injection current density and the threshold optical pump intensity for various In alloy contents are studied. The differential gain as functions of indium alloy content, charge density and the dot radii in the Ga1-xInxN/Al0.2Ga0.8N quantum dot are investigated. The exciton binding energy is calculated in order to obtain the exciton density, the optical gain and the threshold current density in the Ga1-xInxN/Al0.2In0.8N quantum dot. The results show that the red shift energy with an increase in In alloy content is found and the differential gain increases with the charge carrier density.  相似文献   

3.
A MoOx(top)/Au/MoOx(bottom) multilayer was systematically designed for transparent electrodes in green OLEDs in terms of optical transmission and series resistance of the device. The enhancement in optical transmission of MoOx/Au/MoOx (MAM) structures is a result of a series of events, including the optical interference within the multilayers and the interaction of light with surface plasmon polaritons in the metal layer. For the maximum transmission, the optical interference occurring within the multilayers was simulated using a transfer matrix model to determine the optimum thickness of MoOx layers, and then the thickness of the Au interlayer was experimentally optimized for extraordinary optical transmission. In addition, the series resistance added by the top MoOx was characterized to confirm its negligible impact on the performance of the device. The optimum MoOx (40 nm)/Au (10 nm)/MoOx (40 nm) structure showed much higher transmission in the green-red region and lower sheet resistance than indium tin oxide (ITO). We have fabricated MAM-based OLEDs the driving voltage of which was significantly reduced to ∼5.5 V at a current density of 20 mA/cm2, and the current efficiency (11.46 Cd/A) was higher than that (10.91 Cd/A) of ITO-based OLEDs, demonstrating that the MAM electrode is a potential replacement for ITO in optical devices.  相似文献   

4.
Ultradisperse particles of CdSexTe1?x (0≤x≤1) were formed in the matrix of a silicate glass by introduction of corresponding prepared compounds into a mixture of SiO2 and Ca, Na, K, and Li oxides. Initially produced particles with an average size of 10–15 nm grow by a factor of 2–3 after additional thermal treatment of the glasses; the optical absorption spectra are noticeably changed only in the case of CdSexTe1?x (x=0.8 or 0.4) solid solutions, but not in the case of CdSe and CdTe binary compounds. All glasses synthesized exhibit similar luminescence bands in the visible region of the spectrum. The features observed are interpreted under the assumption that two crystalline modifications (wurtzite and sphalerite) are separated in the process of thermal treatment of glasses activated by solid solutions.  相似文献   

5.
From the charge state and closeness of the covalent radii of molecules of the solution-forming components, the possibility of the formation of the solutions Si1 ? x Ge x , Si1 ? x Sn x , (Si2)1 ? x (SnC) x , Ge1 ? x Sn x , (Ge2)1 ? x (SiSn) x , (SiC)1 ? x (GeC) x , (GeC)1 ? x (SnC) x , and (SiGe)1 ? x (SnC) x based on chemical elements of Group IV has been predicted. Single-crystal films of the substitutional solid solution Ge1 ? x Sn x (0 ≤ x ≤ 0.03) have been grown on Ge substrates by liquid-phase epitaxy. X-ray diffraction patterns, spectral photosensitivity, and the I–V characteristics of the obtained n-Ge-p-Ge1 ? x Sn x heterostructures have been investigated. The lattice parameters of the epitaxial film and the substrate a f = 5.6812 Å and a s = 5.6561 Å have been determined. The spectral photosensitivity of the n-Ge-p-Ge1 ? x Sn x heterostructures encompasses the photon energy range from 0.4 to 1.4 eV. It is shown that the forward portion of the I–V characteristics of the investigated structures at low voltages (up to 0.5 V) is described by the exponential dependence I = I 0exp(qV/ckT) and at high voltages (V > 0.5 V), by the power dependence IV α with the values α = 2 at V = (0.5–0.9) V, α = 1.3 at V = (0.9–1.4) V, and α = 2 at V > 1.4 V. The experimental data are explained within the double injection model for the n-p-p structure using the drift mechanism of current transport in the ohmic relaxation mode taking into account the inertia of the electron exchange inside a recombination complex.  相似文献   

6.
The current response of AlxGa1−x As graded-gap layers to optical and X-ray radiation was studied. A graded-gap electric field in the 15-μm-thick AlxGa1−x As layers, with x varying from 0 to 0.4, ensures the complete collection of charges generated by ionizing radiation and makes it possible to attain the value of 0.25 A/W for the current-power sensitivity of AlxGa1−x As. In the layers with a lowered doping level of the narrow-gap region of the graded-gap AlxGa1−x As layer, the voltage-power sensitivity to X-ray radiation with energy lower than 15 keV is as high as 1.6×103 V/W in the photovoltaic mode. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 1, 2002, pp. 124–128. Original Russian Text Copyright ? 2002 by J. Požela, K. Požela, Šilėnas, Jasutis, Dapkus, Kinduris, Jucienė.  相似文献   

7.
An increase in the dark current (by 2–3 orders of magnitude) in GaAs/AlxGa1−x As multilayer quantum-well structures with x⋍0.4 is observed after illumination of the structures with optical light (λ<1.3 μm). This increase is sustained for an extended time (more than 103 s) at low temperatures. It then decreases to its initial value upon heating of the sample. A model of the barrier with local sag of the conduction band facilitating tunneling is proposed. The conduction band sag and the magnitude of the current grow due to optical ionization of uncontrolled deep level clusters present in the barrier and decrease due to subsequent capture of electrons from the conduction band by the deep levels upon heating. Fiz. Tekh. Poluprovodn. 32, 209–214 (February 1998)  相似文献   

8.
It is shown that the ground state transition energy in quantum dots in heterostructures grown by atmospheric-pressure MOCVD can be tuned in the range covering both transparence windows of the optical fiber at wavelengths of 1.3 and 1.55 μm by varying the thickness and composition of the thin GaAs/InxGa1−x As double cladding layer. These structures also exhibit a red shift of the ground state transition energy of the InxGa1−x As quantum well (QW) as a result of the formation of a hybrid QW InxGa1−x As/InAs (wetting layer) between the quantum dots (QDs). The Schottky diodes based on these structures are characterized by an increased reverse current, which is attributed to thermally activated tunneling of electrons from the metal contact to QD levels. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 4, 2004, pp. 448–454. Original Russian Text Copyright ? 2004 by Karpovich, Zvonkov, Levichev, Baidus, Tikhov, Filatov, Gorshkov, Ermakov.  相似文献   

9.
Many solar cells incorporating SiNx films as a rear surface passivation scheme have not reached the same high level of cell performance as solar cells incorporating high‐temperature‐grown silicon dioxide films as a rear surface passivation. In this paper, it is shown by direct comparison of solar cells incorporating the two rear surface passivation schemes, that the performance loss is mainly due to a lower short‐circuit current while the open‐circuit voltage is equally high. With a solar cell test structure that features a separation of the rear metal contacts from the passivating SiNx films, the loss in short‐circuit current can be reduced drastically. Besides a lower short‐ circuit current, dark I–V curves of SiNx rear surface passivated solar cells exhibit distinct shoulders. The results are explained by parasitic shunting of the induced floating junction (FJ) underneath the SiNx films with the rear metal contacts. The floating junction is caused by the high density of fixed positive charges in the SiNx films. Other two‐dimensional effects arising from the injection level dependent SRV of the Si/SiNx interfaces are discussed as well, but, are found to be of minor importance. Pinholes in the SiNx films and optical effects due to a different internal rear surface reflectance can be excluded as a major cause for the performance loss of the SiNx rear surface passivated cells. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

10.
The forward bias impedance characteristics of GaAs1-xPx LED's have been determined. In all cases, the equivalent parallel capacitance reaches a maximum and then either saturates (x = 0.4) or becomes negative at certain frequencies (x = 0.85 and x = 1). The current densities at which Cp maxima are reached are below typical values for display, multiplexing or optical emitters applications (i.e. JF = 1 A/cm2 for x = 0.85). It is suggested large series resistances for x = 0.4, and conductivity modulation effects for x > 0.4 are responsible for the above impedance behavior.  相似文献   

11.
The ZnS is a direct and wide band gap material and it is used in optoelectronics and especially in photovoltaic solar cell applications. We tried to improve some physical characteristics of ZnS films by Cd incorporation. In this work, Zn1−xCdxS semiconductor films were produced by ultrasonic spray pyrolysis (USP) technique. Zn1−xCdxS films were obtained with incorporation of Cd element into ZnS at different concentrations (0⩽x⩽1). The electrical, optical, structural and morphological properties were investigated. The current–voltage characteristics were taken to see the electrical conduction mechanism and to determine the electrical conductivities of the films. Optical band gaps of the films were determined by optical method and structural properties were analyzed using X-ray diffraction (XRD) patterns. Also, scanning electron microscope (SEM) images were taken to see the distribution on the surface and energy dispersive X-ray spectroscopy (EDS) was used for elemental analysis. It was seen that some Cd incorporated films have higher conductivity values and more homogeneous distributions on the surface than ZnS films. Also, crystallinity level of the films increased. Finally, we think that different experimental parameters and Cd incorporation will improve the properties of ZnS films to be used in optoelectronics and photovoltaic solar cells.  相似文献   

12.
The dependence of the optical band gap for Zn1?x MnxTe and Cd1?x MnxTe semiconductor compounds was investigated by the methods of cathodoluminescence and optical reflection. It was found that, for Zn1?x MnxTe compounds in the region x?0.2, the band gap is additionally broadened by a magnitude of about 0.08 eV, which is related to the high density of interstitial-type defects in single crystals. For x?0.3, the probability of the existence of these defects decreases substantially, which is related to the distortion of tetrahedra of the crystal lattice of Zn1?x MnxTe by Mn atoms, which are incorporated into each tetrahedron.  相似文献   

13.
The influence of the thickness of atomic layer deposited Zn1−xSnxOy buffer layers and the presence of an intrinsic ZnO layer on the performance of Cu(In,Ga)Se2 solar cells are investigated. The amorphous Zn1−xSnxOy layer, with a [Sn]/([Sn] + [Zn]) composition of approximately 0.18, forms a conformal and in‐depth uniform layer with an optical band gap of 3.3 eV. The short circuit current for cells with a Zn1−xSnxOy layer are found to be higher than the short circuit current for CdS buffer reference cells and thickness independent. On the contrary, both the open circuit voltage and the fill factor values obtained are lower than the references and are thickness dependent. A high conversion efficiency of 18.0%, which is comparable with CdS references, is attained for a cell with a Zn1−xSnxOy layer thickness of approximately 13 nm and with an i‐ZnO layer. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

14.
A unique watermelon‐like structured SiOx–TiO2@C nanocomposite is synthesized by a scalable sol–gel method combined with carbon coating process. Ultrafine TiO2 nanocrystals are uniformly embedded inside SiOx particles, forming SiOx–TiO2 dual‐phase cores, which are coated with outer carbon shells. The incorporation of TiO2 component can effectively enhance the electronic and lithium ionic conductivities inside the SiOx particles, release the structure stress caused by alloying/dealloying of Si component and maximize the capacity utilization by modifying the Si–O bond feature and decreasing the O/Si ratio (x‐value). The synergetic combination of these advantages enables the synthesized SiOx–TiO2@C nanocomposite to have excellent electrochemical performances, including high specific capacity, excellent rate capability, and stable long‐term cycleability. A stable specific capacity of ≈910 mAh g?1 is achieved after 200 cycles at the current density of 0.1 A g?1 and ≈700 mAh g?1 at 1 A g?1 for over 600 cycles. These results suggest a great promise of the proposed particle architecture, which may have potential applications in the improvement of various energy storage materials.  相似文献   

15.
SiCl4-based reactive ion etching (RIE) is used to etch MgxZn1−xO (0≤x≤0.3) films grown on r-plane sapphire substrates. The RIE etch rates are investigated as a function of Mg composition, RIE power, and chamber pressure. SiO2 is used as the etching mask to achieve a good etching profile. In comparison with wet chemical etching, the in-plane etching anisotropy of MgxZn1−xO (0≤x≤0.3) films is reduced in RIE. X-ray photoelectron spectroscopy measurements show that there is no Si and Cl contamination detected at the etched surface under the current RIE conditions. The influence of the RIE to the optical properties has been investigated.  相似文献   

16.
PbSnTe/PbTe double hetero-diode structures were grown by temperature difference method under controlled vapor pressure (TDM–CVP) liquid-phase epitaxy (LPE). These laser diode (LD) structures were of the PbTe (Bi)/Pb1−xSnxTe/PbTe (undoped substrate) double hetero (DH) type. The peak shift of the wavelength emitted by the fabricated diodes was recorded and it was found that they successfully lased from 15 K to over 77 K (liquid nitrogen temperature) at a slightly lower threshold current density than standard LPEs fabricated via the slow-cooling method. In addition, the lasing peak wavelength was longer than spontaneous emissions. The laser spectra of diodes with varying Sn concentrations (x) in the active layer were observed, and their intensities were recorded as a function of the wavelength. Very sharp lasing spectra were obtained between 6.5 μm and 9.4 μm (x=0–0.11), clarifying that the stoichiometry control possible with TDM–CVP is suitable for fabricating optical devices. In addition, it was demonstrated that TDM–CVP is appropriate for fabricating infrared optical devices constructed from PbxSn1−xTe systems.  相似文献   

17.
A self‐assembled GeOx/reduced graphene oxide (GeOx/RGO) composite, where GeOx nanoparticles are grown directly on reduced graphene oxide sheets, is synthesized via a facile one‐step reduction approach and studied by X‐ray diffraction, transmission electron microscopy, energy dispersive X‐ray spectroscopy, electron energy loss spectroscopy elemental mapping, and other techniques. Electrochemical evaluation indicates that incorporation of reduced graphene oxide enhances both the rate capability and reversible capacity of GeOx, with the latter being due to the RGO enabling reversible utilization of Li2O. The composite delivers a high reversible capacity of 1600 mAh g?1 at a current density of 100 mA g?1, and still maintains a capacity of 410 mAh g?1 at a high current density of 20 A g?1. Owing to the flexible reduced graphene oxide sheets enwrapping the GeOx particles, the cycling stability of the composite is also improved significantly. To further demonstrate its feasibility in practical applications, the synthesized GeOx/RGO composite anode is successfully paired with a high voltage LiNi0.5Mn1.5O4 cathode to form a full cell, which shows good cycling and rate performance.  相似文献   

18.
In this present study, we have reported the preparation of yttrium doped polycrystalline Ca2−xYxCo2O5 (x=0.0–1.0) material by a molten flux method and its various properties like electrical, optical, dielectric and magnetic behaviors. Characterization techniques have been adopted to confirm its physical nature and properties. X-ray diffraction results confirmed the crystal structure of prepared Ca2−xYxCo2O5 as orthorhombic and the scanning electron microscope pictured the presence of platelet-shaped particles with the dimensions of 150–300 nm. It also reveals the state of higher concentration of yttrium (Y3+) controls the grain size of Ca2−xYxCo2O5 ceramics. Further, we find out that the higher concentration of yttrium (Y3+) increases the optical band gap due to the occurrence of metal–insulator transition and also the same in electrical resistivity from 0.2  cm to 0.5  cm, which is due to the replacement of holes by Y3+ ions. The result of dielectric studies proves that the conduction mechanism of yttrium doped calcium cobalt oxide is due to space charge polarization. The magnetic saturation behavior shows the decreasing area in the hysteresis curve while the Y3+ concentration is increased, which is due to the phase transition of ferromagnetic to paramagnetic.  相似文献   

19.
The structural, optical and electrical properties of MgxZn1−xO (x=0.05–0.3) ternary alloy thin films deposited by the sol–gel method on the glass substrate were investigated. The presence of Mg in deposited samples was confirmed through EDAX. XRD spectra revealed that the deposited Mg doped ZnO films were polycrystalline in nature. The optical band gap of the films was tailored between 3.2 and 3.45 eV by varying Mg mole concentration between 0.05 and 0.3. IV characteristics showed decrease in current with increase in the Mg mole concentration. These results explore the applicability of MgZnO to form effective and efficient heterostructures with ZnO as an active layer for efficient carrier confinement in light emitting devices.  相似文献   

20.
A first-principal technique is employed to investigate the concentration dependence of the structural, electronic band structure, optical and chemical bonding properties of Zn1−xMgxS, Zn1−xMgxSe and Zn1−xMgxTe alloys. Structural parameters such as lattice constants and bulk moduli are found to vary non-linearly with changing concentration x and deviating from Vegard׳s law. Parent binaries as well as ternary alloys have a direct band gap (Γ–Γ) which increases non-linearly with increment in concentration. Chemical bonding nature changes from strong covalency to partial ionic character in increasing Mg-contents. The direct band gap and high optical activity in visible and ultraviolet range reveal the implication of these alloys in the optoelectronic devices applications.  相似文献   

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