Effect of the dopant concentration on the luminescence properties of InGaAs/GaAs spin light-emitting diodes with a mn δ layer

The luminescence properties of light-emitting diodes based on GaAs/InGaAs heterostructures containing Mn-doped layers are studied. The dependences of the degree of electroluminescence circular polarization on the growth parameters, specifically, the Mn content and the hole concentration are obtained. A steady increase in the degree of electroluminescence circular polarization and in the Curie temperature of the ferromagnetic structure with increasing hole concentration is observed, and a change in sign of the degree of circular polarization under variations in the Mn content is revealed. The data are interpreted on the basis of well-known models of ferromagnetism in structures based on ferromagnetic semiconductors.     

Influence of PVK ： NPB hole transporting layer on the characteristics of organic light-emitting devices

A doping system consisting of NPB and PVK is employed as a composite hole transporting layer （CHTL）. By adjusting the component ratio of the doping system, a series of devices with different concentration proportion of PVK ： NPB are constracted. The result shows that doping concentration of NPB enhances the competence of hole transporting ability, and modifies the recombination region of charge as well as affects the surface morphology of doped film. Optimum device with a maximum brightness of 7852 cd/m^2 and a power efficiency of 1.75 lm/W has been obtained by choosing a concentration proportion of PVK ： NPB at 1：3.     

Influence of spatial arrangements of π-spacer and acceptor of phenothiazine based dyes on the performance of dye-sensitized solar cells

Three phenothiazine based organic dyes PTA, PDTA and PTDA with D–π–A, π–D–π–A and A–π–D–π–A frameworks were designed and synthesized for the dye sensitized solar cells (DSSCs). Phenothiazine with octyloxyphenyl moiety acts as donor while thiophene and cyanoacetic acid units act as a π-spacer and an acceptor, respectively. The effects of the molecular structures of the dyes on the performance of the DSSCs were investigated systematically along with their photophysical and photoelectrochemical properties. The dye PTDA with A–π–D–π–A framework exhibited a better light harvesting capacity and an effective electron extraction pathway from the electron donor to the TiO₂ surface, leading to an efficiency of 6.82% under 100 mW cm⁻² light illumination, while the dyes PTA and PDTA with D–π–A and π–D–π–A frameworks delivered efficiencies of 6.34% and 5.12%, respectively.     

Extremely low driving voltage electrophosphorescent green organic light-emitting diodes based on a host material with small singlet–triplet exchange energy without p- or n-doping layer

In order to achieve low driving voltage, electrophosphorescent green organic light-emitting diodes (OLEDs) based on a host material with small energy gap between the lowest excited singlet state and the lowest excited triplet state (ΔE_ST) have been fabricated. 2-biphenyl-4,6-bis(12-phenylindolo[2,3-a] carbazole-11-yl)- 1,3,5-triazine (PIC–TRZ) with ΔE_ST of only 0.11 eV has been found to be bipolar and used as the host for green OLEDs based on tris(2-phenylpyridinato) iridium(III) (Ir(ppy)₃). A very low onset voltage of 2.19 V is achieved in devices without p- or n-doping. Maximum current and power efficiencies are 68 cd/A and 60 lm/W, respectively, and no significant roll-off of current efficiency (58 cd/A at 1000 cd/m² and 62 cd/A at 10,000 cd/m²) have been observed. The small roll-off is due to the improved charge balance and the wide charge recombination zone in the emissive layer.     

Effect of rapid thermal annealing on the parameters of gallium-arsenide low-barrier diodes with near-surface δ-doping

The results of experimental studies of the effect of rapid thermal annealing on low-barrier diode structures used in the fabrication of microwave detectors for imaging arrays are indicative of an increase in the effective barrier height. Assuming that this effect is related to the diffusion spreading of the silicon δ-doped layer, which determines charge transport in the modified diode, a theoretical model is developed and the diffusion coefficient for silicon in the near-surface region of gallium arsenide (D ≈ 2 × 10^?14 cm²/s at 600°C) is estimated. A comparison with published data makes it possible to assume that diffusion in the near-surface layers is greatly facilitated compared to that in the bulk. It is suggested that the cause of acceleration of the diffusion can be a high electric field formed by the charged plane of the detector and it can also be related to an increased density of defects near the surface. The practical result consists in the emerging possibility of increasing (within a certain range) the effective barrier height in the grown structures, which will make it possible to adapt the parameters of low-barrier diodes to the optimal value in order to obtain sensitive detectors.     

Intermolecular interactions in organic semiconductors based on annelated β-oligothiophenes and their effect on the performance of organic field-effect transistors

A series of derivatives based on annelated β-oligothiophenes were synthesized and characterized as active layer in organic field-effect transistors (OFETs). Highest field-effect mobility of 0.52 V^?1 s^?1 for 2,5-dibiphenyl-dithieno[2,3-b:3′,2′-d]thiophene (DBP-DTT), 2.2 cm² V^?1 s^?1 for 2,5-distyryl-dithieno[2,3-b:3′,2′-d]thiophene (DEP-DTT), and 0.16 cm² V^?1 s^?1 for 1,4-di[2-dithieno[2,3-b:3′,2′-d] thiophen-2-yl-vinyl]benzene (DDTT-EP) were obtained, while 2,5-diphenyl-dithieno [2,3-b:3′,2′-d]thiophene (DP-DTT) presents no field-effect behaviors. Their thermal, optical and electrochemical properties, topographical and X-ray diffraction patterns of films, and the single crystal structures were also investigated. With the end-capping groups changing in these materials, the intermolecular interactions could transform from S–S in DP-DTT to S–C in DBP-DTT, to S–π in DEP-DTT, and to the coexisting of S–S and S–π in DDTT-EP. According to the device performances and the results of transfer integral calculations, it was revealed that S–π intermolecular interaction benefits not only improving the mobility but also reducing the threshold voltage (V_T), while S–S intermolecular interaction is not favorable for promoting the mobility.     

Effect of multi-intermediate bands on the behavior of InAs1-xNx/GaAs1-ySby quantum dot solar cell

A mathematical model of quantum dot intermediate band solar cells (QDIBSCs) is investigated using two intermediate bands (IBs). These two IBs arise from the quantum dot (QD) semiconductor material within the bandgap energy. Some parameters such as the width of the QD (W_QD) and the barrier thickness or the inter-dot distances between the QDs (B_T) are studied to show their influence on the performance of the QDIBSC. The time-independent Schrödinger equation, which is solved using the Kronig-Penney model, is used to determine the position and bandwidth energies of the two IBs. In our proposed model, the cubic shape of the QDs from InAs_0.9N_0.1 and the barrier or host semiconductor material from GaAs_0.98Sb_0.02 are utilized. It is shown from the results obtained that changing the parameters W_QD and B_T has more influence on the bandwidth energy for the first IB, Δ₁, than in the case of the second IB, Δ₂. The optimum power conversion efficiencies (PCEs) of the QDIBSCs with two IBs for the model under study are 58.01% and 73.55% at 1 Sun and maximum solar concentration, respectively. One can observe that, in the case of the two IBs, an improvement of the PCE is achieved.     

Effect of joint spatial correlation on the diversity performance of space?time block codes

We characterize the effect of joint spatial correlation on the diversity performance of multiple-input multiple-output (MIMO) systems. The joint spatial correlation is structured by the coupling matrix whose elements determine the average power coupling between the transmit and receive eigenmodes. We first derive the closed-form expression for the exact symbol error probability (SEP) of orthogonal space?time block codes over jointly correlated MIMO Rayleigh-fading channels. We then show that the achievable diversity order is equal to the number of nonzero elements of the power coupling matrix and establish the Schur monotonicity theorems on the SEP and the effective fading figure as a functional of elements of the power coupling matrix. Diversity, orthogonal space?time block code (OSTBC), Schur monotonicity, spatial correlation, symbol error probability (SEP).     

Effects of the p-AlInGaN/GaN superlattices’structure on the performance of blue LEDs

The advantages of the p-AIInGaN/GaN superlattices＇ （SLs） structure as an electron blocking layer （EBL） for InGaN blue light-emitting diodes （LEDs） were studied by experiment and APSYS simulation. Elec- troluminescence （EL） measurement results show that the LEDs with the p-AllnGaN/GaN SLs＇ structure EBL ex- hibited better optical performance compared with the conventional A1GaN EBL due to the enhancement of hole concentration and hole carrier transport efficiency, and the confinement of electrons＇ overflow between multiple quantum-wells （MQWs） and EBL.     

Research on quantum well intermixing of 680 nm AlGaInP/GaInP semiconductor lasers induced by composited Si–Si3N4 dielectric layer

The optical catastrophic damage that usually occurs at the cavity surface of semiconductor lasers has become the main bottleneck affecting the improvement of laser output power and long-term reliability. To improve the output power of 680 nm AlGaInP/GaInP quantum well red semiconductor lasers, Si–Si₃N₄ composited dielectric layers are used to induce its quantum wells to be intermixed at the cavity surface to make a non-absorption window. Si with a thickness of 100 nm and Si₃N₄ with a thickness of 100 nm were grown on the surface of the epitaxial wafer by magnetron sputtering and PECVD as diffusion source and driving source, respectively. Compared with traditional Si impurity induced quantum well intermixing, this paper realizes the blue shift of 54.8 nm in the nonabsorbent window region at a lower annealing temperature of 600 °C and annealing time of 10 min. Under this annealing condition, the wavelength of the gain luminescence region basically does not shift to short wavelength, and the surface morphology of the whole epitaxial wafer remains fine after annealing. The application of this process condition can reduce the difficulty of production and save cost, which provides an effective method for upcoming fabrication.     

Growth behavior and improved water–vapor-permeation-barrier properties of 10-nm-thick single Al2O3 layer grown via cyclic chemical vapor deposition on organic light-emitting diodes

We have investigated the growth behavior and water vapor permeation barrier properties of cyclic chemical vapor deposition (C-CVD)-grown 10-nm-thick single layer of Al₂O₃. Al₂O₃ layers grown by C-CVD showed a high density of 3.298 g/cm³ and were amorphous without grain boundaries. A deposition rate of 0.46 nm/cycle was obtained. The C-CVD system was self-limiting, as in the case of atomic layer deposition, which enables precise control of the thickness of the Al₂O₃ layer. A water vapor transmission rate of 1.51 × 10⁻⁵ (g/m²)/day was obtained from a Ca degradation test performed at 85 °C and 85% relative humidity. Moreover, the performance of organic light-emitting diodes, passivated by a C-CVD-grown 10-nm-thick Al₂O₃ single layer, was not affected after 24,000 h of turn-on time; this is strong evidence that C-CVD-grown Al₂O₃ layers effectively prevent water vapor from diffusing into the active organic layer.     

Modelling of the electronic structure for an AlGaAs/GaAs/AlGaAs HFET with a δ-doping layer inside the quantum well

The effect of a δ-doping layer inside the quantum well of an AlGaAs/GaAs/AlGaAs HFET is studied by a self-consistent modelling of the band structure across the device in dependence on the geometric dimensions, the δ-doping density, and the gate voltage. The energy position of the δ-like donors inside the quantum well is attached to the lowest subband energy. Especially the results show the possibility to increase the channel charge and to control its spatial distribution which could make possible an increase of the mobility of the device. It is shown that the potential obtained by a Modified Thomas-Fermi Approximation is very suitable as a starting potential for the self-consistent calculation or even as a final result in special cases.     

Highly efficient emission and high-CRI warm white light-emitting diodes from ligand-modified CsPbBr3 quantum dotsOA

All-inorganic CsPbBr₃ perovskite quantum dots(QDs) have received great attention in white light emission because of their outstanding properties. However, their practical application is hindered by poor stability. Herein, we propose a simple strategy to synthesize excellent stability and efficient emission of CsPbBr₃ QDs by using 2-hexyldecanoic acid(DA) as a ligand to replace the regular oleic acid(OA) ligand. Thanks to the strong binding energy between DA ligand and QDs, ...     

Effect of thermal annealing on the photoluminescence of structures with InGaAs/GaAs quantum wells and a low-temperature GaAs layer δ-doped with Mn

The effects of isochronal thermal annealing (at 325–725°C) on the radiative properties of InGaAs/GaAs nanoheterostructures containing a low-temperature GaAs layer δ-doped with Mn grown by laser deposition are studied. A decrease in the photoluminescence intensity and increase in the ground transition energy are observed upon thermal impact for quantum wells located near the low-temperature GaAs layer. The distribution of Mn atoms in the initial and annealed structures is obtained by secondary-ion mass spectrometry. A qualitative model of the observed effects of thermal annealing on the radiative properties of the structures is discussed; this model takes into account two main processes: diffusion of point defects (primarily gallium vacancies) from the GaAs coating layer deep into the structure and Mn diffusion in both directions by the dissociation mechanism. Magnetization studies show that, as a result of thermal annealing, an increase in the proportion of the ferromagnetic phase at room temperature (presumably, MnAs clusters) in the low-temperature GaAs coating layer takes place.     

Effect of precursor molar ratio of [S2?]/[Zn2+] on the lifetime of ZnS nanocrystals

Undoped ZnS nanocrystals(NCs) with different precursor molar ratios of [S2-]/[Zn2+] are prepared by the chemical precipitation method.The structural and optical properties of the samples are characterized by the X-ray diffraction(XRD) spectra,photoluminescence(PL) spectra and PL decay spectra.The XRD analysis shows that the crystal quality of ZnS NCs becomes better and the grain size is larger at higher [S2-]/[Zn2+] ratios.The PL peaked at 430 nm decreases with the [S2-]/[Zn2+] ratio increasing,which is asc...     

Low-temperature (77–300 K) current-voltage characteristics of 4H-SiC p+-p-n+ diodes: Effect of impurity breakdown in the p-type base

The effect of impurity breakdown on the low-temperature (77–300 K) current-voltage (I–V) characteristics of 4H-SiC diodes with a p-type base has been studied. Experimental samples were fabricated from CVD-grown (chemical vapor deposition) commercial p ⁺-p-n ⁺ 4H-SiC structures. A high electric field in the p-type base was created by applying a forward bias to the diodes. It was found that, at temperatures of 136, 89, and 81 K, the commonly observed “diode” portion of the I–V characteristics is followed by a portion in which the current grows more rapidly due to the impact ionization of frozen-out Al acceptor atoms in the ground (unexcited) state. At temperatures of 81 and 77 K, this portion is followed by one with a negative differential resistance due to the regenerative dynistor-like switching of the diode, caused by impact ionization of aluminum atoms in the excited state.     

Effect of ICT integration on SC flexibility,agility and company’ performance: the Mexican maquiladora experience

Wireless Networks - This article reports a structural equation model (SEM) with four latent variables to measure the relationship between information and communication technologies (ICT)...     

Analysis of the Effect of Spacer Layers on Nonlinear Distortions of the Current–Voltage Characteristics of GaAlAs/InGaAs pHEMTs

Semiconductors - The paper presents the results of modeling the electrophysical parameters of AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (pHEMT) structures via...     

Light-emitting diodes of “Warm” white luminescence on the basis of p-n heterostructures of the InGaN/AlGaN/GaN type coated with phosphors made of yttrium-gadolinium garnets

Semiconductors - Electroluminescence spectra and color characteristics of light-emitting diodes of white luminescence based on p-n heterostructures of the InGaN/AlGaN/GaN type with blue emission...