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Electrochemical capacitance-voltage profiling of nonuniformly doped GaAs heterostructures with SQWs and MQWs for LED applications
摘要： Light-emitting heterostructures with single and multiple GaAs/InGaAs quantum wells have been investigated by means of electrochemical capacitance-voltage (ECV) profiling. Capacitance-voltage characteristics were measured; concentration profiles of free charge carriers over the heterostructure depth as well as the intensity of quantum well filling by charge carriers were obtained. In heterostructures with a single quantum well (QW) we considered limitations of capacitance techniques for undoped QW profiling, which is situated near the metallurgic border of the p–n –junction. We made a detailed consideration of phenomena related to Debye smearing and we developed and analyzed the dependence of the space charge region width on the doping. Special attention was paid to investigation of the “blind” area. This was inspired by the practical problem from capacitance spectroscopy of semiconductors, when the researcher poses the task of obtaining a free charge carrier depth distribution profile as deep as possible in the space charge region, i.e. where the intensity of the electric field is maximum. Generally, the active QW of a LED heterostructure is placed deep in the space charge region, so reaching these regions is extremely important for practical problems. We present an evolution of capacitance-voltage characteristics during ECV profiling of nonuniformly doped p – n– heterostructures. For a heterostructure with multiple quantum wells we registered a response from 6 QWs.
关键词： capacitance-voltage profiling,heterostructure,quantum well,nonuniform doping,Electrochemical capacitance-voltage profiling,quantum dot,light-emitting diodes
更新于2025-11-14 17:28:48
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High dielectric polymer and its application on electro-optical Kerr effect of blue phase liquid crystal
摘要： We present a high-dielectric polymer with a lateral ?uorine group, and its dielectric constant exhibits larger than 20 at 1 kHz. This well-soluble polymer can solely stabilize blue phase liquid crystals (BPLCs) while reducing the operating voltage by 30% and increasing the Kerr constant by nearly 70.6%. The in?uence of the polymer’s dielectric property on the operating voltage is investigated based on the potential distribution. The theoretical result predicts that the operation voltage can be further reduced by 50% when the dielectric constant of the chiral dopant is the same as the high-dielectric polymer. The potential application of high-dielectric materials for the improvement of BPLC devices is foreseeable.
关键词： Kerr constant,blue phase liquid crystals,high-dielectric polymer,electro-optical Kerr effect,operating voltage
更新于2025-11-14 17:28:48
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Tailored nanocomposite energy harvesters with high piezoelectric voltage coefficient through controlled nanowire dispersion
摘要： Composites composed of piezoelectric nanomaterials dispersed in a flexible polymer have emerged as promising materials for highly durable and flexible energy harvesters and sensors. Although piezoelectric materials in their bulk form have a high electromechanical coupling coefficient and can efficiently convert mechanical energy to electrical energy, the ceramic form has low fracture toughness and thus they are limited in certain applications due to difficulty in machining and conforming to curved surfaces. Recently, additive manufacturing processes such as direct write, have been developed to incorporate piezoelectric nanowires into a polymer matrix with controlled alignment to realize printed piezoelectrics. Given the multiphase structure of a nanocomposite, it is possible to control the material structure such that the piezoelectric coupling and dielectric properties can be varied independently. In this paper, experimentally validated finite element (FE) and micromechanics models are developed for calculation and optimization of the piezoelectric voltage coefficient, g31, of a nanocomposite. It is shown that by using high aspect ratio nanowires with controlled alignment, the piezoelectric coupling can be disproportionately increased with respect to the dielectric constant which yields a g31 coefficient that can be enhanced more than seven times compared to the bulk piezoelectric material. Moreover, it is demonstrated that the use of high aspect ratio nanowires in the energy harvester resulted in significant improvement on the output electrical power of an energy harvester.
关键词： Energy harvesting,Nanowires,Finite element modeling (FEM),Voltage coefficient,Piezoelectric,The Mori-Tanaka method,Direct write,Nanocomposite
更新于2025-11-14 17:28:48
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Admittance of Organic LED Structures with an Emission YAK-203 Layer
摘要： The current-voltage characteristics and admittance of multilayer structures for organic LEDs based on the PEDOT:PSS/NPD/YAK-203/BCP system have been experimentally investigated in a wide range of the measurement conditions. It is shown that at voltages corresponding to the effective radiative recombination of charge carriers, a significant decrease in the differential capacitance of the structures is observed. The frequency dependences of the normalized conductance of LED structures are in good agreement with the results of numerical simulation in the framework of the equivalent circuit method. Changes in the frequency dependences of the admittance with a change in temperature are most pronounced in the temperature range of 200–300 K and less noticeable in the temperature range of 8–200 K. From the frequency dependences of the imaginary part of impedance, the charge carrier mobilities are found at various voltages and temperatures. The mobility values obtained by this method are somewhat lower than those determined by the transient electroluminescence method. The dependence of the mobility on the electric field is well approximated by a linear function. As the temperature decreases from 300 to 220 K, the mobility decreases several times.
关键词： frequency dependence of imaginary part of impedance,LED structure,current-voltage characteristic,transient electroluminescence,organic semiconductor,charge carrier mobility,method of equivalent circuits,admittance
更新于2025-11-14 17:28:48
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Low-Voltage, Full-Swing InGaZnO-Based Inverters Enabled by Solution-Processed, Ultra-Thin AlxOy
摘要： High-performance, full-swing inverters implemented with InGaZnO thin-film transistors (TFTs) have been demonstrated capable of operating at a very low voltage. The threshold voltage of the load and drive TFTs were modified through careful change of the gate dielectric anodization voltage. Both the load and drive TFTs show excellent electrical properties including a current on/off ratio > 106 and a subthreshold swing close to the theoretical limit. As a result, the inverters show high voltage gains up to 34 at a supply voltage of only 1 V as well as high noise margins > 92% of the theoretical maximum. The devices and the fabrication process might have potential applications in future wearable and disposable electronics where low cost and low power are vital.
关键词： InGaZnO,one-volt operation,high voltage gain and noise margins,full-swing inverters
更新于2025-11-14 17:28:48
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Highly Stretchable, High‐Mobility, Free‐Standing All‐Organic Transistors Modulated by Solid‐State Elastomer Electrolytes
摘要： Highly stretchable, high-mobility, and free-standing coplanar-type all-organic transistors based on deformable solid-state elastomer electrolytes are demonstrated using ionic thermoplastic polyurethane (i-TPU), thereby showing high reliability under mechanical stimuli as well as low-voltage operation. Unlike conventional ionic dielectrics, the i-TPU electrolyte prepared herein has remarkable characteristics, i.e., a large specific capacitance of 5.5 μF cm?2, despite the low weight ratio (20 wt%) of the ionic liquid, high transparency, and even stretchability. These i-TPU-based organic transistors exhibit a mobility as high as 7.9 cm2 V?1 s?1, high bendability (Rc, radius of curvature: 7.2 mm), and good stretchability (60% tensile strain). Moreover, they are suitable for low-voltage operation (VDS = ?1.0 V, VGS = ?2.5 V). In addition, the electrical characteristics such as mobility, on-current, and threshold voltage are maintained even in the concave and convex bending state (bending tensile strain of ≈3.4%), respectively. Finally, free-standing, fully stretchable, and semi-transparent coplanar-type all-organic transistors can be fabricated by introducing a poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid layer as source/drain and gate electrodes, thus achieving low-voltage operation (VDS = ?1.5 V, VGS = ?2.5 V) and an even higher mobility of up to 17.8 cm2 V?1 s?1. Moreover, these devices withstand stretching up to 80% tensile strain.
关键词： free-standing all-organic transistors,stretchable and conformal electronics,high-mobility,elastomer electrolyte,low-voltage operation
更新于2025-11-14 17:28:48
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Effects of repetitive polarization switching on the coercive voltage of Pt/Pb(Zr0.52Ti0.48)O3/Pt thin films analyzed using impedance spectroscopy
摘要： We investigated the effect of repetitive switching of polarization on the ferroelectric Pt/Pb(Zr0.52Ti0.48)O3/Pt thin film capacitor by using impedance spectroscopy. From the Cole-Cole plot, the equivalent circuit is described as a combination of the bulk part (a capacitor), the interface part (the constant phase element (CPE), and a parallelly-connected resistor). The circuit parameters were analyzed at various stages of switching. An early increase and a subsequent decrease of the bulk capacitance may represent the wake-up and fatigue phenomena, respectively. The change in the interface part was characterized by an increase in resistance and the growth of n, the exponent of CPE, which may have come from a reduction of defects and the diminished inhomogeneity in the interfacial layer, respectively. The change in the resistance and the coefficient of the CPE in the interface part collectively resulted in an increase in the interfacial impedance. The coercive voltage, which may have intrinsically increased due to the repetitive switching, was even larger as a result of the increased interfacial impedance.
关键词： Impedance spectroscopy,Wake-up,Coercive voltage,PZT,Fatigue
更新于2025-11-14 17:28:48
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Determination of physical mechanism responsible for the capacitance-voltage weak inversion “hump” phenomenon in n-InGaAs based metal-oxide-semiconductor gate stacks
摘要： Weak inversion capacitance-voltage (C-V) “hump” is a widely observed phenomenon at n-InGaAs based metal oxide semiconductor (MOS) structures. The mechanism responsible for this phenomenon is still under discussion. The C-V hump can be explained as an interaction of interface states with either one or both semiconductor energy bands. Each of the proposed mechanisms leads to a different interpretation of C-V hump. Simulating the mechanisms by relevant equivalent circuits, the capacitance and conductance characteristics of the MOS structure were calculated and compared with experimental results. The mechanism responsible for the C-V hump was determined.
关键词： interface states,equivalent circuits,n-InGaAs,metal-oxide-semiconductor,capacitance-voltage hump
更新于2025-11-14 17:28:48
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Enabling low voltage losses and high photocurrent in fullerene-free organic photovoltaics
摘要： Despite significant development recently, improving the power conversion efficiency of organic photovoltaics (OPVs) is still an ongoing challenge to overcome. One of the prerequisites to achieving this goal is to enable efficient charge separation and small voltage losses at the same time. In this work, a facile synthetic strategy is reported, where optoelectronic properties are delicately tuned by the introduction of electron-deficient-core-based fused structure into non-fullerene acceptors. Both devices exhibited a low voltage loss of 0.57 V and high short-circuit current density of 22.0 mA cm?2, resulting in high power conversion efficiencies of over 13.4%. These unconventional electron-deficient-core-based non-fullerene acceptors with near-infrared absorption lead to low non-radiative recombination losses in the resulting organic photovoltaics, contributing to a certified high power conversion efficiency of 12.6%.
关键词： non-fullerene acceptors,power conversion efficiency,voltage losses,charge separation,organic photovoltaics
更新于2025-11-14 15:18:02
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[IEEE 2018 IEEE PES/IAS PowerAfrica - Cape Town (2018.6.28-2018.6.29)] 2018 IEEE PES/IAS PowerAfrica - Estimation of Inverter-Based Solar PV Penetration on Medium Voltage Networks Using Grid Impedance
摘要： Installation and control of connecting inverter-based generation to medium voltage networks are constrained by network grid structure and by technical regulations that limits its penetration into the network. Medium voltage networks form the backbone to which low-voltage inverter-based generation such as solar PV systems are connect to. However, these networks generally have inconsistent impedances that vary with line lengths, conductor types and load distribution and therefore make them not as flexible and cost effective to efficiently allow adequate penetration of solar PV type distributed generation (capacity in kW) to be integrated. A generic model that mimics a medium voltage network is analyzed in this paper to determine how inverter-based generation can be maximized on the network in terms of its location by focusing on line impedance ratios to achieve voltage regulation.
关键词： voltage regulation,Inverter-based generation,line impedance ratio,conductor type,medium voltage,line lengths
更新于2025-09-23 15:23:52