Carrier Concentration Distribution Research Articles

Enhancing the Carrier Mobility and Bias Stability in Metal-Oxide Thin Film Transistors with Bilayer InSnO/a-InGaZnO Heterojunction Structure.

In this study, the electrical performance and bias stability of InSnO/a-InGaZnO (ITO/a-IGZO) heterojunction thin-film transistors (TFTs) are investigated. Compared to a-IGZO TFTs, the mobility (µFE) and bias stability of ITO/a-IGZO heterojunction TFTs are enhanced. The band alignment of the ITO/a-IGZO heterojunction is analyzed by using X-ray photoelectron spectroscopy (XPS). A conduction band offset (∆EC) of 0.5 eV is observed in the ITO/a-IGZO heterojunction, resulting in electron accumulation in the formed potential well. Meanwhile, the ∆EC of the ITO/a-IGZO heterojunction can be modulated by nitrogen doping ITO (ITON), which can affect the carrier confinement and transport properties at the ITO/a-IGZO heterojunction interface. Moreover, the carrier concentration distribution at the ITO/a-IGZO heterointerface is extracted by means of TCAD silvaco 2018 simulation, which is beneficial for enhancing the electrical performance of ITO/a-IGZO heterojunction TFTs.

SIMULATION OF DYNAMIC PROCESSES IN A p - i - n DIODE BY THE METHODS OF PERTURBATION THEORY

In the paper a mathematical model of the dynamic process of the electron-hole plasma formation in the active region ( i - region) of a semiconductor p - i - n - diode in the direct bias mode with a harmonic signal fed on the diode is developed. The basis of the model is a nonlinear nonstationary sin- gularly perturbed boundary value problem for a system of continuity equations of electron-hole currents and Poisson's equation. The algorithm for searching the charge carrier concentration distributions and the potential distribution is based on the asymptotic method of boundary functions and the Fourier method. In the course of the research, a technique for decomposing a nonlinear problem based on the development of perturbation theory me- thods was proposed. The initial nonlinear problem is reduced to a recurrent sequence of linear stationary boundary value problems, solved by classical and partially original analytical-numerical methods. The identification of the boundary functions in the solution of the problem provides, in particular, in contrast to the classical approximation of ambipolar diffusion, an adequate description of the electric field strength behavior in the active region of p - i - n - diodes. The obtained research results shed light on the peculiarities of the formation of the impedance characteristics of p - i - n - structures. The results of the work reveal more deeply the nature of the physical processes in the studied technical system and are aimed at improving the methodology for modeling and designing control semiconductor devices.

Improved breakdown performance in recessed-gate normally off GaN MIS-HEMTs by regrown fishbone trench

This work develops a regrown fishbone trench (RFT) structure in selective area growth (SAG) technique to fabricate recessed-gate normally off GaN metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs). The RFT structure effectively modulates the electric field at high drain and gate biases, thus allowing the device to feature improved off-state and gate breakdown performance with a high positive Vth of 2 V. The simulated carrier concentration and electric field distributions reveal the mechanism of electric field weakening by RFT architecture. Meanwhile, the current collapse phenomenon is significantly suppressed, and the gate voltage swing is also enlarged. The maximum gate drive voltage of 9.2 V for 10-year reliability of RFT GaN MIS-HEMT, together with the improved linearity and block voltage, broadens the applications of SAG devices. Furthermore, the RFT structure also provides an etching-free method for fabricating normally off GaN MIS-HEMTs with multi-dimensional gates.

The Remarkable Role of Indium in Synergistically Optimizing Carrier Concentration and Phase Distribution of AgCuTe-Based Materials.

Carrier regulation has proven to be an effective approach for optimizing the thermoelectric performance of materials. One common method to adjust the carrier concentration is through element doping. In the case of AgCuTe-based materials, it tends to form with cation vacancies, resulting in a high hole concentration and complex phase composition at low temperatures, which also hinders material stability. However, this also offers additional opportunities to manipulate the carrier concentration. In this study, the improved performance of AgCuTe through indium doping is reported, which leads to a reduction in hole concentration. In combination with a significant increase in the effective mass of the carriers, the enhanced Seebeck coefficient is also realized. Particularly, a notable improvement in power factor is observed in the hexagonal phase near room temperature. Furthermore, a lower electron thermal conductivity is achieved, contributing to an average figure of merit value of ≈1.21 (between 523 and 723K). Additionally, the presence of indium inhibits the formation of the second phase and ensures a homogeneous phase distribution, which reduces the instability arising from phase transition. This work significantly enhances the potential of AgCuTe-based materials for low to medium-temperature applications.

Multi-wavelength and broadband AlGaN-based LED for versatile and artificial UV light source

This study focuses on modeling and analyzing a multi-wavelength (MW) ultraviolet light-emitting diode (UV LED) equipped with grading transition layers, which holds potential as a versatile and artificial UV light source. Commencing with the exploration of simple dual and triple-wavelength UV LEDs, we delve into the device mechanism, including the role of the grading transition layer and the control of emission intensity ratios. The grading transition layer connects modules with different emission wavelengths, effectively enhancing hole injection by diminishing the effective hole barrier and providing three-dimensional hole gas (3DHG). Besides, the emission intensity ratio of different modules is modulated through electron overflow, which is finely and coarsely controlled respectively by altering the quantum well number and the Al composition of electron controlling layers (ECLs). Modulating the ECL composition and quantum well number has good unilaterality facilitated by using grading transition layers, promoting a lower overall design complexity. Band diagrams, current dynamics, and carrier concentration distribution are analyzed to uncover various device mechanisms. After investigating dual-wavelength and triple-wavelength LEDs, a broadband UV LED is designed and demonstrated through the numerical method. The LED incorporates five emission modules, and each module has a similar emission intensity, contributing to a near 100 nm width UV spectrum. We expect this work lays the foundation for MW and broadband UV LED designs, fostering advancements in the AlGaN-based UV LED community.

Understanding and Hindering the Electron Leakage in Green InP Quantum‐Dot Light‐Emitting Diodes

Indium phosphide (InP) quantum‐dot light‐emitting diodes (QLEDs) are considered as one of the most promising candidates for emerging displays owing to their good luminous performance and environmentally friendly properties. The operation of green InP QLEDs relies on the radiative recombination of electrically generated excitons, as in most QLEDs; however, the electrons injected into green InP QLEDs can easily pass through the quantum‐dot (QD) layer, resulting in a carrier imbalance and low external quantum efficiency (EQE). Herein, the mechanism of electron leakage in green InP QLEDs is revealed. Based on comparative experiments and simulations of the carrier concentration distribution, the path of electron leakage is determined and it is found that the root cause is the large Fermi energy difference between green InP QDs and indium tin oxide (ITO). To solve this problem, an ultrathin LiF layer is applied to modify the work function of the ITO, which simultaneously hinders electron leakage and enhances hole injection. Benefiting from a more balanced carrier injection, the maximum EQE of green InP QLEDs improves from 4.70% to 9.14%. In these findings, a universal mechanism is provided for hindering electron leakage in green InP QLEDs, indicating the feasibility of developing highly efficient green InP QLEDs.

P‐67: Research of photoelectric performance GaN based green Micro‐LED †

GaN‐based light‐emitting diode (LED) arrays are a promising technology in a wide range of applications. Research on temperature dependence performance is important in GaN‐ based LED. Display applications are still the focus of GaN‐ based LEDs, especially high‐definition (HD) displays. It is of great importance for HD display to researching green Micro‐LED device. we study the performance issues of 80μm green Micro‐LED devices include ideality factor at different temperatures, carrier concentration distribution, and optical properties. This research can help understand and fabrication high‐performance green Micro‐LED devices.

P‐10.8: Research of photoelectric performance GaN based green Micro‐LED †

GaN-based light-emitting diode (LED) arrays are a promising technology in a wide range of applications. The photoelectric performance of 80um green Micro-LED has been studied in depth, including the temperature dependence current-voltage, ideality factor, capacitance-voltage, carrier concentration distribution, external quantum efficiency (EQE), and luminance. The results of this research have demonstrated that the Micro-LED has excellent performance, with high EQE.

InP/InGaAs Uni-Traveling-Carrier Photodiode (UTC-PD) With Improved EM Field Response

In this article, a unique structure of InP/InGaAs uni-traveling-carrier photodiode (UTC-PD) is proposed. Compared with the one-sided junction photodiode, the UTC-PD has the advantages of a simpler epitaxial layer structure while maintaining the characteristics of high bandwidth and high output power loss profile. Simulated results show that a large built-in electric field can be generated under illumination, which aids UTC carrier velocity. The merits of the new structure are compared to a standard UTC-PD photodiode in terms of improved electric field and carrier concentration response. It is demonstrated that the photogeneration and light absorption of UTC-PDs are improved by incorporating a step-like internal texture of cones and dots profile in the photo absorption layer. The simulated device shows a peak electrical 3-dB bandwidth of 65 GHz at a low light intensity and reverse bias voltage. The performance characteristics of 1-D and 2-D UTC-PD simulations, including internal electric field distribution, energy band diagram, carrier concentration, and power loss distribution, are carefully studied. A theoretical discussion of the working principle and key performance characteristics of a UTC-PD enhanced by heterojunction design is reported. The entire physical environment is modeled and simulated through the finite element method (FEM) using commercial software. The proposed photodiode structure configuration is designed and optimized for photodetectors for high RF frequencies at different light intensities. To the best of our knowledge, the obtained bandwidth and electric field response is the fastest among those reported for other various higher wavelength photodiodes.

SIMULATION OF DIFFUSION-DRIFF PROCESSES IN THE ELECTRON-HOLE PLASMA OF THE P-I-N-DIODES ACTIVE REGION UNDER THE CONDITIONS OF A MW PENETRATING IN THE PLASMA BY THE PERTURBATION THEORY METHODS

Background. The problem of developing tools for mathematical modeling of the state of electron-hole plasma in the p-i-n structures active region under the influence of an additional factor - a powerful microwave electromagnetic field is considered. The task is important for specialists in the field of microwave electronics, since p-i-n structures are used, in particular, for switching powerful electromagnetic fields and as protective devices for the input paths of radio engineering systems.
 Objective. It consists in developing a methodology for modeling the electron-hole plasma concentration distribution in the p-i-n- diodes active region taking into account the effect on the dynamics of charge carriers of microwave radiation penetrating into the active region and developing asymptotic methods for solving the corresponding singularly perturbed nonlinear problems.
 Methods. Achieving the goal is ensured by the use of boundary layer method, complex amplitudes method and classical analytic-numerical methods for solving boundary value problems for systems of ordinary differential equations.
 Results. A generalized mathematical model of the electron-hole plasma stationary state in the p-i-n diodes active region in the hydrodynamic approximation, which takes into account the effect of microwave radiation on processes in the plasma, is proposed. The model basis is a nonlinear singularly perturbed boundary value problem for the system of electron-hole currents continuity equations and the Poisson. The model boundary value problem is reduced to a recurrent sequence of linear boundary value problems. Solutions of the stated problem are found in the form of asymptotic series containing stationary and non-stationary components. A feature of the proposed mathematical model is that it reflects the effect of detecting an electromagnetic microwave TE-like wave on the charge carrier concentration distribution inhomogeneity in the p-i-n-diode active region.
 Conclusions. The methodology for modeling the electron-hole plasma stationary state in the p-i-n-diodes active region taking into account the effect on the charge carriers dynamics of microwave radiation penetrating into the active region has been developed.

Corrosion reaction kinetics and high‐temperature corrosion testing of contact element strips in ultra‐high voltage bushing based on the phase‐field method

For the structural characteristics of power transmission equipment such as bushings, the plug-in structure is mostly used for current-carrying connections owing to the large size and long distance at high voltage levels. The contact element strip is the key component of the current-carrying structure, carrying the combined electrical–thermal effect. Its electrical current-carrying performance is important. In recent years, discharge failures caused by the overheating failure of electrical connections have occurred from time to time. However, there have been relatively few studies on the failure mechanism of the electrical connection structures of high-voltage power transmission equipment, such as bushings. In this study, from the perspective of corrosion reaction kinetics, a two-dimensional phase-field model of high-temperature corrosion is established to obtain the carrier concentration distribution in the film. The effects of temperature, gas partial pressure, film thickness, and applied electric field on the growth rate of corrosion reaction film were calculated using the finite element method. At the same time, with the contact element strips used in the bushing as the test object, a corrosion test was carried out in SF6 atmosphere to simulate the high-temperature corrosion caused by the uneven current carrying of the contacts in actual operating conditions. Combined with the effect of temperature on the film growth rate, the contact area was the most severely corroded location. The simulation can provide a qualitative analysis for the contact degradation test and a new method for studying the factors affecting the corrosion mechanism of contact element strips.

Sign reversal of anisotropic magnetoresistance and anomalous thickness-dependent resistivity in Sr2CrWO6/SrTiO3 films

High-quality Sr2CrWO6 (SCWO) films have been grown on SrTiO3 (STO) substrate by pulsed laser deposition under low oxygen pressure. With decrease of the film thickness, a drastic conductivity increase is observed. The Hall measurements show that the thicker the film, the lower the carrier density. An extrinsic mechanism of charge doping due to the dominance of oxygen vacancies at SCWO/STO interfaces is proposed. The distribution and gradient of carrier concentration in SCWO films are considered to be related to this phenomenon. Resistivity behavior observed in these films is found to follow the variable range hopping model. It is revealed that with increase of the film thickness, the extent of disorder in the lattice increases, which gives a clear evidence of disorder-induced localization charge carriers in these films. Magnetoresistance measurements show that there is a negative magnetoresistance in SCWO films, which is considered to be caused by the magnetic scattering of magnetic elements Cr3+ and W5+. In addition, a sign reversal of anisotropic magnetoresistance (AMR) in SCWO film is observed for the first time, when the temperature varies across a characteristic value, T M. Magnetization–temperature measurements demonstrate that this AMR sign reversal is caused by the direction transition of easy axis of magnetization from the in-plane ferromagnetic order at T > T M to the out-of-plane at T < T M.

Distribution of excess charge carriers in bilateral macroporous silicon with the same thickness of porous layers

In this work, to calculate the distribution of the excess minority carrier concentration in bilateral macroporous silicon, the solution of the diffusion equation for stationary conditions is used, which is written for a monocrystalline substrate and macroporous layers. The solution to the diffusion equation is supplemented by boundary conditions at the interface between macroporous layers and a monocrystalline substrate and at the boundaries of a bilateral macroporous silicon sample. The dependence of the distribution of the excess minority carrier concentration in bilateral macroporous silicon with the same thickness of porous layers on the depth of macropores, the thickness of the sample of bilateral macroporous silicon, and the bulk lifetime of minority charge carriers is calculated. It is shown that the distribution function of the excess minority carrier concentration in bilateral macroporous silicon exhibits two maxima. The maxima are located in the frontal macroporous layer, near the surface of the sample, and in a monocrystalline substrate, near the interface, the frontal macroporous layer - monocrystalline substrate.

Boxcar Averaging Scanning Nonlinear Dielectric Microscopy.

Scanning nonlinear dielectric microscopy (SNDM) is a near-field microwave-based scanning probe microscopy method with a wide variety of applications, especially in the fields of dielectrics and semiconductors. This microscopy method has often been combined with contact-mode atomic force microscopy (AFM) for simultaneous topography imaging and contact force regulation. The combination SNDM with intermittent contact AFM is also beneficial for imaging a sample prone to damage and using a sharp microscopy tip for improving spatial resolution. However, SNDM with intermittent contact AFM can suffer from a lower signal-to-noise (S/N) ratio than that with contact-mode AFM because of the shorter contact time for a given measurement time. In order to improve the S/N ratio, we apply boxcar averaging based signal acquisition suitable for SNDM with intermittent contact AFM. We develop a theory for the S/N ratio of SNDM and experimentally demonstrate the enhancement of the S/N ratio in SNDM combined with peak-force tapping (a trademark of Bruker) AFM. In addition, we apply the proposed method to the carrier concentration distribution imaging of atomically thin van der Waals semiconductors. The proposed method clearly visualizes an anomalous electron doping effect on few-layer Nb-doped MoS2. The proposed method is also applicable to other scanning near-field microwave microscopes combined with peak-force tapping AFM such as scanning microwave impedance microscopy. Our results indicate the possibility of simultaneous nanoscale topographic, electrical, and mechanical imaging even on delicate samples.

Влияние электронной температуры на распределение концентрации в поперечном сечении газоразрядной плазмы

The electron temperature and the concentration of charged particles associated with it in a gas-discharge plasma can lead to a change in the properties of the corresponding electronic devices: a change in the space charge. Even an insignificant space charge, due to the difference in the concentrations of charged particles in the plasma, can cause instabilities and lead to the formation of undamped longitudinal and transverse waves (strata) in the plasma of the positive gas discharge column. In a magnetized gas-discharge plasma, the space charge decreases due to a decrease in the parameters of motion of charged particles, and with a transverse magnetic field B = B0 = (bebp)-1/2 vanishes and the plasma becomes homogeneous. In the case when the magnetic weakly affects the plasma, it is necessary that the concentration of charge carriers be the same, i.e. the plasma is homogeneous. Therefore, it is necessary to determine the minimum value of the electron temperature at which the Maxwellian plasma is homogeneous. Goal – To estimate the effect of electron temperature on the distribution of charge carrier concentration, analyze the electron balance equation in two cases: at zero and real boundary conditions.

On the Current Saturation of Vertical Transistors With Conductive Network Electrodes

Vertical field effect transistors (VFETs) based on conductive network electrodes feature high current density and compatibility in printing processes. Here, the device structures of VFETs are designed and optimized toward good current saturation and a better ON–OFF ratio. Among the three different structures, a simple structure stands out as the best: a semiconducting layer is inserted below the source electrode to increase the injected area of carriers and to enhance L-type channels (the channels along the semiconductor–dielectric interface and then to the drain), whereas an insulating layer is added on the top and two sides of the source electrode to generate a depletion region and to suppress I-type channels (the channels from the top of the source to the drain). The introduction of moderate Schottky barriers to the source electrodes further benefits the current saturation and gate tuning. The 2D-technology computer-aided design (TCAD) simulations are performed to analyze the physical mechanisms by quantifying the distribution of potentials, carrier concentrations, and current densities. The simulated current–voltage relations show a differential output resistance over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega \cdot $ </tex-math></inline-formula> cm and an ON–OFF ratio over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> , indicating that the problems of current saturation and the ON–OFF ratio in short-channel VFETs have been theoretically solved to some extent.

Evaluation of the double-tuned functionally graded thermoelectric material approach for the fabrication of n-type leg based on Pb0.75Sn0.25Te

Thermoelectric (TE) technologies realize the generation of electrical energy from the waste heat. The one bottleneck, which significantly restricts the wide use of these technologies, relates to the low energy conversion efficiency of the commercial devices. In this work, the double-tuned functionally graded thermoelectric material (DT-FGTM) approach was proposed to achieve the high-performance TE leg through the increase in the average TE figure of merit (ZT)ave. The essence of this idea is connected with the precise control of the bandgap Eg and chemical potential μc over the entire temperature range. Considering Pb0.75Sn0.25Te solid solution, as an example, and using the three band Kane model, we evaluated the best conditions for the highest thermoelectric performance in this material. Within the offered herein DT-FGTM approach, we fabricated the thermoelectric n-type Pb0.75Sn0.25Te1−xIx leg and measured its output energy characteristics. The efficiency of energy conversion for the prepared DT-FGTM leg reaches a very high value of ∼12.0% at temperature difference ΔT = 540 K. Furthermore, the thermal treatment of the fabricated leg should not injure the carrier concentration distribution through the leg, as the hot end of the leg is heavily doped, and the chemical diffusion between segments would be only beneficial. Our demonstration shows that the DT-FGTM approach has significant practical interest and can be utilized for the other TE materials.

Simulation Study on Novel GaN‐Based n−p−n Heterojunction Bipolar Transistors with a Quaternary AlGaInN Emitter and a Two‐Dimensionally Conductive Base

Herein, a simulation study on novel GaN‐based n−p−n heterojunction bipolar transistors (HBTs) with a quaternary n‐AlGaInN emitter and a thin GaInN quantum well (QW) layer inserted in its p‐GaN base is reported. The idea of the quaternary AlGaInN emitter facilitates the design and independent growth of the energy bandgaps and lattice strain. In addition, the p‐GaN base inserted with the thin GaInN QW is expected to be effective in enhancing its lateral conduction via 2D hole gases (2DHGs). The simulation results indicate that the designed GaInN QW definitely functions to generate and transport the 2DHGs and ultimately contributes to the improvement of the device performance. In other words, the lateral resistivity of the p‐GaN base is reduced from 1.8 × 10−1 to 7.0 × 10−2 Ω cm with the use of the GaInN QW insertion layer. Further, the simulation study focusing on the lateral distance between the n‐emitter and p‐base electrodes exhibits stable device characteristics for the HBT with the GaInN QW insertion layer compared with the conventional HBT structure. Dynamic analysis of the carrier concentration distribution indicates that the QW functions as a low‐resistance current path and it has the effect of avoiding the punch‐through phenomenon.

Performance Enhancement of InGaN Light-Emitting Diodes with InGaN/GaN/InGaN Triangular Barriers

InGaN light-emitting diodes (LEDs) with InGaN/GaN/InGaN triangular (IGIT) barriers were designed and investigated on a theoretical basis. The carrier concentration and radiative recombination rate distribution in multiple quantum wells, energy band diagrams, light output power–current–voltage performance curves, and internal quantum efficiency of the LEDs with IGIT barriers were studied. The simulations showed that the InGaN LEDs with IGIT barriers have higher output light power, lower turn-on voltage, and less efficiency droop than that of LEDs with conventional GaN and InGaN barriers. These improvements originate from the appropriately designed energy band diagram of the LEDs with IGIT barriers, which improves injection efficiency of holes and confinement of electrons.

Free-carrier generation dynamics induced by ultrashort intense terahertz pulses in silicon.

We report the results of experimental studies and numerical simulation of the dynamics of the electron-hole pairs formation in silicon under the action of a two-period terahertz pulse with a maximum electric field strength of up to 23 MV/cm. It is shown that an inhomogeneous distribution of the charge carrier concentration over the depth of the silicon sample is formed, which persists for several microseconds. This inhomogeneity is formed due to a sharp increase in the rate of filling the conduction band with free carriers in the subsurface input layer of the silicon wafer, which occurs at a field strength above 15 MV/cm.