Total Carrier Research Articles

Characteristic voltages and times from capacitance–voltage analysis of quantum dot light-emitting diodes

The characteristic voltages in the capacitance–voltage (C–V) curve of quantum dot light-emitting diodes (QLEDs) are usually linked to the start of charge injection and recombination in a working device. However, it may lead to a misunderstanding of the carrier process in QLEDs. This is because capacitance change only reflects an electrical response of additional carriers induced by a small signal loaded on an applied DC voltage but does not directly correlate with the total free carrier response governed by the working voltage. In this work, we study the frequency-dependent C–V characteristics of a blue QLED, focusing on the characteristic voltages, characteristic times, and their relationships. First of all, we identify that the charge injection point of QLEDs should be extracted by the current density–voltage–luminance characteristics rather than the C–V curve. As for the characteristic voltages obtained from the C–V curve, they are determined by voltage-dependent characteristic times in different time domains. Furthermore, the C–V characteristic is helpful to evaluate charge accumulation or leakage in blue QLED, serving as an accessible analysis tool in the carrier transport process. Our work provides a definite physical meaning of characteristic voltages in the C–V curve and exhibits the usefulness of C–V characteristics for analyzing the charge dynamics of QLED.

The bacterial patterns suggesting the dynamic features of tick-associated microorganisms in hard ticks

BackgroundTicks are blood-feeding significant arthropods that can harbour various microorganisms, including pathogens that pose health risks to humans and animals. Tick-symbiont microorganisms are believed to influence tick development, but the intricate interactions between these microbes and the relationships between different tick-borne microorganisms remain largely unexplored.ResultsBased on 111 tick pool samples presenting questing and engorged statuses including 752 questing tick and 1083 engorged tick from cattle and goats, which were collected in two types of geographic landscape (semi-desert and alpine meadow). We observed significant variations in the composition of tick-borne microorganisms across different environments and blood-engorgement statuses, with a pronounced divergence in symbionts compared to environmental bacteria. Metabolic predictions revealed over 90 differential pathways for tick-borne microorganisms in distinct environments and more than 80 metabolic variations in response to varying blood engorgement statuses. Interestingly, nine pathways were identified, particularly related to chorismate synthesis and carbohydrate metabolism. Moreover, microbial network relationships within tick-borne microorganism groups were highly distinct across different environments and blood-engorgement statuses. The microbial network relationships of symbionts involve some pathogenic and environmental microorganisms. Regression modelling highlighted positive correlations between the Coxiella symbiont and related pathogens, while some environmental bacteria showed strong negative correlations with Coxiella abundance. We also identified commensal bacteria/pathogens in bacterial cooccurrence patterns. Furthermore, we tested pathogenic microorganisms of each tick sample analysis revealed that 86.36% (1601/1855) of the tick samples carried one or more pathogenic microorganisms, The total carrier rate of bacterial pathogens was 43.77% ((812/1855). Most blood samples carried at least one pathogenic microorganism. The pathogens carried by the ticks have both genus and species diversity, and Rickettsia species are the most abundant pathogens among all pathogens.ConclusionOur findings underscore that the bacterial pattern of ticks is dynamic and unstable, which is influenced by the environment factors and tick developmental characteristics.

Low frequency of SLC26A4 c.919-2A > G variant among patients with nonsyndromic hearing loss in Yunnan of Southwest China

BackgroundGene variants are responsible for more than half of hearing loss, particularly in nonsyndromic hearing loss (NSHL). The most common pathogenic variant in SLC26A4 gene found in East Asian populations is c.919-2A > G followed by c.2168A > G (p.H723R). This study was to evaluate their variant frequencies in patients with NSHL from special education schools in nine different areas of Southwest China’s Yunnan.MethodsWe performed molecular characterization by PCR-products directly Sanger sequencing of the SLC26A4 c.919-2AG and c.2168 A > G variants in 1167 patients with NSHL including 533 Han Chinese and 634 ethnic minorities.ResultsThe SLC26A4 c.919-2A > G variant was discovered in 8 patients with a homozygous state (0.69%) and twenty-five heterozygous (2.14%) in 1167 patients with NSHL. The total carrier rate of the c.919-2A > G variant was found in Han Chinese patients with 4.50% and ethnic minority patients with 1.42%. A significant difference existed between the two groups (P < 0.05). The c.919-2A > G allele variant frequency was ranged from 3.93% in Kunming to zero in Lincang and Nvjiang areas of Yunnan. We further detected the SLC26A4 c.2168 A > G variant in this cohort with one homozygotes (0.09%) and seven heterozygotes (0.60%), which was detected in Baoshan, Honghe, Licang and Pu`er areas. Between Han Chinese group (0.94%) and ethnic minority group (0.47%), there was no statistical significance (P > 0.05). Three Han Chinese patients (0.26%) carried compound heterozygosity for c.919-2A > G and c.2168 A > G.ConclusionThese data suggest that the variants in both SLC26A4 c.919-2A > G and c.2168 A > G were relatively less frequencies in this cohort compared to the average levels in most regions of China, as well as significantly lower than that in Han-Chinese patients. These results broadened Chinese population genetic information resources and provided more detailed information for regional genetic counselling for Yunnan.

Recombination dynamics and pronounced re-absorption effect in ZnO single crystals under two-photon excitation

Time-resolved photoluminescence measurements were conducted on ZnO single crystals using two-photon (2P) excitation at low temperatures ranging from 25 to 260 K. The decay constants of various emission peaks are determined and compared between one-photon and two-photon excitations using a recently modified localized-state ensemble model. The analysis is focused on the redshift of the phonon-assisted free exciton transition energy with increasing temperature. A significantly longer radiative recombination lifetime of approximately 840 ps is observed under 2P excitation. The extended lifetime of excitons during 2P excitation is achieved through the interplay of multiple mechanisms. Photon-recycling, enabled by high absorption coefficients and total internal reflection, facilitates re-absorption and new carrier generation. Phonon scattering lowers photon energy, allowing their escape from the crystal, while exciton–polariton interactions delay photon travel, collectively contributing to the extension of exciton lifetimes. The re-absorption effect and elongated carrier lifetime observed from our work could be beneficial for applications of ZnO materials in 2P imaging, particularly of biological samples.

Ultrafast Subpicosecond Magnetization of a 2D Ferromagnet.

Strong spin-charge interactions in several ferromagnets are expected to lead to subpicosecond (sub-ps) magnetization of the magnetic materials through control of the carrier characteristics via electrical means, which is essential for ultrafast spin-based electronic devices. Thus far, ultrafast control of magnetization has been realized by optically pumping a large number of carriers into the d or f orbitals of a ferromagnet; however, it is extremely challenging to implement by electrical gating. This work demonstrates a new method for sub-ps magnetization manipulation called wavefunction engineering, in which only the spatial distribution (wavefunction) of s (or p) electrons is controlled and no change is required in the total carrier density. Usinga ferromagnetic semiconductor (FMS) (In,Fe)As quantum well (QW), instant enhancement, as fast as 600fs, of the magnetization is observed upon irradiating a femtosecond (fs) laser pulse. Theoreticalanalysis shows that the instant enhancement of the magnetization is induced when the 2D electron wavefunctions (WFs) in the FMS QW are rapidly moved by a photo-Dember electric field formed by an asymmetric distribution of the photocarriers. Because this WF engineering method can be equivalently implemented by applying a gate electric field, these results open a new way to realize ultrafast magnetic storage and spin-based information processing in present electronic systems.

The NGS panel for genetic testing in cardiology: from the evaluation of disease risk to pharmacogenetics

Cardiovascular diseases (CVD) are a leading cause of mortality in many countries worldwide. Genetic testing is an integral part of CVD prevention. The most common hereditary diseases in the practice of a cardiologist are cardiomyopathy and channelopathy (arrhythmogenic syndromes), as well as familial hypercholesterolemia, which causes a high risk of atherosclerosis and coronary heart disease (CHD). The total carrier frequency of pathogenic variants is 1:100. Timely genetic diagnosis is necessary for conditions that can lead to sudden cardiac death (for example, long QT syndrome, Brugada syndrome, arrhythmogenic cardiomyopathies). Pharmacogenetic testing is also important in cardiology, since it allows taking into account the role of genetic factors in the formation of a response to therapy. Incorporating individual patient characteristics can increase efficiency and minimize the likelihood of complications. The design of modern targeted cardiopanels must necessarily take into account monogenic and oligogenic forms of dyslipidemia and cardiovascular pathologies, polymorphic markers associated with a violation of the lipid spectrum of blood plasma and the early development of CVD in a particular population, as well as a minimum set of pharmacogenetic markers according to modern recommendations for clinical pharmacologists. In this review we provide a justification for the optimal design of such a panel for use in medical practice and scientific research.

Bee pollen usage as carrier material in the drying of honey and some properties of honey-bee pollen powders

PurposeThe aim of this study was to produce an enriched honey powder with active compounds coming from bee pollen and investigate the effects of bee pollen addition as a carrier material on honey powder.Design/methodology/approachThe effects of bee pollen addition as carrier material in corporation with gum arabic at different ratios (25, 50 and 75% of total carrier material amount) on vacuum-dried honey-bee pollen powder were investigated.FindingsThe bee pollen concentration raise in the mixture increased the particle size, total phenolic, flavonoid and sugar contents and antioxidant activity, whereas decreased the Hauser ratio and Carr index values, hygroscopicity and solubility of enriched honey powder samples. The honey powder samples had passable and poor flow properties and very hygroscopic (>20%) structure because of the high sugar content. The phenolic and flavonoid contents of honey powder samples with bee pollen changed between 1531.59 and 3796.00 mg GAE/kg and 424.05–1203.10 mg QE/kg, respectively, and these values were much higher than the control sample. On the basis of linear correlation analysis, there was a very high positive correlation between total phenolic, flavonoid and antioxidant activity, while there was a very high negative correlation between these parameters and solubility.Originality/valueThe study evaluated that enriching of honey powders with pollen, which is a product of both plant and bee origin, rather than enriching with different plant and animal sources has an innovative approach. Additionally, the usage of bee pollen as a carrier agent in food drying has not been previously reported in any study.

Crystal strain engineering of AgBr/TiO2 for visible-light photocatalysis: Balancing light absorption and charge carrier kinetics

Addition of noble metals and/or their halides certainly improves the visible-light photocatalytic activity of TiO2, but whether this improvement is due to better photoabsorption capacity of the noble metal or enhanced photoelectrical properties of TiO2 itself, is still a subject of debate. Furthermore, the optimized load of noble metal halides at which best photocatalytic activity in TiO2 occurs hasn’t been explained in the literature consistently. Herein, we investigate the change in intrinsic lattice strain of TiO2 at different AgBr loadings which imparts selective optoelectronic properties turning AgBr/TiO2 system into a visible-light photocatalyst. XRD analysis reveals that beyond a maximum strain developed at an optimum AgBr loading level, the grain boundary interface can no longer withstand the increased strain at Ti—Ti, and Ti—O bonds and a chain of thermodynamically governed crystalline phase transformation within TiO2 begins. Faster dye degradation kinetics corroborate the hypothesis that the catalyst possessing maximum lattice strain shows superior photocatalytic properties. Photoelectrochemical studies was used to quantify the rate of charge transfer (kct) and rate of recombination (kr) of photogenerated electrons and holes. These studies revealed that although higher AgBr concentration may increase charge transfer through plasmon resonance but ultimately kr controls the total charge carrier flux that determines the photocatalytic efficicency of TiO2. Our work highlights methods in which the optimum loading of AgBr can be determined and presents fundamental insight into the role of lattice strain in balancing optical and electrical properties of TiO2 for constructing high-performance photocatalysts suitable for visible light application.

The modelling and simulation of perovskite solar cell consisting textile-based electrodes

Perovskite solar cell (PSC) consisting textile-based electrodes has been created novel features for future energy supply. Recently, Cs0.05(FA0.85MA0.15)0.95Pb(I0.85Br0.15)3 perovskite has appeared as a favourable candidate for flexible perovskite solar cells. However, a confined performance was acquired when the conventional Spiro-OMeTAD were used as hole transport layer (HTL) material because of suboptimal valance band offset (ΔEV) between Perovskite/HTL layers. In this study, a theoretical drift–diffusion​ modelling is used by finite volume method (FVM) to investigate performance of textile perovskite solar cell with double hole transport layers (HTLs) with graded band gap energies. Copper thiocyanate (CuSCN) and Nickel Oxide (NiO) are replaced as double HTLs, which dramatically enhanced the performance due to optimal upward step by step valance band offsets (ΔEV) between Perovskite/Textile Composite Electrode layers. It is shown that the decreasing of the metal–semiconductor schottky barrier height of electrodes leads to significant increase in fill factor (FF). Also, it is revealed that the enriching of perovskite carrier diffusion length by equipoising of carrier capture cross section, carrier total defect density and carrier thermal velocity substantially promote the overall device efficiency. The short-circuit current (Jsc) of 20.65 mA/cm 2, open-circuit voltage (Voc) of 1.19 V, fill factor (FF) of 73.57%, and power conversion efficiency (PCE) of 18.20% have been obtained by optimization of electrodes properties and perovskite layers. Remarkably, the advantageous of low cost, flexible, and chemical stable conducive textile composite, extends new opportunities in the commercial expansion of highly efficient photovoltaic textile in optoelectronic industry field.

Broadband nonlinear optical response of titanium nitride in the visible spectral range

Epsilon-near-zero (ENZ) materials, a new class of materials with vanishing permittivity, which can significantly enhance the interaction between incident light and matters. Here, we investigated the third-order nonlinear optical response of titanium nitride (TiN), an ENZ material, in the visible range by using Z-scan method, and obtained a maximum nonlinear absorption coefficient β of −3.78 × 103 cm/GW at its ENZ wavelength. Furthermore, the carriers dynamic characteristics of TiN are revealed by time-resolved pump-probe measurement, including the intraband and interband excitation, the former is mainly derived from laser-induced to form a non-equilibrium distribution of hot electrons, resulting in the electron energy redistribution process in the conduction band, and the latter is the electrons located in the valence band being promoted to the conduction band, increasing the total free carrier density and thus causing a change in the optical properties. Our results indicate the great potential applications of TiN in nonlinear optical and all-optical modulation devices.

Improved detection of SBDS gene mutation by a new method of next-generation sequencing analysis based on the Chinese mutation spectrum.

Next-generation sequencing (NGS) is a useful molecular diagnostic tool for genetic diseases. However, due to the presence of highly homologous pseudogenes, it is challenging to use short-read NGS for analyzing mutations of the Shwachman-Bodian-Diamond syndrome (SBDS) gene. The SBDS mutation spectrum was analyzed in the Chinese population, which revealed that SBDS variants were primarily from sequence exchange between SBDS and its pseudogene at the base-pair level, predominantly in the coding region and splice junction of exon two. The c.258+2T>C and c.185_184TA>GT variants were the two most common pathogenic SBDS variants in the Chinese population, resulting in a total carrier frequency of 1.19%. When analyzing pathogenic variants in the SBDS gene from the NGS data, the misalignment was identified as a common issue, and there were different probabilities of misalignment for different pathogenic variants. Here, we present a novel mathematical method for identifying pathogenic variants in the SBDS gene from the NGS data, which utilizes read-depth of the paralogous sequence variant (PSV) loci of SBDS and its pseudogene. Combined with PCR and STR orthogonal experiments, SBDS gene mutation analysis results were improved in 40% of clinical samples, and various types of mutations such as homozygous, compound heterozygous, and uniparental diploid were explored. The findings effectively reduce the impact of misalignment in NGS-based SBDS mutation analysis and are helpful for the clinical diagnosis of SBDS-related diseases, the research into population variation, and the carrier screening.

Carrier frequency and incidence estimation of RPE65-associated inherited retinal diseases in East Asian population by population database-based analysis

BackgroundInherited retinal diseases (IRDs) are clinically and genetically heterogenous disorders leading to visual impairment and blindness. Because gene therapy for RPE65-associated IRDs was recently approved, it is necessary to predict the carrier frequency and prevalence for RPE65-associated IRDs. This study aimed to analyze the carrier frequency and expected incidence of RPE65-associated IRDs in East Asians and Koreans using exome data from the Genome Aggregation Database (gnomAD) and the Korean Reference Genome Database (KRGDB).MethodsWe analyzed 9,197 exomes for East Asian populations from gnomAD comprising 1,909 Korean and 1,722 Korean genomes from KRGDB. All identified RPE65 variants were classified according to the 2015 American College of Medical Genetics and Genomics and the Association for Molecular Pathology guidelines.ResultsThe total carrier frequencies of East Asians and Koreans from both gnomAD and KRGDB were 0.10% (11/10,919) and 0.06% (2/3,631), respectively. The estimated incidence of RPE65-associated IRDs was 1/3,941,308 in East Asians and 1/13,184,161 in Koreans.ConclusionThis study identified carrier frequencies of RPE65-associated IRDs in East Asians and Koreans using gnomAD and KRGDB. We confirmed that the carrier frequency of RPE65-associated IRDs patients was low in Koreans among all East Asian populations, and the incidence was also predicted to be lower than in other East Asian populations. The variant spectrum of RPE65 gene in East Asian and Korean populations differed greatly from those of other ethnic groups.

An Analytical Drain Current Model of ZnO-Based Amorphous Oxide Semiconductor Thin-Film Transistors

An analytical one-piece drain current model of ZnO-based amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) is presented in this article. This model is able to solve the main obstacle in a lack of analytical and physics-based nonregional device modeling for AOSTFTs and is suitable to be implemented into circuit simulators. Based on the effective-charge-density approach, free carrier density and localized carrier density, including tail and deep states, are unified into total carrier density. Then, one-piece surface potential is derived analytically from equivalent 1-D Poisson’s equation described in an effective-charge-density approach. It is also possible that channel carrier mobility is calculated from the ratio between free carrier and effective total carrier densities. Furthermore, drain current expression is derived analytically and validated by experimental data. Good agreements of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> characteristics prove that the proposed model could serve as a useful simulation tool implemented into circuit simulators.

Highly sensitive detection of polystyrene by on-line splitless pyrolysis-gas chromatography/mass spectrometry with cryo-trapping of pyrolyzates and forced venting of carrier gas

Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) has been extensively used as a powerful tool for polymer analysis. In Py-GC/MS measurements, GC methods have usually employed split injection conditions for qualitative and quantitative analysis, but splitless injection of pyrolyzates to GC/MS has been reported to obtain higher sensitivity for small amount of analytes, since split ratio is inversely related to the amount of analyte entering the detection systems. However, the slower total carrier gas flow rate of splitless injection, which is necessary to keep the column flow rate at around a few mL/min, can increase residence time in the pyrolysis chamber, which can cause unfavorable secondary reactions of pyrolyzates such as decomposition and recombination in the pyrolyzer. In this study, we developed a new on-line splitless Py-GC/MS method called the Forced-Venting-and-Trap-Splitless (F-Splitless) method, based on cryo-trapping of pyrolyzates and forced venting of carrier gas under high carrier gas flow rate. Calibration curves measured by the F-Splitless method for polystyrene (PS) using the styrene monomer and trimer as key compounds show a good linearity over the concentration range from 0.01 ng to 100 ng. Limit of detection (LOD) and limit of quantification (LOQ) were 17 pg and 56 pg for the styrene monomer (S) based on the criterion of LOD: 3σ/a and LOQ: 10σ/a, where a is the slope of the calibration curve and σ is the standard deviation of the peak area of the minimum concentration, using the selected ion monitoring (SIM) mode. At a trace concentration level of PS, contamination from the environment was recognized. However, 100 pg of PS showed a signal to noise ratio (S/N) of 570 for S in SIM mode and 1.8 pg of PS could be quantified according to the criterion of LOQ based on signal to noise ratio (S/N), i.e., S/N = 10.

Resonant two-photon terahertz quantum cascade laser.

Lasers that can emit two photons from a single electron relaxation between two states of the same parity have been discussed since the early days of the laser era. However, such lasers have seen only limited success, mainly due to a lack of suitable gain medium. We propose that terahertz (THz) frequency quantum cascade lasers (QCLs) are an ideal semiconductor structure to realize such two-photon emissions. In this work, we present a THz QCL heterostructure designed to emit two resonant photons from each electronic relaxation between two same-parity states in the active region. We present coupled Maxwell-Bloch equations that describe the dynamics of such a two-photon laser and find analytical solutions for the steady-state light intensity, the steady-state energy-resolved carrier densities, and the total threshold carrier density. Due to the two-photon emission from each excited state relaxation and an increased photon-driven carrier transport rate, our simulations predict a significant enhancement of light intensity in our designed resonant two-photon THz QCL when compared to an exemplar conventional THz QCL structure.

Investigation of Modulation Bandwidth of InGaN Green Micro-LEDs by Varying Quantum Barrier Thickness

InGaN-based micro light-emitting diodes (micro-LEDs) with 5, 10, and 13 nm quantum barrier (QB) thickness were fabricated by metal-organic chemical vapor deposition (MOCVD) to investigate the influence of quantum-confined Stark effect (QCSE) on modulation bandwidth and luminous performance of devices. The room-temperature photoluminescence (PL), low-temperature time-resolved PL (TRPL), and electroluminescence (EL) results show that the decrease of QB thickness is beneficial to reduce QCSE of the device. The thinner QB thickness is good for improving the modulation bandwidth because the thinner QB is more beneficial to increase the total carrier recombination rate, but it is not conducive to the improvement of external quantum efficiency (EQE) due to degraded crystal quality. In addition, the modulation bandwidth of the device was calculated by using ABC model in combination with simulation. The calculation is in good agreement with the measured value. What is more, an optical link using an orthogonal-frequency division multiplexing (OFDM) modulation scheme was demonstrated. The transmission data rate increases with the increase of QB thickness from 1.309 to 1.773 Gbps, even though the modulation bandwidth decreases from 245 to 169 MHz. This work provides a way to balance the quantum efficiency and communication performance of green micro-LEDs.

(Digital Presentation) Calculation of the Energy Band Diagram and Estimation of Electronic Transport Parameters of Metastable Amorphous Ge2Sb2Te5

Phase change memory (PCM) is a high speed, high density non-volatile resistive memory technology that utilizes different phases (crystalline and amorphous) of phase change materials such as Ge2Sb2Te5 (GST) to store information [1]. Here, the material undergoes two types of reversible switching phenomena: (i) Ovonic Threshold Switching (OTS), which causes the amorphous phase of the material to switch from a highly resistive state to conductive state with application of high electric fields, resulting in current flow and (ii) Ovonic Memory Switching (OMS), which is due to the change of the phase of the material between amorphous and crystalline phases induced by heating [2]. Even though PCM entered high volume manufacturing, the electronic properties of the phase change materials are still not well understood [3,4]. In this work, we construct the energy band diagram of amorphous GST as a function of temperature using a temperature dependent model of effective activation energy of conduction in metastable amorphous GST [5], which we obtained from high-speed experiments on GST line-cells [6]. Assuming the bandgap energy to linearly decrease with temperature [7,8] and p-type conduction (based on positive Seebeck coefficients measured in a wide temperature range [9]) , we determine a temperature dependent Fermi energy level from 0K to melting temperature, Tmelt ~ 858 K. Liquid GST is expected to become metallic (bandgap collapsing to 0) at ~ 894K, based on the experimental results. We also estimate the carrier concentration at Tmelt utilizing the latent heat of fusion (126 kJ/kg) [10] to be pmelt = 1.47 x 1022 cm-3. Using the melt resistivity measured on GST thin film, we calculate the carrier mobility at melting point as µmelt ~0.187 cm2/V-s, close to the previously reported value of 0.15 cm2/V-s based on crystalline state mobility and a density of states calculation [2]. Assuming a weak temperature dependence of the mobility [5], we obtain the carrier concentration of ~3.37× 1017 cm-3 at room temperature which lies within the ~1017-1018 cm-3 range estimated in a former study [3]. Finally, we calculate conduction activation energy of as-deposited amorphous GST from temperature dependent Seebeck coefficient measured simultaneously with the resistance [9]. The activation energy varies as a parabolic function of temperature where it starts from 0 eV at 0 K, reaches a peak of ~0.257 eV near glass transition temperature (~400 K) with the room temperature value of ~0.24 eV and becomes 0 eV again at ~810 K. We also utilize the Seebeck coefficient measurements along with the band edges and Fermi energy level information from the energy band diagram to calculate the ratio of minority carrier concentration to the total carrier concentration as a function of temperature; this is useful to predict the temperature beyond which bipolar conduction becomes significant.Acknowledgment: Analysis is performed with the support of US National Science Foundation (NSF) award ECCS 1711626. The experimental data used for this analysis were collected with the support of US NSF DMR-1710468 on devices fabricated with the support of US Department of Energy Office of Basic Energy Sciences.

(Digital Presentation) Calculation of the Energy Band Diagram and Estimation of Electronic Transport Parameters of Metastable Amorphous Ge2Sb2Te5

We calculate critical electronic conduction parameters of the amorphous phase of Ge2Sb2Te5 (GST), a common material used in phase change memory. We estimate the room temperature bandgap of metastable amorphous GST to be Eg (300K) = 1.84 eV based on a temperature dependent energy band model. We estimate the free carrier concentration at the melting temperature utilizing the latent heat of fusion to be 1.47 x 1022 cm-3. Using the thin film melt resistivity, we calculate the carrier mobility at melting point as 0.187 cm2/V-s. Assuming that metastable amorphous GST is a supercooled liquid with bipolar conduction, we compute the total carrier concentration as a function of temperature and estimate the room temperature free carrier concentration as p(300K) ≈ n(300K) = 1.69×1017 cm-3. Free electrons and holes are expected to recombine over time and the stable (drifted) amorphous GST is estimated to have p-type conduction with p(300K) ≈ 6×1016 cm-3.

Oxygen vacancy and pyroelectric polarization collaboratively enhancing PEC performance in BaTiO3 photoelectrodes

The efficient separation and transfer of electrons-holes is a key problem in photoelectric catalysis. Herein, oxygen vacancies are introduced into BaTiO3 and combined with pyroelectric polarization to regulate the photoelectric catalytic performance, improving the separation efficiency of carriers. Under 20–50 °C hot-cold cycle, illumination and bias, the maximum current density of BaTiO3−X-5% after oxygen vacancies introduced is 0.77 mA·cm−2, which is higher than the current density of BaTiO3 under light alone (0.17 mA·cm−2), and the current density of BaTiO3 under temperature fluctuation and light (0.35 mA·cm−2). This is because oxygen vacancies are characterized by prolonged light absorption and improved the use utilization of solar energy, it can be used as the capture center of excited electrons to inhibit excited electron-hole pairs recombination. In addition, the generation of photogenerated and pyrogenerated carriers increases the total carrier concentration, and the formation of polarized electric field promotes the separation and transfer of carriers. This offers an idea for development of high performance photoelectrodes in photoelectric catalytic water splitting.

Recovering the carrier number conservation in SPICE simulation of PIN diodes and IGBT devices

In SPICE simulations of PIN diodes and IGBT devices using finite difference method, one discretizes an undepleted N− region into several equally spaced nodes with a time-dependent distance of Δx(t), and then transforms the ambipolar diffusion equation, a time–space partial differential equation, into a set of time-dependent ordinary differential equations. However, the time-dependent property of Δx(t) destroys the carrier number conservation. In this paper, we propose an approach to correct the effect of the Δx(t) by introducing an auxiliary system. It has the same total current and the total carrier number in the undepleted N− region as the real system, but has different electron and hole current components. The difference is caused by adding compensation current terms with the equal amplitude and opposite sign to the electron and hole current terms in the auxiliary system. These compensation current terms are proportional to the boundary speed of the undepleted N− region and do not change the total current. The auxiliary system can be easily solved using SPICE behavior models and its carrier density is a good approximation to the real one. Our simulations show that the compensation current correction is important for fast switching PIN diodes, but may not be very important in IGBT devices due to their large gate-related capacitance.