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We report the observation of three different crystalline layers in hydrothermally grown BiFeO3 (BFO) thick films on SrRuO3/SrTiO3 substrates. High-resolution X-ray diffraction and transmission electron microcopy results suggest that compressively strained, partially relaxed epitaxial layers, and a mixture of polycrystalline and amorphous BFO layers, were successively formed from the bottom to the top of the films. The resistance and capacitance of the mixed layer were significantly lower than those of the epitaxial layers. The atomic concentrations of Bi and Fe in the mixed layer were fluctuating for each point. Based on the observed three crystalline layers, we have discussed the growth mechanism and the leakage current of hydrothermally grown BFO thick films. [ABSTRACT FROM AUTHOR]

The crystallization of amorphous semiconductors is a strongly exothermic process. Once initiated the release of latent heat can be sufficient to drive a self-sustaining crystallization front through the material in a manner that has been described as explosive. Here, we perform a quantitative in situ study of explosive crystallization in amorphous germanium using dynamic transmission electron microscopy. Direct observations of the speed of the explosive crystallization front as it evolves along a laser-imprinted temperature gradient are used to experimentally determine the complete interface response function (i.e., the temperature-dependent front propagation speed) for this process, which reaches a peak of 16m/s. Fitting to the Frenkel-Wilson kinetic law demonstrates that the diffusivity of the material locally/immediately in advance of the explosive crystallization front is inconsistent with those of a liquid phase. This result suggests a modification to the liquid-mediated mechanism commonly used to describe this process that replaces the phase change at the leading amorphous-liquid interface with a change in bonding character (from covalent to metallic) occurring in the hot amorphous material. [ABSTRACT FROM AUTHOR]

We report the structural and magnetotransport properties of ultrathin superparamagnetic Co/ZnO and Co/ZnAlO films deposited by sequentially sputtering Co layers and semiconductor layers. The films consisting of Co nanodots embedded in an amorphous semiconductor matrix exhibit large room temperature tunneling magnetoresistance with a maximum value of over 7%. The singlelayer- nanodot structures gradually develop in the films with thicknesses below 8 nm, where tunneling processes existing only between nanodots that lie in a plane are realized. The tunneling magnetoresistance ratio at room temperature is as high as 5% although the thickness of the Co/ZnAlO film is as thin as 3.2 nm. These single-layer-nanodot films having high tunneling magnetoresistance ratios and superparamagnetic behavior can be used in transparent nano-granular in gap sensors. [ABSTRACT FROM AUTHOR]

Amorphous CoSiB/Pt multilayer is a perpendicular magnetic anisotropy material to achieve high squareness, low coercivity, strong anisotropy, and smooth domain wall (DW) motion, because of the smoother interface compared with crystalline multilayers. For [CoSiB(6Å)/Pt (14Å)]N multilayers with N=3, 6, and 9, we studied the field-induced DW dynamics. The effective anisotropy constant K1eff is 1.5 x 106 erg/cm3 for all the N values, and the linear increment of coercive field Hc with N gives constant exchange coupling J. By analyzing the field dependence of DW images at room temperature, a clear creep motion with the exponent μ=1/4 could be observed. Even though the pinning field Hdep slightly increases with N, the pinning potential energy Uc is constant (=35 kBT) for all the N values. These results imply that the amorphous [CoSiB/Pt]N multilayers are inherently homogeneous compared to crystalline multilayers. For N≦6, the pinning site density ρpin is less than 1000/μm2, which is about 1 pinning site per the typical device junction size of 30 x 30 nm2. Also, the exchange stiffness constant Aex is obtained to be 0.48 x 10-6 erg/cm, and the domain wall width is expected to be smaller than 5.5 nm. These results may be applicable for spin-transfer-torque magnetic random access memory and DW logic device applications. [ABSTRACT FROM AUTHOR]

Computer simulations of structure formation in network forming materials (such as amorphous semiconductors, glasses, or fluids containing hydrogen bonds) are challenging. The problem is that large structural changes in the network topology are rare events, making it very difficult to equilibrate these systems. To overcome this problem, Wooten, Winer, and Weaire [Phys. Rev. Lett. 54, 1392 (1985)] proposed a Monte Carlo bond-switch move, constructed to alter the network topology at every step. The resulting algorithm is well suited to study networks at zero temperature. However, since thermal fluctuations are ignored, it cannot be used to probe the phase behavior at finite temperature. In this paper, a modification of the original bond-switch move is proposed, in which detailed balance and ergodicity are both obeyed, thereby facilitating a correct sampling of the Boltzmann distribution for these systems at any finite temperature. The merits of the modified algorithm are demonstrated in a detailed investigation of the melting transition in a two-dimensional 3-fold coordinated network. [ABSTRACT FROM AUTHOR]

A charge‐trap flash (CTF) device is fabricated using atomic‐layer‐deposited zinc tin oxide (ZTO) as an n‐type amorphous oxide semiconductor (AOS) channel layer and its program/erase characteristics are examined. When a positive voltage of 20 V is applied to the gate electrode, electrons are fluently injected into the adopted SiNx charge trap layer, resulting in a program operation showing a threshold voltage (Vth) shift of 3.7 V. However, even when −20 V is applied for up to 10 s, the trapped electrons are not detrapped. Instead, it is possible to recover Vth to its initial value only by the irradiation of white light. To understand this phenomenon, a ZTO CTF device is modeled using the technology computer‐aided design (TCAD) simulation package. The high hole injection barrier between the source/drain and the ZTO channel prohibits hole injection, which is the cause of the inefficient erasing. It is also confirmed that an AOS CTF with sufficient program and erase speed would be limited by the inherent energy band structure of AOS with its wide bandgap of over 3 eV. An alternative method of using the fringing field effect according to channel length scaling is proposed. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate scaled back-end-of-line (BEOL) compatible indium oxide (In2O3) transistors by atomic layer deposition (ALD) with channel thickness (Tch) of 1.0-1.5 nm, channel length (Lch) down to 40 nm, and equivalent oxide thickness (EOT) of 2.1 nm, with record high drain current of 2.0 A/mm at VDS of 0.7 V among all oxide semiconductors. Enhancement-mode In2O3 transistors with ID over 1.0 A/mm at VDS of 1 V are also achieved by controlling the channel thickness down to 1.0 nm at atomic layer scale. Such high current density in a relatively low mobility amorphous oxide semiconductor is understood by the formation of high density 2D channel beyond $4\times 10^{13}$ /cm2 at HfO2/In2O3 oxide/oxide interface. [ABSTRACT FROM AUTHOR]

Self-powered ultraviolet (UV) photodetectors (PDs) that use a vertical p-n junction generally involve a complex fabrication process if they are to be integrated with optoelectronic integrated circuits (OEICs). This study demonstrates the fabrication of a self-powered metal-semiconductor-metal (MSM) UV PD with simple planar structure using nontoxic and earth abundant ZnSnO (ZTO). The self-powering characteristic is realized using a localized UV-assisted thermal annealing (LUV-TA) process that selectively modifies the surface states underneath different contacts and creates asymmetric Schottky barrier heights (SBHs) for the MSM PD. The a-ZTO MSM PD with assymmetric SBHs operates at a zero bias and has a responsivity of 18.2 mA/W at 350 nm. The open-circuit voltage is 0.40 V under UV illumination at a wavelength of 365 nm (50 mW/cm2). The device exhibits a fast response speed, with a rise time of 38 ms and a decay time of 180 ms. This study demonstrates that this strategy can be extended to other MSM PDs, particularly those that use an amorphous oxide semiconductor as the active layer. [ABSTRACT FROM AUTHOR]

The main dynamical aspects of excitons as charged composite quasi-particles in an amorphous solid are examined by means of a powerful theoretical treatment. In fact, on the basis of that an exciton is a bound quantum state of an electron-hole pair after the hydrogen-atom model, the absolute value of an averaged (with respect to weighted discrete energy levels) exciton energy is defined and calculated for amorphous solids with parabolic energy bands. In particular, amorphous semiconductors of parabolic energy bands are considered. Prior to these considerations, an associated new reformulation of the non-relativistic, static, Schrödinger equation is given. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) is one of the best transparent conducting oxide (TCO) materials with a wide bandgap and good electrical and optical properties. Its low cost, nontoxicity and transparency in the optical region of the electromagnetic spectrum make it very promising candidate for solar cell applications. In this work, zinc acetate precursor was used to grow a ZnO thin film by using sol-gel spin-coating technique. The surface morphological study using scanning electron microscope (SEM) was carried out to confirm the growth pattern and crystal distribution. The optical properties, transmission (T), reflection (R), optical bandgap (Eg), refractive index (n), and extinction coefficient (k) were extracted and investigated to be used in the simulation of ZnO/Cu2O heterostructure solar cell, where ZnO thin film plays a double role: as the TCO window, as well as the emitter of the n-p junction. However, the solar cell showed weak external quantum efficiency (EQE) compared to those prepared by using zinc nitrate and diethyl zinc precursors. TCAD numerical simulation was used to clarify the origin of this weak EQE by taking into account two parameters. The first studied parameter is the root-mean-square interface roughness, RMS, in Haze modeling approach, H, which describes how much of incident light is scattered at the interface. The second studied parameter is the density of defects in the ZnO bulk with continuous distribution of states in its bandgap similar to an amorphous semiconductor made of tail bands and Gaussian distribution deep level bands. Consequently, and by adjusting and investigating the effect of the σRMS and the constituents of the bandgap states, we were able to obtain a good agreement between simulated and measured EQE characteristics of the solar cell. [ABSTRACT FROM AUTHOR]

The goal of the present work is to optimize the composition of amorphous molecular semiconductor (AMS) films based on poly(N-vinylcarbazole), to upgrade the process of registration of light fields, and to reveal the role of volume charges in the formation of ordered nanostructures, using reversible templates. It is found that, when gold condenses on the AMS surface, the surface relief increases, and the distribution and symmetry of localized gold clusters are determined by the electric field pattern on the AMS surface. The role of the absorption parameter and the composite substrate is determined, basing on the study of the absorption parameters of the composite with photo-induced charge. The optimal conditions of the composite application for the study of the spectral characteristics of the investigated structures are determined. [ABSTRACT FROM AUTHOR]

Solution processing of amorphous oxide semiconductors (AOS) is used for electronic and optoelectronic applications. However, the device performance is much lower than that for a device that is fabricated using vacuum processing. This study uses acetylacetone (acac) as an additive in the precursor solution to reduce the nanocluster size in a ZnSnO (ZTO) film. A metal-semiconductor-metal (MSM)-type UV photodetector (PD) is fabricated using as-prepared ZTO film. ZTO film that features a smaller nanocluster size, so more oxygen vacancies are induced, which produces more electrons and the photocurrent is increased. The surface at the metal/semiconductor interface is smoother so there is greater contact with fewer interface states and the dark current is decreased. An extremely high photo-to-dark current ratio (PDCR) of 1314 is achieved for a solution-processed ZTO MSM-type PD. [ABSTRACT FROM AUTHOR]

We investigated the electrical properties and operational stability of amorphous indium-tin-zinc-oxide (a-ITZO) thin-film transistors (TFTs). We fabricated the a-ITZO TFTs using deposition by radio frequency sputtering at room temperature followed by a rapid thermal annealing (RTA) process at different temperatures and oxygen pressure (PO2). This is a more practical annealing route compared to a conventional furnace. Based on film densification and oxygen vacancy optimization, the a-ITZO TFTs exhibited 9.8 cm2 Vs−1, 0.82 V/decade and 1.39 V, for saturation mobility, sub-threshold swing and threshold voltage, respectively. Operation stability tests and hysteresis behavior of a-ITZO TFTs suggest that oxygen vacancy concentration of a-ITZO thin films gradually decreases under higher PO2, consequently affecting the threshold voltage and the shift seen after a gate bias stress test. This observation suggests that gate bias stress and hysteresis stability of an a-ITZO device is due to the effect of oxygen-controlled pressure in the RTA process. This a-ITZO TFTs electrical characterization qualitatively coincides with x-ray photoelectron spectroscopic analyses of oxygen vacancy concentration in a-ITZO thin films. Thus, our systematic a-ITZO thin film optimization using the oxygen-ambient RTA process is a practical basis for high-performance amorphous oxide semiconductor TFT post-annealing methods. [ABSTRACT FROM AUTHOR]

An extraction technique for flat band voltage (${V}_{\textit {FB}}$) in an amorphous InGaZnO (a-IGZO) thin-film transistor (TFT) using the frequency-independent ${C}-{V}$ relationship which is taken from the measured multi-frequency ${C}-{V}$ characteristics, is proposed. The proposed method comprises the consideration of multiple physical parameters for accurate ${V}_{\textit {FB}}$ extraction, including the sub-gap density of states, doping concentration, gate oxide capacitance, and series resistance. The method was verified by comparing both the measured current–voltage characteristics and the extracted ${V}_{\textit {FB}}$ value with the technology computer-aided design simulation results. Moreover, we confirmed the versatility of the method by extracting ${V}_{\textit {FB}}$ from devices with different oxygen contents. The proposed physical-based technique showed better accuracy and compatibility with amorphous oxide semiconductor (AOS) TFTs compared with classical empirically based methods. We believe that our technique is useful for the experimental design and optimization of the gate metal-dielectric-AOS stack for high-performance AOS TFTs. [ABSTRACT FROM AUTHOR]

Amorphous oxide semiconductors have gained significant attention in the past few decades and have emerged as a promising material for thin-film transistors (TFTs) because they offer high carrier mobility (> 10–50 cm2/V s) and uniformity. In particular, amorphous indium-gallium-zinc-oxide (a-IGZO) has been widely employed as an active channel material in TFTs owing to its high mobility. However, indium-based TFTs suffer from stability problems under positive, negative, and illumination bias stress conditions, which limits their applications in flat-panel displays. Moreover, the limited supply of indium and growing demand for high-stability TFTs with better electrical performance has led to the introduction of tin oxide as a promising solution to replace indium in TFTs. This review provides an overview on the progress and recent developments in indium-free tin oxide-based TFTs for large-area electronics, with special emphasis on the sputtering technique. In addition, the source of the dual conductivity of tin oxide is addressed, which will be helpful in designing complementary metal oxide semiconductor devices. The instability problems and approaches to improve the electrical performance of tin oxide TFTs are also discussed. [ABSTRACT FROM AUTHOR]

Ultraviolet-ozone (UV/O3) treatment was adopted to the fabrication of solution-processed amorphous In-Ga-Zn-O thin-film transistors (TFTs), with metal composition of In:Ga:Zn = 1:1:1 represented by InGaZnO4. By applying UV/O3 treatment In-Ga-Zn-O gel films, their condensation was notably enhanced through decomposition of organic- and hydrogen-based elements, which drastically improved the quality of the amorphous InGaZnO4 films. As a result, high TFT performance, with values of on/off ratio, 108; subthreshold swing, 150 mV/decade; threshold voltage, 9.2 V; and field-effect mobility, 5.1 cm2 V-1 s-1, was achieved. [ABSTRACT FROM AUTHOR]

Based on density-functional theory calculations, the effects of cation compositions on electronic structures of In-Sn-Zn-O amorphous semiconductors were investigated. We considered various composition ratios of In, Sn, and Zn in O stoichiometric condition, and found that the conduction band minimum (CBM) energy level decreases and the valence band tail (VBT) energy level extent increases as the sum of In and Sn ratios (RIn+RSn) increases. The CBM lowering is attributed to the increased overlap of the In-5s and Sn-5s orbitals as the RIn+RSn increases, and correspondingly the electron effective masses (me*) are found to be reduced. The VBT increase is found to be due to the increased density of the In and Sn atoms, near which the O-2p inter-site ppσ* coupling is larger than that near the Zn atoms. The acute O-(In,Sn)-O angles are suggested to be structurally important, giving the stronger O-O ppσ* coupling. [ABSTRACT FROM AUTHOR]

Analysis of impedance spectra by a random-walk approach is proposed for the study of ionic-transport materials with a silver-containing chalcogenide glass as a case example. Through a full analysis of complex impedance spectra including the electrode polarization effect, some important physical parameters, such as the number of mobile ions in bulk and interface regions, the diffusion coefficient, etc., are extracted without using the conventional equivalent electric circuit analysis. A detailed discussion on electrode polarization, which is highly dependent on signal amplitude, is also presented. [ABSTRACT FROM AUTHOR]

The dynamic reflection spectra of amorphous blue phase III were investigated. When an electric field is applied to a blue phase III cell, the reflected wavelength does not shift obviously, but the intensity of reflection increases or decreases in a few ms. This fast intensity-tunable phenomenon in blue phase III relates to the dielectric anisotropies and chiralities of the liquid crystal and can be explained by the double twist model consisting of randomly orientated double-twisted cylinders. This study shows that blue phase III can act as a fast intensity-tunable reflector for a specific wavelength. [ABSTRACT FROM AUTHOR]

This study presents a novel high gain operational amplifier (op‐amp) and a comparator using n‐type all enhancement amorphous indium‐gallium‐zinc‐oxide (a‐IGZO) thin‐film transistors (TFTs). The proposed op‐amp employs regulated cascode topology in conjunction with capacitive bootstrap load, which enhances the gain to 159.87% (V/V) as compared to op‐amp with bootstrapping load. In addition, common mode feedback is introduced in the circuit which improves the common‐mode rejection ratio (CMRR) of the amplifier without hampering the output voltage swing. The proposed op‐amp offers a voltage gain of 46.2 dB, phase margin of 67°, CMRR of 51.8 dB, unity gain frequency of 215 kHz and power consumption of 0.22 mW. Furthermore, a novel comparator circuit at a clock frequency of 50 kHz is reported. The power consumption of the circuit is 0.248 mW and it can discriminate a minimum voltage of 50 mV. The performance of the proposed circuits is demonstrated using an analytical model of a‐IGZO in Cadence environment with a channel length of 20 µm at a supply voltage of 10 V. Further with the help of the circuits reported in this work, many sensing systems of practical importance can be developed, such as smart packaging and bio‐medical wearable devices using flexible electronics. [ABSTRACT FROM AUTHOR]

Pulsed excitation methods followed by time-resolved measurements have been questioned as a valid procedure to deduce transport properties of halide perovskites (HaPs). Measurements of both the majority and minority carrier's phototransport properties, under illumination conditions as close as possible to one sun, are needed to obtain reliable information on recombination mechanisms. In this work, we show that the moving photocarrier grating technique (MGT) fulfills the above-mentioned conditions. In this method, both carriers mobilities and the common recombination lifetime are deduced from the DC short circuit current induced by the movement of an interference pattern along the sample surface. We show that the method, originally developed to measure the transport parameters of amorphous semiconductors, can be fully applied to HaPs films. We briefly describe the technique, we perform measurements as a function of the grating period and the light intensity, and we discuss the best approach to extract the transport parameters from MGT measurements. Finally, we find the exponents that describe the intensity dependence of the transport parameters of majority and minority carriers in a HaP sample. [ABSTRACT FROM AUTHOR]

We report a novel technique for separating the parasitic source (${R} _{\text {S}}$) and drain (${R} _{\text {D}}$) resistances in MISFETs using the open drain and the open source configurations based on an alternating-current(AC) signal. We conducted impedance analysis for the AC signal in the open drain for ${R} _{\text {S}}$ and the open source configuration for ${R} _{\text {D}}$. The proposed technique is independent of the I-V equation of MISFETs with various influencing parameters for separate extraction of ${R} _{\text {S}}$ and ${R} _{\text {D}}$ through the physics-based equivalent circuit of MISFETs. So the proposed technique is applicable to every single device as long as the device is an insulated gate MISFET structure, regardless of the presence or absence of the body terminal. This technique is applied to amorphous oxide semiconductor thin-film transistors with the gate length $= 10~\mu \text{m}$ without the body contact. As a result, parasitic resistances were separately extracted to be ${R} _{\text {S}} =2.1\,\,\text{k}\Omega $ , ${R} _{\text {D}} =1.7\,\,\text{k}\Omega $ for ${W} = 600~\mu \text{m}$ , ${R} _{\text {S}} = {R} _{\text {D}} =1.1\,\,\text{k}\Omega $ for ${W} = 1000~\mu \text{m}$ , and ${R} _{\text {S}} = {R} _{\text {D}} =0.6\,\,\text{k}\Omega $ for ${W} = 2000~\mu \text{m}$ independent of gate bias. [ABSTRACT FROM AUTHOR]

Thin‐film transistors (TFTs) based on transparent amorphous oxide semiconductors (TAOSs) have become essential building blocks for a broad range of electronics, since TAOSs facilitate large‐scale fabrication at moderate temperatures and hence feature compatibility with flexible substrates. An emerging indium‐free alternative to the widely commercially exploited indium gallium zinc oxide (IGZO) is amorphous zinc tin oxide (ZTO); however, according to previous reports, achieving acceptable performance of ZTO‐based devices fabricated at temperatures below 300 °C is still challenging to date. Here, key properties of the first all‐oxide and fully transparent metal‐semiconductor field‐effect transistors (MESFETs), metal‐insulator‐semiconductor field‐effect transistors (MISFETs) and junction field‐effect transistors (JFETs) based on amorphous ZTO are compared, employing PtOx, HfOy, and p‐type NiO as gate, respectively. All individual layers have been deposited exclusively at room temperature and do not require any additional postdeposition annealing to obtain sufficient device functionality. Demonstrated TFTs exhibit reasonable current on/off ratios of over six orders of magnitude with subthreshold swings as low as 61 mV dec–1 at room temperature. Transistor characteristics have been recorded for several weeks to study performance consistency over time and are further investigated regarding their stability under bias stress. [ABSTRACT FROM AUTHOR]

Amorphous indium‐gallium‐zinc‐oxide (a‐IGZO) based memristive devices with molybdenum contacts as both top and bottom electrodes are presented aiming to be used in neuromorphic applications. Devices down to 4 µm2 are fabricated using conventional photolithography processes, with an extraordinary yield of 100%. X‐ray photoelectron spectroscopy and transmission electron microscopy performed on the developed structures confirm the presence of a thin intermixed oxide layer (4–5 nm) containing Mo6+ oxidation state at the interface with the bottom contact. This results in Schottky diode‐like characteristics at the pristine state with a rectification ratio of 3 orders of magnitude. The devices have electroforming‐free and area‐dependent analog resistive switching properties. Temperature analysis of resistive switching I–V data reveals barrier height variations of the junction. Several synaptic functions, such as synaptic potentiation and depression as response to programmed pulses, short‐ to long‐term plasticity transition (STP to LTP) and "learning experience" properties are presented. The Mo/IGZO/Mo memristive device shows potential application of an electronic synapse for brain‐inspired computing application. Integration in System‐on‐Panel architectures is possible at negligible cost, because all materials are used in commercial IGZO thin‐film transistor fabrication. [ABSTRACT FROM AUTHOR]

The accumulation of dust on any given photovoltaic (PV) module surface depends on the type of dust, environment, surroundings, weather, module properties, and its installation design. In this research, equations were developed for the preliminary evaluation and comparison of the reduction in power from PV modules because of dust soiling. Use of these equations shows that dust accumulation decreases solar irradiance and thus the power output of modules, and that there is a linear relationship between the power output degradation and density or amount of accumulated dust. The equations can be used to conduct analysis of average photon energy and the PV module power output reduction from accumulated dust. The study also showed that type of PV module can also affect the degree of power output reduction. The amorphous silicon PV modules are more affected compared to poly crystalline silicon PV modules as the latter has a spectrum response which still has the range that can produce full energy and therefore, dust soiling has lesser impact on them. PV power plants should regularly clean the modules, if not, production of electricity decreases, and so too the revenue from selling electricity, making the payback of the power plant longer. [ABSTRACT FROM AUTHOR]

Recently, Jun et al. (Adv. Mater.2018, 30, 1706573) reported Sn‐doped amorphous phases of CuI (a‐CuI) as a new class of transparent p‐type semiconductors. It is surprising that high mobilities are found despite amorphous structures tend to localize carriers, particularly the directional p orbitals of anions. To reveal the microscopic origin of the new p‐type amorphous semiconductors, density functional theory calculations are performed, and structural and electrical properties of a‐CuI are investigated. Amorphous models from melt‐quench simulations consist of structural motifs that resemble local orders in crystalline polymorphs of CuI. Despite the absence of translational symmetry, states at valence band maximum (VBM) are substantially extended in linear ways due to the hybridization between I‐5p states, explaining the high hole mobilities in the experiment. Sn‐doped a‐CuI is also investigated and it is found that Sn atoms stabilize the amorphous structure without disturbing the hole transport. Furthermore, results on nonstoichiometric models show that Cu‐deficiency increases the hole concentration in a‐CuI and also enhances the delocalization of VBM states, which is consistent with the experimental observation that the hole mobility increases with doping concentrations. Herein, the origin of hole conduction in amorphous CuI is enlightened, which is believed to contribute in the development of high‐performance p‐type amorphous materials. [ABSTRACT FROM AUTHOR]

We examine an amorphous oxide semiconductor (AOS) of ZnRhCuO. The a-ZnRhCuO films are deposited at room temperature, having a high amorphous quality with smooth surface, uniform thickness and evenly distributed elements, as well as a high visible transmittance above 87% with a wide bandgap of 3.12 eV. Using a-ZnRhCuO films as active layers, thin-film transistors (TFTs) and gas sensors are fabricated. The TFT behaviors demonstrate the p-type nature of a-ZnRhCuO channel, with an on-to-off current ratio of ∼ 1 × 103 and field-effect mobility of 0.079 cm2V–1s–1. The behaviors of gas sensors also prove that the a-ZnRhCuO films are of p-type conductivity. Our achievements relating to p-type a-ZnRhCuO films at room temperature with TFT devices may pave the way to practical applications of AOSs in transparent flexible electronics. [ABSTRACT FROM AUTHOR]

Recent advances in the field of integrated circuits based on sustainable and transparent amorphous oxide semiconductors (AOSs) are presented, demonstrating ultrahigh performance operating state-of-the-art integrated inverters comprising metal–semiconductor field-effect transistors (MESFETs) with amorphous zinc tin oxide (ZTO) as a channel material. All individual circuit layers have been deposited entirely at room temperature, and the completed devices did not require undergoing additional thermal annealing treatment in order to facilitate proper device functionality. The demonstrated ZTO-based MESFETs exhibit current on/off ratios of over 8 orders of magnitude a field-effect mobility of 8.4 cm2 V−1 s−1, and they can be switched within a voltage range of less than 1.5 V attributed to their small subthreshold swing as low as 86 mV decade−1. Due to adjustments of the circuit layout and, thus, the improvement of certain geometry-related transistor properties, the associated Schottky diode FET logic inverters facilitate low-voltage switching by exhibiting a remarkable maximum voltage gain of up to 1190 with transition voltages of only 80 mV while operating at low supply voltages ≤3 V and maintaining a stable device performance under level shift. To the best of our knowledge, the presented integrated inverters clearly exceed the performance of any similar previously reported devices based on AOS, and thus, prove the enormous potential of amorphous ZTO for sustainable, scalable low-power electronics within future flexible and transparent applications. [ABSTRACT FROM AUTHOR]

This study presents a novel voltage‐programmed, amorphous‐indium–gallium–zinc oxide (a‐IGZO) thin‐film transistor (TFT)‐based active‐matrix organic light‐emitting diode (AMOLED) pixel circuit. The circuit utilises the threshold voltage (VTH) sensing ability of a diode‐connected transistor to compensate for the spatial as well as the temporal variation of the threshold voltage of the driving transistor and supply a constant current to the OLED. The circuit has been simulated in Cadence Spectre using a‐IGZO TFT and OLED simulation program with integrated circuit emphasis (SPICE) models, and the analysis is presented to prove the VTH compensating capability of the proposed circuit. For small currents, about 50nA, the error is suppressed to <9% whereas for large currents, about 2.5 µA, the error is only 1.05%. This performance has been achieved using only five TFTs and two storage capacitors. [ABSTRACT FROM AUTHOR]

We investigated high‐performance amorphous metal‐oxide semiconductor based optoelectronics using low‐temperature and solution process technologies. In particular, metal‐oxide and quantum dots hybrid phototransistors exhibited ultra‐high photodetectivity up to 4×1017Jones in a broad range of detection wavelength from ultraviolet to infrared ranges. In addition, we employed artificial visual perception circuit based on metal‐oxide synaptic transistors with metal chalcogenide semiconductors for optoelectronic neuromorphic devices. We also demonstrated large‐scaled ultra‐flexible and stretchable device showing promising next‐generation wearable optoelectronics. [ABSTRACT FROM AUTHOR]

A Complementary Low‐temperature Poly‐Crystalline Silicon and Oxide (LTPO) technology based on p‐type Low‐temperature Poly‐Crystalline Silicon (LTPS) and n‐type oxide Thin‐Film Transistors (TFTs) was developed and demonstrated. New pixel circuits and Gate‐on‐Array (GOA) circuits were designed and fabricated using this technology. By combining the superior driving capability of LTPS and ultra‐low leakage of oxide semiconductor, all the pixel circuits and GOA circuits can operate between 1 Hz and 120 Hz, which enables both high refresh rate and low standby power display applications. [ABSTRACT FROM AUTHOR]

Photochemistry has emerged in the last few years as a powerful tool for the low‐temperature processing of metal oxide thin films prepared by solution methods. Today, its implementation into the fabrication procedure makes possible the integration of amorphous semiconductors or functional crystalline oxides into flexible electronic systems at temperatures below 350 °C. In this review, the effects of UV irradiation at the different stages of the chemical solution deposition of metal oxide thin films are presented. These stages include from the synthesis of the precursor solution to the formation of the amorphous metal‐oxygen network in the film and its subsequent crystallization into the oxide phase. Photochemical reactions that can be induced in both the solution deposited layer and the irradiation atmosphere are first described, highlighting the role of the potential reactive chemical species formed in the system under irradiation, such as free radicals or oxidizing compounds. Then, the photochemical effects of continuous UV light on the film are shown, focusing on the decomposition of the metal precursors, the condensation and densification of the metal‐oxygen network, and the nucleation and growth of the crystalline oxide. All these processes are demonstrated to advance the formation and crystallization of the metal oxide thin film to an earlier stage, which is ultimately translated into a lower temperature range of fabrication. The reduced energy consumption of the process upon decreasing the processing temperature, and the prospect of using light instead of heat in the synthesis of inorganic materials, make photochemistry as a promising technique for a sustainable future ever more needed in our life. [ABSTRACT FROM AUTHOR]

The authors present the implementation of two amplifiers in a commercial flexible amorphous Indium Gallium Zinc Oxide (a-IGZO) thin-film transistor (TFT) technology: a Cherry Hooper (CH) amplifier and a 4-stage common source amplifier. The CH amplifier is designed as a pre-amplifier for wireless receivers. It is optimised for a high gain-bandwidth product (GBW). From a supply voltage of $V_{{\rm DD}}=8$VDD=8 V it provides 19.4 dB gain and has a $-3\,{\rm dB}$−3dB -bandwidth of 5.3 MHz, while consuming 0.2 mW. It has a GBW of 49.35 MHz, which is more than a factor two better than previously reported a-IGZO TFT amplifiers. The 4-stage common source amplifier is designed as output buffer, has a very wide range of operating conditions and strong robustness against manufacturing tolerances. From a supply voltage of $V_{{\rm DD}}=8$VDD=8 V it provides 28.9 dB gain, has a $-3\,{\rm dB}$−3dB -bandwidth of 1.2 MHz, and a GBW product of 33.43 MHz, while consuming 14.2 mW. Both circuits can operate from a supply voltage between 2.5 and 10 V. [ABSTRACT FROM AUTHOR]

New deposition techniques for amorphous oxide semiconductors compatible with silicon back end of line manufacturing are needed for 3D monolithic integration of thin‐film electronics. Here, three atomic layer deposition (ALD) processes are compared for the fabrication of amorphous zinc tin oxide (ZTO) channels in bottom‐gate, top‐contact n‐channel transistors. As‐deposited ZTO films, made by ALD at 150–200 °C, exhibit semiconducting, enhancement‐mode behavior with electron mobility as high as 13 cm2 V−1 s−1, due to a low density of oxygen‐related defects. ZTO deposited at 200 °C using a hybrid thermal‐plasma ALD process with an optimal tin composition of 21%, post‐annealed at 400 °C, shows excellent performance with a record high mobility of 22.1 cm2 V–1 s–1 and a subthreshold slope of 0.29 V dec–1. Increasing the deposition temperature and performing post‐deposition anneals at 300–500 °C lead to an increased density of the X‐ray amorphous ZTO film, improving its electrical properties. By optimizing the ZTO active layer thickness and using a high‐k gate insulator (ALD Al2O3), the transistor switching voltage is lowered, enabling electrical compatibility with silicon integrated circuits. This work opens the possibility of monolithic integration of ALD ZTO‐based thin‐film electronics with silicon integrated circuits or onto large‐area flexible substrates. [ABSTRACT FROM AUTHOR]

Fractional partial differential equations with time-space fractional derivatives describe some important physical phenomena. For example, the subdiffusion equation (time order 0 < α < 1) is more suitable to describe the phenomena of charge carrier transport in amorphous semiconductors, nuclear magnetic resonance (NMR) diffusometry in percolative, Rouse, or reptation dynamics in polymeric systems, the diffusion of a scalar tracer in an array of convection rolls, or the dynamics of a bead in a polymeric network, and so on. However, the superdiffusion case (1 < α < 2) is more accurate to depict the special domains of rotating flows, collective slip diffusion on solid surfaces, layered velocity fields, Richardson turbulent diffusion, bulk-surface exchange controlled dynamics in porous glasses, the transport in micelle systems and heterogeneous rocks, quantum optics, single molecule spectroscopy, the transport in turbulent plasma, bacterial motion, and even for the flight of an albatross (for more physical applications of fractional sub-super diffusion equations, one can see Metzler and Klafter in 2000). In this work, we establish two fully discrete numerical schemes for solving a class of nonlinear time-space fractional subdiffusion/superdiffusion equations by using backward Euler difference 1 < α < 2 or second-order central difference 1 < α < 2 /local discontinuous Galerkin finite element mixed method. By introducing the mathematical induction method, we show the concrete analysis for the stability and the convergence rate under the L 2 norm of the two LDG schemes. In the end, we adopt several numerical experiments to validate the proposed model and demonstrate the features of the two numerical schemes, such as the optimal convergence rate in space direction is close to O h k + 1 . The convergence rate in time direction can arrive at O τ 2 − α when the fractional derivative is 0 < α < 1. If the fractional derivative parameter is 1 < α < 2 and we choose the relationship as h = C ′ τ (h denotes the space step size, C ′ is a constant, and τ is the time step size), then the time convergence rate can reach to O τ 3 − α . The experiment results illustrate that the proposed method is effective in solving nonlinear time-space fractional subdiffusion/superdiffusion equations. [ABSTRACT FROM AUTHOR]

For the amorphous SiZnSnO (a‐SZTO) thin‐film transistor (TFT), Si can suppress oxygen vacancies, mainly due to higher bonding strength with O compared with Zn or Sn in amorphous oxide ZnSnO semiconductors. When these devices are driven at a low power, a nonideal transfer characteristic of hump phenomenon is observed. As Si concentration increases, this phenomenon is also found even at high voltage. The Si doping changes not only the electrical performance but also the bandgap state. As the Si concentration increases, the conduction band (Ec) raises up to vacuum level. In general, when metal and semiconductor are contacted, a band bending phenomenon occurs at a contact interface due to different work function. This change in Ec caused by the bandgap change due to Si doping also affects the band bending that can form different barriers at the interface between the metal and the channel. When low drain‐to‐source voltage (Vds) is induced, band bending can act as a barrier and cause a hump. So, the hump phenomenon is carefully observed if low Vds is applied to TFT. To make a low‐power device, the work function difference between metal and semiconductor must be considered. [ABSTRACT FROM AUTHOR]

Nanosecond near resonant excitation in As50S50 thin films leads to strong nonlinear optical response, i.e. nonlinear absorption coefficient up to 4 × 106 cm GW−1 and nonlinear refractive index of 8.5 cm2 GW−1, both of which are the strongest ever reported in amorphous semiconductors. We propose a three-level energy band model to explain this effect, which indicates that the nonlinear process is reverse saturable absorption in nature, mediated by excited-state absorption from slow interband transition between the conduction and valence band. On the other hand, observation of negative nonlinear refractive index reveals the occurrence of self-defocusing effect. Finally, benefitting from the strong nonlinear response, we demonstrate a promising application of As50S50 thin films as an optical limiter for optoelectronic sensors. [ABSTRACT FROM AUTHOR]

In this article, we have developed an amorphous CuNiSnO (a-CNTO), which is a p-type amorphous oxide semiconductor (AOS). The a-CNTO thin films were deposited by the pulsed laser deposition method, having high amorphous quality with a rather smooth surface. The a-CNTO films grown at 100 °C exhibited the smoothest surface (root-mean-square roughness of 0.25 nm), highest visible transparency (~85%), and most favorable p-type conductivity (hole concentration of ~1015 cm−3), which are very suitable for electronic device fabrication. Thus, the obtained p-type a-CNTO thin-film transistors (TFTs) have an ON-to- OFF current ratio of ~ 1.2 × 105, the threshold voltage of −2.3 V, the field-effect mobility of 1.37 cm2/Vs, and subthreshold swing of 0.70 V/decade. As a new kind of p-type AOS, the achievement of the p-type a-CNTO TFTs and the low-temperature processes may open the door for practical applications in transparent and flexible electronics. [ABSTRACT FROM AUTHOR]

Deposition of semiconductors on bendable substrates is a crucial step toward flexible circuitry and deposition by a roll-to-roll process. Since most bendable substrates have limited temperature stability (normally degradation starts between 150 °C and 300 °C), processing temperatures are typically below that of rigid substrates. Amorphous oxide semiconductors (AOSs) such as indium gallium zinc oxide (IGZO) can be fabricated at room temperature (RT) and exhibit electron mobilities >10 cm2 V−1 s−1 being a pre-requisite for application in backplanes of displays. While IGZO is already commercially exploited, the search for alternative materials is highly relevant because indium and gallium are rare and expensive. Zinc tin oxide (ZTO) is a promising AOS since zinc and tin are highly abundant and cheap. In this letter, we discuss RT-fabricated n-type ZTO thin films used as the channel material in flexible inverter circuits based on junction field-effect transistors. RT-fabricated nickel oxide is used as a semitransparent p-type gate material. The devices are fabricated on flexible polyimide and exhibit an excellent peak gain magnitude of 464 and uncertainty level as low as 130 mV at a supply voltage of only 3 V. They are characterized before and after bending at various radii. Even after bending at 2 mm radius, the inverters behave still very well. [ABSTRACT FROM AUTHOR]

This study is on the degradation phenomenon of oxide semiconductor thin-film transistor under dynamic stress applied to the drain. The current reduction that occurs during the rise and fall of the pulse was clearly observed through electrical measurements and the cause of the current drop was investigated via a two-dimensional device simulation. The results confirmed that while the instantaneous rise of the pulse provides high energy to the electrons ejected to the drain, the rapid drop of the pulse only produces impact ionization rates in very small areas with an electronic backflow to the drain. Furthermore, a model based on these relationships is proposed for asymmetric local degradation by high energy (hot) electrons. [ABSTRACT FROM AUTHOR]

Efficient charge‐carrier injection is a critical requirement for high‐performance organic electronic devices, such as light‐emitting diodes, solar cells, and field‐effect transistors. In this work, a significantly improved charge‐carrier injection from high work‐function metal‐oxide electrodes in organic field effect transistors (OFETs) is demonstrated for amorphous organic semiconductors (OSCs) by using organic interlayers with a high ionization energy (IE). Molybdenum oxide (MoO3) exhibits limited injection into amorphous 2,2′,7,7′‐tetrakis(N,N‐diphenylamino)‐9,9‐spirobifluorene (Spiro‐TAD) and tris(4‐carbazoyl‐9‐ylphenyl)amine (TCTA) active layers, resulting in high contact resistance and threshold voltage. By inserting an interlayer of a few nanometers thick with high IE between the MoO3 electrode and the amorphous OSC films, the Spiro‐TAD and TCTA OFETs show a substantial enhancement in hole current, subthreshold swing, and effective charge carrier mobility due to the decreased contact resistance. However, for discontinuous interlayers formed on distinct grain domains as in the case of polycrystalline 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophene (C8‐BTBT) films, the effect of the interlayer reduces. These results demonstrate that the utilization of smooth interlayers with IE higher than the semiconductor is a general approach to elevate the hole injection into amorphous OSCs with high IE in OFETs. [ABSTRACT FROM AUTHOR]

'Phase-change' memory materials, such as the canonical composition Ge2Sb2Te5, are being actively researched for non-volatile resistive random-access memory applications. In these devices, ultra-rapid reversible transformations between metastable highly electrically conducting (degenerate-semiconducting) crystalline and more electrically resistive (semiconducting) glassy phases are produced by the application of appropriate voltage pulses. Multilevel programming, wherein more than two metastable resistance states can be stored in the memory material as different proportions of partially glassy/crystalline regions, allows more than one bit to be stored per memory cell. However, this route to increasing data density, without recourse to device-size down-scaling, is threatened by the phenomenon of 'resistance drift', wherein the electrical resistance of the glassy phase slowly increases with time, following a weak power-law dependence, after being written with a voltage pulse. In this paper, we propose an intrinsic electronic mechanism for the resistance drift, particularly valid at ambient temperature and below, by identifying it with the phenomenon of persistent photoconductivity that is commonly observed in a wide range of disordered semiconductors. We develop a model for it in terms of the long-time, deep-trap release and subsequent recombination of charge carriers, akin to that which is believed to be responsible for the long-time photocurrent decay in amorphous semiconductors, such as hydrogenated amorphous silicon. In this case, the parameters controlling the resistance drift are the widths of the (localized) valence- and conduction-band tails in the vicinity of the bandgap. Hence, there is the potential for mitigating resistance drift in the amorphous state of phase-change memory materials by suitable material engineering (e.g. via compositional or fabricational control) to control the extent of band-tailing, thereby facilitating the future introduction of multistate memory. [ABSTRACT FROM AUTHOR]

X-ray diffraction, Amorphous silicon, Multi-objective optimization, Monte Carlo methods. This paper addresses a difficult inverse problem that involves the reconstruction of a three-dimensional model of tetrahedral amorphous semiconductors via inversion of diffraction data. By posing the material-structure determination as a multiobjective optimization program, it has been shown that the problem can be solved accurately using a few structural constraints, but no total-energy functionals/forces, which describe the local chemistry of amorphous networks. The approach yields highly realistic models of amorphous silicon, with no or only a few coordination defects (≤1%), a narrow bond-angle distribution of width 9–11.5°, and an electronic gap of 0.8–1.4 eV. These data-driven information-based models have been found to produce electronic and vibrational properties of a-Si that match accurately with experimental data and rival that of the Wooten-Winer-Weaire models. The study confirms the effectiveness of a multiobjective optimization approach to the structural determination of complex materials, and resolves a long-standing dispute concerning the uniqueness of a model of tetrahedral amorphous semiconductors obtained via inversion of diffraction data. [ABSTRACT FROM AUTHOR]

The effects of radiation on tungsten doped indium oxide (IWO) thin-film transistors (TFTs) have been well investigated in this Letter. In order to achieve high stability and excellent electrical performance simultaneously even in high ionizing radiation damage ambient, different concentrations of tungsten dopant have been introduced for the TFT device fabrication. It is interesting that the high energy ionizing radiation may significantly increase the conductivity and influence the total concentration of oxygen vacancy in the transparent amorphous oxide semiconductor material, which may be completely different from the traditional radiation damage effect for silicon based CMOS devices. However, that abnormal phenomenon will be effectively suppressed by the powerful carrier suppressor, tungsten, which may have a high oxygen bond dissociation energy. Therefore, IWO devices with a 4% tungsten oxide dopant might be the optimized result even after high dosage ionizing radiation exposure. Hence, it may provide a promising radiation hardness approach to improve both the electrical characteristics and reliability for next generation displays, which can be used in the control system of nuclear power generation or space technology. [ABSTRACT FROM AUTHOR]