Donor-like States Research Articles

Atomic and Electronic Structure of Defects in hBN: Enhancing Single-Defect Functionalities.

Defect centers in insulators play a critical role in creating important functionalities in materials: prototype qubits, single-photon sources, magnetic field probes, and pressure sensors. These functionalities are highly dependent on their midgap electronic structure and orbital/spin wave function contributions. However, in most cases, these fundamental properties remain unknown or speculative due to the defects being deeply embedded beneath the surface of highly resistive host crystals, thus impeding access through surface probes. Here, we directly inspected the atomic and electronic structures of defects in thin carbon-doped hexagonal boron nitride (hBN:C) by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Such investigation adds direct information about the electronic midgap states to the well-established photoluminescence response (including single-photon emission) of intentionally created carbon defects in the most commonly investigated van der Waals insulator. Our joint atomic-scale experimental and theoretical investigations reveal two main categories of defects: (1) single-site defects manifesting as donor-like states with atomically resolved structures observable via STM and (2) multisite defect complexes exhibiting a ladder of empty and occupied midgap states characterized by distinct spatial geometries. Combining direct probing of midgap states through tunneling spectroscopy with the inspection of the optical response of insulators hosting specific defect structures holds promise for creating and enhancing functionalities realized with individual defects in the quantum limit. These findings underscore not only the versatility of hBN:C as a platform for quantum defect engineering but also its potential to drive advancements in atomic-scale optoelectronics.

Investigation of Donor-like State Distributions in Solution-Processed IZO Thin-Film Transistor through Photocurrent Analysis

The density of donor-like state distributions in solution-processed indium–zinc-oxide (IZO) thin-film transistors (TFTs) is thoroughly analyzed using photon energy irradiation. This study focuses on quantitatively calculating the distribution of density of states (DOS) in IZO semiconductors, with a specific emphasis on their variation with indium concentration. Two calculation methods, namely photoexcited charge collection spectroscopy (PECCS) and photocurrent-induced DOS spectroscopy (PIDS), are employed to estimate the density of the donor-like states. This dual approach not only ensures the accuracy of the findings but also provides a comprehensive perspective on the properties of semiconductors. The results reveal a consistent characteristic: the Recombination–Generation (R-G) center energy ET, a key aspect of the donor-like state, is acquired at approximately 3.26 eV, irrespective of the In concentration. This finding suggests that weak bonds and oxygen vacancies within the Zn-O bonding structure of IZO semiconductors act as the primary source of R-G centers, contributing to the donor-like state distribution. By highlighting this fundamental aspect of IZO semiconductors, this study enhances our understanding of their charge-transport mechanisms. Moreover, it offers valuable insight for addressing stability issues such as negative bias illumination stress, potentially leading to the improved performance and reliability of solution-processed IZO TFTs. The study contributes to the advancement of displays and technologies by presenting further innovations and applications for evaluating the fundamentals of semiconductors.

Critical and controversial issues pertaining to the growth and properties of Cu2O in the context of energy conversion

Cu2O has been deposited on m-, r-, and a-Al2O3 by reactive sputtering of Cu using Ar with different contents of O2 followed by annealing under carefully optimized conditions at 500 °C under Ar:H2 in order to prevent the oxidation and reduction of the Cu2O layers, which have a cubic crystal structure and are bulk-relaxed. We find that the content of O2 influences the structural and optical properties of the Cu2O layers that exhibited a detailed spectral structure and distinct peaks at 2.75, 2.54, and 2.17 eV corresponding to the indigo, blue, and yellow direct gap transitions of Cu2O as observed by ultrafast pump–probe spectroscopy at room temperature. However, we also observed a transition at 1.8 eV that is related to the occurrence of states ∼0.4 eV below the conduction band minimum of Cu2O. We discuss the controversial origin of these states, which are usually attributed to donor-like oxygen vacancy states, and suggest that the origin of these states may be related to traps at the interfaces of CuO/Cu2O nanostructures, which is important in the context of energy conversion pertaining to solar cells and photocatalysis.

Analysis of degradation of Sb2Se3 thin film solar cells deploying a time-dependent approach linked with 1D-AMPS simulation

In this paper, we have developed a time-dependent model to study defect growth in the absorber layer of Sb2Se3 thin film solar cells. This model has been integrated with the AMPS-1D simulation platform to investigate the impact of increasing defect density at different positions within the Sb2Se3 layer on the electrical parameters of the solar cell. We adopted the Gloeckler standard model for thin films in AMPS to represent Sb2Se3 materials. The study focuses on tracking the degradation of device performance parameters as donor-like mid-gap states accumulate in the Sb2Se3 layer over time. We monitored the variation of key electrical parameters, including efficiency (η), fill factor (FF), open-circuit voltage (Voc), and short-circuit current (Jsc), at three different positions: the interface with CdS, the bulk of the Sb2Se3 layer, and the interface with the top contact. These positions are susceptible to increasing defect density during prolonged operation and irradiation. To pinpoint the most sensitive part of the Sb2Se3 layer to defect accumulation, we divided the layer into three sub-layers. Our simulation results highlight that the CdS/Sb2Se3 interface is the most vulnerable position in the cell when it comes to defect accumulation. The practical implication of this study is that special attention should be given to the CdS/Sb2Se3 interface during material deposition and the development of high-stability Sb2Se3 thin film solar cells.“

Study of Electrical Characteristics for Dual-Gate TFTs With Asymmetric Defect Distributions and Gate Work Functions

Combined effects of asymmetric defect distributions and asymmetric gate work functions (WFs) on the performances of self-aligned dual-gate poly-Si TFTs are investigated. Normally, small grains with plentiful grain boundaries (GBs) or other structural defects appear at different positions of the poly-Si film, which is dependent on the growth process of the film. Subgap states of acceptor-like tail, acceptor-like deep-level, donor-like tail, and donor-like deep-level states are used to emulate the defects. Two sets of density of states (DOS) are employed. We find that defects at different positions of the source-side and drain-side channels exhibit different influences on TFT performance and the influences are dependent on the WFs of the gates. TFTs with a higher gate WF can have a higher tolerance to the depth of the defect region. Besides the electrical characteristics, the combined effects of defects and gate WFs on current density distributions and electric field distributions in the channel regions are explored. The performance variations caused by the asymmetric defects along with asymmetric gate WFs can be explained.

Looking Outside the Square: The Growth, Structure, and Resilient Two-Dimensional Surface Electron Gas of Square SnO2 Nanotubes.

Nanotechnology has delivered an amazing range of new materials such as nanowires, tubes, ribbons, belts, cages, flowers, and sheets. However, these are usually circular, cylindrical, or hexagonal in nature, while nanostructures with square geometries are comparatively rare. Here, a highly scalable method is reported for producing vertically aligned Sb-doped SnO2 nanotubes with perfectly-square geometries on Au nanoparticle covered m-plane sapphire using mist chemical vapor deposition. Their inclination can be varied using r- and a-plane sapphire, while unaligned square nanotubes of the same high structural quality can be grown on silicon and quartz. X-ray diffraction measurements and transmission electron microscopy show that they adopt the rutile structure growing in the [001] direction with (110) sidewalls, while synchrotron X-ray photoelectron spectroscopy reveals the presence of an unusually strong and thermally resilient 2D surface electron gas. This is created by donor-like states produced by the hydroxylation of the surface and is sustained at temperatures above 400°C by the formation of in-plane oxygen vacancies. This persistent high surface electron density is expected to prove useful in gas sensing and catalytic applications of these remarkable structures. To illustrate their device potential, square SnO2 nanotube Schottky diodes and field effect transistors with excellent performance characteristics are fabricated.

Nitrogen-Dependent Electronic Properties of Threading Edge Dislocations in 4H-SiC

The dependence of the electronic properties of threading edge dislocations (TEDs) on the nitrogen (N) doping of 4H silicon carbide (4H-SiC) is investigated by combining first-principles calculations and experiments. First-principles calculations indicate that N atoms tend to accumulate at the cores of TEDs during the N doping of 4H-SiC, giving rise to the formation of TED-N complexes in N-doped 4H-SiC. The accumulation of N donors at the cores of TEDs leads to the donor-like behavior of TEDs in n-type 4H-SiC. With Kelvin probe force microscopy measurements, we verify that TEDs induce acceptor-like and donor-like states in undoped and N-doped 4H-SiC, respectively. For N-doped 4H-SiC, the resistivity decreases when the N concentration increases. In the meantime, the difference in the local Fermi energy between a TED and the perfect 4H-SiC becomes smaller, indicating that the N accumulation at the cores of TEDs may be saturated.

Diversity Analysis of Defect Distribution and Carriers Quantization in Cu 2 ZnSnS 4/Cu2ZnSn(S,Se) 4 Kesterite Quantum Well Solar Cell

Kesterite materials, with a major advantage of direct bandgap and earth abundant material,are popular for low cost and thin film solar cell applications. Despite the popularity, the material fails to achieve significant efficiency due to the emergence of defect states during the growth process. In this paper multiple approaches have been investigated focusing on implementation of Quantum Wells(QW) to enhance the performance of solar cell. QW structure are created using CZTS x Se 1−x and Cu 2 ZnSnS 4 as QW and barrier material layers respectively. The performance evaluation of the QW solar cell is also carried out with the presence of most popular donor-like defect states in a gaussian and tail distribution way. The behavior of the device is investigated in presence of broad range of QWs from 2 to 100QWs to ensure the effect of defects on rise in QWs. The worst case performance of the solar cell is obtained to be efficiency of 9.6% under a high level of defect states. A remarkable observation on the effect of increase in number of QWs and defect states on solar cell parameters solar cell are concluded.

Investigation and modeling of trap states in ambipolar organic field-effect transistor

This work presents a compact analytical model for charge carrier transport in an ambipolar OFET (a-OFET) based on trap-limited conduction (TLC). The model accounts for tail traps in the band gap of the organic semiconductor (OSC) in order to analyse the transistor behaviour in above threshold regime. For the sub-threshold operation of ambipolar OFET, both deep and interface trap states are accounted for, thus accurately describing the transistor behaviour comprising of drift and diffusion elements respectively. A detailed description of surface potential and field-effect mobility for both the electron and hole carriers, in consequence to these trap states has been presented. Individual current components, obtained as a result of modeling tail, deep and interface trap states are combined using the hyperbolic tangent transition function and are in good agreement with the available experimental data. • This work presents modeling of ambipolar OFET using trap-limited conduction (TLC) approach. • Presented work includes modeling of ambipolar current in both above and below threshold regime, by considering tail, deep and interface acceptor and donor-like states in organic semiconductor. • Subthreshold modeling includes both drift and diffusion components. • Dependence of the mobility of electrons and holes on the characteristic temperatures of the distributions of both tail and deep acceptor and donor-like states has been studied. • The model accurately describes the transfer characteristics of ambipolar OFET.

Detection of defect levels in vicinity of Al2O3/p-type GaN interface using sub-bandgap-light-assisted capacitance–voltage method

Defect levels in the vicinity of the Al2O3/p-type GaN interface were characterized using a sub-bandgap-light-assisted capacitance–voltage (C–V) method. For metal–oxide–semiconductor (MOS) diodes prepared using p-type GaN (p-GaN) and Al2O3 formed by atomic layer deposition, the C–V curves measured in the dark showed capacitance saturation at a negative bias and a large negative voltage shift compared with ideal curves, which implied the effects of donor-like gap states in the vicinity of the Al2O3/p-GaN interface. Upon illumination with monochromated sub-bandgap light with photon energies higher than 2.0 eV under a large positive bias, the subsequently measured C–V curves showed three plateaus. The plateau under the positive bias voltage due to the surface inversion appeared despite the sub-bandgap illumination, which did not appear at 1.8 eV light illumination, indicating the existence of midgap defect levels. Moreover, the other plateaus were attributed to defect levels at 0.60 and 0.7–0.8 eV above the valence band maximum. For a sample whose surface was prepared by photo-electrochemical (PEC) etching to a depth of 16.5 nm, the C–V curve measured in the dark showed a reduced voltage shift compared with the unetched sample. Furthermore, sub-bandgap-light-assisted C–V curves of the sample with PEC etching showed no plateau at a positive bias, which indicated the reduction in the density of the midgap defect states. Possible origins of the detected defect levels are discussed. The obtained results showed that the interface control can improve the properties of p-GaN MOS structures.

In-Gap States of HfO2 Nanoislands Driven by Crystal Nucleation: Implications for Resistive Random-Access Memory Devices

Envisioned extremely scaled, high-performance memory devices request to conduct the step from thin semiconductor films to nanoscale structures and the use of promising high-k materials such as hafnium oxide (HfO2). HfO2 is well suited for use in resistive random-access memory (ReRAM) devices based on the valence change mechanism. Here, we provide a decidedly scaled system, namely, HfO2 nanoislands that are grown by van der Waals epitaxy on highly oriented pyrolytic graphite (HOPG). The electronic and structural properties of these well-separated, crystalline HfO2 nanoislands are investigated by scanning probe methods as well as ab initio methods. The topography reveals homogeneously formed HfO2 nanoislands with areas down to 7 nm2 and a thickness of one unit cell. They exhibit several acceptor- and donor-like in-gap states in addition to the bulk band gap, implying bulk properties. X-ray photoelectron spectroscopy indicates hafnium carbide formation as one possible origin for defect states. Going further to the crystal nucleation of HfO2, nanocrystals with a diameter of 2.7–4.5 Å are identified next to carbon vacancies in the topmost HOPG layer, indicating that carbon is incorporated into the islands at early nucleation stages. A precise description of these nuclei is accomplished by the simulation of small HfmOn(:C) clusters (m = 3 to 10; n = 3 to 22) with and without carbon incorporation using ab initio methods. The comparison of the theoretically determined lowest-energy clusters and electronic states with the experimental results allows us to identify the structure of the most relevant HfO2 sub-nanometer crystals formed during the first nucleation steps and the nature of the in-gap states found at the surfaces of HfO2 nanoislands. That way, a model system is derived that consists of distinct structural units, related to surface states or defect states, respectively, that will promote the tailoring of in-gap states of smallest HfO2 structures and thus the scalability of memory devices.

Ambipolarity of diluted hydrogen in wide-gap oxides revealed by muon study

Muon spin rotation has long been recognized as one of the few methods for experimentally accessing the electronic state of dilute hydrogen (H) in semiconductors and dielectrics, where muon behaves as a pseudo-H (designated by the elemental symbol Mu). Meanwhile, predictions on the electronic state of H in these materials by density functional theory (DFT) do not always agree with the observed states of Mu. Most notably, Mu frequently occurs in wide-gap oxides simultaneously in a neutral (Mu0) and a diamagnetic state (Mu+ or Mu−), which DFT calculations do not explain; they predict that H is stable only in a diamagnetic state with the polarity determined by the equilibrium charge-transition level (E+/−) vs the Fermi level. To address this issue, we developed a semi-quantitative model that allows a systematic understanding of the electronic states reported for Mu in the majority of oxides. Our model assumes that muons interact with self-induced excitons to produce relaxed-excited states corresponding to donor-like (MuD) and/or acceptor-like (MuA) states and that these states correspond to the non-equilibrium electronic level (E+/0 or E0/−) predicted by DFT calculations for H. The known experimental results are then explained by the relative position of E+/0 and E0/− in the host’s energy band structure. In addition, the model sheds new light on the polaron-like nature of the electronic states associated with shallow donor Mu complexes.

Investigation on Stability in Solution-Processed In-Zn-Sn-O TFT Array Under Various Intensity of Illumination

The effect of light illumination intensity on the stability of In-Zn-Sn-O (IZTO) thin-film transistors (TFTs) array fabricated by solution processed is investigated. Comparison with positive bias stress, the light illumination suppresses the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> shift under positive bias illumination stress because of the increase in the free electrons induced by the ionized oxygen vacancies in the IZTO channel layer, but transfer characteristics show two-stage degradation under negative bias illumination stress (NBIS). The hump phenomenon is induced after NBIS, and the light illumination intensity is higher, the hump phenomenon becomes more serious. The hump phenomenon is relevant to ionized oxygen vacancies, which act as shallow donor-like states near the conduction-band minimum in IZTO.

Nitrogen Decoration of Basal-Plane Dislocations in 4H - SiC

Basal-plane dislocations (BPDs) pose a great challenge to the reliability of bipolar power devices based on the 4H silicon carbide (4H-SiC). It is well established that heavy nitrogen (N) doping promotes the conversion of BPDs to threading edge dislocations (TEDs) and improves the reliability of 4H-SiC-based bipolar power devices. However, the interaction between N and BPDs, and the effect of N on the electronic properties of BPDs are still ambiguous, which significantly hinder the understanding on the electron-transport mechanism of 4H-SiC-based bipolar power devices. Combining molten-alkali etching and the Kelvin probe force microscopy (KPFM) analysis, we demonstrate that BPDs create acceptor-like states in undoped 4H-SiC, while acting as donors in N-doped 4H-SiC. First-principles calculations verify that BPDs create occupied defect states above the valence band maximum (VBM) and unoccupied defect states under the conduction-band minimum (CBM) of undoped 4H-SiC. The electron transfer from the defect states of intrinsic defects and native impurities to the unoccupied defect states of BPDs gives rise to the acceptor-like behavior of BPDs in undoped 4H-SiC. Defect formation energies indicate that N atoms can spontaneously decorate BPDs during the N doping of 4H-SiC. The binding between N and BPD is strong against decomposition. The accumulation of N dopants at the core of BPDs results in the accumulation of donor-like states at the core of BPDs in N-doped 4H-SiC. This work not only enriches the understanding on the electronic behavior of BPDs in N-doped 4H-SiC, but also helps understand the electron transport mechanism of 4H-SiC-based bipolar power devices.

Extraction of SnO Subbandgap Defect Density by Numerical Modeling of p-Type TFTs

Recently, p-type tin monoxide (SnO) thin-film transistors (TFTs) have gained interest for all-oxide complementary metal–oxide semiconductor (CMOS) circuits for flexible electronics and back-end-of-line integration with Si. However, most SnO TFTs demonstrated so far exhibit a low on– off-current ratio and limited field effect mobility. To understand and improve SnO TFT performance, it is necessary to quantitatively characterize the subbandgap defects in SnO and at its dielectric interface. In this work, we establish numerical models which provide this understanding. By concurrent fitting of simulated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text{D}}$ </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">${V}_{\text{GS}}$ </tex-math></inline-formula> and effective mobility versus <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text{GS}}$ </tex-math></inline-formula> to experimentally measured data, we can accurately extract SnO defect state profiles. Using the extracted simulation models, we then identify ways to improve SnO TFT performance. Specifically, a reduction in the density of shallow, bulk Gaussian acceptor states, is necessary to reduce the off-current, while reducing the contact resistance and interface donor-like tail state density can improve the SnO field effect mobility.

Influences of vacuum annealing induced oxygen defects on the transfer characteristics of a-ITO thin-film transistors

Amorphous indium–tin-oxide (a-ITO) films are fabricated by pulsed laser deposition at room temperature and annealed in vacuum. Although vacuum annealing could ameliorate the carrier mobility and subthreshold swing, the threshold voltage shows a negative shift upon vacuum annealing at 450 K, and a hump emerges in the subthreshold region. The density of electronic states extracted by Grünewald method demonstrate that the hump is caused by shallow donor-like states. Furthermore, the X-ray photoelectron spectra and the photoconductivity experiment reveal that the shallow donors are ascribed to the increased oxygen defects upon thermal annealing.

Establishment and resilience of transplanted gut microbiota in aged mice

SummaryThe maintenance of healthy and resilient gut microbiota is critical for the life quality and healthspan of the elderly. Fecal microbiota transplantation (FMT) has been increasingly used to restore healthy gut microbiota. We systemically studied the establishment and resilience of transplanted microbiota after autologous versus heterologous FMT in aged recipients. Gut microbiota of aged mice (20 months old) failed to restore their original diversity and composition over 8 weeks via spontaneous recovery after antibiotics treatment; in contrast, FMT using either autologous or heterologous (2 months old from a different vendor) donors facilitated the recovery successfully, established donor-like microbiota states, and affected host gene expression profile. Furthermore, the transplanted microbiota established by heterologous FMT is not resilient during chemical-induced colonic inflammation, in contrast to that of autologous FMT. Our findings highlighted the need to monitor the long-term stability of transplanted gut microbiota and to perform multiple FMT when necessary.

Influence of sub-band gap density of states on the electrical performance of amorphous SiZnSnO thin film transistor

Fabrication, electrical characterizations and numerical simulations are performed on radio-frequency sputtered amorphous SiZnSnO thin film transistors (TFTs). Experimental transfer curves are compared with numerically simulated results to extract the nature of sub-band gap density of states (DOS) of the amorphous channel materials. Defect states arising due to disorder induced localization of electronic wave functions is considered in the numerical simulation process. The extracted DOS for conduction band tail is found to be roughly two order of magnitude lower than that of the a-Si:H. Moreover, disorder asymmetry is also observed between conduction and valence band tail states. In addition to band tails, Gaussian shallow donor-like states and deep level acceptor-like traps are also taken into consideration. The influence of these defect states on the electrical performance of SiZnSnO TFTs has been investigated in detail. Such studies are useful for fundamental understanding of device physics and further improvement of amorphous SiZnSnO based TFT performance and stability.

Long-Term Efficacy of Low-Intensity Single Donor Fecal Microbiota Transplantation in Ulcerative Colitis and Outcome-Specific Gut Bacteria.

Aims: To assess the long-term efficacy and safety of single-donor, low-intensity fecal microbiota transplantation (FMT) in treating ulcerative colitis (UC), and to identify the outcome-specific gut bacteria.Design: Thirty-one patients with active UC (Mayo scores ≥ 3) were recruited, and all received FMT twice, at the start of the study and 2∼3 months later, respectively, with a single donor and a long-term follow-up. The fecal microbiome profile was accessed via 16S rRNA sequencing before and after FMT.Results: After the first FMT, 22.58% (7/31) of patients achieved clinical remission and endoscopy remission, with the clinical response rate of 67.74% (21/31), which increased to 55% (11/20) and 80% (16/20), respectively, after the second FMT. No serious adverse events occurred in all patients. During 4 years of follow-up, the mean remission period of patients was 26.5 ± 19.98 m; the relapse rate in the 12 remission patients was 33.33% within 1 year, and 58.3% within 4 years. At baseline, UC patients showed an enrichment in some proinflammatory microorganisms compared to the donor, such as Bacteroides fragilis, Clostridium difficile, and Ruminococcus gnavus, and showed reduced amounts of short-chain fatty acid (SCFA) producing bacteria especially Faecalibacterium prausnitzii. FMT induced taxonomic compositional changes in the recipient gut microbiota, resulting in a donor-like state. Given this specific donor, UC recipients with different outcomes showed distinct gut microbial features before and after FMT. In prior to FMT, relapse was characterized by higher abundances of Bacteroides fragilis and Lachnospiraceae incertae sedis, together with lower abundances of Bacteroides massiliensis, Roseburia, and Ruminococcus; Prevotella copri was more abundant in the non-responders (NR); and the patients with sustained remission (SR) had a higher abundance of Bifidobacterium breve. After FMT, the NR patients had a lower level of Bifidobacterium compared to those with relapse (Rel) and SR, while a higher level of Bacteroides spp. was observed in the Rel group.Conclusion: Low-intensity single donor FMT could induce long remission in active UC. The gut microbiota composition in UC patients at baseline may be predictive of therapeutic response to FMT.

A comprehensive density-of-states model for oxide semiconductor thin film transistors

In this paper, a novel and comprehensive density-of-states model is presented to understand the origin of conductivity and the performance of p-type and n-type oxide semiconductor thin film transistors (TFTs). To validate the model, the simulated I–V characteristics are compared with measured results of p-type Cu2O and SnO and n-type SnO2 TFTs. It was observed that cation vacancies are responsible for hole conduction in p-type TFTs, while anion vacancies and/or metal interstitials are responsible for electron conduction in n-type TFTs. This was observed by assigning the cation vacancies to acceptor-like Gaussian states and anion vacancies and/or metal interstitials to donor-like Gaussian states. The characteristic slopes in conduction/valence band-tail states are due to disorders present in the oxide semiconductors. The model successfully delivers the physical insight and pathway to circuit simulation of large-scale integration of pixel circuits in active matrix liquid crystal display/active matrix organic light-emitting diodes.