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Strain imaging is a critical aspect in the design and characterization of opto-electronics, microelectronics, flexible electronics, and on-chip photonics. However, strain mapping techniques are often material specific and strain measurements in amorphous materials remain a challenge. Here, we demonstrate strain mapping and optical characterization of an amorphous semiconductor using scanning reflectance anisotropy microscopy. Using reflection anisotropy spectroscopy and finite element simulations on evaporated amorphous germanium films, we showcase the strain sensitivity of the ellipsometric parameters. We demonstrate nondestructive mapping for simple and complex strain states in amorphous systems. The sub-degree phase and amplitude sensitivity of the microscope is able to determine strain states on the order of 10 − 3 . [ABSTRACT FROM AUTHOR]

Amorphous oxide semiconductor photodetectors (PDs) are promising ultrasensitive and power-efficient ultraviolet (UV) PDs because they generate low dark current in the dark and exhibit high photoresponse under UV irradiation owing to their superior UV absorption and photocarrier transport characteristics. Herein, we demonstrate UV-sensitive and power-efficient oxide phototransistors through the nanometer-scale engineering of oxide semiconductors and appropriate modulation of gate bias conditions. The dark current and photocurrent of an oxide phototransistor exhibit a trade-off relationship in terms of the thickness of the oxide semiconductor film. Ultrathin InZnO is disadvantageous for fabricating UV-sensitive PDs because of its low photoresponse. In contrast, excessively thick InZnO is disadvantageous for fabricating power-efficient UV PDs owing to its high dark current. However, the InZnO film with an optimal film thickness of 8 nm can simultaneously provide the advantages of both ultrathin and excessively thick cases owing to its low intrinsic carrier concentration and sufficient UV absorption depth. Consequently, an InZnO phototransistor with high UV-sensing performance (Smax = 1.25 × 106), low-power operation capability (Idark = ∼10−13A), and excellent repeatability is realized by using an 8-nm-thick InZnO semiconductor and applying appropriate gate bias modulation (constant gate bias for maximized photosensitivity and temporal positive bias pulse for persistence photocurrent elimination). [ABSTRACT FROM AUTHOR]

With the advancement of artificial intelligence technology, memristors have aroused the interest of researchers because they can realize a variety of biological functions, good scalability, and high running speed. In this work, the amorphous semiconductor material silicon carbide (SiC) was used as the dielectric to fabricate the memristor with the Ag/SiC/n-Si structure. The device has a power consumption as low as 3.4 pJ, a switching ratio of up to 105, and a lower set voltage of 1.26 V, indicating excellent performance. Importantly, by adjusting the current compliance, the strength of the formed filaments changes, and the threshold characteristic and bipolar resistance switching phenomenon could be simultaneously realized in one device. On this basis, the biological long- and short-term memory process was simulated. Importantly, we have implemented leakage integration and fire models constructed based on structured Ag/SiC/n-Si memristor circuits. This low-power reconfigurable device opens up the possibilities for memristor-based applications combining artificial neurons and synapses. [ABSTRACT FROM AUTHOR]

In this Letter, an amorphous In-Ga-Zn-O (InGaZnO) thin-film transistor (TFT) structure with a vacuum-gap as a dielectric layer is proposed and investigated. Field-effect conduction at the vacuum/InGaZnO interfaces exhibits extraordinary effective mobility (μ) up to 65 ± 20 cm2 V−1 s−1, while the μ is only around 10 cm2 V−1 s−1 at the SiO2/InGaZnO interfaces with similar film processing conditions. Temperature-dependent transport is performed for deeper insight of the physical origin of the much higher μ at the vacuum/InGaZnO interface. We have found the density of states (DOS) of tail states is notably lower for the transport near the vacuum (8 × 1017 compared to 1.1 × 1019 cm−3 eV−1 at the SiO2/vacuum interface). These indicate that traditional dielectric materials like SiO2 have strong effects on the charge transport degradation in InGaZnO TFTs by introducing extra energetic disorders, and the intrinsic charge transport in InGaZnO is potentially approaching those in poly-silicon TFTs. Exploring a high-quality dielectric layer should be one effective way to further optimize the electrical performance in TFTs based on amorphous oxide semiconductors. [ABSTRACT FROM AUTHOR]

Maintaining gate bias stability under negative bias stress (NBS) and positive bias stress (PBS) is a long-standing issue in amorphous oxide semiconductor thin-film transistors (TFTs). The passivation of the channel layer is crucial for improving device stability. We show that amorphous gallium oxide, which possesses appropriate energy levels (lower electron affinity and higher ionization potential) for indium–tin–zinc oxide (ITZO) TFTs, can be etched selectively by tetramethyl ammonium hydroxide-containing developers that enable self-alignment passivation, such as easy contact hole formation during the drain and source lithography processes. The self-aligned passivation process led to a-ITZO TFTs with high mobility (>50 cm2 V−1 s−1) and low subthreshold swing (<90 mV/dec). The threshold voltage shifts under NBS and PBS using a bias gate voltage of ±20 V for 1 h were −0.09 and 0.15 V, respectively. This passivation can obviate the need for the conventional CVD-derived passivation process by utilizing the DC sputtering of gallium oxide, which may reduce hydrogen issues. [ABSTRACT FROM AUTHOR]

Maintaining gate bias stability under negative bias stress (NBS) and positive bias stress (PBS) is a long-standing issue in amorphous oxide semiconductor thin-film transistors (TFTs). The passivation of the channel layer is crucial for improving device stability. We show that amorphous gallium oxide, which possesses appropriate energy levels (lower electron affinity and higher ionization potential) for indium–tin–zinc oxide (ITZO) TFTs, can be etched selectively by tetramethyl ammonium hydroxide-containing developers that enable self-alignment passivation, such as easy contact hole formation during the drain and source lithography processes. The self-aligned passivation process led to a-ITZO TFTs with high mobility (>50 cm2 V−1 s−1) and low subthreshold swing (<90 mV/dec). The threshold voltage shifts under NBS and PBS using a bias gate voltage of ±20 V for 1 h were −0.09 and 0.15 V, respectively. This passivation can obviate the need for the conventional CVD-derived passivation process by utilizing the DC sputtering of gallium oxide, which may reduce hydrogen issues. [ABSTRACT FROM AUTHOR]

In this study, we fabricated light-emitting diodes (LEDs) on glass substrates at a maximum process temperature of 200 °C using amorphous oxide semiconductor (AOS) materials as emission layers. Amorphous gallium oxide films doped with rare-earth elements (Eu, Pr, and Tb) were employed as AOS emission layers, and the LEDs emitted clear red, green, and pink luminescence upon direct-current application even in the ambient environment. Resonance photoelectron spectroscopy revealed the difference in the electronic structure of the films for each rare-earth dopant, suggesting different emission mechanisms, viz., electron–hole recombination and impact excitation. Although it is widely believed that amorphous materials are unsuitable for use as emission layers of LEDs because of their high concentrations of mid-gap states and defects, the developed rare-earth-doped AOS materials show good performance as emission layers. This study provides opportunities for the advancement of flexible display technologies operating in harsh environments. [ABSTRACT FROM AUTHOR]

In this study, the effect of radiation on an amorphous semiconductor InWZnO (IWZO) thin film has been investigated. From the x-ray photoelectron spectroscopy in-depth analysis, most of the oxygen vacancies in pristine IWZO films are located at the bottom of the film. As the radiation dose increases, the proportion of oxygen vacancies at the bottom of the film increases. However, the top of the IWZO film is hardly affected by the radiation dose. In addition, the resistive switching behavior of an IWZO memristor under irradiation has also been investigated. A forming process and a bipolar I–V curve of the IWZO memristor vary with the radiation dose. The high resistance state of the memristor is significantly degraded at a radiation dose of 1000 krad, which is due to the more defects in the IWZO film. The retention time of the IWZO memristor is up to 104 s at 85 °C with 100 krad. The damaged site in the IWZO film is observed and fabricated into memristors under radiation. The IWZO film as the resistive switching layer exhibits great potential in harsh environments such as polar regions, space technology, nuclear military, and medical imaging. [ABSTRACT FROM AUTHOR]

Selective doping is a key technology for integrated circuit (IC) fabrication since it enables ultrahigh density transistors with various electrical characteristics to be integrated on a single substrate. Also, for vertical IC integration, low-processing temperature compatibility is an essential feature since the annealing of additional ICs fabricated on top should not compromise the characteristics of underlying ICs. For amorphous oxide semiconductor (AOS) thin-films, which are actively being pursued for vertical integration, a selective doping process combined with a low temperature activation thermal annealing process has not been demonstrated. In this Letter, we demonstrate a low-temperature selective doping process that enables selective multi-level n-type doping of insulating amorphous In2O3 (a-In2O3) thin-films. By applying multiple H plasma processes on lithographically defined areas, a monolithic planar In2O3 inverter circuit was demonstrated. Also, the doping process was used to fabricate and demonstrate the operation of an In2O3 thin-film transistor with a 30 nm spaced channel, showing that our process may be used for back-end-of-line vertical integration of AOS devices. [ABSTRACT FROM AUTHOR]

Molecular engineering of organic semiconductors through different synthetic routes has remarkably improved the understanding of the structure–property relationship and charge transport physics, particularly in organic field-effect transistors (OFETs). Emerging OFETs with reliable charge-carrier mobilities exceeding >1 cm2 V−1 s−1 have been demonstrated. However, the field-effect mobilities of amorphous conjugated polymer semiconductors have still showed the values below 10−2 cm2 V−1 s−1 over the past two decades. Here, we report on highly reproducible amorphous organic PTB7 transistors with an exceptional mobility of 0.80 cm2 V−1 s−1 (μavg ≈ 0.51 ± 0.16 cm2 V−1 s−1) operating at 2 V comparable to that of inorganic amorphous silicon semiconductor devices (0.5–1 cm2 V−1 s−1). This remarkable performance is enabled by the use of high-capacitance electrolyte dielectric (Ci = 48.42 μF cm−2), allowing easily attainable lower contact resistance of < 400 Ω cm and improved charge carrier density in the transistor channel, compared to those fabricated using low-k poly(methyl methacrylate) (Ci = 6.2 nF cm−2) and high-k poly(vinylidene fluoride-co-hexafluoropropylene) (Ci = 49.8 nF cm−2) gate dielectrics. This work contributes an opportunity for understanding and improving device performances of amorphous conjugated polymer semiconductors. [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]

Transparent amorphous oxide semiconductors (TAOSs) based transparent thin-film transistors (TTFTs) with high field effect mobility (μFE) are essential for developing advanced flat panel displays. Among TAOSs, amorphous (a-) SnO2 has several advantages against current a-InGaZnO4 such as higher μFE and being indium-free. Although a-SnO2 TTFT has been demonstrated several times, the operation mechanism has not been clarified thus far due to the strong gas sensing characteristics of SnO2. Here we clarify the operation mechanism of a-SnO2 TTFT by electric field thermopower modulation analyses. We prepared a bottom-gate top-contact type TTFT using 4.2-nm-thick a-SnO2 as the channel without any surface passivation. The effective thickness of the conducting channel was ∼1.7 ± 0.4 nm in air and in vacuum, but a large threshold gate voltage shift occurred in different atmospheres; this is attributed to carrier depletion near at the top surface (∼2.5 nm) of the a-SnO2 due to its interaction with the gas molecules and the resulting shift in the Fermi energy. The present results would provide a fundamental design concept to develop a-SnO2 TTFT. [ABSTRACT FROM AUTHOR]

Since the initial development of semiconductor heterostructures in the 1960s, researchers exploring the potential of artificially structured materials for applications in quantum electronic, optoelectronic, and energy conversion devices have sought a combination of metals and semiconductors, which could be integrated at the nanoscale with atomically sharp interfaces. Initial demonstration of such metal/semiconductor heterostructures employed elemental polycrystalline metal and amorphous semiconductors that demonstrated electronic tunneling devices, and more recently, such heterostructures were utilized to demonstrate several exotic optical phenomena. However, these metal/semiconductor multilayers are not amenable to atomic-scale control of interfaces, and defects limit their device efficiencies and hinder the possibilities of superlattice growth. Epitaxial single-crystalline TiN/Al0.72Sc0.28N metal/semiconductor superlattices have been developed recently and are actively researched for thermionic emission-based waste heat to electrical energy conversion, optical hyperbolic metamaterial, and hot-electron solar-to-electrical energy conversion devices. Most of these applications require controlled Schottky barrier heights that determine current flow along the cross-plane directions. In this Letter, the electronic band alignments and Schottky barrier heights in TiN/Al0.72Sc0.28N superlattice interfaces are determined by a combination of spectroscopic and first-principles density functional theory analyses. The experimental EF(TiN)-EVBM(Al0.72Sc0.28N) at the interfaces was measured to be 1.8 ± 0.2 eV, which is a bit smaller than that of the first-principles calculation of 2.5 eV. Based on the valence band offset and the bandgap of cubic-Al0.72Sc0.28N, an n-type Schottky barrier height of 1.7 ± 0.2 eV is measured for the TiN/Al0.72Sc0.28N interfaces. These results are important and useful for designing TiN/Al0.72Sc0.28N metal/semiconductor superlattice based thermionic and other energy conversion devices. [ABSTRACT FROM AUTHOR]

We have observed and identified two crystalline peaks at ∼270 cm−1 and ∼400 cm−1 in nanocrystalline silicon during both compression and decompression. We attribute the first peak to the orthorhombic Imma phase (Si-XI) and the second one to the TO mode of the silicon metallic β-Sn phase (Si-II). Also, in the process of decompression, we observed a first-order-like transition from a highly coordinated metallic crystalline β-Sn phase to the normal tetrahedral LDA phase of the amorphous semiconductor. When the pressure is completely relieved, the powder regains its initial crystalline structure, which suggests that the amorphous phase has retained some structural features of the parent crystalline phase. [ABSTRACT FROM AUTHOR]

Room temperature fabrication of amorphous oxide semiconductors enables a cost-efficient production of devices on flexible and large-area substrates. Metal-semiconductor field-effect transistors using amorphous zinc-tin-oxide (ZTO) thin films with a cation composition of 1:1 Zn:Sn are presented. The n-type ZTO channel is deposited by long-throw magnetron sputtering from a ceramic target at room temperature on glass substrates. Reactively sputtered platinum is used as a gate contact material. We report on/off current ratios as high as 1.8 × 106, a threshold voltage of 0.47 V, and a sub-threshold swing of 124 mV dec−1 for as-fabricated devices. Using negative bias treatment, an improvement in device properties is observed, namely, a decrease in the off-current by two orders of magnitude and a reduction of the sub-threshold swing. An inverter based on as-deposited ZTO metal-semiconductor field-effect transistors exhibits a high peak gain magnitude of 119 and a small uncertainty level of 160 mV for a supply voltage of 3 V. [ABSTRACT FROM AUTHOR]

The photocurrent (IPH) of amorphous InZnO thin film transistors in the off-state is investigated as a function of incident optical power (P). The results show that IPH exhibits a nonlinear dependence on P. Additionally, the dependence of IPH on P exhibits a strong photon energy (hv)-dependent feature. When P is relatively low, IPH is shown to be proportional to Pγ, where γ is greater than 1. The γ >1 behavior may be ascribed to the source-barrier-lowering effect due to the accumulation of photo-induced positive charges at the source side. When P is relatively high, while IPH remains proportional to Pγ under the incident light with hv larger than the optical bandgap (Eg) of a-IZO, it turns to increase at an exponential rate with P if ht of the incident light is smaller than the Eg. The exponential increase in IPH is attributed to the source-barrier-thinning effect, which leads to a significantly enhanced tunneling current. [ABSTRACT FROM AUTHOR]

The electrical properties of amorphous-indium-gallium-zinc-oxide (a-IGZO) thin films were investigated after thermal annealing and plasma treatment under different gas conditions. The electrical resistivity of a-IGZO thin films post-treated in a hydrogen ambient were lower than those without treatment and those annealed in air, regardless of the methods used for both thermal annealing and plasma treatment. The electrical properties can be explained by the quantity of hydrogen incorporated into the samples and the changes in the electronic structure in terms of the chemical bonding states, the distribution of the near-conduction-band unoccupied states, and the band alignment. As a result, the carrier concentrations of the hydrogen treated a-IGZO thin films increased, while the mobility decreased, due to the increase in the oxygen vacancies from the occurrence of unoccupied states in both shallow and deep levels. [ABSTRACT FROM AUTHOR]

Electrical and magnetotransport properties have been studied on pulsed laser deposition grown amorphous InGaZnO4 thin films exhibiting different disorder. A crossover from strong to weak localization was observed as disorder (quantified by a parameter kfl) decreases. The sample with kfl value 0.04 showed strong localization behavior whereas for the sample with kfl>1, electron transport is governed by weak localization. The samples with kfl>1 showed negative magnetoresistance (MR) because of the suppression of weak localization. From the MR study, we estimated the phase coherence length which scales with temperature as T-3/4. The maximum phase coherence length was found to be 130 nm at 5K for the sample with kfl=1.71 and this can significantly influence the spintronic research in amorphous semiconductors. [ABSTRACT FROM AUTHOR]

Zinc oxynitride (ZnOxNy) has attracted much attention as an amorphous semiconductor with high electron mobility. Recent studies reported that ZnOxNy thin films grown by sputtering contained nanocrystals, which might reduce their electron mobility through grain boundary scattering. In this study, we fabricated amorphous ZnOxNy thin films on a glass substrate by a less-energetic nitrogen-plasma-assisted pulsed laser deposition (PLD) to suppress the formation of the nanocrystals. Grown by PLD under optimized conditions, these ZnOxNy thin films exhibited extremely flat surfaces with a root-mean-squared roughness (Rrms) of less than 0.3nm. The Hall mobility of these films exceeded 200 cm2V-1s-1 at a critical carrier concentration of ~1×1019 cm-3, which was twice as high as the reported values for sputter-deposited films. Meanwhile, the mobility of films with larger Rrms was limited to ~160 cm2V-1s-1 even at the critical carrier concentration and comparable with that of the sputter-deposited ZnOxNy films. The substantial enhancement in mobility in extremely flat ZnOxNy films demonstrated that suppressing the formation of nanocrystals is the key to fabricating amorphous ZnOxNy thin films with very high mobility. [ABSTRACT FROM AUTHOR]

Zinc oxynitride (ZnOxNy) has attracted much attention as an amorphous semiconductor with high electron mobility. Recent studies reported that ZnOxNy thin films grown by sputtering contained nanocrystals, which might reduce their electron mobility through grain boundary scattering. In this study, we fabricated amorphous ZnOxNy thin films on a glass substrate by a less-energetic nitrogen-plasma-assisted pulsed laser deposition (PLD) to suppress the formation of the nanocrystals. Grown by PLD under optimized conditions, these ZnOxNy thin films exhibited extremely flat surfaces with a root-mean-squared roughness (Rrms) of less than 0.3nm. The Hall mobility of these films exceeded 200 cm2V-1s-1 at a critical carrier concentration of ~1×1019 cm-3, which was twice as high as the reported values for sputter-deposited films. Meanwhile, the mobility of films with larger Rrms was limited to ~160 cm2V-1s-1 even at the critical carrier concentration and comparable with that of the sputter-deposited ZnOxNy films. The substantial enhancement in mobility in extremely flat ZnOxNy films demonstrated that suppressing the formation of nanocrystals is the key to fabricating amorphous ZnOxNy thin films with very high mobility. [ABSTRACT FROM AUTHOR]

The enhancement in electrical conductivity and optical transparency induced by a phase transition from amorphous to polycrystalline in lightly silicon-doped indium oxide (InSiO) thin films is studied. The phase transition caused by simple thermal annealing transforms the InSiO thin films from semiconductors to conductors. Silicon atoms form SiO4 tetrahedra in InSiO, which enhances the overlap of In 5s orbitals as a result of the distortion of InO6 octahedral networks. Desorption of weakly bonded oxygen releases electrons from deep subgap states and enhances the electrical conductivity and optical transparency of the films. Optical absorption and X-ray photoelectron spectroscopy measurements reveal that the phase transition causes a Fermi energy shift of ∼0.2 eV. [ABSTRACT FROM AUTHOR]

The doping mechanism in organic-semiconductor films has been quantitatively studied via ultrahigh-sensitivity ultraviolet photoelectron spectroscopy of N,N-bis(1-naphthyl)-N,N-diphenyl-1,1-biphenyl-4,4-diamine (α-NPD) films doped with hexaazatriphenylene-hexacarbonitrile [HAT(CN)6]. We observed that HOMO of α-NPD shifts to the Fermi level (EF) in two different rates with the doping concentration of HAT(CN)6, but HOMO distributions of both pristine and doped amorphous α-NPD films are excellently approximated with a same Gaussian distribution without exponential tail states over ∼5 × 1018 cm-3 eV-1. From the theoretical simulation of the HAT(CN)6-concentration dependence of the HOMO in doped films, we show that the passivation of Gaussian-distributed hole traps, which peak at 1.1 eV above the HOMO onset, occurs at ultralow doping [HAT(CN)6 molecular ratio (MR) < 0.01], leading to a strong HOMO shift of ∼0.40 eV towards EF, and MR dependence of HOMO changes abruptly at MR∼0.01 to a weaker dependence for MR>0.01 due to future of the dopant acceptor level. [ABSTRACT FROM AUTHOR]

Sputter deposited amorphous Ge thin films had their nanostructure altered by irradiation with high-energy Ar+ ions. The change in the structure resulted in a reduction in medium range order (MRO) characterized using fluctuation electron microscopy. The pulsed laser crystallization kinetics of the as-deposited versus irradiated materials were investigated using the dynamic transmission electron microscope operated in the multi-frame movie mode. The propagation rate of the crystallization front for the irradiated material was lower; the changes were correlated to the MRO difference and formation of a thin liquid layer during crystallization. [ABSTRACT FROM AUTHOR]

SnO is one of the few candidates for p-type oxide thin film transistors (TFTs) because it retains a reasonable high hole mobility in a nanocrystalline film. However, the high off-current of SnO TFT limits its usefulness. In this work, SnO TFTs were fabricated using thermal evaporation under ultra-high vacuum. In order to decrease the off-current in p-type SnO thin film transistors (TFTs), we used yttrium to reduce n-type minority charges in the channel. The on/off ratio of the TFT increases from 102 to 5 × 104 and the mobility of the TFT in the saturated regime reduces from 1.6 to 1.4 cm2/V s when the SnO channel is doped with 1 wt. % of Y. Grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy reveal that the reduction of SnO2 in the Y-doped SnO TFT channel is the main reason for the improvement in the TFT characteristics. [ABSTRACT FROM AUTHOR]

The thermal properties of polymers are intricately related to the structural elements. Using equilibrium molecular dynamics simulations, we study the thermal conductivity of ultrathin amorphous polystyrene films versus density, ρ, film thickness, dz, and the ratio of thickness to the radius of gyration, dz/Rg, known as the chain confinement indicator. We find that the thermal conductivity increases linearly as dz/Rg increases, or in other words, that stronger confinement and less entanglement lead to lower thermal conductivity. This underlines the fundamental difference in heat conduction between amorphous polymers and crystalline polymers. [ABSTRACT FROM AUTHOR]

Ferroelectric polarization switching of poly(vinylidene difluoride-trifluoroethylene) is investigated in different thin-film device structures, ranging from simple capacitors to dual-gate thin-film transistors (TFT). Indium gallium zinc oxide, a high mobility amorphous oxide material, is used as semiconductor. We find that the ferroelectric can be polarized in both directions in the metal-ferroelectric-semiconductor (MFS) structure and in the dual-gate TFT under certain biasing conditions, but not in the single-gate thin-film transistors. These results disprove the common belief that MFS structures serve as a good model system for ferroelectric polarization switching in thin-film transistors. [ABSTRACT FROM AUTHOR]

We demonstrate the impacts of Ag doping on the local atomic structure of amorphous GeTe phase-change material. The variations of phonon vibrational modes, boding nature, and atomic structure are shown by Raman, X-ray photoelectron spectroscopy, and ab initio calculation. Combining the experiments and simulations, we observe that the number of Ge atoms in octahedral site decreases and that in tetrahedral site increases. This modification in local order of GeTe originating from the low valence element will affect the crystallization behavior of amorphous GeTe, which is verified by differential scanning calorimetry and transmission electron microscope results. This work not only gives the analysis on the structural change of GeTe with Ag dopants but also provides a method to enhance the thermal stability of amorphous phase-change materials for memory and brain-inspired computing applications. [ABSTRACT FROM AUTHOR]

The pressure induced crystalline collapse at 14.7 GPa of the semiconductor clathrate Sr8Ga16Ge30 and its polyamorphic structures are reported up to 35 GPa. In-situ total scattering measurements under pressure allow the direct microscopic inspection of the mechanisms associated with the pressure induced amorphization in these systems, as well as the structure of the recovered phase. It is observed that, between 14.7 and 35 GPa, the second peak in the structure factor function gradually disappears. Analysis of the radial distribution function extracted from those data indicates a systematic lengthening of the nearest-neighbor framework bonds. This feature is associated with gradual cage collapse and breakdown of the tetrahedral structure. This suggests a change in the local bonding in the high density amorphous form, similarly to that observed in other semiconductor clathrates and elemental silicon. Upon recovery from high pressure, the sample remains amorphous and, while there is some indication of the guest-host cage reforming, it does not seem that the tetrahedral coordination is fully reestablished. As such, the compression-decompression process in these systems gives rise to three distinct amorphous forms. [ABSTRACT FROM AUTHOR]

In this study, we evaluated the effects of microwave irradiation (MWI) post-deposition-annealing (PDA) treatment on the gate bias stress instability of amorphous indium-gallium-zinc oxide thinfilm transistors (a-IGZO TFTs) and compared the results with a conventional thermal annealing PDA treatment. The MWI-PDA-treated a-IGZO TFTs exhibited enhanced electrical performance as well as improved long-term stability with increasing microwave power. The positive turn-on voltage shift (ΔVON) as a function of stress time with positive bias and varying temperature was precisely modeled on a stretched-exponential equation, suggesting that charge trapping is a dominant mechanism in the instability of MWI-PDA-treated a-IGZO TFTs. The characteristic trapping time and average effective barrier height for electron transport indicate that the MWI-PDA treatment effectively reduces the defects in a-IGZO TFTs, resulting in a superior resistance against gate bias stress. [ABSTRACT FROM AUTHOR]

To avoid the problem of air sensitive and wet-etched Zn and/or Ga contained amorphous oxide transistors, we propose an alternative amorphous semiconductor of indium silicon tungsten oxide as the channel material for thin film transistors. In this study, we employ the material to reveal the relation between the active thin film and the transistor performance with aid of x-ray reflectivity study. By adjusting the pre-annealing temperature, we find that the film densification and interface flatness between the film and gate insulator are crucial for achieving controllable high-performance transistors. The material and findings in the study are believed helpful for realizing controllable high-performance stable transistors. [ABSTRACT FROM AUTHOR]

The magneto-mechanical coupling effect of amorphous Co40Fe40B20 (CoFeB) films (10-200 nm) on flexible polyethylene terephthalate substrates were investigated in detail. The normalized rema-nent magnetization (Mr/Ms) of CoFeB films changes significantly (up to 62%) under small tensile or compressive strain. Moreover, the thickness dependence of the magneto-mechanical coupling effect for the flexible CoFeB films was demonstrated. These results provide important information for the development of CoFeB-based magnetic tunnel junction used in flexible spintronic devices. [ABSTRACT FROM AUTHOR]

Self-heating effect is recently considered to play an essential role in the degradation of amorphous oxide thin film transistors (TFTs). Previous thermal analysis on amorphous oxide TFTs based on conventional infrared thermography, however, had limitations in studying short-channel TFTs due to its low spatial-resolution. Here, we investigated self-heating effect of short-channel amorphous In-Ga-Zn-O TFTs by using high-resolution thermoreflectance microscopy. For the TFT with a channel length of 15 lm and a distance of 10.8 lm between source and drain electrodes on an etch stopper, the device temperature due to self-heating reached 70-80 °C, and local heating arose close to the center of the channel compared to the drain side in the literature. The channel length dependence of thermal distribution revealed that the asymmetry of local heating weakened with the decreasing channel length due to a heat dissipation by the source and drain electrodes. Transient thermal analysis under a bias stress unveiled that the maximum temperature as a function of stress time strongly depends on bias stress conditions. The temporal behavior of temperature is possibly attributed to the interaction between self-heating and local degradation. [ABSTRACT FROM AUTHOR]

A time-dependent trap-limited conduction scheme is used to analyze the transient behavior of bistable homogeneous amorphous semiconductors when either the electric field or the current density is prescribed. Numerical outcomes confirm that, for a current-controlled system, the working point is unique and stable in any region of the current-voltage characteristic, while in a field-controlled system the negative differential-resistance region is unstable even in absence of circuit parasitics. The proposed theoretical approach represents a valid tool to grasp the relevant time-dependent features of the Ovonic switching in chalcogenide materials. [ABSTRACT FROM AUTHOR]

The origin of the deep subgap states in amorphous indium gallium zinc oxide (a-IGZO), whether intrinsic to the amorphous structure or not, has serious implications for the development of p-type transparent amorphous oxide semiconductors. We report that the deep subgap feature in a-IGZO originates from local variations in the oxygen coordination and not from oxygen vacancies. This is shown by the positive correlation between oxygen composition and subgap intensity as observed with X-ray photoelectron spectroscopy. We also demonstrate that the subgap feature is not intrinsic to the amorphous phase because the deep subgap feature can be removed by low-temperature annealing in a reducing environment. Atomistic calculations of a-IGZO reveal that the subgap state originates from certain oxygen environments associated with the disorder. Specifically, the subgap states originate from oxygen environments with a lower coordination number and/or a larger metal-oxygen separation. [ABSTRACT FROM AUTHOR]

Photostructural changes in a hybrid photonic crystal fiber with chalcogenide nanofilms inside the inner surface of the cladding holes are experimentally demonstrated. The deposition of the amorphous chalcogenide glass films inside the silica capillaries of the fiber was made by infiltrating the nanocolloidal solution-based As25S75, while the photoinduced changes were performed by side illuminating the fiber near the bandgap edge of the formed glass nanofilms. The photoinduced effect of the chalcogenide glass directly red-shifts the transmission bandgap position of the fiber as high as ~20.6nm at around 1600 nm wavelength, while the maximum bandgap intensity change at ~1270nm was –3dB. [ABSTRACT FROM AUTHOR]

We demonstrated lasing in localized modes of an optimized photonic amorphous structure with short-range order. The InGaAsP multiple quantum wells embedded in a free-standing InGaAsP slab were employed as an active medium by optical pumping at room temperature. The high index contrast between air and InGaAsP, combined with uniformity of local topology and short-range order, enables strong confinement of light via multiple scattering. We confirmed the characteristic of lasing modes in the complex geometry with numerical simulations based on the real images of fabricated samples. [ABSTRACT FROM AUTHOR]

Time-resolved threshold switching characteristics including transient parameters such as delay time and holding voltage are reported for a nanoscale GeTe6 Ovonic threshold switching (OTS) device. The voltage dependence of the threshold switching process has been studied, revealing switching in less than 5 ns in the fastest case. A constant holding voltage is observed for the different voltage pulses applied, which is an indicative for a stable on state in the amorphous phase. In addition, the potential of GeTe6 devices as OTS selectors is validated. [ABSTRACT FROM AUTHOR]

Electron traps in amorphous In-Ga-Zn-O (a-IGZO) thin films were studied using isothermal capacitance transient spectroscopy (ICTS). Broad peaks that shifted toward a longer elapsed time with an increase in the filling pulse width were detected from the ICTS spectra for metal-oxide-semiconductor diodes consisting of a Mo/SiO2/a-IGZO structure. The time constant of the peak position at 180 K was found to be from ∼1 m to ∼100 ms, corresponding to a range of energy level from ∼170 to ∼230 meV below the conduction band edge. The total trap density around the peak was estimated to be ∼1 × 1016 cm-3·eV-1. Further, according to the biasing voltage dependence of the ICTS signal, the density of the trap states increases by about three orders of magnitude near the interface between the a-IGZO and the gate dielectric layers. The electron transport in electronic devices using an a-IGZO could be influenced by the trap states detected in the present study. [ABSTRACT FROM AUTHOR]

We analyzed the intrinsic electrical characteristics of amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) using a gated-four-probe method. Based on the back channel potential, the extraction of intrinsic field-effect mobility (μFEi) and parasitic resistance in source (Rs) and drain (Rd) electrodes was performed especially for low VGS and VDS conditions. The resulting μFEi showed typical VGS dependency of amorphous semiconductor TFTs. However, Rs and Rd showed that there can be non-uniformity in source/drain parasitic resistance, which indicates that a separate analysis of the parameters of each electrode is essential for further improvement of the performance of a-IGZO TFTs. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate an on-chip polycrystalline PbTe photoconductive detector integrated with a chalcogenide glass waveguide. The device is monolithic ally fabricated on silicon, operates at room-temperature, and exhibits a responsivity of 1.0 A/W at wavelengths between 2.1 and 2.5 µm. [ABSTRACT FROM AUTHOR]

Demonstrates the effect of a short-pulse crystallization of amorphous silicon on quartz that causes surface roughening via the freezing of capillary waves excited in the silicon melt. Velocity and viscous damping of the capillary waves; Variation of volume change of the silicon during solidification; Observation of the film thickness variation.

We report an experimental evidence that some hydrogens passivate electron traps in an amorphous oxide semiconductor, a-In-Ga-Zn-O (a-IGZO). The a-IGZO thin-film transistors (TFTs) annealed at 300 °C exhibit good operation characteristics; while those annealed at ≥400 °C show deteriorated ones. Thermal desorption spectra (TDS) of H2O indicate that this threshold annealing temperature corresponds to depletion of H2O desorption from the a-IGZO layer. Hydrogen re-doping by wet oxygen annealing recovers the good TFT characteristic. The hydrogens responsible for this passivation have specific binding energies corresponding to the desorption temperatures of 300-430 °C. A plausible structural model is suggested. [ABSTRACT FROM AUTHOR]

The skin pigment melanin is one of a few bio-macromolecules that display electrical and photo-conductivity in the solid-state. A model for melanin charge transport based on amorphous semiconductivity has been widely accepted for 40 years. In this letter, we show that a central pillar in support of this hypothesis, namely experimental agreement with a hydrated dielectric model, is an artefact related to measurement geometry and non-equilibrium behaviour. Our results cast significant doubt on the validity of the amorphous semiconductor model and are a reminder of the difficulties of electrical measurements on low conductivity, disordered organic materials. [ABSTRACT FROM AUTHOR]

In this work, we report on the structural and electronic properties of amorphous In2O3 obtained with ab initio molecular dynamics. Our results show crystal-like short range InO6 polyhedra having average In-O distance consistent with x-ray spectroscopy data. Structural disorder yields band tailing and localized states, which are responsible of a strong reduction of the electronic gap. Most importantly, the appearance of a peculiar O-O bond imparts n-type character to the amorphous compound and provides contribution for interpreting spectroscopic measurements on indium based oxidized systems. Our findings portray characteristic features to attribute transparent semiconductive properties to amorphous In2O3. [ABSTRACT FROM AUTHOR]

We investigate the influence of thermal annealing on the passivation quality of crystalline silicon (c-Si) surfaces by intrinsic and n-type hydrogenated amorphous silicon (a-Si:H) films. For temperatures up to 255 °C, we find an increase in surface passivation quality, corresponding to a decreased dangling bond density. Due to the combined chemical and field effect passivation of the intrinsic/n-type a-Si:H layer stack, we obtained minority carrier lifetimes with a value as high as 13.3 ms at an injection level of 1015 cm-3. For higher annealing temperatures, a decreased passivation quality is observed, which is attributed to hydrogen effusion. [ABSTRACT FROM AUTHOR]

The origin of instability under positive bias stress (PBS) in amorphous Si-In-Zn-O (SIZO) thin film transistor (TFT) with different Si concentration has been investigated by x-ray photoelectron spectroscopy (XPS) and density of states (DOSs) analysis. It is found that stability of SIZO-TFT with 3 wt. % Si under PBS became more deteriorated than that of 1 wt. % Si incorporated SIZO-TFT due to the increased oxygen related trap distributed in energy range from conduction band to ∼0.3 eV below the conduction band. The origin of instability under PBS was discussed in terms of oxygen related trap derived from DOSs and XPS analysis. [ABSTRACT FROM AUTHOR]

We have performed an ab initio theoretical investigation of a graphene sheet adsorbed on amorphous SiO2 surface (G/a-SiO2). We find that graphene adsorbs on the a-SiO2 surface through van der Waals interactions. The inhomogeneous topology of the a-SiO2 clean surface promotes a total charge density displacement on the adsorbed graphene sheet, giving rise to electron-rich as well as hole-rich regions on the graphene. Furthermore, the adsorbed graphene sheet exhibits a net total charge density gain. In this case, the graphene sheet becomes n-type doped, however, no chemical bonds form at the graphene-SiO2 interface. The electronic charge transfer from a-SiO2 to the graphene sheet occurs upon the formation of a partially occupied level lying above the Dirac point. We find that this partially occupied level comes from the three-fold coordinated oxygen atoms in the a-SiO2 substrate. [ABSTRACT FROM AUTHOR]

This study calculates the contribution of electrons and holes to HfO2 conductivity in Si/HfO2/Ni structures using experiments on injection of minority carriers from n- and p-type silicon. Results show that electrons and holes contribute to the conductivity of HfO2, allowing HfO2 to exhibit two-band conductivity. [ABSTRACT FROM AUTHOR]

Amorphous indium gallium zinc oxide (a-IGZO) thin films of the highest transmittance reported in literature were initially deposited onto flexible polymer substrates at room temperature. The films were annealed in vacuum, air, and oxygen to enhance their electrical and optical performances. Electrical and optical characterizations were done before and after anneals. A partial reversal of the degradation in electrical properties upon annealing in oxygen was achieved by subjecting the films to subsequent vacuum anneals. A model was developed based on film texture and structural defects which showed close agreement between the measured and calculated carrier mobility values at low carrier concentrations (2-6 × 1019 cm-3). [ABSTRACT FROM AUTHOR]

A thin amorphous silicon interlayer, inserted between the III-V semiconductor and the gate dielectric is expected to prevent III-V oxidation, as required for high-mobility channel transistors. We demonstrate that the addition of a thin Al2O3 barrier layer between the a-Si and the high-k HfO2, together with optimized post-metallization annealing, is the key to reduce the a-Si consumption and to achieve a highly scaled gate stack with equivalent oxide thickness of ∼0.8 nm. The evolution of the interfaces during growth and the quality of the stack are investigated by in-situ X-ray photoelectron spectroscopy and electrical measurements on metal-oxide-semiconductors capacitors. [ABSTRACT FROM AUTHOR]