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The hole mobility of an organic semiconductor film that consists of N,N'‐di (1‐naphthyl)‐N,N'‐diphenyl‐benzidine (α‐NPD) is evaluated at various film formation processes, such as vacuum deposition and capillary injection. The mobility varies with the film formation process. From the temperature dependence of mobility, the Poole−Frenkel model and disorder model are discussed. From the analysis based on the Poole−Frenkel model, activation energies of the vacuum‐deposited film, the slowly cooled‐melted film, and the rapidly cooled‐melted film are 0.28, 0.20, and 0.40 eV, respectively. This result suggests that organic semiconductor thin films formed by different film formation methods have different molecular aggregation states. [ABSTRACT FROM AUTHOR]

Three‐terminal memristor devices with a channel length of 70 μm and a width of 5 μm are fabricated using undoped zinc oxide (ZnO), fluorine‐doped zinc oxide (ZnO:F), and nitrogen‐doped zinc oxide (ZnO:N) semiconductor thin films via atomic layer deposition. To observe the effects of humidity and hydrogen doping on their gate‐tunable memristive behavior, gate‐tunable memristive behaviors are measured with a drain bias (VD) ± 10 V at different gate voltages (VG) from 50 to −50 V under humidity of 40%, 55%, and 70%. Resistive switching behavior caused by the hydrogen doping effect is observed, and the on/off ratio increases with increasing humidity, whereas the gate tunability decreases. The conductance and gate tunability of all devices decrease with an increase in humidity due to the hydrogen doping effect. As this study adopts a three‐terminal structure with an oxide memristor, it clearly shows the moisture effect on the memristive behavior of oxide‐based memristors. [ABSTRACT FROM AUTHOR]

Transient photoluminescence (PL) decay imaging is conducted for visualizing carrier transport in luminescent polymer semiconductor thin films. The method is simple, but enables a real‐time observation of carrier motion on the scale of several millimeters in luminescent thin films. Decrease in the PL intensity of the channel region in organic field‐effect transistor (OFET) is observed in accordance with the device operation. Upon application of pulse voltages to the source electrode for carrier injection, the transient PL decay motion is visualized using a conventional charge‐coupled device (CCD) camera. By analyzing the PL decay motion, hole and electron mobilities of poly(9,9‐di‐n‐octylfluorene‐alt‐benzothiadiazole) (F8BT) thin film are evaluated as 1.3 × 10−4 cm2 (V s)−1 and 3.2 × 10−5 cm2 (V s)−1, respectively. Mobility anisotropy is also visualized by using round‐shaped electrode as the source electrode, and the difference of mobility anisotropy for hole and electron of F8BT is clearly identified. [ABSTRACT FROM AUTHOR]

A fundamental understanding of N2 and O2 plasma-induced damage on AlGaN surface is needed in order not to severely degrade electrical characteristics and in order to intelligently achieve the normally-off operation of AlGaN/GaN-based electronic devices. A difference between the damage characteristics of Al0.24Ga0.76N thin film surfaces irradiated with N2 and O2 plasmas is reported, from the perspective of impact of ultraviolet (UV) photons emitted from the plasmas. With the lengthening irradiation time, N2 plasma irradiation introduced a large degree of nitrogen deficiency under the influence of near-UV photons with energies of 3.68 and 3.93 eV larger than the AlGaN band-gap energy, compared to O2 plasma irradiation without the emission of near-UV photons. In a short irradiation time, O2 plasma irradiation introduced a larger degree of nitrogen deficiency. With increasing gas pressure, O2 plasma-induced damage on the surface was more enhanced than N2 plasma-induced damage. The degree of aluminum deficiency was more enhanced than that of gallium deficiency, the amount of oxides incorporated into the surface was suppressed, and the etch-pit density comparable to the dislocation density was introduced on the surface. These findings can be attributed to the impacts of vacuum ultraviolet photons and energetic O+ ions from the O2 plasma. [ABSTRACT FROM AUTHOR]

We evaluate the potential of three-dimensional (3D) thin-film silicon solar cells in the superstrate configuration deposited on hexagonally ordered arrays of ZnO nanocolumns (NCs). These nanostructures are prepared by hydrothermal growth, which is an effective and versatile method to obtain ZnO NCs of high optical and electrical quality at low temperature. For the periods P investigated, varied between 0.9 and 1.4 μm, 3D solar cells based on hydrogenated amorphous silicon (a-Si:H) exhibit a photocurrent ( JSC) boost in the red wavelength range as compared to flat cells; this JSC gain (by more than 1.5 mA cm−2 for P = 0.9 μm) is explained mostly by the increased effective optical thickness of the absorber layer grown on the vertical walls of the NCs. Combining this 3D concept with randomly textured interfaces, rigorous 3D optical simulations based on the finite element method predict that photocurrents significantly higher than those obtained with state-of-the-art substrates (up to 20 mA cm−2) are within reach, if the experimental obstacles specific for 3D design are overcome. [ABSTRACT FROM AUTHOR]

In this work, (0-10 nm) Zn/100 nm ZnO:Ga ultrathin films are deposited on glass substrate at room temperature by magnetron sputtering, with a post-rapid thermal annealing (RTA) at 500 °C for 1 min, which causes a dramatic improvement in carrier concentration due to elimination of Zn-vacancy defects. Depositing different Zn thickness, only 8 nm Zn/100 nm GZO thin film exhibits the highest carrier concentration of 1.02 × 1021 cm−3 and the lowest resistivity of 4 .0 × 10−4 Ω cm. Higher electronic concentration shifts the zero-crossover of the real permittivity below 1.3 μm, which confirms the metal-like optical properties in the near-infrared (NIR) range. Optical losses in these annealed Zn/GZO films are four times smaller than conventional Ag films in the NIR. The average transmittances of all the annealed GZO thin films were above 84% in the visible range. The GZO ultrathin film deposited by this method is a promising low-loss alternative material to conventional metals for plasmonic devices operating in the NIR. [ABSTRACT FROM AUTHOR]

The sputtered-Zn(O,S) and -CdS films were prepared as a buffer layer in CuInSe2 (CIS) in the bottom cell of a Cu(In,Ga)Se2 (CIGS)-tandem-structured solar cell. We characterized the thermal stability and long wavelength response of the CIS solar cell. The thermal stability of CIS solar cell is tested in increasing annealing temperature up to 500 °C in a vacuum for 60 min. The optical response of CIS solar cell was measured by using long-wavelength pass filter to verify availability as a bottom cell. The power conversion efficiency (PCE) of the sputtered-Zn(O,S)/CIS cell showed a slight drop from 9.73% as-fabricated to 9.61% after 60 min of annealing at 300 °C, whereas the 7.97% as-fabricated PCE of the sputtered-CdS/CIS cell fully deteriorated above 300 °C at 60 min of annealing. The PCE of as-fabricated-Zn(O,S)/CIS was 5.46% by using the selective 715 nm long-pass filter. This value remains almost unchanged after post-annealing, whereas the 4.36% PCE of as-fabricated-CdS/CIS solar cell by using the 715 nm long-pass filter continuously dropped after 60 min of 300 °C annealing. The high-temperature-stability of the Zn(O,S) buffer was attributed to the smaller diffusivity of Zn atoms than that of Cd atoms. [ABSTRACT FROM AUTHOR]

The interface formation between epitaxial CuInSe2(112) films and ZnO deposited by metal-organic MBE is investigated by photoelectron spectroscopy. Reaction of diethyl-zinc with CuInSe2 leads to the formation of an intrinsic ZnSe layer and copper depletion of the interface. This is associated with Zn doping of the chalcopyrite surface and a Fermi-level shift toward the conduction band. The implications on the band alignment are discussed. [ABSTRACT FROM AUTHOR]

Indium sulfide thin films were successfully deposited on soda lime glass substrates by modulated flux deposition (MFD) at significantly lower substrate temperatures than in previous experiments. The influence of both experimental parameters sulfur source temperature ( TS) and substrate temperature ( T) on the optical, structural, and chemical properties were studied. Amorphous indium sulfide layers were obtained at T = 100 °C and crystallized as β-In2S3 for T ≥ 150 °C. Quite high values were required for the TS parameter in order to ensure the formation of transparent β-In2S3 thin films. No other polycrystalline phases were detected. Direct optical bandgaps of 2.58 eV (amorphous In2S3) and 2.73 eV (β-In2S3) were estimated for film thicknesses of around 100 nm. [ABSTRACT FROM AUTHOR]

Transition metal (TM)‐doped amorphous gallium oxide (a‐GO:TMx) is studied as an inorganic thin‐film phosphor. Cr is selected as an emission center based on preliminary screening. The most intense red photoluminescence (PL) with a broad emission band of 620–800 nm from the a‐GO:Crx films deposited at room temperature is attained by optimizing the Cr concentration (x = 0.001) and the oxygen partial pressure (PO2 = 10 Pa) during the film growth. Post‐deposition thermal annealing at 400 °C in O2, which is lower than the crystallization temperature, improves internal quantum efficiency (IQE) of PL to 0.3%. Crystallized films by 800 °C annealing further improves the IQE to 20%. The improvement of PL by crystallization is commonly observed for conventional inorganic phosphors, but opposite to that of previously reported rare‐earth (RE)‐doped a‐GO:REx thin‐film phosphors. It is explained by different solubility of Cr and RE in the β‐Ga2O3 host. Transition metal‐doped amorphous oxide semiconductor thin‐film phosphors are realized based on ultra‐wide bandgap amorphous gallium oxide doped with chromium ion. The thin films emit red light derived from the emission center of Cr3+ even deposited at room temperature on glass. [ABSTRACT FROM AUTHOR]

Multi‐color inorganic thin‐film phosphors are deposited at room temperature on glass substrates using ultra‐wide bandgap amorphous gallium oxide (a‐GO) as a host material. All of the a‐GO films doped with four kinds of rare‐earth ions (a‐GO:REx) emit visible light, originating from the RE ions, by 238–257 nm ultraviolet light excitation; that is, blue & red emission from RE = Pr3+, red from Sm3+, green from Tb3+, and blue and yellow from Dy3+. The a‐GO:Prx and a‐GO:Tbx films emit bright light clearly visible by human eyes. Although the internal quantum efficiencies of unannealed a‐GO:Pr0.02 and a‐GO:Tb0.02 films are 0.2 and 1.8%, respectively, those are improved to 2.4 and 3.8 %, respectively, by post‐deposition thermal annealing in O2 at 400 °C through desorption of weakly‐bonded oxygen and structural relaxation. On the other hand, the annealing temperature to improve photoluminescence is limited by crystallization (onset temperatures 400–500 °C). Multi‐color light‐emitting amorphous oxide semiconductor thin films using ultra‐wide bandgap amorphous gallium oxide doped with rare earth ions are fabricated at room temperature on glass. The thin films emit red, blue/red, blue/yellow, and green lights originating from the emission centers of Pr3+, Sm3+, Eu3+, Tb3+, and Dy3+, which will lead to amorphous oxide semiconductor‐based self‐emitting devices. [ABSTRACT FROM AUTHOR]

Operational stability of FTO/CdS/Sb2S1.08Se1.92/C‐Ag thin film solar cells under solar radiation is presented. These solar cells are produced on fluorine‐doped SnO2 (FTO) by thermal evaporation of Sb2S3 and Sb2Se3 powders. Thin film of Sb2S1.08Se1.92 (300 nm) shows a bandgap of 1.45 eV. Its electrical conductivity is 10−7 Ω−1 cm−1 (dark) and 10−5 Ω−1 cm−1 under illumination. Thin film of CdS (120 nm) for the solar cell is obtained on FTO by chemical deposition. Antimony chalcogenide film is deposited on FTO/CdS substrates maintained at 425 °C via thermal evaporation from a mixture of Sb2S3 and Sb2Se3 powders. Subsequently, graphite paint and silver paint electrodes of area 0.49–0.64 cm2 are applied on it. Efficiency of conversion (η) is 5.9 % for the best solar cell and 5.6% on an average for eight cells. Open circuit voltage (Voc) of the cell is 0.453 V; short circuit current density (Jsc), 24.7 mA cm−2; and fill factor, 0.53. For solar cells placed under the sun over 5 days in the exterior with exposure of 24 kWh m−2, η dropped to 5%. Under 30 suns, Voc of 0.54 V and Jsc of 130 mA cm−2 are recorded. The cells remained functional. Thin film solar cells of FTO/CdS/Sb2S1.08Se1.92/C‐Ag with absorber thicknesses of 280–320 nm show good operational stability under the sun. Cells are of conversion efficiency, 5.9% with open circuit voltage of 0.453 V and short circuit current density, 24.7 mA cm−2. Under 30 suns, Voc is 0.54 V and Jsc, 130 mA cm−2. [ABSTRACT FROM AUTHOR]

Thermal annealing of SrTiO3 substrates is used in a wide range of applications, including films and nanoparticle growth, electronic devices, catalysis, and photocatalysis. To predict and control reaction kinetics during high temperature treatments, it is essential to understand dynamics in real time. For this purpose, in‐situ electron microscopy techniques are increasingly used, as structural changes can be monitored at the nanoscale. Herein, the authors report on the surface evolution of the (110) and (001) surfaces of SrTiO3 nanocuboids observed in‐situ during thermal treatment at 800 °C, using aberration corrected high‐resolution transmission electron microscopy. By establishing a threshold for the cumulative electron dose, below which only temperature induced growth occurs, the authors observe the formation of epitaxial, faceted TiO islands, in agreement with previously reported results on the thermal treatment of (001) surfaces of SrTiO3 in reducing environments. When surface evolution is a consequence of the combined effects of electron beam damage and temperature‐induced growth, structural modification of the cuboids is highly dynamic. In this case formation of faceted islands occurs rapidly in conjunction with sublimation of the cuboids at considerably larger speeds than in the case of thermal treatment. This work investigates thermal annealing of SrTiO3 nanocuboids by in‐situ aberration corrected high‐resolution transmission electron microscopy (HRTEM). Below a fixed cumulative electron dose, in a temperature‐induced growth regime, the authors observe the formation of epitaxial, well‐faceted TiO islands. The combined effect of electron beam damage and temperature‐induced growth induces highly dynamical structural modification of the cuboids, including the formation of nanoparticles. [ABSTRACT FROM AUTHOR]

The effect of thermal annealing on the luminescence of wurtzite ZnMgO alloys in the films and ceramics produced by solid state reaction route is investigated. Formation of hexagonal ZnMgO phase is proved by X‐ray diffraction, micro‐Raman, photoluminescence (PL), and PL excitation methods. Mg starts incorporating into ZnO lattice at 700 °C, and its content increases with the increase of the annealing temperature up to 1000 °C. Nevertheless, in the PL spectra of the films annealed in air at 1000 °C, excitonic and defect‐related emissions from residual ZnO phase dominate, while those from the ZnMgO alloy are weak. The annealing in Zn vapor results in even weaker ZnMgO PL. In ceramics sintered in the air at 1000 °C, the PL from wurtzite ZnMgO phase is found to be strongly supressed on the surface and bright in the depth of a pellet. The gettering of Na, K, and Ca residual impurities at the surface of the samples under annealing is proved by Secondary ion mass spectrometry. It is proposed that degradation of ZnMgO PL in the near surface region is caused mainly by intense thermal decomposition of wurtzite ZnMgO phase accompanied by generation of non‐radiative defects. High‐temperature solid state reaction is used to prepare ZnMgO alloyed films and ceramics. Wurtzite Zn‐rich ZnMgO, cubic Mg‐rich ZnMgO, and ZnO phases are revealed. Wurtzite ZnMgO alloy starts forming at 700 °C. At the surface, intensity of ZnMgO exciton photoluminescence is much lower than that of ZnO. Thermal decomposition of ZnMgO is supposed to be more pronounced than that of ZnO. [ABSTRACT FROM AUTHOR]