The resistive switching behavior of the solution processed SiOx device was investigated by inserting TiO2 nanoparticles (NPs). Compared to the pristine SiOx device, the TiO2 NPs inserted SiOx (SiOx@TiO2 NPs) device achieves outstanding switching characteristics, namely a higher ratio of SET/RESET, lower operating voltages, improved cycle-to-cycle variability, faster switching speed, and multiple-RESET states. Density functional theory calculation (DFT) and circuit breaker simulation (CB) were used to detail the origin of the outstanding switching characteristic of the SiOx@TiO2 NPs. The improvement in resistive switching is mainly based on the difference in formation/rupture of the conductive path in the SiO2 and SiO2@TiO2 NPs devices. In particular, the reduction of resistance and lower switching voltage of TiO2 NPs control the formation and rupture of the conductive path to achieve more abrupt switching between SET/RESET with higher on/off ratio. This method of combined DFT calculation and CB offers a promising approach for high-performance non-volatile memory applications.

TiO x -based resistive switching devices have recently attracted attention as a promising candidate for next-generation non-volatile memory devices. A number of studies have attempted to increase the structural density of resistive switching devices. The fabrication of a multi-level switching device is a feasible method for increasing the density of the memory cell. Herein, we attempt to obtain a non-volatile multi-level switching memory device that is highly transparent by embedding SiO 2 nanoparticles (NPs) into the TiO x matrix (TiO x @SiO 2 NPs). The fully transparent resistive switching device is fabricated with an ITO/TiO x @SiO 2 NPs/ITO structure on glass substrate, and it shows transmittance over 95% in the visible range. The TiO x @SiO 2 NPs device shows outstanding switching characteristics, such as a high on/off ratio, long retention time, good endurance, and distinguishable multi-level switching. To understand multi-level switching characteristics by adjusting the set voltages, we analyze the switching mechanism in each resistive state. This method represents a promising approach for high-performance non-volatile multi-level memory applications.

The effects of the neutron irradiation treatment on indium-gallium-zinc oxide (IGZO) are investigated as a function of the neutron irradiation time. With an increase in neutron irradiation time, the oxygen vacancies associated the oxygen deficient states increase, and both shallow and deep band edge states below the conduction band also increase. Moreover, the conduction band offset continuously decreases because of the increase in the oxygen vacancies with increasing the neutron irradiation time. In IGZO TFTs with the neutron irradiation time for 10 s, superior device performance demonstrates such as the lower threshold voltage, higher field effect mobility, smaller sub-threshold gate swing, larger on-off current ratio, and improved bias stability, comparing those of other IGZO TFTs.

The key to full understanding of the degradation mechanism of oxide thin film transistors (Ox-TFTs) by gate bias stress is to investigate dynamical changes of the electron trap site at the channel region while a real-time gate bias is applied to the actual thin film transistor (TFT) structure.

The transparent conducting properties of vanadium-doped indium zinc oxide (VIZO) have been investigated as a function of V doping concentration. The VIZO film demonstrated an average transmittance of above 86% in the visible range, and the sheet resistance showed 10.81 Ω/square with a V doping concentration of 0.18%. In order to verify the applicability as a transparent conductor, the figure of merit was obtained to be 2.07 × 10−2 Ω−1. The changes of electrical characteristics could be correlated with the changes of the electronic structure, such as the oxidation state and the band edge defect states below the conduction band. By applying the optimal condition, the VIZO film achieved a high workfunction of 5.16 eV.

This study suggests a sequential ambient annealing process as an excellent post-treatment method to enhance the device performance and stability of W (tungsten) doped InZnO thin film transistors (WIZO-TFTs). Sequential ambient annealing at 250 °C significantly enhanced the device performance and stability of WIZO-TFTs, compared with other post-treatment methods, such as air ambient annealing and vacuum ambient annealing at 250 °C. To understand the enhanced device performance and stability of WIZO-TFT with sequential ambient annealing, we investigate the correlations between device performance and stability and electronic structures, such as band alignment, a feature of the conduction band, and band edge states below the conduction band. The enhanced performance of WIZO-TFTs with sequential ambient annealing is related to the modification of the electronic structure. In addition, the dominant mechanism responsible for the enhanced device performance and stability of WIZO-TFTs is considered to be a change in the shallow-level and deep-level band edge states below the conduction band.

An all-sputtered oxide TFT process combined with simultaneous ultraviolet and thermal (SUT) treatment for consecutive fabrication processes at low temperatures.

We evaluated the change in the chemical structure between dielectrics (AlOx and HfOx) grown by atomic layer deposition (ALD) and oxidized black phosphorus (BP), as a function of air exposure time. Chemical and structural analyses of the oxidized phosphorus species (PxOy) were performed using atomic force microscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, first-principles density functional theory calculations, and the electrical characteristics of field-effect transistors (FETs). Based on the combined experiments and theoretical investigations, we clearly show that oxidized phosphorus species (PxOy, until exposed for 24 h) are significantly decreased (self-reduction) during the ALD of AlOx. In particular, the field effect characteristics of a FET device based on Al2O3/AlOx/oxidized BP improved significantly with enhanced electrical properties, a mobility of ∼253 cm2 V-1 s-1 and an on-off ratio of ∼105, compared to those of HfO2/HfOx/oxidized BP with a mobility of ∼97 cm2 V-1 s-1 and an on-off ratio of ∼103-104. These distinct differences result from a significantly decreased interface trap density (Dit ∼ 1011 cm-2 eV-1) and subthreshold gate swing (SS ∼ 270 mV dec-1) in the BP device caused by the formation of stable energy states at the AlOx/oxidized BP interface, even with BP oxidized by air exposure.

This study employed experimental results and theoretical calculations to investigate Mn-adsorbed g-C3N4 as a potential photocatalyst with high efficiency. Mn was chosen as the incorporating element, because among the 3d transition metals it exhibits the highest binding energy and most suitable band edge positions. The photocatalytic efficiency of Mn-adsorbed g-C3N4 is 3 times higher that of pristine g-C3N4. Although small variations in the phase and surface morphology were observed, which were confirmed to not be the determining factors to improve efficiency. The factors that affect the high photocatalytic efficiency are therefore the electronic structure, optical absorption, and band edge variations after Mn-adsorption. The Mn atoms stably are bonded with N atoms, due to the strong absorption energy and ionic bond. Moreover, reduction of the g-C3N4 band gap after Mn-adsorption results in a red shift of the absorption band edge. The half-filled Mn 3d state introduces impurity states into the forbidden band gap, which will increase the life time of charge carriers. In addition, the up-shifting of band edges of Mn-adsorbed g-C3N4 leads to inhibition of the electron-hole recombination. As a consequence, the photocatalytic efficiency of Mn-adsorbed g-C3N4 is enhanced due to the combination of the aforementioned effects. (C) 2017 Elsevier B.V. All rights reserved.

The changes of the defect states below the conduction band in atomic-layered HfO2 film grown on SiC substrate were examined as a function of the post-nitridation annealing temperature in an NH3 ambient. As the post-nitridation annealing temperature increased up to 600°C, the incorporated nitrogen into the HfO2/SiC interface was gradually increased. The band gap and valence band offset were mostly increased as a function of the post-nitridation annealing temperature and the band alignment of HfO2 films changed. O K-edge absorption features revealed two distinct band edge states below the conduction band edge in HfO2 films, and these defect states were dramatically reduced with increasing of the post-nitridation annealing temperature. The reduction of defect states in HfO2/SiC improved the electrical properties such as the leakage current density, breakdown voltage, and trap charge density in the HfO2 film and interface of HfO2/SiC.

W-doped InZnO (WIZO) thin-film transistors (TFTs) were fabricated by co-sputtering with different W doping concentrations. We varied the W doping concentration to change the device performance and stability of the WIZO TFTs. WIZO TFTs with a W doping concentration of ∼1.1% showed the lowest threshold voltage shift and hysteresis. We correlated the device characteristics with the evolution of the electronic structure, such as band alignment, chemical bonding states, and band edge states. As the W doping concentration increased, the oxygen-deficient bonding states and W suboxidation states decreased, while the conduction-band offset and the incorporation of the WOx electronic structure into the conduction band increased.

The semiconducting properties of Au ion-irradiated ZnO thin films were investigated as a function of ion irradiation dose at room temperature. The Au ion irradiation was conducted with acceleration energy of 130 MeV in the ion dose range from 1 × 1011 to 5 × 1012 ions/cm2. The physical properties showed no change regardless of the Au ion irradiation dose; however, the electrical properties of Au ion-irradiated ZnO thin films changed, depending on the Au ion irradiation dose. The electronic structure drastically changed with the evolution of hybridized molecular orbital structure for the conduction band and band edge states below the conduction band. These remarkable changes in electronic structure correlate with changes in electrical properties, such as carrier concentration and mobility.

자발형성법으로 InP (001) 기판에 성장한 InAs/InAlGaAs 양자점(QDs, quantum dots)의 광학적 특성을 PL (photoluminescence)과 TRPL (time-resolved PL)을 이용하여 분석하였다. InAs 양자점 시료는 single layer InAs/InAlGaAs QDs (QD1)과 7-stacked InAs/InAlGaAs QDs (QD2)를 사용하였다. 저온(10 K)에서 QD1과 QD2 모두 1,320 nm에서 PL 피크가 나타났으며, 온도를 300 K까지 증가하였을 때 각각 178 nm와 264 nm의 적색편이(red-shift)를 보였다. QD1의 PL 소멸시간은 PL 피크인 1,320 nm에서 1.49 ns이고, PL 피크를 중심으로 장파장과 단파장으로 이동하면서 점차 짧아졌다. 그러나 QD2의 PL 소멸시간은 발광파장이 1,130 nm에서 1,600 nm까지 증가할 때 1.83 ns에서 1.22 ns로 점진적으로 짧아졌다. 이러한 QD2의 PL과 TRPL 결과는 평균 양자점의 크기가 InAs/InAlGaAs 층이 증가함에 따라 점차 증가하기 때문으로 single layer인 QD1에 비해 양자점 크기의 변화가 더 크기 때문으로 설명된다. Self-assembled InAs/InAlGaAs quantum dots (QDs) grown on an InP (001) substrate have been investigated by using photoluminescence (PL) and time-resolved PL measurements. The single layer (QD1) and seven stacks (QD2) of InAs/InAlGaAs QDs grown by the conventional S-K growth mode were used. The PL peak at 10 K was 1,320 nm for both QD1 and QD2. As the temperature increases from 10 to 300 K, the PL peaks for QD1 and QD2 were red-shifted in the amount of 178 and 264 nm, respectively. For QD1, the PL decay increased with increasing emission wavelength from 1,216 to 1,320 nm, reaching a maximum decay time of 1.49 ns at 1,320 nm, and then decreased as the emission wavelength was increased further. However, the PL decay time for QD2 decreased continuously from 1.83 to 1.22 ns as the emission wavelength was increased from 1,130 to 1,600 nm, respectively. These PL and TRPL results for QD2 can be explained by the large variation in the QD size with stacking number caused by the phase separation of InAlGaAs.