L. W. Ji

Ultraviolet ZnO Nanorod Photosensors

This study fabricates and characterizes ultraviolet (UV) photosensors with ZnO nanorods (NRs). The NR arrays were selectively grown in the gap between interdigitated (IDT) electrodes of devices using hydrothermal solution processes and a lithography-based technique. Compared with a conventional ZnO photosensor without NRs, the proposed UV NR photosensors have much higher photoresponse in the UV region. Additionally, the photoconductive gain of an NR photosensor increased as UV illumination time increased; it varied at 34.45-5.32 x 10(2) under illumination by 18.28 mW/cm(2) optical power. Consequently, the substantial photoconductive gain can be attributed to high surface-to-volume ratio of ZnO NRs. The high density of hole-trap states on NR surfaces lead to a persistent photoconductivity (PPC) state, promoting the transport of carriers through devices.

TiO2-Based Thin Film Transistors with Amorphous and Anatase Channel Layer

In this study, TiO 2 films were deposited on FTO (fluorine-doped tin oxide)/glass substrate by radio frequency magnetron sputtering. Amorphous and anatase structure of TiO 2 were achieved without and with thermal process, respectively. Further, TiO 2 -based thin-film transistors (TFTs) with different structure were fabricated. After the electrical characteristics measurement, it was found that the amorphous TiO 2 TFTs can be operated in the enhancement mode with a threshold voltage of 3.8 V. It was also found that the field-effect mobility and on/off current of the TiO 2 TFT with amorphous channel layer were 0.087 cm 2 V ―1 s ―1 and 10 3 , respectively. On the other hand, the TiO 2 TFTs with anatase structure were also tested. It was found that the anatase TiO 2 TFTs have the lower threshold voltage of 2.3 V than amorphous one. Besides, it was also found that the field effect mobility and on/off current ratio of the anatase TiO 2 TFTs were both increased to 10.7 cm 2 V ―1 s ―1 and 10 4 , respectively. In other words, the performance of TiO 2 TFTs was related to the structure of the channel layer.

UV Enhanced Field Emission Performance of Mg-Doped ZnO Nanorods

Vertical Mg-ZnO nanorods were synthesized on glass substrates using a low-temperature hydrothermal method. The field emission performance of Mg-ZnO nanorods was greatly enhanced by UV light illumination. It was found that the Mg-ZnO nanorods grown at 80 °C were structurally uniform and well oriented with pure wurtzite structure. Mg-ZnO nanorod exhibited turn-on fields was 2.27 V/μm, and field enhancement factors (β) was 2212. UV illumination of the Mg-ZnO nanorod reduced the turn-on electrical field from 2.27 to 1.97 V/μm and enhanced the β from 2212 and 4136.

Noise Properties of Mg-Doped ZnO Nanorods Visible-Blind Photosensors

In this investigation, Mg-doped ZnO nanorods were synthesized successfully on a glass substrate at 80 °C by hydrothermal method. The average length and diameter of the Mg-ZnO nanorods were 609 nm and approximately 50 nm, respectively. The X-ray diffraction spectrum showed the Mg-ZnO nanorods had a wurtzite hexagonal phase. The Mg-doped ZnO nanorods are found to be single crystals grown along the c-axis. The photosensors showed good stability properties in ultraviolet (UV) illumination. The resulting Mg-doped ZnO nanorods have excellent potential for application in a UV photodetector (PD) because of the Mg-doped ZnO nanorods UV PD has a high UV-to-visible ratio, fast rise/fall time. Furthermore, the dynamic response of the Mg-doped ZnO nanorods PD with Au electrodes was stable and reproducible with an on/off current contrast ratio of approximately 4 × 103. The ultraviolet-to-visible rejection ratio of the sample is approximately 400 when biased at 1 V, and the fabricated UV PD is visible-blind with a sharp cutoff at 350 nm. The low-frequency noise spectra obtained from the UV PD were caused purely by the 1/f noise. The noise-equivalent power and normalized detectivity (D*) of the Mg-ZnO nanorod PD were 0.335 × 10-9 W and 1.49 × 108cm · Hz0.5 · W-1, respectively.

Effect of Oxygen Plasma Treatment on Characteristics of TiO

In this study, titanium dioxide (TiO2) films were prepared on Corning glass substrates by radio frequency (RF) magnetron sputtering and treated with different O2 plasma conditions, and then were used to fabricate metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors (PDs). The effects of the changes on TiO2 films were investigated by using field-emission scanning electron microscope (FE-SEM), photoluminescence (PL) system and four-point probe measurement. With a 360-nm illumination and 5 V applied bias, it was found that the responsivities of the fabricated TiO2 PDs with 0, 1, 2, and 3 min O2 plasma treatment were 36, 144, 153, and 53 A/W, respectively.

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In this research, applications of different TiO2 electrode structures on Dye-Sensitized Solar Cell were investigated. The different TiO2 electrode structures include: (1) synthesis of TiO2 nano-particles and TiO2 film electrode by sol-gel and spin-coating method; (2) fabrication of the TiO2 film electrode by RF Sputtering; (3) fabrication of the rod TiO2 electrode by photo lithography. X-ray diffraction patterns show that the best sintering temperature of nano-TiO2 thin film is 500oC, at which TiO2 anatase phase forms best and the smallest particle-size (8-10 nm) can be obtained. Ultraviolet-visible absorption spectra reveal that the rod TiO2 electrode with TCPP sensitizer adsorbed on has the best optical absorption from 400 nm to 700 nm. The results of current-voltage analyses reveal that the solar cell with rod TiO2 electrode has higher conversion efficiency than the others. This result also provides clear evidence for the contact area between TiO2 electrode and TCPP sensitizer plays an important role on the efficiency of dye-sensitized solar cell.

Photodetectors

In this study, the aqueous solution method was employed to synthesize one-dimensional well-aligned ZnO nano-array on ITO glass substrate. We can find that the dimension of ZnO nanorod will changes with different growth temperature. X-ray diffraction patterns show that the nanorods are high-quality crystals growing along [001] direction with a high consistent orientation perpendicular to the substrate while the growth temperature is equal to 80. SEM images show that the average diameters of ZnO nanorods are about 60-90 nm by changing growth temperature. The smallest diameter of ZnO nanorods is observed while the growth temperature is equal to 75 degc. The UV/Vis spectra analyses show the absorption peaks appear at 330 nm, 370 nm and 390 nm while growth temperature increases from 65 degc to 85 degc.

Study of Different TiO2 Electrode Structures on Dye-Sensitized Solar Cell

The scope of the special issue is as follows. Nanomaterials which provide one of the greatest potentials for improving performance and extended capabilities of products in a number of industrial sectors are a new class of materials, having dimensions in the 1~100?nm range. Nanostructures can be divided into zero-dimensional, one-dimensional, and two-dimensional based on their shapes. The recent emphasis in the nanomaterials research is put on 1D nanostructures at the expense of 0D and 2D ones, perhaps due to the intriguing possibility of using them in a majority of short-term future applications. The most successful examples are seen in the microelectronics, where “smaller” has always meant a greater performance ever since the invention of transistors: for example, higher density of integration, faster response, lower cost, and less power consumption. In recent years, applications of advanced nanomaterials on microelectronic and photonic devices have been a highly developing field, due to the flexibility and light weight for daily use, which has the potential to be deployable. This special issue selects many papers about advanced nanomaterials on microelectronic and photonic devices topics. It enables interdisciplinary collaboration between science and engineering technologists in the academic and industrial fields

Growth Of ZnO Nanorods by Hydrotherothermal Method Under Different Temperatures

This study demonstrates that anatase TiO2 thin films were grown on Corning glass substrates by radio frequency magnetron sputtering and were then used to fabricate metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors (PDs) with different contact electrodes (Ag or Au). With a 320-nm illumination and 5 V applied bias, the responsivities for the Ag/TiO2/Ag and Au/TiO2/Au MSM PDs were 4.31 and 16.6 A/W, respectively. Additionally, the photoconductive gain and Schottky barrier height at the Ag/TiO2 and Au/TiO2 interfaces were also discussed in the investigation.

Applications of advanced nanomaterials to microelectronic and photonic devices

Downloa Erratum: ZnO Metal-Semiconductor-Metal Ultraviolet Photodiodes with Au Contacts [J. Electrochem. Soc., 154, H26 (2007)] S. J. Young, L. W. Ji, S. J. Chang, and X. L. Du Institute of Microelectronics and Department of Electrical Engineering, National Cheng Kung University, Tainan 70101, Taiwan Institute of Electro-Optical and Material Science, National Formosa University, Yunlin 632, Taiwan Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China