Ya-Hui Chen

Effects of Na content on the luminescence behavior, conduction type, and crystal structure of Na-doped ZnO films

This study investigates the effect of Na content on the structural, optical, and electrical properties of sol-gel Na-doped ZnO films using x-ray diffraction, photoluminescence, and conductivity measurements. It is shown that a p-type conversion of the Na-doped ZnO film might be due to a combined effect of the increased substitutional-Na density and the decreased oxygen-vacancy (VO) density. However, excess Na incorporation into ZnO shows an ambiguous carrier type due to the increase in the donorlike VO density. These results indicate that compensation effects limit the hole concentration in the Na-doped ZnO films. In addition, when more Na is substituted into the ZnO system, the difference in the ionic radii of Zn2+ and Na+ starts playing an increasingly important role, causing the presence of tensile stress in the Na-doped ZnO film.

Effects of Li content on the structural, optical, and electrical properties of LiZnMgO films

This study investigates the effect of Li content on the structural, optical, and electrical properties of sol-gel LiZnMgO films by x-ray diffraction, scanning electron microscopy, photoluminescence, and conductivity measurements. A dependence of crystallite size and conduction type upon Li content has been found. The abnormal shift of the (002) diffraction peak position determined from x-ray diffraction measurements and conduction type determined by Hall effect measurements are closely related to the defects/different defect types. It is shown that n-type conversion of LiZnMgO films is a result of the increase in the donor density based on the change in stoichiometry.

Effects of oxygen deficiency in the sol–gel ZrOx film on the electrical properties of Au/ZrOx/n-type Si/In devices

The ZrOx permittivity and leakage currents through Au/ZrOx/n-type Si/In structures are studied. The electrical conduction investigations suggest that the leakage behaviour is governed by the Schottky emission. The leakage current strongly depends on the O/Zr atomic concentration ratio of ZrOx films and an increase in the number of oxygen-vacancy-related defects may result in a decrease in the ZrOx permittivity, enhancing the leakage conduction of the Au/ZrOx/n-type Si/In devices. In addition, the discrepancy in the ZrOx permittivity determined in the current density-electric field and capacitance–voltage characteristics is attributed to the formation of the intermediate ZrSixOy layer.

An optomechatronic curvature measurement array based on fiber Bragg gratings

This study investigated an optomechatronic array-integrated signal processing module and a human–machine interface based on fiber Bragg grating sensing elements embedded in an elastic support matrix that involves using a self-located electromagnetic mechanism for curvature sensing and solid contour reconstruction. Using bilinear interpolation and average calculation methods, the smooth and accurate surface contours of convex and concave lenses are reconstructed in real-time. The elastic supporting optical sensing array is self-balanced to reduce operational errors. Compared with our previous single-head sensor, the sensitivity of the proposed array is improved by more than 15%. In the curvature range from −20.15 to +27.09 m−1, the sensitivities are 3.53 pm m for the convex measurement and 2.15 pm m for the concave measurement with an error rate below 8.89%. The curvature resolutions are 0.283 and 0.465 m−1 for convex and concave lenses, respectively. This array could be applied in the curvature measurement of solar collectors to monitor energy conversion efficiency or could be used to monitor the wafer-level thin-film fabrication process.

Evaluating solar microsensors packaged with MEMS covers for improving light tracking efficiency

A novel solar microsensor with microelectromechanical system (MEMS)-based packaging for improving solar tracking efficiency was proposed and a functional solar power sensing array was also developed. Solar energy as a renewable energy source in the world is the most important issue. The microsensor with different shapes of masks as light inlet was fabricated on silicon wafers to provide variable attenuation effect of the sunlight. To detect light incident elevation and azimuth accurately, a circuit module for a maximum power tracking system is developed conducting the automatic tracking function by feedback control technique. The best angle related sensitivity for the microsensors covered with inside-shrunk and inside-extended windows are 128.6 Ω/degree and 150.2 Ω/degree, respectively. The collimated process of the incident solar power by developed solar microsensor keeps maximum solar energy collection with the best long-term efficiency in photovoltaic energy conversion. The microsensor to sense collimated solar intensity is designed to promote solar energy collection efficiency and an intelligent bi-axes dynamic solar tracking device will develop in the future.

Effects of H2O2 treatment on the temperature-dependent behavior of carrier transport and the optoelectronic properties for sol–gel grown MoS2/Si nanowire/Si devices

The effects of H2O2 treatment on the temperature-dependent behavior of carrier transport and the optoelectronic properties of a MoS2/Si nanowire (SiNW)/n-Si device are studied. The MoS2 thin films are prepared using the sol–gel method. The thermionic emission–diffusion model is the dominant process in the MoS2/SiNW/n-Si device when there is no H2O2 treatment. However, carrier transport in MoS2/SiNW/n-Si devices that are subject to H2O2 treatment is dominated by thermionic emission, so it demonstrates reliable rectification. Passivation of the SiNW surface increases the responsivity to solar irradiation. There is a low trap density at the MoS2/SiNW interfaces so the increase in photocurrent density for the MoS2/SiNW/n-Si device that is subject to H2O2 treatment is due to greater internal power conversion efficiency. The photo-response results for MoS2/SiNW/n-Si devices that are subject to (are not subject to) H2O2 treatment confirm that the decay in the photocurrent is due to the dominance of long-lifetime (short-lifetime) charge trapping. MoS2/SiNW/n-Si devices that are subject to H2O2 treatment exhibit reliable responsivity to solar irradiation.

A metal-oxide doped SnO 2 -based microsensor for measuring H 2 S concentration

This study focused on developing a hydrogen sulfide (H2S) gas microsensor using nanometal oxides of copper oxide-doped tin dioxide. Electrospinning and high-temperature calcination were adopted to fabricate a high-surface area and porous hollow nanofibrous gas sensing film. The film that served as a sensing mechanism on the heterojunction of the microsensor exhibited a high resistance change rate; therefore, the gas-sensing sensitivity was effectively improved. The ceramic ring-based sensor was coated with a nanosensing film, on which gold sensing electrodes were formed through sputtering by using a shadow mask. Thus, a sensing mechanism was completed that allowed the absorption of the gases to be tested. A heating wire was designed in the chamber of the ceramic ring to control the local temperature of the sensing structure. The response level and repeatability of the device to the gases were effectively enhanced. Results indicated that the microsensor could sense H2S at a concentration of 1–100 ppm, had a sensitivity of 0.39 MΩ/ppm, and possessed response and restoration times of 5 ± 0.12 s and 12 ± 0.24 s, respectively.