Jian-Kai Liou

Bio: Jian-Kai Liou is an academic researcher from National Cheng Kung University. The author has contributed to research in topics: Light-emitting diode & Saturation current. The author has an hindex of 11, co-authored 26 publications receiving 343 citations.

On the Ammonia Gas Sensing Performance of a RF Sputtered NiO Thin-Film Sensor

Abstract: An interesting ammonia gas sensor based on a p-type NiO thin film, prepared by a radio frequency sputtering process, is studied and demonstrated. As compared with conventional n-type metal-oxide sensors, the studied device shows comparable and good sensing performance, including a high-sensing response ratio of 289%, a lower response time of 31 s, and a lower recovery time of 78 s, under an introduced 1000 ppm NH3/air gas at 250 °C and 350 °C, respectively. In addition, the studied sensor device exhibits a lower detection limit (<5 ppm NH3/air) at 250 °C. Consequently, based on these advantages and inherent benefits of low cost, chemical stability, and easy fabrication, etc., the studied NiO thin-film sensor shows the promise for high-performance ammonia gas sensing applications.

Study of an electroless plating (EP)-based Pt/AlGaN/GaN Schottky diode-type ammonia sensor

Abstract: An ammonia sensor based on a Pt/AlGaN/GaN Schottky diode, fabricated by the electroless plating (EP) technique, has been studied in this work. The studied sensor device shows a significant sensing response under an extremely low ammonia concentration of 10 ppb NH 3 /air at 115 °C. As exposed to a 1000 ppm NH 3 /air gas, a high sensing response of 16.22 with a response (recovery) time of 8.73 (2.04) min is obtained. Even at room temperature (25 °C), the studied sensor exhibits good ammonia sensing performance with a sensing response of 2.68 at 1000 ppm NH 3 /air and a low detection limit of 1 ppm NH 3 /air. Based on the excellent sensing performance and inherent advantages of low-power consumption and low-temperature operation, the studied sensor device provides the promise for high-performance ammonia sensing applications.

Improved Performance of an InGaN-Based Light-Emitting Diode With a p-GaN/n-GaN Barrier Junction

Abstract: An InGaN-based light-emitting diode with a p-GaN/n-GaN barrier junction is fabricated and investigated. Due to the built-in potential induced by this junction, superior current spreading performance is achieved. In addition, the suppression of the current-crowding phenomenon yields a reduced parasitic effect. Therefore, under an injection current of 20 mA, improved behaviors, including lower turn-on voltage, lower parasitic series resistance, and reduced p-n junction temperature, are achieved. In addition, due to the improved current-spreading ability, longer life-time, driving at medium current injection (60 mA), as well as significantly enhanced electrostatic discharge performance, are obtained.

Improved Light Extraction Efficiency of a High-Power GaN-Based Light-Emitting Diode With a Three-Dimensional-Photonic Crystal (3-D-PhC) Backside Reflector

Abstract: An interesting approach to improving the light extraction efficiency of high-power GaN-based light-emitting diodes (LEDs) by the use of a 3-D-photonic crystal (3-D-PhC) backside reflector is studied. A 3-D-PhC backside reflector is formed by coating a self-assembled SiO2 nanosphere monolayer between the hybrid reflector and backside of a sapphire substrate. The 3-D-PhC structure is used to enhance light scattering. At 350 mA, as compared with a conventional LED (with a hybrid reflector while only without the 3-D-PhC structure), the studied device exhibits 23.6% enhancement in the light output power without the degradation of electrical properties. Therefore, the performance of high-power GaN-based LEDs could be further improved by using a 3-D-PhC backside reflector.

Enhancement of hydrogen sensing performance of a GaN-based Schottky diode with a hydrogen peroxide surface treatment

Abstract: In this work, enhanced hydrogen sensing characteristics of a GaN-based Schottky diode-type sensor with a GaOx layer are studied and demonstrated. A thin GaOx layer inserted in Pd/GaN interface is oxidized by the immersion in an H2O2 solution at room temperature. Experimentally, a significantly high hydrogen sensing response of 1.8 × 105 and a large Schottky barrier height variation ratio of 33.1% are found upon exposure to a 1% H2/air gas at 300 K. In addition, a very low detection limit of 0.1 ppm H2/air at 300 K is obtained. These improved properties could be attributed to the effective dissociation of hydrogen molecules and rougher Pd surface caused by the presence of the GaOx layer. The response (recovery) time constant of 13.3 (23.6) s is obtained upon exposure to a 1% H2/air gas at 300 K. The related hydrogen adsorption analysis of the proposed device is also studied and demonstrated.

Semiconductor Gas Sensors: Materials, Technology, Design, and Application

Abstract: This paper presents an overview of semiconductor materials used in gas sensors, their technology, design, and application. Semiconductor materials include metal oxides, conducting polymers, carbon nanotubes, and 2D materials. Metal oxides are most often the first choice due to their ease of fabrication, low cost, high sensitivity, and stability. Some of their disadvantages are low selectivity and high operating temperature. Conducting polymers have the advantage of a low operating temperature and can detect many organic vapors. They are flexible but affected by humidity. Carbon nanotubes are chemically and mechanically stable and are sensitive towards NO and NH3, but need dopants or modifications to sense other gases. Graphene, transition metal chalcogenides, boron nitride, transition metal carbides/nitrides, metal organic frameworks, and metal oxide nanosheets as 2D materials represent gas-sensing materials of the future, especially in medical devices, such as breath sensing. This overview covers the most used semiconducting materials in gas sensing, their synthesis methods and morphology, especially oxide nanostructures, heterostructures, and 2D materials, as well as sensor technology and design, application in advance electronic circuits and systems, and research challenges from the perspective of emerging technologies.

Review of recent progress of III-nitride nanowire lasers

Abstract: One-dimensional compound semiconductor nanolasers, especially nanowire (NW)-based nanolasers utilizing III-nitride (AlGaInN) materials system, are an emerging and promising area of research. Significant achievements have been made in developing III-nitride NW lasers with emission wavelengths from the deep ultraviolet (UV) to the near-infrared spectral range. The types of lasers under investigation include Fabry-Perot, photonic crystal, plasmonic, ring resonator, microstadium, random, polariton, and two-dimensional distributed feedback lasers. The lasing thresholds vary by several orders of magnitude, which are a direct consequence of differing NW dimensions, quality of the NWs, characteristics of NW cavities, and coupling with the substrate. For electrically injected, such as ultralow-threshold and continuous-wave III-nitride NW lasers that can operate at room temperature, the following obstacles remain: carrier loss mechanisms including defect-related nonradiative surface recombination, electron overflow, and poor hole transport; low radiative recombination efficiency and high surface recombination; poor thermal management; and highly resistive ohmic contacts on the p -layer. These obstacles must be overcome to fully realize the potential of these lasers.

Ultrasensitive and low detection limit of nitrogen dioxide gas sensor based on flower-like ZnO hierarchical nanostructure modified by reduced graphene oxide

Abstract: Hierarchical rGO/ZnO hybrids with a flower-like morphology of ZnO and flexible rGO sheets were synthesized by a facile solution-processed method. The structures and morphologies of the hybrids were investigated by different kinds of techniques, including X-ray diffraction, field-emission electron scanning microscopy, transmission electron microscopy, and energy dispersive spectroscopy. The gas sensing properties of hierarchical rGO/ZnO hybrids toward nitrogen dioxide were studied via a static system. The response of rGO/ZnO hybrids to 50 ppb NO 2 was 12, which was seven times higher than that of pristine ZnO at 100 °C. The limit of detection could be achieved as low as 5 ppb. The enhanced sensor response was attributed to the presence of local p - n heterojunctions between rGO sheets and hierarchical structure of ZnO.

Hydrogen gas sensing properties of MoS2/Si heterojunction

Abstract: Molybdenum disulfide (MoS 2 ) thin films were deposited on (1 0 0) Si substrates using magnetron sputtering technique and MoS 2 /Si heterojunctions were fabricated X-ray diffraction patterns revealed that (0 0 1) crystal orientation is preferable in the films Atomic force microscopy illustrated that the surface of the film is composed of dense nano-level grains The current–voltage characteristics of the heterojunctions were investigated The results showed that the heterojunctions exhibited obvious sensing properties to hydrogen gas (H 2 ) at room temperature (RT) when reverse voltages were applied on the heterojunctions The sensing performance was featured by a high sensitivity, fast response and recovery, as well as good reversibility, and stable steady states The sensing mechanisms were discussed in terms of the energy-band structure of the MoS 2 /Si heterojunction