Tzong-Bin Wang

Bio: Tzong-Bin Wang is an academic researcher from National Cheng Kung University. The author has contributed to research in topics: Schottky barrier & Schottky diode. The author has an hindex of 7, co-authored 11 publications receiving 221 citations.

Comparison of hydrogen sensing characteristics for Pd/GaN and Pd/Al0.3Ga0.7As Schottky diodes

Abstract: The hydrogen sensing characteristics of Pd/GaN and Pd/Al0.3Ga0.7As Schottky diodes are systematically studied and compared over wide hydrogen concentration and temperature ranges. Experimentally, upon exposing to hydrogen-containing gases, both of the studied Schottky-type hydrogen sensors can be operated under bi-polarity applied voltages attributed to the substantial increases of forward- and reverse-biased currents with increasing the hydrogen concentration. The Pd/GaN Schottky diode can be operated under higher temperature with larger Schottky barrier height modulation than that of Pd/Al0.3Ga0.7As. According to the van’t Hoff equation, the hydrogen adsorption heat values are −18.24 and −10.36 kJ mol−1 for the Pd/GaN and Pd/Al0.3Ga0.7As Schottky diodes, respectively. Experimentally, the Pd/Al0.3Ga0.7As and Pd/GaN Schottky diodes manifest faster adsorption and desorption responses at higher temperature (≥400 K).

Characteristics of In/sub 0.425/Al/sub 0.575/As-InxGa/sub 1-x/As metamorphic HEMTs with pseudomorphic and symmetrically graded channels

Abstract: In/sub 0.425/Al/sub 0.575/As-In/sub x/Ga/sub 1-x/As metamorphic high electron mobility transistors (MHEMTs) with two different channel designs, grown by molecular beam epitaxy (MBE) system, have been successfully investigated. Comprehensive dc and high-frequency characteristics, including the extrinsic transconductance, current driving capability, device linearity, pinch-off property, gate-voltage swing, breakdown performance, unity-gain cutoff frequency, max. oscillation frequency, output power, and power gain, etc., have been characterized and compared. In addition, complete parametric information of the small-signal device model has also been extracted and discussed for the pseudomorphic channel MHEMT (PC-MHEMT) and the V-shaped symmetrically graded channel MHEMT (SGC-MHEMT), respectively.

High breakdown characteristic /spl delta/-doped InGaP/InGaAs/AlGaAs tunneling real-space transfer HEMT

Abstract: A novel /spl delta/-doped InGaP/InGaAs/AlGaAs tunneling real-space transfer high-electron mobility transistor (TRST-HEMT) has been successfully fabricated by low-pressure metal organic chemical vapor deposition (LP-MOCVD). Three-terminal N-shaped negative differential resistance (NDR) phenomenon due to the hot electrons real-space transfer (RST) at high electric field is observed. Two-terminal gate-to-drain breakdown voltage is more than 40 V with a leakage current as low as 0.27 mA/mm. High three-terminal on-state breakdown voltage as high as 19.2 V and broad plateau of current valley as high as 15 V are achieved. These characteristics are attributed to the use of high Schottky barrier height, high bandgap of InGaP Schottky layer, /spl delta/-doping, and GaAs subspacer layers. The measured maximum peak-to-valley ratio (PVR) value is 2.7.

High-temperature thermal stability performance in /spl delta/-doped In/sub 0.425/Al/sub 0.575/As--In/sub 0.65/Ga/sub 0.35/As metamorphic HEMT

Abstract: We report, to our knowledge, the best high-temperature characteristics and thermal stability of a novel /spl delta/-doped In/sub 0.425/Al/sub 0.575/As--In/sub 0.65/Ga/sub 0.35/As--GaAs metamorphic high-electron mobility transistor. High-temperature device characteristics, including extrinsic transconductance (g/sub m/), drain saturation current density (I/sub DSS/), on/off-state breakdown voltages (BV/sub on//BV/sub GD/), turn-on voltage (V/sub on/), and the gate-voltage swing have been extensively investigated for the gate dimensions of 0.65/spl times/200 /spl mu/m/sup 2/. The cutoff frequency (f/sub T/) and maximum oscillation frequency (f/sub max/), at 300 K, are 55.4 and 77.5 GHz at V/sub DS/=2 V, respectively. Moreover, the distinguished positive thermal threshold coefficient (/spl part/V/sub th///spl part/T) is superiorly as low as to 0.45 mV/K.

Investigation of Hydrogen-Sensing Characteristics of a Pd/GaN Schottky Diode

Abstract: The hydrogen sensing and response characteristics of a catalytic Pd/GaN metal-semiconductor (MS) Schottky diode are systematically studied in this paper. The current-voltage characteristics, hydrogen detection sensitivity ratios, Schottky barrier height variations, adsorption heat, and transient responses for different hydrogen concentration are measured over wide temperature range. The Pd/GaN Schottky diode reveals a remarkable capability of hydrogen detection at high temperature and relatively wide operating temperature range under bipolarly applied voltages. Experimentally, extremely low hydrogen concentration for 14 ppm H2 in air can be detected. A very high hydrogen detection sensitivity ratio of 12744 and a large Schottky barrier height variation Δφb of 253 meV are obtained when a 9970 ppm H2 in air gas is introduced at 300 K. In addition, according to the van't Hoff equation, the hydrogen adsorption heat value of the studied device is calculated as -18.24 kJ mole. Finally, considerably short response time is found in the studied device.

Improved Hydrogen Monitoring Properties Based on p-NiO/n-SnO2 Heterojunction Composite Nanofibers

Abstract: Here we demonstrate the preparation and improved hydrogen monitoring properties based on p-NiO/n-SnO2 heterojunction composite nanofibers via the electrospinning technique and calcination procedure. NiO/SnO2 heterojuction composite nanofibers were spin-coated on the ceramic tube with a pair of Au electrodes for the detection of hydrogen. Extremely fast response−recovery behavior (∼3s) has been obtained at the operable temperature of 320 °C, based on our gas sensor, with the detection limit of approximate 5 ppm H2. The role of the addition of NiO into the SnO2 nanofibers and the sensing mechanism has also been discussed in this work.

Enhancement of hydrogen monitoring properties based on Pd-SnO2 composite nanofibers

Abstract: A nano-gas sensor based on Pd–SnO2 composite nanofibers is fabricated by electrospinning technique and calcination procedure. The morphology, structure and composition of the as-prepared nanofibers are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), respectively. The nano-gas sensor shows excellent hydrogen sensing properties such as high sensitivity and extremely fast response–recovery behavior (∼9 s) at a lower operation temperature (280 °C). The detection limit of approximately 4.5 ppm H2 is demonstrated. The function of adding Pd into the SnO2 nanofibers and the sensing mechanism have also been discussed in this work.

Advances of SiC-based MOS capacitor hydrogen sensors for harsh environment applications

Abstract: SiC-based hydrogen sensors have attracted much attention due to applications in harsh environments. In this paper, harsh environment is defined. Characteristics of SiC-based hydrogen sensors for harsh environment applications are reviewed. Various types of SiC-based field effect hydrogen sensor in terms of their respective history, structure, advantages and disadvantages have been discussed. SiC-based MOS capacitor hydrogen sensor will be conferred in detail. The reasons for selecting SiC in fabricating MOS capacitor hydrogen sensor for harsh environment applications are elucidated. Different hydrogen sensing mechanisms depend on the temperatures and the conditions of catalytic metal layer are highlighted. MOS capacitor SiC-based sensors fabricated by previous research groups are listed. Each catalytic electrodes and oxide layers selected have their significant properties. Examples of nanostructured materials that have been used in forming oxide layer are illustrated. The future challenges in terms of material (metal electrodes and oxide layers) properties and surface properties of materials are described. It is concluded that MOS capacitor SiC-based hydrogen sensors promote green technology.

Characteristics of ZnO nanorods-based ammonia gas sensors with a cross-linked configuration

Abstract: Cross-linked ZnO nanorods (NRs)-based ammonia gas sensors have been fabricated and investigated. The influences of interdigitated electrode spacing d and working temperature on ammonia sensing performance are studied. It is found that when the electrode spacing d is reduced, the ammonia sensor response S would be increased due to the configuration transformation of ZnO NRs. The optimal working temperature is about 573 K due to the temperature dependence on reactions of oxygen species. The studied sensor with an electrode spacing d of 2 μm shows a maximum ammonia sensor response S of 81.6 under exposing to a 1000 ppm NH 3 /air gas at 573 K. Also, a lower detection limit of 10 ppm NH 3 /air is achieved. The improved ammonia detecting capability could be attributed to the formation of more cross-linked configurations. The adsorption-time ( τ a ) and desorption-time ( τ b ) constants of the studied sensor with an electrode spacing d of 2 μm, at 573 K, are 74 and 29 s, respectively. Finally, the studied sensor exhibits good gas sensing response and repeatability toward NH 3 gas. Thus, the studied sensor with a cross-linked configuration gives a promise for high-performance ammonia sensing applications.

Advances in Hydrogen, Carbon Dioxide, and Hydrocarbon Gas Sensor Technology Using GaN and ZnO-Based Devices.

Abstract: In this paper, we review our recent results in developing gas sensors for hydrogen using various device structures, including ZnO nanowires and GaN High Electron Mobility Transistors (HEMTs). ZnO nanowires are particularly interesting because they have a large surface area to volume ratio, which will improve sensitivity, and because they operate at low current levels, will have low power requirements in a sensor module. GaN-based devices offer the advantage of the HEMT structure, high temperature operation, and simple integration with existing fabrication technology and sensing systems. Improvements in sensitivity, recoverability, and reliability are presented. Also reported are demonstrations of detection of other gases, including CO2 and C2H4 using functionalized GaN HEMTs. This is critical for the development of lab-on-a-chip type systems and can provide a significant advance towards a market-ready sensor application.