| Summary: | 碩士 === 國立成功大學 === 化學工程學系碩博士班 === 93 === In this study, electroless plating (EP) method was employed to deposit palladium film on doped epitaxial Al0.3Ga0.7As and GaN
films for fabrication of palladium Schottky diodes as hydrogen
sensors. The perfectness of Schottky interface, I-V rectifying
properties, and hydrogen sensing performances were investigated.
The hydrogen adsorption mechanisms on the EP diodes were also
studied. Moreover, the sensing performances of EP were compared
with those of TE.
From the experimental results of EP Pd/Al0.3Ga0.7As Schottky
diode, it reveals that the Pd-Al0.3Ga0.7As Schottky interfacial
quality is quite good with less thermal damage. This diode exhibits the better I-V rectifying properties with higher turn-on voltage and lower reverse leakage currents than the TE one. Based on the thermionic emission model, the Schottky barrier height (SBH) of the EP diode is 998 meV and its ideality factor is closed to unity. For hydrogen-sensing performances, the EP diode exhibits the lowest detection limit which is less than 100 ppm H2/air, and detection range is from 100 pm to 1 % H2/air. In addition, the relative saturation sensitivity even reaches 3.61 at 1% H2/air. For transient detections, the response rate is extremely fast and it takes within 1 minute for response and recovery. However, the operating temperature regime is over 303 ~ 343 K limited to low band gap of Al0.3Ga0.7As substrate.
From the experimental results of EP Pd/GaN Schottky diode, it
reveals that the studied EP diode exhibits better I-V rectifying
properties than TE one. At 303 K, the EP diode exhibits the lowest detection limit which is less than 50 ppm H2/air, and at hydrogen concentration of 1 % H2/air, the relative saturation sensitivity reaches 2.9�e105. However, due to the high band gap of GaN substrate, the device can be operated over a wide temperature region of 303 ~ 523 K.
For hydrogen transient detections by the EP Pd/GaN diode, the
response rate can be promoted by increasing either hydrogen
concentration or operating temperature. It takes only 30 seconds
for response and 10 seconds for recovery. However, at above 423 K, the response is retarded due to the formation of OH and H2O
species. More interesting, a two-stage transient response is
observed at 423 K, which is verified due to the oxygen adsorption of the are GaN surface via porous Pd gate.
|
|---|
