本研究以無電鍍法分別在砷化鋁鎵與氮化鎵兩種摻雜磊晶膜之基材上沈積鈀膜，以製備鈀蕭特基二極體作為氫氣感測器。文中探討此兩種元件之界面品質、電性整流特性、氫氣檢測表現與氫氣吸附機制之分析，並與傳統蒸鍍法之元件來作比較。

　　由無電鍍鈀/砷化鋁鎵蕭特基二極體之實驗結果顯示，以無電鍍法製備之鈀-砷化鋁鎵蕭特基界面並無熱破壞之現象。在I-V電性上，此二極體擁有高啟動電壓與低反向漏電流，其電性整流特性優於蒸鍍元件。以熱游離模式分析，其蕭特基能障值可高達 998 meV，且理想常數值接近1。在氫氣感測方面，此元件於343 K下，偵檢極限達到100 ppm以下，偵檢範圍為100 ppm ~ 1 %，相對飽和靈敏度最高可達3.61，且其響應迅速，響應時間與回復時間皆在1分鐘內，但受限於砷化鋁鎵基材之低能隙值，故僅適用於303 ~ 343 K之操作溫度範圍。

　　在無電鍍鈀/氮化鎵蕭特基二極體之研究中發現，此元件之電性整流特性相較於蒸鍍元件更佳。在氫氣感測方面，303 K時，偵檢極限達到50 ppm以下，而當氫氣濃度為1 %時，其相對飽和靈敏度更可高達2.9105。此元件因氮化鎵基材之高能隙值，故感測溫度範圍較廣，可適用於303 ~ 523 K間。

　　在氫氣暫態響應方面，提高操作溫度與氫氣濃度可增進響應速率，其響應時間僅需30秒且回復時間僅需10秒。但在423 K以上，由於鈀膜表面有OH與H2O之生成反應，而抑制其響應速率，甚至使I-t圖中出現兩段暫態響應(two-stage transient response)之現象，實驗中並證實，此現象係因無電鍍鈀膜不緻密而使氧氣吸附於裸露之氮化鎵基材所導致。

　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105. 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.

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