在本論文中，我們利用低壓有機金屬化學汽相沉積法成長及研製砷化鎵材料系列之異質結構場效電晶體。接著使用硫化銨((NH4)2Sx)溶液進行元件表面之處理，並進一步探討硫化技術對元件特性之影響。在論文中所探討的元件經過硫化處理之後，展現出良好的元件特性，如高崩潰電壓、低漏電流、高線性度及優異的微波特性。更進一步，為了獲得較大的功率增益及頻寬，我們使用深紫外線光罩微影系統來研製具次微米閘極尺寸之場效電晶體。此外，我們也研製了一種具有駝峰式閘極及複合式通道結構之場效電晶體。實驗上，所研製的元件具有良好的直流、微波及高溫操作特性。這些優點顯示元件非常適合應用於高速和高功率電路中。
　　首先，我們探討利用硫化銨溶液在砷化鋁鎵/砷化銦鎵/砷化鎵擬晶性高電子移動率場效電晶體上進行表面鈍化處理，研究其對元件特性所造成的影響，並將其結果與未進行硫化處理之傳統元件做比較。同時，我們完成了次微米閘極元件，而且也進一步地提昇了元件的特性。從實驗結果我們得知，砷化鋁鎵表面在經過硫化處理之後能夠有效的減少表面鍵結電荷及相對應的電容。因此，經過硫化處理之元件具有較低的漏電流及較佳的高頻特性。
　　其次，在磷化銦鎵/砷化銦鎵/砷化鎵擬晶性高電子移動率場效電晶體上，我們使用硫化銨溶液進行磷化銦鎵表面鈍化處理。我們也利用此結構研製了次微米閘極元件來增進高頻特性。對於有潛力的磷化銦鎵材料而言，硫化處理能更進一步地減少表面復合速度及表面態密度。實驗結果顯示，元件經過硫化處理之後可得到較佳的元件特性，如高崩潰電壓、低漏電流以及好的高頻響應。
　　最後，我們將n+型磷化銦鎵/p+型磷化銦鎵/n型砷化鎵駝峰式閘極結構及砷化銦鎵/砷化鎵複合式通道結構應用在一異質結構場效電晶體中。此種駝峰式結構的使用讓元件具有較大的閘極位障。另外，於複合式通道結構中，使用砷化銦鎵層可以增加載子的傳輸特性，而砷化鎵層亦可改善元件在高電場下之操作能力。所以，藉由應用上述兩種結構之優點，使得元件能夠具有良好的直流、微波及高溫操作特性。

　　In this thesis, three GaAs-based heterostructure field-effect transistors (HFETs), grown by a low-pressure metal organic chemical vapor deposition (LP-MOCVD) system, have been fabricated and investigated. In addition, the influences of sulfur ((NH4)2Sx) treatment technique on studied HFETs are also studied. With the aid of sulfur passivation, the studied devices proposed in this work reveal higher breakdown voltage, lower leakage current, better device linearity, and superior microwave performances. For obtaining more power gain and bandwidth of transistors, we also fabricate sub-micron meter gate devices with resorting to deep ultraviolet (UV) photolithography. Besides, we employ the camel-gate and composite channel structure to fabricate a novel HFET. Experimentally, the studied devices show good DC and microwave characteristics and high temperature operation capability. These advantages suggest that the proposed devices are suitable for high-speed and high-power integrated circuit applications.
　　First, we report the characteristics of an AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility field-Effect transistor (PHEMT). In addition, the influences of surface passivation using (NH4)2Sx solution are also compared and studied. Experimentally, the sulfur passivation on AlGaAs surface effectively reduces the surface bound charges and hence the corresponding capacitance. Thus, the studied device with sulfur treatment can suppress the leakage current and shows good microwave characteristics with flat and wide operation regime. Moreover, a sub-micron meter gate structure is also fabricated and higher device performances are obtained.
　　Second, we report the characteristics of an InGaP/InGaAs/GaAs PHEMT. Also, the influences of surface passivation on InGaP layer are studied. For the promising wide-gap InGaP material, the surface recombination velocity and surface states are further reduced by sulfur passivation. As a result, high breakdown voltage, low leakage current, and good frequency response are obtained in the studied device. In the meanwhile, we also develop sub-micron meter gate device to further improve the high-frequency device performances.
　　Finally, an n+-InGaP/p+-InGaP/n-GaAs camel-like gate sturcture and InGaAs/GaAs composite channel structure are introduced to fabricate a new HFET. The employed n+-InGaP/p+-InGaP/n-GaAs camel-gate structure provides a larger barrier height. In addition, composite channel structures with the n-InGaAs channel to improve the carrier transport properties and the n-GaAs channel to improve the operation capability under higher electric field are employed in the studied device. Therefore, good DC and microwave properties and higher temperature operation capability are simultaneously obtained.

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