在本論文中，我們研究以「金屬有機化學氣相沉積法」成長的高載子遷移率電晶體，它使用階梯狀結構的通道層，以改善電晶體的特性。
當我們使用階梯狀結構的通道層時，通道傳導帶將會形成V字型的谷，而通道中的大部分電子會聚集在V型的谷底，因此二維電子雲會較遠離AlGaAs/InGaAs的接面，庫侖散射（Coulomb scattering）會降低，而提高電子遷移率，所以可獲得高的電流密度和增益，同時階梯狀結構的通道層會增加閘極工作電壓擺幅（gate voltage swing）。
在室溫下，閘極的尺寸為1.2×100 ?m2時，元件的最大汲極飽和電流為385 mA/mm，最大轉導值為148 mS/mm，且可得閘極工作電壓擺幅?1.9伏特。另外閘極和汲極兩端的崩潰電壓為16伏特。我們也同時描述了元件的高頻特性，截止頻率為9.5GHz，最大振盪頻率為37GHz。
使用階梯狀結構的通道層結構的高載子遷移率電晶體顯示了良好的特性，使元件預期可以利用於高速和放大器的應用。

In this thesis, the high electron mobility transistors (HEMT’s) with step-composition channel grown by metalorganic chemical vapor deposition (MOCVD) have been studied. The improvement can be expected by using a novel channel structure.
By using the step graded channel the electrons in the channel will be confined well in the bottom of the V-shape conduction band. The electrons are also far away from the AlGaAs/InGaAs interface, thus Coulomb scattering is reduced. Consequently the electron mobility will increase. Then the high drain current density and large gate voltage swing can be obtained.
For a 1.2×100 μm2 gate dimension, the maximum saturation drain current density is 385 mA/mm and the maximum extrinsic transconductance is 148 mS/mm along with the gate voltage swing of 1.9V. Besides, the gate-to-drain breakdown voltage of 16 V is obtained.
The microwave performance of our structure is also described. The current gain cut-off frequency ( ) and maximum oscillation frequency ( ) are 9.5 GHz and 37 GHz, respectively.
These good performances show that the studied structure with step-composition channel HEMT has good potential for high speed and amplification capability.

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