在本文中，我們以有機金屬氣相沉積系統成功研製了對稱漸變式通道(AlGaAs / InxGa1-xAs (x=0.12→0.18→0.12))的高電子移動率電晶體，並改善其特性。

　　首先我們先薄化蕭基層，因而有效地改善了元件的效能。由實驗結果顯示，較薄的簫基層增進了元件的夾止特性並提高了異質轉導值。可得到最佳的異質轉導值為178 mS/mm、崩潰電壓-32V、截止頻率和震盪頻率分別為19.3 GHz和50.1 GHz、此外在2.4 GHz量得輸出功率為16.37 dBm 、最小的雜訊值0.72 dB。

　　此外,我們將縮減閘極凹槽的寬度及雙閘極凹槽來改善元件的特性。它們的寬度分別為5µm、3µm及 雙閘極凹槽寬度7_3 µm。由實驗結果得知閘極凹槽寬度為3µm將最大的異質轉導值由178 mS/mm 增加至220 mS/mm，最大汲極電流420 mA/mm由增加至480 mA/mm。而其截止頻率和震盪頻率更分別由 19.3 GHz 增加至23.75 GHz和 50.1 GHz 至71.6 GHz。雖然閘極寬度 = 3 µm的電晶體可改善大部分特性，但是其崩潰電壓由-32降至 -11 V 。這個結果使得元件輸出功率由 16.37 dBm 降至 15.78 dBm。於是利用雙閘極凹槽蝕刻的製程來改善元件的功率特性，雖然犧牲了一些異質轉導值（202 mS/mm），但是卻大幅提昇了崩潰電壓（-28V），進而提升了功率特性。使得輸出功率由16.37 dBm增加至17.42 dBm。由實驗結果得知利用雙閘極凹槽的製程可得到 最佳的元件特性。

　　我們同時也探討了對稱漸變式通道( AlGaAs / InxGa1-xAs ( x=0.12→0.18→0.12) )的高電子移動率電晶體的溫度特性。由於改善了直流特性，所以其高頻、功率、雜訊特性也獲得大幅的提升。

　In this thesis, the symmetrical graded channel AlGaAs / InxGa1-xAs (x=0.12→0.18→0.12) High Electron Mobility Transistors have been successfully fabricated by metal organic chemical vapor deposition (MOCVD) system, and we improved their characteristics.

　By thinning undoped AlGaAs Schottky layer, the device performance can be proved. The results show that the thinner Schottky layer can enhance the pinch-off characteristic and extrinsic transconductance obviously. The maximum extrinsic transconductance is about 178 mS/mm and it，s ft and fmax is 19.3 GHz and 50.1 GHz. At 2.4 GHz, the output power is 16.37dBm, and the NFmin is 0.72dB.

　In order to improve the characteristics of our devices, we reduce the recess width. Their recess width is 3 µm, 5 µm, and 7_3 µm (double recess), respectively. It，s maximum extrinsic transconductance could be from 178 mS/mm to 220 mS/mm. It，s maximum drain current density is from 420 mA/mm to 480 mA/mm. It，s ft could be from19.3 GHz to 23.75 GHz and it，s fmax could be from 50.1 to 71.6 GHz. Although HEMTs with recess width =3 µm could ameliorate a great part of DC performance, their breakdown voltage is from -32V to -11V. The result limits the power characteristics. The output power is from 16.37 dBm to 15.78 dBm. So we use the double-recess process. Although we sacrifice a little extrinsic transconductance (202 mS/mm)，we could get higher breakdown voltage (-28V) and improve it，s power characteristics. The output power is from 16.37 dBm to 17.42 dBm. The temperature-dependent characteristics of symmetrical graded channel AlGaAs / InxGa1-xAs (x=0.12→0.18→0.12) HEMTs with different recess width and double-recess [10-15] width have also been studied. Because of improving DC characteristics of symmetrical graded channel AlGaAs / InxGa1-xAs ( x=0.12→0.18→0.12) HEMTs，the RF, power, and noise characteristics could be ameliorated effectively.

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