在本篇論文中，為了改善傳統高電子移動率電晶體 (HEMT)閘極電壓擺幅太小的問題，我們採用了以磷化銦為基板並具有反向漸變式通道的高電子移動率電晶體（IGC-HEMT）。實驗的結果顯示，具有反向漸變式通道的高電子移動率電晶體除了提升閘極電壓擺幅外，同時具有極佳的熱穩定性。閘極擺幅電壓之所以會增加是因為閘極調變能力和電子飽和速度之間的平衡所造成;熱穩定性的提高則是因為反向漸變式通道提高了通道與阻擋層介面的導帶不連續，因此使通道侷限載子的能力提升所致。
反向漸變式通道中銦的含量隨深度增加而上升，電子飽和速度亦隨銦含量增加而遞增，這可補償閘極電極與等效二維電子氣位置間距因閘極電壓下降造成的增加。這使得元件即使操作在較寬的閘極電壓範圍下，轉導值都得以維持不變。反向漸變式通道中銦的含量隨深度增加而上升，使通道的能隙隨深度增加而遞減，最後在通道與阻擋層介面獲得了最大的導帶不連續。這提供了良好的侷限載子能力，進而使之具有極佳的熱穩定性。
IGC-HEMT的實驗結果如下: 飽和汲極電流(IDSS0 = 381 mA/mm)、異質轉導值（gm,max = 314 mS/mm)，高頻特性 (fT = 46 GHz, fmax = 55 GHz)。崩潰電壓 (BVoff = 7.1 V)，功率特性 (Pout = 12.8 dBm, power gain = 19.5 dB, P.A.E. = 42.0 %)。飽和汲極電流在420 K仍維持300 K時的90.7 ％(IDSS0 = 345.4 mA/mm)，異質轉導值在420 K也維持300 K時的94.4 ％（gm,max = 296.4 mS/mm)。因此，具有反向漸變式通道的高電子移動率電晶體（IGC-HEMT）相當適合高溫方面的應用。
針對高移動率需使用高銦含量通道，使之無法得到大的崩潰電壓，因而使功率無法提升的問題，我們設計了「具有張力通道之變晶型高電子移動率電晶體」 (TS-MHEMT)。首先我們降低了通道中銦的含量來改善衝擊游離效應並進而提高崩潰電壓。藉由張力通道與V型漸變結構的幫助，仍可保持高電子移動率與高載子量。為了降低磷化銦基板的高成本，我們採用了以砷化鎵為基板的變晶式設計。
TS-MHEMT 的實驗如下：TS-MHEMT具有高飽和汲極電流(IDSS0 = 514 mA/mm)、高異質轉導值（gm,max = 404 mS/mm)，及較佳的高頻特性 (fT = 58.5 GHz, fmax = 72.2 GHz)。崩潰電壓提升 (BVoff = 9.6 V)，並進而改善了元件的功率特性 (Pout = 17.2 dBm, power gain = 21.1 dB, P.A.E. = 49.4 %)。因此，張力變晶型高電子移動率電晶體 (TS-MHEMT)可同時滿足高頻以及高功率方面的需求。

In this thesis, in order to improve the small gate voltage swing of conventional high electron mobility transistors (HEMT), we adopt the HEMT with inversely-graded channel (IGC-HEMT) grown on InP substrate. The experimental results show that the IGC-HEMT has not only wider gate voltage swing but also good thermal stability. The reason for the wider gate voltage swing is that the balance between gate modulation capability and electron saturation velocity. The reason for good thermal stability is that the inversely-graded channel increases the conduction band discontinuity (ΔEC) at the channel/barrier interface and therefore improves the carrier confinement.
The indium composition in the inversely-graded channel elevates with the increase of the depth and the electron saturation velocity also increases with the increase of the indium composition. The increase of electron saturation velocity can compensate for the increase of the distance from gate electrode to the effective 2-DEG position due to the decrease of gate voltage. This design makes the extrinsic transconductance unchanged even though the device is operated at wider gate voltage range. The indium composition in the inversely-graded channel elevates with the increase of the depth and therefore the bandgap decreases with the increase of the depth. Consequently, the maximum conduction band discontinuity is achieved at the channel/barrier interface. The maximum conduction band discontinuity provides good carrier confinement; hence, it has excellent thermal stability.
The experimental results of IGC-HEMT are as follows: The drain-source saturation current density at VGS = 0 V (IDSS0), extrinsic transconductance (gm,max), fT, and fmax are 381 mA/mm, 314 mS/mm, 46 GHz and 55 GHz. The off-state breakdown voltage, maximum output power (Pout), associated gain (GA) and power added efficiency (P.A.E.) are 7.1 V, 12.8 dBm, 19.5 dB and 42.0 %. The IDSS0 at 420 K maintains at 90.7 % of the value at 300 K and the gm,max also maintains at 94.4 % of the value at 300 K. Therefore, the IGC-HEMT is suitable for high-temperature applications.
In order to solve the problem that high mobility comes from In-rich channel which leads to small breakdown voltage, we design the “Tensile-strained metamorphic HEMT” (TS-MHEMT). First, we decrease the Indium composition in the channel to reduce impact ionization and increase breakdown voltage. High mobility and high carrier concentration are still maintained because of the tensile-strained channel and “V”-shaped graded channel structure. Additionally, we adopt the design which uses metamorphic HEMT grown on GaAs substrate to decrease the cost.
The experimental results of TS-MHEMT are as follows: TS-MHEMT has high drain-source saturation current density (IDSS0 = 514 mA/mm), high extrinsic transconductance (gm,max = 404 mS/mm) and better microwave characteristics (fT = 58.5 GHz and fmax = 72.2 GHz). The breakdown voltage is elevated and therefore improve the power characteristics (Pout = 17.2 dBm, GA = 21.1 dB, P.A.E. = 49.4 %). Consequently, the tensile-strained metamorphic HEMT can fulfill the requirement of high-frequency and high-power at the same time.

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