在本文中，我們研究了以分子束磊晶法成長的四元InAlGaAs/InGaAs/InAlGaAs 異質結構場效電晶體的特性。當四元化合物InAlGaAs層被使用時，因為鋁原子數量被減少，所以特性被改善是可以期待的。
我們利用濕蝕刻的方式薄化蕭基層，因而有效的改善了元件的效能。由實驗結果顯示，較薄的蕭基層增進了元件的夾止特性並提高異質轉導值。在閘極長度為1.5m時，最大的異質轉導值為165mS/mm，而在Vgs=2V時汲極電流密度為241mA/mm。而增強式異質結構電晶體最大的異質轉導值為127mS/mm，而在Vgs=2V時汲極電流密度為180mA/mm。
InAlGaAs/InGaAs/InAlGaAs 異質結構場效電晶體的高頻、功率、雜訊特性也被討論。其截止頻率為14.5GHz，最大震盪頻率為25.8GHz。元件輸出功率為15.56dBm，相當於180mW/mm，而相關的附加功率效率為62.6%，線性功率增益為12.6dB。當元件操作在2.4GHz時，其最小雜音指數為1.9dB，增益為12.82dB。

In this thesis, the characteristics of the quaternary InAlGaAs/InGaAs/InAlGaAs heterostructure field-effect transistors grown by molecular beam epitaxy (MBE) have been studied. An improvement in the quaternary InAlGaAs layer can be expected by degrading the Al atom.
By wet etching the InAlGaAs Schottky layer, the device performance can be improved. The results show that the thinner Schottky layer enhances the pinch-off characteristics and the extrinsic transconductance obviously. The maximum extrinsic transconductance is 165mS/mm, and the saturation drain current density is 241mA/mm at VGS=2V for gate length of 1.5m. The maximum extrinsic transconductance for the enhancement-mode FET is 127mS/mm, and the saturation drain current density is 180mA/mm at VGS=2V.
The microwave, power, noise performances of the InAlGaAs/InGaAs/InAlGaAs heterostructure field-effect transistors have also been described. The current gain cut-off frequency (ft) and maximum oscillation frequency (fmax) are 14.5GHz and 25.8GHz, respectively. The device exhibited an output power of 15.56dBm which corresponding to 180mW/mm. The associated power-added efficiency is 62.6%, and the linear power gain is 12.6dB. The device exhibited a minimum noise figure as 1.9dB with 12.82dB for the gain at 2.4GHz.

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