在本論文中，我們利用有機金屬化學氣相沉積系統成長氮化鋁鎵/氮化鎵異質接面，並將其製作成高電子遷移率電晶體來探討元件特性。傳統磊晶結構所製作出來的氮化鋁鎵/氮化鎵高電子遷移率電晶體具有很大的夾止漏電流，經由元件的分析結果發現，此現象可能是由於氮化鎵在成長時，非故意摻雜濃度太高所產生，導致載子在通道內的侷限力較差，在氮化鎵層有額外的漏電流路徑。為了改善此現象我們改變磊晶的結構，利用多重量子井的概念的來增加載子的侷限能力，進而減少元件的夾止漏電流。
本篇論文有兩大實驗主軸，第一部份我們著重於製程結構改善，利用不同製程結構來提升元件特性。這部份製作了雙層絕緣層的金絕半高電子遷移率電晶體、掘入式閘極高電子遷移率電晶體及掘入式閘極金絕半高電子遷移率電晶體。在雙層絕緣層的金絕半高電子遷移率電晶體部分，利用電漿輔助化學氣相沈積來成長二氧化矽及氮化矽作為閘極與半導體之間的絕緣層，此結構能有效改善傳統元件之閘極漏電流問題，但也會使得元件轉導值及臨界電壓特性變差，因此我們透過調整二氧化矽及氮化矽的成長厚度及其成長順序來得到其最佳化參數。為了改善元件的轉導值及臨界電壓的特性，我們製作了掘入式閘極的結構，利用感應耦合式電漿離子蝕刻將閘極下氮化鋁鎵阻障層做蝕刻，較薄的氮化鋁鎵阻障層可以使閘極控制能力提升，進而改善元件的轉導值及臨界電壓的特性，但此結構也會使得汲極電流下降，除此之外利用乾式蝕刻會使得氮化鋁鎵層受到破壞而造成閘極漏電流，為了改善此閘極漏電流我們用濺鍍的方式成長10奈米的二氧化矽，製作一個掘入式閘極金絕半高電子遷移率電晶體，此結構能有效改善閘極漏電流，但其他特性卻比一般結構來的差，我們推測可能是濺鍍二氧化矽的電漿會造成半導體的表面破壞。
第二部份我們則著重於磊晶結構改善，傳統磊晶結構製作出來的氮化鋁鎵/氮化鎵高電子遷移率電晶體具有很大的夾止漏電流，為了要改善此問題我們使用多層磊晶結構來增加載子的侷限能力。多層磊晶結構我們也做了許多的變化，像是改變通道數量及加厚底層氮化鋁鎵的厚度等，在元件的結構上也加上雙層絕緣層的金絕半結構來改善閘極漏電流問題。使用此磊晶結構，最佳的夾止漏電流可以從 126 mA/mm 下降至2.5 mA/mm，亦即減少98 %，隨著磊晶參數的微調夾止漏電也會有些許的不同，但減少幅度都大於94 %。

In this thesis, the AlGaN/GaN heterostructures structure was made by metal organic chemical vapor deposition (MOCVD). The high electron mobility transistor (HEMT) was fabricated and the characteristic was investigated. The most serious problem for the device was that the pinch off leakage was too large for the conventional epitaxial structure to be turned off, which is due to the highly unintentionally doped GaN concentration. If the GaN unintentionally doped was too high that will result in the poor carrier confinement and extra leakage current path in GaN. Therefore we use the multilayer structure to solve this problem.
This thesis was made up of two parts. In the first part, we focused on various device structures in order to improve the device performance. Here, we will investigate the characteristics of conventional structure, bilayer metal insulator semiconductor (MIS) HEMT, recessed gate HEMT, and recessed gate MISHEMT. For the bilayer MISHEMT, the SiO2 and Si3N4 were inserted between the gate metal and semiconductor as insulator by plasma-enhanced chemical vapor deposition (PECVD). The gate leakage could be improved by bilayer MISHEMT, but the threshold voltage and transconductance characteristics for this structure were worse. Therefore, we change the insulators thickness and their sequence to find the optimal parameter. Moreover, in order to improve the threshold voltage and transconductance characteristics for device, the recessed gate HEMT was used. For recessed gate structure, the AlGaN barrier under the gate region was etched by ICP. When the device with thinner AlGaN barrier, the threshold voltage and the transconductance characteristics will be improved due to the better gate control ability, but the drain current would be degraded. Moreover, the recessed gate structure would increase gate leakage by the damage caused by ICP etching and thinner AlGaN. In order to reduce the gate leakage, we add the 10nm SiO2 between gate metal and AlGaN by sputter. The recessed gate MISHEMT only could improve the gate leakage current while the other characteristics were worse than conventional HEMT. Because the sputter used for SiO2 deposition will induce damages trapping carriers in channel.
In the second part, we focused on the improvement of epitaxial structure. For the conventional epitaxial structure, there is a pinch off leakage current problem in device. Therefore, the multilayer structures were used in effort to reduce the pinch off leakage current due to its better carrier confinement. Here, we changed the epitaxial structure with different channel numbers and thickness of AlGaN back barrier. Moreover, the double insulator also was utilized in the multilayer structures. The best performance of the pinch off leakage current decreased by 98 % from 126 mA/mm to 2.5 mA/mm. For all multilayer structures with MISHEMT, the pinch off leakage also could be reduced by more than 94%.

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