 異質接面雙極性電晶體，由於具有高速操作及高電流驅動能力，近幾年來已被廣泛的應用在數位及微波積體電路上。本論文將研究具有突出部射極結構之磷化銦鎵/砷化鎵異質接面雙極性電晶體，包含在元件特性量測分析及其應用於微波頻率上的特性。此外，基於突出部射極結構的使用，由實驗結果可看出元件的表面復合速度及態位密度明顯降低，且此元件可操作在較低的集極電流區，因而可提供使用者在低功率電子電路上的應用。而且，具有突出部射極結構的元件也表現出較佳的高頻表現特性。
 另一方面，一種新穎之磷化銦鎵/砷化鋁鎵/砷化鎵的組合式射極異質接面雙極性電晶體，其元件特性將在第三章中予以研究及討論。有著線性漸變分佈的砷化鋁鎵層組合式射極異質接面雙極性電體，由於其射極到基極間能隙以漸變式減小，且適當的選取鋁的莫耳分率(x=0.11)可使元件呈現出幾乎連續性的導電帶結構。實驗結果顯示組合式射極異質接面雙極性電晶體具有良好的直流與高頻特性，像較低的集極-射極補償電壓，極低的集極電流範圍和一個較寬廣的集極電流操作區域。
第 一 章
導 論
近年來，隨著磊晶技術不斷進步，帶動了三五族化合物半導體產業的發展。而異質接面雙極性電晶體因具有極佳的微波特性及高電流驅動能力，因此，已被廣泛應用在高頻和高功率元件與電路上，例如無線通訊和功率放大器等。除此之外，異質接面雙極性電晶體的價電帶不連續特性及大能隙射極層的使用，使得異質接面雙極性電晶體之基極層摻雜濃度可大幅被提升進而降低基極層電阻值，元件亦具有高線性度及較佳的直流輸出特性，而基-射極的導通電壓也較容易控制。

在第一章中，吾人先對於異質接面雙極性電晶體作一番介紹，且對所使用的材料做一番描述，並與同質接面雙極性電晶體做比較。
對三五族材料系統而言，囿於材料具較高之表面態位密度及較多之表面複合中心，造成少數載子類型之元件特性劣化及可靠性衰減。有鑑於異質接面雙極性電晶體表面複合電流所產生之不良影響，在第二章中，吾人研製一種具有突出部射極結構之異質接面雙極性電晶體，以圖改善元件之相關特性。由實驗結果得知，具突出部射極結構之元件除可在極低之集極電流區下操作，該元件亦具有較低之漏電流及較佳之高頻表現。

對於異質接面雙極性電晶體而言，由於射-基接面之導電帶不連續值（DEC）的存在使得元件特性受其影響而不盡理想，雖現階段常用之磷化銦鎵/砷化鎵材料系統比起砷化鎵/砷化鋁鎵材料系統而言，其具一較小之導電帶不連續值，然此導電帶不連續值及其衍生之缺點依舊影響元件之操作。在第三章中，吾人研製一新穎之組合式射極異質接面雙極性電晶體，並於此章中就元件之直流特性做一完整之研究與探討。最後，我們再對本論文做一個結論，及未來發展性做一個完整適當規劃。

第 二 章
具有突出部射極結構之磷化銦鎵/砷化鎵之異質接面雙載子電晶體
由於異質接面雙極性電晶體具有高密度之表面態位密度及大的表面複合電流，因此，在元件製造的過程中，表面氧化層所產生之缺陷嚴重地降低元件之特性及可靠度。在本章中，吾人將研製具射極突出部結構之磷化銦鎵/砷化鎵異質接面雙極性電晶體，並研究其直流特性及高頻特性；藉由此製程技術，可以減少元件的表面的複合速度及表面態位密度，且在實驗結果發現，相較於一般傳統元件，具射極突出部結構的元件可以操作在低於0.3nA集極電流，並且有比較寬廣的電流操作區域。在高頻特性表現方面，具有突出部射極結構元件具較佳的單一電流增益截止頻率（fT）及最大振盪頻率（fmax）分別為40GHZ及30.6GHZ。

另一方面，我們也比較具有突出部射極結構與一般傳統之元件在常溫及變溫下的兩端、和三端直流特性，包括導通電壓、電流增益和理想因子及高頻表現。從射極周長面積比和電流增益倒數的關係中，由於表面複合電流的減小，我們可以發現具突出部射極結構的元件有較輕微的射極尺寸效應。
第 三 章
磷 化 銦 鎵/砷 化 鋁 鎵/砷 化 鎵 之 研 究 組 合 式 射 極 異 質 接 面 雙 極 性 電 晶 體
於本章中，吾人將研製一種新穎以磷化銦鎵/砷化鋁鎵/砷化鎵為組合式射極結構之異質接面雙極性電晶體，當鋁的莫耳分率為0.11時，磷化銦鎵和砷化鋁鎵可以達到晶格匹配之條件，所以我們可以發現射極和基極接面間的導電帶差趨近於零。

實驗上，由於能障趨近於零，我們可以發現此元件展現相當不錯的直流增益、較低的電壓補償和較小的射極-基極導通電壓。而且從集極電流理想因子趨近於1，更可以證明射極和基極接面能隙差幾乎被削減。此外，此元件可以操作在極低的集極電流區域和寬廣的電流操作區域，所以此元件可以應用於低電壓和低功率系統上。

第 四 章
結 論 與 未 來 展 望
於本論文中，吾人研製以砷化鎵材料系統為基礎之改良型異質接面及組合式射極雙極性電晶體。其中包括磷化銦鎵/砷化鎵具突出部射極結構異質接面雙極性電晶體與一具有組合式射極層之砷化鋁鎵/磷化銦鎵/砷化鎵異質接面雙極性電晶體。組合式射極層之砷化鋁鎵/磷化銦鎵/砷化鎵異質接面雙極性電晶體，組合式射極層之使用旨在射-基接面形成一連續之導電帶，藉以強化元件特性。此外，吾人對傳統之磷化銦鎵/砷化鎵異質接面雙極性電晶體設計一種具突出部射極結構以圖改善其直流及高頻之特性表現。

我們雖對元件製程已有了初步的成果，但仍有一些需改進及加強的部分，就目前所做之成果，吾人將提出數種改善元件的方法，其中包括：
1. 設計新的光罩以縮小元件的面積，冀能減小元件的寄生電阻及電容，使得元件在高頻表現更完善。
2. 研發空橋式製程技術，可有效的減低鈍化層之影響（鈍化層品質不佳之因素，可經由空橋的使用完全的排除），有效的強化元件高頻特性，提高其高頻效能。
3. 由先前的實驗結果發現，鈍化層的品質會嚴重影響高頻的表現，所以在縮小面積的同時，研製一種優良的鈍化層並縮小鈍化層的面積，以期在高頻有更好的表現。
4. 設計指叉狀結構，以減小射極擁擠效應，進而增加元件的功率表現，以提高fT與fmax值。
5. 在具有穿透式射極障壁之異質接面雙極性電晶體結構加上組合式基極漸變層或基極濃度漸變層，以改進元件高頻和直流特性。
6. 完成MMIC’s電路設計，將所研製之元件實際應用於電路上。

　Recently, due to the excellent current driving capability and microwave performances, Heterojunction bipolar transistors (HBTs) have extensively employed on digital and analogy applications. In this thesis, the theoretical analyses and experimental results of InGaP/GaAs HBTs with emitter ledge structure are systematically studied and demonstrated. Based on the use of emitter ledge passivation, the surface recombination velocity and surface state are effectively reduced. The device with ledge passivation can be operated under extremely low collector current region, which offers the promise for low-power electronics applications. Furthermore, the studied devices with ledge passivation show superior microwave performance.

　In addition, the DC characteristics of a novel InGaP/AlxGa1-xAs/GaAs composite emitter heterojunction bipolar transistor (CEHBT) is fabricated and studied in chapter 3. The CEHBT with a linear-graded AlxGa1-xAs layer exhibits a nearly continuous conduction band structure and the absence potential spike at emitter-base junction. Experimental results show that the CEHBT presents good DC and microwave performances, such as a lower collector-emitter offset voltage, an extremely low collector current level and a wide collector current operating regime.

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