【正文】 kTqUneneneneE?????????? ?????????????如從擴散方程出發(fā) ， 利用邊界條件 ， 可得到 Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices ? ? ? ?10 。 如從擴散方程出發(fā) ， 利用邊界條件 ， 得到 Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 近似認為集電區(qū)中非平衡空穴亦是線性分布，且在 x ＝ x2 + LpC 處非平衡空穴密度為零，利用邊界條件 ? ?? ? nCnCkTqUnCnCppepxpC002???Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 于是，集電區(qū)中非平衡空穴的分布為 ? ? ? ?? ?2200。 類似地，從擴散方程出發(fā)考慮邊界條件，解得集電區(qū)中非平衡空穴的分布為 Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices ? ? ? ?220 。 Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 假定晶體管的發(fā)射區(qū)、基區(qū)及集電區(qū)中不存在電場也就是說各區(qū)域的電流只考慮擴散電流。 Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 考慮到 UE kT / q ，且為正值，為形式上與以后公式一致，將上式改寫為 ? ? ????????? 10kTqUbpbnbnBEeWnqDxJChapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 如從下式出發(fā)， ? ????????????????????????????????? ???????????nbbnbkTqUpbnbbkTqUpbpbLWshLxshenLxWshenxnCE1100Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices ? ????????????????????????????????? ???????????nbbnbkTqUpbnbbkTqUpbnbnbnBLWshLxchenLxWchenLqDxJCE1100得基區(qū)電子的擴散電流密度為 Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 分別求 JnB(0) 及 JnB(Wb)，可以發(fā)現(xiàn) x ＝ 0 處的電子電流密度比 x ＝ Wb 處大，表明基區(qū)是存在復合的。11xxeepxp peE LxxkTqUnene ????????????Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 求得發(fā)射區(qū)中空穴電流密度分布為 ? ?? ?10。 Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 不計發(fā)射結(jié)勢壘區(qū)的復合即 JnE ( x1 ) ＝ JnB( 0 ) 于是得發(fā)射極電流密度為 ? ? ? ? ? ? ? ??????????????????????????1000111kTqUpenepebpbnbpEnBpEnEEEeLpDWnDqxJJxJxJJChapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 或者有 ??????????????????????????????????????????1c sc1000kTqUnbbnbpbnbkTqUpenepenbbnbpbnbEEEeLWhLnDqeLpDLWc t hLnDqJChapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 由 ? ? ? ?? ?2200。12xxeeppxpxppCCLxxkTqUnCnCnCnC??????????????Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 則集電區(qū)的空穴電流密度分布為 ? ?20。 Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 集電極電流密度也應等于集電區(qū)內(nèi)電子和空穴的電流密度之和 。 它們是均勻基區(qū)晶體管最基本的方程 。 Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 均勻基區(qū)晶體管的短路電流放大系數(shù) Short Circuit Current amplify Factor of Transistor with uniform Base Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 發(fā)射效率 Emitting Efficiency 根據(jù) npn 晶體管發(fā)射效率 γ 的定義 nEpEpEnEnEEnEJJJJJJJ?????11?Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 把已求得的 JpE 、 JnE 代入上式，有 pepbnbbnepenEpELnDWpDJJ00?Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 根據(jù)嚴格計算的結(jié)果，上式成立有兩個條件： 集電結(jié)短路 ( UC = 0 )； 基區(qū)寬度 Wb 比基區(qū)中電子的擴散長度 Lnb 小得多 Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 類似地， 在后面導出 γ 、 β *、 α * 等量時， 均要求 UC = 0。 Chapter 2 Basic Properties of Bipolar Junction Transistors Fundamental of Semiconductor Devices 得