矽/矽鍺異質接面雙極性電晶體之研究

Abstract

在微波及數位切換應用上，異質接面雙極性電晶體具有高電流增益及高 速度操作的優異特性。在這篇論文□，我們製作並分析以矽鍺合金為基極 的異質接面雙極性電晶體，所有的電晶體結構都是利用冷壁式超高真空化 學氣相沉積法在矽基板上成長而成。超高真空化學氣相沉積技術可以精確 地控制材料的組成及雜質摻雜分佈。在元件製造上，我們使用高台式結構 ；另外，我們使用快速退火技術來保留矽鍺基極層的初成長情形，並減少 摻雜的外擴散。對不同的基極摻雜分佈設計所得之異質接面雙極性電晶體 ，其電流增益大約為5到356，而最大的截止頻率大約為19.5GHz。由集極 截距電流和溫度的關係，我們可以估算出矽鍺基極和矽射極間的能隙差； 另外，我們也討論了元件特性和溫度的關係，結果顯示電流增益和截止頻 率隨溫度的降低而增加。 Heterojunction bipolar transistors (HBTs) exhibit high current gain and high speed operation in both microwave and digital switching application. In this thesis, HBTs with SiGe base were fabricated and analysized. All the HBT structures are grown on silicon substrate by cold-wall ultrahigh vacuum chemical vapor deposition (UHVCVD). UHVCVD technique allows precise control of material composition and impurity doping profiles. A mesa-type structrure is used for device fabrication. Rapid thermal annealing is implemented to preserve the as-grown condition of the SiGe base layer and minimize dopant out-diffusion. The measured current gains are from 5 to 356 for HBTs with different base profile designs. The maximum cutoff frequency is about 19.5 GHz. The band-gap difference between the SiGe base and the Si emitter is estimated by the temperature dependence of the collector intercept current from 210K to 473K. The temperature dependence of the characteristics for fabricated transistors are also discussed. It is shown that both the current gain and the cutoff frequency increase with decreasing temperature.