利用電荷控制修正模型探討量子井發光電晶體中載子傳輸動態機制

Abstract

本論文主要以理論模型去探討發光電晶體的各項載子傳輸的重要特性。首先，我們研究InGaP/GaAs為異質接面的發光電晶體元件的接面溫度特性。在以往異質接面電晶體的研究中，由於具有電流增益大的特性，異質接面電晶體常用於功率放大器。而在高功率操作下，功率耗散會轉換成熱能被釋放出來，並會造成元件電性上之影響，因此，研究異質接面電晶體對溫度變化的特性一直都是重要的問題。在此，我們基於前人對異質接面電晶體之熱研究，用來建立發光電晶體的熱特性之理論基礎。藉由變換外界溫度，進行發光電晶體的電性量測，並基於熱電阻理論對實驗數據進行萃取，進一步得到發光電晶體的接面溫度及熱電阻。以不包含基極量子井的異質接面電晶體結構作為對照組，比較傳統異質接面電晶體及發光電晶體之間的熱特性。 本論文的另外一個重點是想試圖建立發光電晶體的電荷修正控制模型去探討發光電晶體的基極量子井對載子傳輸的影響。同樣是研究InGaP/GaAs為異質接面的發光電晶體元件。從擴散連續方程式下手，具體描述少數載子濃度在基極的分布狀況，寫下基極、集極、射極電流的關係式，對直流及交流電性作分析。將發光電晶體主要的載子傳輸做分類，並將載子捕捉、逃脫、擴散的過程利用修正後的異質接面電晶體的電荷控制模型進行描述。為了更準確地描述基極量子井在發光電晶體中之影響，利用模擬軟體解出載子在量子井的機率分布，並根據費米黃金定則解出載子在量子井中自發躍遷複合的波長，定量出載子在量子井中填入能階的高度及濃度。 最後，將不同狀況代入電荷修正控制模型，如基極偏壓電流、溫度、不同量子井的位置。我們分析實際元件的載子捕捉及逃脫時間和等效基極傳輸時間的關係，及其對應的光頻寬大小，此模型分析有助於未來設計發光電晶體的結構，進一步提升發光電晶體的電光特性。

This thesis focuses on developing theoretical model to investigate the critical carrier transport characteristics of light-emitting transistors. First, we present the junction temperature of InGaP/GaAs light-emitting transistors. In the past research, heterojunction bipolar transistors play an important role in power amplifiers due to high current gain. Under high-power operation, power dissipation is a big issue that produces extra heat and affects the electrical characteristics of devices. Therefore, accurate modeling of thermal impedance is still an active research area. Here we base on these research of thermal resistance, and establish the thermal extraction theory of light-emitting transistors. By changing the ambient temperatures and bias currents, we obtain the experimental data of D. C. measurement. We extract the junction temperature and thermal resistance by using the extraction equation of thermal resistance. Then we compare the junction thermal characteristics of the heterojunction bipolar transistors with light-emitting transistors and investigate the effect of incorporating quantum wells in the base region. Another focus of this thesis is to propose a more accurate charge control model of light-emitting transistors. We present how the base quantum wells affect carrier transport dynamics in the base region of light-emitting transistors by using the modified charge control model. We describe the minority carrier concentration distribution in the base region using current diffusion continuity equation, and write down the equation of base, collector, and emitter current. Then we do the D.C. and A.C. analysis using the modified charge control model of light-emitting transistors. We introduce three main carrier transport mechanisms: carrier diffusion process, carrier capture and escape process in the modified charge control model. In order to explain the effect of the quantum wells in the base, we simulate the carrier probability distribution in quantum wells. According to Fermi’s golden role, we can expect the corresponding wavelength of the most possible spontaneous transition. Hence, we can precisely solve the carrier concentration in the quantum wells and the corresponding occupied energy levels. Finally, we vary base bias current, temperature, and different quantum well position in the base region and analyze the relationship between the carrier escape time and effective base transit time, and the corresponding optical bandwidth. The modified charge control model can be useful for future layer structure design of light-emitting transistors to further improve the overall characteristics of both electrical and optical signals.