砷化鎵發光電晶體特性的研究

Abstract

本篇論文主要在於探討砷化鎵發光電晶體的特性。由於發光電晶 體是由雙極性接面電晶體的基本結構與特性加以改良而來，因此， 我們會先簡介雙極性接面電晶體的基本特性。我們使用了實驗室開 發的程式，解波松方程式和漂移，擴散方程式，並且在高電場時的 砷化鎵區域，使用速度－電場飽和曲線模型。 本文中，分析了兩個發光電晶體結構並和實驗做比較：一個在基 極區域放置量子井（砷化銦鎵），稱作”LET”，另一個沒有放量 子井而以未摻雜的砷化鎵代替，稱作”HBT”。我們發現，電流增 益在HBT裡比在LET中大，但是，發光率卻是在LET中較高，這是 因為當電子由射極擴散到基極時，他會和在基極區域的電洞複合， 或是繼續擴散進而被集極所收集形成集極電流。由於元件操作時溫 度會上升，當溫度上升時，HBT的集極電流會下降，但是LET的集 極電流會上升。進而，我們利用載子的熱逃脫時間來近似載子穿越 基極所需的時間，當基極電流上升時，所需的時間下降，並且可達 到20ps，也和實驗吻合。 最後，我們分析了影響元件操作的各種不同因素，以提供元件設 計者設計元件的方向，並且發現，當射極摻雜較高，2×1018 cm−3， 元件操作在基極電流為5毫安培時，所有由基極注入電流並且在量 子井中複合發光的比例高達73%，電流增益為2.94，基極傳輸時間 為50.6 ps。

In the thesis, we study the characteristics of the light emitting transistors. We first introduce the basic properties of the bipolar junction transistor, because the light emitting transistor was based on the concept of the bipolar junction transistor. To investigate the dynamics of the device, we use the poisson drift-diffusion solver developed in our lab. We apply the velocity saturation model at high electric field on the intrinsic layer of GaAs materials. We analyzed two structures and compared it with experiment data: one without QWs in the base region is called as ”heterojunction bipolar transistor”(HBT); another with QWs in the base region is called as ”light emitting transistors”(LET). The current gain(IC/IB) is much larger in the HBT case than in the LET case. However, the ecombination rate in LET case is larger. Because when electrons diffuse into the base region, they either recombine with holes or are swept to the collector port as the collector current. Besides, because when temperature increases, the mobility will decrease. This will lead to lower collector current in HBT, higher in LET. Furthermore, we approximate the base transit time as the thermionic escaping time. The base transit time can be up to 20 ps which is fast and close to the experimental data. We also analyzed a series of factors affecting the device performance for designers a direction and optimized the device. We found that the higher emitter doping level can get better recombination rate and current gain. At 2 × 1018 cm−3 of the emitter doping level, and the work condition under IB=5mA, we can achieve that the recombination percentage in QWs 73%, the current gain 2.94, and the base transit time 50.6 ps.