穿隧接面發光電晶體之直流與射頻特性分析

Abstract

本篇論文的主要研究為穿隧接面發光電晶體的製程與其元件特性量測分析，我們將發光電晶體的AlGaAs/InxGa(1-x)As基-集極接面設計成高濃度的穿隧接面，同時比較銦含量分別為5 %及2.5 %的穿隧接面發光電晶體在直流及高頻特性上的差異。基-集極穿隧接面可提供額外的電洞回補到基極量子井提供額外的放光，使發光電晶體的輸出光強度和頻寬得以提升。可以藉由理論計算得知銦含量5 %的穿隧接面因為有較小的能隙而有較高的穿隧機率。此外，電晶體的基-集極接面為高摻雜濃度形成的穿隧接面，並透過直接穿隧(direct tunneling)及法蘭茲-凱爾迪西效應(Franz-Keldysh photon assisted tunneling)使得發光電晶體除了有電流調變的能力外還多了基-集極的電壓調變能力，這使得穿隧接面發光電晶體可以做為訊號混成元件。當元件操作在負微分電阻(negative differential resistance)區域時，會使光頻率響應出現鬆弛振盪造成高達12 GHz的光輸出頻寬。另外透過小訊號模型來萃取穿隧接面發光電晶體的小訊號參數，我們的到銦含量5 %的穿隧接面有較小的基-集極接面電阻驗證了5 %的穿隧接面發光電晶體有較高的穿隧機率及光輸出頻寬。 此外，我們製作出第一顆InAs/GaAs量子點發光電晶體。量子點因其特殊的量子能階及電子侷限能力在過去十年被應用在許多元件上，例如: 二極體雷射、發光二極體及光偵測器等。因此我們將量子點加入發光電晶體的基極當作主動區，並量測其輸出的電訊號及光訊號的特性曲線。

This thesis presents the fabrication and characterization of tunnel junction light-emitting transistors (TJLET) with 2.5 % and 5 % indium mole fraction at the AlGaAs/InxGa(1-x)As base-collector tunnel junctions. The collector tunnel junction is an additional source of holes resupply to the base, and to recombination, providing the higher optical output and optical modulation bandwidth. The experimental data can be explained by calculating the tunneling probability. In addition, high p+ and n+ tunnel junction doping can be more effectively controlled by the change of voltage via direct tunneling and Franz-Keldysh photon-assisted tunneling, which makes possible a direct scheme of voltage modulation in addition to the usual current modulation. This is an advantage for signal processing. A resonant optical modulation bandwidth up to 12 GHz is obtained via direct voltage modulation when the TJLET is operated in negative differential resistance region. An analytical understanding of these physical characteristics is developed based on experimental data and small-signal equivalent circuit model of TJLET. From the parasitic element extraction, we find out the base-collector resistance is the key component in the operation of TJLET. Moreover, the first InAs/GaAs quantum dot light-emitting transistor (QDLET) is fabricated. The δ-function-like density of state and strong localization of electronic wave function make the QDs attractive for many device applications. In this work, the electrical and optical characteristics of QDLET are demonstrated. The emission wavelength is near ~ 1100 nm and suitable for optical communication.