發光電晶體基極主動區域設計的研究

Investigation of Base Active Region Design of Light-Emitting Transistors

陳郁文(Yu-Wen Chern)

指導教授 ： 吳肇欣

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.01081

摘要

在本論文中，我們先量測並比較不同偏壓條件下的發光電晶體的光調變頻寬，藉以探討基極主動區域與電壓有關的載子移除機制的影響。 光調變頻寬在一固定的2 mA的輸入電流情況下可以藉由電壓的調變從338 MHz（電晶體飽和操作）大幅提升到1.338 GHz（電晶體順向主動操作），我們演示Giga-Hz的發光電晶體自發光調變速度不僅僅類似發光二極體受到輸入電流的影響，還強烈的受到基極─集極接面的偏壓的影響。藉由改變獨特第三端─集極的負偏壓，不同的載子分布輪廓可以被建立並表現獨特的光調變頻寬。
此外，我們使用計算機模擬工具（TCAD）著手建立發光電晶體的模擬，我們希望在製程之前藉由改變元件的結構得到優化的結構，以期達到高電流增益、強放光輸出及快速的光頻率響應。我們成功演示了發光電晶體的直流及射頻的電跟光的特性，我們先表現了異質接面電晶體及發光電晶體的電流增益、放光增益、能帶圖、發光分布，從異質接面電晶體到發光電晶體，在集極電流為12 mA下，電流增益會從52.02減少至2.02，基極發光復和速度則會從1.22×10^15提升到1.95×10^16 #/s。最後利用小訊號的模型分析，將量子井嵌入異質接面電晶體，基極傳輸時間會從7.9提升到85.5 ps。
最後，我們提出並比較不同發光電晶體基極主動區域設計，改變不同的基極參雜，材料的組成、量子井的寬度、位置，藉以得到優化的結構。我們集中討論不同量子井位置對發光電晶體電流增益、放光強度與微波特性的影響，我們在量子井較靠近射極的發光電晶體結構中，集極電流為12.4 mA下得到較小的電流增益（1.52）、較大的基極發光復和速度（1.52×10^16 #/s）、較大的基極傳輸時間（87.5 ps），較小的等效基極復合時間（133 ps），並利用直流分析、微波分析及載子控制模型分析加以整理討論。

關鍵字

發光電晶體 ； 計算機模擬工具 ； 光通訊 ； 載子移除機制 ； 傾斜載子分布 ； 量子井 ； 基極主動區域設計

並列摘要

In the thesis, the optical modulation bandwidths of light-emitting transistors (LETs) at different bias conditions are measured and compared to investigate the influence of the voltage-dependent charge-removing mechanism within the active region. The modulation bandwidth increases dramatically from 338 MHz (transistor saturation operation) to 1.338 GHz (forward-active operation) due to voltage modulation under a constant input current of 2 mA. We show that Giga-Hz spontaneous bandwidths of LETs depend not only on the input currents, which is similar to light-emitting diodes, but also are strongly related to the voltages of base-collector junction. By varying the reverse bias of collector terminal, different charge distribution profiles can be established to perform distinct optical modulation bandwidths.
Moreover, we want to obtain the optimized structure which has high current gain, large light output, and fast optical response by changing the device structure before fabrication. The dc and microwave analysis of electrical and optical characteristics for light-emitting transistors are demonstrated by using software of technology computer-aided design, TCAD. We demonstrate the dc characteristics of heterojunction bipolar transistors and light-emitting transistors, i.e. current gain, optical gain, band diagram and optical distributions. The electrical current gain is decreased from 52.2 to 2.02 and the base radiative recombination rate is enhanced from 1.22×10^15 to 1.95×10^16 #/s when transistor changes from HBT to LET at the collector current of 12 mA. Based on microwave analysis and small signal equivalent circuit, corresponding base transit time is enhanced from 7.9 ps to 85.5 ps by incorporating QW in the HBT.
Finally, different base active region design of the light-emitting transistors is presented and compared in order to obtain the optimized design, i.e. different base doping, compositions, QW widths, and QW positions. We focus on the effect of QW position design of light-emitting transistors on the electrical gain, optical output and microwave characteristics. Smaller electrical gain of 1.52, larger base radiative recombination rate of 1.52×10^16 #/s, larger base transit time of 87.5 ps, and smaller effective base recombination lifetime of 133 ps at the collector current of 12.4 mA can be obtained in the device with quantum well position closer to the emitter. These results can be discussed and organized through the dc, microwave and charge control model analyses.

並列關鍵字

Light-emitting transistors ； TCAD ； optical communication ； charge-removing mechanism ； tilted-charge distribution ； base active region design

參考文獻

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