利用兩段整合式發光電晶體探討異質接面光電晶體特性分析與邏輯閘應用

Abstract

在資訊爆炸的時代，將光訊號與電訊號整合於同一晶片上形成光電積體整合電路(OEICs, OptoElectronic Integrated Circuits)是未來重要的研究發展之一。發光電晶體(Light-Emitting Transistor, LET)有著獨特的電訊號輸入、光訊號與電訊號同時輸出的雙輸出的特性，且具有快速的載子複合速度。此外，發光電晶體與傳統光電晶體(Heterojunction phototransistor, HPT)磊晶結構相仿，同樣都在基極、集極與次集極間形成p-i-n二極體的光吸收層，因此可將發光電晶體作為光電晶體來當作光偵測器使用。由上述可知，發光電晶體集合了光源與接收端的特性，使之成為下一世代光電積體整合電路重要的發展元件之一。 本研究將兩顆發光電晶體整合於同一元件上，形成一個兩段式整合元件，其中一者為光訊號輸出端，另一者為光訊號之接收端。同時操作下，分析其作為光接收端的元件，在外部光注入下其直流電訊號與高頻特性的改變。隨著操作偏壓、工作電流以及光注入的改變，光電晶體的光響應度可達711.4 A/W。我們另外將穿隧接面引入元件的結構中，發現若有額外的穿隧電流的影響，則穿隧式光電晶體的光響應度可達3404.8 A/W。在元件的高頻特性部分，在有光訊號注入之後，光電晶體的截止頻率由1.4 GHz推至1.51 GHz，我們利用等效小訊號模型分析元件受到電容電阻寄生效應的影響。最後我們利用發光電晶體設計一個以光訊號為主的邏輯電路，形成AND閘與OR閘，並可以得到顯著的光訊號邏輯變換特性。 為了增進元件特性表徵，未來可以以「電晶體雷射」取代發光電晶體，以及設計波導結構來提升元件光訊號輸出與準直性，並可設計NAND閘與NOR閘，使光電邏輯電路運用廣泛。

In an era of information explosion, combining optical and electrical signals into a single chip to form OptoElectronic Integrated Circuits (OEICs) is one of the most important researches and developments in the future. In 2004, Milton Feng and Nick Holonyak, Jr. invented the first light-emitting transistor (LET) in UIUC. The III-V LETs with a direct bandgap and carrier injection have made themselves as three-port (an electrical input, an electrical output and a “third-port” optical output) devices. The LETs has a similar epitaxial structure to the conventional heterojunction bipolar transistor (HBT). The base, collector and subcollector layer of the LET can be employed to form a p-i-n diode for photon detection, which works as a heterojunction phototransistor (HPT). Therefore, the LET has the unique characteristics to function like a photon transmitter and receiver, which has the potential to become a building block for next-generation OEICs. In this thesis, we demonstrate an integrated two-section light-emitting transistor with one section working as a light emitter and the other one working as a phototransistor. Firstly, we use this two-section device to characterize the HPT with different operation points (IB and VCE) and injected optical power. The responsivity of the HPT is 711.4 A/W. A tunnel junction is then incorporated to form a tunnel junction heterojunction phototransistor (TJ-HPT). With the help of the tunnel junction, the responsivity can be enhanced to 3404.8 A/W. Secondly, we characterize the microwave performance of the LET under different optical injections. Through the analysis of small-signal equivalent circuit models, we can analyze the transist time by deembedding the circuit paracistics effect. The cut-off frequency enhances from 1.4 GHz to 1.51 GHz under an optical power injection. Thirdly, we design and demonstrate the optical logic gates in the form of an AND gate and OR gate utilizing the characteristics of phototransistors. The AND gate and OR gate have a significant on/off ratio with injecting optical power. In the future, we can enhance the performance of the two-section device by substituting theLET with the transistor laser (TL). Also we can design an optical NAND gate and NOR gate for future application of OEIC design.