光電晶體之研製與特性分析應用在光電積體電路

Abstract

發光電晶體(Light-Emitting Transistor, LET)是一種特殊的三端(Three port)電晶體，同時具有電訊號輸入、電訊號輸出與光訊號輸出的半導體元件，與傳統電晶體同樣具有電訊號傳輸的功能，同時在基極端的量子井可產生光訊號的輸出，使得發光電晶體成為一種新型的雙輸出電晶體元件，而發光電晶體其磊晶結構與傳統的異質接面雙極性電晶體(Heterojunction bipolar tranisitor)相似，基極、集極與次級極形成一p-i-n二極體可接收光訊號，故我們可以將發光電晶體當作是一個光接收器來操作，即為光電晶體(Heterojunction phototransisitor)，實現積體化光接收器(Receiver)的構想。發光電晶體集合了傳輸器(Transceiver)與接收器(Receiver)的特性，使之成為下一代光電積體整合電路(OEIC, OptoElectronic Integrated Circuits)的重要發展元件。 在本篇論文中，我們利用發光電晶體的光輸出特性與光接收特性，製作出單晶積體整合發光電晶體與側面耦合式光電晶體，一端作為光源，一端視為光接收器，量測其光/電訊號的特性。我們發現將光電晶體的集基極區域當作一個p-i-n diode時，其響應度只有0.1~0.23A/W之間，若我們將他操作至電晶體的模式下，其響應度可增加至1.3 A/W，若我們將利用三端操作的方式操作光電晶體，可以發現電流增益(β=IC/IB)可以得到改善，其增益可從1.35上升至12.3。 本篇論文中發光電晶體與光電晶體的整合積體化，尚有許多可以改善之空間，首先是兩元件之間的耦合，可以藉由波導之製作來改善，並且發光電晶體更可以進一步的製作成電晶體雷射(Transistor laser, TL)，增加光強度輸出與準直性；在光電晶體的部分其收光面積以及材料對於光子吸收的極限都是可以藉由材料、磊晶與光罩設計進行改善。

The heterojunction bipolar transistor (HBT) can be modified and operated as a three-port light-emitting device (an electrical input, an electrical output, and a third port optical output) by incorporating one or more quantum wells in the base region, thus becoming a heterojunction bipolar light-emitting transistor (LET). The epitaxy structure of the LET is very similar to the HBT so that we can operate the LET like a heterojunction phototransistor (HPT). The base, collector and sub-collector layers of a LET are designed to implement the p-i-n photodiode. The LET have the transiever and receiver characteristics, which becomes one of the best candidate of next generation OptoElectric Integrated Circuits (OEIC). In this thesis, we have designd and fabricated the monolithic intergrated light-emitting transistor and heterojunction phototransistor utilizing the optical output and receiver charactrics of the LET. Typcial p-i-n mode current-voltage characteristics have been measured for an HPT with the optical input from the LET. The responsivity of p-i-n photodiode is about 0.1~0.23 A/W, but when operating the HPT at transistor mode the responsivity can be improved to 1.3 A/W. The HPT also can be measured with three-terminal configuration. We found that the current gain of HPT with three-terminal configuration has large improvement with small base current input (1 μA) from 1.35 to 12.3 due to the light absorption. We can still improve the integration of the LET and HPT to enhance the performance. Firstly, we can fabricate wave guide between two devices to increase the coupling coefficient of two devices. Secondly, the LET can be substituted by the transistor laser (TL) due to the larger optical output. Finally, the area of optical window and the absorption litmit can be improved by the epitaxy of material and layout design.