電晶體雷射電壓調變物理模型與藍光發光電晶體製作之研究

Physical Model with Voltage Modulation in Transistor Lasers and Fabrication of the Blue Light-Emitting Transistor

張棋翔(Chi-Hsiang Chang)

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(2016年)

https://doi.org/10.6342/NTU201602077

摘要

電晶體雷射(TL)與發光電晶體(LET)除了保有傳統電晶體的特性以外，其光訊號擁有可以高速調變的特性，因此成為下一代光電積體電路元件以及光通訊系統光源的候選人之一。在本論文中，我們提出一個電晶體雷射的理論模型，其中包含直流電(DC)與交流電(AC)的特性模擬。傳統的半導體雷射大多以速率方程式來描述其雷射特性，不只是直流訊號，光的大訊號、小訊號模型以及頻率響應…等，都可以藉由速率方程式得到。為了能夠清楚地描述雷射輸出特性，我們建立電晶體雷射的速率方程式，並將法蘭茲-凱爾迪西效應(Franz-Keldysh effect)考慮至方程式中。從過去電晶體雷射的實驗中可以發現，隨著集極與射極間的跨壓增加，電晶體雷射的閾值電流會有越來越高的現象，且雷射輸出功率對輸入電流曲線的斜率也會有漸漸變小的趨勢，從這個理論模型我們也可以模擬出與實驗相同的趨勢，並且能夠更加了解其中的物理機制。更特別的是，由於法蘭茲-凱爾迪西效應的關係，電晶體雷射除了以電流來調變光訊號外，也能夠以電壓調變光訊號，我們可以利用速率方程式來計算電壓調變下得到的本質光頻率響應。在一般二極體雷射(DL)或面射型雷射(VCSEL)中，光的頻率響應會受到寄生元件(parasitic element)的影響，因此我們結合了本質光頻率響應與電路轉移函數，來描述在電壓調變下電晶體雷射的動態特性。此外，我們將探討經由小訊號電壓調變後所引起的頻率啁啾(frequency chirping)，並以此理論模型模擬出電晶體雷射操作在某個頻率範圍內，以小訊號電壓調變下所造成的頻率啁啾之效應會比一般半導體雷射還要小。
另一方面，我們製作出第一顆GaN/InGaN量子井發光電晶體，並量測其電訊號及光訊號的特性曲線。由電致發光頻譜可看出此發光電晶體的放光波段約在435奈米附近，為藍光波段，適合應用在未來的可見光通訊系統中。

關鍵字

發光電晶體 ； 電晶體雷射 ； 法蘭茲-凱爾迪西效應 ； 光頻率響應 ； 頻率啁啾 ； 可見光通訊

並列摘要

Possessing the transistor property and high-speed optical modulation characteristics, light-emitting transistors (LETs) and transistor lasers (TLs) have become one of the suitable candidates for next-generation optoelectronic integrated circuit (OEIC) device and optical communication light source. In the thesis, the theoretical model including direct-current (DC) and alternating-current (AC) characteristics of the TL is proposed. To describe the lasing characteristics in the TL, we discuss the effect of the Franz-Keldysh (F-K) absorption using the modified rate equations. Different threshold currents and slopes of the light-versus-current (LI) curves under different voltage biases can be observed in experiments and these phenomena can be described clearly from this model. For AC characteristics, the TL provides not only current modulation but direct voltage-controlled modulation scheme of optical signals via FK photon-assisted tunneling effect. A complete model composed of the intrinsic optical transfer function and an electrical transfer function is proposed to explain the behaviors of voltage modulation. Moreover, we discuss the small-signal frequency chirping under voltage modulation of the TL. The decreasing frequency chirping effect for small-signal high-speed modulation is demonstrated.
In addition, we fabricate the first quantum-well-embedded blue LET. The electrical and optical characteristics of the blue LET are demonstrated in this work. The center wavelength of the electroluminescence (EL) spectrum is about 435 nm. The visible wavelength shows that it has great potential for visible light communication system.

並列關鍵字

Light-emitting transistors ； transistor lasers ； optical frequency response ； Franz-Keldysh effect ； frequency chirping ； visible light communication

參考文獻

[4] M. Feng, N. Holonyak Jr, and W. Hafez, “Light-emitting transistor: Light emission from InGaP/GaAs heterojunction bipolar transistors,” Appl. Phys. Lett., 84, 151 (2004).

[5] M. Feng, N. Holonyak Jr, and R. Chan, “Quantum-well-base heterojunction bipolar light-emitting transistor,” Appl. Phys. Lett., 84, 1952 (2004).

[6] G. Walter, N. Holonyak Jr., M. Feng, and R. Chan, “Laser operation of a heterojunction bipolar light-emitting transistor,” Appl. Phys. Lett., 85, 4768 (2004).

[7] Walid Hafez, William Snodgrass, and Milton Feng, “12.5 nm base pseudomorphic heterojunction bipolar transistors achieving fT= 710GHz and fMAX= 340GHz,” Appl. Phys. Lett. 87, 252109 (2005).

[8] William Snodgrass, Walid Hafez, Nathan Harff, and Milton Feng, “Pseudomorphic InP/InGaAs Heterojunction Bipolar Transistors (PHBTs) Experimentally Demonstrating fT= 765 GHz at 25°C Increasing to fT= 845 GHz at -55°C,” IEEE Intl. Electron Devices Meeting (IEDM), pp. 1-4 (2006).