藍光二極體陣列之特性及藍光電晶體熱效應之探討

Abstract

本篇論文的主要研究為藍光發光二極體陣列特性的研究與探討，分別從陣列數目對光輸出強度、調變頻寬、等效電路模型、資料傳輸之表現作分析。目前已經有許多研究致力於開發高速藍光二極體，分別從磊晶、幾何、製程著手，希望可以追求更高的調變速度以之後可運用於可見光通訊，一般來說，達到高調變速度的通則是縮小元件面積，由於小尺寸的元件能夠承受更高的電流密度以及較低的接面溫度，達到較高的調變頻寬，但縮小元件面積的同時會犧牲輸出光強，運用於可見光通訊作為光源的元件，必須兼具傳輸速度與照明功能，因此，如何開發高速藍光二極體同時兼具照明功能是一大必須克服的問題。本篇論文透過將微米發光二極體透過並列的方式，整合成不同陣列數目的元件，探討陣列數目對發光功率及調變速度的影響，我們獲得了光強度隨陣列數目增加而現性增加的結果，且在相同電流密度下，不同陣列元件的調變速度表現相同，相較於單一式發光二極體，陣列式發光二極體除了能提升光強度外，並不會損失調變速度。我們進一步量測不同陣列數目相對的資料傳輸特性，得到越多陣列數目的元件在資料傳輸特性表現上更好的結果，因此在元件尺寸縮小時，透過此陣列結構，能增強光強度且維持調變速度，使元件資料傳輸特性更好。 此外，接續我們實驗室之前成功製造出第一個藍光量子井(QW) 發光電晶體，並呈現其基本光電特性及頻譜外，我們更進一步調查藍光發光電晶體的熱效應現象，傳統異質雙極性電晶體的電流增益隨溫度上升而變小，是由於溫度升高時，基極和射極接面能帶差變小，導致回流載子變多，電流增益變小，不同於傳統異質雙極性電晶體在熱效應表現的現象，由於載子經過基極裡的量子井，會有捕捉與逃脫機制， 而載子的逃脫時間方程式又與溫度成反比，也就是溫度上升，載子逃脫時間越短，逃脫出來的載子則會跑到集極形成集極電流，使得發光電晶體的電流增益隨溫度增加而變大，形成電流增益，透過此機制，發光電晶體可應用於溫度感測器，與一般紅外光的發光電晶體不同，藍光發光電晶體由於是可見光，將更容易被偵測與應用。為了進一步了解溫度對發光電晶體的影響，我們使用載子控制模型，透過解邊界條件並帶入實驗結果的參數，可獲的不同溫度下載子在基極區分布的情形。藉由以上特性，藍光發光電晶體將是未來可見光通訊與光互連的關鍵元件。

The core of this paper is the research and discussion of the characteristics of blue light-emitting diode arrays, including analyzed the effect of the array numbers on the light intensity, modulation bandwidth, equivalent circuit model and data transmission. At present, there are many studies devoted to the development of high-speed blue light diodes, starting from epitaxy, geometry, and manufacturing processes. Pursuing higher modulation speeds to be applied to visible light communication. Generally speaking, the higher modulation speed can be achieved by scaling down the device area. Because the small size component can withstand higher current density and lower junction temperature to achieve higher modulation width. However, reducing the component area will sacrifice light intensity. As a component of the light source for visible light communication, it must have both modulation speed and illumination function. Therefore, how to develop a high-speed blue LED and simultaneously have a lighting function is a major problem that must be overcome. In this paper, by integrating the micro-light emitting diodes into a parallel array, the effects of the number of arrays on the luminous power and the modulation speed are discussed. We have obtained a linearly increase in the light intensity as the array number increases. The modulation bandwidth of the different arrays behave the same at the same current density, which means the array configurations can enhance the optical power while not lose the modulation speed. We further measure the data rate characteristics of different arrays, and find that the device with more array numbers can exhibit better performance in data transmission characteristics. In summary, the light intensity can be enhanced and better data transfer quality can be obtained through the array structures. In addition, after our lab successfully manufacture the first blue quantum well (QW) luminescent transistor, and present its basic optoelectronic characteristics and spectrum, we further investigate the thermal effects of blue luminescent transistors. The current gain of the traditional heterogeneous bipolar becomes smaller as the temperature rises. When the temperature rises, the difference between the base and emitter junctions becomes smaller, resulting in more reflow carriers and smaller current gain. Different from traditional heterogeneous bipolar, the thermal effect on LETs is very different. Because the capture and escape mechanism in the QW, the carrier escape time equation is inversely proportional to the temperature, that is, the temperature rises, and the carrier escape time is shorter. The escaped carrier will run to the collector to form a collector current, so that the current gain of the light-emitting transistor becomes larger as the temperature increases. Through this mechanism, the light-emitting transistor can be applied to the temperature sensor. What’s more, the blue light-emitting transistors are more easily detected than GaAs-based (infrared) light-emitting transistors. As a result, blue LET is more suitable for thermal sensor application because they are visible light. Furthermore, we use the carrier control model to learn more about the thermal effect on the LET. By solving the boundary conditions and bringing in the parameters of the experimental results, we can obtain the distribution of carriers in the base region under different temperature. With the above characteristics, blue light-emitting transistors will be the key components for future visible light communication and optical interconnection.