量子點主要是三維侷限的量子結構，如此在狀態密度上是呈現delta-function的函數形式，並且三維侷限的庫倫作用力會使量子侷限史塔克效應增強。因此以三維侷限量子點結構來應用於電致光吸收調變器將會有許多優勢。本論文中將以砷化鎵為基板，利用自聚性長晶法成長一層砷化銦(InAs)量子點之p-i-n異質接面材料，來製作與驗證量子點電致光吸收調變器。
而在元件的製作上主要利用濕蝕刻製程，而其目的是為了得到很平滑的蝕刻表面以降低元件的光損耗，以及檸檬酸液選擇性的蝕刻材料造成主動層底切蝕刻，而達到高速的效果。量測証實元件的電致發光波長約在基態為1280 ~ 1320 nm波段以及激發態為1220 ~ 1240 nm波段。而吸收波長在1280 ~ 1320 nm波段，隨著外加逆偏壓的變大，其波長紅位移偏移量與外加逆偏壓呈二次關係，證實為量子局限史塔克效應(Q.C.S.E.)現象，而於7 V偏壓下的紅位移量約20 nm，以及頻寬變大的現象產生。量測波導長度為300 μm之光波導傳輸系數可以得知元件的調變效果在7 V偏壓下約5 dB，相較於量子井結構，量子點的調變吸收量均會比量子井還少兩個數量級，而量子點調變器的調變強度比量子井小約一個數量級，可知量子點材料上，有很強的史塔克效應現象，很適合往後作高效率調變元件用。高速的電光頻率響應上，在3 dB頻寬約3.34 GHz，主要受限於製程上的雜散電容值過大。經過最佳化的量子點結構與元件寄生電容，量子點的電致吸收調變器在電場調變下是有潛力可以達到高速的調變能力。

Quantum dot (QD) has been known as three-dimensional quantum confined structure. Thus, a delta-function type of density with three-dimensional coulomb interaction can have strong dependence on field-driven optical absorption, i.e. Quantum Confine Stark Effect (QCSE), leading to lots of advantages for applications of electroabsorption modulator (EAM). In this work, based on a GaAs substrate, a self-assembly InAs quantum dot (QD) based p-i-n heterostructure is applied for fabricating electroabsorption modulator.
The quantum dot electroabsorption modulation is fabricated by wet-etching technique, where the active region is formed by undercut wet-etching technique using selective etching solution (citric acid). In the device characterization, electro luminescence (EL) is first used to examine the optical transition of QD, showing 1280-1320 nm for ground state and 1220-1240 nm for the excite state. Using the photocurrent spectrum measurement, the red shift of 20 nm in photocurrent peaks from 0 V to 7 V is observed. Also, the peaks exhibit a quadratic relation against with bias, confirming QCSE effect of Q.D.. In the optical transmission measurement, 1300 nm light excites on a 300 μm long device, obtaining 5 dB extinction by voltage swing of 7 V. By comparing with quantum well (QW) structure, the modulation efficient is in the same order of magnitude. However, the active region of QD volume is at least two orders less than QW, indicating strong QCSE can be obtained from QD and QD can have potential for high-efficient modulation. High-speed EO response with -3 dB bandwidth of 3.34 GHz is also obtained, where the main speed limitation is on the electrical isolation on the n-type GaAs substrate. Through optimizing Q.D. structure and also parasitic capacitance, Q.D. EAM can have a great potential for the application of high-speed optical modulation in optoelectronic fields.

目錄 1
致謝 3
中文摘要 5
英文摘要 7
第一章 簡介 8
1.1 前言 8
1.2 研究動機 9
1.3 論文架構 14
第二章 量子點的高調變及高速機制 15
2.1 量子局限史塔克效應 15
2.2 吸收係數 18
2.3 載子跳脫機制 27
第三章 元件製程 33
3.1 製程元件設計與光模態模擬 33
3.2 量子點材料結構 34
3.3 製程步驟 37
3.4 製程結論 56
第四章 量測結果 59
4.1 金屬接觸電阻 59
4.2 電激發光 64
4.3 吸收頻譜 66
4.4 光波導傳輸系數 68
4.5 自發輻射發光 72
4.6 電-光頻率響應 74
4.7 相關製程討論 77
第五章 結論 79
參考文獻 80

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