砷化鎵銦量子點微碟共振腔之製作及光學量測

Fabrication and Optical Measurements of Microdisks Embedded with InGaAs Quantum Dots

陳建安(Chien-An Chen)

指導教授 ： 毛明華

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.00043

摘要

在微碟共振腔圓柱對稱的結構中，電磁場藉由在碟緣牆面上全反射環繞而形成共振，產生所謂的WGM(whispering gallery mode)模態，透過濕式蝕刻，讓微碟上下表面暴露於空氣中，使相對折射率差異大，因而場型更能夠對稱地被侷限在微碟共振腔內。
在微碟材料內搭配砷化鎵銦(InGaAs)量子點主動層，透過量子點大小不一致所造成的非均質寬化現象(inhomogeneous broadening)，形成寬頻的增益頻譜(gain spectrum)，以便於我們能夠在一個寬的能量範圍裡觀察到多個模態，並提供較寬的波長選擇性。
我們成功地利用電子束直寫系統技術，定義半徑2與5 μm兩種大小的微碟尺寸，製作出單層與雙層的微碟結構。我們在不同的溫度下進行了微光激發螢光實驗。室溫底下，在量子點的發光頻譜內，兩種大小的微碟都觀察到徑向模態(radial mode)，其模態平均間距對於半徑2與5 μm微碟分別為30 nm 和12.7 nm；當溫度降到77K，觀察到許多WGM模態，對於半徑2與5 μm微碟，其WGM模態平均間距分別為9~11 nm與3~4 nm，與模擬結果11.1 nm和4.4 nm相近。受限於量測儀器的解析度，我們量到最小的模態半高寬為70 pm，對應的Q值約為14000，而實際上的Q值將更大。改變不同的激發光強度，在半徑5 μm的微碟，觀察到了發出雷射光(lasing)的現象，其發出雷
射光有效臨界激發強度(threshold)，對於單層與雙層微碟分別約為394 μW和417 μW。

關鍵字

量子點 ； 微碟 ； 共振腔 ； 砷化鎵銦

並列摘要

Owing to the geometrical symmetry of microdisk (MD) cavities, they support whispering gallery modes (WGMs) in which light circulates around the periphery of the structure and is confined by total internal reflections at both the sidewall and the top and bottom surfaces of the MD. Being cladded symmetrically by the air at both surfaces, light is well confined inside the MD due to the large refractive index difference. With the InGaAs quantum dots (QDs) as the active region in the MD, the much broader gain spectrum allows more resonant WGMs to be observed due to the inhomogeneous broadening of size-dispersed QDs. By e-beam lithography, we defined MDs of 2 μm and 5 μm in radius, respectively.
After carefully applying both dry and wet etching processes, we successfully fabricated both single-layer and double-layer MDs. We performed micro-photoluminescence experiments at both room temperature (RT) and 77K. At RT, we observed radial modes in both sizes of MDs. The mode spacing for 2 μm and 5 μm MDs is 30 nm and 12.7 nm, respectively. As the temperature is reduced to 77K, we observed several WGMs with the mode spacing 9~11nm and 3~4 nm on average for 2 μm and 5 μm MDs, which agree very well with our simulation results of 11.1 nm and 4.4 nm, respectively. Limited by the resolution of the spectrometer, the minimum full width at half maximum (FWHM) of 70 pm was obtained, which corresponds to a high Q-factor of 14000. The real Q-factor will be even larger. By varying the pumping power at low temperature, we observed the lasing behavior in 5-μm MD with the lasing threshold of 394 μW and 417 μW for single and double-layer MDs, respectively.

並列關鍵字

Microdisks ； InGaAs ； Quantum Dots ； QDs ； Resonator

參考文獻

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