- 學位論文
奈米矽晶微碟全光開關元件之特性研究
All Optical Switching in a Silicon-Nanocrystal-Based Microdisk Resonator
摘要
我們以奈米矽晶為主要材料製作微碟全光開關元件，以錐形光纖耦合的方式進行量測，以中心波長1541nm之寬頻光源SLD (Super Luminescent Diode)進行穿透頻譜量測，驗證微碟共振腔的製程完整度及確定回音廊模態位置；另外以脈衝產生器配合藍光雷射達成波長405nm的脈衝雷射，可調整脈衝寬度及頻率，以其作激發─探測量測，觀察在小時間尺度下載子接受激發光之能量後產生的折射率擾動，以及回音廊模態波長位移現象，以此現象討論材料作為光開關元件的合適性。 首先以電漿增強式化學氣相沈積法成長富矽介電質，並在1200度高溫熱退火下形成奈米矽晶的薄膜，黃光製程將定義的圖形轉化至奈米矽晶薄膜，最後六氟化硫乾式蝕刻完成了內含奈米矽晶的20μm微碟共振腔，在穿透頻譜量測下，觀察到一階及二階徑向模態產生，Q值分別為2500及2100。 激發─探測實驗觀察到元件的開關速度相較於奈米矽晶之載子生命周期已有近十倍的提升，佐證元件的製作對其速度提升有所助益，如何再調整材料的成長來增快開關的速度，將是一大挑戰。
並列摘要
We successfully fabricated an all-optical switch using a Si nanocrystal microdisk resonator and we used the tapered fiber coupling method for measurement. The transmission spectrum is measured with a Super Luminescent Diode whose center wavelength is 1541nm. This diode can be used to verify the perfection of microdisk resonators fabrication and show the characteristic modal structure of whispering-gallery modes. Furthermore, we combined a pulse generator and a blue laser as a 405nm pulse laser whose pulse width and frequency can be adjusted. Then we used it in the pump-probe measurement and observed the refractive index variation that caused by the pumped carriers under short-time scale. The refractive index variation causes the wavelength shift of WGMs. In the summary, we discussed the appropriateness of this material based on our measured results. First we deposited Si-rich oxide by plasma enhanced chemical vapor deposition (PECVD). Then we used the 1200ᵒC post-annealing process to form the Si nanocrystals thin film. Subsequently, we used standard lithography to transform our patterns onto the nanocrystals thin film and dry etched the underlying Si substrate by SF6 . Finally, we successfully fabricated a 20μm microdisk resonator. From the transmission spectrum, we can observe first and second order radial modes. The quality factors are 2500 and 2100, respectively. The switching time of Si nanocrystal microdisk resonators is ten times better than the carrier lifetime of nanocrystal. It indicates that the fabrication of microdisk devices is helpful for improving the switching speed.