埋覆硒化鎘/硫化鋅膠狀量子點介電質微碟共振腔之雷射應用

Abstract

本文中微碟共振腔採用硒化鎘/硫化鋅膠狀量子點為主動材料，以二倍頻532奈米Nd:YAG固態雷射激發，實現於可見光600奈米附近的微碟共振腔雷射。我們製作微碟以二氧化矽層中間埋覆硒化鎘/硫化鋅膠狀量子點，直徑8微米和10微米。8微米的微碟Q值約3000，並且在10微米的微碟共振腔在室溫環境下成功量測到迴音廊模態，其Q值大約3100，雷射閾值約85μw。 相較大部分研究半導體微碟雷射，二氧化矽介電質微碟製程簡單並且成本較低。若要製作尺寸更小的微碟，在光感測器、積體電路上等方面加以應用，考慮損耗會隨尺寸愈小而增加，所以我們更進一步製作氮化矽微碟。氮化矽折射率高於二氧化矽，可增進微碟邊緣與周圍空氣的折射率差，光的侷限性更好，Q值越高。然而，二氧化矽微碟在雷射激發無損壞的問題，但氮化矽微碟卻會因雷射功率過大產生損壞，改變氮化矽成長參數矽甲烷的流量，雖降低了氮化矽折射率，但結構較不容易損壞。矽甲烷125sccm的微碟，直徑4微米觀察到Q值約1000；矽甲烷76sccm的微碟，我們在直徑6微米與8微米皆觀察到迴音廊模態，Q值約400。本文也對於此加以做製程上的討論並改善，期望能達到更好的量測結果。

In this thesis, dielectric microdisk resonators embedded with CdSe/ZnS colloidal quantum dots were demonstrated in the visible range of 600 nm. We fabricated silicon dioxide microdisks embedded with CdSe/ZnS colloidal quantum dots with diameters of 8 μm and 10 μm, respectively. Lasing has been observed for the 10-μm-diameter microdisk resonator, and the quality factor and the threshold pump power are about 3,100 and 85 μW, respectively. Since silicon nitride has higher refractive index than silicon dioxide, better optical confinement and higher quality factor can be expected in silicon nitride microdisk resonators. However, silicon nitride microdisk resonators could be damaged with excessive pump power. The problem can be relieved by decreasing the flow rate of silane in the silicon nitride deposition process at the cost of lowering refractive index. The quality factor of a 4-μm-diameter microdisk resonator with silane flow rate of 125 sccm is about 1,000. For microdisk resonators with silane flow rate of 76 sccm, whispering gallery modes can also be observed for diameters of 6 μm and 8 μm, and the quality factors are about 400. We also discuss and improve the fabrication process to achieve better measurement results.