奈米矽晶於光子晶體發光元件之應用

Abstract

矽基光源整合在光通訊以及光電系統中是非常吸引人的應用，主要是因為它能利用現有廉價成熟的CMOS 製程來實現，在矽基板上整合CMOS 電路與光電主被動元件成為光電系統晶片已是未來的潮流。但受限於矽本身為間接能隙的材料，作為發光光源並沒有效率，然而發展光波導與光偵測器元件仍可獲得極佳的效率。為發展矽基半導體光源，我們以兩方面來著手，一材料本質利用鍺奈米微晶材料作為發光主動層，因為其具有可調的激發頻譜以及高於矽塊材的內部量子效 率;外部結構上，因為光子晶體具有優異控制光的能力，可以利用來提昇外部出光效率。而且，因為光子晶體，元件的維度得以大量縮小以整合在晶片上。光子晶體用來增加外部出光效率的方式有二，一為利用光子晶體能隙; 二為利用光子晶體光錐上不受侷限的出光膜態，在此我們利用的是第二種方式，光因為相位連續會耦合到不受侷限的出光膜態。在此我們也利用第二種方式，以在元件上方量測的室溫微光致激發螢光以探討其垂直方向出光增益。 我們主題分為兩部分，在第一部份我們利用文獻的資料以驗證模擬，其利用光子晶體增加外部出光強度的方式為能帶邊緣近Γ點低群速的膜態。我們利用光子晶體出光態密度的觀念模擬預測出光頻譜，模擬的出光頻譜與文獻上的量測頻譜有非常高的相似度，除了特定頻譜區域深谷差異，我們利用此差異將在後續對模擬有詳細探討。在第二部份我們以實驗加以佐證，我們選用內嵌鍺奈米微晶的奈米孔洞二氧化矽當作塊材，製作直角方形孔洞二維光子晶體於上以嘗試製作矽基光源，使峰值出光強度增加了一點五到三倍。我們利用之前模擬出光態密度的方式以實驗量測頻譜驗證，結果預測頻譜與量測頻譜相似度非常高。

Silicon-based light sources are attractive components in optical communication and optoelectronic systems, since one can take advantage on widely-available CMOS technology; however bulk silicon fails for light source applications in optoelectronics due to an indirect band gap of 1.1 eV. Here, we employ two approaches to overcome the drawbacks. Internally, germanium (Ge) nanocrystals were employed in the matrix for optical applications because of tunable spontaneous emission and better internal quantum efficiency compared to bulk Silicon. Externally, due to good capability to modify light extraction, photonic crystals were employed to enhance light extraction efficiency. Moreover with photonic crystals, dimension of devices can be scaled down much to integrate electronic devices on a chip. Enhancement of light extraction from photonic crystals can be distinguished into two ways. One is carried out by the vertical modes of photonic band gap. The other is performed by Bloch modes above light cone. In the work, we investigate the Bloch modes above light cone. The emitted light couples to radiation modes in accordance with phase match. We investigate the spectra of vertical radiation on samples by micro-photoluminescence experiments measured normal to the surface at room temperature. We separate the subject into two parts. In the first part, we make use of data from paper for simulation. The way to enhance external light extraction efficiency is by low group velocity flat band modes near Γ point. We employ the concept about photonic density of states (DOS) to simulate light extraction spectrum. The simulated spectrum resembles the measured one on paper well besides a dip. By the difference between them, detail discussion about DOS simulation was as follow in context. In the second part, We investigate light extraction characteristics from two-dimensional photonic crystals with a square lattice of air box. The photonic crystals are fabricated on mesoporous silica film with embedded Ge quantum dots for potential applications in Silicon-based light sources. The peak emission from photonic crystals exhibit 1.5- to 3-fold enhancement. Moreover, the spectral features are well explained by the calculations of photonic density of states near the in-plane wavevector of zero magnitude.