具有局部缺陷氮化鎵二維光子晶體面射型雷射光學特性之研究

Abstract

本篇論文研究具有局部缺陷氮化鎵二維光子晶體面射型雷射光學特性以及局部缺陷對雷射共振造成的影響。根據理論，在光子晶體周期結構中，雷射出射必須滿足布拉格繞射條件。因此，考慮樣品光致發光光譜中心波長400奈米，根據平面波展開法而設計光子晶體元件之晶格常數範圍190奈米。我們設計了四種不同的光子晶體元件，一種是沒有缺陷，而有缺陷的分為從中心到旁邊有三、四、五個週期光子晶體被挖空。沒有缺陷之光子晶體雷射發光波長為400奈米，隨著不同的缺陷大小，雷射波長以及雷射閾值會有所不同。為了了解其中變化的差異我們利用平面波展開法模擬光子晶體TE能帶圖。從實驗數據研究光子晶體雷射之正規化頻率正好相對於Γ1 之能帶邊界，表示雷射發生只在特定能帶邊界上。從極化狀態可證實雷射模態確實存在Γ1能帶邊緣。再來利用變角度解析螢光頻譜可以量測到對於不同缺陷之光子晶體雷射的E-K圖是類似的。於是我們利用共振腔之共振波長隨著腔長周期性變化的理論，算出對於不同缺陷大小之光子晶體雷射波長的變化。我們可以發現不同缺陷之光子晶體雷射分別對應到398奈米(H3) 392奈米(H4) 390奈米(H5)，是由於共振腔長之改變造成雷射波長的位移，而模擬的結果也和實驗吻合。此外，關於雷射閾值功率隨著缺陷變大而逐漸升高，是由於當光子晶體層數減少時，反射率以及共振之強度也隨之下降所造成之結果。

In this thesis, we investigated the optical characteristics and the effect of defects in GaN-based 2D photonic crystal surface emitting lasers (PCSELs). According to the theory, the lasing behavior in the photonic crystal grating structure could only happen as the Bragg condition is satisfied. Therefore, the lattice constant is determined to be 190 nm considering PL peak of the samples centered at a wavelength of 400nm by the plane wave expansion theory. We designed four types of PCSELSs, one is without defect, the other is with there periods PC missing, the other is with four periods missing , another is with five periods missing .Lasing wavelengths and lasing threshold powers varies with different defect size. In order to realize the difference between these devices, we use plane wave expansion method (PWEM) to simulate the TE band diagram. Normalized frequency of investigated PC lasing wavelength can correspond to band-edge frequency (Γ1), which indicates the lasing action can only occur at specific band-edge mode. Polarization states further confirm the existence of lasing modes at band-edge (Γ1) mode. By the angle-resolved micro -photoluminescence measurement, we find out that the band structure of these band edge modes with or without defect are similar. Based on the cavity mode theory , cavity modes shifts with cavity length, we calculated cavity mode detuning with cavity lengths which indicates H3 corresponding to 398nm, H4 corresponding to 392 nm and H5 corresponding to 390 nm respectively. Besides, lasing threshold power increasing with larger defect size is the result of coupling and feedback strength decreasing with photonic crystal.