新穎氮化鎵光子晶體雷射之研究

Abstract

在過去幾十年中，氮化鎵系列材料由於具有寬直接能隙與强鍵結力特性，因此吸引了許多注意並且廣泛的運用在各種光電元件中，包含發光二極體、雷射二極體、光偵測器與太陽能電池等。為了在這些光電元件中更能夠操控光的特性並且實現不同功能之高效能的光電元件，光子晶體便是一種可以提升元件效率並且能夠控制光的傳播方向。在此篇論文中，不同維度的光子晶體結構如一維、二維與類光子晶體結構被應用於氮化鎵系列材料上並且發展了不同功能性之氮化鎵光子晶體雷射。 首先，我們製作並分析了氮化鎵一維光子晶體又稱高折射比光柵之反射鏡以及面射型雷射。所製作出之氮化鎵薄膜高折射比光柵反射鏡厚度為160 nm，在藍光波段460 nm以及TE極化下可達到高於90%以及高頻寬60 nm之反射率。另一方面，我們也實現了在室溫操作下之氮化鎵高折射比光柵面射型雷射。以次波長高折射比光柵作為橫向共振腔，所量測到之雷射閾值條件為0.56 mJ/cm2，而雷射波長為394 nm且有著73%的極化率，且有著大範圍雷射面積之特性。 第二部分中，我們實現並且分析氮化鎵二維光子晶體面射型雷射以及非極性高品質奈米共振腔。對於氮化鎵光子晶體面射型雷射，我們研究了針對Γ1、K2以及M3之能帶邊緣模態以及三種不同晶格類型包含三角、正方及蜂窩晶格，利用多重散射法計算出實空間以及倒空間之共振模態與閾值增益並與實驗結果做比較，其中蜂窩晶格之光子晶體面射型雷射有著較低的閾值條件為1.6 mJ/cm2。另一方面，我們也製作出氮化鎵非極性高品質奈米共振腔。在低溫77K之下，在388nm量測到一個主要之共振模態，其品質因子為4.3×103且在m軸向有著64%之極化率。 在最後一部分中，我們利用奈米壓印以及再磊晶成長的技術製作並分析了氮化鎵類光子晶體奈米柱之雷射特性。使用小面積雷射光點約15 μm2激發樣品後，量測到之雷射波長為369nm而閾值條件為40 mJ/cm2，並且在近場影像中發現一侷域性雷射模態，產生之侷域性雷射光點約為3.6 μm。此外量測到雷射之發散角為5.2度與近場量測雷射光點結果吻合。此實驗結果以多重散射法之理論計算之實空間以及倒空間之雷射模態作為驗證。 以上所研究包含一維、二維及類光子晶體之氮化鎵光子晶體雷射展現了不同的雷射特性以及功能性，我們相信此結構所研究之氮化鎵光子晶體雷射元件可以應用在可見光及藍紫光雷射等高功率雷射、光積體電路、雷射顯示以及微投影系統及等應用中。

During the past decade, GaN-based materials, which provide wide direct bandgap and strong binding energy, have been drew great attention and widely used in various optoelectronic devices including light emitting diodes, laser diodes, photon-detectors and solar cells. For further manipulation of light characteristics and realization different function of high efficiency optoelectronic devices, photonic crystals (PCs) are a great candidate to achieve high efficiency optoelectronic devices and control of light propagation. In this thesis, different types of PC structure including one, two dimensional and photonic quasi crystal were applied on the GaN-based materials to develop different functional GaN-based PC lasers. First, GaN-based one dimensional PC also called high contrast grating (HCG) reflectors and surface emitting lasers (SELs) were fabricated and analyzed. The fabricated GaN membrane HCG reflectors revealed high reflectivity (over 90%) at 460 nm band with large stopband width of 60 nm in the TE polarization. On the other hand, GaN-based SELs using HCG were demonstrated at room temperature. The threshold energy density supported by the Fano resonance was measured to be 0.56 mJ/cm2 and the lasing wavelength was 393.6 nm with degree of polarization of 73%. Second, GaN-based two dimensional PC surface emitting lasers (PCSELs) and nonpolar high Q nanocavities were demonstrated and characterized. For GaN-based PCSELs, the multiple scattering method was carried out to calculate the mode pattern in real, reciprocal space and threshold gains for Γ1, K2 and M3 band-edge modes. The PCSELs with different lattice geometry were also studied and compared with simulation results. GaN-based honeycomb PCSELs showed a lowest threshold condition of 1.6 mJ/cm2 among all PCSEL devices. All the simulation results showed a similar tendency to the experimental ones. One the other hand, the nonpolar GaN high quality factor (Q) PC nanocavities were demonstrated. One dominated peak of PC H2 defect nanocavities was observed at 388 nm and Q factor was measured to be approximately 4.3×103 with degree of polarization of 64% along the m-axis at 77K. Finally, GaN photonic quasi crystal nanopillars were fabricated. Lasing action was observed at threshold condition of 40 mJ/cm2 and lasing wavelength of 369 nm under smaller pumping spot of about 15 μm2 at room temperature. One localized lasing mode was observed in the near field image and confirmed by mode pattern in real and reciprocal space. The localized lasing spot was estimated to be 3.6 μm which was matched to the divergence angle. These abovementioned GaN-based PC lasers presented various characteristics and functions. We believe these GaN-based PC lasers can be applied to visible light and UV lasers in high power laser, photonic integrated circuit, laser display application and projection system.