氮化鎵二維面射型光子晶體分散回饋式雷射之研究

Abstract

本論文主要是探討氮化鎵二維面射型光子晶體分散回饋式雷射之製做與研究。在模擬方面，我們是利用平面波展開法來計算元件的光能帶圖。在製作方面，我們利用電子束微影技術，製作了不同晶格常數的元件(晶格常數從190到300奈米)。在量測方面，我們利用光激發系統在室温下進行元件的特性測量，我們觀測到不同的元件(不同的晶格常數)都會有雷射的發光現象，其臨界激發光能量密度大約為3.5mJ/cm2 ，雷射波長從397至425奈米，半高寬約為1.1Å。除此之外，我們對於其它雷射的特性也做了相關量測，例如，極化程度(53%)、發散角(<10∘)、雷射發光情形等… 。其中，在光學顯微鏡的觀測下，我們發現幾乎整個光子晶體的區域都會有雷射發光現象，並且由雷射的發光頻譜可以得知，此雷射在單一波長下操作。最後，我們也比較了實驗量測及理論模擬的正規化頻率。由實驗數據可發現其正規化頻率可分為幾個群組，這些群組都可以對應到相對的理論模擬結果，而這些對應的點則都是位於布里淵區的邊界，這是因為在這些布里淵區的邊界會滿足布拉格繞射條件。由以上的敘述，說明了我們可以獲得大面積單模態的氮化鎵藍光面射型雷射。

In this thesis, we study the fabrication and characteristics of GaN-based two-dimensional surface-emitting photonic crystal distributed-feedback (2D SEPC DFB) laser. We also simulated the band diagram of the PC structure to realize the lasing mechanism by using plane-wave expansion (PWE) method. We fabricated these devices with different lattice constant (from 190nm to 300nm) by using electron-beam lithography (EBL). The laser action of photonic crystal devices was achieved under the optical pumping at room temperature. The clear threshold characteristic was observed at different devices (a=190-300nm). All these devices show a similar threshold pumping energy densities to be about 3.5mJ/cm2. The GaN-based 2D SEPC DFB laser emits violet wavelength (from 397nm to 425nm) with a linewidth of about 1.1Å. In addition, the degree of polarization (53%)、divergence angel (<10∘) and emission image of the laser was also measured. In emission image of the laser, we obtain a stimulated emission of GaN-based 2D SEPC DFB laser over a large area. All emission light normal to the sample surface is collected into a spectrometer/CCD, and the lasing spectrum shows just one lasing mode in the whole lasing area. So, it is clear, the single mode GaN-based 2D SEPC DFB laser with large lasing area was demonstrated. Finally, we compare experiment results with simulation results. We are able to classify the normalized frequency into few groups. Different groups of the normalized frequency occur at different points of Brillouin-zone boundary, Γ、M、K points. All points of normalized frequency can exactly correspond to points of Brillouin-zone boundary because the Bragg condition only satisfies at these points.