具氮化鎵與氮化鋁鎵布拉格反射鏡之紫外光波段氮化鎵雷射之特性研究

Abstract

由於氮化鎵材料具有直接寬能隙引起大家的關注並且廣泛的製作成各種應用光電元件像發光二極體與雷射二極體。高亮度的氮化鎵發光二極體使它應用在交通號誌、液晶顯示器背光源和固態照明的可行性。此外，藍光雷射二極體是其中廣受應用在高密度的數位儲存工具的光源。本論文旨在研究具二十五對的氮化鎵與氮化鋁鎵布拉格反射鏡之紫外光波段微型圓盤以及四方晶格之光子晶體氮化鎵雷射。此布拉格反射鏡具85%的高反射率。接著我們研究不經深蝕刻或下部蝕刻的製程製做出大小為4.7μm的氮化鎵微型圓盤紫外波段光雷射。經過光性量測系統的量測，得到具低截止功率密度為0.03kW/cm2的雷射。藉由有限差分時域分析模擬我們去研究迴音壁模態的共振模態。關於在四方晶格的光子晶體雷射，我們觀察到一強雷射訊號從氮化鎵光子晶體結構而且此訊號是落在布拉格反射鏡結構的高反射波段區內。藉由三維平面波展開法以及有限差分時域分析模擬，我們去研究此光子晶體的邊帶模態。接著我們在n-型的氮化鎵層製做出大面積的氮化鎵準光子晶體奈米柱結構，藉由奈米壓印微影技術之後在準光子晶體奈米柱結構頂部以再磊晶成長出氮化銦鎵與氮化鎵結構之成對金字塔狀的量子井。經過光性量測系統的量測，我們觀察到具低截止功率的紫外光波段訊號且同時具有從量子井產生綠光。我們用有限元素分析法去分析準光子晶體的雷射模態。接著我們展現了在室溫下從一金屬鍍膜之氮化鎵奈米共振腔觀察到雷射訊號。我們觀察到了單一模態的紫外波段雷射訊號，其波長約略三百七十奈米在截止功率0.042kW/cm2. 我們也藉由有限元素分析法模擬的方式來分析此鍍金屬的奈米共振腔的雷射模態與能帶，我們相信此雷射模態是由波導的模態和表面電漿的模態所混合而成的。

Wide and direct bandgap of GaN-based materials have been attracted much attention for applications such as light emitting diodes (LED) and laser diodes (LD). The high brightness GaN-based light emitting diodes (LEDs) have made it possible to apply in traffic signals, backlight in liquid crystal displays, and solid state lighting. Besides, the blue LD can serve as the light source of high density data storage in high definition digital versatile disk(HD-DVD) which is one of the popular data storage tools. In this thesis, we are focus on the design and fabrication of the optical pumped ultraviolet GaN-based microdisk and square lattice of photonic crystal lasers with 25 pair AlN/AlGaN distributed Bragg reflectors. The distributed Bragg reflector provides a high reflectivity of 85%. We demonstrated a 4.7 μm GaN-based microdisk laser in ultraviolet range without undercut or deeply-etching procedures. Under optical pumping conditions, the lasing action was observed with a low threshold power density of 0.03 kW/cm2. We also characterized the whispering gallery mode(WGM) profiles of the microdisk with finite-different time-domain simulation. About square lattice of photonic crystal lasers, a strong lasing emission was observed from GaN photonic crystals within high reflectivity region of DBR. The photonic crystal bandedge mode was also characterized with three-dimensional plane-wave expansion (PWE) and finite-difference time-domain (FDTD) simulation. And large-area GaN-based photonic quasicrystal (PQC) nanopillars structure was fabricated on an n-GaN layer by using nanoimprint lithography technology. The regrown InGaN/GaN multiple quantum wells (MQWs) form nano-pyramid structure on the top of PQC nanopillars. Under optical pump condition, a lasing action was observed at ultra-violet wavelength with an ultralow threshold power, and the green color emission from InGaN/GaN MQWs was also achieved simultaneously. We characterized the lasing mode with finite-element method (FEM) simulation. Then a metal-coated GaN nanostripe laser was operated at room temperature. The ultraviolet lasing mode was observed at a wavelength of approximately 370 nm with a low threshold power density of 0.042 kW/cm2. The lasing mode and band diagram of the metal-coated nanostripe were also characterized using FEM simulation. We believed that this lasing mode was a combination of waveguide mode and surface plasmon mode.