氮化鎵奈米柱製程與雷射特性之研究

Abstract

本論文中，我們利用快速熱退火( rapid thermal annealing, RTA) 將鎳聚成奈米小球，再使用電漿離子耦合反應系統(ICP-RIE)將氮化鎵蝕刻成柱狀，將小球洗掉後，成長一層氮化鎵在奈米柱的表面。我們使用刀鋒量測來得知雷射光點大小，以便估算雷射能量密度。在特性分析中, 包含了結構與光學特性上的相關研究。在發光特性方面，所利用的是脈衝光激發螢光光譜((Microphotoluminescence, μ-PL)，以及變角度和低溫光譜等進行樣品的光學與電特性分析。 藉由變功率脈衝雷射激發去探討室溫時氮化鎵奈米柱的雷射特性，比起未包覆一層氮化鎵的奈米柱，會有更低的閾值功率密度，和較高的自發放射因子(β value)。氮化鎵奈米柱的雷射波長會隨著光點範圍增大而有所紅移，且閾值功率密度和模態間距隨之下降。變角度實驗結果顯示做成奈米柱後，重新包覆過後的斜面結構使樣品的出光散射現象，存在方向性(10˚, -15˚)。另外由低溫量測中，我們可以得知奈米柱的特徵溫度約153K。由於氮化鎵雷射具有許多優越的光學特性，我們相信此結構可以應用在可見光及藍紫光雷射等高功率、大範圍及多用途之光電元件中。

In this study, we studied GaN nanopillars structure fabricated by combined two methods top-approch and bottom-approch. The sample of GaN nanopillars etched down by ICP-RIE with Ni nano mask ,then regrowth GaN passivation layer in the sidewalls. The spotsize dependent photoluminescence (PL), and angle-resolved PL and low temperature were performed to investigate the optical properties of the GaN nanopillars. This research intends to investigate the lasing characteristics of GaN nanopillars under optical pumping. GaN nanopillars has lower threshold power density and higher β value than etched pillars without passivation. The spotsize dependence of the lasing PL spectrum has been observed. As excitation spotsize increasing, the central position of lasing peak wavelength was gradual red-shift, threshold power density decreased and the number of lasing multi-peak modes dreased. We suggest that the peak shift effect of lasing peak was attributed to the change of material gain spectrum under different pumping condition, not related to the pumping power intensity under change of spot size. The angle-resolved PL results show the degree of emission anlges corresponding to the normal direction ( 10˚, -15˚ ) respectively. Moreover, it was observed that the increase in temperature (from 77K to 322K) leads to an increase in threshold excitation energy. It is due to the increase of non-radiated recombination and decrease of radiated recombination. The characteristic temperature T0, was estimated to be 153 K in the temperature range of 77K to 322K.