檯面圖案化氮化鎵孔洞結構上生長氮化鋁鎵的應變鬆弛行為研究

Abstract

本研究中，我們準備生長在不同結構的氮化鎵模板上共16種氮化鋁鎵樣品，用以探討平台及奈米孔洞結構對其上氮化鋁鎵層應力釋放的行為。氮化鋁鎵是以分子束磊晶技術生長，氮化鎵模板則是利用有機金屬氣相沉積方法生長。這些樣品包含兩個系列:系列一之氮化鋁鎵是在製作檯面圖案及孔洞結構後再生長；系列二則是先生長氮化鋁鎵在氮化鎵模板上，再製作檯面圖案及孔洞結構。我們利用倒易空間圖譜技術來量測這些樣品中氮化鋁鎵拉伸應變鬆弛百分比，因為所生長的氮化鋁鎵層超過臨界厚度，會產生或強或弱的應變鬆弛現象。我們發現由檯面和奈米孔洞結構所引起的氮化鎵層壓應變鬆弛導致氮化鎵晶格尺寸沿a軸增加，這結果導致氮化鋁鎵層中的拉伸應變變強，因此其應變鬆弛行為也就更強。然而，我們發現在檯面結構製作前先生長氮化鋁鎵層的樣品內，平臺結構對氮化鋁鎵的應變鬆弛影響不大，因為檯面結構在氮化鎵與氮化鋁鎵層中同時形成。

Sixteen AlGaN-on-GaN samples are prepared for studying the AlGaN strain relaxation behaviors when mesa and porous structures are fabricated in the GaN template based on the hybrid growth of metalorganic chemical vapor deposition and molecular beam epitaxy. The samples include two groups with the AlGaN layers overgrown after and before the fabrications of mesa and porous structures. The technique of reciprocal space mapping is used for measuring the tensile AlGaN strain relaxation percentages in those samples. It is found that the compressive strain relaxation in GaN caused by mesa and/or porous structure fabrications leads to the increase of GaN lattice size along the a-axis, resulting in a stronger tensile strain in the AlGaN layer and hence a stronger strain relaxation behavior in this layer since the AlGaN overgrown thickness is larger than the critical thickness. However, when we overgrow AlGaN before mesa fabrication, the mesa structure does not produce a significant effect on AlGaN strain relaxation because the mesa is formed in both GaN and AlGaN layers.