週期性線狀圖案a-plane藍寶石基板成長半極性氮化鎵薄膜之研究

Abstract

一般在藍寶石基板(a、c-plane sapphire substrate)上成長GaN發光二極體時，都會沿著極性c軸的GaN晶面成長，如此一來便會產生內建電場造成能帶扭曲，使得電子電洞復合機率下降，減少內部量子效率，同時也因能帶扭曲會有發光波長紅移-藍移的現象，而解決或降低能帶扭曲現象的其中一個方法就是使磊晶成長方向沿著非c軸方向成長，也就是非極性或半極性GaN晶面，因此本研究希望製作出a-plane線狀圖案化藍寶石基板成長半極性的GaN晶面。

在第一組實驗與平邊平行的a-plane線狀圖案化藍寶石基板中，利用乾蝕刻的方式分別製作出Pyramid-DPSS與Flat-DPSS做比較，發現不管在SEM表面形貌、XRC半高寬、PL發光強度…等等量測都顯現出Flat-DPSS具有較好特性，但是XRD鑑定晶面後發現所成長出來的仍為極性GaN晶面，而Pyramid-DPSS則是利用側壁成功成長出半極性的(10-11)GaN晶面。

而第二組實驗與平邊夾三十度的a-plane線狀圖案化藍寶石基板中，利用乾加濕蝕刻的方式裸露出特定(13-46)sapphire斜面，濕蝕刻同時也改善了受到乾蝕刻受損的表面，並且成功在上成長半極性的(10-11)GaN晶面，但該晶面的成長速率仍然偏慢，且表面形貌仍有點粗糙，若未來改善該晶面的成長速率以及表面的平整度，對於後續製作成LED元件時，預估將對發光波長紅移-藍移的現象有很大的改善。

As generally recognized, built-in electric field will emerge along the polar c-axis of GaN epitaxial layers when growing the GaN base LEDs on a-、c-plane sapphire substrates. This may cause distortions of energy band gap, thereby decreases the recombination probability of electron-hole pairs and affects the internal quantum efficiency of such a structure. Moreover, energy band gap distortions will also produce red-blue shift in the emission wavelength. In order to alleviate this built-in electric field, non-polar or semi-polar GaN should be grown on sapphire instead. In this thesis, a-plane line patterned sapphire substrates followed by growth of LED structure are fabricated and non-polar or semi-polar GaN is expected to grow on sapphire substrates.

In the first experiment, the dry etching method is employed to produce both Pyramid-DPSS and Flat-DPSS with line patterns parallel to the flat of sapphire substrates. And the Flat-DPSS is observed to possess better properties in SEM surface morphology、FWHM of XRC and PL intensity…etc. However, it is examined to still be polar c-plane GaN under XRD θ-2θ scan. On the other hand, the semi-polar (10-11)GaN successfully grows on Pyramid-DPSS by its side walls.

In the second experiment, the a-plane line patterned sapphire substrates with 30° miscut to sapphire flat is fabricated. The semi-polar (10-11)GaN is successfully grown on specific (13-46)sapphire plane exposed by hybrid dry plus wet etching. And the wet etching method can repair the damaged surface caused by dry etching. Nevertheless, problems of growth rate and surface morphology still exist. The red-blue shift issues exist in LED devices manufacture may be resolved if these problems are overcome in the future research.