氮化鎵/氮化鋁奈米結構之光學特性研究

Abstract

在本論文中，我們利用有機金屬氣相沉積法在藍寶石基板上成長氮化鎵/氮化鋁奈米結構，並且對其光學特性做了一系列的研究分析。 從原子力顯微鏡影像中，我們發現在樣品表面上形成了類似奈米柱的結構。根據拉曼光譜的分析結果，我們觀察到位於605 cm−1的氮化鎵E2H模態，說明了在這種奈米柱結構中存在氮化鎵類量子點結構。從光激發螢光光譜中我們發現有兩個峰值，波長分別為310nm以及360nm，通過理論計算，這兩個峰值可分別對應於GaN/AlN奈米結構和GaN/AlN量子井的發光。在陰極射線發光映射圖中也驗證了310nm的發光確實來自於奈米結構。 從光激發螢光光譜量測結果中，我們發現由於微小的奈米結構，造成電子電洞波函數的高度重疊，使得在奈米結構中受到量子侷限史塔克效應(Quantum confined Stark effect, QCSE)的影響很小。在此奈米結構中，我們也觀察到載子侷限的效應。 在時間解析光激發螢光光譜量測結果中，我們發現在奈米結構中，其輻射復合時間比量子井發光峰值的輻射復合時間小了近一個數量級，說明了奈米結構擁有比量子井更好的載子限制效果。因此其內部量子效率可達到41.6%。 最後，我們觀察到在奈米結構中存在x或y方向的極化特性，其極化率為23.8%，可能是由於平面的各向異性所造成。

In this study, we studied the optical properties of GaN/AlN nanostructures grown on c-plane sapphire substrate by metal-organic chemical vapor deposition (MOCVD). By atomic force microscopy (AFM), nano-rod-like structures were observed on the surface. In raman spectra, a peak centered at about 605 cm-1 related to E2H mode of GaN QDs was observed, demonstrating the presence of the GaN quantum dots (QDs). Two peaks with wavelength of 310nm and 360nm were observed in PL spectra, which can be attributed to the nanostructures and QW emission respectively by theoretical calculations. Moreover, CL mapping also revealed the emission of 310 nm was from the nanostructures. In PL measurement, it demonstrated that the screening effect of QCSE in the nanostructures was unobvious due to the large overlap of electron and hole wave functions resulted from small size nanostructures, and the carrier localization characteristic is observed. TRPL measurement showed short radiative recombination time and higher room-temperature internal quantum efficiency in the nanostructures, and it indicated that nanostructures had stronger carrier confinement effect than QW. Finally, the polarization characteristic demonstrated x- or y-polarization with DOP of 23.8% due to anisotropy of in-plane strain in the nanostructures.