氮化銦奈米點受覆蓋層影響之研究

Abstract

在本論文中，我們研究氮化銦奈米點在長晶過程中加上覆蓋層對其在表面形貌，組成變化，以及光學特性方面的影響。此氮化銦奈米點樣本是以流率中斷法於有機金屬氣相磊晶系統中所成長。我們藉由原子力顯微鏡系統探討氮化銦奈米點表面形貌變化。由原子力顯微鏡影像所顯示，當未有覆蓋層時，氮化銦類圓盤狀奈米點結構所呈現的平均密度為3.9×108 cm-2以及平均高度為24.3nm。隨著覆蓋層溫度增加時，氮化銦奈米點的形狀開始改變以及平均密度也隨之降低。其相似的趨勢也在螢光光譜上被觀察到。螢光光譜量測所示，氮化銦奈米點發光位置約在0.77eV。這與最近文獻上所提到的結果是相符合的。此外，對於氮化銦奈米點螢光強度隨著覆蓋層溫度增加的變化趨勢，與由原子力顯微鏡影像所呈現的結果是一致的。此外，另有兩個強度很明顯的可見光螢光訊號被觀察到。其位置分別落於2.975eV(紫光)以及2.37eV(綠光)。藉由高繞射角X光繞射光譜的分析，我們發先有兩個譜峰位置分別在71.7°及70.2°。比對螢光光譜和X光繞射光譜的關係，我們發現這個變化明顯地是由覆蓋層所影響而且推測那兩個可見光螢光訊號可能是來自於氮化鎵銦的組成變化。此外，其他的成因也不能完全排除,例如深層能階的缺陷態。我們進一步由近場光學顯微系統分析此螢光訊號的空間對應關係，並且也提出我們的解釋，此螢光訊號是來自於覆蓋層以及氮化銦奈米點與氮化鎵緩衝層間的中間層。

In this study, we investigated the capping effects on InN nano-dots which were grown by flow-rate-interruption method using metal organic chemical vapor deposition (MOCVD) in terms of morphology, composition, and optical properties aspect. The InN nano-dots morphology was examined by atomic force microscopy (AFM). AFM images showed the disk-like dots with average density of 3.9×108 cm-2 and dot height of 24.3nm, respectively for uncapped InN. By increasing the capping temperature the dots were deformed and the dot density decreased. The similar trend was also observed in photoluminescence (PL) spectra. The InN band to band emission appeared clearly around 0.77eV that agreed with recent reports. Besides that is consistent, the PL intensity of InN emission decreased with the increasing capping temperature with AFM observations. Moreover, another two strong visible emission bands at 2.975eV (violet emission) and 2.37eV (green emission) were observed. From the analysis of high angle X-ray diffraction curves of capped samples, we found two peaks at 71.7° and 70.2° that may be due to InGaN formation. It is likely that the visible emissions are from InGaN formed by capping processes, though other causes such as deep levels defects cannot be excluded completely. We further analyzed the spatial distribution of PL signals by NSOM mapping and suggest that the visible emissions come from both the capping and interface layers.