氮化鋁鎵薄膜表面微結構之近場光學特性

Abstract

本論文主要針對有機化學氣相磊晶系統 (MOCVD system) 所成長的氮化鋁鎵薄膜表面上微結構作一系列的近場光譜分析。氮化鋁鎵薄膜成長於不同材料的緩衝層 (buffer layer) 上，因薄膜所受的應力不同，表面會形成形貌相異之微結構。不同類型的六角丘狀 (Hexagonal hillock) 結構出現於以氮化鋁作緩衝層的樣品上，而V形缺陷則可在以氮化鎵作緩衝層的樣品上觀察到。針對不同類型的六角丘狀結構和平坦處比較，譜峰位置會有紅移，之前已有論文[1],[2]指出這現象是因不同的鋁組成分佈所造成的。然而，從近場光譜分析可知，隨著不同類型的六角丘狀結構，其光學特性和其表面形貌也有其特殊的相關性。而另一樣品上V形缺陷則可觀察到額外的發光譜峰 （∼3.578eV），有別於近帶躍遷的譜峰位置（∼3.693eV），有文獻指出此能階是由鎵空缺所造成的[3]。本論文中利用近場光學顯微鏡 (NSOM) 就單一不同形貌六角丘狀結構以及V形缺陷作光學性質之分析。

In this article, we analyzed the optical properties of the microstructures on AlGaN films with near-field scanning optical microscopy (NSOM). Different types of hillocks (mesa-like, tent-like, and pyramid-like) appeared on the film with AlN buffer layer while V-shape pit formed in the sample with GaN buffer layer. In the NSOM spectra, the emission from the apexes of hillocks of different types of hillock is red-shifted in comparison with that from the plain surface. It may be due to the fluctuation of Al content [1], [2]. Since the spatial resolution of NSOM (∼100 nm) is capable of observing different regions inside single hillock. The luminescence from various probed regions on different types of hillock reflects their properties in detail. The spectra showed an extra peak （∼3.578eV）from the V-shape pit that differs from the near-band edge emission （∼3.693eV）. We suggested that this emission could be attributed to Ga vacancy [3]. From the intensity-mapping image, Ga vacancies seemed to be accumulated at the pit.