- 學位論文
三族氮化物低維次奈米材料之磊晶成長及物性分析
Epitaxial Growth and Fundamental Properties of III-nitride Low-dimensional Nanomaterials
摘要
本論文中分子束磊晶成長方法被應用在三族氮化物的異質磊晶成長。在缺少三族氮化物基板的情況下，三族氮化物的成長方式通常是經由異質磊晶成長法。在眾多基板的選擇中，低價位且擁有高品質的矽基板是一個很好的選擇。本論文的重點將著重在在矽基板上以分子束磊晶法成長三維、一維及零維三族氮化物的異質磊晶成長技術。 在矽基板上成長三維度的氮化物薄膜方面，我們利用相稱的晶格匹配(commensurate lattice match)技術來解決矽基板與氮化物之間晶格不匹配的問題。利用此技術，我們成功的成長出單晶結構的氮化鋁/氮化矽(AlN/Si3N4)雙層緩衝層。並進一步的利用此雙層緩衝層成長高品質的氮化鎵、氮化銦鎵及氮化銦磊晶薄膜。 在零維度的三族氮化物量子點的成長方面，此論文提出以Stranski-Krastanow (S-K) 機制成長氮化銦量子點的實驗結果。藉著高能反射式高能電子繞射方法，我們可以即時的觀測到量子點成長時由二維成長轉換成三維成長的變化過程。而利用原子力顯微鏡我們可清楚的分析氮化銦量子點的尺寸大小及分佈情況。 在一維度的三族氮化物奈米柱的成長方面，我們提出利用分子束磊晶法成功的在矽基板上成長出氮化鎵、氮化銦鎵及氮化銦奈米柱的磊晶技術。以此技術成長出的三族氮化物有著單晶結構且自發性垂直成長的特性。此論文並深入的分析奈米柱的發光特性。氮化銦奈米柱在室溫下可清楚的量測到紅外光波段的光激發螢光，但若與氮化銦薄膜比較，其螢光強度反而比較弱，且在變溫的光激發光譜的量測上展現出異常的溫度效應。我們認為這樣異常的溫度行為表現是來自於晶格結構的失序及表面電子聚集的效應所造成。氮化鎵奈米柱的室溫螢光波段在紫外光區( 3.4 eV)。除了很微弱的黃色螢光外，並無觀測到任何缺陷造成的螢光，說明了氮化鎵奈米柱的高品質結構。
並列摘要
Plasma-assisted molecular-beam epitaxy (PA-MBE) is applied in this thesis work for III-nitride epitaxy. Due to lack of suitable substrates, III-nitride semiconductors are typically grown by heteroepitaxial growth. Low cost and excellent crystal quality Si wafer is a good choice as the substrate material for III-nitride epitaxy if the difficulty of lattice mismatch can be overcome. In this thesis, we demonstrate that III-nitride semiconductors can be heteroepitaxially grown as thin films as well as zero-, and one-dimensional structures on Si(111) substrates by PA-MBE. For growing III-nitride epilayers on Si, we utilize the concept of commensurate lattice match (CLM) to overcome the problem of large lattice mismatch. It was found in our group that high quality III-nitride epilayers can be grown on Si(111) substrates using a commensurately matched AlN/Si3N4 double buffer layer structure. In this technique, a single crystal Si3N4 layer is used as a diffusion barrier to prevent intermixing and autodoping effects. And, the AlN layer, which is nearly lattice match with GaN and commensurate lattice matched with InN, is used as the second buffer layer. Based on this growth technique, InGaN epilayers covering the entire InGaN composition have also been grown on Si(111) substrates by PA-MBE. For zero dimensional III-nitrides, we find that InN quantum dots (QDs) can be spontaneously formed on AlN and GaN surfaces by PA-MBE under the Stranski-Krastanow (S-K) mode. By using the technique of reflection high-energy electron diffraction (RHEED), we can observe the 2D-3D transition of S-K growth mode and the lattice constant varied can observe drastically at the 2D-3D transition point from AlN to InN lattice constant. For one-dimensional III-nitrides, we demonstrate that vertically aligned InN, GaN and InGaN nanorods can be grown on Si(111) by plasma-assisted molecular-beam epitaxy. For the case of InN nanorods, near-infrared photoluminescence (PL) can be clearly observed at room temperature. However, in comparison to the InN epitaxial films, the PL efficiency is significantly lower. Moreover, the variable-temperature PL measurements of InN nanorods exhibit anomalous temperature effects. We propose that these unusual PL properties are results of considerable structural disorder and strong surface electron accumulation effect. For the case of GaN nanorods, room temperature (300 K) high-intensity PL peak is at the 3.4 eV near-bandedge transition without yellow defect emission. GaN free and donor bound exicton peaks can be clearly observed in low-temperature PL spectra, indicative of high crystal quality of GaN nanorods.