Optical and Material Studies of InGaN/GaN Multi-Quantum Wells Light Emitting Diodes and Thin Films of GaGdN and GaCrN

本論文主要分為兩大部分:第一部分是分析氮化銦鎵/氮化鎵多重量子井的光學與材料結構特性，透過拉曼光譜、X光繞射、光激螢光光譜、光激螢光激發光譜以及時間鑑別光激螢光頻譜，來研究其材料結構與光學特性；第二部份為分析氮化釓鎵和氮化鉻鎵薄膜的光學特性研究。 在第一部份裡，我們研究在氮化銦鎵/氮化鎵多重量子井中對最靠近頂端的兩層位障寬度做變化 (由25埃、40埃、75埃、150埃和300埃) 之樣品的光學及材料結構特性。首先由X 光繞射實驗，我們可以得知樣品的量子井厚度以及量子井中的銦含量。接著，經由光激螢光光譜、光激螢光激發光譜以及時間鑑別光激螢光頻譜，我們可以得到位障寬度較薄的發光效率較高且衰退時間較小。實驗的結果對於將來光電元件發光效率的增加可提供一個重要的貢獻。 在第二部份中，我們探討有機金屬氣相磊晶系統成長不同濃度的稀有元素(釓和鉻)參雜在氮化鎵上形成氮化釓鎵和氮化鉻鎵薄膜，稱之為稀磁性半導體。稀磁性半導體獨特的優點是能顯示出材料的鐵磁性可共存在固體電子與光電子學間。在此，我們利用拉曼光譜和光激螢光光譜初步了解氮化釓鎵和氮化鉻鎵薄膜的光學特性。This thesis mainly divides into two parts: the first part is analyzed the optical properties and material characteristics of InGaN/GaN multi-quantum wells LED structure. By the Raman scattering, X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL), photoluminescence excitation (PLE), time-resolved photoluminescence (TRPL) experiments were carried out to study the optical and material structure properties; the second part is studied on the optical properties of GaGdN and GaCrN thin films. (1) InGaN/GaN MQW LEDs with different Barrier widths structures: We studied the optical and material structure properties of the blue emission MQW LED samples with different barrier widths (25 Å, 40 Å, 75 Å, 150 Å and 300 Å) near the top layer. First, from the XRD experimental results, we can determine the period thickness and indium composition of the samples. From the Photoluminescence, photoluminescence excitation and time-resolved photoluminescence experiments, we can find that the luminescence efficiency is higher and the decay time is small on the sample with thinner barrier widths. The experimental results shown here can serve as important clue for the enhancement of the luminescence efficiency in the future optoelectronic devices. (2) GaGdN and GaCrN thin films by MOCVD: Second, we discussed the metal elements (gadolinium and chromium) doped on GaN grown by metal organic chemical vapor deposition (MOCVD) with different concentration. GaGdN and GaCrN thin films are dilute magnetic semiconductors (DMS). The unique advantage of DMS is that they can exhibit ferromagnetism in materials compatible with those used for solid state electronics and optoelectronics. Here, we studied the optical characteristics on GaGdN and GaCrN thin films by Raman scattering and photoluminescence spectra