以氫氣處理之氮化銦鎵/氮化鎵多重量子井結構及生長於氮化鎵上不同長晶溫度條件之氧化鋅薄膜結構之穿透式電子顯微術分析研究

Abstract

在這個研究中，我們針對位障層有經過氫氣處理和未經過氫氣處理的氮化銦鎵/氮化錠的多重量子井結構作了材料以及光學的分析。同時，我們也針對在不同長晶溫度下以氮化鎵為基底的氧化鋅薄膜結構進行研究。材料分析的方法包括：高解析度X光繞射、高解析度穿透式電子顯微術以及應變分析。基本光學特性的分析則利用激發螢光光譜方法。 我們將探討在氮化鎵/氮化銦鎵多重量子井結構當中生長位障層時加入氫氣的效果。在激發螢光光譜的結果當中，我們發現在未經氫氣處理的樣品中，銦原子聚集的現象相當明顯。而且，激發螢光光譜的峰值會隨著探測晶圓不同處而變化。在高解析度穿透式電子顯微術結果中，我們發現經由氫氣的處理，銦原子主要侷限於井層，同時也減輕晶圓的邊緣處的銦密集的效應。而對高解析度穿透式電子顯微術的影像做應變分析，我們可以看到在晶圓的中心處的量子井結構比邊緣處的量子井結構來得清晰。在高解析度X光繞射的結果中，我們觀察到來自晶圓中心的多重量子井的訊號比邊緣強得許多，而且，透過氫氣的處理，試片中的平均銦原子濃度也變得比較低。 然後，我們將三種在不同長晶溫度的條件下，以氮化鎵為基底所成長的氧化鋅薄膜結構進行比較。雖然在較高溫度成長的結構當中，我們觀察到了有螺旋狀的不連續結構(寬大概100 奈米)，但是它的晶體結構不論在與氮化鎵間的界面或是遠離界面的地方，都比低溫成長的樣品來得好。全程高溫成長的樣本，在靠近氮化鎵的界面，是呈現柱狀的結構；全程低溫成長的樣本，則是比較像是薄膜的結構；而先以低溫成長，再以高溫長晶的樣本，則一開始是薄膜的形式，大約200 奈米後，便呈現柱狀的結構。而以高溫成長的樣本，通常會具有較好的發光效率。

In this research, we perform the optical and material analyzes of five InGaN/GaN multiple quantum wells of different H2 process conditions in growing barriers. Also, ZnO thin film structures on GaN grown at different temperatures are studied. The material analysis methods include high-resolution X-ray diffraction (HRXRD), high-resolution transmission electron microscopy (HRTEM), and strain state analysis (SSA) In optical characterization the fundamental optical properties are obtained with photoluminescence spectroscopy. We study the effect of H2 process in barriers of InGaN/GaN quantum well structures. In the PL results, we find that aggregation structures exist in the sample without H2 process. Also, the PL spectral peak vary over the wafer. In TEM results, we find that H2 process lead to stronger indium confinement in the well layers and can suppress the spinodal decomposition in the rim part of the wafer. By analyzing TEM images with SSA, we find that strong strains exist in the sample with H2 process such that spinodal decomposition become weaker. Besides, in 3D SSA images, we can see that the central part of the wafer have a better-defined quantum-well structure than that in the rim part. In XRD results, we find that the signal of quantum-well structures is quite strong in the central part of the wafer. Also, with the H2 process, the average content of indium in the sample is decreased. Then, we compare the nano-structures of three samples of ZnO thin films grown on GaN with different growth temperature conditions. Although disconnected spiral domain structures (at the order of 100 nm in width) were observed in the samples of high-temperature growth, the crystal quality is generally better than the one grown at the low temperature, either near the sapphire interface or far away from the interface. In the sample of high temperature growth through the whole process, the domain structures extend from the interface with a smaller scale and almost vertical sharp boundaries. The sample grown at the low temperature showed a connected structure from the interface. However, its crystal quality is quite poor. In the sample with initial low temperature growth and then high temperature growth, the ZnO layer started with a connected structure, like the sample of low temperature growth. However, it evolved into domain structures like the sample of high temperature growth beyond about 200 nm in thickness. The samples of high-temperature growth generally have higher photon emission efficiencies. The sample grown at the high temperature through the whole growth process has the highest quantum efficiency.