- 學位論文
不同矽摻雜條件氮化銦鎵薄膜光學與材料特性研究
Studies on Optical and Material Properties of InGaN Thin Films with Different Silicon Doping Conditions
摘要
在本研究中，我們針對大於臨界厚度的無摻雜與矽摻雜的兩片氮化銦鎵薄膜樣品，有系統地探討了它們的光學與材料特性。在第一部份的研究中，我們針對原始成長的不同矽摻雜樣品做了有系統的光學及材料分析。在光激螢光光譜分析中，我們發現有矽摻雜的氮化銦鎵薄膜具有較強的侷域能階放光，其頻譜峰值隨溫度變化呈現S型變動，而在無摻雜的樣品中則不明顯。此外，根據室溫下的螢光光譜以及隨溫度變化之時間解析螢光發光實驗結果，我們發現由於矽摻雜效應能夠降低氮化銦鎵薄膜中的缺陷，使得其發光效率提升並增長了螢光光譜的衰減時間。從空間解析陰極螢光影像以及高解析度穿透式電子顯微鏡影像中顯示出矽摻雜效應的確可以改變材料微結構特性。在第二部份的研究中，我們針對兩種樣品做攝氏800度，為時30分鐘的成長後熱退火處理。在光激螢光光譜以及空間解析陰極螢光中，我們發現熱退火處理能夠增加矽摻雜樣品中接近表層富銦叢聚的密度進而增強其侷域能階的發光強度，但由於熱退火造成的熱引致非放射缺陷，使得整體發光效率降低。此外，在原子力顯微鏡影像中可以看出熱退火處理降低了氮化銦鎵表面的粗糙程度。在第三部份的研究中，為了探討深層的氮化銦鎵薄膜發光特性，我們採用不同深度的表面蝕刻，並且做該深度下的光學量測。我們發現在深層底下的氮化銦鎵具有較強烈的侷域能階發光，顯示在深層含有較強的富銦叢聚結構存在。對照在無蝕刻樣品上不同加速電壓的電子束所量測的陰極螢光光譜實驗，我們發現頻譜峰值位置隨加速電壓增加而有位移的現象，在無摻雜樣品中為紅移，而在矽摻雜樣品中為藍移。其趨勢與各樣品蝕刻後所量得之螢光光譜大略一致。該紅藍移趨勢之差異可歸因於矽摻雜在氮化銦鎵薄膜中使得存在於氮化鎵銦之間的應力能夠獲得較佳的釋放所致。
並列摘要
In this research, the optical properties and material nano-structures of an undoped and a Si-doped InGaN thin films beyond the critical layer thickness are studied. First, we systematically conduct the optical and nano-material analyses on the as-grown samples. From the results of photoluminescence (PL) measurements, we find that Si-doping results in stronger localized state emission. Cathodoluminescence (CL) and high-resolution transmission electron microscopy results show that Si-doping can alter the nano-structures of the In-rich clusters. Second, we study the thermal annealing effects on the properties of the InGaN thin films. From the results of PL and CL measurements, it is found that the localized state emission is enhanced due to the increased density of In-rich clusters near the surface during thermal annealing process. However, the integrated PL intensity is suppressed due to the formation of thermally induced nonradiative defects. In the third part of this research, we compare the depth-dependent optical and nano-material properties by etching the surfaces of the InGaN thin films. In either sample, the emission peaks corresponding to the localized states in both PL and CL measurements become dominant with increasing depth, implying stronger clustering in deep layers. By using various acceleration electron voltage in CL measurements, it is found that the trends of CL spectral peak shift are opposite between the two samples (red-shift in undoped sample, and blue-shift in Si-doped sample) This result is consistent with that from measurement of various etching depths. The difference between the two samples is attributed to the better strain relaxation in deeper layers of the Si-doped sample.