摻雜稀土元素於磷砷化銦鎵與介孔矽質奈米材料之光學特性研究

Optical studies of the rare-earth-doped InGaAsP epilayers and meso-porous siliceous nano-materials

李粵堅(Yueh-Jian Lee)

指導教授 ： 沈志霖

中原大學/理學院/應用物理研究所/博士(2004年)

https://doi.org/10.6840/cycu200400009

摘要

本論文研究磷砷化銦鎵磊晶層摻雜稀土元素的光學性質以及介孔矽質MCM-41和MCM-48的發光機制。內容共分成五部分：
(1) 磷砷化銦鎵磊晶層摻雜稀土元素的光學性質：
我們分別使用光激螢光、光電導和無接點電場調制等光譜量測研究摻雜稀土元素磷砷化銦鎵磊晶層的光學性質。在光激螢光光譜中，其峰值的半高寬會隨稀土元素鈥摻雜量增加而明顯變窄。在無接點電場調制光譜中，磷砷化銦鎵訊號的展寬因子也有變窄的現象。從光電導的實驗中，我們利用Urbrach模型去分析吸收尾端的變化，可以得到相關的Urbrach能量值，進而發現Urbrach能量值會隨鈥的摻雜量增加而減少。以上的實驗結果都證實了摻雜稀土元素於磷砷化銦鎵磊晶層中可有效的改善液相磊晶的晶體品質。
(2) 磷砷化銦鎵磊晶層摻雜稀土元素的持續光電導效應：我們對磷砷化銦鎵磊晶層進行持續光電導效應的量測，認為持續光電導的現象是來自樣品中類DX雜質的晶格鬆弛效應。另外，我們也對一系列摻雜鈥元素的磷砷化銦鎵磊晶層進行持續光電導的測量，發現持續光電導的衰減時間和電子捕捉能障都會隨鈥的摻雜量增加而減少。因此我們推論此現象與鈥元素會與樣品中的施子雜質作用有關。
(3)磷砷化銦鎵磊晶層摻雜稀土元素的拉曼散射研究：
我們測量了不同稀土元素含量磷砷化銦鎵磊晶層的拉曼散射，並且利用“空間相關”的模型來分析拉曼訊號的形狀。發現拉曼訊號的不對稱性不會隨稀土元素的摻雜含量而改變。因此，我們認為稀土元素在磊晶過程中有改善磊晶品質的效果，但沒有大量殘留在磊晶層中。
(4) 介孔矽質MCM-41和MCM-48之紅色螢光特性研究：
我們觀察到MCM-41和MCM-48的紅色螢光會包含兩個能量峰值1.9 eV和2.16 eV。這兩個尖峰分別可以歸因於非橋氧電洞中心和與扭曲鍵相關的非橋氧電洞中心。紅色螢光的強度會隨增加快速熱退火處理的溫度而有增強的趨勢，這是因為樣品表面的氫鍵和單一矽氫氧基群相結合而導致非橋氧電洞中心的濃度增加。在激發光源持續激發時，螢光強度會隨時間而衰減，我們認為是超氧分子和樣品表面產生化學鍵結所造成。
(5) 介孔矽質MCM-41之藍綠色螢光特性研究：
我們利用不同的光激螢光技術來研究MCM-41材料在藍綠色螢光的發光機制。由偏振光激螢光和光激螢光激發的結果，可以證實藍綠色螢光的起源來自於樣品表面的二摺疊配位矽中心之三重態至單重態的躍遷。另外，我們提出一個模型來解釋溫度變化的時間鑑別光激螢光實驗。

關鍵字

磷砷化銦鎵 ； 介孔矽質 ； 光電導 ； 光激螢光 ； 拉曼 ； 稀土元素

並列摘要

This thesis studies the optical properties of the rare-earth doped InGaAsP epilayers and mesoporous materials. Different optical techniques such as photoluminescence (PL), photoconductivity (PC), contactless electroreflectance (CER), micro-Raman, polarized PL, PL excitation measurements are carried out to investigate the physical properties of the rare-earth doped InGaAsP epilayers and mesoporous materials. These results are presented in the following parts:
(1) Influence of rare-earth elements doping on the optical properties of quaternary InGaAsP epitaxial layers:
The PL, PC, and CER measurements were used to study the influence of rare-earth doping on the optical properties of InGaAsP layers grown by liquid phase epitaxy (LPE). Both the full width at half maximum (FWHM) of PL and the broadening parameter of CER were found to reduce as the doping amount of Ho element increases. The absorption tails were analyzed with the Urbach tail model and the Urbach energies were obtained from these fits. It is found that the Urbach energy decreases with increasing the doping amount of Ho elements, indicating the Ho doping leads to the decrease of impurity concentrations. The Nd-deoped InGaAsP layers exhibit the similar results and the narrowest value of the FWHM of PL peak is 7.5 meV with Nd of 0.031 wt%. We demonstrate that the introduction of the rare-earth elements can greatly reduce the residual impurities of LPE-grown layers.
(2) Large-lattice-relaxation model for persistent photoconductivity in quaternary InGaAsP epitaxial layers:
We report the first observation of persistent photoconductivity (PPC) in In1-xGaxAsyP1-y epilayers. Under the excitation-energy, temperature, and alloy composition dependence of the PPC effects, it is found that the lattice relaxation of DX-like impurity is responsible for PPC in In1-xGaxAsyP1-y. PPC was also investigated in Ho-doped InGaAsP epilayers with Ho concentrations in the range of 0-0.15 wt%. As the Ho doping increases, the decay-time constant and the electron-capture barrier were found to decrease. We suggest that the introduced Ho elements may chemically react with donor impurities, suppressing lattice relaxation and hence reducing the electron-capture barrier. Also, the rare earth doping is demonstrated to be an effective method of improving the quality of InGaAsP epilayers.
(3) Raman scattering study of rare-earth elements doped InGaAsP epilayers:
Raman scattering measurements have been used to study the structural properties of the rare-earth doped InGaAsP epilayers. Using a spatial correlation model, we found the asymmetric broadening of lineshape of the Raman signal is not influenced by the rare-earth doping. It indicates that no large amounts of the rare-earth elements are being incorporated into the epitaxial layers during the purification.
(4) Red-light emission in MCM-41 and MCM-48 meso-porous nanostructure:
PL was used to study the emission of light from siliceous MCM-41 and MCM-48 that has undergone rapid thermal annealing (RTA). Two PL bands were observed at 1.9 and 2.16 eV and assigned to the non-bridging oxygen hole centers (NBOHCs) and the NBOHCs associated with broken bonds, respectively. The PL intensity is enhanced after RTA. Based on the surface chemistry, the enhancement is explained by the generation of NBOHCs that originates from the hydrogen-bonded and single silanol groups on the MCM-41 and MCM-48 surfaces. The PL intensity degrades with time during photoexcitation. The dominant mechanism of PL degradation involves the formation of the chemisorbed oxygen-related complexes (probably O2－ molecules) on the surface, which are adsorbed onto the surface and act as an efficient quencher of PL.
(5) Blue-green photoluminescence in MCM-41 meso-porous nanotubes:
Different PL techniques have been used to study the blue-green emission from siliceous MCM-41. It is found that the intensity of the blue-green PL is enhanced after RTA. This enhancement is explained by the generation of the two-fold coordinated Si centers and the non-bridge oxygen hole centers according to the surface properties of MCM-41. Through the analysis of PL with RTA, polarized PL, and PL excitation, we suggest that the triplet-to-singlet transition of two-fold coordinated silicon centers is responsible for the blue-green PL in MCM-41. In addition, we suggest a model to explain the temperature dependence of the carrier time constant and the PL intensity.

並列關鍵字

InGaAsP ； Raman ； Photoconductivity ； Rare-earth ； Photoluminescence ； Meso-porous siliceous

參考文獻

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