含氧化銦及氮化銦量子點奈米複合薄膜之光激發光性質研究

Abstract

本論文研究以貼靶濺鍍法（Target-attachment Sputtering Method）製備含氧化銦（In2O3）、氮氧化銦（InOxNy）及氮化銦（InN）量子點（Quantum Dot，QD）之奈米複合薄膜（Nanocomposite Thin Films）。微觀結構分析發現量子點均以單晶微粒的形式均勻分佈於介電質（Dielectric）基材中。為確認In2O3 QD之波耳半徑（Bohr Radius）及與發生量子效應的關聯，本研究以調變濺鍍功率、貼靶面積與燒結條件等方式以製備不同大小的QD，並量測其光激發光光譜（Photoluminescence，PL）以分析含In2O3 QD奈米複合薄膜之發光特性，實驗結果顯示當In2O3 QD半徑小於1.32 nm時，不僅發光之藍位移（Blue Shift）程度明顯變大，其發光效率亦顯著的提升，理論計算與實驗結果之比對可推論其Bohr Radius應落於1.32 nm左右。本研究並屏除量子侷限效應（Quantum Confinement Effect），利用施體載子（Donor Carrier）與授體載子（Acceptor Carrier）遷移方向的不同以釐清In2O3之可見光發光機制，由於其紅光與藍光強度與施體載子之對應，且藍光與In2O3材料內之In/O之化學劑量比之偏離程度呈正比關係，可確認紅光及藍光之發光分別源自銦間隙原子（Indium Interstitial， ）及氧空缺（Oxygen Vacancy， ）缺陷能階之遷移；綠光強度與授體載子分佈一致，亦可推得綠光來源與銦空缺（Indium Vacancy， ）缺陷能階之遷移有關。 在濺鍍製程中導入氮氣（Nitrogen，N2）後發現介電侷限效應（Dielectric Confinement Effect）可抑制In2O3之綠光之發光效益，由於介電侷限效應主要影響QD表面處之授體載子，此結果證明綠光與銦空缺缺陷能階之遷移的相關性。導入N2亦造成In2O3 QD之氮摻雜效果並伴隨著紫光的產生，且其摻雜量在採用氮化銦靶材後有明顯增加，由X光電子能譜（X-ray Photoemission Spectroscopy，XPS）分析證實，所摻雜的氮佔據In2O3中之氧空缺位置並形成 之缺陷，此一缺陷能階之遷移推論為紫光發光之來源。 本研究亦以貼靶濺鍍法製備含InN QD之奈米複合薄膜，除了成功完成於室溫下即可發出紅外光（Infrared）之含InN QD的奈米複合薄膜之外，亦觀察到導帶邊緣（Conduction Band Edge）於費米穩定化能階（Fermi Stabilization Level）之釘扎效應（Pinning Effect），此效應為本研究中InN QD之能隙（Bandgap）無法再以量子侷限效應進行寬化的主要原因。另外，由變溫PL量測中可發現，InN QD之PL光譜中低能端與高能端的不對稱性分別起因於帶尾效應（Band Tailing）及熱分佈效應（Thermal Population Effect），且可藉由降低溫度改善其對稱性。

Photoluminescence (PL) properties of nanocomposite thin films containing In2O3, InOxNy and InN quantum dots (QDs) prepared by the target-attachment sputtering method are presented. Microstructures analysis revealed the fine dispersion of single crystalline semiconductor QDs embedded in the SiO2 or Si dielectric matrices of nanocomposite thin films. In order to identify the Bohr radius of In2O3 QD and its correlation with the quantum confinement effects, this study prepares the In2O3 QDs of various sizes by adjusting the sputtering power, the surface coverage ratio of pellets attached on target and the sintering condition of pellets. The PL analysis of samples observed not only an obvious blue shift but also an increase of luminescence efficiency when the size of In2O3 QD approached 1.32 nm. In conjunction with theoretical calculation, the Bohr radius of In2O3 QD was identified as 1.32 nm. Nanocomposite thin films containing In2O3 QDs with sizes greater than 1.32 nm were also prepared in order to eliminate the quantum confinement effect so that the origins of visible emissions in such samples could be analyzed. The red and blue emissions were found to correlate with the presence of donor carriers and the stoichiometry deviation of In2O3 was also found to affect the PL intensity of blue emission. This implied that the red and blue emissions are originated from the transitions of indium interstitial ( ) and oxygen vacancy ( ) defect levels, respectively. The presence of acceptor carriers affected the PL intensity of green emission, indicating such an emission is originated from the transition of indium vacancy ( ) defect level. The suppression of green emission in nanocomposite thin films containing In2O3 QDs caused by the dielectric confinement effect was observed by introducing nitrogen (N2) during the sputtering deposition of samples. This further illustrated that the correlation of green emission with indium vacancy in In2O3 since the dielectric confinement effect mainly affects the acceptor carriers at the QD surface. The introduction of N2 also led to the N-incorporation in In2O3 QDs and consequently resulted in the violet emission. The N-incorporation in In2O3 QDs was further enhanced by adopting the InN pellets for target-attachment sputtering deposition. X-ray photoemission spectroscopy (XPS) analysis revealed that the N2 atoms occupy oxygen vacancy sites of In2O3 QDs and generate a new defect type, . The implied that the transition of defect level results in the violet emission of nanocomposite thin films containing In2O3 QDs. Finally, the nanocomposite thin films containing InN QDs were prepared by the target-attachment sputtering method. The samples were able to emit the infrared (IR) emission at room temperature and the pinning effect of conduction band edge at Fermi stabilization level was observed. The pinning effect was the major cause for the absence of quantum confinement effect in bandgap (Eg) tuning of InN. In addition, the band tailing and thermal population effects was found to cause the asymmetry at low and high energy wings of PL spectra and such an asymmetry can be suppressed by reducing the measurement temperature.