披覆銻砷化鎵層之第二型砷化銦量子點的光學特性研究

Abstract

本論文藉由光激螢光技術研究披覆銻砷化鎵層的砷化銦量子點之光學特性。透過改變激發功率及時間解析的螢光光譜，我們確認了其第二型的能帶排列。根據變溫的量測，我們分辨出受電洞侷限影響的不同載子復合路徑：受限於銻砷化鎵層中電洞侷限態的長距離復合在低溫時占有很大的比重，而在高溫時大部分的復合皆由量子點附近能帶彎曲範圍內的短距離復合所主導。接著，我們研究了快速熱退火對於第二型量子點發光特性的影響。除了量子點發光的大量藍移及線寬縮減外，退火也導致輻射復合速率的增加以及消除了銻砷化鎵層中的電洞侷限態。我們論證了透過熱退火可以調變第二型量子點的能帶排列、波函數重疊率及復合動力學。最後，我們利用理論模擬了第二型量子點的能帶排列、發光能量及復合速率。我們發現當銻含量上升到15%時確實有第一型到第二型結構的轉變，造成了更長的生命期及較低的激子束縛能。特別的是，受到材料應變的影響，銻砷化鎵層中的電洞是被侷限於量子點的兩側而非正上方。

Optical properties of InAs quantum dots (QDs) capped with a thin GaAs1-xSbx layer were investigated by photoluminescence (PL). Both the power dependence of PL peak shift and the long decay time constants confirm the type-II band alignment at the InAs-GaAs1-xSbx interface. Different recombination path have been clarified by temperature dependent measurements. The long-range recombination with the hole trapped by localized states in the GaAs1-xSbx quantum well is significant at low temperatures. At higher temperatures, the recombination is dominated by the holes confined to the band-bending region surrounding the QDs. Then, we study the effects of thermal annealing on the emission properties of type-II QDs. Apart from large blueshifts and a pronounced narrowing of the QD emission peak, the annealing process also leads to enhanced radiative recombination rates and reduced localized states in the GaAs1-xSbx layer. We demonstrate that annealing can tailor the band alignment, wavefunction overlaps, and the recombination dynamics in the type-II QDs. Finally, we simulate the band alignment, the emission energy, and the recombination rate of type-II QDs by theoretical calculation. When the Sb composition exceeds ~15%, a transition from type-I to type-II band alignment occurs, resulting in a longer lifetime and a lower exciton binding energy. Noticeably, hole, which is in the GaAs1-xSbx layer, is confined around the InAs QDs rather than on the top due to the material strain.