砷化銦量子點光激發螢光藍移現象之研究

Abstract

本論文主要針對單一層自組式砷化銦（砷化鎵）量子點的光激發螢光行為進行探討。我們觀察到低溫下（20K）樣品光激發頻譜峰值隨著激發光功率增強有ㄧ『藍移現象』，此現象肇因於電子在量子點間穿隧效應所需的時間與電子電洞對輻射復合時間相匹配，而使電子在量子點間有ㄧ重新分佈的行為，不能再將量子點視為獨立的量子點，低光激發功率下由低基態能階量子點發光主導，高光激發功率時則換成高基態能階量子點發光主導；此現象與量子點密度多寡、量子點基態能階高低有密切關係。 根據上述實驗，我們另外建構了模型進行峰值『藍移現象』的模擬。模擬中除了利用穿隧效應以外，尚引入了雙激子發光進行模擬。在高密度量子點樣品模擬中，頻譜波峰的藍移現象確實與實際實驗中觀察到的藍移現象ㄧ致，證實頻譜波峰的藍移現象確實來自於載子在量子點間的重新分佈行為；而在低密度量子點樣品模擬中，並沒有得到載子重新分佈行為造成的藍移現象，反而必須加入雙激子發光才有實際實驗中觀察到的藍移現象，證實了在低密度量子點中的頻譜藍移現象來自於量子點中雙激子發光的影響。

In this paper, we are talking about the optical properties of single layer self-assembled InAs/GaAs QDs. At the low temperature（20K）, we have found that the peak position of the photoluminescence spectrum will have a blue-shift as the power of the photoluminescence increasing. This phenomenon comes from the tunneling time of the carriers between QDs is compatible to the carrier recombination time in QDs. The carrier will re-distribute in QDs during the radiative process, so each QD couldn’t be treated as independent one. The amount of the blue-shift is strongly affected by the density and the ground state energy of QDs. The higher density and the higher ground state energy, the bigger shift of the PL peak position. Based on the experiment above, we also set up a model to check out our explanation of “blue-shift” phenomenon. In the model, beside the “tunneling effect” we also introduce the “bi-exciton effect”. In high density QDs’ sample, simulated PL peak moves like experiment’s doing. So the blue-shift phenomenon comes from the carrier’s “re-distribution” in QDs in high density QDs’ sample. But in low density QDs’ sample, the simulated PL peak doesn’t change whether having “tunneling effect” or not. Until we introduce “bi-exciton effect” to our model, it moves like experiment’s doing. So the blue-shift in low density QDs’ sample comes from the “bi-exciton effect”.