不同尺寸銦化砷銦化鎵量子點的光學特性研究

Abstract

本論文主要利用光學技術，進行不同尺寸InAs/GaAs量子點的光學特性研究，主要分成兩個部份： 第一部份為零維量子點結構變激發功率下螢光特性研究。大尺寸量子點，當激發功率增加，峰值位置有些微紅移現象，因為雷射局部加熱所導致的。小尺寸高密度量子點，峰值有明顯藍移現象，是因為電子重新分配效應使峰值往高能量移動造成的。 第二部份，由螢光激發光譜結果比較不同尺寸量子點載子鬆弛行為，將歸因於分立能階位於不同能態密度quasi-continuum上，導致載子會有兩種不同鬆弛機制。LA coupling效率和量子點大小相關也和激發態位於quasi-continuum不同能態密度相關，導致PLE光譜有所不同。

In this dissertation we used photoluminescence (PL) and photoluminescence excitation (PLE) techniques to investigate size dependence of the optical properties in InAs/GaAs quantum dots (QDs). This thesis is composed of two parts： In first part of the thesis, we report results of power dependent PL measurements of InAs QDs in different sizes. For the large QDs, the ground state energy was found to shift to lower energy when excitation power was increased. This phenomenon can be explained by the cause of laser heating. On the contrary, for QDs in smaller size, the energy of ground state was blue-shifted with increasing excitation power due to the re-distribution of photoexcited carriers. In the second part, we investigated the influence of the intrinsic continuous density of electron-hole states (transitions between bound to delocalized states) on PLE spectra of InAs QDs with different sizes and different numbers of bound states. We compared results from measurements of the PLE and PL spectroscopy at low temperature and under high magnetic field (up to 14 Tesla). The coupling efficiency of the photoexcited carriers to the LA phonons depends not only on the size of the QDs but also on the position of the discrete states with respect to the quasi-continuum background. The PLE resonance associated with the bound transition in small QDs was disintegrated and broadened due to the high joint density states from the continuum background and strong coupling to the LA phonons. However, for larger QDs, the PLE resonances are still visible and they show Zeeman splitting and diamagnetic shift in energy when the magnetic field was applied.