覆蓋砷化銦鎵之砷化銦量子點光學特性研究

Optical properties of InAs/GaAs quantum dots with InGaAs overgrown layer

汪長剛(Chang-Kang Wang)

指導教授 ： 沈志霖

中原大學/理學院/應用物理研究所/碩士(2005年)

https://doi.org/10.6840/cycu200500199

摘要

摘要

我們利用光激螢光研究自我組成之砷化銦/砷化鎵量子點與砷化銦鎵 (應力緩衝) 覆蓋層之光學特性。由光激螢光激發光譜實驗中可發現，侷限激子之激發態中的高精細結構，顯示砷化銦/砷化鎵量子點中激子的量子尺寸效應。藉由量測濕層之輕電洞與重電洞能量分裂證明砷化銦鎵覆蓋層可減緩量子點層之應力。我們也利用時間鑑別光激螢光光譜研究隨溫度變化的螢光衰減時間，發現150 K之前，螢光衰減時間會隨溫度上升而增長，而在更高的溫度則縮短。隨溫度增長的螢光衰減時間可解釋為，受熱重新分佈的電子電洞對從量子點能階進入濕層後再補捉的現象。有砷化銦鎵覆蓋層的砷化銦/砷化鎵量子點，熱重新分佈之效應較顯著。高溫時(大於150 K)，非輻射再結合效應導致螢光衰減時間縮短。此外，我們以波長976 nm 雷射(其光子能量小於濕層能量)作為激發光源，發現較長的螢光衰減時間。當溫度增加時，發現螢光衰減時間有兩次增長與減少 (最大值約為50 K 與 150 K)。此現象可由熱導致光激發載子的重新分佈來解釋。

關鍵字

光激螢光 ； 砷化銦 ； 量子點 ； 砷化銦鎵

並列摘要

Abstract

We study the optical properties of self-organized InAs/GaAs quantum dots (QDs) and InAs/GaAs QDs with InGaAs overgrown (strain-reduced) layers by using photoluminescence (PL). A rich fine structure in the excited states of confined excitons were observed in photoluminescence excitation (PLE) measurements, indicating the quantum-size effect of exciton transitions in InAs/GaAs QDs. The strain relaxation due to the InGaAs overgrown layer was demonstrated by measuring the energy spitting of the heave-hole and light-hole in wetting layers. We also studied the temperature dependence of the PL decay times of InAs/GaAs QDs by time-resolved photoluminescence (TRPL). It is found the decay times first increase with increasing temperature up to ~ 150 K, then decrease at higher temperatures. The increased decay times can be explained by the thermal redistribution of electron-hole pairs from quantum dot states into the wetting layer followed by recapture. The effect of the thermal redistribution is more pronounced in the InAs/GaAs QDs with InGaAs overgrown layers. The decay-time decrease at higher temperatures is attributed to nonradiative recombination. By using a 976- nm laser with the photon energy smaller than the wetting-layer energy, an extra decay time of PL was observed. The dependence of the extra decay time on temperature was also investigated. The decay times first increase with increasing temperature and show two maxima (50 K and 150 K) as a function of temperature. The initial increase of PL decay times has been attributed to the thermally induced redistribution of the photoexcited carriers among the ground state and the first excited state in InAs/GaAs QDs.

並列關鍵字

quantum dot ； InAs ； InGaAs

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