熱退火處理之砷化銦/砷化鎵量子點光性研究

Abstract

我們以PL量測不同厚度的InAs/GaAs量子點與其經過不同退火溫度後的特性，樣品中InAs的沉積厚度分別為1、1.65、2.31與2.49 ML。在變溫PL量測上，我們發現在低溫時量測到的PL光譜為所有量子點的放射總合，但在較高溫時量測到的訊號是較大量子點放射的訊號。我們觀察到沉積1ML的InAs尚無法形成量子點，但對於沉積1.65ML的InAs樣品已形成了量子點結構。對於量子點分佈較不均勻的樣品，我們觀察到隨著溫度增加半高寬有減少的趨勢，但當溫度足夠高時，半高寬會隨著溫度上升而增加。對於2.31ML與7.56ML未經8000C熱退火樣品我們發現其放射能量隨溫度變化不遵守Varshni法則，同時此兩片樣品有兩個不同放射能量的發光，經實驗證實為兩群不同大小量子點所造成的。在退火樣品量測方面，我們發現7000C退火會造成鎵原子擴散不均勻而導致樣品放射訊號半高寬變大，而在經過8000C退火後放射訊號半高寬明顯變小，我們推論是由於鎵原子擴散較均勻與量子點的大小分佈較集中所導致。

The InAs/GaAs quantum dots samples after annealing at different temperature have been investigated by temperature-dependent photoluminescence. The quantum dots with the InAs thickness varying from 1, 1.65, 2.31 to 2.49 monolayer(ML) are studied. At low temperature, the PL spectrum are determined by a combining effect of quantum dots of different sizes, and at room temperature are determined by the quantum dots of larger size. From the PL spectrum, we concluded that the 1ML sample displayed only quantum well behavior, but the 1.65, 2.31 and 2.49ML samples showed the typical feature of quantum dots. We observed a decrease in PL linewidth with increasing temperature for samples with inhomogeneous dot sizes. However, when temperature is high enough, the linewidth was observed to increase with increasing temperature. For the 2.31 and the 2.49ML samples, the relationship of emission energy versus temperature was found to deviate from the Varshni law, probably resulting from different quantum-dot size effect. At low (hight) temperature, the faster redshift of emission energy is dominated by the emission from the group of small (large) quantum dots. The broadening of linewidth after annealing at 7000C indicates an inhomogeneous diffusion of Ga atoms. When the samples were annealed at 8000C, a narrower PL linewidth was observed and was attributed to homogeneous Ga concentration and narrow size distribution.