分子束磊晶成長自聚性碲化鋅/硒化鎂鋅量子點經熱退火之光學特性研究

Abstract

利用分子束磊晶系統以Stranski Krastanov成長模式在硒化鎂鋅上成長碲化鋅量子點，量子點的厚度分別是3.0、3.5、4.0、4.5、5.0、5.5與6.0原子層。並利用快速熱退火和光激發螢光譜實驗技術來探討其物理特性。 分別對4.0原子層和6.0原子層的碲化鋅量子點做350度到550度的快速熱退火分析，經由光激螢光光譜發現兩個熱退火的效應，分別為成熟機制與互擴散。在退火溫度大於470度時，4.0原子層的量子點光激螢光譜峰值能量突然發生紅移(約35meV)的現象，是由於量子點的成熟機制所導致；然而，6.0原子層的量子點光激螢光譜峰值能量隨著溫度上升卻出現逐漸藍移的現象，這是因為互擴散所主導。為了闡明在成熟機制與互擴散的角逐關係，對5.0原子層的碲化鋅量子點做350度到550度的快速熱退火分析。觀察到峰值能量不會隨著溫度而改變，這個結果是由於成熟機制與互擴散之間達到相等的貢獻。本研究論證可以經由覆蓋厚度及熱退火的溫度來控制量子點的尺寸及密度，也闡述成熟機制與互擴散這兩者熱退火效應可以根據量子點覆蓋厚度決定。

ZnTe quantum dots (QDs) were grown on Zn1-XMgXSe with coverage varied from 3.0 to 6.0 MLs by molecular beam epitaxy using the Stranski Krastanov (SK) growth mode. The photoluminescence (PL) were used to investigate the effect of rapid thermal annealing on the optical properties of QDs. ZnTe QDs with coverage of 4.0MLs and 6.0MLs were rapidly thermal annealed from 350°C to 550°C. Two kinds of annealing effects, which were attributed to the ripening and inter-diffusion, were investigated by the analysis of PL spectra. In the case of 4.0MLs sample, the PL peak energy of QDs exhibited an abrupt red-shift (about 35meV) when the annealing temperature (TA) > 470°C. It is due to the ripening effect of QDs. However, for the 6.0MLs sample, as the TA was increased, the PL peak energy of QDs exhibited gradual blue-shift. In this case, the inter-diffusion dominates the ripening. In order to clarify the competition between the ripening and inter-diffusion, ZnTe QDs with 5.0MLs were rapidly thermal annealed from 350°C to 550°C. The peak energy was found to be independent of TA due to the equal contribution from the ripening effect and inter-diffusion. This study demonstrates that the dot size and dot density can be controlled by the coverage and the annealing temperature. The effect of rapid thermal annealing on the ripening process and inter-diffusion depends on the QD coverage.