不同錳濃度碲化鋅/硒化錳鋅量子點的磊晶成長與磁極化子之研究

Abstract

本論文利用分子束磊晶系統成長第二型能帶結構碲化鋅/硒化錳鋅自聚性量子點，其中碲化鋅/硒化錳鋅量子點平均厚度被控制在2.0，2.2，2.4，2.6，3.0，3.5和4.0原子層。在平均厚度低於3.0原子層時，由光激螢光光譜可以發現兩個峰值，較高能量的峰值由濕層貢獻，而較低能量的峰值則由量子點所貢獻，並利用原子力顯微鏡觀察表面形貌證明量子點的形成。 接著成長一系列不同濃度的碲化鋅/硒化錳鋅量子點來觀察錳濃度對磁極化子的影響。在第二型能帶結構中，電洞與電子會被分別侷限在量子點內與量子點外，此時在量子點外的電子會極化錳自旋，因而形成磁極化子。在低溫時間解析光譜中，可發現錳濃度從2.8%增加到7.2%時，碲化鋅/硒化錳鋅量子點樣品中磁極化子的形成時間從96.2奈秒縮短至8.4奈秒，而形成所需的能量從9.0毫電子伏特增加至36.4毫電子伏特，由此現象可知透過錳濃度的調控，可以控制磁極化子的形成動態。

Type II ZnTe/Zn1-xMnxSe quantum dots (QDs) with different ZnTe coverages from 2.0 to 4.0 monolayers (MLs) were grown by molecular beam epitaxy system. When the coverages of ZnTe QDs were less than 3.0 MLs, two peaks in the photoluminescence (PL) spectra were observed. The higher energy peak was attributed to the emission from the ZnTe wetting layer, and the lower energy peak was due to the emission from the QDs. The formation of ZnTe QDs was confirmed by the surface topography study of atomic force microscope (AFM). A series of ZnTe/Zn1-xMnxSe QDs with different Mn concentration were grown to study the influence of Mn concentration on the formation of magnetic polaron. The type II ZnTe/Zn1-xMnxSe QDs confine holes inside non-magnetic ZnTe QDs and the electrons situate outside the QDs and spin polarize Mn ions, which lead to the formation of magnetic polaron. The time-resolved PL shows the decreasing formation time of magnetic polaron from 96.2 ns to 8.4 ns as the Mn concentration increasing from 2.8% to 7.2%. Accordingly, the emission peak shift caused by the formation of magnetic polaron increases from 9.0 meV to 36.4 meV. Current study illustrates that the formation dynamics of magnetic polaron could be manipulated by the control of Mn concentration.