分子束磊晶法成長摻雜氧的硒化鎘 量子點之光激發螢光特性分析

Photoluminescence properties of oxygen incorporated CdSe quantum dots grown by molecular beam epitaxy

陳志典(Chih-Tien Chen)

指導教授 ： 王智祥

中原大學/理學院/應用物理研究所/碩士(2009年)

https://doi.org/10.6840/cycu200900929

摘要

摘要

運用電漿輔助式分子束磊晶系統在硒化鋅緩衝層上成長摻雜氧的硒化鎘自聚性量子點，並且利用原子力顯微鏡、光激發螢光光譜、時間解析光激發螢光光譜等實驗技術來探究其物理特性。我們發現在硒化鋅緩衝層上先沉積極少量的氧原子時，其量子點螢光峰值能量呈現藍位移，推論此少量的氧原子增加了成核的密度，導致量子點尺寸變小 。然而，進一步地增加氧原子的含量，其量子點螢光峰值能量呈現紅位移，可能是由於量子點尺寸變大或者活性氧原子進入到量子點內部形成能帶彎曲效應。由變溫光激發螢光光譜繪出峰值能量對溫度的關係圖，發現所有樣品皆呈現自聚性量子點典型的S型變化，並發現沉積在硒化鋅表面的氧原子增加時，此S型變化的深度與寬度也明顯增加，顯示氧原子的增加會造成量子點尺寸均勻度變差；此外，由變溫光激發螢光光譜繪出螢光強度對溫度的關係圖，計算得知量子點活化能隨著摻雜氧原子而下降。由功率變化之光激發螢光光譜我們發現當激發光源的功率增加時，量子點峰值能量隨著激發光源功率的上升先增加然後持平，這可能是因為有氧原子加入的樣品，量子點內有產生一些侷限態。藉由時間鑑別光激發螢光光譜發現兩種不同的載子生命期，表示螢光峰值能量是由量子點及界面缺陷的侷限態所貢獻，且载子生命期隨著氧原子的含量以及成長中斷時間的增加而變長。

關鍵字

量子點 ； 氧原子 ； 硒化鎘

並列摘要

英文摘要

Self-assembled CdSe quantum dots (QDs) with oxygen incorporation have been grown on ZnSe buffer layers by using plasma-assisted molecular beam epitaxy. Atomic force microscopy (AFM), photoluminescence (PL) and time-resolved photoluminescence (TRPL) were employed to investigate the surface morphology and optical properties of CdSe QDs. The PL spectra showed that the peak energy of the CdSe QDs was blue-shifted when an extremely small amount of atomic oxygen was supplied. This result indicated that atomic oxygen probably played the role of the nucleation sites, and therefore increased the density of QDs and resulted in the size of CdSe QDs decreasing. However, the peak energy became red-shifted when the amount of atomic oxygen increased further, and finally the degree of red-shift increased with the amount of atomic oxygen raised. We proposed that the energy red-shift arised from the atomic oxygen may enhance the surface migration leading the QDs to increase the size, or/and the band-gap bowing effect of the CdSeO ternary materials. In addition, the temperature dependence of the PL peak energy showed that all samples followed the typical S-shape of QDs and the depth and width of the S-shape was increased as the amount of atomic oxygen was raised. The result was attributed to the size fluctuation of QDs was increased due to the incorporation of atomic oxygen. The activation energy, which was determined from the PL peak intensity versus temperature plot, showed a decrease after exposing to the atomic oxygen. Power dependent PL measurements showed that the peak energy increased gradually and saturated finally with raising the excitation power. We suggested localized states were produced when the oxygen were incorporated. Two exponential decay lifetimes were observed in the time-resolved PL measurements. The result indicated the origin of PL peak was from the transitions of excitons and localized states, respectively. The lifetimes increased as the amount of atomic oxygen and the time of the growth interruption increased.

並列關鍵字

CdSe ； quantum dot ； MBE ； oxygen ； migration enhance

參考文獻

J. L. Merz, and J. K. Furdyna, Appl. Phys. Lett. 73, 23 (1998)

E. Norman, and M. Pepper, Appl. Phys. Lett. 76, 25 (2000)

[4] M. Haase, J. Qiu, J. Depuydt, H. Cheng, Appl. Phys. Lett. 59,

[6] I. N. Stranski, L. Krastanow, Sitz. Ber. –Akad. Wiss. Math. –Nat.

[7] M. Volmer, A. Weber, Z. Phys. Chem. 119, 277 (1926)