以分子束磊晶法成長硒化鎘鋅磊晶層及硒化鎘鋅/硒化鋅量子井之光學特性及內部量子效率研究

Abstract

本論文利用分子束磊晶法成長不同鎘濃度的硒化鎘鋅磊晶層及不同厚度之硒化鎘鋅/硒化鋅單一量子井，利用能量色散X-射線光譜得到硒化鎘鋅磊晶層鎘濃度分別為20%、25%、39% 與54%，並利用低溫光激螢光光譜及變溫度光激螢光光譜來探討樣品之光學特性及量子井的內部量子效率。由10K下的低溫螢光光譜發現隨著鎘濃度的增加，譜峰的半高寬會有上升的趨勢，同時缺陷發光也變明顯；由變溫螢光光譜得到的峰值對溫度關係，鎘濃度較高的樣品其峰值隨溫度上升有藍移的趨勢可歸因於侷限態的產生，另外，由積分強度對溫度導數擬合出的活化能會隨著鎘濃度升高而有下降的趨勢。量子井寬為3.8 nm 及6.4 nm的發光位置相對於磊晶層的發光位置藍移了139 meV及84 meV，利用激子與聲學及縱向光學聲子的交互作用分析了譜峰半高寬隨溫度上升而變寬的趨勢，變溫螢光強度擬合而得的活化能隨著井寬變寬而升高，對應到較寬的井寬所擁有較低的次能階，量子井寬為3.8 nm 及6.4 nm的樣品在室溫下內部量子效率為1.1%及0.22%。

Zn1-xCdxSe epilayers of various Cd content and Zn0.80Cd0.20Se/ZnSe single quantum well (QW) were grown by molecular beam epitaxy. The Cd composition (x) were confirmed as 20%, 25%, 39%, and 54% by energy dispersive spectroscopy. Temperature dependent photoluminescence (PL) measurement were employed to characterize the optical property and internal quantum efficiency (IQE). As the Cd content is increased, the energy peak of PL at 10K shows a redshift and the defect-related emission becomes stronger. For epilayer with high Cd composition, blueshift of emission peak with increasing temperature can be ascribed to existence of localized state. Furthermore, activation energy extracted from Arrhenius fitting decreases with the increasing Cd content. The PL peaks of the quantum well with well thickness of 3.8 nm and 6.4 nm respectively blueshift 139 meV and 84 meV compared with the epilayer due to quantum confinement effect. Linewidth broadening effect is analyzed by the exciton-acoustic and LO phonon interaction. The larger activation energy corresponds to the lower sub-band energy level for thicker QW. The internal quantum efficiency at room temperature is 1.1% for 3.8 nm thick QW and 0.22% for 6.4 nm thick QW.