同電子性銦摻雜對氮化鋁鎵薄膜之光特性研究

Abstract

在本論文中，我們利用光激發螢光光譜(Photoluminescence, PL)、時析光激發螢光光譜(Time-Resolved Photoluminescence, TRPL)與螢光激發光譜(Photoluminescence excitation, PLE)等方法，研究銦摻雜之氮化鋁鎵薄膜的光學特性。光激發螢光光譜顯示，當摻入銦的量增加時，Inbe峰半高寬有變窄的趨勢，黃色螢光強度減弱，並且產生一個新的銦相關螢光躍遷(IIn)。另外，整個光譜出現紅移的現象，Inbe與IIn的紅移能量相等。在時析螢光光譜上，當銦摻入後由於非輻射躍遷的機率增加，使得Inbe的躍遷生命週期減少。考慮激發光強度對螢光光譜變化的關係可以得知，Inbe、IIn、Ix三個躍遷過程並不屬於施子受子對(DAP)的躍遷。由變溫光激發螢光光譜中Inbe譜峰位置隨溫度的移動，可以看到所謂「S-shape」的現象，其成因是由於樣品在空間上有不均勻的組成濃度分佈，例如高濃度鋁(Al-rich)區域形成的侷限能態(localized states)。由實驗結果發現，大約在溫度70 K附近是其能由溫度提供脫離區域侷限的能量。此處我們用變溫PL強度所做的阿瑞尼士圖(Arrhenius plot)來計算，對於未摻雜銦的樣品，激子的侷限能(Eloc)是6meV，Inbe的活化能(Ea)為25meV。Eloc的能量若換算成溫度約為70K，剛好與「S-shape」的特殊變化之轉變溫度相符。摻雜最大流率的TMIn(450sccm)後，Inbe的活化能升高至35meV。而由於摻雜銦產生的IIn之活化能則由39.3meV下降至33.7meV。由前述資料，我們嘗試提出以下的解釋：銦摻入後，創造了新的躍遷能態(IIn)，使得氮化鋁鎵原本的主要躍遷(Inbe)的能態量減少，載子在Inbe上的躍遷機率下降，而IIn的躍遷機率上升，兩者的活化能則相對有所增減。最後我們利用PLE的結果，結合活化能的資料，畫出氮化鋁鎵的能階圖，並定義出Eloc、Ea、與Inbe、Inbe-1LO、IIn、Ix等之間的能階位置。銦摻雜所產生的雜質能階可同時貢獻在原本的Ix和IIn的發光躍遷。

We have studied optical properties of various isoelectronic In-doped AlGaN films grown by metalorganic chemical vapor phase epitaxy. From 20 K photoluminescence (PL) spectra, as In-doping was increased, the narrowing of full width at half maximum of the near-band-edge transition, the decreasing of the yellow luminescence and a new emission (i.e. IIn) were observed. Additionally, the red shift of Inbe and IIn was observed with equivalent shift energy. In order to determine the characteristics of Inbe, Ix and IIn, their excitation power dependent measurements were carried out indicating that they are not from donor-acceptor pair (DAP) transitions. Furthermore, the temperature dependence of PL was studied and the S-shape behavior was observed in the spectrum as due to the spatial fluctuation of Al content, for instance, Al-rich formed localized states. From the Arrhenius plot, the Inbe activation energy of 25 meV and the exciton localization energy of 6 meV in un-doping AlGaN film were obtained. However, after In doped into AlGaN, the Inbe activation energy increases to 35 meV and the IIn activation energy decreases from 39.3 to 33.7 meV. By using the photoluminescence excitation (PLE) technique, we found that the In isoelectronic doping created new energy levels that are responsible for the original Ix and a new IIn emissions. Finally, the significant increase of IIn and decrease of Inbe are resulted from the relative changes in activation energies.