Type-II GaSb/GaAs Nano-Structures Prepared by Molecular Beam Epitaxy and Their Applications in Light-Emitting Devices

分子束磊晶成長之 Type-II 銻化鎵/砷化鎵奈米結構及其在發光元件的應用結構及其在發光元件的應用

曾祺哲(Chi-Che Tseng)

指導教授 ： 吳孟奇 ； 林時彥

國立清華大學/電機資訊學院/電子工程研究所/博士(2011年)

https://doi.org/10.6843/NTHU.2011.00113

摘要

在本文中我們將探討銻化鎵量子點形成與光學操作機制和其應用。藉由觀察原子力顯微鏡與反射式高能電子繞射圖形可以判斷形成銻化鎵量子點需要的臨界厚度是~2.5 ML。也研究與觀察到銻化鎵量子點在不同成長溫度與不同五三比例均會影響成長結果；其中隨著五/三比例由2遞減至1，銻化鎵量子點成長模式將由IMF轉為SK模式。為了提升銻化鎵量子點的光特性，本篇論文利用銻分子浸泡法於成長銻化鎵量子之前後，使得光特性有所改善。其原因推測於銻化鎵量子點在較長時間的銻分子浸泡下不僅保護銻化鎵量子點成長後不受到砷與銻原子交互作用而破壞形貌，也減少銻化鎵/砷化鎵之間介面的缺陷產生，將有助於提升光元件應用。在銻分子浸泡過程中隨著砷分子比例增加，發現銻化鎵量子點形貌逐漸變成環狀。其原因推測銻化鎵量子點在高比例的砷分子環境中會有較多的砷原子與量子點表面接觸，以至於發生砷與銻原子置換而形成銻化鎵量子環。我們也藉由掃描穿遂電流系統針對不同砷-銻分子比例的銻化鎵試片進行表面單一量子結構掃描，驗證其量子結構的改變。
隨著改善銻化鎵量子點的光特性，我們成功的研究出單一層銻化鎵/砷化鎵量子點發光二極體，也順利的在室溫下操作。銻化鎵/砷化鎵量子點的電激發光訊號也隨著元件操作在順向偏壓而觀察到。由於銻化鎵/砷化鎵量子點發光二極體的能隙接面是屬於型態二，因此針對銻化鎵/砷化鎵量子點元件給於不同順向電流和射入不同功率的雷射，其研究電激發光與光激發光訊號均有發現螢光會伴隨輸入能量增強而有藍移現象。且螢光藍移位置的與輸入功率的三次方根呈線性關係，此現象是能隙接面屬於型態二的最佳證明。研究發光二極體在不同溫度下操作時觀察光特性在100K實有最佳強度，且當元件操作溫度由10K提升至100K時，其螢光訊號會有特殊的藍位移。為了更進一步了解型態二的發光二極體之間的載子傳輸機制與量子機制，因此研究低溫下元件在不同功率下的發光與電流趨勢。發現電洞在價帶裡因受量子侷限而有重電洞與輕電洞兩者能階的差異。因此根據對銻化鎵/砷化鎵量子點一系列的研究與改善其光電特性，將有助於未來對型態二的發光二極體有更深入的了解。

關鍵字

銻化鎵 ； 量子點

並列摘要

In this thesis, the critical thickness of GaSb QDs is determined to be ~ 2.5 ML by RHEED patterns and AFM measurements. The formation of GaSb QDs under different V/III ratios is investigated. The growth mode of the GaSb QDs would gradually change from IMF mode to the SK mode with decreasing V/III ratios. The different growth temperatures on the GaSb QDs are also investigated. The influence of Sb soaking times that optical property of QDs is improve when the increasing time of Sb soaking is investigated. The results suggest that long soaking time would not only protect GaSb QDs from As-Sb exchange during GaAs capping layer growth but also prevent defect formation in the GaSb/GaAs interfaces, which are advantageous for the fabrication and applications of optical device. The influence of background As on the morphologies of GaSb QDs is investigated. With increasing background As pressures, QD-to-QR transition is observed while similar QD/QR diameters are observed. The As atoms would actually act as a driller to drill down the QDs such that GaSb QRs would be observed with high As background pressures. The STM image of a single GaSb QR shown in this section has revealed that the rings are assembles of even smaller QDs instead of rings with smooth circle surfaces.
GaSb/GaAs QD LED with a single GaSb QD layer is investigated. Significant EL is observed for the device under forward biases, which suggests that pronounced dipole transitions occur at the GaSb/GaAs interfaces. With increasing forward biases, the observed EL peak blue shift confirms that the origin of luminescence is from the type-II GaSb/GaAs QD structures. The linear dependence of PL and EL peaks over the third root of the excitation densities has confirmed that the type-II GaSb/GaAs QDs should be responsible for the luminescence. In the temperature-varying EL measurements lower than 100 K, the device has exhibited a unique optical characteristic of increasing EL intensity and peak blue shift with increasing temperatures. To enhance the device performances, additional carrier confinement schemes are required in the future. The understanding of the operation mechanisms for the device is advantageous for the practical application of type-II LEDs. The 10 K EL spectrums of the device near the turn-on voltage have revealed a dominant luminescence transition from the optical recombination of holes in the LH to HH states with increasing voltages. The large energy separation between HH and LH states suggests that large strain accumulation is observed for the GaSb QDs.

並列關鍵字

GaSb ； quantum dot

參考文獻

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