自聚型砷化銦量子點光學特性及表面型態之研究

The Study of the Optical Characteristics and Surface Morphologies of Self-assembled InAs Quantum Dots

鍾東勳(Tung-Hsun Chung)

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/碩士(2009年)

https://doi.org/10.6843/NTHU.2009.00155

摘要

本論文係主要探討自聚型砷化銦量子點的表面型態及光學特性。根據實驗結果顯示：利用砷銻化鎵緩衝層，於適當銻原子濃度範圍內( 14 %)，可有效增加砷化銦量子點的密度及降低因鄰近量子點聯結而成島狀物的密度，這可歸因於砷銻化鎵會降低銦原子的移動能力所致。而變溫光激螢光頻譜中，波峰之半高寬隨溫度改變的趨勢，指出於砷銻化鎵是成長之量子點分佈有寬化的情形，而其強度隨溫度上升而下降的趨勢，會隨著銻原子濃度的增加，而有增快的趨勢，此係因於：介面中，過剩的銻原子會形成非輻射性放射的再復合中心所導致的結果。而砷銻化鎵覆蓋在砷化銦量子點上，則有削減介面應力，進而降低缺陷密度的功用，所以可運用於增強砷化銦量子點之發光特性。此外，於砷化銦量子點上覆蓋砷銻化鎵或砷化鎵，量子點密度趨勢呈現不同走向，砷銻化鎵覆蓋後量子點密度維持一定，而砷化鎵覆蓋的量子點則先增後降。此可歸因為砷銻化鎵具有較高的移動能力所致。據此，部分覆蓋砷銻化鎵的量子點結構，可提供原子力顯微鏡取得更近似內層量子點的密度。另一方面，於砷化銦量子點紅外線偵測器中，若改變砷化銦量子點的厚度，則可發現偵測波長並不會隨著厚度的增加而有所變易，這起因為：光激螢光激發頻譜指出導電帶中。因吸收光能而產生躍遷的起始能階之間之能量差並不會隨著厚度增減而明顯地有所異動。但隨著砷化銦厚度增加，光激螢光激發頻譜中屬於沾濕層的重電洞及輕電洞之間的能量差則會增加，從這結果，我們認為在砷化銦/砷化鎵量子點系統中，大部分的應力都是積聚在沾濕層而非量子點區域裡。

關鍵字

砷化銦 ； 砷化銻鎵 ； 量子點紅外線偵測器 ； 光激螢光激發頻譜 ； 沾濕層 ； 變溫光激螢光頻譜

並列摘要

In this thesis, the optical properties and surface morphologies of the self-assembled InAs quantum dots (QDs) are investigated. First, the InAs QDs grown on GaAsSb buffer layers with different Sb compositions are investigated. The enhanced InAs dot densities are obtained with increasing Sb composition. However, when the Sb composition exceeds 14 %, severe QD coalsence is observed. Second, the influence of GaAsSb strain-relaxed layers (SRLs) on the InAs QDs is investigated. Due to the strain-reducing effect, the enhanced photoluminescence (PL) intensity is demonstrated for the sample with the SRL. Also observed are the surface morphologies of InAs QDs with GaAs and GaAsSb partial capping layers. The results suggest that the GaAsSb partial capping layers are useful for maintaining the actual InAs QD surface morphology. Finally, the photoluminescence excitation (PLE) spectrums and spectral responses of InAs/GaAs QD infrared photodetectors with different InAs coverage are investigated. Increasing energy separation between heavy-hole state (HH) and light-hole state (LH) in the wetting layer (WL) region is observed in the QD PLE spectrums with increasing InAs coverage. The results suggest that most of the strain resulted from the InAs/GaAs lattice mismatch is accumulated in the WL instead of the QD region. Also observed are the similar energy separations of energy levels responsible for the intra-band absorption in the PLE spectrums of the QDIPs such that similar detection wavelengths are observed for the devices.

並列關鍵字

InAs ； GaAsSb ； QDIP ； PLE ； wetting layer ； TDPL

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