砷化銦量子點在不同條件與已圖樣化的砷化鎵基板上成長之研究

本論文主旨在於探討量子點的表面形態與發光特性，其主要內容在於嘗試調變不同的磊晶參數與方式。首先，我們在改變砷的供應步驟實驗當中得知，只要初始條件能供應充足的砷原子與銦原子鍵結成砷化銦量子點，其量子點結構就能展現出相似的表面形態與光激發螢光光譜，反之，若磊晶開始時砷的供應量不足，就無法形成均勻的量子點。這是由於砷化鎵基板上的砷含量不足，使得鄰近的銦原子群容易積聚成較大的砷化銦島狀結構。此外，就砷化銦量子點紅外線偵測器的元件效果來看，與標準的量子點成長方式比起來，藉由增加遷移距離所成長出的量子點具有較高的均勻性。後者的成長方式所製作成的紅外線偵測器具有較長的偵測波段與降低的正面入射吸收。對於具有不同銦含量的砷化鎵銦量子點而言，降低銦含量會形成體積較大的量子點以及光激發螢光光譜會有藍位移的現象產生。這是由於能隙大小會隨著鎵含量的上升而增加所致。當砷化鎵銦量子點的覆蓋程度在5與6 ML時，量子點的分布密度可以提升至7x1010 cm-2，但是當覆蓋程度增加到7 ML時，卻會有分布密度降低與光激發螢光光譜藍位移的現象產生。最後，適當的調整成長條件，高品質的量子點甚至能成長在僅50奈米厚的砷化鎵緩衝層上。在已圖樣化的砷化鎵基板進行再成長的磊晶實驗，使用銻砷化鎵作為緩衝層能達到更平坦的表面。

關鍵字

量子點；分子束磊晶；已圖樣化

並列摘要

In this thesis, the surface morphologies and optical characteristics of quantum dot (QD) samples grown under different conditions are investigated. Similar surface morphologies and photoluminescence (PL) spectra are observed for the InAs/GaAs QDs grown with both the As shutter always-opened and initially-opened procedures, while no uniform QD formation are observed with the As shutter initially-closed procedure. The phenomenon is attributed to the In droplet formation at the GaAs surface under the As-deficient condition. Additionally, compared with the standard QD growth mode on the device performance of the InAs/GaAs quantum-dot infrared photodetectors (QDIPs), better QD size uniformity is obtained for the QDs grown by migration-enhanced (ME) growth mode. Longer QDIPs detection wavelengths and reduced normal incident absorption are observed for the device with QDs grown by ME growth mode. For InGaAs QDs with different In compositions, larger QD sizes are observed with decreasing In compositions. Also observed is the PL peak energy blue shift with decreasing In composition, which is attributed to the increase of bandgap with increasing Ga composition. Uniform InGaAs QDs with dot densities up to 7x1010 cm-2 are observed for the samples with InGaAs coverage 5 and 6 ML. For the sample with 7 ML InGaAs coverage, QD density reduction and PL wavelength blue shift are observed. Finally, with proper growth condition, high-quality QD structure could be obtained with mere 50 nm GaAs buffer. Compared with GaAs regrown layer, the regrowth of GaAsSb material on patterned GaAs substrates has demonstrated much smooth surfaces.

並列關鍵字

quantum dot ； MBE ； pre-pattern

參考文獻

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國際替代計量

砷化銦量子點在不同條件與已圖樣化的砷化鎵基板上成長之研究

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