砷化銦鎵/砷化鎵量子點光發射源

In(Ga)As/GaAs Quantum Dot Light Sources

謝東坡(Tung-Po Hsieh)

指導教授 ： 綦振瀛

國立中央大學/資訊電機學院/電機工程學系/博士(2007年)

摘要

本論文旨在利用砷化銦鎵/砷化鎵量子點為先進光源的發射源，主要內容包含傳統及量子光源兩大部分，在傳統光源部分，由於砷化銦量子點成長在砷化鎵基板上，晶格常數差異極大，量子點受到應力影響，因此一般量子點基態發光波長只能維持在1.2 mm左右，可以利用兩種不同的方式來延伸發光波長，1.成長體積較大砷化銦量子點，造成量子能階深化 2.利用砷化銦鎵披覆層除了可以降低應力影響所造成的發光波長藍位移，還可利用相分離使量子點體積更大，造成量子能階深化。然而，砷化銦鎵/砷化鎵量子點在長波長 (> 1.4 mm) 發光效率卻會嚴重的衰減，我們針對這個瓶頸，提出到兩種不同的發光衰減機制，包括：1.量子點的體積增大容易造成後續磊晶品質低劣及 2.用於延伸波長的批覆層，容易造成量子點鄰近區域的位障淺化，而降低量子點對載子的侷限能力。於此，我們分別提出兩種不同的方法來增強量子點的發光效率，我們磊晶成長高品質的批覆層及覆蓋層，來降低容易產生非輻射復合中心的機率，並利用電洞阻擋層有效地抑制發光效率的衰減，於此，我們是世界上首先將發光波長延伸至1.55 mm的團隊，至今仍是世界記錄。
第二部分是量子光源，傳統的量子點光源研究大部分聚焦在量子點的群體發光結果，如：發光二極體、半導體雷射等等，單一量子點所產生的單光子源是未來量子計算及量子通訊的基石，我們成長低密度量子點藉此隔離出單一量子點，並得到其所發出的單光子源，利用Hanbury Brown and Twiss量測方式，可以得到連續兩個有效的入射光子時間差的機率分佈圖，觀察到單光子源的反集束(antibunching)現象，發表台灣第一個光激發單光子光源。然而，用傳統的磊晶成長模式藉由應力方式自然形成量子點，量子點的形成呈現隨機分佈，無法正確的預測量子點的產生位置，對於單光子源實際應用將是很嚴重的考驗，於此，我們利用曝光及蝕刻等黃光製程，並藉由特殊磊晶成長砷化鎵緩衝層的方式形成奈米平台(40-50 nm)，利用選擇性成長技術縮減量子點成長的平面，在六角錐頂端的奈米平面定位單一量子點，藉此控制量子點形成的位置，也成功地觀察到單光子源的反集束現象，是第一個在(100)砷化鎵基板上控制單一顆量子點並實現單光子源的團隊。

關鍵字

單光子源 ； 量子點 ； 有機金屬氣相磊晶成長

並列摘要

This thesis is aimed to demonstrate advanced semiconductor light sources from InGaAs/GaAs quantum dots (QDs). The research of self-assembled QDs formed by Stranski-Krastanov growth mode has been of great interest in recent years. The QDs of this kind exhibit very good optical quality so that several QD based optical devices have been demonstrated. Base on this approach, the content of this thesis is divided into two main topics, including typical QD light sources emitted from QD ensemble and non-classical light sources from a single QD.
The thesis discusses typical QD light sources for the first topic. Since QD laser offers several advantages, the pursuit of 1.3 and 1.55 μm QD lasers for last-mile access-point optical fiber networks becomes a focused area of research. However, the typical emission wavelength of InAs QDs in GaAs matrix is often limited to 1.2 mm, an overgrown InGaAs layer on the InAs quantum dots is always used to extend the lasing wavelength to 1.3 mm. However, further extension of the emission wavelength to 1.55 mm has been difficult due to the unknown problem. In this work, we figured out the main problems and then appropriately solved them. We demonstrated that the emission wavelength of In(Ga)As quantum dot heterostructures on GaAs can be tuned from 1.1 mm to as long as 1.55 mm by a 9-nm-thick InGaAs overgrown layer with various indium compositions. Besides, 1.47 mm QD light-emitting diodes were also demonstrated.
However, the luminescence efficiency of the QDs still decreases significantly as the emission wavelength is extended to 1.5 mm. It is found that the loss of holes from QDs to their proximity via the high indium composition of InGaAs overgrown layer is one of the main reasons. We further enhance the optical efficiency of InAs QDs on GaAs emitting at the wavelength of 1.5 mm by inserting a carrier blocking layer, into the GaAs capping matrix. The method can improve the photoluminescence intensity of QD by five times at 1.5 mm.
In the second part of the thesis, non-classical QD light source is the major topic. Single photon source, which is one of so-called non-classical light sources, has been intensively pursued for quantum cryptography and quantum computing in recent years. Here, we report the preparation of low density self-assembled InGaAs on GaAs for single photon sources. Through using a set of optimized growth parameters, including the arsine partial pressure, total coverage of quantum dots, and growth temperature, high optical quality quantum dots with density as low as 5 × 106 cm−2 have been obtained. The spectral lines associated with the exciton, biexciton, multi-exciton, and charged exciton have been resolved and identified. Single photon emission from the single QD is verified by its anti-bunching behavior observed by a Hanbury-Brown and Twiss interferometer.
However, one of the major challenges that need to be overcome is the deterministic control over QD position as self-assembled QDs are of random distribution nature. Understanding and manipulation of QDs thus becomes an important and interesting subject for scientists. This work also demonstrates a single photon emitter based on a spatially-controlled QD grown on a self-constructed (100) nano-plane. A single QD was selectively grown on the nano-plane of a multi-faceted structure. Another advantage of this method is to eliminate other QD emissions because the structure is free of QDs, except for the QD on the nano-plane. Photon correlation measurements show that the single quantum dot can successfully emit antibunched photons.

並列關鍵字

single photon ； Quantum dot ； MOCVD

參考文獻

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