In(Ga)As/GaAs Quantum Dot Light Sources
| Autor: | Tung-Po Hsieh, 謝東坡 |
|---|---|
| Rok vydání: | 2007 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 96 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. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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