Study of GaN-based Microcavity Light Emitting Devices
| Autor: | Bo, Siao Cheng, 鄭柏孝 |
|---|---|
| Rok vydání: | 2012 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 100 For several decades, GaN-based material has attracted much attention of academia and industry and widely used in several optoelectronic devices due to its wide direct bandgap and strong binding energy, such as light emitting diodes, laser diodes, and photon-detectors which can be applied in lighting, optical storage, display, and biotechnology. The thesis is focus on the design and fabrication of the electrically pumped GaN-based microcavity light emitting devices with hybrid distributed Bragg reflectors and an AlN current blocking layer. We have recently demonstrated the continuous wave (cw) current injection of GaN-based VCSEL with hybrid mirrors at 77K with 240 nm ITO and 300 K with 30 nm sputtered ITO. Meanwhile, the room temperature operation of GaN-based VCSEL devices was reported using optical cavities sandwiched by double dielectric DBRs. The major improvements of these devices to achieve room temperature operation are by using a thinner transparent conducting layer of about 50 nm to improve the current spreading and by using the GaN substrate to ensure the good crystal quality of active layers. However, to form VCSELs with double dielectric DBRs required complex fabrication process, such as laser lift-off or elaborated polishing and bonding process. Despite of demonstration of room temperature current injected GaN-based VCSELs, the lateral optical confinement and the transparent conductive ITO film was still a lack in these VCSEL structures, resulting in higher optical loss and difficulty in controlling the quality of output beams. About ITO characteristics improvement, the study consists of the design, fabrication, and characteristics of the ITO films. In order to improve the optical confinement of these devices, we investigated a microcavity light emitting device (MCLED) with a buried AlN current aperture, which can also be used as a lateral optical confinement layer. Since a pre-defined current aperture with a small diameter is introduced in the MCLED structure, the transparent current spreading layer can be omitted from the optical path. The current still can be injected effectively in the current aperture and the optical loss introducing by the transparent current spreading layer could be neglected. The emission from the MCLED with a buried AlN layer shows a very narrow linewidth of 0.52 nm, corresponding to a cavity Q-value of 846, and a dominant emission peak wavelength at 440 nm. The measured cavity mode spacing is approximately 0.7 nm, which is consistent with the estimated value, demonstrating the effect of lateral optical confinement provided by the AlN layer. In addition, the emission peak wavelength as a function of the current is almost invariant with an increasing injection current indicating potential temperature-sensitive applications. Further optimization of bottom DBR growth and crystal quality in this structure would promise to realize low threshold GaN-based VCSELs or GaN-based polariton lasers. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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