Fabrication and Characterization of Dielectric Microdisks with Embedded Colloidal Quantum Dots
Date Issued
2010
Date
2010
Author(s)
Chen, Tso
Abstract
The primary objective in creating a microdisk using dielectric media is to create a disk fabrication procedure that avoids expensive, time-consuming, and high maintenance equipments of semiconductor fabrication systems. And, in doing so, the operable wavelength of the microdisk microcavity is targeted towards the visible wavelength range to cover a wider variety of applications as opposed to optical communication available mostly only to infrared frequencies. This research produces such microdisk microcavity using silicon dioxide and silicon nitride material with embedded CdSe colloidal quantum dots.
Silicon dioxide has been focused by many as promising dielectric material for creating microcavities such as micropillars, microspheres, and even recently in photonic crystals to support whispering gallery modes. However, its low refractive index imposes a limit on how well this dielectric material can confine electromagnetic waves especially with decreasing structure dimensions. Silicon nitride is introduced to resolve this need with an increased index of approximately 2.05 compared to the 1.45 of silicon dioxide. With many similar qualities and properties to silicon dioxide, silicon nitride can substitute silicon dioxide in the fabrication of microdisks with embedded (「sandwiched」) colloidal CdSe/ZnS quantum dots if a fabrication process can be successfully developed. In this thesis, using a combination of PECVD, RIE, photo-lithography, and wet etching, silicon nitride microdisks are fabricated with diameters in the proximity of 10 μm and are capable of supporting whispering gallery modes. However, the best observed modes were seen in 10 and 12 μm microdisks. In addition, only the 12 μm microdisks are capable of supporting higher order radial modes. Active silicon nitride microdisks with evident WGM have also been fabricated through a similar fabrication method with the change of wet etching to undercut the microdisk structures.
Whispering gallery modes are observed in both silicon dioxide and silicon nitride microdisks through a home-made micro-photoluminescence experimental setup using an excitation source of 532 nm green laser. The effect of sandwiching has shown significant improvements in repeatability in fabricating microdisks that are capable of supporting whispering gallery modes despite relatively low quality factors from our preliminary measurement results. Study on passive silicon nitride microdisks with the same fabrication technique developed here shows very high quality factors larger than 104. This indicates the huge application potentials of silicon nitride as suitable dielectric materials for optical microcavities. Whispering gallery modes of the same active silicon nitride microdisks, however, failed to be detected via far-field detection setup. According to sources listed in this thesis, this concurs with theoretical analysis due to the nature of higher confinement allowing less light to be radiated in such microdisks and therefore making far-field detection of such microdisks less likely.
Subjects
microdisk
microcavity
semiconductor
quantum dot
colloidal quantum dot
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-99-R97941105-1.pdf
Size
23.32 KB
Format
Adobe PDF
Checksum
(MD5):da03ba5ea7a4bc47f115a85b3d9f0cc8