Silicon-based nanobeam photonic crystal light emitting devices
Tuesday, November 16th, 2010 10:30 am (refreshments 10:15 am)
Ph. D. Candidate: Yiyang Gong
Research Advisor: Jelena Vuckovic
Committee: Mark Brongersma, Shanhui Fan, David Miller
Location: Center for Nanoscience 232
Silicon compatible light emitting materials can enable a new class of cost-efficient opto-electronic devices, as optical devices and electronic devices can be integrated on the same platform. However, the low emission efficiency of such materials has hampered the development of silicon light emitting devices. We explore the use of photonic cavities to enhance the emission properties of silicon nano-crystals (Si-NCs) in oxide and Er-doped silicon nitride, as high Q, low mode volume cavities enhance the light-matter interaction.
Two dimensional photonic crystal (2D- PC) cavities have been developed for the enhancement of emission for various materials, and cavities with quality (Q-) factors greater than 105 have been experimentally demonstrated in materials with index of refraction n = 3.5. However, materials such as Si-NC doped oxide and nitride have low index of refraction (n ≤ 2.0), and 2D PC cavities have been experimentally demonstrated with Q-factors up to only 3,400 in such low index systems. We investigate one dimensional nanobeam PC cavities, which are versatile and enable high Q cavities for various indices of refraction. We describe the design and fabrication of nanobeam cavities in silicon dioxide (n = 1.5), with experimental Qs over 5,000 in the visible wavelengths. We also study nano-optomechanical effects in passive Si-based nanocavities. We then fabricate nanobeam cavities in silicon oxide with embedded Si-NCs and Er-doped amorphous silicon nitride. We demonstrate Q > 9,000 for the Si-NC material, and analyze the signature of free carrier absorption for this type of material. In addition, we demonstrate nanobeam cavities in the Er-doped nitride material with Q > 15,000. We observe linewidth narrowing in the Er material with increasing pump power, which is a signature of absorption saturation and differential gain, at both room temperature and cryogenic temperatures. Compared to previous designs using high index Si as part of the cavity, we observe a reduction of absorption losses arising from the material, and correspondingly larger decreases in linewidth. By using time resolved measurements, we calculate that optical transparency of the material is reached at high pump powers.
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