Dr. Anuranjita Tewary Profile

Dr. Anuranjita Tewary

at Stanford Univ

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Publications (3)

Proceedings Article | 18 October 2006 Paper

Synthesis and optimization of luminescent Si nanoparticles by CO₂ laser annealing and Si nanocrystal light emission in microcavities

Rohan Kekatpure, Anuranjita Tewary, Mark Brongersma

Proceedings Volume 6368, 636801 (2006) https://doi.org/10.1117/12.686562

KEYWORDS: Silicon, Luminescence, Nanocrystals, Annealing, Gas lasers, Resonators, Carbon monoxide, Nanoparticles, Transmission electron microscopy, Semiconductor lasers

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We report synthesis and photoluminescence optimization of luminescent Si nanocrystals in silicon rich oxide films using a CO₂ laser beam. Laser annealing allows for a very localized heat deposition. This results in appreciable temperature rise in an area that is equivalent to only a few spot sizes. This could be important in CMOS back-end compatible processing where high temperatures on the entire wafer scale might not be acceptable. Furthermore, temperature optimization studies in furnace annealing are time consuming because the furnaces have to be programmed to each individual temperature and the stabilization takes long times. In CO₂ laser annealing, the entire temperature range for nanocrystal formation is available along the radial and axial directions of the laser spot - thereby allowing temperature optimization in a single short experiment. Presence of crystalline nanoparticles is ascertained using structural analysis techniques like transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). We also report luminescence optimization with respect to laser power and annealing time. It is observed that laser annealing in an air ambient results in two peaks in the luminescence spectrum - on in the visible at 570 nm and one in the near infra read at 800 nm. Origin of luminescence in these two peaks is probed by hydrogen passivation and time resolved measurements. In the second part of the paper, we focus on continuous wave characterization of photoluminescence from Si nanocrystals embedded in microdisk resonators. There have been numerous reports on observation of continuous-wave and transient gain in planar optical waveguides with Si nanocrystal active layer. However, there are relatively very few investigations focusing on photoluminescence emission from Si nanocrystals (quantum dots) embedded in on-chip optical microcavities. Microcavities spectrally filter the luminescence from the quantum dots and, depending on the (Q/V) ratio, can significantly alter the spontaneous photoemission from the quantum confined excitons. In our work, planar microcavities are patterned on the emitter layer by high resolution electron beam lithography and a combination of dry and wet chemical etching. Fabrication procedure is optimized to maximize the ratio of the quality factor and the mode volume. Continuous-wave photoluminescence measurements are performed by top-pumping the resonators with a 488 nm line of an argon ion laser. We study the photoemission from the microdisks for the polarization dependence, and quality factors. Contributions of various mechanisms leading to the observed loss are estimated. We believe that our studies will help gain further insight into photoemission physics of the group-IV nanostructures.

Proceedings Article | 2 October 2006 Paper

Transmission properties of tapered air-core photonic bandgap fibers

Aydogan Ozcan, Anuranjita Tewary, Michel Digonnet, Gordon Kino

Proceedings Volume 6389, 63890W (2006) https://doi.org/10.1117/12.685420

KEYWORDS: Optical fibers, Cladding, Single mode fibers, Silica, Optical filters, Telecommunications, Fabry–Perot interferometers, Microscopes, Waveguides, Resonators

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Proceedings Article | 1 March 2006 Paper

Silicon-nanocrystal-coated silica microsphere thermo-optical switch

Anuranjita Tewary, Michel Digonnet, Mark Brongersma, Joo-Yeon Sung, Jung Shin

Proceedings Volume 6125, 61250U (2006) https://doi.org/10.1117/12.669392

KEYWORDS: Switching, Optical spheres, Nanocrystals, Switches, Silicon, Silica, Argon, Fiber lasers, Absorption, Coating

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