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Title: Combined Light and Carrier Localization in High-Refractive Index Silicon Nanocrystal Structures: A Novel Approach for Si-Based Lasers (NSF-CAREER)

Participants: Nate Lawrence (PhD ’13) and Professor Luca Dal Negro

Funding: National Science Foundation (NSF)

Background: The quest for an efficient Silicon-based CMOS compatible light source that can be integrated on-chip is a long standing challenge within the field of integrated optics. Long-haul optical communication, through the use of optical fibers, has already revolutionized global communication due to the large bandwidths that are achievable. As the speed of computer computations increases, systems are becoming limited not by single operation times but instead by the ability to move data within the system where optical communication can also be used to greatly increase bandwidth. Even today the fastest machines in the world are relying more and more on optical communication. Many of the necessary components for on-chip optical communication have been realized but an on-chip light source that can be integrated into the same materials platform as the majority of the semiconductor industry is still out of reach.

(a-b) Room temperature electroluminescence from Er-doped nitride LEDs fabricated in our Lab by reactive sputtering and lithographic processes. The green spot is the emission from higher energy states of Erbium atoms, as pictured by a digital camera. (c) Erbium-doped light emitting pillar arrays fabricated in our group by Electron Beam Lithography (EBL). (d) Erbium-doped micro-disk resonator fabricated in our group by EBL and etching processes.

(a-b) Room temperature electroluminescence from Er-doped nitride LEDs fabricated in our Lab by reactive sputtering and lithographic processes. The green spot is the emission from higher energy states of Erbium atoms, as pictured by a digital camera. (c) Erbium-doped light emitting pillar arrays fabricated in our group by Electron Beam Lithography (EBL). (d) Erbium-doped micro-disk resonator fabricated in our group by EBL and etching processes.

In addition to use in optical communication, many biological and chemical sensing systems, such as Raman sensing and localized Plasmon resonance sensing, rely on optical methods to detect chemical and biological materials. The integration of such devices could greatly be enhanced by increased efficiency of a semiconductor light source.

Description: In this NSF-funded work, we hope to increase the Erbium-doped Silicon Nitride (Er:SiNx) light emission by creating aperiodic arrays of pillars that can alter the rate of light emission materials and change the direction of that light emission. We grow Er:SiNx at BU via magnetron sputter and have optimized the light emission by changing Si content and annealing of the material. We pattern the material using Electron-beam lithography in which features of a few tens of nm are achievable. A metal mask is deposited by electron-beam evaporation and reactive ion etching is used to anisotropically etch pillar structures. Characterization is done in our lab where we measure a 30 times increase in the emission of light at 1.54um wavelength.

Results: Above are an aperiodic spiral structure of Er:SiNx pillar and a normalized PL spectrum showing a signal from a spiral as compared to a background measurement which has been multiplied by a factor of 10.

Website: www.bu.edu/nano

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