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Lasing Consequences of Silicon Nanostructures

This research could have implications in removing data transmission bottlenecks.

While silicon electronics has been a success in modem technologies, silicon photonics is still in development and in need of a laser source. Many approaches have been explored, from anodized silicon luminescence, to generating direct emissions by quantum-confinement, and to indirect down-conversion of a shorter wavelength laser light via silicon's nonlinear dielectric responses. One approach that was developed has led to the demonstration of laser emission in silicon-on-insulator at cryogenic temperatures (<85K).

Silicon's inability to emit light and to 'lase' is rooted in the particular atomic arrangement (lattice) of silicon atoms in their crystalline form. As such, the creation of an all-silicon laser or merely an efficient all-silicon light emitter would necessarily begin at the atomic level. Emissive deformation centers (or 'designer defects') were created in the silicon lattice. These emissive centers exist naturally in silicon. In electronics, they are either detrimental to device performance or are a source of unwanted variation.

One example of such centers is called the G-center, which is formed by moving a silicon atom from its normal lattice site and substituting a carbon atom in its place. When the substituted carbon pairs up with a second carbon atom nearby, a local lattice deformation or emissive center is created and an electron captured at the site can then emit light directly. One way to make silicon more optically active is to increase the density of these G-centers, without adversely increasing electrical and optical losses, so as to allow laser action.

A nano-patterning technique was developed that uses an etch mask made of a regular array of oxide (AAO). In the etching process, this AAO mask is placed directly on a slice of silicon. The etching through the mask results in a pattern of silicon structures. The extreme uniformity of the approach helped to keep optical losses low, the large field size provided sufficient total optical gain, the small feature sizes minimized scattering loss, and the hardness of the AAO stood up well against the deep etching process and protected the underlying silicon everywhere except where the nano-pores were to be etched.

The same nano-patterned etching pro - cess also created local lattice deformation and strain field in the side-wall region (-4 nm thick) and a band-gap narrowing. Both benefited optical emission by facilitating the gathering of electron-hole pairs from the surrounding silicon to the emission centers in the side-wall layer of the etched pore. This itself also benefited from the fact that the nano-pores are much closer together than the electron diffusion length within crystalline silicon.

A future option is to combine patterned implantation with the strain effects that can aid in optical activity, both through direct lattice deformation and indirect selection and stabilization of the desired emissive deformation centers.

This work was done by Jimmy Xu of Brown University for the Office of Naval Research.

ONR-0012

Topics:
Lasers Nanomaterials Nanotechnology Optics Photonics Research and development
This Brief includes a Technical Support Package (TSP).
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Lasing Consequences of Silicon Nanostructures

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    Defense Tech Briefs Magazine

    This article first appeared in the February, 2009 issue of Defense Tech Briefs Magazine (Vol. 3 No. 1).

    Read more articles from this issue here.

    Read more articles from the archives here.

    Overview

    The document presents a comprehensive report on advancements in silicon nanostructures and their potential for laser emission, primarily authored by Jimmy Xu and his team at Brown University. The research focuses on overcoming silicon's inherent limitations in light emission, which stem from its atomic arrangement in crystalline form. The report outlines the successful achievement of optically pumped laser emission at cryogenic temperatures (below 85K) using carbon-implanted nano-patterned silicon-on-insulator substrates.

    Key methodologies employed in the research include ion implantation and solid-phase epitaxy for recrystallization, which resulted in a remarkable 30-fold improvement in luminescence intensity. The nano-patterning was achieved through reactive-ion-etching, utilizing an anodized aluminum oxide membrane as a mask. These techniques are crucial for enhancing the optical properties of silicon, making it a viable candidate for laser applications.

    The document emphasizes the significance of these findings, suggesting that the ability to create silicon lasers could lead to innovative devices and applications that have not yet been conceived. Potential benefits include improved optical and electronic integration, which could alleviate data transmission bottlenecks within computer chips and facilitate the mass production of low-cost micro-gadgets. These gadgets could utilize infrared light emitted from silicon chips for medical diagnostics, showcasing the practical implications of the research.

    Additionally, the report includes a list of publications and awards related to the research, highlighting the contributions of various authors and their collaborative efforts in advancing the field. The findings lay a solid foundation for future research aimed at achieving room-temperature lasing in silicon, which would represent a significant milestone in the development of silicon-based optoelectronic devices.

    In summary, this document encapsulates a pivotal moment in silicon nanotechnology, illustrating the potential for silicon to serve as an emissive optical medium. The research not only addresses the challenges associated with silicon's light emission but also opens avenues for future innovations in laser technology and integrated photonics.

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