Active silicon nanophotonics
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| Luminescense enhancement from Si-rich nitride membrane by linear 3-defect cavity. |
The Idea:
- Design 2-D photonic crystal (PC) nanocavities to improve emission from
silicon CMOS compatible materials, and evaluate their potential for creating a laser.
Reasons:
- Enhanced emission through Purcell effect
- Higher luminescence efficiency due to directed radiation pattern
- Can be pumped electrically => LED
- Integration with Si electronics
- Understanding optical processes in material
Materials studied:
- Er doped silicon-rich silicon nitride
- Photonic crystal nanocavities were fabricated in silicon membranes covered by thermally annealed silicon-rich nitride films
with Erbium-doped silicon nanocrystals. Silicon nitride films were deposited by sputtering on top of silicon on insulator wafers.
The nanocavities were carefully designed in order to enhance emission from the nanocrystal sensitized Erbium at the 1540 nm wavelength.
Experimentally measured quality factors of 15000 were found to be consistent theoretical predictions.
We observe a 20-fold enhancement of Erbium luminescence. [APL 92, 161107 (2008); Erratum].
We also observe linewidth narrowing at cryogenic temperatures.
- Silicon nitride grown by LPCVD with Si nanocrystals
- We demonstrated an up to sevenfold enhancement of photoluminescence from
silicon-rich silicon nitride film due to a single photonic crystal cavity.
Experimentally measured cavity quality factors vary in the range of 200-300,
showing excellent agreement with calculations.
The emission peak can be tuned to any wavelength
in the 600-800 nm range. [APL 89, 221101 (2006)]
- Epitaxially grown germanium on silicon:
- Germanium is an attractive material for light emission due to its process compatibility with silicon.
Ordinarily germanium does not emit light since it is an indirect bandgap semiconductor; however, by heavily doping the germanium with electrons,
the Fermi level can approach the direct bandgap valley and promote radiative recombination at 1.5 um.
Electroluminescence in germanium-on-silicon diodes was demonstrated with this approach--
that is, heavy N-type doping increased the output light significantly Op. Ex. 17, 10019 (2009).
Currently we are working on trying to make a laser out of this material.
- Silicon nitride grown by PECVD with Si nanocrystals
- Strained Ge quantum wells and quantum dots
- Silicon oxide with Si nanocrystals
- Luminescent porous Si produced by anodic etching
Techniques:
While many experiments on nanocavities such as photonic crystal cavities can be performed using conventional free space optics, there are certain limitations on the efficiencies of injecting
and extracting optical signals. Transferring light in and out of nanocavities can also be readily accomplished by drawing a conventional optical fiber down to ~1 um in diameter and positioning
the waveguide near the cavities. This process has many advantages since the tapered fiber provides an additional channel to inject and extract multiple signals.
Efficiencies have been shown to be high, and rapid characterization of numerous devices can be done very quickly [1-3].
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| Images of tapered fiber aligned to single photonic crystal cavity |
1. Hwang, In-Kag et al., APL 87, 131107 (2005).
2. Smith, C., Physica B 394, 289 (2007).
3. Srinivasan, K., IEEE J. Sel. Areas Comm. 23, 1321 (2005).
Collaborators
- Er doped silicon-rich silicon nitride: Rui Li, Joe Warga, Prof. Luca Dal Negro, Boston University (2007-present)
- Porous Si and LPCVD nitride growth: Hiroyuki Sanda, Prof. Yoshio Nishi (2004-2007)
- PECVD nitride: Szu-Lin Cheng, Prof. Yoshio Nishi (2007-present)
- Strained Ge quantum wells and quantum dots: Shen Ren, Prof. David Miller, Yijie Huo, Prof. Jim Harris. (2007-present)
- Oxide with Si nanocrystals growth: Rohan Kekatpure, Prof. Mark Brongersma (2005)