Silicon germanium photonics
A germanium LED
A germanium microdisk side coupled to a fiber taper
- Develop a CMOS-compatible laser source at 1.5 microns based on strained and doped epitaxial germanium on silicon
- Need for CMOS-compatibility for laser sources in optical interconnects
- Germanium can be easily integrated monolithically on silicon
- Can be electrically contacted well
- Understanding optical processes in material
Germanium is an indirect band gap semiconductor and as such it is ordinarily a poor optical emitter. However the indirect band edge is only 0.13 eV below the direct
band edge and by heavily doping the material or by applying a sufficient strain, the material can become quasi-direct band gap. Finding suitable fabrication methods
to heavily dope or inject carriers into germanium are difficult and we are exploring this area in order to overcome this hurdle.
- Electroluminescence in germanium-on-silicon diodes was demonstrated with the band filling approach--
that is, heavy N-type doping increased the output light significantly Op. Ex. 17, 10019 (2009).
- We also demonstrated cavity coupled photoluminescence from germanium microdisks, collected from a fiber taper APL
97, 241102 (2010)
- Recently we developed an electrically injected cavity LED that showed direct gap electroluminescence coupled to microdisk whispering gallery modes. To be published
Images of tapered fiber aligned to single photonic crystal cavity
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].
- Hwang, In-Kag et al., APL 87, 131107 (2005).
- Smith, C., Physica B 394, 289 (2007).
- Srinivasan, K., IEEE J. Sel. Areas Comm. 23, 1321 (2005).
last modified on Thursday November 10, 2011