Recently, there has been increasing interest in light emission from silicon for optoelectronic circuits and chip-to-chip interconnections. In this work, the requirements for creating a chip-to-chip optical link were determined. Different silicon-based devices were studied for their potential use in an optical link including silicon diodes and waveguides with silicon nanocrystals and rare earth ions. The luminescence efficiency and performance of silicon diodes fabricated using both standard CMOS and solar-cell process technologies were analyzed. Photoluminescence (PL) and electroluminescence were measured from both implanted and gas-source diffused devices. Peak PL intensity from implanted-annealed junctions is approximately an order of magnitude lower than for unprocessed silicon. Silicon light-emission efficiency was improved by reducing the surface/contact recombination, and bulk recombination (Auger and Shockley-Read-Hall). This can be done by using gas-source diffusion,
passivating and texturing the surfaces, and depositing anti-reflective coatings.

The challenge is that the radiative recombination lifetime is long because silicon is an indirect bandgap material and carriers are removed by slow spontaneous emission and diffusion rather than stimulated emission and drift. The result is slow switching speeds. In addition, the light is incoherent preventing its use with many high-speed refractive or phase modulators, photonic crystals, etc. Conversely, waveguides with silicon nanocrystals and optical or preferably electrical pumping show promise as a source of coherent light. Modeling parameters for the optical power and optimal wavelength required for an optical link were determined by the photodetector, transimpedance amplifier, coupling losses, noise, and frequency of operation. The prospects for creating a silicon-based optical link look promising.