Sub-bandgap light detection in bulk CMOS

We have been working on techniques to detect subbandgap light in bulk CMOS for a couple of years. Since silicon has a bandgap of 1.14eV, light can only be absorbed if it has a wavelength below 1.1μm. Therefore, silicon cannot be used for the traditional telecommunication wavelengths, namely 1.31μm and 1.55μm.

Using a Schottky photodiode instead of a pn-photodiode in silicon, we can detect these wavelengths since the Schottky barrier is low enough for photons with a telecom wavelength. We are currently investigating how this principle can be used for other applications.