  Silicon is an extremely attractive material platform for integrated optics at
telecommunications wavelengths, particularly for integration with CMOS
circuits. Developing detectors and electrically pumped lasers at telecom
wavelengths are the two main technological hurdles before silicon can become a
comprehensive platform for integrated optics. We report on the generation of
free carriers in unimplanted SOI ridge waveguides, which we attribute to
surface state absorption. By electrically contacting the waveguides, a
photodetector with a responsivity of 36 mA/W and quantum efficiency of 2.8% is
demonstrated. The photoconductive effect is shown to have minimal falloff at
speeds of up to 60 Mhz.
