Butt-Coupled Germanium Photodetectors
Figure 15 shows the fabrication process of the butt-coupling scheme. Ge is selectively grown to fill trenches opened through a \(SIO_2\) layer then a chemical mechanical polish is used to planarize the excess grown Ge[16]. A silicon waveguide of 500 nm wide by 200 nm in height is used for single mode operation at 1550 nm wavelength. Coulpling efficiency is estimated to 86\(\%\) from simulations. Figure 16 shows the responsivity of a 50 \(\mu m\) long Ge photodetector at 3V reverse bias. It be seen that the response is significant at 1520 nm, this shift from 1550 nm can be explained by the shift in the bandgap from Ge on Si changing the peak of absorption.