High-Responsivity Low-Voltage 28-Gb/s Ge p-i-n Photodetector With Silicon Contacts

We report on lateral pin germanium photodetectors selectively grown at the end of silicon waveguides. A very high optical bandwidth, estimated up to 120GHz, was evidenced in 10 µm long Ge photodetectors using three kinds of experimental set-ups. In addition, a responsivity of 0.8 A/W at 1550 nm was measured. An open eye diagrams at 40Gb/s were demonstrated under zero-bias at a wavelength of 1.55 µm.

A compact pin Ge photodetector is integrated in submicron SOI rib waveguide. The detector length is reduced down to 15 microm using butt coupling configuration which is sufficient to totally absorb light at the wavelength of 1.55 microm. A -3 dB bandwidth of 42 GHz has been measured at a 4V reverse bias with a responsivity as high as 1 A/W at the wavelength of 1.55 microm and a low dark current density of 60 mA/cm(2). At a wavelength of 1.52 microm, a responsivity of 1 A/W is obtained under -0.5 V bias. The process is fully compatible with CMOS technology.

We report on evanescently coupled Ge waveguide photodetectors that are grown on top of Si rib waveguides. A Ge waveguide detector with a width of 7.4mum and length of 50 mum demonstrated an optical bandwidth of 31.3 GHz at -2V for 1550nm. In addition, a responsivity of 0.89 A/W at 1550 nm and dark current of 169 nA were measured from this detector at -2V. A higher responsivity of 1.16 A/W was also measured from a longer Ge waveguide detector (4.4 x 100 mum2), with a corresponding bandwidth of 29.4 GHz at -2V. An open eye diagram at 40 Gb/s is also shown.