Silicon-germanium p-i-n photodiodes with double heterojunction: high-speed operation at 10 Gbps and beyond

We present recent results on high-speed waveguide p-in photodetectors with lateral hetero-structured Silicon-Germanium-Silicon (Si-Ge-Si) junctions monolithically integrated on Silicon-on-Insulator substrates. Optical photodetectors leverage a unique integration strategy, combining butt-waveguide-coupling and lateral Si-Ge-Si p-in hetero-junctions. Fabrication is then easier, more robust and fully compatible with available Si-foundry processes. Under a low-voltage operation, 1 µm wide devices have dark currents of at most 150 nA, high responsivity of 1.2 A/W, and-3dB cutoff frequency of 12 GHz. Furthermore, an errorless detection is experimentally achieved for a conventional 10 Gbps data rate, with power sensitivity down to-13.9 dBm with a bit-error-rate (BER) of 10-9. Moreover, under avalanche operation, a 0.8 µm wide p-in diode offers attractive improvements in opto-electrical performances. In particular, initial results show that device responsivity is enhanced from 0.42 A/W up to 2.79 A/W thanks to an avalanche multiplication gain of 6.7. The cutoff frequency remains larger than 17 GHz with a gain of 10.6, resulting in a gain-bandwidth product greater than 180 GHz. These promising results also yield error-free communication at 10-9 with 28 Gbps signal, providing power sensitivities down to-12.7 dBm at 10-9 BER. These results make hetero-structured p-in photodetectors appealing choice for high-bit-rate systems in integrated silicon nanophotonics.