1.1 GHz MSM photodiodes on relaxed Si/sub 1-x/Ge/sub x/ grown by UHV-CVD

The growing market for /spl lambda/=850 nm data links that operate at bit rates >1 Gbit/sec has increased the interest in Si-based monolithically integrated photoreceivers due to the reduced cost arising from their compatibility with existing Si manufacturing technology. However, Si integrated photoreceivers have had difficulty achieving frequency performance comparable to traditional GaAs monolithic photoreceivers, mainly due to the long absorption length (/spl alpha//sup -1/=20 /spl mu/m) for 850 nm radiation in Si. Si/sub 1-x/Ge/sub x/ alloys emerge as a means of overcoming the inherent speed/responsivity trade-offs of bulk Si photodiodes, due to the much shorter absorption length and the higher carrier mobilities of Si/sub 1-x/Ge/sub x/ alloys compared to Si. Though recent results using strained Si/sub 1-x/Ge/sub x/ layers on Si have shown promise for improved photoreceiver performance, strained-layer absorbing regions have limitations because the overall Ge composition must be kept low enough to avoid dislocation formation. In this paper, we present results on MSM photodiodes fabricated on relaxed absorbing layers of single-crystal Si/sub 0.75/Ge/sub 0.25/ grown epitaxially on Si substrates. These photodiodes have bandwidths in excess of 1 GHz and have the distinct advantage of being fully compatible with Si-SiGe high-electron mobility transistors (HEMTs).