A traveling-wave model for optimizing the bandwidth of p-i-n photodetectors in silicon-on-insulator technology

The paper presents an efficient design method for predicting the bandwidth of traveling-wave photodetectors (TWPD's) in silicon-on-insulator (SOI) cop lanar technology, First the transmission-line parameters describing the pro pagation mechanism in the structure are computed up to optical Frequencies, as a function of the geometry and of the carrier concentrations. Next, a t raveling-wave equivalent model is derived, which takes into account the pro pagation mechanism of the optical beam into the silicon active area and the carriers transit time in the p-i-n junction. Using the model enables us to theoretically optimize the radio-frequency output power of the p-i-n struc ture over a wide frequency range by a judicious choice of the optical and R F loads at the accesses of the equivalent opto-electronic coupler formed by the TWPD, SOI coplanar TWPD's supporting a traveling optical wave exhibit an improvement of the 3-dB bandwidth by more than 50% compared with uniform ly illuminated SOI PD's or with GaAs TWPD's of same geometry and the bandwi dth-efficiency product can be enhanced by achieving adequate reflection con ditions for the optical signal at the ends of the SOI device.