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) coplanar technology. First the transmission-line parameters describing the propagation mechanism in the structure are computed up to optical frequencies, as a function of the geometry and of the carrier concentrations. Next, a traveling-wave equivalent model is derived, which takes into account the propagation 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 structure over a wide frequency range by a judicious choice of the optical and RF 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 uniformly illuminated SOI PD´s or with GaAs TWPD´s of same geometry and the bandwidth-efficiency product can be enhanced by achieving adequate reflection conditions for the optical signal at the ends of the SOI device