Analysis of partially depleted absorber waveguide photodiodes

This paper presents the analysis and characterization of partially depleted absorber (PDA) photodiodes. Coupling to these photodiodes is achieved through a planar short multimode waveguide (PSMW) structure. Electric transport in the PDA structure has been investigated and an equivalent electric circuit was developed. Measurements on 5/spl times/20 /spl mu/m/sup 2/ PSMW PDA photodiodes have shown 0.80 A/W responsivity with a fiber mode diameter as high as 6 /spl mu/m. The transverse electric/transverse magnetic polarization dependence was <0.5/spl plusmn/0.3 dB with -1-dB input coupling tolerances as high as /spl plusmn/2.0 and /spl plusmn/1.3 /spl mu/m for horizontal and vertical directions. The -3-dB bandwidth was 50 GHz, and the -1-dB compression current at 40 GHz was 17 mA corresponding to +4.5 dBm radio frequency (RF) power. Compared to similar evanescently coupled p-i-n photodiodes, the saturation current has been significantly improved while maintaining comparable bandwidth and high responsivity.