Design guidelines for edge-coupled waveguide unitravelling carrier photodiodes with improved bandwidth

This study presents experimental and simulation results for edge-coupled waveguide unitravelling-carrier (UTC) photodiodes based on an InGaAs/InP heterostructure. Experimental results are used to calibrate the numerical device simulator. The authors study how different aspects of the UTC photodiode epistructure and contacts impact on the overall device bandwidth, calculating the photoresponse for different structural parameters and doping concentration profiles. The effect of these parameters on the 3-dB cut-off frequency is studied, and design guidelines for UTC photodiodes with improved performance are presented. The UTC photodiode simulated using authors’ design guidelines has a 3 dB cut-off frequency of 49 GHz, a factor of 2 larger than the 25 GHz cut-off of the fabricated UTC photodiode.