Design of broadband and high-output power uni-traveling-carrier photodiodes

In this paper, the bandwidth and saturation current of uni-traveling-carrier photodiode (UTC-PD) is investigated by using physics-based modeling. To further improve the performance, novel device structures are proposed. On the one hand, graded bandgap structure is employed in the absorption layer. It is shown that similar to the effect of graded doping method, the electric field in the absorption layer is increased, and thus the bandwidth is improved. Moreover, both the graded doping and graded bandgap structure are optimized. It is found that for the considered UTC-PD, combining use of the optimized graded doping and graded bandgap structure in the absorption layer leads to an improvement of 39.4% in bandwidth. On the other hand, linear doping profile and Gaussian doping profile are proposed to be used in the collection layer. It is shown that the distribution of electric field in the depletion region is improved, which leads to better saturation performance. For the considered UTC-PD, by using the optimized linear doping profile and the Gaussian doping profile, the improvement in saturation current is 18.7% and 25.8%, respectively.