Edge-coupled InGaAs PIN photodiode with a light funnel waveguide

Abstract

We have successfully fabricated InGaAs edge-coupled photodiodes (EC-PDs) with a light funnel integrated (LIFI) in front of the coupling aperture, called LIFI EC-PD, based on the self-terminated oxide polish (STOP), the crystallographic slope etching of InP, and the self-aligned diffusion (SAD) techniques. The LIFI EC-PD presents not only a lower dark current density (/spl sim/ 4.4 mA/cm/sup 2/) but also a higher responsivity (/spl sim/ 0.4 A/W) than that of the mesa EC-PD (27 mA/cm/sup 2/ and 0.26 A/W, respectively). Furthermore, the thick oxide film serves as the funnel in front of active-region aperture to enhance the coupling efficiency and to lower the bonding pad capacitance down to 50 fF. The lowered bonding pad capacitance can be beneficial in designing a device with a higher transit-time-limited frequency response of beyond 30 GHz. The LIFI EC-PD with a 1-/spl mu/m thick absorption layer exhibits a 3-dB bandwidth of 20 GHz and a responsivity of /spl sim/ 0.4 A/W.