Surface versus lateral illumination effects on an interdigitated Si planar PIN photodiode

Abstract

The planar PIN Photodiode (PD) has profound advantages compared to the vertical surface/edge illuminated PIN PD. A two dimensional interdigitated silicon PIN PD with a 58 microns × 80 microns active area and finger width of 2 microns and finger spacing of 10 microns respectively was modeled and simulated in a novel approach using Silvaco ATHENA and ATLAS software. The device was illuminated from the surface and laterally and comparison analysis was performed. At a reverse bias of -10 V, the dark current was 1 ps. Photocurrent of 500 nA was obtained for a 5 Wcm^-2 optical beam power for both the surface and lateral illumination at a -10 V reverse bias. The total quantum efficiency of the laterally illuminated PIN PD at a wavelength of 850 nm was 95% (responsivity=0.65 A/W) and 75% (responsivity=0.52 A/W) for the surface illuminated PIN PD respectively. The -3dB cutoff frequency of the surface illuminated device was at ~10 kHz and for the laterally illuminated PIN PD, the frequency was at ~0.1 MHz. Lateral illumination in an interdigitated Si planar PIN PD produces higher photocurrent contributing to higher quantum efficiency, responsivity and frequency response as compared to surface illumination.