Cascade GaN-based micro-photodiodes for photonic integration

Photonic integrated circuit have attracted increasing attentions in many applications, such as visible light communication (VLC), optical on-chip interconnects, etc. In this work, we focus the study on photonic integration of GaN-based light-emitting diode (LED) and photodiode (PD). Integrated LED and multi-stage cascade PDs were designed and fabricated. Experimental results have demonstrated that the equivalent capacitance decreases continuously as the number of PD stages increasing. Compared to a single PD, the four-stage cascade PD can reduce the equivalent capacitance by 60%, making the cut-off frequency increased by 37%. Meanwhile, the cascade technique greatly reduces the dark current down to 20 pA and further improves the photo-to-dark current ratio up to 1.2 x 10(6) under a negative 5 V bias. Thus, the finding and experimental results in this work could enable a noval method to further improve VLC performances of photonic integrated devices.