Nonlinearity in ESD robust InGaAs p-i-n photodiode

A guard ring (GR) protected InGaAs p-i-n photodiode with high linearity is fabricated and the effect of the GR protection structure on the linearity of the photodiode is studied. For the electrostatic discharge (ESD) protected photodiode, both the single second order (SSO) intermodulation and the single triple beat intermodulation are below 80 dBc. The GR can enhance the ESD robustness of the photodiode but degrades the photodiode's linearity about 3.5 dB for SSO at 854 MHz. The photodiode's nonlinearity is mainly due to the photodiode junction capacitance variation, which is caused by the photocurrent and bias voltage changes that are resulted from the change of incident laser power. The distortion caused by the photodiode's bias voltage is much larger than that caused by the photocurrent. The GR integrated into the photodiode aggregates the capacitance variation with the bias voltage and therefore increases the distortion. The calculated SSO distortion using the experimentally measured differential capacitances matches the experimental data.