Improved interface and dark current properties of InGaAs photodiodes by high-density N2 plasma and stoichiometric Si3N4 passivation

•Optimized passivation process by using high-density N2 plasma and adjusting N2, SiH4 flow and deposition temperature.•Interface state density decreases several times by using high-density N2 plasma and adjusting N2 and SiH4 flow rates to 17 and 11 sccm.•Dark current can be reach 13 nA/cm2 at 190 K and a −10 mV reverse bias by using high-density N2 plasma and adjusting N2 and SiH4 flow rates to 17 and 11 sccm.•Surface current is negligible compared with the bulk current at room temperature.