A low dark-current, planar InGaAs p-i-n photodiode with a quaternary InGaAsP cap layer

In0.53Ga0.47As p-i-n photodiodes have become the most suitable photodectectors for long wavelength ( m) optical fiber communication systems due to their low dark-currents. Further reduction of the dark-current to subnanoampere range will bring significant improvement in receiver sensitivity at low bit rates. In this paper, we report the successful fabrication of In0.53Ga0.47p-i-n diodes with room temperature dark-currents as low as 0.1 nA at -10 V bias by introducing a quaternary InGaAsP cap layer on the ternary InGaAs. In this new structure the InGaAsP cap layer undergoes the surface treatment and faces the dielectric silicon nitride film, but the p-n junction is still located inside the InGaAs layer. Since the addition of the wide bandgap cap layer results in low dark-current, the reduction of dark-current may be attributed to surface effects. Analysis of the temperature and voltage dependence of the dark-current indicates that at room temperature the ohmic conduction through the shunt formed on the surface limits the dark-current in this new diode structure.