Low dark current InGaAs/InP mesa structured PIN diode detectors for operation at 1.1-1.7 μm have been fabricated. Dark current densities of 16 μA/cm2 were achieved. The diodes have been passivated by polyimide, SiO2 and SiN layers and their effects on the dark current were studied. It was conclusively proved that polyimide passivation had the best results in terms of low dark current, reproducibility and long-term stability of the device.