Passivation of AlGaAsSbInGaAsSbGaSb photodiodes using aqueous (NH ₄) ₂S solution and polyimide encapsulation

We studied passivation effects of treatment in aqueous (NH4) 2 S (ammonium sulfide) solution and polyimide encapsulation on AlGaAsSbInGaAsSbGaSb mesa photodiodes. X-ray photoelectron spectroscopy on InGaAsSb material revealed that (NH4) 2 S passivation reduces oxide bonds, increases III-V bonds, and produces sulfide bonds. Auger electron spectroscopy depth profiling shows a 1:1 replacement of oxygen by sulfur. The percentage of oxygen replaced by sulfur is about 30% at the surface and decays with the depth. Polyimide encapsulation of the photodiode mesa sidewall not preceded by (NH4) 2 S passivation reduces the dark current of the photodiodes at -0.5 V bias by 3.6 times while additional 9. 2 times reduction is obtained when it is preceded by (NH4) 2 S passivation. The dark current performance of devices did not degrade for 240 days after the combined passivation, indicating a promising long-term stability. The capacitance of devices treated with the combined passivation exhibits a standard deviation three times smaller than those with polyimide encapsulation only.