Abstract
We studied passivation effects of treatment in aqueous (NH4)2S (ammonium sulfide) solution and polyimide encapsulation on AlGaAsSb∕InGaAsSb∕GaSb mesa photodiodes. X-ray photoelectron spectroscopy on InGaAsSb material revealed that (NH4)2S 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)2S passivation reduces the dark current of the photodiodes at −0.5V bias by 3.6 times while additional 9.2 times reduction is obtained when it is preceded by (NH4)2S 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.
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