It is shown in this work that sulfur passivation followed by deionized water rinse reduces the dark current of InGaAs/ InP PIN photodetectors significantly. This improvement, however, is short-lived unless the devices are immediately capped with a suitable dielectric. Our experiments show that a polyimide capping layer, which protects the beneficial effects of sulfur passivation, is more effective than silicon nitride in achieving stable low dark current for photodetectors. (C) 2004 Elsevier B.V. All rights reserved.