Low dark current InAs/GaAs quantum-dot infrared photodetectors ͑QDIPs͒ are demonstrated. The dark current is reduced by over three orders of magnitude by using a thin AlGaAs current blocking layer. This thin AlGaAs layer reduces the dark current much more than the response signal. The responsivity at 0.5 V is 0.08 A/W with a peak detection wavelength at 6.5m. The corresponding detectivity is 2.5ϫ10 9 cm Hz 1/2 /W 1/2 , which is the highest detectivity reported for a QDIP at 77 K.

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