Normal incidence InAs/In0.15Ga0.85As dots-in-a-well detectors operating at T = 78 K with lambda(p) similar to 7 mum and a broad spectral width (Deltalambda/lambda) of 35% are reported. Effect of a current blocking AlGaAs layer on the device performance : is studied. Temperature-dependent dark current, spectral response and calibrated blackbody measurements were undertaken to determine the responsivity and detectivity of the detectors at 78 K. A correction factor was introduced to include the effect of scattering and reflections in the undoped substrate. (C) 2003 Elsevier Science B.V. All rights reserved.