The effect of post-growth rapid thermal annealing on 35-layer In0.50Ga0.50As/GaAs quantum dot infrared photodetector (QDIP) with quaternary In0.21Al0.21Ga0.58As capping has been investigated. Transmission electron microscopy showed sonic as-grown defects were removed by post growth annealing treatment. An increase in the compressive strain in the heterostructure due to annealing was identified from X-ray diffraction curve. A two-color photoresponse in the long-wave region (8.5 and 10.2 mu m) was observed in both as-grown device and those annealed at 650 degrees C temperature. A three-fold enhancement in peak responsivity was observed in the QDIPs annealed at 650 degrees C (1.19 A/W) compared to that in the as-grown (0.34 A/W). Detectivity also increased by two fold from as-grown to 650 degrees C annealed device. The changes are attributed to the removal of as-grown defects and dislocations during epitaxial growth. These removals changed the confinement potential profile, which resulted in an improvement in the detectivity and responsivity of the annealed sample. (C) 2012 Elsevier Ltd. All rights reserved.