We present the effect of post-growth rapid thermal annealing on multilayer, uncoupled In0.50Ga0.50As/GaAs quantum dot infrared photodetectors (QDIPs) with a combination of quaternary In0.21Al 0.21Ga0.58As and GaAs capping. Long wave photoresponse (~ 0.11 eV or 10.2 μm) with narrow spectral width (14%) is obtained from as-grown QDIPs. The spectral width increases to 45% for QDIP annealed at 800 C. It is likely that a large inter-diffusion effect because of annealing changes the composition of the quantum dots and capping layer, thus increasing the QDIP spectral width. Dark current as well as noise current is decreased for 650 C annealed QDIP compared to as-grown detector. Passivation of as-grown defect by post growth annealing predicted the improvement of dark current. Such improvement and broadening of characteristics may render such QDIPs suitable for use in broadband infrared imaging applications. © 2013 Elsevier B.V.