In a superlattice (SL) photodetector, each period of the SL includes first and second semiconductor layers having different compositions, at least one of which comprises indium arsenide (InAs). At least one of these two semiconductor layers has a graded composition. In embodiments, the first semiconductor layer comprises InAs and the second semiconductor layer is a graded layer comprising indium arsenide antimonide (InAsSb), wherein the antimony (Sb) concentration is varied. In examples, the Sb concentration in the second layer gradually increases from the top and bottom toward the middle of the layer.