The subject invention comprises the realization of P-on-N type II InAs/GaSb superlattice photodiodes. A high-quality InAsSb layer lattice-mismatched to GaSb is used as a buffer to prepare the surface of the substrate prior to superlattice growth. The InAsSb layer also serves as an effective n-contact layer. The contact layer has been optimized to improve device performance, most notably performance that is similar to traditional N-on-P structures.