The quaternary Sb‐based materials are attractive for use in TPV devices due to the versatility associated with being able to grow InGaAsSb and AlGaAsSb material with a wide range of band gaps lattice matched to a GaSb substrate. Photodiodes (0.60 eV) consisting of an InGaAsSb p/n junction grown on GaSb were fabricated and characterized to establish baseline electrical performance of the material. In order to fabricate monolithic interconnected modules (MIMs) from these photodiodes using a conductive GaSb substrate, an electrical isolation layer must be added between the active layers and the substrate. For this purpose, AlGaAsSb cell isolation diodes (CIDs) were developed and characterized with respect to their ability to block current in reverse bias. These structures were combined in the first MIM structures grown and fabricated from Sb‐based materials on GaSb substrates. © 2003 American Institute of Physics