Wide direct band gap III nitride materials have opened up many new optoelectronic applications because they allow access to a very wide spectral range, from 200 nm to 1.77 mu m, from a single material system. Both light emission sources and photodetectors with advanced properties can be achieved through tailoring layered III nitride structures with various layer orders, chemical compositions, conductivities, and thicknesses. In addition, substrate selection plays an important role in the fabrication of these devices as well as in achieving desired device properties. Along with the efficiency of detection, in most cases it is important to provide selectivity of the optical radiation sensed by the optical device. Such selectivity can be achieved by using spectral properties of optical radiation. In this article the authors present results on the modeling of dual-band photodiode structures based on III nitrides, grown on silicon substrates. UV/IR visible- and solar-blind UV/IR photodetectors have been demonstrated. The peak responsivities of the dual-band photodetectors are 3.8 and 5 5 mA/W at wavelengths of 349 and 1000 nm, respectively. Results on the modeling of the dual-band photodiodes in order to optimize the IR response and realize the solar-blind capability are presented. (C) 2008 American Vacuum Society.