Two-color radiation detector array and methods of fabricating same

An array of radiation detectors each of which is responsive to electromagnetic radiation within a plurality of spectral bands, comprising:

• a substrate having first and second opposed major surfaces;
• a plurality of first regions disposed adjacent to the first surface of the substrate, each of the first regions being comprised of a first semiconductor material having a first type of electrical conductivity and having a significant responsivity to electromagnetic radiation having wavelengths within a first spectral band;
• an electrically conductive layer comprised of a second semiconductor material overlying an exposed area of the first surface of the substrate and also overlying the plurality of first regions, the layer being comprised of semiconductor material having a second type of electrical conductivity for forming a plurality of first heterojunctions with the underlying first regions, the second semiconductor material having a significant responsivity to electromagnetic radiation having wavelengths within a second spectral band that may or may not significantly overlap the first spectral band;
• and
• a plurality of second regions overlying the layer, individual ones of the second regions being in registration with and disposed above a corresponding one of the first regions, the second regions being comprised of a third semiconductor material having the first type of electrical conductivity for forming a plurality of second heterojunctions with the underlying layer, the third semiconductor material further having a significant responsivity to electromagnetic radiation having wavelengths within a third spectral band that does not significantly overlap either the first or the second spectral bands.