Abstract: A radiation detector having a pair of adjacent mesas disposed on a common layer. The common layer comprises a first semiconductor layer having a first conductivity type and an energy bandgap responsive to radiation in a first spectral region. Each of the mesas comprises: a second semiconductor; and a third semiconductor layer disposed on the second semiconductor layer having the first conductivity type and an energy bandgap responsive to radiation in a second spectral region. The second semiconductor layer may have a conductivity type opposite the first conductivity type or the three layers may provide an nBn or pBp structure. The third semiconductor layer of the second mesa produces minority carriers, in response to the radiation in the second spectral region, flowing as unwanted carriers into the common layer towards the first mesa. A barrier region is disposed in the common layer to prevent the unwanted carriers from passing from the second mesa to the first mesa.