In this letter we present a device, based on amorphous silicon material, able to detect infrared light through capacitance measurement at room temperature. The device is ap-c-nstacked structure, wherecindicates a compensated amorphous silicon absorber layer. Operation is based on transitions between extended states in the valence band and defects in the forbidden gap excited by the infrared radiation. We found that the measured capacitance is sensitive to radiation from 800 nm to 5 &mgr;m. ©1998 American Institute of Physics.