Resonant-cavity infrared photodetector (RCID) devices that include a thin absorber layer contained entirely within the resonant cavity. In some embodiments, the absorber region is a single type-II InAs—GaSb interface situated between an n-type region comprising an AlSb/InAs n-type superlattice and a p-type AlSb/GaSb region. In other embodiments, the absorber region comprises one or more quantum wells formed on an upper surface of the n-type region. In other embodiments, the absorber region comprises a “W”-structured quantum well situated between two barrier layers, the “W”-structured quantum well comprising a hole quantum well sandwiched between two electron quantum wells. In other embodiments, an RCID in accordance with the present invention includes a thin absorber region and an nBn or pBp active core within a resonant cavity.