Enhancing the Infrared Photoresponse of Silicon by Controlling the Fermi Level Location within an Impurity Band

wileyonlinelibrary.com detectivity of extrinsic photoconductive detectors depends on the ratio of optical carrier generation to thermal carrier generation. Traditionally, extrinsic silicon photodetectors have been limited by either high thermal impurity ionization or low optical carrier generation due to low absorption of sub-band gap radiation. Commonly used group III or V dopants (B, Al, Ga, P, As, and Sb) have high solubilities in solid silicon, but these impurities introduce shallow defect states that are thermally ionized at room-temperature, so extremely low operating temperatures (below ∼40 K) are required for their use in extrinsic photodetectors. [ 1,3 ] Alternatively, lattice defects, which can be introduced by bombardment with Si + ions, Ar + ions, protons, or neutrons, can be optically active without producing thermally generated free carriers, but they typically result in relatively low sub-band gap absorption coeffi cients, α ≈ 0.5–50 cm −1 . [ 4–8 ]