Dark current in long-wave cascade-transport infrared up-converters

Abstract

Reducing the dark current in an infrared (IR) photodetector is one of the most important aspects in improving the detector’s performance. This article attempts to clarify the dominant paths of dark current and reduce it in a long-wave cascade-transport IR up-converter (CIUP), which has been reported to be a potential candidate for very-large-scale IR detection/imaging. The four paths of the dark current are considered, including the ground state sequential tunneling, thermionic emission onto the continuum, thermally-assisted transition onto the excited state of the absorption quantum well (QW) or some energy levels in the transport region. Accordingly three designs of the band structure are proposed for long-wave CIUPs, with miniband-to-miniband intersubband transition, bound-to-miniband transition and step-bound-to-miniband transition. Samples based on these designs are fabricated and measured. Both the calculated electron concentration distributions and the measured dark currents show that the step-bound-to-miniband structure is the most effective in cutting down the dark current, in which the superlattice barrier and InGaAs absorption QWs help to reduce dark current related to tunneling, thermionic emission and thermally-assisted tunneling.