Optical concentration in fully delineated mid-wave infrared T2SL detectors arrays

Abstract

The dependence of quantum efficiency (QE) on fill factor and pixel pitch is studied theoretically and experimentally in fully delineated type-II superlattice (T2SL) detectors. Theoretically, a 2-dimensional simulation model is used to compute the absorption in the array geometry, which shows an insensitivity of the optical response to the fill factor. This is a result of the photodiode array (PDA) geometry concentrating the light in the pixel area. QE measurements on PDAs with varying pixel pitch (from 225 to 10 μm) and fill factors (from 98% to 64%) confirm this independence of the QE on the fill factor and results in a 50% increase in the photocurrent density in 10 μm pitch PDAs compared to 225 μm pitch PDAs. Furthermore, measurements of the dark current density vs pixel size revealed an absence of surface leakage in these PDAs, which, combined with the increased photocurrent density results in an improved signal-to-noise ratio when reducing the pitch in these T2SL detectors. Finally, this result resolves the QE-modulation transfer function trade-off, as the electrical isolation of the pixel is carried out without impacting the QE of the array.

Simulation and Characterization of the Modulation Transfer Function in Fully Delineated Type-II Superlattices Infrared Detectors

“…However, state-of-the-art MWIR T2SL detectors implement a fully delineated geometry with appropriate passivation of the mesa sidewalls to suppress surface leakage currents [14], [15]. In addition, thanks to this geometry, optical concentration in the pixel has been observed as the pixel pitch reduces, thus mitigating the fill factor loss due to the trench etching and increasing the signal-to-noise ratio in smaller pixel size [7], [16], [17]. The pixels in such arrays are electrically isolated by etching a trench down in the semiconductor, consequently, only the optical crosstalk in the array geometry degrades the MTF.…”