Enhancement of the spectral sensitivity of photodiodes for the mid-IR spectral range

A new method is used to raise the spectral sensitivity of photodiodes based on GaSb/GaInAsSb/GaAlAsSb heterostructures for the spectral range 1.1–2.4 $\mu$m. It is shown that, with a profile formed as pits on the metal-free unilluminated rear surface area of the photodiode chip, it is possible to improve the spectral sensitivity of the photodiodes at wavelengths in the range 1.8–2.4 $\mu$m. The most pronounced increase of up to 53% at the sensitivity maximum, compared with the sensitivity of conventional photodiodes with a fully metallized rear surface of the chip, is observed for photodiodes with shallow pits 30 $\mu$m in radius on their rear surface. These devices can find wide application in systems measuring the amount of water in petroleum products and the moisture content of paper, soil and grain.