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 μm. 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 μm. 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 μm 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.